HYDRAULIC FLUID COMPOSITION

Info

Publication number: 20150376542
Type: Application
Filed: Mar 25, 2014
Publication Date: Dec 31, 2015
Applicant: JX NIPPON OIL & ENERGY CORPORATION (Chiyoda-ku, Tokyo)
Inventors: Kazuhiro YAGISHITA (Chiyoda-ku, Tokyo), Toru HIRANO (Chiyoda-ku, Tokyo), Tadashi OSHIO (Chiyoda-ku, Tokyo)
Application Number: 14/766,870

Abstract

The present invention provides a hydraulic oil composition comprising: a lubricating base oil; and 0.2 to 40% by mass, based on a total amount of the hydraulic oil composition, of at least one copolymer selected from olefin copolymers having a number-average molecular weight of 18000 or lower and copolymers of an α-olefin and a dicarboxylic ester, having a number-average molecular weight of 20000 or lower.

Description

Description

TECHNICAL FIELD

The present invention relates to a hydraulic oil composition. The present invention relates particularly to a hydraulic oil composition containing a viscosity index improver and having a high energy efficiency.

BACKGROUND ART

In recent years, energy-saving hydraulic oils have been developed as one of responses to global warming. There are some conventional energy-saving hydraulic oils allowing achieving the reduction of energy consumption of apparatuses at starting, for example, by decreasing their low-temperature viscosity.

There are also developed energy-saving hydraulic oils whose viscosity change is made small by blending a viscosity index improver to thereby reduce energy consumption in the steady-state operation after the fluid temperature is raised. In the energy-saving hydraulic oils, the fluid leakage (internal leakage) from construction machines' characteristic various hydraulic apparatus interiors is prevented by making small the viscosity change (making the viscosity index high) of the hydraulic oils, and the reduction of the energy consumption is achieved (for example, see Patent Literatures 1 to 3).

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Application Laid-Open No. 2005-307197

Patent Literature 2: Japanese Patent Application Laid-Open No. 2011-046900

Patent Literature 3: Japanese Patent Application Laid-Open No. 2012-180535

SUMMARY OF INVENTION Technical Problem

In the case of the energy-saving hydraulic oils as described in the above Patent Literatures 1 to 3, however, the high viscosity index of the hydraulic oils causes an increase in the loss due to the plumbing resistance. Hence, even if the energy consumption can be reduced by the internal leakage prevention, there is still room for improvement in the point of improving the energy efficiency of the hydraulic system as a whole.

The present invention has been achieved in consideration of such a real situation, and an object thereof is to provide a hydraulic oil composition enabling both the internal leakage prevention and the plumbing resistance reduction to be compatibly achieved, and enabling the energy efficiency of a hydraulic system as a whole to be improved.

Solution to Problem

As a result of exhaustive studies, the present inventors have found that a hydraulic oil composition obtained by blending a lubricating base oil with a specific amount of a specific copolymer has viscosity characteristics excellent in compatibly achieving both the internal leakage prevention and the plumbing resistance reduction of a hydraulic system, and this finding has led to the completion of the present invention.

That is, the present invention provides a hydraulic oil composition comprising a lubricating base oil, and 0.2 to 40% by mass, based on the total amount of the hydraulic oil composition, of at least one copolymer selected from olefin copolymers having a number-average molecular weight of 20000 or lower and copolymers of an α-olefin and a dicarboxylic ester, having a number-average molecular weight of 20000 or lower.

Further in the above hydraulic oil composition, it is preferable that the hydraulic oil composition has the viscosity index of 155 or higher, and the ratio (A/B) of (A) a kinematic viscosity (unit: mm²/s) at 80° C. to (B) a shear viscosity (unit: mPa·s, shear condition: 10⁶/s) at 80° C. is 1.3 or lower.

Advantageous Effects of Invention

The hydraulic oil composition according to the present invention has a low kinematic viscosity as opposed to a high shear viscosity, enables both the internal leakage prevention and the plumbing resistance reduction to be compatibly achieved, and exhibits a remarkable effect of enabling the energy efficiency of a hydraulic system as a whole to be improved.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a preferred embodiment according to the present invention will be described.

A hydraulic oil composition according to an embodiment of the present invention comprises a lubricating base oil and at least one selected from olefin copolymers having a number-average molecular weight of 20000 or lower and copolymers, of an α-olefin and a dicarboxylic ester, having a number-average molecular weight of 20000 or lower.

