Composition Comprising Ester of Epoxy, Unsaturated Fatty Acid Dimer or Trimer and Acid Containing Addition Polymer, and Aqueous Coating Compositions Prepared Therefrom

This invention relates to compositions suitable for coatings. In particular, the compositions of this invention are self-emulsifiable in water, comprise a non-gelled hydroxy ester copolymer containing carboxyl groups, and are substantially free of oxirane functionality. The hydroxy-ester copolymer is the esterification reaction product of an acidic addition copolymer and an epoxy resin which has been partially defunctionalized by reaction with a dimer or a trimer of an unsaturated fatty acid.

The acidic addition copolymer is a solution copolymer of monoethylenically unsaturated monomers comprising at least about 10 weight percent of monoethylenically unsaturated carboxylic acid, based on the total weight of monomers. The partially defunctionalized epoxy resin constitutes at least about 25 weight percent of the total resin solids content and has sufficient oxirane groups to provide a ratio of oxirane groups to carboxyl groups in the acidic copolymer of from 0.5:1 to 0.05 to 1. The epoxy resin is partially defunctionalized by esterification with a fatty acid dimer or trimer. At least some of the carboxyl groups in the final copolymer-epoxy resin hydroxy ester are reacted with a base to render the composition self-emulsifiable in water. The resulting compositions are useful as coatings, particularly as metal primers containing pigment, which are cured by baking. An aminoplast or phenoplast resin in small proportion may be added to enhance the cure on baking.

Epoxy resins, particularly those containing a plurality of aromatic groups, are joined together by ether linkages and provide excellent physical and chemical properties. It has been difficult to employ such resins in aqueous media because they lack storage stability. This often is desirable and is of particular importance when spray application is contemplated. The slightest change in the pH of the aqueous composition as a result of hydrolytic instability results in a marked change in the viscosity and application properties of the coating.

To obtain aqueous coatings of proper resin solids content and viscosity, it has often been necessary in the trade to employ an emulsion system in which a water immiscible component is suspended in an aqueous continuous phase with an emulsifying agent. Such emulsion systems are intrinsically unpredictable since the particle size of the emulsion will vary with the agitation of the composition. This invention provides self-emulsifiable compositions in which the particle size of the emulsion is substantially the same regardless of whether high speed agitation is used or whether the mixture with water is barely stirred.

Compositions which are similar in some respects to the composition of this invention are disclosed in U.S. Pat. No. 4,111,870 and pending U.S. application Ser. No. 95,682, filed Nov. 19, 1979, but there are significant differences which will be apparent from the subsequent disclosure.

U.S. Pat. No. 4,111,870 discloses graft-copolymers which include copolymerized acrylic or methacrylic acid in the backbone, and an epoxy component and a dimerized fatty acid component in the "graft" portion of the molecule. The graft copolymer is prepared by first forming an epoxy ester prepolymer of an epoxy polyether resin and a dimer dicarboxylic fatty acid in which one terminal epoxy group is reacted with an aliphatic, aromatic or cycloaliphatic monocarboxylic acid. The prepolymer is then reacted with an alpha, beta-ethylenically unsaturated monocarboxylic acid which reacts with the epoxy group of the prepolymer, and the resulting product is polymerized with ethylenically unsaturated backbone monomer units to form the graft copolymer. The graft copolymers are used as coatings applied from solvent solutions.

The pending U.S. application of George Brown and Arthur T. Spencer, Ser. No. 95,682 filed Nov. 19, 1979, discloses aqueous compositions which are the esterification product of an acidic addition copolymer and a mixture containing epoxy resin which has been partially defunctionalized by reaction with an epoxy reactive material, such as a phenol; a bisphenol; an acid, such as benzoic acid or octanoic acid; or an alcohol, such as octanol. Dimerized fatty acids are not mentioned as defunctionalizing agents.

