GB2039498A - Preparation of copolymers containing hydroxyl groups by simultaneous esterification and copolymerisation. - Google Patents

Abstract

In a process for the manufacture of copolymers which are based on vinyl compounds, alpha, beta-unsaturated monocarboxylic acids and monoglycidyl compounds, carry hydroxyl groups and are soluble in organic solvents, by heating the reactants in an inert organic solvent with simultaneous esterification and copolymerisation, there is employed as the epoxycarboxy catalyst at least one alkali metal compound. Lacquers are formed from the copolymers combined with aminoplast resins or polyisocyanates.

Description

SPECIFICATION Manufacture of copolymers carrying hydroxyl Process for the manufacture of copolymers which carry hydroxyl groups and are soluble in organic solvents, by simultaneous esterification and copolymerisation in the presence of an epoxy-carboxy catalyst.

German Patent Specification 1,038,754 describes a process for the manufacture of esterified polyhydroxy copolymers. This known process is characterised in that (a) a short-chain a, ss-unsaturated monocarboxylic acid, (b) a vinyl monomer with only one active, terminal CH2=C \ group capable of addition polymerisation and (c) a monoepoxide, which is an alkylene oxide, which is optionally substituted by alkyl, or an ether or ester with only one three-membered epoxide substituent, the monoepoxide having no other reactive group, are reacted at the same time and in the presence of an epoxy-carboxy catalyst and of a catalyst for vinyl polymerisation. With this process, the reaction must always be carried out in the presence of an epoxy-carboxy catalyst and of a catalyst for vinyl polymerisation, at the same time.As repetition of the examples given in this specification has shown, these known copolymers give yellow to brownish coloured solutions. The lacquer films produced therefrom display an undesirable yellow to brown coloration after evaporation of the solvent, so that these products can find only very restricted application.

French Patent Specification 1,390,572 also describes a process for the manufacture of esterified polyhydroxy copolymers, the addition reaction between the epoxy group and the carboxy group taking place during or after the copolymerisation. The use of this process principle has been described by the inventor of the present invention in the following Patent Specifications: German Offenlegungsschrift 2,054,231, Swiss Patent Specification 523,961, German Offenlegungsschrift 2,021,141, German Patent Specification 2,626,900, German Auslegeschrift 2,603,259, German Auslegeschrift 2,659,853, Swiss Patent Specification 519,532, German Offenlegungsschrift 2,515,705;German Offenlegungsschrift 2,603,624, German Offenlegungsschrift 2,618,809 and German Offenlegungsschrift 2,065,770.

The disadvantage of these known processes on an industrial scale is that relatively long reaction times (12 to 15 hours) are required for the reactions, that is to say esterification and copolymerisation, to go to completion. With these long reaction times, undesired side reactions take place, since the carboxyl group of the a,ss-unsaturated monocarboxylic acid reacts, before and after its copolymerisation with the other monomers, with reactive groups, for example with the hydroxyl groups and/or glycidyl groups, with the formation of an ester, and the glycidyl groups react with one another or with the hydroxyl groups, to form structures containing an ether bond.Reaction batches of this type are therefore very sensitive to the conditons under which the reaction is carried out, so that on an industrial scale it is necessary to adhere very precisely to the reaction parameters in order reliably to manufacture copolymers with the desired characteristics in comparable quality. Moreover, even when the reaction is carried out very carefully, the formation of gel particles with particle diameters of about 5 to 25 m always takes place to a certain extent; specialists in the lacquer field term these particles "specks" in the lacquer films produced using such copolymers, and the particles make it impossible to obtain a high quality lacquer coating.

German Offenlegungsschrift 1,668,510 also describes a process for the manufacture of esterified polyhydroxy copolymers, but in this process the addition reaction between the epoxy groups and the carboxy groups is carried out before, after or during the copolymerisation. In the case of the embodiment in which the esterification is carried out during or after the copolymerisation, what has already been stated above applies and the process has the indicated disadvantages.In the case of the embodiment in which two reactants, that is to say the a,t3-unsaturated monocarboxylic acid and the epoxy compound, which is a glycidyl ester of a tertiary aliphatic monocarboxylic acid, are first processed on their own, in the absence of esterification catalysts, to give a precursor in the form of an ester (as is also carried out in German Patent Specifications 2,709,784 and 2,709,782), the surprising disadvantage which results is that the copolymer solutions are obtained as turbid solutions and the lacquer films produced therefrom are likewise cloudy.

Furthermore, further difficulties can very easily arise because the a,ss-unsaturated carboxylic acid tends to undergo self-polymerisation and, as a result of this, the homopolymers formed likewise cause turbidity.

Such findings are also confirmed by the statements in column 9, line 43 to column 10, line 8 of German Patent Specification 1,038,754 and in column 10, lines 1 to 39 of German Patent Specification 2,626,900.

The object of the present invention is substantially to eliminate the disadvantages, described above, of the known processes of the abovementioned type, some of which are carried out on an industrial scale, that is to say: 1. The copolymer solutions should be colourless and clear. This means that the lacquer films produced therefrom should also be "speck-free" or have a very "low speck content" and should not yellow, despite the presence of the catalyst.

2. Even on an industrial scale, the reaction conditions should be relatively non-critical for the manufacturing process, so that, after the optimum reaction parameters have been determined, usable copolymers capable of high performance are always obtained even if there are small deviations in the reaction conditions, and undesired side reactions should also be very extensively eliminated by the catalyst, during copolymerisation and during use of the copolymers.

3. It should be possible to carry out the manufacturing process, especially on an industrial scale, by the one-pot process with a considerably shortened reaction time, in order thus to effect a quite substantial increase in the productivity of the production unit, as a result of the considerably shorter time for which the kettle is in use, and thus to lower production costs.

4. The manufacturing process should also permit the manufacture of improved copolymers based on a known or novel monomer composition.

5. The copolymers manufactured by the process should give non-tacky, water-resistant and elastic films on very diverse substrates or be suitable as binders for pigments, finishing paints and fleeces and also should be suitable for use as binder components, the coatings or sheet-like structures produced therewith having advantageous characteristics of various types.

The object of the invention has been achieved by carrying out the esterification stage with simultaneous copolymerisation in the presence of selected epoxycarboxy catalysts.

