EP0115484A1

EP0115484A1 - Acrylic hydroxy-epoxyhigh solids coating compositions

Info

Publication number: EP0115484A1
Application number: EP82903089A
Authority: EP
Inventors: Mohinder S. Chattha; Ares N. Theodore
Original assignee: Ford Werke GmbH; Ford France SA; Ford Motor Co Ltd; Ford Motor Co
Current assignee: Ford Werke GmbH; Ford France SA; Ford Motor Co Ltd; Ford Motor Co
Priority date: 1982-08-09
Filing date: 1982-08-09
Publication date: 1984-08-15
Also published as: EP0115484A4; WO1984000771A1

Abstract

Composition de revêtement thermodurcissable avec une excellente adaptation aux conditions météorologiques, adaptée pour être utilisée comme couche ou revêtement supérieur d'automobile et qui, après polymérisation, forme un revêtement résistant, vitreux, dur. La composition de revêtement, qui réagit in situ pendant la polymérisation, a pour caractéristique d'être composée d'un mélange: (A) de copolymère acrylique portant des groupes hydroxyles pendants et dont le poids moléculaire numérique moyen (Mn) varie entre approximativement 1000 et 5000, (B) d'anhydride d'acide dicarboxylique comprenant au moins 50 % en poid d'anhydride alcoyle hexahydrophtalique, (C) d'époxy portant un groupe époxyde ou plus par molécule et dont le poids moléculaire (Mn) varie entre approximativement 130 et 1500, et (D) d'agent amino-aldéhyde de liaison transversale.Thermosetting coating composition with excellent adaptation to weather conditions, suitable for use as a top coat or coating for automobiles and which, after polymerization, forms a resistant, glassy, hard coating. The coating composition, which reacts in situ during the polymerization, has the characteristic of being composed of a mixture: (A) of acrylic copolymer carrying pendant hydroxyl groups and whose average numerical molecular weight (Mn) varies between approximately 1000 and 5000, (B) of dicarboxylic acid anhydride comprising at least 50% by weight of alkyl hexahydrophthalic anhydride, (C) of epoxy carrying one or more epoxide groups per molecule and whose molecular weight (Mn) varies between approximately 130 and 1500, and (D) cross-linking amino aldehyde agent.

Description

ACRYLIC HYDROXY-EPOXY HIGH SOLIDS COATING COMPOSITIONS

Reference is made to commonly assigned and concurrently filed U.S. applications Serial No. entitled "Glycidyl-Hydroxy-Acrylic High

Solids Coating Compositions" and Serial No. entitled "High Solids Coating

Compositions", both to Chattha et al.

Technical Field

This invention relates to high solids, thermosetting coating compositions, which when cured, exhibit excellent weatherability and are adapted to provide an automotive topcoat which demonstrates hardness, high gloss and excellent resistance to solvents and water. More particularly, the coating compositions of this invention comprise a mixture of a low molecular weight hydroxyacrylic copolymer, dicarboxylic acid anhydride including at least about 50 weight percent of an alkyl hexahydrophthatic anhydride, epoxy, and amine-aldehyde crosslinking resins. The composition mixture reacts in situ during curing at elevated temperature to form the coating.

BACKGROUND OF THE INVENTION

Because of increasingly strict solvent emission regulations in recent years, low solvent emission paints have become very desirable. A number of high solids paint compositions have been proposed to meet these low solvent emission requirements. However, many of the compositions are deficient because of difficulty in application, slow curing rates, complex and/or time consuming composition formulation, poor durability and low solvent and water resistance of the coating.

One composition, which has been proposed to overcome these deficiencies is taught in U.S. application Serial No. 334,684, filed December 12, 1981 in the name of the inventors of this application. In that composition, hydroxy functional acrylic copolymers react with anhydrides of dicarboxylic acids to produce hydroxy acid and polyacid copolymers. The composition of such a mixture is largely dictated by the stoichiometry of the reactants employed. These acid products are then reacted with epoxies to produce hydroxy functional resins. Subsequently a composition comprising ' a mixture of these hydroxy functional resins and amine-aldehyde crosslinking agent can be applied to a substrate and cured at elevated temperatures to obtain a crosslinkεd structure. Unexpectedly, we have now found that all the materials used to prepare this prior composition can be singly combined and all of the aforementioned reactions can be carried out in situ during curing on the substrate to obtain high solids coatings with excellent physical properties.. While not wishing to be bound by theory, it is believed that in this reaction sequence the hydroxyl functionality of the hydroxy acrylic copolymer reacts with the anhydride to produce acid functionality which further reacts with the epoxide to produce hydroxy moiety; then at higher temperatures, the amine-aldehyde reacts with hydroxyl functionality to produce a crosslinked network. This crosslinking reaction is facilitated by the unconsumed acid present in the, composition.

Disclosure of the Invention

The thermosetting coating composition of this invention preferably contains greater than about 60% by

OMPI

_3&_r__ wIPO →J&r. weight, more preferably greater than 70% by weight, of nonvolatile solids. The composition is characterized in that it comprises a mixture of:

(A) acrylic copolymer bearing pendant hydroxyl groups and having a number average molecular weight (M_n) of between about 1000 and about 5000, preferably between about 1500 and about 3500;

(B) dicarboxylic acid anhydride comprising at least about 50 weight percent, preferably greater than about 80 weight percent, of alkyl hexahydrophthalic anhyd ide;

(C) epoxy having one or more, preferably two, epoxide groups per molecule and having a number average molecular weight (^_n) of between about 130 and 1500; and (D) amine-aldehyde crosslinking agent.