In general, any polyfunctional epoxy resin containing more than one 1,2-epoxy group and having an epoxy equivalent weight of 200 to about 1000 can be used to prepare the compositions of this invention. Preferably, the epoxy resin is an aromatic polyether polyepoxide.

Aromatic polyethers, polyether epoxides and particularly diglycidyl ethers, are well known and available in commerce. The usual aromatic polyether backbone of the epoxy resin is based on a bisphenol which defines a pair of phenolic groups joined together through an intervening divalent hydrocarbon. The preferred bisphenols have the formula: ##STR1## in which R and R.sub.1 are hydrogen or alkyl groups containing up to 8 carbon atoms. Bisphenol A is particularly preferred. In this compound, the two OH groups are in the para position and R and R.sub.1 are each methyl. The epoxy resins which are used herein possess hydroxy groups in addition to epoxy groups. The higher the molecular weight of the epoxy resin the more hydroxy groups are present. In addition, when the epoxy resin is partially defunctionalized by reaction with the dimerized or trimerized fatty acid additional hydroxy groups are provided. These hydroxy groups can participate in the final curing reaction.

Dimerized and trimerized fatty acids are also available articles of commerce. They comprise the dimerization or trimerization products of ethylenically unsaturated C.sub.12 to C.sub.24 drying oil fatty acids. Typical of the commercially available materials are materials known as "Empol 1010", "Empol 1014", "Empol 1022" and "Empol 1024" available from Emery Industries, Inc. A particularly useful material contains the dimerization product of linoleic acid as its main constituent.

The remaining main component of the final copolymer compositions of this invention is an addition copolymer of monoethylenically unsaturated monomers comprising at least about 10 weight percent of monoethylenically unsaturated carboxylic acid, based on the total weight of monomers. These copolymers are themselves well known. The balance of the copolymer is preferably non-reactive under the contemplated conditions of polymerization, prereaction with the epoxy resin, and cure, but small amounts of other reactive monomers may be tolerated. Examples of other suitable reactive monomers are hydroxy monomers such as 2-hydroxy ethyl methacrylate, amide monomers such as acrylamide, and N-methylol monomers such as N-methylol acrylamide.

The non-reactive monomers are, for example, acrylate and methacrylate esters, such as ethyl acrylate, methyl methacrylate or isobutyl methacrylate, styrene, para-methyl styrene, vinyl toluene, vinyl acetate, vinyl chloride, vinylidene chloride, acrylonitrile, and the like. Their function is to enhance solvent solubility and film formation.

The carboxyl-functional monomer must be present in the addition copolymer in a relatively high amount so that the final polymer reaction with the epoxy-dimer ester will contain the requisite carboxyl groups. The preferred minimum proportion of carboxyl monomer is 10 weight percent of the weight of the monomers. Methacrylic acid provides the best hydrolytic stability and is very much preferred, but other acids are also useful, such as fumaric acid, acrylic acid, crotonic acid, itaconic acid, and the like. Up to about 25 weight percent of the monomers can be carboxyl functional, but the maximum proportion is more generally determined by retention of solvent solubility of the copolymer. Generally, the carboxyl monomer content is in the range of 10-20 weight percent to give a polymer with an acid number in the range of 95-130. The number average molecular weight (M.sub.n) of the carboxyl containing addition copolymer is generally in the range of 2500 to 7500 to give a glass transition temperature of from -25.degree. to +25.degree. C. Molecular weight can be controlled by monomer content during polymerization or catalyst concentration, or polymerization temperature, these being known expedients for this purpose. Mercaptan chain termination is preferably avoided when sanitary can use is contemplated as mercaptans have an offensive odor.

The partially defunctionalized epoxy resin is prepared by reacting the epoxy resin and the dimerized or trimerized fatty acid in a solvent at an elevated temperature until the acid number is less than 2 and the epoxy content is 0.25 to 0.75 meq./g. Typically, the proportions of epoxy resin and dimerized or trimerized fatty acid are such that the ratio of carboxyl equivalents to epoxy equivalents is in the range of 0.3:1 to 0.7:1.