The invention relates to a process for the manufacture of copolymers which are based on vinyl compounds, u,ss-unsaturated monocarboxylic acids and monoglycidyl compounds, carry hydroxyl groups and are soluble in organic solvents, by heating the reactants in the presence of an epoxy-carboxy catalyst, esterification taking place, with, at the same time, copolymerisation by means of polymerisation initiators, in inert organic solvents and, if desired, in the presence of chain stoppers, characterised in that at least one alkali metal compound is employed as the epoxy-carboxy catalyst.

The esterification catalysts which are based on an alkali metal compound, and can be employed are all sodium, lithium, potassium, rubidium and caesium compounds - on their own or in a mixture - which are soluble in the reaction mixture consisting of the a,s-unsaturated monocarboxylic acid, the monoglycidyl compound and at least two further vinyl compounds or at least go into solution when they are added and/or when the reaction batch is kept at the reaction temperature in order to effect esterification by an addition reaction with simultaneous copolymerisation; however, the alkali metal compound employed should be free from those constituents which can have an adverse effect during the copolymerisation of the addition product, which is an ester.

Examples of compounds which can be used are the carbonates, bicarbonates and formates and the hydroxides of the abovementioned alkali metals.

On an industrial scale, lithium hydroxide and potassium hydroxide - on their own or as a mixture - have proved most suitable.

For use on an industrial scale, potassium hydroxide is particularly advantageously employed, because of the inexpensive price and the outstanding catalyst characteristics. Appropriately, the alkali metal hydroxide employed, or the alkali metal compound or mixtures of alkali metal compounds employed, is dissolved in the (r,(3-u nsatu rated monocarboxylic acid to be esterified.However, it is also possible first to manufacture the alkali metal salt of the cr,B-unsatu rated monocarboxylic acid, for use as the catalyst, from the alkali metal compound, for example alkali metal hydroxides, alkali metal carbonates or alkali metal bicarbonates, and the said acid and then to dissolve the alkali metal salt of the u,ís-unsaturated carboxylic acid in the reaction mixture or to bring the said salt into solution by heating, whilst carrying out the esterification and copolymerisation.

In general, it suffices to add from about 0.005% by weight to about 0.5% by weight of an alkali metal compound of the type already mentioned, based on the weight of the ester-forming components, for the addition reaction. Preferably, however, about 0.01% by weight to about 0.3% by weight of the alkali metal compound is added.

The most preferred range for the addition is about 0.02% by weight to about 0.1% by weight of alkali metal compounds, and amongst the alkali metal compounds, potassium compounds and lithium compounds are then very particularly advantageously used.

The a.li-ethylenically unsaturated monocarboxylic acids used are acrylic acid, methacrylic acid and/or crotonic acid, on their own or as a mixture. In addition, half-esters of maleic acid and fumaric acid with saturated alcohols which contain 1 to 10 carbon atoms are also suitable.

The monoepoxides include substituted alkyl compounds and also ethers and esters, if these contain a three-membered epoxy ring.

Examples of monoepoxides substituted by alkyl are propylene oxide, but-2-ene oxide, hex-2-ene oxide, oct-2-ene oxide and styrene oxide.

Examples of substituted ether monoepoxides are butyl glycidyl ether, hexyl glycidyl ether, octyl glycidyl ether and phenyl glycidyl ether.

Examples of ester monoepoxides are the glycidyl esters of the following acids: acetic acid, propionic acid, butyric acid, caproic acid, caprylic acid, 2-ethylhexanoic acid, isononanoic acid and (t,(t- dialkylalkanemonocarboxylic acids in which the hydrogen atoms of the alkanemonocarboxylic acid which are in the u-position relative to the carboxyl group are replaced by alkyl radicals, so that there is a tertiary carbon atom having the formula

in which R', R2 and R3 denote alkyl groups, the total sum of the carbon atoms of all the alkyl groups being 3 to 25. The glycidyl esters of a,a-dialkylalkanemonocarboxylic acids having 9 C atoms to 13 C atoms in the radical containing the alkyl groups are preferred.

The most preferred glycidyl ester of an a,a-dialkylalkanemonocarboxylic acid has the empirical formula C1H24Os.

Vinyl compounds which can be used are the aromatic vinyl compounds, for example styrene, vinyltoluene, a-methylstryrene and halogenostyrene, which, apart from the vinyl group, do not possess any group capable of reaction with the carboxyl group.

Vinyl compounds which can be used are the esters of acrylic, methacrylic and crotonic acid were saturated alcohols which contain 1 to 10 carbon atoms in the alcohol radical, such as, for example, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec.-butyl, tert.-butyl, amyl, hexyl, heptyl, octyl, nonyl and decyl radicals, on their own or as a mixture.

Examples of vinyl esters which can be used are: vinyl esters of ,a-diaIkyIalkanemonocarboxyIic acids having the formula

in which R', R2 and R3 denote alkyl groups and the total sum of the carbon atoms in all alkyl groups is 3 to 25, and amongst these compounds vinyl esters having the following empirical formula CgH19-CO-O-CH=CH2 are preferred. Vinyl acetate and vinyl propionate can also be used as vinyl esters.

a,j-Ethylenically unsaturated compounds carrying hydroxyl groups which can be used are hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate and also butanediol monoacrylate andlor butanediol monomethacrylate, on their own or as a mixture. Furthermore, ether-esters carrying hydroxyl groups, such as polypropylene glycol monomethacrylate and/or polyethylene glycol monomethacrylate and/or polyethylene glycol monomethacrylate with average molecular weights of between wabout 175 and about 390, can also be used.

In a preferred embodiment of the process, the reaction is carried out using the a,íj-unsaturated monocarboxylic acid in an amount which is less than the equivalent amount up to 1 equivalent, the molar ratio of monoepoxide: a,íS-unsaturated monocarboxylic acid being 1 : 0.95 to 1. The copolymers should have acid numbers of 3 to 5. The hydroxyl numbers of the copolymers should be 40 to 200.

A further preferred embodiment of the process consists in using xylene, monoglycol ether-acetates or mixtures of xylene and monoether-acetates as the organic solvent, 0.8 to 1.5% by weight of di-tert. -butyl peroxide being employed as the polymerisation initiator and, if desired, up to 1% by weight of dodecylmercaptan being employed as the chain stopper; the percentage by weight data for the polymerisation initiator and the chain stopper are based on the sum of the weights of the monomers employed for the reaction.

