EP0670867A1

EP0670867A1 - Process for applying a primary coat or a single layer of lacquer on plastic materials with an aqueous coating agent

Info

Publication number: EP0670867A1
Application number: EP94901847A
Authority: EP
Inventors: Andreas Holst; Harald Borgholte; Heinz-Peter Rink; Hans-Josef Oslowski; Hartmut Metzdorf
Original assignee: BASF Lacke und Farben AG
Current assignee: BASF Farben und Fasern AG
Priority date: 1992-11-26
Filing date: 1993-11-23
Publication date: 1995-09-13
Also published as: JPH08504449A; BR9307534A; WO1994012579A1; DE4239695A1

Abstract

A process is disclosed for applying a primary coat or a single layer of lacquer on plastic materials with an aqueous coating agent which contains as film-building material one or several emulsion polymers, as well as a water-dilutable polyurethane resin. The process is characterised in that the aqueous coating agent contains an emulsion polymer. The emulsion polymer is prepared in a two-step emulsion polymerization from ethylenically unsaturated monomers. The conditions in which the reaction takes place are selected so that the thus obtained emulsion polymer has an average molar mass between 200,000 and 2,000,000 and a hydroxyl number from 2 to 100 and the absolute difference between the glass transition temperature (Tg1) of the polymer obtained during the first step and the glass transition temperature (Tg2) of the polymer which would be obtained if only the monomer used during the first step or only the mixture of ethylenically unsaturated monomers used during the second step was polymerized is comprised between 10 and 170 °C.

Description

Process for priming or single-layer painting of plastics with an aqueous coating agent

The present invention relates to a method for priming or single-layer coating of plastics with an aqueous coating agent.

Plastics are used in almost all areas of application, especially in the automotive industry. In the case of motor vehicles, the plastic parts should not differ from the metallic parts of the body neither visually nor through less resistance to stone chips, weather, etc. In order to achieve this, efforts are being made to paint the plastic parts in such a way that they do not differ from the metallic parts of the body in terms of appearance and resistance to stone chips, weather, etc. A simple overpainting with the paints used for the metallic parts does not lead to success, however, because adhesion problems and / or poor cold impact strength and / or poor resistance to stone chips occur. To solve these problems, plastic parts are coated with a primer, on which a top coat can then be applied. For ecological and economic reasons, efforts are being made to coat with water-based primer use means. When using aqueous coating compositions for priming plastics, insufficient cold impact strength and / or insufficient adhesion between substrate and primer, in particular between primer and overpainted topcoat, are repeatedly observed.

Aqueous plastic primer, the film-forming material emulsion polymers and water-dilutable

Containing polyurethane resins are known. such

Plastic primers have insufficient cold impact strength and flexibility. There are also disadvantages with regard to other technological properties, such as liability.

Impact modifiers for PVC are known from US Pat. No. 4,443,585, which are based on emulsion polymers of the multi-stage type. The emulsion polymers are polymers which are obtained in an at least three-stage emulsion polymerization process.

EP-A-426 391 discloses core-shell type emulsion polymers which are used for the production of lacquers and coating compositions for paper. The core-shell polymers have a hydrophilic core and a hydrophobic shell. The object on which the present invention is based is to provide a method for priming or single-layer coating of plastics with an aqueous coating composition, with the aid of the coating compositions used it should be possible to prime plastics in such a way that there are no problems with the cold impact resistance Cold impact flexibility and / or liability occur. The coatings obtained should have a toothy transition below -10 ° C. This object is surprisingly achieved by a process for priming or single-layer coating of plastics with an aqueous coating composition which contains, as film-forming material, an emulsion polymer or several emulsion polymers and a water-thinnable polyurethane resin which is characterized in that the aqueous coating composition contains an emulsion polymer which is obtainable is by a) polymerizing in a first stage 10 to 90 parts by weight of an ethylenically unsaturated monomer or a mixture of ethylenically unsaturated monomers in aqueous phase in the presence of one or more emulsifiers and one or more radical-forming initiators and b) after at least 80 parts by weight % of that in the first

Stage used ethylenically unsaturated monomer or monomer mixture have been reacted, in a second stage 90 to 10 parts by weight of an ethylenically unsaturated monomer or a mixture of ethylenically unsaturated monomers are polymerized in the presence of the polymer obtained in the first stage, the reaction conditions being chosen so that that the emulsion polymer obtained has a number average molecular weight of 200,000 to 2,000,000 and the ethylenically unsaturated monomer or monomer mixture used in the first stage and the ethylenically unsaturated monomer or mono used in the second stage the type and amount of the mixed mixture are selected so that the emulsion polymer has a hydroxyl number from 2 to 100 and the absolute difference between the glass transition temperature (T _g1 ) of the polymer obtained in the first stage (a) and the glass transition temperature (T _g2 ) of ^the polymer, which was obtained by polymerizing only the monomer used in the second stage (b) or the mixture of ethylenically unsaturated monomers used in the second stage (b) is 10 to 170 ° C.

The multi-stage emulsion polymers used according to the inventive method are known in part from DE-A-39 42 804. According to this document, the multi-stage emulsion polymers are used in pigmented aqueous base coating compositions. These are effect coatings on automobile bodies, in particular metallic effect coatings with a good metallic effect. According to DE-A-39 42 804, the aqueous base coating compositions are applied to the substrate, a suitable transparent top coating composition is then applied to the base layer obtained, then the base layer is dried together with the top layer at temperatures below 100.degree.

The emulsion polymers used in the process according to the invention can be prepared by a two-stage emulsion polymerization in an aqueous medium in known apparatus, for example in a Ruhr kettle with a heating and cooling device. The monomers can be added in such a way that a solution of all the water, the emulsifier and part of the initiator is introduced and the monomer or

Monomer mixture and separately from it, but in parallel the rest of the initiator at the polymerization temperature tur is slowly added. However, it is also possible to introduce some of the water and the emulsifier and to prepare a pre-emulsion from the rest of the water and the emulsifier and from the monomer or from the monomer mixture, which is slowly added at the polymerization temperature, the initiator again being added separately becomes.

