CA1126103A - Coating process - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Improved application characteristics of spray-applied coatings, particularly for automobile bodies, are obtained when the composition applied comprises (A) a film-forming polyester or alkyd resin, (B) a volatile liquid solvent for the resin and (C) polymer microparticles which are stably dispersed in the solution of the resin in the solvent. Improvements observed include increased resistance to "sagging" and better metal control when the compositions contain metallic flake pigments.

Description

This invention rela`tes to a process for the production of protective and decorative coatings upon surfaces, particularly the surfaces of automo~ile bodies.
It is well known to formulate coating compositions, especially those for use in the automobile industry, upon polyester resins. Such resins may be of the air-drying alkyd type, containing autoxidisable groupings derived from natural drying oil 57 in which case curing of the resin to form a film occurs by the action of atmospheric oxygen~
Alternatively, they may contain no autoxidisable qroupings but instead rely for curing upon the reaction of residual hydroxyl or carboxyt groups present with a cross-linking agent such as an amino resin, effected in a curing step su~sequent to the application of the coating composition to the substrate. A combination of both curing mechanisms is frequently utilisedO These po~yester-based compositions, however, give rise to certain difficulties, especially under the conditions of spray application as normally used in the painting of car bodies. In those cases where such a composition is employed for the final finishing of the car body, the need to achieve good flow-out of the coating after application, in order to maximise gloss, may require the incorporation of ~ilm-forming components of very low molecular weightf these, however, tend to cause excessive flow o the composition during the spraying operation, with the occurrence of "sagging"7 In other cases, where a polyester-based composition is used as a pigmented basecoat, especially one containing

- 2 -.
.

3~21E~3 metallic flake pigment, upon which an unpigmented topcoat is subsequently applied by the conventional wet-on-wet procedure, there is a prime requirement that the application of the topcoat shall not soften the basecoat and hence disrupt the control of orientation o the metallic flake (whereby a "glamour metallic" or "flip" effect is achieved).
To meet this reguirement, film-forming material of high molecular weight is needed, but it is often difficult to select appropriate polyester formulations which will enable high molecular weights to be obtained without accompanying problems of high viscosity or a risk of gelation during manufacture.
It has now been found that an improvement in the spray application properties of a coating composition based on a polyester resin can be achieved by incorporating in the composition a proportion of polymer microparticles of specified type.
According to the present invention there is :-provided a process for the production of a surface coating upon a substrate which comprises applying by spray to the substrate surface a composition comprising (A) a film-forming :
polyestsr resin as hereinafter defined; (B) a volatile organic liquid diluent in which the polyester resin (A) is dissolved;
(C) polymer microparticles as hereinafter defined, in an amount of at least 3% of the aggregate weight of the resin (A) and the microparticles, which are insoluble in and stably dispersed in the solution of the polyester resin (A) in the diluent (B) 9 and subsequently evaporating the volatile diluent to form a polymer film upon the surface.

,~

_ 3 _ .

- . . ., : ~--., :: :

.
- .

By the term ~'film-forming polyester resin" we mean any of those resin~ which are known in the art for use in surface coating compositions and which are essentially the products of condensation of polyhydric alcohols and polycarboxylic acids. We include in this term the alkyd resins which are obtained from such starting materials with the addition of constituents supplying residues of fatty acids derived from natural drying oils, or semi-drying oils, or even oils having no air-drying capabilities. We also include polyester resins not incorporating any natural oil residuesO All these resins normally contain a proportion o~
free hydroxyl and/or carboxyl groups which are available for reaction with suitable cross-linking agents, ~hich are discussed in more detail below. Where a cross-lin~ing agent is employed, this is, for the purposes of the foregoing de~inition of the invention, considered to be a part of the film-forming constituent (A~.
Suitable;polyhydric alcohols for the production of polyester resins include ethylene glycol, propylene glycol, butylene glycol, 1:6-hexylene glycol, neopentyl glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, glycerol, trimethylolpropane, trimethylolethane, pentaeryth-ritol, dipentaerythritol, tripentaerythritol, hexane triol, oligomers of styrene and allyl alcohol (for example that sold by Monsanto Chemical Company under the designation RJ 100) and the condensation products of trimethylolpropane with ethylene oxide or propylene oxide ~such as the produ~ts known commercially as "Niax" triols). Suitable polycarboxy~ic acids * Trade Mark ~ B ~ :
., . . ~ . ~ . ` , . . . ~ .

. . . .... . .

include succinic acid (or its anhydride), adipic acid, azelaic acid, sebacic acid, maleic acid (or its anhydride), fumaric acid, muconic acid, itaconic acid, phthalic acid (or its anhydride), isophthalic acid, terephthalic acid, trimellitic acid (or its anhydride) and pyromellitic acid (or its anhydride). Where it is desired to produce air-drying alkyd resins, suitable drying oil fatty acids which may be used include those derived from iinseed oil, soya bean oil, tall oil, dehydrated castor oil, fish olls or tung oi?. Other oil fatty acids, of semi-drying or non-drying types, which may be used include those derived from sa~flower oil, sunflower oil and cottonseed oil~ Normally it is preferred that the oil length of such an alkyd resin should not exceed 50%.
Monofunctional saturated carboxyl acids may also be incorporated in order to confer plasticity on the polyester. Such acids may be, for example, C4 - C20 saturated aliphatic acids benzoic acid, p-tertbutyl benzoic acid and abietic acld; these may, in fact, be the only fatty acids present, in those cases where the poly-ester resin is to be cured by subsequent reaction of residual hydroxyl or carboxyl groups with a cross-linking agent. In addition, monofunctional hydroxy compounds may be incorporated in order to control the chain length of the polyester or to confer certain desirable compatibility properties upon it; suitable monohydroxy compounds include benzylalcohol, cyclohexyl alcohol, saturated or unsaturated fatty alcohols and condensation products of ethylene oxide or propylene oxide with monofunctional alcohols (e.g. the methoxy-polyethylene glycol obtained by reaction of ethylene oxide with methanol).
Suitable film-forming polyester resins also include . ~ ; :
:: : : : : : - :
~: ` : : ;

~Z6;1~

'lmodified" alkyd resins, for example styrenated or methacrylated alkyds, urethane alkyds and epoxy alkyds.
The volatile organic liquid constituent (B) o~ the composition used in the process may be any of the liquids, or mixtures of liquids, which are conventionally used as polymer solvents in coating compositions, for example aromatic hydrocarbons such as toluene and 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 actual liquid or mixture of liquids selected as the diluent (B) will depend upon the nature of the polyester resin (A~, according ~o principles which are well ~nown in the coatings art, in order that the resin shall be soluble in the diluent.
The polymer microparticles (C) present in the composition used according to the invention are polymer particles of colloidal dimensions, having a diameter of from 0.01 - 10 microns, which are insoluble in the solution of the polyester resin (A) in the diluent (B) and which are stably dispersed therein (in the sense that they do not undergo flocculation or aggregation) whilst dispersed in that medium.
The insolubility of the microparticles may be achieved by suitable selection of the composition of the microparticle polymer, that is to say, the polymer may be one which is inherently insoluble in that solution, but preferably it is achieved by introducing a su~ficient degree of cross-linking into a polymer which, if not cross-linkec3, would actually be .

