Porous polytetrafluoroethylene membrane

Abstract

The present invention relates to microporous and ultrafine polytetrafluoroethylene (PTFE) membranes of high permeability, excellent mechanical strength, and good chemical inertness, and to methods for their preparation. According to the method of the present invention, a porous PTFE substrate having a first pore rating is compressed to provide a porous membrane having a second pore rating, wherein the second pore rating is smaller than the first pore rating. The PTFE substrate can be contacted with one or more fibrous sheets during the compression step, which is preferably performed by passing the substrate, and fibrous sheets, if appropriate, between two calender rolls. The resulting porous PTFE membrane then can optionally be stretched and/or sintered, and preferably has a water permeability of at least about 0.5 l/hr/m2/kPa.

Dependencies are inferred from the claim text.