Battery Separator

Abstract

A multiply sheet product useful as a battery separator having at least two plies each in the form of a microporous sheet of predetermined length and breadth and a thickness of less than 10 mils wherein (a) at least one of said ply being a sheet capable of transforming to a substantially non-porous membrane at a temperature between about 80° and 150° C. while essentially maintaining its length and breadth dimensions and (b) at least one ply being a sheet capable of maintaining its dimensions and porosity at temperatures from ambient to at least about 10° C. greater than the transformation temperature of sheet (a).