Color Plus Clear Coating System Utilizing Organo-Modified Clay

A coating system gaining wide acceptance, particularly in the automotive industry, is one which is known as "color plus clear". In this system the substrate is coated with one or more applications of a pigmented basecoating composition, which is in turn coated with one or more applications of a generally clear topcoating composition.

However, there are several difficulties in employing "color plus clear" coating systems especially as attempts are made to employ coating compositions having high solids contents and also as metallic flake pigments are used to provide a special variable appearance to the coated substrate as it is viewed from different angles to a direction normal to the surface of the substrate. This variable appearance is sometimes referred to as "flop" in the coatings industry. For example, it is important in a "color plus clear" coating system that the applied basecoat not be attacked by components of the topcoating composition, particularly solvents, at the interface of the two, a phenomenon often referred to as strike-in. Strike-in adversely affects the final appearance properties of the coated product. Strike-in is an especially serious problem when metallic-flake pigments are employed in the basecoating composition. Strike-in, among other things, can destroy the desired metallic-flake orientation in the basecoat.

Additionally, irrespective of the problems associated with strike-in, it is important to prevent sagging during curing of the coating composition after application to a nonhorizontal substrate. Also, especially where metallic-flake pigments are employed, it is important to achieve and maintain proper pigment orientation in the pigmented basecoating composition during the curing or drying operation.

One attempt to address some of these problems has been to incorporate in the basecoating composition as part of the organic polymer system present, a proportion of organic, insoluble polymer microparticles as described for example in U.S. Pat. No. 4,220,679 to Backhouse. Another attempt to address at least some of the problems of achieving proper metallic-flake orientation in a high solids basecoat has been to substantially increase the amount of metallic-flake pigment in the basecoating composition as described in U.S. Pat. No. 4,359,504 to Troy.

It has now been found that the incorporation of an effective amount of an organo-modified clay in the basecoating composition permits the basecoating composition to be formulated for example at a high solids content and alleviates the problems of strike-in, the problems of achieving excellent metallic-pattern control where metallic-flake pigments are employed, and the problem of sagging of the coating composition on a nonhorizontal substrate during curing or drying.

The present invention provides a method for coating a substrate comprising the steps of: (A) coating the substrate with one or more applications of a basecoating composition comprising (1) an organic film-forming resin, and where the film-forming resin can be crosslinked, optionally a crosslinking agent for the film-forming resin, (2) an organo-modified clay stably dispersed in the basecoating composition, (3) a solvent system for the film-forming resin and the optional crosslinking agent for the film-forming resin, and (4) pigment particles, to form a basecoat, and optionally before allowing the basecoating composition to become substantially cured or hardened; (B) coating the basecoat with one or more applications of a topcoating composition comprising (1) an organic film-forming resin, which may be the same or different from the film-forming resin of the basecoating composition, and where the film-forming resin of the topcoating composition can be crosslinked, optionally a crosslinking agent for the film-forming resin of the topcoating composition, and (2) a solvent system for the organic film-forming resin of the topcoating composition and the optional crosslinking agent for the film-forming resin of the topcoating composition, to form a transparent topcoat.

The film-forming resin of the basecoating composition may be any of the film-forming resins useful for coating compositions. The film-forming resins of the basecoating composition can be film-forming thermoplastic resins and/or thermosetting resins. Examples of such film-forming thermoplastic resins and/or thermosetting resins include the generally known cellulosics, acrylics, aminoplasts, urethanes, polyesters, epoxies, and polyamides. These resins, when desired, may also contain functional groups characteristic of more than one class, as for example, polyester amides, uralkyds, urethane acrylates, urethane amide acrylates, etc. As indicated above, the film-forming resin may be thermoplastic or it may be thermosetting. As used herein, the term thermosetting is intended to include not only those resins capable of being crosslinked upon application of heat but also those resins which are capable of being crosslinked without the application of heat. In preferred embodiments of the present invention, the film-forming resin of the basecoating composition is selected from thermosetting acrylic resins and thermosetting polyester resins.

Cellulosics refer to the generally known thermoplastic polymers which are derivatives of cellulose, examples of which include: nitrocellulose; organic esters and mixed esters of cellulose such as cellulose acetate, cullulose propionate, cellulose butyrate, and cellulose acetate butyrate; and organic ethers of cellulose such as ethyl cellulose.

Acrylic resins refer to the generally known addition polymers and copolymers of acrylic and methacrylic acids and their ester derivatives, acrylamide and methacrylamide, and acrylonitrile and methacrylonitrile. Examples of ester derivatives of acrylic and methacrylic acids include such alkyl acrylates and alkyl methacrylates as ethyl, methyl, propyl, butyl, hexyl, ethylhexyl and lauryl acrylates and methacrylates, as well as similar esters, having up to about 20 carbon atoms in the alkyl group. Also, hydroxyalkyl esters can readily be employed. Examples of such hydroxyalkyl esters include 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl-4-hydroxybutyl methacrylate, and mixtures of such esters having up to about 5 carbon atoms in the alkyl group. In some instances, corresponding esters of other unsaturated acids, for example, ethacrylic acid, crotonic acid, and other similar acids having up to about 6 carbon atoms can be employed. Where desired, various other ethylenically unsaturated monomers can be utilized in the preparation of arylic resins examples of which include: vinyl aromatic hydrocarbons optionally bearing halo substituents such as styrene, alphamethyl styrene, vinyl toluene, alpha-chlorostyrene, alpha-bromostyrene, and para-fluorostyrene; nonaromatic monoolefinic and diolefinic hydrocarbons optionally bearing halo substituents such as isobutylene, 2,3-dimethyl-1-hexene, 1,3-butadiene, chloroethylene, chlorobutadiene and the like; unsaturated organosilanes such as gamma-methacryloxypropyltriethoxysilane, gamma-acryloxypropyltriethoxysilane, vinyltrimethoxysilane and the like; esters of organic and inorganic acids such as vinyl acetate, vinyl propionate, and isopropenyl acetate; and vinyl chloride, allyl chloride, vinyl alpha-chloroacetate, dimethyl maleate and the like.

The above polymerizable monomers are mentioned as representative of the ##STR1## containing monomers which may be employed; but essentially any copolymerizable monomer can be used.

Aminoplast resins refer to the generally known condensation products of an aldehyde with an amino- or amido-group containing substance examples of which include the reaction products of formaldehyde, acetaldehyde, crotonaldehyde, benzaldehyde and mixtures thereof with urea, melamine, or benzoguanimine. Preferred aminoplast resins include the etherified (i.e., alkylated) products obtained from the reaction of alcohols and formaldehyde with urea, melamine, or benzoguanimine. Examples of suitable alcohols for preparing these etherified products include: methanol, ethanol, propanol, butanol, hexanol, benzylalcohol, cyclohexanol, 3-chloropropanol, and ethoxyethanol.

Urethane resins refer to the generally known thermosetting or thermoplastic urethane resins prepared from organic polyisocyanates and organic compounds containing active hydrogen atoms as found for example in hydroxyl, and amino moieties. Some examples of urethane resins typically utilized in one-pack coating compositions include: the isocyanate-modified alkyd resins sometimes referred to as "uralkyds"; the isocyanate-modified drying oils commonly referred to as "urethane oils" which cure with a drier in the presence of oxygen in air; and isocyanate-terminated prepolymers typically prepared from an excess of one or more organic polyisocyanates and one or more polyols including, for example, simple diols, triols and higher alcohols, polyester polyols and polyether polyols. Some examples of systems based on urethane resins typically utilized as two-pack coating compositions include an organic polyisocyanate or isocyanate-terminated prepolymer (first pack) in combination with a substance (second pack) containing active hydrogen as in hydroxyl or amino groups along with a catalyst (e.g., an organotin salt such as dibutyltin dilaurate or an organic amine such as triethylamine or 1,4-diazobicyclo-(2:2:2) octane). The active hydrogen-containing substance in the second pack typically is a polyester polyol, a polyether polyol, or an acrylic polyol known for use in such two-pack urethane resin systems. Many coating compositions based on urethanes (and their preparation) are described extensively in Chapter X Coatings, pages 453-607of Polyurethanes: Chemistry and Technology, Part II by H. Saunders and K. C. Frisch, Interscience Publishers (N.Y., 1964).

