CH615967A5 - Process for the production of carrier webs which have been impregnated and coated with curable synthetic resins for surface coating - Google Patents

Description

The invention relates to a process for producing a paper backing sheet impregnated and coated with curable synthetic resins for surface treatment, in particular of wood-based panels, the backing sheet first being soaked and predried with an aqueous solution of aminoplast resin precondensate such that the backing sheet is 40 to 60% by weight. Aminoplast resin precondensate, based on paper weight, and the content of volatile constituents during the pressing is as low as possible, and then in a second operation this soaked and pre-dried carrier web with an aqueous dispersion of curable polymer in an amount such that a perfect surface is obtained during pressing is coated.

It has long been known to impregnate and coat paper webs with aqueous solutions of aminoplast resin precondensates in order to temper the surface of materials, in particular wood-based panels, with the process products. The advantage of the aminoplast resin precondensates is that they are water-soluble and penetrate and envelop the hydrophilic paper fiber well. Due to the affinity of the resin to the paper fiber, splitting phenomena are avoided in the cured finished product and uniform surfaces are formed. A disadvantage of the aminoplast resin precondensates, in particular the melamine resin precondensates, is that the cured products are relatively brittle, as a result of which the surfaces obtained can be susceptible to cracking. Another disadvantage is that the resins split off volatile constituents during curing, so that relatively high pressing pressures are necessary to achieve a uniform surface. Another disadvantage is the inadequate resistance to acid chemicals for some purposes and a relatively low weather resistance.

Attempts have therefore already been made to use polymerization resins as coating resins. The advantage of the polymerization resins is that, when cured, they release virtually no volatile constituents, depending on the structure, form more or less chemical-resistant surface layers and are relatively weatherproof. However, they have the decisive disadvantage that they are insoluble in water and must therefore be used in the form of a solution in organic solvents or a dispersion. The use of an organic solution is unfavorable in several respects, since on the one hand the solvents are undesirable because of their flammability and because of the recovery required for economic reasons. In addition, the organic solutions of the polymers penetrate poorly into the hydrophilic fiber, so that after drying and pressing, surfaces are obtained in which the carrier webs can split.

When using an aqueous dispersion of the curable polymers, the disadvantages of the solvent are eliminated, but here too the penetration of the paper fibers with the dispersed particles is insufficient, so that paper splitting cannot be avoided after curing.

Attempts have therefore been made to use curable precondensate resins together with the curable polymer resin, and two process variants are used for this purpose. In one case, the carrier web is impregnated and coated with the dispersion of a polymer resin, which additionally contains aminoplast resin precondensates. Examples of such a procedure2

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For example, German patent specification 1 060137 describes impregnation solutions containing synthetic resin, which are characterized in that they polymerize polyesters from polybasic acids, which consist predominantly of α, ß-unsaturated dicarboxylic acids, and polyhydric alcohols, water-soluble melamine-formaldehyde Contain condensation products, water and a water-soluble ketone as a solvent for the polyester. This method has also been followed recently, as can be seen from German Offenlegungsschrift 2,135,072 (dispersion of an acrylate resin, which contains water-soluble aminoplast resin).

Although glossy surfaces are obtained in this way after pressing, the coatings are either cloudy due to the poor compatibility with the use of melamine-formaldehyde resin and are therefore not usable for the production of clear, translucent surfaces when using high-quality decorative papers, or this occurs the use of pure urea-formaldehyde resin has insufficient resistance to water vapor or water.

The second method is to first impregnate the paper web with the aqueous solution of an aminoplast resin precondensate, the precondensate being used in such quantities that the carrier web is completely penetrated and encased by the resin. The drying of the pre-soaked carrier web must be carried out so far

