Lubricating oil composition

Abstract

Provided is a lubricating oil composition capable of maintaining excellent defoaming performance for a long time period, the lubricating oil composition including: a hydrocarbon-based synthetic oil (X1); an ester-based synthetic oil (X2); and a phosphorus-containing copolymer (Y), wherein the phosphorus-containing copolymer (Y) includes a constituent unit (a) derived from a specific alkyl (meth)acrylate (A), a constituent unit (b) derived from a specific hydroxy group-containing (meth)acrylate (B), and a constituent unit (c) derived from a specific phosphorus-containing (meth)acrylate (C).

Description

Technical Field

[0001] The present invention relates to a lubricating oil composition.Background Art

[0002] From the viewpoints of, for example, a reduction in environmental load and the depletion of fossil fuels, wind power generation utilizing renewable energy has been expected to further increase in demand in the future. The wind power generation includes: converting the kinetic energy of wind into motive power by using a propeller or any other rotor that rotates by receiving the wind; and driving a generator with the motive power to convert the motive power into electric energy. In such wind power generation, a speed increaser is used in consideration of the power generation efficiency of the generator because the rotational speed of the rotor is slow. Various speed increasers have been known, and for example, a planetary gear type power transmission device has been frequently used. A speed increaser oil composition for wind power generation to be used in the planetary gear type power transmission device or the like is required to be, for example, operable in a maintenance-free manner for a long time period.

[0003] In Examples of PTL 1, as the speed increaser oil composition for wind power generation, there is a disclosure of, for example, a composition obtained by adding various additives such as an extreme pressure agent to a mixed base oil of a poly-α-olefin-based base oil and an ester-based base oil.

[0004] In addition, various load-bearing additives such as an extreme pressure agent have each been proposed as an additive for a lubricating oil. For example, a phosphorus-containing (meth)acrylate-based copolymer has been known as such additive (see PTL 2).Citation ListPatent Literature

[0005] PTL 1: JP 2021-187911 A PTL 2: JP 7061242 B1 Summary of InventionTechnical Problem

[0006] Incidentally, in a lubricating oil composition, foaming caused by air entrainment or the like may occur at the time of the operation of a mechanical device. Foam generated in the lubricating oil composition leads to a reduction in lubrication performance thereof, a reduction in sealing performance thereof, the acceleration of its oxidative degradation, a reduction in cooling efficiency thereof, a reduction in power transmission efficiency thereof, and the like. Accordingly, the lubricating oil composition is required to have defoaming performance. In particular, for a speed increaser oil composition for wind power generation to be operated in a maintenance-free manner for a long time period, requirements for its defoaming performance are strict, and it is required for the speed increaser to maintain excellent defoaming performance for a long time period.

[0007] However, a lubricating oil composition using a mixed base oil of a poly-α-olefin-based base oil and an ester-based base oil like PTL 1 has involved a problem in that the composition is liable to foam, and hence it is difficult for the composition to maintain excellent defoaming performance for a long time period. In addition, in PTL 2, no investigation has been made on the foaming of the lubricating oil composition.

[0008] Accordingly, an object of the present invention is to provide a lubricating oil composition capable of maintaining excellent defoaming performance for a long time period.Solution to Problem

[0009] The present invention provides the following items [1] and [2]. [1] A lubricating oil composition, including: a hydrocarbon-based synthetic oil (X1); an ester-based synthetic oil (X2); and a phosphorus-containing copolymer (Y), wherein the phosphorus-containing copolymer (Y) includes a constituent unit (a) derived from an alkyl (meth)acrylate (A) represented by the following general formula (a-1), a constituent unit (b) derived from a hydroxy group-containing (meth)acrylate (B) represented by the following general formula (b-1), and a constituent unit (c) derived from a phosphorus-containing (meth)acrylate (C) represented by the following general formula (c-1): wherein in the general formula (a-1), R a1< represents a hydrogen atom or a methyl group, and R a2< represents an alkyl group having 8 to 20 carbon atoms; wherein in the general formula (b-1), R b1< represents a hydrogen atom or a methyl group, R b2< represents an alkylene group having 2 to 4 carbon atoms, m1 represents an integer of from 1 to 10, and when m1 represents an integer of 2 or more, a plurality of R b2< s may be identical to or different from each other; wherein in the general formula (c-1), R c1< represents a hydrogen atom or a methyl group, R c2< represents an ethylene group, m2 represents an integer of from 1 to 6, when m2 represents an integer of 2 or more, a plurality of R c2< s may be identical to or different from each other, "n" represents an integer of 1 or 2, when n=1, R c3< represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, provided that at least one of a plurality of R c3< s represents a hydrogen atom, and when n=2, R c3< represents a hydrogen atom. [2] A method of producing a lubricating oil composition, including a step of mixing a hydrocarbon-based synthetic oil (X1), an ester-based synthetic oil (X2), and a phosphorus-containing copolymer (Y), wherein the phosphorus-containing copolymer (Y) includes a constituent unit (a) derived from an alkyl (meth)acrylate (A) represented by the following general formula (a-1), a constituent unit (b) derived from a hydroxy group-containing (meth)acrylate (B) represented by the following general formula (b-1), and a constituent unit (c) derived from a phosphorus-containing (meth)acrylate (C) represented by the following general formula (c-1): wherein in the general formula (a-1), R a1< represents a hydrogen atom or a methyl group, and R a2< represents an alkyl group having 8 to 20 carbon atoms; wherein in the general formula (b-1), R b1< represents a hydrogen atom or a methyl group, R b2< represents an alkylene group having 2 to 4 carbon atoms, m1 represents an integer of from 1 to 10, and when m1 represents an integer of 2 or more, a plurality of R b2< s may be identical to or different from each other; wherein in the general formula (c-1), R c1< represents a hydrogen atom or a methyl group, R c2< represents an ethylene group, m2 represents an integer of from 1 to 6, when m2 represents an integer of 2 or more, a plurality of R c2< s may be identical to or different from each other, "n" represents an integer of 1 or 2, when n=1, R c3< represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, provided that at least one of a plurality of R c3< s represents a hydrogen atom, and when n=2, R c3< represents a hydrogen atom. Advantageous Effects of Invention

[0010] The present invention can provide the lubricating oil composition capable of maintaining excellent defoaming performance for a long time period.Description of Embodiments

[0011] The upper limit values and lower limit values of numerical ranges described herein may be freely combined. For example, when the range of "from A to B" and the range of "from C to D" are described as numerical ranges, the numerical range of "from A to D" and the numerical range of "from C to B" are also included in the scope of the present invention.

[0012] In addition, the numerical range of "from a lower limit value to an upper limit value" described herein means that a physical property value is the lower limit value or more and the upper limit value or less unless otherwise stated.

[0013] In addition, in this description, the numerical values of Examples are numerical values that may each be used as an upper limit value or a lower limit value.

[0014] The term "(meth)acrylate" means an acrylate or a methacrylate, and the same applies to any other similar term. For example, the term "poly(meth)acrylate" means a polyacrylate or a polymethacrylate.

[0015] In addition, in this description, an additive such as a phosphorus-containing copolymer (Y) may be blended with any other component in the form of a solution, which is obtained by dissolving the additive in a diluting oil, in consideration of, for example, its solubility in a base oil. In such case, in this description, the content of the additive such as the phosphorus-containing copolymer (Y) is a content in terms of an active component (in terms of resin content) excluding the diluting oil.[Aspect of Lubricating Oil Composition]

[0016] A lubricating oil composition according to an embodiment of the present invention includes a hydrocarbon-based synthetic oil (X1), an ester-based synthetic oil (X2), and a phosphorus-containing copolymer (Y).

[0017] The phosphorus-containing copolymer (Y) includes a constituent unit (a) derived from an alkyl (meth)acrylate (A) represented by the following general formula (a-1), a constituent unit (b) derived from a hydroxy group-containing (meth)acrylate (B) represented by the following general formula (b-1), and a constituent unit (c) derived from a phosphorus-containing (meth)acrylate (C) represented by the following general formula (c-1): wherein in the general formula (a-1), R a1< represents a hydrogen atom or a methyl group, and R a2< represents an alkyl group having 8 to 20 carbon atoms; wherein in the general formula (b-1), R b1< represents a hydrogen atom or a methyl group, R b2< represents an alkylene group having 2 to 4 carbon atoms, m1 represents an integer of from 1 to 10, and when m1 represents an integer of 2 or more, a plurality of R b2< s may be identical to or different from each other; wherein in the general formula (c-1), R c1< represents a hydrogen atom or a methyl group, R c2< represents an ethylene group, m2 represents an integer of from 1 to 6, when m2 represents an integer of 2 or more, a plurality of R c2< s may be identical to or different from each other, "n" represents an integer of 1 or 2, when n=1, R c3< represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, provided that at least one of a plurality of R c3< s represents a hydrogen atom, and when n=2, R c3< represents a hydrogen atom.

[0018] The inventors of the present invention have made intensive investigations in order to solve the above-mentioned problems. As a result, the inventors have surprisingly found that the "phosphorus-containing copolymer (Y)," which has been blended for the purpose of imparting load-bearing performance to a lubricating oil composition including the "hydrocarbon-based synthetic oil (X1)" and the "ester-based synthetic oil (X2)," can impart excellent defoaming performance thereto over a long time period.

[0019] The mechanism via which the "phosphorus-containing copolymer (Y)" can impart excellent defoaming performance over a long time period to the lubricating oil composition including the "hydrocarbon-based synthetic oil (X1)" and the "ester-based synthetic oil (X2)" is not clear. However, for example, a long-chain alkyl group and a polar group of the "phosphorus-containing copolymer (Y)" are presumed to exhibit some influence on the suppression of the foaming of the composition by, for example, controlling the surface tension of a foam surface.

[0020] In the following description, the "hydrocarbon-based synthetic oil (X1)," the "ester-based synthetic oil (X2)," and the "phosphorus-containing copolymer (Y)" are also referred to as "component (X1)," "component (X2)," and "component (Y)," respectively.

[0021] The lubricating oil composition of this embodiment may include only the component (X1), the component (X2), and the component (Y), but may further include any other component except the component (X1), the component (X2), and the component (Y).

[0022] The total content of the component (X1), the component (X2), and the component (Y), in the lubricating oil composition of this embodiment is preferably 50 mass% or more, more preferably 60 mass% or more, still more preferably 70 mass% or more, still further more preferably 80 mass% or more, yet still further more preferably 85 mass% or more with respect to the total amount of the lubricating oil composition.

[0023] In addition, the total content of the component (X1), the component (X2), and the component (Y) is typically 100 mass% or less.

[0024] The respective components in the lubricating oil composition of this embodiment are described in detail below.<Hydrocarbon-based Synthetic Oil (X1)>

[0025] The lubricating oil composition of this embodiment includes the hydrocarbon-based synthetic oil (X1) as a base oil.

