US20170175029A1

US20170175029A1 - Lubricating-oil composition

Info

Publication number: US20170175029A1
Application number: US15/300,163
Authority: US
Inventors: Nobuaki Watanabe
Original assignee: Idemitsu Kosan Co Ltd
Current assignee: Idemitsu Kosan Co Ltd
Priority date: 2014-03-31
Filing date: 2015-03-30
Publication date: 2017-06-22
Also published as: JPWO2015152143A1; WO2015152143A1; JP6729866B2

Abstract

By using a lubricating oil composition containing (1) a base oil comprising a base oil A having a kinematic viscosity at 100° C. of 2 mm²/s or more and 7 mm²/s or less and a viscosity index of 120 or less, (2) at least one selected from an acrylate-based polymer and an olefin-based polymer each having a mass average molecular weight of 40,000 or less, and (3) a lubricating oil additive comprising a sulfur-based extreme pressure agent; and having a kinematic viscosity at 100° C. of more than 9.3 mm²/s and 12.5 mm²/s or less and a high temperature high shear viscosity at 150° C. of 2.9 mPa·s or more, a lubricating oil composition capable of making both a lowering in viscosity for fuel saving properties and fatigue resistance for improvement of fatigue life compatible with each other and also having excellent low-temperature viscosity properties is provided.

Description

TECHNICAL FIELD

The present invention relates to a lubricating oil composition having excellent fuel saving properties and fatigue resistance and having excellent low-temperature viscosity properties. In detail, the present invention relates to a lubricating oil composition for internal combustion engine, which is capable of lubricating gears or bearings as a two-wheeled vehicle engine oil, a transmission oil, and so on.

BACKGROUND ART

At the request of energy conservation or reduction of carbon dioxide, fuel saving properties are also required in lubricating oils for internal combustion engine (engine oil). With respect to engine oils to be used for four-wheeled vehicles, as means for enhancing the fuel saving properties, a lowering in viscosity or an improvement in viscosity index has hitherto been performed, and a variety of polymers, such as viscosity index improvers, etc., to be used therefor, and so on have also been proposed (see, for example, PTLs 1 to 8). But, when an engine oil whose viscosity is lowered from the viewpoint of fuel saving properties is, for example, used for two-wheeled vehicles, there was a case where a variety of problems are generated due to a difference in mechanical structure between a four-wheeled vehicle and a two-wheeled vehicle (see, for example, PTL 9).

CITATION LIST

Patent Literature

PTL 1: JP 10-114895 A
PTL 2: Japanese Patent No. 3955573
PTL 3: Japanese Patent No. 4359807
PTL 4: Japanese Patent No. 4283120
PTL 5: JP 2008-208221 A
PTL 6: JP 2009-221382 A
PTL 7: JP 2010-280821 A
PTL 8: Japanese Patent No. 5319996
PTL 9: JP 2011-195734 A

SUMMARY OF INVENTION

Technical Problem

That is, in general, the two-wheeled vehicle has a structure in which lubrication of a variable transmission is performed along with lubrication of an engine by the same engine oil. In consequence, for example, when a viscosity-lowered engine oil (for example, a 10W-30 viscosity grade oil) is used in a two-wheeled vehicle, the possibility that a fatigue damage, such as pitching, etc., is generated in gears or bearings of a variable transmission (particularly radial needle bearings within a crank shaft) becomes large.
In the light of the above, for example, in an engine oil for two-wheeled vehicle, since it lubricates gears or bearings of a variable transmission, in addition to a lowering in viscosity of the engine oil, an improvement of fatigue life, namely an improvement of fatigue resistance, is a problem. In consequence, in the case where it is contemplated to lower the viscosity of an engine oil to be used for a two-wheeled vehicle to improve the fuel consumption reducing properties, it is necessary to solve these problems.
A problem of the present invention is to provide a lubricating oil composition capable of making both lowering in viscosity for fuel saving properties and fatigue resistance for improvement of fatigue life compatible with each other and also having excellent low-temperature viscosity properties.

Solution to Problem

In view of the foregoing problem, the present inventor made extensive and intensive investigations. As a result, it has been found that the foregoing problem of the present invention can be solved by blending a specified low-molecular weight polymer in a viscosity-lowered lubricating oil in which a kinematic viscosity at 100° C. and a high temperature high shear viscosity (HTHS viscosity) at 150° C. are prescribed to specified ranges, respectively, leading to accomplishment of the present invention.
Specifically, the present invention is as follows.
[1] A lubricating oil composition containing (1) a base oil including a base oil A having a kinematic viscosity at 100° C. of 2 mm²/s or more and 7 mm²/s or less and a viscosity index of 120 or less, (2) at least one selected from an acrylate-based polymer and an olefin-based polymer each having a mass average molecular weight of 40,000 or less, and (3) a lubricating oil additive including a sulfur-based extreme pressure agent; and having a kinematic viscosity at 100° C. of more than 9.3 mm²/s and 12.5 mm²/s or less and a high temperature high shear viscosity at 150° C. of 2.9 mPa·s or more.
[2] The lubricating oil composition as set forth above in [1], which has a CCS viscosity at −25° C. of 7,000 mPa·s or less and a viscosity index of 135 or more.
[3] The lubricating oil composition as set forth above in [1] or [2], wherein the acrylate-based polymer and/or the olefin-based polymer each having a mass average molecular weight of 40,000 or less is a poly-α-olefin obtained from at least one selected from α-olefins having a carbon number of 8 or more and 12 or less and having a kinematic viscosity at 100° C. of 100 mm²/s or more and 2,000 mm²/s or less.
[4] The lubricating oil composition as set forth above in any of [1] to [3], wherein a central oil film thickness in the measurement of an oil film thickness in the elastohydrodynamic lubrication (EHL) state is 50 nm or more at a rolling speed of 1.6 m/s.
[5] The lubricating oil composition as set forth above in any of [1] to [4], wherein in the evaluation of fatigue life of a radial rolling bearing, a 50% failure probability (L50) is 3.0×10⁶times or more.
[6] The lubricating oil composition as set forth above in any of [1] to [5], wherein the base oil further includes a base oil having a viscosity index of more than 120.
[7] The lubricating oil composition as set forth above in any of [1] to [6], wherein a kinematic viscosity at 100° C. after a shear test of the lubricating oil composition is 9 mm²/s or more.
[8] The lubricating oil composition as set forth above in any of [1] to [7], which is used for internal combustion engines.
[9] The lubricating oil composition as set forth above in any of [1] to [8], which is used for two-wheeled vehicle internal combustion engines.
[10] A production method of a lubricating oil composition including blending (1) a base oil including a base oil A having a kinematic viscosity at 100° C. of 2 mm²/s or more and 7 mm²/s or less and a viscosity index of 120 or less with (2) at least one selected from an acrylate-based polymer and an olefin-based polymer each having a mass average molecular weight of 40,000 or less and (3) a lubricating oil additive including a sulfur-based extreme pressure agent, to produce a lubricating oil composition having a kinematic viscosity at 100° C. of more than 9.3 mm²/s and 12.5 mm²/s or less and a high temperature high shear viscosity at 150° C. of 2.9 mPa·s or more.
[11] An internal combustion engine for which a lubricating oil composition containing (1) a base oil including a base oil A having a kinematic viscosity at 100° C. of 2 mm²/s or more and 7 mm²/s or less and a viscosity index of 120 or less, (2) at least one selected from an acrylate-based polymer and an olefin-based polymer each having a mass average molecular weight of 40,000 or less, and (3) a lubricating oil additive including a sulfur-based extreme pressure agent; and having a kinematic viscosity at 100° C. of more than 9.3 mm²/s and 12.5 mm²/s or less and a high temperature high shear viscosity at 150° C. of 2.9 mPa·s or more, is used.
[12] A lubrication method of an internal combustion engine to be lubricated using a lubricating oil composition containing (1) a base oil including a base oil A having a kinematic viscosity at 100° C. of 2 mm²/s or more and 7 mm²/s or less and a viscosity index of 120 or less, (2) at least one selected from an acrylate-based polymer and an olefin-based polymer each having a mass average molecular weight of 40,000 or less, and (3) a lubricating oil additive including a sulfur-based extreme pressure agent; and having a kinematic viscosity at 100° C. of more than 9.3 mm²/s and 12.5 mm²/s or less and a high temperature high shear viscosity at 150° C. of 2.9 mPa·s or more.

