| 摘要 |
A process is disclosed for the preparation of a polyurethane rigid foam having a low thermal conductivity. This process comprises reacting an organic and/or modified organic polyisocyanate with at least one higher molecular weight compound having at least two reactive hydrogen atoms, and optionally lower molecular weight chain extending agents and/or crosslinking agents in the presence of a blowing agent and a catalyst. The blowing agent consists of cyclopentane or of a mixture comprising cyclopentane and/or cyclohexane and at least one compound homogeneously miscible with cyclopentane and/or cyclohexane, such compound preferably having a boiling point below 35.degree.C and being selected from the group consisting of alkanes, cycloalkanes having a maximum of 4 carbon atoms, dialkylethers, cycloalkylene ethers and fluoroalkanes. The cyclopentane or above mixture is used in conjunction with water. The so obtained polyurethane rigid foam can be used in the low temperature appliance industry and as an insulating material in a heating and composite element. |
