High solids coating composition adapted for use as automotive topcoat--#4

Claim 1

A thermosetting coating composition adapted for low temperature bake applications which contains greater than about 60% by weight of nonvolatile solids, and which, exclusive of pigments, solvents and other nonreactive components, consists essentially of: (A) a bifunctional copolymer bearing hydroxy functionality and pendent epoxy functionality, having a number average molecular weight (Mn) of between about 1500 and about 10,000 and a glass transition temperature (Tg) of between about 31 25° C. and about 70° C., said copolymer consisting essentially of (i) between about 5 and about 25 weight percent of monoethylenically unsaturated monomers bearing glycidyl functionality and between about 5 and about 25 weight percent of monoethylenically unsaturated monomer bearing hydroxy functionality, with the total of said glycidyl and hydroxy functional monomers being not greater than about 30 weight percent of the monomers in said bifunctional copolymer and (ii) between about 90 and about 70 weight percent of other monoethylenically unsaturated monomers; (B) a reactive catalyst comprising hydroxy functional organophosphate ester having the formula: ##STR3## wherein n=1 to 2 and R is selected from the group consisting of mono or dihydroxy alkyl, cycloalkyl, or aryl radicals; (C) an amine-aldehyde crosslinking agent; and (D) up to about 45 weight percent based on the total weight of (A), (B), (C) and (D) of a hydroxy functional additive having a number average molecular weight (Mn) of between about 150 and about 6000, said organophosphate ester being included in said composition in an amount sufficient to provide between about 0.67 and about 1.4 equivalents of acid functionality for each equivalent of pendent epoxy functionality on said bifunctional copolymer, and said amine-aldehyde crosslinking agent being included in said composition in an amount sufficient to provide at least about 0.4 equivalents of nitrogen crosslinking functionality for each equivalent of hydroxy functionality included in said composition either as (i) an organic hydroxyl group on said organophosphate ester, (ii) a hydroxyl group on on said bifunctional copolymer, (iii) a hydroxyl group on said hydroxy functional additive, or (iv) as a result of esterification of said pendent epoxy functionality of said bifunctional copolymer during cure of said coating composition.