GB1270954A - Process for the production of oriented polyolefin films - Google Patents

Abstract

1,270,954. Process for the production of oriented films. W. R. GRACE & CO. 14 April, 1969 [18 April, 1968], No. 19096/69. Heading B5B. A process for preparing an oriented film from tubular cross-linked polyolefin material which comprises (a) passing the tubular cross-linked polyolefin material through a first set of pinch rollers; (b) inflating the tubular material by internal gas pressure; (c) heating the inflated material to a temperature above its flow temperature; (d) biaxially orienting the inflated material by stretching it in a single stage by internal gas pressure while at such a temperature; and (e) without further stretching, collapsing the expanded material by passing it through a second set of pinch rollers after cooling the material below its flow temperature. The term flow temperature is the point at which the film exhibits self adhesion. The term polyolefin denotes polymers and blends in which all the structural units are derived from an ethylenically unsaturated hydrocarbon, preferably ethylene with a density of 0.94 g./c.c. A typical composition in Example 1 is 65% by weight ethylene/butene-1 (95:5) copolymer and 35% polyethylene (d 0.92 g./c.c.). Prior to orienting the polyethylene film is cross-linked to the equivalent of at least 2 x 10<SP>6</SP> rads by irradiating or chemical means. The film in the form of a tube is oriented by stretching by internal gas pressure while at 17‹ to 110‹ C. above its crystalline melting point. The resulting oriented polyethylene film which may be used as a shrinkable packaging film has an oxygen transmission rate of at least 5300 c.c./24 hr./atms. m.<SP>2</SP>/mil. and a moisture vapour transmission of at least 0À28 gm./24 hr./100 m<SP>2</SP>./mil.