| 摘要 |
Layers of thermoplastic polymeric materials are bonded together by surface-activating at least one layer, applying a layer of the other material to the activated surface, and irradiating the layers with ultraviolet light through the more U.V.-transparent layer. The second layer may be applied by coating, as by extrusion or dipping in a solution or emulsion. One layer may be a polyolefin film and this, whether or not the activated layer, is in general that through which the U.V. irradiation is effected. The other layer may be a film of (a) vinylidene chloride copolymerized with a small proportion of other monomer such as acrylonitrile, vinyl chloride, alkyl methacrylate or alkyl acrylate or mixtures thereof (many other examples are given in the Specification), or (b) a polyester such as polyethylene terephthalate, or other reaction product of a glycol with a dibasic acid such as adipic, sebacic, isophthalic, azelaic, maleic, bibenzoic, hexahydroterephthalic, or 1,5-, 2,6- or 2,7-naphthalene dicarboxylic acids. Surface activation is preferably effected by electrical discharge but may be by flaming or treatment with concentrated or fuming sulphuric acid, sulphur trioxide, hot sodium hydroxide or with gaseous borontrifluoride, aluminium chloride or titanium tetrachloride, or a liquid co-ordinated complex thereof. Films used may be oriented, and the products embodying polyolefins may be used for making heat-sealable and heat-shrinkable bags and wrappers, particularly for foodstuffs and, in the case of polythene-polyethylene terephthalate products, for "boil-in-bag" applications such as heat-sterilizable hermetically sealed packages of pharmaceuticals. Examples refer to (a) a film of a 75/25 blend of low density/high density polythene activated by electric discharge and coated by dipping with an aqueous dispersion of a copolymer of vinylidene chloride/methyl acrylate/itaconic acid in weight ratio 92,5 : 7,5 : 1, the product being U.V. irradiated through the polythene; (b) a biaxially oriented, heat-set film of polyethylene terephthalate coated with an aqueous dispersion of a 94 : 6 : 1 copolymer of vinylidene chloride/acrylonitrile/itaconic acid and activated by electric discharge on its coated surface, the coated film being subsequently melt-extrusion coated on the coated surface with polythene, the product thereafter being irradiated with U.V. through the polythene. |
