Patent ID: 8029635

Claim:
A method for forming a porous PTFE layer, comprising the steps of: (1) combining one or at least two unburned porous polytetrafluoro ethylene (PTFE) films and a plate shaped support body that can withstand a heating condition in the following process (2) by disposing the PTFE film on one face of the plate shaped support body and bending a peripheral section having a width of at least 1 cm in the PTFE film to the rear side of the support body; and (2) heating the matter resulted from the above process (1) at a temperature less than the melting point of the PTFE film; wherein the at least two unburned porous PTFE films are bonded to each other by using a binder resin in advance, and the heating treatment in the process (2) is carried out at a temperature in the range of the melting point of the used binder resin to 320° C. for the range of 10 to 60 minutes.