PTFE membrane

• US 20060157893A1
• Filed: 11/23/2005
• Published: 07/20/2006
• Est. Priority Date: 11/24/2004
• Status: Active Grant

• Current Assignee: Donaldson Company Incorporated
• Original Assignee: Donaldson Company Incorporated
• Inventors: Patel, Kirit
• Granted Patent: US 7,922,946 B2
• Time in Patent Office: Days
• US Class Current: 264/322
• CPC Class Codes: B01D 2323/08 Specific temperatures applied
• CPC Class Codes: B01D 2323/081 Heating
• CPC Class Codes: B01D 2323/10 Specific pressure applied
• CPC Class Codes: B01D 2325/20 Specific permeability or cut-off range
• CPC Class Codes: B01D 67/0027 by stretching
• CPC Class Codes: B01D 67/0083 Thermal after-treatment
• CPC Class Codes: B01D 67/0086 Mechanical after-treatment
• CPC Class Codes: B01D 69/02 characterised by their properties
• CPC Class Codes: B01D 71/36 Polytetrafluoroethene
• CPC Class Codes: B29C 2071/027 Tempering, i.e. heating an object to a high temperature and quenching it
• CPC Class Codes: B29C 43/22 of articles of indefinite length
• CPC Class Codes: B29C 43/46 Rollers
• CPC Class Codes: B29C 71/02 Thermal after-treatment B29C71/0063 and B29C71/0072 take precedence
• CPC Class Codes: B29K 2027/18 PTFE, i.e. polytetrafluorethene , e.g. ePTFE, i.e. expanded polytetrafluorethene
• CPC Class Codes: B29L 2031/755 Membranes, diaphragms
• CPC Class Codes: C08J 2327/18 Homopolymers or copolymers of tetrafluoroethylene
• CPC Class Codes: C08J 5/2237 containing fluorine

Abstract

A method for improving the dimensional stability of PTFE membranes by the application of elevated temperature and elevated pressure to a PTFE membrane. The process reduces and/or eliminates the relaxation stress normally associated with PTFE membranes made using previously existing methods.

Claims

1. A method of affecting the dimensional stability of a PTFE membrane, comprising:

a) subjecting the PTFE membrane to an elevated temperature above the melting point of the PTFE membrane for a given exposure time; and

b) subjecting the PTFE membrane to an elevated pressure for a given exposure time,

wherein the PTFE membrane is simultaneously subjected to the elevated temperatures and elevated pressures, and wherein the effects on the dimensional stability are dictated at least in part by the combination of the temperature, pressure and exposure time.

2. The method of affecting the dimensional stability of a PTFE membrane of claim 1, wherein the membrane is elevated to a temperature above about 327°

C.

3. The method of affecting the dimensional stability of a PTFE membrane of claim 1, wherein the membrane is elevated to a temperature above about 340°

C.

4. The method of affecting the dimensional stability of a PTFE membrane of claim 1, wherein the membrane is elevated to a temperature above about 325°

C. and below about 400°

C.

5. The method of affecting the dimensional stability of a PTFE membrane of claim 1, wherein the membrane is elevated to a temperature above about 350°

C. and below about 360°

C.

6. The method of affecting the dimensional stability of a PTFE membrane of claim 1, wherein the membrane is elevated to a temperature above about 360°

C. and below about 380°

C.

7. The method of affecting the dimensional stability of a PTFE membrane of claim 1, wherein the membrane is elevated to a temperature above about 325°

C. and below about 400°

C.

8. The method of affecting the dimensional stability of a PTFE membrane of claim 1, wherein the membrane is heated to an elevated temperature using a roller having a temperature in excess of about 340°

C.

9. The method of affecting the dimensional stability of a PTFE membrane of claim 1, wherein the membrane is heated to an elevated temperature using a roller having a temperature in excess of about 360°

C.

10. The method of affecting the dimensional stability of a PTFE membrane of claim 1, wherein the membrane is heated to an elevated temperature above about 327°

C. while simultaneously being compressed under a pressure of at least 1 pound per square inch.

11. The method of affecting the dimensional stability of a PTFE membrane of claim 1, wherein the membrane is heated to an elevated temperature above about 327°

C. while simultaneously being compressed under a pressure of at least 5 pounds per square inch.

12. The method of affecting the dimensional stability of a PTFE membrane of claim 1, wherein the membrane is heated to an elevated temperature above about 327°

C. while simultaneously being compressed under a pressure of at least 20 pounds per square inch.

13. The method of affecting the dimensional stability of a PTFE membrane of claim 1, wherein the given exposure time is from 0.1 to 1 second.

14. The method of affecting the dimensional stability of a PTFE membrane of claim 1, wherein the given exposure time is from 0.05 to 0.5 seconds.

15. A PTFE membrane produced using the process of claim 1.

16. The PTFE membrane of claim 15, wherein the PTFE membrane has air permeability of at least 4 liters per minute per square centimeter at 0.7 bar.

17. The PTFE membrane of claim 15, wherein the PTFE membrane has a Coulter Porometer of at least 0.25 MFP.

18. The PTFE membrane of claim 15, wherein the PTFE membrane has shrinkage of less than 10 percent in the machine direction.

19. The PTFE membrane of claim 15, wherein the PTFE membrane has shrinkage of less than 5 percent in the machine direction.

20. A method of processing a PTFE membrane, the comprising the steps of:

a) providing an oriented PTFE membrane that has been at least unilaterally oriented;

b) simultaneously subjecting the PTFE membrane to a temperature of at least 340°

C. for a period of less than I second and a pressure of at least 1 pound per square inch.