that the volatile content is as low as possible. A dry value of ^ 6 should be aimed for. A drying value of <5 is particularly preferred. The carrier web so impregnated with aminoplast resin precondensate and then dried is then coated with the dispersion of a curable polymer resin. The polymer is now deposited on the coated paper fiber, so that during curing the aminoplast resin envelops the paper fiber, while the cured polymer predominantly forms the surface. This avoids paper splitting and, on the other hand, the advantages of the curable polymers, which determine the surface properties of the tempered material, are exploited. An example of such a mode of operation is the procedure described in German Auslegeschrift 1 174 143. This process is characterized in that the base paper is impregnated in the first stage with a formaldehyde condensation resin which releases only small amounts of volatile constituents, especially aminoplast resin, in such amounts that the resin content in the paper is about 2 to 50, especially 10 to 33 Is percent by weight, and that after drying or further condensation in the second stage with the amount of a prepolymer of a curable polymer resin based on esters of saturated polybasic carboxylic acids with unsaturated alcohols, especially a diallyl phthalate resin, required to achieve good bondability and a perfect surface, coated and dried or further treated in the usual way. However, the process products are not tack-free, which can give rise to separation of the resin from the substrate. In addition, the two resin layers are only compatible to a limited extent.

The object of the present invention is to find optimal resins for impregnation and coating using the last-described procedure, which must have the following properties: The impregnated and coated carrier web must be stable in storage, tack-free and elastic until it is pressed under curing conditions. After pressing, the process product must result in surface layers which must be crack-resistant, transparent, high-gloss, acid and alkali-resistant and weather-resistant.

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This can only be achieved if a combination of aminoplast resin precondensates and curable polymers can be found for impregnation and coating, which are sufficiently compatible with one another so that no opaque interfaces form, and if the aminoplast resin precondensates used do not become brittle and hardened in the hardened state on the other hand, the cured polymer resins have resistance to acid and alkalis and to weathering.

A method that is described in the following literature and patent citations offers itself as a possibly suitable networking principle: «J. A. Simms "Journal of Appi. Pole. Sci », V (1961), p. 58; A. Ravve «Journal of Pol. Be », Part A 3 (1965), p. 1775; Y. Iwakura et al. "Macromolecular Chemistry", 97 (1966), p. 128, GB-PS 809 257 and US-PS 3 323 946 and US-PS 2 604 463.

The process according to the invention is now characterized in that the aminoplast resin precondensate is a urea-formaldehyde precondensate or additionally contains melamine-formaldehyde precondensate in a weight amount which is at most twice the amount by weight of the urea-formaldehyde precondensate, and that mixed polymer is used as the curable polymer in the aqueous dispersion mentioned will that out

A) a hard-brittle copolymer which is obtained by polymerizing a) 60 to 84.9% by weight of styrene and / or alkyl methacrylate with 1 to 20 carbon atoms in the alkyl radical,

b) 0 to 20% by weight of alkyl acrylates with 1 to 8 carbon atoms in the alkyl radical,

c) 1 to 20% by weight of the glycidyl ester of acrylic or methacrylic acid,

d) 1 to 20 wt .-% acrylic or methacrylic acid and / or an anhydride of an unsaturated dicarboxylic acid and / or a hydroxyalkyl ester of acrylic or methacrylic acid with 2 to 4 carbon atoms in the hydroxyalkyl radical and / or the amide of acrylic or methacrylic acid and e ) 0 to 20% by weight of acrylonitrile,

wherein the sum of components a) to e) is 100% by weight, has been obtained, and

B) a rubber-elastic copolymer which has a glass transition point of not more than + 10 ° C. and which is obtained by polymerizing a) 78 to 99% by weight of an acrylic acid alkyl ester with 1 to 8 carbon atoms in the alkyl radical,

b) 1 to 20% by weight of acrylic or methacrylic acid and / or an anhydride of an unsaturated dicarboxylic acid or a hydroxyalkyl ester of acrylic or methacrylic acid with 2 to 4 carbon atoms in the hydroxyalkyl radical and / or an acid reamide of acrylic or methacrylic acid and c 0 to 2% by weight of a crosslinking monomer with at least two reactive non-conjugated olefinic double bonds in the molecule,

the sum of components a) to c) giving 100% by weight has been obtained,

exists, the weight ratio of hard-brittle copolymer A: rubber-elastic copolymer B is 3: 1 to 20: 1.

Maleic anhydride or itaconic anhydride can be used as the anhydride of an unsaturated dicarboxylic acid (monomer component d) or b) of the polymer A or B).

