04248924 is referenced by 55 patents and cites 8 patents.

Porous film materials composed of polytetrafluoroethylene having an asymmetric structure are produced by stretching the film using a pair of revolving rolls which are heated to a temperature lower than the melting point of the film. Stretching is produced by revolving the two rolls at different speed which also tends to produce a compressive force in the thickness of the film. The rolls are heated to different temperatures to produce a temperature difference of preferably 50.degree. C. or more. The combination of the compressive force and the temperature gradient in the thickness of the film is believed to produce the asymmetric structure in the resulting porous film materials which are characterized by a fiber structure in the front surface which is different from that in the back surface.

Title
Asymmetric porous film materials and process for producing same
Application Number
5/830288
Publication Number
4248924
Application Date
September 2, 1977
Publication Date
February 3, 1981
Inventor
Koichi Okita
Osaka
JP
Agent
Sughrue Rothwell Mion Zinn and Macpeak
Assignee
Sumitomo Electric
JP
IPC
B29D 27/00
D01D 5/12
B01D 13/04
B32B 27/02
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