|Title of Invention
A PROCESS FOR PREPARATION OF YELLOW PIGMENT
|A process to prepare Pigment Yellow 138 having high surface area, exhibiting strong color strength and transparency while also having good lightfastness. The process is a mill process which may be carried out in any conventional apparatus such as a kneader, ball mill apparatus or any suitable such container. The process uses Pigment Yellow 138 alone or along with salt in a mill container.
The Patent Act 1970,
(39 of 1970)
The Patent rule 2003
(See Section 10 and Rule 13)
1. TITLE OF THE INVENTION
"A process for preparation of yellow pigment."
2. APPLICANT (S):
(a) NAME : GHARDA CHEMICALS LTD.
(b) NATIONALITY : INDIA
(c) ADDRESS : B-27/29, MIDC, PHASE 1, DOMBVLI.
DIST. THANE, PIN 421 203, MAHARASHTRA, INDIA
3. PREAMBLE TO THE DESCRIPTION
The following specification describes the invention
A process for preparation of yellow pigment.
BACKGROUND OF THE INVENTION
Pigment Yellow 138 is well known to be a very lightfast and weatherfast green-shade yellow pigment with good heat stability. Pigment Yellow 138, also known as quinophthalone, is typically used in plastics and paint applications. The most common commercial Pigment Yellow 138 has a relatively low specific surface area of approximately 25 m2/gm, which gives good hiding power in systems where opacity is desirable. For most ink systems however, it is desirable to have a high degree of transparency, therefore, pigments having a high specific surface area are required. Pigment Yellow 138 may be prepared by various means of comminution, including ball milling or kneading in the presence of a grinding agent. However, it has not been known how to prepare Pigment Yellow 138 having high surface area, exhibiting strong color strength and transparency while also having good lightfastness. The preparation of quinophthalone pigments is described in the prior art. For example, condensation of 2-methylquinoline derivatives (quinaldine derivatives) with aromatic ortho-dicarboxylic acids or their anhydrides is carried out in the presence of inert high-boiling diluents such as ortho-dichlorobenzene, trichlorobenzene, nitrobenzene, naphthalene, diphenyl ordiphenyl ether (Chimia 24, 328, 1970; GB-A1.091.734). U.S. Pat. No. 5,106,980 discloses a process for the preparation of quinophthalones by condensation of 8-aminoquinaldine with phthalic anhydride optionally monosubstituted or polysubstituted by chlorine or bromine, in the presence of a diluent, resulting in relatively low specific surface area and opaque pigment. U.S. Pat. No. 3,622,583 describes a process for the preparation of yellow dye quinophthalone derivatives by heating 8-aminoquinaldine with tetrachlorophthalic anhydride or tetrabromophthalic anhydride in the presence of other solvents and at a temperature of 130-300°C. According to the Industrial Organic Pigments, by Herbst, W. and Hunger, K. VCH., Yellow 138 pigment that possess higher surface area exhibit somewhat lower lightfastness properties. However, the prior art processes result in relatively low specific surface area Pigment Yellow 138 and therefore are mostly
opaque till recently Patent US 7060835 describes use of grinding agents like inorganic salts to have a transparent pigment, wherein a particle of said transparent Pigment Yellow 138 has a surface area of greater than about 50 m2 /g to about 100 m2/g.
SUMMARY OF THE INVENTION
It has now been found that, the above objectives can be realized by a process for preparing transparent Pigment Yellow 138 comprising of
(a) grinding Pigment Yellow 138 in the absence of grinding agent or using an organic salt based grinding agent;
(b) preparing a slurry of the ground pigment with an alcohol or other organic solvents for example pyridine, dimethylformamide, dimethylacetamide , glacial acetic acid, chlorobenzene, dichlorobenzene, nitrobenzene at ambient temperature, Also the whole operation can be effected at reflux temperature or under pressure at an elevated temperature.
(c) filtering said slurry resulting in a filter cake containing particles of transparent Pigment Yellow 138.
The present invention also provides a process for improving transparency and color strength in an ink or a plastic composition comprising adding transparent Pigment Yellow 138 to said composition. Other objectives and advantages of the present invention will become apparent from the following description.
DETAILED DESCRIPTION OF INVENTION
The present invention is a process for preparing a more transparent Pigment Yellow 138, which surprisingly exhibits little, if any, loss in strength, chroma or hue in the ink masstone while exhibiting good lightfastness. The process is a mill process which may be carried out in any conventional apparatus such as a kneader, ball mill apparatus or any suitable such container. The process combines Pigment Yellow 138 alone and or a salt, which are milled, and then the prepared pigment is isolated with
alcohol or water at 30°C and dried.
The starting pigment is any Pigment Yellow 138 or quinophthalone yellow, such as that commercially available from GHARDA - GAFAST PY 138 or PY 138 from BASF, typically, between 95 parts or whole of pigment along with 5% of organic salt or no salt at all.
