WO1997047701A1

WO1997047701A1 - Coating composition based on polyglycidyl resin and polyacid curing agent

Info

Publication number: WO1997047701A1
Application number: PCT/US1997/009285
Authority: WO
Inventors: Mark A. Wozniak; Debra L. Singer; Stephen A. Kesicki; Dennis A. Simpson; Kurt G. Olson
Original assignee: Ppg Industries, Inc.
Priority date: 1996-06-13
Filing date: 1997-05-30
Publication date: 1997-12-18

Abstract

A curable coating composition made from a polyepoxide and a polyacid where the polyepoxide is at least one blend of at least two epoxy-containing acrylic copolymers, each containing (a) an ethylenically unsaturated monomer having at least one epoxy group and (b) a polymerizable ethylenically unsaturated monomer which is free of epoxy groups. The two epoxy-containing acrylic copolymers can be polymerized separately and blended together or preferably the two epoxy-containing acrylic copolymers are polymerized in the same reaction vessel using a successive step polymerization process. The curable coating composition is useful as an automotive topcoat in a composite color-plus-clear coating and provides for improved intercoat adhesion. A method of making the polyepoxide where the at least two epoxy-containing copolymers are polymerized in the same reaction vessel using a successive step polymerization.

Description

COATING COMPOSITION BASED ON POLYGLYCIDYL RESIN AND POLYACID CURING AGENT

The present invention relates to curable coating compositions based on poly epoxides and poly acid curing agents, to the process of preparing such a composition and to the use of such compositions in a process for preparing multi-layered coated articles comprising a pigmented or colored base coat and a transparent or clear coat, and to the coated articles themselves.

Original equipment finish coating systems for automobiles have utilized color- plus-clear technology for a number of years. This technology involves the application of a pigmented or otherwise colored base coat to a substrate, followed by the application of a transparent or clear topcoat to the base coat. The clear coat imparts high gloss and distinctness of image to the system as well as protecting the base coat from environmental attack.

However, a problem frequently encountered with such systems is poor adhesion between coating layers ("intercoat adhesion"). This can occur when a base coat or clear coat layer is applied over another clear coat layer during on-line repairs of original equipment paint jobs, and when a clear coat is applied over an electrocoat layer or a base coat is applied over a clear coat layer during custom two-tone painting. Two-tone painting involves the application of a base coat and clear coat system to an entire automotive part or portion thereof, after which an area is covered or "masked" so that the remaining exposed area can be painted with a different colored base coat followed by a clear coat. In these situations a base coat may be applied on top of a clear coat layer or on top of an electrocoated layer onto which clear coat overspray has deposited. Also, a clear coat layer may be applied directly on top of a previously applied clear coat layer.

It would be desirable to provide a color-plus-clear coating system which is useful as an original finish for automobiles with reduced intercoat adhesion problems from those of prior art systems, while maintaining other important properties for the coating such as mar resistance. It is especially desirable to improve intercoat adhesion for polyepoxide-polyacid coating systems such as those described in U.S. Patent 4,681,811.

SUMMARY OF THE TNVRNTION In accordance with the present invention, there is provided a curable coating composition having at least a polyepoxide with a polyacid curing agent and a process for making the coating. Also provided are a process for applying the composite coating to a substrate and the resultant coated article. The composite coating is formed by applying a film-forming composition to a substrate to form a base coat followed by applying to the base coat a film forming composition to form a transparent or clear coat over the base coat. The curable coating composition of the present invention can be the base coat or clear coat of the composite coating composition. The polyepoxide of the curable coating composition is at least one blend of at least two epoxy-containing acrylic copolymers, each containing at least (a) an ethylenically unsaturated monomer having at least one epoxy group, and (b) a polymerizable ethylenically unsaturated monomer which is free of epoxy groups. The' two epoxy-containing acrylic copolymers can be polymerized separately and blended together or preferably the two epoxy-containing acrylic copolymers are polymerized in the same reaction vessel using a successive step polymerization process. The use of the term "copolymer" includes at least the (a) and (b) aforementioned monomers and any additional monomers that are polymerized to produce each copolymer reaction product for the polyepoxide.

DETAILED DESCRIPTION OF THE INVENTION The polyepoxide and polyacid type of curable coating composition of the present invention can be solvent-borne, water-borne, or a powder coating film forming formulation. The water-borne coatings include those that are water- dilutable, where film forming binders are either molecular dispersed solutions in water or water/solvent blends or binders in the form of dispersions or emulsions. By the term "film forming" , it is meant that the resinous material upon curing at ambient or elevated temperature forms a self-supporting continuous film on at least a horizontal surface and even includes polymeric materials that upon removal of any solvents or carriers present in the polymer emulsion, dispersion, suspension or solution, can coalesce to form a film on at least a horizontal surface and is capable of curing into a continuous film. Preferably the curable coating composition of the present invention is a liquid crosslinkable clear coating composition for a base coat and clear coat composite coating composition. The at least one blend of the at least two epoxy-containing acrylic polymers or copolymers for the curable coating composition optionally may have additional blends of two epoxy-containing acrylic copolymers. Additionally, a blend can contain more than two epoxy-containing polymers, but two is preferred.

Each epoxy-containing acrylic copolymer, hereinafter referred to as "epoxy copolymer" , is a copolymer of at least (a) an ethylenically unsaturated monomer having at least one epoxy group and (b) a polymerizable ethylenically unsaturated monomer which is free of epoxy groups. Hereinafter, for a blend of epoxy copolymer (a^ and (b,) will designate the components of the first epoxy copolymer, and (a₂) and (b₂) will designate the components of the second epoxy copolymer. Generally (a,) and (a₂) can be the same type or different types of ethylenically unsaturated monomers having at least one epoxy group, as well as (b,) and (b₂) can be the same type or different types of polymerizable ethylenically unsaturated monomer which is free of epoxy groups. Optionally, one or more of the epoxy copolymers can contain in addition to the (a) and (b) monomers additional ethylenically unsaturated monomers free of epoxy groups, which can be the same or different from one epoxy copolymer to another epoxy copolymer. For optimal intercoat adhesion properties, the amount of such additional monomers should be less than 20, preferably less than 10 percent by weight of the solids of the epoxy copolymer.

Ethylenically unsaturated monomers containing epoxy groups suitable for use in the epoxy copolymer are those containing 1,2-epoxy groups as are known to those skilled in the art. Nonexclusive examples include glycidyl acrylate, glycidyl methacrylate, 3,4-epoxycyclohexylmethyl(meth)acrylate; 2-(3,4- epoxycyclohexyl)ethyl (meth)acrylate and allyl glycidyl ether. The epoxy group-containing ethylenically unsaturated monomer is preferably used in amounts of from about 30 to 70 and more preferably about 40 to 70 percent by weight of the total monomers used in preparing each epoxy-containing acrylic copolymer.

Ethylenically unsaturated monomers which do not contain epoxy groups can be any such monomers known to those skilled in the art that can react by free radical addition polymerization with epoxy-containing unsaturated monomers to form a copolymer with epoxy functionality. Nonexclusive examples of such 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 include: ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, benzyl acrylate, isobornyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, isobornyl methacrylate, isodecyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, and mixtures thereof. 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, vinyl propionate, and vinyl pivalate; hydroxyl functional free radical polymerizable monomers like hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl methacrylate, hydroxypropyl acrylate, hydroxybutyl methacrylate, and hydroxybutyl acrylate; and alkoxysilane monomers having free radical polymerizable functionality such as the vinyl-containing alkoxy silane like trialkoxy vinylsilane, methacrylate-functional silanes like polyalkoxysilylalkyl methacrylate such as trimethoxysilylpropyl methacrylate and other silanes that are free radically polymerizable such as those having the general formula Rx-Si-R'₍₄._X) where R is an organo group such as alkyl and/or alkoxy groups along with the aforedescribed type of unsaturation and R' is an alkyl and/or alkoxy group generally with 1 to 10 carbon atoms, and x is an integer of 1 or 2. Of course, as mentioned supra where more than one of the ethylenically unsaturated monomers which do not contain epoxy groups are present in the epoxy copolymer, the amount of this second such monomer should be less than 20, preferably less than 10 percent by weight of the solids of the epoxy copolymer in the blend or blends of epoxy copolymers. The ethylenically unsaturated acrylic monomer free of epoxy groups is preferably used in an amount for the first such monomer of from 30 to 70 and more preferably 30 to 60 percent by weight of the total monomers used in preparing each epoxy copolymer. The total weight percent of the monomers to prepare each epoxy copolymer should equal 100 percent.

