GB1039787A - Coating composition and method - Google Patents

Abstract

Conductive surfaces are electrophoretically coated by anodic deposition of organic resinous coatings from aqueous emulsions comprising a continuous aqueous phase having dispersed therein a salt of a base and the heat reaction product of an aliphatic a , b -ethylenically unsaturated carboxylic acid with a polyester of an unsaturated fatty acid and an aliphatic polyhydric alcohol, said heat reaction product having an acid number of at least 40, and an oil soluble phase, stably dispersed in the aqueous phase, comprising a resinous polyol at least partially esterified with a monocarboxylic acid, the heat reaction product and polyol ester being present in a weight ratio of 10/90 to 90/10. Preferred bases are ammonia, volatile amines and alkali metal hydroxides and carbonates. The heat reaction products may be derived from dehydrated castor, soya, linseed, tung, oiticica or safflower oil and fumaric, maleic, crotonic, acrylic or sorbic acid. The polyol may be a hydroxyl functional polyester, a polyepoxide such as epichlorohydrin/bisphenol A condensated, a copolymer of allyl alcohol or a homologue thereof, a saponified vinyl chloride/ vinyl acetate copolymer or a polymer of hydroxyethyl acrylate or methacrylate. The monocarboxylic acid may be a linseed, coconut, cotton seed, dehydrated castor or tall oil acid. The compositions may also comprise organic solvents, aminoplast resins and pigments; and may be used to form coatings,e.g. on automobile bodies, by the passage of D.C. The coating deposited may be cured by baking. In an example zinc phosphate treated steel is coated using an aqueous ammonia solution of fumarated soya oil, a tall oil acid esterified styrene/allyl alcohol copolymer, aromatic hydrocarbon solvents, pine oil, lead chromate and titanium dioxide.ALSO:Aqueous emulsions adapted for electrophoretic film deposition comprise a continuous aqueous phase having dispersed therein a salt of a base with the heat reaction product of an aliphatic a ,b -ethylenically unsaturated carboxylic acid with a polyester of an unsaturated fatty acid and an aliphatic polyhydric alcohol, said heat reaction product having an acid number of at least 40, and an oil-soluble phase, stably dispersed in the aqueous phase, comprising a resinous polyol at least partially esterified with a monocarboxylic acid, the heat reaction product and polyol ester being present in a weight ratio of 10/90 to 90/10. Preferred heat reaction products are of dehydrated castor, soya, linseed, tung, oiticica or safflower oil with fumaric, maleic, crotonic, acrylic or sorbic acid. Preferred bases are volatile nitrogeneous bases, e.g. ammonia, methylamine, dimethylamine, diethylamine, triethylamine and morpholine, or alkali metal hydroxides or carbonates. Specified resinous polyols are hydroxyl functional polyesters derived from phthalic and adipic acids, and glycerine and pentaerythritol, optionally together with ethylene glycol or butane diol; copolymers of allyl and methallyl alcohols with styrene or substituted styrenes, vinyl esters, acrylic or methacrylic esters, or acrylic acid; polyepoxides such as the diglycidyl ether of bisphenol A; saponified vinyl chloride-vinyl acetate copolymers; and polymers of hydroxyethyl acrylate and methacrylate. The monocarboxylic acid may be saturated or unsaturated, e.g. derived from linseed, coconut, cotton-seed, dehydrated castor or tall oil, and esterification may be effected directly with the acid or by transesterification with the oil. The oil-soluble phase may comprise minor proportions of organic solvents, e.g. toluene and xylene, aminoplasts, e.g. derived from urea or melamine and formaldehyde, and preferably esterified with butanol. The compositions may also comprise pigments, e.g. lead chromate, titanium dioxide, barytes, talc, calcium carbonate and iron oxide. Examples describe the preparation of a composition comprising an aqueous ammonia solution of fumarated soya oil, a tall oil acid esterified styrene-allyl alcohol copolymer, aromatic hydrocarbons, pine oil, lead chromate and titanium dioxide.