Abstract: A process for producing polyurethane rigid foams comprises reactinga) organic polyisocyanatesb) relatively high molecular weight compounds containing at least two respective hydrogen atoms and, if desired,c) low molecular weight chain extenders and/or crosslinkers in the presence ofd) blowing agentse) catalysts and, if desired,f) auxiliaries and additives,wherein the relatively high molecular weight compounds containing at least two reactive hydrogen atoms comprise a mixture ofa1) one or more high-functional, polyether alcohols having functionalities of from 6 to 8 and mean equivalent masses of from 125 to 200,a2) one or more polyether alcohols based on aliphatic amines having functionalities of from 3 to 4 and mean equivalent masses of from 70 to 130,a3) one or more low-functional polyether alcohols having functionalities of from 2 to 3 and mean equivalent masses of from 67 to 250, anda4) an OH-containing fatty acid ester.

Abstract: The invention provides UV-stabilizer concentrates, which, relative to the total weight, consist ofA) 40 to 80 weight-% of at least one thermoplastic polyurethaneB) 10 to 30 weight-% 1,3,5-tri-glycidyl-isocyanurate andC) 10 to 30 weight-% 2-(2-hydroxy-3,5,-di-tert-amyl-phenyl)-2H-benzotriazole and/or 1,6-hexane-di-yl-bis-(3-(3-benzotriazole-N-yl)-4-hydroxy-5-tert-butyl)-phe nyl-propanoate.The invention also discloses a process for their production, and their utilization to stabilize TPU against UV- and thermal-degradation.