Highly porous separator foil
AssigneeTreofan Germany GmbH & Co. KG
InventorsDetlef Busch, Bertram Schmitz, Dominic Klein
Life of this patent
Estimating the term…
Abstract
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.
Claims17
A biaxially oriented, single layer or multilayer porous film, porosity of which is generated by transformation of β-crystalline polypropylene during stretching of the film, which comprises at least one porous layer, which layer contains at least one propylene polymer and β-nucleating agent, wherein the film has a Gurley value of <250 s and wherein when the propylene polymer is a propylene block polymer, the propylene block polymer has a melting range that begins at over 120° C.
A method for producing a single layer or multilayer porous polypropylene film in which in a first longitudinal stretching process propylene polymer and β-nucleating agents are melted in an extruder and extruded through a flat nozzle onto a take-off roller, on which the melt film cools down and solidifies, forming β-crystallites, and this film is then stretched longitudinally, cooled and wound up, and in a second, transverse stretching process, this longitudinally stretched, wound up film is unwound, heated to a transverse stretching temperature and stretched in the transverse direction, wherein the advance speed of the longitudinal stretching process is greater or less than the advance speed of the transverse stretching process.
Dependencies are inferred from the claim text.