| 摘要 |
A process for producing CFC-free polyurethane rigid foams having reduced thermal conductivity comprises reacting a) isocyanate semiprepolymers modified with urethane groups and containing from 31 to 20% by weight of NCO, based on aromatic polyisocyanates and at least one aromatic and/or preferably aliphatic polyester-polyol having a hydroxyl number of from 22 to 400, b) at least one relatively high molecular weight compound containing at least two reactive hydrogen atoms, which advantageously have arylene units bonded to them, and, if desired, c) low molecular weight chain extenders and/or crosslinkers in the presence of d) blowing agents, preferably cyclopentane and/or cyclohexane in combination with water, e) catalysts and, if desired, f) additives. The CFC-free polyurethane rigid foams are preferably used as insulation material in refrigeration appliances and as insulation in composite and heating elements, for example for insulating remote heating pipes.
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