Polyester resins are generally known and are prepared by conventional techniques utilizing polyhydric alcohols and polycarboxylic acids. Examples of suitable polyhydric alcohols include: ethylene glycol; propylene glycol; diethylene glycol; dipropylene glycol; butylene glycol; glycerol; trimethylolpropane; pentaerythritol; sorbitol; 1,6-hexanediol; 1,4-cyclohexanediol; 1,4-cyclohexanedimethanol; 1,2-bis(hydroxyethyl)cyclohexane; and 2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl-3-hydroxypropionate. Examples of suitable polycarboxylic acids include: phthalic acid; isophthalic acid; terephthalic acid; trimellitic acid; tetrahydrophthalic acid; hexahydrophthalic acid; tetrachlorophthalic acid; adipic acid; azelaic acid; sebacic acid; succinic acid; maleic acid; glutaric acid; malonic acid; pimelic acid; suberic acid; 2-2-dimethylsuccinic acid; 3,3-dimethylglutaric acid; 2,2dimethylglutaric acid; maleic acid; fumaric acid; and itaconic acid. Anhydrides of the above acids, where they exist, can also be employed and are encompassed by the term "polycarboxylic acid." In addition, certain substances which react in a manner similar to acids to form polyesters are also useful. Such substances include lactones such as caprolactone, propylolactone and methyl caprolactone, and hydroxy acids such as hydroxy caproic acid and dimethylol propionic acid. If a triol or higher hydric alcohol is used, a monocarboxylic acid, such as acetic acid and benzoic acid may be used in the preparation of the polyester resin. Moreover, polyesters are intended to include polyesters modified with fatty acids or glyceride oils of fatty acids (i.e., conventional alkyd resins) Alkyd resins typically are produced by reacting the polyhydric alcohols, polycarboxylic acids, and fatty acids derived from drying, semi-drying, and non-drying oils in various proportions in the presence of a catalyst such as litharge, sulfuric acid, or a sulfonic acid to effect esterification. Examples of suitable fatty acids include saturated and unsaturated acids such as stearic acid, oleic acid, ricinoleic acid, palmitic acid, linoleic acid, linolenic acid, licanic acid, elaeostearic acid, and clupanodonic acid.

Epoxy resins, often referred to simply as "epoxies", are generally known and refer to compounds or mixtures of compounds containing more than one 1,2-epoxy group of the formula ##STR2## i.e., polyepoxides. The polyepoxides may be saturated or unsaturated, aliphatic, cycloaliphatic, aromatic or heterocyclic. Examples of suitable polyepoxides include the generally known polyglycidyl ethers of polyphenols and/or polyepoxides which are acrylic resins containing pendant and/or terminal 1,2-epoxy groups. Polyglycidyl ethers of polyphenols may be prepared, for example, by etherification of a polyphenol with epichlorohydrin or dichlorohydrin in the presence of an alkali. Examples of suitable polyphenols include: 1,1-bis(4-hydroxyphenyl)ethane; 2,2-bis(4-hydroxyphenyl)propane; 1,1-bis(4hydroxyphenyl)isobutane; 2,2-bis(4-hydroxytertiarybutylphenyl)propane; bis(2-hydroxynaphthyl)methane; 1,5-dihydroxynaphthalene; 1,1-bis(4-hydroxy-3-allylphenyl)ethane; and the hydrogenated derivatives thereof. The polyglycidyl ethers of polyphenols of various molecular weights may be produced, for example, by varying the mole ratio of epichlorohydrin to polyphenol in known manner.

Epoxy resins also include the polyglycidyl ethers of mononuclear polyhydric phenols such as the polyglycidyl ethers of resorcinol, pyrogallol, hydroquinone, and pyrocatechol.

Epoxy resins also include the polyglycidyl ethers of polyhydric alcohols such as the reaction products of epichlorohydrin or dichlorohydrin with aliphatic and cycloaliphatic compounds containing from two to four hydroxyl groups including, for example, ethylene glycol, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, propane diols, butane diols, pentane diols, glycerol, 1,2,6-hexanetriol, pentaerythritol, and 2,2-bis(4-hydroxycyclohexyl)propane.

Epoxy resins additionally include polyglycidyl esters of polycarboxylic acids such as the generally known polyglycidyl esters of adipic acid, phthalic acid, and the like.

Addition polymerized resins containing epoxy groups may also be employed. These polyepoxides may be produced by the addition polymerization of epoxy functional monomers such as glycidyl acrylate, glycidyl methacrylate and allyl glycidyl ether optionally in combination with ethylenically unsaturated monomers such as styrene, alpha-methyl styrene, alpha-ethyl styrene, vinyl toluene, t-butyl styrene, acrylamide, methacrylamide, acrylonitrile, methacrylonitrile, ethacrylonitrile, ethyl methacrylate, methyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, and isobornyl methacrylate.

Many additional examples of epoxy resins are described in the Handbook of Epoxy Resins, Henry Lee and Kris Neville, 1967, McGraw Hill Book Company.

When desired, generally known crosslinking agents may be utilized in the method of the invention particularly when thermosetting resins containing active hydrogen atoms, for example, from moieties such as hydroxyl, carboxyl, amino, and amido, are employed in the coating compositions.

As will be appreciated by one skilled in the art, the choice of crosslinking agent depends on various factors such as compatibility with the film-forming resin, the particular type of functional groups on the film-forming resin and the like. The crosslinking agent may be used to crosslink the film-forming resin either by condensation or addition or both. When the thermosetting reactants include monomers having complementary groups capable of entering into crosslinking reactions, the crosslinking agent may be omitted if desired.

Representative examples of crosslinking agents include blocked and/or unblocked diisocyanates, diepoxides, aminoplasts, phenoplasts, and silane crosslinking agents. When aminoplast resins are employed as crosslinking agents, particularly suitable are the melamine-formaldehyde condensates in which a substantial proportion of the methylol groups have been etherified by reaction with a monohydric alcohol such as those set forth previously in the description of aminoplast resins suitable for use as film-forming resins in compositions of the invention.

The term "solvent system" as used herein, for example in the phrase "solvent system for the film-forming resin and optional crosslinking agent", is employed in a broad sense and is intended to include true solvents as well as liquid diluents for the film-forming resin and for the optional crosslinking agent which are not true solvents for these components. The solvent system generally is organic. It may be a single compound or a mixture of compounds. Ordinarily the solvent system does not comprise water. However when the solvent system does comprise both water and an organic portion, the components are usually miscible in the proportions employed. The relationship between the solvent system and the film-forming resin, and also between the solvent system and the organo-modified clay (described infra), depends upon the absolute and relative natures of these materials and upon the relative amounts used. Such factors as solubility, miscibility, polarity, hydrophilicity, hydrophobicity, lyophilicity and lyophobicity are some of the factors which may be considered. Illustrative of suitable components of the solvent system which may be employed are alcohols such as lower alkanols containing 1 to 8 carbon atoms including methanol, ethanol, propanol, isopropanol, butanol, secondary-butyl alcohol, tertiary-butyl alcohol, amyl alcohol, hexyl alcohol and 2-ethylhexyl alcohol; ethers and ether alcohols such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol dibutyl ether, propylene glycol monomethyl ether, diethylene glycol monobutyl ether, diethylene glycol dibutyl ether, dipropylene glycol monoethyl ether, and dipropylene glycol monobutyl ether; ketones such as acetone, cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, methyl amyl ketone and methyl N-butyl ketone; esters such as ethyl acetate, butyl acetate, 2-ethoxyethyl acetate and 2-ethylhexyl acetate; aliphatic and alicyclic hydrocarbons such as the various petroleum naphthas and cyclohexane; aromatic hydrocarbons such as benzene, ethyl benzene, toluene and xylene; chlorinated hydrocarbon solvents such as methylene chloride, chloroform, carbontetrachloride, chloroethane, and 1,1,1-trichloroethane; and water.

