| 摘要 |
1,196,543. Caps for containers. W. R. GRACE & CO. 7 Feb., 1969 [9 Feb., 1968], No. 6592/68. Heading B8T. [Also in Divisions B4-B5] A method of forming gaskets in plastics closures for containers in which a thermoplastic gasket-forming material is introduced into the closure, heated and formed into a gasket of desired profile, is characterized in that the material introduced contains particles of an electrically inductive material which is conductive and/or ferromagnetic; or a thin layer of electrically inductive material is placed between the gasket-forming material and the closure inner surface; and the thermoplastic material is heated by subjecting the closure contents to a high-frequency magnetic field. The gasket material may be a vinyl resin plastisol and the closure containing it may be rapidly spun to distribute it over the inner surface thereof and subjected to the high-frequency field until it is fluxed and then cooled. Alternatively the material is heated in the closure by the field until it is sufficiently soft and is then moulded. The inductive material may comprise aluminium, copper, iron or an alloy of iron and nickel, or silver, gold, carbon, graphite or barium ferrite. The gasket forming material may include a blowing agent to produce a foamed gasket. |