The esterification reaction between the oxirane groups of the partially defunctionalized epoxy resin and carboxyl groups of the addition copolymer is a conventional reaction which is normally carried out in the presence of a small amount of a tertiary amine esterification catalyst, e.g., N,N-dimethylethanolamine. The catalyst is normally used in an amount of from 1 to 6 weight percent of the materials subjected to esterification. Preferably, the catalyst comprises 3 to 5 weight percent of the reactants. The proportions of partially defunctionalized epoxy resin and acidic addition copolymer are such that the ratio of oxirane groups in the defunctionalized epoxy resin to the carboxyl groups in the addition copolymer is from 0.5:1 to 0.05:1, preferably 0.25:1 to 0.1:1. The reaction is conducted until the acid member of the product is between about 35 and 75 mg. KOH/g, preferably 50 to 60 mg. KOH/g.

The compositions of this invention form films with reasonably good properties on baking in the absence of any external curing agent. However, from 1-25 weight percent of the curing agents such as aminoplast resins, phenoplast resins and mixtures thereof will serve to enhance the cure. With analogous prior art polymers at least 15 weight percent of curing agent, based on the total weight of polymer is normally required. While such levels of curing agents are useful with the hydroxy ester copolymers of this invention, this invention is unusual in enabling the achievement of a superior cure using a smaller proportion of curing agent. For example, 2-12 weight percent is entirely sufficient to cure films containing the hydroxy ester copolymers of this invention. The advantage is using reduced amounts of curing resin is that the small proportion of curing agent needed to provide the desired solvent insolubility results in less brittleness in the cured film.

The preferred curing agents are water dispersible. These will be illustrated by hexamethoxy methyl melamine, or by A stage phenol-formaldehyde resols. However, the compositions of this invention are emulsions and water dispersibility in the curing agent is not essential.

The curing of compositions containing curing agent by baking, is entirely conventional in the art. Presumably, the methylol groups introduced by the curing agent react with the hydroxy and carboxyl groups present in the copolymer, and with the hydroxy present in the aromatic polyether devoid of oxirane functionality. Acidic curing agents are commonly employed to facilitate the cure, though this is not essential, especially when a phenoplast curing agent is used.

In the preferred use of the compositions of this invention from about 3 to about 10 weight percent of water dispersible aminoplast resin is added to the mixture to assist in cure on baking.

The resins of this invention are typically used by dissolution in a volatile organic solvent. A wide variety of solvents are suitable. In general, any solvent which does not interfere with the achievement of an emulsion when the acidic copolymer salts are diluted with water can be used. The point at which an emulsion is achieved is easily observed. It occurs when the aqueous system changes from clear to milky.

Organic solvents of limited water miscibility, such as xylene, toluene, and butanol are useful, and they may be used alone or together with water miscible solvents, such as 2-ethoxy ethanol or methyl ethyl ketone.

The aqueous coating compositions of this invention are primarily useful for coating aluminum, tinplated steel, pretreated metals, steel, or metals coated with the same or different resin compositions, i.e., a second coat. These aqueous compositions also can be used for coating other substrates, such as wood. The most preferred and advantageous use of the coating compositions is metal primers containing large amounts of pigments, e.g. 1 to 60 weight percent. Such compositions contain enough amine for salt formation with from 50 to 90 percent of the available carboxyl groups and enough water to provide a final solids content of about 10 to about 50 weight percent. The pH of these compositions is generally 6-9, preferably 7-8, and they have a viscosity of about 10 to 1000 centipoise. After application, the coating is baked for about 5 seconds to about 30 minutes at between about 250.degree. F. and about 600.degree. F. A typical bake is for about 2 minutes at about 400.degree. F.

The invention is illustrated in the following non-limiting examples. Proportions are by weight.

