GB2118192A - Coating composition - Google Patents

Abstract

A coating composition comprises a cross-linkable film-forming polymer in, a cross-linking agent dissolved in, and insoluble cross-linked copolymer particles dispersed in, a volatile organic liquid diluent, in which the copolymer is of alpha , beta -ethylenically- unsaturated monomers and carries a resinous portion including an ampho- ionic group of the formula <IMAGE> wherein R is optionally substituted phenylene or C1-12 alkylene and Y is COOH or SO3H.

Description

SPECIFICATION Coating composition Coating compositions having high solids contents, and comprising cross-linked polymeric microparticles dispersed in a conventional coating composition containing a film-forming resinous vehicle, have recently been developed and are of particular interest for use in the automobile industry.

The particles comprise polymer cross-linked to the extent that it is insoluble in the organic diluent in which the particles are dispersed. The polymer is finely divided and stably dispersed in the coating composition. Such dispersions are sometimes known as "microgels".

One known method for preparing microgels comprises preparing finely divided polymer particles by emulsion polymerisation from ethylenically-unsaturated monomers and cross-linkable, polymerisable monomers in an aqueous medium, and separating the microgel particles by solvent exchange, azeotropic distillation, centrifugal separation, filtering or drying. Another known method is the so-called "non-aqueous dispersion" (NAD) procedure, which involves reacting ethylenicallyunsaturated monomer and copolymerisable, cross-linking monomer in a non-aqueous organic solvent in which the monomers, but not the product, are soluble.

The first method is generally preferred in industry, because the particle formation and removal of heat of reaction can be performed conveniently. However, this procedure involves the additional step of the removal of water from the emulsion which is formed. Further, since a relatively low molecular weight compound, usually an anionic or cationic surfactant, is usually used as an emulsifier in order to ensure effective dispersion of the monomers in the aqueous medium, the polymer particles tend to carry this compound adhered to their surfaces. In use of the resultant coating composition, the surfactant may be introduced into the coating and this may have undesirable effects on the performance of the resultant film, e.g. low water-resistance.A further problem is that water is used in the emulsion polymerisation step, while it is usual to use a volatile organic diluent in the formulation of coating compositions. The emulsifier used to assist dispersion in the aqueous medium is not usually of assistance in achieving a stable dispersion of microparticles in a coating composition formulated with a volatile organic liquid, and it is therefore necessary to take special steps to achieve the desired stable dispersion.

In the NAD method, a non-aqueous organic solvent is used, and the product can be added directly to a coating composition. If desired, the microparticles can be separated by simple filtration. A problem associated with the NAD method is that particular dispersion stabilising agents are required in the copolymerisation step, whereby a microgel is obtained. The stabilising agent is often a graft copolymer comprising a polymer backbone which is not solvated by the organic medium, and a plurality of pendant polymer chains which are solvated. The graft copolymer must be carefully selected, in consideration of the affinities for polymer particles and organic medium, in dependence on the types of monomers and medium used.Further, since the organic liquid is usually a liquid of low polarity, comprising mainly aliphatic hydrocarbons, and a relatively highly polar organic solvent is used in the formulation of coating compositions, the dispersion stabilising agent used in the microgel formation is often useless for the stabilisation of microgels in the coating composition.

Japanese laid-open Patent Applications Nos. 133234/78, 133235/78, 1 33236/78 and 1 50439/79, in proposing a solution to this last problem, suggest that, after formation of the microgels, monomers capable of forming polymers with the same composition as that of the film-forming polymer used in the coating composition should be polymerised on the surfaces of the microgel particles, thereby modifying the polymer surfaces in accordance with the changing circumstances of use. It would nevertheless be desirable to avoid the need for such a step.

According to the present invention, a coating composition comprises a film-forming polymer, a cross-linking agent, cross-linked copolymer particles and a volatile organic liquid diluent, in which the film-forming polymer has functional groups capable of reacting with the cross-linking agent, in which the cross-linking agent is dissolved in the diluent, in which the copolymer particles have an average diameter of from 0.02 to 40 4 and are stably dispersed in the diluent, and in which the copolymer is of -ethylenically-unsaturated monomers and carries a resinous portion including an ampho-ionic group of the formula -N-R-Y wherein R is optionally substituted C16 alkylene and Y is COOH or SO3H.

The film-forming polymer may be of the type conventionally used in coating compositions.

Examples of such polymers are acrylic, alkyd and polyester resins bearing functional groups such as hydroxyl and carboxyl groups. Usually, they have an acid value of 0.5 to 60, a hydroxyl number of 20 to 200 and a number average molecular weight of 500 to 10,000.

The cross-linking agent may be any of those customarily used in this field, providing that it is soluble in the organic liquid diluent and capable of reacting with the functional groups of the filmforming polymer. Examples are diisocyanates, diepoxides and aminoplast resins. Particularly preferred cross-linking agents are melamine-formaldehyde condensation products in which a substantial proportion of the methylol groups are etherified with butanol or methanol.

The film-forming polymer is carried in the volatile organic liquid diluent in the form of a dispersion or solution, or maybe partly in dispersion and partly in solution. The cross-linking agent is in solution.

Examples of suitable volatile organic liquid diluents are aromatic hydrocarbons such as toluene, xylene and petroleum fractions of various boiling point ranges having a significant aromatic content, esters such as butyl acetate, ethylene glycol diacetate and 2-ethoxyethyl acetate, ketones such as acetone and methyl isobutyl ketone, and alcohols such as butyl alcohol.

The copolymer particles are insoluble in the combination of the film-forming polymer and the diluent because of the cross-linking, and are maintained in a stabilised state of dispersion in the coating composition because of the presence of the resinous portion having a dipolar ionic radical. The average particle diameter is preferably from 0.02 to 40 microns. Such polymeric microparticles may be classified in the following two groups, as to the mode of inclusion of the resinous portion having the ampho-ionic radical in the copolymer.

A first group of polymeric microparticles is composed of cross-linked copolymer of ,- ethylenically-unsaturated monomers to which the ampho-ionic radical is adhered mechanically. Fine particles of cross-linking-type acrylic polymer may be advantageously prepared by the copolymerisation of at least one a,P-ethylenically-u nsatu rated monomer and at least one cross-linking monomer which is difunctional with respect to the polymerisation reaction, in an aqueous or organic solvent.

