| 摘要 |
1392334 Laminated films W R GRACE & CO 28 March 1972 [30 March 1971] 14463/72 Headings B5B and B5N [Also in Division C3] A flexible laminate, suitable for use in heatshrink packaging comprises the following layers in the order given:- (i) a layer comprising an oriented copolymer of ethylene and vinyl acetate containing 5-20% by weight (preferably 8-12%) of units derived from vinyl acetate, the copolymer preferably being cross-linked; (ii) a barrier layer of low oxygen permeability such that the oxygen transmission rate of the laminate is no more than 70 c.c./sq.m./24 hrs./ atm. (measured at 73‹ F. and 0% relative humidity, according to A.S.T.M. Standard D1434; and (iii) a layer comprising (a) a copolymer of ethylene and vinyl acetate containing 5-20% by weight of units derived from vinyl acetate, or (b) a blend of isotactic polypropylene, atactic polypropylene or polybutene-1, or (c) a propylene, ester or amide polymer. Preferably the barrier layer is a vinylidene chloride copolymer with at least one other ethylenically unsaturated monomer, (e.g. vinyl chloride), the copolymer containing at least 50% by weight of vinylidene chloride derived units, and may contain 70-85% vinylidene chloridederived units and 30-15% of vinyl chloride derived units and the preferred vinylidene chloride polymer being a mixture of 5-40% (especially 5-15%) polymer obtained by suspension polymerization and 60-95% (especially 85-95%) polymer obtained by emulsion polymerization. The barrier layer may also contain 2-10%, especially 4-6%, of epoxy resin, and at least 5% of the vinylidene chloride polymer in the barrier layer may be of a liquid coating grade. Preferably, substantially all the vinylidene chloride polymer in the barrier layer is obtained by emulsion polymerization and 5- 40% thereof is liquid coating grade. In a preferred method, the laminate is made by melt extruding the ethylene/vinyl acetate copolymer layer (i) from die head 11 to form a tube, which is water quenched at cooling ring 12, collapsed and fed into irradiation vault 14 where it is irradiated with electrons from an iron core transformer accelerator 16, suitably at a dosage of 2-15 megarads. The tubing is then slightly inflated, but not stretched significantly, and passes through vacuum chamber 21 to a laminating or coating die 22. A second tubular film is melt-extruded therefrom and directly adhered to the tube 10 to form a two-ply tubular laminate 24. Die 22 (Figs. 2 and 3) is a circular crosshead die having an adaptor 26 attached thereto to provide an opening 27 for the tube 10. The path of the coating material 23 is shown by the arrows. Vacuum chamber 21 draws film 23 while still molten against tubing 10, to prevent bubble formation. The two ply film 24 passes to the laminating or coating die 32 while still hot, and a third layer is melt-extruded therefrom and directly adhered to the two ply tubular laminate 24 to form a three-ply tubular laminate 34, which is water quenched at 39, and wound up. Biaxial orientation is effected by passing previously wound-up film through hot water bath 44 as shown. After the orientation temperature has been attained, bubble 54 is blown in the film out of the water and the film is stretched in both the transverse and longitudinal directions in a preferred ratio of 1 : 1À5 to 1 : 6, especially 1 : 2 to 1 : 4. |
