IE43511B1 - Process for the manufacture of plastics dispersions - Google Patents

Abstract

An aqueous polymer dispersion which is suitable for the preparation of paints having high wet adhesion is prepared by copolymerisation in aqueous medium of vinyl esters of saturated monocarboxylic acids in the presence of an olefinically unsaturated acetoacetate. The vinyl ester employed is vinyl acetate, vinyl propionate, vinyl butyrate and/or vinyl isobutyrate together with vinyl esters of saturated monocarboxylic acids having 5 to 20 carbon atoms whose carboxyl group is bonded to a tertiary or quaternary carbon atom. The resultant dispersions are suitable for the preparation of gloss emulsion paints having high wet adhesion to non-sorptive substrates and have high resistance to hydrolysis.

Description

This invention relates to a process for the manufacture of plastics dispersions suitable for making dispersion paints having a good wet adhesion, i.e. when wetted after drying.

The problem of the wet adhesion, i.e. the adhesion of dried paints on wetting, of dispersion paints on smooth non-absorbent surfaces has long restricted the use of such dispersion paints. Dispersion paints having a low pigment content, which dry on the substrate with formation of a glossy or slightly dull film, have a poor adhesion to smooth D non-absorbent surfaces when the paints are re-wetted after drying. The wet adhesion is especially unsatisfactory with fresh paints which have not yet undergone ageing.

Dispersion paints of low pigment content are chosen when a washable coat of paint is desired. Owing to the high binder content of the paint a non-porous washable film is formed. Dispersion paints drying with formation of a glossy or slightly dull film also have a pigment content of less than 40% by volume, generally from about 10 to 25%. They also contain about 3 to 20% of organic D solvents to improve the gloss and flow, to prolong the working time and for improving film consolidation, for example water-miscible polyhydric alcohols having up to 6 carbon atoms, especially ethylene and propylene glycol, or the monomethyl to monobutyl ethers thereof. To improve the film consolidation, there are used solvents having a restricted solubility in water, such as the monoglycol ethers of carboxylic acids and more particularly esters 43S1 - 3 of carboxylic acids with monoalkyl ethers of glycols or oligoglycols. Butyl diglycol acetate is one of the most widely used representatives of this group. The combination of a low pigment content with a relatively high solvent content has a very detrimental effect on the wet adhesion of the coats of dispersion paints.

With poor wet adhesion, paints formulated to give washable coats do not have this property when applied to smooth non-absorbent surfaces, for example old coats of alkyd or oil paints. In moist rooms, such as kitchens, bath rooms, or industrial premises, where condensation may form, the new coat may detach from the substrate if the wet adhesion is insufficient. Moreover, a poor wet adhesion complicates painting. When, for example, the base and the upper half of a wall or the wall and the ceiling are to be painted in different colours, the first coat of paint may be soiled with the different paint by inaccurate handling of the brush. In principle, the different paint could be wiped off with a wet cloth or sponge, but with a poor wet adhesion the first paint may then be damaged or even removed simultaneously.

Therefore, many attempts have been made to modify plastics dispersions in such a manner that the dispersion paints made therewith have the desired wet adhesion.

In British Patent Specification No. 1,138,960 it has been proposed to prepare plastics dispersions by polymerizing suitable monomers in aqueous emulsion using as comonomers 0.2 to 15% by weight, calculated on the total monomers, of compounds carrying oxirane groups and then to react the copolymer at room temperature with ammonia or an amine.

Suitable oxirane compounds are, above all, glycidyl esters of acrylic and methacrylic acids, allyl glycidyl ethers and vinyl glycidyl ethers. 43521 Dispersion paints prepared with plastics dispersions of this type have quite a good wet adhesion, but for many applications the wet adhesion is not at all sufficient.