Examples of suitable a,-ethylenically-unsaturated monomers are the following: (1) carboxyl-bearing monomers such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid and fumaric acid; (2) hydroxyl-bearing monomers such as 2-hydroxyethyl acrylate, hydroxypropyl acrylate, 2hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, ally alcohol and methallyl alcohol; (3) nitrogen-containing alkyl acrylates and methacrylates such as dimethylaminoethyl acrylate and dimethylaminoethyl methacrylate; (4) polymerisable amides such as acrylamide and methacrylamide; (5) polymerisable nitriles such as acrylonitrile and methacrylonitrile; (6) alkyl acrylates and methacrylates such as methyl acrylate, methyl methacrylate, ethyl acrylate, n-butyl acrylate, n-butyi methacrylate and 2-ethylhexyl acrylate;; (7) polymerisable aromatic compounds such as styrene, a-methylsWrene, vinyltoluene and tbutylstyrene; (8) a-olefins such as ethylene and propylene; (9) vinyl compounds such as vinyl acetate and vinyl propionate; and (10) dienes such as butadiene and isoprene.

These monomers are used alone or in combinations of two or more.

The cross-linking monomer may be any of the known monomers of functionality of two or greater than two. One preferred group comprises the so-called polyfunctional monomers, having two or more ethylenical unsaturations in its molecule, e.g. polymerisable unsaturated monocarboxylic esters of polyhydric alcohols, polymerisable unsaturated alcoholic esters of polycarboxylic acids, and aromatic compounds substituted with two or more vinyl groups.Examples of such compounds are ethylene glycol diacrylate or dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, 1 4-butanediol diacrylate, neopentyl glycol diacrylate, 1 ,6-hexanediol diacrylate, pentaerythritol diacrylate, pentaerythritol triacrylate, tetraacrylate, dimethacrylate, trimethacrylate or tetramethacrylate, glycerol diacrylate or dimethacrylate, glycerol allyloxydimethacrylate, 1,1,1 -tris- hydroxymethylethane triacrylate, dimethacrylate or tri trimethacrylate, 1,1,1 -tris-hydroxymethylpropane diacrylate, triacrylate, dimethacrylate or trimethacrylate, triallyl cyanurate, triallyl isocyanurate, triallyl trimellitate, diallyl terephthalate, diallyl phthalate and divinylbenzene. Cross-linking monomers may also be of a combination of two ethylenically-unsaturated monomers each bearing mutually-reactive funcational groups such as, for example, the combination of epoxy-bearing ethylenically-unsaturated monomers such as glycidyl acrylate or methacrylate, and carboxyl-bearing ethylenically-unsaturated monomers such as acrylic, methacrylic or crontonic acid. Other examples of combinations of mutuallyreactive functional groups are amine and carbonyl, epoxide and acid anhydride, amine and acid chloride, alkyleneimine and carbonyl, organoalkoxysilane and carboxyl and hydroxyl and isocyanate groups.

The a, -ethylenically-unsaturated monomers and cross-linking monomers may be reacted in an aqueous or organic liquid medium in conventional manner, to obtain microparticles or cross-linked copolymer. In the present invention, the polymerisation is carried out in the presence of a resin having the specified ampho-ionic radical. Examples of such resins are alkyd, polyester, modified epoxy, acrylic, melamine and polyether resins having an ampho-ionic group of the formula --NN--R-C000 or orNsRSo3(3 wherein R is as defined above. These resins can exhibit specific behaviour in respect of reactivity, surface activity, and electrochemical properties owing to the presence of the ampho-ionic radical, and can act as emulsifier or stabilising agent in the polymerisation reaction.

Alkyd and polyester resins are characterised by forming a series of ester chains, using as essential components polycarboxylic acid and polyhydric alcohol. For use in the invention, a part of the polyhydric alcohol is replaced by, for example, a compound of the formula

wherein R, is hydroxyalkyl, R2 and R3 are independently selected from hydrogen and optionally substituted alkyl, and A is optionally substituted C16 alkylene or phenylene. For reference, see Japanese Kokai Nos. 34725/81 and 51727/81. Of these resins, those having an acid value of 30 to 150, especially 40 to 150, and a number average molecular of 500 to 5000, especially 700 to 3000, are preferred for use in this invention.

Modified epoxy resins having the characteristic ampho-ionic radical are disclosed in Japanese Kokai No. 40522/82. In general, epoxy resins are characterised by having an oxirane ring at or near the end of the chain. Therefore, it is possible to obtain a modified epoxy resin having at the end of the polymer chain a proportion of such radicals as those of the formula

wherein R4 and R5 are each hydrogen or methyl, R6 is an optionally substituted alkyl group non-reactive with epoxy groups, and A is as defined above, by reaction of an epoxy resin of formula II with a compound of formula Ill

R6-NH-A-503M (III) wherein M is an alkali metal or ammonium cation and R4, R5, R6 and A have the same meanings as defined above.The hydrophilicity of the modified epoxy resin increases in proportion to the quantity of the ampho-ionic groups. Reference may again be made, in this connection, to Japanese Kokai No.

40522/82.

Acrylic resins having the ampho-ionic radical therein can be advantageously prepared by solution polymerisation, using a free radical initiator, from the combination of at least one polymerisable amino acid compound of the formulae

wherein R7, R8, R, and R10 are independently selected from H, CH3 and C2H R,1 hydrogen or C ~20 alkyl optionally including in the chain -SO-, -COO- and/or -0- groups; R,2 is C,~,2 alkylene optionally substituted by -OH, -SH, -SR13 (in which R13 is C14 alkyl) or one or more C14 alkyl radicals; and Y is as defined above;

wherein R,4, R,5 and R,6 are independently selected from hydrogen and C16 alkyl;R,7 is Rr, as defined above or a further radical of the formula

and R,8 is C2~,2 alkylene optionally substituted with one or more C16 alkyl radicals;