: : :

soluble in the solution of the polyester resin (A) in the diluent (B). Where insolubility of the microparticles is achieved through cross-linking, it is preferred that the degree of cross-linking should not be greater than that 5 necessary to render the polymer insoluble. Insolubility of the microparticles in the solution of polyes~er resin (A) in diluent (B) may be checked by means of the following test.
The microparticles (1 part by weight) are shaken for 30 minutes with the diluent (B) ~100 parts by weight); the suspension is then centrifuged at 17,000 r p.m. for 30 minutes. ~
The supernatant liquid is decanted off and the residual polymer ~-then dried for 30 minutes at 150C, after which its weight is compared with that of the microparticles originally taken.
This test may be difficult to apply where the specific gravity of the diluent is close to or greater than that of the micro-particles, but such diluents ~e5g. chlorinated solvents) would not normally be used in the compositions under consideration.
Where the result of this test indicates that the microparticles are acceptably insoluble in the diluent (B) alone9 it can be assumed that the particles will be at least equally insoluble when the polyester resin tA) is a~so present in solution in the diluent; there would be practical dificulties in carrying out the test actually in a solution of polyester resin (A) in diluent (B).
The microparticulate polymer may be of various types~
It may, for example, be an addition polymer, derived from one or more ethylenically unsaturated monomers; in particular, it may be a polymer or copolymer of one or more alkyl esters of :
:

acrylic acid or methacrylic acid, optionally together with other monomers such as vinyl acetate, acrylonitrile, styrene, acrylic acid or methacrylic acid. Suitable acrylic and methacrylic esters include methyl methacrylate, ethyl metha-crylate, propyl methacrylate, butyl methacrylate9 ethylacrylate, butyl acrylate and 2-ethylnexyl acrylate. Where it is desired that such a polymer should be cross-linked, this may be achieved by either of two general methods : firstly, by including in the monomers from which the polymer is derived a minor proportion of a monomer which is polyfunctional with respect to the polymerisation reaction, e.g. ethylene glycol dimethacrylate or divinylbenzene; or secondly, by including in those monomers minor proportions of two othe~ monomers carrying pairs of chemical groupings which can be caused to react with one another either during or after the polymerisation reaction, such as epoxy and carboxyl (e.g. glycidyl methacrylate and methacrylic acid)~ anhydride and hydroxyl or isocyanate and hydroxyl. Alternatively, the microparticles may be composed of a condensation polymer, for example a polyester prepared 2 from any of the polyhydric alcohols and polycarboxylic acids described above. Again, such polymers may be cross-linked if desired, by the incorporation of materials of functionality greater than two, in the starting composition, although in this case, because of the characteristically broad distribution of molecular species formed in a condensation polymerisation, it may be difficult to ensure that all those species are in fact cross-linked. ~
The chemical compositions and degree of cross-linking .

- , . : . : ~ : : .:

of the microparticulate polymer may be such that it has a Tg (glass-rubber transition temperature) below room temperature~ in which case the microparticles will be rubbery in nature; alternatively it may be such that the Tg is above room temperature9 that is to say the particles will be hard and glassy.
As already stated9 it is necessary that the polymer microparticles be stably dispersed in the solution of the polyester resin in the liquid diluent. By "stably dispersed"
is meant that the particles are prevented from flocculating or aggregating by means of a steric barrier around the particles, of polymer chains which are solvated by the said solution and hence are in a chain-extended configuration. In this context the term "solvated" implies that the polymer chains in question, if they were independent molecules, would be actually soluble in the polyester resin solution; however, because the chains are in fact attached to the microparticles at one or more points along thelr length, the steric barrier remains permanently attached to the particles. It will be understood that the stabilising polymer chains to be used in any particular instance will be selected with reference to the nature of the liquid diluent and film-forming polyester resin concerned. In general terms this means that the chains will be of a degree of polarity similar to that of the dlluent and film~forming resin, so that the combination of the latter will be inherently a solvent for the polymer of which the chains are composed. Since, in the automobile finishes to which the present invention is primarily directed, ~/
_ 9 _ :. . - , . .. .
:., ~ .

.
.....
. . : -. . .:~

the liquid diluent will conventionally be of a relatively high degree of polarity ~containing, for example, a substantial proportion of "strong" ester and ketone solvents) it follows that the stabilising chains on the microparticles will usually require to be o~ a composition such that they are inherently soluble in that ty~e of liquid.
The mode of anchoring of the stabilisinq chains to the microparticles is conveniently discussed in connection with methods of making the particles, as ~ollows.
The polymer microparticles may be produced in a variety of ways. Preferably they are produced by the dispersion polymerisation of monomers, in an organic liquid in which the resulting polymer is insoluble~ in the presence of a steric stabiliser for the particles. Suitable processes of dispersion polymerisation are well-known and extensively described in the literature. Thus, so far as the dispersion polymerisation of ethylenically unsaturated monomers such as acrylic or methacrylic acid esters, vinyl esters and styrene or its derivatives are concerned, the procedure is basically one of polymerising the monomers in an inert liquid in which the monomers are soluble but the resulting polymer is not soluble, in the presence dissolved in the liquid of an amphipathic stabilising agent or of a polymeric precursor which, by copolymerisation or graftin~ with a portion of the monomers, can give rise in situ to such a stabilising agent.
Reerence may be made, for example, to British Patent Speciications Nos. 941,305; 1,052,Z41; 1,122,397 and 1,231,614 for a general description of the principles involved, as well ., .
- 10 -~

~ , as to "Dispersion Polymerisation in Oryanic Media~ ed~
K.E.J. Barrett (John Wiley and Sons, 1975). Suitable ethylen-ically unsaturated monomers include methyl methacrylate, ethyl methacrylate, butyl methacrylate~ ethyl acrylate, butyl acrylate, 2-hydroxyethyl acrylate, vinyl acetate, vinyl propionate, styrene and vinyl toluene. The production specifically of dispersions of cross-linked addition polymer particles can be achieved by including, in the monomers selected, pairs of monomers containing (in addition to the polymerisable unsaturated groups~ groups capable o~ entering into chemical reaction with each other; for example, the epoxide and carboxyl groups contained in glycidyl methacrylate and methacrylic acid. By following the procedures particularly described in British Patent Specifications Nos.
1,095,288 and 1,156,012, for example, particles are obtained in which there are present such complementary groups which, although not at that stage co-reacted, can be caused to co-react and so ~orm cross-links by subsequently heating the dispersion to a suitably elevated temperature~ Cross-linked addition polymers may also be prepared in dispersion by including in the monomers undergoing dispersion polymerisation a minor proportion of a monomer which is difunctional with respect to the polymerisation reaction, such as ethyleneglycol dimethacrylate or divinylbenzene.
O~ the unsaturated monomers mentioned above, methyl methacrylate is an appropriate choice where it is desired that the polymer microparticles should have a high Tg value. Where the microparticles are required to be of low Tg, ethyl acrylate , . , : - . .
- : ~