The composition reacts in situ during curing at elevated temperatures to form the coating.

The acrylic copolymer is prepared from a monomer mixture comprising: (i) between about 10 and about 40 weight percent of monoethylenically unsaturated hydroxy alkyl esters of acrylic acid or methacrylic acid and (ii) between about 90-60 weight percent of other monoethylenically unsaturated monomers. The dicarboxylic acid anhydride is included in an amount so as to provide between about 0.25 and about 1.5, preferably about 0.30 and 1.20, anhydride groups for each hydroxyl group on the acrylic copolymer. The epoxy is included in an amount so as to provide at least about 1.0, preferably between about 1.1 and 1.2 epoxide groups per anhydride group. The amine-aldehyde is included in the composition in amount sufficient to provide at least about 0.60, preferably between about 0.75 and 2.75, nitrogen crosslinking functional groups for each hydroxyl group initially present on the acrylic copolymer (A).

OMPI In addition, the coating composition of this invention may include additives such as solvents, catalysts, antioxidants, U.V. absorbers, flow control or wetting agents, antistatic agents, pigments, plasticizers, etc. The compositions of this invention are also compatible with non-aqueous dispersions (NAD's), which are generally used as flow control additives.

This invention overcomes the above mentioned deficiencies of prior high solids coating compositions and provides a high solids composition particularly suitable for use as an automotive topcoat, clear or pigmented, which exhibits outstanding weatherability.

Advantageously, since the composition of this invention is applied to the substrate ^: as an essentially unreacted mixture of low molecular weight materials, little or no solvent is required to maintain a desirable low application viscosity, i.e., the composition can be of very high solids level.

The composition of this invention, being of essentially single step formulation, offers a distinct commercial advantage over those compositions whose formulation includes a series of reaction steps prior to curing, since such reaction steps generally require heat, agitation and monitoring for extended periods of time. Advantageously, during the in situ reactions during curing of the composition of this invention, carboxyl functionality is generated which, until it is later consumed by further reaction, acts as a catalyst for the crosslinking reaction.

Best Mode for Carrying Out the Invention

The coating compositions of this invention provide a system which is particularly suitable for those applications requiring a coating having high gloss, hardness, adhesion, high solvent and water resistance and

OMPI superior weatherability. The components of the coating composition of this invention are combined to form a homogeneous mixture which is then applied to a substrate and cured at elevated temperatures. Each of the components of the coating composition, the amounts of each of the components required to achieve the desired results of the invention and a method for applying the composition are described hereinafter in greater detail.

(A) Hydroxy Functional Acrylic Polymer

One material in the high solids coating composition of this invention is a hydroxy functional acrylic copolymer, i.e., a copolymer bearing pendant hydroxyl groups, which may be prepared by conventional free radical induced polymerization of suitable alpha-beta unsaturated monomers. The term "copolymer" as used herein refers to a copolymer of two or more different monomers at least one of which contains pendant hydroxyl groups.

The copolymers used in the coating composition of this invention have a number average molecular weight (M_n) of between about 1000-5000, preferably between about 1500-3000. The monomers used to prepare the copolymer include between about 10 and about 40 weight percent of one or more monoethylenically unsaturated monomers bearing hydroxyl functionality.

The monoethylenically unsaturated hydroxy functional monomers useful in preparation of the copolymer and providing the hydroxyl functionality to the copolymer may be selected from a long list of hydroxy functional monomers. Preferably, however, the hydroxy functional monomers are acrylates and may be selected from the group consisting of, but not limited to the following esters of acrylic or methacrylic acids and aliphatic alcohols: 2-hydroxyethyl acrylate; 3-chloro-2-hydroxyρroρyl acrylate; 2-hydroxy-l-methylethyl acrylate; 2-hydroxy- propyl acrylate; 3-hydroxypropyl acrylate; 2,3 dihydroxy- propyl acrylate; 2- ydroxybutyl acrylate; 4-hydroxybutyl acrylate; diethylene glycol acrylate; 5-h roxypentyl acrylate; 6-hydroxyhexyl acrylate; triethyleneglycol acrylate; 7-hydroxyheptyl acrylate; 2 hydroxymethyl ethacrylate; 3-chloro-2-hydroxypropyl methacrylate; 2-hydroxy-l-methylethyl methacrylate; 2-hydroxyρropyl methacrylate; 3-hydroxypropyl methacrylate; 2,3-dihydroxy- propyl methacrylate; 2-hydroxybutyl methacrylate; 4-hydroxybutyl methacrylate; 3,4-dihydroxybutyl methacrylate; 5-hyd oxypentyl methacrylate; 6-h droxyhexyl methacrylate; l,3-dimethyl-3-hydroxybutyl methacrylate; 5,6 dihydroxyhexyl methacrylate; and 7-hydroxyheptyl methacrylate.

Although one of ordinary skill in the art will recognize that many different hydroxyl bearing monomers, including those listed, above could be employed, the preferred hydroxy functional monomers for use in the copolymer of the invention are C₅ - C7 hydroxy alkyl acrylates and/or Cg - Cs hydroxy alkyl methacrylates, i.e., esters of C2 - C4 dihydric alcohols and acrylic or methacrylic acids.

