Patent ID: 8889284
Filing Date: 2014-11-18
Classification: B29C,B29D,B29K,C08J,C08K,C08L,H01G,H01M,Y02E,Y10T

Abstract:
1. A method for producing a single layer or multilayer porous polypropylene film which comprises melting a propylene copolymer and β-nucleating agent in an extruder and extruding through a flat die nozzle onto a drawing-off roller, on which the melt film cools and solidifies, forming β-crystallites, and this film is then stretched in the longitudinal direction with a neck-in ratio of less than 10%, and subsequently is stretched in the transverse direction, wherein during the transverse stretching the film is stretched at a slow stretching speed of less than 40%/sec, and the porous polypropylene film has a Gurley value of <250 s after production.