The present invention provides a process for the preparation of aqueous plastics dispersions which impart to paints manufactured therefrom an especially good wet adhesion on non-absorbent and slightly absorbent substrates which comprises copolymerizing in an aqueous system the following monomers: (A) (B) (C) (D) from 5 to 50% by weight, preferably from 15 to 35% by weight, relative to the total monomers, of at least one vinyl ester of a saturated monocarboxylic acid, the carboxyl group of which is directly linked to a tertiary or quaternary carbon atom and the carboxylic acid radical of which contains from 5 to 20, preferably from 5 to 11, carbon atoms; from 40 to 94.5% by weight, relative to the total monomers, of at least one vinyl ester of a saturated carboxylic acid having from 2 to 4 carbon atoms; from 0 to 30% by weight, relative to the total monomers, of at least one other alpha -betaunsaturated compound copolymerizable with the above monomers; and from 0.5 to 10% by weight, preferably from 1 to 5% by weight, relative to the total monomers, of an acetoacetic acid ester of the formula 0 R R' ί! II ί f CHg-C-CH2-C-X-C=CH 4351ί where X is -0-, -O-CIL-, -0-CH.-CH--0-C2 i ί || or O-CH2-CH2-CH2-O-C-f and each of R and R' is H or CH3.

The compound (D) is for example, vinyl or allyl acetoacetate or an acetoacetic acid ester of β-hydroxy-ethylacrylate, methacrylate or crotonate, or hydroxy-propylacrylate, methacrylate or crotonate. Preferably, allyl acetoacetate is used since it yields the best results.

Vinyl esters of saturated monocarboxylic acids the carboxyl groups of which are directly linked to a tertiary or quaternary carbon atom (A) are especially vinyl pivalate, vinyl isononanoate or, preferably, 'Versatic' acid vinyl esters, as described for example in British Patent Specification No. 993,470. 'Versatic'-10-acid vinyl ester is especially preferred. Mixtures of any two or more such monomers may also be used. (The word 'Versatic' is a registered Trade Mark. Versatic acid is a mixture of saturated tertiary monocarboxylic acids having 9, 10 and 11 carbon atoms, and Versatic-10-acid is a saturated tertiary monocarboxylic acid having 10 carbon atoms).

Suitable vinyl esters (B) are vinyl acetate, vinyl propionate, vinyl butyrate and vinyl isobutyrate, or mixtures of any two or more of these compounds. Preferably, vinyl acetate is employed.

Alpha-beta-unsaturated compounds (C) are, for example acrylic, methacrylic, crotonic, maleic and fumaric acids and esters of acrylic, methacrylic and crotonic acids, diand monoesters of maleic and fumaric acids, the alcohol radicals thereof having from 1 to 30 preferably from 1 to carbon atoms, and other derivatives of these acids such as (meth-)acrylamide, (meth-)acrylonitrile and maleic anhydride.

The copolymerization process of the present invention is carried out under conventional conditions for the manufacture of plastics dispersions. Xn the first place, care should be taken that the polymers formed yield a coherent film under the drying conditions of the paints of which they are components and the monomers for making the copolymers should be selected in such a manner that, depending on the respective polymerization parameters, the formation of copolymers from the monomers bearing keta groups can be expected.

If desired, two or more of the compounds (C) may be used simultaneously.

When monomers which yield water-soluble homopolymers are to be copolymerised, the amounts should be chosen in such a manner that the water-sensitivity of the dispersion films or the paint films is not excessive. For example, (meth-)acrylic acid, crotonic, maleic and fumarie acids (meth)-acrylamide and maleic anhydride should each be copolymerized in amounts not exceeding 5%, relative to the total weight of the monomers.

The aqueous plasties dispersions in accordance with the present invention suitably have solids contents of from 20 to 70^ preferably from 40 to 60S by weight. Such aqueous plastics dispersions may be manufactured according to usual processes known to those skilled in the art.

Plastic dispersions are extremely complex systems, and the manufacture of high-quality dispersions according to the present invention requires the application of great skill and experience. Departure from the established rules of emulsion polymerization may therefore adversely affect important properties, for example water resistance, of the dispersion films or paint films. thsse reasons, the dispersions should not contain substantially more than the usual amounts of up to 3%, preferably up to 2%, of ionic emulsifiers, or of up to 6%, preferably up to 4%, of non-ionic emulsifiers, relative to the weight of the polymer.

Suitable non-ionic emulsifiers are, for example, alkyl polyglycol ethers, such as the ethoxylation products of lauryl, oleyl or stearyl alcohol or of mixtures such as coconut fatty alcohol; alkyl-phenol polyglycol ethers such as the ethoxylation products of octyl- or nonyl-phenol, diisopropyl-phenol, triisopropyl-phenol or di- or tritert .butyl-phenol; or ethoxylation products of polypropylene oxide.

