Abstract: A cross-linkable nitrile rubber composition comprising a nitrile rubber (A1) including an ?,?-ethylenically unsaturated nitrile monomer unit and having iodine value of 120 or less, silica (B1) having CaO value determined by X-ray fluorescence composition analysis of 0.5 wt % or more, and a crosslinking agent (C1). According to the present invention, a cross-linkable nitrile rubber composition, capable of giving a highly-saturated cross-linked nitrile rubber having excellent mechanical properties such as elongation and small compression set, and excellent in workability, and a cross-linked rubber obtained by crosslinking the rubber composition can be provided.

Abstract: A nitrile group-containing copolymer rubber comprising 10 to 40 wt % of ?,?-ethylenically unsaturated nitrile unit (a), 10 to 60 wt % of ?,?-ethylenically unsaturated carboxylic acid ester unit (b), and 20 to 70 wt % in total of conjugated diene unit (c) and saturated conjugated diene unit (d), wherein a content ratio “x” of a conjugated diene unit (c) based on the total content of said conjugated diene unit (c) and said saturated conjugated diene unit (d) is 0.08 or smaller, and “x·A” defined as a product of said ratio “x” and a content ratio “A” (%) of said ?,?-ethylenically unsaturated nitrile unit (a) is 1.5 or smaller. According to the present invention, a nitrile group-containing copolymer rubber capable to provide a rubber vulcanizate highly balanced in mechanical strength, heat aging resistance, oil resistance, cold resistance and ozone resistance, and a vulcanizable rubber composition using the rubber can be provided.