| 摘要 |
1,060,183. Seaming non-metallic sheet material. MONSANTO CHEMICALS Ltd. Jan. 7. 1966 [Feb. 12, 1965], No. 6153/65. Heading B5K. A seal 1 between a biaxially orientated thermoplastic synthetic resin sheet and a thermoplastic synthetic resin surface extends continuously around the edges of and between a series of perforations 4 in the sheet, the perforations 4 being spaced at intervals from one another so as to form a line of weakness along which the sheet can be torn so as to break the seal when required. Specified resins for the sheet are polystyrene, isotactic polyethylene or polypropylene, styrene copolymers, e.g. styrene-acrylonitrile copolymers, polyacrylates, polymethacrylates, polycarbonates, polyvinyl chloride and polyethylene terephthalate. The surface to which the sheet is sealed may be of any of the above specified resins or a toughened polystyrene or a styrene/ acrylonitrile/butadiene copolymer. Preferably the seal 1 is made between two biaxially orientated polystyrene sheets 2, 3. The orientated sheet may have a thickness of 0À0005-0À020 inch, e.g. a cover of 0À001-0À005 inch thickness is sealed to a container made from a sheet 0À01 inch thick. The perforations 4 may be circular, elliptical, square, rectangular or triangular. The major dimension of each perforation is 0À01-0À2 inch, preferably 0À02-0À1 inch. Preferably, the perforations 4 are evenly spaced with the distance between adjacent perforations being approximately the same as their major dimension. The seal may be produced by a heat scaling method or an adhesive may be used. The former method may be effected by an electrically heated tool 11, Figs. 2 and 3 (both not shown), having a line of teeth 12 with flat sealing surfaces 13 therebetween, both the teeth 12 and the surfaces 13 being coated with polytetrafluoroethylene to prevent the resin adhering thereto. A silicone rubber anvil 14 is provided. The operation is preferably performed at a temperature between 175‹ and 300‹ F. and at a pressure between 5 and 14 lbs. per square inch. A thermostat may be provided to maintain the tool at the sealing temperature. The tool may be maintained in contact with the sheet for up to 5 seconds, e.g. between 0À75 and 4 seconds. If it is desired to form a seal which is stronger on one side of the line of perforations 4, then the tool 11 or the anvil 14 is asymmetrically shaped or the anvil 14 is constructed of two materials of differing hardness to apply a greater pressure on one side. Alternatively, differential heating is employed, e.g. the tool 11 or the anvil 14 is constructed of two materials of different thermal conductivity. The seal of the invention may be used to seal a flat cover around three sides of a square container with a conventional seal on the fourth side to be used as a hinge. After sealing, the flat cover may be heat shrunk by radiation. |
