Process for producing a porous track membrane

• US 20050252883A1
• Filed: 07/26/2005
• Published: 11/17/2005
• Est. Priority Date: 05/29/2003
• Status: Active Grant

• Current Assignee: Dressel Pte Limited
• Original Assignee: Dressel Pte Limited
• Inventors: Desyatov, Andrey Viktorovich, Egorov, Alexei Valerievich
• Granted Patent: US 7,597,815 B2
• Time in Patent Office: Days
• US Class Current: 216/56
• CPC Class Codes: B01D 2323/42 Details of membrane preparation apparatus
• CPC Class Codes: B01D 67/0027 by stretching
• CPC Class Codes: B01D 67/0032 by elimination of segments of the precursor, e.g. nucleation-track membranes, lithography or laser methods
• CPC Class Codes: B01D 71/34 Polyvinylidene fluoride

Abstract

Porous track membranes are produced by exposing a polymeric film to a bombardment of heavy ions to provide the film with a track density, and etching pores into the resulting tracked film with an etching solution to provide the film with a density of the pores corresponding to the track density under conditions to maintain turbulent flow. An alkaline etching solution is used that contains salts of alkali metals in sufficient concentration to increase the boiling point of the resulting alkali-metal-containing solution to temperatures in excess of about 100 up to about 150° C.

Claims

1. A process for producing a porous track membrane useful in the separation of materials from a fluid comprising the steps of:

a) exposing a polymeric film to a bombardment of heavy ions to provide the film with a track density; and

b) etching pores into the resulting tracked film with an etching solution to provide the film with a density of the pores corresponding to the track density under conditions to maintain turbulent flow.

2. The process of claim 1, wherein said heavy ions are selected from the group of ions consisting of krypton, argon, xenon, bismuth, and combinations thereof.

3. The process of claim 1, wherein said track density is in a range of about 10⁷ cm⁻

2 to about 10⁹ cm<sup>−

2</sup>.

4. The process of claim 1, wherein the diameter of said pores is in a range of about 0.01 to about 1 μ

m.

5. The process of claim 1, wherein said etching solution is an alkaline solution.

6. The process of claim 5, wherein said polymeric film is a fluoropolymeric film.

7. The process of claim 6, wherein said fluoropolymeric film is polyvinylidene fluoride.

8. The process of claim 7, wherein said alkaline solution is an alkaline solution of potassium permanganate

9. The process of claim 8, wherein said alkaline solution also contains salts of alkali metals in sufficient concentration to increase the boiling point of the resulting alkali-metal-containing solution to temperatures in a range of about 100 to about 150°

C.

10. The process of claim 9, wherein said etching is carried out at temperatures greater than 100°

C.

11. The process of claim 10, wherein said etching solution is passed in contact with said tracked film at a flow rate to produce a Reynolds Number from about 100 to about 500.

12. The process of claim 11, wherein said etching is carried out for a period in a range of about 1 to about 24 hours.

13. The process of claim 12, wherein at least the temperature, flow rate and time are controlled so that the etching step takes place with overheating of the etching solution of not more than 10°

C.

14. The process of claim 13, wherein said alkali metal salt is sodium chloride.

15. A process for producing a porous track membrane useful in the separation of materials from a fluid comprising the steps of:

a) exposing a fluoropolymeric film to a bombardment of heavy ions to provide the film with a track density;

b) cutting the resulting tracked film into a plurality of separate sections; and

c) etching the sections of tracked film with an etching solution to provide the sections of film with a density of pores corresponding to the track density under conditions to maintain turbulent flow.

16. The process of claim 15, wherein said heavy ions are selected from the group of ions consisting of krypton, argon, xenon, bismuth, and combinations thereof.

17. The process of claim 16, wherein said track density is in a range of about 10⁷ cm⁻

2 to about 10⁹ cm<sup>−

2</sup>.

18. The process of claim 17, wherein the diameter of said pores is in a range of about 0.01 to about 1 μ

m.

19. The process of claim 18, wherein said etching solution is in an alkaline solution.

20. The process of claim 19, wherein said fluoropolymeric film is polyvinylidene fluoride.

21. The process of claim 20, wherein said alkaline solution is an alkaline solution of potassium permanganate

22. The process of claim 21, wherein said alkaline solution also contains salts of alkali metals in sufficient concentration to increase the boiling point of the resulting alkali-metal-containing solution to temperatures in a range of about 100 to about 150°

C.

23. The process of claim 22, wherein said etching is carried out at temperatures greater than 100°

C.

24. The process of claim 23, wherein said etching solution is passed in contact with said tracked film at a flow rate to produce a Reynolds Number from about 100 to about 500.

25. The process of claim 24, wherein said etching is carried out for a period in a range of about 1 to about 24 hours.

26. The process of claim 25, wherein said conditions of temperature, flow rate and time are controlled so that the etching step takes place with overheating of the etching solution of not more than 1°

C.

27. The process of claim 26, wherein said alkali metal salt is sodium chloride.

28. The process of claim 15, wherein the section of cut tracked film is placed within a cassette to carry out step (c) by fixing one ending of the film on one of a plurality of fixed supports, extending the free end of the film around the remainder of the fixed supports, fixing the free end to a turning support, and turning the turning support to provide a preliminary stretching of the film before etching.

29. The process of claim 28, wherein the cassette is placed in the etching solution.

39. The process of claim 23, wherein said etching solution is passed in contact with said tracked film at a flow rate to produce a Reynolds Number from about 100 to about 500.

40. The process of claim 24, wherein said etching is carried out for a period in a range of about 1 to about 24 hours.

41. The process of claim 25, wherein said conditions of temperature, flow rate and time are controlled so that the etching step takes place with overheating of the etching solution of not more than 1°

C.

42. The process of claim 26, wherein said alkali metal salt is sodium chloride.

30. A process for producing a porous track membrane useful in the separation of materials from a fluid comprising the steps of:

a) exposing a continuous roll of polymeric film to a bombardment of heavy ions to provide the film with a track density; and

a) etching the continuous roll of tracked film as the roll passes through an etching solution to provide the sections of film with a density of pores corresponding to the track density under conditions to maintain turbulent flow.

31. The process of claim 30, wherein said heavy ions are selected from the group of ions consisting of krypton, argon, xenon, bismuth, and combinations thereof.

32. The process of claim 31, wherein said track density is in a range of about 10⁷ cm⁻

2 to about 10⁹ cm<sup>−

2</sup>.

33. The process of claim 32, wherein the diameter of said pores is in a range of about 0.01 to about 1 μ

m.

34. The process of claim 33, wherein said etching solution is in an alkaline solution.

35. The process of claim 34, wherein said fluoropolymeric film is polyvinylidene fluoride.

36. The process of claim 35, wherein said alkaline solution is an alkaline solution of potassium permanganate

37. The process of claim 36, wherein said alkaline solution also contains salts of alkali metals in sufficient concentration to increase the boiling point of the resulting alkali-metal-containing solution to temperatures in a range of about 100 to about 150°

C.

38. The process of claim 37, wherein said etching is carried out at temperatures greater than 100°

C.