Technical Field
[0001] The present invention relates to a hydraulic oil composition.
Background Art
[0002] 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.
[0003] 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
4
the oil temperature is raised. In,the energy-saving hydraulic oils, the
oil 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 cxample,
see Patent Literatures 1 to 3).
Citation List
Patent Literature
[0004] Patent Literature 1: Japanese Patent Application Laid-Open No.
2005-307197
Patent Literature 2: Japanese Patent Application Laid-Open No.
25 201 1-046900
Patent Literature 3: Japanese Patent Application Laid-Open No.
I
2012-180535
Summary of Inven~on
Technical Problem
[0005] 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.
[0006] 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 a$hieved, and enabling
the energy efficiency of a hydraulic system as a whole to be improved.
Solution to Problem
[0007] As a result of earnest studies, the present inventors have found a
composition exhibiting excellent viscosity characteristics 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.
[0008] That is, the present invention provides a hydraulic oil
composition comprising a lubricating base oil having a kinematic
viscosity at 40°C of 15 to 50 rnm2/s, a viscosity index of 125 or lower,
and an aromatic content of 1% by mass or higher, and 1 to 40% by mass
based on the total amount of the hydraulic oil composition of a
polymethacrylate having a number-average molecular weight of 28000
or lower.
[0009] The hydraulic oil composition preferably has the ratio (Am) of
(A) a kinematic viscosity (unit: mm2/s) at 80°C to (B) a high shear
viscosity (unit: rnPas, shear condition: 10 ~1so) f 1.15 or lower.
Advantageous Effects of Invention
[0010] The present invention can provide a hydraulic oil composition
which enables both the internal leakage prevention and the plumbing
resistance reduction to be compatibly achieved, and enables the energy
efficiency of a hydraulic system as a whole to be improved.
Description of Embodiments
[0011] Hereinafter, a preferred embodiment according to the present
invention will be described.
4 [0012] A hydraulic oil composition according to the present
embodiment comprises a lubricating base oil having a kinematic
viscosity at 40°C of 15 to 50 rnm2/s, a viscosity index of 125 or lower,
and an aromatic content of 1% by mass or higher, and 1 to 40% by mass
based on the total amount of the hydraulic oil composition of a
polymethacrylate having a number-average molecular weight of 28000
or lower.
[0013] The lubricating base oil to be used in the present embodiment
includes mineral oils, and synthetic hydrocarbon oils. These
lubricating base oils can be used singly or in combinations of two or
more.
[0014] The mineral oil is not especially limited, but examples thereof
include paraffmic 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 refming treatments including solvent deasphalting, solvent
extraction, hydrocracking, solvent dewaxing, catalytic dewaxing,
hydrorefining, sulfuric acid cleaning and clay treatment.
[0015] Examples of the synthetic hydrocarbon oil include
poly-a-olefins (polybutene, 1-octene oligomers, 1-decene oligomers
and the like), alkylbenzenes and alkylnaphthalenes.
[0016] The kinematic viscosity at 40°C of the lubricating base oil is 15
to 50 mm2/s, preferably 20 to 45 mm2/s, more preferably 25 to 40
rnm2/s, and still more preferably 25 to 35 mm2/s. When the kinematic
viscosity at 40°C is 15 rnm2/s or higher, the case is preferable in the
points of being capable of preventing the lowering of the flash point,
and of the evaporation. Further when the kinematic viscosity at 40°C
is 50 mm2/s or lower, the plumbing resistance can be reduced.
[0017] The viscosity index of the lubricating base oil is 125 or lower,
and preferably 120 or lower. Further the viscosity index of the
lubricating base oil is preferably 90 or higher, more preferably 100 or
higher, and still more preferably 105 or higher. When the viscosity
index is 90 or higher, since when the kinematic viscosity at high
temperatures is secured, the kinematic viscosity at low temperatures is
suppressed in becoming high, the lowering of the efficiency of a
hydraulic system can be suppressed.
[0018] Here, the "kinematic viscosity" and the "viscosity index" in the
25 present invention mean values measured according to JIS K 2283.
[0019] The aromatic content of the lubricating base oil is 1% by mass
or higher, preferably 1.5% by mass or higher, and more preferably 2%
by mass or higher. When the aromatic content is 1% by mass or
higher, the solubility and the viscosity-increasing effect of the
polymethacrylate are likely to be improved. The upper limit of the
aromatic content of the lubricating base oil is not especially limited, but
the aromatic content of the lubricating base oil is, for example, 35% by
mass or lower.
[0020] The sulfur content of the lubricating base oil is not especially
limited, but is preferably 5000 ppm by mass or lower, more preferably
3000 ppm by mass or lower, still more preferably 1000 ppm by mass or
lower, and most preferably 300 ppm by mass. When the sulhr content
is 5000 ppm by mass or lower, the case is preferable in the points of the
oxidation stability and the corrosion resistance.
