Ion exchange membrane and method for producing dry ion exchange membrane

An ion exchange membrane containing a fluorinated polymer having a group represented by —SO3M (M is a hydrogen atom, an alkali metal or a quaternary ammonium cation) and, in the main chain, a group represented by —CF2—, 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.