The most preferred embodiment of the invention is characterised in that the solvent, that is to say xylene or a mixture of xylene and ethylglycol acetate, is heated with the glycidyl ester to 140 to 1 80"C, a further mixture consisting of acrylic acid, in which the catalyst has been dissolved, is then added with the further monomeric vinyl compounds, di-tert.-butyl peroxide and dodecylmercaptan at a uniform rate in the course of 2 to 5 hours and the polymerisation and condensation reactions are carried out for a further 4 to 5 hours at constant temperature.

Solvents suitable for the manufacture of the new copolymers are those which do not contain any active hydrogen atoms, such as xylene, monoglycol ether-acetates or mixtures of monoglycol ether-acetate and xylene, examples of monoglycol ether-acetates which may be mentioned being methylglycol acetate, ethylglycol acetate, isopropylglycol acetate or n-butylglycol acetate.

Polymerisation initiators which can be employed are, for example, a diacyl peroxide, for example di-benzyl peroxide, peresters, for example tertiary butyl peroctoate, and dialkyl peroxides, for example di-tert.-butyl peroxide, and also all peroxides which have half-lives in a temperature range of 50 to 150"C.

The proportion of peroxide is about 0.5 to 5% by weight, based on the total proportion of the a,ss-ethylenically unsaturated monomers, including the esterified monoepoxides.

The chain regulators optionally employed are, for example, octylmercaptan, decylmercaptan, laurylmercaptn and the branched dodecylmercaptan. The proportion of chain regulators, based on the total proportion of the ethylenically unsaturated monomers, including the esterified monoepoxides, is0 to 2.5% by weight.

These new copolymers can be used as component A in reactive lacquers, together with a polyisocyanate component B.

Polyisocyanates which can be employed as component B are, for example, the following: toluylene 2,4-diisocyanate, toluylene 2,6-diisocyanate, diphenyl methane 4,4'-diisocyanate, naphthylene 1,5diisocyanate, triphenylmethane 4,4'-4" -trilsocyanate, 1 -lisocyanatophenyl I-ethyl isocyanate or xylylene diisocyanate, fluorine-substituted diisocyanates, ethylene glycol diphenyl ether 2,2'-diisocyanate, diethylene glycol diphenyl ether 2,2'-diisocyanate, 1,1 '-dinaphthyl 2,2'-diisocyanate, biphenyl 2,4'-diisocyanate, biphenyl 4,4'-diisocyanate, benzophenone 3,3'-diisocyanate, fluorene 2,7-diisocyanate, anthraquinone 2,6-di isocyanate, pyrene 3,8-diisocyanate, chrysene 2,8-diisocyanate, 1 -methyl-benzene 2,4,6-triisocyanate, naphthalene 1 ,3,7-triisocyanate, biphenylmethane 2,4,4'-triisocyanate, triphenylmethane 4,4',4" triisocyanate, 3'-methoxyhexane diisocyanate, octane diisocya nate, w,w-diisocyanato-1 4- dimethylnaphthalene, cyclohexane 1 ,2-diisocyanate, 1 -isopropylbenzene 2,4-diisocyanate, 1 -chlorobenzene 2,4-diisocyanate, 1 4luorobenzene 2,4-diisocyanate, 1-nitrobenzene 2,4-diisocyanate, 1 -chloro-4- methoxybenzene 2,5-diisocyanate, azobenzene 4,4'-diisocyanate, benzeneazonaphthalene 4,4'-diisocyanate, diphenyl ether 2,4-diisocyanate and diphenyl ether 4,4'-diisocyanate and also polyisocyanates based on isophorone diisocyanate with isocyanurate structures and a functionality between 3 and 4.Further compounds which may be mentioned are reaction products which contain isocyanate groups and are obtained from polyhydric alcohols and polyisocyanates, for example the reaction product of 1 mol of trimethylolpropane with 3 mols of toluylene diisocyanate, and also trimerised or polymerised isocyanates.

In addition, a reaction product which contains biuret groups and is obtained from 1 mol of water and 3 mols of hexamethylene diisocyanate and has a NCO content of 16 to 17% by weight can also be used. The last-mentioned reaction product of water and hexamethylene diisocyanate is particularly preferred. The NCO content of the reaction product is that for a 75 % strength solution in xylene/ethylglycol acetate.

For use of the new copolymers, the mixtures of solvent-containing copolymers A, which contain hydroxyl groups, and polyisocyanate B are applied by the simplest conceivable means, say after the addition of known auxiliaries, such as levelling agents, pigments or dyes, by spraying, dipping, coating, brushing or other suitable means, to the corresponding substrates and the sheet-like structure is dried at room temperature; in special cases, the coatings can be baked; this essentially depends on the substrates used and on the requirements which the coatings have to meet in practice. The additional use of reactive melamine resins can also be advantageous. The reactive melamine resins can be added, say, in amounts of 1 to 10% by weight, based on the weight of the binder component, and as a result of this, in particular, an increase in the gloss of the sheet-like structure can be observed.

When the new copolymers are used in the reactive lacquers already mentioned, the reaction and the application of the sheet-like structures to the substrate are carried out in solution. Suitable solvents are, for example, ethyl acetate, butyl acetate, ether-acetates, diethylglycol diacetate and also aromatic compounds, such as benzene, toluene or xylene. The concentration of the solutions can vary within wide limits and essentially depends on the solubility of te components. Solutions with a solids content of 20 to 80% by weight are preferably used.

When the new copolymers are used in reactive lacquers, component A and B are preferably used in the following amounts: (A) 60 to 95% by weight of hydroxyl group-containing copolymers prepared according to the invention and (B) 5 to 40% by weight of an organic polyisocyanate, the numerical values for (A) and (B) together having to add up to 100% by weight.

Example 1 A mixture consisting of 294.0 g of xylene, 150.0 g of ethylglycol acetate and 144.5 g of the glycidyl ester of an (t,cx-dialkylalkanemonocarboxylic acid of the following empirical formula C13H2403 with an epoxide equivalent of 245 to 253 (boiling range 5 to 90% at 710 mm Hg of 251 to 278"C, = 0.59 epoxide equivalent, = 21.72 % by weight) is heated under reflux at about 146"C in a reaction vessel fitted with a stirrer, a reflux condenser and a thermometer. (The glycidyl ester is described in Technical Bulletin RES/CAX/1 from Shell Chemicals unde the title: "Shell Resin Intermediates Cardura E 10".Its structure can be represented by the following formula, which is based on a synthetic, saturated, highl branched monocarboxylic acid having 10 C atoms

in which R1, R2 and R3 represent straight-chain alkyl groups, at least one of which is always a methyl group).