Except in those instances wherein a specific compound is named, the term "acrylate" is used in this specification to include esters of both acrylic and methacrylic acid, i.e., acrylates and methacrylates.

The remainder of the monomers forming the copolymer, i.e., between about 90 and about 60 weight percent of the monomers of the copolymer, are other monoethylenically unsaturated monomers. These other monoethylenically usaturated monomers are preferably alpha-beta olefinically unsaturated monomers, i.e., monomers bearing olefinic unsaturation between the two carbon atoms in the alpha and beta positions with respect to the terminus of an aliphatic carbon-to-carbon chain. Among the alpha-beta olefinically unsaturated monomers which may be employed are other acrylates (meaning esters of either acrylic or methacrylic acids not containing hydroxyl functionality), as well as mixtures of other acrylates and monovinyl hydrocarbons. Preferably, in excess of 50 weight percent of the total of the copolymer monomers are acrylates (this total including hydroxy functional acrylates and other acrylates). These other acrylates are preferably selected from esters of C_j_ - C 2 monohydric alcohols and acrylic or methacrylic acids, i.e., methyl methacrylate, ethylacrylate, butylacrylate, ( iso)-butylmethacrylate, hexylacrylate, 2-ethylhexyl acrylate, lauryl ethacrylate, etc. Monovinyl hydrocarbons when they are employed,^' should preferably constitute less than 50 weight percent of the copolymer. Among the monovinyl hydrocarbons suitable for use in forming the copolymers are those containing 8 to 12 carbon atoms and including styrene, alpha methylstyrene, vinyl toluene, t-butylstyrene and chlorostyrene. Other such monovinyl hydrocarbon monomers as vinyl chloride, acrylonitrile, methacrylonitrile, and vinyl acetate may be included in the copolymer as modifying monomers. However, when employed, these modifying monomers should constitute only between about 0 and about 30 weight percent of the monomers in the copolymer. Small amounts of ethylencally unsaturated carboxylic acids can also be used in preparing the copolymer, such as acrylic acid, methacrylic acid, crontonic acid, itaconic acid, aleic acid and the like.

A preferred embodiment of this invention comprises a copolymer of 2-hydroxyethyl acrylate, methyl methacrylate, isobutyl methacrylate and styrene.

In preparing the copolymer, the hydroxy functional monomers and the other monoethylenically unsaturated monomers are mixed and reacted by conventional free radical initiated polymerization in such proportions as to obtain the copolymer desired. A large number of free radical initiators are known to the art and are suitable for the purpose. These include: benzoyl peroxide; lauryl peroxide; t-butylhydroxy peroxide; acetylcyclohexylsulfonyl peroxide; diisobutyryl peroxide; di(2-ethylhexyl) peroxydicarbonate; diisopropylproxy- dicarbonate; t-butylperoxypivalate; decanoyl peroxide; azobis - (2-methylpropionitrile), etc. The polymerization is preferably carried out in solution using a solvent in which the epoxide-functional, hydroxyl-functional copolymer is soluble. Included among the suitable solvents are toluene, methyl amyl ketone, xylene, dioxane, butanone, etc. If the hydroxy- functional copolymer is prepared in solution, the solid copolymer can be precipitated by pouring the solution at .a slow rate into a nonsolvent for the copolymer such as hexane, octane, or water under suitable agitation conditions.

The copolymer useful in the compositions of this invention can also be prepared by emulsion polymerization, suspension polymerization, bulk polymerization, or combinations thereof, or still other suitable methods. In these methods of preparing copolymers, chain transfer agents may be required to control molecular weight of the copolymer to a desired range. When chain transfer agents are used, care must be taken so they do not decrease the shelf stability of the composition by causing premature chemical reactions.

Various mixtures of these types of copolymers may also be employed within the scope of the compositions of the invention described herein.

(B) Dicarboxylic Acid Anhydride

The anhydride used in this composition comprises at least about 50 percent by weight, and up to 100 percent by weight, of alkyl hexahydrophthalic anhydride,

^' wherein the alkyl group preferably comprises up to about 7 carbons, more preferably up to 4 carbons. Most preferably the alkyl hexahydrophthalic anhydride comprises methyl hexahydrophthalic anhydride. The remainder of the anhydrides, i.e., 0 to about 50 weight percent, more preferably 0 to about 20 weight percent, and most preferably 0 to about 10 percent by weight, are selected from a variety of anhydrides, which include but are not limited to, hexahydrophthalic, 2-dodecene-l-ylsuccinic, tetrahydrophthalic, methyl tetrahydrophthalic and camphoric anhydrides, and mixtures of suitable anhydrides.

The anhydride is included in the composition in an amount sufficient to provide between about 0.25 and about 1.2, more preferably between about 0.30, and about 1.2 most preferably between about 0.5 and 1.1 anhydride groups for each hydroxyl group initially present on the copolymer. During curing, it appears that the anhydride reacts with hydroxyl groups on the copolymer forming carboxyl groups. In compositions wherein excess anhydride (i.e., relative hydroxyl groups) is present, it appears that the excess anhydride will later react with the hydroxyl groups generated by previous carboxyl/epoxide reactions to form more carboxyl groups. Since the epoxide is present in an amount substantially corresponding to the anhydride, these carboxyl groups will subsequently be reacted with epoxide to form (i.e., regenerate) hydroxyl functionality.

