GB1331387A - Packaging film - Google Patents

Abstract

1331387 Laminated films DOW CHEMICAL CO 24 Sept 1971 [25 Sept 1970] 44623/71 Heading B5B A four-layered laminated film comprises (1) a first surface layer of an ethylene/vinyl acetate copolymer; (2) a barrier layer of a copolymer vinylidene chloride and vinyl chloride containing 4 to 12 wt. per cent of an ethylene/ vinylacetate copolymer disposed adjacent the first surface layer; (3) a second layer of an ethylene/vinylacetate copolymer disposed between the barrier layer and a second surface layer; and (4) a second surface layer of a polyethylene, the difference in heat sealing temperatures of the first and second surface layers being at least 16‹ C. The copolymers used in layers (1) and (3) preferably contain 90 to 60 wt. per cent ethylene and 10 to 40 wt. per cent vinyl acetate and have a melt index of from 2 to 30. The barrier layer (2) is preferably a copolymer of 70 to 80 wt. per cent vinylidene chloride and 30 to 20 wt. per cent vinyl chloride intimately blended with a copolymer containing 60 to 86 wt. per cent ethylene and 40 to 14 wt. per cent vinyl acetate. In an example a four-layer film of the invention is prepared by melt co-extrusion and chill roll casting. Comparative examples describe the preparation of four-layer laminates in which the ethylene-vinyl acetate copolymeric modifier is missing from the barrier layer or is present in an amount of less than 4% by weight.