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Abstract

The present invention provides a thermosetting powder coating composition comprising: (A) an epoxy-containing resin; and (B) a curing agent containing acid anhydride (a) and at least one species selected from the group consisting of acid anhydride (b) and dibasic acid (c), the acid anhydride (a) being represented by formula X--COO--[CO--(CH.sub.2).sub.m --COO].sub.n --CO--X (1) wherein the two X's are the same or different and independently represent a C.sub.4-12 alkyl group having a branched structure, R.sub.1 --O--CO--R.sub.2 --, R.sub.1 --CO--R.sub.2 -- or R.sub.1 --CO--NH--R.sub.2 -- in which R.sub.1 is a C.sub.1-10 monovalent saturated hydrocarbon group; R.sub.2 is a C.sub.1-10 bivalent saturated hydrocarbon group; m is an integer of 6 to 18; and n is an integer of 8 to 50, the acid anhydride (b) being represented by the formula HO--[CO--(CH.sub.2).sub.p --COO].sub.q --H (2) wherein p is an integer of 6 to 18 and q is an integer of 2 to 18, and having carboxyl groups at both ends, the dibasic acid (c) being represented by the formula HOOC--(CH.sub.2).sub.t --COOH (3) wherein t is an integer of 6 to 18, the molar ratio of carboxyl groups to acid anhydride groups in the curing agent being in the range between 0.15:1 and 2:1, and the molar ratio of the total of carboxyl groups and acid anhydride groups in the curing agent (B) to epoxy groups in the epoxy-containing resin (A) being in the range between 0.7:1 and 1.2:1. The present invention further provides a method for forming a topcoat according to a 2-coat 1-bake system comprising the steps of applying to a substrate a thermosetting aqueous colored base coating composition, applying to the uncured surface of the base coat a clear coating composition, and curing the two coats by heating, wherein the clear coating composition is the above-mentioned thermosetting powder coating composition.

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First Claim