[0026] A hydrocarbon-based synthetic oil generally used as a base oil for forming a lubricating oil composition may be used as the hydrocarbon-based synthetic oil (X1) without particular limitation.

[0027] Specific examples of the hydrocarbon-based synthetic oil (X1) include: a poly-α-olefin (hereinafter also referred to as "PAO"); an alkylbenzene; an alkylnaphthalene; and a GTL base oil produced by the hydroisomerization dewaxing of a residual wax (gas-to-liquid wax) in a GTL process. Among them, a PAO is preferred from the viewpoint of appropriately adjusting the kinematic viscosity of the lubricating oil composition with ease and the viewpoint of improving the viscosity index thereof.

[0028] Specific examples of the PAO include polybutene, polyisobutylene, a 1-decene oligomer, and an ethylene-propylene copolymer, and hydrogenated products thereof.

[0029] The 100°C kinematic viscosity of the hydrocarbon-based synthetic oil (X1) is preferably from 20 mm 2< / s to 55 mm 2< / s, more preferably from 25 mm 2< / s to 50 mm 2< / s, still more preferably from 30 mm 2< / s to 45 mm 2< / s.

[0030] The viscosity index of the hydrocarbon-based synthetic oil (X1) is preferably 100 or more, more preferably 110 or more, still more preferably 115 or more.

[0031] The kinematic viscosity and viscosity index of the base oil are values measured or calculated in conformity with JIS K2283:2000.

[0032] The hydrocarbon-based synthetic oils (X1) may be used alone or in combination thereof.

[0033] Herein, in the lubricating oil composition of this embodiment, the hydrocarbon-based synthetic oil (X1) preferably includes a low-viscosity hydrocarbon-based synthetic oil (X11) having a 100°C kinematic viscosity of from 1.5 mm 2< / s to 11.0 mm 2< / s and a high-viscosity hydrocarbon-based synthetic oil (X12) having a 100°C kinematic viscosity of from 50.0 mm 2< / s to 350.0 mm 2< / s from, for example, the viewpoints of improving the wear resistance of the lubricating oil composition and ensuring the low-temperature characteristics thereof.

[0034] In the lubricating oil composition of this embodiment, the total content of the low-viscosity hydrocarbon-based synthetic oil (X11) and the high-viscosity hydrocarbon-based synthetic oil (X12) is preferably from 50 mass% to 100 mass%, more preferably from 60 mass% to 100 mass%, still more preferably from 70 mass% to 100 mass%, still further more preferably from 80 mass% to 100 mass%, yet still further more preferably from 90 mass% to 100 mass%, even more preferably from 95 mass% to 100 mass% with respect to the total amount of the hydrocarbon-based synthetic oil (X1).(Low-viscosity Hydrocarbon-based Synthetic Oil (X11))

[0035] The low-viscosity hydrocarbon-based synthetic oil (X11) contributes to ensuring the low-temperature characteristics of the lubricating oil composition.

[0036] In the lubricating oil composition of this embodiment, the 100°C kinematic viscosity of the low-viscosity hydrocarbon-based synthetic oil (X11) is preferably from 1.5 mm 2< / s to 11.0 mm 2< / s, more preferably from 2.0 mm 2< / s to 9.0 mm 2< / s, still more preferably from 3.0 mm 2< / s to 5.0 mm 2< / s from the viewpoint of improving the low-temperature characteristics of the lubricating oil composition.

[0037] Specific examples of the low-viscosity hydrocarbon-based synthetic oil (X11) include those given as specific examples of the hydrocarbon-based synthetic oil (X1) and each having a 100°C kinematic viscosity in the above-mentioned ranges specified for the low-viscosity hydrocarbon-based synthetic oil (X11). Among them, a PAO having a 100°C kinematic viscosity in the above-mentioned ranges specified for the low-viscosity hydrocarbon-based synthetic oil (X11) is preferred.

[0038] Specific examples of the PAO are as described above.

[0039] The low-viscosity hydrocarbon-based synthetic oils (X11) may be used alone or in combination thereof.

[0040] Herein, in the lubricating oil composition of this embodiment, the content of the low-viscosity hydrocarbon-based synthetic oil (X11) is preferably 10 mass% or more, more preferably 15 mass% or more, still more preferably 18 mass% or more with respect to the total amount of the lubricating oil composition from the viewpoints of ensuring the low-temperature characteristics of the lubricating oil composition and suppressing a reduction in flash point thereof. In addition, the content is preferably 40 mass% or less, more preferably 35 mass% or less, still more preferably 30 mass% or less.(High-viscosity Hydrocarbon-based Synthetic Oil (X12))

[0041] The high-viscosity hydrocarbon-based synthetic oil (X12) contributes to improvements in wear resistance, fatigue life, and the like of the lubricating oil composition by maintaining the kinematic viscosity of the base oil (A) high.

[0042] In the lubricating oil composition of this embodiment, the 100°C kinematic viscosity of the high-viscosity hydrocarbon-based synthetic oil (X12) is preferably from 50.0 mm 2< / s to 350.0 mm 2< / s, more preferably from 100.0 mm 2< / s to 300.0 mm 2< / s, still more preferably from 120.0 mm 2< / s to 200.0 mm 2< / s from the viewpoint of more easily improving the wear resistance, fatigue life, and the like of the lubricating oil composition.

[0043] Specific examples of the high-viscosity hydrocarbon-based synthetic oil (X12) include those given as specific examples of the hydrocarbon-based synthetic oil (X1) and each having a 100°C kinematic viscosity in the above-mentioned ranges specified for the high-viscosity hydrocarbon-based synthetic oil (X12). Among them, a PAO having a 100°C kinematic viscosity in the above-mentioned ranges specified for the high-viscosity hydrocarbon-based synthetic oil (X12) is preferred.

[0044] Specific examples of the PAO are as described above.

[0045] The high-viscosity hydrocarbon-based synthetic oils (X12) may be used alone or in combination thereof.

[0046] Herein, from the viewpoint of further increasing the viscosity index of the lubricating oil composition, the high-viscosity hydrocarbon-based synthetic oil (X12) is more preferably a poly-α-olefin obtained by using a metallocene catalyst (hereinafter also referred to as "mPAO").

[0047] The mPAO has an increasing effect on the viscosity index of the lubricating oil composition because the mPAO has a viscosity index higher than that of a PAO produced by using a non-metallocene catalyst (Ziegler catalyst or the like).

[0048] The mPAO is a poly-α-olefin or a hydrogenated product thereof obtained by using preferably α-olefins each having 8 to 12 carbon atoms alone or in combination thereof as a raw material, and producing (polymerizing) the raw material in the presence of the metallocene catalyst.

[0049] Although the α-olefin having 8 to 12 carbon atoms, which serves as the raw material of the mPAO, may be a linear α-olefin or a branched α-olefin, a linear α-olefin is preferably used. In addition, examples of the α-olefin having 8 to 12 carbon atoms, which serves as the raw material of the mPAO, include 1-octene, 1-nonene, 1-decene, 1-undecene, and 1-dodecene. Among them, a decene oligomer obtained through polymerization by using 1-decene as a raw material is preferred.

[0050] A complex having a conjugated 5-membered carbon ring containing a Group 4 element of the periodic table, that is, a metallocene complex and an oxygen-containing organoaluminum compound may be used in combination as the metallocene catalyst that is a polymerization catalyst used for the production of the mPAO.

[0051] The Group 4 element of the periodic table in the metallocene complex is, for example, one or more selected from titanium, zirconium, and hafnium. Among them, zirconium is preferred. In addition, a complex having a substituted or unsubstituted cyclopentadienyl ligand is generally used as the complex having a conjugated 5-membered carbon ring.

[0052] Suitable examples of the metallocene complex include bis(n-octadecylcyclopentadienyl)zirconium dichloride, bis(trimethylsilylcyclopentadienyl)zirconium dichloride, bis(tetrahydroindenyl)zirconium dichloride, bis[(t-butyldimethylsilyl)cyclopentadienyl]zirconium dichloride, bis(di-t-butylcyclopentadienyl)zirconium dichloride, (ethylidene-bisindenyl)zirconium dichloride, biscyclopentadienylzirconium dichloride, ethylidenebis(tetrahydroindenyl)zirconium dichloride, and bis[3,3-(2-methyl-benzindenyl)]dimethylsilanediylzirconium dichloride.

[0053] The metallocene complexes may be used alone or in combination thereof.

[0054] Examples of the oxygen-containing organoaluminum compound include methylaluminoxane, ethylaluminoxane, and isobutylaluminoxane.

[0055] The oxygen-containing organoaluminum compounds may be used alone or in combination thereof.

[0056] The mPAOs may be used alone or in combination thereof.

[0057] In the lubricating oil composition of this embodiment, the content of the high-viscosity hydrocarbon-based synthetic oil (X12) is preferably 50 mass% or more, more preferably 55 mass% or more, still more preferably 60 mass% or more with respect to the total amount of the lubricating oil composition from the viewpoint of easily preparing a lubricating oil composition excellent in wear resistance and fatigue life by maintaining the kinematic viscosity of the lubricating oil composition high. In addition, the content is preferably 80 mass% or less, more preferably 75 mass% or less, still more preferably 70 mass% or less.<Ester-based Synthetic Oil (X2)>

[0058] The lubricating oil composition of this embodiment includes the ester-based synthetic oil (X2) as a base oil.

[0059] The incorporation of the ester-based synthetic oil (X2) into the lubricating oil composition contributes to, for example, an improvement in detergent dispersion action of the lubricating oil composition and an improvement in thermal stability thereof.

[0060] An ester-based synthetic oil generally used as a base oil for forming a lubricating oil composition may be used as the ester-based synthetic oil (X2) without particular limitation.

[0061] Specific examples of the ester-based synthetic oil (X2) include a diester, an aromatic ester, a polyol ester, and a complex ester. Among them, a polyol ester is preferred.

[0062] The ester-based synthetic oils (X2) may be used alone or in combination thereof.

[0063] The 100°C kinematic viscosity of the ester-based synthetic oil (X2) is preferably from 2 mm 2< / s to 15 mm 2< / s, more preferably from 3 mm 2< / s to 10 mm 2< / s, still more preferably from 4 mm 2< / s to 7 mm 2< / s.

[0064] The viscosity index of the ester-based synthetic oil (X2) is preferably 70 or more, more preferably 80 or more, still more preferably 90 or more.

[0065] The kinematic viscosity and viscosity index of the base oil are values measured or calculated in conformity with JIS K2283:2000.

[0066] Although the polyol ester may be a partial ester or complete ester of a polyol, the complete ester of the polyol is preferably used from the viewpoint of improving the defoaming performance of the lubricating oil composition.