Advantageous Effects of Invention

In accordance with the present invention, it is possible to provide a lubricating oil composition capable of making both a lowering in viscosity for fuel saving properties and fatigue resistance for improvement of fatigue life compatible with each other and also having excellent low-temperature viscosity properties.
In addition, in accordance with the present invention, it is possible to provide a lubricating oil composition capable of lubricating any of an engine and a variable transmission as a lubricating oil composition for two-wheeled vehicle internal combustion engine.

DESCRIPTION OF EMBODIMENTS

The present invention is hereunder described in more detail.
The lubricating oil composition of the present invention is one containing (1) a base oil including a base oil A having a kinematic viscosity at 100° C. of 2 mm²/s or more and 7 mm²/s or less and a viscosity index of 120 or less, (2) at least one selected from an acrylate-based polymer and an olefin-based polymer each having a mass average molecular weight of 40,000 or less, and (3) a lubricating oil additive including a sulfur-based extreme pressure agent; and having a kinematic viscosity at 100° C. of more than 9.3 mm²/s and 12.5 mm²/s or less and a high temperature high shear viscosity (hereinafter referred to as “HTHS viscosity”) at 150° C. of 2.9 mPa·s or more.

[(1) Base Oil]

The base oil that is used for the lubricating oil composition of the present invention includes a base oil A having a kinematic viscosity at 100° C. of 2 mm²/s or more and 7 mm²/s or less and a viscosity index of 120 or less. As a base oil that may be used for a viscosity-lowered lubricating oil, though a high-quality base oil having a high viscosity index has hitherto been used, in the present invention, a relatively low-quality base oil having a low viscosity index can also be used as the base oil. That is, from the viewpoints of lowering the viscosity and reducing the costs, preferably, a base oil A having a kinematic viscosity at 100° C. of 3 mm²/s or more and 6 mm²/s or less and a viscosity index of 110 or less can be used. Specifically, mineral oil-based base oils belonging to Group I and Group II in the API (American Petroleum Institute) base oil category can also be used.
The viscosity index and the kinematic viscosity at 100° C. of the base oil can be measured in conformity with JIS K2283 (ASTM D445).
From the aforementioned viewpoints, the base oil in the lubricating oil composition of the present invention contains the aforementioned base oil A in an amount of preferably 70 mass % or more, more preferably 80 mass % or more, and still more preferably 100 mass %.
It is arbitrary to use other base oil together with the base oil A in the base oil in the present invention. Though the base oil that may be used is not particularly limited, so long as the effects of the present invention are not impaired, from the viewpoint of low-temperature viscosity properties, a base oil whose viscosity index is more than 120 can also be used. Specifically, mineral oils or synthetic base oils belonging to Group III in the API base oil category can be used. Such a base oil is contained in an amount of preferably less than 30 mass % in the base oil in the present invention.
The base oil A-including base oil that is the base oil in the lubricating oil composition of the present invention is not particularly limited so long as its properties are satisfied with properties prescribed with respect to the obtained lubricating oil composition.
As the mineral oil-based base oil that may be used in the present invention, for example, all of a base oil obtained through refining by subjecting a lubricating oil distillate that is obtained by atmospheric distillation of a crude oil, or distillation under reduced pressure of an atmospheric residue given by atmospheric distillation of a crude oil, to one or more treatments of solvent deasphalting, solvent extraction, hydro-cracking, solvent dewaxing, hydrorefining, and the like; a mineral oil produced by isomerizing a mineral oil-based wax or a wax produced by a Fischer-Tropsch process or the like (gas-to-liquid wax); and the like are exemplified.
Meanwhile, as the synthetic oil, poly-α-olefins, polybutene, polyol esters, dibasic acid esters, aromatic esters, phosphate esters, polyphenyl ethers, alkylbenzenes, alkylnaphthalenes, polyoxyalkylene glycols, neopentyl glycol, silicone oil, trimethylolpropane, pentaerythritol, hindered esters, and the like can be used.