(C) Epoxy

This composition also includes an epoxy having one or more epoxide groups per molecule and having a number average molecular weight (M_n) between about 130 and about 1500. Preferably, the epoxy used in the invention composition is a diepoxide. It is believed that, during curing, the carboxyl group opens the epoxide ring of the epoxy in an esterification reaction which generates hydroxyl groups. The epoxy is present in the composition in an amount sufficient to provide at least about 1.0 more preferably between about 1.0 and 1.2, most preferably between about 1.0 and 1.1 epoxide groups for each anhydride group present in the composition, i.e., essentially all of the pendant carboxyl groups resulting from the initial hydroxy copolymer anhydride reaction and, in the case of excess anhydride, the carboxyl groups resulting from subsequent hydroxyl-excess anhydride reactions will be reacted with an epoxide to regenerate hydroxyl functionality.

The epoxy suitable for use in this invention is a low molecular weight epoxy which can ^:be a liquid or a solid and can be either a single epoxy or a mixture of suitable epoxies. Examples of suitable epoxies include, but are not limited to, C4 _ Cig monoepoxies such as alkylene oxides, cyclic oxides, glycidyl esters and glycidyl ethers. Amoung numerous examples of such monoepoxides are 1,2 epoxy pentane, 1,2-epoxy decane, styrene oxide, cyclohexene oxide, n-butyl glycidyl ether, glycidyl acetate and glycidol. Suitable diepoxides include those which are the condensation products of bisphenol-A with epichlorohydrin, examples of which are commercially available as Epon 828, 1001, 1004, 1007 and 1009 (marketed by Shell Chemical Company, Houston, Texas), Araldite 6010 and 8001 (marketed by Ciba-Geigy Corp., Ardsley, New York); ester type diepoxides such as diglycidyl phthalate, diglycidyl adipate and diglycidyl glutarate; cycloaliphatic diepoxides such as dicycopentaxediene and vinyl _ cyclohexane dioxide; and aliphatic ether type diepoxides such as ethylene glycol diglycidyl ether, 1,2-propylene glycol, diglycidyl ether and 1,4-butanediol diglycidyl ether such as Araldite RD-2 (marketed by Ciba-Geigy). Epoxies having more than two epoxide groups per molecule such as triepoxy resins XB2818 (Ciba-Geigy) and Dion 711 (Diamond Shamrock Chemical Co., Morristown, N.J.) and tetraepoxy resin 0163 (Ciba-Geigy) may also be used. The epoxies may be substituted by non-interferring functionality such as hydroxyl or the carbon chain may be interrupted by oxygen, and may contain ethylenic unsaturation; however a saturated epoxy and one containing no hydroxyl functionality is preferable. It is also preferred that the epoxy of this composition contain terminal epoxide groups.

Catalysts are generally included in the composition to accelerate the epoxide/carboxyl reaction. Suitable catalyst for this epoxide/carboxyl reaction are well known in the art. Preferred catalysts useful for this reaction are the tetralkyl ammonium salts such as tetra methyl ammonium chloride, tetraethyl ammonium bromide and trimethyl benzyl ammonium chloride as well as metal salts of a carboxylic acid, such as potassium octoate or chromium III octoate. Other useful catalysts include: metal halides such as chromium trichloride, ferric trichloride, and aluminum trichloride; mercaptans and thioethers such as octyl mercaptan, dimercapto propanol and dimercapto-diethyl ether; ^* tertiary amines such as triethyl amine, pyridine, dimethylandine, quinoline, β-picoline, ethylpyridine, and the like. Still other catalysts known to catalyze the carboxyl/epoxide reaction will be apparent to those skilled in this art.

(D) Amino Crosslinking Agent

Another essential component of the paint compositions of this invention is an amine-aldehyde crosslinking agent. Amine-aldehyde crosslinking agents suitable for crosslinking hydroxy functional bearing materials are well known in the art. Typically, these crosslinking materials are products of reactions of melamine, or urea with formaldehyde and various alcohols containing up to and including 4 carbon atoms. Preferably, the amine-aldehyde crosslinking agents useful in this invention are amine-aldehyde resins such as condensation products of formaldehyde with melamine, substituted melamine, urea, benzoquanamine or substituted benzoquanamine. Preferred members of this class are methylated melamine-formalade yde resins such as hexamethoxylmelamine. These liquid crosslinking agents have substantially 100 percent nonvolatile content as measured by the foil method at 45°C for 45 minutes. For the purpose of the preferred high solids coatings of the invention it should be recognized that it is important not to introduce extraneous diluents that would lower the final solids content of the coating. Other suitable amine-aldehyde crosslinking agents would be apparent to one skilled in the art.

