GB1446138A - Method and apparatus for manufacture of tubular biaxially stretched film - Google Patents

Abstract

1446138 Tubular film SHOWA DENKO KK 18 April 1974 [3 May 1973] 17023/74 Heading B5B A tubular biaxially stretched film of synthetic resin preferably polypropylene is made by passing raw film 1 (Fig. 1) through nip rollers 2 into a pre-heater barrel 4 incorporating within its walls indirect heaters 3, the upper end of the barrel being closed by a head portion 5, then into a stretching barrel 8 which incorporates within its walls indirect heaters 7, cooling the film by a cooling jacket 9 disposed so as to intercept the radiant heat from the heater in the wall, and finally through nip rollers 14 disposed below stabilizer plates 12. The rollers 14 rotate at a speed in excess of rollers 2, the pairs of rollers forming seals for the enclosed gas and at the same time stretching longitudinally the film 1. Disposed below the rollers 14 are a nozzle 13 for injecting gas into the tube and gas sealing rolls 15. In addition a draught tube 11 and an air cooling ring 10 is disposed to increase cooling of the film. Furthermore the raw film may be preheated by a circulation type heater unit 23 and slit heaters 24 to provide local heating to portions of film having a greater thickness. Slit heaters may be positioned inside the preheater barrel. The head portion 5 prevents the flow of gas from the panel but allows the passage of the film and comprises either an air curtain, Figs. 3 and 4, where heated air 19, via inlet 16 is spurted out at 17 against the film 1 and optionally a portion is recycled through a suction inlet 18 or a rubber seel unit, Figs. 5-10, where a rubber sheet 20 is held in a frame 22 by bolts 21.