Title of Invention	RECORDING INK, INKJET RECORDING METHOD AND INKJET RECORDING APPARATUS
Abstract	There is provided a recording ink containing at least: water; a water-soluble organic solvent; a surfactant; and a carbon black having a hydrophilic group on a surface thereof, wherein the carbon black releases humic acid in an aqueous dispersion of the carbon black, which is recovered from the recording ink, a concentration of the humic acid released in the aqueous dispersion containing 20 % by mass of the carbon black of is expressed with a maximum absorbance at a wavelength of 230 nm to 260 nm, and the recording ink has the maximum absorbance of 5.0 to 20.0 at the wavelength of 230 nm to 260 nm.

Title of Invention

RECORDING INK, INKJET RECORDING METHOD AND INKJET RECORDING APPARATUS

Abstract

There is provided a recording ink containing at least: water; a water-soluble organic solvent; a surfactant; and a carbon black having a hydrophilic group on a surface thereof, wherein the carbon black releases humic acid in an aqueous dispersion of the carbon black, which is recovered from the recording ink, a concentration of the humic acid released in the aqueous dispersion containing 20 % by mass of the carbon black of is expressed with a maximum absorbance at a wavelength of 230 nm to 260 nm, and the recording ink has the maximum absorbance of 5.0 to 20.0 at the wavelength of 230 nm to 260 nm.

