Patent GB-941898-A (GB)
IPC: B29C48/08
Abstract: 941,898. Polyolefin films; laminates and laminating. UNION CARBIDE CORPORATION. July 19, 1961 [July 21, 1960], No. 26080/61. Headings B5B and B5N. [Also in Division B2] A polyolefin film comprises a highly uniaxially oriented crystalline polyolefin film having a melting-point above 120 C., a density of at least 0.94 and a tensile strength of from 30,000 to 80,000 pounds per square inch. The film may be of a high density homopolymer of propylene, ethylene or butylene or a copolymer of said olefins with themselves, or a copolymer of propylene and ethylene with vinyl chloride or acetate. The film may be coated with a homopolymer of ethylene, propylene or butylene, or a copolymer of said olefins with themselves, or a copolymer of propylene or ethylene with vinyl chloride or acetate. The heat sealable coated film may be formed by continuously passing a seamless tubing of highly crystalline polyolefin 38 having a coating 40 of a polyolefin, having a melting-point lower than that of the tubing, bonded to at least one surface thereof, through a heated zone 48 maintained at a temperature below the melting point of the crystalline polyolefin but above the temperature at which it is drawable and above the melting- point of the coating but below its degradation point, to preserve the bond of the thermoplastic coating to the crystalline polyolefin tubing, while simultaneously introducing and maintaining in the tubing a bubble of a fluid medium, e.g. air, to prevent the tubing from collapsing, stretching the tubing at least 700% in the longitudinal direction to cause high orientation thereof in said direction, flattening the oriented tubing and recovering the coated film. The oriented tubing 38 may be coated with a polyolefin film having a melting-point lower than that of the oriented tubing by simultaneously extruding a second tubing 40 of the polyolefin having a lower melting-point, the second tubing being concentric to the oriented tubing and adhering thereto. The coated tubing may be formed by extruding a melt of the highly crystalline polyolefin through an annular orifice of die 14 to form a seamless tubing, simultaneously extruding therewith a melt of the thermoplastic coating material through a concentric annular orifice of die 14, whereby it is deposited on to the polyolefine tubing being co-extruded, continuously with drawing the coated tubing from the point of extrusion, e.g. by squeeze rolls 46, flattening the tubing, e.g. by rolls 50, at a point spaced from the extrusion point, a bubble of fluid medium being maintained under pressure in the tubing between these points to cause distension thereof, and passing the coated tubing through the heated zone and stretching as above. The coating may have a melting-point of less than 115 C., and a density of up to 0.93. The coated film may be used as a tear tape 58 comprising a crystalline polyolefin backing film 60 having a thermoplastic coating 62, applied internally to surface 68 (Fig. 5) or externally to surface 64 (Fig. 4), of a packing film 66 which may be of low or high density polyethylene, fibrous cellulose material, e.g. paper, or non- fibrous material, e.g. regenerated cellulose. As shown in Fig. 2, the tear tape 58 may be notched at 70 and strip 72 torn out between guides 74. Alternatively, the tape may have tab 76 as in Fig. 3. The coated or uncoated crystalline polyolefin film may be treated, e.g. flame, ozone, chlorination or corona discharge treatment, or metallized, before or after orientation, and may be coated with a pressure-sensitive adhesive or a magnetic layer.