Claims
- 1. A method to form an electrolyte permeable diaphragm for an electrolytic cell for producing chlorine and an alkali metal hydroxide comprising:
- (a) combining about 1 to about 50 parts by weight polytetrafluoroethylene powder having an average particle size of about 100 to about 1,000 microns diameter with about 50 to about 98 parts by weight of a solid pore-forming powder having an average particle size of about 0.1 to about 100 microns diameter, and about 10 to about 1,000 parts by weight of a nonaqueous liquid capable of wetting the polytetrafluoroethylene and incapable of dissolving substantial amounts of the pore-forming powder;
- (b) mixing the combination with a shearing means sufficiently to reduce the average particle sizes of the polytetrafluoroethylene to leas than about 50 microns diameter;
- (c) removing a portion of the liquid from the mixture of step (b) until the mixture has a liquid to solid weight ratio of about 0.05 to about 1;
- (d) rolling the compressed mixture a plurality of times to form a sheet;
- (e) heating the sheet sufficiently to sinter the sheet material; and
- (f) removing at least a portion of the solid pore-forming powder from the sintered sheet by contacting the sheet with a liquid medium to produce a porous polytetrafluoroethylene sheet with a thickness of from about 5 to about 100 mils, an average pore size of from about 0.1 to about 100 microns, a gas permeability of from about 1 to about 100 seconds, a liquid permeability factor of from about 1 to about 60, and a tensile strength of from about 100 to about 1000 pounds per square inch.
- 2. The method of claim 1 wherein steps (a) and (b) are performed substantially simultaneously.
- 3. The method of claim 1 wherein the polytetrafluoroethylene powder and the pore-forming powder are combined in a weight ratio of about 1:2 to about 1:9.
- 4. The method of claims 1 or 3 wherein a water wettable filter powder with an average particle size of less than about 100 microns is combined in step (a) in an amount of about 5 to about 500 weight percent of the polytetrafluoroethylene.
- 5. The method of claim 4 wherein the filler powder is at least one material selected from the group consisting of carbon, silicon dioxide and titanium dioxide.
- 6. The method of claim 4 wherein dry water wettable filler and pore-forming powder are mixed together before combining with the nonaqueous liquid in step (a).
- 7. The method of claim 1 wherein the liquid in step (b) is an aliphatic hydrocarbon.
- 8. The method of claim 1 wherein the liquid is present in an amount of about 100 to about 400 parts by weight.
- 9. The method of claim 1 including the additional step of drying the sheet of step (f) at a temperature of up to about 85.degree. C.
- 10. The method of claim 1 wherein the sheet of step (f) is about 40 to about 80 mils thick.
- 11. The method of claim 1 wherein the sheet of step (f) is from about 60 to about 90 percent porous.
- 12. The method of claim 1 wherein the liquid permeability factor of the sheet of step (f) is about 5 to about 25.
- 13. The method of claim 1 wherein the thickness of the sheet of step (f) is about 40 to about 80 mils, the average pore size dimension is about 1 to about 20 microns, the gas permeability is from about 60 to about 90 seconds, the liquid permeability factor is from about 5 to about 25, the tensile strength is about 150 to about 700, said diaphragm is about 70 to about 80 percent porous, and about 85 to about 95 percent of the pores are of a size within two orders of magnitude from each other.
- 14. The method of claim 13 wherein the tensile strength of the sheet is about 250 to about 600 pounds per square inch.
- 15. The method of claim 1 including the additional step of compressing the mixture of step (c) at a pressure of about 10 to about 100 pounds per square inch gauge before rolling.
REFERENCE TO PRIOR APPLICATION
This application is a continuation-in-part of patent application Ser. No. 877,060, filed Feb. 13, 1978, now U.S. Pat. No. 4,224,130, which was a continuation of application Ser. No. 777,868, filed Mar. 15, 1977, now abandoned.
US Referenced Citations (10)
Foreign Referenced Citations (2)
Number |
Date |
Country |
725704 |
Jan 1966 |
CAX |
1081046 |
Aug 1967 |
GBX |
Continuations (1)
|
Number |
Date |
Country |
Parent |
777868 |
Mar 1977 |
|
Continuation in Parts (1)
|
Number |
Date |
Country |
Parent |
877060 |
Feb 1978 |
|