wherein R,9, R20 and R21 are independently selected from H and CH3; R22 is C,~20 alkyl having at least one hydroxyl group and optionally containing in the chain -0- or -COO-; R23 is a group as defined for R22, hydrogen or C,~20 alkyl;R24 is optionally substituted (CH2)n (in which n is an integer of from 1 to 6); and ye is COOS or SO3e; and

wherein Rrg, R20, R21, R24 and ye are as defined above; and either R28 and R29 are the same or different and are each cycloalkyl or C,~20 alkyl optionally containing in the chain -0-or -COO-, or R28 and R29 are taken together and form a heterocyclic ring containing the nitrogen atom; with at least one polymerisable monomer selected from hydroxy-bearing monomers, carboxyl-bearing monomers, glycidyl-bearing monomers, alkyl acrylates or methacrylates, N-containing alkyl acrylates or methacrylates, polymerisable amides, polymerisable nitriles, polymerisable aromatic compounds, - olefins, vinyl compounds and diene compounds, of the type described above.As to the details of these polymerisable amino acid compounds, reference should be made to Japanese Kokai Nos. 51050/80, 53251/80,145249/81 and 145250/81; as to ampho-ionic radical-bearing acrylic resins, to the published version of Japanese Patent Application No. 71864/81. Preferably, these acrylic resins should have an acid value of 30 to 180, more preferably 40 to 160, and a number average molecular weight of 500 to 10,000, more preferably 700 to 6000.

Melamine resins having the specified ampho-ionic radical may be prepared by using at least one hydroxyl-bearing aminosulfonic-type ampho-ionic compound of the formulae

wherein R22 is as defined above, R35 is as defined above for R22, hydrogen, C18 alkyl or -cH2-CHR36-SO3H, and R36 is hydrogen or methyl, together with melamine and formalin, and reacting them by conventional means. The reaction conditions and procedures used are not critical; in this connection, reference should be made to, for example, "A guide of synthetic resins for coating composition" by K. Kitaoka, published 25th May 1974, Kobunshi Kankokai, pages 134 to 139. These hydroxy-bearing aminosulfonic-type ampho-ionic compounds are described more specifically in Japanese Kokai No.92859/81.

Polyether resins having the specified ampho-ionic group may be prepared, as stated in Japanese Kokai No. 40522/82, by reacting a compound of the formula R33-NH-A-SO3M (oil) wherein R33 is a substituent non-reactive with epoxy groups, A is alkylene or phenylene, and M is as defined above, with a polyether-type epoxy resin having at the end of the polymer chain a group of formula 11, thereby obtaining a modified polyether-type epoxy resin having at the end of polymer chain a group of the formula

wherein R4, R5 and R33 are as defined above. Various polyether-type epoxy resins are commercially available.

All of the resins described above possess the characteristic ampho-ionic group required in the invention. Other resin portion-containing copolymers for use in the invention can be obtained similarly.

The resins may be prepared either in water-soluble or organic solvent-soluble form. When watersoluble, they are useful as emulsifier and dispersing agent in the emulsion polymerisation of a,,3- ethylenically-unsaturated monomers in an aqueous medium and can therefore be used, without using any additional emulsifier, to prepared microparticles of cross-linked copolymer used in the present invention.

The polymerisation may preferably and advantageously be carried out by adding a mixture of defined amounts of monomers, including cross-linking monomer, to an aqueous medium containing the ampho-ion-type resin, in the presence of a polymerisation initiator. The amount of the ampho ionic-type resin may vary within a wide range; in general, it is from 0.3 to 8, and preferably 0.5 to 6, % by weight of the total amount of monomers to be copolymerised. The cross-linking monomer preferably constitutes 0.01 to 20, more preferably 0.1 to 10, % by weight of the total polymerisable monomers. This amount must be sufficient to make the microparticle polymer insoluble in the combination of film-forming polymer and organic liquid diluent.This insolubility may be checked by means of the following test: the microparticles (1 part by weight) are shaken for 30 minutes with the organic liquid diluent (e.g. tetrahydrofuran) (100 parts by weight). The suspension is then centrifuged at 17,000 rpm for 30 minutes. The supernatant liquid is decanted off and the residual polymer is dried and weighed. The weight of the polymer is compared with the original weight of the microparticles.

Where the result of this test indicates that the microparticles are acceptably insoluble in the diluent alone, it can be assumed that the particles will be at least equally insoluble in the combination of the film-forming polymer and the diluent.

The reaction medium, i.e. water, may be used in an amount which gives a resinous emulsion of 2 to 65, preferably 20 to 60, % non-volatile solids content. In order to assist the solubilisation of the ampho-ionic resin, a quantity of base equivalent to the acid value may be present in the reaction medium. Suitable bases include alkali metal hydroxides, but by reason of their volatility and lack of inorganic ions to be released in the form coating, preference is given to ammonia and organic amines.

The aqueous medium may also contain a water-miscible organic solvent, if required.

As the polymerisation initiator, any of those known in the art may satisfactorily be used, including organic peroxides such as benzoyl peroxide, t-butyl peroxide and cumene hydroperoxide, organic azo compounds such as azobiscyanovaleric acid, azobisisobutyronitrile, azobis(2,4-dimethyl)valeronitrile, and azobis(2-amidinopropane)hydrochloride, inorganic water-soluble radical initiators such as potassium persulfate, ammonium persulfate and hydrogen peroxide, and redox-type initiators comprising a combination of an inorganic water-soluble radical initiator and sodium pyrosulfite, sodium hydrogen sulfite or bivalent Fe ion. They may be used alone or in combination. Such initiators may be present in the reaction medium or may be added to the reaction system simultaneously with the monomers.The amount of initiator is usually from 0.05 to 5, more preferably 0.1 to 3, % by weight of the total monomers to be copolymerised. If desired, a conventional chain transfer such as lauryl or hexyl mercaptan may be present, in an appropriate amount.

By the adoption of the emulsion polymerisation technique, a stably-dispersed, milky or creamy resinous emulsion can be obtained, the average diameter of the microparticles therein being from 0.02 to 0.5 y. When water is removed from the emulsion by spray-drying, solvent replacement, azeotropic distiilation, centrifugal separation, filtering, drying or other appropriate means, a partially agglomerated polymeric mass having a maximum particle diameter of about 40 y can be obtained; this need not be a fused mass. Such a product may be used directly or, after pulverisation, as the microparticles in the novel coating composition. For drying the emulsion, spray-drying is most preferred because of the ease of operation and the particle diameterpbtainable therewith.

