Patent GB-1230128-A (GB)
IPC: B29C48/10
Filed: 1968-08-05
Abstract: 1,230,128. Tubular films. MITSUBISHI JUSHI K.K. 5 Aug., 1968 [11 Aug., 1967; 12 Oct., 1967; 13 Nov., 1967], No. 37270/68. Heading B5B. A tubular resinous film 10 is extruded from an annular nozzle 11 and passes over a plurality of inner rollers 12 having axes of rotation substantially perpendicular to the direction of extrusion of the film (indicated by arrow A) and mounted on an inner support 13, to be urged against the inner surface of the film. Inner support 13 is mounted on rotary shaft 14 which also carries a rotary cooling former 15 which is journalled by a stationary cooling former 16 having a smaller diameter than the rotary former so that inner rollers 12 can revolve in the circumferential direction along the inner surface of tubular resinous film 10. Rotary and stationary formers 15 and 16 are in the form of hollow cylinders and are cooled by water, the rotary former being disposed to contact the inner surface of the resinous film. Stationary former 16 is secured to extrusion nozzle 11 and has a diameter slightly smaller than that of the rotary former, so that there is a small gap between the periphery of the stationary former and the tubular resinous film. Cooling gas, e.g. air, is admitted through inlet pipe 17 and discharged through outlet pipe 18 to form a thin film of cooling gas in the gap. A plurality of outer rollers 19 supported by an outer support 20 are provided to contact the outer surface of film 10, each of said outer rollers 19 being opposed to a corresponding one of inner rollers 12 and having an axis of rotation substantially parallel to the axis of the corresponding inner roller. As in Fig. 2, four pairs of co-operating inner and outer rollers may be provided, each located on one side of a square. Thus when rotary shaft 14 and outer support 20 are revolved in the circumferential direction of the film at the same angular speed the film is twisted circumferentially. As rollers 12 and 19 are rotated in the direction of extrusion A of the film said revolution does not interfere with the movement of the film. Stationary cooling former 16 cools the film immediately after extrusion thereof from the nozzle. Rotary cooling former 15 which is rotated with inner rollers 12 effectively cools the tubular resinous film while at the same time assisting twisting thereof. As shown in Fig. 3, film 10 is cooled by stationary cooling former 16 and rotary cooling former 15 immediately after extrusion, then twisted circumferentially by inner and outer rollers 12 and 19, heated and softened by heat from heater 22 and expanded and stretched by air supplied from inlet pipe 17, prior to being folded into a flat sheet by pinch rollers 21a and then wrapped around a take-up roll 21. The apparatus is shown in more detail in Figs. 4, 5 and 7 (not reproduced). When portions of uneven thickness are formed in the extruded film due to irregularities in the extrusion nozzle 11, their positions are definite and lost by the action of twist imparted to the film in the manner described, so that such thick portions are ultimately uniformly distributed along the length of the take-up roll, thus eliminating any bulge in the roll of the film. In a modified method, twist is imparted intermittently or twists in opposite directions are imparted alternately to the film. Thus the tubular film 10 may be twisted in one direction by revolving inner and outer rollers 12 and 19 for a period of time equal to that required for the film to travel from extrusion nozzle 11 to the point M surrounded by heater 22 at which the film begins to expand. Thereafter, twisting is interrupted for the same period of time, and twist is then imparted in the opposite direction for the same period by revolving the inner and outer rollers in the opposite direction. This cycle of operations is repeated. Specified materials include polyethylene and polyvinyl. chloride.