Each epoxy copolymer can be prepared separately generally by any method known to those skilled in the art but preferably by solution polymerization techniques in the presence of suitable catalysts such as organic peroxides, such as di-t-amyl peroxide, t-butyl perbenzoate, t-amyl peracetate, t-butyl peracetate or ethyl-3,3-di(t-amylperoxy) butyrate or azo compounds, such as benzoyl peroxide, N,N'-azobis(isobutyronitrile) or alpha, alpha-dimethylazobis(isobutyronitrile). Other free radical polymerization methods and other catalysts or initiators known to those skilled in the art for preparing epoxy copolymers can also be used. The polymerization can be carried out in an organic solution in which the monomers are soluble as known to those skilled in the art. Suitable solvents are aromatic solvents such as xylene toluene and mixtures thereof, ketones such as methyl amyl ketone or ester solvents such as ethyl 3-ethoxypropionate. Also other materials may be present for or during the polymerization; for example, a chain transfer agent such as alpha-methyl styrene dimer is preferably present in conventional chain transfer amounts. Generally such a polymerization process is disclosed along with additional examples of both ethylenically unsaturated monomers with and without epoxy functionality in U.S. Patent 4,681,811.

After such polymerization, any two such prepared epoxy copolymers can be blended together. The blend can contain from about 5 to 95 percent of the first epoxy copolymer, and from 5 to 95 percent of the second epoxy polymer, where the percentages are based on weight of resin solids of the blend. If one of the epoxy copolymers present in the blend is derived from polymerization with more than one ethylenically unsaturated monomer without epoxy functionality, the total amount of that epoxy copolymer in the blend should be less than 20, preferably less than about 10 percent by weight of the resin solids of the blend. Preferably, the two epoxy copolymers are polymerized in the same reaction vessel using a successive step polymerization process.

The first step in the successive step polymerization process consists of adding (ai), the ethylenically unsaturated monomer having at least one epoxy group, and (b,), the ethylenically unsaturated monomer which is free of epoxy groups, of the first epoxy copolymer into a suitable reaction vessel and polymerizing the monomers in the presence of a suitable initiator and optionally solvents as described above. After components (a,) and (b,) have essentially completely reacted, the next step of the process is to add components (a₂) and (b₂) for the formation of the second epoxy copolymer to the same reaction vessel. These monomers are polymerized in the presence of the epoxy copolymer reaction product of monomer components (a_t) and (b,), a suitable initiator and optionally solvents as described above. Preferably, when additional epoxy copolymers are present in the blend of epoxy copolymers, each additional epoxy copolymer is successively polymerized by adding its components to the reaction vessel after the preceding epoxy copolymer has essentially completely reacted, and the components are polymerized in the presence of all previously polymerized acrylic polymers, a suitable initiator, and optionally solvents as described above. This process can be used for as many epoxy copolymers that are blended together to form the polyepoxide of the coating composition of the present invention.

By the terms "essentially completely reacted", it is meant that the addition of the components of the second or any subsequent epoxy copolymer should not start before at least 80, preferably at least 90 percent by weight of the components of the first or previous epoxy copolymer have reacted. Most preferably, the components of the second or subsequent epoxy copolymer should not be added to the reaction vessel until the components of the first previous epoxy copolymer have essentially completely reacted. A benefit of polymerizing in a successive step process is that any free monomer remaining from the previous polymerization step is scavenged and used in the polymerization of the next epoxy copolymer. This will reduce the need to purge the copolymer blend of excess monomer with excess initiator. The above-described successive polymerization process listed only two components for the first and second epoxy copolymers; however, the process can also be used if any, some, or all of the epoxy copolymers contain additional ethylenically unsaturated monomers as mentioned above. The epoxy copolymers typically have a range of molecular weights and a range of glass transition temperatures (Tg). For instance the weight average molecular weight can be between about 1000 and 20,000, preferably about 1000 to 10,000, and more preferably about 1000 to 5000. The molecular weight is determined by gel permeation chromatography using a polystyrene standard. Preferably, the epoxy copolymers for liquid coatings have a glass transition temperature (Tg) less than 50°C, more preferably less than 30°C, but for powder coatings higher Tg's can be used. The Tg is described in PRINCIPLES OF POLYMER CHEMISTRY, Flory, Cornell University Press, Ithaca, New York, 1953, pages 52-57. The Tg can be calculated as described by Fox in Bull. Amer. Physic. Society, 1,3, page 123 (1956). The Tg can be measured experimentally by using a penetrometer such as a Du Pont 940 Thermomedian Analyzer. The Tg of the polymers as used herein refers to the calculated values unless otherwise indicated. It is also most preferred that the two or more epoxy copolymers are essentially free of non-epoxy -containing acrylic polymer species. This means that in preparing either or both of the copolymers that whenever an amount of one or more of the ethylenically unsaturated monomers free of epoxy functionality are added for polymerization that the addition is accompanied by the addition of at least one ethylenically unsaturated monomer containing at least one epoxy group. The relative amounts of the accompanying addition can be any amount that results in the proper amount of the monomers for polymerization to the epoxy-containing acrylic copolymer as discussed herein.

The blend of the epoxy copolymers are polyepoxides in the polyepoxide and polyacid curable coating composition of the present invention. These polyepoxides are present in the coating composition in amounts of about 10 to 90 percent by weight, preferably from 20 to 80 percent by weight and more preferably from 30 to 70 percent by weight based on total weight of resin solids of the composition.

In addition to the blend of the epoxy copolymers described above, certain polyepoxide monomers and oligomers can also be present . Examples of these materials are described in U.S. Patent No. 4,102,942 in column 3, lines 1-16. Specific examples of such low molecular weight polyepoxides are 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate and bis(3,4-epoxycyclohexylmethyl) adipate. These low molecular weight polyepoxides may be used to increase the cure response and solids content of the curable compositions. When used, they are present in amounts up to 30, preferably 5 to 30 percent by weight based on the total weight of resin solids in the curable composition. The curable coating composition of the present invention further includes a polyacid component having a high average acid functionality. More specifically, the polyacid curing agent of the present invention on average contains greater than two acid groups per molecule, more preferably three or more and most preferably, four or more, such acid groups being reactive with the polyepoxide to form a cured or crosslinked coating as indicated by its resistance to organic solvent. The parameter of greater than two acid groups per molecule is intended to encompass polyacid curing agents that are di-functional curing agents and tri- or higher functionality polyacid curing agents and mixtures thereof. Polyacid curing agent mixtures including up to about 50 percent of a di-functional curing agent with a tri-functional curing agent are suitable. Also higher percentages of di-functional material can be useful alone or with the remainder of the curing agent mixtures as higher than tri-functional or when the polyepoxide component is highly functional. The acid functionality is preferably carboxylic acid, although acids such as phosphorus -based acid may be used. When the curable, non-gelled coating composition of the present invention is a powder coating, the polyacid can be 1 ,12- dodecanedicarboxylic acid. Preferably, the polyacid curing agent is a carboxylic acid terminated material having, on average, greater than two carboxylic acid groups per molecule. Among the polyacid curing agents which may be used include 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 cyclic 1 ,2-acid anhydrides or acid functional polyesters derived from polyols and polyacids or 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 fluid compositions while maintaining outstanding properties such as gloss and distinctness of image.

The half-ester is obtained by reaction between a polyol and a cyclic 1 ,2-acid anhydride under conditions sufficient to ring open the anhydride forming the half-ester with substantially no polyesterification occurring. Such reaction products are of relatively low molecular weight with narrow molecular weight distributions and low viscosity and provide lower volatile organic contents in the coating composition while still providing for excellent properties in the resultant coating. By substantially no polyesterification occurring means that the carboxyl groups formed by the reaction of the anhydride are not further esterified by the polyol in a recurring manner. By this it is meant that less than 10, preferably less than 5 percent by weight high molecular weight polyester is formed.

Two reactions may occur in combining the anhydride and the polyol together under suitable reaction conditions. The desired reaction mode involves ring opening the anhydride ring with hydroxyl, i.e.,

X-(-O-C-R-C-OH)_A

II II o o where X is the residue of the polyol after the polyol has been reacted with a 1 ,2-dicarboxylic acid anhydride, R is an organic moiety associated with the anhydride and A is equal to at least 2.

Subsequently, carboxylic acid groups formed by opening of the anhydride ring may react with hydroxyl groups to give off water via a condensation reaction. Although this latter reaction can be used, it is not preferred since it can lead to a polycondensation reaction resulting in products with higher molecular weights.

To achieve the desired reaction, the 1 ,2-acid anhydride and polyol are contacted together usually by mixing the two ingredients together in a reaction vessel. Preferably, reaction is conducted in the presence of an inert atmosphere such as nitrogen and in the presence of a solvent to dissolve the solid ingredients and/or to lower the viscosity of the reaction mixture. Examples of suitable solvents are high boiling materials and include, for example, ketones such as methyl amyl ketone, diisobutyl ketone, methyl isobutyl ketone; aromatic hydrocarbons such as toluene and xylene; as well as other organic solvents such as dimethyl formamide, n-amyl propionate, ethyl benzene, propylene glycol monomethylether acetate, ethyl 3-ethoxypropionate and N-methyl-pyrrolidone.