It is preferred to add the monomer or monomer mixture in the form of a pre-emulsion in the first stage and in the second stage the monomer or monomer mixture in bulk, i.e. without adding water and emulsifier and adding the initiator separately, but in parallel. It is particularly preferred in the first stage to first prepare a seed polymer from a part (generally about 30% by weight of the total preemulsion to be used) of the preemulsion to be used in the first stage and then to add the rest of the preemulsion to be used in the first stage .

The polymerization temperature is generally in the range from 20 to 100 ° C., preferably 40 to 90 ° C.

The quantitative ratio between the monomers and the water can be selected so that the resulting dispersion has a solids content of 30 to 60% by weight, preferably 30 to 45% by weight.

An anionic emulsifier is preferably used alone or in a mixture as the emulsifier.

Examples of anionic emulsifiers are the alkali metal salts of sulfuric acid half-esters of alkylphenols or alcohols, furthermore the sulfuric acid half-esters of oxyethylated alkylphenols or oxyethylated alcohols, preferably the alkali metal salts of sulfuric acid half ester of a 4 to 5 moles of ethylene oxide per mole of reacted nonylphenol, alkyl or aryl sulfonate, sodium lauryl sulfate, sodium lauryl ethoxylate sulfate and secondary sodium alkane sulfonates, the carbon chain of which contains 8 to 20 carbon atoms. The amount of the anionic emulsifier is 0.1 to 5.0% by weight, based on the monomers, preferably 0.3 to 3.0% by weight. Furthermore, to increase the stability of the aqueous dispersion, a nonionic emulsifier of the ethoxylated alkylphenol or fatty alcohol type, for example an addition product of one mole of nonylphenol and 4 to 25 moles of ethylene oxide, can be used in a mixture with the anionic emulsifier. A radical initiator is preferably one

Peroxide compound used. The initiator is water-soluble or monomer-soluble. A water-soluble initiator is preferably used. Suitable initiators are the customary inorganic per compounds, such as ammonium persulfate, potassium persulfate, ammonium or alkali metal peroxodiphosphate and organic peroxides, such as e.g. Benzoyl peroxide, organic peresters, such as

Perisopivalate, partly in combination with reducing agents, such as sodium disulfide, hydrazine, hydroxylamine and catalytic amounts of accelerators, such as iron,

Cobalt, cerium and vanadyl salts. Alkali metal or ammonium peroxodisulfates are preferably used. Redox initiator systems disclosed in EP-A-107 300 can also be used.

In the first stage, 10 to 90, preferably 35 to 65 parts by weight of an ethylenically unsaturated monomer or a mixture of ethylenically unsaturated monomers are emulsion polymerized. After at least 80 wt .-%, preferably at least 95 wt .-%, of the ethylenically unsaturated used in the first stage have been reacted in a second stage (b), 90 to 10, preferably 65 to 35 parts by weight of an ethylenically unsaturated monomer or a mixture of ethylenically unsaturated monomers are emulsion polymerized in the presence of the polymer obtained in the first stage. It is essential that the reaction conditions are chosen so that the emulsion polymer obtained has a number average molecular weight of 200,000 to 2,000,000 and the ethylenically unsaturated monomer or monomer mixture used in the first stage and the ethylenically unsaturated monomer or Monomer mixture in type and amount are selected so that the emulsion polymer has a hydroxyl number of 2 to 100 mg KOH / g, preferably 10 to 50 mg KOH / g, and the absolute difference between the glass transition temperature (T _g1 ) of the in the first Step (a) of the polymer obtained and the glass transition temperature (T _g2 ) of the polymer which would be obtained solely by polymerizing the monomer used in the second step (b) or the mixture of ethylenically unsaturated monomers used in the second step (b), 10 to 170 ° C, preferably 80 to 150 ° C.

Because the glass transition temperature of emulsion polymers according to the equation

T _g = glass transition temperature of the copolymer in K.

W _n = weight fraction of the nth monomer

T _gn = glass transition temperature of the homopolymer from the nth monomer x = the number of different monomers can be calculated approximately, the person skilled in the art has no problem selecting the monomer or monomer mixture to be used in the first stage and the monomer or monomer mixture to be used in the second stage (b) such that the absolute Difference between the glass transition temperature (T _g1 ) of the polymer obtained in the first stage (a) and the glass transition temperature (T _g2 ) of the polymer, which is obtained solely by polymerizing the monomer used in the second stage (b) or that in the second stage ( b) used mixture of ethylenically unsaturated monomers would be obtained, is 10 to 170 ° C.

The emulsion polymer used in the process according to the invention should have a number average molecular weight (determination: gel permeation chromatography using polystyrene as the standard) of 200,000 to 2,000,000, preferably 300,000 to 1,500,000, and usually acid numbers of less than 100 mg KOH / g and an OH number of Have 2 to 100 mg KOH / g. The person skilled in the art knows how to select the reaction conditions during the emulsion polymerization so that he obtains emulsion polymers which have the number-average numbers given above

Have molecular weights (see e.g. chemistry, physics and technology of plastics in individual representations, dispersions of synthetic high polymers, part 1 of F.

Hölscher, Springer Verlag, Berlin, Heidelberg, New York, 1969).

According to the process of the invention, the aqueous coating compositions contain, in addition to the emulsion polymer described above or in addition to the emulsion polymers described above, a water-dilutable polyurethane resin as the film-forming agent Material.

In the process according to the invention for priming or single-layer coating of plastics, an aqueous coating composition is very particularly preferably used which contains as the film-forming material an emulsion polymer obtained by a multistage polymerization, in which the polymer obtained in the first stage (a) has a glass transition temperature (T _g1 ) from -60 ° C to + 20 ° C and in which the monomer used in the second stage (b) or the mixture used in the second stage (b) is selected from ethylenically unsaturated monomers so that a sole polymerization of the in the second stage used monomer or in the second stage

Stage used mixture of ethylenically unsaturated monomers would lead to a polymer with a glass transition temperature (T _g2 ) of +30 to + 110 ° C. When such emulsion polymers are used in the process according to the invention, coatings are obtained on plastic substrates which have particularly good low-temperature impact strength and low-temperature flexibility. Examples of monomers which can be used in the first stage are: vinylaromatic hydrocarbons, such as styrene, α-alkylstyrene and vinyltoluene, esters of acrylic acid or methacrylic acid, in particular aliphatic and cycloaliphatic acrylates or methacrylates with up to 20 carbon atoms in the alcohol radical, such as methyl, ethyl, propyl, butyl, hexyl, ethylhexyl, stearyl, lauryl and cyclohexyl acrylate or methacrylate, acrylic and / or methacrylic acid, acrylic and / or methacrylamide, N-methylolacrylamide and / or N-methylol methacrylamide, hydroxyalkyl esters of acrylic acid, methacrylic acid or another α, β-ethylenically unsaturated carboxylic acid, such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, 2-hydroxyethyl methacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate,

Monomers containing carboxyl or sulfonic acid groups, such as acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, acrylamidomethylpropanesulfonic acid.