A 5 liter reaction vessel was charged with 1000.0 grams of Cellosolve which was heated to 115.degree. C. under a nitrogen atmosphere. A mixture of 303.8 grams of glacial methacrylic acid, 1146.6 grams of butyl acrylate, 215.6 grams of methyl methacrylate, 294.0 grams of hydroxyethyl methacrylate and 39.2 grams of t-butyl perbenzoate were added dropwise in four hours. The reaction mixture was held at 115.degree. C. for one hour after the addition was complete at which point an additional 9.8 grams of t-butyl perbenzoate were added. After an additional one hour at 115.degree. C. the reactor was discharged to afford an acrylic copolymer with a calculated glass transition temperature of -7.degree. C., a Gardner-Holdt viscosity of Z4-Z5, a number and weight average molecular weight (vs. a polystyrene standard) of 5,6326 and 18,850, respectively, a non-volatile content of 65.1 percent, and an acid number of 96.1 mg KOH/gram.

The procedure of Example 1 was repeated with several different monomer charges to obtain polymers whose constitution and properties are summarized in Table 1.

Araldite 6084 (294.0 gms, 1.12 meq. epoxy/gm) was reacted for one hour at 150.degree. C. with Empol 1010 Dimer Acid (47.0 gms, 3.50 meq. carboxyl/gm) in the presence of 15.0 gms of Butyl Cellosolve and 1.0 g of tri-n-butylamine to afford a product with an acid number of less than one mg KOH/gm and an epoxy value of 0.43 meq. epoxy/gm. This epoxy-ester was subsequently reacted for one hour at 125.degree. C. with 840.0 gms of the preformed acrylic copolymer from Example 1 in the presence of 43.7 gms of dimethylethanolamine. The resulting epoxy-ester acrylic copolymer was reduced with 1293.6 gms of deionized water to yield a dispersion with the following properties: pH=7.37, Viscosity=60 cps, Acid Number=57.0 mg KOH/gm, and %NV=34.5. A sample of this material was combined with 15% of Resimene 714, applied to a 25 mil Alodine treated aluminum panel at 0.7 mil dry film thickness and baked 20 minutes at 325.degree. F. The resulting film showed greater than 100 MEK double rubs, had a Knoop hardness of 20 KHN, and passed a 12 in. lb. reverse impact test with no cracks or tape off when tested with Scotch tape.

Epon 1004 (378.0 gms, 1.12 meq. epoxy/gm) was reacted for one hour at 150.degree. C. with Empol 1010 Dimer Acid (72.0 gms, 3.50 meq. carboxyl/gm) in the presence of 20.0 gms. of Butyl Cellosolve and 1.4 g of tri-n-butylamine to afford a product with an acid number of less than one mg KOH/gm and an epoxy value of 0.34 meq. epoxy/gm. This epoxy-ester, with 15.0 gms of Butyl Cellosolve, was subsequently reacted for one hour at 125.degree. C. with 770.0 gms of the preformed acrylic copolymer of Example 2 in the presence of 45.2 gms of dimethylethanolamine. The resulting epoxy-ester acrylic copolymer was reduced with 1304.1 gms of deionized water to yield a dispersion with the following properties: pH=7.29, Viscosity=250 cps, Acid Number=57.5 mg KOH/gm, and %NV=34.4.

Epon 1004 (294.0 gms, 1.12 meq. epoxy/gm) was reacted for one hour at 150.degree. C. with Empol 1010 Dimer Acid (30.0 gms, 3.50 meq. carboxyl/gm) in the presence of 15.0 gms of Butyl Cellosolve and 1.0 g of tri-n-butylamine to afford a product with an acid number of less than one mg KOH/gm and an epoxy value of 0.63 meq. epoxy/gm. This epoxy-ester was subsequently reacted for one hour at 125.degree. C. with 840 gms of the preformed acrylic copolymer of Example 4 in the presence of 43.7 gms of dimethylethanolamine. The resulting epoxy-ester acrylic copolymer was reduced with 1462.0 gms of deionized water to yield a dispersion with the following properties: pH=7.76, Viscosity=550 cps, Acid Number=50.9 mg KOH/gm, and %NV=32.6.

