EXTENDED BIAXIALLY ORIENTED THERMALLY SHRINKABLE MULTILAYER FILM Russian patent published in 1999 - IPC

FIELD: chemical industry. SUBSTANCE: described is extended biaxially oriented thermally shrinkable multilayer film consisting of central oxygen-barrier layer composed of mixture comprising ethylene-vinyl alcohol copolymer and polyamide, intermediate adhesive layers made of adhesive based on maleic anhydride modified polyethylene, and outer layer based on polyolefins having density greater than 0.914 g/cubic cm. Central layer is made of mixture containing 70-85 wt % of ethylene-vinyl alcohol copolymer having melting temperature from 162 to 178 C and containing 36-44 wt % of ethylene and 15-30 wt % of polyamide which is polyε-caprolactam-nylon copolymer derived from adipinic acid and hexamethylene diamine containing 85 mole % of polyε caprolactam in copolymer. Thickness of central layer is 1.27-2.54 mcm and oxygen permeability through layer is more than 35 cubic cm/sq.m/ 24 h, and each intermediate adhesive layer is made of mixture containing 35-80 wt % of ethylene-α-olefin copolymer having density of less than 0.914 g/cu.cm, 20-40 wt % of adhesive based on maleic anhydride modified polyethylene having melt index of less than 1.7 g/10 min, or adhesive based on maleic anhydride modified ethylene-vinyl acetate copolymer having melt index of less than 0.5 g/10 min and not greater than 40 wt % of ethylene-vinyl acetate copolymer having melt index of not greater than 1 and containing 7-15 wt % of vinyl acetate. Mixture has average melt index and average melting temperature lower than melting temperature of polymeric mixture of central layer, and thickness of each adhesive layer is 2.5-5 % of film thickness first outer layer is self-thermally weldable and is made of polyolefin having density of less than 0.914 g/cu.cm and containing not more than 45 wt % of ethylene-vinyl acetate copolymer having melt index of not greater than 1 and melting temperature lower than melting temperature of polymeric mixture of central layer. Thickness of central layer is 20-35 % of film thickness, and at least one of outer layers has melting temperature of at least 105 C, and film has at least 30% free shrinkage at 90 C in transversal direction and total film thickness of 38.1-88.9 mcm. EFFECT: improved thermal shrinkage and physical properties. 19 cl, 8 ex, 14 tbl, 2 tbl