|Title of Invention||
AN ADHESIVE STICK
|Abstract||The present invention relates to an adhesive stick consisting of a water based preparation of at least one starch ether with a viscosity below 2.000.000 mPas as the adhesive component and a soap gel as the shaping gel-forming component and, optionally, other auxiliaries, characterized in that it contains 15 to 25% by weight sucrose, based on the total weight of the stick.|
This invention relates to an adhesive stick consisting of a water-based preparation of starch ethers as the adhesive component and a soap gel as the shaping gel-forming component and, optionally, other auxiliaries. The invention also relates to a process for the production of such sticks and to their use.
Adhesive sticks (= stick-like adhesives which are displaceably mounted in a closeable tube which leave behind a tacky film when rubbed onto a receiving surface) are now part of everyday life. They contain in particular (see DE-PS 18 11 466) water-soluble or water-dispersible synthetic polymers of adhesive character, more particularly polyvinyl pyrrolidone (PVP), dissolved in an aqeous/organic liquid phase together with a shaping gel-forming component. The gel-forming component is selected in particular from alkali metal or ammonium salts of aliphatic carboxylic acids, more particularly containing from about 12 to 22 carbon atoms. If the basically high-tack water-based preparations of the polymer substances of adhesive character are heated together with small quantities of the gel-forming component based on fatty acid soaps to relatively high temperatures, more particularly above 50°C, and if this solution is subsequently left standing to cool, the mixture solidifies to a more or less stiff soap gel in which the shaping and comparatively rigid micelle structure of the soap gels is predominantly in evidence at first. This provides for the known production and handling of such adhesives in stick form in closeable tubes. When the stick is rubbed onto a receiving surface, the micelle structure is destroyed so that the rigid mixture is converted into a paste-like state in which its adhesive character is predominant.
An adhesive stick corresponding to the preamble of the main claim is described in EP 596 958. Besides the starch ethers, other
macromolecular substances - for example polyvinyl pyrrolidone (PVP) -may also be present as adhesive components. The adhesive stick in question has high adhesive strength sufficient for most applications. However, there are also situations where it could be higher, for example after storage for several months under varying climatic conditions.
The problem addressed by the invention was to provide an adhesive stick which would have higher adhesive strength higher after storage for several months under varying climatic conditions without any deterioration in other important properties, such as initial tack and handling behavior (rubbing, compressive strength). These properties, too, would be improved.
It has surprisingly been found that an adhesive stick such as this is obtained if at least one viscosity-reduced starch ether is used together with sucrose as the adhesive component.
Accordingly, the problem addressed by the invention is solved by an adhesive stick consisting of a water-based preparation of at least one starch ether with a viscosity below 2,000,000 mPas and sucrose as the adhesive component and a soap gel as the shaping gel-forming component
adhesive composition is preferably 15 to 25 and more preferably 18 to 22% by weight, based on the total weight of the stick. The sucrose is preferably used in solid form.
"Viscosity-reduced" starch ethers are understood to be starch ethers which not only have been etherified in largely polymer-analog form, but in addition have been chemically or physically destructured so that their viscosity is below about 2,000,000 mPas (30% solution, 20oC, Brookfield).
According to Ullmann, Encyklopadie der technischen Chemie, 4th Edition, Verlag Chemie, Weinheim/Bergstrasse (1974), starch ethers are formally products of the condensation between the hydroxy groups of the anhydroglucose units (AGU) of starch molecules and alcoholic hydroxy
groups of other compounds. Only a few water-soluble starch ethers of this type are produced on a relatively large scale and industrially used. They include certain hydroxyalkyl starches, more particularly hydroxyethyl and hydroxypropyl starch and also carboxymethyl starch. Reaction products of native starches with ethylene oxide, propylene oxide, butylene oxide and/or glycidols have proved to be particularly suitable for the purposes of the invention. More particularly, starch derivatives having relatively high degrees of substitution, preferably nonionic starch ethers, can advantageously be adjusted to a relatively low viscosity level by mechanical treatment in aqueous systems which promotes the degradation of crystalline structures and/or oxidative, acid-hydrolytic, enzymatic and thermal degradation and are therefore particularly suitable. Accordingly, viscosity-reduced nonionic starch ethers, particularly hydroxyalkyi starch, are particularly preferred because the desired adhesive sticks are best obtained with them. The degree of substitution (DS) should preferably be 0.1 to 2.0 and, more preferably, 0.2 to 1.0. Mixed etherification products may of course also be successfully used in accordance with the invention. The adhesive sticks according to the invention preferably contain 5% by weight to 50% by weight viscosity-reduced starch ethers. These percentages by weight are based on the total weight of the stick.