In the first stage, a mixture of al) 47 to 99% by weight, preferably 75 to 90% by weight, of a cycloaliphatic or aliphatic ester of acrylic acid or methacrylic acid or a mixture of such esters, a2) 1 to 20% by weight, is preferably used .-%, preferably 5 to 15 wt .-%,

of a monomer carrying at least one hydroxyl group and copolymerizable with (a1), (a3) and (a4) or a mixture of such monomers, a3) 0 to 8% by weight, preferably 2 to 6% by weight, of at least one carboxyl - or sulfonic acid group-bearing monomers which can be copolymerized with (a1), (a2) and (a4) or a mixture of such monomers and a4) 0 to 25% by weight, preferably 2 to 15% by weight,

another monomers copolymerizable with (a1), (a2) and (a3) or a mixture of such monomers is used, the sum of the parts by weight of (a1), (a2), (a3) and (a4) always being 100% by weight. -%. Examples of components (a1) that can be used are: cyclohexyl acrylate, cyclohexyl methacrylate, alkyl acrylates and acrylic methacrylates with up to 20 carbon atoms in the alkyl radical, such as methyl, ethyl, propyl, butyl, hexyl, ethylhexyl, stearyl and lauryl acrylate and methacrylate or mixtures of these monomers.

Examples of components (a2) which can be used are: hydroxyalkyl esters of acrylic acid, methacrylic acid or another α, β-ethylenically unsaturated carboxylic acid. These esters can be derived from an alkylene glycol esterified with an acid, or they can be obtained by reacting the acid with an alkylene oxide. Hydroxyalkyl esters of acrylic acid and are preferably used as component (a2)

Methacrylic acid in which the hydroxyalkyl group contains up to 4 carbon atoms, or mixtures of these hydroxyalkyl esters. Examples of such hydroxyalkyl esters are 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, 2-hydroxyethyl methacrylate, 4-hydroxybutyl acrylate or 4-hydroxybutyl methacrylate. Corresponding esters of other unsaturated acids such as ethacrylic acid, crotonic acid and similar acids with up to about 6 carbon atoms per molecule can also be used. Acrylic acid and / or methacrylic acid and / or acrylamidomethylpropanesulfonic acid are preferably used as component (a3). However, other ethylenically unsaturated acids with up to 6 carbon atoms in the molecule can also be used. Examples of such acids are ethacrylic acid, crotonic acid, maleic acid, fumaric acid and itaconic acid. The following can be used as component (a4): vinylaromatic hydrocarbons, such as

Styrene, α-alkyl styrene and vinyl toluene, acrylic and

Methacrylamide and acrylonitrile and methacrylonitrile or mixtures of these monomers.

Examples of monomers which can be used in the second stage (b) are: vinylaromatic hydrocarbons, such as styrene, α-alkylstyrene and vinyltoluene, esters of acrylic acid or methacrylic acid, in particular aliphatic and cycloaliphatic acrylates or methacrylates with up to 20 carbon atoms in the alcohol residue, such as methyl, ethyl, propyl, butyl, hexyl, ethylhexyl, stearyl, lauryl and cyclohexyl acrylate or methacrylate, acrylic and / or methacrylic acid, acrylic and / or methacrylamide, N-methylolacrylamide and / or N-methylol methacrylamide, hydroxyalkyl esters of acrylic acid, methacrylic acid or another α, ß-ethylenically unsaturated carboxylic acid, such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, 2-hydroxyethyl methacrylate, Hydroxybutyl acrylate, 4-hydroxybutyl methacrylate. In the second stage, preference is given to using ethylenically unsaturated monomers or mixtures of ethylenically unsaturated monomers which are essentially free of hydroxyl and carboxyl groups. “Substantially free” is intended to mean that it is preferred to use monomers or monomer mixtures which are free from hydroxyl and carboxyl groups, but that the monomers or monomer mixtures used also contain small amounts of hydroxyl and, for example as a result of impurities / or may contain carboxyl groups. The content of monomers with hydroxyl, carboxyl or other hydrophilic groups should be in the second stage of the emulsion polymerization compared to the content of these monomers in the first stage be significantly reduced. In the second stage (b), a mixture of b1) 100 to 60% by weight, preferably 99.5 to 75% by weight, of a cycloaliphatic or aliphatic ester of acrylic acid or methacrylic acid or a mixture of such esters and b2 is preferred ) 0 to 40% by weight, preferably 0.5 to 25% by weight, of a monomer copolymerizable with (b1) or a mixture of such monomers, the sum of the parts by weight of b1) and b2) always being 100% by weight. -% results.

The following can be used as component b1): cyclohexyl acrylate, cyclohexyl methacrylate,

Alkyl acrylates and alkyl methacrylates with up to 20 carbon atoms in the alkyl radical, e.g. Methyl, ethyl, propyl, butyl, hexyl, ethylhexyl, stearyl and lauryl acrylate and methacrylate or mixtures of these monomers.

As component (b2) e.g. can be used:

vinyl aromatic hydrocarbons such as styrene, α-alkyl styrene and vinyl toluene, acrylic and methacrylamide and acrylonitrile and methacrylonitrile or mixtures of these monomers.

