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AssigneeNippon Valqua Kogyo Kabushiki Kaisha
InventorsNobuo Kawahigashi, Shigesou Hashida, Yasunobu Kojima
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A process for producing a polytetrafluoroethylene porous film having excellent mechanical strength wherein pores have a substantially perfect circle and it is possible to uniformly control its pore size to a predetermined size. The porous film is obtained by compression molding polytetrafluoroethylene resin molding powders obtained by a suspension polymerization method to prepare a preform, sintering said preform at a temperature of at least 327.degree. C., forming it into a film, resintering the film at a temperature of at least 327.degree. C., quenching it at a cooling rate of at least 70.degree. C. per hour to reduce the crystallinity of polytetrafluoroethylene to 55% or below, and thereafter stretching said film at a stretch ratio of from 1.3 to 6.5 while heating it to a temperature of from 100.degree. to 320.degree. C.
A process for producing a polytetrafluoroethylene porous film which comprises the steps of compression molding polytetrafluoroethylene resin molding powders of average particle diameter of from 1 to 900 micrometers obtained by a suspension polymerization method to prepare a polytetrafluoroethylene preform, sintering said preform at a temperature of at least 327.degree. C., forming it into a film, then sintering the resulting film at a temperature of at least 327.degree. C., thereafter quenching it at a cooling rate of at least 70.degree. C. per hour to reduce the crystallinity of polytetrafluoroethylene to 55% or below, and then uniaxially or biaxially stretching said film at a stretch ratio of from 1.3 to 6.5 while heating it to a temperature of from 100.degree. to 320.degree. C.
Dependencies are inferred from the claim text.