Full Text	DESCRIPTION [Technical Field The present invention relates to recording ink appropriate for inkjet recording, an Inkjet recording method and an inkjet recording apparatus. Background Art A coloring agent for inkjet recording ink is mainly based on-a dye, and there are disadvantages that the dye ink is inferior in water resistance and weather resistance and also easily oozes out on plain paper. In order to eliminate these disadvantages, such ink has been proposed that pigments, for example, carbon black, are used. The pigment ink is excellent in water resistance and weather resistance and also able to record images which ooze out to a less extent but is inferior in fixing property, which is a problem. Therefore, an attempt has been made that various resins are added to improve the fixing property. For example, Patent Literature 1 has described a recording solution which contains carbon black and a soap-free emulsion. In records obtained by using the above-described recording solution, a resin emulsion forms a film after drying of ink to fix a pigment, thereby imparting scratch resistance and water resistance, but carbon black contained in the recording solution is dispersed by a surfactant and therefore does not have a hydrophilic group directly on the surface. There is found a disadvantage that the above-described recording solution dispersed by a surfactant is poor in dispensability due to detachment of the surfactant adsorbed on the surface of the pigment with the lapse of time and may easily increase in viscosity and cause aggregation. Further, Patent Literature 2 has described a method in which hypohalogen is used to acid-treat carbon black. Since this method is able to introduce an aqueous dispersible functional group onto the surface by acid treatment of carbon black, the dispersion stability is better than that attained by using a surfactant. However, carbon black is known to generate humic acid due to acid treatment and the dispersion tends to decrease in pH with the lapse of time, thereby causing a decrease in dispersion stability and the deterioration of members inside an ink-used recording apparatus. Still further, Patent Literature 3 has described an ink composition containing two or more types of resins in which a pigment that can be dispersed or dissolved in water without a dispersing agent is used. Carbon black which is contained in the above-described ink composition and can be dispersed or dissolved in water without a dispersing agent is acid-treated by using hypochlorous acid or ozone. Since there are provided no measures for the pH decrease with the lapse of time due to elusion of humic acid, the ink is not satisfactory in terms of storage stability. In addition, Patent Literature 4 has described that attention is given to humic acid contained in acid-treated carbon black and where the concentration of humic acid is found to be one or lower in terms of the absorbance, there is provided an excellent feature of preventing clogging at a nozzle or a pen tip due to the development of solids. However, there is a problem that where humic acid is abundantly contained in a recording solution, pH is decreased with the lapse of time to deteriorate the storage stability. [Patent Literature l] Japanese Patent (JPB) No.3489289 [Patent Literature 2] JPB No. 3405817 [Patent Literature 3] Japanese Patent Application Laid-Open (JPA) No. 2004-204079 [Patent Literature 4] JPA No. 11349309 Disclosure of Invention An object of the present invention is to provide a recording ink excellent in fixing property and image density on a recording medium, also excellent in prolonged storage stability of ink and capable of forming a high-quality image not only on plain paper or paper exclusively used for inkjet printing but also on coated paper for commercial printing poor in water absorption, and an inkjet recording method as well as an inkjet recording apparatus. In order to solve the above problem, the present inventor and others have diligently conducted research, finding that humic acid released from carbon black is contained into ink at a predetermined quantity to increase the ink viscosity on water evaporation, by which the carbon black undergoes a quick aggregation on a recording medium to form an image, thereby providing a high image density. It has been found that a pH buffering agent is formulated into ink, thereby making it possible to retain the storage stability thereof, although a humic acid-containing recording ink tends to decrease in pH with the lapse of time. Further, in recent years, it has been desired that since inkjet printing does not require plate-making procedures to attain an easy printing and water-based ink is lower in environmental impact, such ink is used to make a high-quality printing for commercial use such as offset printing and gravure printing. Since paper used in offset printing and gravure printing is coated with inorganic pigments such as calcium carbonate and kaoline or not provided with a water absorbing layer as provided on paper exclusively used for inkjet printing, it is inferior in absorption of water-based ink. It has been found that in the recording ink of the present invention, a coloring material undergoes a quick aggregation on a recording medium to effect drying, thus making it possible to make a high-quality recording on the recording medium poor in absorption of the water-based ink. The following are means for solving the above problem- A recording ink containing at least: water; a water-soluble organic solvent; a surfactant; and a carbon black having a hydrophilic group on a surface thereof, wherein the carbon black releases humic acid in an aqueous dispersion of the carbon black, which is recovered from the recording ink, a concentration of the humic acid released in the aqueous dispersion containing 20 % by mass of the carbon black is expressed with a maximum absorbance at a wavelength of 230 nm to 260 nm, and the recording ink has the maximum absorbance of 5.0 to 20.0 at the wavelength of 230 nm to 260 nm. The recording ink according to , wherein a content of the carbon black is from 5 % by mass to 15 % by mass with respect to the total amount of the recording ink. The recording ink according to any of or , wherein the recording ink has a ratio B/A of from 5.0 or more to less than 550 when the recording ink has a water evaporation rate of 34% by mass to 41% by mass relative to a total mass of the recording ink, where A is an initial viscosity of the recording ink and B is a viscosity after water evaporation. The recording ink according to any one of to , further containing a pH buffering agent. The recording ink according to , wherein the pH buffering agent is at least one organic pH buffering agent selected from Good's buffer solutions. The recording ink according to any one of to , wherein the carbon black having a hydrophilic group has a volume average particle size of from 60 nm to 200 nm at the time being dispersed in water. The recording ink according to any one of to , further containing resin fine particles having a volume average particle size of from 50 nm to 200 nm. The recording ink according to any one of to , wherein at least a part of a terminal of the hydrophilic group on the carbon black is substituted with an alkali metal. The recording ink according to , wherein a quantity of the alkali metal contained in the recording ink is from 100 ppm or more to 1500 ppm or less. The recording ink according to any one of to , wherein the recording ink has a viscosity of 6 mPa-s to 20 mPa-s at 25°C. An inkjet recording method including at least: applying a stimulus to the recording ink as defined in any one of to , and ejecting the recording ink from a recording head so as to form an image on a recording medium, wherein the recording head is configured to have an ink discharge opening on a face of a nozzle plate, and to have an ink repellent layer formed on the face of the nozzle plate where the ink discharge opening is placed. The inkjet recording method according to , wherein the stimulation is at least one selected from the group consisting of heat, pressure, vibration and light. The inkjet recording method according to any of or , wherein the ink repellent layer contains either a fluorine-based material or a silicone-based material. The inkjet recording method according to any one of to , wherein the ink repellent layer has a surface roughness Ra of 0.2 µm or less. The inkjet recording method according to any one of to , wherein the ink repellent layer is formed so to have an opening along with the ink discharge opening, and the opening of the ink repellent layer is formed so that a cross-sectional area of a face perpendicular to a center line of the opening becomes gradually larger as a distance from the face of the nozzle plate increases in a vicinity of the opening. The inkjet recording method according to any one of to , wherein the ink repellent layer has a critical surface tension yc of from 5 mN/m to 40 mN/m. The inkjet recording method according to any one of to , wherein the recording medium has a support and a coating layer at least on one face of the support. The inkjet recording method according to any one of to , wherein the recording medium has a purified water transfer amount of 2 mL/m2 to 45 ml/m2 when measured at 23°C and 50% RH for a contact time of 100 ms by using a dynamic scanning absorptometer, and has a purified water transfer amount of 3 mL/m2 to 50 mL/m2 when measured at 23°C and 50% RH for the contact time of 400 ms by using a dynamic scanning absorptometer. The inkjet recording method according to any one of to , wherein an applied amount of the coating layer is from 0.5 g/m2 to 20.0 g/m2 on a dry basis. The inkjet recording method according to any one of to , wherein the recording medium has a basis weight of 50 g/m2 to 250 g/m2. An inkjet recording apparatus containing at least: an ink ejecting unit configured to apply a stimulus to the recording ink as defined in any one of to , and to eject the recording ink so as to record an image on a recording medium. The inkjet recording apparatus according to , wherein the stimulus is at least one selected from the group consisting of heat, pressure, vibration and light. Brief Description of the Accompanying Drawings FIG. 1 is a schematic view for illustrating one example of an ink cartridge used in the present invention. FIG. 2 is a schematic view which also includes a case (outer covering) of the ink cartridge given in FIG. 1. FIG. 3 is a perspective view for explaining a state that the cover of an ink cartridge loading portion is opened in an inkjet recording apparatus of the present invention. FIG. 4 is a schematic block diagram for explaining a whole constitution of the inkjet recording apparatus of the present invention. FIG. 5 is a schematic enlarged view for illustrating one example of an inkjet head used in the inkjet recording apparatus of the present invention. FIG. 6 is an enlarged element view for illustrating one example of the inkjet head used in the inkjet recording apparatus of the present invention. FIG. 7 is an enlarged sectional view in an inter-channel direction for illustrating major parts of the exemplified inkjet head used in the inkjet recording apparatus of the present invention. FIG. 8 is a schematic sectional view for illustrating one example of a nozzle plate on the inkjet head used in the inkjet recording apparatus of the present invention. FIG. 9A is a schematic view for explaining the nozzle plate on the inkjet head used in the inkjet recording apparatus of the present invention. FIG. 9B is a schematic view for explaining the nozzle plate on the inkjet head used in. the inkjet recording apparatus of the present invention. FIG. 9C is a schematic view for explaining the nozzle plate on the inkjet head used in the inkjet recording apparatus of the present invention. FIG. 10A is a schematic view for explaining a nozzle plate on the inkjet head for comparison. FIG. 10B is a schematic view for explaining another nozzle plate on the inkjet head for comparison. FIG. 10C is a schematic view for explaining still another nozzle plate on the inkjet head for comparison. FIG. 11 is a view for illustrating a state at which a silicone resin is coated by using a dispenser to form a ink repellent film. FIG. 12A is a view for showing a relationship between a coating hole at the needle tip used in the present invention and a coating width on the nozzle plate, which is an object to be coated. FIG. 12B is a view for showing a relationship between a general needle tip and a coating width on the nozzle plate, which is an object to be coated. FIG. 13 is a view for illustrating coating motions when the dispenser is used. FIG. 14 is a view for illustrating a state at which an ink repellent layer of the silicone resin is formed on the inner wall of the nozzle up to a desired depth. FIG. 15 is a view for illustrating one example of the inkjet head on the inkjet recording apparatus of the present invention and also a state at which the nozzle port is formed by excimer laser machining. FIG. 16 is a view for illustrating a constitution of the excimer laser machine used on machining the nozzle port. FIG. 17A is a view for illustrating a base material of the nozzle forming member used in a step of manufacturing the nozzle plate in manufacturing the inkjet head. FIG. 17B is a view for illustrating a step of forming a SiO 2 thin film layer on the surface of a resin film. FIG. 17C is a view for illustrating a step of coating a fluorine-based water repellent. FIG. 17D is a view for illustrating a step of allowing the film to stand in the atmosphere after deposition of the water repellent film. FIG. 17E is a view for illustrating a step of attaching an adhesive tape thereon. FIG. 17F is a view for illustrating a step of machining the nozzle port. FIG. 18 is a view for briefly illustrating an apparatus to be used on manufacture of the inkjet head by a method for manufacturing the inkjet head. FIG. 19 is a view for showing a relationship between a quantity of water evaporation and ink viscosity. Best Mode for Carrying Out the Invention The recording ink of the present invention contains at least water, a water-soluble organic solvent, a surfactant and carbon black having a hydrophilic group on the surface, and also contains other components, if necessary. The concentration of humic acid released in an aqueous dispersion containing 20% by mass of carbon black recovered from the recording ink is from 5.0 to 20.0 in terms of a maximum absorbance measured at a wavelength of 230 nm to 260 nm. The humic acid is an organic acid generated on oxidation treatment of carbon black, having an aromatic ring and a plurality of functional groups such as a carboxyl group and a hydroxyl group. Although the constitution thereof is not identified, it has been known that the humic acid exhibits a maximum absorbance at a wavelength of 230 nm to 260 nm. It is, therefore, possible to determine the concentration of humic acid by measuring the absorbance. The humic acid is generated in a process of oxidization of carbon black, and is removed by washing as much as possible during dispersion preparation. However, when a highly oxidized and bulky carbon black is used, it will not be completely removed by washing, and humic acid is likely to remain in the carbon black. In a stored ink, residual humic acid is released to reduce the ink's pH. The reduction of pH may cause aggregation and thickening of ink, as well as corrosion of members used in the ink flow paths inside a printer. When printed with such an ink, the ink may not be normally discharged. On the other hand, when humic acid is remained in the carbon black, evaporation of water causes a reduction in the ink's pH, producing a high image density due to aggregation and thickening of ink. Therefore, the humic acid preferably remains at a certain concentration. The first step of a method for quantification of humic acid released in an aqueous dispersion containing 20% by mass of carbon black recovered from the recording ink involves separation of such additives as a surfactant, rust-preventive agent and ultraviolet absorbing agent by column chromatography or the like for recovery of a carbon black. The thus obtained carbon black is then subjected to vacuum drying by using a dryer at 50 °C for sufficient evaporation of water and solvent, and is diluted with water to a concentration of 20% by mass. Fifty grams of the diluted solution is measured into in a beaker, and passed through an ultra-filter (Pellicon Biomax 50 manufactured by Millipore) for 30 minutes to obtain a brown liquid. This liquid is diluted 10 times with ion exchanged water and read on a spectrophotometer (U3310 manufactured by Hitachi High-Technologies Corporation) equipped with a quartz cell (light path length, 10 mm) at a wavelength of 230 nm to 260 nm. The thus obtained maximum absorbance was increased 10 times to determine the concentration of humic acid. The thus determined concentration of humic acid is preferably in a range of 5.0 to 20.0 in terms of maximum absorbance measured at a wavelength of 230 nm to 260 nm, and more preferably from 10.0 to 15.0. Where the maximum absorbance is less than 5.0, there may be found a poor image density on a recording medium such as a plain paper or a coated paper. In contrast, where the maximum absorbance is more than 20.0, there is found a tendency that pH is decreased to a greater extent with the lapse of time and aggregation or increase in viscosity takes place after a prolonged storage. There is also found a tendency that the ink is increased in viscosity to a greater extent on water evaporation, which may affect the discharge stability of the ink. In other words, it has been found that when a certain quantity of humic acid is present in the ink, a recorded image high in concentration can be obtained. This may be due to a fact that solids are quickly increased in viscosity and undergo aggregation on evaporation of water on the surface of the recording medium. A better understanding can be obtained for the relationship between viscosity increasing behaviors on water evaporation and image density. In other words, if such a condition is satisfied that when a quantity of water evaporation relative to a whole mass of ink is in a range of 34 % by mass to 41 % by mass, the viscosity is increased from 5.0 times or more to less than 550 times with respect to an initial viscosity, the ink is provided with an excellent discharge stability to increase the image density of a record. Regarding a relationship between the concentration of humic acid in ink and ink viscosity increasing behaviors on water evaporation, there is found a tendency that the higher the concentration of humic acid is, that is, the higher the value of absorbance determined by the above-described method is, to the higher extent the viscosity associated with water evaporation is elevated, and the lower the concentration of humic acid is, that is, the lower the value of absorbance is, to the lower extent the viscosity associated with water evaporation is elevated. Further, a quantity of the alkali metal contained in the ink will also affect ink viscosity increasing behaviors on water evaporation. The alkali metal contained in ink includes mainly lithium, sodium and potassium, which are mainly those added as a neutralizer of a hydrophilic group on the surface of carbon black and a neutralizer of a resin emulsion, although some of the alkali metals are derived from a surfactant or other additives. The quantity of the alkali metal contained in the ink is preferably from 100 ppm to 1500 ppm and more preferably from 200 ppm to 1200 ppm. Where the quantity of the alkali metal is less than 100 ppm, the image density tends to decrease, and where the quantity is more than 1500 ppm, ink may be deteriorated in storage and discharge performance. - Carbon black - Carbon black having a hydrophilic group used in the recording ink of the present invention is that manufactured by using known carbon black, including that manufactured, for example, by a channel method, an oil furnace method, a furnace method, an acetylene black method, a thermal black method or the like. It is noted that carbon black made by the channel method is available only in the limited variations due to a reduced manufacturing quantity in recent years, and carbon black made by the furnace method is now widely used due to availability of wider variations. There is no particular restriction on the types of carbon black, and general types of carbon black manufactured by any of the above-described methods are usable. Preferable are those in which the primary particle size is from 10 nm to 40 nm, and the specific surface area determined by BET method is from 50 m2/g to 300 m2/g. The carbon black preferably has a DBP oil absorption from 50 mL/100 g to 300 mL/100 g, and more preferably 100 mL/100 g to 300 mL/100 g. The DBP oil absorption can be obtained from an amount of DBP that is needed to fill voids of 100 g of carbon black by applying droplets of DBP dibutyl phthalate to the carbon black for penetration into the voids. There is no particular restriction on the carbon black, and any appropriate carbon black may be appropriately selected, including, for example, # 2700, # 2650, # 2600, # 2450B, # 2400B, # 2350, # 230, # 1000, # 990, # 980, # 970, # 960, # 950, # 900, # 850, # 750B, MCF 88, # 650B, MA 600, MA 77, MA 7, MA 8, MA 11, MA 100, MA 100R, MA 100S, MA 220, MA 230, MA 200RB, MA 14, # 52, # 50, # 47, # 45, # 45L, # 44, # 40, # 33, # 32, # 30, # 25, # 20, # 10, # 5, # 95, # 85, CF 9, and # 260 (all of which are manufactured by Mitsubishi Chemical Corporation); Raven 700, 5750, 5250, 5000, 3500 and 1255 (all of which are manufactured by Colombia Corporation; Rega 1400R, 330R, 660R, MogulL, Monarch 700, 800, 880, 900, 1000, 1100, 1300, and 1400 (all of which are manufactured by Cabot Corporation); Color Black FW1, FW2, FW2V, FW18, FW200, S150, S160, S170, Printex 35, U, V, 140U, 140V, Special Black 6, 5, 4A and 4 (all of which are manufactured by Degussa AG); Toka Black # 8500, # 8300, # 7550, # 7400, # 7360, # 7350, # 7270 and # 7100 (all of which are manufactured by Tokai Carbon Co., Ltd.); Fat-soluble (Shiyou) Black N110, N220, N234, N339, N330, N326, N330T, MAF and N550, (all of which are manufactured by Cabot Japan K.K.). The carbon black can be stably dispersed without using any dispersing agent by modifying the surface, and at least one type of hydrophilic group is bonded on the surface of the carbon black directly or through another atomic group. There is no particular restriction on the above described method for modifying the surface. Any method may be appropriately selected, depending on the intended purpose, including, for example, gas-phase oxidation using an oxidative gas such as ozone or liquid-phase oxidation using a liquid oxidizing agent. The liquid oxidizing agent includes hydrogen peroxide, iodine water, hypochloride, chlorite, nitrate, permanganate, dichromate and persulfate. The hydrophilic group includes, for example, COOM, -SO 3M, PO3HM, PO3M2, -SO2NH2 and SO2NHXCOR (in the formula, M denotes a hydrogen atom, alkali metal, ammonium or organic ammonium, and R denotes an alkyl group of 1 to 12 carbon atoms, a phenyl group which may have a substituent group or a naphthyl group which may have a substituent group.). In particular preferable are those in which -COOM or -SO3M is bonded on the surface. "M" given in the hydrophilic group includes, for example, lithium, sodium and potassium as an alkali metal. The organic ammonium includes, for example, mono- or tri-methyl ammonium, mono- or tri-ethyl ammonium, and mono-or trimethanol ammonium. In view of obtaining a higher image density, alkali metals such as potassium and sodium are preferably used. The volume average particle size in a state that the carbon black having the hydrophilic group is dispersed in water is preferably from 60 nm to 200 nm and more preferably from 80 nm to 180 nm. Where the volume average particle size is less than 60 nm, there is a failure in obtaining a sufficient image density. Where it is more than 200 nm, clogging may take place on a nozzle more often, resulting in deterioration of the discharge performance. In this instance, the volume average particle size can be measured by using Microtrac UPA (manufactured by Nikkiso Co., Ltd.). An amount of the carbon black having the hydrophilic group is preferably from 5 % by mass to 15 % by mass, and more preferably from 6 % by mass to 12 % by mass, with respect to the total mass of the ink. Where the content is less than 5 % by mass, there may be a failure in obtaining a sufficient image density. Where it is more than 15 % by mass, ink may be increased in viscosity to result in deterioration of the discharge stability. - Watersoluble organic solvent - There is no particular restriction on the water-soluble organic solvent. Any solvent may be used, depending on the intended purpose, including, for example, polyvalent alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, ethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3-propane diol, 1,3-butane diol, 2,3'butane diol, 1,4 butane diol, 3-methyl-l,3-butane diol, 1,5-pentane diol, tetraethylene glycol, l,6hexane diol, 3-methyl-1,5-pentane diol, 2-methyl-2,4-pentane diol, polyethylene glycol, glycerol, 1,2,6-hexane triol, 1,2,4-butane triol, 1,2,3-butane triol and petriol; polyvalent alcohol alkyl ethers such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethylether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetra-ethylene glycol monomethyl ether and propylene glycol monoethyl ether." polyvalent alcohol aryl ethers such as ethylene glycol monophenyl ether, and ethylene glycol monobenzyl ether; nitrogen-containing heterocycle compounds such as Nmethyl-2-pyrolidone, N-hydroxy ethyl-2-pyrolidone, 2-pyrolidone, 1,3-dimethylimidazolidinone, ecaprolactam; amides such as formamide, N-methyl formamide, formamide, and N,N-dimethyl formamide; amines such as monoethanol amine, diethanol amine, triethanol amine, monoethyl amine, diethyl amine and triethyl amine; sulfur-containing compounds such as dimethyl sulfoxide, sulfolane and thiodiethanol; propylene carbonate and ethylene carbonate. These substances may be used solely or in combination of two or more of them. Among the above substances, in view of obtaining the solubility and excellent effects in preventing poor jetting properties on water evaporation, in particular preferable are glycerin, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3-butane diol, 2,3-butane diol, 1,4-butane diol, 3-methyl-l,3-butane diol, 1,5-pentane diol, tetra-ethylene glycol, 1,6-hexane diol, 3-methyl-l,5-pentane diol, 2methyl-2,4-pentane diol, polyethylene glycol, l,2,4butane triol, 1,2,6-hexane triol, thiodiglycol, 2pyrolidone, N-methyl-2-pyrolidone, and N-hydroxy ethyhl-2-pyrolidone. The amount of the water-soluble organic solvent in the recording ink is preferably from 15 % by mass to 40 % by mass, and more preferably from 20 % by mass to 35 % by mass. Where the content is excessively low, a nozzle may be more likely to dry, thus resulting in a poor discharge of ink droplets. Where the content is excessively high, ink viscosity may be increased to exceed an appropriate range of the viscosity. - Surfactant - The surfactant may be used solely by selecting any one of those consisting of anionic surfactants, cationic surfactants, nonionic surfactants, amphoteric surfactants and fluorochemical surfactants or in combination of two or more of them. Among these, nonionic surfactants and fluorochemical surfactants are in particular preferable. The anionic surfactants include, for example, alkylallyl, alkylnaphthalene sulfonate, alkyl phosphate, alkyl sulfate, alkyl sulfonate, alkylether sulfate, alkyl sulfosuccinate, alkylester sulfate, alkylbenzene sulfonate, alkyldiphenyl ether disulfonate, alkylaryl ether phosphate, alkylaryl ether sulfate, alkylaryl etherester sulfate, olefin sulfonate, alkane olefin sulfonate, polyoxyethylene alkylether phosphate, polyoxyethylene alkylether sulfate ester, ether carboxylate, sulfosuccinate, asulfo fatty acid ester, fatty acid salt, condensate of fatty acid with amino acid, and naphthenic acid salt. The nonionic surfactants include, for example, an acetylene glycol-based surfactant, polyoxyethylene alkylether, polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ester, polyoxyethylene sorbitan fatty acid ester. The cationic surfactants include, for example, alkyl amine salt, dialkyl amine salt, aliphatic amine salt, benzalkonium salt, quaternary ammonium salt, alkylpyridinium salt, imidazorinium salt, sulfonium salt and phosphonium salt. The amphoteric surfactants include, for example, imidazoline derivatives such as imidazorinium betaine; dimethylalkyl lauryl betaine, alkylglycine and alkyldi(aminoethyl) glycine. The fluorochemical surfactants may preferably include a compound expressed by any one of the following general formulae (I) to (III). However, in the general formula (I), m denotes an integer of 0 to 10, and n denotes an integer of 1 to 40. However, in the general formula (II), Rf denotes CF3 or CF2 CF3 . Further, n, m and p respectively denote an integer of 1 to 4, that of 6 to 25 and that of 1 to 4. However, in the general formula (III), q denotes an integer of 1 to 6, Rf denotes CF3 or CF2CF3. R1 denotes SO3- and R2 denotes NH4 + . The fluorochemical surfactants may include commercially available products, for example, Surflon S-111, S112, S-113, S121, S-131, S132, S-141 and S-145 (all of which are manufactured by Asahi Glass Co., Ltd.); Fullard FC-93, FC-95, FC-98, FC129, FC135, FC170C, FC-430, FC431 and FC-4430 (all of which are manufactured by Sumitomo 3M Limited); Megafack F-470, F1405 and F-474 (all of which are manufactured by Dainippon Ink and Chemicals Incorporated); Zonyl FS-300, FSN, FSN100 and FSO (all of which are manufactured by Dupont Inc.); Ftop EF-351, 352, 801 and 802 (all of which are manufactured by Jemco Inc.). - Resin fine particles - Resin fine particles are allowed to be added to the recording ink of the present invention. The resin fine particles are those in which a water-insoluble resin is dispersed in water, and on evaporation of a solvent, the resin fine particles are fused to each other to form a film, thereby developing an effect of fixing a coloring agent on a medium. Further, when the solvent is deposited, the resin fine particles tend to increase in viscosity and undergo aggregation, inhibiting the penetration of coloring compositions to provide a high image density. They are also effective in preventing strike through. Resin compositions in the resin fine particles include, for example, acrylic resin, vinyl acetate resin, styrene-butadiene resin, vinyl chloride resin, acrylstyrene resin, acryl silicone resin, butadiene resin, styrene resin, urethane resin, and acryl-urethane resin. The resin emulsion is preferably contained from 0.1 % by mass to 40 % by mass with respect to a whole quantity of ink and more preferably from 1 % by mass to 25 % by mass. Where the resin emulsion is contained in a quantity of less than 0.1 % by mass, there may be a failure in obtaining a sufficient fixing property. Where it is contained in excess of 40 % by mass, the ink is abundant in solids and scarce in solvents, which may deteriorate the storage stability or result in frequent drying and solidification of the ink at a nozzle to decrease the discharge performance. The resin fine particles are preferably from 50 nm to 200 nm in volume average particle size and more preferably from 60 nm to 80 nm. Where the volume average particle size is less than 50nm, the resin emulsion may be increased in viscosity, thereby causing difficulty in providing the ink viscosity which can be discharged by an inkjet printer, and where it is in excess of 200 nm, resin fine particles may be clogged inside the nozzle of the inkjet printer to result in failure of discharge. The resin fine particles are preferably added to the carbon black from 0.05 parts by mass to 1.2 parts by mass with respect to the carbon black of 1 part by mass, and more preferably from 0.2 parts by mass to 1.0 part by mass. Where the resin fine particles are added in a quantity of less than 0.05 parts by mass, there may be a failure in obtaining a sufficient fixing property. Where they are added in excess of 1.2 parts by mass, the storage stability may be deteriorated or the discharge performance may be decreased. - Penetrating agent - The penetrating agent includes a diol compound having the carbon number of 7 to 11. Where the carbon number is less than 7, there is a failure in obtaining a sufficient penetration, thereby spoiling a recording medium when the medium is printed on both faces, or there is found an insufficient spread of ink on the recording medium to result in a poor filling of pixels, thereby deteriorating the quality of characters or the image density. Where the carbon number is in excess of 11, the storage stability may be decreased. The diol compounds preferably include, for example, 2-ethyl-1,3 hexane diol and 2,2,4-trimethyl-1, 3 pentanediol. The diol compound is preferably added from 0.1 % by mass to 20 % by mass and more preferably from 0.5 % by mass to 10 % by mass. Where the compound is added in an excessively small quantity, ink is poorly permeated into paper, which may lead to a case where the paper is rubbed by transfer rollers and blemished, ink attached on a transfer belt on reversing the recording face of a recording medium for printing on both faces thereof may spoil the recording medium, or there may be a failure in providing a high-speed printing or both-face printing. In contrast, where the compound is added in an excessively large quantity, the printing dot diameter is made larger, which may widen the line of characters or decrease the image sharpness. pH buffering agent - In order to prevent a pH decrease in the ink during a prolonged storage, in the present invention, usable are conventionally known solutions such as a phosphate buffer solution, acetate buffer solution, ethanol amine buffer solution, boric acid buffer solution, citric acid buffer solution, tartaric acid buffer solution, and Good's buffer solution. Among these buffer solutions, an organic pH buffering agent selected from Good's buffer solution is particular preferable. The Good's buffer solution is zwitter ion amino acids such as N-substituted taurine and N-substituted glycine, and known as an organic buffering agent suitable for bio-chemical uses. The Good's buffer solution has specific structures which are as follows: necessary, which includes, for example, pH adjusting agent, anti-septic/anti-mildew agent, rust-preventive agent, anti-oxidizing agent, ultraviolet absorbing agent, oxygen abosrbent and light stabilizer. The anti-septic/anti-mildew agent includes, for example, 1,2-benzoisothiazoline-3-on, sodium dehydroacetate, sodium sorbate, 2-pyridinethioll-sodium oxide, sodium benzoate and sodium pentachlorophenol. There is no particular restriction on the pH adjusting agent, as long as it does not affect ink to be formulated and is able to retain pH at 7 or higher. Any given substance may be used, depending on the intended purpose. The pH adjusting agent includes, for example, amines such as diethanol amine and triethanol amine,' hydroxides of alkali metal elements such as lithium hydroxide, sodium hydroxide and potassium hydroxide; carbonates of alkali metals such as ammonium hydroxide, quaternary ammonium hydroxide, quaternary phosphonium hydroxide, lithium carbonate, sodium carbonate and potassium carbonate. The rust-preventive agent includes, for example, acid sulfite, sodium thiosulfate, ammonium thiodiglycolate, diisopropyl ammonium nitrite, pentaerithritol tetranitrate and dicyclohexyl ammonium nitrite. The anti-oxidizing agents include, for example, phenol anti-oxidizing agents (including hindered phenol anti-oxidizing agents), amine anti-oxidizing agents, sulfur anti-oxidizing agents, and phosphorus anti-oxidizing agents. The phenol anti-oxidizing agents (including hindered phenol anti-oxidizing agents) include, for example, butylated hydroxy anisole, 2,6-di-tert-butyl-4-ethylphenol, stearyl-ß-(3,5ditert-butyl-4-hydroxyphenyl) propionate, 2,2'-methylenebis (4-methyl-6-tert-butylphenol), 2,2'-methylenebis (4-ethyl-6-tertbutylphenol), 4,4'-butylidenebis (3-methyl-6-tert-butylphenol), 3,9-bis [1, 1-dimethyl-2- [ß-(3tertbutyl-4-hydroxy-5-methylphenyl) propyonyloxy]ethyl] 2,4,8,10-tetraixaspiro [5, 5] undecane, 1,1,3-tris (2methyl-4-hydroxy-5-tertbutylphnyl) butane, l,3,5trimethyl-2,4,6-tris (3,5-di-tertbutyl-4hydroxy benzyl) benzene, and tetrakis [methylene-3-(3', 5'-di-tert-butyl-4'-hydroxy phenyl) propionate] methane. The amine anti-oxidizing agents include, for example, phenyl-ß-naphthyl amine, a-naphthyl amine, N,N'-disec-butyl-pphenylene diamine, phenothiazine, N,N'-diphenyl-pphenylene diamine, 2,6-ditert-butyl-p-cresol, 2,6-ditertbutylphenol, 2,4-dimethyl-6-tertbutyl-phenol, butylhydroxy anisole, 2,2'-methylene-bis (4-methyl-6tert-butylphenol), 4,4'-butylidene-bis (3-methyl-6-tertbutylphenol), 4,4'-thiobis (3methyl-6-tert-butylphenol), tetrakis [methylene-3 (3,5ditert-butyl-4dihydroxyphenyl) propionate] methane, and 1,1,3-tris (2methyl-4-hydroxy-5-tert-butylphenyl) butane. The sulfur anti-oxidizing agents include, for example, dilauryl 3,3'-thiodipropionate, distearyl tiodipropionate, laurylstearyl thiodipropionate, dimyristyl 3,3'-thiodipropionate, distearylB,B'-thiodipropionate, 2-mercaputo benzoimidazole, and dilauryl sulfide. The phosphorus anti-oxidizing agents include, for example, triphenyl phosphite, octadecyl phosphite, triisodecyl phosphite, trilauryl trithio phosphite, and trinonyl phenyl phosphite. The ultraviolet absorbing agents include, for example, benzophenone ultraviolet absorbing agents, benzotriazole ultraviolet absorbing agents, salicylate ultraviolet absorbing agents, cyanoacrylate ultraviolet absorbing agents, and nickel complex salt ultraviolet absorbing agents. The bezophenone ultraviolet absorbing agents include, for example, 2hydroxy-4noctoxy benzophene, 2-hydroxy-4-n-dodecyl. oxybenzophenone, 2,4-dihydroxy benzophenone, 2hydroxy-4-methoxybenzophenone, and 2,2',4,4'-tetrahydroxybenzophenone. The benzothiazole ultraviolet absorbing agents include, for example, 2(2'-hydroxy-5'-tert-octylphenyl) benzotriazole, 2(2'hydroxy-5'-methyl phenyl) benzoriazole, 2-(2'-hydroxy-4'-octoxyphenyl) benzotriazole, and 2-(2'-hydroxy-3'-tert-butyl-5'-methyl phenyl)-5-chlorobenzotriazole. The salicylate ultraviolet absorbing agents include, for example, phenyl salicylate, p-tert-butylphenyl salicylate, and poctylphenyl salicylate. The cyanoacrylate ultraviolet absorbing agents include, for example, ethyl-2-cyano-3,3'-diphenyl acrylate, methyl-2-cyano-3methyl-3-(p-methoxyphenyl) acrylate, and butyl-2-cyano-3-methyl-3-(pmethoxyphenyl) acrylate. The nickel complex salt ultraviolet absorbing agents include, for example, nickelbis (octylphenyi)sulfide, 2,2'-thiobis (4tertoctylphalate)-n-butylamine nickel (II), 2,2'thiobis (4-tert-octyylphalate)-2ethylhyxyl amine nickel (II), and 2,2'-thiobis (4-tert-octylphalate) triethanol amine nickel (II). There is no particular restriction on physical properties of the recording ink of the present invention. The physical properties may be appropriately selected, depending on the intended purpose. It is preferable that, for example, the solids content, viscosity surface tension and pH preferably fall under the following ranges. The solids content of the recording ink is preferably in a range of 5 % by mass to 20 % by mass and more preferably from 6 % by mass to 15 % by mass. Where the solids content is less than 5 % by mass, there may be a failure in obtaining a sufficient image density. In this instance, the solids content of the ink in the present invention substantially means the water-insoluble coloring agent and resin fine particles. The viscosity is preferably from 6 mPaa to 20 mPas at 25°C, and more preferably from 6.5 mPas to 12 mPas. Where the viscosity exceeds 20 mPa*s, there may be a difficulty in securing the discharge stability. The surface tension is preferably in a range of 25 mN/m to 55 mN/m at 20°C. Where the surface tension is less than 25 mN/m, ink may apparently ooze out on a recording medium to result in a failure of obtaining a stable jetting. Where the surface tension exceeds 55 mN/m, the ink will not penetrate into the recording medium sufficiently to result in a prolonged drying time. The pH is preferably, for example, from 7 to 10. A prolonged storage of the recording ink may change the physical properties. In particular, when the ink is stored after heating, it undergoes an increase in viscosity and a decrease in pH. It is desirable to keep the change in physical properties to the least possible extent. For example, the increase in viscosity after two-week storage at 60°C is preferably within 5%, and the decrease in pH is preferably within -5%. The recording ink of the present invention is favorably used in various fields and effectively used in an image recording apparatus (a printer or the like) based on an inkjet recording system. For example, ink having such a function that paper to be recorded and the recording ink are heated at temperatures of 50°C to 200°C during printing or before or after printing to promote printing fixing can be used in a printer or the like. This ink can be in particular preferably used in an ink cartridge, an ink record, an inkjet recording apparatus and an inkjet recording method of the present invention. The recording ink of the present invention is able to form a high-quality image not only on paper exclusively used for inkjet printing and plain paper but also on coated paper poor in water absorption. In this instance, the coated paper poor in water absorption is printing coated paper in which a coating layer is provided at least on one of two faces of a support and a quantity of purified water transferred to the recording medium measured at the contact time of 100 ms by using a dynamic scanning liquid absorbing system is in a range of 3 mL/m2 to 15 mL/m2. In the above-described recording medium, a quantity of the recording ink of the present invention transferred to the recording medium at the contact time of 100 ms measured by using a dynamic scanning absorptometer is preferably from 2 mL/m2 to 40 mL/m2, and more preferably from 3 mL/m2 to 30 mL/m2. Further, a quantity of purified water transferred to the recording medium is preferably from 2 mL/m2 to 45 mL/m2 and more preferably from 3 mL/m2 to 30 mL/m2. Where a quantity of the recording ink and that of the purified water transferred at the contact time of 100 ms are excessively small, beading may take place more frequently. Where they are excessively great, the ink dot diameter after the recording may be made smaller than desired. A quantity of the recording ink of the present invention transferred to the recording medium at the contact time of 400 ms measured by using a dynamic scanning absorptometer is from 3 mL/m2 to 50 mL/m2, and preferably from 4 mL/m2 to 40 mL/m2. Further, a quantity of purified water transferred to the recording medium is preferably from 3 mL/m2 to 50 mL/m2 and more preferably from 4 mL/m2 to 40 mL/m2. Where the quantity transferred at the contact time of 400 ms is excessively small, ink is not sufficiently dried and spur marks may develop easily. In contrast, where the quantity is excessively great, bleeds may take place easily and the gloss of an image portion after drying may be decreased. In this instance, the dynamic scanning absorptometer (DSA, Journal of the Japan Technical Association of the Pulp and Paper Industry, Vol. 48, May 1994, page 88-92, authored by Mr. Shigenori Kuga is a device capable of exactly measuring an absorbed quantity in an extremely short time. The dynamic scanning absorptometer is able to read a speed of liquid absorption directly from the movement of the meniscus in a capillary tube. A sample is formed into a disk shape, on which an absorption head is scanned helically. An automatic measurement is realized by a method in which the scanning speed is allowed to change according to previously established patterns and one sheet of the sample is used to make measurements only by the number of points required. A liquid supply head to paper samples is connected to the capillary tube via a Teflon (registered trade mark)made tube, and the position of the meniscus in the capillary tube is automatically read by an optical sensor. More specifically, the dynamic scanning absorptometer (K350 series D type, manufactured by Kyowa Seiko Co., Ltd.) is used to measure a quantity of purified water or ink transferred. Quantities transferred at the contact time of 100 ms and at the contact time of 400 ms can be determined by interpolating measurements of the quantities transferred at adjacent contact times of the respective contact times. The measurements are made at 23°C and RH of 50%. - Support - There is no particular restriction on the support. Any substance may be selected depending on the intended purpose, including, for example, paper mainly based on wood fibers or sheet-like substances such as non-woven fabrics mainly based on wood fibers and synthetic fibers. There is no particular restriction on the paper. Any known paper may be appropriately used depending on the intended purpose, including, for example, wood pulp and waste paper pulp. The wood pulp includes, for example, broad-leaved wood bleached kraft pulp (LBKP) and coniferous wood bleached kraft pulp (NBKP), NBSP, LBSP, GP, and TMP. Materials of the waste paper pulp include high-quality white paper, clean envelops, cream-white paper, cards, special white paper, wood containing white paper, simili paper, white-color paper, Kent paper, white art paper, special high-quality paper cuttings, high-quality paper cuttings, newspapers ad magazines as listed in the table of waste paper standard specifications issued by the Paper Recycling Promotion Center. More specifically, the materials include waste paper and waste paperboard, for example, printer paper used in information-related fields such as non-coated computer paper, thermal recording paper and pressure sensitive paper; office waste paper such as PPC paper; coated paper such as art paper, coat paper, finely coated paper and matt paper; non-coated paper such as wood-free paper, colored wood-free paper, notebook paper, letter paper, package paper, decorative paper, wood containing paper, paper for gazettes, woody paper, package paper used in supermarkets and the like, simili paper, machine glazed paper and milk carton paper; chemical pulp-containing paper and high-yield pulp containing paper. These materials may be used solely or in combination of two or more of them. The waste paper pulp is in general manufactured by a combination of the following four steps. (1) Pulping is a step in which a pulper is used to treat waste paper mechanically and chemically, disintegrating the paper to give a fiber form, thereby removing printing ink from fibers. (2) Dust removal is a step in which foreign matter (plastics and others) and waste contained in waste paper are removed by screening, cleaning and others. (3) Ink removal is a step in which printing ink removed from fibers by using a surfactant is removed from a system by using a floating method or a washing method. (4) Bleaching is a step in which oxidation or reduction is used to improve the whiteness of fibers. A mixing ratio of waste paper pulp to a whole pulp content on mixture of the waste pulp is preferably 40% or less, with consideration given to measures against a possible curling of paper after recording. Internal additives used in the support include, for example, conventionally known pigments as white pigments. The white pigments include, for example, white inorganic pigments such as light calcium carbonate, heavy calcium carbonate, kaolin, clay, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, zinc carbonate, satin white, aluminum silicate, diatomaceous earth, calcium silicate, magnesium silicate, synthetic silica, aluminum hydroxide, alumina, lithopone, zeolite, magnesium carbonate, and magnesium hydroxide; organic pigments such as styrene-based plastic pigment, acrylic plastic pigment, polyethylene, microcapsule, urine resin, and melamine resin. The pigments may be used solely or in combination of two or more of them. Internal sizing agents used in making the support include, for example, a neutral rosin sizing agent used in making neutralized paper, alkenyl succinic anhydride (ASA), alkylketene dimer (AKD), and a petroleum resin-based sizing agent. Of these agents, the neutral rosin sizing agent and alkenyl succinic anhydride are in particular preferable. The alkylketen dimer can be used in a smaller quantity because of its higher sizing effect. However, there is a case where the friction coefficient on the surface of recording paper (medium) is decreased to result in an easy slippage, the use of which is not favorable in terms of transferring the paper on inkjet recording. - Coating layer - The coating layer contains a pigment and a binder (binding agent), and also contains a surfactant and other compositions, if necessary. Usable as the pigment is an inorganic pigment or a combination of an inorganic pigment with an organic pigment. The inorganic pigment includes, for example, kaoline, talc, heavy calcium carbonate, light calcium carbonate, calcium sulfite, amorphous silica, titanium white, magnesium carbonate, titanium dioxide, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, and chlorite. Of these pigments, kaoline is in particular preferable because it is excellent in gloss development property and able to provide a texture close to that of paper for offset printing. The kaoline includes delaminated kaoline, calcinated kaoline and engineered kaoline by surface modification. When the gloss development property is taken into account, it is preferable that kaoline having such a particle size distribution that the particle size of 2 µm or less is 80 % by mass accounts for 50 % by mass or more with respect to a total quantity of kaoline. The kaoline is preferably added at 50 parts by mass or more with respect to 100 parts by mass of a total quantity of pigments on the coating layer. Where the addition is less than 50 parts by mass, there may be a failure in obtaining a sufficient gloss. There is no particular restriction on the added quantity. The kaoline is more preferably added at 90 parts by mass or less in terms of coating suitability, with consideration given to the fluidity of kaoline and increase in viscosity under a high sheering force in particular. The organic pigment includes a water-soluble dispersion, for example, styrene acryl copolymer particles, styrenebutadiene copolymer particles, polystyrene particles, and polyethylene particles. Two or more of the pigments may be mixed. The organic pigment is added preferably from 2 parts by mass to 20 parts by mass with respect to 100 parts by mass of a total quantity of pigments on the coating layer. Since the organic pigment is excellent in gloss development property and smaller in specific gravity than an inorganic pigment, it is able to provide a coating layer high in bulk, great in gloss and favorable in surface covering property. Where it is added at less than 2 parts by mass, the above-described effects are not obtained. Where it is added at a quantity exceeding 20 parts by mass, there is found deterioration in the fluidity of a coating solution to result in a decreased coating operation, which is not desirable in terms of cost. The organic pigment is available in a solid type, a hollow type, a donut type and other. When the gloss development property, surface covering property and fluidity of a coating solution are comprehensively considered, the hollow type having an average particle size of 0.2 µm to 3.0 µm is preferably employed, and that having a void percentage of 40% or higher is more preferably employed. An aqueous resin is preferably used as the binder. At least one of a water-soluble resin and an aqueous dispersible resin may be favorably used as the aqueous resin. There is no particular restriction on the water-soluble resin, and any resin may be appropriately selected, depending on the intended purpose. The resins include, for example, a modified product of polyvinyl alcohols such as polyvinyl alcohol, anion modified polyvinyl alcohol, cation modified polyvinyl alcohol and acetal modified polyvinyl alcohol; polyurethane; a modified product of polyvinyl pyrolidone such as a copolymer of polyvinyl pyrolidone and polyvinyl pyrolidone with vinyl acetate, a copolymer of vinyl pyrolidone and dimethyl amnoethyl/methacrylate, a copolymer of quaternary vinyl pyrolidone with dimethyl aminoethyl/methcrylate, and a copolymer of vinyl pyrolidone with methacrylamide propyl tri methyl ammonium chloride; cellulose such as carboxymethyl cellulose, hydroxyethyl cellulose and hydroxypropyl cellulose; a modified product of cellulose such as cationic hydroxyethyl cellulose; a synthetic resin such as polyester, polyacryl acid(ester), melamine resin, and their modified products, and a copolymer of polyester with polyurethane; poly(meta)acrylic acid, poly(meta)acrylamide, acidified starch, phosphorylated starch, internally modified starch, cationic starch, various types of modified starch, polyethylene oxide, polyacrylic acid soda, and alginate soda. These resins may be used solely or in combination of two or more of them. Of these resins, in view of ink absorption, in particular preferable are polyvinyl alcohol, cation modified polyvinyl alcohol, acetal modified polyvinyl alcohol, polyester, polyurethane, and a copolymer of polyester with polyurethane. There is no particular restriction on the aqueous dispersible resin. Any resin may be appropriately selected, depending on the intended purpose, including, for example, poly vinyl acetate, ethylene/vinyl acetate copolymer, polystyrene, styrene/(meta) acryl ester copolymer, (meta)acryl ester polymer, vinyl acetate(meta)acrylic acid(ester) copolymer, styrene/butadiene copolymer, ethylene/propylene copolymer, polyvinyl ether, and silicone/acryl copolymer. These resins may contain a cross-linking agent such as methylolated melamine, methylolated urea, methylolated hydroxy propylene urea, and isocyanate and also have a copolymer containing a unit of N-methylol acrylamide with a self cross-linking property. These aqueous resins may be used in a plurality. The aqueous resin is added preferably from 2 parts by mass to 100 parts by mass with respect to 100 parts by mass of the pigments, and more preferably from 3 parts by mass to 50 parts by mass. The aqueous resin is added in such a quantity that the recording medium can obtain a desired absorption property. Where an aqueous dispersible coloring agent is used as the coloring agent, it is not always necessary to formulate a cationic organic compound. There is no particular restriction on the coloring agent. Any agent may be appropriately selected depending on the intended purpose, including, for example, a primary to a tertiary amine which reacts with a sulfonic acid group, a carboxyl group, an amino group or others in a direct dye or an acid dye in water-soluble ink to form an insoluble salt, monomer, oligomer and polymer of quaternary ammonium salt. Of these substances, the oligomer or the polymer is preferable. The cationic organic compound includes, for example, dimethyl amine/epichloruhydrine polycondensate, dimethyl amine/ammonia/epichloruhydrine condensate, poly (trimethyl aminoethyl methcrylate/methyl sulfate), diallyl amine hydrochloride/acrylamide copolymer, poly (diaryl amine hydrochloride/sulfur dioxde), polyaryl amine hydrochloride, poly (aryl amine hydrochloride/diaryl amine hydrochloride), acrylamide/diaryl amine copolymer, polyvinyl amine copolymer, dicyandiamide, dicyandiamide/ammonium chloride/urea/formaldehyde condensate, polyalkylene polyamine/dicyandiamide ammonium salt condensate, dimethyldiallyl ammonium chloride, polydiallyl methyl amine hydrocloride, poly (diallyldimethyl ammonium chloride), poly (diallyldimethyl ammonium chloride/sulfur dioxide), poly (diallyldimethyl ammonium chloride/diallyl amine hydrochloride derivative), acrylamide/diallyldimethyl ammonium chloride copolymer, acrylate/acrylamide/diallyl amine hydrochloride copolymer, ethylene imine derivatives such as polyethylene imine and acryl amine polymer, and polyethylene imine alkylene oxide modified products. These substances may be used solely or in combination of two or more of them. Of these substances, it is preferable to use in combination of a lowmolecularweight a cationic organic compound such as dimethyl amine/epichloruhydrine polycondensate or polyallyl amine hydrochloride with another relatively-high-molecular-weight cationic organic compound such as poly (diallydimethyl ammonium chloride). The combined use makes it possible to improve the image density and reduce feathering to a greater extent as compared with sole use. The cationic organic compound is treated by a colloid titration method (in which polyvinyl potassium sulfate and truidine blue are used) to determine a cationic equivalent, which is preferably in a range of 3 meq/g to 8 meq/g. Where the cationic equivalent falls in this range, favorable results are obtained in the above-described range of the drying attachment quantity. In this instance, in determining the cationic equivalent by the colloid titration method, the cationic organic compound is diluted with distilled water so as to give 0.1 % by mass on a dry solid basis, without adjustment of pH. The cationic organic compound is preferably from 0.3 g/m2 to 2.0 g/m2 in drying attachment quantity. Where the cationic organic compound is less than 0.3 g/m2 in drying attachment quantity, there may be a failure in sufficiently improving the image density or effectively decreasing feathering. There is no particular restriction on the surfactant, and any surfactant may be appropriately selected depending on the intended purpose, including, for example, an anionic active agent, a cationic active agent, an amphoteric active agent and a non-ionic active agent. Of these agents, the non-ionic active agent is in particular preferable. The surfactant is added, by which the water resistance of an image can be improved and the image density is also increased, thus resulting in the improvement of bleeding. The non-ionic active agent includes, for example, a higher alcohol ethylene oxide addition, an alkyl phenol ethylene oxide addition, a fatty acid ethylene oxide addition, a polyvalent alcohol fatty acid ester ethylene oxide addition, a higher aliphatic amine ethylene oxide addition, a fatty acid amide ethylene oxide addition, an ethylene oxide addition of fat, a poly propylene glycolethylene oxide addition, a fatty acid ester of glycerol, a fatty acid ester of pentaerithritol, a fatty acid ester of sorbitol or sorbitan, a fatty acid ester of sucrose, an alkylether of polyvalent alcohol and fatty acid amides of alkanol amines. These substances may be used solely or in combination of two or more of them. There is no particular restriction on the polyvalent alcohol. Any substance may be appropriately selected depending on the intended purpose, including, for example, glycerol, trimethykik propane, pentaerithritol, sorbitol and sucrose. Further, an effectively usable ethylene oxide addition is that in which ethylene oxide is partially substituted with alkylene oxide such as propylene oxide or butylene oxide to an extent of retaining the water solubility. It is preferably substituted at 50% or less. HLB (hydrophile-lipophile balance) of the non-ionic active agent is preferably from 4 to 15 and more preferably from 7 to 13. The surfactant is added preferably from 0 parts by mass to 10 parts by mass with respect to 100 parts by mass of the cationic organic compound, and more preferably from 0.1 parts by mass to 1.0 part by mass. Other compositions may be added to the coating layer, whenever necessary, to such an extent that will not affect the object or effect of the present invention. These other compositions include additives such as alumina powder, a pH adjusting agent, an anti-sceptic agent and an antioxidizing agent. There is no particular restriction on a method for forming the coating layer, and any appropriate method may be appropriately selected depending on the intended purpose. The coating layer can be formed by a method in which a layer-coating solution is impregnated or coated on the support. There is no particular restriction on a method for impregnating or coating the layer-coating solution, and any method may be appropriately selected depending on the intended purpose. The coating can be performed by using various types of coaters such as a conventional size press, a gate roll size press, a film transfer size press, a blade coater, a rod coater, an air knife coater, and a curtain coater. In particular, preferable in terms of cost is a method in which the conventional size press, the gate roll size press or the film transfer size press mounted on a paper machine is used to impregnate or attach the coating solution, thereby giving an on-machine finishing. There is no particular restriction on an applied amount of a coating solution for the coating layer. The applied amount may be appropriately selected depending on the intended purpose, preferably from 0.5 g/m2 to 20 g/m2, and more preferably from 1 g/m2 to 15 g/m2 on a dry basis. Where the applied amount is less than 0.5 g/m2, the ink which is not sufficiently absorbed may ooze out to blur characters. Where the applied amount is more than 20 g/m2, the texture is spoiled for paper to result in a fact that the paper is difficult to fold and additional writing with a writing instrument is not easy. The coated film may be dried, whenever necessary, after the impregnation or coating. There is no particular restriction on temperatures at which the drying is effected in this instance. The temperatures may be appropriately selected depending on the intended purpose and preferably from 100°C to 250°C. The recording medium may be also provided with a back layer on the back face of a support and another layer between the support and the coating layer or between the support and the back layer. Further, a protective layer may be provided on the coating layer. These layers may be provided in a single layer or plural layers. The recording medium may include commercially-available offset printing coat paper and gravure printing coat paper, in addition to inkjet recording media, if their absorption property falls under the above-described range. The recording medium preferably has basis weight of 50 g/m2 to 250 g/m2, more preferably of from 60 g/m2 to 200 g/m2. Where the basis weight is less than 50 g/m2, defective transfer such as a jammed recording medium may take place more often in the course of transferring the recording medium due to lack of consistency. In contrast, where the basis weight exceeds 250 g/m2, there may also cause defective transfer in which the consistency becomes excessively great, thereby the recording medium is not successfully bent at a curved portion in the transfer course to result in jamming of a recording medium. (Ink cartridge) An ink cartridge of the present invention is to accommodate the recording ink of the present invention in a container and also provided with other members and others appropriately selected, whenever necessary. There is no particular restriction on the container, which may be appropriately selected for shape, dimensions, structure, material or the like, depending on the intended purpose. The container may be, for example, that having an ink bag formed with an aluminum-laminated film, a resin film or the like. Next, an explanation will be made for the ink cartridge by referring to FIG. 1 and FIG. 2. In this instance, FIG. 1 is a view for illustrating one example of the ink cartridge of the present invention, and FIG. 2 is a view which also includes a case (outer covering) of the ink cartridge given in FIG. 1. As illustrated in FIG. 1, the ink cartridge 200 is loaded into an ink bag 241 from an ink filling port 242 and the ink filling port 242 is closed by fusion after air is discharged. When the ink cartridge is used, an ink discharge port 243 made with a rubber member is punctured with a needle on the apparatus main body to supply ink to the apparatus. The ink bag 241 is formed with a package member such as an aluminum-laminated film devoid of air permeability. As illustrated in FIG. 2, the ink bag 241 is usually housed into a plastic-made cartridge case 244 and used so as to be removably attached to various types of inkjet recording apparatus. The ink cartridge of the present invention is able to accommodate the recording ink of the present invention and usable so as to be removably attached to various types of inkjet recording apparatuses. Further, the ink cartridge is in particular preferably used so as to be removably attached to an inkjet recording apparatus of the present invention, which will be described later. (Inkjet recording apparatus and inkjet recording method) An inkjet recording apparatus of the present invention is provided with at least a unit configured to shoot ink and also provided with other units which can be selected whenever necessary, for example, a unit to generate stimulation and a unit to gain control. An inkjet recording method of the present invention includes at least an ink shooting step and also includes other steps which can be selected whenever necessary, for example, steps of generating stimulation and gaining control. The inkjet recording method of the present invention can be employed by the inkjet recording apparatus of the present invention, and the ink shooting step can be favorably carried out by using the unit configured to shoot ink. The above-described other steps are also favorably carried out by using the above-described other units. - Ink shooting step and unit configured to shoot ink - The ink shooting step is a step of applying stimulation to the recording ink of the present invention, thereby shooting the recording ink from a recording head to record an image on a recording medium. The unit configured to shoot ink is a means to apply stimulation to the recording ink of the present invention, thereby shooting the recording ink from the head to record an image on a recording medium. There is no particular restriction on the unit configured to shoot ink, including, for example, various types of ink discharging nozzles. In the present invention, it is preferable that the liquid chamber portion, the fluid resistance portion, the diaphragm and the nozzle member of the inkjet head are at least partially formed with a material at least containing one of silicon and nickel. Further, the inkjet nozzle is preferably 30 µm or less in nozzle diameter and more preferably from 1µm to 20 µm. Such a constitution is also preferable that a sub-tank for supplying ink is provided on the inkjet head and the ink is supplied to the sub-tank via a supply tube from the ink cartridge. The stimulation can be generated, for example, by the unit to generate stimulation. There is no particular restriction on such stimulation. Any stimulation may be appropriately selected depending on the intended purpose, including, for example, heat (temperature), pressure, vibration, light and the like. They may be used solely or in combination of two or more of them. Among other things, heat and pressure are preferably used. It is noted that the unit to generate stimulation includes, for example, a heating device, a pressure device, a piezoelectric element, a vibration generating device, an ultrasonic generator and a lighting device. More specifically, included are, for example, a piezcrelectric actuator such as a piezoelectric element, a thermal actuator which uses an electrothermal converter such as a heat element to utilize the change in phase resulting from the film boiling of a liquid, a shape memory alloy actuator which uses the change in metal phase resulting from the change in temperature, and an electrostatic actuator which uses an electrostatic force. There is no particular restriction on an aspect of shooting the recording ink, which is different depending on the types of stimulation. Where the stimulation is, for example, "heat," such a method is available that thermal energy corresponding to a recording signal is applied to the recording ink inside a recording head, for example, by using a thermal head or the like, bubbles are generated in the recording ink by the thermal energy, thereby a pressure coming from these bubbles is utilized to discharge and jet the recording ink as ink droplets from the nozzle port of the recording head. Further, where the stimulation is "pressure," such a method is available that, for example, voltage is applied to a piezoelectric element attached to a position which is called a pressure chamber inside an ink flow path on a recording head, by which the piezoelectric element is bent to reduce the volume of the pressure chamber, thus discharging and jetting the recording ink as ink droplets from the nozzle port of the recording head. The to-be-shot ink droplets of the recording ink are preferably, for example, from 3 pL to 40 pL in size and, the discharging/jetting speed is preferably from 5m/s to 20m/s, the driving frequency is preferably at 1 kHz or more, and a resolution is preferably at 300 dpi or more. It is preferable to provide a unit configured to reverse the recording face of a recording medium so as to print on both faces thereof. The reversing unit includes, a transfer belt having an electrostatic force, a unit configured to retain the recording medium by pneumatic absorption and a combination of transfer rollers with spurs. It is preferable to provide an endless transfer belt and a unit configured to transfer a recording medium while retaining the recording medium, with the surface of the transfer belt being electrified. In this instance, it is particularly preferable to give AC bias of ± 1.2 kV to ± 2.6 kV to an electrification roller, thereby electrifying the transfer belt. It is noted that there is no particular restriction on the unit configured to gain control, as long as it does not restrict the movement of each of the above-described units. Any unit may be appropriately selected depending on the intended purpose, including, for example, devices such as a sequencer, a computer and the like. Where ink with a relatively low surface tension is used such as the recording ink used in the inkjet recording method of the present invention, it is preferable that a nozzle plate is excellent in water repellency and ink repellency. This is because the nozzle plate excellent in water repellency and ink repellency is used, by which even ink low in surface tension can be used to form the meniscus of ink, resulting in a favorable formation of ink droplets (granulation). The meniscus is formed normally, thus there is no chance that ink is pulled toward one direction on jetting of the ink. As a result, such images are obtained that jetting of ink and high in dot position accuracy. Where printing is made on a medium low in absorption, for example, a recording medium (sheet) used in the inkjet recording method of the present invention, whether the position accuracy is high is remarkably influences the image quality. In other words, ink is less likely to spread on an absorption-low medium, there is developed a void, or a portion at which ink fails in filling the recording medium if the position accuracy is decreased even to a slight extent. This portion at which ink fails in filling the medium will eventually cause variance in image density or decrease in image density to deteriorate the image quality. However, the inkjet head used in the present invention is able to realize a high dot position accuracy even if ink low in surface tension is used, by which the ink successfully fills a recording medium which is low in absorption, thus making it possible to provide printed matter with a high image quality free of variance in image density or decrease in image density. An explanation will be made for one aspect at which an inkjet recording method of the present invention is performed by using an inkjet recording apparatus of the present invention with reference to the drawings. The inkjet recording apparatus shown in FIG. 3 is provided with an apparatus main body 101, a paper feeding tray 102 for feeding sheets loaded on the apparatus main body 101, a paper discharging tray 103 for storing an image-recorded (formed) sheet loaded on the apparatus main body and an ink cartridge loading portion 104. An operation portion 105 including an operation key and a display is arranged on the upper face of the ink cartridge loading portion 104. The ink cartridge loading portion 104 is provided with an opening/closing front cover 115 for attaching or detaching an ink cartridge 200. As illustrated in FIG. 4 and FIG. 5, inside the apparatus main body 101, a guide rod 131 and a stay 132 which are guide members placed laterally on the right and left side plates are used to retain a carriage 133 so as to slide in a main scanning direction, and the carriage is moved and scanned by a main scanning motor (not illustrated) to the direction given by the arrow