In principle, any native starches may be used for the production of the starch derivatives used in accordance with the invention. Suitable starches can be found in Ullmann, loc, cit., Vol. 22, sub-chapters 6.2 to 6.4 to the chapter entitled "Starke (Starch)". In addition to cereal starches, such as corn starch, wheat starch or rice starch, and also tuber or root starches, such as potato or tapioca starch, pulse starches, such as pea starch or bean starch, are also suitable.
The water-based preparations of the viscosity-reduced starch ethers are preferably prepared by mixing the starch ethers with water and -substantially irreversibly - degrading the superstructures of the starch
ethers by physical, more particularly mechanical, action and/or by chemical, for example oxidative, acid-catalytic, enzymatic or thermal degradation of the starch ethers. A combination of physical and chemical action is also possible. Concentrated systems having a starch ether content of about 20% by weight to 70% by weight are preferred because it has been found that the preparations are easiest to handle in these concentration ranges. The water-based preparations may then be combined with the other components in the described manner. If desired, the starch derivative preparations may be diluted before mixing with the other components, preferably to a starch ether content of 20% by weight to 40% by weight.
The aqueous systems may be mechanically destructured in machines known to the expert, preferably at the high concentrations mentioned. Suitable destructuring machines are kneaders, extruders, stator-rotor machines and/or stirrers. The degree to which the superstructures of the aqueous starch derivative systems are mechanically degraded is dependent on concentration, temperature, residence time and shearing. The degree of degradation of the starch superstructures should advantageously lie close to the limit. The degree of degradation can be determined by measurement of the solution viscosities. The starch superstructures can also be degraded without any disadvantages during the production of the adhesive sticks in mixing machines in which a sufficient degree of degradation of the starch superstructures can be achieved.
The mechanical degradation of the starch or starch ether superstructures can be supported or replaced by chemical degradation of the starch molecules to the viscosity level according to the invention. The partial chemical degradation of the starch or starch ether molecules may be carried out both before and after mechanical degradation of the starch superstructures. The two processes may also be carried out alone
independently of one another. The viscosity reduction or tne starcn einer solution may also be carried out solely by chemical degradation to the viscosity level according to the invention. The starch molecules may be degraded by the oxidative, acid-hydrolytic, enzymatic or thermal methods of degradation known to the expert.
The processes normally used for degrading starches are described in detail in "Ullmanns Encyklopadie der technischen Chemie" 4th Edition, Verlag Chemie, Weinheim (1974). Preferred oxidizing agents for oxidative degradation are chromic acid, permanganate, hydrogen peroxide, nitrogen dioxide, hypochlorite, periodate and peracids such as, for example, peracetic acid. Preferred acids for acid-hydrolytic degradation are hydrochloric acid, sulfuric acid and phosphoric acid, although other acids, such as for example acetic acid, oxalic acid, sulfurous acid, perchloric or trichloroacetic acid, may also be used. Alpha- and beta-amylases and also the glucoamylases and debranching enzymes may be used as starch-degrading enzymes.
In the context of the invention, an adequate degree of degradation is preferably reached when a 30% by weight aqueous solution of the starch ether used has a Brookfield viscosity at 20oC in the range from about 100 to 1,000,000 mPas, preferably in the range from 2,000 to 100,000 mPas and, more preferably, in the range from 3,000 to 30,000 mPas, as measured on a solution with a 30% solids content. Adhesive sticks containing 5% by weight to 10% by weight of the starch ethers according to the invention with a viscosity of 1,000,000 to 50,000 mPas or 10 to 30% by weight with a viscosity of 100,000 to 2,000 mPas or 30 to 50% by weight with a viscosity of 30,000 to 100 mPas have proved to be particularly suitable. In addition, other polymers may be added as the adhesive component in a total quantity of up to 50% by weight. The percentages by weight are based on the total weight of the adhesive stick.
