| 摘要 |
<p>1,222,399. Laminated bags. W. R. GRACE & CO. 22 May, 1968 [11 Aug., 1967], No. 31758/70. Divided out of 1,222,398. Heading B8K. A thermoplastic pouch comprises a tubular section of laminated heat-shrinkable material, the section having one end closed by a heat seal 29 and the other end having an inwardly curling edge 30, 31. The tubular section is made by extrusion coating a tubular plastics substrate with a plastics layer from a circular die to which vacuum is applied to prevent occlusion of gas, cooling, heating to the substrate orientation temperature and stretching to orientate the substrate. The inward curl in the finished bag is due to the stress in the substrate. Between said cooling and heating, further layers may be applied by extrusion. The substrate is preferably polyethylene which has been cross-linked, but may be polypropylene or polyvinyl chloride. Preferably the first coating is ethylene-vinyl acetate copolymer containing 3-28 wt. per cent vinyl acetate and the second coating, if applied, is polyamide; other suitable coatings are polyurethane and polymers of vinyl or vinylidene chloride.</p> |