The following mixture, which is at room temperature in a dropping funnel and consists of 26.2 (3.94 % by weight) of the vinyl ester of an cr,cr-dialkylalkanemonocarboxylic acid having the formula C9H19CO-O- CH=CH2 in which the radical CgH19 to a large extent can be characterised by the structure C2H5 - C - CH3 C5H11 116.1 g (= 17.45 % by weight) of hydroxyethyl methacrylate, 26.0 g (= 3.9 % by weight) of polypropylene glycol monomethacrylate with an average molecular weight of 350 to 387 and a hydroxyl member of 145 to 160 (the above product can be represented by the following formula:: CH3 CH3 CH2 = C - COO - (CH2 - CHO)n - H in which n denotes the numerical values 5 to 6), 192.0 g )= 28.85 by weight) of styrene, 118.0 g (= 17.7 % by weight) of methyl methacrylate, 6.4 g of di-tert.-butyl peroxide, 6.4 g of dodecylmercaptan, 42.0 g (= 6.388 % by weight and 0.583 acid equivalent) of acrylic acid and 0.3 g of potassium hydroxide, the potassium hydroxide having first been dissolved in the acrylic acid, is added dropwise at a uniform rate, in the course of 4 hours, to the mixture which is at 146"C and the resulting mixture is then copolymerised for a further 5 to 6 hours.The copolymer solution has a solids content of 61.8 %. The viscosity of the solution diluted to 50 % strength with xylene gives a flow time of 115 seconds, measured in a DIN cup with a 4 mm nozzle. The acid number of the copolymer is 3.3.

Further advantageous embodiments of the invention are given in Patent Claims 2 to 18.

The calculation of reaction batches for the manufacture of copolymers with a specific hydroxyl group content has been described by the same inventor in columns 5 and 6 of German Auslegeschrift 2,603,259 and also in German Auslegeschrift 2,626,900.

TABLE I Examples 2 to 7 Example Example Example Example Example Example Example 2 3 4 5 5 6 7 8 Item Xylene 294 g 294 g 294 g 294 g 294 g 294 g 220 g xylene and 111 g Solesso 100 Item Ethylglycol 150 g 150 g 150 g 150 g 150 g 150 g 111 g butyl acetate acetate Item 3 Glycidyl ester 160 g 160 g 145 g 145 g 155 g 155 g 155 g from Example 1 Item 4 Acrylic acid 46 g 46 g 42 g 42 g 45 g 45 g 45g Item 5 Polypropylene 19.6 g 19.6 g 26 g 26 g 33 g 33 g 33 g glycol monomethacrylate from Example 1 Item 6 Styrene 190.4 g 190.4 g 198 g 198 g 197.7 g 158.2 g 159.2 g Item 7 Methyl meth- 126 g 126 g 112 g 100 g 118.6 g 158.2 g 158.2 g acrylate Item 8 Hydroxyethyl 116.2 g 116.2 g 116.1 g 116 g 109.6 g 110 g 110 g methacrylate Item 9 Vinyl ester of an - - 21 g 26 g - - &alpha;,&alpha;;-dialkylalkanemonocarboxylic acid TABLE I (cont...) Example 2 to 7 Example Example Example Example Example Example Example 2 3 4 5 6 7 8 Iten 10 Potassium 0.3 g - - - 0.1 g 0.1 g 0.1 g hydroxide Item 11 Lithium - 0.1 g 0.1 g 0.1 g 0.1 g - hydroxide Item 12 Dodecylmercaptan 7.4 g 7.4 g 6.4 g 6.4 g - 7.4 g Item 13 Di-tert.-butyl 6.4 g 6.4 g 6.4 g 6.4 g 6.4 g 6.4 g 6.4 g peroxide Time taken for Items 4 hours 4 hours 4 hours 4 hours 2 hours 4 hours 4 hours to 13 to run in Copolymerisation time 5 hours 6 hours 6 hours 4 hours 5 hours 5 hours 5 hours after all of the items have run in Flow time of the solution 109 98 95 98 382 98 192 seconds dilueted to 50 % strength seconds seconds seconds seconds seconds seconds DIN 4x DIN 4 DIN 4 DIN 4 DIN 4 DIN 4 DIN 4 Acid number 4.0 4.2 4.0 4.3 4.8 4.8 4.6 Solids content 62% 61.3% 61.3% 60.8% 62.4% 62.5% Iodine colour value < 1 < 1 < 1 < 1 < 1 < 1 < 1 according to DIN 6162 In Examples 2 to 7,the solvents and the glycidyl ester are heated,as described in Example 1,to 144 to 148 C and the monomers and the catalyst dissolved therein,which have been kept at room temperature,are added at a uniform rate to the mixture,which is kept at the boil,and the resulting mixture is then copolymerised.

x Diluted with ethylglycol acetate to a 50% by weight copolymer solid content.

Comparison tests to demonstrate the technical advance achieved compared with German Patent Specification 1,038,754.

Comparison Example 1 The procedure was as described in Example 1, but, for the purpose of the comparison tests, the types and amounts of the solvents and monomers used were those indicated in Example 2. An exceptionally small amount of catalyst was chosen in order to keep the degree of yellowing of the resin solution as low as possible, since with larger amounts of catalyst intensive brown discolorations already arise. Therefore, 0.3 g of triethylamine was employed. The product had a solids content of 62 % by weight and after dilution to 50 % with xylene had a viscosity of 88 seconds flow time, measured in a DIN cup with a 4 mm outlet nozzle at 200C.

The acid number was 5.8. The DIN method gave a value of 2 to 3 for the iodine colour value, and the copolymer solution was thus intensely yellowish. The pigmented films obtained with TiO2 also displayed yellowing.

Comparison Example 2 The procedure was as in Comparison Example 1 except that 1 g of a 40 % strength methanolicsolution of benzyltrimethylammonium hydroxide was employed in place of triethylamine. The product was found to have a solids content of 61.6% by weight and a flow time of 117 seconds, measured as a 50% strength solution in xylene, and an acid number of 5.3. The DIN method gave a value of 2 for the iodine colour value, and the copolymer solution was thus intensely yellowish, whilst the films pigmented with TiO2 displayed yellowing.