Furthermore, both in the first stage (a) and in the second stage (b), tetrahydrofurfuryl acrylate, tetrahydrofurfuryl methacrylate, furfuryl acrylate, furfuryl methacrylate, phenoxyethyl acrylate and phenoxy ethyl methacrylate and crosslinking monomers such as hexanediol diacrylate, hexanediol dimethacrylate, glycol diacrylate, glycol dimethacrylate, butanediol acrylate, butanediol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, divinylbenzene, allyl methacrylate and allyl methacrylate are used. However, the proportion of these crosslinking monomers should be kept relatively low. In the process according to the invention, the polymers described in DE-A-39 42 804 and obtainable by multi-stage emulsion polymerization can also be used as the film-forming material of the aqueous coating compositions. In the case of these emulsion polymers, that obtained in the first stage (a)

Polymer has a glass transition temperature (T _g1 ) of + 30 to + 110 ° C, the monomer used in the second stage (b) or the mixture of ethylenically unsaturated monomers used in the second stage (b) is selected so that a sole polymerization of the monomer used in the second stage or of the mixture of ethylenically unsaturated monomers used in the second stage would lead to a polymer with a glass transition temperature (T _g2 ) of -60 ° C. to + 20 ° C. With regard to the production of these multi-stage emulsion polymers, reference is made to the corresponding statements in DE-A-39 42 804. In addition to the suitable monomers mentioned in the two-stage emulsion polymerization, the following monomers can also be used in the first and in the second stage of the emulsion polymerization: tetrahydrofurfuryl acrylate, tetrahydrofurfuryl methacrylate, furfuryl acrylate, furfuryl methacrylate, phenoxyethyl acrylate, phenoxyethyl methacrylate, low methylene acrylate, and diaoxyethyl methacrylate, as well as low methoxy acrylate, and diaoxyethyl methacrylate, Glycol dimethacrylate, Butanediol acrylate, butanediol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, allyl acrylate, allyl methacrylate. The aqueous coating compositions used in the process according to the invention contain water-thinnable polyurethane resins as film-forming material in addition to the multi-stage emulsion polymers. The film-forming material contained in the aqueous coating composition preferably consists of 20 to 80% by weight, particularly preferably 30 to 70% by weight, of the emulsion polymer (s) and 80 to 20% by weight, particularly preferably 70 to 30% by weight. , of the water-thinnable polyurethane resin, the proportions each relating to the solids content and their total always being 100% by weight.

As water-thinnable polyurethane resins e.g. water-thinnable, urea-containing polyurethane resins in question, which have a number average molecular weight (determination: gel chromatography with polystyrene as standard) of 1000 to 250,000 and an acid number of 5 to 70 mg KOH / g and by reaction, preferably chain extension of prepolymers containing isocyanate groups with polyamines and / or hydrazine can be produced.

The preparation of the prepolymer containing isocyanate groups can be carried out by reaction of polyalcohols having a hydroxyl number of 10 to 1800, preferably 50 to 500 mg KOH / g, with excess polyisocyanates at temperatures up to 150 ° C., preferably 50 to 130 ° C., in organic solvents cannot react with isocyanates. The equivalence ratio of NCO to OH groups is 1.5 to 1.0 and 1.0 to 1.0, preferably between 1.4 and 1.2 to 1. The for the preparation of the Pra polymeric polyols used can be low molecular weight and / or high molecular weight and they can contain inert anionic groups.

Low molecular weight polyols can be used to increase the hardness of the polyurethane. You have a

Molecular weight from 60 to about 400 and can contain aliphatic, alicyclic or aromatic groups. Amounts of up to 30% by weight of the total polyol constituents, preferably about 2 to 20% by weight, are used. The low molecular weight polyols with up to about 20 carbon atoms per molecule, such as ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butylene glycol, 1,6, are advantageous -Hexanediol, trimethylolpropane, castor oil or hydrogenated castor oil, ditrimethylolpropane ether, pentaerythritol, 1,2-cyclohexanediol, 1,4-cyclohexanedimethanol, bisphenol A, bisphenol F, neopentylglycol, hydroxypivalic acid neopentylglycol ester, hydroxyethylated or hydroxypropylated bisphenolated or hydroxypropylated bisphenylated or hydroxypropylated, bisethylphenylated or hydroxypropylated, bisethylphenylated or hydroxypropylated, bisphenolated or hydroxyethylated or hydroxypropylated

Mixtures.

In order to obtain a high flexibility NCO prepolymer, a high proportion of a predominantly linear polyol with a preferred hydroxyl number of 30 to 150 mg KOH / g should be added. Up to 97% by weight of the total polyol can consist of saturated and unsaturated polyesters and / or polyesters and / or polyethers with a molecular weight M _n of 400 to 5000. Suitable high molecular weight polyols are aliphatic polyether diols of the general formula H- (0 - (- CHR) _n -) _m -OH, in which R = hydrogen or a lower alkyl radical which is optionally provided with different substituents, where n = 2 to 6, is preferably 3 to 4 and m = 2 to 100, preferably 5 to 50. Examples are linear or branched polyether diols, such as poly (oxyethylene) glycols, poly (oxypropylene) glycols and / or Poly (oxybutylene) glycols. The selected polyether diols should not introduce excessive amounts of ether groups, because otherwise the polymers formed in

Swell water. The preferred polyether diols are (poly) oxypropylene) glycols in the molecular weight range M _n from 400 to 3000. Polyester diols are prepared by esterification of organic dicarboxylic acids or their anhydrides with organic diols or are derived from a hydroxycarboxylic acid or a lactone. To produce branched polyester polyols, polyols or polycarboxylic acids with a higher valency can be used to a small extent. The dicarboxylic acids and diols can be linear or branched aliphatic, cycloaliphatic or aromatic dicarboxylic acids or diols.

The diols used to prepare the polyesters consist, for example, of alkylene glycols, such as ethylene glycol, propylene glycol, butylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol and other diols, such as dimethylolcyclohexane. The acid component of the polyester consists primarily of low molecular weight dicarboxylic acids or their anhydrides with 2 to 30, preferably 4 to 18, carbon atoms in the molecule. Suitable acids are, for example, o-phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, maleic acid, fumaric acid, glutaric acid, hexachloroheptanedicarboxylic acid, tetrachlorophthalic fatty acid and /. Instead of these acids, their anhydrides, if they exist, can also be used. Smaller amounts of carboxylic acids with 3 or more carboxyl groups, for example trimellitic anhydride or the adduct of maleic anhydride with unsaturated fatty acids, can also be present in the formation of polyester polyols.

According to the invention, polyester diols are also used, which are obtained by reacting a lactone with a diol. They are characterized by the presence of a terminal hydroxyl group and recurring polyester components of the formula - (- CO- (CHR) _n -CH ₂ -O -) -.

