GB1417970A - Processes and means for producing or treating films of plastics material - Google Patents

Abstract

1417970 Treatment of polymeric films LAMBEG INDUSTRIAL RESEARCH ASSOCIATION 8 Dec 1972 [18 Dec 1971] 58905/71 Heading B5B A sheet of molecularly orientable synthetic thermoplastic polymeric film is passed between two moving surfaces forming a pressurized nip, the surfaces being cooled so that on passing through the nip the film material goes from the plasticized to the unplasticized state, the film being mechanically worked to break up spherulites as it passes through the nip so that its tendency to fibrillate is decreased. The film may be polypropylene, high density polyethylene, polyamide or polyester and may include small amounts of polystyrene or chalk. Preferred apparatus consists of a 2¢ inch extruder 10 having a 20 inch slot die with lips 0À022 inch apart at 260‹ C. to give a film of 0À005 inch. The extrudate is nipped between a smooth chill roll 16 at 30‹ C. and a silicone rubber roll 18 at 85‹ C., both rolls having a peripheral speed of 50 feet/min. The surface of the roll 18 is kept cool by a spring-loaded cooling roll at 30‹ C. The film is slit by blades 22, drawn in a ratio of 1 : 7 in a hot air oven 24 at 150‹ C., annealed at 160‹ C. in oven 30, and shrunk by 4% on godet rolls 32. The product may be woven and used as a carpet backing, or twisted to form fibrillated twine. Instead of being slit and annealed the film may be passed through a pinned roll fibrillator (Fig. 2, not shown). In other arrangements (Figs. 3-7, not shown), one or both rolls may be cooled by partial immersion in a cooling bath, a silicone rubber belt passing round either roll may form one of the nip surfaces, or the rubber roll may be above or below the chill roll. One or both nip surfaces may be roughened to give an opaque film, e.g. by depressions or protuberances having a frequency of at least 100 per inch. The rolls may be wider than the film so that the driven roll drives the other by direct contact.