| 摘要 |
1,075,189. Extrusion machines. KOPPERS CO. Inc. Jan. 7, 1965, No. 832/65. Heading B5A. [Also in Division B1] In an extrusion moulding machine for use in producing expanded or expandable thermoplastic polymeric material, the screw is provided with integral chokes 82, 84, 86, 88 etc. which divide the barrel 18 into annular channels 80d, 80e, 80f, 80g etc. whose volumes sequentially increase towards the exit end of the barrel and wherein the respective screw flights 79d, 79e, 79f, 79g &c. are formed with sequentially decreasing pitch so that the throughput of the machine remains constant. Each choke, Fig. 3 (not shown), is provided with axial grooves (98), and a cylindrical portion (94) is situated adjacent an inlet, as at (31), which is used for the introduction of liquid or gaseous material under pressure, e.g. a blowing agent, into the grooves of the choke as the latter rotates. By this means plasticized material passing from one side of each choke to the other has thoroughly admixed therewith material from inlets 31, 30, 29, 28 &c., Fig. 1. Prior to choke 82, material entering from a hopper 14 is plasticized in passing from annular channel 80a to channels 80b and 80c. The increase in volume of the annular channels 80d, 80e, 80f, 80g etc. allows cooling of the foaming agent/ thermoplastic mix with consequent rise in viscosity thereof, Fig. 7 (not shown), and ease of extrusion. In one embodiment, Fig. 5 (not shown), foamable polystyrene beads are made by injecting expanding agent, e.g. pentane, through lines (29), (30) and (31), with line (28) used likewise or for the injection of additives such as plasticizers, dyes, light stabilizing agents, antioxidants or flame-retarding agents. A multi-orifice die (132) produces strands of extrudate (134), shock-cooled by water in a bath (136) to prevent expansion, and the strands are granulated by a chopper (142). In a second embodiment, Fig. 6 (not shown), a foam film (154) is produced continuously from die head (152), which is blown, collapsed by plates (156), slit by a device (164) and collected in the form of two sheets by rolls (170), (172). Other polymeric thermoplastic materials mentioned include homopolymers and copolymers derived from hydrocarbon vinyl monomers and in particular impact polystyrene, i.e. an admixture of polystyrene with natural or synthetic rubber. Various blowing agents are mentioned, the preferred variety being voltatile organic compounds of a saturated aliphatic hydrocarbon containing from 4-7 carbon atoms in the molecule and perchlorofluoro carbons, which compounds have a molecular weight of at least 58 and a boiling point not greater than 95‹ C. and are added in amounts of up to 15 parts by weight per 100 parts by weight of polymer. The cell size of the resulting product may be controlled by using an agent such as a carbon dioxide liberating material and boric acid or an organic acid having at least about 3À0 milliequivalents of acidic hydrogen per gram, which agent may be added via hopper 14. |
