PROCESS FOR PREPARING COLOUR-PLUS-CLEAR COATED ARTICLES USING HIGH SOLIDS COATING COMPOSITIONS CONTAINING A POLYEPOXIDE AND A COPOLYMER OF AN ALPHA-OLEFIN AND AN OLEFINICALLY UNSATURATED MONOANHYDRIDE

Abstract: The invention provides a curable, liquid coating composition containing organic solvent and a resinous binder, characterised in that said resinous binder comprises: (a) a polyepoxide, and (b) a copolymer of an alpha-olefin or a cycloolefin and an olefinically unsaturated monoanhydride which may include a partial ester thereof, and said coating composition has a resin solids content of at least 40 percent by weight.

Description: The present invention relates to a process for preparing color-plus-clear coated articles and to the coated articles themselves. Color-plus-clear coatings involve the application of a colored or pigmented base coat to a substrate followed by the application of a transparent or clear top coat to the base coat. The composite coatings are becoming increasingly popular as original finishes for automobiles. The color-plus-clear coatings have outstanding gloss and distinctness of image, and the clear coat is particularly important for these properties. Two-pack clear coat compositions comprising polyols such as polyester polyols, polyurethane polyols and acrylic polyols and polyisocyanate curing agents give outstanding gloss and distinctness of image along with good humidity resistance and mar resistance. However, the polyisocyanates are difficult to handle being sensitive to moisture and require cumbersome safety precautions because of their toxicity. U.S. Patent No. 4,650,718 discloses crosslinkable coating compositions which avoid the problems of polyisocyanate curing agents. The crosslinkable coating compositions are based on polyepoxides and polyacid curing agents. Although these compositions can be formulated to produce cured coatings with excellent adhesion, gloss and distinctness of image (i.e., ability to reflect images in a clear, well-defined manner), the resultant cured coatings do not have optimum humidity and mar resistance. The present invention provides a process for applying a composite coating to a substrate which comprises applying to the substrate a coloured film-forming composition to form a base coat and applying to said base coat a clear film-forming composition to form a transparent top coat over the base coat in which the clear film-forming composition comprises a curable liquid coating composition containing organic solvent and a resinous binder, characterised in that said resinous binder comprises: (a) a polyepoxide, and (b) a copolymer of an alpha-olefin or a cycloolefin and an olefinically unsaturated monoanhydride and/or a partial ester of such copolymer, and said coating composition has a resin solids content of at least 40 percent by weight and preferably at least 55% by weight. The invention further provides for the resultant coated article. The essential ingredients of the crosslinkable compositions used in the method of the present invention are the polyepoxide, the copolymer of an alpha-olefin or cycloolefin and an olefinically unsaturated mono-anhydride which may include a partial ester thereof and preferably a polyacid. Among the polyepoxides which can he used are epoxy-containing acrylic polymers which are preferred, epoxy condensation polymers such as polyglycidyl ethers of alcohols and phenols and certain polyepoxide monomers and oligomers. The epoxy-containing acrylic polymer may be a copolymer of an ethylenically unsaturated monomer having at least one epoxy group and at least one polymerizable ethylenically unsaturated monomer which is free of epoxy groups. Examples of ethylenically unsaturated monomers containing epoxy groups are those containing 1,2-epoxy groups and include glycidyl acrylate, glycidyl methacrylate and allyl glycidyl ether. Examples of ethylenically unsaturated monomers which do not contain epoxy groups are alkyl esters of acrylic and methacrylic acid containing from 1 to 20 atoms in the alkyl group. Specific examples of these acrylates and methacrylates are methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethyl acrylate, butyl acrylate and 2-ethylhexyl acrylate. Examples of other copolymerizable ethylenically unsaturated monomers are vinyl aromatic compounds such as styrene and vinyl toluene; nitriles such as acrylonitrile and methacrylonitrile; vinyl and vinylidene halides such as vinyl chloride and vinylidene fluoride and vinyl esters such as vinyl acetate. Acid group-containing copolymerizable ethylenically unsaturated monomers such as acrylic and methacrylic acid are preferably not used because of the possible reactivity of the epoxy and acid group. The epoxy group-containing ethylenically unsaturated monomer is preferably used in amounts of from about 5 to 60, more preferably from 20 to 50 percent by weight of the total monomers used in preparing the epoxy-containing acrylic polymer. Of the remaining polymerizable ethylenically unsaturated