Besides the viscosity-reduced starch ethers according to the
invention, the adhesive stick may contain other water-soluble and/or water-dispersible polymers (for example polyurethane dispersions, polyvinyl pyrrolidone and/or poiyacryiates) as an adhesive component. The total percentage content of the adhesive components should be between 15 and 50% by weight. The PVP content is preferably 0%.
The adhesive sticks according to the invention preferably contain sodium salts of C12-22 fatty acids of natural or synthetic origin as the soaps for forming the gel structure. C14.18 fatty acids and mixtures thereof are preferred. The sodium salts of the fatty acids, i.e. the soaps, are present in quantities of 3 to 20% by weight, based on the weight of the adhesive stick, and preferably in quantities of 5 to 10% by weight.
The auxiliaries typically used in adhesive sticks may also be used in the adhesive sticks according to the invention in quantities of 0 to 25% by weight, based on the adhesive stick. The auxiliaries in question are, for example, plasticizers and/or moisture regulators, i.e. organic water-soluble solvents, which are normally used in adhesive sticks. Other suitable auxiliaries are polyfunctional alcohols, such as propylene glycol, glycerol, polyglycerols, trimethylol propane, polyether glycols and also sorbitol and/or low molecular weight starch hydrolyzates which have been converted into the corresponding polyols by reduction with hydrogen. For example, a mixture of glycerol and polyethylene glycol may be used. The non-volatile organic solvents mentioned should be used in quantities of at most up to 50% by weight, based on the water content of the sticks. The content of glycerol and propylene glycol is preferably 0%.
In addition to the main components mentioned, typical auxiliaries, for example substances which promote easy and soft rubbing, may also be used. Substances such as these are, for example, aminocarboxylic acids and/or their lactams. Suitable aminocarboxylic acids or lactams should contain up to 12 carbon atoms and, more particularly, from 4 to 8 carbon atoms. The preferred representative in terms of practical application is £-
caprolactam or the 7-aminocaproic acid derived therefrom. The quantity in which the lactams or corresponding aminocarboxylic acids are used is normally no more than 15% by weight and, for example, between 1% by weight and 10% by weight, based on the stick as a whole.
The adhesive sticks according to the invention may contain pigments, dyes, perfumes, preservatives and the like as further auxiliaries. These auxiliaries are present in the usual small quantities. Other possible additives are, for example fillers, optical brighteners, dextrins, cellulose derivatives and non-destructured starch derivatives. Mannans, more particularly gaiactomannans, may be present as further additives in the adhesive sticks according to the invention. Gaiactomannans from the fruit of the carob tree and from guar flour are particularly suitable. The destructured ethers may also be replaced to a small extent by destructured mannans.
The individual components are preferably present in the adhesive stick in the following quantities: 3 to 10% by weight sodium soaps, 5 to 40% by weight viscosity-reduced starch ethers, 15 to 25% by weight sucrose and 0 to 25% by weight auxiliaries, of which 0 to 20% by weight may be water-soluble or water-dispersible polymers. The balance to 100% is water.
The adhesive sticks according to the invention are produced by initially preparing an aqueous, preferably highly concentrated system of suitable starch derivatives with degradation of the superstructures by mechanical action and/or by chemical degradation, mixing the resulting system with sucrose and then thoroughly mixing this preparation, optionally diluted with water, with the components forming the soap gel and optionally with the other auxiliaries, heating the mixture to temperatures of at least 50°C and preferably to 80°C until a uniform mixture is obtained and leaving the mixture thus obtained to cool in the absence of mechanical action to form a gel. The mixtures obtained, which are easy to pour in the
temperature range mentioned, are preferably introduced directly into stick tubes or similar containers and left to solidify in the absence of mechanical action to form the required gels.
The adhesive sticks according to the invention show particularly high adhesive strength which does not weaken even after storage under various climatic conditions; substrate failure (paper) at least still occurs. Accordingly, in addition to the surface-to-surface bonding of substrates, the adhesive sticks according to the invention may be used in particular for the permanent bonding of paper and/or board. In addition, they may also be produced, if desired, without using water-soluble plasticizers (water-soluble organic solvents) or moisture regulators (again water-soluble organic solvents).
The adhesive sticks according to the invention are distinguished by good soft-rubbing characteristics, a uniform film with no unevenness being obtained with little effort.
