| 摘要 |
1518847 Extruding foamed plastics FURUKAWA ELECTRIC CO Ltd 15 Oct 1975 [22 Oct 1974 20 Nov 1974] 42351/75 Heading B5A [Also in Division C3] An extruded thermoplastic polymer board of thickness not more than 200 mm., which comprises opposed non-foamed skin layers of thickness 0.5 to 3 mm., a non-foamed layer of thickness 0À1 to 2 mm. intermediate of the skin layers and a foamed layer separating the intermediate layer from each skin layer, each foamed layer being composed of cells which are elongated between a skin layer and the intermediate layer, the volume occupied by cells having an average diameter (as defined) of more than 5 mm. being more than 50% of the volume of the board (Fig. 1) is made by (a) extruding into the atmosphere a mixture comprising 100 parts by weight of the thermoplastic polymer, 2 to 20 parts by weight of a volatile foaming agent which is soluble in the polymer at the extrusion temperature, and 0À1 to 3 parts by weight of a nucleating agent so as to form a board, the extrusion temperature being between the softening or melting point of the mixture and a temperature 30‹ C. higher than the softening or melting point of the thermoplastic polymer; (b) rapidly cooling opposed surfaces of the extruded board so as to form the skin layers; and (c) slowly cooling the board substantially.in the absence of shearing stress and at a rate of cooling which allows the material to foam to form the foamed layers, the opposed surfaces of the board being restrained during step (c) by expansion restricting means such that the thickness of the resulting board is 50 to 95% of the theoretical maximum thickness. In Fig. 3, board 7 is extruded from die 6 and cooled rapidly by water-cooled pipe 8 thereby forming skin layers 4, expansion is then controlled by restricting means 9 in which heat medium can be passed thereby forming cells 2 and higher density layer 3 in foamed board 1 which is taken up by roll 10. In Examples 1-4 polyethylene and polypropylene were extruded as above into foamed boards using calcium carbonate as nucleating agent and trichlorofluoromethane as foaming agent. The boards were joined together by compression of heated facing sides in Example 5 or by mechanical arrangement of boards having a depression and projection respectively (Fig. 2, not shown) in Example 3. |