In contrast to the above, the copolymer solutions according to the invention were colourless, and the films pigmented with TiO2 also displayed no yellowing.

Further comparison tests (With reference to German Auslegeschrift 2,626,900 for demonstrating the technical advance achieved).

Preparation of copolymer 1 according to German Auslegeschrift 2,626,900 Example 1 325 g of xylene, 155 g of ethylglycol acetate and 214 g of glycidyl esters of a,a- dialkylalkanemonocarboxylic acids of the following empirical formula C13H2403 are heated under reflux at 147"C and a mixture consisting of 145 g of methyl methacrylate, 135 g of hydroxyethyl methacrylate, 2 g of tert-dodecylmercaptan, 160 g of styrene, 63 g of acrylic acid and 7 g of di-tert.-butyl peroxide is added at a uniform rate in the course of 2 hours and the resulting mixture is subjected to polymerisation and condensation reactions for about 6 hours at 140 to 145"C. The product is found to have a solids content of 60% by weight.A solution diluted to a 50% solids content with xylene gives viscosities of 350 seconds, measured in a DIN cup with a 4 mm outlet orifice at 200C. The value of the acid number of the copolymer is 8.0. No further change in the acid number took place when the batch was kept under reflux for a further period.

Comparison copolymer according to the invention The procedure was as described in Example 1 of German Auslegeschrift 2,626,900, except that, in addition, 0.32 g of lithium hydroxide was dissolved beforehand in the acrylic acid and mixed with the other compounds of the feed mixture.

The course of the reaction was determined by determining the acid number, based on the copolymer.

One hour after all of the constituents had run in Acid number 8.9 Two hours after all of the constituents had run in Acid number 7.5 Three hours after all of the constituents had run in Acid number 5.6 Four hours after all of the constituents had run in Acid number 4.5 Five hours after all of the constituents has run in Acid number 4.0 Six hours after all of the constituents had run in Acid number 4.0 Further comparison tests (With reference to German Auslegeschrift 2,603,259 for demonstrating the technical advance achieved) Preparation of copolymer 2 according to German Auslegeschrift 2,603,259 Example 2 705 g of xylene, 337 g of ethylglycol acetate and 403 g of glycidyl esters of a,adialkylalkanemonocarboxylic acids of the following empirical formula C13H2403 are heated under reflux at 138"C and a mixture consisting of 124 g of acrylic acid, 293 g of hydroxyethyl methacrylate, 423 g of styrene, 315 g of methyl methacrylate, 15.2 g of di-tert.-butyl peroxide and 17 g of dodecylmercaptan is added at a uniform rate and the resulting mixture is subjected to simultaneous polymerisation and condensation reactions for about 6 hours at 135"C. The solids content is 61% by weight. The viscosity of a solution diluted to a 50% by weight solids content with xylene is 140 seconds, measured in a DIN cup with a 4 mm outlet orifice at 230C. The acid number is 8.2, based on the copolymer.

Comparison copolymers according to the invention The procedure was as described in Example 2 of German Auslegeschrift 2,603,259, except that, in addition, 0.71 g of lithium hydroxide was dissolved beforehand in the acrylic acid and mixed with the other compounds ofthe feed mixture.

The course of the reaction was determined by determining the acid number, based on the copolymer.

One hour after all of the constituents had run in acid number 9 Two hours after all of the constituents had run in acid number 7.2 Three hours after all of the constituents had run in acid number 5.8 Four hours after all of the constituents had run in acid number 4.6 Five hours after all of the constituents had run in acid number 3.9 Six hours after all of the constituents had run in acid number 3.9 The comparison tests show that the copolymers obtained according to the invention have acid numbers of the desired lower values, so that the incorporation of the glycidyl ester is more complete than in the case of the processes of the prior art.

A comparison of the reactions as a function of the time which elapses after all of the monomers have run in shows that lower acid numbers are obtained only 2 hours after all of the monomers have run in, whilst the products which are obtained by the process of the prior art require a reaction time of at least 6 hours after all of the monomers have run in in order to obtain acid numbers which approach these values.

Example 9 Preparation ofa reactive lacquer: The viscosity of 100 g of copolymer solution, obtained according to Example 2, and 20 g of a 75% strength solution of an aliphatic triisocyanate which contains biuret groups, has been obtained by reacting three mols of hexamethylene diisocyanate with one mol of water and has a NCO content of 21% by weight, dissolved in 1:1 xylene/ethylglycol acetate, is adjusted to the spraying viscosity with a solvent mixture consisting of 1:1 xylene/butyl acetate and the resulting mixture is used to coat steel sheets to give a dry film coating thickness of 45 m, and the coatings are cured for 10 days at room temperature. The films had an excellent gloss and good stability towards xylene.

A particularly preferred reactive lacquer contains: (A) 63 to 68% by weight of manufactured copolymers containing hydroxyl groups and (B) 32 to 37% by weight of an organic triisocyanate which has been obtained by reacting 3 mols of hexamethylene diisocyanate with 1 mol of water, the numerical values for (A) and (B) having to add up to 100% by weight.

The main fields of application for the copolymers - in combination with aliphatic and aromatic polyisocyanates or mixtures thereof - are air-drying and oven-drying lacquer coatings on metal, wood and plastic. Two-component lacquers of this type are preferably used when the characteristics expected from the air-dried or force-dried lacquers are those which customarily are offered only by stoving lacquers.

These new reactive lacquers are employed as binders, especially for the car repair lacquer field and for lacquer-coating buses and lorries.

In combination with aliphatic polyisocyanates, yellowing-free lacquer coatings of good body and with excellent stability to weathering and gloss retention are obtained.

A certain degree of yellowing must be expected with aromatic polyisocyanates are used for crosslinking.

In accordance with their higher crosslinking density, reactive lacquers on the basis of the invention display a high scratch-resistance and abrasion-resistance, coupled with good stability to solvents, compared with comparable good commercially available products for the same purpose.

The good stability to water and chemicals should also be singled out.

Lacquers of this type can not only be air-dried but can also be stoved within a wide temperature range; thus, for example, the films are completely cured in 30 minutes at 130"C.

The resistance to weathering of the lacquer coatings cured at room temperature is not inferior to that of the stoved films.

The copolymers have a high pigment pick-up. All neutral pigments and fillers are suitable for pigmenting.

