Diphenylmethane diisocyanate based polyisocyanates containing allophanate groups and having blocked isocyanate groups

摘要

The present invention relates to polyisocyanates prepared from diphenylmethane diisocyanate wherein at least 95% of the isocyanate groups are blocked with diethyl malonate and wherein the polyisocyanates have, based on solids,PPA) a content of unblocked and blocked isocyanate groups (calculated as NCO) of 9% to 13%,P PB) a content of allophanate groups (calculated as C.sub.2 HN.sub.2 O. sub.3, molecular weight 101) of 3% to 9% andPPC) a calculated average functionality of 2.0 to 2.5.PPThe present invention also relates to a process for the production of these polyisocyanates and to their use as crosslinking agents for organic polyhydroxyl compounds in polyurethane stoving lacquers.