monomers, preferably from 40 to 95 percent, more preferably from 50 to 80 percent by weight of the total monomers are the alkyl esters of acrylic and methacrylic acid. In preparing the epoxy-containing acrylic polymer, the epoxide functional monomers and the other ethylenically unsaturated monomers can be mixed and reacted by conventional free radical initiated organic solution polymerization as generally described above. The epoxy-containing acrylic polymer typically has a number average molecular weight between about 1000 and 20,000, preferably 1000 to 10,000, and more preferably 1000 to 5000. The molecular weight is determined by gel permeation chromatography using a polystyrene standard. In determining molecular weights in this fashion, it is not the actual molecular weights which are measured but an indication of the molecular weight as compared to polystyrene. The values which are obtained are commonly referred to as polystyrene numbers. However, for the purposes of this invention, they are referred to as molecular weights. The epoxy condensation polymers which are used are polyepoxides, that is, those having a 1,2-epoxy equivalency greater than 1, preferably greater than 1 and up to about 3.0. Examples of such epoxides are polyglycidyl ethers of polyhydric phenols and of aliphatic alcohols. These polyepoxides can be produced by etherification of the polyhydric phenol or aliphatic alcohol with an epihalohydrin such as epichlorohydrin in the presence of alkali. Examples of suitable polyphenols are 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), 1,1-bis(4-hydroxyphenyl)ethane and 2-methyl-1,1-bis(4-hydroxyphenyl)propane. Examples of suitable aliphatic alcohols are ethylene glycol, diethylene glycol, 1,2-propylene glycol and 1,4-butylene glycol. Also, cycloaliphatic polyols such as 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,2-bis(hydroxymethyl)cyclohexane and hydrogenated bisphenol A can also be used. Besides the epoxy-containing polymers described above, certain polyepoxide monomers and oligomers can also be used. Examples of these materials are those containing the cyclohexane oxide moiety. These polyepoxides are of relatively low molecular weight and of relatively high reactivity thus enabling the formation of high solids coating compositions with excellent cure response. The polyepoxides should have an average 1,2-epoxy equivalency of greater than one. The preferred polyepoxides are diepoxides, that is, having a 1,2-epoxy equivalency of two. Various polyepoxides containing the cyclohexane oxide moiety are known. Particularly preferred in this regard is 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate. Also, the diepoxide bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate can be used. These epoxides are commercially available from Union Carbide Corporation as ERL 4221 and ERL 4299, respectively. Also, epoxies containing the cyclohexane moiety are described in U.S. Patents Nos. 2,890,194; 2,890,195; 2,890,196; 2,890,197; 2,890,210; 3,023,174 and 3,027,357. Mixtures of polyepoxides, particularly mixtures of epoxy-containing acrylic polymers and polyepoxides containing a cyclohexane moiety, are preferred because they result in coating compositions which have high solids content and a good combination of coating properties, i.e., gloss, distinctness of image, adhesion, hardness and solvent resistance. The polyepoxide is typically present in the liquid crosslinkable composition in amounts of about 20 to 75, preferably from 30 to 60 percent by weight based on total weight of resin solids. The compositions of the present invention also contain a copolymer of an alpha-olefin or cycloolefin and an olefinically unsaturated monoanhydride which may include a partial ester thereof. The copolymer is typically present in the coating composition in amounts of 1 to 40, preferably 5 to 30 percent by weight based on weight of resin solids. The copolymer provides for good mar resistance and humidity resistance in the resultant cured coating. Amounts greater than 40 percent by weight are less preferred because they adversely affect the hardness and Distinctness of Image (DOI) of the cured coating. Among the alpha-olefins which may be used in the reaction with the olefinically unsaturated anhydride are those having from 4 to 14, preferably 4 to less than 10 carbon atoms. Alpha-olefins of less than 4 carbon atoms are undesirable because they are gaseous and difficult to handle; whereas alpha-olefins of 10 or more carbon atoms are less preferred because of poor hardness and DOI. Examples of alpha-olefins are 1-butene, 1-hexene, 1-octene, 2-methyl-1-heptene, 2,4,4-trimethyl-1-pentene, 1-nonene, 1-decene, 1-dodecene, 1-tridecene, 1-tetradecene and vinyl cyclohexane, with 1-octene being preferred. Examples of cycloolefins include cyclohexene and cyclooctene. Mixtures of alpha-olefins and cycloolefins can be used. The olefinically unsaturated anhydride is of the structure: where R and R₁ are the same or different and are