Patent ID: 8614273

Claim:
A carbon fiber composite material seal member comprising a hydrogenated acrylonitrile-butadiene rubber (HNBR) and carbon nanofibers, wherein the seal member has a number of cycles to fracture of 7000 or more when subjected to a tension fatigue test at a temperature of 70° C., a maximum tensile stress of 4 N/mm, and a frequency of 1 Hz, the seal member includes 10 to 60 parts by mass of the carbon nanofibers and 0 to 100 parts by mass of a filler having an average particle diameter of 5 to 100 nm based on 100 parts by mass of the hydrogenated acrylonitrile-butadiene rubber (HNBR), the amount of the carbon nanofibers and the amount of the filler satisfy the following expressions (1) and (2), Wt= 0.1 W 1 +W 2 (1) 20 ≦Wt≦ 60 (2) W1: amount (parts by mass) of filler, and W2: amount (parts by mass) of carbon nanofibers, the carbon nanofibers have an average diameter of 10 to 20 nm, the carbon nanofibers have an average rigidity of 3 to 12 before the carbon nanofibers are mixed into the hydrogenated acrylonitrile-butadiene rubber (HNBR), the rigidity being defined by Lx÷D (Lx: distance between adjacent defects of carbon nanofiber, D: diameter of carbon nanofiber), and the carbon fiber composite material in an uncrosslinked form has a fraction (fnn) of components having a second spin-spin relaxation time of 0 to 0.2 measured for 1 H at 150° C. by the Hahn-echo method using the pulsed NMR technique.