| 摘要 |
1427006 Extruding foamed plastics; foam plastics laminates BRITISH VISQUEEN Ltd 8 March 1973 [10 April 1972] 16488/72 Headings B5A and B5N [Also in Division C3] An extruded olefine polymer foam (which may be laminated) is made by heating in an extruder a mixture of an olefine polymer and water to a temperature above 100‹ C. and at which the polymer is molten and at a pressure sufficient to prevent vaporization of the water, there being also present in the mixture a thermally decomposable blowing agent that will generate a gas at or below the said temperature at normal atmospheric pressure, and thereafter releasing the pressure of the mixture by extrusion to allow the polymer to foam, the ratio of water to blowing agent being 4 : 1 to 20 : 1 by weight. In the example mixtures of pigmented polyethylene, water and azodicarbonamide were extruded together with polyethylene on its own to form a foam/film laminate. The two polymers were each fed to screw extruders and extruded through the downstream and upstream orifices respectively so that two layers were extruded concurrently and coaxially through a 2-layer tubular film extrusion head, with the non-foaming layer innermost. The laminate was air-cooled after extrusion and during blowing. |
