Composite ultrafiltration membranes

• US 4,824,568 A
• Filed: 05/16/1986
• Issued: 04/25/1989
• Est. Priority Date: 05/16/1986
• Status: Expired due to Term

• Current Assignee: Millipore Investment Holdings, Ltd. (Merck & Co., Inc.)
• Original Assignee: Millipore Corporation (Merck & Co., Inc.)
• Inventors: Allegrezza, Anthony E. Jr., Burke, Edmund T.
• Primary Examiner(s): Spear, Frank
• Application Number:
  US06/864,074
• Time in Patent Office: 1,075 Days
• Field of Search: 210/490, 210/500.41, 210/500.42, 210/506, 427/244, 427/245, 427/246
• US Class Current: 210/490
• CPC Class Codes: B01D 69/12 Composite membranes; Ultra-thin membranes

Abstract

Composite ultrafiltration membranes are disclosed which are produced by forming an ultrafiltration membrane structure on a preformed microporous membrane.

Claims

1. In a method of forming a composite membrane suitable for ultrafiltration by casting a solution of polymer dissolved in a solvent onto a porous support and thereafter precipitating the polymer under conditions whereby an assymetric skinned membrane is formed on the porous support:

the improvement of employing a microporous membrane as the porous support and treating the micrporous membrane prior to casting the solution of polymer and solvent thereon with an agent which results in membrane pore structure upon casting of the solution of polymer dissolved in a solvent onto the microporous membrane support to provide the composite membrane with a porosimitry bubble point significantly increased over that of the same composite membrane formed without treatment of the microporous membrane with said agent.

2. The improvement of claim 1 wherein said agent is a liquid miscible with water.

3. The improvement of claim 2 wherein said agent comprises a glycol or glycerine.

4. The improvement of claim 3 wherein said glycol or glycerine is dissolved in an alcohol solution.

5. The improvement of claim 4 wherein said microporous membrane comprises a polyvinylidene difluoride microporous membrane.

6. The improvement of claim 5 wherein said polymer dissolved in a solvent comprises polyvinylidene difluoride.

7. A composite membrane suitable for ultrafiltration formed by the method of claim 6.

8. The improvement of claim 4 wherein said polymer dissolved in a solvent comprises polysulfone.

9. A composite membrane suitable for ultrafiltration formed by the method of claim 8.

10. A composite membrane suitable for ultrafiltration formed by the method of claim 1.

11. A method for forming a composite membrane suitable for ultrafiltration comprising pretreating a surface of a polyvinylidene difluoride microporous membrane by contacting said surface with a solution of glycerine in an alcohol solvent, drying said pretreated surface, casting a solution of polyvinylidene difluoride in a solvent upon the treated surface of the polyvinylidene difluoride microporous membrane and thereafter precipitating polyvinylidene difluoride from the casting solution under conditions sufficient to from an assymetric skinned polyvinylidene difluoride membrane on the treated surface of the microporous membrane and an intermediate membrane zone between the assymetric skinned membrane and microporous membrane, said intermediate membrane zone having a finer pore structure than the microporous membrane.

12. A membrane formed by the method of claim 11.

13. A composite integral membrane comprising a preformed microporous membrane having an average pore diameter of below about 0.65 micrometers and having an assymetric skinned membrane formed therein and an intermediate membrane zone having a pore structure finer than that of said microporous membrane, said integral membrane having a bubble point significantly higher than that of said preformed microporous membrane.

14. A composite integral membrane of claim 13 wherein said composite membrane is formed from polyvinylidene difluoride.

15. A composite integral membrane consisting essentially of a microporous membrane, an assymetric skinned membrane and an intermediate membrane zone of finer pore structure than the microporous membrane, said composite membrane having a porosimetry bubble point of greater than about 60 psi.

16. A method of producing a composite membrane, comprising

a. applying a solution of glycerine in a solvent to the surface of a preformed polyvinylidene difluoride microporous membrane to wet the surface of said preformed membrane;

b. drying the wet surface of the preformed microporous membrane to provide a surface thereof treated with glycerine;

c. dissolving polyvinylidene difluoride in a solvent therefor to form a solution of polyvinylidene difluoride;

d. applying the solution of polyvinylidene difluoride to the glycerine-treated surface of said preformed polyvinylidene difluoride microporous membrane;

e. precipitating polyvinylidene fluoride from said solution onto the glycerine treated surface of the preformed polyvinylidene difluoride microporous membrane under conditions whereby an assymetric skinned membrane of polyvinylidene difluoride is formed on the microporous membrane and an intermediate membrane zone having a pore structure finer than that of the microporous membrane is additionally formed to provide a composite polyvinylidene difluoride membrane having a porosimetry bubble point significantly increased over that of the preformed polyvinylidene difluoride microporous membrane.

17. A composite polyvinylidene difluoride membrane formed by the process of claim 16.