For the desired ring opening reaction and half-ester formation, a 1,2-dicarboxylic anhydride is used. Reaction of a polyol with a carboxylic acid instead of an anhydride would require esterification by condensation and elimination of water which would have to be removed by distillation. Under these conditions this would promote undesired polyesterification. Also, the reaction temperature is preferably low, that is, no greater than 135 °C, preferably less than 120°C, and usually within the range of 70°-135°C, preferably 90°-120°C. Temperatures greater than 135 °C are generally undesirable because they promote polyesterification, whereas temperatures less than 70 °C are undesirable because of sluggish reaction. The time of reaction can vary somewhat depending principally upon the temperature of reaction. Usually the reaction time will be from as low as 10 minutes to as high as 24 hours.

The equivalent ratio of anhydride to hydroxyl on the polyol is preferably at least about 0.8:1 (the anhydride being considered monofunctional) to obtain maximum conversion to the desired half-ester. Ratios less than 0.8: 1 can be used but such ratios result in increased formation of lower functionality half-esters.

Among the anhydrides which can be used in formation of the 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, glutaric 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, itaconic anhydride, citraconic anhydride and maleic anhydride. Among the polyols which can be used are simple polyols, that is, those containing from about 2 to 20 carbon atoms, as well as oligomeric polyols and polymeric polyols such as polyester polyols, polyurethane polyols and acrylic polyols. Among the simple polyols are diols, triols, tetrols and mixtures thereof. Examples of the polyols are preferably those containing from 2 to 10 carbon atoms such as aliphatic polyols. Specific examples include but are not limited to the following compositions: di-trimethylol propane; pentaerythritol; 1,2,3,4-butanetetrol; sorbitol; trimethylol propane; trimethylol ethane; 1 ,2,6-hexanetriol; glycerine; trishydroxyethyl isocyanurate; dimethylolpropionic acid; 1,2,4-butanetriol; TMP/epsilon-caprolactone triols; ethylene glycol; 1,2-propanediol; 1,3-propanediol; 1 ,4-butanediol; 1,5-pentanediol; 1 ,6-hexanediol; neopentyl glycol; diethylene glycol; dipropylene glycol;

1 ,4-cyclohexanedimethanol, 2,2,4-trimethyl-l ,3-pentanediol, and l-(2,2-dimethyl-3- hydroxypropyl) 2,2-dimethyl-3-hydroxypropionate.

With regard to oligomeric polyols, suitable polyols are polyols made from reaction of diacids with triols, such as trimethylol propane/cyclohexane diacid and trimethylol propane/adipic acid.

With regard to polymeric polyols, the polyester polyols are prepared by esterification of an organic polycarboxylic acid or anhydride thereof with organic polyols and/or an epoxide. Usually, the polycarboxylic acids and polyols are aliphatic or aromatic dibasic acids or acid anhydrides and diols.

The polyols which are usually employed in making the polyester include trimethylol propane, di-trimethylol propane, alkylene glycols such as ethylene glycol, neopentyl glycol and other glycols such as hydrogenated bisphenol A, cyclohexanediol, cyclohexanedimethanol, the reaction products of lactones and diols, for example, the reaction product of epsilon-caprolactone and ethylene glycol, hydroxy-alkylated bisphenols, polyester glycols, for example, poly(oxytetramethylene)glycol and the like. The acid component of the polyester consists primarily of monomeric carboxylic acids or anhydrides having 2 to 18 carbon atoms per molecule. Among the acids which are useful are phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, methylhexahydrophthalic acid, adipic acid, azelaic acid, sebacic acid, maleic acid, glutaric acid, chlorendic acid, tetrachlorophthalic acid and other dicarboxylic acids of varying types. Also, there may be employed higher polycarboxylic acids such as trimellitic acid and tricarballylic acid. However, the use of these higher functionality polycarboxylic acids are not preferred because of resultant high viscosities. Anhydrides that can be used can be those previously listed. Besides the polyester polyols formed from polybasic acids and polyols, polylactone-type polyesters can also be employed. These products are formed from the reaction of a lactone such as epsilon-caprolactone and a polyol such as ethylene glycol, diethylene glycol and trimethylolpropane.

Besides polyester polyols, polyurethane polyols such as polyester-urethane polyols which are formed from reacting an organic polyisocyanate with a polyester polyol such as those described above can be used. The organic polyisocyanate is reacted with a polyol so that the OH/NCO equivalent ratio is greater than 1 : 1 so that the resultant product contains free hydroxyl groups. The organic polyisocyanate which is used in preparing the polyurethane polyols can be an aliphatic or aromatic polyisocyanate or a mixture. Diisocyanates are preferred, although higher polyisocyanates such as triisocyanates can be used, but they do result in higher viscosities. Examples of suitable diisocyanates are 4,4'-diphenylmethane diisocyanate,

1 ,4-tetramethylene diisocyanate, isophorone diisocyanate and

4,4'-methylenebis(cyclohexyl isocyanate). Examples of suitable higher functionality polyisocyanates are polymethylene polyphenol isocyanates.

It is also possible to use acid-functional acrylic crosslinkers made from copolymerizing methacrylic acid and/or acrylic acid monomers with other ethylenically unsaturated copolymerizable monomers as the polyacid curing agent.

Alternatively, acid-functional acrylics can be prepared from hydroxy-functional acrylics reacted with cyclic anhydrides.

Alternatively, the reaction between polyol and a polyacid or cyclic anhydride can be conducted at higher temperatures through a condensation reaction to form acid functional polyesters of higher molecular weights.

The polyacid curing agent is present in the crosslinkable composition in amounts of about 10 to 90, preferably 20 to 80, more preferably 30 to 70 percent by weight based on total weight of resin solids. The curable coating compositions of the present invention may optionally contain an aminoplast resin. Typically, when used, the aminoplast resin is present in the composition in amounts up to about 30 percent by weight, more preferably from about 2 to 20 percent by weight based on total weight of resin solids in the curable composition. Also, blocked or unblocked isocyanate curing agents as are well known in the art can also be used in art recognized amounts. Also, mixtures of aminoplast resin and blocked isocyanate can be used.

Optionally, the crosslinkable composition can contain silane functionality which can be incorporated into the composition by using a reactive silane group-containing material such as gamma-methacryloXypropyltrimethoxysilane or mercaptopropyltrimethoxysilane which can be used in the preparation of the epoxy copolymers, as previously discussed. Such materials co-react with the polymerizing monomers or polymers forming a polymer with silane curing groups. Alternately, a silane group-containing material such as methyltrimethoxysilane in an amount up to 20, preferably 2 to 15 percent by weight, can be included in the composition.

The composition may optionally contain an aliphatic monocarboxylic acid containing at least 6, preferably from 8 to 22 carbon atoms such as described in U.S. Patent No. 4,764,430, column 6, line 48, to column 7, line 9. Examples of such acids include lauric acid and isostearic acid, which as preferred. These monocarboxylic acids, when used, are present in amounts up to 15 percent, preferably 0.5 to 10 percent by weight based on total weight of resin solids of the curable composition.

The composition may also contain an anhydride, preferably an anhydride which is a liquid at 25°C. The presence of such an anhydride in the composition provides for improved cure response. Examples of suitable anhydrides include dodecenyl succinic anhydride and alkyl-substituted hexahydrophthalic anhydrides wherein the alkyl group contains up to 7 carbon atoms, more preferably up to 4 carbon atoms, such as methyl hexahydrophthalic anhydride. The amount of the anhydride which is used in the curable composition can vary from about 0 to 40 percent, preferably from about 5 to 25 percent by weight based on total weight of resin solids of the curable composition.

To form one-package compositions, the curable coating composition of the present invention is substantially free of basic esterification catalyst. Although the absence of catalyst has a negative effect on the cure of the composition, it provides for a stable composition and is also beneficial in reducing or eliminating cure inhibition between layers in a color-plus-clear composite coating when the base coat contains an acid-catalyzed resinous binder. The high functionality associated with the polyepoxides and polyacid provide for sufficient cure response. In a preferred embodiment, the composition of the present invention has no or only small amounts of basic esterification catalyst such that the composition is stable for a time sufficient to allow formulation of the composition as a single component; i.e., one-package, composition.

