Separating film, separating film element, separating film module, sewage and waste water treatment device, and separating film manufacturing method

Abstract

A separation membrane has a porous substrate and a porous resin layer on at least one surface of the porous substrate and the porous resin layer contains a resin. Part of the resin permeates through the porous substrate to form a composite layer. At least one of the following relationships (1) and (2) is satisfied: (1) the porous resin layer has an average pore size in the range of 0.01 to 0.2 μm and a standard variation of the pore size of 0.1 μm or less at the surface, and (2) the porous resin layer has macrovoids having short diameters of 0.05×A or more wherein A represents the thickness of the porous substrate, and the rejection of micro particles having an average particle size of 0.9 μm is at least 90%. This separation membrane can be readily produced by a method for making a separation membrane according to the present invention.

What is claimed is:  
     
         1 . A separation membrane comprising a porous substrate and a porous resin layer on at least one surface of the porous substrate, where the porous resin layer comprises a resin, a part of the resin permeating into the porous substrate to form a composite layer with the porous substrate, and at least one of the following relationships (1) and (2) is satisfied: 
 (1) the porous resin layer has an average pore size in the range of 0.01 to 0.2 μm and a standard variation of the pore size of 0.1 μm or less at the surface; and    (2) the porous resin layer has macrovoids having short diameters of 0.05×A or more, wherein A represents the thickness of the porous substrate, and the rejection of micro particles having an average particle size of 0.9 μm is at least 90%.    
     
     
         2 . The separation membrane according to  claim 1 , wherein 
 B≧0.2×A, and    C/B≧0.1    wherein A represents the thickness of the porous substrate, B represents the thickness of the porous resin layer and C represents the thickness of the composite layer.    
     
     
         3 . The separation membrane according to  claim 1 , wherein the porous substrate has a density of 0.7 g/cm 3  or less.  
     
     
         4 . The separation membrane according to  claim 1 , wherein the porous substrate comprises an organic fiber.  
     
     
         5 . The separation membrane according to  claim 1 , wherein the porous substrate comprises a nonwoven fabric.  
     
     
         6 . The separation membrane according to  claim 1 , wherein the resin comprises polyvinylidene fluoride as the major component.  
     
     
         7 . A separation membrane comprising a porous substrate and a porous resin layer on at least one surface of the porous substrate, the porous substrate comprising an organic fiber and having a density of 0.7 g/cm 3  or less, the porous resin layer comprising a resin, part of the resin permeating into the porous substrate to form a composite layer with the porous substrate, wherein 
 B≧0.2×A, and    C/B≧0.1    wherein A represents the thickness of the porous substrate, B represents the thickness of the porous resin layer, and C represents the thickness of the composite layer, and wherein the porous resin layer has macrovoids having short diameters of 0.05×A or more, and the rejection of micro particles having an average particle size of 0.9 μm is at least 90%.    
     
     
         8 . A separation membrane comprising a porous substrate and a porous resin layer on at least one surface of the porous substrate, the porous resin layer comprising a resin and permeating into part of the porous substrate to form a composite layer with the porous substrate, wherein 
 B≧0.2×A, and    C/B≧0.1    wherein A represents the thickness of the porous substrate, B represents the thickness of the porous resin layer and C represents the thickness of the composite layer, and wherein the porous resin layer has an average pore size in the range of 0.01 to 0.2 μm and a standard variation of the pore size of 0.1 μm or less at the surface.    
     
     
         9 . The separation membrane according to  claim 1 , wherein the porous substrate has the porous resin layers on two surfaces, and 
 2d A ≦d C      2d B ≦d C      wherein d A  represents the average pore size at the surface of one of the porous resin layers, d B  represents the average pore size at the surface of the other porous resin layer, and d C  represents the average pore size in the central cross-section of the separation membrane in the thickness direction.    
     
     
         10 . A separation membrane element comprising a supporting plate and the separation membrane according to  claim 1  on at least one face of the supporting plate.  
     
     
         11 . The separation membrane element according to  claim 10  used in sewage separation.  
     
