| abstract |
The object of the present invention is to provide a base oil for hydraulic oil suitably used for hydraulic systems having filters of which micropore diameter is 50 μm or less, which is capable to improve the decrease of flow in a hydraulic pump at low temperature like −30° C. or less and capable to normally operate the hydraulic systems. The invention also provides a hydraulic oil composition using the above base oil, especially a hydraulic oil composition suitably used for such as tractors, transmissions, and common systems thereof having the hydraulic systems. In order to achieve the object, provided is a base oil for hydraulic oil comprising mineral oil, wherein the mineral oil is defined by kinematic viscosity at 100° C.: 1.5˜6 mm 2 /s, pour-point: −10° C. or less, viscosity index: 100 or more, % C P : 70 or more, % C A : 2 or less, and aniline point: 106° C. or more; and wherein, the mineral base oil is treated by catalytic dewaxing process and/or contains tertiary carbon atoms at a ratio of 7.4% or more to the total carbon atoms. |