Here, n is preferably 4 to 6 and the substituent R is hydrogen, an alkyl, cycloalkyl or alkoxy radical. No substituent contains more than 12 carbon atoms. The total number of carbon atoms in the substituent does not exceed 12 per lactone ring. Examples include hydroxycaproic acid, hydroxybutyric acid, hydroxydecanoic acid and / or hydroxystearic acid. The lactone used as the starting material can be represented by the following general formula, CH ₂ - (CR ₂ ) _n - C = 0 in which n and R have the meaning already given. Unsubstituted ε-caprolactone, in which n is 4 and all R substituents are hydrogen, is preferred for the preparation of the polyester diols. The reaction with lactone is started by low molecular weight polyols, such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, dimethylolcyclohexane. However, other reaction components, such as ethylenediamine, alkyldialkanolamines or even urea, can also be reacted with caprolactone.

Also suitable as higher molecular weight diols are polylactam diols which are produced by reacting, for example, ε-caprolactam with low molecular weight diols. Aliphatic, cycloaliphatic and / or aromatic polyisocyanates with at least two isocyanate groups per molecule are used as typical multifunctional isocyanates. Suitable aromatic diisocyanates are phenylene diisocyanate, tolylene diisocyanate, Xylylene diisocyanate, biphenylene diisocyanate, naphthylene diisocyanate and diphenylmethane diisocyanate.

Due to their good resistance to ultraviolet light, (cyclo) aliphatic diisocyanates produce products with a low tendency to yellowing. Examples include isophorone diisocyanate, cyclopentylene diisocyanate and the hydrogenation products of aromatic diisocyanates, such as cyclohexylene diisocyanate, methylcyclohexylene diisocyanate and dicyclohexylmethane diisocyanate. Examples of aliphatic diisocyanates are trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, propylene diisocyanate, ethylethylene diisocyanate, dimethylethylene diisocyanate, methyltrimethylene diisocyanate and trimethylhexane diisocyanate. Isophorone diisocyanate and dicyclohexylmethane diisocyanate are particularly preferred as diisocyanates.

The polyisocyanate component used to form the prepolymer can also contain a proportion of higher-quality polyisocyanates, provided that this does not cause gel formation. Products which have proven useful as triisocyanates are those obtained by trimerization or oligomerization of diisocyanates or by reaction of diisocyanates with polyfunctional OH or

Compounds containing NH groups are formed. These include, for example, the biuret of hexamethylene diisocyanate and water, the isocyanurate of hexamethylene diisocyanate or the adduct of isophorone diisocyanate with trimethylolpropane.

The average functionality can optionally be reduced by adding monoisocyanates. Examples of such chain terminating monoisocyanates are phenyl isocyanate, cyclohexyl isocyanate and stearyl isocyanate. Polyurethanes are generally not compatible with water unless special components are incorporated and / or special manufacturing processes involved in their synthesis steps are taken. So large an acid number is incorporated that the neutralized product can be dispersed stably in water. For this purpose, compounds are used which contain two H-active groups reacting with isocyanate groups and at least one group capable of forming anions. Suitable groups which react with isocyanate groups are, in particular, hydroxyl groups and primary and / or secondary amino groups. Groups capable of forming anions are carboxyl, sulfonic acid and / or phosphonic acid groups. Carboxylic acid or carboxylate groups are preferably used. They should be so inert that the isocyanate groups of the diisocyanate preferably react with the other groups of the molecule that are reactive toward isocyanate groups. Alkane acids with two substituents on the α-position carbon atom are used for this. The substituent can be a hydroxyl group, an alkyl group or an alkylol group. These polyols have at least one, generally 1 to 3 carboxyl groups in the molecule. They have two to about 25, preferably 3 to 10, carbon atoms. Examples of such compounds are dihydroxypropionic acid, dihydroxysuccinic acid and dihydroxybenzoic acid. A particularly preferred group of dihydroxyalkanoic acids are the α, β-dimethylolalkanoic acids, which are characterized by the structural formula RC (CH ₂ OH) ₂ COOH, where R = hydrogen or an alkyl group having up to about 20 carbon atoms. Examples of such compounds are 2,2-dimethylol acetic acid, 2,2-dimethylol propionic acid, 2,2-dimethylol butyric acid and 2,2-dimethylol pentanoic acid. The preferred dihydroxyalkanoic acid is 2,2-dimethylolpropionic acid. Compounds containing amino groups are, for example, diaminovaleric acid, 3,4-diaminobenzoic acid, 2,4-diaminotoluenesulfonic acid and 2,4-diaminodiphenyl ether sulfonic acid. The polyol containing carboxyl groups can be 3 to 100% by weight, preferably account for 5 to 50% by weight of the total polyol constituents in the NCO prepolymer.

The amount of ionizable carboxyl groups available as a result of the carboxyl group neutralization in salt form is generally at least 0.4% by weight, preferably at least 0.7% by weight, based on the solid. The upper limit is about 6% by weight. The amount of dihydroxyalkanoic acids in the unneutralized prepolymer gives an acid number of at least 5, preferably at least 10. The upper limit of the acid number is 70, preferably 40 mg KOH / g, based on the solid.

Before the reaction with isocyanates, this dihydroxyalkanoic acid is advantageously neutralized at least in part with a tertiary amine in order to avoid a reaction with the isocyanates.

The NCO prepolymers used according to the invention can be prepared by simultaneously reacting the polyol or polyol mixture with an excess of diisocyanate.

On the other hand, the implementation can also be carried out step by step in the prescribed order. Examples are described in DE-OS-26 24 442 and DE-OS-32 10 051. The reaction temperature is up to 150 ° C, with a temperature in the range of 50 to

130 ° C is preferred. The reaction continues until practically all of the hydroxyl functions have been converted. The NCO prepolymer contains at least about 0.5% by weight of isocyanate groups, preferably at least 1% by weight of NCO, based on the solid. The upper limit is approximately 15% by weight, preferably 10% by weight, particularly preferably 5% by weight. The reaction can optionally be carried out in the presence of a catalyst such as organotin compounds and / or tertiary amines. To keep the reactants in a liquid state and better temperature control during the reak tion is to allow the addition of organic solvents that have no active hydrogen after

Zerewitinoff included, possible. Usable solvents are, for example, dimethylformamide, esters, ethers, such as diethylene glycol dimethyl ether, keto esters, ketones, such as

Methyl ethyl ketone and acetone, ketones substituted with methoxy groups, such as methoxy-hexanone, glycol ether esters, chlorinated hydrocarbons, aliphatic and alicyclic hydrocarbon pyrrolidones, such as N-methyl pyrrolidone, hydrogenated furans, aromatic hydrocarbons and mixtures thereof. The amount of solvent can vary within wide limits and should be sufficient to form a prepolymer solution with a suitable viscosity. Mostly 0.01 to 15 wt .-% solvent, preferably 0.02 to 8 wt .-% solvent, based on the solid. If the water-insoluble solvents boil lower than the water, they can be gently distilled off after the urea-containing polyurethane dispersion has been prepared by vacuum distillation or thin-film evaporation.

