| 摘要 |
1317323 Extruding polyvinylchloride KONINKLIJKE MACHINEFABRIEK STORK NV 24 June 1970 [24 June 1969] 30582/70 Heading B5A Unstabilized polyvinyl chloride polymer is moulded, e.g. by extrusion or injection, by pressurizing particles thereof in a first zone to a temperature between the glass transition and melting points, i.e. 80‹ to 120‹C., and then melting the particles, i.e. at 180‹ to 220‹ C., predominantly by shear, but which may be supplemented by conducted heat, in a second processing zone over a residence time of less than 20 sees., e.g. 10 to 20 seconds, and through which the polymer is passed to be formed, by means of the pressure developed in the first processing zone. The zones, which are independently heated and/or cooled are preferably insulated from each other, e.g. by an air gap, and in an injection machine, the nozzle thereof serves as the second zone. In an extruder the screw or screws, of low or zero compression ratio, comprise the first zone acting as a conveyer to the second zone wherein the shear is developed by a mandrel, spider, or the tip of the screw which may be varied in speed independently of the screw conveying portion thereof. In the examples: (1) suspension polymerized polyvinyl chloride powder is extruded, at 90‹ C., by a 15 length to diameter ratio and average 4 mm. channel depth screw into a second zone at 190‹ C. comprising a tubular die of 2 mm. depth and from which a 70 Á film is blown; (2) a rod is extruded utilizing an 8 length to diameter ratio non-compressive screw of 3 mm. channel depth, and which is provided with a conical tip of the same angle as that of the die entry; (3) and (4) non-compressive twin screws, heated to 90‹ C. by oil circulating therein, extrude into a second zone defined by screw tip clearances which decrease from 10 to 4 mm., followed by a torpedo and a 2 mm. clearance tube die from which film is blown;(5) the screw of example (1) is provided with a cylindrical tip joined thereto by a conical portion. |
