Coating composition catalyzed with phosphonic acid derivative - #1

Claim 1

A thermosetting coating composition adapted for low temperature bake applications which, exclusive of pigments, solvents and other nonreactive components, consists essentially of: (A) a copolymer bearing pendent epoxy functionality and being free of pendent hydroxy functionality, and having a number of average molecular weight (M n ) of between about 1500 and about 10,000 and a glass transition temperature (Tg) of between about -25° C. and about 70° C., said copolymer consisting of between about 10 and about 30 weight percent of monoethylenically unsaturated monomers bearing glycidyl functionality and between about 90 and about 70 weight percent of other monoethylenically unsaturated monomers; (B) a reactive catalyst comprising at least one phosphonic acid derivative having the formula: ##STR3## wherein n=1 to 2 and R is selected from the group consisting of alkyl, cycloalkyl and aryl radicals; (C) an amine-aldehyde resin crosslinking agent; and (D) up to 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 (M n ) of between 150 and about 6000, said phosphonic acid derivative being included in said composition in an amount sufficient to provide between about 0.8 and about 1.4 equivalents of acid functionality for each equivalent of pendent epoxy functionality on said copolymer, and said amine-aldehyde resin 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 as a group on an initial component thereof or generated in situ as a result of esterification of said pendent epoxy functionality of said copolymer during cure of said coating composition.