High-boiling solvents should be water-soluble and remain in the aqueous polyurethane dispersion to facilitate the confluence of the polymer particles during film formation, or they are largely removed by azeotropic distillation. Particularly preferred solvents are N-methylpyrrolidone, optionally in a mixture with ketones, such as methyl ethyl ketone. The anionic groups of the NCO prepolymer are at least partially neutralized with a tertiary amine. The resulting increase in dispersibility in water is sufficient for infinite dilutability. It is also sufficient to consistently disperse the neutralized polyurethane containing urea groups. Suitable tertiary amines are, for example, trimethylamine, triethylamine, dimethylethylamine, Diethylmethylamine, N-methylmorpholine. After neutralization, the NCO prepolymer is diluted with water and then results in a finely divided dispersion. Shortly thereafter, the isocyanate groups still present are reacted with di- and / or polyamines with primary and / or secondary amino groups as chain extenders. This reaction leads to a further linkage and an increase in the molecular weight. The competitive reaction between amine and water with the isocyanate must be well coordinated to obtain optimal properties

(Time, temperature, concentration) and well monitored for reproducible production. Water-soluble compounds are preferred as chain extenders because they increase the dispersibility of the polymeric end product in water. Hydrazine and organic diamines are preferred because they generally build up the highest molecular weight without gelling the resin. However, the prerequisite for this is that the ratio of the amino groups to the isocyanate groups is selected appropriately. The amount of chain extender is determined by its functionality, the NCO content of the prepolymer and the duration of the reaction. The ratio of the active hydrogen atoms in the chain extender to the NCO groups in the prepolymer should generally be less than 2: 1 and preferably in

Range from 1.0: 1 to 1.75: 1. The presence of excess active hydrogen, especially in the form of primary amino groups, can result in polymers with undesirably low molecular weights.

Polyamines are essentially alkylene polyamines having 1 to 40 carbon atoms, preferably about 2 to 15 carbon atoms. They can carry substituents that have no hydrogen atoms that are reactive with isocyanate groups. Examples are polyamines with a linear or branched aliphatic, cycloaliphatic or aromatic structure and at least two primary amines no groups. As diamines are to be mentioned ethylenediamine, propylenediamine, 1,4-butylenediamine, piperazine, 1,4-cyclohexyldimethylamine, hexamethylenediamine-1,6, trimethylhexamethylenediamine, methanediamine, isophoronediamine, 4,4'-diaminodicyclohexylmethane and aminoethylethanolamine. Preferred diamines are alkyl or cycloalkyl diamines, such as propylenediamine and 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane.

The chain can be extended at least partially with a polyamine which has at least three amine groups with a reactive hydrogen. This type of polyamine can be used in such an amount that unreacted amine nitrogen atoms with 1 or 2 reactive hydrogen atoms are present after the polymer has been extended. Such useful polyamines are diethylene triamine, triethyl tetraamine, dipropylene triamine and dibutylene triamine.

Preferred polyamines are the alkyl or cycloalkyl triamines, such as diethylenetriamine. To prevent gelling during chain extension, small amounts of monoamines, such as ethylhexylamine, can also be added.

The water-dilutable polyurethane resins to be used according to the invention and their production are also described in EP-A-89 497 and US Pat. No. 4,719,132.

The aqueous coating compositions used in the process according to the invention can optionally, in addition to the emulsion polymer and the water-dilutable

Polyurethane resin advantageously also contain other compatible water-thinnable synthetic resins, such as Aminoplast resins, polyesters and polyethers.

The aqueous coating compositions used in the process according to the invention can optionally also contain other customary additives, such as organic solvents, Contain leveling agents, light stabilizers, rheology aids, pigments, fillers and catalysts. When ready for application, the coating compositions generally contain 30 to 80, preferably 45 to 70% by weight of water, 0 to 50, preferably 0 to 10

% By weight of organic solvents, 6 to 70, preferably 15 to 45% by weight of the film-forming material, 0 to 40, preferably 5 to 25% by weight of pigments and / or fillers and 0 to 10% by weight of other additives , such as Catalysts, thickeners, leveling agents, etc., where the percentages by weight are based on the overall formulation of the paints in the ready-to-apply state (i.e. e.g. with spray viscosity). Since the plastic substrates to which the aqueous coating compositions are applied are generally sensitive to temperature, the aqueous coating compositions generally have to be cured at temperatures of up to 100 ° C. for thermoplastics and up to 140 ° C. for thermosets.

In principle, according to the method according to the invention for priming or single-layer painting of plastics, all plastics can be primed or painted in one layer. Examples of suitable plastics are: ABS, AMMA, ASA, CA, CAB, EP, UF, CF, MF, MPF, PF, PAN, PA, PC, PE, HDPE, LDPE, PETP, PMMA, PP, PS, SB, PUR, PVC, RF, SAN, PP-EPDM and UP (short names according to DIN 7728T1). Preferred plastic substrates are: polycarbonate, polypropylene-EPDM and polyamide. The plastics to be painted can of course be polymer blends, modified plastics or fiber-reinforced plastics. In many cases it is advisable to use suitable plastics before painting

Methods (e.g. flame treatment, corona treatment, coating pretreatment with an adhesion promoter, such as chlorinated polyolefins etc.).

The aqueous coating compositions used in the process according to the invention are preferably used for priming plastics and can be applied, for example, by spraying, knife coating or dipping. The primed plastics can easily, e.g. with single-layer

Solid or metallic effect paints or with two-coat solid or metallic effect paints of the base coat clear coat type are overcoated.

