| 摘要 |
PROBLEM TO BE SOLVED: To obtain a hydraulic oil compsn. for buffers, which is excellent in low-temp. viscosity characteristics, vaporizability, and shear stability and has a stable damping power at from low to high temps. SOLUTION: This compsn, is prepd, by compounding, based on the compsn., at least 94 wt.% base oil comprising a mixed mineral oil consisting of (a) a deeply dewaxed mineral oil and (b) a low-viscosity mineral oil in a wt, ratio of (97/3)-(99/1) with 4-6 wt.% non-dispersion-type polymethacrylate viscosity index improver as an additive, and has a kinematic viscosity of 3-3.5 mm2/s at 100 deg.C and 20.5-23.5 mm2/s at 20 deg.C, a viscosity index of 160-170, a Brookfield viscosity of 1,350-1,600 mPa.s at -40 deg.C, an amt. of NOACK evaporation of 6 wt.% or lower, and a viscosity decrease of 7% or lower at 100 deg.C in the shear stability test by the sound wave method. |