The lubricating base oil to be used in the present embodiment includes mineral oils, synthetic hydrocarbon oils, synthetic oxygen-containing oils, and fats and oils. These lubricating base oils can be used singly or in combinations of two or more.

The mineral oil is not especially limited, but examples thereof include paraffinic mineral oils or naphthenic mineral oils refined by subjecting lubricating oil fractions obtained by atmospheric pressure distillation and reduced pressure distillation of crude oils to suitably combined refining treatments including solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfuric acid cleaning and clay treatment.

Examples of the synthetic hydrocarbon oil include poly-α-olefins (polybutene, 1-octene oligomers, 1-decene oligomers and the like), alkylbenzenes and alkylnaphthalenes.

As the synthetic oxygen-containing oil, there are used, for example, esters such as monoesters of a monohydric alcohol and a monovalent fatty acid, and polyol esters of a polyhydric alcohol and a monovalent fatty acid; and polyoxyalkylene glycols.

As the fats and oils, there are used, for example, vegetable fats and oils such as palm oil, palm kernel oil, rapeseed oil, soybean oil, high oleic rapeseed oil and high oleic sunflower oil.

Among these, mineral oils and synthetic hydrocarbon oils are preferably used and mineral oils are more preferably used.

The kinematic viscosity at 40° C. of the lubricating base oil is not especially limited, but is preferably 15 mm²/s or higher, more preferably 20 mm²/s or higher, still more preferably 25 mm²/s or higher, and most preferably 30 mm²/s or higher. Further the kinematic viscosity at 40° C. of the lubricating base oil is preferably 50 mm²/s or lower, more preferably 45 mm²/s or lower, still more preferably 40 mm²/s or lower, and most preferably 35 mm²/s or lower. When the kinematic viscosity at 40° C. of the lubricating base oil is 15 mm²/s or higher, the case is preferable in the point of evaporation; and when the kinematic viscosity at 40° C. of the lubricating base oil is 50 mm²/s or lower, the case is preferable because the plumbing resistance can be reduced.

The viscosity index of the lubricating base oil is not especially limited, but is preferably 150 or higher, more preferably 160 or higher, still more preferably 170 or higher, and most preferably 175 or higher. When the viscosity index is 150 or higher, since the kinematic viscosity at low temperatures is suppressed in becoming high when the kinematic viscosity at high temperatures is secured, the case is preferable in the point of being capable of suppressing the efficiency decrease of a hydraulic system. On the other hand, the upper limit value of the viscosity index is not especially limited, but is, for example, 250.

Here, the “kinematic viscosity” and the “viscosity index” in the present specification mean values measured according to JIS K 2283.

The content of the lubricating base oil is preferably 50% by mass or higher, more preferably 60% by mass or higher, and still more preferably 70% by mass or higher based on the total amount of the hydraulic oil composition. Further the content of the lubricating base oil is preferably 99% by mass or lower, and more preferably 98% by mass or lower based on the total amount of the hydraulic oil composition. When the content of the lubricating base oil is 50% by mass or higher, the excellent advantages of the hydraulic oil are easily fully exhibited.

The hydraulic oil composition according to the present embodiment comprises at least one selected from olefin copolymers having a number-average molecular weight of 20000 or lower and copolymers, of an α-olefin and a dicarboxylic ester, having a number-average molecular weight of 20000 or lower.

Here, the “number-average molecular weight” in the present specification refers to a number-average molecular weight in terms of polystyrene determined by gel permeation chromatography (GPC) (reference material: polystyrene).

The olefin copolymer is a cooligomer or a copolymer of ethylene and an α-olefin. The α-olefin includes propylene, 1-butene and 1-pentene, and propylene is preferably used. The copolymer of ethylene and an α-olefin is not especially limited, and may be a random polymer or a block polymer.

The number-average molecular weight of the olefin copolymer is 18000 or lower, preferably 16000 or lower, more preferably 14000 or lower, and still more preferably 10000 or lower. Further the number-average molecular weight of the olefin copolymer is preferably 700 or higher, more preferably 1000 or higher, and still more preferably 1500 or higher. When the number-average molecular weight is 18000 or lower, the case is preferable in the point of the pump efficiency; and when the number-average molecular weight is 700 or higher, the case is preferable because the effect of improving the viscosity index becomes large.