in FIG. 5. The carriage 133 is provided with a recording head 134 made up of four inkjet recording heads for discharging recording ink droplets of individual colors of yellow (Y), cyan (C), magenta (M) and black (B) arranged in such a direction that a plurality of ink discharging ports are crossed in a main scanning direction, with the direction of discharging ink droplets faced downward. The inkjet recording head constituting the recording head 134 is provided with a piezoelectric actuator such as a piezoelectric element, a thermal actuator which uses an electrothermal converter such as a heat element to utilize the change in phase resulting from the film boiling of a liquid, a shape memory alloy actuator which uses the change in metal phase resulting from the change in temperature, and an electrostatic actuator which uses an electrostatic force or the like as a unit configured to generate energy for discharging recording ink. Further, the carriage 133 is equipped with a sub-tank 135 of each color for supplying each ink to the recording head 134. The recording ink of the present invention is supplied through a recording ink supply tube (not illustrated) from the ink cartridge 200 of the present invention filled at ink cartridge loading portion 104 and refilled to the sub-tank 135. On the other hand, a paper feeding portion for feeding sheets 142 placed on the sheet placing portion (pressure plate) 141 of the paper feeding tray 102 is provided with a crescent gear (paper feeding gear 143) for separating the sheets 142 from the sheet placing portion 141 and supplying them one by one and a separation pad 144 which is opposed to the paper feeding gear 143 and made with a material large in friction coefficient. The separation pad 144 is urged to the paper feeding gear 143. A transfer portion for transferring the sheets 142 fed from the paper feeding portion below the recording head 134 is provided with a transfer belt 151 for electrostatically adsorbing and transferring the sheets 142, a counter roller 152 for transferring the sheets 142 sent via a guide 145 from the paper feeding portion, with the sheets held with respect to the transfer belt 151, a transfer guide 153 for changing the direction of the sheets 142 sent above approximately perpendicularly at about 90 degrees to follow on the transfer belt 151, and a leading-end pressure gear 155 urged to the transfer belt 151 by the presser member 154. It is also provided with an electrification roller 156, which is a unit configured to electrify the surface of the transfer belt 151. The transfer belt 151 is an endless belt, stretched between a transfer roller 157 and a tension roller 158 and able to rotate in a belt transfer direction. The transfer belt 151 is provided, for example, with a surface layer acting as a sheet adhesion face formed with a resin material of about 40 µm free of rheostatic control, for example, a copolymer of tetrafluoroethylene with ethylene (ETFE) and a back layer (middle resistive layer, ground layer) which is made with the same material as the surface layer to which rheostatic control is effected by carbon black. A guide member 161 is provided at the back of the transfer belt 151 so as to correspond to an imaging area by the recording head 134. It is noted that a paper discharge portion for discharging the sheets 142 recorded by the recording head 134 is provided with a separation nail 171 for separating the sheets 142 from the transfer belt 151, a paper discharge roller 172 and a paper discharge gear 173. A paper discharging tray 103 is arranged below the paper discharge roller 172. A both-face paper feeding unit 181 is removably attached to the back face portion of the apparatus main body 101. The both-face paper feeding unit 181 captures the sheets 142 returned by a reverse rotation of the transfer belt 151 to reverse the sheets 142, thereby feeding the sheets again between the counter roller 152 and the transfer belt 151. It is noted that a manual paper feeding portion 182 is provided on the upper face of the bothface paper feeding unit 181. A recording completion signal or a signal of indicating that the training end of the sheet 142 has arrived at a recording area, by which recording motions are completed to discharge the sheet 142 onto the paper discharging tray 103. Then, when recording ink inside the sub-tank 135 is detected for the near end of residual quantity, the recording ink is refilled at a predetermined quantity from the ink cartridge 200 to the sub-tank 135. In the inkjet recording apparatus, a housing of the ink cartridge 200 can be disassembled to exchange only an ink bag thereinside when recording ink inside the ink cartridge 200 is used up. Further, the ink cartridge 200 is able to supply the recording ink stably, even when constituted so as to fill the ink vertically from the front face. Therefore, where the ink cartridge is arranged, with the apparatus main body 101 being closed above, for example, a case where the ink cartridge is accommodated inside a rack or an object is placed on the upper face of the apparatus main body 101, the ink cartridge 200 can be exchanged easily. In this instance, an explanation was made by referring to an example applied to a serial type (shuttle-type) inkjet recording apparatus at which the carriage scans. The inkjet recording apparatus of the present invention is also applicable to a line-type inkjet recording apparatus equipped with a line-type head. Further, the inkjet recording apparatus and the inkjet recording method of the present invention are applicable to various types of recording by an inkjet recording method, and in particular preferably applicable, for example, to an inkjet recording printer, a facsimile device, a copying device, and a multifunction device of printer/facsimile/copier. Next, an explanation will be made for an inkjet head. FIG. 6 is an enlarged view of elements of an inkjet head to which the present invention is applied. FIG. 7 is an enlarged sectional view in an inter-channel direction for illustrating major parts of the inkjet head. The inkjet head is constituted with a frame 10 engraved so as to form an ink supply port (not illustrated) (ink is supplied from the surface direction to the rear direction in FIG. 6 (direction of the back face of paper)) and a common liquid chamber 12, a fluid resistance portion 21, a flow path plate 20 which is engraved so as to form a pressure liquid chamber 22 and provided with a port 23 for communicatively connecting to a nozzle 31, a nozzle plate 30 which forms the nozzle 31, a projected portion 61, a diaphragm 60 equipped with a diaphragm portion 62 and an ink flowing port 63, a laminated piezoelectric element 50 joined to the diaphragm 60 via a bonding layer 70, and a base 40 which fixes the laminated piezoelectric element 50. The base 40 is made with barium titanate-based ceramic and is joined to the laminated piezoelectric elements 50 which are arranged in two arrays. The laminated piezoelectric element 50 is prepared by alternately laminating a piezoelectric layer 51 of lead zirconate titanate (PZT) with a thickness of 10 µm to 50 µm/one layer and an internal electrode layer 52 made with silver/palladium (AgPd) with a thickness of several µm/one layer. The internal electrode layer 52 is connected at both ends to an external electrode 53. The laminated piezoelectric element 50 is divided into a comb shape by a half-cut dicing process and used as a driving portion 56 and a supporting portion 57 (non-driving portion) for each division (refer to FIG. 7). Of the two external electrodes 53, one of them (connected to one end of the internal electrode layer 52 in the surface direction or the rear direction in the drawing (direction on the back face of paper)) is restricted in length by a process, for example, notching so as to be divided at the outer end by a half-cut dicing process, and these divisions are given as a plurality of individual electrodes 54. The other is not subjected to division by the dicing process but made conductive and given as a common electrode 55. FPC (80) is joined by soldering to the individual electrodes 54 at the driving portion. Further, the common electrode 55 is provided with an electrode layer at the edge of the laminated piezoelectric element and turned around so as to be joined to the ground electrode of the FPC (80). A driver IC (not illustrated) is loaded into the FPC (80), thereby controlling a driving voltage applied to the driving portion 56. The diaphragm 60 is provided with a thin-film diaphragm portion 62, an islet projected portion (island portion) 61 joined to the laminated piezoelectric element 50 which is given as a driving portion 56 formed at the center of the diaphragm portion 62, a thick-film portion including a beam joined to a supporting portion (not illustrated), and an opening port which is given as an ink flowing port 63 formed by laminating two layers of Ni plated film by electro molding method. The diaphragm portion is 3 µm in thickness and 35 µm in width (one side). Connection of the islet projected portion 61 of the diaphragm 60 with the movable portion 56 of the laminated piezoelectric element 50 and that of the diaphragm 60 with the frame 10 are made by patterning a bonding layer 70 which contains a gap material. The flow path plate 20 is engraved by using a silicon mono-crystalline substrate to give a fluid resistance portion 21 and a pressure liquid chamber 22 and provided with a through hole which acts as a communicatively connected port 23 at a position opposed to a nozzle 31 through patterning by an etching process. A remaining portion after the etching is given as a partition wall 24 of the pressure liquid chamber 22. In this instance, the head is provided with a portion which is made narrow in etching width, and the portion is given as the fluid resistance portion 21. The nozzle plate 30 is made with a metal material, for example, Ni plated film by an electro-molding process and provided with many nozzles 31, that is, fine discharging ports for shooting ink droplets. This nozzle 31 is formed in a horn shape (approximately cylindrical shape or trapezoidal cylindrical shape) as an internal shape (inner shape). Further, the nozzle 31 is from 20 µm to 35 µm in diameter at the outlet of ink droplets. The nozzles are to give 150 dpi at each array. The nozzle plate 30 is provided on the ink discharging face (front face of the nozzle) with an ink repellent layer 90. A water repellent film prepared by PTFE-Ni eutectoid plating, electro-coating of a fluorine resin, vapor-deposition coating of a vaporizing fluorine resin (for example, fluoridated pitch), baking of a silicone-based resin or a fluorine-based resin after coating of a solvent or the like, is formed, depending on physical properties of ink, so that the shape of ink droplets and shooting properties can be stabilized to obtain a high-quality image. - Surface roughness - An ink repellent layer used in the present invention is preferably 0.2 µm or less in surface roughness of Ra. The surface roughness of Ra is made to be 0.2 µm or less, by which the remainder after wiping can be reduced. FIG. 8 and FIG. 9A through FIG. 9C are sectional views for illustrating a nozzle plate of the inkjet head used in the present invention. In the present embodiment, it is preferable that the nozzle plate 32 of the inkjet head is made by Ni electro-casting, the surface of which is provided with an ink repellent film 31 or a silicone resin film with a thickness of 1Å (0.1 nm) or more, and the surface roughness is made to be Ra = 0.2 µm or less. Further, the ink repellent film 31 is preferably 0.1pm or more in thickness and more preferably 0.5 µm or more. As illustrated in FIG. 9C, when ink 3 is filled, the meniscus (liquid level) P resulting from a silicone resin film is formed on the border between the ink repellent film 31 and the nozzle plate 32. An ink repellent film formed on a nozzle plate having an ink discharging opening (nozzle) of the inkjet head is formed so as to have an opening along with the ink discharging opening, and the opening is formed so that the cross-sectional area on the flat face perpendicular to the center line of the opening becomes gradually larger as the distance from the face of the nozzle plate increases in the vicinity of the opening. The shape of the ink repellent film in the vicinity of the opening is preferably in a curved face. Further, the curvature radius of the curve in the vicinity of the opening of an ink repellent film at the cross section of a flat face including the center line of the opening is preferably greater than the thickness of the ink repellent film. Further, it is preferable that a curve from the brim of the opening of the ink repellent film at the cross section on a flat face including the center line of the opening to the vicinity of the opening is approximately an arc curve and the curvature radius of the arc is greater than the thickness of the ink repellent film. It is also preferable that a tangent line passing through the brim of the opening of the ink repellent film at the cross section of the flat face including the center line of the opening forms an angle of 90 degrees with respect to the surface of the nozzle member including the edge thereof. The opening of the nozzle plate 32 is formed in such a way that the cross section of the flat face perpendicular to the center line indicated by the single dot and dash line in FIG. 9 A through FIG. 9C is approximately circular at the center of the center line. Further, the ink repellent film 31 formed on an ink discharging face of the nozzle plate 32 is formed so that the cross-sectional area of the opening of the flat face perpendicular to the center line becomes larger as it moves away from the nozzle plate 32. More specifically, as illustrated in FIG. 9A, the opening of the ink repellent film 31 is provided with a curve from the brim of the opening of the nozzle plate 32 to the vicinity of the opening, which is given a round shape with a curvature radius of r. The curvature radius of r is preferably greater than the thickness of d except for the vicinity of the opening of the ink repellent film 31. The thickness of d is a thickness at parts other than the round part which is the opening of the ink repellent film 31 and may be preferably a maximum thickness of the ink repellent film. As described above, the opening of the ink repellent film 31 connected to the opening of the nozzle plate 32 is shaped to be free of approximately sharp edges (a smooth curve free of acuminate portions) and given a curve free of catching portions, thereby making it possible to remove such a defect where a wiper made with a material, for example, rubber, is used to wipe, sharp portions are caught by the wiper and the ink repellent film 31 is detached from the nozzle plate 32. Further, as illustrated in FIG. 9B, it is preferable that a tangent line passing through the brim of the opening of the ink repellent film 31 at the cross section of the flat face including the center line of the opening of the nozzle plate 32 forms an angle 0 of less than 90 degrees with respect to the surface of the nozzle plate 32 including the brim of the opening of the nozzle plate 32 connected to the brim of the opening. Since an angle of 9 which a tangent line at the brim of the opening of the ink repellent film 31 forms with the surface of the nozzle plate is less than 90 degrees, as illustrated in FIG. 9C, the meniscus (liquid level) P is stably formed at a border between the ink repellent film 31 and the nozzle plate 32. Therefore, such a possibility can be greatly reduced that the meniscus P is formed at other portions. As a result, a meniscus-forming face is made stable, by which ink can be jetted stably and favorably when an image is formed by using an image forming apparatus in which an inkjet head including the nozzle plate 32 is used. The silicone resin used in the present embodiment is preferably a liquid silicone resin which cures at room temperature and more preferably that involved in hydrolysis reaction. SR 2411 manufactured by Dow Corning Toray Co., Ltd. was used in the examples to be described later. Table A below shows the results of evaluation made for the shape of the nozzle plate 32 from the brim of the opening to the vicinity of the brim of the opening on the ink repellent film 31 at the inkjet head of the present embodiment, ink retained around the nozzle, edge detachment, and jetting stability. The results of Table A reveal that where approximately sharp edges are included in the edge portion of the ink repellent film 31 (near the brim of the opening), ink is retained around the nozzle, and the edge is detached when the ink is wiped. There is found no ink retained where the ink head has round shape, i.e. no shape edge. However, a partial edge detachment is found, where r is smaller than d as illustrated in FIG. 10A. Where 9 is greater than 90 degrees as illustrated in FIG. 10B, ink droplets are unstably jetted. Further, where r is smaller than d and 6 is greater than 90 degrees as illustrated in FIG. 10C, there are cases where the meniscus (liquid level) P is formed at a border between the ink repellent film 31 and the nozzle plate 32 on ink filling, and where the meniscus Q is formed at a projected portion toward the center of the opening on the ink repellent film 31' (a portion at which the cross-sectional area perpendicular to the center line of the opening is made smallest). As a result, there may be found a variance in jetting stability of ink when an inkjet recording apparatus equipped with an inkjet head including the nozzle plate 32 is used to record images. Next, an explanation will be made for a method for producing a nozzle member of the inkjet head related to the present embodiment. FIG. 11 is a view for illustrating a constitution in which a silicone resin is coated by using a dispenser 34 related to the present embodiment to form the ink repellent film 31. A dispenser 4 is arranged for coating a silicone solution on the ink discharging face of the nozzle 32 prepared by Ni electro-casting, and the dispenser 4 is scanned while silicone is discharged from the leading end of a needle 35 in such a way that the nozzle plate 32 is kept away from the leading end of the needle 35 at a predetermined distance, by which a silicone resin film can be formed selectively on the ink discharging face of the nozzle plate 32, as illustrated in FIG. 8 and FIG. 9A through FIG. 9C. The silicone resin used in the present embodiment was a silicone resin which cures at room temperature, that is, SR 2411 (Dow Corning Toray Co., Ltd., viscosity: 10 mPa•s). However, there was found some silicone entered around the nozzle port and the back face of the nozzle plate. The thus selectively formed silicone resin film was 1.2 µm in thickness and 0.18 µm in surface roughness (Ra). As illustrated in FIG. 12A, a coating hole at the leading end of the needle 35 related to the present embodiment is secured to be wide only by the width to be coated on the nozzle plate 32, which is a target to be coated. This fact makes it possible to completely coat all over the target to be coated by scanning the dispenser 34 only once toward the coating direction. In other words, a scanning direction for coating motions can be set only in one direction, thereby eliminating the necessity for changing the direction or conducting a reverse scanning as in FIG. 12B. In this instance, as illustrated in FIG. 12B, the leading end of a general-type needle 35 is much narrower than the width to be coated on the nozzle plate 32, which is a target to be coated. Therefore, in order to completely coat all over the target to be coated, it is necessary to move the target by changing the scanning direction for coating motions by 90 degrees or conducting a reverse scanning in several different directions, thus making it difficult to coat all over the target to be coated at a uniform thickness. According to the present embodiment, a coating hole at the leading end of the needle 35 is secured to be wide only by the width to be coated on the nozzle plate 32, which is a target to be coated. Thereby, the target to be coated can be coated all over at a uniform thickness to provide an accurate surface finishing. FIG. 13 is a view for illustrating coating motions when the dispenser 34 of the present embodiment is used. Although similar in basic constitution as in FIG. 11, silicone is coated while a gas 36 is jetting from a nozzle port (opening) of the nozzle plate 32. The gas 36 may include any type of gas which is less likely to cause chemical reactions with silicone to be coated. For example, air may be used. The gas 36 is coated while being jetted from the nozzle port, thereby making it possible to form a silicone resin film only on the surface of the nozzle except for the nozzle port of the nozzle plate 32. Further, as described above, the gas 36 is not jetted but a similar silicone resin is used to coat, thereby the silicone resin is allowed to enter into a predetermined depth. Thereafter, the gas 36 is jetted from the nozzle 32, thus making it possible to form an ink repellent layer of the silicone resin up to a desired depth on the inner wall of the nozzle (for example, about several µm), as illustrated in FIG. 14. In other words, besides the ink repellent film 31 on the ink discharging face, it is possible to form quite a thin ink repellent film 31a (ink repellent film on the inner wall of the opening) up to a predetermined depth from the brim of the opening on the nozzle plate 32. The thus prepared ink repellent film 31 of the nozzle plate was wiped by using EPDM rubber (rubber hardness of 50 degrees). As a result, after the ink repellent film 31 of the nozzle plate was wiped 1000 times, it was able to retain favorable ink repellency. Further, a nozzle member on which the ink repellent film was formed, was submerged into ink at 70°C for 14 days. As a result, ink repellency was successfully retained, which remained unchanged thereafter. FIG. 15 is a view for illustrating one example of the inkjet head of the present invention and also a state at which the nozzle port is formed by excimer laser machining. The nozzle plate 43 is such that in which a resin member 121 is joined with a highly rigid member 125 with a thermoplastic adhesive agent 126. The resin member 121 is prepared by sequentially laminating a SiO2 thin film layer 122 and a fluorine-based water repellent layer 123 on the surface thereof. The resin member 121 is provided with a nozzle port 44 having a predetermined diameter, and the highly rigid member 125 is provided with a port 127 which is communicatively connected to the nozzle port 44. The SiO2 thin film layer 122 is formed by a method which is relatively low in thermal consumption, that is, in which the film can be formed in a temperature range where the resin member is not thermally influenced. More specifically, preferable are sputtering ion beam enhanced deposition, ion plating, CVD (chemical vapor deposition), PCVD (plasma chemical vapor deposition) and others. It is desirable in terms of the processing time and material cost to make the SiO2 thin film layer 122 as thin as possible to such an extent as to secure adhesion. Where the layer is excessively thick, there may be found a problem in processing a nozzle port by excimer laser. In other words, even where the resin member 121 is neatly machined into a nozzle port shape, a part of the SiO2 thin film layer 122 is not satisfactorily treated, with some of the layer not being treated. Therefore, specifically, when consideration is given to a fact that adhesion is secured and no SiO2 thin film layer 122 is left untreated on treatment by the excimer laser, the thickness is preferably in a range of 1 Å to 300 A (0.1 nm to 30 nm) and more preferably from 10 Å to 100 Å (1 nm to 10 nm). Experimental results revealed that the thickness of the SiO2 thin film of 30 Å (3 nm) yielded a sufficient adhesion and no problem was found at all in relation to excimer laser machining. Further, the SiO2 thin film layer 122 was left untreated only to a slight extent at 300 Å (30 nm) and still usable. Where the thickness exceeded 300 Å (30 nm), a relatively large part of the film layer was left untreated and the nozzle was deformed to an unusable extent. The ink repellent layer may be made with any material, as long as it is able to repel ink. Specifically, included are fluorine-based water-repellent materials and silicone-based water repellent materials. Various materials are known as fluorine-based water repellent materials. In this instance, a mixture of perfluoro polyoxetane with modified perfluoro polyoxetane (product name: Optool DSX, manufactured by Daikin Industries, Ltd.) is deposited to give a thickness of 1 Å to 30 Å (0.1 nm to 3 nm), thereby obtaining a necessary water repellency. Experimental results revealed that there was no difference in water repellency and wiping resistance when the thickness of Optool DSX was 10 Å, 20 Å or 30 Å. Thus, with the cost taken into account, the thickness is preferably from 1 Å to 20 Å (0.1 nm to 2 nm). However, some of ink to be used may be kept for performance for a longer time when a water repellent film is made thicker in view of reliability. In this instance, the thickness is preferably from 100 Å to 200 Å (10 nm to 20 nm). Further, an adhesive tape 124 prepared by coating an adhesive material on a resin-made film is pasted on the surface of the fluorine-based water repellent layer 123, thereby giving a supplementary function on treatment by an excimer laser. Silicone-based water repellent materials are also usable. The silicone-based water repellent materials include a silicone resin and an elastomer which can cure at room temperature. They are preferably coated on the surface of a base material and subjected to polymerization and curing when allowed to stand at room temperature in the atmosphere, thereby forming an ink repellent film. The above-described silicone-based water repellent material is a heat-curable liquid silicone resin or elastomer. The material may be such that which is coated on the surface of a base material and cured after heat treatment, thereby forming an ink repellent film. The silicone-based water repellent material may be an ultraviolet-ray curable liquid silicone resin or elastomer, which is coated on the surface of a base material and cured on exposure to ultraviolet rays, thereby forming an ink repellent film. The silicone-based water repellent material is preferably 1000 cp (centipoise) or less in viscosity. FIG. 16 is a view for illustrating a constitution of the excimer laser machine used in machining the nozzle port. Excimer laser beam 82 emitted from a laser oscillator 81 is reflected by mirrors 83, 85, 88, and led to a processing table 90. A beam expander 84, a mask 86, a field lens 87 and an image forming optical system 89 are provided at predetermined positions on a light path until the laser beam 82 arrives at the processing table 90 so that an optimal beam can be given to a work piece. The work piece (nozzle plate) 91 is placed on the processing table 91 to receive the laser beam. The processing table 90 is constituted with a known XYZ table or the like and designed to move the work piece 91, when necessary, and radiate the laser beam at a desired point. In this instance, the laser was explained by referring to excimer laser. A laser is usable in various types as long as it is an ultraviolet-ray laser of a short wavelength by which ablation processing can be conducted. FIG. 17A to FIG. 17E are views for graphically illustrating a step of manufacturing a nozzle plate in a method for manufacturing the inkjet head of the present invention. FIG. 17A illustrates a material which is used as a base material of a nozzle forming member. In this instance, a polyimide film manufactured by Dupont Inc., for example, Kapton (product name) film free of particles is used as a resin film 121. Regarding a general-use polyimide film, particles of SiO2 (silica) or others are added to the film material in view of the handling property (lubricating property) in a roll-film handling apparatus. When a nozzle port is machined by the excimer laser, particles of SiO2 (silica) are poorly machined by the excimer laser, thereby resulting in deformation of the nozzle. For this reason, in the present invention, such a film is used that the particles of SiO2 (silica) are not added. Further, as a base material of the plate, Upilex, a polyimide film manufactured by Ube Industries, Ltd., may be used. Upilex is extremely fine in particles and can be used as it is, as a result of being free from any machining problems. FIG. 17B is a view for illustrating a step of forming a SiO2 thin film layer 122 on the surface of the resin film 121. The SiO2 thin film layer 122 is desirably formed by a sputtering method which is conducted at a vacuum chamber, with the preferable film thickness being in a range from about 1Å to 300Å (0.1 nm to 30 nm). In this instance, the film is formed from about 10Å to 100Å (1 nm to 10 nm) in thickness. The sputtering is effectively conducted by a method in which after Si is sputtered, the surface of Si is exposed to O2 ion, thereby forming a SiO2 film, due to a fact that the SiO2 film is improved in adhesion on the resin film 121 to provide uniform and compact film, which is more effective in improving the wiping resistance of water repellent film. FIG. 17C is a view for illustrating a step of coating a fluorine-based water repellent 123a. This repellent can be coated by methods such as spin coating, roller coating, screen printing and spray coating. A film form method by vacuum deposition is more effective because of improvement in adhesion of the water repellent film. Further, the vacuum deposition is conducted, as it is, at a vacuum chamber after formation of the SiO2 thin film layer 122 given in FIG. 17B, thereby providing better effects. Conventionally, after formation of the SiO2 thin film layer 122, a work piece is once taken out from the vacuum chamber and impurities or the like may attach on the surface, which may affect the adhesion of the film layer. It is noted that various types of fluorine-based water repellent materials are known. In this instance, perfluoro polyoxetane, modified perfluoro polyoxetane, or a mixture of them is used as a fluorineamorphous compound, thus making it possible to obtain water repellency required for ink. The previously described Optool DSX manufactured by Daikin Industries, Ltd. is from time to time called "alcoxysilane terminal modified perfluoropoly ether." FIG. 17D is a view for illustrating a step of allowing the water repellent film after vacuum deposition to stand in the atmosphere. This step makes it possible that the fluorine-based water repellent 123a and the SiO2 thin film layer 122 are chemically bonded through water contained in the atmosphere to form a fluorine-based repellent layer 123. FIG. 17E is a view for illustrating a step of pasting an adhesive tape 124. The adhesive tape 124 is pasted on the face on which the fluorine-based water repellent layer 123 is coated. The adhesive tape 124 should be pasted so as not to generate bubbles. There may be a case where a nozzle port formed at a position where bubbles are present is deteriorated in quality by attachments on machining due to the presence. FIG. 17F is a view for illustrating a step of machining a nozzle port 44. In this step, the excimer laser is radiated from the side of polyimide film 121 to form the nozzle port 44. After the nozzle port 44 is machined, the adhesive tape 124 is removed to use the nozzle port. It is noted that an explanation was omitted for a highly rigid member 125 used in increasing the rigidity of the nozzle plate 43 given in FIG. 15. This step is preferably conducted between the step given in FIG. 17D and that given in FIG. 17E. FIG. 18 is a view for briefly illustrating an apparatus used in manufacturing an inkjet head by a method for manufacturing the inkjet head of the present invention. The apparatus is that for realizing a method called "meta mode process" which has been developed by OCLI (Optical Coating Laboratory Inc., USA) and used in preparing an anti-reflection film and an anti-fouling film used on a display or the like. As illustrated in FIG. 18, a Si sputter 202, an O2 ion gun 203, a Nb sputter 204 and an Optool deposition 205, which are stations, are arranged at four sites around a drum 210, and they are all at a vacuum chamber. First, the Si sputter 202 is used to effect sputtering, and the O2 ion gun 203 is then used to radiate O2 ions to Si, thereby producing SiO2. Thereafter, the Nb sputter 204 and the Optool deposition 205 are used to appropriately deposit Optool DSX. In manufacturing an anti-reflection film, the necessary number of Nb and SiO2 are overlapped at a predetermined thickness and then deposited. Since the present invention does not require a function of the anti-reflection film, it is sufficient to paste SiO2 and Optool DSX, with one layer each, without using Nb. As described above, this apparatus makes it possible to vacuum-deposit Optool DSX, as it is, at a vacuum chamber after formation of the SiO2 thin film layer 122. The ink repellent layer is preferably from 5 mN/m to 40 mN/m in critical surface tension and more preferably from 5 mN/m to 30 mN/m. Where the critical surface tension exceeds 30 mN/m, there is found a phenomenon that ink is excessively wet on a nozzle plate when used for a long time to result in a bend discharging of the ink or abnormal granulation after a repeated printing. Where it exceeds 40 mN/m, there is found a phenomenon that the ink is excessively wet on the nozzle plate from the beginning to result in a bend discharging of the ink or abnormal granulation from the beginning. The ink-repellent materials listed in Table B were actually coated on an aluminum substrate, heated and dried to manufacture a nozzle place having an ink repellent layer. An ink repellent layer was measured for critical surface tension to obtain the results shown in Table 2. In this instance, the critical surface tension can be measured by using the Zisman method. In other words, a liquid, the surface tension of which is known, is dropped on the ink repellent layer to measure the contact angle of θ, the surface tension of the liquid is plotted on the x axis and cos θ is plotted on the y axis, thereby obtaining a line on the downward side (Zisman Plot). When this line is to give Y = 1 (θ =0), the surface tension can be calculated as a critical surface tension, Yc The critical surface tension can be measured also by such methods as Fowkes method, the Owens and Wendt method and the Van Oss method. Further, a nozzle plate having an ink repellent layer was used to manufacture an inkjet head by a method similar to that for manufacturing the head. The cyan ink described below was used and jetted through the inkjet head. A shooting process of the ink was videotaped and observed to confirm that a normal granulation took place when either of the nozzle plates was used and discharge was also stable. The results are shown in Table B. Copper phthalocyanine pigment-containing polymer fine particle dispersion of 20.0 % by mass, 3-methyl 1,3-butane diol of 23.0 % by mass, glycerin of 8.0 % by mass, 2-ethyl-l,3-hexane diol of 2.0 % by mass, FS-300 (manufactured by Dupont) of 2.5 % by mass as a fluorochemical surfactant, Proxel LV (manufactured by Abecia Inc.) of 0.2 % by mass as an anti-septic/anti-mildew agent, 2-amino-2-ethyl-1,3-propane diol of 0.5 % by mass and an appropriate quantity of ion exchanged water were added to give 100 % by mass, and, thereafter, the resultant was filtered through a membrane filter with an average pore size of 0.8 µm. The cyan ink was prepared by the above procedures. A frame 10, which is to form an ink supply port and engraved to give a common liquid chamber 12 in FIG. 6, is manufactured by resin molding. In the thus constituted inkjet head, a driving wave pattern (pulse voltage of 10 V to 50 V) is applied to a driving portion 56 according to recording signals, by which the driving portion 56 is displaced toward a direction of lamination, and a pressure liquid chamber 22 is given pressure via a nozzle plate 30 to result in pressure elevation, thereby ink droplets are discharged from a nozzle 31. Thereafter, when ink droplets are completely discharged, ink pressure inside the pressure liquid chamber 22 is decreased to develop a negative pressure inside the pressure liquid chamber 22 due to the inertia of ink flow and electrical discharge process of the driving pulse. The step is then moved to an ink filling step. In this instance, ink supplied from an ink tank flows into a common liquid chamber 12, passing a fluid resistance portion 21 through an ink flowing port 63 from the common liquid chamber and is filled into the pressure liquid chamber 22. The fluid resistance portion 21 is effective in attenuating the residual pressure oscillation after the discharge but resistive to refill by utilizing the surface tension. An appropriate fluid resistance portion is selected, thereby the residual pressure is attenuated in conformity with the refill time, making it possible to shorten the time necessary for moving on to the next ink droplet discharging motion (driving cycle). An ink recorded matter made by the inkjet recording apparatus according to the inkjet recording method of the present invention is provided with an image formed on a recording medium by using the recording ink of the present invention. The ink record matter is high in image quality, free of oozed ink and excellent in stability with the lapse of time, therefore, finding favorably a variety of applications as documents and others in which various types of printing and imaging are recorded. Examples Hereinafter, an explanation will be made for examples of the present invention. It should be, however, noted that the present invention is not restricted by the examples in any way. (Preparation Example 1) -Preparation of a surface treated carbon black pigment dispersion - 1 mol/L sodium persulfate was added to 100 g of carbon black having a primary particle size of 16 nm, specific surface area of 260 m2/g, and DBP oil absorption of 69 mL/100g (#960, manufactured by Mitsubishi Chemical Corporation), and the mixture was stirred at 80°C for 10 hours so as to proceed with an oxidation treatment. Then, the resultant was washed with purified water and dried, thereafter, dispersed again in water and neutralized with sodium hydroxide so as to give pH of 7, with remaining salts being separated by an ultra-filter. Water to be added was adjusted so as to the pigment concentration of 20% by mass, and a membrane filter with a pore size of 0.8 µm was used to remove large particles therefrom. The thus prepared dispersion was 1.35 mS/cm in electric conductivity and 123 nm in volume average particle size. It is noted that the carbon black was measured for a volume average particle size by using Microtrac UPA (manufactured by Nikkiso Co., Ltd.). (Preparation Example 2) -Preparation of surface-treated carbon black pigment dispersion- 1 mol/L sodium hypochlorite was added to 100 g of carbon black having a primary particle size of 16 nm, specific surface area of 260 m2/g, and DBP oil absorption of 69 mL/100g (#960, manufactured by Mitsubishi Chemical Corporation), and the mixture was stirred at 80°C for 10 hours so as to proceed with an oxidation treatment. Then, the resultant was washed with purified water and dried, thereafter, dispersed again in water and neutralized with potassium hydroxide so as to give pH of 7, with remaining salts being separated by an ultra-filter. Water to be added was adjusted so as to attain the pigment concentrations of 20 % by mass, and a membrane filter with a pore size of 0.8 µm was used to remove large particles. The thus obtained dispersion was 1.3 mS/cm in electric conductivity and 128 nm in volume average particle size. It is noted that the carbon black was measured for a volume average particle size by using Microtrac UPA (manufactured by Nikkiso Co., Ltd.). (Preparation Example 3) -Preparation of surface-treated carbon black pigment dispersion- 3L of purified water was added to 100 g of carbon black having a primary particle size of 16 nm, specific surface area of 260 m2/g, and DBP oil absorption of 69 mL/100g (#960, manufactured by Mitsubishi Chemical Corporation), and the mixture was stirred for 5 minutes. Then, ozone gas was introduced so as to proceed with an oxidation treatment for 1 hour. The resultant was washed with purified water and dried, thereafter, dispersed again in water and neutralized with sodium hydroxide so as to give pH of 7, with remaining salts being separated by an ultra-filter. Water to be added was adjusted so as to attain the pigment concentration of 20% by mass, and a membrane filter with a pore size of 0.8 µm was used to remove large particles. The thus obtained dispersion was 1.25 mS/cm in electric conductivity and 132 nm in volume average particle size. It is noted that the carbon black was measured for a volume average particle size by using Microtrac UPA (manufactured by Nikkiso Co., Ltd.). (Preparation Example 4) -Preparation of surface-treated carbon black pigment dispersion- 1 mol/L sodium hypochlorite was added to 100 g of carbon black having a primary particle size of 16 nm, specific surface area of 260 m2/g, and DBP oil absorption of 69 mL/100g (#960, manufactured by Mitsubishi Chemical Corporation), and the mixture was stirred at 100°C for 15 hours so as to proceed with an oxidation treatment. Then, the resultant was washed with purified water and dried, thereafter, dispersed again in water and neutralized with potassium hydroxide so as to give pH of 7, with remaining salts being separated by an ultra-filter. Water to be added was adjusted so as to attain the pigment concentration of 20% by mass, and a membrane filter with the pore size of 0.8 µm was used to remove large particles. The thus obtained dispersion was 1.38 mS/cm in electric conductivity and 126 nm in volume average particle size. It is noted that the carbon black was measured for a volume average particle size by using Microtrac UPA (manufactured by Nikkiso Co., Ltd.). (Preparation Example 5) -Preparation of surface-treated carbon black pigment dispersion- 1 mol/L sodium persulfate was added to 100 g of carbon black having a primary particle size of 21 nm, specific surface area of 135 m2/g, and DBP oil absorption of 53 mL/100g (#7550, manufactured by Tokai Carbon Co., Ltd.), and the mixture was stirred at 80°C for 10 hours so as to proceed with an oxidation treatment. Then, the resultant was washed with purified water and dried, thereafter, dispersed again in water and neutralized with sodium hydroxide so as to give pH of 7, with remaining salts being separated by an ultra-filter. Water to be added was adjusted so as to attain the pigment concentration of 20% by mass, and a membrane filter with a pore size of 0.8 µm was used to remove large particles. The thus obtained dispersion was 1.2 mS/cm in electric conductivity and 61 nm in volume average particle size. It is noted that the carbon black was measured for a volume average particle size by using Microtrac UPA (manufactured by Nikkiso Co., Ltd.). (Preparation Example 6) -Preparation of surface-treated carbon black pigment dispersion- 1 mol/L sodium persulfate was added to 100 g of carbon black having a primary particle size of 24 nm, specific surface area of 120 m2/g, and DBP oil absorption of 57 mL/100g (MA8, manufactured by Mitsubishi Chemical Corporaton), and the mixture was stirred at 80°C for 10 hours so as to proceed with an oxidation treatment. Then, the resultant was washed with purified water and dried, thereafter, dispersed again in water and neutralized with sodium hydroxide so as to give pH of 7, with remaining salts being separated by an ultra-filter. Water to be added was adjusted so as to attain the pigment concentration of 20 % by mass, and a membrane filter with a pore size of 0.8 µm was used to remove large particles. The thus obtained dispersion was 1.23 mS/cm in electric conductivity and 55 nm in volume average particle size. It is noted that the carbon black was measured for a volume average particle size by using Microtrac UPA (manufactured by Nikkiso Co., Ltd.). (Preparation Example 7) -Preparation of surface-treated carbon black pigment dispersion- 1 mol/L sodium persulfate was added to 100 g of carbon black having a primary particle size of 20 nm, specific surface area of 140 m2/g, and DBP oil absorption of 131 mL/100g (MA600, manufactured by Mitsubishi Chemical Corporaton), and the mixture was stirred at 80°C for 10 hours so as to proceed with an oxidation treatment. Then, the resultant was washed with purified water and dried, thereafter, dispersed again in water and neutralized with sodium hydroxide so as to give pH of 7, with remaining salts being separated by an ultra-filter. Water to be added was adjusted so as to attain the pigment concentration of 20 % by mass, and a membrane filter with a pore size of 0.8 µm was used to remove large particles. The thus obtained dispersion was 1.35 mS/cm in electric conductivity and 205 nm in volume average particle size. It is noted that the carbon black was measured for a volume average particle size by using Microtrac UPA (manufactured by Nikkiso Co., Ltd.). (Example 1) An ink composition with the following formulation was prepared and triethanol amine was added so as to attain pH of 9. Thereafter, the composition was filtered by using a membrane filter with an average pore size of 0.8 pm to prepare ink. •Carbon black dispersion of Preparation Example l: 9.0 % by mass (solids content) • 1,5-pentane diol- 22.5 % by mass •Glycerin: 7.5 % by mass •Surfactant (Softanol EP 7025, manufactured by Nippon Shokubai Co., Ltd.): 1.0 % by mass •Ion exchanged water: 60.0 % by mass (Example 2) An ink composition with the following formulation was prepared and triethanol amine was added so as to attain pH of 9. Thereafter, the composition was filtered by using a membrane filter with an average pore size of 0.8 µm to prepare ink. •Carbon black dispersion of Preparation Example 2' 8.0 % by mass (solids content) •Acryl resin fine particles (Aquabrid 4720 manufactured by Daicel Chemical Industries, Ltd., volume average particle size = 95nm): 5.0 % by mass (solids content) •3-methyl-l,3-butane diol: 21.0 % by mass • Glycerin: 7.0 % by mass • Surfactant (Softanol EP 7025, manufactured by Nippon Shokubai Co., Ltd.): 1.0 % by mass •pH buffering agent expressed by the following formula (4): 0.1 % by mass (HOCH2CH2)2NCH2COOH: formula (4) •Ion exchanged water: 57.9 % by mass (Example 3) An ink composition with the following formulation was prepared and triethanol amine was added so as to attain pH of 9. Thereafter, the composition was filtered by using a membrane filter with an average pore size of 0.8 µm to prepare ink. •Carbon black dispersion of Preparation Example 5: 8.0 % by mass (solids content) •Acryl resin fine particles (Aquabrid 4720 manufactured by Daicel Chemical Industries, Ltd., volume average particle size = 95 nm - 5.0 % by mass (solids content) •3methyl-l,3butane diol: 21.0 % by mass •Glycerin: 7.0 % by mass • Surfactant (Softanol EP 7025, manufactured by Nippon Shokubai Co., Ltd.): l.o % by mass •pH buffering agent expressed by the following formula (8): 0.1 % by mass •Ion exchanged water: 57.9 % by mass (Example 4) An ink composition with the following formulation was prepared and triethanol amine was added so as to attain pH of 9. Thereafter, the composition was filtered by using a membrane filter with an average pore size of 0.8 µm to prepare ink. •Carbon black dispersion of Preparation Example 6: 8.0 % by mass (solids content) •Acryl resin fine particles (Aquabrid 4720 manufactured by Daicel Chemical Industries, Ltd., volume average particle size = 95 nm) : 5.0 % by mass (solids content) •3-methl-1,3-butane diol: 21.0 % by mass •Glycerin: 7.0 % by mass • Surfactant (Softanol EP 7025, manufactured by Nippon Shokubai Co., Ltd.): 1.0 % by mass •Ion exchanged water: 58.0 % by mass (Example 5) An ink composition with the following formulation was prepared and triethanol amine was added so as to attain pH of 9. Thereafter, the composition was filtered by using a membrane filter with an average pore size of 0.8 µm to prepare ink. •Carbon black dispersion of Preparation Example 7: 8.0 % by mass (solids content) •Acryl resin fine particles (Aquabrid 4720 manufactured by Daicel Chemical Industries, Ltd., volume average particle size = 95 nm): 5.0 % by mass (solids content) •3- methyl-l,3-butane diol: 21.0 % by mass •Glycerin: 7.0 % by mass •Surfactant (Softanol EP 7025, manufactured by Nippon Shokubai Co., Ltd.): 1.0 % by mass •Ion exchanged water: 58.0 % by mass (Example 6) An ink composition with the following formulation was prepared and triethanol amine was added so as to attain pH of 9. Thereafter, the composition was filtered by using a membrane filter with an average pore size of 0.8 µm to prepare ink. •Carbon black dispersion of Preparation Example 1 : 14.0 % by mass (solids content) •Acryl resin fine particles (Aquabrid 4720 manufactured by Daicel Chemical Industries, Ltd., volume average particle size = 95 nm): 2.0 % by mass (solids content) • l,3butane diol: 21.0 % by mass •Glycerin: 7.0 % by mass • Surfactant (Softanol EP 7025, manufactured by Nippon Shokubai Co., Ltd.): 1.0 % by mass •Ion exchanged water: 55.0 % by mass (Example 7) An ink composition with the following formulation was prepared and triethanol amine was added so as to attain pH of 9. Thereafter, the composition was filtered by using a membrane filter with an average pore size of 0.8 µm to prepare ink. •Carbon black dispersion of Preparation Example l: 4.0 % by mass (solids content) •Acryl resin fine particles (Aquabrid 4720 manufactured by Daicel Chemical Industries, Ltd., volume average particle size = 95 nm): 2.0 % by mass (solids content) • 1,6-hexane diol: 24.0 % by mass •Glycerin: 8.0 % by mass •Surfactant (Softanol EP 7025, manufactured by Nippon Shokubai Co., Ltd.): 1.0 % by mass •Ion exchanged water: 61.0 % by mass (Example 8) An ink composition with the following formulation was prepared and triethanol amine was added so as to attain pH of 9. Thereafter, the composition was filtered by using a membrane filter with an average pore size of 0.8 µm to prepare ink. •Carbon black dispersion of Preparation Example 1- 7.0 % by mass (solids content) •Acryl resin fine particles (Aquabrid 4720 manufactured by Daicel Chemical Industries, Ltd., volume average particle size = 95 nm): 4.0 % by mass (solids content) • 1,3-butane diol: 21.0 % by mass •Glycerin-' 7.0 % by mass •Surfactant expressed by the formula (l) (m =2, n =10): 1.0 % by mass •Ion exchanged water: 61.0 % by mass (Example 9) An ink composition with the following formulation was prepared and triethanol amine was added so as to attain pH of 9. Thereafter, the composition was filtered by using a membrane filter with an average pore size of 0.8 µm to prepare ink. •Carbon black dispersion of Preparation Example 1: 16.0 % by mass (solids content) • 1,3-butane diol: 21.0 % by mass •Glycerin: 7.0 % by mass •Surfactant (Softanol EP 7025, manufactured by Nippon Shokubai Co., Ltd.): 1.0 % by mass •Ion exchanged water: 55.0 % by mass (Example 10) An ink composition with the following formulation was prepared and sodium hydroxide was added so as to attain pH of 9. Thereafter, the composition was filtered by using a membrane filter with an average pore size of 0.8 µm to prepare ink. •Carbon black dispersion of Preparation Example l: 7.0 % by mass (dry solid basis) •Acryl resin fine particles (Aquabrid 4720 manufactured by Daicel Chemical Industries, Ltd., volume average particle size = 95 nm): 4.0 % by mass (solids content) • 1.3butane diol: 21.0 % by mass •Glycerin: 7.0 % by mass •Surfactant (Softanol EP 7025, manufactured by Nippon Shokubai Co., Ltd.): 1.0 % by mass Ion exchanged water: 60.0 % by mass (Comparative Example 1) An ink composition with the following formulation was prepared and triethanol amine was added so as to attain pH of 9. Thereafter, the composition was filtered by using a membrane filter with an average pore size of 0.8 µm to prepare ink. •Carbon black dispersion of Preparation Example 3: 6.0 % by mass (solids content) •3-methyl-l,3-butane diol: 21.0 % by mass •Glycerin:7.0 % by mass •Surfactant (Softanol EP 7025, manufactured by Nippon Shokubai Co., Ltd.): 1.0 % by mass •Ion exchanged water: 63.0 % by mass (Comparative Example 2) An ink composition with the following formulation was prepared and triethanol amine was added so as to attain pH of 9. Thereafter, the composition was filtered by using a membrane filter with an average pore size of 0.8 µm to prepare ink. • Carbon black dispersion of Preparation Example 4: 8.0 % by mass (solids content) •3methyl-1,3butane diol: 21.0 % by mass •Glycerin: 7.0 % by mass • Surfactant (Softanol EP 7025, manufactured by Nippon Shokubai Co., Ltd.) - 1.0 % by mass •Ion exchanged water: 62.0 % by mass (Comparative Example 3) • Carbon black A (# 47 manufactured by Mitsubishi Chemical Corporation): 15 % by mass • Joncryl 68 (manufactured by Johnson polymer Co., Ltd.): 5 % by mass •Glycerin: 10 % by mass •Ion exchanged water: 70 % by mass The above materials were dispersed with glass beads in a sand mill for 3 hours, and then filtered through a membrane filter with an average pore size of 5pm to obtain a carbon black dispersion A. Using the obtained carbon black dispersion A, an ink composition with the following formulation was prepared and triethanol amine was added so as to attain pH of 9. Thereafter, the composition was filtered through a membrane filter with an average pore size of 0.8 µm to prepare ink. •Carbon black dispersion A: 7.0 % by mass (solids content) • 1,3-butane diol: 22.5 % by mass •Glycerin: 7.5 % by mass •Surfactant (Softanol EP 7025, manufactured by Nippon Shokubai Co., Ltd.): 1.0 % by mass •2,2,4-trimethyl-1, 3 pentanediol: 2.0 % by mass •Ion exchanged water: 67 % by mass Each of the thus obtained recording ink was evaluated for various properties as shown below. Tables 1 to 4 show each of the ink formulations and the results. Each recording ink was diluted with purified water and measured for a volume average particle size (D50%) by using a particle size distribution measuring device (Microtrac UPA, manufactured by Nikkiso Co., Ltd.). Measurement was made for the viscosity at 25°C by using RL-500 (manufactured by Toki Sangyo Co., Ltd.). Measurement was made for the surface tension at 23°C ± 2°C by using a static surface tension balance (BVP-Z, manufactured by Kyowa Interface Science Co., Ltd.). Measurement was made for the pH at 23°C ± 2°C by using a pH meter (HM-A, manufactured by DKKToa Corporation). Each of the thus obtained recording ink was used to test the imaging performance by using the inkjet printer shown in FIG. 3 through FIG. 7. A silicone resin film (room-temperature curing silicone resin SR 2411, manufactured by Dow Corning Toray Co., Ltd.) was formed on the surface of the nozzle plate of the inkjet printer, with a thickness of 1.2 µm, surface roughness (Ra) of 0.18 µm and critical surface tension of 21.6 mN/m. The imaging test was conducted at the super-fine mode by using high-grade plain paper under conditions of 23°C and 50 % RH. Further, the head driving wave pattern was adjusted so that the ink can be discharged at a constant quantity. The inkjet printer shown in FIG. 3 to FIG. 7 in which each recording ink prepared in Examples 1 through 10 and Comparative Examples 1 through 3 was filled was used to print on type 6200 paper (manufactured by NBS Ricoh Co., Ltd.) at a resolution of 600 dpi. After drying, measurement was made for the image density by using a reflection-type color spectrophotometer (manufactured by X-Rite). The inkjet printer shown in FIG. 3 to FIG. 7 in which each recording ink prepared in Examples 1 through 10 and Comparative Examples 1 through 3 was filled was used to print on type 6200 paper (manufactured by NBS Ricoh Co., Ltd.) at a resolution of 600 dpi. After drying, printed parts were rubbed with a cotton cloth ten times, and pigment transferred to the cotton cloth was macroscopically observed and evaluated on the basis of the following criteria. [Evaluation criteria] A: Substantially no pigment is transferred to the cotton cloth. B: Pigment is transferred to some extent. C : Pigment is clearly transferred. The inkjet printer shown in FIG. 3 to FIG. 7 in which each recording ink prepared in Examples 1 through 10 and Comparative Examples 1 through 3 was filled was used to print on type 6200 paper (manufactured by NBS Ricoh Co., Ltd.) at a resolution of 600 dpi. The printing was conducted continuously on 200 sheets of the paper to evaluate the discharge disturbance and discharge failure on the basis of the following criteria. [Evaluation criteria] A: No discharge disturbance or discharge failure is found. B: Discharge disturbance or discharge failure is found in three or less nozzles. C: Discharge disturbance or discharge failure is found in four or more nozzles. atmosphere> The inkjet printer shown in FIG. 3 to FIG. 7 in which each recording ink prepared in Examples 1 through 10 and Comparative Examples 1 through 3 was filled was used to conduct an all color cleaning. Thereafter, the ink was allowed to stand under the conditions of 32°C and 30 %RH for one month. Then, nozzles were checked for the printing performance to evaluate discharge disturbance and discharge failure on the basis of the following criteria. [Evaluation criteria] A: No discharge disturbance or discharge failure is found. B: Discharge disturbance or discharge failure is found in three or less nozzles. C : Discharge disturbance or discharge failure is found in four or more nozzles. Recording ink prepared in Examples 1 through 10 and Comparative Examples 1 through 3 were filled into cartridges and stored at 60°C for two weeks. Observation was made for an increased viscosity of the ink and change in pH. It is noted that the increased viscosity was defined as (increased viscosity of ink, %) = [(viscosity after storage) /(viscosity before storage) - 1 ] x 100. The inkjet printer shown in FIG. 3 to FIG. 7 in which each recording ink prepared in Examples 1 through 12 and Comparative Examples 1 through 3 was filled was used to print on a matt paper (Hokuetsu Paper Mills, Ltd.) at a resolution of 600 dpi. Evaluation was made for blurred characters and variance in color at a solid part. It is noted that the a matt paper was measured for a quantity of purified water transferred to a recording medium at the contact time of 100 ms by using a dynamic scanning absorptometer (DSA, manufactured by Kyowa Seiko Co., Ltd.), finding that the quantity was 3.6 mL/m2. [Evaluation criteria for blurred characters] A: Characters are very clearly printed, with no blur found. B: Characters are printed less clearly, with some blur found. C : Characters are not clearly printed, with a marked blur found. [Evaluation criteria for variance in color at solid part] A: Image is clear, with substantially no variance in color. B: Image is relatively poor in clearness, with some variance in color. C: Image is not clear, with a marked variance in color. At first, column chromatography was performed to remove additives such as a surfactant, a rust-preventive agent and an ultraviolet absorbing agent from the recording ink prepared in Examples 1 through 10 and Comparative Examples 1 through 3 and recovered a carbon black. The thus obtained carbon black was subjected to vacuum drying by using a dryer at 50 °C for sufficient evaporation of water and solvent and then diluted with water to a concentration of 20 % by mass. Fifty grams of the diluted solution was measured in a beaker, and passed through an ultra-filter (Pellicon Biomax 50, manufactured by Millipore) for 30 minutes to obtain a brown liquid. This liquid was diluted 10 times with ion exchanged water and read on a spectrophotometer (U-3310, manufactured by Hitachi High-Technologies Corporation) equipped with a quartz cell (light path length of 10 mm) at a wavelength of 230 nm to 260 nm. The thus obtained maximum absorbance was increased 10 times to determine the concentration of humic acid. Recording ink prepared in Examples 1 through 10 and Comparative Examples of 1 through 3 was diluted 10 times with ion exchanged water and measured for concentrations of sodium and potassium contained in the ink by using a high-frequency induction plasma emission analyzer (ICP-1000IV, manufactured by Shimadzu Corporation). The thus obtained values were respectively multiplied by 10 times and totaled to give the concentration of alkali metals. A predetermined quantity of the ink prepared in Examples 1, 5, 7, 9 and Comparative Examples of 1 through 3 was allowed to stand under the conditions of 50°C and 10% humidity, and measured for a change in ink mass after the passage of a certain time and the viscosity at 25°C. It is noted that a quantity of water evaporation and an increased viscosity relative to an initial viscosity were determined by the following formulae. • (Quantity of water evaporation [%]) = [ (mass of initial ink ) — (mass of ink after water evaporation)] / (mass of initial ink) x 100 • (Increased viscosity relative to initial viscosity) = (viscosity of ink after water evaporation) / (initial viscosity) FIG. 19 shows a relationship between the quantity of water evaporation (%) and the viscosity of ink (mPa•s). Further, Table 5 shows an increased viscosity relative to the initial viscosity when the water evaporation rate is from 34 % by mass to 41 % by mass. (Production Example A) —Production of Support— A support having a basis weight of 79g/m2 was produced by papermaking a slurry containing 0.3% by mass of the following formulation using a fourdrinier papermaking machine. In a size press step of the papermaking process, an aqueous solution of oxidized starch was applied to a surface of the support such that the deposited solid amount is 1.0g/m2 per one surface. •Broad-leaved wood bleached kraft pulp (LBKP): 80 parts by mass • Coniferous wood bleached kraft pulp (NBKP): 20 parts by mass •Precipitated calcium carbonate (product name: TP-121, manufactured by Okutama Kogyo Co., Ltd.): 10 parts by mass •Aluminum sulfate:1.0 part by mass •Amphoteric starch (product name: Cato3210, manufactured by Nippon NSC Ltd.): 1.0 part by mass •Neutral rosin sizing agent (product name: NeuSize M-10, manufactured by HARIMA CHEMICALS,INC.): 0.3 parts by mass •Retention aid (product name: NR-11LS, manufactured by HYMO Co..Ltd.): 0.02 parts by mass (Production Example B) —Production of Recording Medium 1— As a pigment 70 parts by mass of clay containing 97 % by mass of particles having a particle diameter of 2µm or less, 30 parts by mass of heavy calcium carbonate having an average particle diameter of 1.1µm, as an adhesive 8 parts by mass of styrenebutadiene copolymer emulsion having a glass transition temperature (Tg) of -5°C, 1 part by mass of phosphated starch, as an auxiliary agent 0.5 parts by mass of calcium stearate, and water were mixed together to prepare a coating solution containing 60 % by mass of solid content. The obtained coating solution was applied on both sides of the prepared substrate using a blade coater such that the deposited solid amount is 8 g/m2 per one surface, dried with hot air, and supercalendered to prepare "Recording Medium 1". (Production Example C) —Production of Recording Medium 2— As a pigment 70 parts by mass of clay containing 97 % by mass of particles having a particle diameter of 2µm or less, 30 parts by mass of heavy calcium carbonate having an average particle diameter of 1.1µm, as an adhesive 7 parts by mass of styrenebutadiene copolymer emulsion having a glass transition temperature (Tg) of -5°C, 0.7 parts by mass of phosphated starch, as an auxiliary agent 0.5 parts by mass of calcium stearate, and water were mixed together to prepare a coating solution containing 60 % by mass of solid content. The obtained coating solution was applied on both sides of the prepared substrate using a blade coater such that the deposited solid amount is 8 g/m2 per one surface, dried with hot air, and supercalendered to prepare "Recording Medium 2". (Production Example D) —Production of Recording Medium 3— A coated paper for gravure printing (product name: Space DX, a basis weight of 56g/m2, manufactured by Nippon Paper Industries Co., Ltd.) was used. (Production Example E) —Production of Recording Medium 4— A coat paper for offset printing (product name: Aurora Coat, a basis weight of 104.7 g/m2, manufactured by Nippon Paper Industries Co., Ltd.) was used. (Production Example F) —Production of Recording Medium 5— A matte coated paper for inkjet printing (product name: SuperFine paper, manufactured by SEIKO EPSON Corp.) was used. Next, the quantity of each of inks in Examples 3 and 5 transferred to the recording media 1 through 5 was measured by using a dynamic scanning absorptometer as follows: Beading, blur characters, drying property and OD value of an image printed in each recording medium were evaluated. The results were shown in Tables 6 and 7. absorptometer> A dynamic scanning absorptometer (K350 series D type, manufactured by Kyowa Seiko Co., Ltd.) was used to measure the quantities of transferred inks of Examples 3 and 5. Quantities transferred at the contact time of 100 ms and at the contact time of 400 ms could be determined by interpolating measurements of the quantities transferred at adjacent contact times of the respective contact times. The measurements were made at 23°C and RH of 50%. The inks of Examples 3 and 5 were printed on the recording media 1 through 5 at a resolution of 600 dpi, and beading was visually observed. [Evaluation criteria] 4: Substantially no beading and uniform printing 3: Slightly beading is observed. 2: Clearly beading is observed. 1: Outstandingly beading is observed. The inks of Examples 3 and 5 were printed on the recording media 1 to 5 at a resolution of 600 dpi, and blur characters was visually observed. [Evaluation criteria] 4: Substantially no blur and clear printing 3: Slightly blur is observed. 2: Clearly blur is observed. 1: Outstandingly blur is observed. The inks of Examples 3 and 5 were printed on the recording media 1 through 5 at a resolution of 600 dpi. Immediately after printing, a plain paper type 6200 paper (manufactured by NBS Ricoh Co., Ltd.) was put on printed parts, and pressed with a finger and then visually observed a degree of transferred on the plain paper. [Evaluation criteria] 4: No transfer is observed. 3: Slightly transfer is observed. 2: Clearly transfer is observed. l: Outstandingly transfer is observed. The inks of Examples 3 and 5 were printed on the recording media 1 through 5 at a resolution of 600 dpi. An image density of a solid image was measured by a color reflection densitometer XRite938. Industrial Applicability The recording ink of the present invention is excellent in fixing property and image density on a recording medium and also excellent in stability after a prolonged storage and able to form a high-quality image not only on plain paper or paper exclusively used for inkjet printing but also on coated paper for commercial printing poor in water absorption, thereby favorably applicable to an inkjet recording apparatus. Further, the inkjet recording apparatus and the inkjet recording method of the present invention are applicable to various types of recording by an inkjet recording method, and in particular preferably applicable, for example, to an inkjet recording printer, a facsimile device, a copying device, and a multifunction device of printer/facsimile/copier. WE CLAIM : 1. A recording ink comprising: water; a water-soluble organic solvent; a surfactant; and a carbon black having a hydrophilic group on a surface thereof, wherein the carbon black releases humic acid in an aqueous dispersion of the carbon black, which is recovered from the recording ink, a concentration of the humic acid released in the aqueous dispersion containing 20 % by mass of the carbon black is expressed with a maximum absorbance at a wavelength of 230 nm to 260 nm, and the recording ink has the maximum absorbance of 5.0 to 20.0 at the wavelength of 230 nm to 260 nm, and wherein a quantity of the alkali metal contained in the recording ink is from 100 ppm or more to 1500 ppm or less. 2. The recording ink as claimed in claim 1, wherein a content of the carbon black is from 5 % by mass to 15 % by mass with respect to the total amount of the recording ink. 3. The recording ink as claimed in any of claim 1 or 2, wherein the recording ink has a ratio B/A of from 5.0 or more to less than 550 when the recording ink has a liquid evaporation rate of 34% by mass to 41% by mass relative to a total mass of the recording ink, where A is an initial viscosity of the recording ink and B is a viscosity after liquid evaporation. 4. The recording ink as claimed in any one of claims 1 to 3, comprising a pH buffering agent. 5. The recording ink as claimed in claim 4, wherein the pH buffering agent is at least one organic pH buffering agent selected from Good's buffer solutions. 6. The recording ink as claimed in any one of claims 1 to 5, wherein the carbon black having a hydrophilic group has a volume average particle size of from 60 nm to 200 nm at the time being dispersed in water. 7. The recording ink as claimed in any one of claims 1 to 6, comprising resin fine particles having a volume average particle size of from 50 nm to 200 nm. 8. The recording ink as claimed in any one of claims 1 to 7, wherein at least a part of a terminal of the hydrophilic group on the carbon black is substituted with an alkali metal. 9. The recording ink as claimed in any one of claims 1 to 8, wherein the recording ink has a viscosity of 6 mPa•s to 20 mPa•s at 25°C. 10. An inkjet recording method comprising: applying a stimulus to the recording ink as defined in any one of claims 1 to 9, and ejecting the recording ink from a recording head so as to form an image on a recording medium, wherein the recording head is configured to have an ink discharge opening on a face of a nozzle plate, and to have an ink repellent layer formed on the face of the nozzle plate where the ink discharge opening is placed. 11. The inkjet recording method as claimed in claim 10, wherein the stimulation is at least one selected from the group consisting of heat, pressure, vibration and light. 12. The inkjet recording method as claimed in any of claim 11 or 12, wherein the ink repellent layer comprises either a fluorine-based material or a silicone-based material. 13. The inkjet recording method as claimed in any one of claims 1 0 to 12, wherein the ink repellent layer has a surface roughness Ra of 0.2 µm or less. 14. The inkjet recording method as claimed in any one of claims 10 to 13, wherein the ink repellent layer is formed so to have an opening along with the ink discharge opening, and the opening of the ink repellent layer is formed so that a cross-sectional area of a face perpendicular to a center line of the opening becomes gradually larger as a distance from the face of the nozzle plate increases in a vicinity of the opening. 15. The inkjet recording method as claimed in any one of claims 1 0 to 14, wherein the ink repellent layer has a critical surface tension Yc of from 5 mN/m to 40 mN/m. 16. The inkjet recording method as claimed in any one of claims 10 to 15, wherein the recording medium has a support and a coating layer at least on one face of the support. 17. The inkjet recording method as claimed in any one of claims 10 to 16, wherein the recording medium has a purified water transfer amount of 2 mL/m2 to 45 ml/m2 when measured at 23°C and 50% RH for a contact time of 100 ms by using a dynamic scanning absorptometer, and has a purified water transfer amount of 3 mL/m2 to 50 mL/m2 when measured at 23°C and 50% RH for the contact time of 400 ms by using a dynamic scanning absorptometer. 18. The inkjet recording method as claimed in any one of claims 16 to 17, wherein an applied amount of the coating layer is from 0.5 g/m2 to 20.0 g/m2 on a dry basis. 19. The inkjet recording method as claimed in any one of claims 10 to 18, wherein the recording medium has a basis weight of 50 g/m2 to 250 g/m2. 20. An inkjet recording apparatus comprising: an ink ejecting unit configured to apply a stimulus to the recording ink as defined in any one of claims 1 to 9, and to eject the recording ink so as to record an image on a recording medium. 21. The inkjet recording apparatus according to claim 20, wherein the stimulus is at least one selected from the group consisting of heat, pressure, vibration and light. ABSTRACT RECORDING INK, INKJET RECORDING METHOD AND INKJET RECORDING APPARATUS There is provided a recording ink containing at least: water; a water-soluble organic solvent; a surfactant; and a carbon black having a hydrophilic group on a surface thereof, wherein the carbon black releases humic acid in an aqueous dispersion of the carbon black, which is recovered from the recording ink, a concentration of the humic acid released in the aqueous dispersion containing 20 % by mass of the carbon black of is expressed with a maximum absorbance at a wavelength of 230 nm to 260 nm, and the recording ink has the maximum absorbance of 5.0 to 20.0 at the wavelength of 230 nm to 260 nm.

