PURPOSE: To obtain a heterogeneous ion exchange membrane with large ion transport no. at high ion concn. by kneading a thermoplastic resin, a finely divided ion exchange resin and low MW PE wax to prepare pellets and extruding the pellets into a membrane after which the membrane is irradiated with radiation to cross link the thermoplastic resin and treated with hot water.

CONSTITUTION: A thermoplastic resin such as high density PE is mixed with a finely divided ion exchange resin such as strongly acidic cation exchange resin in a ratio of 75:25W25:75 by wt., and to the mixt. is added PE wax with an average MW of about 500W5000 as a lubricant, followed by kneading. The kneaded material is extrusion molded into pellets, and the pellets are supplied to an extruder and extrusion molded into an about 0.1W1.0 mm thick membraneous product. The product is then irradiated with radiation to cross link the thermoplastic resin as the matrix polymer and the wax, and the cross linked product is held in hot water of above 60, esp. above 70°c for about 30W60 min to obtain a desired ion exchange membrane.