[0067] Although the polyol serving as a raw material of the polyol ester is not particularly limited, an aliphatic polyol is preferred, and examples thereof may include: dihydric alcohols, such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, trimethylene glycol, tetramethylene glycol, and neopentyl glycol; trihydric alcohols, such as glycerin, trimethylolethane, and trimethylolpropane; and tetrahydric or higher polyhydric alcohols, such as diglycerin, triglycerin, pentaerythritol, dipentaerythritol, mannitol, and sorbitol. Among them, trimethylolpropane and pentaerythritol are preferred, and pentaerythritol is more preferred.

[0068] A fatty acid for forming the polyol ester is preferably a saturated fatty acid or unsaturated fatty acid having 4 to 20 carbon atoms, more preferably a saturated fatty acid or unsaturated fatty acid having 4 to 16 carbon atoms, still more preferably a saturated fatty acid or unsaturated fatty acid having 4 to 12 carbon atoms, still further more preferably a saturated fatty acid or unsaturated fatty acid having 4 to 11 carbon atoms, yet still further more preferably a saturated fatty acid or unsaturated fatty acid having 5 to 9 carbon atoms.

[0069] In particular, when the fatty acid for forming the polyol ester is a saturated fatty acid or unsaturated fatty acid having 4 to 11 (preferably 5 to 9) carbon atoms, the defoaming performance of the lubricating oil composition is easily exhibited over a long time period. In addition, when the fatty acid for forming the polyol ester is a saturated fatty acid or unsaturated fatty acid having 4 to 11 carbon atoms, and the polyol for forming the polyol ester is pentaerythritol, the following effect is more easily obtained: the defoaming performance of the lubricating oil composition is easily exhibited over a long time period.

[0070] Accordingly, the ester-based base oil (X2) preferably includes an ester of pentaerythritol and a fatty acid having 4 to 11 carbon atoms, more preferably includes an ester of pentaerythritol and a fatty acid having 5 to 10 carbon atoms, and still more preferably includes an ester of pentaerythritol and a fatty acid having 8 to 10 carbon atoms.

[0071] The fatty acid for forming the polyol ester may be linear or branched, but is preferably linear.

[0072] In the lubricating oil composition of this embodiment, the content of the ester-based synthetic oil (X2) is preferably 0.5 mass% or more, more preferably 1.0 mass% or more, still more preferably 1.5 mass% or more, still further more preferably 3.0 mass% or more, yet still further more preferably 5.0 mass% or more, even more preferably 7.0 mass% or more with respect to the total amount of the lubricating oil composition from the viewpoints of, for example, improving the detergent dispersion action of the lubricating oil composition and improving the thermal stability thereof. In addition, the content is preferably 15 mass% or less, more preferably 13 mass% or less, still more preferably 12 mass% or less.<Total Content of Hydrocarbon-based Synthetic Oil (X1) and Ester-based Synthetic Oil (X2)>

[0073] In the lubricating oil composition of this embodiment, the total content of the hydrocarbon-based synthetic oil (X1) and the ester-based synthetic oil (X2) is preferably 75 mass% or more, more preferably 78 mass% or more, still more preferably 80 mass% or more with respect to the total amount of the lubricating oil composition. In addition, the total content is preferably 99.9 mass% or less.

[0074] The total content of the component (X1) and the component (X2) is preferably from 50 mass% to 100 mass%, more preferably from 60 mass% to 100 mass%, still more preferably from 70 mass% to 100 mass%, still further more preferably from 80 mass% to 100 mass%, yet still further more preferably from 90 mass% to 100 mass%, even more preferably from 95 mass% to 100 mass% with respect to the total amount of the base oil in the lubricating oil composition.<Content Ratio of Hydrocarbon-based Synthetic Oil (X1) to Ester-based Synthetic Oil (X2)>

[0075] In the lubricating oil composition of this embodiment, the content ratio [(X1) / (X2)] of the hydrocarbon-based synthetic oil (X1) to the ester-based synthetic oil (X2) is preferably from 5.0 to 50.0, more preferably from 6.0 to 45.0, still more preferably from 7.0 to 40.0 in terms of mass ratio.<Content Ratio of Low-viscosity Hydrocarbon-based Synthetic Oil (X11) to High-viscosity Hydrocarbon-based Synthetic Oil (X12)>

[0076] In the lubricating oil composition of this embodiment, when the hydrocarbon-based synthetic oil (X1) includes the low-viscosity hydrocarbon-based synthetic oil (X11) and the high-viscosity hydrocarbon-based synthetic oil (X12), the content ratio [(X11) / (X12)] of the low-viscosity hydrocarbon-based synthetic oil (X11) to the high-viscosity hydrocarbon-based synthetic oil (X12) is preferably from 0.10 to 0.80, more preferably from 0.15 to 0.70, still more preferably from 0.20 to 0.50 in terms of mass ratio.<Other Base Oil>

[0077] The lubricating oil composition of this embodiment may include any other base oil except the component (X1) and the component (X2).

[0078] Examples of the other base oil include a mineral oil, and a synthetic oil except the component (X1) and the component (X2).

[0079] Examples of the mineral oil include: an atmospheric residue obtained by the atmospheric distillation of a crude oil, such as a paraffin-base crude oil, an intermediate-base crude oil, or a naphthene-base crude oil; a distillate obtained by the vacuum distillation of such atmospheric residue; and a mineral oil obtained by subjecting the distillate to one or more refining processes, such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining.

[0080] Examples of the synthetic oil except the component (X1) and the component (X2) include: various ethers such as polyphenyl ether; a polyalkylene glycol; an alkylbenzene; and an alkylnaphthalene.

[0081] The mineral oils may be used alone or in combination thereof.

[0082] The synthetic oils except the component (X1) and the component (X2) may be used alone or in combination thereof.

[0083] In addition, one or more kinds of mineral oils, and one or more kinds of synthetic oils except the component (X1) and the component (X2) may be used in combination.<Phosphorus-containing Copolymer (Y)>

[0084] The lubricating oil composition of this embodiment includes the phosphorus-containing copolymer (Y).

[0085] The phosphorus-containing copolymer (Y) includes the constituent unit (a) derived from the alkyl (meth)acrylate (A) represented by the following general formula (a-1), the constituent unit (b) derived from the hydroxy group-containing (meth)acrylate (B) represented by the following general formula (b-1), and the constituent unit (c) derived from the phosphorus-containing (meth)acrylate (C) represented by the following general formula (c-1): wherein in the general formula (a-1), R a1< represents a hydrogen atom or a methyl group, and R a2< represents an alkyl group having 8 to 20 carbon atoms; wherein in the general formula (b-1), R b1< represents a hydrogen atom or a methyl group, R b2< represents an alkylene group having 2 to 4 carbon atoms, m1 represents an integer of from 1 to 10, and when m1 represents an integer of 2 or more, a plurality of R b2< s may be identical to or different from each other; wherein in the general formula (c-1), R c1< represents a hydrogen atom or a methyl group, R c2< represents an ethylene group, m2 represents an integer of from 1 to 6, when m2 represents an integer of 2 or more, a plurality of R c2< s may be identical to or different from each other, "n" represents an integer of 1 or 2, when n=1, R c3< represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, provided that at least one of a plurality of R c3< s represents a hydrogen atom, and when n=2, R c3< represents a hydrogen atom.

[0086] In the following description, the alkyl (meth)acrylate (A), the hydroxy group-containing (meth)acrylate (B), and the phosphorus-containing (meth)acrylate (C) are also referred to as "monomer (A)," "monomer (B)," and "monomer (C)," respectively.

[0087] In this embodiment, although the phosphorus-containing copolymer (Y) may include only the constituent unit (a) derived from the monomer (A), the constituent unit (b) derived from the monomer (B), and the constituent unit (c) derived from the monomer (C), the copolymer may include any other constituent unit except the constituent units (a), (b), and (c) to such an extent that the effects of the present invention are not impaired.

[0088] In this embodiment, the total content of the constituent units (a), (b), and (c) in the phosphorus-containing copolymer (Y) is preferably from 70 mol% to 100 mol%, more preferably from 80 mol% to 100 mol%, still more preferably from 90 mol% to 100 mol% with respect to all the constituent units of the phosphorus-containing copolymer (Y).

[0089] The alkyl (meth)acrylate (A), the hydroxy group-containing (meth)acrylate (B), and the phosphorus-containing (meth)acrylate (C) are described in detail below.<<Alkyl (Meth)acrylate (A)>>

[0090] The alkyl (meth)acrylate (A) to be used in this embodiment is represented by the following general formula (a-1).

[0091] The constituent unit (a) derived from the alkyl (meth)acrylate (A) mainly plays a function of causing the phosphorus-containing copolymer (Y) to exhibit oil solubility. In addition, in order to cause the lubricating oil composition to exhibit defoaming performance over a long time period, the constituent unit is presumed to be responsible for the defoaming performance by controlling the surface tension of a foam surface.

[0092] The alkyl (meth)acrylates (A) may be used alone or in combination thereof. Accordingly, the phosphorus-containing copolymer (Y) may include one kind of the constituent units (a) each derived from the alkyl (meth)acrylate (A) alone, or may include two or more kinds thereof.

[0093] In the general formula (a-1), R a1< represents a hydrogen atom or a methyl group. That is, the alkyl (meth)acrylate (A) has an acryloyl group or a methacryloyl group as a polymerizable functional group.

[0094] A monomer in which R a1< represents a hydrogen atom or a methyl group is easily available and is excellent in polymerizability.

[0095] Herein, in this embodiment, R a1< preferably represents a hydrogen atom from the viewpoint of easily adjusting the molecular weight of the phosphorus-containing copolymer (Y). That is, the alkyl (meth)acrylate (A) preferably has an acryloyl group as a polymerizable functional group.

[0096] In the general formula (a-1), R a2< represents an alkyl group having 8 to 20 carbon atoms.

[0097] When the number of the carbon atoms of the alkyl group falls within the above-mentioned range, the oil solubility of the phosphorus-containing copolymer (Y) can be easily ensured.

[0098] Examples of the alkyl group having 8 to 20 carbon atoms that may be selected as R a2< include chain alkyl groups, such as an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, and an icosyl group. Those groups may be linear or branched.

[0099] Herein, from the viewpoint of more easily ensuring the oil solubility of the phosphorus-containing copolymer (Y), the number of the carbon atoms of the alkyl group is preferably from 10 to 18, more preferably from 10 to 16, still more preferably from 10 to 14.<<Hydroxy Group-containing (Meth)acrylate (B)>>

[0100] The hydroxy group-containing (meth)acrylate (B) to be used in this embodiment is represented by the following general formula (b-1).

