GB903794A - Improvements in and relating to a method for the manufacture of organic thermoplastic tubular film and products resulting therefrom - Google Patents

Abstract

<PICT:0903794/IV(a)/1> <PICT:0903794/IV(a)/2> An apparatus for the production of organic thermoplastic tubular film (which may subsequently, if desired, be slit to convert it into flat film) comprises a die 3 having an annular orifice 2 through which organic thermoplastic material is extruded in the form of a tube 1, quenched by means not shown, and then passed in a partially collapsed state between nip rolls 4. A tubular probe 5 mounted on the die 3 projects through the nip of the rolls 4 and has perforations at 6. Air issues from the perforations 6 to form an air cushion between the probe 5 and the shaped grooves 7 in the nip rolls 4. The grooved portions of the nip rolls are formed from a resilient material such as sponge rubber. The film 8 assumes a lenticular shape on its passage between the nip rolls and the perforated part 6 of the tubular probe 5 is also so shaped. Air from the air cushion escapes into the space 11 between the die and the nip rolls, the pressure in this space being controlled by an exit pipe 9. The pressure at 10 is greater than that in the space 11 and is used to inflate the film in the drawing stage, but the pressure at 10 is less than that inside the probe at the perforations 6. This is brought about by restricting the opening at the end of the probe 12 and also allowing the air in the drawing bubble controllably to escape. When higher air cushion pressures are needed, as in the case of polypropylene film manufacture, a separate air supply may be provided for the perforations. For example, the interior of the probe may be provided with a second air supply pipe for supply of air under moderate pressure to the space 10, while supplying air to the perforations at a higher pressure through an outer channel in the probe. The second air supply pipe and the probe are then sealed into each other at the end of the probe so that air from the outer channel does not escape to the space 10. In either case the air discharged through the perforations 6 reduces contact pressure between the tubular film and the probe 5 so that scratching of the tubular film is reduced. Specifications 787,479 and 843,113 are referred to.