Ion exchange membrane and method for producing dry ion exchange membrane
An ion exchange membrane containing a fluorinated polymer, wherein in a case where by Raman spectroscopy, polarized light orthogonal to the thickness direction of the ion exchange membrane is irradiated to obtain a spectrum chart, whereby the ratio of the peak area a2 of Raman shift 680 to 760 cm −1 to the peak area al of Raman shift 1,025 to 1,095 cm −1 is taken as A1, and by Raman spectroscopy, to a cross section in the thickness direction of the ion exchange membrane, polarized light parallel with the thickness direction is irradiated to obtain a spectrum chart, whereby the ratio of the peak area b2 of Raman shift 920 to 1,025 cm −1 to the peak area b1 of Raman shift 1,025 to 1,095 cm −1 is taken as B1, B1/A1 is at least 1.05.
1. An ion exchange membrane containing a fluorinated polymer having a group represented by —SO 3 M (M is a hydrogen atom, an alkali metal or a quaternary ammonium cation) and, in the main chain, a group represented by —CF 2 —, wherein
in a case where by Raman spectroscopy, to a cross section in the thickness direction of the ion exchange membrane, polarized light orthogonal to the thickness direction is irradiated to obtain a spectrum chart, whereby the ratio of the peak area a2 of Raman shift 680 to 760 cm −1 to the peak area a1 of Raman shift 1,025 to 1,095 cm −1 is taken as A1, and
by Raman spectroscopy, to a cross section in the thickness direction of the ion exchange membrane, polarized light parallel to the thickness direction is irradiated to obtain a spectrum chart, whereby the ratio of the peak area b2 of Raman shift 680 to 760 cm −1 to the peak area b1 of Raman shift 1,025 to 1,095 cm −1 is taken as B1,
the ratio of said B1 to said A1 is at least 1.05,
wherein the ion exchange capacity of the fluorinated polymer is 1.25 to 2.05 meq/g dry resin, and
wherein the fluorinated polymer further has an ether bond site in a side chain, and
in a case where by Raman spectroscopy, to a cross section in the thickness direction of the ion exchange membrane, polarized light orthogonal to the thickness direction is irradiated to obtain a spectrum chart, whereby the ratio of the height h2 of the highest peak within a range of Raman shift 920 to 1,025 cm −1 to the height h1 of the highest peak within a range of Raman shift 1,025 to 1.095 cm −1 is taken as H1, and
by Raman spectroscopy, to a cross section in the thickness direction of the ion exchange membrane, polarized light parallel to the thickness direction is irradiated to obtain a spectrum chart, whereby the ratio of the height h4 of the highest peak within a range of Raman shift 920 to 1,025 cm −1 to the height h3 of the highest peak within a range of Raman shift 1,025 to 1,095 cm −1 is taken as H2,
the ratio of said H2 to said H1 is at least 1.15.
2. The ion exchange membrane according to claim 1 , wherein the fluorinated polymer has a unit represented by the formula (1):
—[CF 2 —CF(-L-(SO 3 M) n )]- Formula (1)
in the formula (1), L is an n+1-valent perfluorohydrocarbon group which may contain an oxygen atom, M is a hydrogen atom, an alkali metal or a quaternary ammonium cation, and n is 1 or 2.
3. The ion exchange membrane according to claim 2 , wherein the ether bond site of the side chain is a site contained in a unit obtained by polymerizing at least one type of monomer selected from the group consisting of the following monomers (A) to (E):
4. The ion exchange membrane according to claim 1 , wherein the ion exchange membrane contains a liquid medium, and the content of the liquid medium in the ion exchange membrane is at most 15 mass % to the total mass of the ion exchange membrane.
5. The ion exchange membrane according to claim 4 , wherein the liquid medium is at least one of water and a water-soluble organic solvent.
6. A method for producing a dry ion exchange membrane, comprising drying a wet ion exchange membrane having an ion exchange membrane containing a fluorinated polymer having a sulfonic acid type functional group wet with a liquid medium, to remove the liquid medium to obtain a dry ion exchange membrane, characterized in that the dimensional change of the dry ion exchange membrane from the wet ion exchange membrane during drying is at least −5% in each of the MD direction and the TD direction,
wherein the drying temperature is at least the softening point of the fluorinated polymer.
7. The method for producing a dry ion exchange membrane according to claim 6 , wherein the content of the liquid medium in the dry ion exchange membrane is at most 15 mass % to the total mass of the dry ion exchange membrane.
8. The method for producing a dry ion exchange membrane according to claim 6 , wherein the dimensional change of the dry ion exchange membrane from the wet ion exchange membrane during drying is at most 50% in each of the MD direction and the TD direction.
9. The method for producing a dry ion exchange membrane according to claim 6 , wherein the content of the liquid medium in the wet ion exchange membrane is at least 20 mass % to the total mass of the wet ion exchange membrane.
10. The method for producing a dry ion exchange membrane according to claim 6 , wherein the wet ion exchange membrane is obtained by contacting the ion exchange membrane containing the fluorinated polymer with the liquid medium at a temperature of at least 60° C.
11. The method for producing a dry ion exchange membrane according to claim 6 , wherein a reinforcing material is contained inside or at the surface of the wet ion exchange membrane.