As will be appreciated by one skilled in the art, the organic solvents, examples of which have been described previously, suitable for the solvent system in the method of the present invention may be broadly classified into five categories which include aliphatic, aromatic, moderately polar, highly polar and chlorinated solvents. Essentially nonpolar aliphatic solvents include normal and branched chain aliphatic hydrocarbons having from about 5 to 12 carbon atoms and cycloaliphatic compounds. Essentially nonpolar aromatic solvents include such materials as benzene, toluene, xylene and ethyl benzene. Moderately polar solvents include ketonic and ester solvents such as acetone, methylethylketone, methylbutylketone, methylisobutylketone, cyclohexanone, ethyl acetate, butyl acetate, ethoxyethyl acetate, and the like. Highly polar solvents include such materials as low molecular weight alcohols such as methanol, ethanol, propanol, 2-propanol, butanol, 2-butanol, and ethoxyethanol. Chlorinated hydrocarbon solvents include such materials as methylene chloride, chloroform, carbon tetrachloride, chloroethane and 1,1,1-trichloroethane.

The basecoating composition also contains a pigment. Examples of opacifying pigments include titanium dioxide (rutile or anatase), zinc oxide, zirconium oxide, zinc sulfide, and lithopone. Examples of coloring pigments include iron oxides, cadmium sulfide, carbon black, phthalocyanine blue, phthalocyanine green, indanthrone blue, ultramarine blue, chromium oxide, burnt umber, benzidine yellow and toluidine red. Examples of reactive pigments include silicate-treated barium metaborate, strontium chromate and lead chromate. Examples of extender pigments include pigmentary silica, barytes, calcium carbonate, barium sulfate, talc, aluminum silicates, sodium aluminum silicates, potassium aluminum silicates and magnesium silicates. Metallic pigments include metallic powders and metallic flakes. Examples of metallic powders include aluminum powder, copper powder, bronze powder and zinc dust. Examples of metallic flakes include aluminum flakes, nickel flakes, copper flakes, bronze flakes, brass flakes and chromium flakes. A single pigment may be used or mixtures of pigments may be employed. It is preferred that at least a portion of the pigment particles be metallic flakes. The metallic flakes usually comprise aluminum flakes.

The principles respecting the formation of solutions, dispersions, pseudodispersions, and emulsions of film-forming resins are generally known in the art. Any of these systems may be utilized in the basecoating and/or topcoating composition.

The method of the invention requires that an organo-modified clay be employed in the basecoating composition. The organo-modified clays which are suitable in the method of the present invention are produced from the reaction of an organic cation, organic anion and smectite-type clay. The clays used to prepare these organo-modified clays suitable for the process of the present invention are smectite-type clays which have a cation exchange capacity of at least 75 milliequivalents per 100 grams of clay. Particularly desirable types of clay are the naturally occurring Wyoming varieties of swelling bentonites and like clays and hectorite, a swelling magnesium-lithium silicate clay.

The clays, especially the bentonite type clays, are preferably converted to the sodium form if they are not already in this form. This can conveniently be done by preparing an aqueous clay slurry and passing the slurry through a bed of cation exchange resin in the sodium form. Alternatively, the clay can be mixed with water and a soluble sodium compound such as sodium carbonate, sodium hydroxide and the like, followed by shearing the mixture with a pugmill or extruder.

Smectite-type clays prepared naturally or synthetically by either a pneumatolytic or, preferably a hydrothermal synthesis process can also be used to prepare the organophilic, organo-modified clays suitable for the present invention. Representative of such clays are montmorillonite, bentonite, beidellite, hectorite, saponite, and stevensite. These clays may be synthesized hydrothermally by forming an aqueous reaction mixture in the form of a slurry containing mixed hydrous oxides or hydroxides of the desired metal with or without, as the case may be, sodium (or alternate exchangeable cation or mixture thereof) fluoride in the proportions for the particular synthetic smectite desired. The slurry is then placed in an autoclave and heated under autogenous pressure to a temperature within the range of approximately 100.degree. to 325.degree. C., preferably 274.degree. to 300.degree. C., for a sufficient period of time to form the desired product.

The cation exchange capacity of the smectite-type clays can be determined by the well-kown ammonium acetate method.

Organo-modified clays of one preferred type which do not require the addition of polar solvent activators (such as acetone, alcohols and the like) for use in the method of the present invention are produced from the reaction of the smectite-type clay with an organic cation and an organic anion described below. Additional description may be obtained from U.S. Pat. No. 4,412,018 which is hereby incorporated by reference.

The organic cationic compounds which are useful in preparing these preferred organo-modified clays suitable for the method of the present invention may be selected from a wide range of materials which are capable of forming an organophilic clay by exchange of cations with the smectite-type clay. The organic cationic compound generally has a positive charge localized on a single atom or on a small group of atoms within the compound. Preferably the organic cation is selected from the group consisting of quaternary ammonium salts, phosphonium salts, sulfonium salts and mixtures thereof wherein the organic cation contains at least one lineal or branched alkyl group having 12 to 22 carbon atoms. The remaining moieties on the central positively charged atoms are chosen from (a) lineal or branched alkyl groups having 1 to 22 carbon atoms; (b) aralkyl groups, that is benzyl and substituted benzyl moieties including fused ring moieties having lineal or branched alkyl groups having 1 to 22 carbon atoms in the alkyl portion of the structure; (c) aryl groups such as phenyl and substituted phenyl including fused ring aromatic substituents; and (d) hydrogen.

The long chain alkyl radicals containing at least one group having 12 to 22 carbon atoms may be derived from naturally occurring oils including various vegetable oils, such as corn oil, coconut oil, soybean oil, cottonseed oil, castor oil and the like, as well as various animal oils or fats such as tallow oil. The alkyl radicals may likewise be petrochemically derived such as from alpha olefins. Additional exemplary radicals include methyl, ethyl, decyl, lauryl, and stearyl.

Additional examples of aralkyl groups, that is benzyl and substituted benzyl moieties would include those materials derived from, e.g. benzyl halides, benzhydryl halides, trityl halides, alpha-halo-alphaphenylalkanes wherein the alkyl chain has from 1 to 22 carbon atoms such as 1-halo-1-phenylethane, 1-halo-1-phenyl propane, and 1-halo-1-phenyloctadecane; substituted benzyl moieties such as would be derived from ortho, meta and para-chlorobenzyl halides, para-methoxybenzyl halides, ortho, meta and para-methoxybenzyl halides, ortho, meta and para-nitrilobenzyl halides, and ortho, meta and para-alkylbenzyl halides wherein the alkyl chain contains from 1 to 22 carbon atoms; and fused ring benzyl-type moieties such as would be derived from 2-halomethylnaphthalene, 9-halomethylanthracene and 9-halomethylphenanthrene, wherein the halo group would be defined as chloro, bromo, iodo, or any other such group which serves as a leaving group in the nucleophilic attack of the benzyl type moiety such that the nucleophile replaces the leaving group on the benzyl type moiety.

