Patent GB-978203-A (GB)
Title: Improvements in or relating to the manufacture of plastic tubes
Inventor: BILD FREDERICK
IPC: B29C48/10
Filed: 1962-12-03
Abstract: 978,203. Tubes and films ; moulding thermoplastic material. IMPERIAL CHEMICAL INDUSTRIES Ltd. April 10, 1963 [Dec. 3, 1962], No. 45467/62. Addition to 787,479. Headings B5A and B5B. In the production of tubular films by inflation, the tube of thermoplastic material is passed between a pair of substantially parallel nip rollers 9 spaced apart to such an extent that the tube is flattened between them, and encircles a stationary probe 15 (Fig. 2), located at the side of and outside the line of the nip, so that creasing of the tube at the edge is prevented. As shown, two such probes 15, 16 of substantially pear-shaped cross-section may be used, or alternatively only one probe may be used, the other edge of the tube passing through the nip. In Fig. 4, one edge only of the tube is internally supported on the stationary probe 25, the other edge 26 projecting outside the nip by an amount which permits a substantially gas-tight seal. to be maintained between the portions of the tube before and after passing through the nip. Probe 15 of Fig. 2 and probe 25 of Fig. 4 are provided with internal conduits enabling inflating gas to be supplied to the tube after passing through the nip. In Fig. 3, inflating gas is supplied through a conduit provided in an additional elliptical probe 20 passing through the nip within the tube. The nip rollers are covered with a layer 18 of a resilient substance, suitably rubber, and in the apparatus of Fig. 3, at least one roller is circumferentially grooved to permit a passage for the probe 20, the grooves 21 being lined with a resilient substance, suitably sponge rubber. In Fig. 1, a tube of plastic material is extruded from a die 2 and passed through a sizing die 3, lubricated with water from pipe 4, the water being removed by a vacuum device 6 having a ring seal 7 and pipe 8 for application of vacuum. The tube 1 is then passed between nip rollers 9, and infra-red heaters 10 which heat it to the orientation temperature, is stretched and the tubular film 11 produced is flattened by guides 12 and hauled off by further nip rollers 13. A conduit 14 passing through the die 2 supplies inflating gas to assist sizing by the sizing die 3, and probe 15 has an internal conduit through which inflating gas is supplied to the tube after it has passed through the nip. A solid probe 16 in front of the probe 15 is also attached to the die. After passage through the rollers 13, the flattened film may be slit at each edge in conventional manner, or may be slit along one edge only, since the use of the probe or probes eliminates creasing at the edges. Tubes having wall thicknesses of less than 0.01 inch, or of 0.01-0.1 inch thickness or greater may be so made. Specified materials include polypropylene, especially isotactic polypropylene, polythene, polyesters, e.g. polyethylene terephthalate, polyamides, vinyl polymers and copolymers, e.g. polyvinyl chloride, polystyrene, polyvinylidene chloride and vinyl chloride/ vinylidene chloride copolymers, and cellulose derivatives, especially cellulose acetate. Specification 954,383 also is referred to.