Cation exchange membrane and method for producing same

A method of producing a cation-exchange membrane, the method comprising:

• impregnating voids of a substrate made of polyolefin-based woven fabric with a polymerizable composition for forming a cation exchange resin, the polymerizable composition containing a polymerization initiator, polyvinyl chloride, and a monomer component which contains a cross-linkable monomer and a monomer containing a sulfonic acid group-introducible functional group or a sulfonic acid group;
• and
• copolymerizing the monomer component in the polymerizable composition for forming the cation-exchange resin after the immersing, wherein, the copolymerizing is performed at 40° C. or higher to lower than 80° C.,
• the polymerizable composition for forming the cation-exchange resin containing 55 parts by mass or more to 98 parts by mass or less of the polyvinyl chloride relative to 100 parts by mass of the monomer component,
• wherein:
• the monomer component includes a-alkylstyrene, and
• a content of the α-alkylstyrene is 1 mass % or more to 13 mass % or less relative to the entire monomer component.