Alternatively, the polymeric microparticles may be prepared in a non-aqueous organic solvent by the so-called NAD method, using the resin having an ampho-ionic radical as dispersion stabilising agent. A low polarity organic solvent is used which can dissolve the monomers but not the polymer; examples are aliphatic hydrocarbons such as hexane, heptane and octane.

As previously mentioned, the ampho-ionic-type resins used in the invention may be organic solvent-soluble and, owing to their specific surface activity and electrochemical properties, they are useful as dispersing and stabilising agents in such circumstances. The reaction initiator to be used, operational details and post-treatment in the NAD method are well known in the art and need not be elaborated here; suffice it to say that, even in the NAD method, polymeric particles having an average diameter of 1 to 40 4 can be obtained.

In either method, a,P-ethylenica I ly-u nsaturated monomers and cross-linking monomers are successfully copolymerised in the presence of the ampho-ionic-type resin, without the necessity of using any additional emulsifier, and microparticles of polymer, cross-linked to the extent that they are insoluble in the organic liquid diluent, are obtained. Furthermore, the micro-particles are always accompanied, through mechanical adhesion, by the ampho-ionic-type resin used, which can have excellent affinity to volatile organic liquid diluents used in the coating composition, and therefore, when formulated as such, can be maintained in stable dispersion.

A second group of polymeric microparticles is composed of cross-linked copolymer of a,5- ethylenically-unsaturated monomers, having integrally incorporated therein a resinous portion having the specified ampho-ionic radical This group of polymeric microparticles may be further divided into two sub-groups.

The first sub-group comprises microparticles composed of cross-linked copolymer of ,/3- ethylenically-unsaturated monomers, to which the resinous portions having the ampho-ionic radicals are anchored by covalent bonds. As indicated above, a resin having the ampho-ionic radical can exhibit specific reactivity and surface activity and thus be useful as an emulsifier or dispersing agent in the polymerisation of cz -ethylenically-unsaturated monomers in aqueous or non-aqueous media.

However, the microparticles have the ampho-ionic-type resin held merely by mechanical adhesion.

Insofar as the ampho-ionic-type resins are anchored by that force, the particles may be maintained in stable dispersion in the coating composition but, once the resins are removed from the microparticles for any reason, the stability of the microparticles would be greatiy reduced. We have found that, by the inclusion of polymerisable a,,3-unsaturation bonding in the ampho-ionic-type resin, additional anchoring of the resin to the microparticles can be attained, without sacrificing the desired properties and functions of the resin.

Thus, in a second aspect of the invention, the polymeric microparticles may be prepared by poiymerising at least one ,-ethylenicaily-unsaturated monomer and at least one cross-linking monomer, in an aqueous or organic medium, in the presence of a resin having the given ampho-ionic radical and a polymerisable a,-unsaturated bond. Examples of such resins are alkyd, polyester, modified epoxy, acrylic, melamine and polyether resins of the types already described. In preparing these ampho-ionic-type resins, the procedure can be modified to make them carry functional groups such as carboxyl or epoxy groups, by the selective use of appropriate monomers to be copolymerised.

The desired polymerisable a,-unsaturation may, therefore, be freely introduced into such a resin, after introduction of the ampho-ionic radical, by reaction between a carboxyl-bearing ampho-ionic-type resin and an epoxy-bearing unsaturated compound such as glycidyl acrylate or methacrylate, or by reaction between an epoxy-bearing ampho-ionic-type resin and an a,-unsaturated carboxylic acid such as acrylic, methacrylic or crotonic acid. By way of example, an alkyd or polyester resin having an ampho-ionic group, of the type described above, may be reacted with glycidyl acrylate or methacrylate, with the carboxyl groups still present, thereby incorporating the desired polymerisable a, - unsaturation.A modified epoxy resin having an ampho-ionic group, of the type described above, may be reacted with an ce"B-unsaturated carboxylic acid, for reaction with the remaining epoxy group.

In the case of acrylic resins, carboxyl or glycidyl-bearing monomers may coexist in the reaction system for the preparation of ampho-ionic-type acrylic resins of the type described above; with the thusobtained resin, an epoxy-bearing unsaturated compound such as glycidyl acrylate or methacrylate, or an a"B-unsaturated carboxylic acid such as acrylic, methacrylic or crotonic acid may be reacted at a later stage. A polyether resin having an ampho-ionic group, of the type described above, may be reacted with acrylic or methacrylic acid, for reaction with the remaining epoxy group. Any appropriate modifications may be made in connection with the preparation of suitable resins having both amphoionic radicals and polymerisable a,-unsaturation.

The resins can exhibit variegated affinities to aqueous and non-aqueous solvents, owing to the presence of the characteristic ampho-ionic group. Hydrophilicity may be increased by the inclusion of hydrophilic groups in the resin. Therefore, in the polymerisation of a"B-ethylenically-unsaturated monomers, they can be effective emulsifying or dispersion stabilising agents in either aqueous or nonaqueous reaction media. Furthermore, since they have the characteristic a" -unsaturation, they can take part in the copolymerisation reaction, thereby giving microparticles of cross-linked copolymer of ,/3-ethylenically-unsaturated monomers, to which both a resinous portion and the specified amphoionic group have been firmly bonded, via covalent bonding.The preparation of microparticles of this type is very similar to that described for the first group of polymeric microparticles.

The second sub-group comprises microparticles directly obtained by the copolymerisation of at least one polymerisable amino acid compound of the formula

in which R41 is a substituent containing a polymerisable ethylenically-unsaturated bond, R42 is hydrogen or optionally substituted C,~30 hydrocarbyl, and R and Y are as defined herein, with other polymerisable ethylenically-unsaturated monomers (examples of which have already been given), at least part of which is cross-linking monomer. These microparticles may also be composed of crosslinked copolymer of a,ss-ethylenically-unsaturated monomers, having pendant resinous portions containing the specified ampho-ionic group.The polymerisable amino acid compound of the given formula may be prepared by reaction between an oxirane compound and an amino acid having primary or secondary amino groups, or by reaction between a benzyl halide and an aminosulfonic compound having primary or secondary amino groups, as disclosed in Japanese Kokai No. 139111/82.