[(2) Acrylate-Based Polymer and Olefin-Based Polymer]

From the viewpoint of improving the fatigue resistance, particularly prolonging the life in fatigue life of radial needle, the lubricating oil composition of the present invention contains at least one selected from an acrylate-based polymer and an olefin-based polymer each having a mass average molecular weight of 40,000 or less.
Examples of the acrylate-based polymer having a mass average molecular weight of 40,000 or less include a polymethacrylate (PMA). As the polymethacrylate, any of a dispersion type and a non-dispersion type can be used. Specifically, there can be exemplified so-called non-dispersion type polymethacrylates, such as various methacrylic esters or copolymers according to an arbitrary combination thereof or hydrides thereof, etc.; so-called dispersion type polymethacrylates obtained through copolymerization of various methacrylic esters containing a nitrogen compound; and the like. These polymethacrylates may be used alone or in combination of any two or more thereof.
Examples of the olefin-based polymer having a mass average molecular weight of 40,000 or less include homopolymers or copolymers of an α-olefin, ethylene-α-olefin copolymers, polybutene, and the like. Of those, the homopolymers or copolymers of an α-olefin are a homopolymer or copolymer of an α-olefin having preferably 2 to 30 carbon atoms, more preferably 4 to 22 carbon atoms, still more preferably 6 to 16 carbon atoms, yet still more preferably 6 to 14 carbon atoms, and especially preferably 8 to 12 carbon atoms, and the copolymer may be either a random copolymer or a block copolymer.
Examples of the α-olefin that may be used include α-olefins having 2 to 30 carbon atoms, such as ethylene, propylene, isobutylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-nonene, 1-decene, 1-dodecene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadene, 1-eicosene, etc.
Examples of the ethylene-α-olefin copolymer include copolymers of ethylene and an α-olefin. As the α-olefin, propylene or an α-olefin the same as those used for the aforementioned homopolymers or copolymers of an α-olefin is useful. The ethylene-α-olefin copolymer may be a random copolymer.
These olefin-based polymers may be used alone or in combination of any two or more thereof.
These olefin-based polymers can be produced by an arbitrary method. For example, the olefin-based polymer can be produced through a thermal reaction in the absence of a catalyst. Besides, the olefin-based polymer can be produced through homopolymerization or copolymerization of an olefin using a known catalyst system inclusive of organic peroxide catalysts, such as benzoin peroxide, etc.; Friedel-Crafts catalysts, such as aluminum chloride, an aluminum chloride-polyhydric alcohol-based catalyst, an aluminum chloride-titanium tetrachloride-based catalyst, an aluminum chloride-alkyltin halide-based catalyst, boron fluoride, etc.; Ziegler type catalysts, such as an organoaluminum chloride-titanium tetrachloride-based catalyst, an organoaluminum-titanium tetrachloride-based catalyst, etc.; metallocene type catalysts, such as an aluminoxane-zirconocene-based catalyst, an ionic compound-zirconocene-based catalyst, etc.; Lewis acid complex type catalysts, such as an aluminum chloride-base-based catalyst, a boron fluoride-base-based catalyst, etc.; and the like. In the present invention, though the aforementioned olefin-based polymer can be used, when taking into consideration its heat or oxidation stability, a hydride of an olefin-based polymer resulting from hydrogenation of a double bond in the olefin-based polymer can also be used.
Of the aforementioned acrylate-based polymer and olefin-based polymer (2), in the present invention, the olefin-based polymer is preferably used from the viewpoint of fatigue resistance. From the viewpoints of a lowering in viscosity and an improvement in fatigue resistance and also an improvement in low-viscosity properties, a poly-α-olefin obtained from at least one selected from α-olefins having a carbon number of 8 or more and 12 or less and having a kinematic viscosity at 100° C. of 100 mm²/s or more and 2,000 mm²/s or less is preferably used (such a poly-α-olefin will be hereinafter referred to as “high-viscosity PAO”).
The carbon number of the α-olefin that is a raw material monomer of the high-viscosity PAO is preferably 8 or more and 12 or less, more preferably 9 or more and 11 or less, and still more preferably 10 from the viewpoints of an improvement in fatigue resistance, workability, lubricating oil adaptability, and so on. Specifically, among the aforementioned α-olefins, those having a carbon number of 8 or more and 12 or less are used. In addition, the kinematic viscosity at 100° C. of the high-viscosity PAO is preferably 100 mm²/s or more and 1,800 mm²/s or less, more preferably 100 mm²/s or more and 1,500 mm²/s or less, and still more preferably 200 mm²/s or more and 1,000 mm²/s or less from the viewpoints of excellent viscosity index improving ability, favorable fluidity, and excellent fatigue resistance.
The kinematic viscosity at 100° C. of the high-viscosity PAO can be measured in conformity with JIS K2283 (ASTM D445).
In the present invention, as the high-viscosity PAO, from the viewpoints of a lowering in viscosity, fatigue resistance, and low-temperature viscosity properties, one having at least one of the following composition (I) and properties (II) and/or one obtained by the following production method (III) can be more preferably used.
(I) In the aforementioned high-viscosity PAO, a proportion of dimer and trimer components is preferably less than 2 mass %, more preferably less than 1.5 mass %, and still more preferably less than 1.0 mass %. According to this, the high-viscosity PAO is small in the molecular weight distribution and has a more uniform composition, so that a polymer having a desired viscosity region can be obtained. The high-viscosity PAO does not substantially contain a performance-lowering component, and hence, it is useful as a lubricating oil component. The proportion of the aforementioned dimer and trimer components can be controlled by a polymerization condition and can be determined by means of gas chromatography.
(II) From the any viewpoint of a lowering in viscosity, fatigue resistance, and low-temperature viscosity properties, it is preferred that the aforementioned high-viscosity PAO has at least one selected from the following four properties.
(II-1) it is amorphous; (II-2) a viscosity index is 150 or more; (II-3) a pour point is −15° C. or lower; and (II-4) an average carbon number is 4 or more and 15 or less.
In view of the fact that as the viscosity index is higher, the temperature dependency becomes smaller, and the low-temperature properties become more favorable, the viscosity index of the high-viscosity PAO is more preferably 1.70 or more. In addition, in view of the fact that as the low-temperature pour point is lower, the low-temperature properties are more favorable, the pour point of the high-viscosity PAO is more preferably −20° C. or lower, and still more preferably −30° C. or lower. Furthermore, the average carbon number of the high-viscosity PAO is more preferably 8 or more and 12 or less.
It is meant by the term “amorphous” as referred to herein that the high-viscosity PAO has properties generally revealed in the case of “amorphous”, for example, a melting point is not present, but only a glass transition temperature is present; transparency is given; a change in volume at the time of cooling for solidification is small, and so on. As for the high-viscosity PAO, the viscosity index can be measured in conformity with JIS K2283 (ASTM D445); the pour point can be measured in conformity with JIS K2269; and the average carbon number can be measured by means of the NMR measurement, respectively.
(III) It is preferred to produce the aforementioned high-viscosity PAO in conformity with, for example, the method described in the pamphlet of WO 2012/035710 A.
That is, specifically, the high-viscosity PAO can be obtained through polymerization of the aforementioned α-olefin alone or a mixture of any two or more thereof using a polymerization catalyst containing (A) a meso-type transition metal compound, (B) at least one compound of (B-1) a compound capable of reacting with the transition metal compound (A) or a derivative thereof to form an ionic complex and (B-2) an aluminoxane, and (C) an organoaluminum compound.
As for the meso-type transition metal compound (A), those described in paragraphs [0036] to [0063] of the pamphlet of WO 2012/035710 A; as for the compound (B), those described in paragraphs [0065] to [0075] of the same pamphlet; as for the organoaluminum compound (C), those described in paragraphs [0077] and [0078] of the same pamphlet; and furthermore, as for the obtained polymerization catalyst, those described in paragraphs [0076] and [0079] to [0089] of the same pamphlet can be used, respectively.
Specifically, as the polymerization catalyst, there can be preferably exemplified (1,1′-ethylene) (2,2′-tetramethyldisilylene)-bis(indenyl)zirconium dichloride, (1,1′-tetramethylenedisilylene) (2,2′-ethylene)-bis(indenyl)zirconium dichloride, (1,1′-tetramethylethylene)(2,2′-tetramethyldisilylene)-bis(indenynzirconium dichloride, (1,1′-tetramethylenedisilylene)(2,2′-tetramethylethylene)-bis(indenyl)zirconium dichloride, (1,1′-dimethylsilylenemethylene) (2,2′-ethylene)-bis(3 methylindenyl) zirconium dichloride, (1,1′-ethylene) (2,2′-dimethylsilylenemethylene)-bis(3-methylindenyl)zirconium dichloride, (1,1′-ethylene) (2,2′-tetramethyldigermirene)-bis(indenyl)zirconium dichloride, (1,1′-tetramethyldigermirene) (2,2′-ethylene)-bis(indenyl)zirconium dichloride,
(1,1′-ethylene)(2,2′-tetramethyldisilylene)-bis(3-methylindenyl)zirconium dichloride, (1,1′-tetramethyldisilylene) (2,2′-ethylene)-bis(3-methylindenyl) zirconium dichloride, (1,1′-tetramethylethylene)(2,2′-tetramethyldisilylene)-bis(3-methylindenyl) zirconium dichloride, (1,1′-tetramethyldisilylene)(2,2′-tetramethylethylene)-bis (3-methylindenyl)zirconium dichloride, (1,1′-dimethylsilylenemethylene)(2,2′-ethylene)-bis(3-methylindenyl)zirconium dichloride, (1,1′-ethylene)(2,2′-dimethylsilylenemethylene)-bis(3-methylindenyl) zirconium dichloride, (1,1′-ethylene)(2,2′-tetramethyldigermirene)-bis(3-methylindenyl)zirconium dichloride, (1,1′-tetramethyldigermirene)(2,2′-ethylene)-bis(3-methylindenyl)zirconium dichloride, and the like, and also compounds obtained by substituting zirconium of these compounds with titanium or hafnium. In addition, analogous compounds of other groups or lanthanoid series metal elements.
Though the polymerization method is not particularly limited, the polymerization can be performed in conformity with the method described in paragraphs [0090] to [0095] of the same pamphlet.
From the viewpoint of fatigue resistance for improvement in fatigue life, the molecular weight of each of the aforementioned acrylate-based polymer and olefin-based polymer (2) is 40,000 or less in terms of a mass average molecular weight. From the same viewpoint, the molecular weight is preferably 35,000 or less, more preferably 30,000 or less, still more preferably 25,000 or less, and especially preferably 20,000 or less. Though a lower limit value thereof is not particularly limited, similarly from the viewpoints of fatigue resistance and low-temperature viscosity properties, it is preferably 5,000 or more. The mass average molecular weight can be measured by the gel permeation chromatography (GPC) method and determined from a calibration curve prepared using polystyrene. For example, the mass average molecular weight of each of the aforementioned polymers can be calculated as a conversion value into polystyrene by the following GPC method.