-or vinyl acetate may be used, but it may be a more convenient alternative to copolymerise methyl methacrylate with minor proportions of '7softeninq" monomers such as butyl acrylate or butyl methacrylate. The proportions used of such softening monomers may, however, need to be limited; otherwise there is a risk that the resulting copolymer may be too soluble, even in low-polarity hydrocarbon diluents, for stable dispersion of microparticles to be obtained. With butyl acrylate as the softening monomer, for example, a proportion of 15% by weight of the total monomers should not be exceeded.
Certain other softening monomers such as 2-ethoxyethyl acrylate or 2-ethoxyethyl methacrylate, may be used in greater proportions than this if desired, but these monomers are not as readily accessible as the corresponding lower alkyl esters~
Small proportions of comonomers incorporating carboxyl- groups, e.g. acrylic acid or methacrylic acid may be included ~where the microparticles are to be cross-linked, such proportions would be in excess of those used in order to achieve cross-llnking by reaction with a co-reactive monomer such as glycidyl methacrylate). Conversely, small (additional) proportions of an epoxide monomer, e.g. glycidyl methacrylate, may be included.
Other functional monomers, such as hydroxyethyl acrylate or acrylamide, may also be included in minor proportions in ~he monomers from which the microparticles are to be derived.
The production of dispersions of condensation polymers is described, for example, in British Patent Specifications Nos~ 1,373,531; 1,403,794 and 1,419,1g9 and methods of obtaining cross-linked polymer particles are ~! included in these descriptions. The general principles ;. ; . . . .
:
- .:, , :, : : : ~ : ; -Z~ 3 involved here are the same as those referred to above in connection with addition polymer dispersions, but there is a difference of detail arising from the commonly more highly polar nature of the monomers or starting materials from which condensation polymers are derived. This is, namely, that the monomers in question are usually insoluble in the inert liquid in which the polymerisation is to be carried out~
Accordingly the first step in the dispersion polymerisation of the monomers is to bring them into a state of colloidal 10 dispersion in the inert liquid, either as liquid or as solid particles. In the second step, polymerisation of the monomers takes place within those same particles. An amphipathic stabilising agent is required in each stage, firstly in order to stabilise the particles of monomer and ~5 secondly in order to stabilise the particles of polymer formed, but in suitable cases a single sta~ilising aqent can be ~ found which will perform both these functions. In place of ; using a preformed amphipathic stabilisin~ agent in this process, there may be employed instead a suitable polymeric precursor which, by copolymerisation or grafting with a portion of the monomers being polymerised, can give rise to such a stabilising agent in_situ. Reference may be made in this connéction to our Canadia~ Patent Serial ~o. 1079884, published ~une 17, 1980 Suitable monomeric starting materials for preparing condensation polymer microparticles are those which are well known for use in making such polymers by melt or solution polymerisation techniques~ For example, suitable materials in the case o~ polyester microparticles are the polyhydric alcohols and polycarboxylic acids mentioned above in connection B ~ ~

.

.~ ~ : ~ :, ., 6~S~3 with the fil~-forming polyester resin (A). In the case of polyamide microparticles, suitable monomeric starting makerials are amino-acids, such as 6-aminocaproic acid or 11-amino-undecanoic acid, or the corresponding lactams, and/or polyamines, such as ethyl~ne diamine, propylene diamine, hexamethylene diamine, diethylene triamine, triethylene tetramine or tris (aminoethyl) methane, in conjunction with the polycarboxylic acids mentioned above. It will, of course~ be understood that, in the case of both polyester and polyamide microparticles, the mixture to be polymerised must incorporate some proportion of a starting monomer which has a functionality greater than two, where it is desired that the microparticles should be cross-linkedO
In all the above-described dispersion polymerisation processes, the amphipathic steric stabilisin~ agent is a substance the molecule of which contains a polymeric component which is solvatable by the liquid in which the dispersion is made and another component which is relatively non-solvatable by that liquid and is capable of associating with the polymer par~icles producedO Such a stabilising agent will be soluble as a whole in the dispersion liquid, but the resulting solution will usually contain both individual molecules and micellar aggregates of molecules, in equilibrium with each other. The type of stabilising agent preferred for use in the invention is a block or graft copolymer containing in the molecule two types of polymeric component : one type consists, as stated above, of polymer chains which are solvatable by the dispersion liquid and the other type consists of polymer chains of different polarity from the first type which accordingly are , not solvatable by that liquid and are capable of becoming anchored to the polymer microparticles. A particularly useful form of such a stabilising agent is a graft copolymer comprising a polymer backbone, which is the non-solvatable or "anchor~ component, and a plurality of solvatable polymer chains pendant from the backbone. Specific examples of such graft copolymers include those in which the backbone is an acrylic polymer chain, derived predominantly from methyl methacrylate, and the pendant chains are residues of poly (12-hydroxystearic acid~ which are readily solvatable by an aliphatic hydrocarbon medium. These copolymers may be made, for example, by first reacting poly~12-hydroxystearic acid) with glycidyl acryIate or glycidyl methacrylate, whereby the terminal - COOH yroup in the polymeric acid is converted to an ester derivative containing a polymerisable unsaturated grouping, and then copolymerising that derivative with methyl methacrylate, optionally together with minor proportions of other copolymerisable monomers. By employing acrylic acid or methacrylic acid as such minor comonomers, it is possible to introduce carboxyl groups into the backbone chain of the graft copolymer with beneficial results inasmuch as the backbone is thereby rendered more polar than it is if composed of methyl methacrylate units alone. This incraased polarity causes the backbone to be even less solvatable by a non-polar diluent such as an aliphatic hydrocarbon, and in consequence enhances the force whereby it becomes anchored to the microparticle.
Although it is preferred to prepare the polymer microparticles by means of dispersion polymerisation processes . ~ .

