Claims
- 1. A process for producing asymmetric porous film materials which comprises
- molding a polytetrafluoroethylene containing a liquid lubricating agent by a paste method to form a film,
- removing the liquid lubricating agent, and
- generating a temperature difference simultaneously with a compressive force in the thickness direction of the film during stretching the film at a temperature lower than the sintering temperature of the polytetrafluoroethylene using rolls
- which have a different revolving ratio and
- which have a temperature difference between each other,
- whereby tension is caused by the stretching direction of the film while a compressive force corresponding to the tension is caused in the thickness direction of the film.
- 2. A process for producing asymmetric porous film materials as set forth in claim 1, wherein the step of stretching is carried out at least twice using rolls having a different revolving ratio, and at least one stretching step is carried out with the rolls having a temperature difference between each other.
- 3. A process for producing asymmetric porous film materials as set forth in claim 1, wherein the step of stretching is carried out using rolls having a different revolving ratio which have a temperature difference of at least 50.degree. C.
- 4. A process for producing asymmetric porous film materials as set forth in claim 1, wherein the temperature of the low speed roll in the rolls having a different revolving ratio is 230.degree. C. or less and the temperature of the high-speed roll is 250.degree. C. or more but lower than the sintering temperature of the polytetrafluoroethylene.
Priority Claims (1)
Number |
Date |
Country |
Kind |
51-105912 |
Sep 1976 |
JPX |
|
Parent Case Info
This is a division of application Ser. No. 830,288, filed Sept. 2, 1977.
US Referenced Citations (6)
Divisions (1)
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Number |
Date |
Country |
Parent |
830288 |
Sep 1977 |
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