| 摘要 |
The invention relates to a seal (gasket) part for a hydraulic cylinder which is obtained by compression moulding an ethylene- alpha -olefin-diene copolymer rubber which has been vulcanised using a peroxide as a vulcanising agent. In the ethylene- alpha -olefin-diene copolymer, (a) the ethylene content is from 60 to 70 % by weight, the alpha -olefin content is from 30 to 40 % by weight, the Mooney viscosity (ML1+4 100 DEG C) is from 35 to 55 and the iodine number is from 20 to 35; (b) the molecular weight distribution satisfies the condition Mw/Mn </= 5.0; and (c) the alpha -olefin contents for in each case 20 % by weight of the EPDM polymers at opposite ends of the molecular weight distribution satisfy the condition C3E - C3I </= 5.0 % by weight, where C3I is the alpha -olefin content at the high-molecular-weight end of the range and C3E is the alpha -olefin content at the low-molecular-weight end of the range. The seal part for the hydraulic cylinder has, in particular, excellent resistance to erosion and resistance to fatigue.
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