Strongly basic pigments and also pigments with soluble metal compouns can exert a catalytic action on the crosslinking, as a result of which the processing time of the lacquer batches, after mixing, is shortened.

Tests on the reaction solution obtained according to Example 9, in order to demonstrate the technical advance achieved: 1. Determination of the pot life, that is to say the stability of the two-component lacquer at20'C: Flow time in seconds (4 mm outlet nozzle) Start 18 after 24 hours 21 after 48 hours 25 after 50 hours 26 after72 hours 46 after 96 hours 280 after 100 hours gelled This result shows that these lacquers have a surprisingly long pot life. On the basis of the processing conditions customary in practice - rise in the viscosity to twice the initial viscosity, that is to say a flow time of at most 36 seconds - this lacquer has a processing time of more than 60 hours. Moreover, lacquer residues which are 96 hours old can be diluted by adding freshly made-up lacquer solutions and can still be processed well.

2. Determination of the curing time ofthe lacquer films: This manufactured two-component lacquer solution is applied to a glass plate in such a way that a dry film coating thickness of about 40item results.

2a Determination ofthe Koniopendulum hardness at20 C: Pendulum hardness after one day 40 seconds after two days 92 seconds after three days 170 seconds after four days 201 seconds The surprising feature in this case is that the clear lacquer has reached its complete film hardness of more than 200 seconds after only a 4 day curing time at 20"C. If this result is compared with the four day open pot life, that is to say no gelling of the lacquer solution takes place within this period, this result was surprising and not foreseeable.

2b Determination of the Konig pendulum hardness after stoving at 80"C with a 30 minute stoving time: Pendulum hardness 80tC 30 minutes 85 seconds after one day at 20"C 125 seconds after two days at 20C 168 seconds after three days at 20"C 200 seconds As a result of the 30 minute drying time at 800C, the virtually complete film hardness of 168 seconds pendulum hardness is obtained after only a further two days' drying at 20"C.

The lacc,uer films resulting therefrom have a very high surface hardness and cannot be damaged by testing with a fingernail. Moreover, these coatings are distinguished by very good fastness to light and stability to solvents, such as xylene, toluene or acetone. When sheet metal samples placed facing south are subjected to weathering in Florida for 11/2 years at 5"C, these lacquer films display no crazing and the gloss is reduced by only 10% compared with the starting gloss, which is 110%, measured by the Lange method.

Comparison tests to demonstrate the technical advance achieved compared with the best, commercially available competitive products, in respect of the pot life: Copolymer according Analogous reactive Analogous to Example 2 of the lacquer, but co- reactive lacinvention - reactive polymer according quer, but lacquer according to to Example 2 of copolymer Example 9 of the German Patent according to invention Specification Example 1 of 2,603,259 German Patent Specification 2,626,900 Determination of the pot life of the reactive lacquer by measuring the flow time in a DIN cup with an outlet nozzle 4 mm in diameter, at 200C in seconds Time at the start 18 18 18 after 24 hours 21 25 28 after 48 hours 25 75 155 after 56 hours 40 280 not measur able, gelled after 60 hours 90 not measurable, gelled Comparison tests to demonstrate the technical advance ach,;;eved compared with the best, commerically available competitive products, in respect of the pot life: In order to determine the pot life, the copolymers prepared according to the invention which are listed in the table above and, for comparison, the best commercially available competitive products were mixed with the aliphatic triisocyanate which had been obtained by reacting 3 mols of hexamethylene diisocyanate with 1 mol of water. The mixing ratios of the copolymers with the polyisocyanate were, based on the solids content, 70% by weight of copolymer: 30% by weight of polyisocyanate.The mixtures were distilled with a solvent mixture consisting of xylene/butyl acetate in a weight ratio of 1:1 to a viscosity of 18 seconds flow time, measured in a DIN cup with 4 mm outlet orifice, and the rise in viscosity was determined as a function of time at 20"C. As can be seen from the above table, the copolymers prepared according to the invention are distinctly superior to the known copolymers according to German Patent Specification 2,603,259 and German Patent Specification 2,626,900. The copolymers prepared according to the invention have a more advantageous pot life in respect of the slower rise in the viscosity and slower gelling. It can be concluded from this that the reactive lacquers have considerably more advantageous processing characteristics.

The copolymers containing hydroxyl groups which are obtainable by the process of the invention can also be used with blocked polyisocyanates, instead of with the polyisocyanates, for the manufacture of stoving lacquers, as is described, for example, in German Offenlegungsschrift 2,623,081 under the title "Stoving lacquers based on film-forming copolymers which contain hydroxyl groups and are soluble in inert organic solvents".Blocked polyisocyanates for this purpose have, for example, been described by the inventor of the present invention in German Offenlegungsschrift and Auslegeschrift 2,612,786 under the title "Blocked diisocyanates, their manufacture from diisocyanatomethyl-norbonane and alkyl acetoacetates and their use as crosslinking agents", in German Offenlegungsschrift and Auslegeschrift 2,612,785 "Blocked diisocyanates, their manufacture from 4,4'-diisocyanato-dicyclohexylmethane and alkyl acetoacetates and their use as crosslinking agents", in German Offenlegungsschrift and Auslegeschrift 2,612,784 "Blocked diisocyanates, their manufacture from hexamethylene 1 ,6-diisocyanate and acetoacetates and their use in crosslinking agents", in German Offenlegungsschrift and Auslegeschrift 2,612,783 "Blocked polyisocyanates obtained from biuret group-contaning polyisocyanate and alkyl acetoacetates" and in German Offenlegungsschrift and Auslegeschrift 2,612,638 "Blocked diisocyanates obtained from 2,2,4-trimethylhexamethylene diisocyanate and alkyl acetoacetates and their use as crosslinking agents".

As, for example, Claims 16 and 18 of the invention show, 70 to 95% by weight of hydroxyl group-containing copolymers, manufactured according to the invention, with 5 to 30% by weight of aminoplast resins can be used as stoving lacquers, the % by weight data having to add up to 100% by weight.

Aminoplast resins which can be used are all aminoplast resins which are compatible with acrylate copolymer resins; these resins are available commercially in large numbers and frequently are synthesised on the basis of urea/formaldehyde and/or melamine/formaldehyde and are in the form of the products etherified with lower alkanols.