[0101] The constituent unit (b) derived from the hydroxy group-containing (meth)acrylate (B) plays a function of making the phosphorus-containing copolymer (Y) a multi-point adsorption type copolymer, and is presumed to contribute to improvements in wear resistance and extreme pressure property of the copolymer. In addition, in order to cause the lubricating oil composition to exhibit defoaming performance over a long time period, the constituent unit is presumed to be responsible for the defoaming performance by controlling the surface tension of a foam surface.

[0102] The hydroxy group-containing (meth)acrylates (B) may be used alone or in combination thereof. Accordingly, the phosphorus-containing copolymer (Y) may include one kind of the constituent units (b) each derived from the hydroxy group-containing (meth)acrylate (B) alone, or may include two or more kinds thereof.

[0103] In the general formula (b-1), R b1< represents a hydrogen atom or a methyl group. That is, the hydroxy group-containing (meth)acrylate (B) has an acryloyl group or a methacryloyl group as a polymerizable functional group.

[0104] A monomer in which R b1< represents a hydrogen atom or a methyl group is easily available and is excellent in polymerizability.

[0105] Herein, in this embodiment, R b1< preferably represents a hydrogen atom from the viewpoint of easily adjusting the molecular weight of the phosphorus-containing copolymer (Y). That is, the hydroxy group-containing (meth)acrylate (B) preferably has an acryloyl group as a polymerizable functional group.

[0106] In the general formula (b-1), R b2< represents an alkylene group having 2 to 4 carbon atoms.

[0107] When the number of the carbon atoms of the alkylene group falls within the above-mentioned range, the oil solubility of the phosphorus-containing copolymer (Y) can be made satisfactory, and the adsorptivity thereof to a metal can also be made satisfactory.

[0108] Herein, from the viewpoint of easily ensuring appropriate oil solubility and appropriate adsorptivity to a metal, the number of the carbon atoms of the alkylene group is preferably from 2 or 3, more preferably 2.

[0109] m1 represents an integer of from 1 to 10. When m1 represents an integer of 2 or more, a plurality of R b2< s may be identical to or different from each other. In addition, a bonding mode within the moiety represented by -(OR b2< ) m1 may be a random bond or a block bond, but is preferably a random bond from the viewpoint of ease of polymerization.

[0110] When m1 falls within the above-mentioned range, appropriate oil solubility can be easily ensured.

[0111] Herein, from the viewpoint of more easily ensuring appropriate oil solubility, m1 represents preferably from 1 to 6, more preferably from 1 to 4, still more preferably 1 or 2, still further more preferably 1.<<Phosphorus-containing (Meth)acrylate (C)>>

[0112] The phosphorus-containing (meth)acrylate (C) to be used in this embodiment is represented by the following general formula (c-1).

[0113] The constituent unit (c) derived from the phosphorus-containing (meth)acrylate (C) is presumed to play a function of improving the wear resistance and extreme pressure property of the phosphorus-containing copolymer (Y) by introducing a phosphoric acid group or a group derived from an acidic phosphoric acid ester into a side chain of the phosphorus-containing copolymer (Y).

[0114] Herein, phosphorus is an element that causes a reduction in thermal stability of the phosphorus-containing copolymer (Y), and hence phosphorus is an element that is not generally introduced from the viewpoint of ensuring the thermal stability. However, a problem of the reduction in thermal stability due to the introduction of phosphorus is alleviated by introducing the constituent unit (c) derived from the phosphorus-containing (meth)acrylate (C) into a copolymer in which the constituent unit (a) derived from the alkyl (meth)acrylate (A) and the constituent unit (b) derived from the hydroxy group-containing (meth)acrylate (B) are combined. Thus, the phosphorus-containing copolymer (Y) as a whole becomes a phosphorus-containing copolymer that is excellent in thermal stability, and is also excellent in wear resistance and extreme pressure property.

[0115] The phosphorus-containing (meth)acrylates (C) may be used alone or in combination thereof. Accordingly, the phosphorus-containing copolymer (Y) may include one kind of the constituent units (c) each derived from the phosphorus-containing (meth)acrylate (C) alone, or may include two or more kinds thereof.

[0116] In the general formula (c-1), R c1< represents a hydrogen atom or a methyl group. That is, the phosphorus-containing (meth)acrylate (C) has an acryloyl group or a methacryloyl group as a polymerizable functional group.

[0117] A monomer in which R c1< represents a hydrogen atom or a methyl group is easily available and is excellent in polymerizability.

[0118] Herein, in this embodiment, R c1< preferably represents a hydrogen atom from the viewpoint of easily adjusting the molecular weight of the phosphorus-containing copolymer (Y). That is, the phosphorus-containing (meth)acrylate (C) preferably has an acryloyl group as a polymerizable functional group.

[0119] In the general formula (c-1), R c2< represents an ethylene group.

[0120] When R c2< represents an ethylene group, the oil solubility of the phosphorus-containing copolymer (Y) can be made satisfactory, and the adsorptivity thereof to a metal can also be made satisfactory.

[0121] m2 represents an integer of from 1 to 6. When m2 represents an integer of 2 or more, a plurality of R c2< s may be identical to or different from each other. In addition, a bonding mode within the moiety represented by -(OR c2< ) m2 may be a random bond or a block bond, but is preferably a random bond from the viewpoint of ease of polymerization.

[0122] When m2 falls within the above-mentioned range, appropriate oil solubility can be easily ensured.

[0123] Herein, from the viewpoint of easily ensuring appropriate oil solubility, m2 represents preferably from 1 to 4, more preferably 1 or 2, still more preferably 1.

[0124] "n" represents an integer of 1 or 2. When n=1, R c3< represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, provided that at least one of a plurality of R c3< s represents a hydrogen atom. When n=2, R c3< represents a hydrogen atom. In the case where n=1, only one of a plurality of R c3< s may represent a hydrogen atom. In this case, the other of the plurality of R c3< s represents a hydrocarbon group having 1 to 3 carbon atoms.

[0125] Herein, in the case where n=1, when the other of the plurality of R c3< s represents a hydrocarbon group having 1 to 3 carbon atoms, the hydrocarbon group is preferably a methyl group or an ethyl group.

[0126] Alternatively, when n=1, the plurality of R c3< s each preferably represent a hydrogen atom.

[0127] Herein, the phosphorus-containing (meth)acrylate (C) preferably contains, as a main component, a phosphorus-containing (meth)acrylate (C1) in which n=1.

[0128] The term "main component" as used herein refers to a component whose content exceeds 50 mass%. That is, the content of the phosphorus-containing (meth)acrylate (C1) in which n=1 is preferably from more than 50 mass% to 100 mass%, more preferably from 60 mass% to 100 mass%, still more preferably from 70 mass% to 100 mass%, still further more preferably from 80 mass% to 100 mass%, yet still further more preferably from 90 mass% to 100 mass% with respect to the total amount of the phosphorus-containing (meth)acrylate (C).

[0129] In addition, the content of a constituent unit (c1) derived from the phosphorus-containing (meth)acrylate (C1) in which n=1 is preferably from more than 50 mass% to 100 mass%, more preferably from 60 mass% to 100 mass%, still more preferably from 70 mass% to 100 mass%, still further more preferably from 80 mass% to 100 mass%, yet still further more preferably from 90 mass% to 100 mass% with respect to the total amount of the constituent unit (c) derived from the phosphorus-containing (meth)acrylate (C).

[0130] In addition, the phosphorus-containing (meth)acrylate (C) to be used in this embodiment has an acid value of preferably from 300 mgKOH / g to 600 mgKOH / g, more preferably from 350 mgKOH / g to 550 mgKOH / g from the viewpoint of more easily improving the wear resistance and extreme pressure property of the phosphorus-containing copolymer (Y).

[0131] In this description, the acid value of the phosphorus-containing (meth)acrylate (C) means a value measured by a potentiometric method specified in JIS K 2501:2003, 7.(Requirement (α): Content Ratio of Constituent Unit (a) to Constituent Unit (b))

[0132] In the phosphorus-containing copolymer (Y), the content ratio [(a) / (b)] of the constituent unit (a) to the constituent unit (b) is preferably from 7 / 3 to 9 / 1, more preferably 8 / 2 in terms of molar ratio from, for example, the viewpoint of the solubility of the copolymer in a base oil.(Requirement (β): Phosphorus Content)

[0133] The phosphorus content of the phosphorus-containing copolymer (Y) is preferably from 0.05 mass% to 1.0 mass%, more preferably from 0.06 mass% to 0.70 mass%, still more preferably from 0.07 mass% to 0.50 mass%, still further more preferably from 0.08 mass% to 0.40 mass%, yet still further more preferably from 0.10 mass% to 0.30 mass% with respect to the total amount of the phosphorus-containing copolymer (Y).

[0134] The phosphorus content of the phosphorus-containing copolymer (Y) may be calculated on the basis of: a result of the measurement of the amount of phosphorus in an organic solvent (e.g., a lubricating base oil) in conformity with JPI-5S-38-03 after the dissolution of a predetermined amount of the phosphorus-containing copolymer (Y) in the organic solvent; and the dissolved amount of the phosphorus-containing copolymer (Y) in the organic solvent.(Other Monomer)

[0135] The phosphorus-containing copolymer (Y) may include, in addition to the above-mentioned constituent units (a), (b), and (c), a constituent unit derived from any other monomer to such an extent that the effects of the present invention are not significantly impaired. The other monomer is, for example, a functional group-containing monomer except the monomers (A), (B), and (C). The other functional group-containing monomer is, for example, a functional group-containing (meth)acrylate except the monomers (A), (B), and (C).

[0136] However, from the viewpoint of more easily improving the effects of the present invention, the total content of the above-mentioned constituent units (a), (b), and (c) in the phosphorus-containing copolymer (Y) is preferably from more than 50 mass% to 100 mass%, more preferably from 60 mass% to 100 mass%, still more preferably from 70 mass% to 100 mass%, still further more preferably from 80 mass% to 100 mass%, yet still further more preferably from 90 mass% to 100 mass% with respect to all the constituent units of the phosphorus-containing copolymer (Y).

[0137] In addition, from the viewpoint of more easily improving the effects of the present invention, the content of the constituent unit derived from the functional group-containing monomer except the monomers (A), (B), and (C) in the phosphorus-containing copolymer (Y) is preferably 50 mass% or less, more preferably less than 40 mass%, still more preferably less than 30 mass%, still further more preferably less than 20 mass%, yet still further more preferably less than 10 mass% with respect to all the constituent units.(Mass Average Molecular Weight (Mw) of Phosphorus-containing Copolymer (Y))

[0138] The mass average molecular weight (Mw) of the phosphorus-containing copolymer (Y) is preferably from 5,000 to 100,000, more preferably from 5,000 to 80,000, still more preferably from 5,000 to 60,000 from the viewpoint of more easily exhibiting the effects of the present invention and the viewpoint of the solubility of the copolymer in a base oil.