[0021] The content of the lubricating base oil is preferably 40% by
mass or higher, more preferably 50% 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, more preferably 98% by mass
or lower, and still more preferably 95% by mass or lower based on the
total amount of the hydraulic oil composition. When the content of the
lubricating base oil is 40% by mass or higher, the excellent advantages
of the hydraulic oil are easily fully exhibited.
[0022] The polymethacrylate which the hydraulic oil composition
according to the present embodiment contains is a polymethacrylate
25 having a number-average molecular weight of 28000 or lower.
Suitable examples of such a polymethacrylate include a non-dispersant
polymethacrylate having a structural unit represented by the following
formula (1) and a dispersant polymethacrylate having a structural unit
represented by the following formula (2).
[0023] [Chemical Formula 11
[In the formula (I), a is an integer of 1 or more, and is an integer such
that the number-average molecular weight of the polymethacrylate is
28000 or lower; and R' represents an alkyl group having 1 to 22 carbon
atoms.]
[0024] [Chemical Formula 21
[In the formula (2), each of b and c is an integer of 1 or more, and is
integer such that the number-average molecular weight of the
polymethacrylate is 28000 or lower; R' represents an alkyl group having
1 to 22 carbon atoms; R~ represents hydrogen or a methyl group; and X
represents a polar group.]
[0025] The number-average molecular weight of the polymethacrylate
is 28000 or lower, preferably 25000 or lower, more preferably 23000 or
lower, and still more preferably 20000 or lower. Further the
number-average molecular weight of the polymethacrylate is preferably
2000 or higher, more preferably 5000 or higher, and still more
preferably 10000 or higher. When the number-average molecular
weight of the polymethacrylate is 28000 or lower, the case is preferable
in the point of an effect of improving the high shear viscosity; and when
that is 2000 or higher, the case is preferable in the point of an effect of
improving the viscosity index.
[0026] The content of the polymethacrylate is 1 to 40% by mass based
on the total amount of the hydraulic oil composition. The content of
the polymethacrylate is preferably 3% by mass or higher, more
preferably 5% by mass or higher, and still more preferably 10% by mass
or higher. Further the content of the polymethacrylate is preferably
30% by mass or lower, more preferably 25% by mass or lower, and still
more preferably 20% by mass or lower. When the content of the
polymethacrylate is 1% by mass or higher, the case is preferable in the
point an effect of improving the high shear viscosity; and when that is
35% by rnass or lower, the case is preferable in the point that the effect
corresponding to the cost can be anticipated.
[0027] The kinematic viscosity at 40°C of the hydraulic oil composition
is preferably 20 mm2/s or higher, more preferably 30 d s or higher,
still more preferably 40 rnm2/s or higher, and most preferably 41.4
25 mm2/s or higher. Further the kinematic viscosity at 40°C is preferably
SO rnm2/s or lower, more preferably 70 mm2/s or lower, still more
preferably 60 mm2/s or lower, and most preferably 50.6 mm2/s or lower.
When the kinematic viscosity at 40°C 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.
[0028] The ratio (A/B) of (A) a kinematic viscosity (unit: mm2/s) at
80°C to (B) a high shear viscosity (unit: &as, shear condition: 106/s)
at 80°C, with respect to the hydraulic oil composition, is preferably 1.15
or lower, more preferably 1.14 or lower, still more preferably 1.13 or
lower, and most preferably 1.12 or lower. When the above ratio (A/B)
is 1.15 or lower, the case is preferable in the points of the pump
efficiency and the plumbing resistance. The lower limit of the above
ratio (AIB) is not especially limited, but is, for example, 1.0 or higher.
[0029] Here, the "high shear viscosity" in the present invention means a
value measured according to ASTM (D4741, D4683, D6616), CEC
(L-36A-90).
[0030] The hydraulic oil composition according to the present
embodiment, in order to more improve its excellent advantages, can
hrther 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.
[0031] Examples of the extreme pressure agent includes sulfur
compounds such as ester sulfides, sulfurized fats and oils and
polysulfides, zinc dithiophosphate, and phosphorus compounds, and
phosphorus compounds are preferable. 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 are esters
of phosphoric acid, phosphorous acid or thiophosphoric acid with an
alkanol or a polyetheric alcohol, and their derivatives.
[0032] Among the above phosphoms 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.
[0033] Examples of the antioxidant include phenolic compounds such
4 as 2,6-ditertiary-butyl-p-cresol (DBPC), aromatic amines such as
phenyl-a-naphthylamine 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.
100341 Examples of the pour point depressant are copolymers of one or
two or more monomers 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.
100351 Examples of the rust-preventive agent are amino acid
derivatives, partial esters of polyhydric alcohols; esters such as lanolm
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; mines; 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.
[0036] 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.
[0037] The hydraulic oil composition can Wher comprise a viscosity
4 index improver other,than the above polymethacrylate. Examples of
the viscosity index improver include non-dispersant viscosity index
improvers such as copolymers of one or two or more monomers
selected from various types of methacrylate esters, or hydrogenated
substances thereof, polyisobutylenes or hydrogenated si~bstances
thereof, hydrogenated styrene-diene copolymers, and polyalkylstyrenes.