The compressive strengths are in the range from about 30 to 70 N/16 mm I.
The adhesive composition according to the invention is stable in storage, i.e. it shows no signs of separation over a period of 72 hours at 72'C, which is crucially important to the production process.
I Starting materials
1. Starch ether according to Example 10a of EP 596 958 B10.
2. Polyvinyl pyrrolidone PVP with a K value of 90.
3. C14-18 monocarboxylic acid mixture.
II Production of the adhesive sticks
The components listed in Table 1 are mixed at ca. 70°C and
processed to adhesive sticks in accordance with page 7 of the present specification.
Ill Properties of the adhesive sticks
1. Bonding and sample preparation The following substrates were bonded:
1. Soennecken Speziai Kopierpapier 5015 to
a) photos (Kodak Royal paper)
b) Soennecken Spexial Kopierpapier 5015
c) Soennecken writing pad paper, square-ruled
d) Pelikan "Rainbow" tinted paper
e) Pelikan "Rainbow" colored fancy paper
2. Photos (Kodak Royal) in photoalbums
0 to 6 months at
a) room temperaure (20°C/50% rel. humidity)
b) 40°C/20% rel. humidity
c) 30X/80% rel. humidity
Tests a) Compressive strength
Compressive strength is understood to be the maxmimum load measured parallel to the longitudinal axis on collapse of the stick under pressure. Compressive strength is measured with an Erichsen Model 464L compressive strength tester, measuring head 709 (manufacturer: Erichsen, Simonshofchen, Wuppertal).
The adhesive cut off with a minimum length of 30 mm immediately above the piston is placed between two holders in the form of approx. 10 mm thick disks of rigid PVC which are formed
with a circular 3 mm deep depression adapted to the particular stick diameters. The stick provided with the holders is placed centrally on the table of the compressive strength tester. The height of the force measuring instrument over the table is adapted to the height of the stick to be tested. The measuring head is then advanced against the stick to be tested at a rate of approx. 70 mm per minute. On reaching the maximum compressive force, the value is read off from the digital display.
b) Setting time
To determine whether the adhesive properties of the sticks are sufficient for the application envisaged, bonding tests are carried out by hand under certain processing conditions and evaluated. The following procedure is adopted:
A supply of white Soennecken 5015 Speciai-Copierpapier (DIN A4, weight per unit area approx. 80 g/m5) and adhesive sticks to be tested are conditioned for at least 24 hours at 20EC/65% relative humidity. The test paper is cut into strips 5 cm wide and approx. 30 cm long. An adhesive stick is rubbed twice longitudinally under uniform pressure over the uncoated side of a paper strip and should produce a uniform film. Immediately afterwards, a second paper strip which has not been coated with adhesive is placed on the coated strip with its uncoated side facing inwards and rubbed on by hand. An attempt is then made to peel the paper strips slowly from one another. The time at which separation in the adhesion zone is only possible with tearing of paper over entire width characterizes the setting time.
c) Open time
The open time is the time after application of the adhesive
within which the materials to be bonded have to be fitted together in order, after setting, to obtain complete tearing of paper in the separation test. The method is the same as that used to determine setting time except that the strips of paper are only fitted together after defined times following application of the adhesive. Beginning with 15 seconds, the open time may be graduated, for example, in intervals of 15 seconds. With slow-setting adhesives having predictably longer open times, correspondingly longer intervals will be selected.
d) Adhesive strength
For bonding, see "setting time".
After the indicated storage time under the specified climatic conditions, the paper strips are pulled apart by hand (manual separation) The "fracture" pattern obtained is visually evaluated on the basis of the following appearances:
1 100% tearing of material
2 50% tearing of material
3 Slight tearing of fibers
4 Adhesion, but with no tearing of material
5 Very weak adhesion (substrate separation)
The results of the adhesive strength tests after storage are set out in Table II.
The individual results are set out in Tables I and 11. They show that it is possible by using sucrose to produce an adhesive stick which shows significantly higher adhesive strength than a formulation of the stick described in EP 596 958, above all after storage for several months under various climatic conditions.
11 Comparison Example based on Example 10 of EP 0 596 958 B1
1. An adhesive stick consisting of a water-based preparation of at least one starch ether with a viscosity below 2,000,000 mPas as the adhesive component and a soap gel as the shaping gel-forming component and, optionally, other auxiliaries, characterized in that it contains sucrose.
