POWDER COATING CROSSLINKING AGENTS CONTAINING URETDIONE GROUPS AND FREE ISOCYANATE

摘要

The present invention relates to polyaddition compounds, which are solid below 40.degree.C and liquid above 125.degree.C, are prepared by the reaction of an isocyanate component containing uretdione groups with a polyol containing ester and/or carbonate groups, other than hydroxypivalic acid neopentylglycol ester, and have a) an average isocyanate functionality of 2.0 to 8.0 and a content of free isocyanate groups (calculated as NCO; molecular weight = 42) of 2.1 to 6.0 wt.%, b) a content of uretdione groups (calculated as C2N2O2; molecular weight = 84) of 10 to 19 wt.%, c) a content of urethane groups (calculated as -NH-CO-O; molecular weight = 59) of 10 to 17 wt.% and d) a content of ester groups -CO-O (calculated as -CO-O; molecular weight = 44) and/or carbonate groups -O-CO-O (calculated as -CO-O; molecular weight = 44) of 1 to 17 wt.%. The present invention also relates to a process for the preparation of these polyaddition compounds to two-component polyurethane powder coating compositions containing these polyaddition compounds as the crosslinking agent and isocyanate-reactive compounds as the binder.