     
         12 . A separation membrane element comprising a separation membrane comprising a porous substrate and a porous resin layer on at least one surface of the porous substrate, the porous resin layer comprising a resin, part of the resin permeating into the porous substrate to form a composite layer with the porous substrate, wherein the porous resin layer has an average pore size in the range of 0.01 to 0.2 μm and a standard variation of the pore size of 0.1 μm or less at the surface.  
     
     
         13 . The separation membrane element according to  claim 12  used in sewage separation.  
     
     
         14 . A separation membrane module comprising a plurality of the separation membrane elements according to  claim 10  and a housing containing the separation membrane elements, the separation membrane elements being arranged substantially parallel to each other so as to form spaces between the adjacent separation membranes.  
     
     
         15 . A separation membrane module comprising a plurality of separation membrane elements and a housing containing the separation membrane elements, each separation membrane element comprising a separation membrane comprising a porous substrate and a porous resin layer on at least one surface of the porous substrate, the porous resin layer comprising a resin, part of the resin permeating into the porous substrate to form a composite layer with the porous substrate, wherein the porous resin layer has an average pore size in the range of 0.01 to 0.2 μm and a standard variation of the pore size of 0.1 μm or less at the surface.  
     
     
         16 . A sewage treatment apparatus comprising the separation membrane module according to  claim 14 , the separation membrane module being immersible into sewage to be treated in use.  
     
     
         17 . A sewage treatment apparatus comprising a separation membrane module comprising a plurality of separation membrane elements and a housing containing the separation membrane elements, each separation membrane element comprising a separation membrane comprising a porous substrate and a porous resin layer on at least one surface of the porous substrate, the porous resin layer comprising a resin, part of the resin permeating into the porous substrate to form a composite layer, wherein the porous resin layer has an average pore size in the range of 0.01 to 0.2 μm and a standard variation of the pore size of 0.1 μm or less at the surface, the separation membrane module being immersible into sewage to be treated in use.  
     
     
         18 . A method for treating sewage, comprising filtering the sewage with the separation membrane according to  claim 1 .  
     
     
         19 . A method for making a separation membrane comprising the steps of: 
 applying a solvent solution containing a resin, a pore-forming agent, and a solvent onto at least one surface of a porous substrate having a density of 0.7 g/cm 3  or less to form a coating film and to impregnate the porous substrate with the solvent; and    immersing the porous substrate into a coagulation bath containing a non-solvent to coagulate the resin and to form a porous resin layer on the surface of the porous substrate.    
     
     
         20 . The method for making the separation membrane according to  claim 19 , wherein the solvent solution comprises 5 to 30 weight percent of the resin, 0.1 to 15 weight percent of the pore-forming agent, and 40 to 94.9 weight percent of the solvent, and the coagulation bath contains at least 60 weight percent of the non-solvent.  
     
     
         21 . The method for making the separation membrane according to  claim 19 , wherein the solvent solution contains a non-solvent.  
     
     
         22 . The method for making the separation membrane according to  claim 21 , wherein the solvent solution comprises 5 to 30 weight percent of the resin, 0.1 to 15 weight percent of the pore-forming agent, 40 to 94.8 weight percent of the solvent, and 0.1 to 20 weight percent of the non-solvent, and the coagulation bath contains at least 80 weight percent of the non-solvent.  
     
     
         23 . The method for making the separation membrane according to  claim 19 , wherein the coating films of the solvent solution are formed on two surfaces of the porous substrate.  
     
     
         24 . The method for making the separation membrane according to  claim 19 , wherein the temperature of the solvent solution is in the range of 15° C. to 120° C. and the temperature of the coagulation bath is in the range of 15° C. to 80° C.  
     
     
         25 . The method for making the separation membrane according to  claim 19 , wherein the porous substrate comprises a nonwoven fabric.  
     
     
         26 . The method for making the separation membrane according to  claim 19 , wherein the resin comprises polyvinylidene fluoride as the major component.  
     
     
         27 . The method for making the separation membrane according to  claim 19 , wherein the resin comprises polyvinylidene fluoride as the major component, and the pore-forming agent comprises a polymer comprising polyethylene glycol having a weight average molecular weight of at least 10,000 as the major component.