As ionic emulsifiers, anionic emulsifiers are primarily used, for example alkali metal or ammonium salts of alkyl, aryl or alkylaryl sulfonates, sulfates, phosphates, phosphonates, or compounds having different anionic end groups, oligo- or polyethylene oxide units possibly being contained between the hydrocarbon radical and the anionic group. Typical representatives are sodium lauryl sulfate, sodium octyl-phenol glycol ether sulfate, sodium dodecyl-benzene sulfonate, sodium lauryl diglycol sulfate and ammonium tri-tert.butyl-phenol penta- and octa-glycol sulfates.

As protective colloids there may be used natural substances such as gum arabic, starch, alginates, or modified natural substances such as methyl, ethyl, hydroxyalkyl or carboxymethyl cellulose, or synthetic substances, for - 8 example polyvinyl alcohol, polyvinyl pyrrolidone, or mixtures of any two or more such substances. Modified cellulose derivatives and synthetic protective colloids are preferred.

To initiate and continue polymerization, oil-soluble and/or preferably water-soluble radical forming agents or redox systems are used, for example hydrogen peroxide, potassium or ammonium peroxydisulfate, dibenzoyl peroxide, lauryl peroxide, di-tert.butyl peroxide, bisazodiisobutyronitrile, either per se or together with reducing components, for example sodium bisulfite, Rongalite, glucose, ascorbic acid, and other compounds having a reducing action (the word 'Rongalite' is a Trade Mark).

The dispersions prepared according to the present invention have the special advantage of being suitable for the manufacture of gloss dispersion paints having a good wet adhesion on non-absorbent substrates, and of displaying a high resistance to saponification.

The following Examples and Comparative Examples illustrate the invention, the parts being by weight unless otherwise stated. The words·Tylose and C^lgon are registered Trade Marks.· EXAMPLE 1: A dispersion liquid consisting of 709 parts water parts polyvinyl alcohol having a degree of hydrolysis of 88 mol 7°, and a viscosity of 18 cP at 20°C in a 4% aqueous solution thereof 0.9 parts sodium vinylsulfonate 1.1 parts sodium dodecylbenzene sulfonate parts nonylphenol polyglycol ether having about 30 ethylene oxide units 43Sli - 9 0.72 part NaIi2PO4.2H2O 1.67 parts Na2HP04.12H20 1.5 parts ammonium peroxydisulfate and parts of a monomer mixture taken from a mixture of 300 parts vinyl acetate, 150 parts 2-ethylhexyl acrylate, 150 parts vinyl pivolate and 18 parts allyl acetoacetate was heated while stirring in a 2 liter three-necked flask placed in a heating bath and equipped with stirrer, reflux condenser, dropping funnel and thermometer, whereby the polymerization was initiated. When the temperature had reached 90°C, addition of the remaining monomer was started.

Immediately after completion of the monomer addition a solution of 0.3 part ammonium peroxydisulfate in 15 parts water was added, heating of the polymerization mixture (70°C) was continued for 2 hours while stirring, and the batch was then slowly cooled.

The dispersion obtained had a solids content of about 47.5%.

EXAMPLE 2 (Comparison): The procedure described in Example 1 was repeated with the exception that no allyl acetoacetate was used in the polymerization.

EXAMPLE 3: In an apparatus as described in Example 1 a dispersion liquor consisting of 618 parts water parts oleyl polyglycol ether having about 25 ethylene oxide units 0.2 part sodium dodecylbenzene sulfonate dssai - 10 12 parts hydroxyethyl cellulose having an average degree of polymerization of about 400 (molecular weight about 100,000) 1.5 part sodium acetate 2.5 parts ammonium peroxydisulfate and parts of a monomer mixture taken from a mixture of 450 parts vinyl acetate 150 parts vinyl isononanoate parts allyl acetoacetate was heated to 70°C and the remaining monomer mixture (549 parts) was metered in within a period of 3 hours at this temperature. When the addition was complete 0.5 part ammonium peroxydisulfate in 15 parts water were added and heating was continued for a further 2 hours. The dispersion had a solids content of about 50%.

EXAMPLE 4 (Comparison): The procedure described in Example 3 was repeated with the exception that no alkyl acetoacetate was used in the polymerization.

