Hollow fiber membrane and method of producing the same

Abstract

A method of producing a hollow fiber membrane includes discharging a polyvinylidene fluoride solution comprising a polyvinylidene fluoride resin and a poor solvent at a temperature above a phase separation temperature into a cooling bath at a temperature below the phase separation temperature to coagulate the polyvinylidene fluoride resin. The hollow fiber membrane comprises a polyvinylidene fluoride resin having spherical structures that have an average diameter in the range of 0.3 to 30 μm.

What is claimed is:  
     
         1 . A method of producing a hollow fiber membrane comprising: 
 discharging a polyvinylidene fluoride solution comprising a polyvinylidene fluoride resin and a poor solvent at a temperature above a phase separation temperature into a cooling bath at a temperature below the phase separation temperature to coagulate the polyvinylidene fluoride resin.    
     
     
         2 . The method according to  claim 1 , wherein the crystallization temperature of the polyvinylidene fluoride solution is in the range of 40° C. to 120° C., the average cooling rate of the polyvinylidene fluoride solution when the temperature of the polyvinylidene fluoride solution reaches the crystallization temperature during cooling is in the range of 2×10 3 ° C./min to 10 6 ° C./min, and the temperature Ts of a spinneret for discharging the polyvinylidene fluoride solution into the cooling bath and the crystallization temperature Tc satisfy the relationship Tc≦Ts≦Tc+90.  
     
     
         3 . The method according to  claim 1 , wherein the polyvinylidene fluoride solution contains at least 20 to 60 percent by weight of the polyvinylidene fluoride resin.  
     
     
         4 . The method according to  claim 1 , wherein the polyvinylidene fluoride solution has a phase separation temperature in the range of 80° C. to 220° C.  
     
     
         5 . The method according to  claim 1 , wherein the cooling bath contains 60 to 100 percent by weight of a poor solvent.  
     
     
         6 . The method according to  claim 1 , wherein the hollow section of the hollow fiber membrane is formed by using a hollow section-forming liquid containing 60 to 100 percent by weight of a poor solvent.  
     
     
         7 . The method according to  claim 1 , wherein the coagulated polyvinylidene fluoride resin is drawn to 1.1 to 5 times at a temperature in the range of 50° C. to 140° C.  
     
     
         8 . A hollow fiber membrane comprising a polyvinylidene fluoride resin having spherical structures that have an average diameter in the range of 0.3 to 30 μm.  
     
     
         9 . The hollow fiber membrane according to  claim 8 , having spherical structures at a density in the range of 10 3 /mm 2  to 10 8 /mm 2  in the interior.  
     
     
         10 . The hollow fiber membrane according to  claim 8 , having micropores with11 an average pore size in the range of 0.01 to 20 μm in the outer surface.  
     
     
         11 . The hollow fiber membrane according to  claim 8 , having a porosity in the range of 40% to 75%.  
     
     
         12 . The hollow fiber membrane according to  claim 8 , having a water permeability in the range of 0.1 to 10 m 3 /m 2 ·hr at 100 kPa and 25° C., a tensile strength in the range of 0.3 to 3 kg per fiber, and an elongation at break in the range of 20% to 1,000%.  
     
     
         13 . The hollow fiber membrane according to  claim 8 , wherein the main chain of the polyvinylidene fluoride has hydrophilic functional groups.  
     
     
         14 . The hollow fiber membrane according to  claim 13 , wherein the hydrophilic functional group is at least one selected from hydroxyl, amino, and carboxyl groups.  
     
     
         15 . A hollow fiber membrane module comprising the hollow fiber membrane according to  claim 8 .  
     
     
         16 . A water separator comprising the hollow fiber membrane module according to  claim 15 .  
     
     
         17 . A method of producing permeated water from raw water using the water separator according to  claim 16 .  
     
     
         18 . A method of producing permeated water from raw water using a membrane comprising a polyvinylidene fluoride resin, the method comprising bringing the membrane into contact with chlorine in an amount corresponding to the organic content in the raw water.  
     
     
         19 . The method according to  claim 17 , wherein the membrane is brought into contact with chlorine in an amount corresponding to the organic content in the raw water.  
     
     
         20 . The method according to either  claim 18  or  19 , wherein the amount of the chlorine is 0.01 to 10 times the total organic carbon content in the raw water.