Examples of aryl groups would include phenyl such as in N-alkyl and N,N-dialkyl anilines, wherein the alkyl groups contain between 1 and 22 carbon atoms; ortho, meta and para-nitrophenyl, ortho, meta and para-alkyl phenyl, wherein the alkyl group contains between 1 and 22 carbon atoms, 2-, 3-, and 4-halophenyl wherein the halo group is defined as chloro, bromo, or iodo, and 2-, 3-, and 4-carboxyphenyl and esters thereof, where the alcohol of the ester is derived from an alkyl alcohol, wherein the alkyl group contains between 1 and 22 carbon atoms, aryl such as a phenol, or aralkyl such as benzyl alcohols; fused ring aryl moieties such as naphthalene, anthracene, and phenanthrene.

Many processes are known to prepare organic cationic salts. For example when preparing a quaternary ammonium salt one skilled in the art would prepare a dialkyl secondary amine, for example, by the hydrogenation of nitriles, see U.S. Pat. No. 2,355,356; form the methyl dialkyl tertiary amine by reductive alkylation using formaldehyde as the source of methyl radical. Also see Shapiro et al U.S. Pat. No. 3,136,819 for forming the quaternary amine halide by adding benzyl chloride or benzyl bromide to the tertiary amine as well as Shapiro et al U.S. Pat. No. 2,775,617. The salt anion is preferably selected from the group consisting of chloride and bromide, and mixtures thereof, and is more preferably chloride, although other anions such as acetate, hydroxide, nitrite, etc., may be present in the organic cationic compound to neutralize the cation.

These organic cationic compounds can be represented by the formulas: ##STR3## wherein X is nitrogen or phosphorus, Y is sulfur, M.sup.- is selected from the group consisting of chloride, bromide, iodide, nitrite, hydroxide, acetate, methyl sulfate, and mixtures thereof; and wherein R.sub.1 is an alkyl group having 12 to 22 carbon atoms; and wherein R.sub.2, R.sub.3 and R.sub.4 are selected from the group consisting of hydrogen; alkyl groups containing 1 to 22 carbon atoms; aryl groups; aralkyl groups containing 1 to 22 carbon atoms on the alkyl chain, and mixtures thereof.

The organic anions useful in preparing these preferred organo-modified clays suitable for the method of the present invention may be selected from a wide range of materials providing they are capable of reacting with the above-described organic cation and form intercalations with a smectite-type clay as an organic cation-organic anion complex. The molecular weight (gram molecular weight) of the organic anion is typically 3,000 or less, and usually 1,000 or less and contains at least one acidic moiety per molecule as disclosed herein. The organic anion is preferably derived from an organic moiety having a pK.sub.A less than about 11.0. As indicated, the source acid must contain at least one ionizable hydrogen having the preferred pK.sub.A in order to allow the formation of the organic cation-organic anion complex and subsequent intercalation reaction to occur.

Also useable is any compound which will provide the desired organic anion on hydrolysis. Representative compounds include:

(1) acid anhydrides including acetic anhydride, maleic anhydride, succinic anhydride and phthalic anhydride;

(2) acid halides including acetylchloride octanoyl, chloride, lauroyl chloride, lauroyl bromide and benzoyl bromide;

(3) 1,1,1-trihalides including 1,1,1-trichloroethane and 1,1,1-tribromooctane; and

(4) orthoesters including ethylorthoformate, and ethylorthostearate.

The organic anions may be in the acid or salt form. Salts may be selected from alkali metal salts, alkaline earth salts, ammonia, and organic amines. Representative salts include: hydrogen, lithium, sodium, potassium, magnesium, calcium, barium, ammonium and organic amines such as ethanolamine, diethanolaine, triethanolamine, methyl diethanolamine, butyl diethanolamine, diethyl amine, dimethyl amine, triethyl amine, dibutyl amine, and so forth, and mixtures thereof. The most preferred salt is sodium as the alkali metal salt.

Exemplary types of suitable acidic functional organic compounds useful in this invention include:

(1) carboxylic acids including:

(a) benzene carboxylic acids such as benzoic acid, ortho, meta and para-phthalic acid, 1,2,3-benzene tricarboxylic acid; 1,2,4-benzene tricarboxylic acid; 1,3,5-benzenetricarboxylic acid; 1,2,4,5-benzene tetracarboxylic acid; 1,2,3,4,5,6-benzene hexacarboxylic acid (mellitic acid);

(b) alkyl carboxylic acids having the formula H--(CH.sub.2).sub.n --COOH, wherein n is a number from 1 to 22, such compounds include acetic acid; propionic acid; butanoic acid; pentanoic acid; hexanoic acid; heptanoic acid; octanoic acid; nonamoic acid; decanoic acid; undecanoic acid; lauric acid, tridecanoic acid; tetradecanoic acid; pentadecanoic acid; hexadecanoic acid; heptadecanoic acid; octadecanoic acid (stearic acid); nonadecanic acid; eicosonic acid;

(c) alkyl dicarboxylic acids having the formula HOOC--(CH.sub.).sub.n --COOH, wherein n is 1 to 8 such as oxalic acid; malonic acid; succinic acid; glutaric acid; adipic acid; pimelic acid; suberic acid; acelaic acid; sacic acid;

(d) hydroxyalkyl carboxylic acids such as citric acid; tartaric acids, malic acid; mandelic acid; and 12-hydroxystearic acid;

(e) unsaturated alkyl carboxylic acids such as maleic acid; fumaric acid; and cinnamic acid;

(f) fused ring aromatic carboxylic acids such as naphthalenic acid; and anthracene carboxylic acid;

(g) cycloaliphatic acids such as cyclohexane carboxylic acid; cyclopentane carboxylic acid; and furan carboxylic acids.

(2) organic sulfuric acids including:

(a) sulfonic acids including:

(1) benzene sulfonic acids such as benzene sulfonic acid; phenol sulfonic acid; dodecylbenzene sulfonic acid; benzene disulfonic acid, benzene trisulfonic acids; para-toluene sulfonic acid; and

(2) alkyl sulfonic acids such as methane sulfonic acid; ethane sulfonic acid; butane sulfonic acid; butane disulfonic acid; sulfosuccinate alkyl esters such as dioctyl succinyl sulfonic acid; and alkyl polyethoxysuccinyl sulfonic acid; and

(b) alkyl sulfates such as the lauryl half ester of sulfuric acid and the octadecyl half ester of sulfuric acid.

(3) organophosphorus acids including:

(a) phosphnic acids have the formula: ##STR4## wherein R is an aryl group or alkyl having 1 to 22 carbon atoms; (b) phosphinic acids having the formula: ##STR5## wherein R is an aryl group or alkyl group having 1 to 22 carbon atoms, such as dicyclohexyl phosphinic acid; dibutyl phosphinic acid; and dilauryl phosphinic acid;

(c) thiophosphinic acids having the formula: ##STR6## wherein R is an aryl group or alkyl group having 1 to 22 carbon atoms such as di-isobutyl dithiophosphinic acid; dibutyl dithiophosphinic acid; dioctadecyl dithiophosphinic acid;

(d) phosphites, that is diesters of phosphorous acid having the formula: HO--P(OR).sub.2 wherein R is an alkyl group having 1 to 22 carbon atoms such as dioctadecylphosphite;

(e) phosphates, that is diesters of phosphoric acid having the formula: ##STR7## wherein R is an alkyl group having 1 to 22 carbon atoms, such as dioctadecyl phosphate;

(4) Phenols such as phenol; hydroquinone, t-butylcatechol; p-methoxyphenol; and naphthols;

(5) thioacids having the formula: ##STR8## wherein R is an aryl group or alkyl group having 1 to 22 carbon atoms, such as thiosalicylic acid; thiobenzoic acid; thioacetic acid; thiolauric acid; and thiostearic acid;

(6) Amino acids such as the naturally occurring amino acids and derivatives thereof such as 6-aminohexanoic acid; 12-aminododecanoic acid; N-phenylglycine; and 3-aminocrotonoic acid;

(7) Polymeric acids prepared from acidic monomers wherein the acidic function remains in the polymer chain such as low molecular weight acrylic acid polymers and copolymers; and styrene maleic anhydride copolymers;

(8) Miscellaneous acids and acid salts such as ferrocyanide; ferricyanide; sodium tetraphenylborate; phosphotungstic acid; phosphosilicic acid, or any other such anion which will form a tight ion pair with an organic cation, i.e., any such anion which forms a water insoluble precipitate with an organic cation.