Full Text

DESCRIPTION
[Technical Field
The present invention relates to recording ink appropriate
for inkjet recording, an Inkjet recording method and an inkjet
recording apparatus.
Background Art
A coloring agent for inkjet recording ink is mainly based
on-a dye, and there are disadvantages that the dye ink is
inferior in water resistance and weather resistance and also
easily oozes out on plain paper. In order to eliminate these
disadvantages, such ink has been proposed that pigments, for
example, carbon black, are used.
The pigment ink is excellent in water resistance and
weather resistance and also able to record images which ooze
out to a less extent but is inferior in fixing property, which is a
problem. Therefore, an attempt has been made that various
resins are added to improve the fixing property.
For example, Patent Literature 1 has described a
recording solution which contains carbon black and a soap-free
emulsion. In records obtained by using the above-described
recording solution, a resin emulsion forms a film after drying of

ink to fix a pigment, thereby imparting scratch resistance and
water resistance, but carbon black contained in the recording
solution is dispersed by a surfactant and therefore does not have
a hydrophilic group directly on the surface. There is found a
disadvantage that the above-described recording solution
dispersed by a surfactant is poor in dispensability due to
detachment of the surfactant adsorbed on the surface of the
pigment with the lapse of time and may easily increase in
viscosity and cause aggregation.
Further, Patent Literature 2 has described a method in
which hypohalogen is used to acid-treat carbon black. Since
this method is able to introduce an aqueous dispersible
functional group onto the surface by acid treatment of carbon
black, the dispersion stability is better than that attained by
using a surfactant. However, carbon black is known to generate
humic acid due to acid treatment and the dispersion tends to
decrease in pH with the lapse of time, thereby causing a
decrease in dispersion stability and the deterioration of
members inside an ink-used recording apparatus.
Still further, Patent Literature 3 has described an ink
composition containing two or more types of resins in which a
pigment that can be dispersed or dissolved in water without a
dispersing agent is used. Carbon black which is contained in
the above-described ink composition and can be dispersed or
dissolved in water without a dispersing agent is acid-treated by

using hypochlorous acid or ozone. Since there are provided no
measures for the pH decrease with the lapse of time due to
elusion of humic acid, the ink is not satisfactory in terms of
storage stability.
In addition, Patent Literature 4 has described that
attention is given to humic acid contained in acid-treated carbon
black and where the concentration of humic acid is found to be
one or lower in terms of the absorbance, there is provided an
excellent feature of preventing clogging at a nozzle or a pen tip
due to the development of solids. However, there is a problem
that where humic acid is abundantly contained in a recording
solution, pH is decreased with the lapse of time to deteriorate
the storage stability.
[Patent Literature l] Japanese Patent (JPB) No.3489289
[Patent Literature 2] JPB No. 3405817
[Patent Literature 3] Japanese Patent Application Laid-Open
(JPA) No. 2004-204079
[Patent Literature 4] JPA No. 11349309
Disclosure of Invention
An object of the present invention is to provide a
recording ink excellent in fixing property and image density on a
recording medium, also excellent in prolonged storage stability
of ink and capable of forming a high-quality image not only on
plain paper or paper exclusively used for inkjet printing but also

on coated paper for commercial printing poor in water
absorption, and an inkjet recording method as well as an inkjet
recording apparatus.
In order to solve the above problem, the present inventor
and others have diligently conducted research, finding that
humic acid released from carbon black is contained into ink at a
predetermined quantity to increase the ink viscosity on water
evaporation, by which the carbon black undergoes a quick
aggregation on a recording medium to form an image, thereby
providing a high image density.
It has been found that a pH buffering agent is formulated
into ink, thereby making it possible to retain the storage
stability thereof, although a humic acid-containing recording ink
tends to decrease in pH with the lapse of time.
Further, in recent years, it has been desired that since
inkjet printing does not require plate-making procedures to
attain an easy printing and water-based ink is lower in
environmental impact, such ink is used to make a high-quality
printing for commercial use such as offset printing and gravure
printing. Since paper used in offset printing and gravure
printing is coated with inorganic pigments such as calcium
carbonate and kaoline or not provided with a water absorbing
layer as provided on paper exclusively used for inkjet printing,
it is inferior in absorption of water-based ink. It has been
found that in the recording ink of the present invention, a

coloring material undergoes a quick aggregation on a recording
medium to effect drying, thus making it possible to make a
high-quality recording on the recording medium poor in
absorption of the water-based ink.
The following are means for solving the above problem-
A recording ink containing at least: water; a water-soluble
organic solvent; a surfactant; and a carbon black having a
hydrophilic group on a surface thereof, wherein the carbon black
releases humic acid in an aqueous dispersion of the carbon black,
which is recovered from the recording ink, a concentration of the
humic acid released in the aqueous dispersion containing 20 %
by mass of the carbon black is expressed with a maximum
absorbance at a wavelength of 230 nm to 260 nm, and the
recording ink has the maximum absorbance of 5.0 to 20.0 at the
wavelength of 230 nm to 260 nm.
The recording ink according to , wherein a content of the
carbon black is from 5 % by mass to 15 % by mass with respect
to the total amount of the recording ink.
The recording ink according to any of or , wherein
the recording ink has a ratio B/A of from 5.0 or more to less than
550 when the recording ink has a water evaporation rate of 34%
by mass to 41% by mass relative to a total mass of the recording
ink, where A is an initial viscosity of the recording ink and B is
a viscosity after water evaporation.
The recording ink according to any one of to ,

further containing a pH buffering agent.
The recording ink according to , wherein the pH
buffering agent is at least one organic pH buffering agent
selected from Good's buffer solutions.
The recording ink according to any one of to ,
wherein the carbon black having a hydrophilic group has a
volume average particle size of from 60 nm to 200 nm at the
time being dispersed in water.
The recording ink according to any one of to ,
further containing resin fine particles having a volume average
particle size of from 50 nm to 200 nm.
The recording ink according to any one of to ,
wherein at least a part of a terminal of the hydrophilic group on
the carbon black is substituted with an alkali metal.
The recording ink according to , wherein a quantity of
the alkali metal contained in the recording ink is from 100 ppm
or more to 1500 ppm or less.
The recording ink according to any one of to ,
wherein the recording ink has a viscosity of 6 mPa-s to 20
mPa-s at 25°C.
An inkjet recording method including at least: applying a
stimulus to the recording ink as defined in any one of to
, and ejecting the recording ink from a recording head so as
to form an image on a recording medium, wherein the recording
head is configured to have an ink discharge opening on a face of

a nozzle plate, and to have an ink repellent layer formed on the
face of the nozzle plate where the ink discharge opening is
placed.
The inkjet recording method according to , wherein
the stimulation is at least one selected from the group consisting
of heat, pressure, vibration and light.
The inkjet recording method according to any of or
, wherein the ink repellent layer contains either a
fluorine-based material or a silicone-based material.
The inkjet recording method according to any one of
to , wherein the ink repellent layer has a surface roughness
Ra of 0.2 µm or less.
The inkjet recording method according to any one of
to , wherein the ink repellent layer is formed so to have an
opening along with the ink discharge opening, and the opening
of the ink repellent layer is formed so that a cross-sectional area
of a face perpendicular to a center line of the opening becomes
gradually larger as a distance from the face of the nozzle plate
increases in a vicinity of the opening.
The inkjet recording method according to any one of
to , wherein the ink repellent layer has a critical surface
tension yc of from 5 mN/m to 40 mN/m.
The inkjet recording method according to any one of
to , wherein the recording medium has a support and a
coating layer at least on one face of the support.

