Preparation for deposition of coatings

摘要

A low temperature curing powder coating composition includes a combination of a branched oligoester polyol and a nonemissive uretdione polyisocyanate cross-linking agent. A powder coating composition comprises a branched hydroxyl terminated oligoester polyol having a hydroxyl value of 15-250, an acid number of 1-25 and a number average molecular weight of 1000-7500, which is the product of a hydroxyl terminated oligoester diol and a poly acid or anhydride having a carboxyl functionality of at least 3 and a uretdione crosslinking agent. The composition cures at less than 160[deg]C with a urethane catalyst and 160[deg]C without catalyst and the cured coating binder has a pencil hardness of at least HB, direct and reverse impact resistances of at least 80 in lb at a cured film thickness of 0.8-4 mils; the composition has a T gof at least 40[deg]C. Independent claims are also included for the following: (a) a process for preparing the composition above comprising blending the reactants above so that there is an equivalent ratio of isocyanate: hydroxyl groups of 0.5-1.8:1; (b) a branched hydroxyl-terminated oligoester polyol composition as above comprising the reaction product of a diol as above having a number average molecular weight of 400-1500 and at least a tri-carboxylic acid; and (c) a process for preparing the branched hydroxyl-terminated oligoester polyol above comprising blending the diol above with a polyacid. This hydroxy-terminated oligoester diol is the reaction product of a diol and a di-acid selected from an open chain aliphatic, cycloaliphatic, or aromatic dicarboxylic acid, anhydride or acid halide and has a number average molecular weight of 400-1500.