The organophilic, organo-modified clays suitable for use in the present invention can be prepared by admixing the clay, organic cation, organic anion and water together, preferably at a temperature within the range from 20.degree. C. to 100.degree. C., more preferably 60.degree. C. to 77.degree. C. for a period of time sufficient for the organic cation and organic anion complex to intercalate with the clay particles, followed by filtering, washing, drying and grinding. The addition of the organic cation and organic anion may be done either separately or as a complex. In using the organophilic clays in emulsions, the drying and grinding steps may be eliminated. When admixing the clay, organic cation, organic anion and water together in such concentrations that a slurry is not formed, then the filtration and washing steps can be eliminated.

The clay is preferably dispersed in water at a concentration of from about 1% to 80% and preferably 2% to 7%, the slurry optionally centrifuged to remove non-clay impurities which constitute about 10% to about 50% of the starting clay composition, the slurry agitated and heated to a temperature in the range from 60.degree. C. to 77.degree. C.

The organophilic, organo-modified clays suitable for use in the method of the present invention may be prepared by admixing the organic anion with a clay and water together, preferably at a temperature between 20.degree. C. and 100.degree. C. for a sufficient time to prepare a homogenous mixture followed by the addition of the organic cation in sufficient amounts to satisfy the cation exchange capacity of the clay and the cationic capacity of the organic anion. The mixture is reached with agitation at a temperature between 20.degree. C. and 100.degree. C. for a sufficient time to allow the formation of an organic cation-organic anion complex which is intercalated with the clay and tne cation exchange sites of the clay are substituted with the organic cation. Reaction temperatures below 20.degree. C. or above 100.degree. C. while useable are not preferred because of the need for additional processing apparatus, namely cooling devices and pressure reactors.

The amount of organic anion added to the clay for purposes of preparing suitable organo-modified clays for the present invention should be sufficient to impart to the organophilic, organo-modified clay, desirable enhanced dispersion characteristics. This amount is defined as the milliequivalent ratio which the number of milliequivalents (M.E.) of the organic anion in the organoclay per 100 grams of clay, 100% active clay basis. The organophilic, organo-modified clays suitable for the method of the present invention, should have an anion milliequivalent ratio of 5 to 100 and preferably 10 to 50. At lower anion milliequivalent ratios the enhanced dispersibility and efficiency of the organophilic, organo-modified clays, are negligible. At higher anion M.E. ratios the efficiency of the organophilic, organo-modified clay reaction product is reduced from nonintercalated organic cation-organic anion complexes or ion pairs.

The organic anion is preferably added to the reactants in the desired milliequivalent ratio as a solid or solution in water under agitation to effect a macroscopically homogenous mixture.

The organic cation is employed in a sufficient quantity to at least satisfy the cation exchange capacity of the clay and the cationic activity of the organic anion. Additional cation above the sum of the exchange capacity of the clay and anion may be optionally used. It has been found when using the smectite-type clays that use of at least 90 milliequivalents of organic cation is sufficient to satisfy at least a portion of the total organic cation requirement. Use of amounts of from 80 to 200 M.E., and preferably 100 to 160 M.E. are acceptable. At lower milliequivalent ratios incomplete reaction between the organic cation and clay or organic anion will occur resulting in the formation of products which are not suitable for the method of the present invention.

A typical process for preparing an organophilic, organo-modified clay may be described more particularly by the following steps which involve: (a) preparing a slurry of smectite-type clay in water at 1 to 80% by weight of the smectite-type clay; (b) heating the slurry to a temperature between 20.degree. C. and 100.degree. C.; (c) adding 5 to 100 milliequivalents of an organic anion per 100 grams of clay, 100% active clay basis and an organic cation in a sufficient amount to satisfy the cation exchange capacity of the smectite-type clay and the cationic activity of the organic anion while agitating the reaction solution; (d) continuing the reaction for a sufficient time to form a reaction product comprising an organic cation-organic anion complex which is intercalated with the smectite-type clay and the cation exchange sites of the smectite-type clay are substituted with the organic cation; and (e) recovering the reaction product.

When organo-modified clays of the preferred type described above are utilized in the method of the invention, it is also preferred that the solvent system be based on moderately to highly polar solvents such as the alcohols, ethers and ether alcohols, ketones, and esters, examples of which are described above. Moderately to highly polar solvents are preferred for this embodiment because of the increased effectiveness of the organo-modified clay as a pattern control agent when employed in the method of the present invention in which the solvent system is based essentially on such moderately to highly polar solvents.

Additional preferred examples of organo-modified clays, which also do not require the addition of polar solvent activators, which may be employed in the method of the present invention particularly when the solvent system is based on moderately polar solvent, or on essentially nonpolar aromatic and nonpolar aliphatic solvents include those described in U.S. Pat. No. 4,391,637 and published U.K. patent application No. GB 2 107 692A, which are hereby incorporated by reference. The organo-modified clays described therein while effective in moderately polar solvents, are particularly effective in both nonpolar aliphatic and aromatic solvents. Clays suitable for preparation of these organo-modified clays are the same smectite-type clays as those described previously herein. These organo-modified clays comprise the reaction product of the smectite-type clay and an organic cationic compound having at least one long chain alkyl group and at least one group selected from a beta,gamma-unsaturated alkyl group or a hydroxyalkyl group having 2 to 6 carbon atoms. Some examples of these organo-modified clays particularly useful in essentially non-polar aromatic and aliphatic solvent systems include reaction products of an organic cationic compound and a smectite-type clay having a cation exchange capacity of at least 75 milliequivalents per 100 grams of the clay, wherein the organic cationic compound contains (a) a first member selected from the group consisting of a beta,gamma-unsaturated alkyl group and a hydroxyalkyl group having 2 to 6 carbon atoms and mixtures thereof, (b) a second member comprising a long chain alkyl group having 12 to 60 carbon atoms and (c) a third and fourth member selected from a member of group (a) above, an aralkyl group, and an alkyl group having 1 to 22 carbon atoms and mixtures thereof; and wherein the amount of the organic cationic compound is from 90 to 140 milliequivalents per 100 grams of the smectite-type clay, 100% active clay basis.

As discussed above the smectite-type clays and their preparation suitable for the preparation of these organophilic, organo-modified clays which are particularly compatible with essentially non-polar aromatic and aliphatic solvents are the same as the smectite-type clays described above which are suitable for preparation of the organophilic, organo-modified clays which are particularly compatible with moderate to highly polar solvents.

The organic cationic compounds useful for preparation of the organophilic, organo-modifed clays which are especially compatible with essentially non-polar aromatic and aliphatic solvents, may be selected from a wide range of materials that are capable of forming an organophilic clay by exchange of cations with the smectite-type clay. The organic cationic compound generally has a positive charge localized on a single atom or on a small group of atoms within the compound. Preferably the organic cation is selected from the group consisting of quarternary ammonium salts, phosphonium salts, and mixtures thereof, as well as equivalent salts, and wherein the organic cation contains at least one member selected from (a) a beta, gamma-unsaturated alkyl group and/or a hydroxyalkyl group having 2 to 6 carbon atoms and (b) a long chain alkyl group. The remaining moieties on the central positive atom are chosen from a member from group (a) above or an aralkyl group and/or an alkyl group having from 1 to 22 carbon atoms.