. : , . . . . .. .
. .
., , . : ~ -6~3 as just described9 it may be necessary to subject the particles so obtained to a further treatment in order to render them suitable for incorporation in the compositions used according to the invention~ This need may arise in the following way. The most convenient inert liquids in which to carry out dispersion polymerisations are liquids of low polarity, for example aliphatic or aromatic hydrocarbons or mixtures thereof; this is because such liquids are non solvents for the majority of polymers, whether of the addition or of the condensation type, and therefore, give scope for the widest ~
choice of polymer or copolymer compositions according to the :
properties which it is desired the microparticles should possess. From the foregoing discusslon it will, however, be appreciated that steric stabilising agents which are suitable for stabilising the microparticles in a simple low polarity liquid environment may no longer effectively stabilise them when they are transferred to the environment of the solution of the film-forming polyester resin (A) in the liquid diluent (B)~ One relevant factor is that (B) is likely to be a relatively highly polar liquid, where the formulation of automobile finishes is concerned, and another, perhaps more important, factor is that the polyester molecules (A) will now be competing with the chains of the stabilising agent for the solvating action of the diluent. The consequence is that transfer of the microparticles to the new environment will result in their de-stabilisation and flocculation~

~ 16 ?3 It is, therefore, a preferred feature of the invention that microparticles which have been made by a dispersion polymerisation process are further associated with a polymer which is soluble in the volatile organic S liquid constituent (B) of the base-coat composition and is also compatible with the film-forming polyester resin (A).
This further polymer, hereinafter referred to as the "auxiliary" polymer, is essentially non-crosslinked. It is believed that, when microparticles with which it is associated are introduced into the more highly polar environment of the solution of film-forming polyester resin (A) in the organic liquid (B), the chains of the auxiliary polymer now become solvated and take over at least in part from the original amphipathic stabiliser the function of 1~ maintaining the microparticles in a deflocculated, dispersed state. The scope of the present invention is not, however, in any way limited by the extent to which this belief is correct.
The microparticles are most conveniently brought into association w~th the auxiliary polymer by following up the dispersion polymerisation process immediately with the polymerisation of further monomer, from which the auxiliary polymer is to be derived, in the original inert liquid medium and in the presence of the original stabilising agent.
In general, the auxiliary polymer will be required to have a composition such that it is compatible with the film~forming polyester resin (A). The monomer or monomers from which the auxiliary polymer is to be derived will be chosen with this requirement in mind, as will be apparent to those skilled in the art.

- 17 _ : , : ,:: ::

:
, . ~ , . . . .

On introducing the microparticles so treated into the solution of the polyester resin (A) in the liquid (B), part of the auxiliary polymer may be dissolved away by that more polar medium, but it is believed that a substantial portion of the auxiliary polymer chains remainsattached to the microparticles (albeit now solvated by the medium), for example by virtue of their having become entangled with the chains of the microparticle polymer during their formation, or as a result of actual grafting on to those chains. If desired, the stability of the treated microparticles in the more polar medium may be enhanced by ensuring that covalent linkages are developed between the chains of the auxiliary polymer and those of the microparticlès. This may be done, for example, by including an unsaturated carboxylic acid in the monomers from which the auxiliary polymer is derived. The carboxyl groups so introduced are able to react with epoxide groups, present in the microparticle polymer as the result of the use of a slight excess of the latter groups for the purpose of cross-linking that polymer by reaction with carboxyl groups in the manner described above.
The incorporation of the microparticles, macle by dispersion polymerisation, into the coating composition may be effected by blending the dispersion of the microparticles (whether treated with auxiliary polymer or not) with a solution of the film-forming polyester resin (A) in a suitable diluent (B). Another possibility is to separate the micro~
particles from the dispersion in which they are made, for example by centrifuging, filtration or spray-drying, and then L2~3 to blend the microparticles with a solution of a polyester resin (A) in a diluent (B) as before.
~ i~l b~ ~ e-r-st-oo~--f-E~om--t-h~--oreg~1F~g---de-sGr~ t~ n that, for the purposes of the definition of the hereinbefore given, the film-forming con~iXuent ~A) is considered to comprise that ~ ~t- f the auxiliary polymer, if such po ~ ~ ~yed, which is dissolved away from the micro ~ when the latter are incorporated into the As an alternative to the use of dispersion poly~er-isation methods, the polymer microparticles may, for example, be produced by aqueous emulsion polymerisation of suitable unsaturated monomers, using procedures well~known in the art.
The microparticles are then obtained in the form of a charge-stabilised dispersion, from which the particles themselves can be separated, e.g. by spray drying. For incorporation into the coating composition, the microparticles are then re-dispersed in the solution in the diluent of the film-forming polyester resin, preferably by methods imparting high shear to the mixture such as pug milling or triple roll milling, in an analogous fashion to the dispersion of a pigment By further analogy to pigment dispersion, the requisite steric stability of the microparticles may then be achieved simply as a result of an innate tendency of the film-forming polyester resin ~which by definition is solvated by the diluent) to associate with the particles, for example through the interaction of polar groups present in the polyester resin and in the micro-particle respectively. In producing the microparticles by : . . . . : .
., , , . - . .
- . .
, 26~3 aqueous emulsion polymerisation, some difunctional unsaturated compounds may be included in the polymerising monomers in order to give rise to a cross-linked polymer which will be insoluble in the solution of the film-forming polyester resin (A) in the diluent (B), whatever the nature of the latter. Here again 9 as in the case of microparticles made by dispersion polymerisation~ it may be desirable to continue the emulsion polymerisation with a second feed of monomers which does not include any difunctional (iOe. cross-linking) material and which gives rise to a polymer which iscompatible with the solution of polyester resin (A) in diluent (B), in other words to associate with the microparticles an 'auxiliary' polymer having the same function as that previously described.
As has already been stated, the polymer microparticles (C) are present in the compositions used according to the invention in an amount of at least 3% of the aggregate weight of the film-forming polyrner (A~ and of the microparticles.
For the purposes of this definition, the term "polymer microparticles" is to be understood as referring, in the case where auxiliary polymer is employed, to the microparticles proper together with that part of the auxiliary polymer associated therewith which cannot be dissolved away from the particles by the diluent (B), under the conditions of the insolubility test described above. When the compositions are intended for use in the production of f;nishing coats (as distinct from their use as basecoats, mentioned below), the amount of the po]ymer microparticles incorporated is preferably .: . , _ 20 -()3 from 3% to 30% of the aggregate weight of the film-forminy polymer and the microparticles~
The compositions used in the process of the invention may incorporate, in addition to the polyester resin (A)g the diluent (B) and the polymer microparticles ~C), pigments as conventionally used in the coatings art. Such pigments may range in particle size from 1 to 50 m~crons and may be ~
inorganic in nature, for example titanium dioxide, iron oxide, chromium oxide, lead chromate or carbon black, or organic in nature, for example phthalocyanine blue, phthalocyanine green, carbazole violet, anthrapyrimidine yellow, flavanthrone yellow, isoindoline yellow, indanthrone blue, quinacridone violet and ~ i~
perylene red. Of particular interest in the context of the invention are metallic pigrnents consisting of flat flakes of aluminium, copper, tin, nickel or stainless steel, by the use of which there may be obtained the so-called "glamour metallic"
finishes whereby a differential light reflection effect, depending upon the viewing angle, is achieved. Any of the above pigments may be present in the coating compositions in a proportion of from 2% to 50% of the aygregate weight of all the film-forming material present. The term "pigment" is-. _. . , :
here meant to embrace also cpnventional fillers ~ j and extenders, such as talc or kaolin.
Such pigments, whether metallic or otherwise, may be incorporated into the compositions with the ald of knowndispersants, for example an acrylic polymer, which are compatible with the polyester resin (A).

