GB1419972A - Method and apparatus for stretching plastic material - Google Patents

Abstract

1419972 Stretching apparatus J D McCALL 23 Nov 1972 54228/72 Heading B5B Thermoplastic film is uniaxially stretched by pulling the film away from the nip of restraining rolls whilst heating the film to soften it. The major part of the heating zone is either within the nip of the restraining rolls or within the area from the nip to a plane extending transversely to the film and tangential to the nip rolls. The heating is uniform across the film throughout the entire heating zone. When the film 11 is heated at the nip, nip roller 16 may be internally heated by means of fluid passing through from inlet 26 to outlet 28 (not shown). When the film is heated after the nip the heater may take the form of a bar 48 placed close to the nip. This bar is preferably a wedge shape, the point 52 being thrust almost into the nip, and having a flat bottom surface 50 close to the film. By inclining the bar 48 at a slight angle α the nip may be shielded from convection currents. When a heating bar is used the roll 16 may be cooled by fluid passing internally through it. Preferably roll 16 has a non-resilient surface and roll 18 a resilient one. Pulling rolls 40 and 42 may also be non- resilient and resilient respectively and 40 may also be cooled. The process is illustrated for polyvinyl alcohol and is stated to give a uniform stretching.