Column: TOSO GMHHR-H(S)HT
Detector: RI detector for liquid chromatography, WATERS 150C

Solvent: 1,2,4-Trichlorobezene
Measurement temperature: 145° C.
Flow rate: 1.0 mL/min
Sample concentration: 2.2 mg/mL
Injection amount: 160 μL
Calibration curve: Universal Calibration
Analysis program: HT-GPC (Ver. 1.0)
From the viewpoints of a lowering in viscosity, fatigue resistance, and low-temperature viscosity properties, the kinematic viscosity at 100° C. of each of the aforementioned acrylate-based polymer and olefin-based polymer (2) is preferably 5 mm²/s or more and 15,000 mm²/s or less, more preferably 50 mm²/s or more and 10,000 mm²/s or less, still more preferably 100 mm²/s or more and 10,000 mm²/s or less, and especially preferably 100 mm²/s or more and 5,000 mm²/s or less.
The viscosity index of each of the aforementioned acrylate-based polymer and olefin-based polymer (2) is preferably 120 or more, and more preferably 150 or more. On the other hand, the viscosity index is preferably 350 or less, and more preferably 250 or less.
In the lubricating oil composition of the present invention, the aforementioned acrylate-based polymer and/or olefin-based polymer (2) is preferably contained in an amount in the range of 0.1 mass % or more and less than 20 mass % on a basis of the whole amount of the composition. So long as this amount falls within the foregoing range, in the obtained lubricating oil composition, an improvement in fatigue resistance is attained together with a lowering in viscosity, and favorable low-temperature viscosity properties are obtained. From the aforementioned viewpoints, the content of the acrylate-based polymer and/or olefin-based polymer is more preferably 0.5 mass % or more and 20 mass % or less, and still more preferably 1 mass % or more and 15 mass % or less on a basis of the whole amount of the composition.

[(3) Lubricating Oil Additive Including Sulfur-Based Extreme Pressure Agent]