Suitable salts for use in the process include salts of naphthalenesulphonic acid condensation products. A preferred salt is sodium, between about 1 to 20 parts based on the starting pigment. The starting pigment alone or alongwith salt are combined in a mill container and milled at a temperature of about 50°C to 80°C. for about thirty minutes to about 10 hours. It is preferred that the temperature be about 70-80°C and the milling continue for about 1 to 2 hours. If a ceramic lined ball mill is used then balls are added, which may be of any appropriate material, such as, but not limited to ceramic, zirconium oxide, and the like. The balls typically have a size of about 22-45 mm and are added at about 100 to 200 parts based on the pigment. Upon completion of the milling process, the mixture is isolated by preparing an aqueous slurry through mixing the mill contents with about 25 to about 150 parts alcohol preferably Isopropylalcohol, then stirring at about 30°C to about 70°C for a period of about thirty minutes to about 3 hours. The resulting slurry is filtered and the filter cake is thoroughly washed with water until equivalent conductivity is attained, followed by deionized water, if desired. The washed filter cake is dried at about 50°C. to about 150°C. The resultant pure and transparent Yellow Pigment 138 may be formulated into a variety of ink systems resulting in yellow inks which are strong, cleaner and more transparent than corresponding inks made from the common commercial Pigment Yellow 138 while exhibiting virtually identical lightfastness and masstone properties. Surprisingly, little if any loss in color strength, chroma or hue in the ink masstone was experienced upon its exposure to light for up to 200 hours. Similar exposure of the reduced ink film (ink tint) demonstrated only a minor decrease in its lightfastness relative to the corresponding film of the common commercial pigment. The process of the present invention is further illustrated by the following non-limiting examples in which all parts and percentages are by weight, unless otherwise indicated.
Pigment with moisture contain less than 0.5% w/w, organic chloride purity min 99% w/w, was charged in ceramic lined ball mill such that 50% mill was occupied by volume of balls and pigment quantity was charged based on the volume equivalent to void volume of balls. The mill was rotated below the critical speed with monitoring of particle size distribution and surface area of 65 m2/gm.
Pigment as in example 1 (95 part), naphthalenesulphonic acid condensation products, sodium salt (5 parts) was charged in ceramic lined ball mill such that 50% mill was occupied by volume of balls and pigment quantity was charged based on the volume equivalent to void volume of balls. The mill was rotated below the critical speed with monitoring of particle size distribution and surface area of 88 m2/gm.
EXAMPLE 3 (COMPARISON)
Pigment Yellow 138 of Example 1 having a surface area of 65 m2/gm was tested for lightfastness compared to conventional commercial Pigment Yellow 138 having a surface area of 25 m2/gm. Both pigments in a suitable vehicle were drawn down on a substrate and exposed to light for up to 200 hours. The larger surface area pigment of Example 1 exhibited comparable lightfastness with the conventional pigment of smaller surface area.
EXAMPLE 4 (COMPARISON)
The pigment of Example 1 having a surface area of 65 m2 /gm was incorporated into a typical solvent ink film and compared with a solvent ink film containing a conventional commercial Pigment Yellow 138 having a surface area of about 25 m2/gm. Both solvent ink films were exposed to 192 hours of sunlight under identical conditions of light, temperature and ambient humidity, and then tested for tint strength and color strength and CIELAB value for [Delta]E* using the spectrophotometer.
EXAMPLE 5 (COMPARISON)
The pigment of Example 1 having a surface area of 65 m2/gm was incorporated into a typical aqueous ink film and compared with an aqueous ink film containing a conventional commercial Pigment Yellow 138 having a surface area of about 25 m2/gm. Both aqueous ink films were exposed to 192 hours of sunlight under identical conditions of light, temperature and ambient humidity, and then tested for tint strength and color strength according to the method of Example 4.
The respective masstones of each aqueous ink film displayed essentially no change in strength or [Delta]E value (relative to their non-exposed areas), while the corresponding ink tints exhibited comparable color strength decreases.
EXAMPLE 6 (COMPARISON)
The pigment of Example 2 having a surface area of about 88 m2/gm was
incorporated into a plastic (LDPE) and compared with a plastic containing a
conventional commercial Pigment Yellow 138 having a surface area of about 25
m2/gm. Both plastics were exposed to temperatures of between 130-250°C to test
for coloristic properties of masstone and color strength by the method set forth in
Little or no differences in the respective [Delta]E values were observable over this
temperature range although the higher surface area pigment of Example 2 exhibited
a significantly stronger shade in the tint (of 45-50%) throughout the range, compared
to the conventional pigment having surface area of about 25 m2/gm.
|Indian Patent Application Number
|PG Journal Number
|Date of Filing
|Name of Patentee
|GHARDA CHEMICALS LTD.
|B-27/29,MIDC, PHASE 1, DOMBIVALI,DIST.THANE.
|PCT International Classification Number
|PCT International Application Number
|PCT International Filing date