POROUS STRETCHED POLYTETRAFLUOROETHYLENE FILM HAVING ELASTICRECOVERY IN THICKNESS DIRECTION, PROCESS FOR PRODUCING THE SAME, AND USE OFTHE POROUS FILM

摘要

A porous stretched polytetrafluoroethylene film which has a residual strain of 11.0% or lower as measured after a load necessary for pushing the front end of a rod into the porous film in the thickness direction at a strain rate of 10 0 %/min to a depth which is 20% of the film thickness is repeatedly imposed 20 times, the rod being a cylindrical rod which has an outer diameter of 2 mm o r larger and at least 1.9 times the film thickness, has a smooth and flat fron t- end surface perpendicular to the axis, and has a modulus in tension of 1.0.times.104 kgf/mm2 or higher. Also provided is a process for producing th e porous film, which includes the step of compressing a porous stretched polytetrafluoroethylene film having a high stretch ratio.