Patent ID: 7893124

Claim:
A process for producing rigid polyurethane foams, comprising: reacting at least one polyisocyanate with a mixture of compounds having at least two hydrogen atoms which are reactive toward isocyanate groups in the presence of blowing agents, wherein the mixture of compounds having at least two hydrogen atoms reactive toward isocyanate groups comprises: from 10 to 50% by weight of a polyether alcohol which has a hydroxyl number of from 360 to 450 mg KOH/g and a viscosity at 25° C. of greater than 12 000 mPa·s obtained by addition of ethylene oxide and/or propylene oxide to a TDA comprising a vicinal TDA, from 25 to 80% by weight of a polyether alcohol which has a functionality of from 5 to 7.5 and a hydroxyl number of from 380 to 480 mg KOH/g obtained by addition of propylene oxide to sorbitol and/or sucrose, and from 10 to 25% by weight of a polyether alcohol which has a functionality of from 2 to 4 and a hydroxyl number of from 140 to 250 mg KOH/g obtained by addition of ethylene oxide and propylene oxide to TDA or amines other than TDA or of propylene oxide to 2-, 3- or 4-functional alcohols or castor oil derivatives, and wherein the polyether alcohol obtained from sorbitol and/or sucrose consists of propylene oxide, sorbitol and/or sucrose and an optional liquid coinitiator, and wherein the at least one polyisocyanate comprises: a mixture of a polyisocyanate having an NCO content of from 30 to 32% by weight and a viscosity of from 2000 to 2200 mPa·s at 25° C. and a polyisocyanate having an NCO content of from 30 to 32% by weight and a viscosity of from 100 to 120 mPa·s at 25° C.