Araldite 6084 (294.0 gms, 1.12 meq. epoxy/gm) was reacted for one hour at 150.degree. C. with Empol 1010 Dimer Acid (47.0 gms, 3.50 meq. carboxyl/gm) in the presence of 15.0 gms of Butyl Cellosolve and 1.0 g of tri-n-butylamine to afford a product with an acid number of less than one mg KOH/gm and an epoxy value of 0.43 meq. epoxy/gm. This epoxy-ester was subsequently reacted for one hour at 125.degree. C. with 840.0 gms of the preformed acrylic copolymer from Example 5 in the presence of 21.9 gms of dimethylethanolamine. The resulting epoxy-ester acrylic copolymer was reduced with 1293.6 gms of deionized water and 21.9 gms of dimethylethanolamine to yield a dispersion with the following properties: pH=7.84, Viscosity=75 cps, Acid Number=54.5 mg KOH/gm, and %NV=34.7.

Epon 1001 (255.0 gms, 1.96 meq. epoxy/gm) was reacted for one hour at 150.degree. C. with Empol 1010 Dimer Acid (95.0 gms, 3.50 meq. carboxyl/gm) in the presence of 15.0 gms of Butyl Cellosolve and 1.0 g of tri-n-butylamine to afford a product with an acid number of less than one mg KOH/gm and an epoxy value of 0.49 meq. epoxy/gm. This epoxy-ester was subsequently reacted for one hour at 125.degree. C. with 769.0 gms of the preformed acrylic copolymer from Example 8 in the presence of 40.0 gms of dimethylethanolamine. The resulting epoxy-ester acrylic copolymer was reduced with 1253.6 gms of deionized water to yield a dispersion with the following properties: pH=7.50, Viscosity=82 cps, Acid number=55.4 mg KOH/gm, and %NV=34.5.

DRH 151 [an epoxy resin supplied by the Shell Chemical Company] (866.0 gms, 4.31 meq. epoxy/gm) was reacted for one hour at 185.degree. C. with 277.7 gms of Bisphenol A and 1.1 gms of triphenylphosphine to yield an epoxy resin with an epoxy value of 1.25 meq. epoxy/gm. This resin (378.0 gms) was reacted for one hour at 150.degree. C. with Empol 1010 Dimer Acid (72.0 gms, 3.50 meq/gm) in the presence of 20.0 gms of Butyl Cellosolve and 1.4 g of tri-n-butylamine to afford a product with an acid number of less than one mg KOH/gm and an epoxy value of 0.36 meq. epoxy/gm. This epoxy-ester was subsequently reacted for one hour at 125.degree. C. with 770.0 gms of the preformed acrylic copolymer of Example 2 in the presence of 45.2 gms of dimethylethanolamine. The resulting epoxy-ester acrylic copolymer was reduced with 1304.1 gms of deionized water to yield a dispersion with the following properties: pH=7.38, Viscosity=160 cps, Acid Number=55.8 mg KOH/gm, and %NV=35.9.

The procedure of Examples 10-15 was repeated with the acrylic polymers obtained in Examples 3-9 and several different epoxy resins to obtain dispersions whose constitution and properties are summarized in Table 2.

In the foregoing Examples the following materials referred to by tradenames are further identified as follows:

ARALDITE 6084--an epoxy resin having a molecular weight of about 1000 which is Bisphenol A--epichlorohydrin reaction product available from Ciba-Geigy.

EMPOL 1010--dimerized fatty acid, primarily dimerized linoleic acid, available from Emery Industries.

EPON 1001, EPON 1002, and EPON 1004--aromatic polyether epoxides which are the reaction products of Bisphenol A and epichlorohydrin having molecular weights of about 900, 1100 and 1400, respectively, and available from Shell.

DRH 151--an aliphatic polyepoxide resin available from Shell having a molecular weight of about 300.

RESIMINE 714--melamine formaldehyde resin available from Monsanto.