EXAMPLE 5i In an apparatus as described in Example 1 a dispersion liquor consisting of: 657 parts water parts nonylphenol polyglycol ether having about 30 ethylene glycol units parts polyvinyl alcohol having a degree of hydrolysis of 88 mol % and a viscosity of 4% aqueous solution of 18 cP at 20°C 0.9 parts sodium vinyl sulfonate 1.5 parts sodium acetate - 11 2.5 parts ammonium peroxydisulfate 48 parts vinyl acetate and parts Versatic-10-acid vinyl ester was heated to 7C°C and at that temperature there were added within a period of 3 hours a mixture of 432 parts vinyl acetate and 108 parts Versatic-10-acid vinyl ester and 9 parts allyl acetoacetate.

When the addition was complete 0.5 part ammonium peroxydisulfate in 15 parts water was added and the dispersion was heated for a further 2 hours. The dispersion had a solids content of approximately 49%.

EXAMPLE 6 (Comparison): The procedure described in Example 5 was repeated with the exception that no allyl acetoacetate was used in the polymerization.

EXAMPLE 7: In an apparatus as described in Example 1 a dispersion liquor consisting of 622 parts water parts nonylphenol polyglyeol ether having about 30 ethylene oxide units 1.5 parts sodium acetate parts hydroxyethyl cellulose having an average degree of polymerization of about 400 (molecular weight about 100,000) 2.5 parts ammonium peroxydisulfate and parts of a monomer mixture prepared from 396 parts vinyl acetate 150 parts Versatic-10-acid vinyl ester, parts n-butyl acrylate - 12 18 parts allyl acetoacetate and 6 parts crotonic acid was heated to 70°C and at that temperature there was added within 3 hours, the remaining monomer mixture (558 parts). When the addition was complete 0.5 part ammonium peroxydisulfate in 15 parts water was added and the dispersion was heated for a further 2 hours. The dispersion had a solids content of about 50%.

EXAMPLE 8 (Comparison): The procedure described in Example 7 was repeated with the exception that no allyl acetoacetate was used in the polymerization.

To prepare dispersion paints having a high wet adhesion, the dispersions obtained according to the preced ing Examples were blended with a pigment suspension. Pigment suspensions or pigment pastes of this type, which are suitable for making dispersion paints of low pigment content and especially gloss paints consist, for example, ι of titanium dioxide uniformly dispersed in water. They contain, in general, protective colloids such as cellulose derivatives, for example hydroxyethyl cellulose, and dispersing agents, for example salts of poly(meth)acrylic acid or sodium polyphosphate. Other conventional constit uents of pigment suspensions are antimicrobic preserving agents, antifoaming agents, pH stabilizers and fillers. Especially suitable titanium dioxide pigments are the rutile and anatase modifications. For the manufacture of gloss paints the average particle diameter of the pigment should be near the lower limit of the wave length of light, i.e. at about 0.4 to 0.2 micron. For making dull paints of low pigment content special large surface silicate - 13 pigments could be concomitantly used. Dull paints of high binder content yield paint coatings that are easy to clean. The pigment paste may, of course, also contain coloured pigments or the desired shade is obtained by adding a shading dyestuff to the dispersion paint containing the white pigment.

The pigment suspension can be prepared in known manner, for example by dispersing the pigment in a dissolver, a ball mill or ^and mill. For use in gloss paints, the pigment suspension should not contain noticeable amounts of pigment aggregates which would affect the gloss.

Auxiliaries such as plasticizers, cross linking agents, buffer substances, thickening agents, thixotropic agents, rust preventing agents, alkyd resins, or drying oils may be added to the dispersion or the finished dispersion paint. Suitable plasticizers are not the solvents initially mentioned as film consolidation agents having a temporary action only but compounds which reduce the filmforming temperature and remain in the polymer for a longer period of time, for example dibutyl phthalate.

To test the wet adhesion, gloss paints were prepared according to the following formulationsi Formulation 1: (1) 41.0 parts water .6 parts of a 3% aqueous solution of Tylose H 20 0.4 part Calgon N (solid) 3.0 parts dispersing agent PA 30 1.0 part ammonia of 25% strength 2.0 parts of preserving agent 3.0 parts of anti-foaming agent 175 parts of titanium dioxide having a particle size of from 0.2 to 0.4 micron .0 parts 1,2-propylene-glycol - 14 were dispersed and then (2) 710 parts of one of the above dispersions (with a solids content of 50%) to which had been added 2.0 parts ammonia of 25% strength if the pH did not exceed approximately 7, were added.

