| 摘要 |
1,180,744. Seaming non-metallic sheet material. BRITISH VISQUEEN Ltd. 31 May, 1967 [6 July, 1966], No. 30288/66. Heading B5K. A heat seal is formed between at least two layers 1, 1<SP>1</SP> of plastics film by pressing together the layers 1, 1<SP>1</SP> between two surfaces at least one of which is heated to a temperature sufficient to effect heat sealing and supplying by conduction additional but less intensive heat on at least one side of the sealing area so as to extend the area of temperature gradient between the heat sealing area and the cold area of the film layers 1, 1<SP>1</SP>. As shown, the layers 1, 1<SP>1</SP> are formed by the walls of a web of flattened tubular film. Heat sealing members 2, 2<SP>1</SP> have secured thereto annealing members 3, 3<SP>1</SP> of lower thermal conductivity than the members 2, 2<SP>1</SP> and comprising silicone rubber blocks which, when the members 2, 2<SP>1</SP> are spaced apart, stand proud of the heat sealing surfaces. A knife 4 is advanced when the members 2, 2<SP>1</SP> are closed to sever the layers 1, 1<SP>1</SP> to form individual bags each with the annealed side of the seam facing the interior of the bag. In another embodiment (not shown), the annealing members are made of rigid material and stand slightly proud of the sealing surfaces but are spring-loaded so as to enable the sealing members to be brought together during sealing. In a further embodiment, the surfaces of the annealing members may be level with the surfaces of the sealing members. The invention is also applicable to machines in which a single heated member works against a surface or in which the film layers are carried by steel bands between heated sealing members. The heat sealing member(s) are made of metal, e.g. mild steel, stainless steel or aluminium. Specified materials for the annealing member(s) are silicone rubber; laminates of paper and thermosetting resins, e.g. phenol formaldehyde resins; glass cloth/epoxy resin laminates; wood-filled or fibre-filled thermosetting resins; hard asbestos and glass-filled nylon. Specified films to be sealed are polythene, polypropylene and polyvinyl chloride films having a thickness of at least 0À006 inch. |