selected from the class consisting of hydrogen, lower alkyl containing from 1 to 4 carbon atoms, lower alkoxy containing from 1 to 4 carbon atoms and halo. Examples of suitable anhydrides include maleic anhydride which is preferred, itaconic anhydride, citraconic anhydride, chloromaleic anhydride, ethylmaleic anhydride and methoxymaleic anhydride. Theoretically, one mole of the olefinically unsaturated anhydride is added to one mole of the alpha-olefin to obtain the desired reaction product. However, in order to obtain an effective addition reaction, a molar excess of olefin is usually employed. The reaction is carried out by heating the reactants together preferably in the presence of organic solvent and in the presence of a free radical initiator such as benzoyl peroxide, tert-amyl peroxyacetate or azo-type initiators at a temperature up to the reflux temperature of the alpha-olefin, generally from about 30 to 220°C., preferably from 80 to 180°C., for a time sufficient to complete the polymerization; typically from 0.5 to 10, preferably 1 to 5 hours. To prepare preferred products, the time, temperature and catalyst are adjusted to prepare a product which has a weight average molecular weight of less than 15,000, more preferably 3000 to 12,000, as determined by gel permeation chromatography using a polystyrene standard. Molecular weights higher than 15,000 are not preferred because it is difficult to formulate coatings with high solids content. Besides the anhydride copolymers, the partial ester derivatives formed by partially esterifying the copolymer with an alcohol can also be used and have been found to provide clear coats with less tendency to yellow. Among the alcohols which may be used include alkyl alcohols such as methanol and ethanol, arylalkyl alcohols such as benzyl alcohol, ether alcohols such as 2-butoxyethanol, and tert-amino alcohols such as dimethylethanolamine. Usually, for each equivalent of anhydride functionality, up to one-half equivalent of alcohol is used. Esterification takes place by heating the anhydride copolymer and the alcohol together at reflux temperature for about 0.5 to 5 hours. Preferably, the coating composition contains a polyacid containing two or more acid groups per molecule which are reactive with the polyepoxide. The polyacid provides for better DOI and hardness in the cured coatings. The acid functionality is preferably carboxylic acid, although acids such as sulfonic acid may be used but their use is not preferred. Preferably, the polyacid curing agent is a carboxyl-terminated material (such as polyester) having at least two carboxyl groups per molecule. Among the polyacid curing agents which may be used are carboxylic acid group-containing polymers such as acrylic polymers, polyesters, and polyurethanes; oligomers such as ester group-containing oligomers and monomers. The preferred polyacid curing agents are ester group-containing oligomers. Examples include half-esters formed from reacting polyols and 1,2-acid anhydrides. The half-esters are preferred because they are of relatively low molecular weight and are quite reactive with epoxy functionality enabling the formulation of high solids compositions while maintaining outstanding properties such as hardness and distinctness of image. The preferred polyacid curing agents are of the structure: where X is the residue of the polyol after reaction with the 1,2-dicarboxylic acid anhydride, R is an organic moiety associated with the anhydride and A is equal to at least 2. Among the anhydrides which can be used in the formation of of desired polyesters are those which exclusive of the carbon atoms and the anhydride moiety contain from about 2 to 30 carbon atoms. Examples include aliphatic, including cycloaliphatic, olefinic and cycloolefinic anhydrides and aromatic anhydrides. Substituted aliphatic aromatic anhydrides are also included within the definition of aliphatic and aromatic provided the substituents do not adversely affect the reactivity of the anhydride or the properties of the resultant polyester. Examples of substituents would be chloro, alkyl and alkoxy. Examples of anhydrides include succinic anhydride, methylsuccinic anhydride, dodecenyl succinic anhydride, octadecenylsuccinic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, alkyl hexahydrophthalic anhydrides such as methylhexahydrophthalic anhydride, tetrachlorophthalic anhydride, endomethylene tetrahydrophthalic anhydride, chlorendic anhydride, citraconic anhydride and maleic anhydride. Among the polyols which can be used are those which contain from about 2 to 20 carbon atoms. Preferred are diols, triols and mixtures thereof. Examples include polyols containing from 2 to 10 carbon atoms. Examples include aliphatic polyols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, glycerol, 1,2,3-butanetriol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 1,4-cyclohexanedimethanol, trimethylolpropane, 2,2,4-trimethylpentane-1,3-diol, pentaerythritol and 1,2,3,4,-butanetetrol. Aromatic