GB1123318A - Process and apparatus for cooling thermoplastic sheets or films - Google Patents

Abstract

1,123,318. Cooling thermoplastic films. ZELLSTOFFABRIK WALDHOF. 21 Dec., 1966 [23 Dec., 1965], No. 57156/66. Headings B5A and B5B. Thermoplastic films or sheets made by a blow moulding process, are cooled with a gaseous media enriched with a mist-like atomized liquid, immediately after extrusion from a tubular die and before drawing off. The film may be cooled on its inside or outside surface. Air enriched with a fine spray of atomized liquid is supplied to a lower cooling ring 8 through pipes 11. Baffles 12, in the annular space 13 effect uniform distribution of the pressure ratio by causing turbulence, thus directing the cooling medium coming from the air gap 14, under an adjustable lip 15, on to all sides of the outside wall of the tubular film 10, the cooling medium streaming upwards along the outside tube wall. Cooling ring 9 works in like manner, the cooling medium being directed downwards through air gap 19. The size of the liquid drops is at or less than 20 Á and the vaporization temperature of the atomized liquid is preferably below the setting point of the film. The amount of liquid coming into contact with the film is such that it vaporizes between the die and the draw-off device. The liquid may be blown off with heated air moving in the direction opposite to the film. Alternatively (Fig. 2), the cooling medium may be introduced into a mandrel head 20 through a pipe 23 passing upwards in the centre of housing head 21, the cooling medium being insulated from the temperature of the housing head by insulation means 27. A baffle 26 directs the cooling medium on to the inside wall of the film, the cooling medium also serving to blow the film. Air is removed through suction pipe 25. Additional cooling from the outside may be effected as above. Films with uniformly grained surfaces may be produced.