Examples of R4, are the groups of the formulae

wherein R43, R44, R45 and R46 are each hydrogen or alkyl. Examples of R42 are hydrogen and C~20 alkyl optionally including in the carbon chain-SO-, -COO- or -0-. Examples of R are C,-,2 alkylene and phenylene, optionally substituted by C14 alkyl groups. Specific examples of the polymerisable amino acid compounds are the following: N-(2-hydroxy-3-allyloxypropyl)taurine, optionally with a N-methyl, N-ethyl, N-propyl, N-butyl, Nheptyl, N-dodecyl, N-heptadecyl, N-(2-octadecylsu Ifinylethyl) or N-(2-stea royloxyethyl) group.

2- or 3-[(2-hydroxy-3-allyloxypropyl)aminoj-1 -propanesulfonic acid 1 -[(2-hydroxy-3-allyloxypropyl)amino]-2-propanesulfonic acid 3- or 4-[(2-hydroxy-3-allyloxypropyl)amino]-2-butanesulfonic acid 2- or 4-[(2-hydroxy-3-allyioxypropyl)amino]-1 -butanesulfonic acid 1 -[(2-hydroxy-3-allyloxypropyl)amino]-2-methyl-2-propanesulfonic acid 3-[(2-hydroxy-3-allyloxypropyl)amino]-2-pentanesulfonic acid 4-[(2-hydroxy-3-allyloxypropyl)amino]-2-methyl-3-pentanesulfonic acid 5-[(2-hydroxy-3-allyloxypropyl)amino]-1 -pentanesulfonic acid 1 0-[(2-hydroxy-3-allyloxypropyl)amino]-1 -decanesulfonic acid N-(2-hydroxy-3-methal Iyloxypropyl)taurine N-( 1 -methyl-2-hydroxy-3-allyloxypropyl)taurine N-(2-hydroxy-3-al lyloxypropyl)glyci ne N-(2-hydroxy-3-methallyloxypropyl)glycine N-(2-hydroxy-3-methal lyloxypropyl)sarcosine N-(2-hydroxy-3-allyloxypropyl)alanine N-(2-hydroxy-3-allyioxypropyl)-p-alanine, optionally with a N-methyl, N-ethyl, N-butyl, N-heptyl, N-dodecyl or N-heptadecyl group N-( 1 -methyl-2-hydroxy-3-allyloxypropyl)-P-al nine N-(2-hyd roxy-3-al Iyloxypropyl)-E-ami noca proic acid N-(2-hydroxy-3-allyloxypropyl)threonine N-(2-hydroxy-3-al lyloxypropyl)cysti ne N-(2-hydroxy-3-allyloxypropyl)methionine N-(2-hydroxy-3-allyloxypropyl)anthranilic acid N-(2-hydroxy-3-allyloxypropyl)-m-aminobenzoic acid N-(2-hydroxy-3-allyloxypropyl)-p-aminobenzoic acid N-(2-hydroxy-3-allyloxypropyl)orthanilic acid N-(2-hydroxy-3-allyloxypropyl)metanilic acid N-(2-hydroxy-3-allyloxypropyl)sulfanilic acid N-(vinylbenzyl)taurine, optionally with a N-methyl, N-ethyl, N-propyl, N-butyl, N-heptyl, Ndodecyl, N-heptadecyl, N-(2-octadecylsulfinylethyl) or N-(2-stearoyloxy ethyl) group N-(isopropenyibenzyl)taurine, optionally with a N-methyl, N-ethyl, N-propyl, N-butyl, N-heptyl, Ndodecyl, N-heptadecyi, N-(2-octadecylsulfinylethyl) or N-(2-stearoylethyl) group 2- or 2-vinylbenzylamino or isopropenylbenzylamino-1 -propanesulfonic acid, any of which 4 compounds optionally has a N-methyl group 1 -vinylbenzylamino or isopropenylbenzylamino-2-propanesulfonic acid 3- or 4-vinylbenzylamino or isopropenylbenzylamino-2-butanesulfonic acid 2- or 4-vinylbenzylamino or isopropenylbenzylamino-1 -butanesulfonic acid 1 -vinylbenzylamino or isopropenylbenzylamino-2-propanesulfonic acid, either of which optionally has a N-methyl group 3-vinylbenzylamino or isopropenylbenzylamino-2-pentanesulfonic acid 4-vinylbenzylamino or isopropenylbenzylamino-2-methyl-3-pentanesulfonic acid 5-vinylbenzylamino or isopropenylbenzamino-1 -pentanesulfonic acid 10-vinylbenzylamino or isopropenylbenzylamino-1 -decanesulfonic acid 2-(N-dodecyl or octadecyl-N-vinylbenzyl or isopropenyl)-amino-1 -propanesulfonic acid N-(vinylbenzyl)octanilic acid N-(isopropenylbenzyl)octanilic acid N-(vinylbenzyi)metanilic acid N-(isopropenylbenzyl)metanilic acid N-(vinylbenzyl)sulfanilic acid and N-(isopropenylbenzyl)sulfanilic acid Since a polymerisable a"l3-unsaturation bond is included in the amino acid compound, it may participate directly in the copolymerisation reaction. Further, this compound can exhibit variegated surface activities and electrochemical characteristics, depending on the ambient conditions, owing to its amphoteric nature. This is especially true in an aqueous medium. Therefore, in the copolymerisation of s 3-ethylenically-unsaturated monomers and cross-linking monomers in an aqueous medium, this compound may act as emulsifier or dispersing agent giving, by emulsion polymerisation, a soap-free emulsion containing microparticles of cross-linked copolymer.

In carrying out the emulsion polymerisation, the amino acid compound may be present in the reaction system in an amount of 0.2 to 30, preferably 0.5 to 1 5, % by weight of the total monomers.

