GB932250A - Acrylic polymers - Google Patents

Abstract

Steel surfaces are sprayed with an organic solvent solution of an acrylic copolymer which comprises 2,5 to 10% of acrylic or methacrylic acid, 2,5 to 15% of acrylonitrile or methacrylonitrile and the balance comprising styrene or a nuclear alkyl styrene and either (a) a C1-C8 alkyl methacrylate or (b) a mixture of a C1-C8 alkyl methacrylate and a C1-C10 alkyl acrylate (see Group IV(a)). The coating compositions may also contain aminoplasts, polyepoxides and phenolic resins. In the examples steel surfaces are coated with solutions of acrylic acid/acrylonitrile/methyl methacrylate/styrene copolymers in methyl ethyl ketone-xylene mixtures, followed by air drying or baking of the coatings.ALSO:A copolymer having a viscosity of from 5 to 22 poises at 77 DEG F as a 50% solution in methyl ethyl ketone comprises from 2.5 to 10% of acrylic or methacrylic acid, 2.5 to 15% of acrylonitrile or methacrylonitrile and the balance comprising a styrene compound having the formula: <FORM:0932250/IV(a)/1> wherein R is a C1-C8 alkyl group and n is 0, 1, 2 or 3 and acrylic ester (A) or a mixture of acrylic esters (A) and (B) having the formulae: <FORM:0932250/IV(a)/2> in which R1 is a C1-C8 alkyl group and R2 is a C1-C10 alkyl group, the proportion of ester (B) in the mixture of (A) and (B) being up to a maximum illustrated on the graph, and the weight ratio of the styrene to the acrylic ester(s) being from 3:1 to 1:9. Also present may be small quantities of other unsaturated acids, e.g. crotonic and itaconic acids and monobutyl maleate. The copolymers are prepared by polymerizing the monomers in a chain stopping solvent, e.g. methyl ethyl ketone, methyl isobutyl ketone or acetone, in the presence of a free-radical catalyst, e.g. benzoyl peroxide or azodiisobutyronitrile. Part of the acid, the styrene compound and the catalyst may be added incrementally as the reaction proceeds. The examples describe the preparation of copolymers from mixtures of styrene, methyl methacrylate, acrylic acid and acrylonitrile. The resulting copolymers are used in coating compositions in the form of solutions in solvents such as benzene, toluene, xylene or ethyl benzene, preferably containing a proportion of a polar solvent, e.g. methyl ethyl ketone, acetone, methyl isobutyl ketone cyclohexanone, diacetone alcohol, dimethyl formamide, ethyl acetate, butyl propionate, isophorone and glycol monoethers. As additional components of the coating compositions there may be used a solventsoluble polymethylol condensation product of urea, melamine or benzoguanamine and formaldehyde esterified with a C3-C8 primary saturated monohydric alcohol, or a polyepoxide having a 1,2-epoxide equivalent greater than 1, together with a basic curing catalyst. Specified polyepoxides are polyglycidyl ethers of bisphenol A, the triglycidyl ether of trimethylol propane and copolymers of glycidyl methacrylate or allyl glycidyl ether with acrylate or methacrylate esters. Together with the polyepoxide there may be used a fusible alkaline condensed phenol-formaldehyde resin, the phenolic constituent of which may be phenol itself, cresols, xylenols, bisphenol A, phenyl phenol, cyclohexyl phenol, tert-butyl phenol, tert-amyl phenol and bi- or tri-functional phenols; and mixtures thereof. Also present in the compositions may be plasticizers, e.g. esters of ricinoleic, phthalic, sebacic and phosphoric acids and low molecular weight alkyd resins.