GB1106994A - Improvements in and relating to thermoplastic films - Google Patents

Abstract

1,106,994. Tubular films. BAKELITE XYLONITE Ltd. 5 July, 1965 [6 July. 1964], No. 27715/64. Heading B5B. In apparatus for extruding a tube of thermoplastic material comprising an extrusion die, means for supplying an inflation pressure, and means for hauling off the tube after inflation while maintaining an inflation pressure within the tube, there are provided means associated with the die for preventing an inflation pressure from rupturing the extruding tube, and a pair of nip rolls for drawing off the tube from the die lips, constructed so that they flatten the tube across only a part of its width so that two opposed portions of the tube are brought into contact with one another in the nip, without forming crease marks in the tube. The ruptureprevention means may be an external solid support, or pressure equalization means, or may be a flexible seal inserted into the tube before the inflation zone and impassible by inflating gas. The extruded tube may be quenched prior to its passage through the nip rolls by passing it through a quenching lath and/or circulating quenching fluid e.g. water or air, through the interior of the tube. To prevent the tube from collapsing as it leaves the die lips, gas may be introduced into the tube between the die lips and a former. In one such embodiment (Figs. 1-3, not shown) tube (6) is extruded from die (1), passed over former (16) below the level of quench bath (2), over seal (19) and through the nip formed between portions (24) of rollers (23). The tube then passed through annular heater (4) inflated at (27) and flattened between rollers (5). Air is passed through tube (14) into channel (13) to create a pressure in space (25) to prevent collapse of the tube as it leaves the die lips. Water, to quench the tube internally is passed into space (26) through tube (11) and removed via tubes (10) and (15). Inflating air, injected through tube (12) below seal (19) carries the seal flange (23) to distort radially and thus seal against the walls of tube (6). In further embodiments, seals which may be increased in efficiency after start-up of the apparatus, comprise an inflatable hollow rubber disc (30) or a flange (23) which may be distorted by manual rotation of a washer (21) (Figs. 4 and 5, not shown). The nip rolls (3) may be of different forms (Figs. 8 and 9, not shown) provided that the nip is less than half the circumference of the tubular film. In apparatus wherein the film is withdrawn upwardly from the surface of the quenching bath (2) (Fig. 6, not shown), a second pair of nip rolls, (3a) similar to rolls (3) are located above the surface of the quench bath (2) and a series of guide rolls (33) may be provided to reduce the curvature of the path followed by the tube (Fig. 7, not shown).