An example of the copolymer of an α-olefin and a dicarboxylic ester includes a compound represented by the following formula (1).

In the above formula (1), R¹represents a linear or branched alkyl group; R²to R⁵may be identical or different, and each represent hydrogen, a linear or branched alkyl group, or an ester group represented by —R⁶—CO₂R⁷or —CO₂R⁸(R⁶represents a linear or branched alkylene group; and R⁷and R⁸may be identical or different, and each represent a linear or branched alkyl group); any two of R²to R⁵are the above ester group; and X and Y may be identical or different, and each represent a positive number.

Here, a partial structure represented by the following formula (2) in the above formula (1) is originated from the α-olefin, and as the α-olefin, one having 3 to 20 carbon atoms is used and one having 6 to 18 carbon atoms is preferably used.

The α-olefin specifically includes propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene and 1-eicosene.

Further a partial structure represented by the following formula (3) in the above formula (1) is originated from the dicarboxylic ester.

The dicarboxylic ester specifically includes maleic acid, fumaric acid, citraconic acid, mesaconic acid and itaconic acid.

The number-average molecular weight of the copolymer of an α-olefin and a dicarboxylic ester is 20000 or lower, preferably 18000 or lower, more preferably 14000 or lower, still more preferably 12000 or lower, and most preferably 10000 or lower. When the number-average molecular weight is 20000 or lower, the case is preferable in the point of the pump efficiency-improving capability. Further the number-average molecular weight of the copolymer of an α-olefin and a dicarboxylic ester is not especially limited, but is preferably 5000 or higher, more preferably 6000 or higher, and still more preferably 8000 or higher. When the number-average molecular weight is 5000 or higher, the case is preferable in the point of the viscosity-improving capability.

The kinematic viscosity at 100° C. of the copolymer of an α-olefin and a dicarboxylic ester is not especially limited, but is preferably 1 mm²/s or higher, more preferably 10 mm²/s or higher, still more preferably 50 mm²/s or higher, and most preferably 200 mm²/s or higher; and further that is preferably 5000 mm²/s or lower, more preferably 3000 mm²/s or lower, still more preferably 2000 mm²/s or lower, and most preferably 1000 mm²/s or lower. When the kinematic viscosity at 100° C. is 1 mm²/s or higher, the case is preferable in the point of making a high viscosity; and when that is 5000 mm²/s or lower, the case is preferable in the point of handling in the production.

In the present embodiment, in the case of concurrently using the olefin copolymer and the copolymer of an α-olefin and a dicarboxylic ester, their ratio is not especially limited, and is arbitrary.

The content of the copolymers is 0.2 to 40% by mass based on the total amount of the hydraulic oil composition. When the content of the copolymers is 0.2% by mass or higher, the blending effect is easily attained. Further when the content is 40% by mass or lower, the case is preferable in the point of the solubility and the stability.

In the case of singly using the olefin copolymer as the copolymer, the content of the copolymer is preferably 20% by mass or lower, more preferably 15% by mass or lower, still more preferably 10% by mass or lower, and most preferably 8% by mass or lower based on the total amount of the hydraulic oil composition. Further the content of the copolymer is preferably 0.2% by mass or higher, more preferably 0.5% by mass or higher, still more preferably 1% by mass or higher, and most preferably 3% by mass or higher based on the total amount of the hydraulic oil composition.

In the case of singly using the copolymer of an α-olefin and a dicarboxylic ester as the copolymer, the content of the copolymer is 40% by mass or lower, preferably 35% by mass or lower, more preferably 30% by mass or lower, and still more preferably 25% by mass or lower based on the total amount of the hydraulic oil composition. Further the content of the copolymer is preferably 1% by mass or higher, more preferably 3% by mass or higher, still more preferably 5% by mass or higher, and most preferably 10% by mass or higher based on the total amount of the hydraulic oil composition.

In the case of concurrently using the olefin copolymer and the copolymer of an α-olefin and a dicarboxylic ester as the copolymers, the content of the copolymers is 40% by mass or lower, preferably 35% by mass or lower, more preferably 30% by mass or lower, and still more preferably 25% by mass or lower based on the total amount of the hydraulic oil composition. Further the content of the copolymers is 0.1% by mass or higher, preferably 1% by mass or higher, more preferably 3% by mass or higher, and still more preferably 5% by mass or higher based on the total amount of the hydraulic oil composition.

