| 摘要 |
The present invention provides a hydraulic oil composition comprising a base oil composed of a mineral oil (A) and/or synthetic oil (B) incorporated with 20 wt% or less, based on the whole composition, of one or more; types of additives (C) including viscosity index improver and/or pour point depressant, and having a kinematic viscosity of 1 to 20 mm2/s at 100.degree.C, a viscosity index of 140 or more and a Brool~eld viscosity of 2000 mPa~s or less at -40.degree.C, wherein the mineral oil (A) is a deeply dewaxed mineral oil (a) having a kinematic viscosity of 2 to 3 mm2/s at 100.degree.C, pour point of -30.degree.C or less and cloud point of -27.5.degree.C or less, or a mixed mineral oil of the deeply dewaxed mineral oil (a) and a low-viscosity mineral oil (b) having a kinematic viscosity of 1.0 to 6.0 mm2/s at 40.degree.C, and the synthetic oil (B) is a poly-a-olefin (c) having a kinematic viscosity of 1.5 to 45 mm2/s at 100.degree.C, and/or an ester compound (d) having a kinematic viscosity of 1.5 to 20 mm2/s at 100.degree.C and pour point of 30.degree.C or less.
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