Powder coating composition for automotive topcoat

Claim 1

A thermosetting powder coating composition of finely divided particles having a particle size of about 1 to 100 microns, wherein the particles are an intimately mixed blend consisting essentially of: A. an acrylic copolymer having 3 to 10 carboxylic acid groups per polymer chain and consisting essentially of (1) about 5 to 30 percent by weight, based on the weight of the copolymer, of methacrylic acid, and (2) about 70 to 95 percent by weight, based on the weight of the copolymer, of other monoethylenically unsaturated monomers which are selected from or a mixture of the following: (a) up to 25% by weight, based on the weight of the copolymer, of styrene or α-methylstyrene, and (b) at least one ester of acrylic or methacrylic acid having the formula ##STR7## where R 1 is selected from the group consisting of hydrogen and the methyl radical, and R 2 is selected from the group consisting of C 1 -C 20 aliphatic hydrocarbon radicals, wherein the copolymer has a number average molecular weight of about 2,000 to 8,000, a weight average molecular weight of about 4,000 to 16,000, and glass transition temperature of about 40° C. to 100° C.; B. a crosslinking agent capable of reacting with carboxylc acid groups of the copolymer, said crosslinking agent being present in an amount sufficient to provide 0.7 to 1.5 carboxyl-reactive functional groups for each carboxylic acid group originally in the copolymer, said crosslinking agent further being selected from the group consisting of hydantoin epoxides containing 2 to 4 epoxide groups, and disubstituted and trisubstituted oxazolines; C. agents capable of preventing the degradation of the coating by ultraviolet light consisting essentially of about 0.3 to 5 percent by weight, based on the weight of the acrylic copolymer, of an ultraviolet screener and about 0.3 to 5 percent by weight, based on the weight of the acrylic copolymer, of a hindered amine light stabilizer, said agents having a weight average molecular weight greater than 400 and a particle size of less than 20 microns and D. about 0.05 to 2.0 percent by weight, based on the weight of the powder coating compositions, of a flow control agent.