polyols such as bisphenol A and bis(hydroxymethyl) xylene can also be used. When the polyacid curing agent is used, it is typically present in the coating composition in amounts of about 5 to 75, preferably 5 to 50 percent by weight based on total weight of resin solids. The equivalent ratio of the reactants present in the composition are preferably adjusted that for each equivalent of epoxy there are 0.5 to 1.5, preferably 0.8 to 1.2 equivalents of carboxyl (anhydride being considered monofunctional). The compositions will also preferably contain catalysts to accelerate the cure of the epoxy and carboxyl groups. Examples of suitable catalysts are basic materials and include organic amines and quaternary ammonium compounds such as pyridine, piperidine, dimethylaniline, diethylenetriamine, tetramethylammonium chloride, tetramethylammonium acetate, tetramethylbenzylammonium acetate, tetrabutylammonium fluoride, and tetrabutylammonium bromide. The amount of catalyst is typically from 0.1 to 10, preferably 0.5 to 3 percent by weight based on weight of resin solids. Also, optional ingredients such as plasticizers, antioxidants, and UV light absorbers can be included in the composition. These ingredients typically are present in amounts of up to 25 percent by weight based on total resin weight. For colored and/or textured coatings, pigments may be included in the compositions. Pigment contents in amounts of up to 75 percent by weight based on total solids can be used. The compositions used in the method of the present invention are liquid compositions and are formulated into liquid high solids coating compositions, that is, those coating compositions containing greater than 40, preferably greater than 55 percent by weight resin solids. The solids content is determined by formulating the coating composition to a No.4 Ford cup viscosity of 25-30 seconds at 76°F (24°C) and heating the composition to 105-110°C for 1 to 2 hours to drive off the volatile material. The curable compositions used in the method of the invention can be applied as coatings to a substrate by any of the conventional coating techniques such as brushing, spraying, dipping or flowing, but it is preferred that spray applications be used since this gives the 5 best appearance. Any of the known spray techniques may be employed such as compressed air spraying, airless spraying, electrostatic spraying and either manual or automatic methods. After application of the coating composition to the substrate, the coated substrate is heated to cure the coating. In the curing operation, solvents are driven off and the film-forming material of the coating composition is crosslinked through reaction of the carboxyl groups and epoxy groups. The heating or curing operation is usually carried out at a temperature in the range of from 160-350°F. (71-177°C.). The thickness of the coating is usually from about 0.1 to 5, preferably 0.1 to 3 mils. Preferably, the compositions of the present invention, particularly those prepared with the aliphatic polyepoxides and with the epoxy-containing acrylic polymers, are used to formulate clear coats for use in a color-plus-clear application. In a color-plus-clear application, a composite coating is applied to a substrate. The process comprises applying to the substrate a pigmented or colored film-forming composition to form a base coat and applying to the base coat a second film-forming composition to form a transparent top coat over the base coat. The film-forming composition of the base coat can be any of the compositions useful in coating applications, particularly automotive applications in which the color-plus-clear coating applications are finding their most use. A film-forming composition conventionally comprises a resinous binder and a pigment to act as a colorant. Particularly useful resinous binders are acrylic polymers, polyesters including alkyds, and polyurethanes. The resinous binder far the base coat can be an organic solvent-based material such as those described in U.S. Patent No. 4,220,679, note column 2, line 24, continuing through column 4, line 40. Also, water-based coating compositions such as those described in U.S. Patent No. 4,403,003 and U.S. Patent No. 4,147,679 can also be used as the binder in the base coat composition. The resinous binder for the base coat can also be the curable composition of the present invention. The base coat composition also contains pigments including metallic pigmentation to give it color. Examples of suitable pigmentations for the base coat are described in the aforementioned U.S. Patents Nos. 4,220,679; 4,403,003 and 4,147,679. Optional ingredients in the base coat composition are those which are well known in the art of formulating surface coatings and include surfactants, flow control agents, thixotropic agents, fillers, anti-gassing agents, organic co-solvents, catalysts and other customary auxiliaries. Examples of these materials and suitable amounts are described in the aforementioned