According to the method according to the invention, coatings are obtained on plastic substrates which have excellent cold impact properties, cold impact flexibility, adhesiveness and excellent wetting properties. The invention is explained in more detail below on the basis of exemplary embodiments. Parts mean parts by weight, unless stated otherwise.

1. Preparation of emulsion polymer dispersions 1 to 3

1.1. Emulsion polymer dispersion 1: 964 g of deionized water and 8.75 g of a 30% strength aqueous solution of the ammonium salt of penta (ethylene glycol) nonylphenyl ether sulfate are placed in a cylindrical glass double-wall vessel with a stirrer, reflux condenser, stirrable feed vessel, dropping funnel and thermometer

(Fenopon EP 110 from GAF Corp., emulsifier 1) and heated to 82 ° C. In the stirrable feed tank from 525 g deionized water, 26.3 g emulsifier 1, 24.5 g methacrylamide, 31.5 g methacrylic acid, 140 g n-butyl methacrylate, 297.5 g n-butyl acrylate, 171.5 g methyl methacrylate, 80.5 g hydroxypropyl methacrylate and 35.0 g furfuryl methacrylate made an emulsion. 30% by weight of this emulsion are added for presentation. 28% by weight of a solution of 2.3 g of ammonium peroxodisulfate (APS) in 138 g of deionized water are then added dropwise over the course of 5 minutes. An exothermic reaction occurs. The reaction temperature is kept between 82 and 88 ° C. 15 minutes after the addition of the ammonium peroxodisulfate solution has ended, the remaining 70% by weight of the emulsion together with the remaining 72% by weight of the ammonium peroxodisulfate solution are added over the course of an hour, the temperature being kept at 85.degree. It is then cooled to 82 ° C. and within two hours a mixture of 7 g methacrylamide, 87.5 g n-butyl acrylate and 686 g methyl methacrylate and 4 g Eikosa (ethylene glycol) nonylphenyl ether (Antarox CO 850 from GAF Corp., emulsifier 2 ) and 250.5 g of deionized water are added. After the addition has ended, the reaction mixture is kept at 82-85 ° C. for two hours. It is then cooled and the dispersion is filtered through a 30 nm mesh. A finely divided dispersion with a non-volatile content of 45% by weight and an acid number of 18 mg KOH / g is obtained.

1.2. Emulsion polymer dispersion 2:

825.5 g of deionized water and 7.5 g of a 30% strength aqueous solution of the ammonium salt of penta (ethylene glycol) nonylphenyl ether sulfate are placed in a cylindrical glass double wall vessel with stirrer, reflux condenser, stirrable feed vessel, dropping funnel and thermometer (Fenopon EP 110 from GAF Corp., emulsifier 1) and heated to 82 ° C. An emulsion is prepared in the stirrable feed vessel from 450 g deionized water, 15 g emulsifier 1, 6.8 g acrylamide, 525 g methyl methacrylate and 120 g n-butyl methacrylate. 30% by weight of this emulsion are added for presentation. 28% by weight of a solution of 2 g of ammonium peroxodisulfate (APS) in 118 g of deionized water are then added dropwise in the course of 5 minutes. An exothermic reaction occurs. The reaction temperature is kept between 82 and 88 ° C. 15 minutes after the addition of the ammonium peroxodisulfate solution has ended, the remaining 70% by weight of the emulsion together with the remaining 72% by weight of the ammonium peroxodisulfate solution are added over the course of an hour, the temperature being kept at 85.degree. It is then cooled to 82 ° C. and within two hours a mixture of 20 g of acrylamide, 27 g of methacrylic acid, 449 g of n-butyl acrylate, 77.5 g of methyl methacrylate, 67.5 g of hydroxypropyl methacrylate, 30 g of furfuryl methacrylate and 13.6 g Eikosa (ethylene glycol) - nonylphenyl ether (Antarox CO 850 from GAF Corp., emulsifier 2) and 204.5 g of deionized water were added. After the addition has ended, the reaction mixture is kept at 85 ° C. for two hours. It is then cooled and the dispersion is filtered through a 30 nm mesh. A finely divided dispersion with a non-volatile content of 45% by weight and an acid number of 15 mg KOH / g is obtained.

1.3. Emulsion polymer dispersion 3 (comparison)

834.5 g of deionized water and 7.5 g of a 30% aqueous solution of the ammonium salt are placed in a cylindrical glass double-walled vessel with a stirrer, reflux condenser, stirrable inlet vessel, dropping funnel and thermometer of penta (ethylene glycol) nonylphenyl ether sulfate

(Fenopon EP 110 from GAF Corp., emulsifier 1) and heated to 82 ° C. In the stirrable feed vessel, 477 g of deionized water, 15 g of emulsifier 1, 3.4 g of eikosa (ethylene glycol) nonylphenyl ether (Antarox CO 850 from GAF Corp., emulsifier 2), 27 g of acrylamide, 603 g of methyl methacrylate, 120 g of n-butyl methacrylate , 449 g of n-butyl acrylate, 27 g of methacrylic acid, 67.5 g of hydroxypropyl methacrylate and 30 g of furfuryl methacrylate. 10% by weight of this emulsion are added for presentation. Then 10% by weight of a solution of 1.95 g of ammonium peroxodisulfate in 327 g of deionized water are added dropwise over the course of five minutes. An exothermic reaction occurs. The reaction temperature is kept between 82 and 88 ° C. 15 minutes after

Completion of the addition of the ammonium peroxodisulfate solution, the remaining 90 wt .-% of the emulsion within three hours and the remaining 90 wt .-% of

Solution of ammonium peroxodisulfate in deionized water is added over a period of four hours, the temperature being kept between 82 and 88 ° C. After the addition has ended, the reaction mixture is kept at 82 ° C. for a further two hours. It is then cooled and the dispersion is filtered through a 30 nm mesh. A finely divided dispersion with a non-volatile content of 45% by weight and an acid number of 14 mg KOH / g is obtained.

