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AssigneeNippon Valqua Kogyo Kabushiki Kaisha
InventorsKawahigashi Nobuo, Hashida Shigesou, Kojima Yasunobu
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A process for the production of PTFE porous membranes is provided wherein a PTFE preform is prepared by compression molding a PTFE molding powder of 1-90 .mu.m obtained by suspension polymerization of tetrafluoroethylene, the preform is sintered at a temperature above 327.degree. C., followed by skiving the heated preform into a film form. The thus-obtained film is heat treated at a temperature above 327.degree. C., the heat treated film is slowly cooled at a cooling rate of less than 70.degree. C./hr so as to adjust the crystallinity of PTFE in the sintered film to 60-75% and the film is stretched either uniaxially or biaxially to 1.3 to 6.5 times while heating at a temperature of 100.degree.-320.degree. C.
A process for the production of polytetrafluoroethylene porous membranes, which comprises preparing a polytetrafluoroethylene preform by compression molding a polytetrafluoroethylene resin molding powder having an average particle diameter of 1-900 .mu.m obtained by suspension polymerization of tetrafluoroethylene, heating the preform at a temperature above 327.degree. C. followed by skiving the heated preform into a film form, heating the obtained film at a temperature above 327.degree. C., slowly cooling the heated film at a cooling rate of less than 70.degree. C./hr so as to adjust the crystallinity of polytetrafluoroethylene in the heated film to 60-75%, and stretching the heated film either uniaxially or biaxially to 1.3 to 6.5 times while heating at a temperature of 100.degree.-320.degree. C.
Dependencies are inferred from the claim text.