Patent GB-1147418-A (GB)
Title: Method and apparatus for making oriented blown tubular film
IPC: B29C48/10
Filed: 1968-01-24
Abstract: 1,147,418. Making oriented inflated tubular film. FMC CORP. 24 Jan., 1968 [2 March, 1967], No. 3771/68. Heading B5B. An apparatus for making an oriented tubular film includes an extrusion die 11 (Figs. 1 and 2) which is mounted on the outlet 13 of a conventional extruder. Molten polymeric material is fed by the extruder into the die and issues from the annular orifice 15 of the die as a continuous tubular film 17. The die 11 is provided with an axial passageway 23 which terminates, at one end, in a concavity 25 and, at its opposite end connects with a sleeve 27. The passageway 23, concavity 25 and sleeve 27 together provide a passage through which gas is exhausted from the tubular film 17 and discharged through a valved outlet 29. Extending through and spaced from the walls of this exhaust passage is a conduit 31 which is slidably supported from the sleeve 27 by a packed bushing 33 for movement into the operative position shown in Fig. 1 or the position at the start of operations shown in Fig. 2. An inflatable ball or balloon 37, formed of flexible and preferably elastic material, is fixed to the conduit 31 by seals 39. At the start of operations the ball 37 is in a collapsed condition and the conduit is in a retracted position (Fig. 2). Molten thermoplastic material is then extruded through the die orifice 15 to form the tubular film 17 and as soon as the film is laced between the nip rolls 19 and 21 and to a collection device, a compressed gas (usually air) is introduced into the tubular film 17 through the conduit 31 and the conduit is then projected into the continuously advancing tubular film. The ball 37 is then inflated by a compressed gas (usually air) delivered through the tubing 43. The molten tubular film 17 issuing from the die orifice 15 is cooled, either by the ambient atmosphere alone or in combination with an air cooling ring an orientation temperature below the first order phase transition temperature and above the second order phase transition temperature of the film material, preferably up to about 50 C. above such transition temperature. Thus, as the tubular film 17 moves beyond the inflated ball 37 the portions thereof cooled to within the orientation temperature range are expanded radially and oriented, by the gas delivered by the conduit 31 and issuing from the baffle 35. The gas then flows, as indicated by the arrows in Fig. 1, past the ball 37 and into the die passageway 23 from which it is exhausted through the valved outlet 29. Since the passage between the ball 37 and the adjacent portion of the advancing and still molten tubular film is restricted, the linear velocity of the gas will increase and reach a maximum as it flows through the restricted passage. The pressure which the gas exerts in the adjacent portion of the tubular film is thereby decreased and thus no significant radial expansion of the still molten portion of the tubular film will occur. Once oriented, the tubular film is cooled to below its second order phase transition temperature by the ambient atmosphere alone or in combination with an air cooling ring before it is advanced between the nip rollers 19 and 21 and collected. In shutting down the apparatus, the ball 37 is first deflated, the conduit 31 retracted to the position shown in Fig. 2, and the delivery of gas into the conduit 31 and the extrusion of molten material discontinued.