Patent ID: 7938941

Claim:
A cation-exchange membrane for electrolysis comprising a fluorine-containing polymer having an ion-exchange group and a porous substrate, characterized in that the membrane has projecting parts comprising a polymer having an ion-exchange group on the surface of an anode side of the membrane; 20≦h≦95, where h is defined as an average value of heights (μm) from the surface of the anode side of the membrane to the tops of the projecting parts; 50≦P≦1,200, where P is defined as a distribution density (piece/cm 2 ) of the projecting parts; 0.001≦S≦0.6, where S is defined as an average value of area fractions (cm 2 /cm 2 ) of the bottom faces of the projecting parts on the same plane as the surface of the anode side of the membrane; T≦0.05, where T is defined as an average value of area fractions (cm 2 /cm 2 ) of the top parts of the projecting parts on the surface of the anode side of the membrane; and 0.5 ≦b/a≦ 0.9 and 0.25 ≦h/a≦ 0.80, where a is defined as an average value of lengths (μm) of the bottom sides of the projecting parts on the same plane as the surface of the anode side of the membrane, and b is defined as an average value of widths (μm) of the projecting parts at the half height h/2 (μm) of the projecting part.