POROUS BIAXIALLY-ORIENTED FILM COMPRISING HIGH MOLECULAR ETHYLENE/ ALPHA-OLEFIN COPOLYMER AND ITS USE

摘要

A porous biaxially oriented film comprising an ethylene/ alpha -olefin copolymer wherein the copolymer is obtained by copolymerising an ethylene and an alpha -olefin having 4 to 8 carbon atoms, wherein the alpha -olefin is present in an amount of from 1.0 to 7.5 per 100 carbon atoms of the copolymer and the intrinsic viscosity [ eta ] of the copolymer is from 3.5 to 10.0 dl/g; wherein (i) the film has a microporous structure in which microfibrils of the ethylene/ alpha -olefin copolymer are uniformly dispersed; (ii) when cooled to room temperature after heat-treatment at 160 DEG C in a constrained state the film loses its air permeating property due to the loss of porosity but still retains the structure which is based on the microfibrils; (ii) at a temperature of not less than 170 DEG C the film breaks up after having lost the gas permeating property.