To form multi-package or multi-component curable coating compositions in which the polyepoxide and polyacid curing agent are present in separate packages and combined shortly before application, an esterification catalyst to promote cure can be included in the composition. A number of such catalysts are known in the art. These catalysts include basic materials such as secondary amine catalysts, for example, piperidine and N-methyldodecylamine; tertiary amine catalysts such as N,N-dimethyldodecylamine, pyridine, and N,N-dimethylaniline; ammonium compounds, including tetrabutylammonium bromide, tetrabutylammonium hydroxide, and tetrabutylammonium acetate; phosphonium compounds, including ethyltriphenylphosphomum acetate and tetrabutyl phosphonium bromide; and other ammonium and phosphonium salts. When used, the catalysts are present in amounts up to 5, preferably 0.5 to 3 percent by weight based on total weight of resin solids of the curable composition.

The curable coating composition of the present invention may also contain a copolymer of an alpha olefin such as 1-octene or 1-decene and an olefϊnically unsaturated anhydride such as maleic anhydride. The anhydride group in such a polymer may be ring-opened with ethanol. The use of these copolymers in polyepoxide-polyacid curable compositions is described more fully in U.S. Patent No. 4,927,868. When used, the copolymers are present in amounts up to 25 percent, preferably 5 to 20 percent by weight based on total weight of resin solids of the curable composition.

Other optional ingredients, such as plasticizers, anti-oxidants, UV light absorbers and stabilizers may be formulated into the curable compositions of the present invention. When used, these ingredients are present (on an individual basis) in amounts up to 10 percent, preferably from about 0.1 to 5 percent by weight based on total weight of resin solids of the curable composition.

The equivalent ratio of the reactants present in the curable coating compositions are adjusted such that for each equivalent of carboxyl (anhydride, if present is considered monofunctional) there is 0.3 to 3.0, preferably 0.8 to 1.5 equivalent of epoxy.

The curable coating compositions preferably are formulated into liquid high solids coating compositions; that is, compositions containing greater than 40 percent, preferably greater than 50 percent by weight resin solids. The solids content is determined by heating a sample of the composition to 105-110°C for 1-2 hours to drive off the volatile material. Although the compositions are preferably liquid coating compositions, they may be formulated as powder coating compositions. The curable coating compositions of the invention may be applied to a substrate by any conventional coating technique such as brushing, spraying, dipping or flowing, but spray applications are preferred. Any of the known spraying techniques may be employed such as compressed air spraying, electrostatic spraying and eitfier 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 materials of the coating composition are crosslinked. The heating or curing operation is usually carried out at a temperature in the range of from 160-350°F (71-177°C) but if needed, lower or higher temperatures may be used as necessary to activate crosslinking mechanisms. The thickness of the coating is usually from about 0.5-5, preferably 1.2-3 mils.

Preferably , the compositions of the present invention are used to formulate clear coats for use in a color-plus-clear composite coatings. In a color-plus-clear composite coating, a pigmented or colored film-forming composition is applied to a substrate to form a base coat and a second film-forming composition is applied to the base coat to form a transparent top coat, or clear coat, over the base coat. The curable coating composition of the present invention also can be used as the base coat of the composite coating composition where the coating would have the pigments and/or colorant added to it along with the typical additives of a base coat. These are more fully discussed infra for the discussion of general base coats that are suitable for the composite coating where the curable coating composition of the present invention is the clear coat. For a composite coating where the curable coating composition is the clear coat, the film-forming composition of the base coat can be any of the compositions useful in coatings applications, particularly automotive applications. The film-forming composition comprises a resinous binder and a pigment to act as the colorant. Particularly useful resinous binders are acrylic polymers, polyesters, including alkyds, and polyurethanes.

The acrylic polymers are copolymers of one or more alkyl esters of acrylic acid or methacrylic acid optionally together with one or more other polymerizable ethylenically unsaturated monomers. These polymers may be either of the thermoplastic type or the thermosetting crosslinking type. Suitable alkyl esters of acrylic acid or methacrylic acid include methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethyl acrylate, butyl acrylate, and 2-ethyl hexyl acrylate. Suitable other copolymerizable ethylenically unsaturated monomers include vinyl aromatic compounds such as styrene and vinyl toluene; nitriles such acrylonitrile and methacrylonitrile; vinyl and vinylidene halides such as vinyl chloride and vinylidene fluoride and vinyl esters such as vinyl acetate.

Where the polymer is of the crosslinking type, suitable functional monomers may be used in addition to the other acrylic monomers mentioned above and include, for example, acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate. The coating composition in such cases contains a crosslinking agent such as an aminoplast. Other crosslinking agents such as polyisocyanates including blocked polyisocyanates may also be used. Also, the acrylic polymer can be prepared with N-(alkoxymethyl)acrylamides and N-(alkoxymethyl)methacrylamides which result in self-crosslinking acrylic polymers.

Besides acrylic polymers, the resinous binder for the base coat composition may be an alkyd resin or a polyester. Such polymers may be prepared in a known manner by condensation of polyhydric alcohols and polycarboxylic acids. Suitable polyhydric alcohols include ethylene glycol, propylene glycol, butylene glycol, 1,6-hexylene glycol, neopentyl glycol, diethylene glycol, glycerol, trimethylol propane, and pentaerythritol.

Suitable polycarboxylic acids include succinic acid, adipic acid, azelaic acid, sebacic acid, maleic acid, fumaric acid, phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, and trimellitic acid. Besides the polycarboxylic acids mentioned above, functional equivalents of the acids such as anhydrides where they exist or lower alkyl esters of the acids such as the methyl esters may be used.

Where it is desired to produce air-drying alkyd resins, suitable drying oil fatty acids may be used and include those derived from linseed oil, soya bean oil, tall oil, dehydrated castor oil, or tung oil.

The polyesters and alkyd resins contain free hydroxyl and/or carboxyl groups which are available for further crosslinking reactions. Suitable crosslinking agents are the amine or amide-aldehyde condensates (aminoplasts) or the polyisocyanate curing agents as are well known in the art. Polyurethanes can also be used as the resinous binder of the base coat.

Among the polyurethanes which can be used are polymeric polyols which are prepared by reacting the polyester polyols or acrylic polyols such as those mentioned above with a polyisocyanate such that the OH/NCO equivalent ratio is greater than 1 :1 so that free hydroxyl groups are present in the product.

The organic polyisocyanate which is used to prepare the polyurethane polyol can be an aliphatic or an aromatic polyisocyanate or a mixture of the two. Diisocyanates are preferred, although higher polyisocyanates can be used in place of or in combination with diisocyanates.

Examples of suitable aromatic diisocyanates are 4,4'-diphenylmethane diisocyanate and toluene diisocyanate. Examples of suitable aliphatic diisocyanates are straight chain aliphatic diisocyanates such as 1,6-hexamethylene diisocyanate. Also, cycloaliphatic diisocyanates can be employed. Examples include isophorone diisocyanate and 4,4'-methylene-bis-(cyclohexyl isocyanate). Examples of suitable higher polyisocyanates are 1,2,4-benzene triisocyanate and polymethylene polyphenyl isocyanate.

Most of the polymers prepared as described above are organic solvent-based polymers, although acrylic polymers can be prepared via aqueous emulsion polymerization techniques and used as aqueous-based base coat compositions. Water-based base coats in color-plus-clear compositions are disclosed in U.S. Patent Nos. 4,403,003 and 5,071,904, and the resinous compositions used in preparing these base coats can be used in the practice of this invention. Also, water-based polyurethanes such as those prepared in accordance with U.S. Patent No. 4,147,679 can be used as the resinous binder in the base coat.

The base coat also typically contains pigments to give it color. Compositions containing metallic flake pigmentation are useful for the production of so-called "glamour metallic" finishes chiefly upon the surface of automobile bodies. Proper orientation of the metallic pigments results in a lustrous shiny appearance with excellent flop. By "flop" is meant the visual appearance of brightness or lightness of the metallic coating with a change in viewing angle, that is, a change from 90 to 180 degrees. The greater the change from light to dark appearance with respect to viewing angle, the better the flop. Flop is important because it accentuates the lines of a curved surface such as on an automobile body. Suitable metallic pigments include in particular aluminum flake, copper bronze flake and mica. Besides the metallic pigments, the base coating compositions of the present invention may contain non-metallic color pigments conventionally used in surface coatings including inorganic pigments such as titanium dioxide, iron oxide, chromium oxide, lead chromate, and carbon black, and organic pigments such as phthalocyanine blue and phthalocyanine green. In general, the pigment is incorporated into the coating composition in amounts of about 1 to 80 percent by weight based on weight of coating solids. The metallic pigment is employed in amounts of about 0.5 to 25 percent by weight based on weight of coating solids.

If desired, the base coat composition may contain additional materials well known in the art of formulated surface coatings. These would include surfactants, flow control agents, thixotropic agents, fillers, anti-gassing agents, organic cosol vents, catalysts, and other customary auxiliaries. These materials can constitute up to 40 percent by weight of the total weight of the coating composition. The base coating compositions can be applied to various substrates to which they adhere. The compositions can be applied by conventional means including brushing, dipping, flow coating, spraying and the like, but they are most often applied by spraying. The usual spray techniques and equipment for air spraying and electrostatic spraying and either manual or automatic methods can be used.