, . . . i ;:

... .

. ~ :
- ' . ~ .

,:

If desired, the compositions may additionally incorporate other known additives, for example viscosity modifiers such as bentone or cellulose acetate butyrate.
As already indicated, there may further be incorporated a cross-llnking agent to effect or assist the curing of the polyester resin ~A). Suitable types of cross-linking agents include diisocyanates, diepoxides and, especially, aminoplast resins, t~at is to say, condensates of formaldehyde with nitrogenous compounds such as urea, melamine, thiourea or benzoguanamine, or the lower alkyl ethers of such condensates in which the alkyl groups contain from 1 to 4 carbon atoms. Particularly suitable are melamine-formaldehyde condensates in which a substantial proportion of the methylol groups are etheriied by reaction with butanol.
The proportion of cross-~inking agent to cross-linkable acrylic or other polymer in the composition may vary widely, but in general a ratio of from 50:50 to 90:10 by weight of polymer to cross-linking agent is satisfactory. The precise proportion to be employed depends upon the properties required in the final ~ilm, but a preferred range afording a good balance of properties is from 60:40 to 85:15 by weight of polymer to cross-linklng agent.
The composition may also incorporate a suitable catalyst for the cross-linking reaction, for example an acid-reacting compound such as acid butyl maleate, acid butylphosphate or p-toluene sulphonic acid. Alternatively, the required catalytlc effect may be provided by carboxyl groups present ln the film-forming polyester resin (A). ~;

!

. , . . . - . . .

`~ ~6:~)3 Following spray application of the coating composition to the substrate surface and evaporation of the volatile liquid diluent so as to form a polymer fiim upon the surface, the polyester resin constituent (A) may then be allowed to cure by atmospneric oxidation, or it may be reacted with a cross-linking agent present, as appropriate.
If desired, the cur;ng process may be assisted by heating the coating, for example to a temperature of up to 160C.
Any of the known spraying procedures may be used for applying the composition, such as compressed air spraying, electrostatic spraying, hot spraying and airless spraying~
and either manual or automatic methods are suitable. Under these conditions of application, coatings of excellent gloss are obtained which possess advantages over the coatings obtained according to the prior art in respect of the reduction of excessive flow on application, particularly at sharp edges or corners of a substrate of complicated shape, or the obliteration of scratch marks in the surface to be coated.
Films of up to 4 mils dry thickness may be applied without any tendency for sagging, or "sheariness" of any metallic pigment present, to occur.
- Alternatively~ the proceSs of the invention may be modified to a two-coat procedure, commonly referred to as a "base-coat/clear-coat" procedure and of special relevance to the productlon of the "glamour metallic" finishes referred to earlier, in which there is first applied to the surface of the substrate a base-coat containing the metallic pigment and formulated to give the maximum "flip" tone effect, and there -- . . : . . . .. :

.
.
. , ~ . . -: , LlZ6~3 is then applied over the base-coat an unpigmented top-coat which yields a high degree of gloss without in a~y way modifying the characteristics of the base-coat. The process according to the invention as hereinbefore defined in which metallic pigment is employed is of special value ~or the production of the base-coat in this type of application procedure.
Thus, according to a further aspect of the invention, there is provided a process for the production of a multilayer coating upon the surface of a substrate, which comprises the steps of : `
(1) applying by spray to the surface a base-coat comprising:-(A) a film-forming polyester resin as hereinbefore defined;
(~) a volatile organic liquid diluent in which the polyester resin (A) is dissolved;
(C) polymer microparticles as hereinbefore defined which are insoluble in and are stably dispersed in the solution of the film-forming polymer in the liquid diluent7 in an amount of at least :
10% of the aggregate weight of the film-forming polymer and the microparticles;
(D) pigment particles also dispersed in the solution of the film-forming polyester resin in the liquid diluent;
(2) forming a polymer filrn upon the surface from the cornposition applied in step (1);

~ y - 24 - :

.
.

: : , : .
.
.. ~ : . ... :

26~3 (3) applying to the base-coat film so obtained a transparent top-coat composition comprising:
(E) a film forming polyrner;
(F) a volatile carrier liquid for the polymer tE);

(4) forming a second polymer film upon the base-coat film from the composition applied in step (3)~

The polyester resins (A), the diluents (B) and the polymer microparticles (C) which are suitable for use in the above process are those previously described herein. The pigment particles (D) may be any of those already described but, as already indicated~ the process is of special relevance to the use of metallic pigments. }t will be noted that a higher maximum proportion of the microparticl s is specified for use in this process~ as compared with the process ; described earlier. This stipulation takes into account the fact that, in a base-coat composition, especially one containing a metallic pigment, a rather higher degree of control of flow of the material during application is required than in a omposition intended for the production of a finishing coat.
Preferably the amount of the microparticles used is from 10%
to 30% of the aggregate weight of the film-forming polymer (A) and the microparticles.
If desired, the base-coat composition may -additionally incorporate other known additives, for example viscosity modifiers such as bentone or cellulose acetate butyrate.

~ 25 -)3 The polymer constituent (E) of the top-coat composition employed in step (3) of the process may in general be any suitable film-forming polymer. Thus, it may be a film-forming polyester resin of any of the types previously described, in which case the top coat composition may additionally contain a cross-linking agent. Alternatively, the polymer (E) may be one of the known acrylic ~ilm-forming polymers, derived predominantly from esters of acrylic or methacrylic acid. Such polymers may be of the thermoplastic type, in which case the step (4) of forming the second polymer film may require no more than evaporation of the volatile carrier liquid; alternatively9 they may be of the thermo-setting type, which require the assistance of a cross-linking agent of similar type to those already descrîbed in connection with the polyester resins, and may also require khe application of heat in step (4). Unlike the polyester resin in the base-coat composition, the polymer (E) in the top-coat composition may be either in solution or in stable dispersion in the volatile carrier liquid (F3 of the composition.
Thus, the carrier liquid (F) may be either a solvent or a non-solvent for the top-coat polymer. Where the liquid is to be a solvent, it may be any of the volatile organic liquids or mixtures thereof previously mentioned as suitable for use in a composition containing the polyester resin. Where the liquid i5 to be a non-solvent, ik will tend to be of rather lower polarity than the former and may consist of one or more aliphatic hydrocarbons such as hexane, heptane or petroleum fractions of low aromatic content, optionally in ;~

--: ,. , . - . - i .

-: :. : :- : .

:: , : : : - : ~ .: : :: . . ~ :
.