The lubricating oil composition of the present invention contains a lubricating oil additive including a sulfur-based extreme pressure agent together with the aforementioned polymer.
Examples of the sulfur-based extreme pressure agent include zinc dithiophosphate (ZnDTP), sulfurized olefins, dialkyl polysulfides, diaryl polysulfides, zinc dithiocarbamate, disulfides, sulfurized oils and fats, sulfurized esters, thiocarbonates, thiocarbamates, and the like.; and examples thereof further include thiophosphite esters, thiophosphate esters, thiophosphonate esters, and amines or metal salts thereof, and the like. The aforementioned sulfur-based extreme pressure agent may be used alone or in combination of any two or more thereof. A content thereof is in the range of preferably 0.01 mass % or more and 10 mass % or less, and more preferably 0.5 mass % or more and 5 mass % or less on a basis of the whole amount of the composition. By using the aforementioned sulfur-based extreme pressure agent, for example, in a two-wheeled vehicle engine, etc. using a wet clutch, it reacts with the metal surface to form a film having a small coefficient of friction, thereby enabling one to contemplate to reduce the friction and improve the lubricity, and hence, such is preferred.
In the lubricating oil composition of the present invention, as other additives, all of additives that are generally used as lubricating oil additives can be used, and those used as lubricating oil additives for two-wheeled vehicle are preferably used. Specifically, lubricating oil additives represented by an extreme pressure agent other than sulfur-based extreme pressure agents, a friction modifier, an ashless dispersant, a metal-based detergent, an antioxidant, a metal deactivator, a rust preventive, a defoaming agent, a demulsifier, a coloring agent, etc., and the like can be used.
Examples of the extreme pressure agent other than sulfur-based extreme pressure agents include phosphorus-containing extreme pressure agents, such as a phosphite ester, a phosphate ester, a phosphonate ester, an alkyl hydrogen phosphite, and an amine or a metal salt thereof, etc., and the like.
In the lubricating oil composition of the present invention, in order to improve the fuel saving properties, a metal-based friction modifier or an ashless friction modifier can be contained. Specifically, examples of the friction modifier include an organic molybdenum-based compound, a fatty acid, a higher alcohol, oils and fats, an amide, a sulfurized ester, a phosphate ester, a phosphite ester, a phosphate ester amine salt, and the like. Though these friction modifiers can be used alone or as an arbitrary combination of plurality kinds thereof, a content thereof is typically in the range of 0.01 mass % or more and 10 mass % or less on a basis of the whole amount of the composition.
Examples of the ashless dispersant include polybutenylsuccinimide, polybutenylbenzylamine, and polybutenylamine, each of which has a polybutenyl group having a mass average molecular weight of 900 or more and 3,500 or less, and a derivative thereof, such as a boric acid-modified product thereof, etc., and the like. Though these ashless dispersants can be used alone or as an arbitrary combination of plural kinds thereof, a content thereof is typically in the range of 0.01 mass % or more and 10 mass % or less on a basis of the whole amount of the composition.
Examples of the metal-based detergent include a sulfonate, a phenate, a salicylate, and a naphthenate of an alkali metal (e.g., sodium (Na), potassium (K), etc.) or an alkaline earth metal (e.g., calcium (Ca), magnesium (Mg), etc.), and the like. These metal-based detergents can be used alone or as an arbitrary combination of plurality kinds thereof. A total base number and a content of such a metal-based detergent may be properly selected according to the required performance of the lubricating oil. The total base number is typically 0 mgKOH/g or more and 500 mgKOH/g or less, and preferably 10 mgKOH/g or more and 400 mgKOH/g or less by the perchloric acid method. In addition, a content thereof is typically in the range of 0.1 mass % or more and 10 mass % or less on a basis of the whole amount of the composition.
As the antioxidant, an arbitrary material can be properly selected and used among known antioxidants that have hitherto been used an antioxidant for an engine oil, and all of a phenol-based antioxidant, an amine-based antioxidant, a molybdenum-based antioxidant, a sulfur-based antioxidant, a phosphorus-based antioxidant, and the like can be used. Specifically, examples thereof include an amine-based antioxidant, such as an alkylated diphenylamine, phenyl-α-naphthylamine, an alkylated phenyl-α-naphthylamine, etc.; a phenol-based antioxidant, such as 2,6-di-tert-butylphenol, 4,4′-methylenebis(2,6-di-tert-butylphenol), isooctyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, octadecyl-di-tert-butyl-4-hydroxyphenyl)propionate, etc.; a sulfur-based antioxidant, such as dilauryl-3,3′-thiodipropionate, etc.; a phosphorus-based antioxidant, such as a phosphite, etc.; and a molybdenum-based antioxidant. These antioxidants can be used alone or as an arbitrary combination of plural kinds thereof. A blending amount thereof is in the range of 0.01 mass % or more and 10 mass % or less on a basis of the whole amount of the lubricating oil composition.
Examples of the metal deactivator include benzotriazole, a triazole derivative, a benzotriazole derivative, a thiadiazole derivative, and the like, and a content thereof is typically in the range of 0.01 mass % or more and 3 mass % or less on a basis of the whole amount of the lubricating oil composition.
Examples of the rust inhibitor include a fatty acid; an alkenyl succinic acid half ester; a fatty acid soap; an alkyl sulfonic acid salt; a sulfonate, a phenate, a salicylate, and a naphthenate of an alkaline earth metal (e.g., calcium (Ca), magnesium (Mg), barium (Ba), etc.); a polyhydric alcohol fatty acid ester; a fatty acid amine; an oxidized paraffin; an alkyl polyoxyethylene ether; and the like, and a content thereof is typically in the range of 0.01 mass % or more and 5 mass % or less on a basis of the whole amount of the composition.
As the defoaming agent, a liquid silicone is suitable, and for example, methyl silicone, fluorosilicone, a polyacrylate, and the like can be used. A preferred content of such a defoaming agent is 0.0005 mass % or more and 0.1 mass % or less on a basis of the whole amount of the composition.
As the demulsifier, an ethylene-propylene block polymer; a sulfonate, a phenate, a salicylate, and a naphthenate of an alkaline earth metal (e.g., calcium (Ca), magnesium (Mg), etc.); and the like can be used, and a content thereof is typically 0.0005 mass % or more and 1 mass % or less on a basis of the whole amount of the composition.
As the coloring agent, a dye, a pigment, and the like can be used, and a content thereof is typically 0.001 mass % or more and 1 mass % or less on a basis of the whole amount of the composition.
As mentioned previously, the lubricating oil composition in which a sulfur-based extreme pressure agent and optionally, various additives selected from an extreme pressure agent other than sulfur-based extreme pressure agents, a friction modifier, an antioxidant, a metal-based detergent, an ashless dispersant, a metal deactivator, a rust inhibitor, a defoaming agent, a demulsifier, a coloring agent, and the like are blended is typically one blending the foregoing additives therein; however, as the case may be, at least a part of the blended additives may be one converted into another compound through a reaction or the like.