By modifying the hard-brittle copolymer A with the rubber-elastic copolymer B, in particular the impact resistance and the resistance to crack formation at changing temperatures and changing humidity as well as the resistance to stress corrosion cracking under the influence of different

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chemical agents improved. The improvement in the resistance to cracking leads to a reduction in the level of soiling. The rubber-elastic copolymer B increases the fluidity necessary for the formation of a perfect surface during curing.

It is particularly advantageous if the rubber-elastic copolymer B is first prepared and the copolymer A is polymerized therein. The polymerization is expediently carried out in the form of emulsion polymerization in a manner known per se, as described, for. B. is described in DT-AS 1 961452.

For better impregnation of the carrier web, the aqueous solution of the aminoplast resin precondensates can be a wetting agent, for. B. a water-soluble adduct of ethylene oxide with alcohols with a chain length of Cs to Cm, can be added.

It has proven to be particularly advantageous to add plasticizer to the copolymer dispersion, the plasticizer content being at most equal to the weight of the polymerization content in the dispersion. The plasticizers have at least two functions: on the one hand, they facilitate film formation when coating and drying the process product, so that the film formation temperature can be reduced. On the other hand, they improve the flow of the film formed when pressed under curing conditions, so that high-gloss surfaces are obtained at low pressure. A distinction can therefore be made between temporary and permanent plasticizers, temporary plasticizers being those which facilitate film formation but largely evaporate when the film dries due to the low boiling point. The permanent plasticizers remain in the film and primarily improve the flow properties when the surface is formed under curing conditions.

The quantitative ratio of temporary to permanent plasticizers should be about 3: 1 to 1: 3.

Examples of temporary plasticizers are alkyl glycols, such as. B. ethyl glycol. Alkyl phthalyl alkyl glycolate has proven itself as a permanent plasticizer, with the lower alkyl radicals having 1 to 4 carbon atoms being essentially suitable as alkyl radicals.

A particularly advantageous form of the process consists in adding a melamine resin precondensate etherified with lower alcohols or other additives capable of crosslinking in an amount of 1 to 20% by weight, calculated as solids and based on the polymer, to the dispersion of the copolymer.

This additive has a favorable influence on the usage properties of the surfaces, especially their hardness and resistance to organic solvents. Alcohols with 1 to 4 carbon atoms in turn serve as lower alcohols in the etherified melamine resin precondensates.

Instead of the etherified melamine resin precondensates, because of their compatibility, tetrakis (methoxymet-hyI) benzoguanamine (reaction product of benzoguanamine and formaldehyde), tetrakis (ethoxy) benzoguanamine (reaction product of benzoguanamine with ethylene oxide) or polyether of hexamethylamine melamine, such as hexamethylamine melamine be used.

Additives which are capable of crosslinking are, in addition to the etherified melamine precondensates, e.g. B. epoxy resins. In general, however, the etherified melamine precondensates are preferred.

The process products can also contain pigments in a manner known per se.

The process products produced according to the invention have the advantages and application properties described at the outset and are clearly superior to the comparative products of the prior art.

The process according to the invention will be explained in more detail with the aid of the following examples. In the examples, the non-stressed preparation of the resins used is first described. Then the impregnation and coating process is explained. This is followed by the testing of the surfaces as obtained by pressing the process products according to the invention.

example 1

a) Preparation of the dispersion to be used according to the invention of a curable two-phase copolymer in a 2-stage process

1st stage «(copolymer B)»: 16 parts of octylphenoxypolyethoxyethanol are dissolved in 250 parts of oxygen-free water, in which a monomer mixture of 5.6 parts (= 87.9% by weight) of n-butyl acrylate, 0.7 parts (= 11.0% by weight) of acrylic acid and 0.07 part (= 1.0% by weight) of allyl methacrylate. Then 1.2 parts (NH4) 2Fe (S04) 2-6 H2O (dissolved in 10 parts water) and 0.28 parts cumene hydroperoxide are added. The reaction proceeding at 25 ° C. under nitrogen is terminated after 4 hours. A 5 ml sample is then taken to determine sales; the yield is 99%.