It is preferable that the content of the viscosity index improver is 0.01 to
15% by mass based on the total amount of the hydraulic oil
composition.
[0038] Examples of the antifoaming agent are silicones such as
dimethylsilicones and fluorosilicones. 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.
[0039] Examples of the demulsifier include polyoxyalkylene glycols,
polyoxyalkylene alkyl ethers, polyoxyalkylene alkylarnides and
polyoxyalkylene fatty acid esters.
[0040] Examples of the oiliness agent include fatty acids, esters and
5 alcohols. It is preferable that the content of the oiliness agent is 0.01 to
I
I 0.5% by mass based on the total amount of the hydraulic oil
I composition.
Examples
[0041] Hereinafter, the present invention will be described more
10 specifically by way of Examples and Comparative Examples, but the
present invention is not any more limited to these contents.
LO0421 In Examples 1 to 3 and Comparative Examples 1 to 3, hydraulic
oil compositions were each prepared by blending a lubricating base oil
4 and additives in a composition shown in Table 1 and Table 2. In the
15 preparation of the hydraulic oil composition, by regulating the amount
of a viscosity index improver to be blended according to its molecular
! weight, the kinematic viscosity at 40°C of the hydraulic oil composition
was regulated so that the IS0 viscosity grade became VG46. The
I
lubricating base oils and the additives used in the Examples and the
I i/ 20 Comparative Examples are as follows.
I
j [0043] !
i
I
i Base oil 1: a solvent refined mineral oil (aromatic content: 30.0% by
1 mass, sulfur content: 2300 ppm by mass, kinematic viscosity at 40°C: 1
28.6 mm2/s, viscosity index: 101)
25 Base oil 2: a solvent refined mineral oil + a hydrorefined mineral oil
(aromatic content: 13.0% by mass, sulfur content: 600 ppm by mass,
kinematic viscosity at 40°C: 26.6 mm2/s, viscosity index: 103)
Base oil 3: a hydrorefmed mineral oil (aromatic content: 2.0% by mass,
sulfur content: 10 ppm by mass or less, kinematic viscosity at 40°C:
29.5 mm2/s, viscosity index: 117)
Base oil 4: hydrorefined mineral oil (aromatic content: 0.5% by mass,
s u l k content: 10 ppm by mass or lower, kinematic viscosity at 40°C:
36.4 mm2/s, viscosity index: 13 1)
Base oil 5: hydrorefined mineral oil (aromatic content: 0.5% by mass,
s u l k content: 10 ppm by mass or lower, kinematic viscosity at 40°C:
39.6 m d s , viscosity index: 130)
[0044] Here, the aromatic content was measured according to
silica-alumina gel chromatography described in "Separation of
High-Boiling Petroleum Distillates Using Gradient Elution Through
1 Dual-Packed (Silica Gel-Alumina Gel) Adsoption Columns,"
Analytical Chemistry, Vol. 44, No. 6, (1972), pp.915-919.
[0045] Further the s u l k content was measured according to ASTM
D495 1, "Standard Test Method for Determination of Additive Elements
in Lubricating Oils by Inductively Coupled Plasma Atomic Emission
Spectrometry."
[0046] Further the kinematic viscosity and the viscosity index were
measured according to JIS K2283.
[0047]
As other additives, tricresyl phosphate, 2,6-ditertiary-butyl-pcresol
(DBPC) and a pour point depressant were used.
[0049] For each hydraulic oil composition obtained in Examples 1 to 3
and Comparative Examples 1 to 3, the kinematic viscosities at 40°C,
80°C and 100°C and the viscosity indices were measured according to
JIS K 2283. Further for each hydraulic oil composition, the high shear
viscosity at 80°C at a shear condition of 106/s was measured according
to ASTM (D4741, D4683, D6616), CEC (L-36A-90). A measuring
instrument used was a USV (Ultra Shear Viscometer) viscometer,
manufactured by PCS Instruments. The results are shown in Table 1
1 and Table 2. I
[0050] An HPV35+35 pump test was carried out on each hydraulic oil
composition obtained in Examples 1 to 3 and Comparative Examples 1
to 3. 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 2.
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

claim
1. A hydraulic oil composition comprising:
i a lubricating base oil having a kinematic viscosity at 40°C of 15
to 50 mm2/s, aviscosity index of 125 or lower, and an I aromatic content 1 5 of 1% by mass or higher; and
I 1 to 40% by mass based on a total amount of the hydraulic oil
I
1 composition of a polymethacrylate having a number-average molecular
weight of 28000 or lower.
I 2. The hydraulic oil composition according to claim 1, wherein the
10 hydraulic oil composition has a ratio (AIB) of (A) a kinematic viscosity
I (unit: m d s ) at 80°C to (B) a high shear viscosity (unit: @as, shear
I ~ condition: 1 06/s) at 80°C of 1.15 or lower.