[Lubricating Oil Composition]

The lubricating oil composition of the present invention contains the aforementioned base oil (1) including a base oil A having a kinematic viscosity at 100° C. of 2 mm²/s or more and 7 mm²/s or less and a viscosity index of 120 or less, the aforementioned acrylate-based polymer and/or olefin-based polymer (2) each having a mass average molecular weight of 40,000 or less, and the aforementioned lubricating oil additive (3) including a sulfur-based extreme pressure agent. According to such a constitution, by regulating the kinematic viscosity at 100° C. to more than 9.3 mm²/s and 12.5 mm²/s or less and the HTHS viscosity at 150° C. to 2.9 mPa·s or more, respectively, a lubricating oil composition capable of making both a lowering in viscosity for fuel saving properties and fatigue resistance for improvement of fatigue life compatible with each other and also having excellent low-temperature viscosity properties is obtained.
In the light of the above, in the lubricating oil composition of the present invention, not only the kinematic viscosity at 100° C. is more than 9.3 mm²/s and 12.5 mm²/s or less, but also the HTHS viscosity is 2.9 mPa·s or more. The HTHS viscosity is a viscosity in a lowered state under the high-temperature high-shear situation, and by regulating the kinematic viscosity at 100° C. and the HTHS viscosity at 150° C. to the foregoing ranges, respectively, it is possible to use the lubricating oil composition of the present invention as a viscosity-lowered two-wheeled vehicle engine oil of a 10W-30 viscosity grade. Also, the lubricating oil composition of the present invention maintains lubricity and realizes a lowering in viscosity, so that it is able to contribute to fuel saving properties. From this viewpoint, the kinematic viscosity at 100° C. of the lubricating oil composition is preferably more than 9.3 mm²/s and 11.0 mm²/s or less, and the HTHS viscosity at 150° C. is preferably 3.0 mPa·s or more. Here, though an upper limit value of the HTHS viscosity at 150° C. is not particularly limited, it is typically about 3.7 mPa·s.
The HTHS viscosity at 150° C. of the lubricating oil composition can be regulated by selecting the viscosity of the base oil, the kind, molecular weight, content, and so on of the acrylate-based polymer or olefin-based polymer, or other viscosity index improver, and the like. In addition, the kinematic viscosity at 100° C. of the lubricating oil composition can be measured in conformity with JIS K2283 (ASTM D445), and the HTHS viscosity at 150° C. can be measured in conformity with JPI-5S-36-03 (ASTM D4683).
Furthermore, in the lubricating oil composition of the present invention, it is preferred that the low-temperature viscosity (CCS viscosity at −25° C.) is 7,000 mPa·s or less, and the viscosity index is 135 or more. By allowing any one of the CCS viscosity at −25° C. and the viscosity index to fall within the foregoing range, the lubricating oil composition of the present invention maintains lubricity and realizes a lowering in viscosity and furthermore, is able to obtain favorable low-temperature viscosity properties, so that it is able to contribute to fuel consumption reducing properties. From this viewpoint, the CCS viscosity at −25° C. of the lubricating oil composition is more preferably 6,000 mPa·s or less, and still more preferably 5,500 mPa·s or less; and the viscosity index is more preferably 137 or more, and still more preferably 140 or more.
The CCS viscosity at −25° C. can be regulated by selecting the viscosity of the base oil, the kind, molecular weight, content, and so on of the acrylate-based polymer or olefin-based polymer, or other viscosity index improver, and the like. The CCS viscosity at −25° C. in the lubricating oil composition can be measured in conformity with JIS K2010 (ASTM D2602), and the viscosity index can be measured in conformity with JIS K2283 (ASTM D445).
Furthermore, with respect to the lubricating oil composition of the present invention, it is preferred that a kinematic viscosity at 100° C. after a shear test is 9 mm²/s or more. When the kinematic viscosity at 100° C. after a shear test is less than 9 mm²/s, the lubricity is not sufficient because of a lowering in viscosity at the time of a high temperature. From the aforementioned viewpoint, the kinematic viscosity at 100° C. after a shear test of the lubricating oil composition of the present invention is more preferably 9.3 mm²/s or more and 11.0 mm²/s or less.
The “kinematic viscosity at 100° C. after a shear test” in the present invention can be, for example, regulated by controlling the molecular weight, content, and so on of the acrylate-based polymer or olefin-based polymer, or other viscosity index improver, or the viscosity of the base oil, and the like. The shearing method is in conformity with JPI-5S-29 (ASTM D3945).
From the viewpoint of providing a lubricating oil composition which is lowered in viscosity for fuel saving properties and is excellent in low-temperature viscosity properties, in the lubricating oil composition of the present invention, a central oil film thickness in the measurement of an oil film thickness in the elastohydrodynamic lubrication (EHL) state is preferably 50 nm or more, more preferably 55 nm or more, and still more preferably 66 nm or more at a rolling speed of 1.6 m/s.
The oil film thickness can be measured using an EHL ultra thin film measurement system, manufactured by PCS Instruments under conditions of load: 20 N, temperature: 120° C., rolling speed: 0.05 to 1.6 m/s, and oil film thickness: 1 to 250 nm
From the viewpoint of providing a lubricating oil composition that is excellent in fatigue resistance for improvement of fatigue life, in the lubricating oil composition of the present invention, in the fatigue life of a radial rolling bearing, a 50% failure probability (L50) as a pitching life is preferably 3.0×10⁶times or more, more preferably 4.0×10⁶times or more, still more preferably 5.0×10⁶times or more, and especially preferably 6.0×10⁶times or more.
The fatigue life can be evaluated using a radial needle bearing fatigue-evaluating tester, manufactured by A&D Company, Limited under conditions of load: 3,000 N, temperature: 120° C., rotation rate: 2,000 rpm, and bearing: radial bearing (solid needle bearing: NSK LM1710).

[Internal Combustion Engine]

In view of the fact that the lubricating oil composition of the present invention has the aforementioned constitution and action and effect, it can be preferably used as a lubricating oil composition for internal combustion engine. Especially, in view of the fact that the lubricating oil composition of the present invention makes both lowering in viscosity for fuel consumption reducing properties and fatigue resistance for improvement of fatigue life compatible with each other and also has excellent low-temperature viscosity properties, it is not only suitable for lubrication of each of members of an engine but also able to be suitably used for two-wheeled vehicle having a structure in which a variable transmission is also lubricated by the same engine oil, namely for lubrication of a two-wheeled vehicle internal combustion engine.

[Production Method of Lubricating Oil Composition]

The present invention is also concerned with a production method of a lubricating oil composition including blending (1) a base oil including a base oil A having a kinematic viscosity at 100° C. of 2 mm²/s or more and 7 mm²/s or less and a viscosity index of 120 or less with (2) at least one selected from an acrylate-based polymer and an olefin-based polymer each having a mass average molecular weight of 40,000 or less and (3) a lubricating oil additive including a sulfur-based extreme pressure agent, to produce a lubricating oil composition having a kinematic viscosity at 100° C. of more than 9.3 mm²/s and 12.5 mm²/s or less and a high temperature high shear viscosity at 150° C. of 2.9 mPa·s or more.
The lubricating oil composition including the aforementioned base oil (1), the acrylate-based polymer and/or olefin-based polymer (2) having a mass average molecular weight of 40,000 or less, and the lubricating oil additive (3) including a sulfur-based extreme pressure agent, and having specified properties is one as described above. The method of blending the base oil (1) with the polymer (2) and the lubricating oil additive (3) is not particularly limited so long as the respective components are blended such that the kinematic viscosity at 100° C. and the HTHS viscosity at 150° C. fall within the foregoing prescribed ranges, respectively, and the blending order, blending conditions, and so on are not particularly limited, too.