U.S. Patents Nos. 4,220,679; 4,403,003 and 4,147,679. The base coat compositions can be applied to the substrate by any of the conventional coating techniques such as brushing, spraying, dipping or flowing, but they are most often applied by spraying. The usual spray techniques and equipment for air spraying, airless spraying and electrostatic spraying in either manual or automatic methods can be used. During application of the base coat to the substrate, a film of the base coat is formed on the substrate typically in a thickness of about 0.1 to 5 and preferably about 0.1 to 2 mils. After forming a film of the base coat on the substrate, solvent, that is, organic solvent and/or water, is driven out of the base coat film by heating or simply an air drying period before application of the clear coat. Preferably, the heating step will only be that sufficient and for a short period of time to insure that the clear top coat composition can be applied to the base coat without the former dissolving the base coating composition, that is, "striking in". Suitable drying conditions will depend on the particular base coat composition, on the ambient humidity with certain water-based compositions, but in general a drying time of from about 1 to 15 minutes at a temperature of about 70-175°F. (21-79°C.) will be adequate to insure that mixing of the two coats is minimized. At the same time, the base coat film is adequately wetted by the clear top coat composition so that satisfactory intercoat adhesion can be obtained. Also, more than one base coat and more than one top coat may be applied to develop optimum appearance. Usually between coats, the previously applied base coat or top coat is flashed, that is, exposed to ambient conditions for about 1 to 20 minutes. The clear top coat composition is applied to the base coat by any of the conventional coating techniques mentioned above, although spray applications are preferred. As mentioned above, the clear top coat is applied to the base coat via a wet-on-wet technique before the base coat has been cured. The two coatings are then heated to conjointly harden both coating layers. Curing conditions such as described above can be used. Clear coats typically have thicknesses of 0.5 to 5, usually 1 to 2.5 mils. The invention will be further defined by reference to the following examples. Unless otherwise indicated, all parts are by weight. PREPARATIONS The following Preparations A-G show the preparation of a polyepoxide, a polyacid and various alpha-olefin-maleic anhydride copolymers which are useful in the practice of the present invention. PREPARATION A An epoxy-containing acrylic polymer was prepared from the following mixture of ingredients: Ingredients Weight (in grams) Solids (in grams) Glycidyl methacrylate 2080.0 40.0 Methyl methacrylate 1716.0 33.0 Butyl acrylate 1300.0 25.0 Styrene 104.0 2.0 VAZO-67 260.0 5.0 (on monomers) Tertiary-butyl perbenzoate 104.0 2.0 (on monomers) Tertiary-butyl perbenzoate (post addition) 26.0 0.5 (on monomers) Xylene (2996.7 grams) was charged to a suitable reactor and heated to reflux to remove water through a Dean-Stark trap. The glycidyl methacrylate, methyl methacrylate, butyl acrylate, and styrene were mixed together. The VAZO-67, first portion of tertiary-butyl perbenzoate and 500.0 grams of xylene were also premixed together. The premixture of vinyl monomers and the premixture of initiators were added simultaneously to the reaction vessel over a period of about three hours while maintaining the reaction temperature at reflux. At the completion of the addition, the reaction mixture was held at reflux for one hour followed by the addition of the second portion of tertiary-butyl perbenzoate and 100 grams of xylene. The reaction mixture was held for two hours at reflux followed by cooling to room temperature. The reaction mixture had a solids content of about 58 percent and a number average molecular weight of about 1,300 as determined by gel permeation chromatography using a polystyrene standard. PREPARATION B A polyacid half-ester of 1-(3-hydroxy-2,2-dimethylpropyl)-3-hydroxy-2,2-dimethylpropionate (ESTER DIOL 204) and methylhexahydrophthalic anhydride was prepared from the following mixture of ingredients: Ingredients Parts by Weight (in grams) ESTER DIOL 204 2550.0 Methylhexahydrophthalic anhydride 4116.0 Methyl isobutyl ketone 1466.5 Ethanol 666.6 The ESTER DIOL 204 and 1466.5 grams of the methyl isobutyl ketone were charged to a reaction vessel and heated under a nitrogen atmosphere to 115°C. The methylhexahydrophthalic anhydride was added over a 90-minute period. The reaction mixture was then held at 115°C. for four hours. The reaction mixture was then cooled to 100°C. followed by the addition of ethanol (to react with residual anhydride) and heating the reaction mixture to reflux and holding for two hours. The reaction mixture was stripped to a pot temperature of 125°C. The reaction mixture was then adjusted to 80 percent solids with methyl isobutyl ketone. PREPARATION