The inkjet recording method according to any one of
to , wherein the recording medium has a purified water
transfer amount of 2 mL/m2 to 45 ml/m2 when measured at 23°C
and 50% RH for a contact time of 100 ms by using a dynamic
scanning absorptometer, and has a purified water transfer
amount of 3 mL/m2 to 50 mL/m2 when measured at 23°C and 50%
RH for the contact time of 400 ms by using a dynamic scanning
absorptometer.
The inkjet recording method according to any one of
to , wherein an applied amount of the coating layer is from
0.5 g/m2 to 20.0 g/m2 on a dry basis.
The inkjet recording method according to any one of
to , wherein the recording medium has a basis weight of 50
g/m2 to 250 g/m2.
An inkjet recording apparatus containing at least: an ink
ejecting unit configured to apply a stimulus to the recording ink
as defined in any one of to , and to eject the recording
ink so as to record an image on a recording medium.
The inkjet recording apparatus according to , wherein
the stimulus is at least one selected from the group consisting of
heat, pressure, vibration and light.
Brief Description of the Accompanying Drawings
FIG. 1 is a schematic view for illustrating one example of
an ink cartridge used in the present invention.

FIG. 2 is a schematic view which also includes a case
(outer covering) of the ink cartridge given in FIG. 1.
FIG. 3 is a perspective view for explaining a state that the
cover of an ink cartridge loading portion is opened in an inkjet
recording apparatus of the present invention.
FIG. 4 is a schematic block diagram for explaining a whole
constitution of the inkjet recording apparatus of the present
invention.
FIG. 5 is a schematic enlarged view for illustrating one
example of an inkjet head used in the inkjet recording apparatus
of the present invention.
FIG. 6 is an enlarged element view for illustrating one
example of the inkjet head used in the inkjet recording
apparatus of the present invention.
FIG. 7 is an enlarged sectional view in an inter-channel
direction for illustrating major parts of the exemplified inkjet
head used in the inkjet recording apparatus of the present
invention.
FIG. 8 is a schematic sectional view for illustrating one
example of a nozzle plate on the inkjet head used in the inkjet
recording apparatus of the present invention.
FIG. 9A is a schematic view for explaining the nozzle
plate on the inkjet head used in the inkjet recording apparatus
of the present invention.
FIG. 9B is a schematic view for explaining the nozzle

plate on the inkjet head used in. the inkjet recording apparatus
of the present invention.
FIG. 9C is a schematic view for explaining the nozzle
plate on the inkjet head used in the inkjet recording apparatus
of the present invention.
FIG. 10A is a schematic view for explaining a nozzle plate
on the inkjet head for comparison.
FIG. 10B is a schematic view for explaining another
nozzle plate on the inkjet head for comparison.
FIG. 10C is a schematic view for explaining still another
nozzle plate on the inkjet head for comparison.
FIG. 11 is a view for illustrating a state at which a
silicone resin is coated by using a dispenser to form a ink
repellent film.
FIG. 12A is a view for showing a relationship between a
coating hole at the needle tip used in the present invention and
a coating width on the nozzle plate, which is an object to be
coated.
FIG. 12B is a view for showing a relationship between a
general needle tip and a coating width on the nozzle plate,
which is an object to be coated.
FIG. 13 is a view for illustrating coating motions when
the dispenser is used.
FIG. 14 is a view for illustrating a state at which an ink
repellent layer of the silicone resin is formed on the inner wall

of the nozzle up to a desired depth.
FIG. 15 is a view for illustrating one example of the inkjet
head on the inkjet recording apparatus of the present invention
and also a state at which the nozzle port is formed by excimer
laser machining.
FIG. 16 is a view for illustrating a constitution of the
excimer laser machine used on machining the nozzle port.
FIG. 17A is a view for illustrating a base material of the
nozzle forming member used in a step of manufacturing the
nozzle plate in manufacturing the inkjet head.
FIG. 17B is a view for illustrating a step of forming a SiO
2 thin film layer on the surface of a resin film.
FIG. 17C is a view for illustrating a step of coating a
fluorine-based water repellent.
FIG. 17D is a view for illustrating a step of allowing the
film to stand in the atmosphere after deposition of the water
repellent film.
FIG. 17E is a view for illustrating a step of attaching an
adhesive tape thereon.
FIG. 17F is a view for illustrating a step of machining the
nozzle port.
FIG. 18 is a view for briefly illustrating an apparatus to
be used on manufacture of the inkjet head by a method for
manufacturing the inkjet head.
FIG. 19 is a view for showing a relationship between a

quantity of water evaporation and ink viscosity.
Best Mode for Carrying Out the Invention
The recording ink of the present invention contains at
least water, a water-soluble organic solvent, a surfactant and
carbon black having a hydrophilic group on the surface, and also
contains other components, if necessary.
The concentration of humic acid released in an aqueous
dispersion containing 20% by mass of carbon black recovered
from the recording ink is from 5.0 to 20.0 in terms of a
maximum absorbance measured at a wavelength of 230 nm to
260 nm.
The humic acid is an organic acid generated on oxidation
treatment of carbon black, having an aromatic ring and a
plurality of functional groups such as a carboxyl group and a
hydroxyl group. Although the constitution thereof is not
identified, it has been known that the humic acid exhibits a
maximum absorbance at a wavelength of 230 nm to 260 nm. It
is, therefore, possible to determine the concentration of humic
acid by measuring the absorbance.
The humic acid is generated in a process of oxidization of
carbon black, and is removed by washing as much as possible
during dispersion preparation. However, when a highly
oxidized and bulky carbon black is used, it will not be
completely removed by washing, and humic acid is likely to

remain in the carbon black.
In a stored ink, residual humic acid is released to reduce
the ink's pH. The reduction of pH may cause aggregation and
thickening of ink, as well as corrosion of members used in the
ink flow paths inside a printer. When printed with such an ink,
the ink may not be normally discharged.
On the other hand, when humic acid is remained in the
carbon black, evaporation of water causes a reduction in the
ink's pH, producing a high image density due to aggregation and
thickening of ink. Therefore, the humic acid preferably
remains at a certain concentration.
The first step of a method for quantification of humic acid
released in an aqueous dispersion containing 20% by mass of
carbon black recovered from the recording ink involves
separation of such additives as a surfactant, rust-preventive
agent and ultraviolet absorbing agent by column
chromatography or the like for recovery of a carbon black. The
thus obtained carbon black is then subjected to vacuum drying
by using a dryer at 50 °C for sufficient evaporation of water and
solvent, and is diluted with water to a concentration of 20% by
mass.
Fifty grams of the diluted solution is measured into in a
beaker, and passed through an ultra-filter (Pellicon Biomax 50
manufactured by Millipore) for 30 minutes to obtain a brown
liquid. This liquid is diluted 10 times with ion exchanged

water and read on a spectrophotometer (U3310 manufactured
by Hitachi High-Technologies Corporation) equipped with a
quartz cell (light path length, 10 mm) at a wavelength of 230 nm
to 260 nm. The thus obtained maximum absorbance was
increased 10 times to determine the concentration of humic acid.
The thus determined concentration of humic acid is
preferably in a range of 5.0 to 20.0 in terms of maximum
absorbance measured at a wavelength of 230 nm to 260 nm, and
more preferably from 10.0 to 15.0. Where the maximum
absorbance is less than 5.0, there may be found a poor image
density on a recording medium such as a plain paper or a coated
paper. In contrast, where the maximum absorbance is more
than 20.0, there is found a tendency that pH is decreased to a
greater extent with the lapse of time and aggregation or
increase in viscosity takes place after a prolonged storage.
There is also found a tendency that the ink is increased in
viscosity to a greater extent on water evaporation, which may
affect the discharge stability of the ink. In other words, it has
been found that when a certain quantity of humic acid is present
in the ink, a recorded image high in concentration can be
obtained.
This may be due to a fact that solids are quickly increased
in viscosity and undergo aggregation on evaporation of water on
the surface of the recording medium.
A better understanding can be obtained for the

relationship between viscosity increasing behaviors on water
evaporation and image density. In other words, if such a
condition is satisfied that when a quantity of water evaporation
relative to a whole mass of ink is in a range of 34 % by mass to
41 % by mass, the viscosity is increased from 5.0 times or more
to less than 550 times with respect to an initial viscosity, the
ink is provided with an excellent discharge stability to increase
the image density of a record.
Regarding a relationship between the concentration of
humic acid in ink and ink viscosity increasing behaviors on
water evaporation, there is found a tendency that the higher the
concentration of humic acid is, that is, the higher the value of
absorbance determined by the above-described method is, to the
higher extent the viscosity associated with water evaporation is
elevated, and the lower the concentration of humic acid is, that
is, the lower the value of absorbance is, to the lower extent the
viscosity associated with water evaporation is elevated.
Further, a quantity of the alkali metal contained in the
ink will also affect ink viscosity increasing behaviors on water
evaporation. The alkali metal contained in ink includes mainly
lithium, sodium and potassium, which are mainly those added as
a neutralizer of a hydrophilic group on the surface of carbon
black and a neutralizer of a resin emulsion, although some of
the alkali metals are derived from a surfactant or other
additives.

The quantity of the alkali metal contained in the ink is
preferably from 100 ppm to 1500 ppm and more preferably from
200 ppm to 1200 ppm. Where the quantity of the alkali metal
is less than 100 ppm, the image density tends to decrease, and
where the quantity is more than 1500 ppm, ink may be
deteriorated in storage and discharge performance.
- Carbon black -
Carbon black having a hydrophilic group used in the
recording ink of the present invention is that manufactured by
using known carbon black, including that manufactured, for
example, by a channel method, an oil furnace method, a furnace
method, an acetylene black method, a thermal black method or
the like. It is noted that carbon black made by the channel
method is available only in the limited variations due to a
reduced manufacturing quantity in recent years, and carbon
black made by the furnace method is now widely used due to
availability of wider variations.
There is no particular restriction on the types of carbon
black, and general types of carbon black manufactured by any of
the above-described methods are usable. Preferable are those
in which the primary particle size is from 10 nm to 40 nm, and
the specific surface area determined by BET method is from 50
m2/g to 300 m2/g.
The carbon black preferably has a DBP oil absorption from
50 mL/100 g to 300 mL/100 g, and more preferably 100 mL/100 g

to 300 mL/100 g. The DBP oil absorption can be obtained from
an amount of DBP that is needed to fill voids of 100 g of carbon
black by applying droplets of DBP dibutyl phthalate to the
carbon black for penetration into the voids.
There is no particular restriction on the carbon black, and
any appropriate carbon black may be appropriately selected,
including, for example, # 2700, # 2650, # 2600, # 2450B, # 2400B,
# 2350, # 230, # 1000, # 990, # 980, # 970, # 960, # 950, # 900, #
850, # 750B, MCF 88, # 650B, MA 600, MA 77, MA 7, MA 8, MA
11, MA 100, MA 100R, MA 100S, MA 220, MA 230, MA 200RB,
MA 14, # 52, # 50, # 47, # 45, # 45L, # 44, # 40, # 33, # 32, # 30,
# 25, # 20, # 10, # 5, # 95, # 85, CF 9, and # 260 (all of which are
manufactured by Mitsubishi Chemical Corporation); Raven 700,
5750, 5250, 5000, 3500 and 1255 (all of which are manufactured
by Colombia Corporation; Rega 1400R, 330R, 660R, MogulL,
Monarch 700, 800, 880, 900, 1000, 1100, 1300, and 1400 (all of
which are manufactured by Cabot Corporation); Color Black
FW1, FW2, FW2V, FW18, FW200, S150, S160, S170, Printex 35,
U, V, 140U, 140V, Special Black 6, 5, 4A and 4 (all of which are
manufactured by Degussa AG); Toka Black # 8500, # 8300, #
7550, # 7400, # 7360, # 7350, # 7270 and # 7100 (all of which are
manufactured by Tokai Carbon Co., Ltd.); Fat-soluble (Shiyou)
Black N110, N220, N234, N339, N330, N326, N330T, MAF and
N550, (all of which are manufactured by Cabot Japan K.K.).
The carbon black can be stably dispersed without using

any dispersing agent by modifying the surface, and at least one
type of hydrophilic group is bonded on the surface of the carbon
black directly or through another atomic group.
There is no particular restriction on the above described
method for modifying the surface. Any method may be
appropriately selected, depending on the intended purpose,
including, for example, gas-phase oxidation using an oxidative
gas such as ozone or liquid-phase oxidation using a liquid
oxidizing agent. The liquid oxidizing agent includes hydrogen
peroxide, iodine water, hypochloride, chlorite, nitrate,
permanganate, dichromate and persulfate.
The hydrophilic group includes, for example, COOM, -SO
3M, PO3HM, PO3M2, -SO2NH2 and SO2NHXCOR (in the
formula, M denotes a hydrogen atom, alkali metal, ammonium or
organic ammonium, and R denotes an alkyl group of 1 to 12
carbon atoms, a phenyl group which may have a substituent
group or a naphthyl group which may have a substituent group.).
In particular preferable are those in which -COOM or -SO3M is
bonded on the surface.
"M" given in the hydrophilic group includes, for example,
lithium, sodium and potassium as an alkali metal. The organic
ammonium includes, for example, mono- or tri-methyl
ammonium, mono- or tri-ethyl ammonium, and mono-or
trimethanol ammonium. In view of obtaining a higher image
density, alkali metals such as potassium and sodium are

preferably used.
The volume average particle size in a state that the
carbon black having the hydrophilic group is dispersed in water
is preferably from 60 nm to 200 nm and more preferably from 80
nm to 180 nm. Where the volume average particle size is less
than 60 nm, there is a failure in obtaining a sufficient image
density. Where it is more than 200 nm, clogging may take place
on a nozzle more often, resulting in deterioration of the
discharge performance. In this instance, the volume average
particle size can be measured by using Microtrac UPA
(manufactured by Nikkiso Co., Ltd.).
An amount of the carbon black having the hydrophilic
group is preferably from 5 % by mass to 15 % by mass, and more
preferably from 6 % by mass to 12 % by mass, with respect to
the total mass of the ink. Where the content is less than 5 % by
mass, there may be a failure in obtaining a sufficient image
density. Where it is more than 15 % by mass, ink may be
increased in viscosity to result in deterioration of the discharge
stability.
- Watersoluble organic solvent -
There is no particular restriction on the water-soluble
organic solvent. Any solvent may be used, depending on the
intended purpose, including, for example, polyvalent alcohols
such as ethylene glycol, diethylene glycol, triethylene glycol,
ethylene glycol, propylene glycol, dipropylene glycol,

tripropylene glycol, 1,3-propane diol, 1,3-butane diol, 2,3'butane
diol, 1,4 butane diol, 3-methyl-l,3-butane diol, 1,5-pentane diol,
tetraethylene glycol, l,6hexane diol, 3-methyl-1,5-pentane diol,
2-methyl-2,4-pentane diol, polyethylene glycol, glycerol,
1,2,6-hexane triol, 1,2,4-butane triol, 1,2,3-butane triol and
petriol; polyvalent alcohol alkyl ethers such as ethylene glycol
monoethyl ether, ethylene glycol monobutyl ether, diethylene
glycol monomethylether, diethylene glycol monoethyl ether,
diethylene glycol monobutyl ether, tetra-ethylene glycol
monomethyl ether and propylene glycol monoethyl ether."
polyvalent alcohol aryl ethers such as ethylene glycol
monophenyl ether, and ethylene glycol monobenzyl ether;
nitrogen-containing heterocycle compounds such as
Nmethyl-2-pyrolidone, N-hydroxy ethyl-2-pyrolidone,
2-pyrolidone, 1,3-dimethylimidazolidinone, ecaprolactam;
amides such as formamide, N-methyl formamide, formamide,
and N,N-dimethyl formamide; amines such as monoethanol
amine, diethanol amine, triethanol amine, monoethyl amine,
diethyl amine and triethyl amine; sulfur-containing compounds
such as dimethyl sulfoxide, sulfolane and thiodiethanol;
propylene carbonate and ethylene carbonate. These substances
may be used solely or in combination of two or more of them.
Among the above substances, in view of obtaining the
solubility and excellent effects in preventing poor jetting
properties on water evaporation, in particular preferable are

glycerin, ethylene glycol, diethylene glycol, triethylene glycol,
propylene glycol, dipropylene glycol, tripropylene glycol,
1,3-butane diol, 2,3-butane diol, 1,4-butane diol,
3-methyl-l,3-butane diol, 1,5-pentane diol, tetra-ethylene glycol,
1,6-hexane diol, 3-methyl-l,5-pentane diol, 2methyl-2,4-pentane
diol, polyethylene glycol, l,2,4butane triol, 1,2,6-hexane triol,
thiodiglycol, 2pyrolidone, N-methyl-2-pyrolidone, and
N-hydroxy ethyhl-2-pyrolidone.
The amount of the water-soluble organic solvent in the
recording ink is preferably from 15 % by mass to 40 % by mass,
and more preferably from 20 % by mass to 35 % by mass.
Where the content is excessively low, a nozzle may be more
likely to dry, thus resulting in a poor discharge of ink droplets.
Where the content is excessively high, ink viscosity may be
increased to exceed an appropriate range of the viscosity.
- Surfactant -
The surfactant may be used solely by selecting any one of
those consisting of anionic surfactants, cationic surfactants,
nonionic surfactants, amphoteric surfactants and fluorochemical
surfactants or in combination of two or more of them. Among
these, nonionic surfactants and fluorochemical surfactants are
in particular preferable.
The anionic surfactants include, for example, alkylallyl,
alkylnaphthalene sulfonate, alkyl phosphate, alkyl sulfate,
alkyl sulfonate, alkylether sulfate, alkyl sulfosuccinate,

alkylester sulfate, alkylbenzene sulfonate, alkyldiphenyl ether
disulfonate, alkylaryl ether phosphate, alkylaryl ether sulfate,
alkylaryl etherester sulfate, olefin sulfonate, alkane olefin
sulfonate, polyoxyethylene alkylether phosphate,
polyoxyethylene alkylether sulfate ester, ether carboxylate,
sulfosuccinate, asulfo fatty acid ester, fatty acid salt,
condensate of fatty acid with amino acid, and naphthenic acid
salt.
The nonionic surfactants include, for example, an
acetylene glycol-based surfactant, polyoxyethylene alkylether,
polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ester,
polyoxyethylene sorbitan fatty acid ester.
The cationic surfactants include, for example, alkyl amine
salt, dialkyl amine salt, aliphatic amine salt, benzalkonium salt,
quaternary ammonium salt, alkylpyridinium salt, imidazorinium
salt, sulfonium salt and phosphonium salt.
The amphoteric surfactants include, for example,
imidazoline derivatives such as imidazorinium betaine;
dimethylalkyl lauryl betaine, alkylglycine and
alkyldi(aminoethyl) glycine.
The fluorochemical surfactants may preferably include a
compound expressed by any one of the following general
formulae (I) to (III).

However, in the general formula (I), m denotes an integer
of 0 to 10, and n denotes an integer of 1 to 40.

However, in the general formula (II), Rf denotes CF3 or
CF2 CF3 . Further, n, m and p respectively denote an integer of
1 to 4, that of 6 to 25 and that of 1 to 4.

However, in the general formula (III), q denotes an
integer of 1 to 6, Rf denotes CF3 or CF2CF3. R1 denotes SO3-
and R2 denotes NH4 + .
The fluorochemical surfactants may include commercially
available products, for example, Surflon S-111, S112, S-113,
S121, S-131, S132, S-141 and S-145 (all of which are
manufactured by Asahi Glass Co., Ltd.); Fullard FC-93, FC-95,
FC-98, FC129, FC135, FC170C, FC-430, FC431 and FC-4430
(all of which are manufactured by Sumitomo 3M Limited);

Megafack F-470, F1405 and F-474 (all of which are
manufactured by Dainippon Ink and Chemicals Incorporated);
Zonyl FS-300, FSN, FSN100 and FSO (all of which are
manufactured by Dupont Inc.); Ftop EF-351, 352, 801 and 802
(all of which are manufactured by Jemco Inc.).
- Resin fine particles -
Resin fine particles are allowed to be added to the
recording ink of the present invention. The resin fine particles
are those in which a water-insoluble resin is dispersed in water,
and on evaporation of a solvent, the resin fine particles are
fused to each other to form a film, thereby developing an effect
of fixing a coloring agent on a medium. Further, when the
solvent is deposited, the resin fine particles tend to increase in
viscosity and undergo aggregation, inhibiting the penetration of
coloring compositions to provide a high image density. They are
also effective in preventing strike through.
Resin compositions in the resin fine particles include, for
example, acrylic resin, vinyl acetate resin, styrene-butadiene
resin, vinyl chloride resin, acrylstyrene resin, acryl silicone
resin, butadiene resin, styrene resin, urethane resin, and
acryl-urethane resin.
The resin emulsion is preferably contained from 0.1 % by
mass to 40 % by mass with respect to a whole quantity of ink
and more preferably from 1 % by mass to 25 % by mass. Where
the resin emulsion is contained in a quantity of less than 0.1 %

by mass, there may be a failure in obtaining a sufficient fixing
property. Where it is contained in excess of 40 % by mass, the
ink is abundant in solids and scarce in solvents, which may
deteriorate the storage stability or result in frequent drying and
solidification of the ink at a nozzle to decrease the discharge
performance.
The resin fine particles are preferably from 50 nm to 200
nm in volume average particle size and more preferably from 60
nm to 80 nm. Where the volume average particle size is less
than 50nm, the resin emulsion may be increased in viscosity,
thereby causing difficulty in providing the ink viscosity which
can be discharged by an inkjet printer, and where it is in excess
of 200 nm, resin fine particles may be clogged inside the nozzle
of the inkjet printer to result in failure of discharge.
The resin fine particles are preferably added to the carbon
black from 0.05 parts by mass to 1.2 parts by mass with respect
to the carbon black of 1 part by mass, and more preferably from
0.2 parts by mass to 1.0 part by mass. Where the resin fine
particles are added in a quantity of less than 0.05 parts by mass,
there may be a failure in obtaining a sufficient fixing property.
Where they are added in excess of 1.2 parts by mass, the storage
stability may be deteriorated or the discharge performance may
be decreased.
- Penetrating agent -
The penetrating agent includes a diol compound having

the carbon number of 7 to 11. Where the carbon number is less
than 7, there is a failure in obtaining a sufficient penetration,
thereby spoiling a recording medium when the medium is
printed on both faces, or there is found an insufficient spread of
ink on the recording medium to result in a poor filling of pixels,
thereby deteriorating the quality of characters or the image
density. Where the carbon number is in excess of 11, the
storage stability may be decreased.
The diol compounds preferably include, for example,
2-ethyl-1,3 hexane diol and 2,2,4-trimethyl-1, 3 pentanediol.
The diol compound is preferably added from 0.1 % by mass
to 20 % by mass and more preferably from 0.5 % by mass to 10 %
by mass. Where the compound is added in an excessively small
quantity, ink is poorly permeated into paper, which may lead to
a case where the paper is rubbed by transfer rollers and
blemished, ink attached on a transfer belt on reversing the
recording face of a recording medium for printing on both faces
thereof may spoil the recording medium, or there may be a
failure in providing a high-speed printing or both-face printing.
In contrast, where the compound is added in an excessively
large quantity, the printing dot diameter is made larger, which
may widen the line of characters or decrease the image
sharpness.
pH buffering agent -
In order to prevent a pH decrease in the ink during a

prolonged storage, in the present invention, usable are
conventionally known solutions such as a phosphate buffer
solution, acetate buffer solution, ethanol amine buffer solution,
boric acid buffer solution, citric acid buffer solution, tartaric
acid buffer solution, and Good's buffer solution. Among these
buffer solutions, an organic pH buffering agent selected from
Good's buffer solution is particular preferable.
The Good's buffer solution is zwitter ion amino acids such
as N-substituted taurine and N-substituted glycine, and known
as an organic buffering agent suitable for bio-chemical uses.
The Good's buffer solution has specific structures which
are as follows:

necessary, which includes, for example, pH adjusting agent,
anti-septic/anti-mildew agent, rust-preventive agent,
anti-oxidizing agent, ultraviolet absorbing agent, oxygen
abosrbent and light stabilizer.
The anti-septic/anti-mildew agent includes, for example,
1,2-benzoisothiazoline-3-on, sodium dehydroacetate, sodium
sorbate, 2-pyridinethioll-sodium oxide, sodium benzoate and
sodium pentachlorophenol.
There is no particular restriction on the pH adjusting
agent, as long as it does not affect ink to be formulated and is
able to retain pH at 7 or higher. Any given substance may be
used, depending on the intended purpose.
The pH adjusting agent includes, for example, amines
such as diethanol amine and triethanol amine,' hydroxides of
alkali metal elements such as lithium hydroxide, sodium
hydroxide and potassium hydroxide; carbonates of alkali metals
such as ammonium hydroxide, quaternary ammonium hydroxide,
quaternary phosphonium hydroxide, lithium carbonate, sodium
carbonate and potassium carbonate.
The rust-preventive agent includes, for example, acid
sulfite, sodium thiosulfate, ammonium thiodiglycolate,
diisopropyl ammonium nitrite, pentaerithritol tetranitrate and
dicyclohexyl ammonium nitrite.
The anti-oxidizing agents include, for example, phenol
anti-oxidizing agents (including hindered phenol anti-oxidizing

agents), amine anti-oxidizing agents, sulfur anti-oxidizing
agents, and phosphorus anti-oxidizing agents.
The phenol anti-oxidizing agents (including hindered
phenol anti-oxidizing agents) include, for example, butylated
hydroxy anisole, 2,6-di-tert-butyl-4-ethylphenol,
stearyl-ß-(3,5ditert-butyl-4-hydroxyphenyl) propionate,
2,2'-methylenebis (4-methyl-6-tert-butylphenol),
2,2'-methylenebis (4-ethyl-6-tertbutylphenol), 4,4'-butylidenebis
(3-methyl-6-tert-butylphenol), 3,9-bis
[1, 1-dimethyl-2- [ß-(3tertbutyl-4-hydroxy-5-methylphenyl)
propyonyloxy]ethyl] 2,4,8,10-tetraixaspiro [5, 5] undecane,
1,1,3-tris (2methyl-4-hydroxy-5-tertbutylphnyl) butane,
l,3,5trimethyl-2,4,6-tris (3,5-di-tertbutyl-4hydroxy benzyl)
benzene, and tetrakis [methylene-3-(3',
5'-di-tert-butyl-4'-hydroxy phenyl) propionate] methane.
The amine anti-oxidizing agents include, for example,
phenyl-ß-naphthyl amine, a-naphthyl amine,
N,N'-disec-butyl-pphenylene diamine, phenothiazine,
N,N'-diphenyl-pphenylene diamine, 2,6-ditert-butyl-p-cresol,
2,6-ditertbutylphenol, 2,4-dimethyl-6-tertbutyl-phenol,
butylhydroxy anisole, 2,2'-methylene-bis
(4-methyl-6tert-butylphenol), 4,4'-butylidene-bis
(3-methyl-6-tertbutylphenol), 4,4'-thiobis
(3methyl-6-tert-butylphenol), tetrakis [methylene-3
(3,5ditert-butyl-4dihydroxyphenyl) propionate] methane, and

1,1,3-tris (2methyl-4-hydroxy-5-tert-butylphenyl) butane.
The sulfur anti-oxidizing agents include, for example,
dilauryl 3,3'-thiodipropionate, distearyl tiodipropionate,
laurylstearyl thiodipropionate, dimyristyl 3,3'-thiodipropionate,
distearylB,B'-thiodipropionate, 2-mercaputo benzoimidazole, and
dilauryl sulfide.
The phosphorus anti-oxidizing agents include, for example,
triphenyl phosphite, octadecyl phosphite, triisodecyl phosphite,
trilauryl trithio phosphite, and trinonyl phenyl phosphite.
The ultraviolet absorbing agents include, for example,
benzophenone ultraviolet absorbing agents, benzotriazole
ultraviolet absorbing agents, salicylate ultraviolet absorbing
agents, cyanoacrylate ultraviolet absorbing agents, and nickel
complex salt ultraviolet absorbing agents.
The bezophenone ultraviolet absorbing agents include, for
example, 2hydroxy-4noctoxy benzophene,
2-hydroxy-4-n-dodecyl. oxybenzophenone, 2,4-dihydroxy
benzophenone, 2hydroxy-4-methoxybenzophenone, and
2,2',4,4'-tetrahydroxybenzophenone.
The benzothiazole ultraviolet absorbing agents include,
for example, 2(2'-hydroxy-5'-tert-octylphenyl) benzotriazole,
2(2'hydroxy-5'-methyl phenyl) benzoriazole,
2-(2'-hydroxy-4'-octoxyphenyl) benzotriazole, and
2-(2'-hydroxy-3'-tert-butyl-5'-methyl
phenyl)-5-chlorobenzotriazole.

The salicylate ultraviolet absorbing agents include, for
example, phenyl salicylate, p-tert-butylphenyl salicylate, and
poctylphenyl salicylate.
The cyanoacrylate ultraviolet absorbing agents include,
for example, ethyl-2-cyano-3,3'-diphenyl acrylate,
methyl-2-cyano-3methyl-3-(p-methoxyphenyl) acrylate, and
butyl-2-cyano-3-methyl-3-(pmethoxyphenyl) acrylate.
The nickel complex salt ultraviolet absorbing agents
include, for example, nickelbis (octylphenyi)sulfide, 2,2'-thiobis
(4tertoctylphalate)-n-butylamine nickel (II), 2,2'thiobis
(4-tert-octyylphalate)-2ethylhyxyl amine nickel (II), and
2,2'-thiobis (4-tert-octylphalate) triethanol amine nickel (II).
There is no particular restriction on physical properties of
the recording ink of the present invention. The physical
properties may be appropriately selected, depending on the
intended purpose. It is preferable that, for example, the solids
content, viscosity surface tension and pH preferably fall under
the following ranges.
The solids content of the recording ink is preferably in a
range of 5 % by mass to 20 % by mass and more preferably from
6 % by mass to 15 % by mass. Where the solids content is less
than 5 % by mass, there may be a failure in obtaining a
sufficient image density.
In this instance, the solids content of the ink in the
present invention substantially means the water-insoluble

coloring agent and resin fine particles.
The viscosity is preferably from 6 mPa*a to 20 mPa*s at
25°C, and more preferably from 6.5 mPa*s to 12 mPa*s. Where
the viscosity exceeds 20 mPa*s, there may be a difficulty in
securing the discharge stability.
The surface tension is preferably in a range of 25 mN/m to
55 mN/m at 20°C. Where the surface tension is less than 25
mN/m, ink may apparently ooze out on a recording medium to
result in a failure of obtaining a stable jetting. Where the
surface tension exceeds 55 mN/m, the ink will not penetrate into
the recording medium sufficiently to result in a prolonged
drying time.
The pH is preferably, for example, from 7 to 10.
A prolonged storage of the recording ink may change the
physical properties. In particular, when the ink is stored after
heating, it undergoes an increase in viscosity and a decrease in
pH. It is desirable to keep the change in physical properties to
the least possible extent. For example, the increase in viscosity
after two-week storage at 60°C is preferably within 5%, and the
decrease in pH is preferably within -5%.
The recording ink of the present invention is favorably
used in various fields and effectively used in an image recording
apparatus (a printer or the like) based on an inkjet recording
system. For example, ink having such a function that paper to
be recorded and the recording ink are heated at temperatures of

50°C to 200°C during printing or before or after printing to
promote printing fixing can be used in a printer or the like.
This ink can be in particular preferably used in an ink cartridge,
an ink record, an inkjet recording apparatus and an inkjet
recording method of the present invention.