2nd stage «(copolymer A)»: 6 parts of Na2HP04 and 1.2 parts of the trisodium salt of ethylenediaminetetraacetic acid are added to the dispersion obtained in the 1st stage.

For this, a monomer mixture consisting of 76 parts (= 70.9% by weight) of methyl methacrylate, 10 parts (= 9.3% by weight) of n-butyl methacrylate, 11.1 parts (= 10.4% by weight) ) Glycidyl methacrylate and 5.1 parts (= 4.8% by weight) of acrylic acid, added and again homogenized. Then 1.2 parts (NHt) 2Fe (S04) 2-6 H2O (dissolved in 10 parts water) and 0.25 parts cumene hydroperoxide (dissolved in 5 parts (= 4.7% by weight) methyl methacrylate) are added dropwise in this way that a temperature of 10 ° C is not exceeded. After 5.5 hours of reaction, a conversion of 95% is achieved; the coagulate content is 1%, the DIN cup viscosity at 20 ° C for 24 seconds and the Staudinger index [t |] = 1.95 [100 ml / g] (chloroform / 20 ° C).

b) modification of the dispersion obtained according to a)

The dispersion is modified with 6 parts of a 55% strength solution of a butyl etherified melamine formaldehyde resin in n-buta-nol and 0.2 part of p-toluenesulfonic acid, based on 100 parts of the dispersion. In addition, 10 parts of methyl phthalyl ethyl glycolate and 10 parts of ethyl glycol as a plasticizer, based on 100 parts of dispersion, are added. To achieve an optimal processing viscosity, 10 parts of an aqueous solution of 5 parts of a copolymer of 2 parts of methacrylic acid, 2 parts of n-butyl acrylate and 6 parts of methyl methacrylate in 100 parts of water are further added, a DIN cup viscosity of 42 seconds at 20 ° C results. The dispersion is then homogenized.

c) Preparation of the melamine-urea-formaldehyde pre-soak resin mixture

A melamine-formaldehyde resin is prepared in the usual way by precondensation of 157 parts of 37% strength aqueous formaldehyde solution, 110 parts of melamine, 3.5 parts of aqueous sodium hydroxide solution (3 molar) and 30 parts of chloroacetic acid from the urea-formaldehyde resin by precondensation of

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188 parts of 37% aqueous formaldehyde solution 77 parts of urea 26.5 parts of phosphoric acid (3 molar)

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44 parts of aqueous sodium hydroxide solution (3 molar) and 50 parts of chloroacetic acid.

50 parts of the melamine and 50 parts of the urea-formaldehyde resin are mixed with the addition of 25 parts of water and 25 parts of ethyl glycol.

d) impregnation of a paper web

A decorative paper with a basis weight of 80 g / m 2 is impregnated with the aqueous resin mixture obtained under c). After the water has evaporated, the basis weight is 120 g / m2; the volatile content is 4.7%.

e) coating of the pre-impregnated paper web, pressing of the film obtained on a particle board and application test

The paper web pre-impregnated according to d) is coated with the modified dispersion and then dried. A tack-free film with a basis weight of 195 g / m2 is obtained. A film stored for one month is only slightly cross-linked and still shows good fluidity during treatment under heat and pressure.

Pressing on a chipboard is done with the help of a highly polished chrome sheet and a press cushion at a pressure of 19 kp / cm2 and a temperature of 145 ° C for 8 minutes. A high-gloss, haze-free surface is obtained, the degree of gloss of which is 90%. The hardened film is resistant to dilute acids and alkalis, alcohol and petrol. Acetone and ethyl acetate, methylene chloride and trichlorethylene attack only moderately after short-term exposure (10 minutes). The pendulum hardness is 118 seconds; the impact tensile strength 32 kp-cm / cm2.

Example 2

a) Preparation of the dispersion to be used according to the invention of a curable, two-phase copolymer in a 2-stage process

The procedure is as in example la). The approach is composed as follows ^

1st stage «(copolymer B)»:

50 parts of water

2 parts of sodium aurium sulfate at 24.5 parts of n-butyl acrylate (= 97.0% by weight)

0.7 parts of acrylic acid (= 2.8% by weight / o)

0.05 parts of allyl methacrylate (= 0.2% by weight)

0.025 part of potassium peroxydisulfate conversion: 98% after 7 hours at 75 ° C.

