Porous polytetrafluoroethylene film and process for preparation thereof

摘要

PCT No. PCT/JP94/00080 Sec. 371 Date Nov. 22, 1994 Sec. 102(e) Date Nov. 22, 1994 PCT Filed Jan. 21, 1994 PCT Pub. No. WO94/16802 PCT Pub. Date Aug. 4, 1994A porous polytetrafluoroethylene film which is excellent as an air filter used in clean rooms in a semiconductor industry, which is suitable for the collection of microparticles floating in a gas such as air and exhibits a low pressure drop is provided. The film has an average pore size of from 0.2 to 0.4 mu m and exhibits a pressure drop of from 20 to 50 mmH2O when air is passed through it at a flow rate of 5.3 cm/sec. The film is prepared by stretching biaxially unsintered polytetrafluoroethylene at specific temperatures.