Ultrafiltration membrane of polyamide
Abstract
Abstract A membrane is disclosed of polyamide, a copolyamide or a mixture of polyamides, suitable for ultrafiltration and composed of an ultrafiltration skin and a backing layer. The pore size in the backing layer increases with distance from the ultrafiltration skin. The membrane is prepared by dissolving a polyamide in at least 75% formic acid, applying a casting solution, containing about 12-22% by weight polyamide and about 1-7% by weight polyethylene glycol in formic acid which has been brought to a temperature of below about 18 DEG C., as a thin layer onto a carrier foil resistant to the components of the solution, introducing the casting solution on the carrier foil into a precipitation and washing bath, withdrawing the casting solution as a coagulated and washed membrane from the carrier foil, stretching in at least one direction and subsequently drying this coagulated and washed membrane.
Inventors
- 👤 Erich Schindler
- 👤 Franz Maier
Bibliographic Details
Claims Analysis
Total Claims: 4References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1989-06-16 | 1989-12-16 | 1990-06-17 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1993-06-16 | 1993-12-16 | 1994-06-17 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1997-06-16 | 1997-12-16 | 1998-06-17 | $7700.00 | Window Closed / Lapsed |