2nd stage «(copolymer A)»:

200 parts of water

6 parts Na2HP04

8 parts of sodium lauryl sulfate

2.4 parts (NH4) 2Fe (S04) 2-6H20

2 parts of trisodium ethylenediaminetetraacetic acid

0.66 parts of cumene hydroperoxide

0.29 parts formaldehyde sulfoxylate

80 parts of n-butyl methacrylate (= 84.2% by weight)

10 parts glycidyl acrylate (= 10.5% by weight)

5 parts of acrylic acid (= 5.3% by weight)

Turnover: 94% after 6 hours at 0 °, maximum 10 ° C.

The coagulum content is 0.5%; the DIN cup viscosity at 20 ° C for 22 seconds; the Staudinger index [t)] = 2.65 [100 ml / g] (chloroform / 20 ° C).

The dispersion obtained is modified with the plasticizers and the thickener (DIN cup viscosity of 44 seconds at 20 ° C.) according to Example 1b), but without using butyl-etherified melamine resin.

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b) coating of the pre-impregnated paper web, compression of the film obtained on an asbestos cement board and application test 5 The paper dispersion pre-impregnated according to Example ld) is coated with the modified dispersion and then dried. A tack-free film with a basis weight of 195 g / m2 is obtained. A film stored for a month is only slightly cross-linked and still shows good flowability under heat and pressure during treatment 10.

The pressing on an asbestos cement plate is done with the help of a satin matt chrome sheet at a pressure of 30 kp / cm2. Adhesion to the asbestos cement board is mediated by an adhesive film consisting of bleached sodium 15 kraft paper (150 g / m2) that has been soaked in alkaline precondensed phenol-formaldehyde resin (molar ratio 1: 2). A silky matt, haze-free surface is obtained which shows no stress corrosion cracking when exposed to methanol or ethanol-water mixtures. The hardened film is resistant to dilute acids and bases, alcohol and petrol. Acetone and ethyl acetate hardly attack after short-term exposure (10 minutes), methylene chloride and trichlorethylene moderate. When exposed to water vapor and stored in cold water, there is no clouding or bubble formation. The pendulum hardness is 95 seconds; the gloss level 70% and the impact tensile strength 35 kp-cm / cm2.

Example 3

a) Preparation of the dispersion to be used according to the invention of a curable two-phase copolymer in a 2-stage process

The procedure is as in example la). The approach is as follows:

35 1st stage «(copolymer B)»:

50 parts of water

2 parts octylphenoxypolyethoxyethanol 24.5 parts ethyl acrylate (= 97.1% by weight)

0.7 parts of acrylic acid (= 2.8% by weight)

40 0.02 parts of allyl methacrylate (= 0.08% by weight)

0.025 parts of potassium peroxydisulfate conversion: 96% after 6.5 hours at 75 ° C.

2nd stage «(copolymer A)»:

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Share Na2HP04

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Parts of trisodium ethylenediaminetetraacetic acid

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Parts of methyl methacrylate (= 70.0% by weight)

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Parts of styrene (= 10.0% by weight)

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Parts of acrylonitrile

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Parts of glycidyl acrylate (= 10.0% by weight)

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Parts of maleic anhydride (= 5.0% by weight)

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Parts of formaldehyde sulfoxylate

55 0.29 parts of cumene hydroperoxide

Turnover: 95% after 5 hours at 0 ° C.

The coagulum content is 1.0%; the DIN cup viscosity at 20 ° C for 19 seconds and the Staudinger index [t]] = 2.05 60 [100 ml / g] (chloroform / 20 ° C).

The dispersion obtained is modified with the plasticizers and the thickener (DIN cup viscosity of 40 seconds at 20 ° C.) according to Example 1b), but without using butyl-etherified melamine resin.