[0139] The mass average molecular weight (Mw) is a value measured or calculated by a method described in Examples to be described later.(Polymerization Mode of Phosphorus-containing Copolymer (Y))

[0140] The polymerization mode of the phosphorus-containing copolymer (Y) is not particularly limited, and may be any of block copolymerization, random copolymerization, and block / random copolymerization. Among them, random copolymerization is preferred from the viewpoint of ease of a polymerization reaction.<Content of Phosphorus-containing Copolymer (Y)>

[0141] In the lubricating oil composition of this embodiment, the content (in terms of resin content) of the phosphorus-containing copolymer (Y) is preferably from 0.10 mass% to 5.0 mass%, more preferably from 0.15 mass% to 3.0 mass%, still more preferably from 0.20 mass% to 2.0 mass% with respect to the total amount of the lubricating oil composition from, for example, the viewpoint of improving the effects of the present invention and the viewpoint of improving the wear resistance of the lubricating oil composition.<<Method of producing Phosphorus-containing Copolymer (Y)>>

[0142] The phosphorus-containing copolymer (Y) is produced by a production method including a step (S) of polymerizing the alkyl (meth)acrylate (A) represented by the general formula (a-1), the hydroxy group-containing (meth)acrylate (B) represented by the general formula (b-1), and the phosphorus-containing (meth)acrylate (C) represented by the general formula (c-1).

[0143] The step (S) of producing the phosphorus-containing copolymer (Y) is described in detail below.(Step (S) of producing (polymerizing) Phosphorus-containing Copolymer (Y))

[0144] The step (S) of producing the phosphorus-containing copolymer (Y) is not particularly limited, and the copolymer is produced by applying any of the known steps (S). Examples of such step (S) include an emulsion polymerization method, a suspension polymerization method, and a solution polymerization method.

[0145] Herein, a solution polymerization method in which a solvent soluble in a lubricating base oil is used as a solvent is preferably adopted as the step (S) of producing the phosphorus-containing copolymer (Y).((Solution Polymerization Method))

[0146] The solution polymerization method is performed by, for example, loading the monomers (A), (B), and (C), and the solvent and an initiator into a reactor, purging the inside of the reactor with nitrogen, and then subjecting the mixture to a reaction while stirring the mixture at from 60°C to 100°C for from 2 hours to 10 hours. Any other monomer except the monomers (A), (B), and (C) is also optionally loaded into the reactor.

[0147] Examples of the solvent to be used in the solution polymerization method include: alcohols, such as methanol, ethanol, propanol, 2-propanol, and butanol; hydrocarbons, such as benzene, toluene, xylene, and hexane; esters, such as ethyl acetate, butyl acetate, and isobutyl acetate; ketones, such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; ethers, such as methoxybutanol, ethoxybutanol, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, propylene glycol monobutyl ether, and dioxane; mineral oils; and synthetic oils, such as a poly-α-olefin, an ethylene-α-olefin copolymer, an alkylbenzene, an alkylnaphthalene, polyphenyl ether, an alkyl-substituted diphenyl ether, a polyol ester, a dibasic acid ester, a hindered ester, a monoester, and a GTL base oil.

[0148] Those solvents may be used alone or in combination thereof.

[0149] Examples of the initiator to be used in the solution polymerization method include: azo-based initiators, such as 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis-(N,N-dimethyleneisobutylamidine) dihydrochloride, and 1,1'-azobis(cyclohexyl-1-carbonitrile); hydrogen peroxide; organic peroxides, such as benzoyl peroxide, t-butyl hydroperoxide, cumene hydroperoxide, methyl ethyl ketone peroxide, and perbenzoic acid; persulfates, such as sodium persulfate, potassium persulfate, and ammonium persulfate; the redox initiators of hydrogen peroxide-Fe 2+< ; and other existing radical initiators.

[0150] The molecular weight of the phosphorus-containing copolymer (Y) is controlled by a known method. The molecular weight of the phosphorus-containing copolymer (Y) may be controlled by, for example, a reaction temperature, a reaction time, the amount of the initiator, the loading amount of each monomer, the kind of the solvent, or the use of a chain transfer agent.((Preferred Aspect 1 in Step (S)))

[0151] In the step (S), from the viewpoint of producing the phosphorus-containing copolymer (Y) satisfying the above-mentioned requirement (α), the blending ratio [(A) / (B)] of the alkyl (meth)acrylate (A) to the hydroxy group-containing (meth)acrylate (B) is adjusted to preferably from 7 / 3 to 9 / 1, more preferably 8 / 2 in terms of molar ratio.((Preferred Aspect 2 in Step (S)))

[0152] In the step (S), from the viewpoint of producing the phosphorus-containing copolymer (Y) satisfying the above-mentioned requirement (β), the blending ratio [(C) / {(A)+(B)}] of the phosphorus-containing (meth)acrylate (C) to the total amount of the alkyl (meth)acrylate (A) and the hydroxy group-containing (meth)acrylate (B) is preferably adjusted to from 0.1 / 100 to 10 / 100 in terms of molar ratio.

[0153] In addition, from the viewpoint of more easily improving the wear resistance and extreme pressure property of the phosphorus-containing copolymer (Y), the ratio [(C) / {(A)+(B)}] is more preferably 0.5 / 100 or more, still more preferably 1.0 / 100 or more.

[0154] Further, from the viewpoint of more easily improving the thermal stability of the phosphorus-containing copolymer (Y), the ratio [(C) / {(A)+(B)}] is more preferably 5.0 / 100 or less, still more preferably 3.0 / 100 or less.

[0155] The upper limit values and lower limit values of those numerical ranges may be freely combined. Specifically, the ratio is more preferably from 0.5 / 100 to 5.0 / 100, still more preferably from 1.0 / 100 to 3.0 / 100.<Other Additive>

[0156] The lubricating oil composition of this embodiment may include an additive except the component (Y) (hereinafter also referred to as "additive for a lubricating oil") to such an extent that the effects of the present invention are not impaired.

[0157] Examples of the additive for a lubricating oil include an antioxidant, a metal deactivator, a demulsifier, a detergent dispersant, a defoamer, and an extreme pressure agent.

[0158] Those additives for a lubricating oil may be used alone or in combination thereof.

[0159] In this description, the additive may be blended with any other component in the form of a solution, which is obtained by dissolving the additive in a diluting oil, in consideration of its handleability and its solubility in a base oil. In such case, in this description, the content of the additive is a content in terms of an active component (in terms of resin content) excluding the diluting oil.

[0160] The details of the above-mentioned respective additives for a lubricating oil are described below.(Antioxidant)

[0161] An amine-based antioxidant, a phenol-based antioxidant, a phosphorus-based antioxidant, a sulfur-based antioxidant, a molybdenum amine complex-based antioxidant, and the like to be used in related-art lubricating oil compositions may each be used as the antioxidant.

[0162] The antioxidants may be used alone or in combination thereof.

[0163] Examples of the amine-based antioxidant include: monoalkyldiphenylamine-based compounds, such as monooctyldiphenylamine and monononyldiphenylamine; dialkyldiphenylamine-based compounds, such as 4,4'-dibutyldiphenylamine, 4,4'-dipentyldiphenylamine, 4,4'-dihexyldiphenylamine, 4,4'-diheptyldiphenylamine, 4,4'-dioctyldiphenylamine, 4,4'-dinonyldiphenylamine, and monobutylphenylmonooctylphenylamine; polyalkyldiphenylamine-based compounds, such as tetrabutyldiphenylamine, tetrahexyldiphenylamine, tetraoctyldiphenylamine, and tetranonyldiphenylamine; and naphthylamine-based compounds, such as α-naphthylamine, phenyl-α-naphthylamine, butylphenyl-α-naphthylamine, pentylphenyl-α-naphthylamine, hexylphenyl-α-naphthylamine, heptylphenyl-α-naphthylamine, octylphenyl-α-naphthylamine, and nonylphenyl-α-naphthylamine.

[0164] Examples of the phenol-based antioxidant include: monophenol-based compounds, such as 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol, and octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; and diphenol-based compounds, such as 4,4'-methylenebis(2,6-di-tert-butylphenol) and 2,2'-methylenebis(4-ethyl-6-tert-butylphenol).

[0165] The content of the antioxidant only needs to be the minimum amount required to maintain the oxidation stability of the lubricating oil composition, and is preferably from 0.01 mass% to 1.5 mass%, more preferably from 0.1 mass% to 1.2 mass% with respect to the total amount of the lubricating oil composition.(Metal Deactivator)

[0166] Examples of the metal deactivator include a benzotriazole-based compound, a tolyltriazole-based compound, a thiadiazole-based compound, an imidazole-based compound, and a pyrimidine-based compound.

[0167] The metal deactivators may be used alone or in combination thereof.

[0168] The content of the metal deactivator is preferably from 0.01 mass% to 5.0 mass%, more preferably from 0.02 mass% to 3.0 mass% with respect to the total amount of the lubricating oil composition from the viewpoint of the effect of its addition.(Demulsifier)

[0169] Examples of the demulsifier include: cationic surfactants, such as a quaternary ammonium salt and imidazolines; a polyoxyalkylene block polymer (e.g., an ethylene oxide (EO)-propylene oxide (PO) block copolymer), a polyoxyalkylene glycol, and a polyoxyalkylene polyglycol; and an alkylene oxide adduct of an alkylphenol-formaldehyde polycondensate.

[0170] The demulsifiers may be used alone or in combination thereof.

[0171] The content of the demulsifier is preferably from 0.0005 mass% to 0.5 mass%, more preferably from 0.0008 mass% to 0.2 mass% with respect to the total amount of the lubricating oil composition.(Detergent Dispersant)

[0172] Examples of the detergent dispersant include succinimides, boron-containing succinimides, benzylamines, boron-containing benzylamines, succinic acid esters, and monovalent or divalent carboxylic acid amides represented by a fatty acid or succinic acid.

[0173] The detergent dispersants may be used alone or in combination thereof.

[0174] The content of the detergent dispersant is preferably from 0.01 mass% to 5.0 mass%, more preferably from 0.02 mass% to 3.0 mass% with respect to the total amount of the lubricating oil composition from the viewpoint of the effect of its addition.(Defoamer)

[0175] Examples of the defoamer include a silicone oil, a fluorosilicone oil, a fluoroalkyl ether, and an acrylate-based compound such as a polymethacrylate.

[0176] Among them, an acrylate-based compound such as a polymethacrylate and a silicone oil are preferred.

[0177] The defoamers may be used alone or in combination thereof.

[0178] The content of the defoamer is preferably from 0.001 mass% to 1.0 mass%, more preferably from 0.002 mass% to 0.5 mass%, still more preferably from 0.003 mass% to 0.3 mass% with respect to the total amount of the lubricating oil composition.(Extreme Pressure Agent)

[0179] An organometallic extreme pressure agent, a sulfur-based extreme pressure agent, a phosphorus-based extreme pressure agent, and a sulfur-phosphorus-based extreme pressure agent to be used in the related-art lubricating oil compositions may each be used as the extreme pressure agent.