Particularly preferred crosslinking agents are ^{t e} amino crosslinking agents sold by American Cyanamid, Wayne, N.J. under the trademark "Cymel" . In particular, Cymel 301, Cymel 303, Cymel 325 and Cymel 1156, which are alkylated melamine-formaldehyde resins, are useful in the compositions of this invention. The crosslinking reactions are known to be catalytically accelerated by acids. Therefore, the unconsumed carboxyl group acts as a catalyst for the crosslinking reaction. In addition, if desired, catalysts may be added to the composition which accelerate the crosslinking reaction. One such catalyst, for example, is p-toluene sulfonic acid and the amine salts thereof. Other useful catalysts are well known to those skilled in the art. Selection of optimal cure temperature would be well within the skill of those in the art. The amine-aldehyde materials function as a crosslinking agent in the composition of the invention by reacting with the hydroxyl groups of the composition, which groups were either present initially on the copolymer and nonreacted or regenerated during subsequent in situ reactions of intially present hydroxyl groups. In order to achieve the outstanding properties which make these coating compositions particularly useful as automotive topcoat materials, it is essential that the amount of amino crosslinking agent be sufficient to substantially crosslink the hydroxyl groups in the coating composition. Therefore, the amino crosslinking agent should be included in the composition in an amount sufficient to provide at least about 0.60 preferably between about 0.75 and about 2.75 of nitrogen crosslinking functional groups for each hydroxyl group included in the composition either as an initially present and unreacted hydroxyl group on the copolymer or as a regenerated hydroxyl group i.e., by means of in situ reactions with anhydride and epoxy. The hydroxyl groups present in the composition and available for crosslinking can therefore be essentially taken to be equal to the hydroxyl groups initially present on the copolymer (A).

Other Materials

In addition to the above discussed components, other materials may be included in the coating compositions of the invention. These include materials such as catalysts, antioxidants, U.V. absorbers, solvents, surface modifiers and wetting agents, as well as pigments.

It is generally suitable and preferable, in order to achieve the preferred high solids content of the coating compositions of the invention, to use little or no volatile solvent in the composition. However, when desirable, suitable solvents which may be employed include those commonly used, such as toluene, xylene, methyl amyl ketone, acetone, butyl acetate, tetrahyd ofuran, ethylacetate, di ethylsuccinate, di^'methylglutarate, dimethyladipate or mixtures thereof. In some embodiments of the subject composition, it may be desirable to incorporate solvent into the coating composition in order to facilitate application of the -coating composition, e.g., spray application. The solvent, in which the hydroxy acrylic copolymer is prepared, may be employed as a solvent for the coating composition thus eliminating the need for, drying the copolymer after preparation, if such is desired. Typical solvents which may be so used are detailed above.

As mentioned above, the nonvolatile solids content of the coating composition is preferably at least 60% and more preferably 70% or more, thus limiting the amount of solvent included in the composition. However, while the composition is particularly suitable for use as a high solids composition, the composition is also suitable for use as low solids compositions. Determination of optimal solids content for a given application would be within the skill of one in the art.

Surface modifiers or wetting agents are comomon additives for liquid paint compositions. The exact mode of operation of these surface modifiers is not known, but it is thought that their presence contributes to better adhesion of the coating composition to the surface being coated and helps formation of thin coatings, particularly on metal surfaces. These surface modifiers are exemplified by acrylic polymers containing 0.1 - 10 percent by weight of copolymerized monoethylenically unsaturated carboxylic acids such as methacrylic acid, acrylic acid or itaconic acid, cellulose acetate butyrate, silicone oils or mixtures thereof. Of course, the choice of surface modifiers or wetting agent is dependent upon the type of surface to be coated and selection of the same is clearly within the skill of the artisan.

The coating composition of the invention also may include pigments. The amount of pigment in the coating composition may vary, but preferably is between about 3 and about 45 weight percent based on the total weight of the paint composition. If the pigment is metallic flake, the amount generally ranges from about 1 to about 20 weight percent.

For many applications of the coating compositions of this invention, particularly high solids compositions, it may be desirable to employ flow control additives to provide sag free coatings. Among numerous such materials, NAD's such as described by Porter (S. Porter, Jr. and B.N. McBane, U.S. Patent 4,025,474, May 24, 1977) are compatible with these coating compositions. These particle dispersions may be included in an amount up to 15% by weight of the total composition. Other types of NAD's such as described by D.L. Maker and S.C. Peng (U.S. Patent 3,814,721, June 4, 1974) or by S.K. Horvath (U.S. application Serial No. 292,853, filed August 14, 1981) also may be included in the paint composition.

Application Techniques

The coating composition can be applied by conventional methods known to those skilled in the art. These methods include roller coating, spray coating, dipping or brushing and, of course, the particular application technique chosen will depend on the particular substrate to be coated and the environment in which the coating operation is to take place.

A particularly preferred technique for applying the high solids coating compositions, particularly when applying the same to automobiles as topcoats, is spray coating through the nozzle of a spray gun. High solids paints have in the past caused some difficulty in spray coating techniques because of the high viscosity of the materials and resultant problems in clogging of spray guns. However, because the compositions of this invention demonstrate relatively low viscosity, considering the high solids content, they can be applied by spray coating techniques.

The invention will be further understood by referring to the following detailed examples. It should be understood that the specific examples are presented by way of illustration and not by way of limitation. Unless otherwise specified, all references to "parts" is intended to mean parts by weight.

