POWDER COATING COMPOSITIONS, A PROCESS FOR THEIR PREPARATION AND THEIR USE FOR THE COATING HEAT RESISTANT SUBSTRATES

Mo-3852 LeA 28,901 POWDER COATING COMPOSITIONS, A PROCESS FOR THEIR PREPARATION AND THEIR USE FOR THE COATING HEAT RESISTANT SUBSTRATES The present invention relates to a powder coating composition having a glass transition temperature of 20 to 80.degree.C and containing A) 56 to 86.9% by weight of a polyacrylate polyol component having a hydroxyl number of 30 to 155 and a glass transition temperature of 30 to 120.degree.C, B) 0.1 to 9% by weight of a polyester polyol component having a hydroxyl number of 40 to 180 and a glass transition temperature of -40 to 80.degree.C and C) 13 to 35% by weight of a polyisocyanate component having a glass transition temperature of -40 to 60.degree.C and containing at least one ketoxime-blocked polyisocyanate selected from (i) polyisocyanate derivatives prepared from 1,6-diisocyanatohexane and containing biuret, isocyanurate, uretdione and/or urethane groups, (ii) polyisocyanate derivatives prepared from mixtures of 1,6-diisocyanatohexane and 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane and containing isocyanurate groups and optionally uretdione groups and (iii) polyisocyanates derivatives prepared from 4,4'-diisocyanato-dicyclohexylmethane and containing urethane groups, and D) at least one catalyst for the reaction between blocked isocyanate groups and hydroxyl groups, wherein i) the percentages of components A), B) and C) are based on the total weight of these components and ii) components A), B) and C) are present in amounts sufficient to provide an equivalent ratio of blocked isocyanate groups to hydroxyl groups of 0.5:1 to 1.5:1. The present invention is also relates to a process for the preparation of this powder coating composition and to heat-resistant substrates, particularly automotive body parts, coated with this powder coating composition.