6~3 admixture with liquids of high polarity as already referred to~ provided that the total mixture is a non-solvent for the top-coat polymer.
Where the top-coat composition is a polymer dispersion, this will in general be a sterically stabilised dispersion in which the polymer particles are stabilised by means of a block or graft copolymer, one polymeric constituent o which is non-solvatable by that liquid and is associated with the disperse polymer. The well-known principles according to which such dispersions may be prepared have been referred to above in connection with the making of the micro-particles of the base-coat composition.
The top coat composition may in some cases contain both polymer in solution and polymer in dispersion. The soluble polymer may be a preformed polymer of different monomer composition from the dispersed polymer which, unlike the latter, is soluble in the carrier liquid (F) and is added as a solution therein to the dispersion. It may alternatively arise during the formation of the disperse polymer as the result of preferential polymerisation of certain of the monomers present.
Again, it may be polymer which is originally formed in dispersion but which, unlike t~e main film-ormer, passes into solutlon when there are added to the continuous phase liquid of the dispersion other liquids o~ stronger solvency than the latter in the course of formulating a paint with the required application characteristics.
Usually, the top-coat composition will be substant-ially colourless so that the pigmentation effect due to the t .

base-coat is not significantly modified, but it may be desirable in some cases to provide a transparent tinting of the top-coat composition.
In the first operational step of the process, the base-coat composition is applied to the surface of the substrate9 which may be previously primed or otherwise treated as conventional in the art. The substrates which are of principal interest in the context of the invention are metals such as steel or aluminium which are commonly used for the fabrication of automobile bodies, but other materials such as glass, ceramics, wood and even plastics can be used ; --provided they are capable of withstanding the temperatures at which final curing of the multilayer coating may be effected. After application of the base-coat composition, a polymer film is formed therefrom upon the surface of the substrate. If desired, this may be achieved by s~bjecting ; the substrate and the applied coating to heat in order to volatilise the organic liquid diluent, and it lies within the scope of the invention to employ a heating temperature sufficient to cross-link the base-coat film in those cases where curing of the polyester resin requires such a procedure.
However, a particular merit of the present process is that it is sufficient to allow only a short period of drying at or about room temperature, i.e. without effecting curing of the polyester resin, in order to ensure that the top-~oat composition can be applied to the base-coat film without there being any tendency for the former to mix with or dissolve the latter in a way which can interfere with the correct ... ; ~

~ ~ :

- ,:
.

Z~ 3 orientation of a metallic pigment, whereby optimum "flip"
effect is achieved. Typically, a drying time of from 1 to

5 minutes at a temperature of from 15Q to 30C ensures that mixing of the two coats is prevented. At the same time, the base-coat film is adequately wetted by the topcoat composition, so that satisfactory intercoat adhesion is obtained.
After application of the top-coat composition to the base-coat film, the coated substrate is subjected to a curing operation in which the base-coat, and optionally the top-coat also, is cured by autoxidation and/or cross-linking with the aid of the cross-linking agent(s) present, as appropriate. This curing operation is carried out at an elevated temperature as is conventional in the thermosetting coating composition art, usually at a temperature in the lS range 100 - 140C, but, if desired, at a lower temperature provided the cross-linking system is sufficiently reactive.
The base-coat composition may be applied to the substrate by any of the spray techniques described above. The top-coat compo~ition may subsequently be applied by any convenient method such as brushing, spraying, dipping or flowing, but it is pre~erréd that spray application again be used since the best results are thereby achieved in regard to gloss o~ the final finish. The use of the base-coat composition containing both polyester resin and polymer micro-particles is found to give a signiicantly improved degree ofcontrol over the orientation of metallic pigment under the conditions of spray application, so ~hat enhanced "flip" can be achieved~

The invention is illustrated but not limited by the following Examples, in which parts and percentages are :-by weight.

~A) Alkyd resin finish composition containing polymer :
., - .

(1) Pre~at~on of Pol~mer_Microparticle_ To a vessel fitted with stirrer, thermometer an~
reflux condenser the following were added:-Aliphatic hydrocarbon ~boiling range 140 - 156C : zero aromatlc content) 20.016 parts Methyl methacrylate 1.776 parts Methacrylic acid 0.036 part lS Azo-diisobutyronitrile 0.140 part Graft copolymer stabiliser ~ ~ (33% solution) (as described below) 0.6~2 part :~ : The vessel and contents were purged with inert gas ~and the temperature then raised to 100 and held there for 1 hour in order to produce a disperse polymer "seed". The following ingredients were pre-mixed and were fed into the :vessel at a uniform rate over a perlod of 6 hours, maintaining ; stirring and heating at 100C :
Methyl methacrylate 32.459 parts ~-Glycidyl methacrylate 0~331 part Methacrylic acid 0.331 part Azo-diisobutyronitrile 0.203 part Dimethylaminoethanol 0.070 part .~,",, .

.

Graft copolymer stabiliser solution (as described below)6.810 parts . .
Aliphatic hydrocarbon (boiling range 140 - 156C) 33.166 parts 100.000 parts The contents of the vessel were held at 100C for a further 3 hours, to give full conversion of the monomers to a fine dispersion containing insoluble polymer gel microparticles (21 - 22% of the total dispersion) together with uncross-linked polymer particles (23% of the total dispersion).
The graft copolymer stabiliser used in the above procedure was obtained as followsO 12-hydroxystearic acid was self-condensed to an acid value of about 31 - 34 mg KOH/g (corresponding to a molecular weight of 1650 - 1800) and~then reatced with an ~quivalent amount of glycidyl methacrylate.
The resulting unsaturated ester was copolymerised at a weight ratio of 2:1 with a mixture of methyl methacrylate and acrylic acid in the proportions o~ 95:5.
(2) Modification oE Microparticles with Auxiliary Polymer To a vessel fitted as described in step (a), there were charged 63.853 parts of the dispersion obtained in step (a) above. The dispersion was heated to 115C and the vessel ~ :
.
was purged with inert gas. The following ingredients were pre-mixed and were ~ed at a steady rate, over a period of 3 hours, to the stirred contents o~ the vessel, the temperature being maintained at 115C :
: .

''~':;' ; ~
~: ,.

... ~ . . . .. .. . .. . .. . . .

Methyl methacrylate 3.342 parts Hydroxyethyl acrylate 1.906 parts Methacrylic acid 0.496 part Butyl acrylate 3.691 parts 2-Ethylhexyl acrylate 3.812 parts Styrene 5~712 parts Azo-diisobutyronitrile 0.906 part Prim-octyl mercaptan 0.847 part Graft copolymer stabiliser solution (as described in 1.495 parts step (a).) On completion of the addition, the contents of the vessel were held at 115C for a further 2 hours to achieve full conversion of the monomers, and 13.940 parts of butyl 1~ acetate were finally added, bringing the total charge to 100.000 parts~ The dispersion so obtained had a total film-forming solids content of 45 - 46%; the content of insolu~le ~el polymer microparticles was 27.0 - 27~5%.
(3) Preparation of Millbase The following ingredients were ground together in a ball mill ~
Titanium dioxide pigment 7.8 parts Middle chrome " 27.8 p~rts Scarlet chrome " 18.1 parts Disperslng resin (49% solids solution in xylene) 29.6 parts Xylene 16.7 parts :
,~
- , . ~ :

