One-component coating compositions containing oxime- or lactam-blocked polyisocyanates which have improved resistance to yellowing

A one-component coating composition which comprises

• a) a blocked polyisocyanate which is the reaction product of a polyisocyanate with
• i) 60 to 99.9 equivalent percent, based on the equivalents of isocyanate groups of the polyisocyanate prior to blocking, of an oxime or lactam blocking agent for isocyanate groups and
• ii) 0.1 to 40 equivalent percent, based on the equivalents of isocyanate groups of the polyisocyanate prior to blocking, of hydrazine and/or a compound which is soluble at a maximum temperature of 80.degree. C. in either the polyisocyanate, the blocking agent or an optional organic solvent for the polyisocyanate and contains the group, H(R)N--NR--CO--, wherein the carbonyl group is bound to carbon or nitrogen and R represents hydrogen or an optionally substituted hydrocarbon radical and
• b) a compound containing at least two isocyanate-reactive groups.

A coated substrate which was prepared by coating a substrate with a one-component coating composition containing acid groups and additionally comprising

• a) a blocked polyisocyanate which is the reaction product of a polyisocyanate with
• i) 60 to 99.9 equivalent percent, based on the equivalents of isocyanate groups of the polyisocyanate prior to blocking, of an oxime or lactam blocking agent for isocyanate groups and
• ii) 0.1 to 40 equivalent percent, based on the equivalents of isocyanate groups of the polyisocyanate prior to blocking, of hydrazine and/or a compound which is soluble at a maximum temperature of 80.degree. C. in either the polyisocyanate, the blocking agent or an optional organic solvent for the polyisocyanate and contains the group, H(R)N--NR--CO--, wherein the carbonyl group is bound to carbon or nitrogen and R represents hydrogen or an optionally substituted hydrocarbon radical and
• b) a compound containing at least two isocyanate-reactive groups.