Powder coating composition for automotive topcoat

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 consisting essentially of polymerized monomers of:
• (1) about 8 to 35 percent by weight, based on the weight of the copolymer, of a monoethylenically unsaturated monomer having the formula ##STR13## where R.sub.1 and R.sub.4 are the same or different and are each selected from the group consisting of hydrogen and the methyl radical, and R.sub.2, R.sub.3, R.sub.5, and R.sub.6, are hydrogen and
• (2) about 65 to 92 percent by weight, based on the weight of the copolymer, of at least one monoethylenically unsaturated monomer which is free of epoxy groups selected from the group consisting of
• (a) styrene;
• (b) esters of acrylic or methacrylic acid having the formula ##STR14## where R.sup.1 is selected from the group consisting of hydrogen and the methyl radical, and R.sup.7 is selected from the group consisting of C.sub.1 -C.sub.20 aliphatic hydrocarbon radicals and C.sub.1 -C.sub.20 aromatic hydrocarbon radicals.
• wherein the copolymer has a number average molecular weight of about 1,500 to 10,000, a weight average molecular weight of about 3,000 to 18,000, and a glass transition temperature of about 30.degree. C. to 100.degree. C;
• B. a carboxy-terminated crosslinking agent consisting of an aliphatic dicarboxylic acid having the formula
• HOOC--(CH.sub.2).sub.n --COOH
• where n is an integer from 8-18;
• said crosslinking agent being present in an amount sufficient to provide 0.9-1.5 carboxylic acid groups for each epoxy group orginially in the copolymer;
• C. a supplementary crosslinking having at least one functional group which is capable of reacting with either hydroxyl groups or carboxylic acid groups, and which will not react until the the carboxylic-terminated crosslinking agent has reacted with the acrylic copolymer said supplementary crosslinking being present in an amount sufficient to provide 0.1-0.7 functional group for each epoxy group originally in the acrylic copolymer and is selected from the group consisting of an alkylated melamine formaldehyde resin, an alkylated glycoluril resin, an aliphatic glycidyl ether having the formula ##STR15## an aliphatic glycidyl ester having the formula ##STR16## where R.sup.8 is selected from the group consisting of the C.sub.1 -C.sub.20 aliphatic hydrocarbon radicals,
• a cycloaliphatic epoxide having the formula ##STR17## a cycloaliphatic epoxide having the formula ##STR18## where R.sup.9 is selected from the group consisting of bivalent C.sub.6 -C.sub.10 aromatic hydrocarbon radicals and bivalent C.sub.2 -C.sub.20 aliphatic hydrocarbon radicals;
• and
• D. at least one agent capable of preventing the degradation of the coating by ultraviolet light
• wherein the agent has a weight average molecular weight of greater than 300 and a particle size of less than 40 microns.