Subsequently a mixture of (3) 10 parts butyl diglycol acetate and 27.0 parts 1,2-propylene-glycol were slowly added while ) stirring.

The liquid or soluble components indicated in (1), with the exception of the 1,2-propylene-glycol, were introduced in the above sequence into a vessel provided with stirrer, and the pigment was then dispersed in this i mixture by means of a dissolver. Subsequently, 1,2propyleneglycol was added. In order to ensure identical conditions for mixing with the different dispersions to be tested, for example in view of pigment dispersion, a large amount of this pigment paste was manufactured. ι Formulation II: Formulation II differed from Formulation I by a larger amount of organic solvent, that is, a mixture of 53 parts 1,2-propyleneglycol and 17 parts butyldiglycol acetate was added to the paint.

Formulation III: Formulation III differed from Formulations I and II by a still larger amount of organic solvents, that is, a mixture of 68.7 parts 1,2-propyleneglycol and 21.3 parts butyldiglycol acetate was added to the practically finished paint. 3 511 - 15 one run.

Formulation IV: Formulation IV differed from Formulation I by a varied composition of the solvent mixture added to the practically finished paint (step 3 of paint manufacture); that is, a mixture of 12.4 parts 1,2-propyleneglycol, 4.6 parts butyldiglycol acetate and 20 parts 2,2,4-trimethylpentanediol1,3-monoisobutyrate-l (Texanol) was added to the paint.

For the manufacture of the individual paints a corresponding proportion of the pigment pastes were mixed according to the process of the above formulations, while slowly stirring, with the dispersions approximately one day old, whereupon the solvents (3) were added. After complete mixing, the paints were passed through a sieve.

These gloss paints were allowed to stand for one day and then spread onto glass plates and steel sheets onto which a pigmented glossy air-drying alkyd resin enamel had been sprayed and which had been aged after drying for 24 hours at 1OO°C. A film applicator was used having a slit diameter of 200 microns. After a drying period of 24 hours the wet adhesion of the gloss paints was tested according to the two following methods: (1) Abrasion test: The glass plates with the dried coating of dispersion paint were inserted in a mechanical abrasion device as described, for example, in German Offenlegungsschrift No. 2,262,956 and similar to the Gardner Washability and Abrasion Machine, but having a stroke length of approximately 1.20 m in a manner such that the applied films of dispersion paint were in a vertical position with respect to the direction of movement of the brush. Due to the long moving distance about 15 paints could be simultaneously tested in A brush with hog's bristles was used which, at the beginning of the test, had been wetted with distilled water. During the test the area on which the brush moved was also wetted with distilled water so that the brushed areas were permanently covered with -a water film. With a poor wet adhesion the dispersion paint was brushed off the substrate after a few strokes of the brush and torn at the boundary between wetted and dry film. The better the wet adhesion, the greater the number of strokes of the brush until the film is shifted aside. The dispersion paint has an optimum wet adhesion when in the wetted area the film is not damaged after 5,000 strokes of the brush, one stroke including a backward and forward movement. 2) Condensation test: A rectangular thermostat chamber was used one half of which was filled with water at 50°C and in the gas space of which above the water level was mounted a fan. The upper opening was covered with the steel sheets with the coated surface facing downwards so that the thermostat chamber was closed. The thermostat was kept in a room maintained at 23°C. Owing to the temperature difference steam condensed on the lower surface of the sheets and acted on the coats of paint. After 15 minutes the sheets were removed and the coatings evaluated.

With an unsatisfactory wet adhesion, blisters form between the film of dispersion paint and the alkyd resin lacquer and the film can be easily shifted aside, for example with the finger-tip. A film having a good wet adhesion is still free of blisters after a period of 6 hours and cannot be shifted.

The test results are listed in the following Table. - 17 43S11 β o •rl P Φ to β Φ Ό β Ο , • β β • • β • β • • (0 to •Η •Η (0 to •Η 10 Ή to to Ρ ρ Ρ ε ε Ρ Ρ ε Ρ ε ρ Ρ to £ί 49 49 49 49 49 49 φ ο ιη ιη ο Ρ Ό ιο ΓΟ cm 10 ιθ ιΡ ιθ <η Φ CM Ν Ν Ν Κ Μ Λ Ο ο Ο Ο ο ο Ο ο Ο Ο ο ο ιη ο ο ιη ο CM ο ο ιη ο ο CM ο rp ιη σι ιη ιη ιη Λ Λ Ν Ν Ν o o o in h of test results β •H P Φ * H 0 β z g s tp M-J β O •H · Ρ β O fl O 55 kl -H atO Φ Ρ H Ρ Ρ Φ ft .5 m Π) β Ή X Οι Ή Ό Μ * * *. <# in \0 > co αι Ρ φ φ % ο υ *