The recording ink of the present invention is able to form
a high-quality image not only on paper exclusively used for
inkjet printing and plain paper but also on coated paper poor in
water absorption. In this instance, the coated paper poor in
water absorption is printing coated paper in which a coating
layer is provided at least on one of two faces of a support and a
quantity of purified water transferred to the recording medium
measured at the contact time of 100 ms by using a dynamic
scanning liquid absorbing system is in a range of 3 mL/m2 to 15
mL/m2.
In the above-described recording medium, a quantity of
the recording ink of the present invention transferred to the
recording medium at the contact time of 100 ms measured by
using a dynamic scanning absorptometer is preferably from 2
mL/m2 to 40 mL/m2, and more preferably from 3 mL/m2 to 30
mL/m2. Further, a quantity of purified water transferred to the
recording medium is preferably from 2 mL/m2 to 45 mL/m2 and
more preferably from 3 mL/m2 to 30 mL/m2.
Where a quantity of the recording ink and that of the

purified water transferred at the contact time of 100 ms are
excessively small, beading may take place more frequently.
Where they are excessively great, the ink dot diameter after the
recording may be made smaller than desired.
A quantity of the recording ink of the present invention
transferred to the recording medium at the contact time of 400
ms measured by using a dynamic scanning absorptometer is
from 3 mL/m2 to 50 mL/m2, and preferably from 4 mL/m2 to 40
mL/m2.
Further, a quantity of purified water transferred to the
recording medium is preferably from 3 mL/m2 to 50 mL/m2 and
more preferably from 4 mL/m2 to 40 mL/m2.
Where the quantity transferred at the contact time of 400
ms is excessively small, ink is not sufficiently dried and spur
marks may develop easily. In contrast, where the quantity is
excessively great, bleeds may take place easily and the gloss of
an image portion after drying may be decreased.
In this instance, the dynamic scanning absorptometer
(DSA, Journal of the Japan Technical Association of the Pulp
and Paper Industry, Vol. 48, May 1994, page 88-92, authored by
Mr. Shigenori Kuga is a device capable of exactly measuring an
absorbed quantity in an extremely short time. The dynamic
scanning absorptometer is able to read a speed of liquid
absorption directly from the movement of the meniscus in a
capillary tube. A sample is formed into a disk shape, on which

an absorption head is scanned helically. An automatic
measurement is realized by a method in which the scanning
speed is allowed to change according to previously established
patterns and one sheet of the sample is used to make
measurements only by the number of points required. A liquid
supply head to paper samples is connected to the capillary tube
via a Teflon (registered trade mark)made tube, and the position
of the meniscus in the capillary tube is automatically read by an
optical sensor. More specifically, the dynamic scanning
absorptometer (K350 series D type, manufactured by Kyowa
Seiko Co., Ltd.) is used to measure a quantity of purified water
or ink transferred. Quantities transferred at the contact time
of 100 ms and at the contact time of 400 ms can be determined
by interpolating measurements of the quantities transferred at
adjacent contact times of the respective contact times. The
measurements are made at 23°C and RH of 50%.
- Support -
There is no particular restriction on the support. Any
substance may be selected depending on the intended purpose,
including, for example, paper mainly based on wood fibers or
sheet-like substances such as non-woven fabrics mainly based on
wood fibers and synthetic fibers.
There is no particular restriction on the paper. Any
known paper may be appropriately used depending on the
intended purpose, including, for example, wood pulp and waste

paper pulp. The wood pulp includes, for example, broad-leaved
wood bleached kraft pulp (LBKP) and coniferous wood bleached
kraft pulp (NBKP), NBSP, LBSP, GP, and TMP.
Materials of the waste paper pulp include high-quality
white paper, clean envelops, cream-white paper, cards, special
white paper, wood containing white paper, simili paper,
white-color paper, Kent paper, white art paper, special
high-quality paper cuttings, high-quality paper cuttings,
newspapers ad magazines as listed in the table of waste paper
standard specifications issued by the Paper Recycling Promotion
Center. More specifically, the materials include waste paper
and waste paperboard, for example, printer paper used in
information-related fields such as non-coated computer paper,
thermal recording paper and pressure sensitive paper; office
waste paper such as PPC paper; coated paper such as art paper,
coat paper, finely coated paper and matt paper; non-coated
paper such as wood-free paper, colored wood-free paper,
notebook paper, letter paper, package paper, decorative paper,
wood containing paper, paper for gazettes, woody paper, package
paper used in supermarkets and the like, simili paper, machine
glazed paper and milk carton paper; chemical pulp-containing
paper and high-yield pulp containing paper. These materials
may be used solely or in combination of two or more of them.
The waste paper pulp is in general manufactured by a
combination of the following four steps.

(1) Pulping is a step in which a pulper is used to treat
waste paper mechanically and chemically, disintegrating the
paper to give a fiber form, thereby removing printing ink from
fibers.
(2) Dust removal is a step in which foreign matter
(plastics and others) and waste contained in waste paper are
removed by screening, cleaning and others.
(3) Ink removal is a step in which printing ink removed
from fibers by using a surfactant is removed from a system by
using a floating method or a washing method.
(4) Bleaching is a step in which oxidation or reduction is
used to improve the whiteness of fibers.
A mixing ratio of waste paper pulp to a whole pulp content
on mixture of the waste pulp is preferably 40% or less, with
consideration given to measures against a possible curling of
paper after recording.
Internal additives used in the support include, for
example, conventionally known pigments as white pigments.
The white pigments include, for example, white inorganic
pigments such as light calcium carbonate, heavy calcium
carbonate, kaolin, clay, talc, calcium sulfate, barium sulfate,
titanium dioxide, zinc oxide, zinc sulfide, zinc carbonate, satin
white, aluminum silicate, diatomaceous earth, calcium silicate,
magnesium silicate, synthetic silica, aluminum hydroxide,
alumina, lithopone, zeolite, magnesium carbonate, and

magnesium hydroxide; organic pigments such as styrene-based
plastic pigment, acrylic plastic pigment, polyethylene,
microcapsule, urine resin, and melamine resin. The pigments
may be used solely or in combination of two or more of them.
Internal sizing agents used in making the support include,
for example, a neutral rosin sizing agent used in making
neutralized paper, alkenyl succinic anhydride (ASA),
alkylketene dimer (AKD), and a petroleum resin-based sizing
agent. Of these agents, the neutral rosin sizing agent and
alkenyl succinic anhydride are in particular preferable. The
alkylketen dimer can be used in a smaller quantity because of
its higher sizing effect. However, there is a case where the
friction coefficient on the surface of recording paper (medium) is
decreased to result in an easy slippage, the use of which is not
favorable in terms of transferring the paper on inkjet recording.
- Coating layer -
The coating layer contains a pigment and a binder
(binding agent), and also contains a surfactant and other
compositions, if necessary.
Usable as the pigment is an inorganic pigment or a
combination of an inorganic pigment with an organic pigment.
The inorganic pigment includes, for example, kaoline, talc,
heavy calcium carbonate, light calcium carbonate, calcium
sulfite, amorphous silica, titanium white, magnesium carbonate,
titanium dioxide, aluminum hydroxide, calcium hydroxide,

magnesium hydroxide, zinc hydroxide, and chlorite. Of these
pigments, kaoline is in particular preferable because it is
excellent in gloss development property and able to provide a
texture close to that of paper for offset printing.
The kaoline includes delaminated kaoline, calcinated
kaoline and engineered kaoline by surface modification. When
the gloss development property is taken into account, it is
preferable that kaoline having such a particle size distribution
that the particle size of 2 µm or less is 80 % by mass accounts
for 50 % by mass or more with respect to a total quantity of
kaoline.
The kaoline is preferably added at 50 parts by mass or
more with respect to 100 parts by mass of a total quantity of
pigments on the coating layer. Where the addition is less than
50 parts by mass, there may be a failure in obtaining a
sufficient gloss. There is no particular restriction on the added
quantity. The kaoline is more preferably added at 90 parts by
mass or less in terms of coating suitability, with consideration
given to the fluidity of kaoline and increase in viscosity under a
high sheering force in particular.
The organic pigment includes a water-soluble dispersion,
for example, styrene acryl copolymer particles,
styrenebutadiene copolymer particles, polystyrene particles,
and polyethylene particles. Two or more of the pigments may
be mixed.

The organic pigment is added preferably from 2 parts by
mass to 20 parts by mass with respect to 100 parts by mass of a
total quantity of pigments on the coating layer. Since the
organic pigment is excellent in gloss development property and
smaller in specific gravity than an inorganic pigment, it is able
to provide a coating layer high in bulk, great in gloss and
favorable in surface covering property. Where it is added at
less than 2 parts by mass, the above-described effects are not
obtained. Where it is added at a quantity exceeding 20 parts by
mass, there is found deterioration in the fluidity of a coating
solution to result in a decreased coating operation, which is not
desirable in terms of cost.
The organic pigment is available in a solid type, a hollow
type, a donut type and other. When the gloss development
property, surface covering property and fluidity of a coating
solution are comprehensively considered, the hollow type having
an average particle size of 0.2 µm to 3.0 µm is preferably
employed, and that having a void percentage of 40% or higher is
more preferably employed.
An aqueous resin is preferably used as the binder.
At least one of a water-soluble resin and an aqueous
dispersible resin may be favorably used as the aqueous resin.
There is no particular restriction on the water-soluble resin, and
any resin may be appropriately selected, depending on the
intended purpose. The resins include, for example, a modified

product of polyvinyl alcohols such as polyvinyl alcohol, anion
modified polyvinyl alcohol, cation modified polyvinyl alcohol and
acetal modified polyvinyl alcohol; polyurethane; a modified
product of polyvinyl pyrolidone such as a copolymer of polyvinyl
pyrolidone and polyvinyl pyrolidone with vinyl acetate, a
copolymer of vinyl pyrolidone and dimethyl
amnoethyl/methacrylate, a copolymer of quaternary vinyl
pyrolidone with dimethyl aminoethyl/methcrylate, and a
copolymer of vinyl pyrolidone with methacrylamide propyl tri
methyl ammonium chloride; cellulose such as carboxymethyl
cellulose, hydroxyethyl cellulose and hydroxypropyl cellulose; a
modified product of cellulose such as cationic hydroxyethyl
cellulose; a synthetic resin such as polyester, polyacryl
acid(ester), melamine resin, and their modified products, and a
copolymer of polyester with polyurethane; poly(meta)acrylic acid,
poly(meta)acrylamide, acidified starch, phosphorylated starch,
internally modified starch, cationic starch, various types of
modified starch, polyethylene oxide, polyacrylic acid soda, and
alginate soda. These resins may be used solely or in
combination of two or more of them.
Of these resins, in view of ink absorption, in particular
preferable are polyvinyl alcohol, cation modified polyvinyl
alcohol, acetal modified polyvinyl alcohol, polyester,
polyurethane, and a copolymer of polyester with polyurethane.
There is no particular restriction on the aqueous

dispersible resin. Any resin may be appropriately selected,
depending on the intended purpose, including, for example, poly
vinyl acetate, ethylene/vinyl acetate copolymer, polystyrene,
styrene/(meta) acryl ester copolymer, (meta)acryl ester polymer,
vinyl acetate(meta)acrylic acid(ester) copolymer,
styrene/butadiene copolymer, ethylene/propylene copolymer,
polyvinyl ether, and silicone/acryl copolymer. These resins may
contain a cross-linking agent such as methylolated melamine,
methylolated urea, methylolated hydroxy propylene urea, and
isocyanate and also have a copolymer containing a unit of
N-methylol acrylamide with a self cross-linking property.
These aqueous resins may be used in a plurality.
The aqueous resin is added preferably from 2 parts by
mass to 100 parts by mass with respect to 100 parts by mass of
the pigments, and more preferably from 3 parts by mass to 50
parts by mass. The aqueous resin is added in such a quantity
that the recording medium can obtain a desired absorption
property.
Where an aqueous dispersible coloring agent is used as
the coloring agent, it is not always necessary to formulate a
cationic organic compound. There is no particular restriction
on the coloring agent. Any agent may be appropriately selected
depending on the intended purpose, including, for example, a
primary to a tertiary amine which reacts with a sulfonic acid
group, a carboxyl group, an amino group or others in a direct

dye or an acid dye in water-soluble ink to form an insoluble salt,
monomer, oligomer and polymer of quaternary ammonium salt.
Of these substances, the oligomer or the polymer is preferable.
The cationic organic compound includes, for example,
dimethyl amine/epichloruhydrine polycondensate, dimethyl
amine/ammonia/epichloruhydrine condensate, poly (trimethyl
aminoethyl methcrylate/methyl sulfate), diallyl amine
hydrochloride/acrylamide copolymer, poly (diaryl amine
hydrochloride/sulfur dioxde), polyaryl amine hydrochloride, poly
(aryl amine hydrochloride/diaryl amine hydrochloride),
acrylamide/diaryl amine copolymer, polyvinyl amine copolymer,
dicyandiamide, dicyandiamide/ammonium
chloride/urea/formaldehyde condensate, polyalkylene
polyamine/dicyandiamide ammonium salt condensate,
dimethyldiallyl ammonium chloride, polydiallyl methyl amine
hydrocloride, poly (diallyldimethyl ammonium chloride), poly
(diallyldimethyl ammonium chloride/sulfur dioxide), poly
(diallyldimethyl ammonium chloride/diallyl amine hydrochloride
derivative), acrylamide/diallyldimethyl ammonium chloride
copolymer, acrylate/acrylamide/diallyl amine hydrochloride
copolymer, ethylene imine derivatives such as polyethylene
imine and acryl amine polymer, and polyethylene imine alkylene
oxide modified products. These substances may be used solely
or in combination of two or more of them.
Of these substances, it is preferable to use in combination

of a lowmolecularweight a cationic organic compound such as
dimethyl amine/epichloruhydrine polycondensate or polyallyl
amine hydrochloride with another
relatively-high-molecular-weight cationic organic compound
such as poly (diallydimethyl ammonium chloride). The
combined use makes it possible to improve the image density
and reduce feathering to a greater extent as compared with sole
use.
The cationic organic compound is treated by a colloid
titration method (in which polyvinyl potassium sulfate and
truidine blue are used) to determine a cationic equivalent, which
is preferably in a range of 3 meq/g to 8 meq/g. Where the
cationic equivalent falls in this range, favorable results are
obtained in the above-described range of the drying attachment
quantity.
In this instance, in determining the cationic equivalent by
the colloid titration method, the cationic organic compound is
diluted with distilled water so as to give 0.1 % by mass on a dry
solid basis, without adjustment of pH.
The cationic organic compound is preferably from 0.3 g/m2
to 2.0 g/m2 in drying attachment quantity. Where the cationic
organic compound is less than 0.3 g/m2 in drying attachment
quantity, there may be a failure in sufficiently improving the
image density or effectively decreasing feathering.
There is no particular restriction on the surfactant, and

any surfactant may be appropriately selected depending on the
intended purpose, including, for example, an anionic active
agent, a cationic active agent, an amphoteric active agent and a
non-ionic active agent. Of these agents, the non-ionic active
agent is in particular preferable. The surfactant is added, by
which the water resistance of an image can be improved and the
image density is also increased, thus resulting in the
improvement of bleeding.
The non-ionic active agent includes, for example, a higher
alcohol ethylene oxide addition, an alkyl phenol ethylene oxide
addition, a fatty acid ethylene oxide addition, a polyvalent
alcohol fatty acid ester ethylene oxide addition, a higher
aliphatic amine ethylene oxide addition, a fatty acid amide
ethylene oxide addition, an ethylene oxide addition of fat, a poly
propylene glycolethylene oxide addition, a fatty acid ester of
glycerol, a fatty acid ester of pentaerithritol, a fatty acid ester of
sorbitol or sorbitan, a fatty acid ester of sucrose, an alkylether
of polyvalent alcohol and fatty acid amides of alkanol amines.
These substances may be used solely or in combination of two or
more of them.
There is no particular restriction on the polyvalent
alcohol. Any substance may be appropriately selected
depending on the intended purpose, including, for example,
glycerol, trimethykik propane, pentaerithritol, sorbitol and
sucrose. Further, an effectively usable ethylene oxide addition

is that in which ethylene oxide is partially substituted with
alkylene oxide such as propylene oxide or butylene oxide to an
extent of retaining the water solubility. It is preferably
substituted at 50% or less. HLB (hydrophile-lipophile balance)
of the non-ionic active agent is preferably from 4 to 15 and more
preferably from 7 to 13.
The surfactant is added preferably from 0 parts by mass
to 10 parts by mass with respect to 100 parts by mass of the
cationic organic compound, and more preferably from 0.1 parts
by mass to 1.0 part by mass.
Other compositions may be added to the coating layer,
whenever necessary, to such an extent that will not affect the
object or effect of the present invention. These other
compositions include additives such as alumina powder, a pH
adjusting agent, an anti-sceptic agent and an antioxidizing
agent.
There is no particular restriction on a method for forming
the coating layer, and any appropriate method may be
appropriately selected depending on the intended purpose. The
coating layer can be formed by a method in which a
layer-coating solution is impregnated or coated on the support.
There is no particular restriction on a method for impregnating
or coating the layer-coating solution, and any method may be
appropriately selected depending on the intended purpose. The
coating can be performed by using various types of coaters such

as a conventional size press, a gate roll size press, a film
transfer size press, a blade coater, a rod coater, an air knife
coater, and a curtain coater. In particular, preferable in terms
of cost is a method in which the conventional size press, the gate
roll size press or the film transfer size press mounted on a paper
machine is used to impregnate or attach the coating solution,
thereby giving an on-machine finishing.
There is no particular restriction on an applied amount of
a coating solution for the coating layer. The applied amount
may be appropriately selected depending on the intended
purpose, preferably from 0.5 g/m2 to 20 g/m2, and more
preferably from 1 g/m2 to 15 g/m2 on a dry basis. Where the
applied amount is less than 0.5 g/m2, the ink which is not
sufficiently absorbed may ooze out to blur characters. Where
the applied amount is more than 20 g/m2, the texture is spoiled
for paper to result in a fact that the paper is difficult to fold and
additional writing with a writing instrument is not easy.
The coated film may be dried, whenever necessary, after
the impregnation or coating. There is no particular restriction
on temperatures at which the drying is effected in this instance.
The temperatures may be appropriately selected depending on
the intended purpose and preferably from 100°C to 250°C.
The recording medium may be also provided with a back
layer on the back face of a support and another layer between
the support and the coating layer or between the support and

the back layer. Further, a protective layer may be provided on
the coating layer. These layers may be provided in a single
layer or plural layers.
The recording medium may include
commercially-available offset printing coat paper and gravure
printing coat paper, in addition to inkjet recording media, if
their absorption property falls under the above-described range.
The recording medium preferably has basis weight of 50
g/m2 to 250 g/m2, more preferably of from 60 g/m2 to 200 g/m2.
Where the basis weight is less than 50 g/m2, defective transfer
such as a jammed recording medium may take place more often
in the course of transferring the recording medium due to lack of
consistency. In contrast, where the basis weight exceeds 250
g/m2, there may also cause defective transfer in which the
consistency becomes excessively great, thereby the recording
medium is not successfully bent at a curved portion in the
transfer course to result in jamming of a recording medium.
(Ink cartridge)
An ink cartridge of the present invention is to
accommodate the recording ink of the present invention in a
container and also provided with other members and others
appropriately selected, whenever necessary.
There is no particular restriction on the container, which
may be appropriately selected for shape, dimensions, structure,
material or the like, depending on the intended purpose. The

container may be, for example, that having an ink bag formed
with an aluminum-laminated film, a resin film or the like.
Next, an explanation will be made for the ink cartridge by
referring to FIG. 1 and FIG. 2. In this instance, FIG. 1 is a
view for illustrating one example of the ink cartridge of the
present invention, and FIG. 2 is a view which also includes a
case (outer covering) of the ink cartridge given in FIG. 1.
As illustrated in FIG. 1, the ink cartridge 200 is loaded
into an ink bag 241 from an ink filling port 242 and the ink
filling port 242 is closed by fusion after air is discharged.
When the ink cartridge is used, an ink discharge port 243 made
with a rubber member is punctured with a needle on the
apparatus main body to supply ink to the apparatus.
The ink bag 241 is formed with a package member such as
an aluminum-laminated film devoid of air permeability. As
illustrated in FIG. 2, the ink bag 241 is usually housed into a
plastic-made cartridge case 244 and used so as to be removably
attached to various types of inkjet recording apparatus.
The ink cartridge of the present invention is able to
accommodate the recording ink of the present invention and
usable so as to be removably attached to various types of inkjet
recording apparatuses. Further, the ink cartridge is in
particular preferably used so as to be removably attached to an
inkjet recording apparatus of the present invention, which will
be described later.

(Inkjet recording apparatus and inkjet recording method)
An inkjet recording apparatus of the present invention is
provided with at least a unit configured to shoot ink and also
provided with other units which can be selected whenever
necessary, for example, a unit to generate stimulation and a unit
to gain control.
An inkjet recording method of the present invention
includes at least an ink shooting step and also includes other
steps which can be selected whenever necessary, for example,
steps of generating stimulation and gaining control.
The inkjet recording method of the present invention can
be employed by the inkjet recording apparatus of the present
invention, and the ink shooting step can be favorably carried out
by using the unit configured to shoot ink. The above-described
other steps are also favorably carried out by using the
above-described other units.
- Ink shooting step and unit configured to shoot ink -
The ink shooting step is a step of applying stimulation to
the recording ink of the present invention, thereby shooting the
recording ink from a recording head to record an image on a
recording medium.
The unit configured to shoot ink is a means to apply
stimulation to the recording ink of the present invention,
thereby shooting the recording ink from the head to record an
image on a recording medium.

There is no particular restriction on the unit configured to
shoot ink, including, for example, various types of ink
discharging nozzles.
In the present invention, it is preferable that the liquid
chamber portion, the fluid resistance portion, the diaphragm
and the nozzle member of the inkjet head are at least partially
formed with a material at least containing one of silicon and
nickel.
Further, the inkjet nozzle is preferably 30 µm or less in
nozzle diameter and more preferably from 1µm to 20 µm.
Such a constitution is also preferable that a sub-tank for
supplying ink is provided on the inkjet head and the ink is
supplied to the sub-tank via a supply tube from the ink
cartridge.
The stimulation can be generated, for example, by the
unit to generate stimulation. There is no particular restriction
on such stimulation. Any stimulation may be appropriately
selected depending on the intended purpose, including, for
example, heat (temperature), pressure, vibration, light and the
like. They may be used solely or in combination of two or more
of them. Among other things, heat and pressure are preferably
used.
It is noted that the unit to generate stimulation includes,
for example, a heating device, a pressure device, a piezoelectric
element, a vibration generating device, an ultrasonic generator

and a lighting device. More specifically, included are, for
example, a piezcrelectric actuator such as a piezoelectric
element, a thermal actuator which uses an electrothermal
converter such as a heat element to utilize the change in phase
resulting from the film boiling of a liquid, a shape memory alloy
actuator which uses the change in metal phase resulting from
the change in temperature, and an electrostatic actuator which
uses an electrostatic force.
There is no particular restriction on an aspect of shooting
the recording ink, which is different depending on the types of
stimulation. Where the stimulation is, for example, "heat,"
such a method is available that thermal energy corresponding to
a recording signal is applied to the recording ink inside a
recording head, for example, by using a thermal head or the like,
bubbles are generated in the recording ink by the thermal
energy, thereby a pressure coming from these bubbles is utilized
to discharge and jet the recording ink as ink droplets from the
nozzle port of the recording head. Further, where the
stimulation is "pressure," such a method is available that, for
example, voltage is applied to a piezoelectric element attached
to a position which is called a pressure chamber inside an ink
flow path on a recording head, by which the piezoelectric
element is bent to reduce the volume of the pressure chamber,
thus discharging and jetting the recording ink as ink droplets
from the nozzle port of the recording head.

The to-be-shot ink droplets of the recording ink are
preferably, for example, from 3 pL to 40 pL in size and, the
discharging/jetting speed is preferably from 5m/s to 20m/s, the
driving frequency is preferably at 1 kHz or more, and a
resolution is preferably at 300 dpi or more.
It is preferable to provide a unit configured to reverse the
recording face of a recording medium so as to print on both faces
thereof. The reversing unit includes, a transfer belt having an
electrostatic force, a unit configured to retain the recording
medium by pneumatic absorption and a combination of transfer
rollers with spurs.
It is preferable to provide an endless transfer belt and a
unit configured to transfer a recording medium while retaining
the recording medium, with the surface of the transfer belt
being electrified. In this instance, it is particularly preferable
to give AC bias of ± 1.2 kV to ± 2.6 kV to an electrification roller,
thereby electrifying the transfer belt.
It is noted that there is no particular restriction on the
unit configured to gain control, as long as it does not restrict the
movement of each of the above-described units. Any unit may
be appropriately selected depending on the intended purpose,
including, for example, devices such as a sequencer, a computer
and the like.
Where ink with a relatively low surface tension is used
such as the recording ink used in the inkjet recording method of

the present invention, it is preferable that a nozzle plate is
excellent in water repellency and ink repellency. This is
because the nozzle plate excellent in water repellency and ink
repellency is used, by which even ink low in surface tension can
be used to form the meniscus of ink, resulting in a favorable
formation of ink droplets (granulation). The meniscus is
formed normally, thus there is no chance that ink is pulled
toward one direction on jetting of the ink. As a result, such
images are obtained that jetting of ink and high in dot position
accuracy.
Where printing is made on a medium low in absorption,
for example, a recording medium (sheet) used in the inkjet
recording method of the present invention, whether the position
accuracy is high is remarkably influences the image quality. In
other words, ink is less likely to spread on an absorption-low
medium, there is developed a void, or a portion at which ink
fails in filling the recording medium if the position accuracy is
decreased even to a slight extent. This portion at which ink
fails in filling the medium will eventually cause variance in
image density or decrease in image density to deteriorate the
image quality.
However, the inkjet head used in the present invention is
able to realize a high dot position accuracy even if ink low in
surface tension is used, by which the ink successfully fills a
recording medium which is low in absorption, thus making it

possible to provide printed matter with a high image quality free
of variance in image density or decrease in image density.
An explanation will be made for one aspect at which an
inkjet recording method of the present invention is performed by
using an inkjet recording apparatus of the present invention
with reference to the drawings. The inkjet recording apparatus
shown in FIG. 3 is provided with an apparatus main body 101, a
paper feeding tray 102 for feeding sheets loaded on the
apparatus main body 101, a paper discharging tray 103 for
storing an image-recorded (formed) sheet loaded on the
apparatus main body and an ink cartridge loading portion 104.
An operation portion 105 including an operation key and a
display is arranged on the upper face of the ink cartridge
loading portion 104. The ink cartridge loading portion 104 is
provided with an opening/closing front cover 115 for attaching or
detaching an ink cartridge 200.
As illustrated in FIG. 4 and FIG. 5, inside the apparatus
main body 101, a guide rod 131 and a stay 132 which are guide
members placed laterally on the right and left side plates are
used to retain a carriage 133 so as to slide in a main scanning
direction, and the carriage is moved and scanned by a main
scanning motor (not illustrated) to the direction given by the
arrow in FIG. 5.
The carriage 133 is provided with a recording head 134
made up of four inkjet recording heads for discharging recording

ink droplets of individual colors of yellow (Y), cyan (C), magenta
(M) and black (B) arranged in such a direction that a plurality of
ink discharging ports are crossed in a main scanning direction,
with the direction of discharging ink droplets faced downward.
The inkjet recording head constituting the recording head
134 is provided with a piezoelectric actuator such as a
piezoelectric element, a thermal actuator which uses an
electrothermal converter such as a heat element to utilize the
change in phase resulting from the film boiling of a liquid, a
shape memory alloy actuator which uses the change in metal
phase resulting from the change in temperature, and an
electrostatic actuator which uses an electrostatic force or the
like as a unit configured to generate energy for discharging
recording ink.
Further, the carriage 133 is equipped with a sub-tank 135
of each color for supplying each ink to the recording head 134.
The recording ink of the present invention is supplied through a
recording ink supply tube (not illustrated) from the ink
cartridge 200 of the present invention filled at ink cartridge
loading portion 104 and refilled to the sub-tank 135.
On the other hand, a paper feeding portion for feeding
sheets 142 placed on the sheet placing portion (pressure plate)
141 of the paper feeding tray 102 is provided with a crescent
gear (paper feeding gear 143) for separating the sheets 142 from
the sheet placing portion 141 and supplying them one by one

and a separation pad 144 which is opposed to the paper feeding
gear 143 and made with a material large in friction coefficient.
The separation pad 144 is urged to the paper feeding gear 143.
A transfer portion for transferring the sheets 142 fed from
the paper feeding portion below the recording head 134 is
provided with a transfer belt 151 for electrostatically adsorbing
and transferring the sheets 142, a counter roller 152 for
transferring the sheets 142 sent via a guide 145 from the paper
feeding portion, with the sheets held with respect to the transfer
belt 151, a transfer guide 153 for changing the direction of the
sheets 142 sent above approximately perpendicularly at about
90 degrees to follow on the transfer belt 151, and a leading-end
pressure gear 155 urged to the transfer belt 151 by the presser
member 154. It is also provided with an electrification roller
156, which is a unit configured to electrify the surface of the
transfer belt 151.
The transfer belt 151 is an endless belt, stretched between
a transfer roller 157 and a tension roller 158 and able to rotate
in a belt transfer direction. The transfer belt 151 is provided,
for example, with a surface layer acting as a sheet adhesion face
formed with a resin material of about 40 µm free of rheostatic
control, for example, a copolymer of tetrafluoroethylene with
ethylene (ETFE) and a back layer (middle resistive layer, ground
layer) which is made with the same material as the surface layer
to which rheostatic control is effected by carbon black. A guide

member 161 is provided at the back of the transfer belt 151 so as
to correspond to an imaging area by the recording head 134. It
is noted that a paper discharge portion for discharging the
sheets 142 recorded by the recording head 134 is provided with a
separation nail 171 for separating the sheets 142 from the
transfer belt 151, a paper discharge roller 172 and a paper
discharge gear 173. A paper discharging tray 103 is arranged
below the paper discharge roller 172.
A both-face paper feeding unit 181 is removably attached
to the back face portion of the apparatus main body 101. The
both-face paper feeding unit 181 captures the sheets 142
returned by a reverse rotation of the transfer belt 151 to reverse
the sheets 142, thereby feeding the sheets again between the
counter roller 152 and the transfer belt 151. It is noted that a
manual paper feeding portion 182 is provided on the upper face
of the bothface paper feeding unit 181.
A recording completion signal or a signal of indicating
that the training end of the sheet 142 has arrived at a recording
area, by which recording motions are completed to discharge the
sheet 142 onto the paper discharging tray 103.
Then, when recording ink inside the sub-tank 135 is
detected for the near end of residual quantity, the recording ink
is refilled at a predetermined quantity from the ink cartridge
200 to the sub-tank 135.
In the inkjet recording apparatus, a housing of the ink

cartridge 200 can be disassembled to exchange only an ink bag
thereinside when recording ink inside the ink cartridge 200 is
used up. Further, the ink cartridge 200 is able to supply the
recording ink stably, even when constituted so as to fill the ink
vertically from the front face. Therefore, where the ink
cartridge is arranged, with the apparatus main body 101 being
closed above, for example, a case where the ink cartridge is
accommodated inside a rack or an object is placed on the upper
face of the apparatus main body 101, the ink cartridge 200 can
be exchanged easily.
In this instance, an explanation was made by referring to
an example applied to a serial type (shuttle-type) inkjet
recording apparatus at which the carriage scans. The inkjet
recording apparatus of the present invention is also applicable
to a line-type inkjet recording apparatus equipped with a
line-type head.
Further, the inkjet recording apparatus and the inkjet
recording method of the present invention are applicable to
various types of recording by an inkjet recording method, and in
particular preferably applicable, for example, to an inkjet
recording printer, a facsimile device, a copying device, and a
multifunction device of printer/facsimile/copier.
Next, an explanation will be made for an inkjet head.
FIG. 6 is an enlarged view of elements of an inkjet head to
which the present invention is applied. FIG. 7 is an enlarged

sectional view in an inter-channel direction for illustrating
major parts of the inkjet head.
The inkjet head is constituted with a frame 10 engraved
so as to form an ink supply port (not illustrated) (ink is supplied
from the surface direction to the rear direction in FIG. 6
(direction of the back face of paper)) and a common liquid
chamber 12, a fluid resistance portion 21, a flow path plate 20
which is engraved so as to form a pressure liquid chamber 22
and provided with a port 23 for communicatively connecting to a
nozzle 31, a nozzle plate 30 which forms the nozzle 31, a
projected portion 61, a diaphragm 60 equipped with a diaphragm
portion 62 and an ink flowing port 63, a laminated piezoelectric
element 50 joined to the diaphragm 60 via a bonding layer 70,
and a base 40 which fixes the laminated piezoelectric element 50.
The base 40 is made with barium titanate-based ceramic and is
joined to the laminated piezoelectric elements 50 which are
arranged in two arrays.
The laminated piezoelectric element 50 is prepared by
alternately laminating a piezoelectric layer 51 of lead zirconate
titanate (PZT) with a thickness of 10 µm to 50 µm/one layer and
an internal electrode layer 52 made with silver/palladium
(AgPd) with a thickness of several µm/one layer. The internal
electrode layer 52 is connected at both ends to an external
electrode 53.
The laminated piezoelectric element 50 is divided into a

comb shape by a half-cut dicing process and used as a driving
portion 56 and a supporting portion 57 (non-driving portion) for
each division (refer to FIG. 7).
Of the two external electrodes 53, one of them (connected
to one end of the internal electrode layer 52 in the surface
direction or the rear direction in the drawing (direction on the
back face of paper)) is restricted in length by a process, for
example, notching so as to be divided at the outer end by a
half-cut dicing process, and these divisions are given as a
plurality of individual electrodes 54. The other is not subjected
to division by the dicing process but made conductive and given
as a common electrode 55.
FPC (80) is joined by soldering to the individual
electrodes 54 at the driving portion. Further, the common
electrode 55 is provided with an electrode layer at the edge of
the laminated piezoelectric element and turned around so as to
be joined to the ground electrode of the FPC (80). A driver IC
(not illustrated) is loaded into the FPC (80), thereby controlling
a driving voltage applied to the driving portion 56.
The diaphragm 60 is provided with a thin-film diaphragm
portion 62, an islet projected portion (island portion) 61 joined
to the laminated piezoelectric element 50 which is given as a
driving portion 56 formed at the center of the diaphragm portion
62, a thick-film portion including a beam joined to a supporting
portion (not illustrated), and an opening port which is given as

an ink flowing port 63 formed by laminating two layers of Ni
plated film by electro molding method. The diaphragm portion
is 3 µm in thickness and 35 µm in width (one side).
Connection of the islet projected portion 61 of the
diaphragm 60 with the movable portion 56 of the laminated
piezoelectric element 50 and that of the diaphragm 60 with the
frame 10 are made by patterning a bonding layer 70 which
contains a gap material.
The flow path plate 20 is engraved by using a silicon
mono-crystalline substrate to give a fluid resistance portion 21
and a pressure liquid chamber 22 and provided with a through
hole which acts as a communicatively connected port 23 at a
position opposed to a nozzle 31 through patterning by an etching
process.
A remaining portion after the etching is given as a
partition wall 24 of the pressure liquid chamber 22. In this
instance, the head is provided with a portion which is made
narrow in etching width, and the portion is given as the fluid
resistance portion 21.
The nozzle plate 30 is made with a metal material, for
example, Ni plated film by an electro-molding process and
provided with many nozzles 31, that is, fine discharging ports
for shooting ink droplets. This nozzle 31 is formed in a horn
shape (approximately cylindrical shape or trapezoidal
cylindrical shape) as an internal shape (inner shape). Further,

the nozzle 31 is from 20 µm to 35 µm in diameter at the outlet of
ink droplets. The nozzles are to give 150 dpi at each array.
The nozzle plate 30 is provided on the ink discharging
face (front face of the nozzle) with an ink repellent layer 90. A
water repellent film prepared by PTFE-Ni eutectoid plating,
electro-coating of a fluorine resin, vapor-deposition coating of a
vaporizing fluorine resin (for example, fluoridated pitch), baking
of a silicone-based resin or a fluorine-based resin after coating
of a solvent or the like, is formed, depending on physical
properties of ink, so that the shape of ink droplets and shooting
properties can be stabilized to obtain a high-quality image.

