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AssigneeDaikin Industries, Ltd.
InventorsOsamu Tanaka, Toshio Kusumi, Jun Asano, Katsutoshi Yamamoto, Osamu Inoue, Shinichi Chaen, Nobuki Uraoka, Shinji Tamaru
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A 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 mmH.sub.2 O 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.
A porous polytetrafluoroethylene film which is prepared by stretching biaxially an unsintered PTFE has an average pore size of from 0.2 to 0.4 .mu.m and exhibits a pressure drop of from 20 to 50 mmH.sub.2 O when air is passed through the film at a flow rate of 5.3 cm/sec.
A process for preparing a porous polytetrafluoroethylene film comprising the steps of stretching lengthwise an unsintered polytetrafluoroethylene tape, which is obtained by paste extruding a polytetrafluoroethylene fine powder and then rolling it, at a temperature of from 250.degree. to 320.degree. C. and subsequently stretching crosswise said lengthwise stretched unsintered polytetrafluoroethylene at a temperature of from 100.degree. to 200.degree. C. to produce a porous polytetrafluoroethylene film having an average pore size of from 0.2 to 0.4 .mu.m.
A porous polytetrafuloroethylene film which is prepared by stretching an unsintered polytetrafuloroethylene tape lengthwise at a temperature between 250.degree. to 350.degree. C.;
Dependencies are inferred from the claim text.