The base coating compositions can be applied over virtually any substrate including wood, metals, glass, cloth, plastic, foam, including elastomeric substrates and the like. They are particularly useful in applications over metals, particularly metals which are primed with an electrodeposition primer, and elastomeric substrates that are found on motor vehicles. During application of the base coat composition to the substrate, a film of the base coat is formed on the substrate. Typically, the base coat thickness will be about 0.01 to 5, preferably 0.1 to 2 mils in thickness.

After application of the base coat to the substrate, a film is formed on the surface of the substrate by driving solvent, i.e., organic solvent or water, out of the base coat film by heating or by an air drying period. Preferably, the heating will only be sufficient and for a short period of time to ensure that the topcoat can be applied to the base coat without the former dissolving the base coat composition. Suitable drying conditions will depend on the particular base coat composition, and on the ambient humidity with certain water-based compositions, but in general a drying time of from about 1 to 5 minutes at a temperature of about 80-250°F (20- 121°C) will be adequate to ensure that mixing of the two coats is minimized. At the same time, the base coat film is adequately wetted by the topcoat composition so that satisfactory intercoat adhesion is obtained. Also, more than one base coat and multiple top coats may be applied to develop the optimum appearance. Usually between coats, the previously applied coat is flashed; that is, exposed to ambient conditions for about 1 to 20 minutes.

When the curable coating composition of the present invention is the clear coat or a composite coating, it is applied to the base coat by any of the conventional coating techniques mentioned above, with spray applications preferred. Typically 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 cure both coating layers. Curing conditions such as described above may be used.

The curable coating compositions of the present invention provide excellent intercoat, repair, or recoat adhesion. By this is meant that the curable coating composition can be applied as a coating to a substrate which has already been coated with one or more layers of coatings with the similar or different compositions, or additional layers of coatings with similar or different compositions which may also be applied on top of the present coating composition. Under these conditions the present coating composition will maintain adhesion to the layers to which it is adjacent. These conditions could occur in a two-tone operation where a portion of the painted article is coated or "recoated" with a different color for decorative purposes. Also, recoating can occur when a portion of the painted article is recoated to repair a defect in the original coating. Intercoat adhesion is typically measured by scribing a coated substrate with a "cross-hatch" pattern and securely applying a piece of adhesive tape onto the scribe. The tape is then removed and the substrate examined for removal of the coating layers. A rating is given based on the area and layers of coating material removed by the tape. As shown in the following examples, the curable compositions of the present invention have excellent intercoat adhesion as measured by this test.

It should be noted that the monomers of the epoxy copolymers can be copolymerized using polymerization techniques, as described above, all in one step to form an epoxy copolymer. However, when the resultant polymer is used in a coating composition, the coating does not exhibit acceptable intercoat adhesion properties. Surprisingly, even though the amounts of the monomers can be identical to the all in one step approach, when the polyepoxide is made by blending more than one epoxy copolymer or by successive step polymerization, and the resultant polyepoxide is used in a coating composition of the present invention, the intercoat adhesion is enhanced.

The invention will be further described by reference to the following examples which are presented for the purpose of illustration only and are not intended to limit the scope of the invention. Unless otherwise indicated, all amounts are listed as parts by weight. EXAMPLES A TO E

Examples A through E show the preparation of polyepoxide resins according to this invention. Table 1 below lists the total percentages of epoxy-containing monomer contained in each polyepoxide of Examples A through E.

TABLE 1

Examples A-E were prepared in accordance with the following general procedure. An initial solvent portion was charged into a four-neck flask, which served as the reaction vessel, and which was equipped with a thermocouple, a reflux condenser and a stirrer. The initial solvent charge was heated to reflux under a nitrogen gas blanket. A "first initiator mixture" was prepared in a separate premix flask. Also, the "first monomer mixture" was prepared in a separate second premix flask. The first initiator mixture was added dropwise from a first addition funnel into the reaction vessel over a period of four hours while maintaining the reaction at reflux and under a nitrogen gas blanket. Five minutes after the start of the initiator addition, the first monomer mixture was added dropwise from a second addition funnel to the reaction vessel over 2.5 hours. After the completion of the addition of the first monomer mixture, the reaction mixture was held at reflux for 30 minutes. During this time the first initiator mixture continued to be added to the reaction vessel. After this period of time a "second monomer mixture" , which was premixed, was added dropwise by an addition funnel to the reaction vessel over 30 minutes. After the completion of the addition of the first initiator mixture, the reaction mixture was held at reflux for 30 minutes. After this period of time a " second initiator mixture", which was premixed, was added dropwise by an addition funnel to the reaction vessel over 30 minutes. (After the completion of each addition a portion of the solvent was added as a rinse.) The reaction was then held at reflux under the nitrogen blanket for two hours after which the reaction mixture was cooled and poured. The reaction mixture was analyzed for solids content, weight average molecular weight as determined by gel permeation chromatography using a polystyrene standard, and epoxy equivalent weight. The percent solids of the copolymer were obtained by a procedure based on the American Society of Testing Materials (ASTM) standard method D-2369. The method used for epoxy equivalent weight was based on a procedure by R. Jay, Anal. Chem., 3_6_, 667, (1964), which is also described in Quantitative Organic Analysis via Functional Groups, by S. Siggia and J. G. Hanna, 4th Ed, Robert E. Kreiger Publishing Company, Malabar, Florida, 1988.

In the preparation of Example A, Solvesso 100 was the solvent which was charged into the reaction vessel in the parts by weight shown in Table 2. The rm-amyl peracetate (60% solution) and Solvesso 100 were mixed together as a "first initiator mixture" in the parts shown in Table 2. Glycidyl methacrylate, butyl methacrylate and methylstyrene dimer were also mixed together as the "first monomer mixture" in the amounts shown in Table 2. The "second monomer mixture" was premixed from glycidyl methacrylate, methyl methacrylate, styrene and methylstyrene dimer in the amounts shown in Table 2. The "second initiator mixture" was premixed from di-terf-amyl peroxide and Dowanol PM acetate in the amounts shown in Table 2. Examples B, C, D and E were synthesized in a similar manner with the components shown in Table 2. TABLE 2

Components Example Example Example Example Example A B C D E

Initial solvent charge

Solvesso 100¹ 496.8 496.8 496.8 496.8 496.8

First initiator mixture tert-Amyl peracetate² j 160.0 160.0 160.0 160.0 160.0

Solvesso 100 80.0 80.0 80.0 80.0 80.0

Rinse (Solvesso 100) 5.0 5.0 5.0 5.0 5.0

First monomer mixture

Glycidyl methacrylate 776.1 678.7 559.6 828.8 428.8

Butyl methacrylate 492.8 652.8 812.8 332.8 972.8

Methylstyrene dimer 24.6 25.9 26.6 22.4 27.7

Rinse (Solvesso 100) 5.0 5.0 5.0 5.0 5.0

Second monomer mixture

Glycidyl methacrylate 183.9 121.3 80.4 291.2 51.2

Methyl methacrylate 3.2 3.2 3.2 3.2 3.2

Styrene 1 12.0 112.0 112.0 112.0 112.0

Methylstyrene dimer 7.39 6.08 5.41 9.6 4.32

Rinse (Solvesso 100) 5.0 5.0 5.0 5.0 5.0

Second initiator mixture

Di-rerf-amyl peroxide³ 16.0 16.0 16.0 16.0 16.0

Dowanol PM acetate⁴ 1 17.9 117.9 117.9 117.9 117.9

Rinse (Dowanol PM acetate) 30.0 30.0 30.0 30.0 30.0

Resin properties

% Solids (110°C/1 hour) 65.3 65.5 63.7 65.2 64.6

Epoxy Equivalent Weight 367.5 445.9 545.1 311.8 734.9

Weight average molecular weight 2597 2468 2201 2693 2696

Available from Exxon.

² Available as a 60% solution in odorless mineral spirits as Lupersol 555 M60 from Elf Atochem North America, Inc.

Available from Elf Atochem North America, Inc.

Propylene glycol monomethylether acetate, commercially available from Dow Chemical. EXAMPLE F (COMPARATIVE)

A comparative polyepoxide resin having an epoxy-containing monomer content of 60 percent was prepared as follows.