The beta,gamma-unsaturated alkyl group may be selected from a wide range of materials. These compounds may by cyclic or acylic, unsubstituted or substituted with aliphatic radicals containing up to 3 carbon atoms such that the total number of aliphatic carbons in the beta,gamma-unsaturated radical is 6 or less. The beta,gamma-unsaturated alkyl radical may be substituted with an aromatic ring that likewise is conjugated with the unsaturation of the beta,gamma moiety or the beta,gamma-radical is substituted with both an aliphatic radical and an aromatic ring.

Representative examples of cyclic beta,gamma-unsaturated alkyl groups include 2-cyclohexenyl and 2-cyclopentanyl. Representative examples of acyclic beta,gamma-unsaturated alkyl groups containing 6 or less carbon atoms include propargyl, allyl (2-propenyl); crotyl (2-butenyl); 2-pentenyl; 2-hexenyl; 3-methyl-2-butenyl; 3-methyl-2-pentenyl; 2,dimethyl-2-butenyl; 1,1-dimethyl-2-propenyl; 1,2-dimethyl-2-propenyl; 2,4-pentadienyl; and 2,4-hexadienyl. Representative examples of acyclic-aromatic substituted compounds include cinnamyl (3-phenyl-2-propenyl); 2-phenyl-2-propenyl; and 3-(4-methoxyphenyl)-2-propenyl. Representative examples of aromatic and aliphatic substituted materials include 3-phenyl-2-cyclohexenyl; 3-phenyl-2-cyclopentenyl; 1,1-dimethyl-3-phenyl-2-propenyl; 1,1,2-trimethyl-3-phenyl-2-propenyl; 2,3-dimethyl-3-phenyl-2-propenyl; 3,3-dimethyl-2-phenyl-2-propenyl; and 3-phenyl-2-butenyl.

The hydroxyalkyl group is selected from a hydroxyl substituted aliphatic radical wherein the hydroxyl is not substituted at the carbon adjacent to the positively charged atom, and has from 2 to 6 aliphatic carbons. The alkyl group may be substituted with an aromatic ring. Representative examples include 2-hydroxyethyl (ethanol); 3-hydroxypropyl; 4hydroxypentyl; 6-hydroxyhexyl; 2-hydroxypropyl (isopropanol); 2-hydroxybutyl; 2-hydroxypentyl; 2-hydroxyhexyl; 2-hydroxycyclohexyl; 3-hydroxycyclohexyl; 4-hydroxycyclohexyl; 2-hydroxycyclopentyl; 3-hydroxycyclopentyl; 2-methyl-2-hydroxypropyl; 1,1,2-trimethyl-2-hydroxypropyl; 2-phenyl-2-hydroxyethyl; 3-methyl-2-hydroxybutyl; and 5-hydroxy-2-pentenyl.

The long chain alkyl radicals may be branched or unbranched, saturated or unsaturated, substituted or unsubstituted and should have from 12 to 60 carbon atoms in the straight chain portion of the radical.

The long chain alkyl radicals may be derived from natural occurring oils including various vegetable oils, such as corn oil, coconut oil, soybean oil, cottonseed oil, castor oil and the like, as well as various animal oils or fats such as tallow oil. The alkyl radicals may likewise be petrochemically derived such as from alpha olefins.

Representative examples of useful branched, saturated radicals include 12-methylstearyl; and 12-ethylstearyl. Representative examples of useful branched, unsaturated radicals include 12-methyloleyl and 12-ethyloleyl. Representative examples of unbranched saturated radicals include lauryl; stearyl; tridecyl; myristal (tetradecyl); pentadecyl; hexadecyl; hydrogenated tallow, docosonyl. Representative examples of unbranched, unsaturated and unsubstituted radicals include oleyl, linoleyl; linolenyl, soya and tallow.

The remaining groups on the positively charged atom are chosen from (a) a member of the group selected from a beta,gamma-unsaturated alkyl group and a hydroxyalkyl group having 2 to 6 carbon atoms, both described above; (b) an alkyl group having 1 to 22 carbon atoms, cyclic and acyclic and (c) an aralkyl group, that is benzyl and substituted benzyl moieties including fused ring moieties having lineal or branched 1 to 22 carbon atoms in the alkyl portion of the structure.

Representative examples of an aralkyl group, that is, benzyl and substituted benzyl moieties would include benzyl and those materials derived from, e.g. benzyl halides, benzhydryl halides, trityl halides, 1-halo-1-phenylalkanes wherein the alkyl chain has from 1 to 22 carbon atoms such as 1-halo-1-phenylethane; 1-halo-1-phenyl propane; and 1-halo-1-phenyloctadecane; substituted benzyl moieties such as would be derived from ortho-, meta- and para-chlorobenzyl halides, para-methoxybenzyl halides; ortho-, meta-, and para-nitrilobenzyl halides; and ortho-, meta- and para-alkylbenzyl halides wherein the alkyl chain contains from 1 to 22 carbon atoms; and fused ring benzyl-type moieties such as would be derived from 2-halomethylnaphthalene, 9-halomethylanthracene and 9-halomethylphenanthrene, wherein the halo group would be defined as chloro, bromo, iodo, or any other such group which serves as a leaving group in the nuclcophilic attack of the benzyl type moiety such that the nuclophile replaces the leaving group on the benzyl type moiety.

Representative examples of useful alkyl groups which may be lineal and branched, cyclic and acyclic include methyl; ethyl; propyl; 2-propyl; iso-butyl; cyclopentyl; and cyclohexyl.

The alkyl radicals may also be derived from other natural oils, both substituted and unsubstituted such as those described above, including various vegtable oils, such as tallow oil, corn oil, soybean oil, cottonseed oil, castor oil and the like, as well as various animal oils and fats.

The salt anion is preferably selected from the group consisting of chloride and bromide, and mixtures thereof, and is more preferably chloride, although other anions such as acetate, hydroxide, nitrite, etc., may be present in the organic cationic compound to neutralize the cation. A representative formula for the salt is ##STR9## wherein R.sub.1 is selected from the group consisting of a beta,gamma-unsaturated alkyl group and hydroxyalkyl group having 2 to 6 carbon atoms and mixtures thereof; R.sub.2 is a long chain alkyl group having 12 to 60 carbon atoms; R.sub.3 and R.sub.4 are selected from a group consisting of an R.sub.1 group, an aralkyl group, and alkyl group having from 1 to 22 carbon atoms and mixtures thereof; X is phosphorous or nitrogen; and wherein M.sup.- is an anion selected from the group consisting of Cl--, Br--, 1--, NO.sub.2 --, OH-- and C.sub.2 H.sub.3 O.sub.2 --.

The organophilic, organo-modified clays which are particularly suitable for use in the method of the present invention when an essentially non-polar aromatic or aliphatic solvent is employed, can be prepared by admixing the smectite-type clay, quaternary ammonium compound and water together, preferably at a temperature within the range of from 20.degree. C. to 100.degree. C., and most preferably from 35.degree. C. to 77.degree. C. for a period of time sufficient for the organic compound to coat the clay particles, followed by filtering, washing, drying and grinding.

The clay is preferably dispersed in water at a concentration from about 1 to 80% and preferably 2% to 7%, the slurry optionally centrifuged to remove non-clay impurities which constitute about 10% of the starting clay composition, the slurry agitated and heated to a temperature in the range of from 35.degree. C. to 77.degree. C. The quaternary amine salt is then added in the desired milliequivalent ratio, preferably as a liquid in isopropanol or dispersed in water and the agitation continued to effect the reaction.

The amount of organic cation added to the smectite-type clay should be sufficient to impart to the clay the enhanced dispersion characteristic desired. This amount is defined as the milliequivalent ratio which is the number of milliequivalents (M.E.) of the organic cation in the organoclay per 100 grams of clay, 100% active clay basis. The organophilic, organo-modified clay should have a milliequivalent ratio of from 90 to 140 and preferably 100 to 130. It will be recognized that the preferred milliequivalent ratio within the range of from 90 to 140 will vary depending on the characteristics of the organic solvent system to be employed with the organophilic, organo-modified clay. These organo-modified clays are effective in both aliphatic and aromatic solvents as well as moderately polar solvents.