[0180] The extreme pressure agents may be used alone or in combination thereof.

[0181] Examples of the organometallic extreme pressure agent include: organomolybdenum-based compounds, such as a molybdenum dialkyldithiocarbamate (MoDTC) and a molybdenum dialkyldithiophosphate (MoDTP); and organozinc-based compounds, such as a zinc dialkyldithiocarbamate (ZnDTC) and a zinc dialkyldithiophosphate (ZnDTP).

[0182] Examples of the sulfur-based extreme pressure agent include a sulfurized oil and fat, a sulfurized fatty acid, a sulfurized ester, a sulfurized olefin, a monosulfide, a polysulfide, a dihydrocarbyl sulfide, a thiadiazole compound, an alkylthiocarbamoyl compound, a thiocarbamate compound, a thioterpene compound, and a dialkyl thiodipropionate compound.

[0183] Examples of the phosphorus-based extreme pressure agent include: phosphoric acid esters, such as an aryl phosphate, an alkyl phosphate, an alkenyl phosphate, and an alkylaryl phosphate; acidic phosphoric acid esters, such as a monoaryl acid phosphate, a diaryl acid phosphate, a monoalkyl acid phosphate, a dialkyl acid phosphate, a monoalkenyl acid phosphate, and a dialkenyl acid phosphate; phosphorous acid esters, such as an aryl hydrogen phosphite, an alkyl hydrogen phosphite, an aryl phosphite, an alkyl phosphite, an alkenyl phosphite, and an arylalkyl phosphite; acidic phosphorous acid esters, such as a monoalkyl acid phosphite, a dialkyl acid phosphite, a monoalkenyl acid phosphite, and a dialkenyl acid phosphite; and amine salts thereof.

[0184] Examples of the sulfur-phosphorus-based extreme pressure agent include: alkylthiophosphoric acid esters, such as a monoalkyl thiophosphate, a dialkyl dithiophosphate, and a trialkyl trithiophosphate, and amine salts thereof; and a zinc dialkyldithiophosphate (ZnDTP).

[0185] Herein, the lubricating oil composition of this embodiment preferably includes, as the extreme pressure agent, an amine salt of an acidic phosphoric acid ester selected from the group consisting of: a monoalkyl acid phosphate; and a dialkyl acid phosphate from the viewpoint of improving its wear resistance.

[0186] The number of the carbon atoms of an alkyl group included in each of the monoalkyl acid phosphate and the dialkyl acid phosphate is preferably from 6 to 20, more preferably from 8 to 16, still more preferably from 10 to 14. In addition, the alkyl group may be linear or branched.

[0187] The content of the extreme pressure agent is preferably from 0.1 mass% to 5.0 mass%, more preferably from 0.2 mass% to 3.0 mass%, still more preferably from 0.3 mass% to 1.0 mass% with respect to the total amount of the lubricating oil composition from the viewpoint of the effect of its addition.

[0188] From the viewpoint of improving the long-term defoaming performance of the lubricating oil composition, the content of the thiocarbamate compound is preferably small. The thiocarbamate compound is, for example, a dialkyl dithiocarbamate compound such as methylenebis(dibutyldithiocarbamate).

[0189] The content of the thiocarbamate compound is preferably less than 0.01 mass%, more preferably less than 0.001 mass% with respect to the total amount of the lubricating oil composition, and it is still more preferred that the lubricating oil composition be free of any thiocarbamate compound.[Physical Properties of Lubricating Oil Composition]

[0190] The lubricating oil composition of this embodiment preferably satisfies the following physical properties.<Kinematic Viscosity and Viscosity Index>

[0191] The 40°C kinematic viscosity of the lubricating oil composition of this embodiment is preferably from 90 mm 2< / s to 1,100 mm 2< / s, more preferably from 135 mm 2< / s to 748 mm 2< / s, still more preferably from 198 mm 2< / s to 506 mm 2< / s, still further more preferably from 288 mm 2< / s to 352 mm 2< / s.

[0192] The viscosity index of the lubricating oil composition of this embodiment is preferably 140 or more, more preferably 160 or more, still more preferably 170 or more, still further more preferably 180 or more.

[0193] The kinematic viscosity and viscosity index of the lubricating oil composition are values measured or calculated in conformity with JIS K2283:2000.<Defoaming Performance>

[0194] In the lubricating oil composition of this embodiment, defoaming performances measured by methods described in Examples to be described later each preferably fall within the following ranges.(Defoaming Performance by Sequences I, II, and III)

[0195] When a defoaming performance evaluation 1 in Examples to be described later is performed, the volume of foam immediately after the completion of air blowing into the lubricating oil composition is preferably 100 mL or less, more preferably 50 mL or less, still more preferably 30 mL or less.

[0196] In addition, when the defoaming performance evaluation 1 in Examples to be described later is performed, the volume of foam after standing for 10 minutes from the completion of the air blowing is preferably 10 mL or less, more preferably 0 mL.(Defoaming Performance by 7-day Continuous Foaming Test)

[0197] When a defoaming performance evaluation 2 in Examples to be described later is performed, the volume of foam in the lubricating oil composition is preferably 50 mL or less, more preferably 40 mL or less, still more preferably 30 mL or less.(Wear Resistance)

[0198] In the lubricating oil composition of this embodiment, the average wear amount of rollers measured by a method described in Examples to be described later is preferably 30 mg or less, more preferably 20 mg or less, still more preferably 10 mg or less.[Method of producing Lubricating Oil Composition]

[0199] A method of producing a lubricating oil composition according to an embodiment of the present invention is not particularly limited.

[0200] For example, the method of producing a lubricating oil composition of this embodiment includes a step of mixing the hydrocarbon-based synthetic oil (X1), the ester-based synthetic oil (X2), and the phosphorus-containing copolymer (Y), and the phosphorus-containing copolymer (Y) includes the constituent unit (a) derived from the alkyl (meth)acrylate (A) represented by the general formula (a-1), the constituent unit (b) derived from the hydroxy group-containing (meth)acrylate (B) represented by the general formula (b-1), and the constituent unit (c) derived from the phosphorus-containing (meth)acrylate (C) represented by the general formula (c-1).

[0201] When the additive for a lubricating oil is blended, the additive for a lubricating oil may be blended simultaneously with the component (Y), or may be blended separately. In addition, the components may each be blended in the form of a solution (dispersion) by adding a diluting oil or the like thereto.

[0202] After the blending of the respective components, the components are preferably stirred and uniformly dispersed by using a known method.

[0203] Preferred aspects of the above-mentioned respective components have already been described above.[Application of Lubricating Oil Composition]

[0204] The lubricating oil composition of this embodiment can maintain excellent defoaming performance for a long time period. Accordingly, the lubricating oil composition of this embodiment may be widely used for lubricating applications each requiring long-term defoaming performance.

[0205] The composition may be suitably used as, for example, a speed increaser oil for a wind turbine, a hydraulic oil, a compressor oil, a gear oil, a cutting oil, a machine tool oil, a refrigerating machine oil, a turbine oil, an internal combustion engine oil, a transmission oil, or an axle unit oil for an automobile. The composition may be particularly suitably used as a speed increaser oil for a wind turbine among them.

[0206] Accordingly, in this embodiment, the following method (1) or (2) is provided. (1) A method of using the lubricating oil composition of this embodiment, wherein the lubricating oil composition is used as a speed increaser oil for a wind turbine, a hydraulic oil, a compressor oil, a gear oil, a cutting oil, a machine tool oil, a refrigerating machine oil, a turbine oil, an internal combustion engine oil, a transmission oil, or an axle unit oil for an automobile. (2) A method of using the lubricating oil composition of the present invention, wherein the lubricating oil composition is used as a speed increaser oil for a wind turbine. In addition, in this embodiment, the following method (3) is also provided. (3) A method of suppressing foaming of a lubricating oil composition including the hydrocarbon-based synthetic oil (X1) and the ester-based synthetic oil (X2) by blending the lubricating oil composition with the phosphorus-containing copolymer (Y). [One Aspect of the Present Invention to be provided]

[0207] In one aspect of the present invention, the following items [1] to

[10] are provided. [1] A lubricating oil composition, including: a hydrocarbon-based synthetic oil (X1); an ester-based synthetic oil (X2); and a phosphorus-containing copolymer (Y), wherein the phosphorus-containing copolymer (Y) includes a constituent unit (a) derived from an alkyl (meth)acrylate (A) represented by the following general formula (a-1), a constituent unit (b) derived from a hydroxy group-containing (meth)acrylate (B) represented by the following general formula (b-1), and a constituent unit (c) derived from a phosphorus-containing (meth)acrylate (C) represented by the following general formula (c-1): wherein in the general formula (a-1), R a1< represents a hydrogen atom or a methyl group, and R a2< represents an alkyl group having 8 to 20 carbon atoms; wherein in the general formula (b-1), R b1< represents a hydrogen atom or a methyl group, R b2< represents an alkylene group having 2 to 4 carbon atoms, m1 represents an integer of from 1 to 10, and when m1 represents an integer of 2 or more, a plurality of R b2< s may be identical to or different from each other; wherein in the general formula (c-1), R c1< represents a hydrogen atom or a methyl group, R c2< represents an ethylene group, m2 represents an integer of from 1 to 6, when m2 represents an integer of 2 or more, a plurality of R c2< s may be identical to or different from each other, "n" represents an integer of 1 or 2, when n=1, R c3< represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, provided that at least one of a plurality of R c3< s represents a hydrogen atom, and when n=2, R c3< represents a hydrogen atom. [2] The lubricating oil composition according to the above-mentioned item [1], wherein the hydrocarbon-based synthetic oil (X1) has a 100°C kinematic viscosity of from 20 mm 2< / s to 55 mm 2< / s. [3] The lubricating oil composition according to the above-mentioned item [1] or [2], wherein the hydrocarbon-based synthetic oil (X1) includes a low-viscosity hydrocarbon-based synthetic oil (X11) having a 100°C kinematic viscosity of from 1.5 mm 2< / s to 11.0 mm 2< / s, and a high-viscosity hydrocarbon-based synthetic oil (X12) having a 100°C kinematic viscosity of from 50.0 mm 2< / s to 350.0 mm 2< / s. [4] The lubricating oil composition according to any one of the above-mentioned items [1] to [3], wherein the ester-based base oil (X2) includes an ester of pentaerythritol and a fatty acid having 4 to 11 carbon atoms. [5] The lubricating oil composition according to any one of the above-mentioned items [1] to [4], wherein a content ratio [(a) / (b)] of the constituent unit (a) to the constituent unit (b) in the phosphorus-containing copolymer (Y) is from 7 / 3 to 9 / 1 in terms of molar ratio. [6] The lubricating oil composition according to any one of the above-mentioned items [1] to [5], wherein a phosphorus content in the phosphorus-containing copolymer (Y) is from 0.05 mass% to 1.0 mass% with respect to a total amount of the phosphorus-containing copolymer (Y). [7] The lubricating oil composition according to any one of the above-mentioned items [1] to [6], wherein the phosphorus-containing copolymer (Y) has a mass average molecular weight (Mw) of from 5,000 to 100,000. [8] The lubricating oil composition according to any one of the above-mentioned items [1] to [7], further comprising one or more kinds of additives selected from the group consisting of: an antioxidant; a metal deactivator; a demulsifier; a detergent dispersant; a defoamer; and an extreme pressure agent. [9] The lubricating oil composition according to any one of the above-mentioned items [1] to [8], wherein the lubricating oil composition is used as a speed increaser oil for a wind turbine, a hydraulic oil, a compressor oil, a gear oil, a cutting oil, a machine tool oil, a refrigerating machine oil, a turbine oil, an internal combustion engine oil, a transmission oil, or an axle unit oil for an automobile.

