Powder coating compositions and their use for coating heat-resistant substrates

A powder coating composition for the production of glossy flexible coatings which is solid below 30.degree. C. and liquid above 120.degree. C. and comprises

• A) a polyisocyanate component which
• i) has a content of blocked isocyanate groups (expressed as NCO, molecular weight=42) of 3.0 to 14.0% by weight,
• ii) has a functionality, based on the blocked isocyanate groups, of 1.9 to 2.3 and
• iii) contains at least one .epsilon.-caprolactam-blocked polyisocyanate based on the reaction product of 4,4'-diisocyanatodicyclohexyl methane with a polyol component having an average molecular weight of 90 to 400 and containing at least 50% by weight, based on the weight of the polyol component, of one or more (cyclo)aliphatic diols containing 4 to 12 carbon atoms,
• B) a polyacrylate polyol component containing at least one polyhydroxy polyacrylate having an OH number of 40 to 120,
• C) an organotin catalyst for the reaction between hydroxyl groups and blocked isocyanate groups and
• D) a positive amount of up to about 5% by weight, based on the weight of
• components A) and B), of at least one trialkyl and/or triaryl phosphite, wherein components A) and B) are present in quantities which correspond to an equivalent ratio of blocked isocyanate groups of the polyisocyanate component to hydroxyl groups of the polyacrylate polyol component of 0.5:1 to 1.2:1.

A coated heat-resistant substrate which is coated with a powder coating composition for the production of glossy flexible coatings which is solid below 30.degree. C. and liquid above 120.degree. C. and comprises

• A) a polyisocyanate component which
• i) has a content of blocked isocyanate groups (expressed as NCO, molecular weight=42) of 3.0 to 14.0% by weight,
• ii) has a functionality, based on the blocked isocyanate groups, of 1.9 to 2.3 and
• iii) contains at least one .epsilon.-caprolactam-blocked polyisocyanate based on the reaction product of 4,4'-diisocyanatodicyclohexyl methane with a polyol component having an average molecular weight of 90 to 400 and containing at least 50% by weight, based on the weight of the polyol component, of one or more (cyclo)aliphatic diols containing 4 to 12 carbon atoms,
• B) a polyacrylate polyol component containing at least one polyhydroxy polyacrylate having an OH number of 40 to 120 and
• C) an organotin catalyst for the reaction between hydroxyl groups and blocked isocyanate groups,
• wherein components A) and B) are present in quantities which correspond to an equivalent ratio of blocked isocyanate groups of the polyisocyanate component to hydroxyl groups of the polyacrylate polyol component of 0.5:1 to 1.2:1.