POROUS STRETCHED POLYTETRAFLUOROETHYLENE FILM HAVING ELASTIC RECOVERY IN THICKNESS DIRECTION, PROCESS FOR PRODUCING THE SAME, AND USE OF THE 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 100 %/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 or larger and at least 1.9 times the film thickness, has a smooth and flat front-end surface perpendicular to the axis, and has a modulus in tension of 1.0x10<4> kgf/mm<2> or higher. Also provided is a process for producing the porous film, which includes the step of compressing a porous stretched polytetrafluoroethylene film having a high stretch ratio.