[10] A method of producing a lubricating oil composition, including a step of mixing a hydrocarbon-based synthetic oil (X1), an ester-based synthetic oil (X2), and a phosphorus-containing copolymer (Y), wherein the phosphorus-containing copolymer (Y) includes a constituent unit (a) derived from an alkyl (meth)acrylate (A) represented by the following general formula (a-1), a constituent unit (b) derived from a hydroxy group-containing (meth)acrylate (B) represented by the following general formula (b-1), and a constituent unit (c) derived from a phosphorus-containing (meth)acrylate (C) represented by the following general formula (c-1): wherein in the general formula (a-1), R a1< represents a hydrogen atom or a methyl group, and R a2< represents an alkyl group having 8 to 20 carbon atoms; wherein in the general formula (b-1), R b1< represents a hydrogen atom or a methyl group, R b2< represents an alkylene group having 2 to 4 carbon atoms, m1 represents an integer of from 1 to 10, and when m1 represents an integer of 2 or more, a plurality of R b2< s may be identical to or different from each other; wherein in the general formula (c-1), R c1< represents a hydrogen atom or a methyl group, R c2< represents an ethylene group, m2 represents an integer of from 1 to 6, when m2 represents an integer of 2 or more, a plurality of R c2< s may be identical to or different from each other, "n" represents an integer of 1 or 2, when n=1, R c3< represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, provided that at least one of a plurality of R c3< s represents a hydrogen atom, and when n=2, R c3< represents a hydrogen atom. Examples

[0208] The present invention is specifically described by way of Examples below. However, the present invention is not limited to Examples below.[Methods of measuring Various Physical Property Values]

[0209] The respective properties of respective raw materials used in each of Examples and Comparative Examples, and a lubricating oil composition of each of Examples and Comparative Examples were measured according to the following procedures.(1) Kinematic Viscosity and Viscosity Index

[0210] The 40°C kinematic viscosity and viscosity index of the lubricating oil composition were measured or calculated in conformity with JIS K2283:2000.(2) Mass Average Molecular Weight (Mw)

[0211] One column "TSKguardcolumn SuperHZ-L" and two columns "TSKSuperMultipore HZ-M" manufactured by Tosoh Corporation were attached to "1515 Isocratic HPLC Pump" and "2414 Differential Refractive Index (RI) Detector" manufactured by Waters Corporation in this order from an upstream side, and the mass average molecular weight of a phosphorus-containing copolymer was measured under the following conditions: a measurement temperature: 40°C, a mobile phase: tetrahydrofuran, a flow rate: 0.35 ml / min, and a sample concentration: 1.0 mg / ml. The mass average molecular weight was determined in terms of standard polystyrene.[Examples 1 to 3, and Comparative Examples 1 to 3]

[0212] The following respective components were mixed to prepare lubricating oil compositions each having the composition shown in Table 1, and the lubricating oil compositions were evaluated as described below.

[0213] The unit of each numerical value in the blending composition in Table 1 is "mass%".

[0214] The details of the respective components used for preparing the lubricating oil compositions each having the composition shown in Table 1 are described below.<Hydrocarbon-based Synthetic Oil>

[0215] ·"PAO-1": PAO-1 is a poly-α-olefin having a 40°C kinematic viscosity of 390 mm 2< / s, a 100°C kinematic viscosity of 39.7 mm 2< / s, and a viscosity index of 152. The poly-α-olefin corresponds to the hydrocarbon-based synthetic oil (X1). ·"PAO-2": PAO-2 is a poly-α-olefin having a 40°C kinematic viscosity of 17.4 mm 2< / s, a 100°C kinematic viscosity of 3.9 mm 2< / s, and a viscosity index of 119. The poly-α-olefin corresponds to the low-viscosity hydrocarbon-based synthetic oil (X11). ·"mPAO": mPAO is a decene oligomer, which is obtained by polymerizing 1-decene through use of a metallocene catalyst, and has a 40°C kinematic viscosity of 1,616 mm 2< / s, a 100°C kinematic viscosity of 147.4 mm 2< / s, and a viscosity index of 202. The oligomer corresponds to the high-viscosity hydrocarbon-based synthetic oil (X12). <Ester-based Synthetic Oil>

[0216] ·"Ester 1": A diester of trimethylolpropane (TMP) and isostearic acid (100°C kinematic viscosity: 13.29 mm 2< / s, viscosity index: 124) ·"Ester 2": A tetraester of pentaerythritol and C5-C9 fatty acids (100°C kinematic viscosity: 4.81 mm 2< / s, viscosity index: 101)

[0217] The C5-C9 fatty acids are fatty acids, which are formed of nonanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, and octanoic acid, and are mainly formed of nonanoic acid.<Phosphorus-containing Copolymer>

[0218] A phosphorus-containing copolymer produced by a production example to be described later was used.<Additive for Lubricating Oil>

[0219] ·"Phenol-based antioxidant": octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate ·"Amine-based antioxidant": monobutylphenylmonooctylphenylamine ·"Alkylthiophosphoric acid ester": a tris[2,4-isoalkyl (C 9 , C 10 ) phenyl] thiophosphate ·"Alkylthiocarbamate": methylenebis(dibutyldithiocarbamate) (S content=30.3%) ·"Alkylbenzotriazole": an N-dialkylaminomethylbenzotriazole (N content=14.6%) ·Amine salt of a C10 isodecyl acid phosphate and trioctylamine ·Amine salt of a C13 tridecyl acid phosphate and trioctylamine ·"EO-PO copolymer": a xylene solution of an EO-PO block copolymer (50%) ·"Alkenyl succinimide": a mixture of 50% of polybutenyl succinimide, 20% of polybutene, and 30% of a mineral oil (base number: 37 mgKOH / g) ·"Defoamer": a defoamer obtained by adding an acrylate-based compound having a component concentration of 5 mass% to 95 mass% of a light oil <Monomer used in Production Example>

[0220] ·"Dodecyl acrylate": Dodecyl acrylate is a compound represented by the general formula (a-1) in which R a1< represents a hydrogen atom, and R a2< represents a dodecyl group (an alkyl group having 12 carbon atoms). The compound was used as the alkyl (meth)acrylate (A). ·"2-Hydroxyethyl acrylate": 2-Hydroxyethyl acrylate is a compound represented by the general formula (b-1) in which R b1< represents a hydrogen atom, R b2< represents an ethylene group (an alkylene group having 2 carbon atoms), and m1=1. The compound was used as the hydroxy group-containing (meth)acrylate (B). ·"P-1A(N)": Light Acrylate P-1A(N) (product name), manufactured by Kyoeisha Chemical Co., Ltd., phosphorus content=14.3 mass%

[0221] P-1A(N) is a mixture containing a compound represented by the general formula (c-1) in which n=1 as a main component, and also containing a compound represented by the general formula (c-1) in which n=2. In each of both the compounds, R c1< represents a hydrogen atom, R c2< represents an ethylene group (an alkylene group having 2 carbon atoms), and m2=1. In addition, in each of both the compounds, R c3< represents a hydrogen atom. The mixture was used as the phosphorus-containing (meth)acrylate (C).

[0222] The acid value of P-1A(N) (value measured by a potentiometric method specified in JIS K 2501:2003, 7) is from 420 mgKOH / g to 520 mgKOH / g.<Production Example: Production of Phosphorus-containing Copolymer>

[0223] 191.56 Grams (797 mmol) of dodecyl acrylate, 23.12 g (199 mmol) of 2-hydroxyethyl acrylate, 4.28 g (21.8 mmol) of P-1A(N), and 192 g of 2-propanol serving as a solvent were loaded into a 1,500 mL 4-necked flask mounted with a temperature gauge, a nitrogen introduction tube, and a stirring machine.

[0224] Next, the inside of the flask was purged with nitrogen, and 0.8 g of 2,2'-azobis(isobutyronitrile) was added as an initiator to the mixture. After that, a temperature in the flask was slowly increased while the mixture was stirred. The mixture was subjected to a reaction for 4 hours while being refluxed at a temperature of from 75°C to 85°C. After the completion of the reaction, the solvent was evaporated under reduced pressure. Thus, a phosphorus-containing copolymer was obtained.

[0225] The mass average molecular weight (Mw) of the phosphorus-containing copolymer was 22,000. In addition, the phosphorus content thereof was 0.13 mass%.

[0226] The phosphorus-containing copolymer was used by being diluted with a mineral oil so that the content of the phosphorus-containing copolymer was 50 mass%.<Evaluation 1: Defoaming Performance Evaluation 1>

[0227] The lubricating oil compositions were each evaluated for its foaming degree and foaming stability by a method compliant with JIS K 2518:2017 in the order of (1) Sequence I (24°C), (2) Sequence II (93°C), and (3) Sequence III (24°C).

[0228] In an evaluation result "X-Y" in Table 1, X represents the volume (unit: mL) of foam immediately after the completion of air blowing into each of the lubricating oil compositions, and Y represents the volume (unit: mL) of foam after standing for 10 minutes from the completion of the air blowing.

[0229] In this Example, a case in which X was 100 mL or less and Y was 10 mL or less was defined as being passable.<Evaluation 2: Defoaming Performance Evaluation 2>

[0230] Air blowing into each of the lubricating oil compositions was started by using a test container and a diffuser stone compliant with JIS K 2518:2017 at a dry air blowing amount of 3 L / h and 60°C, and the volume of foam after 7 days was measured.

