Patent ID: 8557887

Claim:
A process for producing rigid polyurethane foams, comprising: reacting polyisocyanates (a) with compounds (b) having at least two hydrogen atoms which are reactive toward isocyanate groups in the presence of blowing agents (c), and a flame retardant (d), wherein the compounds (b) having at least two hydrogen atoms which are reactive toward isocyanate groups comprise: at least one aromatic polyester alcohol (bi), which is prepared using a fatty acid, at least one polyether alcohol (bii) having a functionality of from 4 to 8, and a hydroxyl number in the range from 300 to 600 mg KOH/g, and at least one polyether alcohol (biii) having a functionality of from 2 to 4 and a hydroxyl number in the range from 100 to less than 300 mg KOH/g, wherein a weight ratio of the at least one aromatic polyester alcohol (bi) to a sum of the at least one polyether alcohol (bii) and the at least one polyether alcohol (biii) is from greater than 0.15 to less than 4, and the average content of the fatty acid of the compounds (b) is greater than 1% by weight and less than 30% by weight based on a total weight of the compounds (b) and the flame retardant (d).