"` ~ 3 (4) Preparation of finish composition The following ingredients were blended :
Millbase (as described in (3) abo~e) 150.34 parts Melamine/formaldehyde resin (62%
solids solution in butanol)63.52 parts Alkyd resin solution ~as described below) 133~43 parts Polymer microparticle dispersion (as described in (2) above)35.46 parts Dipentene 24.00 parts Butyl acetate 8.00 parts Xylene 51.00 parts The alkyd resin solUtion used in the above formulatlon was a 63% solids solution in xylene of a 34%
: 15 oil length resin made by condensing coconut oil, trimethylol-propane, glyceroll benzoic acid and phthalic anhydride in the molar proportions 00806 : 3.273 : 0~192 : 0.581 : 3.906 respectively.
~: (B) Alkyd res;in finish not containing polymer The ~ollowing ingredients were blended:-Millbase as described in A(3) above 150.34 parts Melamine/formaldehyde resin (62%
solids solution in butanol)63.52 parts 25 . Alkyd resin solution tas described in A(4) above) 157.58 parts Dip~ntene 24.00 parts Butyl acetate 8.00 parts Xylene 51.00 parts ; ~3 .

.

.. . .

6~3 (C) Applicat_on of finishes The compositions prepared as described in (A) and(B) above were applied by spray on to vertical primed steel panels which were punched with 0.25" diameter holes at l"
intervals, in such a way that the film thickness progressively increased from the top to the bottom of the panel~ The applied coatings were allowed to flash off for 45 minutes and were then stoved at 130C for lO minutes.
The film thickness at which sagging of the coatings at the rims of the holes first occurred was then estimated.
For the composition (A) containing polymer micropartic:Les, the minlmum film thickness was 0.0038"; for the composîtion (B) not containing the microparticles, the minimum film thickness was only 0.0024"~
lS EXAMPLE 2 Base-coat/clear~top coat process utilising base-coat (A) Preparation of Base-coat compos_tion The following ingredients were blended:

Melamine/formaldehyde resin (67%
solution in butanol) 38.0Q parts Polymer microparticles dispersion : ~ (as described in Example:l, part A(2)~) 83.56 parts Alkyd resin soIution (as described below) 26.64 parts Dispersion of Carbazole Violet (6.1% in xylene) lO.12 parts Dispersion of Phthalocyanine Blue (9.7% in xylene) 20.28 parts Dispersion of Carbon Black (14.2% in xylene) 2.52 parts - 34 ~

, Dispersion of Aluminium ~lake (35% paste in xylene) 81.04 parts 2-Ethoxyethyl acetate 50.64 parts Butyl Acetate 35.00 parts The alkyd resin solution used in the above formulation was a 70% solids solution in xylene of a resin made by condensing coconut oil, trimethylolpropane, glycerol and phthalic anhydride in the molar proportions 1.0 : 4.05 : 0.5 : 5.14 D
B. Coati q process 100 parts of the basecoat composition prepared as in (A) was thinned by addition of 87 parts of butyl acetate, to give a viscosity of 23.25 secs. in a B.S. B3 cup at 25C. The thinned paint was applied by spray to a primed metal panel so as to give a film of thickness 0.000~3" after loss of all solvents. After a 2 minute flash-off period at room temperature, the panels were over-coated with two coats of a thermosetting acrylic ~-clear composition, a 2 minute flash-off period being allowed between coats9 The dry film thickness of the clear coat was 0.0025". A~ter a final flash-off period of 10 minutes at room temperature~ the panels and coatings were stoved at 127C for 30 minutes.
The finishes thus obtained were of excellent appearance, having an even aluminium metal effect with no trace oP movement of the metal flake (i.e. absence of "shear"). There was no sinkage of the clear top coat into the basecoat7 50 that the very high gloss level associated with the clear coat was in no way impaired by !

' ,: , . .. . ~

., : ` ', , . :, : , : .

~2~ 3 the basecoat, and yet there was excellent intercoat adhesion of the stoved panels. The coating also had good flexibility and humidity resistance.
The acrylic clear composition used as the topcoat in the above procedure was made up as follows:-Butylated melamine-formaldehyde resin, 60% solution in butanol 22.0 parts Dipentene 9.5 parts Butyl ~lycollate 4.5 parts Butanol ~ 2~5 parts 2% solution of silicone oil0.4 part Non aqueous dispersion in aliphatic/
aromatic hydrocarbon mixture of thermosetting acrylic resin? 42~
solids 50.0 parts ;~ ~ Solution of thermosett1ng acrylic resin, in xylene/butanol, 50%
solids 19.8 parts :: : : :
The COmpoSItiOn had a viscosity of 60 seconds when measured at 25C in`a B3 cup according to B.S. 1733:
1955.

The~procedure of Example 2 was repeatéd, except tha~ the 26.64 parts of allcyd resin solution there described ; ~ 25 were replaced by 31.07 parts o~ a 60% solution in xylene of an alkyd resin obtained by condensing azel.aic acid, phthalic anhydride,~ trimethylolpropane and neopentylglycol ;~
in the molar proportions of 0.346 : 0.654 : 0.369 : 0.777 respectively.
~C~
Alkyd resin finish compositions containing polymer ~ ~5~ _Ies at different _ight proportions :; ~ ' :'" ' :
~; - 36 -~6~
, ~
Three compositions, designated I, II and III, were obtained by blending the following ingredients in the proportions shown:-I II III

Melamine/formaldehyde resin (62% solids solution in Butanol) 60.0 72.560~0 White mill base containin~
TiO2 119.2 119.2 119~2 Alkyd resin solution (as described in Example 2)143.1 107.9128.2 Silicone oil solution ~2%) 1~2 1~2 1.2 Isobutyl alcohol 8.0 8.0 8.0 Dipentene 20.0 20~0:20.0 :~
Xylene 56.0 50.083~0 ;

: Polymer microparticle dispersion ~as described in Example 1, part A t2)) 32.965.8 Thermosetting acrylic ~; 20 polymer, (65%:solution) - - 22.9 ~:: : Determined solids content, % ~ 51.14 50.59 50.03 Microparticle content, % non-volatile (based on non-volatile resin components 5 10 0 Primed metal panels were sprayed with each of the three composltions so as to give a "wedge" coat of gradually varying film thickness. Each panel was allowed to stand vertically for 45 minutes and was then stoved, again in a vertical position, for 10 minutes at 130C.
The film thickness at which "sagging" first .occurred was then determined each case. The panel ~inished with - 37 _ ~ ~:

- : .: .: . , . : .: . : ~

composition III sagged at a film thickness of 60 - 65 microns and above, but the panels finished with compositions I and II sagged only at a film thickness of 75 microns and above.
Example 5 Polyester rinish composition containing polymer microparticles, using an alternative cross-The ~ollowing ingredients were ground in a ball mill:-Hydroxyl group-containing polyester, (hydroxyl content 801%~ 90% solution in 2-butoxyethyl acetate) 17.1l parts Polymer microparticle dispersion (as described in Example 1, part A (2)~ 8.39 parts Butyl acetate 6.20 parts Titanium dioxide 34.30 parts After grinding and removal from the ball mill, the following ingredients were added:- ~
Zinc octoate (containing 22% Zn) 0.8~0 part Silicone oil solution (2%)2.00 parts 2 Ethoxyethyl acetate 3.10 parts Butyl acetate 2.80 parts To the above charge there was added 15.i5 parts of an aliphatic polyisocyanate (100% non-volatile content, NC0 content 23.5%). After mixing, the resulting composition was sprayed on to a primed panel in the manner described in Example 4, allowed to flash off for 30 minutes and then stoved for 30 minutes at 80C.

