EXPANDED POROUS POLYTETRAFLUOROETHYLENE FILM HAVING ELASTIC RECOVERY PROPERTY IN THICKNESS-WISE DIRECTION OF THE FILM, PRODUCTION PROCESS THEREOF, AND USE OF THE POROUS FILM

摘要

An expanded porous polytetrafluoroethylene film having residual strain of at most 11.0% as measured after a load required to indent a rod, which is in a columnar form that its outer diameter is at least 2 mm and at least 1.9 times as much as the thickness of the film, and has a smooth plane perpendicular to its axis at a free end surface thereof and a modulus of longitudinal elasticity of at least 1.0 × 10 4 kgf/mm 2 , up to 20% of the film thickness at a strain rate of 100%/min from the free end surface is applied repeatedly 20 times, and a production process of the porous film, in which a step of compressing an expanded porous polytetrafluoroethylene film having a high draw ratio is provided.