Primer composition of an acrylic epoxy ester graft copolymer, a high molecular weight epoxy resin and a heat reactive condensate

Claim 1

A coating composition comprising a solution of 5-60% by weight of film-forming constituents in an organic solvent; wherein the film-forming constituents consist essentially of (1) 20-85% by weight of an acrylic epoxy ester graft copolymer having a relative viscosity of about 1.040-1.100 measured at 0.5% polymer solids in dichloroethylene solvent at 25° C. and consisting essentially of 10-75% by weight of a polymeric backbone segment and 90-25% by weight of polymer side chain segments; wherein (a) the polymeric backbone segment of the graft copolymer consists essentially of polymerized monomers selected from the group consisting of methyl methacrylate, styrene and mixtures thereof; and about 0.5-5% by weight, based on the weight of the copolymer, of polymerized methacrylic acid or acrylic acid monomers; and about 0.5-10% by weight, based on the weight of the copolymer, of polymerized adhesion promoting acrylic monomers selected from the group consisting of hydroxyaminopropyl methacrylate, diethylaminoethyl methacrylate, dimethylaminoethyl methacrylate, 2-aminopropyl methacrylate, 2-aminoethyl methacrylate, t-butyl aminoethyl methacrylate, 2-(1-aziridinyl)-ethyl methacrylate, N-2-hydroxypropyl methacrylamide, N-2-hydroxyethyl methacrylamide and 3-(2-methacryloxyethyl)-2,2-spirocyclohexyloxazolidine; (b) the polymeric side chain segments are grafted into the backbone segment and consist essentially of the following formula which is shown as being grafted into the backbone segment ##STR11## wherein R is H or CH 3; Z is the residual of an epoxy hydroxy polyether resin that has the following recurring structural unit ##STR12## where n is a positive integer sufficiently large to provide a weight average molecular weight of 500-4,000 and R 1 is an alkylene group; X is the residual of a dimer dicarboxylic fatty acid in which the carboxyl groups of the fatty acid are reacted with terminal epoxy groups of th expoxy hydroxy polyether resin; and Y is the residual of an aromatic, cycloaliphatic or aliphatic monocarboxylic acid in which the carboxyl group is reacted with a terminal epoxy group of the epoxy hydroxy polyether resin; (2) 5-70% by weight of an epoxy hydroxy polyether resin of the formula ##STR13## where R 1 is an alkylene group and n is an integer sufficiently large to provide a weight average molecular weight of about 30,000-200,000; and (3) 10-35% by weight of a heat reactive condensate selected from the group consisting of an alkylated melamine formaldehyde, an alkylated urea formaldehyde, an alkylated benzoguanamine formaldehyde or mixtures thereof wherein the alkyl groups have 1-4 carbon atoms. pg,27