An initial solvent portion was charged into a four-neck flask, which served as the reaction vessel, and which was equipped with a thermocouple, a reflux condenser and a stirrer. The initial solvent charge was heated to reflux under a nitrogen gas blanket. Charge 2 was prepared in a separate premix flask and was added dropwise from a first addition funnel into the reaction vessel over a period of time 4 hours while maintaining the reaction at reflux and under a nitrogen gas blanket. Fifteen minutes after the start of the initiator addition, Charge 3, which was prepared in a separate second premix flask, was added dropwise from a second addition funnel to the reaction vessel over 2.5 hours. After the completion of the addition of Charge 3, the reaction mixture is held at reflux for 30 minutes. During this time Charge 2 continued to be added to the reaction vessel. After this period of time Charge 4, which was premixed, was added dropwise by an addition funnel to the reaction vessel over 30 minutes. After the completion of the addition of Charge 2, the reaction mixture was held at reflux for one hour. The reaction mixture was then cooled to 130°C. Charge 5, which was premixed, was added dropwise by an addition funnel to the reaction vessel over 1 hour. The reaction was then held at 130°C under the nitrogen blanket for one hour. Charge 6, which was premixed, was added dropwise by an addition funnel to the reaction vessel over 1 hour. The reaction was then held at 130°C under the nitrogen blanket for one hour. Charge 7, which was premixed, was added dropwise by an addition funnel to the reaction vessel over one hour. After the addition of Charge 7 was complete, the reaction was held at 130°C under a nitrogen blanket for two hours after which the reaction mixture was cooled and poured. The reaction mixture was analyzed for solids content, weight average molecular weight as determined by gel permeation chromatography using a polystyrene standard, and epoxy equivalent weight as described above.

In the preparation of Example F, xylene and ethyl 3-ethoxypropionate were the solvents which were charged into the reaction vessel in the parts by weight shown in Table 3. The tert-amyl peracetate (60% solution) and ethyl 3- ethoxypropionate were mixed together as the Charge 2 in the parts shown in Table 3. Glycidyl methacrylate, methyl methacrylate, butyl methacrylate, styrene and methylstyrene dimer were also mixed together as Charge 3 in the amounts shown in Table 3. Charge 4 was premixed from methyl methacrylate, butyl methacrylate, styrene and methylstyrene dimer in the amounts shown in Table 3. Charges 5, 6, and 7 were premixed from tert-butyl perbenzoate and ethyl 3- ethoxypropionate in the amounts shown in Table 3.

¹ Commercially available as EKTAPRO EEP from Eastman Chemicals

³ Available from Elf Atochem North America, Inc.

EXAMPLE G (COMPARATIVE)

A comparative polyepoxide resin having an epoxy-containing monomer content of 40 percent was prepared as follows. An initial solvent portion was charged into a four-neck flask, which served as the reaction vessel, and which was equipped with a thermocouple, a reflux condenser and a stirrer. The initial solvent charge is heated to reflux under a nitrogen gas blanket. Charge 2 was prepared in a separate premix flask and was added dropwise from a first addition funnel into the reaction vessel over a period of 4 hours while maintaining the reaction at reflux and under a nitrogen gas blanket. Fifteen minutes after the start of Charge 2, the Charge 3, which was prepared in a separate second premix flask, was added dropwise from a second addition funnel to the reaction vessel over 2.5 hours. After the completion of the addition of Charge 3, the reaction mixture is held at reflux for 30 minutes. During this time Charge 2 continued to be added to the reaction vessel. After this period of time Charge 4, which was premixed, was added dropwise by an addition funnel to the reaction vessel over 30 minutes. After the completion of the addition of Charge 2, the reaction mixture was held at reflux for one hour. After this period of time Charge 5, which was premixed, was added dropwise by an addition funnel to the reaction vessel over 30 minutes. (After the completion of each addition a portion of the solvent was added as a rinse.) The reaction is then held at 130°C under the nitrogen blanket for two hours after which the reaction mixture is cooled and poured. The reaction mixture was analyzed for solids content, weight average molecular weight as determined by gel permeation chromatography using a polystyrene standard, and epoxy equivalent weight as described above.

In the preparation of Example G, Solvesso 100 was the solvent which was charged into the reaction vessel in the parts by weight shown in Table 4. The tert-amyl peracetate (60% solution) and Solvesso 100 were mixed together as Charge 2 in the parts shown in Table 4. Glycidyl methacrylate, methyl methacrylate, butyl methacrylate and styrene were also mixed together as the Charge 3 in the amounts shown in Table 4. Charge 4 was premixed from butyl methacrylate and styrene in the amounts shown in Table 4. Charge 5 was premixed from di-tert-amyl peroxide and Dowanol PM acetate in the amounts shown in Table 4. TABLE 4

1 Available from Exxon.

Available as a 60% solution in odorless mineral spirits as Lupersol 555 M60 from Elf Atochem North America, Inc.

Available from Elf Atochem North America, Inc.

⁴ Propylene glycol monomethylether acetate, commercially available from Dow Chemical.

EXAMPLE H A polyacid curing agent was prepared as follows. An initial solvent portion and the pentaerythritol were charged into a four-neck flask, which served as the reaction vessel, and which was equipped with a thermocouple, a reflux condenser and a stirrer. The initial charge was heated to 125 °C under a nitrogen gas blanket. Charge 2 was added dropwise from an addition funnel into the reaction vessel over a period of 1 to 2 hours while maintaining the reaction at 125 °C and under a nitrogen gas blanket. After the completion of the addition, the reaction mixture was cooled to 115°C and held at that temperature for 4 hours. Charge 3 was then added to the reaction mixture. The reaction was then held at 105°C under a nitrogen blanket for 30 minutes, after which the reaction mixture was cooled and poured. The reaction mixture was analyzed for solids content, acid number and weight average molecular weight as determined by gel permeation chromatography using a polystyrene standard. The aforementioned measured characteristics of the copolymer were obtained by procedures based on the following American Society of Testing Materials (ASTM) standard methods: D-2369 for percent solids and D- 1639 for acid number. In the preparation of Example H, n-amyl propionate and pentaerythritol were the components of the initial charge which were charged into the reaction vessel in the parts by weight shown in Table 5. The methylhexahydrophthalic anhydride was added as Charge 2 in the parts shown in Table 5. n-Propyl alcohol was added as Charge 3 in the parts by weight shown in Table 5.

TABLE 5

Clear coat compositions were prepared in Examples 1 through 8 using the polyepoxide resins of Example A through G, and the polyacid curing agent of Example H. Examples 1 and 2 are comparative examples using the comparative polyepoxides of Examples F and G. Example 8 was a comparative clear coat in which the polyepoxide was comprised of 75 percent of the polyepoxide of comparative Example F and 25 percent of the polyepoxide of comparative Example G, the percentages based on epoxy equivalents. Examples 3 through 7 were clear coats made utilizing the polyepoxides made according to this invention of Examples A through E.

Each clear coat composition of Examples 1 through 8 was made by first mixing together in a can under agitation TINUVIN 328, TINUVIN 123, polybutylacrylate, ethyl 3-ethoxypropionate, and CYMEL 202. To this mixture was added under agitation the appropriate polyepoxide from Examples A to G, followed by the polyacid curing agent of Example H. The amounts of each component used are listed in each of the Examples 1 to 8.

EXAMPLE 1 (COMPARATIVE) A clear coat composition was prepared from the polyepoxide of comparative

Example F, having an epoxy monomer content of 60 percent.

2-(2'-Hydroxy-3',5'-ditert-amylphenyl) benzotriazole UV light stabilizer available from Ciba-Geigy Corp.

Sterically hindered tertiary amine light stabilizer available from Ciba Geigy Corporation with aminoether which is bis-(l-octyloxy-2,2,6,6-tetramethyl-4-pi-peridinyl) sebacate.

Butylated and methylated melamine-formaldehyde resin available from CYTEC Industries, Inc.

EXAMPLE 2 (COMPARATIVE)

A clear coat composition was prepared from the polyepoxide of comparative Example G, having an epoxy monomer content of 40 percent.

EXAMPLE 3 A clear coat composition was prepared from the polyepoxide of Example E, having an epoxy monomer content of 30 percent.

EXAMPLE 4

A clear coat composition was prepared from the polyepoxide of Example C, having an epoxy monomer content of 40 percent.

EXAMPLE 5 A clear coat composition was prepared from the polyepoxide of Example B, having an epoxy monomer content of 50 percent.

EXAMPLE 6

A clear coat composition was prepared from the polyepoxide of Example A, having an epoxy monomer content of 60 percent.

EXAMPLE 7

A clear coat composition was prepared from the polyepoxide of Example D, having an epoxy monomer content of 70 percent.

EXAMPLE 8 (COMPARATIVE) A clear coat composition was prepared with a polyepoxide that consists of

75 percent of the polyepoxide of comparative Example F and 25 percent of the polyepoxide of comparative Example G, the percentages based on epoxy equivalents.

The spray viscosity, as measured by a #4 Ford Cup, and the percent weight solids of the clear coats of Examples 1 through 8 are listed below in Table 6.

TABLE 6

EXAMPLE 9 The clear coat compositions of Examples 1 through 8 were tested as follows.

