Patent GB-1395765-A (GB)
Title: Method and apparatus for producing laminar thermoplastic film
IPC: B29C48/10
Filed: 1972-05-01
Abstract: 1395765 Oriented laminar film; laminates MITSUBISHI YUKA KK and M SUDO 1 May 1972 [1 May 1971 10 May 1971 13 May 1971] 20225/72 Headings B5A B5B and B5N [Also in Division B8] Molten thermoplastic resin of the same or different kind is extruded from each of at least two concentric annular orifices 12, 22, of inner and outer dies I, II, Fig. 2, which either rotate in opposite directions, or one of which rotates whilst the other is stationary. The inner tubular extrudate 23 is inflated, by air admitted through a die passage 13, into fusing and expanding contact with the outer extruded tubular film 24 to produce a laminar film, e.g. for heat sealing into bags, of enhanced mechanical properties due to the inclined molecular orientations C, C<SP>1</SP> of the films arising from the relative rotation between the dies I, II. The inner die I rotates at a bearing 9 and at a seal 7 upon a stationary member 8 through which molten thermoplastic from an extruder is supplied to the die I, and the outer die II rotates at a bearing 20 and a seal 18 with respect to a similar stationary member 19. In the Fig. 4 embodiment (not shown), a three layer film is produced by the provision of a further outer rotatable die having an annular orifice. With the Fig. 2 embodiment and with the inner and outer dies rotating in opposite directions, tubular films are produced having an inner layer of high density polyethylene oriented at 45 degrees to an outer layer either also of high density polyethylene, or of polypropylene. With the outer die rotating and the inner stationary, a film is produced with an outer polypropylene layer oriented at 80 degrees to the tube axis, and an axially oriented inner high density polyethylene layer. With the Fig. 4, embodiment, the inner and outer dies may rotate in opposite directions with the intermediate die stationary to produce a tubular film having an intermediate layer of low density polyethylene, and inner and outer layers of high density polyethylene producing an increased heat sealing strength as compared to the high density polyethylene layered film of the Fig. 2, embodiment. As an alterative to the intermediate low density polyethylene layer there may be employed a co-polymer of ethylene and vinyl acetate or ethyl acrylate, polycarbonate, vinyl chloride, or vinyl/vinylidene chloride co-polymer. The outer and intermediate dies may rotate in opposite directions with the inner die stationary to produce a tubular film having outer, intermediate, and inner layers respectively of high density polyethylene, polypropylene and low density polyethylene. The outer die may rotate faster, with the intermediate die rotating slowly in the same direction, or being stationary, with the inner die being stationary to produce a tubular film having outer and intermediate layers of high density polyethylene, and an inner layer of low density polyethylene. With the dies of the Fig. 2, embodiment, rotating in opposite directions or the outer rotating and the inner stationary, the tubular film may be fused into a single flat film upon passage through nip rolls upstream of which the outer layer has been air cooled. Such a flat film may be produced with outer high density polyethylene layers and inner low density polyethylene layers, or alternatively with outer layers of high density polyethylene, polypropylene, polycarbonate, or vinyl/vinylidene chloride co-opolymer and inner layers of low density polyethylene, ethylene-vinyl acetate or ethyl acrylate co-oplymer, or vinyl chloride.