Additional description of organo-modified clays suitable for the method of the present invention can be found in U.S. Pat. Nos. 4,105,578, 2,531,427 and published U.K. patent application No. GB 2 107 693A the disclosures of which are hereby incorporated by reference.

In addition to the above components, the basecoating and/or the topcoating compositions employed in the invention may contain optional ingredients which may be employed in their customary amounts for their customary purposes provided they do not seriously interfere with good coatings practice. Examples of these optional ingredients include various fillers; plasticizers; antioxidants; mildewcides and fungicides; surfactants; various catalysts to promote drying or curing; resinous pigment dispersants or grinding vehicles; various flow control agents including, for example, thixotropes and additives for sag resistance and/or pigment orientation based on organic polymer microparticles (sometimes referred to as microgels) described for example in U.S. Pat. Nos. 4,025,474; 4,055,607; 4,075,141; 4,115,472; 4,147,688; 4,180,489; 4,242,384; 4,268,547; 4,220,679; and 4,290,932 the disclosures of which are hereby incorporated by reference; and other such formulating additives.

Where desired the topcoating composition may also contain an organo-modified clay.

The basecoating composition and topcoating compositions are usually prepared by simply admixing the various ingredients for the respective compositions at room temperature although elevated temperatures may be used.

The amounts of the materials in the basecoating composition including the organo-modified clay can vary widely. Generally the film-forming resin constitutes from about 10 percent to about 95 percent by weight, typically from about 25 percent to about 50 percent by weight, of the basecoating composition. Generally the amount of organo-modified clay can range from about 1 percent to about 20 percent by weight, typically from about 1 percent to about 12 percent by weight, based on the sum of the weights of the organic film-forming resin, optional crosslinking agent, and organo-modified clay.

The amount of solvents and/or diluents constituting the solvent system for the film-forming resin also may vary widely. Generally the total amount of solvents and/or diluents may range from about 0 to about 80 percent by weight, typically from about 35 to about 65 percent by weight, of the basecoating composition.

The amount of the optional crosslinking agent for the film-forming resin of the basecoating composition generally may range from 0 to 50 percent by weight, typically from 10 to 40 percent by weight based on the sum of the weights of the organic film-forming resin, optional crosslinking agent, and organo-modified clay.

The amount of pigment particles present in the basecoating composition is likewise subject to wide variation. Generally the pigment is present in an amount ranging from about 2 to about 50 percent by weight, typically from about 3 to about 30 percent by weight, based on the sum of the weights of the film-forming resin, optional crosslinking agent, and the organo-modified clay. When metallic flakes are employed as pigment on the basecoating composition, they generally are present in the range of from about 2 to about 30 percent by weight, typically from about 10 to about 20 percent by weight, based on the sum of the weights of the film-forming resin, optional crosslinking agent, and the organo-modified clay present in the basecoating composition.

The film-forming resin of the topcoating composition can be any of the film-forming resins useful for coating compositions and can be the same or different from the film-forming resin of the basecoating composition. Likewise, film-forming resins for the topcoating composition can be film-forming thermoplastic resins and/or thermosetting resins. Illustrative examples of film-forming resins suitable for the topcoating composition have been described previously in the discussion of examples of film-forming resins suitable for the basecoating composition. The solvent systems described with respect to the basecoating composition also can be employed for the film-forming resin of the topcoating composition. For example, the film-forming resin of the topcoating composition may be dissolved in the solvent system or it may be dispersed in the solvent system. Like the solvent system for the film-forming resin of the basecoating composition, the solvent system for the topcoating composition may be organic or aqueous, but typically is essentially organic, and may be a single compound or a mixture of compounds. Illustrative of components suitable for the solvent system include those described previously.

As for the film-forming resin of the basecoating composition, the film-forming resin of the topcoating composition may be present in the coating composition in the form of a solution, dispersion, emulsion or pseudodispersion. Likewise, the topcoating composition may contain optional ingredients such as various fillers, plasticizers, antioxidants, mildewcides and fungicides, surfactants, various catalysts to promote drying or curing, and various flow control agents as described previously with respect to the basecoating composition.

Where a crosslinkable film-forming resin is utilized in the topcoating composition, optionally a crosslinking agent can be incorporated in the topcoating composition. Examples of such crosslinking agents include those described previously with respect to the basecoating composition.

The topcoating composition is formulated so that when it is applied to the basecoat, it forms a clear topcoat so that the pigmentation of the basecoat will be visible through the topcoat. It should be understood that the topcoat, while being transparent, may contain small amounts of dyes and/or tints to modify the overall appearance where desired. However, it is usually preferable not to employ even small amounts of dyes and/or tints in the topcoating composition. Although the topcoating composition may contain transparent extender pigments and optionally a small amount of coloring pigment, it should not contain so much coloring pigment that it interferes with the general transparency of the topcoat. Usually it is preferable not to utilize even small amounts of coloring pigment in the topcoating composition.

The amounts of the film-forming resin and solvent system employed in the topcoating composition generally are as described with respect to the amounts of these components for the basecoating composition.

Where an organo-modified clay is utilized in the topcoating composition, the amount of organo-modified clay generally is as described previously with respect to the amount of organo-modified clay for the basecoating composition.

The method of the invention can be employed utilizing a wide variety of substrates such as metals, wood, glass, cloth, plastics, fiberglass, foams and the like as well as over primers. The basecoating composition and topcoating composition can be applied to the substrate using any application technique known in the art such as roll coating, curtain coating, dip coating, doctor blade coating, spraying and the like although spraying is most often employed.

In the method of the invention the basecoating composition containing organic film-forming resin, the solvent system for the film-forming resin, pigment particles, and organo-modified clay is first applied to the substrate. The basecoating composition, depending on the choice of thermoplastic and/or thermosetting resin, may be dried or cured at ambient temperature or with applied heat to a degree sufficient to allow the clear topcoating composition to be applied to the basecoat without undesirable strike-in. Thermoplastic coating compositions are typically hardened by evaporation of the volatile solvent system (sometimes referred to as curing although hardening of thermoplastic coatings ordinarily does not involve a crosslinking process). Thermosetting coating compositions can be cured (i.e. crosslinked) in a variety of ways, typically at temperatures in the range of from about 20.degree. C. to about 260.degree. C. Some of the thermosetting film-forming resins such as air-curable alkyds for example may be cured by exposure to the oxygen in air. Many of the coating compositions contain a crosslinking agent. When a crosslinking agent is present, the coating compositions are usually cured by the application of heat. Although the curing temperature may vary widely it is typically in the range of about 80.degree. Celsius (C.) to about 150.degree. C. Similarly, curing times may be subject to wide variation, but typically range from about 10 minutes to about 45 minutes. Where a plurality of superimposed basecoats or topcoats are to be applied, each coating composition may be cured prior to application of the next coating composition. It is preferable, however, to utilize coating systems which will permit the application of two or more superimposed coatings which can be cured together in a single curing operation. For example, a thermosetting basecoat may be somewhat cured prior to application of a thermosetting topcoat, although it is preferred to use coating systems which will permit the topcoating composition to be applied to a substantially uncured basecoat and to cure them simultaneously in one operation, i.e. an essentially "wet on wet" procedure. Thus in a preferred embodiment of the invention the topcoating composition is applied to the basecoat before allowing the basecoating composition to become substantially cured. Particularly when heat curing is employed, it is sometimes desirable to allow the basecoating composition to flash at ambient temperature for up to about 30 minutes, typically up to about 5 minutes, before the topcoating composition is applied to the basecoat. Such solvent flashing may be utilized with either basecoating compositions containing thermoplastic film-forming resins or with basecoating compositions containing thermosetting film-forming resins (i.e., those which involve some degree of crosslinking during cure). However the period of solvent flashing in a "wet on wet" procedure is not so long as to allow a substantial degree of hardening or curing of the basecoat (for example as can be measured by resistance to degradation by organic solvents).