C A 1-decene-maleic anhydride copolymer was prepared as follows: To a reaction vessel fitted with a condenser, thermometer, nitrogen sparging inlet and agitator was charged 1123 grams (g.) (8 moles) of 1-decene. As the 1-decene was heated at a reflux temperature of 145°C., a first mixture of 147.5 g. of tert-amyl peroxyacetate (available from Pennwalt Corporation as a 60 percent solids solution in mineral spirits as LUPERSOL 555-M60) and 80 g. of butyl acetate was added over a period of three hours. Beginning a half hour after the start of the first addition, a second mixture of 393.2 g. (4 moles) of maleic anhydride, 401.2 g. of acetone and 246.9 g. of butyl acetate was added over a period of two hours. After completion of the additions, heating was continued at 145-146°C. for one hour. Thereafter, solvent was removed by distillation with a total distillate of 290 g. being removed. The reaction mixture was cooled to room temperature and thinned with butyl acetate to a solids content of 75.4 percent. The copolymer had a number average molecular weight of about 1,697 and a weight average molecular weight of about 3,620. PREPARATION D A 1-octene-maleic anhydride copolymer was prepared as follows: To a reaction vessel equipped as described in Preparation C was charged 1821.6 g. (16.23 moles) of 1-octene. As the 1-octene was heated at a reflux temperature of 120°C., a first mixture of 458.9 g. of benzoyl peroxide (available as 78 percent by weight aqueous mixture from Pennwalt Corporation as LUCIDOL 78) and 3781.8 g. of butyl acetate was added over a period of three hours. Beginning a half hour after the start of the first addition, a second mixture of 794.8 g. (8.1 moles) of maleic anhydride and 1890.9 g. of butyl acetate was added over a period of two hours. After completion of the additions, heating at reflux was continued for one hour. Thereafter, solvent was removed by distillation with a total distillate of 5457 g. removed. The copolymer had a solids content of 75.9 percent, a number average molecular weight of about 1061 and a weight average molecular weight of about 2731. PREPARATION E A 1-hexene-maleic anhydride copolymer was prepared as follows: To a reaction vessel equipped as described in Preparation C was charged 109 g. (1.3 moles) of 1-hexene. As the 1-hexene was heated to reflux, a first mixture of 36.7 g. of LUCIDOL 78 and 302.5 g. of butyl acetate was added over a period of 2 1 / 2 hours. Beginning a half hour after the start of the first addition, a second mixture of 63.6 g. (0.65 moles) of maleic anhydride and 151.3 g. of butyl acetate was added over a period of 1 1 / 2 hours. After completion of the additions, heating at reflux was continued for one hour. Thereafter, solvent was removed by distillation with a total distillate of 396.3 g. being removed. The copolymer had a solids content of 66 percent, a number average molecular weight of 1000 and a weight average molecular weight of 4274. PREPARATION F A 1-octene-maleic anhydride copolymer was prepared as follows: To a reaction vessel equipped as described in Preparation C was charged 3024 g. (27 moles) of 1-octene. As the 1-octene was heated to reflux temperature at 120°C., a first mixture of 182 g. of LUPERSOL 555-M60 and 825 g. of butyl acetate was added over a period of three hours. Beginning a half hour after the start of the first addition, a second mixture of 1323 g. (13.5 moles) of maleic anhydride and 3407 g. of butyl acetate was added over a period of two hours. After completion of the additions, heating at reflux was continued for one hour. Thereafter, solvent was removed by distillation with a total distillate of 5453 g. being removed. The remaining product had a solids content of 97 percent, number average molecular weight of 2217 and a weight average molecular weight of 5906. PREPARATION G The benzyl alcohol half-ester of a 1-octene-maleic anhydride copolymer was prepared as follows: To a reaction vessel equipped with a condenser, thermometer, nitrogen sparging inlet and agitator was charged 1129.6 g. (3.9 moles) of the maleic anhydride-1-octene copolymer of Preparation D and 70.4g of benzyl alcohol. The ingredients were heated to 105°C. and held for one hour followed by cooling to room temperature. Comparative Example The following Example shows the formulation of a clear coat containing no alpha-olefin-maleic anhydride copolymer. A base mix was formulated from the following ingredients: Ingredient Parts by Weight (in grams) Solids (in grams) TINUVIN 328 3.0 3.0 TINUVIN 292 1.0 1.0 Polybutylacrylate 0.4 0.25 MULTIFLOW 0.5 0.25 ARMEEN DM-12D 4.0 4.0 25/75 hexyl acetate/methyl isobutyl ketone 16.0 - RESIMINE 717 16.4 13.8 Silica grind 12.5 5.4 (4.4 resin, 1.0 pigment) The ingredients were mixed in the order indicated with a low shear mixer to form the base mix. The base mix was mixed with the following ingredients to form the coating composition. Ingredients Parts by Weight (in grams) Solids (in grams) Base Mix 53.8 27.7 ERL 4299 19.6 19.6 Epoxy-containing