[0231] In this Example, a case in which the volume of the foam was 50 mL or less was defined as being passable.<Evaluation 3: Evaluation of Transparency>

[0232] Each of the lubricating oil compositions was loaded into a transparent glass container, and the glass container was placed on a laboratory bench covered with white paper, followed by the evaluation of the transparency of the lubricating oil composition. The evaluation of the transparency was performed under an environment at 20°C.

[0233] The results are shown in Table 1.

[0234] The content of the phosphorus-containing copolymer in Table 1 is a content including a diluting oil.

[0235] In addition, the term "C12:OH" of the phosphorus-containing copolymer in Table 1 means a molar ratio between a constituent unit derived from dodecyl acrylate and a constituent unit derived from 2-hydroxyethyl acrylate.[Table 1]

[0236] Table 1Comparative Example 1Comparative Example 2Comparative Example 3Example 1Example 2Example 3Composition of lubricating oil composition (unit: mass%)PAO-189.986.1687.9mPAO61.9365.9065.86PAO-224.2321.3121.31Ester 1 (diester of TMP and isostearic acid)10.0010.0010.00Ester 2 (tetraester of pentaerythritol and C5-C9 fatty acids)10.0010.0010.00Phosphorus-containing copolymer (C12:OH=8:2, Mw: 22,000)2.001.001.00Phenol-based antioxidant0.500.500.500.50Amine-based antioxidant0.500.500.500.50Alkylthiophosphoric acid ester0.400.40Alkylthiocarbamate1.651.65Alkylbenzotriazole0.050.050.050.05Amine salt of acidic phosphoric acid ester (C10) isodecyl acid phosphate and trioctylamine0.580.580.58Amine salt of acidic phosphoric acid ester (C13) tridecyl acid phosphate and trioctylamine0.62EO-PO copolymer0.010.010.010.01Alkenyl succinimide0.050.050.050.05Defoamer (5% of acrylate-based defoamer+95% of light oil)0.1000.1000.1000.1000.1000.100Total100.00100.00100.00100.00100.00100.00Physical property of mixed base oil100°C kinematic viscosity mm 2< / s39.739.734.1139.740.2140.19Physical properties of lubricating oil composition40°C kinematic viscosity mm 2< / s330320-320320320Viscosity index150145-147186186EvaluationFoaming (1) 24°C (ml)0-00-0150-00-030-020-0Foaming (2) 93°C (ml)0-00-010-00-010-010-0Foaming (3) 24°C (ml)0-00-0180-100-010-020-0Continuous foaming test foaming amount after 7 days (ml)580140-302030

[0237] The following can be seen from Table 1.

[0238] It can be seen that the lubricating oil compositions of Examples 1 to 3 each exhibit excellent defoaming performance over a long time period.

[0239] Meanwhile, it can be seen that the lubricating oil compositions of Comparative Examples 1 and 2 are each poor in long-term defoaming performance.

[0240] In addition, it can be seen that when the low-viscosity hydrocarbon-based synthetic oil, the high-viscosity hydrocarbon-based synthetic oil, and the ester-based synthetic oil are included, and the phosphorus-containing copolymer is not added like Comparative Example 3, the initial defoaming performance of the lubricating oil composition is poor.

[0241] Each of the lubricating oil compositions of Examples 1 to 3 was transparent and showed no cloudiness.<Evaluation 4: FE8 Bearing Wear Test>

[0242] The lubricating oil compositions of Comparative Example 2, and Examples 2 and 3 were each evaluated for its wear resistance by measuring a bearing wear amount in conformity with DIN 51819-3.(Experimental Conditions)

[0243] Testing machine: FE8 manufactured by FAG (DIN 51819-1) Material of roller bearing: high strength brass Number of revolutions: 7.5 rpm Load: 100 kN (2.1 GPa) Oil temperature: 80°C Test time: 80 hours×2 (no oil change) (Evaluation Method)

[0244] The evaluation was performed on the basis of the total (mg) of the wear amounts of two roller bearings. The result is the average value of two experiments (n=2). In this Example, a case in which the average wear amount of the roller bearings was 30 mg or less was defined as being passable.

[0245] The results are shown in Table 2.

[0246] The content of the phosphorus-containing copolymer in Table 2 is also a content including a diluting oil.

[0247] In addition, the term "C12:OH" of the phosphorus-containing copolymer in Table 2 means a molar ratio between a constituent unit derived from dodecyl acrylate and a constituent unit derived from 2-hydroxyethyl acrylate.[Table 2]

[0248] Table 2Comparative Example 2Example 2Example 3Composition of lubricating oil composition (unit: mass%)PAO-186.16mPAO65.9065.86PAO-221.3121.31Ester 1 (diester of TMP and isostearic acid)10.00Ester 2 (tetraester of pentaerythritol and C5-C9 fatty acids)10.0010.00Phosphorus-containing copolymer (C12:OH=8:2, Mw: 22,000)1.001.00Phenol-based antioxidant0.500.500.50Amine-based antioxidant0.500.500.50Alkylthiophosphoric acid ester0.40Alkylthiocarbamate1.65Alkylbenzotriazole0.050.050.05Amine salt of acidic phosphoric acid ester (C10) isodecyl acid phosphate and trioctylamine0.580.58Amine salt of acidic phosphoric acid ester (C13) tridecyl acid phosphate and trioctylamine0.62EO-PO copolymer0.010.010.01Alkenyl succinimide0.050.050.05Defoamer (5% of acrylate-based defoamer+95% of light oil)0.1000.1000.100Total100.00100.00100.00Physical property of mixed base oil100°C kinematic viscosity mm 2< / s39.740.2140.19Physical properties of lubricating oil composition40°C kinematic viscosity mm 2< / s320320320Viscosity index145186186EvaluationFE8 D-7.5 / 100-80 average wear amount of rollers mg1400.52.0

[0249] It can be seen from Table 2 that the lubricating oil compositions of Examples 2 and 3 are each excellent in wear resistance.

Claims

1. A lubricating oil composition, comprising: a hydrocarbon-based synthetic oil (X1); an ester-based synthetic oil (X2); and a phosphorus-containing copolymer (Y), wherein the phosphorus-containing copolymer (Y) comprises a constituent unit (a) derived from an alkyl (meth)acrylate (A) represented by the following general formula (a-1), a constituent unit (b) derived from a hydroxy group-containing (meth)acrylate (B) represented by the following general formula (b-1), and a constituent unit (c) derived from a phosphorus-containing (meth)acrylate (C) represented by the following general formula (c-1): wherein in the general formula (a-1), Ra1 represents a hydrogen atom or a methyl group, and Ra2 represents an alkyl group having 8 to 20 carbon atoms; wherein in the general formula (b-1), Rb1 represents a hydrogen atom or a methyl group, Rb2 represents an alkylene group having 2 to 4 carbon atoms, m1 represents an integer of from 1 to 10, and when m1 represents an integer of 2 or more, a plurality of Rb2s may be identical to or different from each other; wherein in the general formula (c-1), Rc1 represents a hydrogen atom or a methyl group, Rc2 represents an ethylene group, m2 represents an integer of from 1 to 6, when m2 represents an integer of 2 or more, a plurality of Rc2s may be identical to or different from each other, "n" represents an integer of 1 or 2, when n=1, Rc3 represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, provided that at least one of a plurality of Rc3s represents a hydrogen atom, and when n=2, Rc3 represents a hydrogen atom.

2. The lubricating oil composition according to claim 1, wherein the hydrocarbon-based synthetic oil (X1) has a 100°C kinematic viscosity of from 20 mm2 / s to 55 mm2 / s.

3. The lubricating oil composition according to claim 1 or 2, wherein the hydrocarbon-based synthetic oil (X1) comprises a low-viscosity hydrocarbon-based synthetic oil (X11) having a 100°C kinematic viscosity of from 1.5 mm2 / s to 11.0 mm2 / s, and a high-viscosity hydrocarbon-based synthetic oil (X12) having a 100°C kinematic viscosity of from 50.0 mm2 / s to 350.0 mm2 / s.

4. The lubricating oil composition according to any one of claims 1 to 3, wherein the ester-based base oil (X2) comprises an ester of pentaerythritol and a fatty acid having 4 to 11 carbon atoms.

5. The lubricating oil composition according to any one of claims 1 to 4, wherein a content ratio [(a) / (b)] of the constituent unit (a) to the constituent unit (b) in the phosphorus-containing copolymer (Y) is from 7 / 3 to 9 / 1 in terms of molar ratio.

6. The lubricating oil composition according to any one of claims 1 to 5, wherein a phosphorus content in the phosphorus-containing copolymer (Y) is from 0.05 mass% to 1.0 mass% with respect to a total amount of the phosphorus-containing copolymer (Y).

7. The lubricating oil composition according to any one of claims 1 to 6, wherein the phosphorus-containing copolymer (Y) has a mass average molecular weight (Mw) of from 5,000 to 100,000.

8. The lubricating oil composition according to any one of claims 1 to 7, further comprising one or more kinds of additives selected from the group consisting of: an antioxidant; a metal deactivator; a demulsifier; a detergent dispersant; a defoamer; and an extreme pressure agent.

9. The lubricating oil composition according to any one of claims 1 to 8, wherein the lubricating oil composition is used as a speed increaser oil for a wind turbine, a hydraulic oil, a compressor oil, a gear oil, a cutting oil, a machine tool oil, a refrigerating machine oil, a turbine oil, an internal combustion engine oil, a transmission oil, or an axle unit oil for an automobile.

10. A method of producing a lubricating oil composition, comprising a step of mixing a hydrocarbon-based synthetic oil (X1), an ester-based synthetic oil (X2), and a phosphorus-containing copolymer (Y), wherein the phosphorus-containing copolymer (Y) comprises a constituent unit (a) derived from an alkyl (meth)acrylate (A) represented by the following general formula (a-1), a constituent unit (b) derived from a hydroxy group-containing (meth)acrylate (B) represented by the following general formula (b-1), and a constituent unit (c) derived from a phosphorus-containing (meth)acrylate (C) represented by the following general formula (c-1): wherein in the general formula (a-1), Ra1 represents a hydrogen atom or a methyl group, and Ra2 represents an alkyl group having 8 to 20 carbon atoms; wherein in the general formula (b-1), Rb1 represents a hydrogen atom or a methyl group, Rb2 represents an alkylene group having 2 to 4 carbon atoms, m1 represents an integer of from 1 to 10, and when m1 represents an integer of 2 or more, a plurality of Rb2s may be identical to or different from each other; wherein in the general formula (c-1), Rc1 represents a hydrogen atom or a methyl group, Rc2 represents an ethylene group, m2 represents an integer of from 1 to 6, when m2 represents an integer of 2 or more, a plurality of Rc2s may be identical to or different from each other, "n" represents an integer of 1 or 2, when n=1, Rc3 represents a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, provided that at least one of a plurality of Rc3s represents a hydrogen atom, and when n=2, Rc3 represents a hydrogen atom.

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