Lubricating oil composition

Abstract

Provided is a lubricating oil composition that maintains excellent defoaming properties over a long period of time. The lubricating oil composition contains a hydrocarbon synthetic oil (X1), an ester synthetic oil (X2), and a phosphorus-containing copolymer (Y). The phosphorus-containing copolymer (Y) includes a structural unit (a) derived from a specific alkyl (meth)acrylate (A), a structural unit (b) derived from a specific hydroxyl group–containing (meth)acrylate (B), and a structural unit (c) derived from a specific phosphorus-containing (meth)acrylate (C).

Description

lubricating oil composition

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

[0002] From the viewpoints of reducing environmental load and the depletion of fossil fuels, demand for wind power generation utilizing renewable energy is expected to further increase in the future. Wind power generation converts the kinetic energy of wind into power using a propeller or other rotor that rotates in response to wind, and this power drives a generator to convert it into electrical energy. In such wind power generation, since the rotation speed of the rotor is slow, a speed increaser is used in consideration of the power generation efficiency of the generator. Various speed increasers are known, and for example, planetary gear type power transmission devices are widely used. Speed ​​increaser oil compositions for wind power generation used in planetary gear type power transmission devices and the like are required to be able to operate without maintenance for a long period of time, etc.

[0003] As an example of a speed-increasing oil composition for wind power generation, Patent Document 1 discloses a mixed base oil of a poly-α-olefin base oil and an ester base oil to which various additives such as extreme pressure agents have been added.

[0004] Various load-bearing additives such as extreme pressure agents have also been proposed as additives for lubricating oils, including, for example, phosphorus-containing (meth)acrylate copolymers (see Patent Document 2).

[0005] JP 2021-187911 A Patent No. 7061242 A

[0006] Incidentally, lubricating oil compositions may foam due to factors such as air entrainment during operation of mechanical devices. Foaming in lubricating oil compositions can lead to reduced lubrication performance, reduced sealing performance, accelerated oxidative degradation, reduced cooling efficiency, and reduced power transmission efficiency. Therefore, lubricating oil compositions are required to have antifoaming performance. In particular, speed-increasing oil compositions for wind power generation, which are operated maintenance-free for long periods of time, have strict requirements for antifoaming performance and are required to maintain excellent antifoaming performance over a long period of time. However, lubricating oil compositions using a mixed base oil of a poly-α-olefin base oil and an ester base oil, as in Patent Document 1, have the problem of being prone to foaming and making it difficult to maintain excellent antifoaming performance over a long period of time. Furthermore, Patent Document 2 does not consider at all the foaming of lubricating oil compositions.

[0007] Therefore, an object of the present invention is to provide a lubricating oil composition that can maintain excellent antifoaming performance for a long period of time.

[0008] According to the present invention, the following items [1] and [2] are provided: [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 structural unit (a) derived from an alkyl (meth)acrylate (A) represented by the following general formula (a-1), a structural unit (b) derived from a hydroxyl group-containing (meth)acrylate (B) represented by the following general formula (b-1), and a structural unit (c) derived from a phosphorus-containing (meth)acrylate (C) represented by the following general formula (c-1): [In the above general formula (a-1), R ａ１ is a hydrogen atom or a methyl group. ａ２ represents an alkyl group having 8 to 20 carbon atoms. [In the above general formula (b-1), R ｂ１ is a hydrogen atom or a methyl group. ｂ２ represents an alkylene group having 2 to 4 carbon atoms. m1 represents an integer of 1 to 10. When m1 is an integer of 2 or more, a plurality of R ｂ２ may be the same or different. [In the above general formula (c-1), R ｃ１is a hydrogen atom or a methyl group. ｃ２ represents an ethylene group. m2 represents an integer of 1 to 6. When m2 is an integer of 2 or more, a plurality of R ｃ２ may be the same or different. n represents an integer of 1 or 2. When n=1, R ｃ３ is a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms. ｃ３ When n=2, at least one of R ｃ３ is a hydrogen atom.] [2] A method for 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 structural unit (a) derived from an alkyl (meth)acrylate (A) represented by the following general formula (a-1), a structural unit (b) derived from a hydroxyl group-containing (meth)acrylate (B) represented by the following general formula (b-1), and a structural unit (c) derived from a phosphorus-containing (meth)acrylate (C) represented by the following general formula (c-1): [In the above general formula (a-1), R ａ１ is a hydrogen atom or a methyl group. ａ２ represents an alkyl group having 8 to 20 carbon atoms. [In the above general formula (b-1), R ｂ１ is a hydrogen atom or a methyl group. ｂ２ represents an alkylene group having 2 to 4 carbon atoms. m1 represents an integer of 1 to 10. When m1 is an integer of 2 or more, a plurality of R ｂ２ may be the same or different. [In the above general formula (c-1), R ｃ１ is a hydrogen atom or a methyl group. ｃ２ represents an ethylene group. m2 represents an integer of 1 to 6. When m2 is an integer of 2 or more, a plurality of R ｃ２ may be the same or different. n represents an integer of 1 or 2. When n=1, R ｃ３ is a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms. ｃ３ When n=2, at least one of R ｃ３ is a hydrogen atom.]

[0009] According to the present invention, it is possible to provide a lubricating oil composition that can maintain excellent antifoaming performance for a long period of time.

