METHOD FOR PRODUCING POROUS POLYTETRAFLUOROETHYLENE FILM AND POROUS POLYTETRAFLUOROETHYLENE FILM

摘要

Provided is a method for producing a porous polytetrafluoroethylene film having good chemical resistance, good heat resistance, a high porosity, and good dimensional stability. The method for producing a porous polytetrafluoroethylene film includes a stretching step of stretching a sheet-like molded body composed of a fluororesin containing polytetrafluoroethylene as a main component in a longitudinal direction and/or a lateral direction at a temperature lower than a melting point of the fluororesin to make a porous fluororesin film, and, after the stretching step, an annealing step of holding the porous fluororesin film in a shape-fixed state, and maintaining the porous fluororesin film at a temperature lower than the melting point of the fluororesin but not lower than a temperature 30°C lower than the melting point for 1 to 20 hours.