When the content of the olefin copolymer and/or the copolymer of an α-olefin and a dicarboxylic ester is the above given amount or larger, the blending effect is easily attained; and when that is the above given amount or smaller, the case is preferable in the point of the solubility and the stability.

The kinematic viscosity at 40° C. of the hydraulic oil composition is not especially limited, but is preferably 20 mm²/s or higher, more preferably 30 mm²/s or higher, still more preferably 40 mm²/s or higher, and most preferably 45 mm²/s or higher. Further the kinematic viscosity at 40° C. of the hydraulic oil composition is preferably 80 mm²/s or lower, more preferably 70 mm²/s or lower, still more preferably 60 mm²/s or lower, and most preferably 50 mm²/s or lower. When the kinematic viscosity at 40° C. of the hydraulic oil composition is 20 mm²/s or higher, the case is preferable in the point of the durability of a hydraulic system; and when that is 80 mm²/s or lower, the case is preferable in the point of the friction reduction.

The viscosity index of the hydraulic oil composition is preferably 150 or higher, more preferably 155 or higher, still more preferably 160 or higher, and most preferably 165 or higher. When the viscosity index is 150 or higher, the case is preferable because an optimum viscosity range can be held over a broad temperature range. On the other hand, the upper limit value of the viscosity index is not especially limited, but is, for example, 250.

The ratio (A/B) of (A) a kinematic viscosity at 80° C. to a shear viscosity (unit: mPa·s, shear condition: 10⁶/s) at 80° C. with respect to the hydraulic oil composition is not especially limited, but is preferably 1.4 or lower, more preferably 1.3 or lower, still more preferably 1.25 or lower, and most preferably 1.2 or lower. When the above A/B is 1.4 or lower, the case is preferable in the point of the pump efficiency and the plumbing resistance. On the other hand, the lower limit value of the above A/B is not especially limited, but is, for example, 1.1.

Here, the “shear viscosity” in the present specification means a value measured according to ASTM (D4741, D4683, D6616), CEC (L-36A-90).

The hydraulic oil composition according to the present embodiment, in order to more improve its excellent advantages, can further comprise, as required, an extreme pressure agent, an antioxidant, a pour point depressant, a rust-preventive agent, a metal deactivator, a viscosity index improver, an antifoaming agent, a demulsifier, an oiliness agent and the like. These additives may be used singly or in combinations of two or more.

The extreme pressure agent includes sulfur compounds such as ester sulfides, sulfurized fats and oils and polysulfides, zinc dithiophosphate, and phosphorus compounds, and it is preferable that phosphorus compounds are used. The phosphorus compounds specifically include phosphate esters, acidic phosphate esters, amine salts of acidic phosphate esters, chlorinated phosphate esters, phosphite esters and phosphorothionate. The phosphorus compounds include esters of phosphoric acid, phosphorous acid or thiophosphoric acid with an alkanol or a polyetheric alcohol, and their derivatives.

Among the above phosphorus compounds, since higher antiwear property can be provided, phosphate esters, acidic phosphate esters, amine salts of acidic phosphate esters are preferable, and among these, phosphate esters are more preferable. It is preferable that the content of the extreme pressure agent is 0.05 to 5% by mass based on the total amount of the hydraulic oil composition.

Examples of the antioxidant include phenolic compounds such as 2,6-ditertiary-butyl-p-cresol (DBPC), aromatic amines such as phenyl-α-naphthylamine, hindered amine compounds, phosphite esters and organometal compounds. It is preferable that the content of the phenolic antioxidant is 0.01 to 2% by mass based on the total amount of the hydraulic oil composition. Further it is preferable that the content of the amine-based antioxidant is 0.001 to 2% by mass based on the total amount of the hydraulic oil composition.

Examples of the pour point depressant are copolymers of at least one monomer selected from acrylate esters and methacrylate esters, and hydrogenated substances thereof. It is preferable that the content of the pour point depressant is 0.01 to 5% by mass based on the total amount of the hydraulic oil composition.

