Patent ID: 6048607
Filing Date: 2000-04-11
Classification: B29C,B29K,C08J,H01M,Y02E,Y10S,Y10T

Abstract:
A porous film of a high molecular weight polyolefin possessing the following physical properties:(1) a tensile strength in at least one direction of at least 15 MPa;(2) a piercing strength of at least 3.0 g/.mu.m;(3) an air-permeability of not more than 200 seconds/100 cc;(4) a bubble point of 0.1-5.0 kg/cm.sup.2 ;(5) a porosity of at least 30%; and(6) a film thickness of 10-200 .mu.m,which is obtained by subjecting an air-impermeable film of a high molecular polyolefin substantially free of a plasticizer and/or a solvent to a thermal treatment for making the film porous at a temperature of 80 to 160.degree. C. for 30 seconds to 5 minutes and stretching the resultant porous film (A) in at least one direction or by stretching the porous film (A) in at least one direction followed by subjecting the stretched film to a thermosetting treatment comprising further heating the porous film (A) and fixing it in two directions.