- Surface roughness -
An ink repellent layer used in the present invention is
preferably 0.2 µm or less in surface roughness of Ra. The
surface roughness of Ra is made to be 0.2 µm or less, by which
the remainder after wiping can be reduced.
FIG. 8 and FIG. 9A through FIG. 9C are sectional views
for illustrating a nozzle plate of the inkjet head used in the
present invention.
In the present embodiment, it is preferable that the nozzle
plate 32 of the inkjet head is made by Ni electro-casting, the
surface of which is provided with an ink repellent film 31 or a
silicone resin film with a thickness of 1Å (0.1 nm) or more, and
the surface roughness is made to be Ra = 0.2 µm or less.

Further, the ink repellent film 31 is preferably 0.1pm or more in
thickness and more preferably 0.5 µm or more.
As illustrated in FIG. 9C, when ink 3 is filled, the
meniscus (liquid level) P resulting from a silicone resin film is
formed on the border between the ink repellent film 31 and the
nozzle plate 32.
An ink repellent film formed on a nozzle plate having an
ink discharging opening (nozzle) of the inkjet head is formed so
as to have an opening along with the ink discharging opening,
and the opening is formed so that the cross-sectional area on the
flat face perpendicular to the center line of the opening becomes
gradually larger as the distance from the face of the nozzle plate
increases in the vicinity of the opening.
The shape of the ink repellent film in the vicinity of the
opening is preferably in a curved face. Further, the curvature
radius of the curve in the vicinity of the opening of an ink
repellent film at the cross section of a flat face including the
center line of the opening is preferably greater than the
thickness of the ink repellent film.
Further, it is preferable that a curve from the brim of the
opening of the ink repellent film at the cross section on a flat
face including the center line of the opening to the vicinity of
the opening is approximately an arc curve and the curvature
radius of the arc is greater than the thickness of the ink
repellent film.

It is also preferable that a tangent line passing through
the brim of the opening of the ink repellent film at the cross
section of the flat face including the center line of the opening
forms an angle of 90 degrees with respect to the surface of the
nozzle member including the edge thereof.
The opening of the nozzle plate 32 is formed in such a way
that the cross section of the flat face perpendicular to the center
line indicated by the single dot and dash line in FIG. 9 A
through FIG. 9C is approximately circular at the center of the
center line. Further, the ink repellent film 31 formed on an ink
discharging face of the nozzle plate 32 is formed so that the
cross-sectional area of the opening of the flat face perpendicular
to the center line becomes larger as it moves away from the
nozzle plate 32.
More specifically, as illustrated in FIG. 9A, the opening of
the ink repellent film 31 is provided with a curve from the brim
of the opening of the nozzle plate 32 to the vicinity of the
opening, which is given a round shape with a curvature radius of
r. The curvature radius of r is preferably greater than the
thickness of d except for the vicinity of the opening of the ink
repellent film 31.
The thickness of d is a thickness at parts other than the
round part which is the opening of the ink repellent film 31 and
may be preferably a maximum thickness of the ink repellent
film.

As described above, the opening of the ink repellent film
31 connected to the opening of the nozzle plate 32 is shaped to
be free of approximately sharp edges (a smooth curve free of
acuminate portions) and given a curve free of catching portions,
thereby making it possible to remove such a defect where a
wiper made with a material, for example, rubber, is used to wipe,
sharp portions are caught by the wiper and the ink repellent
film 31 is detached from the nozzle plate 32.
Further, as illustrated in FIG. 9B, it is preferable that a
tangent line passing through the brim of the opening of the ink
repellent film 31 at the cross section of the flat face including
the center line of the opening of the nozzle plate 32 forms an
angle 0 of less than 90 degrees with respect to the surface of the
nozzle plate 32 including the brim of the opening of the nozzle
plate 32 connected to the brim of the opening.
Since an angle of 9 which a tangent line at the brim of the
opening of the ink repellent film 31 forms with the surface of the
nozzle plate is less than 90 degrees, as illustrated in FIG. 9C,
the meniscus (liquid level) P is stably formed at a border
between the ink repellent film 31 and the nozzle plate 32.
Therefore, such a possibility can be greatly reduced that the
meniscus P is formed at other portions. As a result, a
meniscus-forming face is made stable, by which ink can be jetted
stably and favorably when an image is formed by using an image
forming apparatus in which an inkjet head including the nozzle

plate 32 is used.
The silicone resin used in the present embodiment is
preferably a liquid silicone resin which cures at room
temperature and more preferably that involved in hydrolysis
reaction. SR 2411 manufactured by Dow Corning Toray Co., Ltd.
was used in the examples to be described later.
Table A below shows the results of evaluation made for the
shape of the nozzle plate 32 from the brim of the opening to the
vicinity of the brim of the opening on the ink repellent film 31 at
the inkjet head of the present embodiment, ink retained around
the nozzle, edge detachment, and jetting stability.

The results of Table A reveal that where approximately
sharp edges are included in the edge portion of the ink repellent
film 31 (near the brim of the opening), ink is retained around
the nozzle, and the edge is detached when the ink is wiped.
There is found no ink retained where the ink head has
round shape, i.e. no shape edge. However, a partial edge
detachment is found, where r is smaller than d as illustrated in
FIG. 10A. Where 9 is greater than 90 degrees as illustrated in

FIG. 10B, ink droplets are unstably jetted.
Further, where r is smaller than d and 6 is greater than
90 degrees as illustrated in FIG. 10C, there are cases where the
meniscus (liquid level) P is formed at a border between the ink
repellent film 31 and the nozzle plate 32 on ink filling, and
where the meniscus Q is formed at a projected portion toward
the center of the opening on the ink repellent film 31' (a portion
at which the cross-sectional area perpendicular to the center
line of the opening is made smallest). As a result, there may be
found a variance in jetting stability of ink when an inkjet
recording apparatus equipped with an inkjet head including the
nozzle plate 32 is used to record images.
Next, an explanation will be made for a method for
producing a nozzle member of the inkjet head related to the
present embodiment.
FIG. 11 is a view for illustrating a constitution in which a
silicone resin is coated by using a dispenser 34 related to the
present embodiment to form the ink repellent film 31.
A dispenser 4 is arranged for coating a silicone solution on
the ink discharging face of the nozzle 32 prepared by Ni
electro-casting, and the dispenser 4 is scanned while silicone is
discharged from the leading end of a needle 35 in such a way
that the nozzle plate 32 is kept away from the leading end of the
needle 35 at a predetermined distance, by which a silicone resin
film can be formed selectively on the ink discharging face of the

nozzle plate 32, as illustrated in FIG. 8 and FIG. 9A through
FIG. 9C.
The silicone resin used in the present embodiment was a
silicone resin which cures at room temperature, that is, SR 2411
(Dow Corning Toray Co., Ltd., viscosity: 10 mPa•s). However,
there was found some silicone entered around the nozzle port
and the back face of the nozzle plate. The thus selectively
formed silicone resin film was 1.2 µm in thickness and 0.18 µm
in surface roughness (Ra).
As illustrated in FIG. 12A, a coating hole at the leading
end of the needle 35 related to the present embodiment is
secured to be wide only by the width to be coated on the nozzle
plate 32, which is a target to be coated. This fact makes it
possible to completely coat all over the target to be coated by
scanning the dispenser 34 only once toward the coating
direction.
In other words, a scanning direction for coating motions
can be set only in one direction, thereby eliminating the
necessity for changing the direction or conducting a reverse
scanning as in FIG. 12B.
In this instance, as illustrated in FIG. 12B, the leading
end of a general-type needle 35 is much narrower than the width
to be coated on the nozzle plate 32, which is a target to be
coated. Therefore, in order to completely coat all over the
target to be coated, it is necessary to move the target by

changing the scanning direction for coating motions by 90
degrees or conducting a reverse scanning in several different
directions, thus making it difficult to coat all over the target to
be coated at a uniform thickness.
According to the present embodiment, a coating hole at
the leading end of the needle 35 is secured to be wide only by
the width to be coated on the nozzle plate 32, which is a target
to be coated. Thereby, the target to be coated can be coated all
over at a uniform thickness to provide an accurate surface
finishing.
FIG. 13 is a view for illustrating coating motions when
the dispenser 34 of the present embodiment is used. Although
similar in basic constitution as in FIG. 11, silicone is coated
while a gas 36 is jetting from a nozzle port (opening) of the
nozzle plate 32. The gas 36 may include any type of gas which
is less likely to cause chemical reactions with silicone to be
coated. For example, air may be used.
The gas 36 is coated while being jetted from the nozzle
port, thereby making it possible to form a silicone resin film
only on the surface of the nozzle except for the nozzle port of the
nozzle plate 32.
Further, as described above, the gas 36 is not jetted but a
similar silicone resin is used to coat, thereby the silicone resin
is allowed to enter into a predetermined depth. Thereafter, the
gas 36 is jetted from the nozzle 32, thus making it possible to

form an ink repellent layer of the silicone resin up to a desired
depth on the inner wall of the nozzle (for example, about several
µm), as illustrated in FIG. 14. In other words, besides the ink
repellent film 31 on the ink discharging face, it is possible to
form quite a thin ink repellent film 31a (ink repellent film on
the inner wall of the opening) up to a predetermined depth from
the brim of the opening on the nozzle plate 32.
The thus prepared ink repellent film 31 of the nozzle plate
was wiped by using EPDM rubber (rubber hardness of 50
degrees). As a result, after the ink repellent film 31 of the
nozzle plate was wiped 1000 times, it was able to retain
favorable ink repellency. Further, a nozzle member on which
the ink repellent film was formed, was submerged into ink at
70°C for 14 days. As a result, ink repellency was successfully
retained, which remained unchanged thereafter.
FIG. 15 is a view for illustrating one example of the inkjet
head of the present invention and also a state at which the
nozzle port is formed by excimer laser machining. The nozzle
plate 43 is such that in which a resin member 121 is joined with
a highly rigid member 125 with a thermoplastic adhesive agent
126. The resin member 121 is prepared by sequentially
laminating a SiO2 thin film layer 122 and a fluorine-based water
repellent layer 123 on the surface thereof. The resin member
121 is provided with a nozzle port 44 having a predetermined
diameter, and the highly rigid member 125 is provided with a

port 127 which is communicatively connected to the nozzle port
44. The SiO2 thin film layer 122 is formed by a method which
is relatively low in thermal consumption, that is, in which the
film can be formed in a temperature range where the resin
member is not thermally influenced. More specifically,
preferable are sputtering ion beam enhanced deposition, ion
plating, CVD (chemical vapor deposition), PCVD (plasma
chemical vapor deposition) and others.
It is desirable in terms of the processing time and
material cost to make the SiO2 thin film layer 122 as thin as
possible to such an extent as to secure adhesion. Where the
layer is excessively thick, there may be found a problem in
processing a nozzle port by excimer laser. In other words, even
where the resin member 121 is neatly machined into a nozzle
port shape, a part of the SiO2 thin film layer 122 is not
satisfactorily treated, with some of the layer not being treated.
Therefore, specifically, when consideration is given to a fact that
adhesion is secured and no SiO2 thin film layer 122 is left
untreated on treatment by the excimer laser, the thickness is
preferably in a range of 1 Å to 300 A (0.1 nm to 30 nm) and more
preferably from 10 Å to 100 Å (1 nm to 10 nm). Experimental

results revealed that the thickness of the SiO2 thin film of 30 Å
(3 nm) yielded a sufficient adhesion and no problem was found
at all in relation to excimer laser machining. Further, the SiO2
thin film layer 122 was left untreated only to a slight extent at

300 Å (30 nm) and still usable. Where the thickness exceeded
300 Å (30 nm), a relatively large part of the film layer was left
untreated and the nozzle was deformed to an unusable extent.
The ink repellent layer may be made with any material,
as long as it is able to repel ink. Specifically, included are
fluorine-based water-repellent materials and silicone-based
water repellent materials.
Various materials are known as fluorine-based water
repellent materials. In this instance, a mixture of perfluoro
polyoxetane with modified perfluoro polyoxetane (product name:
Optool DSX, manufactured by Daikin Industries, Ltd.) is
deposited to give a thickness of 1 Å to 30 Å (0.1 nm to 3 nm),
thereby obtaining a necessary water repellency. Experimental
results revealed that there was no difference in water repellency
and wiping resistance when the thickness of Optool DSX was 10
Å, 20 Å or 30 Å. Thus, with the cost taken into account, the
thickness is preferably from 1 Å to 20 Å (0.1 nm to 2 nm).
However, some of ink to be used may be kept for performance for
a longer time when a water repellent film is made thicker in
view of reliability. In this instance, the thickness is preferably
from 100 Å to 200 Å (10 nm to 20 nm). Further, an adhesive
tape 124 prepared by coating an adhesive material on a
resin-made film is pasted on the surface of the fluorine-based
water repellent layer 123, thereby giving a supplementary
function on treatment by an excimer laser. Silicone-based

water repellent materials are also usable.
The silicone-based water repellent materials include a
silicone resin and an elastomer which can cure at room
temperature. They are preferably coated on the surface of a
base material and subjected to polymerization and curing when
allowed to stand at room temperature in the atmosphere,
thereby forming an ink repellent film.
The above-described silicone-based water repellent
material is a heat-curable liquid silicone resin or elastomer.
The material may be such that which is coated on the surface of
a base material and cured after heat treatment, thereby forming
an ink repellent film.
The silicone-based water repellent material may be an
ultraviolet-ray curable liquid silicone resin or elastomer, which
is coated on the surface of a base material and cured on
exposure to ultraviolet rays, thereby forming an ink repellent
film.
The silicone-based water repellent material is preferably
1000 cp (centipoise) or less in viscosity.
FIG. 16 is a view for illustrating a constitution of the
excimer laser machine used in machining the nozzle port.
Excimer laser beam 82 emitted from a laser oscillator 81
is reflected by mirrors 83, 85, 88, and led to a processing table
90. A beam expander 84, a mask 86, a field lens 87 and an
image forming optical system 89 are provided at predetermined

positions on a light path until the laser beam 82 arrives at the
processing table 90 so that an optimal beam can be given to a
work piece. The work piece (nozzle plate) 91 is placed on the
processing table 91 to receive the laser beam. The processing
table 90 is constituted with a known XYZ table or the like and
designed to move the work piece 91, when necessary, and radiate
the laser beam at a desired point. In this instance, the laser
was explained by referring to excimer laser. A laser is usable
in various types as long as it is an ultraviolet-ray laser of a
short wavelength by which ablation processing can be conducted.
FIG. 17A to FIG. 17E are views for graphically
illustrating a step of manufacturing a nozzle plate in a method
for manufacturing the inkjet head of the present invention.
FIG. 17A illustrates a material which is used as a base
material of a nozzle forming member. In this instance, a
polyimide film manufactured by Dupont Inc., for example,
Kapton (product name) film free of particles is used as a resin
film 121. Regarding a general-use polyimide film, particles of
SiO2 (silica) or others are added to the film material in view of
the handling property (lubricating property) in a roll-film
handling apparatus. When a nozzle port is machined by the
excimer laser, particles of SiO2 (silica) are poorly machined by
the excimer laser, thereby resulting in deformation of the nozzle.
For this reason, in the present invention, such a film is used
that the particles of SiO2 (silica) are not added. Further, as a

base material of the plate, Upilex, a polyimide film
manufactured by Ube Industries, Ltd., may be used. Upilex is
extremely fine in particles and can be used as it is, as a result of
being free from any machining problems.
FIG. 17B is a view for illustrating a step of forming a SiO2
thin film layer 122 on the surface of the resin film 121. The
SiO2 thin film layer 122 is desirably formed by a sputtering
method which is conducted at a vacuum chamber, with the

preferable film thickness being in a range from about 1Å to 300Å
(0.1 nm to 30 nm). In this instance, the film is formed from
about 10Å to 100Å (1 nm to 10 nm) in thickness. The
sputtering is effectively conducted by a method in which after Si
is sputtered, the surface of Si is exposed to O2 ion, thereby
forming a SiO2 film, due to a fact that the SiO2 film is improved
in adhesion on the resin film 121 to provide uniform and
compact film, which is more effective in improving the wiping
resistance of water repellent film.
FIG. 17C is a view for illustrating a step of coating a
fluorine-based water repellent 123a. This repellent can be
coated by methods such as spin coating, roller coating, screen
printing and spray coating. A film form method by vacuum
deposition is more effective because of improvement in adhesion
of the water repellent film. Further, the vacuum deposition is
conducted, as it is, at a vacuum chamber after formation of the
SiO2 thin film layer 122 given in FIG. 17B, thereby providing

better effects. Conventionally, after formation of the SiO2 thin
film layer 122, a work piece is once taken out from the vacuum
chamber and impurities or the like may attach on the surface,
which may affect the adhesion of the film layer. It is noted that
various types of fluorine-based water repellent materials are
known. In this instance, perfluoro polyoxetane, modified
perfluoro polyoxetane, or a mixture of them is used as a
fluorineamorphous compound, thus making it possible to obtain
water repellency required for ink. The previously described
Optool DSX manufactured by Daikin Industries, Ltd. is from
time to time called "alcoxysilane terminal modified perfluoropoly
ether."
FIG. 17D is a view for illustrating a step of allowing the
water repellent film after vacuum deposition to stand in the
atmosphere. This step makes it possible that the
fluorine-based water repellent 123a and the SiO2 thin film layer
122 are chemically bonded through water contained in the
atmosphere to form a fluorine-based repellent layer 123.
FIG. 17E is a view for illustrating a step of pasting an
adhesive tape 124. The adhesive tape 124 is pasted on the face
on which the fluorine-based water repellent layer 123 is coated.
The adhesive tape 124 should be pasted so as not to generate
bubbles. There may be a case where a nozzle port formed at a
position where bubbles are present is deteriorated in quality by
attachments on machining due to the presence.

FIG. 17F is a view for illustrating a step of machining a
nozzle port 44. In this step, the excimer laser is radiated from
the side of polyimide film 121 to form the nozzle port 44. After
the nozzle port 44 is machined, the adhesive tape 124 is removed
to use the nozzle port. It is noted that an explanation was
omitted for a highly rigid member 125 used in increasing the
rigidity of the nozzle plate 43 given in FIG. 15. This step is
preferably conducted between the step given in FIG. 17D and
that given in FIG. 17E.
FIG. 18 is a view for briefly illustrating an apparatus
used in manufacturing an inkjet head by a method for
manufacturing the inkjet head of the present invention.
The apparatus is that for realizing a method called "meta
mode process" which has been developed by OCLI (Optical
Coating Laboratory Inc., USA) and used in preparing an
anti-reflection film and an anti-fouling film used on a display or
the like. As illustrated in FIG. 18, a Si sputter 202, an O2 ion
gun 203, a Nb sputter 204 and an Optool deposition 205, which
are stations, are arranged at four sites around a drum 210, and
they are all at a vacuum chamber. First, the Si sputter 202 is
used to effect sputtering, and the O2 ion gun 203 is then used to
radiate O2 ions to Si, thereby producing SiO2. Thereafter, the
Nb sputter 204 and the Optool deposition 205 are used to
appropriately deposit Optool DSX. In manufacturing an
anti-reflection film, the necessary number of Nb and SiO2 are

overlapped at a predetermined thickness and then deposited.
Since the present invention does not require a function of the
anti-reflection film, it is sufficient to paste SiO2 and Optool DSX,
with one layer each, without using Nb. As described above, this
apparatus makes it possible to vacuum-deposit Optool DSX, as it
is, at a vacuum chamber after formation of the SiO2 thin film
layer 122.
The ink repellent layer is preferably from 5 mN/m to 40
mN/m in critical surface tension and more preferably from 5
mN/m to 30 mN/m. Where the critical surface tension exceeds
30 mN/m, there is found a phenomenon that ink is excessively
wet on a nozzle plate when used for a long time to result in a
bend discharging of the ink or abnormal granulation after a
repeated printing. Where it exceeds 40 mN/m, there is found a
phenomenon that the ink is excessively wet on the nozzle plate
from the beginning to result in a bend discharging of the ink or
abnormal granulation from the beginning.
The ink-repellent materials listed in Table B were
actually coated on an aluminum substrate, heated and dried to
manufacture a nozzle place having an ink repellent layer. An
ink repellent layer was measured for critical surface tension to
obtain the results shown in Table 2.
In this instance, the critical surface tension can be
measured by using the Zisman method. In other words, a liquid,
the surface tension of which is known, is dropped on the ink

repellent layer to measure the contact angle of θ, the surface
tension of the liquid is plotted on the x axis and cos θ is plotted
on the y axis, thereby obtaining a line on the downward side
(Zisman Plot). When this line is to give Y = 1 (θ =0), the
surface tension can be calculated as a critical surface tension, Yc
The critical surface tension can be measured also by such
methods as Fowkes method, the Owens and Wendt method and
the Van Oss method.
Further, a nozzle plate having an ink repellent layer was
used to manufacture an inkjet head by a method similar to that
for manufacturing the head. The cyan ink described below was
used and jetted through the inkjet head. A shooting process of
the ink was videotaped and observed to confirm that a normal
granulation took place when either of the nozzle plates was used
and discharge was also stable. The results are shown in Table
B.

Copper phthalocyanine pigment-containing polymer fine
particle dispersion of 20.0 % by mass, 3-methyl 1,3-butane diol
of 23.0 % by mass, glycerin of 8.0 % by mass, 2-ethyl-l,3-hexane
diol of 2.0 % by mass, FS-300 (manufactured by Dupont) of 2.5 %
by mass as a fluorochemical surfactant, Proxel LV
(manufactured by Abecia Inc.) of 0.2 % by mass as an
anti-septic/anti-mildew agent, 2-amino-2-ethyl-1,3-propane diol
of 0.5 % by mass and an appropriate quantity of ion exchanged

water were added to give 100 % by mass, and, thereafter, the
resultant was filtered through a membrane filter with an
average pore size of 0.8 µm. The cyan ink was prepared by the
above procedures.

A frame 10, which is to form an ink supply port and
engraved to give a common liquid chamber 12 in FIG. 6, is
manufactured by resin molding.
In the thus constituted inkjet head, a driving wave
pattern (pulse voltage of 10 V to 50 V) is applied to a driving
portion 56 according to recording signals, by which the driving
portion 56 is displaced toward a direction of lamination, and a
pressure liquid chamber 22 is given pressure via a nozzle plate
30 to result in pressure elevation, thereby ink droplets are
discharged from a nozzle 31.
Thereafter, when ink droplets are completely discharged,
ink pressure inside the pressure liquid chamber 22 is decreased
to develop a negative pressure inside the pressure liquid
chamber 22 due to the inertia of ink flow and electrical
discharge process of the driving pulse. The step is then moved
to an ink filling step. In this instance, ink supplied from an
ink tank flows into a common liquid chamber 12, passing a fluid

resistance portion 21 through an ink flowing port 63 from the
common liquid chamber and is filled into the pressure liquid
chamber 22.
The fluid resistance portion 21 is effective in attenuating
the residual pressure oscillation after the discharge but
resistive to refill by utilizing the surface tension. An
appropriate fluid resistance portion is selected, thereby the
residual pressure is attenuated in conformity with the refill
time, making it possible to shorten the time necessary for
moving on to the next ink droplet discharging motion (driving
cycle).

An ink recorded matter made by the inkjet recording
apparatus according to the inkjet recording method of the
present invention is provided with an image formed on a
recording medium by using the recording ink of the present
invention.
The ink record matter is high in image quality, free of
oozed ink and excellent in stability with the lapse of time,
therefore, finding favorably a variety of applications as
documents and others in which various types of printing and
imaging are recorded.
Examples
Hereinafter, an explanation will be made for examples of

the present invention. It should be, however, noted that the
present invention is not restricted by the examples in any way.
(Preparation Example 1)
-Preparation of a surface treated carbon black pigment
dispersion -
1 mol/L sodium persulfate was added to 100 g of carbon
black having a primary particle size of 16 nm, specific surface
area of 260 m2/g, and DBP oil absorption of 69 mL/100g (#960,
manufactured by Mitsubishi Chemical Corporation), and the
mixture was stirred at 80°C for 10 hours so as to proceed with
an oxidation treatment. Then, the resultant was washed with
purified water and dried, thereafter, dispersed again in water
and neutralized with sodium hydroxide so as to give pH of 7,
with remaining salts being separated by an ultra-filter. Water
to be added was adjusted so as to the pigment concentration of
20% by mass, and a membrane filter with a pore size of 0.8 µm
was used to remove large particles therefrom.
The thus prepared dispersion was 1.35 mS/cm in electric
conductivity and 123 nm in volume average particle size.
It is noted that the carbon black was measured for a
volume average particle size by using Microtrac UPA
(manufactured by Nikkiso Co., Ltd.).
(Preparation Example 2)
-Preparation of surface-treated carbon black pigment dispersion-
1 mol/L sodium hypochlorite was added to 100 g of carbon

black having a primary particle size of 16 nm, specific surface
area of 260 m2/g, and DBP oil absorption of 69 mL/100g (#960,
manufactured by Mitsubishi Chemical Corporation), and the
mixture was stirred at 80°C for 10 hours so as to proceed with
an oxidation treatment. Then, the resultant was washed with
purified water and dried, thereafter, dispersed again in water
and neutralized with potassium hydroxide so as to give pH of 7,
with remaining salts being separated by an ultra-filter. Water
to be added was adjusted so as to attain the pigment
concentrations of 20 % by mass, and a membrane filter with a
pore size of 0.8 µm was used to remove large particles.
The thus obtained dispersion was 1.3 mS/cm in electric
conductivity and 128 nm in volume average particle size.
It is noted that the carbon black was measured for a
volume average particle size by using Microtrac UPA
(manufactured by Nikkiso Co., Ltd.).
(Preparation Example 3)
-Preparation of surface-treated carbon black pigment dispersion-
3L of purified water was added to 100 g of carbon black
having a primary particle size of 16 nm, specific surface area of
260 m2/g, and DBP oil absorption of 69 mL/100g (#960,
manufactured by Mitsubishi Chemical Corporation), and the
mixture was stirred for 5 minutes. Then, ozone gas was
introduced so as to proceed with an oxidation treatment for 1
hour. The resultant was washed with purified water and dried,

thereafter, dispersed again in water and neutralized with
sodium hydroxide so as to give pH of 7, with remaining salts
being separated by an ultra-filter. Water to be added was
adjusted so as to attain the pigment concentration of 20% by
mass, and a membrane filter with a pore size of 0.8 µm was used
to remove large particles.
The thus obtained dispersion was 1.25 mS/cm in electric
conductivity and 132 nm in volume average particle size.
It is noted that the carbon black was measured for a
volume average particle size by using Microtrac UPA
(manufactured by Nikkiso Co., Ltd.).
(Preparation Example 4)
-Preparation of surface-treated carbon black pigment dispersion-
1 mol/L sodium hypochlorite was added to 100 g of carbon
black having a primary particle size of 16 nm, specific surface
area of 260 m2/g, and DBP oil absorption of 69 mL/100g (#960,
manufactured by Mitsubishi Chemical Corporation), and the
mixture was stirred at 100°C for 15 hours so as to proceed with
an oxidation treatment. Then, the resultant was washed with
purified water and dried, thereafter, dispersed again in water
and neutralized with potassium hydroxide so as to give pH of 7,
with remaining salts being separated by an ultra-filter. Water
to be added was adjusted so as to attain the pigment
concentration of 20% by mass, and a membrane filter with the
pore size of 0.8 µm was used to remove large particles.

The thus obtained dispersion was 1.38 mS/cm in electric
conductivity and 126 nm in volume average particle size.
It is noted that the carbon black was measured for a
volume average particle size by using Microtrac UPA
(manufactured by Nikkiso Co., Ltd.).
(Preparation Example 5)
-Preparation of surface-treated carbon black pigment dispersion-
1 mol/L sodium persulfate was added to 100 g of carbon
black having a primary particle size of 21 nm, specific surface
area of 135 m2/g, and DBP oil absorption of 53 mL/100g (#7550,
manufactured by Tokai Carbon Co., Ltd.), and the mixture was
stirred at 80°C for 10 hours so as to proceed with an oxidation
treatment. Then, the resultant was washed with purified water
and dried, thereafter, dispersed again in water and neutralized
with sodium hydroxide so as to give pH of 7, with remaining
salts being separated by an ultra-filter. Water to be added was
adjusted so as to attain the pigment concentration of 20% by
mass, and a membrane filter with a pore size of 0.8 µm was used
to remove large particles.
The thus obtained dispersion was 1.2 mS/cm in electric
conductivity and 61 nm in volume average particle size.
It is noted that the carbon black was measured for a
volume average particle size by using Microtrac UPA
(manufactured by Nikkiso Co., Ltd.).
(Preparation Example 6)

-Preparation of surface-treated carbon black pigment dispersion-
1 mol/L sodium persulfate was added to 100 g of carbon
black having a primary particle size of 24 nm, specific surface
area of 120 m2/g, and DBP oil absorption of 57 mL/100g (MA8,
manufactured by Mitsubishi Chemical Corporaton), and the
mixture was stirred at 80°C for 10 hours so as to proceed with
an oxidation treatment. Then, the resultant was washed with
purified water and dried, thereafter, dispersed again in water
and neutralized with sodium hydroxide so as to give pH of 7,
with remaining salts being separated by an ultra-filter. Water
to be added was adjusted so as to attain the pigment
concentration of 20 % by mass, and a membrane filter with a
pore size of 0.8 µm was used to remove large particles.
The thus obtained dispersion was 1.23 mS/cm in electric
conductivity and 55 nm in volume average particle size.
It is noted that the carbon black was measured for a
volume average particle size by using Microtrac UPA
(manufactured by Nikkiso Co., Ltd.).
(Preparation Example 7)
-Preparation of surface-treated carbon black pigment dispersion-
1 mol/L sodium persulfate was added to 100 g of carbon
black having a primary particle size of 20 nm, specific surface
area of 140 m2/g, and DBP oil absorption of 131 mL/100g (MA600,
manufactured by Mitsubishi Chemical Corporaton), and the
mixture was stirred at 80°C for 10 hours so as to proceed with

an oxidation treatment. Then, the resultant was washed with
purified water and dried, thereafter, dispersed again in water
and neutralized with sodium hydroxide so as to give pH of 7,
with remaining salts being separated by an ultra-filter. Water
to be added was adjusted so as to attain the pigment
concentration of 20 % by mass, and a membrane filter with a
pore size of 0.8 µm was used to remove large particles.
The thus obtained dispersion was 1.35 mS/cm in electric
conductivity and 205 nm in volume average particle size.
It is noted that the carbon black was measured for a
volume average particle size by using Microtrac UPA
(manufactured by Nikkiso Co., Ltd.).
(Example 1)
An ink composition with the following formulation was
prepared and triethanol amine was added so as to attain pH of 9.
Thereafter, the composition was filtered by using a membrane
filter with an average pore size of 0.8 pm to prepare ink.