Claims (16)

1. A process for the preparation of an aqueous plastics dispersion which comprises copolymerizing in an aqueous system the following monomers: (A) from 5 to 50% by weight, relative to the total monomers, of at least one vinyl ester of a saturated branched monocarboxylie acid having from 5 to 20 carbon atoms, the carboxyl groups of which are directly linked to a tertiary or quaternary carbon atom; (B) from 40 to 94.5% by weight, relative to the total monomers of at least one vinyl ester of a saturated carboxylic acid containing 2 to 4 carbon atoms; (C) from 0 to 30% by weight, relative to the total monomers, of at least one other alpha-betaunsaturated compound copolymerizable with the above monomers; and (D) from 0.5 to 10% by weight, relative to the total monomers, of at least one acetoacetic acid ester of the formula II 0 R R' II CH 3 -c-ch 2 -c-x-c=ch where X is -ο-, -o-ch 2 -, -o-ch 2 -ch 2 -o-cor -o-ch 2 -ch 2 -ch 2 -0-CII II - 19 and each of R and R' is H or CHg.

2. A process as claimed ir. claim 1 wherein the aceto acetic acid ester is used in an amount ciom 1 to M. by weight.

3. A process as claimed in claim 1 or claim 2, wherein the acetoacetic acid ester is vinyl acetoacetate, allyl acetoacetate, or the acetoacetic acid ester of βhydroxy ethyl- or β-hydroxy propyl-acrylate, methacrylate or crotonate.

4. A process as claimed in claim 1 or claim 2, wherein the acetoacetic acid ester is allyl acetoacetate.

5. A process as claimed in any one of claims 1 to 4, wherein component (A) is present in an amount from 15 to 35% by weight.

6. A process as claimed in any one of claims 1 to 5 wherein component (A) is vinyl pivalate, vinyl isononanoate or the vinyl ester of a mixture of saturated tertiary monocarboxylic acids having 8, 10 and 11 carbon atoms.

7. A process as claimed in any one of claims 1 to 5, wherein component (A) is the vinyl ester of a saturated tertiary monocarboxylic acid having 10 carbon atoms.

8. A process as claimed in any one of claims 1 to 7, wherein component (Bi is vinyl acetate.

9. A process as claimed in any one of claims 1 to 8, wherein component (C) is acrylic, methacrylic, crotonic, maleic or fumaric acid or an ester thereof with an alcohol containing from 1 to 30 carbon atoms or another polymerizable derivative of such an acid.

10. A process as claimed in claim 9, wherein component (C) is a monomer that when homopolymerized is water-soluble and is present in an amount not exceeding 5% by weight of the total monomer. - 20 LO

11. A process as claimed in claim 1, conducted substantially as described in any one of Examples 1, 3, 5 and 7 herein.

12. An aqueous plastics dispersion whenever produced by the process as claimed in any one of claims 1 to 11.

13. An aqueous plastics dispersion as claimed in claim 12 having a total solids content of from 20 to 70% by weight.

14. An aqueous plastics dispersion as claimed in claim 12 having a total solids content of from 40 to 60% by weight.

15. A copolymer comprising, by weight, calculated on the copolymers L5 !0 •5 (A) from 5 to 50% of units derived from at least . one vinyl ester of a saturated branched monocarboxylic acid having from 5 to 20 carbon atoms, the carboxyl groups of which are directly linked to a tertiary or quaternary carbon atom? (B) from 40 to 94.5% of units derived from at least one vinyl ester of a saturated carboxylic acid containing 2 to 4 carbon atoms; (c) from 0 to 30% of units derived from at least one other alpha-beta-unsaturated compound copolymerizable with (A) and (b); and (D) from 0.5 to 10% of units derived from at least one acetoacetic acid ester of the formula 0 0 · R R' ch 3 -c-ch 2 -C-X-C=CH where X, R and R 1 have the meanings specified in claim 1.

16. A copolymer as claimed in claim 15 substantially as described in any one of Examples 1, 3, 5 and 7 herein.