Highly porous separator foil

摘要

The invention relates to a biaxially oriented single- or multilayer porous foil, the porosity of which is generated by transformation of ss-crystalline polypropylene during orientation of the foil. The Gurley value of the foil is <250 s. The invention also relates to a process for producing the foil by using a low transverse stretching velocity for the transverse orientation process.

主权项

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.