Powder coating compositions, a process for their production and their use for coating heat-resistant substrates

A powder coating composition having a glass transition temperature of 20.degree. to 80.degree. C. which is prepared by a process which comprises

• a) homogeneously dissolving in an inert solvent or solvent mixture having a boiling point or range between 50.degree. and 150.degree. C.
• A) a polyol component having a hydroxyl value of 30 to 155 and a glass transition temperature of 30.degree. to 120.degree. C. and containing at least one hydroxy-functional copolymer of olefinically unsaturated monomers,
• B) a polyisocyanate component containing blocked isocyanate groups, having a glass transition temperature of -45.degree. to +45.degree. C. and containing at least one ketoxime-blocked polyisocyanate selected from the group consisting of
• i) polyisocyanates containing one or more biuret, isocyanurate, uretdione or urethane groups and prepared from 1,6-diisocyanatohexane,
• ii) polyisocyanates containing isocyanurate groups and prepared from mixtures of 1,6-diisocyanatohexane and 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl cyclohexane and
• iii) polyisocyanates containing isocyanurate groups and uretdione groups and prepared from a mixture of 1,6-diisocyanatohexane and 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl cyclohexane and
• C) a catalyst component containing at least one catalyst for the reaction between blocked isocyanate groups and hydroxyl groups components, wherein components A) and B) are present in an amount which are sufficient to provide an equivalent ratio of blocked isocyanate groups to hydroxyl groups of 0.5:1 to 1.5:1,
• b) freeing the resulting solution from the solvent and
• c) simultaneously and/or subsequently converting the solid obtained into powder form.

A coated heat-resistant substrate which has been coated with the powder coating composition having a glass transition temperature of 20.degree. to 80.degree. C. and prepared by a process comprising

• a) homogeneously dissolving in an inert solvent or solvent mixture having a boiling point or range between 50.degree. and 150.degree. C.
• A) a polyol component having a hydroxyl value of 30 to 155 and a glass transition temperature of 30.degree. to 120.degree. C. and containing at least one hydroxy-functional copolymer of olefinically unsaturated monomers,
• B) a polyisocyanate component containing blocked isocyanate groups, having a glass transition temperature of -45.degree. to +45.degree. C. and containing at least one ketoxime-blocked polyisocyanate selected from the group consisting of
• i) polyisocyanates containing one or more biuret, isocyanurate, uretdione or urethane groups and prepared from 1,6-diisocyanatohexane,
• ii) polyisocyanates containing isocyanurate groups and prepared from mixtures of 1,6-diisocyanatohexane and 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl cyclohexane and
• iii) polyisocyanates containing isocyanurate groups and uretdione groups and prepared from a mixture of 1,6-diisocyanatohexane and 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl cyclohexane and
• C) a catalyst component containing at least one catalyst for the reaction between blocked isocyanate groups and hydroxyl groups components,
• wherein components A) and B) are present in an amount which are sufficient to provide an equivalent ratio of blocked isocyanate groups to hydroxyl groups of 0.5:1 to 1.5:1,
• b) freeing the resulting solution from the solvent and
• c) simultaneously and/or subsequently converting the solid obtained into powder form.