PROCESS FOR PRODUCING ETHYLENE/TETRAFLUOROETHYLENE COPOLYMER POROUS MATERIAL, AND ETHYLENE/TETRAFLUOROETHYLENE COPOLYMER POROUS MATERIAL
To provide a method for easily producing an ethylene/tetrafluoroethylene copolymer porous material having excellent chemical resistance and filtration performance and has a high heat resistance, within a wide range of the porosity, and an ethylene/tetrafluoroethylene copolymer porous material obtained by such a process. A process for producing an ethylene/tetrafluoroethylene copolymer porous material which comprises a step of dissolving an ethylene/tetrafluoroethylene copolymer having repeating units based on ethylene and repeating units based on tetrafluoroethylene at a temperature of at most 300° C. in a solvent which can dissolve the ethylene/tetrafluoroethylene copolymer at a temperature of at most 300° C., to achieve a predetermined concentration to obtain a solution, a step of forming the solution to obtain a formed product, and a step of cooling the formed product to a temperature of at most the phase separation temperature of the solution to solidify the ethylene/tetrafluoroethylene copolymer.
1 . A process for producing an ethylene/tetrafluoroethylene copolymer porous material, which comprises a step (A) of dissolving an ethylene/tetrafluoroethylene copolymer having repeating units based on ethylene and repeating units based on tetrafluoroethylene, in a solvent which can dissolve the ethylene/tetrafluoroethylene copolymer, at a temperature of at most 300° C. and at least the phase separation temperature of a solution obtainable, to achieve a predetermined concentration to obtain a solution; a step (B) of forming the solution at a temperature of at most 300° C. and at least the phase separation temperature of the solution to obtain a formed product; and a step (C) of cooling the formed product at a temperature of at least the phase separation temperature of the solution, to a temperature of at most the phase separation temperature of the solution to solidify the ethylene/tetrafluoroethylene copolymer.
2 . The process for producing an ethylene/tetrafluoroethylene copolymer porous material according to claim 1 , wherein the dissolution in the step (A) is carried out at a temperature of at least the phase separation temperature of the solution and at most the melting point of the ethylene/tetrafluoroethylene copolymer.
3 . The process for producing an ethylene/tetrafluoroethylene copolymer porous material according to claim 1 , wherein the predetermined concentration in the step (A) is from 15/85 to 65/35 by the mass ratio of the ethylene/tetrafluoroethylene copolymer to the solvent as represented by the ethylene/tetrafluoroethylene copolymer/the solvent, in the solution.
4 . The process for producing an ethylene/tetrafluoroethylene copolymer porous material according to claim 1 , wherein the cooling in the step (C) is carried out in a cooling liquid.
5 . The process for producing an ethylene/tetrafluoroethylene copolymer porous material according to claim 1 , wherein the solvent is at least one member selected from the group consisting of a fluorinated aromatic compound, an aliphatic compound having at least one carbonyl group and a hydrofluoroalkyl ether.
6 . The process for producing an ethylene/tetrafluoroethylene copolymer porous material according to claim 1 , wherein in the step (A), the solution is prepared to contain a powder having a primary particle size of from 10 nm to 1 μm.
7 . The process for producing an ethylene/tetrafluoroethylene copolymer porous material according to claim 4 , wherein the step (B) is carried out by discharging the solution as an extruded product.
8 . The process for producing an ethylene/tetrafluoroethylene copolymer porous material according to claim 7 , wherein the cooling in the step (C) is carried out by passing the extruded product immediately after the step (B) through a dry portion having a length of from 0.1 to 100 mm at a temperature of at least 0° C. and at most the phase separation temperature of the solution, and then introducing the extruded product to the above cooling liquid.
9 . The process for producing an ethylene/tetrafluoroethylene copolymer porous material according to claim 4 , wherein the cooling liquid is a non-solvent for the ethylene/tetrafluoroethylene copolymer.
10 . The process for producing an ethylene/tetrafluoroethylene copolymer porous material according to claim 1 , which further has a step (D) of extracting the solvent.
11 . An ethylene/tetrafluoroethylene copolymer porous material in the form of a film or a hollow fiber, obtained by the production process as defined in claim 1 .
12 . The ethylene/tetrafluoroethylene copolymer porous material according to claim 11 , which has a porosity of from 20 to 90% and has an average pore size of the pores of from 0.01 to 20 μm.