| 摘要 |
PURPOSE:To obtain the membrane enabling stable production of caustic alkali having high concn. with high current efficiency at low electrolytic voltage over a long period of time by forming a layer of an F-contg. copolymer with a porous layer contg. specified inorg. particles as one of surface layers and a layer of a specified Fcontg. copolymer as the other. CONSTITUTION:This membrane is composed of two surface layers. One of the layers is a layer of an F-contg. copolymer having carboxylic acid groups and consisting of monomers represented by formulae I, II. This layer has 1-4% water content (W) in 40% aq. NaOH soln. and 5-50mum thickness. A porous layer contg. 30-95wt.% alkali- proof particles of one or more kinds of oxides, nitrides or carbides of group IV elements having <=0.2mum primary particle diameter and a hydrophilic F-contg. polymer as a binder has been formed on the surface of the copolymer layer by 0.1-10mg/cm<2>. The other of the surface layers is a layer of an F-contg. copolymer having sulfonic acid and/or carboxylic acid groups and consisting of monomers represented by formulae I-III (where each of X1 and X2 is F, Cl, H or CF3, X3 is F or CF3, (n) is 0, 1 or 2, (m) is 1, 2 or 3 and M is an alkali metal). This layer has 3-10% water content W and 5-200mum thickness. This membrane passes a specified amt. or less of water together with Na<+> entering a cathode chamber. |