The desired dispersion stability is difficult to obtain at lower levels than 0.2% by weight; too large a quantity, though being not harmful to the reaction per se, may adversely affect film performance. As to the amount of cross-linking monomer used and polymerisation details, there are no critical differences between this case and those described above. The particle size may be 0.08 to 0.2 ,u. The particles can be maintained in stable dispersion in the coating composition.

Though emulsion polymerisation is particularly preferred, the microparticles may also be prepared by suspension or mass polymerisation, using a suitable initiator, and pulverising the product by mechanical means, e.g. crushing or grinding, or by using the NAD method described above.

In the present invention, the microparticles are added to film-forming polymer, organic liquid diluent and cross-linking agent, to give a high solids coating composition. The ratio of these four components may be varied over a wide range, depending on the application and the desired effect. In general, 50 to 99.5 parts by weight of the film-forming polymer (in terms of solids content) are mixed with 50 to 0.5 parts by weight of the microparticles. The amount of cross-linking agent, is in general, 5 to 100 parts by weight per 100 parts of the aggregate weight of the film-forming polymer and the microparticles (i.e. polymeric components), and the amount of organic liquid diluent is preferably 10 to 2000 parts by weight per 100 parts of the aggregate weight of polymeric components and the crosslinking agent (i.e. solid matter).

If desired, coating compositions of this invention may additionally contain conventional additives such as antioxidants, UV-absorbers, surface modifiers, viscosity modifiers, pigments and metal powder or flakes. The compositions may be prepared using conventional techniques and apparatus.

The novel coating compositions possess adequate fluidity for spray coating, and can provide thick coatings without sagging. The coatings can be of high gloss and excellent film-performance. Since the compositions contain neither low molecular weight emulsifying agents nor graft polymer dispersing agents, the coatings may comprise only resinous material, integrally cross-linked and hardened, formed from the microparticles, film-forming polymer and cross-linking agent, they can be useful as decorative coatings for automobile bodies and other articles. When the microparticles are made using amino acid compounds, the composition may additionally have good low temperature curing characteristics.

The following Examples illustrate the invention; unless otherwise stated, parts and % are by weight.

Reference Example 1 (a) Preparation of polyester resin having an ampho-ionic group Into a 2 litre flask fitted with stirrer, nitrogen inlet pipe, thermo-regulator, condenser and decanter, were placed 1 34 parts bishydroxyethyltaurine, 130 parts neopentyl glycol, 236 parts azelaic acid, 1 86 parts phthalic anhydride and 27 parts xylene. The mixture was heated, while removing the formed water azeotropicaily with xylene. The temperature was raised to 1 900C over about 2 hours from the commencement of reflux, and stirring and dehydration were continued until the acid value reached to 145. The reaction mixture was then allowed to cool to 1 400C. At that temperature, 314 parts of Cardura E-1 0 (glycidyl versatate, manufactured by Shell Chem. Co.) were added dropwise over 30 minutes. After continuing stirring for 2 hours, the reaction was over. The thus-obtained polyester resin had acid value 59, hydroxyl number 90 and number-average molecular weight 1054.

(b) Preparation of polymer microparticles Into a 1 litre reaction vessel fitted with stirrer, condenser and thermo-regulator, were placed 282 parts deionised water, 10 parts of the polyester resin obtained in paragraph (a) and 0.75 part dimethylethanolamine. The mixture was heated, while stirring, to 800C, to give a clear solution. 4.5 parts azobiscyanovaleric acid dissolved in a combined solution of 45 parts deionised water and 4.3 parts dimethylethanolamine were added and then, dropwise, a mixture of 70.7 parts methyl methacrylate, 94.2 parts n-butyl acrylate, 70.7 parts styrene, 30 parts 2-hydroxyethyl acrylate and 4.5 parts ethylene glycol dimethacrylate, over 60 minutes. 1.5 parts extra azobiscyanovaleric acid dissolved in a combined solution of 1 5 parts deionised water and 1.4 parts dimethylethanolamine were then added and the mixture was stirred at 800C for 60 minutes to obtain an emulsion having solids content 45%, pH 7.2, viscosity 92 cps (250C) and particle diameter 0.156 . Polymer microparticles were obtained by subjecting this emulsion to spray-drying.

Reference Example 2 (a) Preparation of modified epoxy resin having an ampho-ionic group Into a similar reaction vessel as used in Reference Example 1 , were placed 73.5 parts taurine sodium salt, 100 parts ethylene glycol and 200 parts ethylene glycol monomethyl ether. The mixture was stirred and heated to 1200 C, to obtain a clear solution. A mixture of 470 parts Epon 1001 (bisphenol A diglycidyl ether-type epoxy resin, epoxy equivalent 470, manufactured by Shell Chem. Co.) and 400 parts ethylene glycol monomethyl ether was added dropwise over 2 hours, and stirring and heating were continued for 20 hours to complete the reaction. After purifying and drying, 518 parts of modified epoxy resin were obtained, acid value 49.4 and sulfur content (fluorescent X ray analysis) 2.8%.

(b) Preparation of polymer microparticles Into a stainless steel vessel were placed 200 parts deionised water and 0.2 parts triethylamine.

While stirring with a mixer, 5 parts of the modified epoxy resin obtained in paragraph (a) were added.

The mixture was heated to 700C and stirred for 10 minutes to obtain a slightly turbid aqueous solution.

This solution was placed in a similar reaction vessel as used in Reference Example 1; 106 parts deionised water were added and the temperature was raised to 800 C. A mixed solution of 4.5 parts of azobiscyanovaleric acid, 4.9 parts triethylamine and 45 parts deionised water was added and, while maintaining the same temperature, a mixture of 1 50 parts methyl acrylate, 142 parts n-butyl acrylate, 1.8 parts glycidyi methacrylate and 1.2 parts methacrylic acid was added dropwise over 1 20 minutes.

A solution of 1.5 parts azobiscyanovaleric acid, 1.6 parts triethylamine and 1 5 parts deionised water was then added, while keeping the same temperature, and the whole was stirred for 60 minutes to obtain an emulsion having solids content 45%, pH 7.2, viscosity 69 cps (250C) and particle diameter 0.172,u. Polymer microparticles were obtained by subjecting the emulsion to spray-drying.

