| 摘要 |
1,110,598. Making thermoplastic film by extrusion. UNION CARBIDE CORPORATION. 17 June, 1965 [17 June, 1964], No. 25720/65. Heading B5B. Thermoplastic film, e.g. of polyethylene or polypropylene, is extruded at 12 in such a way as to have beaded edges and is taken up by an internally cooled cooling roll 15, an air cushion being maintained between the cooling roll and the part of the film between the beads to prevent surface or other defects such as scratches, gel tack marks, puckers and blotches, The air cushion is obtained by the motion of the roll which may have a matt surface over most of its width for this purpose. The diameter of the roll between the parts contacting the beads of the film may be reduced to increase the separation between the film and roll. Regulation of the quantity of air in the cushion is effected by air knife 18 across the film between the beads at the point at which the beads first contact the roll. This contact is assisted by air jets 20 above each bead. A vacuum knife 22 reduces turbulence at the point where the air cushion is formed. Heaters 24 remove any volatiles from the roll surface. The film beads may be produced by providing the extruder 12 with end plate heaters which causes the plastic to extrude faster at the edges than the middle. The film may be extruded horizontally, vertically downwards or upwards or in an inclination direction. Fourteen examples of extrusion of polyethylene and polypropylene film, some with erucamide as slip agent, are given, together with full details of process parameters. |