Examples of the rust-preventive agent are amino acid derivatives, partial esters of polyhydric alcohols; esters such as lanolin fatty acid esters, alkyl succinate esters and alkenyl succinate esters; sarcosine; polyhydric alcohol partial esters such as sorbitan fatty acid esters; metal soaps such as fatty acid metal salts, lanolin fatty acid metal salts and oxidized wax metal salts; sulfonates such as calcium sulfonate and barium sulfonate; oxidized waxes; amines; phosphoric acid; and phosphate salts. It is preferable that the content of the rust-preventive agent is 0.01 to 5% by mass based on the total amount of the hydraulic oil composition.

Examples of the metal deactivator are benzotriazole compounds, thiadiazole compounds and imidazole compounds. It is preferable that the content of the metal deactivator is 0.001 to 1% by mass based on the total amount of the hydraulic oil composition.

The hydraulic oil composition according to the present embodiment can further comprise a viscosity index improver other than the above copolymers. Specific examples thereof include non-dispersive viscosity index improvers such as copolymers of at least one monomer selected from methacrylate esters and hydrogenated substances thereof, polyisobutylenes and hydrogenated substances thereof, hydrogenated styrene-diene copolymers and polyalkylstyrenes. It is preferable that the content of the viscosity index improver other than the above copolymers is 0.01 to 15% by mass based on the total amount of the hydraulic oil composition.

Examples of the antifoaming agent are silicones such as dimethylsilicones and fiuorosilicones. It is preferable that the content of the antifoaming agent is 0.001 to 0.05% by mass based on the total amount of the hydraulic oil composition.

Examples of the demulsifier include polyoxyalkylene glycols, polyoxyalkylene alkyl ethers, polyoxyalkylene alkylamides and polyoxyalkylene fatty acid esters.

The oiliness agent includes fatty acids, esters and alcohols. It is preferable that the content of the oiliness agent is 0.01 to 0.5% by mass based on the total amount of the hydraulic oil composition.

EXAMPLES

Hereinafter, the present invention will be described more specifically by way of Examples and Comparative Examples, but the present invention is not any more limited to these contents.

In Examples 1 to 4 and Comparative Examples 1 to 4, hydraulic oil compositions were each prepared by blending a lubricating base oil and additives in a composition shown in Table 1 and Table 2. The lubricating base oils and the additives used in the Examples and the Comparative Examples are as follows.

Base oil 1: hydrorefined mineral oil (total aromatic content: 0.0% by mass, sulfur content: 10 ppm by mass or lower, 40° C. kinematic viscosity: 20 mm²/s, viscosity index: 124)

Base oil 2: hydrorefined mineral oil (total aromatic content: 0.0% by mass, sulfur content: 10 ppm by mass or lower, 40° C. kinematic viscosity: 26 mm²/sec, viscosity index: 131)

Base oil 3: hydrorefined mineral oil (total aromatic content: 0.0% by mass, sulfur content: 10 ppm by mass or lower, 40° C. kinematic viscosity: 46 mm²/sec, viscosity index: 127)

Here, the total aromatic content was measured according to silica-alumina gel chromatography described in “Separation of High-Boiling Petroleum Distillates Using Gradient Elution Through Dual-Packed (Silica Gel-Alumina Gel) Adsorption Columns,” Analytical Chemistry, Vol. 44, No. 6, (1972), pp. 915-919.

Further the sulfur content was measured according to ASTM D4951, “Standard Test Method for Determination of Additive Elements in Lubricating Oils by Inductively Coupled Plasma Atomic Emission Spectrometry.”

Further the kinematic viscosity and the viscosity index were measured according to JIS K 2283.

A: ethylene-propylene copolymer (Mitsui Chemicals, Inc., Lucant HC2000, number-average molecular weight: 13100)

B: copolymer of an α-olefin and a dicarboxylic ester (Ketjenlube, KL2700, number-average molecular weight: 9800, kinematic viscosity at 100° C.: 700 mm²/sec)

C: styrene-diene copolymer (Infineum International Ltd., SV151, number-average molecular weight: 144000)

D: polymethacrylate (Sanyo Chemical Industries, Ltd., number-average molecular weight: 40000)

E: polymethacrylate (Sanyo Chemical Industries, Ltd., number-average molecular weight: 100000)

F: olefin copolymer (Chevron Corp., Paratone 8451, number-average molecular weight: 230000)

In Examples 1 to 4 and Comparative Examples 1 to 4, as other additives, tricresyl phosphate, 2,6-ditertiary-butyl-p-cresol (DBPC) and a pour point depressant were each blended in 0.5% by mass based on the total amount of the hydraulic oil composition.