A similar composition was prepared but omitting the polymer microparticles. On spray application as described in Example 4, this was observed to have significantly poorer resistance to sagging then the above composition containing the microparticles.
5xam~1e 5 Polyester "metallic" finish composition, with The following series of ingredi~nts, identified in columns I and II respectively, were blended I II
Butylated melamine/formalde-hyde resin (67% solids in butanol) 39.3 parts 39.3 parts Dispersion of phthalocy-anine blue (9.7% in xylene) 3063 parts 3.83 parts Dispersion of phthalocy-anine green-blue (8.65%
in xylene)2.34 parts 2.34 parts Alkyd resin solution (as described below)59783 parts 117.6 parts Butyl acetate20.1 parts 20.1 parts Methyl ethyl ketone20.1 parts 20.1 parts Flow-promoting polymer (10% solution in xylene) 0.9 parts 0.9 parts Dipentene30.0 parts 30.0 parts Modified microparticle dispersion (as described in Example 1 A (2))77.31 parts Dispersion of aluminium flake (20% paste in xylene)18.15 parts 18.14 parts Xylene - 20.0 parts - : . ~ . : . , ~ :, . ,. . , : . . - . , , .: : : :~ :
: ~: . , .: . : :, Læ~3 The alkyd resin used in the above formulation was a 70% solids solution in a 4:1 by weight ~ixture of xylene and isobutanol of a 34% oil length resin made by condensing coconut oil, trimethylolpropane, glycerol and phthalic anhydride in the molar proportions 1.0 : 4.05 :
0.5 : 5 14 respectively.
Both compositions I and II had a viscosity of 33 secs. measured in B.S. B3 cup at 25C.
Four coats of each composition were applied wet-on-wet to primed metal panels, allowing a l-minute flash-off period between coats. After a final 10-minute flash-off period, the panels were stoved at 127C for 30 minutesO
The control of the aluminium flake pigment on : 15 application, as observed by absence of "shear" effects and "black-edginy" in the coatings obtained, was found to be superior in the case of composition I to that in the case of composition II.

~, :. . , -~ , , , . ' : . , ~

Claims (10)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for the production of a surface coating upon a substrate which comprises applying by spray to the substrate surface a composition comprising:
(A) a film-forming polyester resin which is selected from the group consisting of products of condensation of a polyhydric alcohol and a polycarboxylic acid and products of condensation of a polyhydric alcohol, a polycarboxylic acid and a constituent supplying the residue of a fatty acid derived from a natural drying, semi-drying or non-drying oil;
(B) a volatile organic liquid diluent in which the polyester resin (A) is dissolved;
(C) polymer microparticles of diameter 0.01 to 10 microns which are insoluble in the solution of the polyester resin (A) in the diluent (B) and are stably dispersed therein in a non-flocculated state by means of a steric barrier around the particles of polymer chains which are solvated by the said solution, in an amount of at least 3% of the aggregate weight of the resin (A) and the microparticles, which are insoluble in and stably dispersed in the soluble of the polyester resin in the diluent (B), said microparticles being further associated with an auxiliary polymer which is soluble in the diluent (B) and which also is compatible with the film-forming resin (A).
and subsequently evaporating the volatile diluent (B) and forming a polymer film upon the surface.

2. A process as claimed in Claim 1, wherein the polymer is a polymer or copolymer of one or more alkyl esters of acrylic acid or methacrylic acid,

3. A process as claimed in Claim 1, wherein the polymer microparticles have been produced by the dispersion polymerisation of monomers in an organic liquid, in which the resulting polymer is insoluble, in the presence of a steric stabiliser for the particles.

4. A process as claimed in Claim 3, wherein the steric stabiliser used in the production of the polymer micro-particles is a graft copolymer comprising a polymer back bone which is not solvatable by the organic liquid and is capable of becoming anchored to the polymer microparticles and a plurality of polymer chains pendant from the back-bone which are solvatable by the organic liquid.

5. A process as claimed in Claim 3, wherein the microparticles have been further associated with a polymer (hereinafter referred to as auxiliary polymer) which is soluble in the volatile organic liquid constituent (B) of the composition and is also compatible with the film-forming resin (A).

6. A process as claimed in Claim 5, wherein the microparticles have been associated with auxiliary polymer by following up the dispersion polymerisation process, whereby the microparticles are obtained, immediately with the polymerisation of further monomer, from which the auxiliary polymer is to be derived, in the original inert liquid medium and in the presence of the original stabilising agent.

7. A process as claimed in Claim 1, wherein the polymer microparticles (C) are present in an amount of from 3% to 30% of the aggregate weight of the film-forming polymer (A) and the microparticles (C).

8. A process as claimed in Claim 1, wherein the composition applied to the substrate additionally contains a metallic flake pigment.

9. A process for the production of a multilayer coating upon the surface of a substrate which comprises the steps of:
(1) applying by spraying to the surface a base-coat composition comprising:
(A) a film-forming polyester resin which is selected from the group consisting of products of condensation of a polyhydric alcohol and a polycarboxylic acid and products of condensation of a polyhydric alcohol, a polycarboxylic acid and a constituent supplying the residue of a fatty acid derived from a natural drying, semi-drying or non-drying oil;
(B) a volatile organic liquid diluent in which the polyester resin (A) is dissolved;
(C) polymer microparticles of diameter 0.01 to 10 microns which are insoluble in the solution of the polyester resin (A) in the diluent (B) and are stably dispersed therein in a non-flocculated state by means of a steric barrier around the particles of polymer chains which are solvated by the said solution which are insoluble in and are stably dispersed in the solution of the film-forming polymer in the liquid diluent, in an amount of at least 10% of the aggregate weight of the film-forming polymer (A) and the microparticles (C).
(D) pigment particles also dispersed in the solution of the film-forming polyester resin in the liquid diluent;

(2) forming a polymer film upon the surface from the composition applied in step (1);
(3) applying to the base-coat film so obtained a transparent top-coat composition comprising;
(E) a film-forming polymer;
(F) a volatile carrier liquid for the polymer (E);
(4) forming a second polymer film upon the base-coat film from the composition applied in step (3).

10. A process as claimed in Claim 9, wherein the polymer microparticles (C) are present in an amount of from 10% to 30% of the aggregate weight of the film-forming polymer (A) and the microparticles (C).