•Carbon black dispersion of Preparation Example l: 9.0 %
by mass (solids content)
• 1,5-pentane diol- 22.5 % by mass
•Glycerin: 7.5 % by mass
•Surfactant (Softanol EP 7025, manufactured by Nippon
Shokubai Co., Ltd.): 1.0 % by mass
•Ion exchanged water: 60.0 % by mass

(Example 2)
An ink composition with the following formulation was
prepared and triethanol amine was added so as to attain pH of 9.
Thereafter, the composition was filtered by using a membrane
filter with an average pore size of 0.8 µm to prepare ink.

•Carbon black dispersion of Preparation Example 2' 8.0 %
by mass (solids content)
•Acryl resin fine particles (Aquabrid 4720 manufactured
by Daicel Chemical Industries, Ltd., volume average particle
size = 95nm): 5.0 % by mass (solids content)
•3-methyl-l,3-butane diol: 21.0 % by mass
• Glycerin: 7.0 % by mass
• Surfactant (Softanol EP 7025, manufactured by Nippon
Shokubai Co., Ltd.): 1.0 % by mass
•pH buffering agent expressed by the following formula
(4): 0.1 % by mass
(HOCH2CH2)2NCH2COOH: formula (4)
•Ion exchanged water: 57.9 % by mass
(Example 3)
An ink composition with the following formulation was
prepared and triethanol amine was added so as to attain pH of 9.
Thereafter, the composition was filtered by using a membrane
filter with an average pore size of 0.8 µm to prepare ink.

•Carbon black dispersion of Preparation Example 5: 8.0 %
by mass (solids content)
•Acryl resin fine particles (Aquabrid 4720 manufactured
by Daicel Chemical Industries, Ltd., volume average particle
size = 95 nm - 5.0 % by mass (solids content)
•3methyl-l,3butane diol: 21.0 % by mass
•Glycerin: 7.0 % by mass
• Surfactant (Softanol EP 7025, manufactured by Nippon
Shokubai Co., Ltd.): l.o % by mass
•pH buffering agent expressed by the following formula
(8): 0.1 % by mass

•Ion exchanged water: 57.9 % by mass
(Example 4)
An ink composition with the following formulation was
prepared and triethanol amine was added so as to attain pH of 9.
Thereafter, the composition was filtered by using a membrane
filter with an average pore size of 0.8 µm to prepare ink.

•Carbon black dispersion of Preparation Example 6: 8.0 %
by mass (solids content)
•Acryl resin fine particles (Aquabrid 4720 manufactured

by Daicel Chemical Industries, Ltd., volume average particle
size = 95 nm) : 5.0 % by mass (solids content)
•3-methl-1,3-butane diol: 21.0 % by mass
•Glycerin: 7.0 % by mass
• Surfactant (Softanol EP 7025, manufactured by Nippon
Shokubai Co., Ltd.): 1.0 % by mass
•Ion exchanged water: 58.0 % by mass
(Example 5)
An ink composition with the following formulation was
prepared and triethanol amine was added so as to attain pH of 9.
Thereafter, the composition was filtered by using a membrane
filter with an average pore size of 0.8 µm to prepare ink.

•Carbon black dispersion of Preparation Example 7: 8.0 %
by mass (solids content)
•Acryl resin fine particles (Aquabrid 4720 manufactured
by Daicel Chemical Industries, Ltd., volume average particle
size = 95 nm): 5.0 % by mass (solids content)
•3- methyl-l,3-butane diol: 21.0 % by mass
•Glycerin: 7.0 % by mass
•Surfactant (Softanol EP 7025, manufactured by Nippon
Shokubai Co., Ltd.): 1.0 % by mass
•Ion exchanged water: 58.0 % by mass
(Example 6)
An ink composition with the following formulation was

prepared and triethanol amine was added so as to attain pH of 9.
Thereafter, the composition was filtered by using a membrane
filter with an average pore size of 0.8 µm to prepare ink.

•Carbon black dispersion of Preparation Example 1 :
14.0 % by mass (solids content)
•Acryl resin fine particles (Aquabrid 4720 manufactured
by Daicel Chemical Industries, Ltd., volume average particle
size = 95 nm): 2.0 % by mass (solids content)
• l,3butane diol: 21.0 % by mass
•Glycerin: 7.0 % by mass
• Surfactant (Softanol EP 7025, manufactured by Nippon
Shokubai Co., Ltd.): 1.0 % by mass
•Ion exchanged water: 55.0 % by mass
(Example 7)
An ink composition with the following formulation was
prepared and triethanol amine was added so as to attain pH of 9.
Thereafter, the composition was filtered by using a membrane
filter with an average pore size of 0.8 µm to prepare ink.

•Carbon black dispersion of Preparation Example l: 4.0 %
by mass (solids content)
•Acryl resin fine particles (Aquabrid 4720 manufactured
by Daicel Chemical Industries, Ltd., volume average particle
size = 95 nm): 2.0 % by mass (solids content)

• 1,6-hexane diol: 24.0 % by mass
•Glycerin: 8.0 % by mass
•Surfactant (Softanol EP 7025, manufactured by Nippon
Shokubai Co., Ltd.): 1.0 % by mass
•Ion exchanged water: 61.0 % by mass
(Example 8)
An ink composition with the following formulation was
prepared and triethanol amine was added so as to attain pH of 9.
Thereafter, the composition was filtered by using a membrane
filter with an average pore size of 0.8 µm to prepare ink.

•Carbon black dispersion of Preparation Example 1- 7.0 %
by mass (solids content)
•Acryl resin fine particles (Aquabrid 4720 manufactured
by Daicel Chemical Industries, Ltd., volume average particle
size = 95 nm): 4.0 % by mass (solids content)
• 1,3-butane diol: 21.0 % by mass
•Glycerin-' 7.0 % by mass
•Surfactant expressed by the formula (l) (m =2, n =10):
1.0 % by mass
•Ion exchanged water: 61.0 % by mass
(Example 9)
An ink composition with the following formulation was
prepared and triethanol amine was added so as to attain pH of 9.
Thereafter, the composition was filtered by using a membrane

filter with an average pore size of 0.8 µm to prepare ink.

•Carbon black dispersion of Preparation Example 1:
16.0 % by mass (solids content)
• 1,3-butane diol: 21.0 % by mass
•Glycerin: 7.0 % by mass
•Surfactant (Softanol EP 7025, manufactured by Nippon
Shokubai Co., Ltd.): 1.0 % by mass
•Ion exchanged water: 55.0 % by mass
(Example 10)
An ink composition with the following formulation was
prepared and sodium hydroxide was added so as to attain pH of
9. Thereafter, the composition was filtered by using a
membrane filter with an average pore size of 0.8 µm to prepare
ink.

•Carbon black dispersion of Preparation Example l: 7.0 %
by mass (dry solid basis)
•Acryl resin fine particles (Aquabrid 4720 manufactured
by Daicel Chemical Industries, Ltd., volume average particle
size = 95 nm): 4.0 % by mass (solids content)
• 1.3butane diol: 21.0 % by mass
•Glycerin: 7.0 % by mass
•Surfactant (Softanol EP 7025, manufactured by Nippon
Shokubai Co., Ltd.): 1.0 % by mass

Ion exchanged water: 60.0 % by mass
(Comparative Example 1)
An ink composition with the following formulation was
prepared and triethanol amine was added so as to attain pH of 9.
Thereafter, the composition was filtered by using a membrane
filter with an average pore size of 0.8 µm to prepare ink.

•Carbon black dispersion of Preparation Example 3: 6.0 %
by mass (solids content)
•3-methyl-l,3-butane diol: 21.0 % by mass
•Glycerin:7.0 % by mass
•Surfactant (Softanol EP 7025, manufactured by Nippon
Shokubai Co., Ltd.): 1.0 % by mass
•Ion exchanged water: 63.0 % by mass
(Comparative Example 2)
An ink composition with the following formulation was
prepared and triethanol amine was added so as to attain pH of 9.
Thereafter, the composition was filtered by using a membrane
filter with an average pore size of 0.8 µm to prepare ink.

• Carbon black dispersion of Preparation Example 4: 8.0 %
by mass (solids content)
•3methyl-1,3butane diol: 21.0 % by mass
•Glycerin: 7.0 % by mass
• Surfactant (Softanol EP 7025, manufactured by Nippon

Shokubai Co., Ltd.) - 1.0 % by mass
•Ion exchanged water: 62.0 % by mass
(Comparative Example 3)
• Carbon black A (# 47 manufactured by Mitsubishi
Chemical Corporation): 15 % by mass
• Joncryl 68 (manufactured by Johnson polymer Co., Ltd.):
5 % by mass
•Glycerin: 10 % by mass
•Ion exchanged water: 70 % by mass
The above materials were dispersed with glass beads in a
sand mill for 3 hours, and then filtered through a membrane
filter with an average pore size of 5pm to obtain a carbon black
dispersion A.
Using the obtained carbon black dispersion A, an ink
composition with the following formulation was prepared and
triethanol amine was added so as to attain pH of 9. Thereafter,
the composition was filtered through a membrane filter with an
average pore size of 0.8 µm to prepare ink.

•Carbon black dispersion A: 7.0 % by mass (solids content)
• 1,3-butane diol: 22.5 % by mass
•Glycerin: 7.5 % by mass
•Surfactant (Softanol EP 7025, manufactured by Nippon
Shokubai Co., Ltd.): 1.0 % by mass
•2,2,4-trimethyl-1, 3 pentanediol: 2.0 % by mass

•Ion exchanged water: 67 % by mass
Each of the thus obtained recording ink was evaluated for
various properties as shown below. Tables 1 to 4 show each of
the ink formulations and the results.

Each recording ink was diluted with purified water and
measured for a volume average particle size (D50%) by using a
particle size distribution measuring device (Microtrac UPA,
manufactured by Nikkiso Co., Ltd.).

Measurement was made for the viscosity at 25°C by using
RL-500 (manufactured by Toki Sangyo Co., Ltd.).

Measurement was made for the surface tension at 23°C ±
2°C by using a static surface tension balance (BVP-Z,
manufactured by Kyowa Interface Science Co., Ltd.).

Measurement was made for the pH at 23°C ± 2°C by using
a pH meter (HM-A, manufactured by DKKToa Corporation).

Each of the thus obtained recording ink was used to test
the imaging performance by using the inkjet printer shown in
FIG. 3 through FIG. 7. A silicone resin film (room-temperature
curing silicone resin SR 2411, manufactured by Dow Corning
Toray Co., Ltd.) was formed on the surface of the nozzle plate of

the inkjet printer, with a thickness of 1.2 µm, surface roughness
(Ra) of 0.18 µm and critical surface tension of 21.6 mN/m. The
imaging test was conducted at the super-fine mode by using
high-grade plain paper under conditions of 23°C and 50 % RH.
Further, the head driving wave pattern was adjusted so that the
ink can be discharged at a constant quantity.

The inkjet printer shown in FIG. 3 to FIG. 7 in which each
recording ink prepared in Examples 1 through 10 and
Comparative Examples 1 through 3 was filled was used to print
on type 6200 paper (manufactured by NBS Ricoh Co., Ltd.) at a
resolution of 600 dpi. After drying, measurement was made for
the image density by using a reflection-type color
spectrophotometer (manufactured by X-Rite).

The inkjet printer shown in FIG. 3 to FIG. 7 in which each
recording ink prepared in Examples 1 through 10 and
Comparative Examples 1 through 3 was filled was used to print
on type 6200 paper (manufactured by NBS Ricoh Co., Ltd.) at a
resolution of 600 dpi. After drying, printed parts were rubbed
with a cotton cloth ten times, and pigment transferred to the
cotton cloth was macroscopically observed and evaluated on the
basis of the following criteria.
[Evaluation criteria]
A: Substantially no pigment is transferred to the cotton

cloth.
B: Pigment is transferred to some extent.
C : Pigment is clearly transferred.

The inkjet printer shown in FIG. 3 to FIG. 7 in which each
recording ink prepared in Examples 1 through 10 and
Comparative Examples 1 through 3 was filled was used to print
on type 6200 paper (manufactured by NBS Ricoh Co., Ltd.) at a
resolution of 600 dpi. The printing was conducted continuously
on 200 sheets of the paper to evaluate the discharge disturbance
and discharge failure on the basis of the following criteria.
[Evaluation criteria]
A: No discharge disturbance or discharge failure is found.
B: Discharge disturbance or discharge failure is found in
three or less nozzles.
C: Discharge disturbance or discharge failure is found in
four or more nozzles.
atmosphere>
The inkjet printer shown in FIG. 3 to FIG. 7 in which each
recording ink prepared in Examples 1 through 10 and
Comparative Examples 1 through 3 was filled was used to
conduct an all color cleaning. Thereafter, the ink was allowed
to stand under the conditions of 32°C and 30 %RH for one month.
Then, nozzles were checked for the printing performance to

evaluate discharge disturbance and discharge failure on the
basis of the following criteria.
[Evaluation criteria]
A: No discharge disturbance or discharge failure is found.
B: Discharge disturbance or discharge failure is found in
three or less nozzles.
C : Discharge disturbance or discharge failure is found in
four or more nozzles.

Recording ink prepared in Examples 1 through 10 and
Comparative Examples 1 through 3 were filled into cartridges
and stored at 60°C for two weeks. Observation was made for an
increased viscosity of the ink and change in pH.
It is noted that the increased viscosity was defined as
(increased viscosity of ink, %) = [(viscosity after storage)
/(viscosity before storage) - 1 ] x 100.

The inkjet printer shown in FIG. 3 to FIG. 7 in which each
recording ink prepared in Examples 1 through 12 and
Comparative Examples 1 through 3 was filled was used to print
on a matt paper (Hokuetsu Paper Mills, Ltd.) at a resolution of
600 dpi. Evaluation was made for blurred characters and
variance in color at a solid part.
It is noted that the a matt paper was measured for a
quantity of purified water transferred to a recording medium at

the contact time of 100 ms by using a dynamic scanning
absorptometer (DSA, manufactured by Kyowa Seiko Co., Ltd.),
finding that the quantity was 3.6 mL/m2.
[Evaluation criteria for blurred characters]
A: Characters are very clearly printed, with no blur found.
B: Characters are printed less clearly, with some blur
found.
C : Characters are not clearly printed, with a marked blur
found.
[Evaluation criteria for variance in color at solid part]
A: Image is clear, with substantially no variance in color.
B: Image is relatively poor in clearness, with some
variance in color.
C: Image is not clear, with a marked variance in color.

At first, column chromatography was performed to remove
additives such as a surfactant, a rust-preventive agent and an
ultraviolet absorbing agent from the recording ink prepared in
Examples 1 through 10 and Comparative Examples 1 through 3
and recovered a carbon black. The thus obtained carbon black
was subjected to vacuum drying by using a dryer at 50 °C for
sufficient evaporation of water and solvent and then diluted
with water to a concentration of 20 % by mass. Fifty grams of
the diluted solution was measured in a beaker, and passed
through an ultra-filter (Pellicon Biomax 50, manufactured by

Millipore) for 30 minutes to obtain a brown liquid. This liquid
was diluted 10 times with ion exchanged water and read on a
spectrophotometer (U-3310, manufactured by Hitachi
High-Technologies Corporation) equipped with a quartz cell
(light path length of 10 mm) at a wavelength of 230 nm to 260
nm. The thus obtained maximum absorbance was increased 10
times to determine the concentration of humic acid.

Recording ink prepared in Examples 1 through 10 and
Comparative Examples of 1 through 3 was diluted 10 times with
ion exchanged water and measured for concentrations of sodium
and potassium contained in the ink by using a high-frequency
induction plasma emission analyzer (ICP-1000IV, manufactured
by Shimadzu Corporation). The thus obtained values were
respectively multiplied by 10 times and totaled to give the
concentration of alkali metals.

A predetermined quantity of the ink prepared in Examples
1, 5, 7, 9 and Comparative Examples of 1 through 3 was allowed
to stand under the conditions of 50°C and 10% humidity, and
measured for a change in ink mass after the passage of a certain
time and the viscosity at 25°C. It is noted that a quantity of
water evaporation and an increased viscosity relative to an
initial viscosity were determined by the following formulae.
• (Quantity of water evaporation [%]) = [ (mass of initial ink ) —

(mass of ink after water evaporation)] / (mass of initial ink) x
100
• (Increased viscosity relative to initial viscosity) = (viscosity of
ink after water evaporation) / (initial viscosity)
FIG. 19 shows a relationship between the quantity of
water evaporation (%) and the viscosity of ink (mPa•s).
Further, Table 5 shows an increased viscosity relative to
the initial viscosity when the water evaporation rate is from
34 % by mass to 41 % by mass.

(Production Example A)
—Production of Support—
A support having a basis weight of 79g/m2 was produced
by papermaking a slurry containing 0.3% by mass of the
following formulation using a fourdrinier papermaking machine.
In a size press step of the papermaking process, an aqueous
solution of oxidized starch was applied to a surface of the
support such that the deposited solid amount is 1.0g/m2 per one
surface.
•Broad-leaved wood bleached kraft pulp (LBKP): 80 parts
by mass
• Coniferous wood bleached kraft pulp (NBKP): 20 parts by

mass
•Precipitated calcium carbonate (product name: TP-121,
manufactured by Okutama Kogyo Co., Ltd.): 10 parts by mass
•Aluminum sulfate:1.0 part by mass
•Amphoteric starch (product name: Cato3210,
manufactured by Nippon NSC Ltd.): 1.0 part by mass
•Neutral rosin sizing agent (product name: NeuSize M-10,
manufactured by HARIMA CHEMICALS,INC.): 0.3 parts by
mass
•Retention aid (product name: NR-11LS, manufactured by
HYMO Co..Ltd.): 0.02 parts by mass
(Production Example B)
—Production of Recording Medium 1—
As a pigment 70 parts by mass of clay containing 97 % by
mass of particles having a particle diameter of 2µm or less, 30
parts by mass of heavy calcium carbonate having an average
particle diameter of 1.1µm, as an adhesive 8 parts by mass of
styrenebutadiene copolymer emulsion having a glass transition
temperature (Tg) of -5°C, 1 part by mass of phosphated starch,
as an auxiliary agent 0.5 parts by mass of calcium stearate, and
water were mixed together to prepare a coating solution
containing 60 % by mass of solid content.
The obtained coating solution was applied on both sides of
the prepared substrate using a blade coater such that the
deposited solid amount is 8 g/m2 per one surface, dried with hot

air, and supercalendered to prepare "Recording Medium 1".
(Production Example C)
—Production of Recording Medium 2—
As a pigment 70 parts by mass of clay containing 97 % by
mass of particles having a particle diameter of 2µm or less, 30
parts by mass of heavy calcium carbonate having an average
particle diameter of 1.1µm, as an adhesive 7 parts by mass of
styrenebutadiene copolymer emulsion having a glass transition
temperature (Tg) of -5°C, 0.7 parts by mass of phosphated starch,
as an auxiliary agent 0.5 parts by mass of calcium stearate, and
water were mixed together to prepare a coating solution
containing 60 % by mass of solid content.
The obtained coating solution was applied on both sides of
the prepared substrate using a blade coater such that the
deposited solid amount is 8 g/m2 per one surface, dried with hot
air, and supercalendered to prepare "Recording Medium 2".
(Production Example D)
—Production of Recording Medium 3—
A coated paper for gravure printing (product name: Space
DX, a basis weight of 56g/m2, manufactured by Nippon Paper
Industries Co., Ltd.) was used.
(Production Example E)
—Production of Recording Medium 4—
A coat paper for offset printing (product name: Aurora
Coat, a basis weight of 104.7 g/m2, manufactured by Nippon

Paper Industries Co., Ltd.) was used.
(Production Example F)
—Production of Recording Medium 5—
A matte coated paper for inkjet printing (product name:
SuperFine paper, manufactured by SEIKO EPSON Corp.) was
used.
Next, the quantity of each of inks in Examples 3 and 5
transferred to the recording media 1 through 5 was measured by
using a dynamic scanning absorptometer as follows:
Beading, blur characters, drying property and OD value of
an image printed in each recording medium were evaluated.
The results were shown in Tables 6 and 7.
absorptometer>
A dynamic scanning absorptometer (K350 series D type,
manufactured by Kyowa Seiko Co., Ltd.) was used to measure
the quantities of transferred inks of Examples 3 and 5.
Quantities transferred at the contact time of 100 ms and at the
contact time of 400 ms could be determined by interpolating
measurements of the quantities transferred at adjacent contact
times of the respective contact times. The measurements were
made at 23°C and RH of 50%.

The inks of Examples 3 and 5 were printed on the
recording media 1 through 5 at a resolution of 600 dpi, and

beading was visually observed.
[Evaluation criteria]
4: Substantially no beading and uniform printing
3: Slightly beading is observed.
2: Clearly beading is observed.
1: Outstandingly beading is observed.

The inks of Examples 3 and 5 were printed on the
recording media 1 to 5 at a resolution of 600 dpi, and blur
characters was visually observed.
[Evaluation criteria]
4: Substantially no blur and clear printing
3: Slightly blur is observed.
2: Clearly blur is observed.
1: Outstandingly blur is observed.

The inks of Examples 3 and 5 were printed on the
recording media 1 through 5 at a resolution of 600 dpi.
Immediately after printing, a plain paper type 6200 paper
(manufactured by NBS Ricoh Co., Ltd.) was put on printed parts,
and pressed with a finger and then visually observed a degree of
transferred on the plain paper.
[Evaluation criteria]
4: No transfer is observed.
3: Slightly transfer is observed.

2: Clearly transfer is observed.
l: Outstandingly transfer is observed.

The inks of Examples 3 and 5 were printed on the
recording media 1 through 5 at a resolution of 600 dpi. An
image density of a solid image was measured by a color
reflection densitometer XRite938.

Industrial Applicability
The recording ink of the present invention is excellent in
fixing property and image density on a recording medium and
also excellent in stability after a prolonged storage and able to
form a high-quality image not only on plain paper or paper
exclusively used for inkjet printing but also on coated paper for
commercial printing poor in water absorption, thereby favorably
applicable to an inkjet recording apparatus.
Further, the inkjet recording apparatus and the inkjet
recording method of the present invention are applicable to
various types of recording by an inkjet recording method, and in
particular preferably applicable, for example, to an inkjet
recording printer, a facsimile device, a copying device, and a
multifunction device of printer/facsimile/copier.

WE CLAIM :
1. A recording ink comprising:
water;
a water-soluble organic solvent;
a surfactant; and
a carbon black having a hydrophilic group on a surface thereof,
wherein the carbon black releases humic acid in an aqueous
dispersion of the carbon black, which is recovered from the recording ink,
a concentration of the humic acid released in the aqueous dispersion
containing 20 % by mass of the carbon black is expressed with a
maximum absorbance at a wavelength of 230 nm to 260 nm, and the
recording ink has the maximum absorbance of 5.0 to 20.0 at the
wavelength of 230 nm to 260 nm,
and wherein a quantity of the alkali metal contained in the
recording ink is from 100 ppm or more to 1500 ppm or less.
2. The recording ink as claimed in claim 1, wherein a content of the
carbon black is from 5 % by mass to 15 % by mass with respect to the
total amount of the recording ink.
3. The recording ink as claimed in any of claim 1 or 2, wherein the
recording ink has a ratio B/A of from 5.0 or more to less than 550 when
the recording ink has a liquid evaporation rate of 34% by mass to 41% by
mass relative to a total mass of the recording ink, where A is an initial

viscosity of the recording ink and B is a viscosity after liquid
evaporation.
4. The recording ink as claimed in any one of claims 1 to 3,
comprising a pH buffering agent.
5. The recording ink as claimed in claim 4, wherein the pH buffering
agent is at least one organic pH buffering agent selected from Good's
buffer solutions.
6. The recording ink as claimed in any one of claims 1 to 5, wherein
the carbon black having a hydrophilic group has a volume average
particle size of from 60 nm to 200 nm at the time being dispersed in
water.
7. The recording ink as claimed in any one of claims 1 to 6,
comprising resin fine particles having a volume average particle size of
from 50 nm to 200 nm.
8. The recording ink as claimed in any one of claims 1 to 7, wherein
at least a part of a terminal of the hydrophilic group on the carbon black
is substituted with an alkali metal.
9. The recording ink as claimed in any one of claims 1 to 8, wherein
the recording ink has a viscosity of 6 mPa•s to 20 mPa•s at 25°C.

10. An inkjet recording method comprising:
applying a stimulus to the recording ink as defined in any one of
claims 1 to 9, and ejecting the recording ink from a recording head so as
to form an image on a recording medium,
wherein the recording head is configured to have an ink discharge
opening on a face of a nozzle plate, and to have an ink repellent layer
formed on the face of the nozzle plate where the ink discharge opening is
placed.
11. The inkjet recording method as claimed in claim 10, wherein the
stimulation is at least one selected from the group consisting of heat,
pressure, vibration and light.
12. The inkjet recording method as claimed in any of claim 11 or 12,
wherein the ink repellent layer comprises either a fluorine-based material
or a silicone-based material.
13. The inkjet recording method as claimed in any one of claims 1
0 to 12, wherein the ink repellent layer has a surface roughness Ra of
0.2 µm or less.
14. The inkjet recording method as claimed in any one of claims 10 to
13, wherein the ink repellent layer is formed so to have an opening along
with the ink discharge opening, and the opening of the ink repellent layer

is formed so that a cross-sectional area of a face perpendicular to a
center line of the opening becomes gradually larger as a distance from
the face of the nozzle plate increases in a vicinity of the opening.
15. The inkjet recording method as claimed in any one of claims 1
0 to 14, wherein the ink repellent layer has a critical surface tension
Yc of from 5 mN/m to 40 mN/m.
16. The inkjet recording method as claimed in any one of claims 10 to
15, wherein the recording medium has a support and a coating layer at
least on one face of the support.
17. The inkjet recording method as claimed in any one of claims 10 to
16, wherein the recording medium has a purified water transfer amount
of 2 mL/m2 to 45 ml/m2 when measured at 23°C and 50% RH for a
contact time of 100 ms by using a dynamic scanning absorptometer, and
has a purified water transfer amount of 3 mL/m2 to 50 mL/m2 when
measured at 23°C and 50% RH for the contact time of 400 ms by using a
dynamic scanning absorptometer.
18. The inkjet recording method as claimed in any one of claims 16 to
17, wherein an applied amount of the coating layer is from 0.5 g/m2 to
20.0 g/m2 on a dry basis.
19. The inkjet recording method as claimed in any one of claims 10 to

18, wherein the recording medium has a basis weight of 50 g/m2 to 250
g/m2.
20. An inkjet recording apparatus comprising:
an ink ejecting unit configured to apply a stimulus to the
recording ink as defined in any one of claims 1 to 9, and to eject the
recording ink so as to record an image on a recording medium.
21. The inkjet recording apparatus according to claim 20, wherein the
stimulus is at least one selected from the group consisting of heat,
pressure, vibration and light.

ABSTRACT

RECORDING INK, INKJET RECORDING METHOD
AND INKJET RECORDING APPARATUS
There is provided a recording ink containing at least: water; a
water-soluble organic solvent; a surfactant; and a carbon black having a
hydrophilic group on a surface thereof, wherein the carbon black releases
humic acid in an aqueous dispersion of the carbon black, which is
recovered from the recording ink, a concentration of the humic acid
released in the aqueous dispersion containing 20 % by mass of the
carbon black of is expressed with a maximum absorbance at a wavelength
of 230 nm to 260 nm, and the recording ink has the maximum
absorbance of 5.0 to 20.0 at the wavelength of 230 nm to 260 nm.

Documents:

02042-kolnp-2008-abstract.pdf

02042-kolnp-2008-claims.pdf

02042-kolnp-2008-correspondence others.pdf

02042-kolnp-2008-description complete.pdf

02042-kolnp-2008-drawings.pdf

02042-kolnp-2008-form 1.pdf

02042-kolnp-2008-form 3.pdf

02042-kolnp-2008-form 5.pdf

02042-kolnp-2008-gpa.pdf

02042-kolnp-2008-international publication.pdf

02042-kolnp-2008-international search report.pdf

02042-kolnp-2008-pct priority document notification.pdf

02042-kolnp-2008-pct request form.pdf

2042-KOLNP-2008-(08-11-2011)-ABSTRACT.pdf

2042-KOLNP-2008-(08-11-2011)-AMANDED CLAIMS.pdf

2042-KOLNP-2008-(08-11-2011)-DESCRIPTION (COMPLETE).pdf

2042-KOLNP-2008-(08-11-2011)-DRAWINGS.pdf

2042-KOLNP-2008-(08-11-2011)-EXAMINATION REPORT REPLY RECIEVED.pdf

2042-KOLNP-2008-(08-11-2011)-FORM 1.pdf

2042-KOLNP-2008-(08-11-2011)-FORM 2.pdf

2042-KOLNP-2008-(08-11-2011)-OTHERS PATENT DOCUMENTS.pdf

2042-KOLNP-2008-(08-11-2011)-OTHERS.pdf

2042-KOLNP-2008-(13-03-2013)-ANNEXURE TO FORM-3.pdf

2042-KOLNP-2008-(13-03-2013)-CORRESPONDENCE.pdf

2042-KOLNP-2008-ASSIGNMENT.pdf

2042-KOLNP-2008-CORRESPONDENCE 1.1.pdf

2042-KOLNP-2008-CORRESPONDENCE 1.2.pdf

2042-KOLNP-2008-EXAMINATION REPORT.pdf

2042-KOLNP-2008-FORM 18 1.1.pdf

2042-kolnp-2008-form 18.pdf

2042-KOLNP-2008-FORM 3 1.2.pdf

2042-KOLNP-2008-FORM 3.1.pdf

2042-KOLNP-2008-FORM 5.pdf

2042-KOLNP-2008-GPA.pdf

2042-KOLNP-2008-GRANTED-ABSTRACT.pdf

2042-KOLNP-2008-GRANTED-CLAIMS.pdf

2042-KOLNP-2008-GRANTED-DESCRIPTION (COMPLETE).pdf

2042-KOLNP-2008-GRANTED-DRAWINGS.pdf

2042-KOLNP-2008-GRANTED-FORM 1.pdf

2042-KOLNP-2008-GRANTED-FORM 2.pdf

2042-KOLNP-2008-GRANTED-SPECIFICATION.pdf

2042-KOLNP-2008-INTERNATIONAL PUBLICATION.pdf

2042-KOLNP-2008-INTERNATIONAL SEARCH REPORT.pdf

2042-KOLNP-2008-PCT REQUEST FORM.pdf

2042-KOLNP-2008-REPLY TO EXAMINATION REPORT.pdf

2042-KOLNP-2008-TRANSLATED COPY OF PRIORITY DOCUMENT.pdf

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Patent Number

256135

Indian Patent Application Number

2042/KOLNP/2008

PG Journal Number

19/2013

Publication Date

10-May-2013

Grant Date

07-May-2013

Date of Filing

21-May-2008

Name of Patentee

RICOH COMPANY, LTD.

Applicant Address

3-6, NAKAMAGOME 1-CHOME, OHTA-KU, TOKYO

Inventors:

#	Inventor's Name	Inventor's Address
1	KOJIMA MARIKO	GRAN DURIE KOMAE 203, 1-2-10, IZUMIHON-CHO, KOMAE-SHI, TOKYO 201-0003
2	GOTOH AKIHIKO	BON MEISON HONATSUGI 701, 3-14-8, NAKA-CHO, ATSUGI-SHI, KANAGAWA 243-0018
3	BANNI AKIKO	MY CASTLE HONATSUGI 902, 1-3-14, KOTOBUKI-CHO, ATSUGI-SHI, KANAGAWA 243-0033
4	INOUE TOMOHIRO	16-15-203, OMARU, TSUZUKI-KU, YOKOHAMA-SHI, KANAGAWA 224-0061
5	NAGAI KIYOFUMI	FINE HILL VILLAGE 102, 2212-1, NARUSE, MACHIDA-SHI, TOKYO 194-0044

PCT International Classification Number

C09D 11/00,B41M 5/00

PCT International Application Number

PCT/JP2007/068227

PCT International Filing date

2007-09-12

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	2006-251589	2006-09-15	Japan