Test panels coated with electrocoat primer, commercially available from PPG Industries, Inc. as ED-5000, were first basecoated, by spray application to a film thickness of 0.6 mils ( 15.2 μ), with a black waterborne base coat, commercially available from PPG Industries, Inc. as HWB-9517. The basecoated panels were then flash baked for 5 minutes at 200°F (93 °C) before spray applying each clear coat to the flash baked base coat. Each clear was spray applied in two coats to a film thickness of 1.7 to 2.3 mils (43.2 μ to 58.4 μ) with a 90 second ambient flash between coats and a five minute ambient flash before baking the composite base coat/clear coat film. One set of test panels of each clear coat composition were baked at 285 °F (140°C) for 30 minutes, and another set of test panels were baked at 315°F (157°C) for 30 minutes. The higher bake temperature represents a more severe recoat condition. The test panels were then recoated either with a full base coat/clear coat system as described above or just with a clear coat. All recoat test panels were baked at 285 °F for 30 minutes. The composite coatings were then tested for intercoat adhesion using the method in ASTM D-3359. In addition, 20° gloss was measured with a Gloss Meter available from Pacific Scientific, and

Distinctness of Image (DOI) was measured with a Dorigon II DOI meter available from Hunter Labs prior to recoating the test panels. Mar resistance was tested using the following procedure.

1. Dry Bon- Ami Cleanser (Feldspar/Calcite cleanser manufactured by Faultless Starch/Bon Ami Company, Kansas City, Missouri) was applied to one half of the test panel.

2. The excess cleanser was tapped off so that a thin film of cleanser remained on the test panel.

3. The acrylic finger of an Atlas AATCC Crockmeter, model CM-5 manufactured by Atlas Electric Devices Company, Chicago, Illinois, was covered with a two inch by two inch piece of felt cloth, obtainable from Atlas Electric Devices.

4. The cleanser coated panel was rubbed with the felt cloth ten times (ten double rubs) using the Crockmeter. 5. The test was repeated at least once changing the felt cloth after each test. 6. After testing, the panel was washed with water to remove the cleanser and then carefully dried. 7. The 20° gloss was measured using a gloss meter manufactured by Pacific Scientific, on both the unmarred part of the panel and the marred parts of the panel. The difference in gloss was a measure of the mar resistance. The smaller the difference the greater the mar resistance.

The test results are listed in Tables 7 and 8. The data of Table 7 shows that generally as the total percentage of epoxy-containing monomer contained in the polyepoxide increases, the mar resistance of a coating composition containing the polyepoxide increases. Comparing the coating of comparative Example 1 (60% epoxy-containing monomer) with the coating made according to this invention described in Example 6 (60% epoxy-containing monomer) shows that the mar resistance is approximately equivalent. At 40% epoxy-containing monomer level, the mar resistance of the comparative coating (Example 2) and the coating prepared according to the present invention (Example 4) are also approximately equal, but lower than at 60% . It has been understood that normally higher levels of epoxy- containing monomer in the polyepoxide can produce better mar resistance, but can produce unacceptable intercoat adhesion properties. Table 8 shows that the coatings made according to the present invention exhibit acceptable adhesion, even at higher levels of epoxy-containing monomer in the polyepoxide of the coating. Comparing the high level of epoxy-containing monomer (60%) of Example 6 with comparative Example 1 shows that intercoat adhesion is greatly increased with this invention.

TABLE 7

* Comparative Example

** The polyepoxide is a mixture containing 75 % of the 60% polyepoxide of Example 1 and 25% of the 50% polyepoxide of Example 2.

¹ Total percentage of epoxy-containing monomer in the polyepoxide of the coating.

² Measured using the Mar Resistance Test described above.

TABLE 8

* Comparative Example

** The polyepoxide is a mixture containing 75 % of the 60% polyepoxide of Example 1 and 25 % of the 50% polyepoxide of Example 2.

1 Total percentage of epoxy-containing monomer in the polyepoxide of the coating.

Tape Adhesion Test per ASTM D-3359 measuring recoat adhesion of base coat/clear coat to base coat/clear coat (BC/CC to BC/CC) and clear coat to base coat/clear coat (CC to BC/CC).

Rating basis: 0 = complete loss of adhesion to 5 = no loss of adhesion. The results tabulated in Tables 7 and 8 show that the claimed invention provides clear coat compositions that have high gloss and DOI while exhibiting necessary mar resistance and intercoat adhesion properties.

Claims

What is claimed is:

1. A coating composition comprising a polyepoxide and a polyacid curing agent, wherein the polyepoxide comprises at least one blend of at least two epoxy-containing acrylic copolymers each epoxy-containing acrylic copolymer comprising (i) a polymerizable ethylenically unsaturated monomer having at least one epoxy group, and (ii) a polymerizable ethylenically unsaturated monomer which is free of epoxy groups.

2. The coating composition of claim 1 wherein the epoxy-containing acrylic copolymers of each blend are polymerized successively, one after another, where after a first epoxy-containing acrylic copolymer successively polymerized epoxy-containing acrylic copolymers are polymerized in the presence of at least one of the preceding polymerized epoxy-containing acrylic copolymers of the blend.

3. The coating composition of claim 2 wherein the blend of at least two epoxy-containing acrylic copolymers from successive polymerization has each copolymer essentially completely polymerized before the formation of the next epoxy-containing acrylic copolymer.

4. The coating composition of claim 1 wherein the polyepoxide is essentially free of non-epoxy-containing acrylic polymer species.

5. The coating composition of claim 1 wherein the polyepoxide is present in the coating composition in an amount of about 10 to 90 percent by weight of resin solids and the polyacid curing agent is present in an amount of about 10 to 90 percent by weight of resin solids.

6. The coating composition of claim 1 wherein the polyepoxide is present in the coating composition in an amount of about 30 to 70 percent by weight of resin solids and the polyacid curing agent is present in an amount of about 30 to 70 percent by weight of resin solids.

7. The coating composition of claim 1 wherein the polymerizable ethylenically unsaturated monomer having at least one epoxy group of a first epoxy-containing acrylic copolymer is present in an amount of about 30 to 70 percent by weight of the first copolymer solids, the polymerizable ethylenically unsaturated monomer having at least one epoxy group of a second epoxy-containing acrylic copolymer is present in an amount of about 30 to 70 percent by weight of the second copolymer solids, and wherein the polymerizable ethylenically unsaturated monomer which is free of epoxy groups of the first epoxy-containing acrylic polymer is present in an amount of about 30 to 70 percent by weight of the first copolymer solids, and the polymerizable ethylenically unsaturated monomer which is free of epoxy groups of the second epoxy-containing acrylic copolymer is present in an amount of about 30 to 70 percent by weight of the second acrylic polymer solid.

8. The coating composition of claim 1 wherein the polymerizable ethylenically unsaturated monomer having at least one epoxy group for both a first and second epoxy-containing acrylic copolymer is present in an amount of about 40 to 70 percent by weight of the first and of the second epoxy-containing acrylic copolymer solids, and the polymerizable ethylenically unsaturated monomer free of epoxy groups for both the first and the second epoxy-containing acrylic copolymer is present in an amount of about 30 to 60 percent by weight of the first and of the second epoxy-containing acrylic copolymer solids, respectively.

9. The coating composition of claim 1 wherein in a blend of epoxy- containing acrylic copolymers, a first epoxy-containing acrylic copolymer is present in an amount of about 5 to 95 percent by weight of resin solids of the blend of epoxy-containing acrylic copolymers, and a second epoxy-containing acrylic copolymer is present in an amount of about 5 to 95 percent by weight of resin solids of the blend of epoxy-containing acrylic copolymers.

10. The coating composition of claim 1 wherein the ethylenically unsaturated monomer having at least one epoxy group is chosen from the group consisting of glycidyl acrylate, glycidyl methacrylate and allyl glycidyl ether and are the same or different from one epoxy-containing acrylic copolymer to the other epoxy-containing acrylic copolymer.

11. The coating composition of claim 1 wherein the at least one ethylenically unsaturated monomer free of epoxy groups is the same or different for each epoxy-containing acrylic copolymer and is chosen from the group consisting of: ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, benzyl acrylate, isobornyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, isobornyl methacrylate, isodecyl methacrylate cyclohexyl methacrylate, benzyl methacrylate, methyl methacrylate, vinyl-containing alkoxy silanes, methacrylate-containing alkoxy silanes and styrene and mixtures thereof, where the second and any additional ethylenically unsaturated monomer free of epoxy groups that is present is in an amount of less than 10 percent by weight of total resin solids for the combined epoxy-containing acrylic copolymers.

12. The coating composition of claim 1 additionally comprising optional components selected from the group consisting of an aminoplast resin, and blocked isocyanate, and mixtures thereof.

