Porous polytetrafluoroethylene membrane, production method thereof, sheet-shaped rolled tetrafluoroethylene molded article and air filter medium

摘要

The fine polytetrafluoroethylene powder is mixed with a liquid lubricant, and the mixture is formed into an amorphous sheet by one or more extrusion and rolling methods. The liquid lubricant is removed from the sheet by one or more heating and extrusion methods. The sheet-like molded article was stretched in the longitudinal direction to provide a crystal melting curve having an endothermic peak in a temperature range of 345 5C when analyzed by a differential scanning calorimeter, and a sheet type polytetrafluoroethylene sheet having a crystallinity of 0.1 to 0.85 and a specific gravity of 1.4 or less An ethylene molded article is produced. Subsequently, the molded product is stretched in the transverse direction to produce a porous polytetrafluoroethylene (PTFE) film. The method of the present invention is effective for producing a useful porous PTFE membrane having a high collection efficiency, a low pressure loss, and a reduced leakage of coarse particles with excellent regeneration.