The solution of the finished copolymer is cooled and the aminoplast solution is introduced, the solvent content being so adjusted that the desired concentration is obtained. Pigments can then be added.

After stoving at 90 to 1809C, the stoving lacquers according to the invention give films which have excellent stability characteristics towards chemicals of all types, such as solvents, acids and alkalis and also super fuels.

The stoving lacquers can be dried at room temperatures. It is not essential that curing is carried out at 120 to 1402C over a period of 30 minutes. At 160"C, for example, the stoving time is reduced to about 15 minutes.

Preferred aminoplasts are condensation products of formaldehyde and melamine, about 4 to 6 mols of formaldehyde per mol of melamine having been reacted, either under weakly acid or under weakly basic conditions, and the products should be etherified to the extent of 80 to 100% with butanol or isobutanol. The reaction products resulting therefrom should have a molecular weight of 400 to 1,200 and be soluble in organic solvents such as xylene and butanol or isobutanol and other alcohols.

The copolymer and the aminoplast are dissolved in the organic solvent in a ratio of 70 to 95 parts of the copolymer to 5 to 30 parts of the aminoplast. The proportions of the copolymer and of the alkylated aminoplast must be so chosen that the two components are compatible not only in the coating solution but also in the finished film. Any suitable concentration of the copolymer and of the aminoplast in the solvent, for example from 1 to 50 per cent by weight, can be used. If a pigment is present, the total solids content in the coating composition is between 5 and 75 per cent by weight. The ratio of pigment to binder (copolymer plus aminoplast) can be between 1: 20 and 1:1.

Solvents which can be used are: hydrocarbons, such as benzene, toluene, xylenes and aromatic naphthenes or mixtures of such solvents; esters, such as ethyl acetate, lactate or propionate, butyl acetate, lactate or propionate, amyl acetate, lactate or propionate, ethoxyethyl acetate, lactate or propionate or methoxyethyl acetate, lactate or propionate, ketones, such as acetone, methyl isopropyl ketone, methyl isobutyl ketone, dioxane, isophorone or cyclohexanone; alcohols, such as n-butanol, t-butanol, isopropyl alcohol, n-propyl alcohol, amyl alcohols and cyclohexanol; esters, such as diethyl ether and the monoethyl, monomethyl and monobutyl ethers of ethylene glycol, and various other solvents, such as dimethylformamide, dimethylacetamide, acetonitrile, nitromethane, nitroethane, nitropropane or nitrobutane, as well as mixtures of 2 or more solvents of the same group and also of several or all of the groups mentioned above.

Pigments which can be added are: inorganic pigments, such as Chrome Yellow, Prussian Blue and Brunswick Green; titanium pigments, for example titanium dioxide, extended titanium pigments (which are extended either with precipitated or natural extenders, such as alkaline earth metal sulphates, or for example calcium sulphate and barium sulphate); shaded titanium pigments and titanates, such as the titanates of barium, zinc, lead and magnesium. Other types of organic pigments can also be used, for example zinc sulphide pigments, such as zinc sulphide, lithopone, extended zinc sulphide pigments, such as lithopone on a calcium base, zinc sulphide extended with natural extenders, zinc oxide or antimony oxide or organic pigments, that is to say organic dyes which are free from sulphonic acid groups, carboxylic acid groups or other groups conferring solubility in water. The term "pigment" also includes other water-insoluble organic dyes, for example the calcium or barium lacquers of azo dyes for lacquers.

The new stoving lacquers can be applied to the substrates in any desired manner, for example by spreading, spraying, dipping or rolling. They are then dried and cured by heating.

Claims (18)

1. Process for the manufacture of copolymers which are based on vinyl compounds, ce,ss-unsaturated monocarboxylic acids and monoglycidyl compounds, carry hydroxyl groups and are soluble in organic solvents, by heating the reactants in the presence of an epoxy-carboxy catalyst, esterification taking place, with, at the same time, copolymerisation by means of polymerisation initiators, in inert organic solvents and, if desired, in the presence of chain stoppers, characterised in that at least one alkali metal compound is employed as the epoxy-carboxy catalyst.

2. Process according to Claim 1, characterised in that d) 11 to 0.5% by weight of an (t,ss-unsaturated carboxylic acid, e) 1.5 to 39% by weight of a monoglycidyl compound and a + b) 50 to 98% by weight of other vinyl compounds are employed for the reaction.

3. Process according to Claim 2, characterised in that (c) up to 30% by weight of one or more vinyl compounds containing a hydroxyl group in the molecule are employed as other vinyl compounds for the reaction.

4. Process according to one of Claims 1 to 3, characterised in that a) styrene and b) acrylates and/or methacrylates having 1 to 12 carbon atoms in the alcohol radical are employed as other vinyl compounds.

5. Process according to one of Claims 1 to 4, characterised in that the compounds employed as other vinyl compounds containing a hydroxyl group in the molecule (c) are hydroxyethyl acrylate, hydroxylpropyl acrylate, butanediol monoacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, butanediol monomethacrylate, polypropylene glycol monomethacrylate and/or polyethylene glycol monomethacrylate with average molecular weights of between about 175 and about 390.

6. Process according to one of Claims 1 to 5, characterised in that d) acrylic acid and'or methacrylic acid, e) monoglycidyl estersor mixtures of monoglycidyl esters of aliphatic saturated monocarboxylic acids having 2 to 19 carbon atoms, a) styrene, b) vinyl esters of saturated monocarboxylic acids, or mixtures of such esters, having 4 to 19 carbon atoms in the carboxylic acid molecule, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, sec.-butyl acrylate, tert.-butyl acrylate, methyl acrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec.-butyl methacrylate, tert.-butyl methacrylate and/or methyl methacrylate and c) hydroxyethyl acrylate, hydroxypropyl acrylate, butanediol monoacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate and/or butanediol monomethacrylate are reacted.

7. Process according to Claim 1, characterised in that d) 6 to 12% by weight of acrylic acid are reacted with e) 18 to 44% by weight of the glycidyl ester of an a,a-dialkylalkanemonocarboxylic acid which has the empirical formula C13H2403 and the structure of which approximately corresponds to

in which R1, R2 and R3 represent straight-chain alkyl groups, at least one of which is methyl group, the molar ratio of glycidyl ester to acrylic acid being 1: 0.98 to 1, and a) 15 to 30% by weight of styrene and/or vinyltoluene, b) 15 to 25% by weight of methyl methacrylate and c) 15 to 25% by weight of hydroxyethyl methacrylate and the reaction is continued until an acid numberof 3 to 5 is obtained, the given percentages by weight having to add up to 100 % by weight.