acrylic polymer of Preparation A 30.5 18.3 Polyacid of Preparation B 54.9 43.9 25/75 hexyl acetate/methyl isobutyl ketone 15.7 - The ingredients were mixed with a low shear mixer in the order indicated to form the coating composition which was then applied as a clear coat over both an aluminum metallic base coat and a black base coat which had been previously spray applied to a primed steel panel. The base coat was given a 15-minute flash at room temperature followed by the application of the clear coat. The clear coat was given a 15-minute flash at room temperature followed by curing the composite coating for 30 minutes at 250°F. (121°C.). The properties of the coating composition and the cured coating are reported in the Table below. The following Examples show the formulation of clear coats using the polyepoxides, polyacid and alpha-olefin-maleic anhydride copolymers of Preparations A-G. Example 1 The following Example shows the formulation of a coating composition with both the polyacid of Preparation B and the 1-octene-maleic anhydride copolymer of Preparation D. Ingredients Parts by Weight (in grams) Solids (in grams) Base Mix of Example 1 53.8 27.7 ERL 4299 20.9 20.9 Epoxy-containing acrylic polymer of Preparation A 32.3 19.4 Polyacid of Preparation B 25.9 20.7 1-octene-maleic anhydride copolymer of Preparation D 27.4 20.8 25/75 hexyl acetate/methyl isobutyl ketone 14.2 - The ingredients were mixed in the order indicated and applied as a clear coat as described in Comparative Example. The properties of the coating composition and the cured composite coatings are reported in the Table below. Example 2 The following Example shows the formulation of a coating composition with no polyacid and the 1-octene-maleic anhydride copolymer of Preparation D. Ingredients Parts by Weight (in grams) Solids (in grams) Base Mix of Example 1 53.8 27.7 ERL 4299 23.4 23.4 Epoxy-containing acrylic polymer of Preparation A 36.2 21.7 1-octene-maleic anhydride copolymer of Preparation D 48.4 36.7 25/75 hexyl acetate/methyl isobutyl ketone 12.7 - The ingredients were mixed in the order indicated and applied as a clear coat as described in Comparative Example. The properties of the coating composition and the cured composite coatings are reported in the Table below. Example 3 The following Example shows the formulation of a coating composition with the benzyl alcohol half-ester of the 1-octene-maleic anhydride copolymer of Preparation G. Ingredients Parts by Weight (in grams) Solids (in grams) Base Mix of Example 1 53.8 27.7 ERL 4299 19.7 19.7 Epoxy-containing acrylic polymer of Preparation A 30.7 18.4 Polyacid of Preparation B 24.5 19.6 Copolymer of Preparation G 33.2 24.1 25/75 hexyl acetate/methyl isobutyl ketone 12.7 - The ingredients were mixed in the order indicated and applied as a clear coat as described in Comparative Example. The properties of the coating composition and the cured composite coatings are reported in the Table below. Example 4 The following Example shows the formulation of a coating composition with the 1-decene-maleic anhydride copolymer of Preparation C. Ingredients Parts by Weight (in grams) Solids (in grams) Base Mix of Example 1 53.8 27.7 ERL 4299 19.4 19.4 Epoxy-containing acrylic polymer of Preparation A 30.0 18.0 Polyacid of Preparation B 24.0 19.2 1-decene-maleic anhydride copolymer of Preparation C 33.4 25.2 25/75 hexyl acetate/methyl isobutyl ketone 13.9 - The ingredients were mixed in the order indicated and applied as a clear coat as described in Comparative Example. The properties of the coating composition and the cured composite coatings are reported in the table below. Example 5 The following Example shows the formulation of a coating composition with the 1-hexene-maleic anhydride copolymer of Preparation E. Ingredients Parts by Weight (in grams) Solids (in grams) Base Mix of Example 1 53.8 27.7 ERL 4299 21.6 21.6 Epoxy-containing acrylic polymer of Preparation A 33.7 20.2 Polyacid of Preparation B 26.8 21.4 1-hexene-maleic anhdride copolymer of Preparation E 29.1 18.6 25/75 hexyl acetate/methyl isobutyl ketone 9.5 - The ingredients were mixed in the order indicated and applied as a clear coat as described in Comparative Example. The properties of the coating composition and the cured composite coatings are reported in the Table below. Example 6 The following Example shows the formulation of a coating composition with the 1-octene-maleic anhydride copolymer of Preparation F. Ingredients Parts by Weight (in grams) Solids (in grams) Base Mix of Example 1 53.8 27.7 ERL 4299 20.9 20.9 Epoxy-containing acrylic polymer of Preparation A 32.3 19.4 Polyacid of Preparation B 25.9 20.7 1-octene-maleic anhydride copolymer of Preparation F 41.6 20.8 25/75 hexyl acetate/methyl isobutyl ketone 9.5 - ¹50 percent solids in methyl isobutyl ketone. The ingredients were mixed in the order indicated and applied as a clear coat as described in Comparative Example. The properties of the coating composition and the cured composite