EXAMPLES

The present invention is hereunder specifically described with reference to Examples, but it should be construed that the present invention is by no means limited by these Examples.

[Evaluation Items and Evaluation Methods]

Respective properties of a lubricating oil composition were measured according to the following methods.
(1) Kinematic viscosity (at 40° C. and 100° C.)
The kinematic viscosity was measured in conformity with JIS K2283 (ASTM D445).

(2) Viscosity Index (VI):

The viscosity index was measured in conformity with JIS K2283 (ASTM D445).

(3) CCS Viscosity (Cold Cracking Simulator):

The viscosity at −25° C. was measured in conformity with JIS K2010 (ASTM D2602).

(4) HTHS Viscosity (High Temperature High Shear):

The HTHS viscosity was measured in conformity with JPI-5S-36-03 (ASTM D4683) under the following conditions.
Device: TBS high-temperature viscometer (tapered bearing simulator)
Shear rate: 10⁶sec⁻¹
Rotation rate (motor): 3,000 rpm
Clearance (rotator/stator): 2 to 3 μm
Sample amount: 20 to 50 mL
Measurement time: calibration, 4 to 6 hours; test, 15 minutes

(5) Shear Test:

The shear test was performed in conformity with JPI-5S-29 (ASTM D3945).

(6) Melting Point:

The melting point was measured using a differential scanning calorimeter (DSC-7, manufactured by PerkinElmer)

(7) Pour Point:

The pour point was measured in conformity with JIS K2269.

(8) Amount of Dimer and Trimer Components:

The amount of the dimer and trimer components was measured by means of gas chromatography (GC).

(9) Average Carbon Number:

The average carbon number was determined from peak areas at 0.9 ppm and 1.2 ppm by means of the NMR measurement.

(10) Evaluation of Fatigue Life:

The fatigue life was measured using the following device under the following conditions.
Device: Radial needle bearing fatigue-evaluating tester, manufactured by A&D Company, Limited
Load: 3,000 N, temperature: 120° C., rotation rate: 2,000 rpm
Bearing: Radial bearing (solid needle bearing: NSK LM1710)
Test conditions: A test oil was filled in 6 devices, and the test was simultaneously started under the aforementioned conditions. A time at which each device reached a vibration limiter or more was recorded as a life. Six data were subjected to Weibull plotting, and from an approximation straight line thereof, a 10% failure probability L10 (times) and a 50% failure probability L50 (times) were calculated.

(11) Measurement of Oil Film Thickness:

The oil film thickness was measured using the following device under the following conditions.
Device: EHL ultra thin film measurement system (EHD2), manufactured by PCS Instruments
Load: 20 N, temperature: 120° C., rolling speed: 0.2 m/s and 1.6 m/s

Examples 1 to 7 and Comparative Examples 1 and 2

As shown in Table 1, a base oil shown in the same table was blended with various additives to prepare lubricating oil compositions, and with respect to each of the obtained lubricating oil compositions, the respective properties inclusive of the kinematic viscosity (at 40° C. and 100° C.), the viscosity index, the HTHS viscosity at 150° C., the CCS viscosity at −25° C., the viscosity (at 100° C.) after a shear test, and so on were measured. In addition, with respect to these lubricating oil compositions, the fatigue life and the oil film thickness were evaluated. As for the blending amount of each polymer in Table 1, a blending amount (mass %) as the resin component is shown.
Those results are shown in Table 1.

TABLE 1

							Compar-	Compar-
							ative	ative
Exam-	Exam-	Exam-	Exam-	Exam-	Exam-	Exam-	Exam-	Exam-
ple 1	ple 2	ple 3	ple 4	ple 5	ple 6	ple 7	ple 1	ple 2

Composition of lubricating oil

Base oil (150N) ⁽¹⁾	wt %	86.04	89.43	86.55	82.82	87.15	79.19	81.26	90.32	88.84
PMA-1 ⁽²⁾	wt %	4.96	—	—	—	—	—	—	—	—
High-viscosity PAO-1 ⁽³⁾	wt %	—	1.57	—	—	—	—	—	—	—
High-viscosity PAO-2 ⁽⁴⁾	wt %	—	—	4.45	—	—	—	—	—	—
High-viscosity PAO-3 ⁽⁵⁾	wt %	—	—	—	8.18	—	—	—	—	—
PAO-a ⁽⁶⁾	wt %	—	—	—	—	3.85	—	—	—	—
PAO-b ⁽⁷⁾	wt %	—	—	—	—	—	11.81	—	—	—
Polybutene ⁽⁸⁾	wt %	—	—	—	—	—	—	9.74	—	—
OCP ⁽⁹⁾	wt %	—	—	—	—	—	—	—	0.68	—
PMA-2 ⁽¹⁰⁾	wt %	—	—	—	—	—	—	—	—	2.16
Package additive ⁽¹¹⁾	wt %	9.00	9.00	9.00	9.00	9.00	9.00	9.00	9.00	9.00
Total	wt %	100.00	100.00	100.00	100.00	100.00	100.00	100.00	100.00	100.00

Properties of lubricating oil

Kinematic	at 40° C.	mm²/s	54.55	58.56	59.14	59.64	62.19	63.04	68.18	66.36	55.36
viscosity	at 100° C.	mm²/s	9.302	9.301	9.305	9.303	9.307	9.301	9.301	9.300	9.320

Viscosity index (VI)	—	154	140	138	136	129	126	114	115	147
CCS viscosity	mPa · s	5790	5292	4775	4643	7967	8649	11736	4400	4650
(at −25° C.)
HTHS viscosity	mPa · s	3.23	2.96	3.03	3.10	3.11	3.05	3.08	3.28	2.92
(at 150° C.)
Kinematic viscosity	mm²/s	9.25	9.29	9.28	9.27	9.29	9.22	9.27	8.62	8.70
after shear test
(at 100° C.)

Performance of lubricating oil

Radial fatigue life	times	2.6	4.6	4.5	4.2	4.7	4.6	5.5	1.3	0.55
(L10) × 10⁶
Radial fatigue life	times	4.5	7.3	7.3	6.7	7.3	7.1	7.1	1.9	1.2
(L50) × 10⁶
Central oil film	nm	65	70	60	55	65	70	75	40	45
thickness at 1.6 m/s
Central oil film	nm	16	16	14	14	17	15	18	10	11
thickness at 0.2 m/s

The base oil and the respective additives as used are as follows.

