Patent GB-1169338-A (GB)
Title: Method and Apparatus for the Heat-Sealing of Plastics Film Layers
IPC: B29C65/74
Filed: 1968-02-29
Abstract: 1,169,338. Seaming non-metallic sheet materials; making bags. CANADIAN INDUSTRIES Ltd. 29 Feb., 1968 [27 March, 1967], No. 9847/68. Headings B5D and B5K. [Also in Division B8] A device for heat sealing and severing successive portions from an edge of an intermittently-advancing plastics web 47 comprising at least two layers of plastics film, comprises a movable heat sealer blade 2 and a resilient support 16 opposed thereto, adapted to compress momentarily between them, during stationary phases of the web, an edge portion thereof, to seal and sever it from the web, the support 16 being movable away from the web in a direction transverse to the direction of movement thereof, after its release from the blade 2, so as to move the position of contact of the blade 2 with the web transversely away from the web. As shown in Figs. 1 and 3, the V-shaped blade 2 is attached, by a bracket 6, a spacer 7 and a screw 8, to a support plate 4 secured to a piston 5 and a V-shaped water-cooled film clamp 3 is resiliently attached to the plate 4 by movable bolts 10 surrounded by helical springs 11. The film support comprises a resilient heat resistant belt 16, preferably made of glass cloth and/or polytetrafluoroethylene, passing around rollers 17, 18 and over an anvil 19 faced with a resilient heat resistant pad 20 preferably made of polytetrafluoroethylene or silicone rubber. The belt 16 is movable by a pinion 21 attached to the roller 18 through a unidirectional clutch 22 and a rack 23 maintained in mesh with the pinion 21 by rollers 24, 25. A film holding roller 31, preferably made of polytetrafluoroethylene, is mounted on an arm 32 pivotable on a shaft 33 and pressed against the film 47 on the belt 16 by a spring 34. An arm 35 on the shaft 33 engages a screw 36 in a bracket 37 fixed to the rack 23. In operation, at the beginning of the cycle, the blade 2 is in its raised position, the rack 23 is at its extreme right-hand position, Fig. 1, and the roller 31 is clear of the film 47. A solenoid 42 is energized so that a valve 38 causes compressed air to be supplied to a cylinder 13 to lower the sealer assembly against the film 47. Simultaneously, a cylinder 28 drives the rack 23 to the left of Fig. 1 to lower the roller 31 on to the film, the belt 16 remaining stationary because the clutch 22 is disengaged. The clamp 3 contacts the film before the blade 2 and clamps the film against the belt 16 under the action of the springs 11. The blade 2 cuts and seals the film. The solenoid 42 is de-energized so that, in the valve 40, a spring 43 forces a valve spool 41 upwardly, to cause the cylinder 13 to raise the sealer assembly, the blade 2 ceasing contact with the film before the clamp 3. Simultaneously, the rack 23 is forced to the right so that the clutch 18 is engaged and the belt 16 moves to the left. As the rack 23 reaches the end of its travels, the roller 31 is raised and the film 47 is moved another step. The sealing cycle is repeated. In a machine for making block bottom plastics bags, Fig. 4, the film 47 is folded longitudinally and provided with a gusseted fold 48 and is advanced intermittently by one bag width. The sealing device 52 of Fig. 1 is positioned to seal and sever a triangular gusset portion at 53, printing ink on the outer film surface preventing sealing together of the two inner plies of the gusset. A unit 51, positioned at a distance equal to an exact number of bag widths from the device 52, seals the film panels transversely with double seals and cuts between two seals to sever the bags from the web.