Each property was measured for each hydraulic oil composition obtained in Examples 1 to 4 and Comparative Examples 1 to 4 as described below. The results are shown in Table 1 and Table 2.

The kinematic viscosity and the viscosity index: which were measured according to HS K 2283.

The shear viscosity: which was measured according to ASTM (D4741, D4683, D6616), CRC (L-36A-90), at 80° C. at a shear condition of 10⁶/s. A measuring instrument used was a USV (Ultra Shear Viscometer) viscometer, manufactured by PCS Instruments.

[HPV35+35 Pump Test]

An HPV35+35 pump test was carried out on each hydraulic oil composition obtained in Examples 1 to 4 and Comparative Examples 1 to 4. Specifically, the rotational torque of the pump was measured under the following test condition, and the total efficiency was calculated. The results are shown in Table 1 and Table 1

The pump name: Komatsu HPV35+35

The discharge volume+the drain volume: 40 L/min

The pump type: a swash plate type

The oil temperature: 80° C.

The pressure: no load, 35 MPa

The rotation of the pump: 2100 rpm

TABLE 1 Example 1 Example 2 Example 3 Example 4 Composition base oil 1 balance — balance balance (% by mass) base oil 2 — balance — — base oil 3 — — — — viscosity index improver A 7.5 5 — 2.5 viscosity index improver B — — 19 9.5 viscosity index improver C — — — — viscosity index improver D — — — — viscosity index improver E — — — — viscosity index improver F — — — — tricresyl phosphate 0.5 0.5 0.5 0.5 DBPC 0.5 0.5 0.5 0.5 pour point depressant 0.5 0.5 0.5 0.5 Properties kinematic viscosity at 40° C. (mm²/s) 46.34 46.59 46.48 44.64 kinematic viscosity at 80° C. (mm²/s) 13.59 13.21 13.12 12.71 kinematic viscosity at 100° C. (mm²/s) 8.74 8.42 8.35 8.12 viscosity index 171 159 157 157 shear viscosity at 80° C. (mPa · s) 11.43 11.19 11.34 11.13 kinematic viscosity at 80° C./ 1.19 1.18 1.16 1.14 shear viscosity at 80° C. Total Efficiency (%) of 66.5 65.8 65.8 65.7 HPV35 + 35 Pump Test [35 MPa, 80° C.]

TABLE 2 Comp. Comp. Comp. Comp. Example 1 Example 2 Example 3 Example 4 Composition base oil 1 — — — — (% by mass) base oil 2 — balance balance balance base oil 3 balance — — — viscosity index improver A — — — — viscosity index improver B — — — — viscosity index improver C — 11.5 — — viscosity index improver D — 5 — — viscosity index improver E — — 10 — viscosity index improver F — — — 7 tricresyl phosphate 0.5 0.5 0.5 0.5 DBPC 0.5 0.5 0.5 0.5 pour point depressant 0.5 0.5 0.5 0.5 Properties kinematic viscosity at 40° C. (mm²/s) 45.21 44.97 47.30 45.23 kinematic viscosity at 80° C. (mm²/s) 11.98 13.75 15.70 13.08 kinematic viscosity at 100° C. (mm²/s) 7.51 8.94 10.44 8.38 viscosity index 132 184 218 164 shear viscosity at 80° C. (mPa · s) 10.10 9.12 11.19 8.70 kinematic viscosity at 80° C./ 1.19 1.51 1.40 1.50 shear viscosity at 80° C. Total Efficiency (%) of 64.7 64.0 65.1 63.6 HPV35 + 35 Pump Test [35 MPa, 80° C.]

Claims

1. A hydraulic oil composition comprising:

a lubricating base oil; and

0.2 to 40% by mass, based on a total amount of the hydraulic oil composition, of at least one copolymer selected from olefin copolymers having a number-average molecular weight of 18000 or lower and copolymers of an α-olefin and a dicarboxylic ester, having a number-average molecular weight of 20000 or lower.

2. The hydraulic oil composition according to claim 1, wherein the hydraulic oil composition has a viscosity index of 150 or higher; and a ratio (A/B) of (A) a kinematic viscosity (unit: mm2/s) at 80° C. to (B) a shear viscosity (unit: mPa·s, shear condition: 106/s) at 80° C. is 1.3 or lower.