coatings are reported in the Table below. ¹Measured with a 20 degree gloss meter manufactured by Hunter Lab. ²Distinctness of Image (DOI) determined on a C-Box manufactured by C-Box I²R Co. ³Crosshatch adhesion determined generally in accordance with the procedures of ASTM 3359. The adhesion was rated 0-5 with 5 indicating excellent adhesion. ⁴Tukon hardness number determined by ASTM E-48. Pencil hardness determined by taking series of standard pencils of varying hardness with H being the hardest and B being the softest and scratching the panels with pencils of increasing hardness until the coating was etched away. ⁵Two (2) drops of xylene are placed on the panel for 3 minutes. The pencil hardness of the spot in contact with the xylene is then determined. How much the coating softens compared to the original pencil hardness is a measure of the xylene resistance. ⁶Humidity resistance determined by using the coated panel as the ceiling of a humidity chamber (QCT chamber) with the coating directed inwardly towards the chamber. The chamber is heated to 140°F. (60°C.) and about a 2-inch (3 cm) level of water is located 3 to 5 inches below the coated panel (panel sloped). After being exposed for 24 hours, the appearance and 20° gloss of the exposed coating was determined and compared with the original appearance and gloss before testing. ⁷Coating scratched with a fingernail. Ratings are poor for heavy marking of the coating; fair for slight marking of the coating and good for no marking. Mar resistance determined over black coatings and other properties determined over the silver coating.

Claims: A process for applying a composite coating to a substrate which comprises applying to the substrate a coloured film-forming composition to form a base coat and applying to said base coat a clear film-forming composition to form a transparent top coat over the base coat in which the clear film-forming composition comprises a curable liquid coating composition containing organic solvent and a resinous binder, characterised in that said resinous binder comprises: (a) a polyepoxide, and (b) a copolymer of an alpha-olefin or a cycloolefin and an olefinically unsaturated monoanhydride and/or a partial ester of such copolymer, and said coating composition has a resin solids content of at least 40 percent by weight. A process as claimed in claim 1, characterised in that the polyepoxide is a copolymer of a monoethylenically unsaturated monomer having at least one epoxy group and at least one monoethylenically unsaturated monomer which is free of epoxy groups. A process as claimed in claim 1, in which the polyepoxide is a cyclohexane oxide moiety containing polyepoxide. A process as claimed in any of the preceding claims, characterised in that the olefinically unsaturated monoanhydride is maleic anhydride. A process as claimed in any of the preceding claims, characterised in that the alpha-olefin contains from 4 to less than 10 carbon atoms. A processn as claimed in claim 5, characterised in that the alpha-olefin is 1-hexene or 1-octene. A process as claimed in any of the preceding claims, characterised in that the copolymer (b) has a weight average molecular weight of less than 15,000. A process as claimed in any of the preceding claims, characterised in that the polyepoxide is present in the crosslinkable composition in an amount of from 20 to 75 percent by weight based on the weight of resin solids. A process as claimed in any of the preceding claims, characterised in that the copolymer (b) is present in the composition in an amount of from 5 to 40 percent by weight based on the weight of resin solids. A process as claimed in any of the preceding claims, characterised in that the resin solids content is at least 55 percent by weight. A process as claimed in any of the preceding claims, characaterised in that the composition also contains a polyacid. A process as claimed in claim 11, characterised in that the polyacid is a carboxyl- terminated material having at least 2 carboxyl groups per molecule. A process as claimed in claim 12, characterised in that the polyacid is a carboxyl- terminated polyester. A process as claimed in claim 13, characterised in that the carboxyl-terminated polyester is a half-ester of the structure: where X is the residue of a polyol after reaction with a 1,2-dicarboxylic acid anhydride, R is an organic moiety associated with the anhydride, and A is equal to at least 2. A process as claimed in any of claims 11 to 14, characterised in that the polyacid curing agent is present in the composition in amounts of about 5 to 50 percent by weight based on the weight of resin solids. A process as claimed in any of the preceding claims, characterised in that the equivalent ratio of carboxyl to epoxy is from 0.8 to 1.2 to 1 and is sufficient to form a cured product.

Inventors: BLACKBURN, WILLIAM PELHAM, SCHIMMEL, KARL FRANCIS
Applicants: PPG INDUSTRIES, INC.
Application year: 1988
Main classification: C09D135
IPC codes: C09D123, C09D163, B05D7