Amine-blocked polyisocyanates and their use in one-component stoving compositions

A blocked polyisocyanate crosslinking agent, which is stable in storage, does not crystallise from solution and is the reaction product of

• A1) 30 to 70 equivalent % of a polyisocyanate component having, an NCO content of 12 to 24 wt. % and containing a lacquer polyisocyanate prepared from a linear or branched aliphatic diisocyanate and having allophanate, biuret, isocyanurate, iminooxadiazindion, uretdione and/or urethane groups, and
• A2) 30 to 70 equivalent % of a polyisocyanate component having an NCO content of 8 to 15 wt. % and containing a lacquer polyisocyanate prepared from a cycloaliphatic diisocyanate and containing allophanate, biuret, isocyanurate, uretdione and/or urethane groups,
• wherein the equivalent percentages of polyisocyanate components A1 and A2 add up to 100 equivalent %, with
• B) 85 to 100 equivalent %, based on the isocyanate groups of components A1+A2, of a secondary aliphatic linear amine having a boiling point of 60 to 110.degree. C. and
• C) 0 to 15 equivalent %, based on the isocyanate groups of components A1+A2, of chemically incorporated hydrazine derivatives corresponding to formula (I) ##STR6## wherein R represents a saturated hydrocarbon residue having 2 to 5 carbon atoms,
• and which contains in admixture
• D) 0.0 to 5.0 wt. %, based on the weight of components A1, A2 and C, of amines having a structural unit corresponding to formula (II). ##STR7##