Reference Example 3 Preparation of acrylic resin varnish Into a vessel fitted with stirrer, thermo-regulator and reflux condenser, were placed 710 parts toluene and 200 parts n-butanol. 200 parts of the following mixture: methacrylic acid 12 parts styrene 264 parts methyl methacrylate 264 parts n-butyl acrylate 360 parts 2-hydroxyethyl acrylate 100 parts azobisisobutylonitrile 10 parts were added, and the contents were stirred and heated. While refluxing, the remaining 810 parts of the mixture were added dropwise over 2 hours, followed by a solution of 3 parts azobisisobutylonitrile in 100 parts of toluene over 30 minutes. The reaction mixture was further stirred and refluxed for 2 hours to complete the reaction, thereby obtaining an acrylic resin varnish having a solids content of 50%.

Reference Example 4 Preparation of alkyd resin varnish Into a reaction vessel fitted with stirrer, thermo-regulator and decanter, were placed the following: dehydrated castor oil 260 parts coconut oil 192 parts trimethylolpropane 403 parts diethylene glycol 65 parts phthalic anhydride 578 parts xylene 45 parts The mixture was stirred and heated, while removing the formed water azeotropically with xylene. When the acid value and hydroxyl number reached 10 and 100, respectively, the reaction was stopped, and the product was diluted with xylene to obtain an alkyd resin varnish having solids content 70% and Gardner viscosity Z.

Reference Example 5 Preparation of polyester resin varnish Into a reaction vessel fitted with stirrer, thermo-regulator and decanter, were placed the following: ethylene glycol 39 parts neopentyl glycol 130 parts azelaic acid 236 parts phthalic anhydride 186 parts xylene 30 parts The mixture was stirred and heated. While removing the formed water azeotropically with xylene, the heating was continued until the acid value reached 1 50. At this point, the mixture was allowed to cool to 1 400C; 314 parts of Cardura E.10 (epoxy resin manufactured by Shell Chem. Co.) were added and stirring continued foc 2 hours.The thus-obtained resin had acid value 9, hydroxyl number 90 and number-average molecular weight 1 050. This was diluted with xylene to obtain a polyester resin varnish having solids content 60% and Gardner viscosity Y.

Example 1 25 parts polymer microparticles of Reference Example 1, 500 parts acrylic resin varnish of Reference Example 3 and 65 parts n-butanol-modified melamine resin were mixed, using a laboratory mixer, in a stainless steel vessel. The mixture was diluted with xylene:ethylene glycol monobutyl ether (1:1) to give a coating composition having a Ford Cup No. 4 viscosity of 25 seconds and a non-volatile (solids) content of 39.6%.

Example 2 The procedure of Example 1 was followed, the solids comprising 5 parts polymer microparticles of Reference Example 2, 13 parts aluminium paste (comprising 64% aluminium flakes,) % stearic acid and 35% mineral spirit) and 200 parts acrylic resin varnish of Reference Example 3. The viscosity was 20 seconds.

Example 3 A coating composition was prepared from 30 parts polymer microparticles of Reference Example 1,200 parts white paste prepared from equal weights alkyd resin varnish of Reference Example 4 and rutile titanium dioxide stirred with a paint conditioner, 35 parts hexamethoxymethyl melamine and 0.1 part p-toluenesulfonic acid. On dilution as in Example 1, the viscosity was 25 seconds. A coating 48 y in dry thickness was obtained by spraying the composition by conventional means (constant speed and interval) and baking at 1 400C for 30 minutes.

Example 4 A coating composition was prepared from 7 parts polymer microparticles of Reference Example 1, 1 90 parts white paste prepared from 100 parts polyester resin varnish of Reference Example 5 and 90 parts rutile titanium dioxide stirred together using a paint conditioner, and 5 parts hexamethylenediisocyanate trimer. A white coating composition was obtained by mixing, with a laboratory mixer, at ambient temperature for 30 minutes, and dilution with 1:1 xylene:butyl acetate (viscosity 25 seconds).

The composition was applied by spraying, followed by drying at 800C for 30 minutes.

Comparative Examples 1 to 4 The procedures of Examples 1 to 4 were followed, except that the polymer microparticles were omitted. In the first two cases, sagging characteristics after spraying were considerably worse than for Examples 1 and 2 while, in the second and fourth cases, the pinhole characteristics and (in the second case) metal orientation were lower than for Examples 2 and 4, respectively. Comparative Example 3 gave a coating of 34 L dry thickness and, in Comparative Example 4, the coating was much thinner than for Example 4.

Reference Example 6 Preparation of polyester resin having both ampho-ionic group and polymerisable a"B- unsaturation Into a 2 litre flask equipped with stirrer, nitrogen inlet tube, thermo-regulator, condenser and decanter, were placed 21 3 parts bishydroxyethyltaurine, 236 parts 1,6-hexanediol, 296 parts phthalic anhydride, 376 parts azelaic acid and 44 parts xylene. The mixture was heated, while removing the formed water azeotropically with xylene. The temperature reached 21 00C about 3 hours from the commencement of reflux, and the reaction was continued under stirring and dehydration until the acid value reached 125. After cooling to 1 400C, 250 parts Cardura E-10 (glycidyl ester of versatic acid, made by Shell Chem. Co.) were added dropwise at that tempurature over 30 minutes, and stirring was then continued for about 2 hours. The reaction mixture was then cooled to 800C. 0.05 part hydroquinone monomethyl ether, 140 parts xylene, 1 70 parts glycidyl methacrylate and 7.5 parts triethylamine were added and reacted at 900C for 3 hours. The thus-obtained resin had acid value 53, hydroxyl number 73, number-average molecular weight 1110 and sulfur value 21.9.

Reference Example 7 Preparation of polymer microparticles Into a reaction vessel equipped with stirrer, condenser and thermo-regulator, were placed 25 parts polyester resin obtained in Reference Example 6, 1.7 parts dimethylethanolamine and 508 parts deionised water. The mixture was heated, with stirring, to 800C. 90 parts of the following initiator solution were added and, immediately thereafter, the following monomer was added dropwise over 60 minutes: Initiator solution azobiscyanovaleric acid 10 parts deionised water 100 parts dimethylethanolamine 10 parts Monomer mixture methyl methacrylate 125 parts n-butyl acrylate 165 parts styrene 125 parts 2-hydroxyethyl acrylate 50 parts ethylene glycol dimethacrylate 10 parts The remaining 30 parts of the initiator solution were then added and stirring was continued for an additional 30 minutes.The thus-obtained emulsion contained a microgel-dispersed phase and an average diameter (measured by transmission-type electron microscope) of 0.083 y. The emulsion was then spray-dried to obtain polymer microparticles.

