Patent ID: 7807221
Filing Date: 2010-10-05
Classification: B01D

Abstract:
1. A method for producing a composite porous membrane comprising the steps of: (a) coating a first membrane-forming solution and then a second membrane-forming solution on a braid using a ring nozzle, wherein the ring nozzle comprises a braid passage through which the braid passes, a first discharge port formed around the entirety of the wall of the braid passage in a circumferential direction, and a second discharge port formed at the exit side and at the peripheral of the braid passage, concentrically with the braid passage, and wherein, after supplying the first membrane-forming solution from the first discharge port to thereby coat the braid, the second membrane-forming solution, which has a greater concentration than the first membrane-forming solution, is supplied from the second discharge port to thereby form a braid coated with the first and second membrane solutions; (b) solidifying the coated membrane-forming solutions in a solidification solution to produce a first porous layer; (c) supplying a solution from the first discharge port, to thereby coat the surface of the first porous layer, which solution does not dissolve the membrane material; (d) coating the second membrane-forming solution from the second discharge port on the surface of the layer from (c) using the ring nozzle through the second discharge port; (e) solidifying the coated second membrane-forming solution from (d) in a solidification solution to produce a second porous layer.