(1) Base Oil:

150N: Kinematic viscosity at 100° C.; 5.28 mm²/s, viscosity index; 104

(2) PMA-1:

Polymethacrylate, mass average molecular weight; about 35,000

(3) High-Viscosity PAO-1:

Mass average molecular weight; about 24,000, kinematic viscosity at 100° C.; 710 mm²/s, amorphous, pour point: −30 to −40° C., amount of dimer and trimer components; 1 mass % or less, raw material monomer; 1-decene

(4) High-Viscosity PAO-2:

Mass average molecular weight; about 12,300, kinematic viscosity at 100° C.; 230 mm²/s, amorphous, pour point: −30 to −40° C., amount of dimer and trimer components; 1 mass % or less, raw material monomer; 1-decene

(5) High-Viscosity PAO-3:

Mass average molecular weight; about 8,000, kinematic viscosity at 100° C.; 130 mm²/s, amorphous, pour point: −30 to −40° C., amount of dimer and trimer components; 1 mass % or less, raw material monomer; 1-decene

(6) PAO-a:

Ethylene-propylene copolymer, mass average molecular weight; about 14,000, kinematic viscosity at 100° C.; 2,000 mm²/s, viscosity index; 300

(7) PAO-b:

SPECTRASYN 100 (poly-α-olefin (polymer of α-olefin having 4 to 22 carbon atoms), manufactured by Exxon Mobil Corporation, mass average molecular weight; about 16,000, kinematic viscosity at 100° C.; 100 mm²/s, viscosity index; 170

(8) Polybutene:

Mass average molecular weight; about 1,300

(9) OCP:

Olefin copolymer (ethylene-propylene copolymer), mass average molecular weight; about 90,000

(10) PMA-2:

Polymethacrylate, mass average molecular weight; about 400,000

(11) Package Additive:

Sulfur-based extreme pressure agent: zinc dithiophosphate (10), ashless dispersant: polybutenylsuccinimide (20), metal-based detergent: Ca phenate (12.2), Ca sulfonate (5.6), antioxidant: amine-based antioxidant (8.9), phenol-based antioxidant (4.4), others: friction modifier, rust inhibitor, and metal deactivator (5.6), and diluent oil (33.3). The numerical values within the parentheses show mass % relative to the whole amount of the package additive.
The compositions of Examples 1 to 7, each of which is the lubricating oil composition of the present invention, are each a composition in which the base oil is blended with the acrylate-based polymer or olefin-based polymer having a molecular weight falling within the scope prescribed in the present invention and the various lubricating oil additives, thereby regulating the kinematic viscosity (at 100° C.) and the HTHS viscosity (at 150° C.) within the scope prescribed in the present invention, and were excellent in all of the radial fatigue life and the central oil film thickness.
On the other hand, the compositions of Comparative Examples 1 and 2, in which the acrylate-based polymer or the olefin-based polymer having a molecular weight falling outside the scope prescribed in the present invention, were inferior in all of the radial fatigue life and the central oil film thickness, even by regulating the kinematic viscosity (at 100° C.) and the HTHS viscosity (at 150° C.) within the scope prescribed in the present invention.

INDUSTRIAL APPLICABILITY

The lubricating oil composition of the present invention makes both a lowering in viscosity for fuel consumption reducing properties and fatigue resistance for improvement of fatigue life compatible with each other and also is excellent in low-temperature viscosity properties. In particular, in view of the fact that the lubricating oil composition of the present invention is able to lubricate all of an engine and a variable transmission as a lubricating oil for internal combustion engine, it can be suitably as a lubricating oil composition for two-wheeled vehicle internal combustion engine.

Claims

1. A lubricating oil composition, comprising:

(1) a base oil comprising a base oil A having a kinematic viscosity at 100° C. of 2 mm²/s or more and 7 mm²/s or less and a viscosity index of 120 or less;

(2) at least one selected from an acrylate-based polymer and an olefin-based polymer each having a mass average molecular weight of 40,000 or less; and

(3) a lubricating oil additive comprising a sulfur-based extreme pressure agent,

wherein the lubricating oil composition has a kinematic viscosity at 100° C. of more than 9.3 mm²/s and 12.5 mm²/s or less and a high temperature high shear viscosity at 150° C. of 2.9 mPa·s or more.

2. The lubricating oil composition according to claim 1, which has a CCS viscosity at −25° C. of 7,000 mPa·s or less and a viscosity index of 135 or more.

3. The lubricating oil composition according to claim 1, wherein the acrylate-based polymer and the olefin-based polymer each having a mass average molecular weight of 40,000 or less is a poly-α-olefin obtained from α-olefins having a carbon number of 8 or more and 12 or less and having a kinematic viscosity at 100° C. of 100 mm²/s or more and 2,000 mm²/s or less.

4. The lubricating oil composition according to claim 1, wherein a central oil film thickness in the measurement of an oil film thickness in the elastohydrodynamic lubrication (EHL) state is 50 nm or more at a rolling speed of 1.6 m/s.

5. The lubricating oil composition according to claim 1, wherein in the evaluation of fatigue life of a radial rolling bearing, a 50% failure probability (L50) is 3.0×10⁶times or more.

6. The lubricating oil composition according to claim 1, wherein the base oil further comprises a base oil having a viscosity index of more than 120.

7. The lubricating oil composition according to claim 1, wherein a kinematic viscosity at 100° C. after a shear test of the lubricating oil composition is 9 mm²/s or more.

8. The lubricating oil composition according to claim 1, wherein the composition is suitable for internal combustion engines.

9. The lubricating oil composition according to claim 1, wherein the composition is suitable for two-wheeled vehicle internal combustion engines.

10. A production method of a lubricating oil composition, the method comprising:

blending (1) a base oil comprising a base oil A having a kinematic viscosity at 100° C. of 2 mm²/s or more and 7 mm²/s or less and a viscosity index of 120 or less with (2) at least one selected from an acrylate-based polymer and an olefin-based polymer each having a mass average molecular weight of 40,000 or less and (3) a lubricating oil additive comprising a sulfur-based extreme pressure agent, to produce a lubricating oil composition having a kinematic viscosity at 100° C. of more than 9.3 mm²/s and 12.5 mm²/s or less and a high temperature high shear viscosity at 150° C. of 2.9 mPa·s or more.

11. An internal combustion engine, comprising at least one member lubricated with a lubricating oil composition, wherein the lubricating oil composition comprises:

(3) a lubricating oil additive comprising a sulfur-based extreme pressure agent, and

the lubricating oil composition has a kinematic viscosity at 100° C. of more than 9.3 mm²/s and 12.5 mm²/s or less and a high temperature high shear viscosity at 150° C. of 2.9 mPa·s or more.