| 摘要 |
Provided is a method including: a step A of extruding a mixture containing a polytetrafluoroethylene (PTFE) fine powder having a standard specific gravity (SSG) of 2.19 or less and a liquid lubricant into a sheet using a flat die so as to obtain a PTFE sheet; a step B of rolling the PTFE sheet by passing the sheet between a pair of rolls in a longitudinal direction of the sheet; a step C of stretching the rolled PTFE sheet in a transverse direction of the sheet; a step D of removing the liquid lubricant from the PTFE sheet; and a step E of stretching the PTFE sheet, from which the liquid lubricant has been removed, both in the longitudinal direction of the sheet and in the transverse direction of the sheet, for example, at an area stretch ratio of 150 to 700, so as to make the sheet porous. According to this production method, it is possible to increase the PF value of the porous PTFE membrane. |
