Process for the preparation of pulverulent polyurethane varnishes free from blocking agents, that have an extended pot life and are curable above 120 degrees centigrade, and pulverulent polyurethane varnishes prepared by this process

摘要

A process for the preparation of blocking agent-free polyurethane powder coatings with high storage stability, which can be hardened above 120 ° C., based on linear uretdione group-containing polyisocyanate addition products with terminally unblocked NCO groups and polyols, a. linear uretdione groups, terminally unblocked isophorone diisocyanate diol polyaddition products whose uretdione-containing isophorone diisocyanate is 98% hot-cleavable in isophorone diisocyanate, of the following formula IMAGE R '= divalent, aliphatic, cycloaliphatic or aromatic diol, araliphatic mean, with an NCO / OH ratio of 1: 0.5 to 1: 0.9, in particular 1: 0.6 to 1: 0.8, a uretdione / diol molar ratio 2: 1 to 6: 5, preferably 3: 2 to 5: 4, a content of free isocyanate up to 8% by weight and preferably 5% by weight, molecular weights between 500 and 4000, preferably between 1450 and 2800, and melting points = 70 ° C. to = 130 ° C, preferably 85 ° C to 120 ° C with b. Polyhydroxyl compounds with an OH functionality of = 2.2 to = 3.5, preferably 2.5 to 3.4, an average molecular weight of 2000-4500, preferably 2300-3900, an OH number of 30 to 100 mg KOH / g, preferably 40-80 mg KOH / g, a viscosity of 80,000 mPa · s, preferably 30,000 mPa · s at 160 ° C and melting points between = 65 ° C and = 120 ° C, preferably 75 ° C - 100 ° C, and with c. conventional additives are implemented in polyurethane chemistry, and the ratio of a. and b. is chosen so that the NCO ratio is between 0.8: 1 to 1.2: 1. Furthermore, the blocking agent-free polyurethane powder coatings produced by the process.