13. The coating composition of claim 1 wherein the polyacid curing agent is a carboxylic acid-terminated material having an average of greater than two carboxylic acid groups per molecule.

14. The coating composition of claim 13 wherein the polyacid curing agent is a carboxylic acid-terminated polyester.

15. The coating composition of claim 14 wherein the carboxylic acid-terminated polyester is of the structure:

X-(-O-C-R-C-OH)_A

O O

where X is a residue of a polyol after the polyol has been reacted with a 1,2-dicarboxylic acid anhydride, R is an organic moiety associated with the anhydride, and A is equal to at least two.

16. The coating composition of claim 15 wherein the polyol is selected from the group consisting of di-trimethylol propane, pentaerythritol, 1,2,3,4-butanetetrol, sorbitol, trimethylol propane, trimethylol ethane, 1,2,6-hexanetriol, glycerin, trishydroxyethyl isocyanurate, dimethylol propionic acid, 1,2,4-butanetriol, neopentyl glycol, 1,6-hexane diol, l-(2,2-dimethyl-3- hydroxypropyl) 2,2-dimethyl-3-hydroxypropionate, and mixtures thereof.

17. The coating composition of claim 1 wherein the equivalent ratio of carboxyl to epoxy is from 0.5 to 1.5: 1.

18. The coating composition of claim 1 wherein in the blend of at least two epoxy-containing acrylic copolymers, at least one of the copolymers is a polymerized reaction product of at least one additional polymerizable ethylenically unsaturated monomer different from the ethylenically unsaturated monomer having at least one epoxy group and a first ethylenically unsaturated monomer free of epoxy groups, and any said additional polymerizable ethylenically unsaturated monomers free of epoxy groups are present in an amount of less than 20 percent by weight of resin solids of said epoxy-containing acrylic copolymer.

19. The coating composition of claim 18 wherein any additional polymerizable ethylenically unsaturated monomers free of epoxy groups are present in an amount of less than 10 percent by weight of resin solids of said epoxy- containing acrylic copolymer.

20. A coating composition comprising from about 30 to 70 percent by weight of resin solids of a polyepoxide and from about 30 to 70 percent by weight of a polyacid curing agent, wherein the polyepoxide comprises a blend of two epoxy-containing acrylic copolymers, each epoxy-containing acrylic copolymer comprising (i) a polymerizable ethylenically unsaturated monomer having at least one epoxy group and (ii) a polymerizable ethylenically unsaturated monomer which is free of epoxy groups, wherein the epoxy-containing acrylic polymers of each blend are polymerized successively, one after another, in the presence of the preceding polymerized epoxy-containing copolymers of the blend.

21. A process for producing a coating composition comprising:

(I) adding (a), a first ethylenically unsaturated monomer having at least one epoxy group, and (b), a first ethylenically unsaturated monomer which is free of epoxy groups into a reaction vessel; (II) polymerizing the monomers (a) and (b) in the presence of an initiator to form a first epoxy-containing acrylic copolymer;

(III) after components (a) and (b) have essentially completely reacted, adding (c) a second ethylenically unsaturated monomer having at least one epoxy group, and (d), a second ethylenically unsaturated monomer which is free of epoxy groups, which are the same or different from the first (a) and

(b), into the same reaction vessel;

(IV) polymerizing (c) and (d) in the presence of an initiator and the first epoxy-containing acrylic copolymer of (II) to form a second epoxy- containing acrylic copolymer and a polyepoxide blend of the first and second epoxy-containing acrylic copolymers; and

(V) mixing together a polyacid curing agent and the polyepoxide blend of (IV) to form a coating composition.

22. The process of claim 21 wherein the polyepoxide is present in the coating composition in an amount of about 10 to 90 percent by weight of resin solids and the polyacid curing agent is present in amount of about 10 to 90 percent by weight of resin solids.

23. The process of claim 21 wherein the polyepoxide is present in the coating composition in an amount of about 30 to 70 percent by weight of resin solids and the polyacid curing agent is present in amount of about 30 to 70 percent by weight of resin solids.

24. The process of claim 21 wherein: (a) is present in an amount of about 30 to 70 percent of the total solids of (a) and (b), (b) is present in an amount of about 30 to 70 percent of the total solids of (a) and (b), (c) is present in an amount of about 30 to 70 percent of the total solids of (c) and (d), and (d) is present in an amount of about 30 to 70 percent of the total solids of (c) and (d).

25. The process of claim 21 wherein (a) and (c) are the same or different and are chosen from the group consisting of glycidyl acrylate, glycidyl methacrylate and allyl glycidyl ether.

26. The process of claim 21 wherein the ethylenically unsaturated monomer free of epoxy groups (c) and (d) for each epoxy-containing acrylic copolymer is chosen from the group consisting of: ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, benzyl acrylate, isobornyl acrylate, isodecyl methacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, isobornyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, methyl methacrylate, vinyl-containing alkoxy silanes, methacry late-containing alkoxy silanes and styrene and mixtures thereof, where the second and any additional ethylenically unsaturated monomer free of epoxy groups that is present is in an amount of less than 20 percent by weight of total resin solids for the combined epoxy-containing acrylic copolymers.

27. The process of claim 26 wherein any additional ethylenically unsaturated monomer free of epoxy groups that is present is in an amount of less than 10 percent by weight of total resin solids for the combined epoxy-containing acrylic copolymers.

28. The process of claim 21 wherein the first epoxy-containing acrylic copolymer is present in the polyepoxide blend in an amount of about 5 to 95 percent by weight and the second epoxy-containing acrylic copolymer is present in the polyepoxide blend in an amount of about 5 to 95 percent by weight, the percentages based on the polyepoxide solids.

29. The process of claim 21 additionally comprising adding an optional component selected from the group consisting of aminoplast resin and blocked isocyanate and mixtures thereof, to the coating composition of (V).

30. The process of claim 21 wherein the polyacid curing agent is a carboxylic acid-terminated material having an average of greater than two carboxylic acid groups per molecule.

31. The process of claim 29 wherein the polyacid curing agent is a carboxylic acid-terminated polyester of the structure:

X-(-O-C-R-C-OH)_A

O O where X is a residue of a polyol after the polyol has been reacted with a 1 ,2-dicarboxylic acid anhydride, R is an organic moiety associated with the anhydride, and A is equal to at least two.

32. The process of claim 30 wherein the polyol is selected from the group consisting of di-trimethylol propane, pentaerythritol, 1,2,3,4-butanetetrol, sorbitol, trimethylol propane, trimethylol ethane, 1,2,6-hexanetriol, glycerin, trishydroxyethyl isocyanurate, dimethylol propionic acid, 1 ,2,4-butanetriol, neopentyl glycol, 1 ,6-hexanediol, l-(2,2-dimethyl-3-hydroxypropyl) 2,2-dimethyl-3- hydroxypropionate, and mixtures thereof.

33. The process of claim 21 wherein the equivalent ratio of carboxyl to epoxy is from 0.5 to 1.5: 1.

34. The process of claim 21 , additionally comprising successively forming additional epoxy-containing acrylic copolymers in the polyepoxide blend by polymerizing an ethylenically unsaturated monomer having at least one epoxy group and an ethylenically unsaturated monomer which is free of epoxy groups of each additional epoxy-containing acrylic copolymer in the presence of an initiator and all previously formed epoxy-containing acrylic copolymers of the polyepoxide blend.

35. The process of claim 21 wherein at least one of the epoxy-containing acrylic reaction products contains at least one additional polymerizable ethylenically unsaturated monomer different from the ethylenically unsaturated monomer having at least one epoxy group and the ethylenically unsaturated monomer free of epoxy groups, and any additional polymerizable ethylenically unsaturated monomers free of epoxy groups are present in an amount of less than 20 percent by weight of resin solids of said epoxy-containing acrylic copolymer.

36. The process of claim 35 wherein any additional polymerizable ethylenically unsaturated monomers free of epoxy groups are present in an amount of less than 10 percent by weight of resin solids of said epoxy-containing acrylic copolymer.

37. A process for applying a composite coating to a substrate which comprises applying to the substrate a colored film-forming composition to form a base coat, and applying to said base coat a clear film forming composition to form a transparent topcoat over the base coat characterized in that the clear film-forming composition is a crosslinkable coating composition comprising a polyepoxide and a polyacid curing agent, wherein the polyepoxide comprises at least one blend of at least two epoxy-containing acrylic copolymers, each epoxy-containing acrylic copolymer comprising (i) a polymerizable ethylenically unsaturated monomer having at least one epoxy group and (ii) a polymerizable ethylenically unsaturated monomer which is free of epoxy groups, wherein the epoxy-containing acrylic polymers of each blend are polymerized successively, one after another, in the presence of the preceding polymerized epoxy-containing polymers of the blend.