| 摘要 |
PROBLEM TO BE SOLVED: To provide a hydraulic oil that has excellent long-term stability and excellent non-corrosive property and can control a vibration of a lofty building caused by an earthquake, a wind or the like by specifying a viscosity index, a volume elasticity and a pour point. SOLUTION: A phenolic antioxidant, amine antioxidant or zinc dialkyldithiophosphate antioxidant in an amount of 0.01-2 wt.% is added to one or more base oil of a hydraulic oil that is selected from a poly(α-olefin), a polyol ester, a polyether produced by carrying out the low polymerization of a hydrocarbon having a double bond at a terminal such as 1-decene or the like and hydrogenating the terminal double bond and that has a kinematic viscosity (at 40 deg.C) of 5-1,000 mm2/s, preferably 15-1,000 mm2/s to produce a hydraulic oil for a vibration damper having a viscosity index of 110-400, preferably 110-120, a volume elasticity of 1.3-2.0 GPa, preferably 1.3-1.8 GPa and a pour point of not more than -25 deg.C, preferably not more than -30 deg.C. The vibration damper is used in such a condition that it is purged with an inert gas and can employ a sealing material excellent in a long-term oil sealing properties, which results in causing few problems in the practical use.
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