Patent ID: 7767778

Claim:
A polyurethane powder coating composition comprising A) a hydroxy-functional binder component which is solid below 40° C. and liquid above 130° C., and has a content of carboxyl groups (calculated as COOH; molecular weight 45) of 0.5 to 2.0 wt. %, and comprises A1) at least one polymeric polyol having an OH number of 15 to 200 mg KOH/g and a number average molecular weight of 400 to 10,000 and A2) optionally at least one compound containing at least one carboxyl group, B) a polyaddition compound which contain uretdione groups and optionally free isocyanate groups, is solid below 40° C. and liquid above 125° C., and is prepared form at least one aliphatic and/or cycloaliphatic diisocyanate, C) at least one zinc compound as hardening catalyst, D) a compound which has a number average molecular weight of 200 to 5000 and contains groups reactive to carboxyl groups, and E) optionally additives for powder coating compositions, wherein i) components A) and B) are present in amounts such that 0.8 to 2.2 isocyanate groups of component B) are present for each hydroxyl group of component A), ii) the term isocyanate groups of component B) means the sum of isocyanate groups present in dimeric form as uretdione groups and free isocyanate groups, iii) components A) and D) are present in amounts such that 0.8 to 2.0 groups of component D) reactive to carboxyl groups are present for each carboxyl group of component A), iv) when aliphatic and/or cycloaliphatic dicarboxylic acids having 4 to 20 carbon atoms and/or aliphatic hydroxycarboxylic acids with 4 to 18 carbon atoms present as component A2), the amount of components A2) and D) in the total amount of components A), B) and D) is less than 10 wt. % and v) the amount of component C) in the total amount of components A) to E) is 0.05 to 5 wt. %.