| 摘要 |
The plastic (pref. polypropylene or polyethylene) is extruded through a slit extrusion nozzle into a low pressure zone defined between concave plates, this zone being maintained at a temperature lower than the extrusion temperature, and the plastic foaming and expanding in this zone so that it contacts the surfaces of the plates and forms a sheet having a cone of elongate cells, and a skin of high density expanded plastic pref. the two concave plates are succeeded by a pair of divergent planar plates, and the foaming agent is an aliphatic hydrocarbon. |