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b) coating of the pre-impregnated paper web, pressing of the film obtained on a particle board and application test

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The paper web pre-impregnated according to Example Id) is coated with the modified dispersion and then dried. A tack-free film with a basis weight of 195 g / m2 is obtained. A film stored for one month is only slightly cross-linked and still shows good fluidity during treatment under heat and pressure.

Pressing on a chipboard is done with the help of a highly polished chrome sheet at a pressure of 20 kp / cm2 and at a temperature of 140 ° C for 10 minutes.

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A high-gloss surface is obtained which shows no stress corrosion cracking when exposed to methanol or ethanol-water mixtures. The hardened film is resistant to dilute acids and alkalis, alcohol and petrol. 5 Acetone and ethyl acetate hardly attack after a short-term exposure (10 minutes), methylene chloride and trichlorethylene moderate. When exposed to water vapor and when stored in cold water, there is no clouding or blistering. The pendulum hardness is 122 seconds; the gloss level 90% and the l0 impact tensile strength 38 kp-cm / cm2.

Claims (4)

615967 PATENT CLAIMS 1. A process for the production of a support web of paper impregnated and coated with curable synthetic resins for surface treatment, in particular of wood-based panels, the support web first being soaked and predried with an aqueous solution of aminoplast resin precondensate in such a way that the support web is 40 to 60% by weight aminoplast resin precondensate , based on paper weight, and the content of volatile constituents during the pressing is as low as possible, and then in a second operation this soaked and pre-dried carrier web with an aqueous dispersion of curable polymer in such an amount that a perfect surface is obtained during pressing , is coated, characterized in that the aminoplast resin precondensate is a urea-formaldehyde precondensate or additionally melamine-formaldehyde precondensate in a weight which is at most twice the weight of the urea-formaldehyde precondensate Contains the right amount, and that the curable polymer used in the aqueous dispersion mentioned is copolymer, which consists of A) a hard-brittle copolymer which is obtained by polymerizing a) 60 to 84.9% by weight of styrene and / or alkyl methacrylate with 1 to 20 carbon atoms in the alkyl radical, b) 0 to 20% by weight of alkyl acrylates with 1 to 8 carbon atoms in the alkyl radical, c) 1 to 20% by weight of the glycidyl ester of acrylic or methacrylic acid, d) 1 to 20 wt .-% acrylic or methacrylic acid and / or an anhydride of an unsaturated dicarboxylic acid and / or a hydroxyalkyl ester of acrylic or methacrylic acid with 2 to 4 carbon atoms in the hydroxyalkyl radical and / or the amide of acrylic or methacrylic acid and e ) 0 to 20% by weight of acrylonitrile, wherein the sum of components a) to e) is 100% by weight, has been obtained, and B) a rubber-elastic copolymer which has a glass transition point of not more than + 10 ° C. and which is obtained by polymerizing a) 78 to 99% by weight of an acrylic acid alkyl ester with 1 to 8 carbon atoms in the alkyl radical, b) 1 to 20 wt .-% acrylic or methacrylic acid and / or an anhydride of an unsaturated dicarboxylic acid or a hydroxyalkyl ester of acrylic or methacrylic acid with 2 to 4 carbon atoms in the hydroxyalkyl radical and / or an acid amide of acrylic or methacrylic acid and c 0 to 2% by weight of a crosslinking monomer with at least two reactive non-conjugated olefinic double bonds in the molecule, the sum of components a) to c) giving 100% by weight has been obtained, exists, the weight ratio of hard-brittle copolymer A: rubber-elastic copolymer B is 3: 1 to 20: 1. 2. The method according to claim 1, characterized in that plasticizer in the weight ratio of ^ 1: 1, based on the polymer, is added to the aqueous copolymer dispersion. 3. The method according to claim 2, characterized in that a mixture of temporary and permanent plasticizers in a weight ratio of 3: 1 to 1: 3 is added as the plasticizer. 4. The method according to any one of the preceding claims, characterized in that a melamine resin precondensate etherified with lower alcohols or other additives capable of crosslinking are added to the aqueous copolymer dispersion in an amount of 1 to 20% by weight, calculated as Solids and based on copolymer, added.