| 摘要 |
A partially cross - linked stretch - oriented mono-olefine polymer foam, optionally having at least one non-porous impervious skin of the same polymer integrally united to the foam, is prepared by adding a foamable composition comprising the cross-linked polymer and foaming agent to an extruder, heating the composition therein, extruding the mixture as a sheet or tube under pressure, quench-chilling one or both surfaces of the foaming extrudate with a stream of compressed gas to give non-porous skins, if desired, prior to uni- or bi-axially stretch-orienting the foamed extrudate. The preliminary cross-linking of the polymer is achieved by radiation, free-radicals derived from known agents or co-polymerization with a di-olefinic hydrocarbon such as di-cyclopentadiene. The preferred polymers are homopolymers of ethylene or propylene although co-polymers of ethylene with a -mono-olefines may be used. Typical foaming agents are organic compounds which decompose to give nitrogen, e.g. p,p1-oxy-bis(benzene-sulphonylhydrazide) or di-nitrosopentamethylene tetramine; mixtures of ammonium, alkali or alkaline earth metal carbonates or bicarbonates and an acidic agent which liberate carbon dioxide, e.g. sodium bicarbonate and citric acid and, finally, volatile liquid hydrocarbons or substitution derivatives thereof absorbed on a solid absorbent, e.g. pentane on silica gel. Other conventional additives may be included in the composition. A suitable extrusion apparatus is described. |