Example 1

A hydroxy acrylic copolymer is prepared from the following monomers:

Wt. g. Wt %

2-hydroxyethyl acrylate 100 25

Isobutyl methacrylate 120 30

Methyl methacrylate 160 40 Styrene 20 5

Twenty (20) grams of tert-butyl perbenzoate is added to the above monomer mixture and the resulting solution added dropwise over a period of 1.5 hours to 325 parts of refluxing xylene. The heating and stirring is continued for half an hour after the addition is complete and then 0.5g of tert-butyl perbenzoate are added portionwise to the reaction mixture. The reaction mixture is refluxed for additional one hour and then allowed to cool to room temperature. Molecular weight ( _n) from gel permeation chrometography was found to be 2700. One hundred (100) parts of this polymer are mixed with 19.8 parts of bis-(3,4-epoxy-6-methylcyclohexane- methyl adipate (Araldite CY-178, Ciba-Geigy), 42 parts of hexamethoxeymethyl melamine (Cymel 325, American Cyahamid) and 0.2 parts of Cordova Accelerator AMC™-2 (Cordova Chemical, Sacramento, California). The above mixture is dissolved in 21 parts of butyl acetate and 15.8 parts of methylhexahydrophthalic anhydride are added to it. The reulting mixture is stirred for one minute and then spray applied to primed panels in three coats with an intermediate flash of one minute and a final flash of five minutes. The panels are baked at 135° C for 20 minutes to obtain clear coatings with excellent hardness, adhesion, gloss and solvent (methyl ethyl ketone and xylene) resistance.

Example 2

Ten (10) parts of the hydroxy polymer from Example 1, 3.2 parts of Eponex DRH 151.3 (Shell Chemical Company) and 6 parts of Cymel 325 (American Cyanamid) are dissolved in 8 parts of butyl acetate and one drop of Cordova Accelerator AMC™-2 is added to • this solution. Methylhexahychrophthalic anhydride (2.2 parts) is added to the above solution and it is well shaken. The resulting formulation is drawn on a primed steel panel and is baked at 130°C for 15 minutes to obtain coatings with excellent xylene and methyl ethyl ketone resistance.

Example 3

A hydroxy acrylic copolymer is prepared from the following monomers:

Wt/grams t. %

Butyl methacrylate 1000 50

Hydroxyethyl acrylate 400 20

Methylmethacrylate 400 20

Styrene 200 10

One hundred (100) grams tert-butyl perbenzoate is added to the above monomer mixture and the resulting solution added dropwise over a period of two hours to 1600 grams of refluxing (145°) methyl amyl ketone (under nitrogen). The heating and stirring is continued for half an hour after the addition is complete and then five (5) grams of tert-butyl perbenzoate are added portionwise to the reaction mixture. The reaction mixture is refluxed for an additional ninety minutes and then allowed to cool to room temperature. The molecular weight is determined by Gel Permeation Chromatography, M_n = 2570.

Sixty-two (62) parts of the above polymer, 12.9 parts of Epon 828 (Shell Chemical Co.), 27 parts of Cymel 325 and 0.1 parts Cordova Accelerator AMC™-2 are dissolved in 21 parts of butyl acetate and 10.8 parts of a solution of 2 parts of methyltetrahydrophthalic anhydride in 8.8 parts of methylhexahydrophthalic anhydride are added to the above solution. The resulting composition is stirred well and spray applied to primed steel panels, which are baked at 135°C for 20 minutes to obtain coatings with excellent hardness, adhesion, gloss and solvent resistance. Example 4

An acrylic copolymer is prepared from the following monomers:

Parts by Weight

Butyl methacrylate 26 Ethylhexyl acrylate 20 Hydroxyethyl acrylate 30 Styrene 24

The preparation is carried out in the same way as outlined in Example 1 by using cellusolve acetate as the solvent and tert-butyl peroctoate (5% of monomers) as initiator to obtain a 70% solution of the polymer. The calculated Tg is -7°C. and the molecular weight of from Gel Permeation Chromatography is M_n = 3070 and ^~M_W/M_n = 2.2. Sixty parts of the above polymer, 16.7 parts of

1,4-butanedioldiglycidyl ether, 18 parts of Cymel 301, 0.3 parts 2-hydroxycyclohexyl-ρ-toluene sulfonate and 0.1 parts of Cordova Accelerator AMC™-2 are dissolved in 17 parts of butyl acetate. Twenty-seven (27).of methyl- hexahydrophthalic anhydride are added to above solution and the resulting formulation is applied by spraying to primed steel panels. The panels are baked at 135°C for 20 minutes to obtain coatings with excellent hardness, gloss, adhesion and xylene resistance. Example 5

Three hundred (300) parts of Ti0₂ are mixed with

210 parts of the polymer solution from Example 4 and 14 parts of n-butyl acetate. The above mixture is placed in a porcelain bottle containing porcelain beads and put on a roller mill for 18 hours.

Forty-two (42) parts of the above mill base, ten parts of the polymer from Example 4, 6 parts of Cymel 325, 10.3 parts of Araldite 178 (Ciba-Geigy) and 0.07 part of Cordova Accelerator AMC™-2 are mixed 7 parts of n-butyl acetate. Nine (9) parts of methylhexahydrophthalic anhydride are added to the above mixture and the resulting formulation is applied by spraying to primed steel panels. The panels are baked at 130°C for 18 minutes to obtain white coatings with excellent hardness, adhesion, gloss and solvent resistance.

Example 6

Five-hundred (500) parts of Ti0₂ and 250 parts of Ferrite Yellow are mixed with 500 parts of polymer from Example 4 and 150 parts of butyl acetate. The mill base is prepared as described in Example 5.