8. Process according to one of Claims 1 to 6, characterised in that d) 5 to 7% by weight of acrylic acid are copolymerised with e) 17 to 25% by weight of the glycidyl ester of an a,a-dialkylalkanemonocarboxylic acid which has the empirical formula C13H2403 and the structure of which approximately corresponds to

in which R1, R2 and R represent straight-chain alkyl groups, at least one of which is a methyl group, the molar ratio of glycidyl ester to acrylic acid being 1: 0.98 to 1, and a) 25 to 30% by weight by styrene, b1) 15 to 20% by weight of methyl methacrylate, c1) 15 to 20% by weight of hydroxyethyl methacrylate, c2) 2 to 6% by weight of polypropylene glycol monomethyacrylate, which has a structure which approximately corresponds to the formula

in which n denotes numbers of 5 to 6, and an average molecular weight of about 350 to 387, and b2) 3 to 10% by weight of the vinyl ester of an a,a-dialkylalkanemonocarboxylic acid which has the approximate formula CgH19-CO-O-CH=CH2, in which the grouping C9H19 largely has the structure

the percentages by weight having to add up to 100% by weight and the copolymerisation being continued until acid numbers of 3 to 5 are obtained.

9. Process according to one of Claims 1 to 8, characterised in that the copolymerisation is carried out with the addition of a chain regulator.

10. Process according to Claim 1, characterised in that copolymers are manufactured from a) 20 to 32% by weight of styrene and/or vinyltoluene, b) 16 to 26% by weight of methyl methacrylate, c) 26 to 16% by weight of hydroxyethyl methacrylate, up to 7% by weight of the hydroxyethyl methacrylate optionally being replaced by polypropylene glycol monomethyacrylate which has the formula

in which n denotes numbers of 5 to 6, and an average molecular weight of about 350 to 387, d) 6 to 9% by weight of acrylic acid and/or methacrylic acid and e) 20 to 30% by weight of glycidyl esters of aliphatic saturated monocarboxylic acids having 9 to 15 carbon atoms, components a, bc, d and e being so chosen that they make up 100% by weight.

11. Process according to Claim 1, characterised in that copolymers are manufactured from a) 10 to 29% by weight of styrene and/or vinyltoluene, b) 18 to 26% by weight of methyl methacrylate, c) 16 to 26% by weight of hydroxyethyl methacrylate, d) 7 to 12% by weight of acrylic acid and/or methacrylic acid and e) 36 to 20% by weight of glycidyl esters of aliphatic saturated monocarboxylic acids having 9 to 15 carbon atoms, components a, b, c, d and e being so chosen that they add up to 100% by weight.

12. Process according to Claim 1, characterised in that copolymers are manufactured from a) 27 to 32% by weight of styrene and/or vinyltoluene, b) 18 to % by weight of methyl methacrylate, c1) 16 to 18% by weight of hydroxyethyl methacrylate, c2) 2 to 6% by weight of polypropylene glycol monomethyacrylate which has the formula

in which n denotes numbers of 5 to 6, and an average molecular weight of about 350 to 387, and an average molecular weight of about 350 to 387, d) 6 to 7% by weight of acrylic acid and/or methacrylic acid and e) 23 to 25% by weight of glycidyl esters of aliphatic saturated monocarboxylic acids having 9 to 15 carbon atoms, components a, b, c, d and e being so chosen that they add up to 100% by weight.

13. Process according to Claim 1, characterised in that copolymers are manufactured from 3 to 40% by weight of a) styrene and/or vinyltoluene and/or b) methyl methacrylate, 10 to 40% by weight of b1) acrylates and or methacrylates of aliphatic saturated monoalcohols having 2 to 12 C atoms, 10 to 30% by weight of c) hydroxyethyl acrylate and/or hydroxyethyl methacrylate or polypropylene glycol monomethacrylate which has the formula CH3 CH3 CH2 = C - COO - (CH2CHO)n - H in which n denotes numbers of 5 to 6, and an average molecular weight of about 250 to 387, 5 to 12% by weight of d) acryclic acid and;or methacrylic acid and 35 to 15% by weight of e) glycidyl esters of aliphatic saturated monocarboxylic acids having 9 to 15 carbon atoms, components a, b, c, d and e being so chosen that they add up to 100% by weight.

14. Process according to Claim 1 orto one of Claims 10 to 13, characterised in that, for copolymers which are intended for crosslinking polyisocyanate, the starting components are so chosen and reacted that copolymers with a hydroxyl group content of about 2 to about 6% by weight, based on the weight of the starting monomers, are obtained.

15. Process according to Claim 14, characterised in that the starting components are so chosen, and reacted for such a time, that copolymers with acid numbers of 2 to 12 and preferably 3 to 6 are obtained.

16. Process according to Claim 15, characterised in that, for copolymers which are intended for crosslinking with aminoplast resins, the starting components are so chosen and reacted that copolymers with a hydroxyl group content of 2 to 4.5% by weight, based on the weight of the starting monomers, and with an acid number of 10 to 15 are obtained.

17. Reactive lacquers based on copolymers, which are based on vinyl compounds, ct,(i-unsaturated monocarboxylic acids and monoglycidyl compounds and carry hydroxyl groups, polyisocyanates, inert organic solvents and, if desired, further additives customary in reactive lacquers, characterised in that the lacquers contain components (A) and (B) in amounts of (A) 60 to 95% by weight of copolymers which contain hydroxyl groups and have been manufactured according to the invention and (B) 5 to 40% by weight of an organic polyisocyanate, the numerical values of (A) and (B) together having to add up to 100% by weight.

18. Stoving lacquers based on copolymers, which are based on vinyl compounds, a,l3-unsaturated monocarboxylic acids and monoglycidyl compounds and contain hydroxyl groups, aminoplast resins, organic solvents and, if desired, further additives customary in stoving lacquers, characterised in that the lacquers contain components (A) and (C) in amounts of (A) 70 to 95% by weight of copolymers which contain hydroxyl groups and have been manufactured according to the invention and (C) 5 to 30% by weight of aminoplast resins, the numerical values of (A) and (C) together having to add up to 100% by weight.