Thermosetting powder coating composition and method for forming a topcoat using the same

Abstract

The present invention provides a thermosetting powder coating composition comprising: (A) an epoxy-containing resin; and (B) a curing agent containing, as an essential ingredient, an acid anhydride (a) represented by the formula HOOC—(CH2)m—[COO—CO—(CH2)m]n—COOR1   (1) wherein R1 represents a C1-10 monovalent saturated hydrocarbon group, m is an integer of 6 to 18, and n is a number of 1 to 20 on average, the molar ratio of carboxyl groups to acid anhydride groups in the curing agent being in the range from 0.15:1 to 2.0:1, 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 from 0.7:1 to 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 thermosetting powder coating composition.

Dependencies are inferred from the claim text.