US Patent 7160926 Ion exchange fluorocarbon resin membrane

An ion exchange fluorocarbon resin membrane having a storage modulus (JIS K-7244), when substituted with tributyl ammonium ions, at a temperature of not less than Tc represented by the following general equations (1-1) to (1-3) of 0.8×106 Pa or more, and a heat of crystal fusion at 270 to 350° C. of 1 J/g or less:Tc (° C.)=55+Tg (EW<750)  (1-1)Tc (° C.)=0.444×EW−278+Tg (750≦EW<930)  (1-2)Tc (° C.)=135+Tg (EW≧930)  (1-3)where Tg designates the peak temperature of loss tangent in the dynamic viscoelasticity measure-ment of the ion exchange fluorocarbon resin membrane (having SO3H as the ends of the side chains).