Fifty-two (52) parts of the above mill base are mixed with 20 parts of polymer from Example 4, 13.5 parts of Ξpon 828 (Shell Chemical Co.), 19 parts of Cymel 325, 0.15 parts of Cordova Accelerator AMC™-2 and 16 parts of butyl acetate. Twelve (12) parts of methylhexa¬ hydrophthalic anhydride are added to the above mixture and the resulting formulation is applied by spraying to primed steel panels which are baked at 130°C for 18 minutes to obtain hard, glossly yellow coatings with excellent solvent resistance. Example 7

Fifty (50) parts of the polymer solution from Example 4 are placed in a round bottom flask and the solvent is distilled-off under reduced pressure to obtain essentially solvent free polymer. Eighteen (18) parts of the above polymer, 20 parts of Cymel 301, 0.2 parts of Cordova Accelerator AMC™-2, 0.2 parts of 2-hydro- cyclohexyl p-toluene sulfonate are dissolved in 10.2 parts of 1,4-butanedioldiglycidyl ether. Seventeen (17) parts of methylhexahydrophthalic anhydride are added to the above mixture and the resulting formulation is drawn on primed steel panels which are baked at 140°C for 17 minutes to obtain solvent-resistant, hard coatings with excellent adhesion.

Example 8

Five (5) parts of phthalo blue pigment are mixed with 45 parts of the polymer from Example 1 and the mill base is ground as described in Example 5.

Twenty-four (24) parts of the above mill base are mixed with 32 parts of the polymer from Example 1, 27 parts of Cymel 325, 14 parts of Epon 828 (Shell Chemical Co.), 8 parts flow control additive (prepared according to U.S. Patent 4,025,474), 0.1 part Cordova Accelerator AMC™-2, 5 parts of aluminum flakes and 18 parts of butyl acetate. Twelve (12) parts of methylhexahydrophthalic anhydride are added to the above mixture and the resulting formulation is applied by spraying in four coats. The panels are baked at 130°C for_, 18 minutes to obtain blud metallic coatings with excellent physical properties. Example 9

A hydroxy acrylic copolymer is prepared from the following monomers:

Wt/g.

Allyl alcohol 5

2-Hydroxyprop l methacrylate 25

Isobutyl methacrylate 60

Vinyl acetate 10

Five (5) grams tert-butyl perbenzoate are added to the above mixture and the polymer is prepared as described in Example 1 to obtain a 62.5% solution in xylene.

Forty-three (43) parts of the above polymer solution are mixed with 14 parts of Epon 825, 19 parts of Cymel 325, 0.1 part of Cordova Accelerator AMC™-2 and 15 parts of butyl acetate. Twelve (12) parts of methylhexa¬ hydrophthalic anhydride are added to above mixture and the resulting formulation is applied by spraying to primed steel panels which are baked at 132°C for 19 minutes to obtain coatings with excellent hardness, adhesion and solvent (xylene and methyl ethyl ketone) resistance.

Industrial Applicability

It will be obvious from the foregoing that this invention has industrial applicability, particularly to the automotive industry, and provide a coating with excellent exterior weatherability and distinct commercial advantages.

Claims

1. A thermosetting coating composition, which reacts in situ during curing at elevated temperatures, characterized in that said composition comprises a mixture of:

(A) acrylic copolymer bearing pendant hydroxyl groups and having a number average molecular weight (M_n) of between about 1000-5000, said copolymer being prepared from a monomer mixture comprising (a) between about 10 and about 40 weight percent of monoethylenically unsaturated hydroxy alkyl esters of acrylic acid or methacrylic acid "^* and (b) between about 90-60 weight ^; percent of other monoethylenically unsaturated monomers;

(B) dicarboxylic acid anhydride comprising at least about 50 percent by weight of alkyl hexahydrophthalic anhydride, said dicarboxylic acid anhydride being included in said composition in an amount so as to provide between about 0.25 and about 1.5 anhydride groups for each hydroxyl group on said acrylic copolymer;

(C) epoxy having one or more epoxide groups per molecule and having a number average molecular weight (M_n) of between about 130-1500, said epoxy being included in said composition in an amount so as to provide at least about 1.0 epoxide group for each anhydride group; and

(D) amine-aldehyde crosslinking agent included in said composition in an amount sufficient to provide at least about 0.60 nitrogen crosslinking functional groups for each pendant hydroxyl group initially present in said composition on said copolymer (A) .

2. A coating composition according to claim 1, wherein said monoethylenically unsaturated hydroxy alkyl ester is selected from the group consisting of C5 - C7 hydroxy alkyl acrylates, C - - C- hydroxy alkyl methacrylates, and mixtures thereof.

3. A coating composition according to claim 2, wherein said other monoethylenically unsaturated monomers are selected from the group consisting of other acrylates, or mixtures of said other acrylates and other monovinyl hydrocarbons.

4. A coating composition according to claim 3, wherein said other acrylates are esters of a C_j - Cs monohydric alcohol and acrylic or methacrylic acid and said other monovinyl hydrocarbons are C3 - C 2 vinyl monomers.

5. A coating composition according to claim 1, wherein said alkyl group of said alkyl hexahydrophthalic anhydride comprises a lower alkyl group having up to about seven carbons.

6. A coating composition according to claim 1, wherein said dicarboxylic acid anhydride comprises at least about 80 percent by weight of alkyl hexahydrophthalic anhydride.

7. A coating composition according to claim 1, wherein said dicarboxylic acid anhydride is included in said composition in an amount so as to provide between about 0.30 and about 1.2 anhydride group for each hydroxyl group on said acrylic copolymer.

/' QMPI

8. A coating composition according to claim 5 or 6, wherein said alkyl hexahydrophthalic anhydride is methyl hexahydrophthalic anhydride.

