GB1469211A - Apparatus for forming extruded tubular thermoplastics film - Google Patents

Abstract

1469211 Cooling extruded tubular film MOBIL OIL CORP 21 Jan 1975 2611/75 Headings B5A and B5B A tubular thermoplastics film 26 is formed by internal inflation, e.g. by air of a tube extruding from a die 14, and externally cooling the inflating tube by fluid, e.g. air at 20‹ to 100‹ C., discharged through apertures 43 in the surrounding surface of a housing 32, which is of increasing diameter in the direction away from the die 14. The apertures 43 are arranged in pairs of circumferentially extending rows 42a, 42b, and with the apertures of each row being directed in a direction away from those of the other row of the pair, and each towards an outlet passage 16 for the fluid from the housing, provided between adjacent pairs of aperture rows. The cooling fluid prevents adhesion of the tube to the housing surface, towards which the extruding tube is drawn by decreased pressures, both in the regions between each row of a pair of rows of apertures, and in the regions in which the fluid enters the passages 16. The apertures of the rows of a pair are directed away from each each at 50‹ to 160‹ C., and preferably 110‹ to 150‹ C., and the temperature and/or velocity of the fluid discharged from the rows may be in an ascending or descending gradient axially of the housing. Each pair of aperture rows is provided in one of a plurality of ring manifolds spaced apart axially to define the passages 16. The apertured housing surface is conical, or paraboloid, and diverges from the axis of the die outlet at an angle which is less than 48 degrees, preferably less than 38 degrees. The distance from the die outlet at which the extruding tube commences its diametral expansion, is preferably 5 to 15% of that to the frost line of the cooling tube. Die outlet widths are specified which are in excess of those which would be employed in processes not using the housing, e.g. in a ratio to the film thickness of more than 10 : 1, and preferably more than 15 : 1. The passages 16 may vent air to atmosphere, or other fluid to a closed reservoir system. The ratio of film to die outlet diameter is from 1À5 to 5, and the preferred film thickness is 0À01 to 0À25 mm. The internal inflating fluid is circulated through the die mandrel. The film may comprise various specified thermoplastics, and is flattened by guides prior to passage through nip rollers.