2. Production of aqueous coating compositions based on emulsion polymer dispersion 1, 2 and 3

(Examples 1, 2 and Comparative Example 1) and preparation of an aqueous coating composition based on the commercially available emulsion polymer dispersion Neocryl XK 70 (Comparative Example 2)

The inventory listed in the table below Parts are weighed in one after the other and dispersed for approx. 20 minutes. The mixture is then processed in a discontinuous agitator mill down to a fineness of 15 μm. The plastic primers obtained are applied to a polycarbonate plastic part at 50% atmospheric humidity and at 23 ° C. at an injection pressure of 4 to 5 bar (layer thickness

25 μm). It is then baked at 80 ° C for 30 minutes.

In Examples 1 and 2, the emulsion polymer dispersions 1 and 2 are used, in Comparative Example 1, the emulsion polymer dispersion 3 and in Comparative Example 2, the dispersion Neocryl XK 70

(Manufacturer: ICI Ltd.), which contains an emulsion polymer.

¹⁾ Assessment criterion: + very good

0 satisfactory

- bad ²⁾ The steam jet test is carried out according to Daimler-Benz delivery specification (DBL) 9014. A steam jet with a steam pressure of 100 bar, an opening angle of 25 °, a temperature of 80 ° C at the nozzle outlet is applied for 2 minutes

painted side of a test plate. The distance between the nozzle and the substrate is 10 cm. The degree of damage to the paint is then assessed. Assessment criterion as for ¹⁾ . ³⁾ The puncture test serves to determine the

Impact resistance, which is defined as the property of the material (also painted material) to react with sudden deformation with high deformation and high force absorption.

The force / deformation curve and the puncture energy that can be calculated from this serve as a measure of the impact strength.

A puncture apparatus is used for the determination, in which a test bolt hits a substrate plate with a test thickness of up to 4 mm with a force of up to 20 kN and a constant speed of up to 12 m / s. In the case of painted panels, the test bolt is opened on the unpainted back of the panel. Since the entire experiment is carried out in a closed, controlled temperature chamber, the sample can be tempered and the measuring temperature can be varied between -70 ° C and 250 ° C. In practice, an investigation is carried out from 25 ° C downwards until the energy required for tough / brittle fracture is low enough, i.e. the puncture leads to breakage in the paint and substrate.

Claims

1. Process for priming or single layer

Painting of plastics with an aqueous coating agent which contains an emulsion polymer or several emulsion polymers as well as a water-dilutable polyurethane resin as the film-forming material, characterized in that the aqueous coating agent contains an emulsion polymer which can be obtained by a) in a first stage 10 to 90 parts by weight of a ethylenically unsaturated monomers or a mixture of ethylenically unsaturated

Monomers are polymerized in the aqueous phase in the presence of one or more emulsifiers and one or more radical-forming initiators and b) after at least 80% by weight of the ethylenically unsaturated monomer or monomer mixture used in the first stage has been reacted, 90 to in a second stage 10 parts by weight of an ethylenically unsaturated

Monomers or a mixture of ethylenically unsaturated monomers are polymerized in the presence of the polymer obtained in the first stage, the reaction conditions being chosen so that the emulsion polymer obtained has a number average molecular weight of 200,000 to 2,000,000 and the ethylenically unsaturated used in the first stage Monomer or monomer mixture and the ethylenically unused used in the second stage Saturated monomer or monomer mixture in type and amount are selected so that the emulsion polymer has a hydroxyl number of 2 to 100 and the absolute difference between the glass transition temperature (T _g1 ) of the polymer obtained in the first stage (a) and the glass transition temperature (T _g2 ) of the polymer, which would be obtained by polymerizing only the monomer used in the second stage (b) or the mixture of ethylenically unsaturated monomers used in the second stage (b), is 10 to 170'C.

2. The method according to claim 1, characterized in that the polymer obtained in the first stage (a) has a glass transition temperature (T _g1 ) of -60 ° C to + 20 ° C and that in the second stage (b) used monomer or the mixture of ethylenically unsaturated monomers used in the second stage (b) is selected such that a sole polymerization of the monomer used in the second stage or of the mixture of ethylenically unsaturated monomers used in the second stage to give a polymer with a glass transition temperature ( T _g2 ) would lead from +30 to + 110 ° C.

3. The method according to claim 1, characterized in that the polymer obtained in the first stage (a) has a glass transition temperature (T _g1 ) of +30 to + 110 ° C and that in the second stage (b) used monomer or The mixture of ethylenically unsaturated monomers used in the second stage (b) is selected such that a sole polymerization of the monomer used in the second stage (b) or of the mixture of ethylenically unsaturated used in the second stage (b) termed monomers would lead to a polymer with a glass transition temperature (T _g2 ) of -60 ° C to + 20 ° C.

4. The method according to claim 1 or 2, characterized in that in the first stage (a) a mixture of a1) 47 to 99 wt .-%, preferably 75 to 90

% By weight of a cycloaliphatic or aliphatic ester of acrylic acid or methacrylic acid or a mixture of such esters, a2) 1 to 20% by weight, preferably 5 to 15% by weight, of an at least one hydroxyl group with (a1) , (a3) and (a4) copolymerizable monomers or a mixture of such monomers, a3) 0 to 8% by weight, preferably 2 to 6% by weight, of a group bearing at least one carboxyl or sulfonic acid group with (a1), (a2) and (a4) copolymerizable monomers or a mixture of such monomers and a4) 0 to 25% by weight, preferably 2 to 15% by weight, of another copolymerizable with (a1), (a2) and (a3) Monomers or a mixture of such monomers is used, the sum of the parts by weight of (a1), (a2), (a3) and (a4) always

Is 100% by weight. 5. The method according to claim 1, 2 or 4, characterized in that in the second stage (b) Mixture of b1) 100 to 60 wt .-%, preferably 99.5 to

75 wt .-%, a cycloaliphatic or aliphatic ester of acrylic acid or

Methacrylic acid or a mixture of such esters and b2) 0 to 40% by weight, preferably 0.5 to

25% by weight, one copolymerizable with (b1)

Monomers or a mixture of such monomers is used, the sum of the parts by weight of b1) and b2) always being 100% by weight.

6. The method according to claim 1 to 5, characterized in that the film-forming material contained in the aqueous coating composition from 20 to 80 wt .-%, particularly preferably 30 to 70 wt .-%, of

Emulsion polymer and 80 to 20 wt .-%, particularly preferably 70 to 30 wt .-%, of the water-dilutable polyurethane resin, the proportions each refer to the solids content and their total is always 100 wt .-%.