9. A coating composition according to claim 1, wherein up to about 50 percent by weight of said dicarboxylic acid anhydride comprises an anhydride selected from the group consisting of hexahydrophthalic anhydride, 2-dodecene-l-ylsuccinic anhydride, tetrahydrophthalic anhydride, methyl tetrahydrophthalic anhydride, camphoric anhydride, and mixtures of the above.

10. A coating composition according to claim 1, wherein said epoxy contains two epoxide groups per molecule.

11. A coating coposition according to claim 1 or 10, wherein said epoxy is a saturated epoxy.

12. A coating composition according to claim 1 or 10, wherein said epoxy contains terminal epoxide functionality.

13. A coating composition according to claim 1, wherein said amine-aldehyde crosslinking agent is selected from the group consisting of condensation products of formaldehyde with melamine, substituted melamine, urea, benzoquanamine and substituted benzoguanamine and mixtures of said condensation products and is included in an amount sufficient to provide between about 0.75 and about 2.75 nitrogen crosslinking functional groups for each hydroxyl group initially present in said composition on said copolymer (A).

OMPI

14. A coating composition according to claim 1, which further comprises up to about 15 weight percent, based on the total weight of the composition, of a flow control additive.

15. A coating composition according to claim 1, wherein said dicarboxylic acid anhydride consists of methyl hexahydrophthalic anhydride and said epoxy is a diepoxide.

16. A high solids thermosetting coating composition, which reacts in situ during curing at elevated temperatures, which contains greater than about 60 weight percent of nonvolatile solids and which, except for pigments and other nonreactive components, is characterized in that it consists essentially of a mixture of:

(A) acrylic copolymer bearing pendant hydroxyl groups and having a number average molecular weight (M_n) of between about 1000 and about 5000, said copolymer being prepared from a monomer mixture comprising (a) between about 10 and about 40 weight percent of monoethylenically unsaturated hydroxy alkyl ester of acrylic acid or methacrylic acid and (b) between about 90-60 weight percent of other monoethylenically unsaturated monomers;

(B) dicarboxylic acid anhydride comprising at least about 50 percent by weight of alkyl hexahydrophthalic anhydride, said dicarboxylic acid anhydride being included in said composition in an amount so as to provide between about 0.25 and about 1.5 anhydride groups for each hydroxyl group on said acrylic copolymer; (C) epoxy having one or more epoxide groups per molecule and having a number average molecular weight (M_n) of between about 130-1500, said epoxy being included in said composition in an amount so as to provide at least about 1.0 epoxide groups for each anhydride group; and

(D) amine-aldehyde crosslinking agent included in said composition in an amount sufficient to provide at least about 0.60 nitrogen crosslinking functional groups for each pendant hydroxyl group initially present in said composition on said copolymer (A)

17. A high solids coating composition according to claim 16, wherein said monoethylenically unsaturated hydroxyl alkyl ester is selected from the group consisting of C5 - C7 hydroxy alkyl acrylates, Cg - Cs hydroxy alkyl methacrylates, and mixtures thereof.

18. A high solids coating composition according to claim 17, wherein said other monoethylenically unsaturated monomers are selected from the group consisting of other acrylates or mixtures of said other acrylates and other monovinyl hydrocarbons. ^•

19. A high solids coating composition according to claim 18, wherein said other acrylates are esters of a C_ - C3 monohydric alcohol and acrylic or methacrylic acid and said other monovinyl hydrocarbons are C3 - Cτ_2 vinyl monomers.

20. A high solids coating composition according to claim 16, wherein said alkyl group of said alkyl hexa¬ hydrophthalic anhydride comprises a lower alkyl group having up to about seven carbons.

21. A high solids coating composition according to claim 16, wherein said dicarboxylic acid anhydride comprises at least about 80 percent by weight of an alkyl hexahydrophthalic anhydride.

22. A high solids coating composition according to claims 16 or 21, wherein said dicarboxylic acid anhydride is included in said composition so as to provide between about 0.30 and about 1.2 anhydride groups for each hydroxyl group on said acrylic copolymer.

23. A high solids coating composition according to claims 20 or 21, wherein said alkyl hexahydrophathalic anhydride is methyl hexahydrophthalic anhydride.

24. A high solids coating composition according to claim 16, wherein up to about 50 percent by weight of said dicarboxylic acid anhydride is selected from the group consisting of hexahydrophthalic anhydride, 2-dodecene-l-ylsuccinic anhydride, tetrahydrophthalic anhydride, methyl tetrahydrophthalic anhydride, camphoric anhydride, and mixtures of the above.

25. A high solids coating composition according to claim 16, wherein said epoxy contains two epoxide groups per molecule.

26. A high solids coating composition according to claims 16 or 25, wherein said epoxy is a saturated epoxy.

27. A high solids coating composition according to claim 26, wherein said epoxy contains terminal epoxide functionality.

OMPI IPO O

28. A high solids coating composition according to claim 16, wherein said amine-aldehyde crosslinking agent is selected from the group consisting of condensation products of formaldehyde with melamine, substituted melamine, urea, benzoquanamine and substituted benzoguanamine and mixtures of said condensation products and is included in an amount sufficient to provide between about 0.75 and about 2.75 nitrogen crosslinking functional group for each hydroxyl group initially present in said composition on said copolymer (A).

29. A high solids coating composition according to claim 16, wherein said dicarboxylic acid anhydride consists of methyl hexahydrophthalic anhydride and said epoxy is a diepoxide.