2. An adhesive stick as claimed in claim 1, characterized in that the starch ethers are nonionic and, in particular, are reaction products of native starches with ethylene oxide, propylene oxide, butylene oxide and/or glycidol.
3. An adhesive stick as claimed in at least one of the preceding claims, characterized in that the degree of substitution (DS) of the starch ethers is from 0.1 to 2.0 and preferably from 0.2 to 1.0.
4. An adhesive stick as claimed in claim 1, 2 or 3, characterized in that the viscosity of the starch ethers is reduced by physical, more particularly mechanical, destructuring and also by chemical destructuring, such as thermal, acid-hydrolytic, enzymatic or, more particularly, oxidative destructuring or by a combination of these methods.
5. An adhesive stick as claimed in any of claims 1 to 4, characterized in that, after destructuring, the starch ethers have a viscosity of 100 to 1,000,000 mPas, preferably 2,000 to 100,000 mPas and, more preferably, 3,000 to 30,000 mPas, as measured in a solution having a solids content of 30% (Brookfield, 20°C).
6. An adhesive stick as claimed in at least one of claims 1 to 5, characterized in that it contains 5 to 10% by weight starch ethers having a viscosity of 1,000,000 to 50,000 mPas or 10 to 30% by weight starch ethers having a viscosity of 100,000 to 2,000 mPas or 30 to 50% by weight starch ethers having a viscosity of 30,000 to 100 mPas, the percentages by weight being based on the adhesive stick as a whole and the viscosity being that of a 30% by weight aqueous solution at 20°C.
7. An adhesive stick as claimed in at least one of the preceding claims, characterized in that the sucrose contents is 15 to 25 and preferably 18 to 22% by weight, based on the total weight of the stick.
8. An adhesive stick as claimed in at least one of the preceding claims, characterized in that sodium salts of C12-22 fatty acids and, more particularly, C14-18 fatty acids of natural or synthetic origin are present as the soap forming the gel structure.
9. An adhesive stick as claimed in at least one of the preceding claims, characterized in that the sodium salts of the fatty acids are present in quantities of 3 to 20% by weight and preferably 5 to 10% by weight, based on the total weight of the stick.
10. An adhesive stick as claimed in at least one of the preceding claims, characterized in that plasticizers, pigments, dyes, perfumes, preservatives and/or moisture regulators and, optionally, other water-soluble and/or water-dispersible polymers are present as further auxiliaries.
11. An adhesive stick as claimed in at least one of the preceding claims, characterized in that it contains
3 to 10% by weight sodium soaps,
5 to 40% by weight viscosity-reduced starch ethers, 15 to 25% by weight sucrose,
0 to 25% by weight auxiliaries,
0 to 20% by weight water-soluble or dispersible polymers; balance to 100% by weight water.
12. A process for the production of the adhesive stick claimed in the
preceding claims, characterized in that an aqueous, preferably highly
concentrated system of suitable starch derivatives is initially prepared with
degradation of the superstructures by mechanical action and/or by
chemical degradation, the resulting system is mixed with sucrose and the
preparation obtained, optionally diluted with water, is then thoroughly mixed with the components forming the soap gel and optionally with the other auxiliaries, heated to temperatures of at least 50°C until a uniform mixture is obtained and the mixture thus obtained is left to cool in the absence of mechanical action to form a gel.
13. The use of the adhesive sticks claimed in claims 1 to 12 for the surface-to-surface bonding of substrates, more particularly paper and/or board.
14. The use of viscosity-reduced starch ethers according to at least one of claims 1 to 5 together with sucrose as the adhesive component in adhesive sticks.
15. An adhesive stick, substantially as hereinabove described and examplified.
|Indian Patent Application Number||IN/PCT/2000/471/CHE|
|PG Journal Number||05/2007|
|Date of Filing||03-Oct-2000|
|Name of Patentee||M/S. HENKEL KOMMANDITGESELLSCHAFT AUF AKTIEN|
|Applicant Address||Henkelstrasse 67 D-40589 Dusseldorf|
|PCT International Classification Number||C09J 103/08|
|PCT International Application Number||PCT/EP1999/001937|
|PCT International Filing date||1999-03-23|