Process for producing solid polyurethane curing agents

A process for producing a solid, internally and externally blocked polyurethane curing agent based on a (cyclo)aliphatic polyisocyanate, in which, in the sequence of steps a) to d),

• a) i) at least one internally blocked (cyclo)aliphatic polyisocyanate,
• wherein the internally blocked (cyclo)aliphatic polyisocyanate is an internally blocked cycloaliphatic polyisocyanate formed from only polyisocyanates having at least one cyclically and at least one acyclically aliphatically bonded isocyanate group, and
• ii) at least one lactam and/or at least one aliphatic alcohol are dissolved in a solvent to produce a reaction mixture,
• wherein the solvent is an ether selected from a group consisting of a diisopropyl ether and a methyl tert butyl ether,
• b) the reaction mixture is heated and reacted,
• c) the reacted reaction mixture is cooled until product precipitates, and
• d) liquid solvent and any unreacted dissolved reactants and precipitated product are mechanically separated from one another.