| 摘要 |
<p>An improvement in a process for the production of polyurethane foam in which a first component is admixed with a second component and in which the first component has a viscosity at least two times the viscosity of the second component, thereby resulting in a non-uniform distribution of the cells of the foam, is disclosed. The improvement comprises admixing the second component with 1-5%, by weight of the second component, of fumed silica prior to admixing the first and second components. The amount of fumed silica is controlled so that the polyurethane foam subsequently obtained has a substantially uniform distribution of cells. A process for the production of a foamed thermoplastic structure in which at least part of the normally liquid chlorofluorocarbon blowing agent is added as a composition comprising an admixture of 5-99%, by weight, of fumed silica and 1-95%, by, weight, of a normally liquid chlorofluorocarbon adsorbed thereon is also disclosed. The composition is in the form of a dry free-flowing powder.</p> |
