| 摘要 |
1,233,088. Extruding foamed thermoplastics. BRITISH PETROLEUM CO. Ltd. 2 June, 1969 [19 July, 1968], No. 34565/68. Heading B5A. In an extrusion process, a thermoplastics containing a blowing agent is extruded into a region of sub-atmospheric pressure. As shown, a glass cylinder 2 sealingly engages an extrusion nozzle having a slit orifice 1, and cylinder 2 is extended downstream by a metal cylinder 6 whose downstream end enters a vacuum manifold 7. The extrudate is initially supported on a heat-resisting support 3, which rests loosely within glass cylinder 2, and is heated to maintain its temperature by infra-red heaters 4 (only one shown) situated externally of tube 2. Alternatively, fluid heated take-off rollers may be used. Subsequent rollers may cool the extrudate which may also be shaped by metal bands. The extrudate emerges via slots 10, 12 defined by a vacuum-retaining rubber sleeve 9 lined with P.T.F.E. This sleeve is supported by wooden flanges 11, 13 whose distance apart may be altered by adjustment of wooden spacers 14. Such adjustment varies the pressure exerted by a sleeve 9 on the extrudate. Thermoplastics mentioned are polymers or copolymers of a vinyl or vinylidene monomer, preferably a hydrocarbon such as ethylene, propylene, 4-methyl pentene-1 or styrene or a substituted monomer such as acrylonitrile, vinyl chloride, vinyl acetate or methyl methacrylate. Polystyrene is particularly preferred. Various standard blowing agents and nucleating agents are mentioned. An example is given. |