Reference Example 8 Preparation of polymer microparticles In the same reaction vessel as used in Reference Example 7, 100 parts polyester resin obtained in Reference Example 6, 6.8 parts dimethylethanolamine and 503 parts deionised water were placed. The mixture was heated, while stirring, to 800 C. 72 parts of the following initiator solution were added and, immediateiy thereafter, the following monomer mixture was added dropwise over 2 hours:: Initiator solution azobiscyanovaleric acid 8 parts deionised water 80 parts dimethylethanolamine 8 parts Monomer mixture methyl methacrylate 80 parts n-butyl acrylate 130 parts styrene 80 parts 2-hydroxyethyl acrylate 50 parts glycidyl methacrylate 1 8.5 parts methacrylic acid 11.5 parts The remaining 24 parts of the initiator solution were then added and stirring was continued for a further 30 minutes. The thus-obtained emulsion contained a microgel dispersed phase and an average diameter of 0.042 y. The emulsion was then spray-dried to obtain polymer micro-particles.

Examples 5 to 8 and comparative examples 5 to 8 The procedures of Examples 1 to 4 and Comparative Examples 1 to 4 were repeated, except that the polymer microparticles of Reference Examples 7 and 8 were used instead of those of Reference Examples 1 and 2. Before dilution, the microparticles used in Example 5 remained dispersed, without sedimentation, after 72 hours. The viscosities of the coating compositions of Examples 5 to 8 were 25, 20, 25 and 25 seconds. The solids contents of Example 5 and Comparative Example 5 were 42.3% and 37.6%, respectively. The thickness of the films obtained in Example 7 and Comparative Example 7 were 47 y and 34,u, respectively. The same improvements in the Examples 5 to 8 over Comparative Examples 5 to 8 were observed as for those of Examples 1 to 4 over Comparative Examples 1 to 4, respectively.

Reference Example 9 Preparation of microgel Into a reaction vessel equipped with stirrer and thermo-regulator, were placed 21 6 parts deionised water. While maintaining the temperature at 80 C and stirring, a mixture of 4.5 parts azobiscyanovaleric acid, 4.28 parts dimethylethanolamine and 45 parts deionised water was added. At the same temperature, a first solution of 6 parts N-methyl-N-(vinylbenzyl)taurine, 2.1 parts dimethylethanolamine, 6 parts 2-hydroxyethyl acrylate and 90 parts deionised water and a second solution of 77.4 parts methyl methacrylate, 103.2 parts n-butyl acrylate, 77.4 parts styrene, 24 parts 2-hydroxyethyl acrylate and 6 parts tetraethylene glycol dimethacrylate were simultaneously added over 60 minutes.After the addition, a mixture of 1.5 parts azobiscyanovaleric acid, 1.42 parts dimethylethanolamine and 1.5 parts deionised water was added. The system was stirred for an additional 60 minutes, to obtain an emulsion having solids content 45%, pH 7.8, viscosity 68 cps (250C) and an average particle size 0.148 4. This emulsion had no coagulates and excellent mechanical stability. The molecular weight of the polymer constituting the emulsion was so high that it could not be dissolved in tetrahydrofuran, and could not be determined by gel permeation chromatography. This emulsion was spray-dried to obtain polymer microparticles.

Reference Example 10 Preparation of microgel Repeating the procedure of Reference Example 9, but substituting 3.7 parts glycidyl methacrylate and 2.3 parts methacrylic acid for tetraethylene glycol dimethacrylate, an emulsion was obtained having solids content 45%, pH 7.2 and mean particle diameter 0.13 y. The tetrahydrofuran-insoluble matter of the polymer constituting the emulsion was 78%. The emulsion was then spray-dried, to obtain microparticles.

Examples 9 to 12 and comparative examples 9 to 12 The procedures of Examples 1 to 4 and Comparative Examples 1 to 4 were repeated, except that the polymer microparticles of Reference Examples 9 and 1 0 were used instead of those of Reference Examples 1 and 2. The viscosities of the coating compositions of Examples 9 to 12 were 25, 20, 25 and 25 seconds. The solids contents of Example 9 and Comparative Example 9 were 41.7% and 37.6%, respectively. Thy thickness of the films obtained in Example 11 and Comparative Example 11 were 45 ,u and 34 4, respectively. The same improvements in the Examples 9 to 12 over Comparative Examples 9 to 12 were observed as for those of Examples 1 to 4 over Comparative Examples 1 to 4, respectively.

Claims (7)

Claims

1. A coating composition which comprises a cross-linkable film-forming polymer in, a crosslinking agent dissolved in, and insoluble cross-linked copolymer particles dispersed in, a volatile organic liquid diluent, in which the copolymer is of a,-ethylenically-unsaturated monomers and carries a resinous portion including an ampho-ionic group of the formula -N-R-Y wherein R is optionally substituted phenylene or Cm~,2 alkylene and Y is COOH or SO3H.

2. A composition according to claim 1, in which the resinous portion is mechanically bound to the copolymer.

3. A composition according to claim 1, in which the resinous portion is integrally incorporated in the copolymer.

4. A composition according to claim 1, in which the resinous portion is covalently bound to the copolymer.

5. A composition according to claim 3, in which the resinous portion is pendant to the copolymer.

6. A composition according to claim 5, in which the copolymer particles are prepared by copolymerising ,-ethylenically-unsaturated monomers, in which one of the monomers includes groups of the formula

wherein R and Y are as defined in claim 1, R, is a substituent including an a,-ethylenicaily- unsaturated group, and R2 is hydrogen or optionally substituted C,~30 hydrocarbyl, and in which another of the monomers is a cross-linker.

7. A composition according to any preceding claim, in which the particles have an average diameter of from 0.02 to 40 y.