Patent ID: 7445735

Claim:
A process for improving the wet out time of an uncoated microporous membrane comprising the steps of: providing an ultrahigh molecular weight polyethylene (UHMWPE); providing a particulate silica filler; providing a processing plasticizer; mixing UHMWPE, filler and processing plasticizer together to form a mixture, having a weight ratio of filler to UHMWPE of from 1:9 to 15:1 by weight; extruding said mixture to form a sheet; calendering said sheet; extracting all or part of said processing plasticizer from said sheet to produce a matrix comprising UHMWPE and said particulate filler, the filler being distributed throughout said matrix, to produce a microporous matrix sheet; and calendering said microporous matrix sheet to produce a microporous membrane; where said microporous membrane exhibits a reduction in wet out time of 50% or more over said microporous matrix sheet.