The color plus clear method of the invention provides a number of advantages. By incorporating the organo-modified clay in the pigmented basecoating composition, the amount of sagging of the basecoating coating composition on a verticle substrate during curing, including curing by heating, can be substantially reduced or even eliminated often without the use of known organic microgels. Moreover, this advantage with respect to sag control is especially important when a high-solids coating composition is utilized in the method of the invention where sag control can be an especially serious problem.

As used herein in reference to the basecoating composition, the term "high solids coating composition" is intended to include basecoating compositions having a total solids content of at least 35 percent by weight, preferably at least 40 percent by weight. A high-solids basecoating composition which can be applied to the substrate by conventional spraying techniques has a No. 4 Ford Cup viscosity of less than 25 seconds when the total solids content of the basecoating composition typically is at least 35 percent by weight, and preferably is at least 40 percent by weight.

As used herein in reference to the topcoating composition, the term "high solids coating composition" is intended to include topcoating compositions having a total solids content of at least 40 percent by weight. A high-solids topcoating composition which can be applied to the substrate by conventional spraying techniques has a No. 4 Ford Cup viscosity of less than 25 seconds when the total solids content of the topcoating composition is at least 40 percent by weight, preferably at least 45 percent by weight.

Moreover, it is preferred that the basecoating and topcoating compositions be applied by conventional spraying to the substrate at a combined total solids content of at least 50 percent by weight of the sum of the basecoating composition and the topcoating composition.

Wherever referred to herein, the solids are understood to include the essentially nonvolatile components of the coating composition including, for example, film-forming resin, organo-modified clay and pigment particles. It is to be understood that the optional crosslinking agents, examples of which have been described above, are intended to be included for the purpose of the determination of the solids content of the coating composition. Particularly where a high-solids coating composition is utilized in the method of the invention, typically the organic film-forming resin will comprise a crosslinkable resin having a weight average molecular weight of from 300 to 20,000 and typically the coating composition will contain a crosslinking agent examples of which include those described previously.

Where metallic flakes are employed as pigment in the basecoating composition, the incorporation of the organo-modified clay provides excellent control of the pigment orientation in the basecoat such that the dried or cured coating exhibits a high degree of pattern control as evidenced by excellent variable appearance when viewed at different angles to a direction normal to the coated surface and also exhibits excellent metallic brightness (sometimes referred to as brightness of face or lightness of face) when viewed from a direction essentially normal to the coated substrate. Moreover, the high degree of pattern control may be achieved in the method of the invention without the necessity of using known organic polymer microgels which have been synthesized for this purpose, although it is to be understood that the scope of the present invention is intended to include the color plus clear coating method of the invention wherein an organic polymer microgel is employed in combination with the organo-modified clay in the basecoating composition and/or where an organic polymer microgel is employed in the topcoating composition optionally in combination with organo-modified clay.

Some further advantages of the method of the invention may obtain because of the nature of the organo-modified clay. For example, coating compositions suitable for use in the method of the invention employing the organo-modified clay tend to be more shelf stable (as measured for example by increase in viscosity on storage for 24 hours in a "hot room" at 60.degree. C.) than for example coatings employing inorganic particles such as silica for rheology control such as certain silicas of colloidal dimensions.

The following examples are intended to further illustrate the present invention. As used in the body of the specification, examples and claims, all percents, ratios and parts are by weight unless otherwise specifically indicated. As used herein, "pbw" means "parts by weight.".

Examples 2 through 4 illustrate the method of the invention in which an organo-modified clay is utilized in a basecoating composition to provide an excellent combination of appearance properties in the resulting cured composite films (i.e., transparent topcoat over pigmented basecoat). Examples 1 and 5 are comparative examples. Example 1 utilizes no organo-modified clay in the basecoating composition. Example 5 utilizes cellulose acetate butyrate but no organo-modified clay in the basecoating composition.

(a) Each of the five basecoating compositions, numbered 1 through 5 respectively in the following TABLE 1 is prepared as follows. Components (1) through (10) in the amounts in parts by weight (pbw) as set forth on TABLE 1 are introduced into a container in the order indicated in TABLE 1 (i.e., component 1 is added before component 2 and so forth). After all of components (1) through (10) have been introduced into the container, the contents of the container are mixed together utilizing a conventional stirrer. Next, component (11) in the amount as set forth in TABLE 1 is admixed with the contents of the container to produce a basecoating composition having the percent by weight total spray solids as indicated in TABLE 1. Each of the basecoating compositions having a total percent by weight spray solids as set forth in TABLE 1 has a No. 4 Ford Cup viscosity of 14 seconds, except for Example 5 which has a No. 4 Ford Cup viscosity of 22 seconds.

(b) Each of the basecoating compositions is spray applied in two coats to each panel of a set of two metal panels with a 2 minute flash at ambient conditions between basecoating applications to form a resulting basecoat on each of the panels. The resulting basecoat on each of the panels is allowed to flash at ambient conditions for two minutes. Immediately thereafter an unpigmented transparent topcoating composition (sometimes referred to herein as a clearcoating composition) as set forth in TABLE 2 is spray applied to the basecoat in two coats with a 2 minute flash at ambient conditions between transparent topcoating applications to form a resulting transparent topcoat on the basecoat of each of the panels (hereafter referred to as a composite basecoat/topcoat). The resulting composite basecoat/topcoat on each of the panels is allowed to flash for 10 minutes at ambient conditions and immediately thereafter is cured for 30 minutes at 250 degrees Fahrenheit (.degree.F.), one of each of the sets of two panels being cured in a horizontal position and one of each of the sets of two panels being cured in a substantially vertical position. The thicknesses of the basecoat and topcoat respectively in each of the cured basecoat/topcoat composites are about 0.8 mil and 1.5 mil respectively.

(c) The resulting cured films are examined and compared visually for pattern control, absence of strike-in of the topcoat into the basecoat, and lightness of face (or metallic brightness). A cured film having excellent pattern control exhibits a completely uniform distribution of metallic flake pigment in a planar direction across the substrate as determined visually and is free of any visually noticeable, localized discontinuities in the distribution of metallic flake pigment and any visually noticeable defects such as, for example, short hairlike features in the pattern (believed to be attributable to an unacceptably high degree of substantially nonhorizontal rather than horizontal alignment to the substrate of small areas of metallic flake pigment). A cured film which is essentially free of strike-in of the topcoat into the basecoat (sometimes alternatively said to exhibit excellent "hold-out") has a high degree of gloss and a high degree of distinctness of image (DOI) such that when the film is viewed from a direction close to the normal to the surface and under, for example, a light fixture such as a fluorescent light fixture having a cross-hatch grid in front of the bulb, the reflected image of the lighted fixture in the film appears clear and sharply distinct and seems to originate deep in the film.

The comparative ratings for pattern control, hold-out, and lightness of face of the resulting cured films of Examples 1 through 5 is as follows:

Control: 3>2>4>5 >>>1

Hold-out: 3 =2.gtoreq.5>4 >>1

Lightness of face: 3.gtoreq.2>5>4 >>>1

In the comparative ratings immediately above .gtoreq. means "slightly better than although close", > means "better than", and >> means "much better than", and = means "equal to".

Thus the cured films prepared according to the method of the invention (i.e., Nos. 2, 3 and 4) provide an excellent combination of pattern control, hold-out, and lightness of face compared to the cured films prepared according to the process utilizing no pattern control agent (No. 1), and the process utilizing cellulose acetate butyrate.