Polytetrafluoroethylene porous film and process for preparing the same
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United States of America Patent
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Oct 25, 1994
Issued Date -
N/A
app pub date -
Jul 6, 1992
filing date -
Jul 4, 1991
priority date (Note) -
Expired
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Abstract
A polytetrafluoroethylene (PTFE) porous film is formed from a PTFE resin molding powder obtained by suspension polymerization. The film has a porosity of 40 to 80% and a removal ratio of uniform particles having a diameter of 0.2 .mu.m less than 99%, or has a porosity of 40 to 80% and a bubble point of not less than 3 kg/cm.sup.2. This PTFE porous film is obtained by a process of compression-molding a PTFE resin molding powder to prepare a preform, sintering the preform at a temperature not lower than the melting point of the unsintered PTFE, processing the preform into films, then laminating at least two of the obtained films, fusing the films to unite them, and subjecting the obtained film to uniaxial or biaxial stretching at a temperature not higher than a melting point of the sintered PTFE. If desired, the finally obtained film may be subjected to heat setting. In the PTFE porous film of the invention, pores are nearly round and the diameters of the pores are almost uniform. Further, the porous film of the invention has a high porosity and is excellent in mechanical strength, so that the film is free from the pinholes even when the thickness of the film is small. The PTFE porous film can be efficiently prepared by sequential biaxial stretching or the like, without breakage.
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