Patent ID: 8044147

Claim:
A nitrile group-containing copolymer rubber comprising 10 to 40 wt % of an α,β-ethylenically unsaturated nitrile unit (a), 10 to 60 wt % of an α,β-ethylenically unsaturated carboxylic acid ester unit (b), and 20 to 70 wt % in total of a conjugated diene unit (c) and a saturated conjugated diene unit (d), wherein the wt % of (a) through (d) is based on a total weight of the nitrile group-containing copolymer rubber, and wherein a content ratio “x” is 0.08 or smaller, and wherein “x” is defined as a ratio of a content of the conjugated diene unit (c) to a sum of a content of the conjugated diene unit (c) and the content of the saturated conjugated diene unit (d); and wherein “x·A” is 1.5 or smaller, wherein “x·A” is defined as a product of said ratio “x” and “A” wherein “A” is a wt % of said α,β-ethylenically unsaturated nitrile unit (a).