[0010] The upper and lower limits of the numerical ranges described herein can be combined arbitrarily. For example, when "A to B" and "C to D" are described as numerical ranges, the numerical ranges "A to D" and "C to B" are also included in the scope of the present invention. Furthermore, the numerical range "lower limit to upper limit" described herein means that it is equal to or greater than the lower limit and equal to or less than the upper limit, unless otherwise specified. Furthermore, in this specification, the numerical values ​​in the examples are numerical values ​​that can be used as upper or lower limits. Note that "(meth)acrylate" means acrylate or methacrylate, and other similar terms have the same meaning. For example, "poly(meth)acrylate" means polyacrylate or polymethacrylate. Furthermore, in this specification, additives such as the phosphorus-containing copolymer (Y) may be blended with other components in the form of a solution dissolved in diluent oil, taking into account solubility in the base oil, etc. In such cases, the content of additives such as the phosphorus-containing copolymer (Y) herein is the content in terms of active ingredient (resin content) excluding the diluent oil.

[0011] [Aspects of Lubricating Oil Composition] The lubricating oil composition of this embodiment contains a hydrocarbon-based synthetic oil (X1), an ester-based synthetic oil (X2), and a phosphorus-containing copolymer (Y). The phosphorus-containing copolymer (Y) contains structural units (a) derived from an alkyl (meth)acrylate (A) represented by the following general formula (a-1), structural units (b) derived from a hydroxyl group-containing (meth)acrylate (B) represented by the following general formula (b-1), and structural units (c) derived from a phosphorus-containing (meth)acrylate (C) represented by the following general formula (c-1): [In the above general formula (a-1), R ａ１ is a hydrogen atom or a methyl group. ａ２ represents an alkyl group having 8 to 20 carbon atoms. [In the above general formula (b-1), R ｂ１ is a hydrogen atom or a methyl group. ｂ２represents an alkylene group having 2 to 4 carbon atoms. m1 represents an integer of 1 to 10. When m1 is an integer of 2 or more, a plurality of R ｂ２ may be the same or different. [In the above general formula (c-1), R ｃ１ is a hydrogen atom or a methyl group. ｃ２ represents an ethylene group. m2 represents an integer of 1 to 6. When m2 is an integer of 2 or more, a plurality of R ｃ２ may be the same or different. n represents an integer of 1 or 2. When n=1, R ｃ３ is a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms. ｃ３ When n=2, at least one of R ｃ３ is a hydrogen atom. ]

[0012] The present inventors have conducted extensive research to solve the above problems. As a result, they have unexpectedly found that a "phosphorus-containing copolymer (Y)" formulated for the purpose of imparting load-bearing performance to a lubricating oil composition containing a "hydrocarbon-based synthetic oil (X1)" and an "ester-based synthetic oil (X2)" can impart excellent defoaming performance over a long period of time. The mechanism by which the "phosphorus-containing copolymer (Y)" can impart excellent defoaming performance over a long period of time to a lubricating oil composition containing a "hydrocarbon-based synthetic oil (X1)" and an "ester-based synthetic oil (X2)" is not clear, but it is speculated that, for example, the long-chain alkyl group and polar group possessed by the "phosphorus-containing copolymer (Y)" have some effect on suppressing foaming by controlling the surface tension of the foam surface.

[0013] In the following description, the “hydrocarbon-based synthetic oil (X1),” the “ester-based synthetic oil (X2),” and the “phosphorus-containing copolymer (Y)” will also be referred to as “component (X1),” “component (X2),” and “component (Y),” respectively.

[0014] The lubricating oil composition of this embodiment may be composed only of component (X1), component (X2), and component (Y), or may further contain components other than component (X1), component (X2), and component (Y). In the lubricating oil composition of this embodiment, the total content of component (X1), component (X2), and component (Y) is preferably 50 mass% or more, more preferably 60 mass% or more, even more preferably 70 mass% or more, still more preferably 80 mass% or more, and even more preferably 85 mass% or more, based on the total amount of the lubricating oil composition. The total content of component (X1), component (X2), and component (Y) is usually 100 mass% or less.

[0015] Each component contained in the lubricating oil composition of this embodiment will now be described in detail.

[0016] <Hydrocarbon-based synthetic oil (X1)> The lubricating oil composition of this embodiment contains a hydrocarbon-based synthetic oil (X1) as a base oil. As the hydrocarbon-based synthetic oil (X1), any hydrocarbon-based synthetic oil commonly used as a base oil for constituting a lubricating oil composition can be used without particular limitation. Specific examples of the hydrocarbon-based synthetic oil (X1) include poly-α-olefins (hereinafter also referred to as "PAO"), alkylbenzenes, alkylnaphthalenes, and GTL base oils produced by hydroisomerization dewaxing residual wax (gas-to-liquid wax) in a GTL process. Among these, PAO is preferred from the viewpoint of making it easier to appropriately adjust the kinematic viscosity of the lubricating oil composition and from the viewpoint of improving the viscosity index. Specific examples of PAO include polybutene, polyisobutylene, 1-decene oligomer, ethylene-propylene copolymer, and hydrogenated products thereof. The 100°C kinematic viscosity of the hydrocarbon-based synthetic oil (X1) is preferably 20 mm ２ / s ~ 55 mm ２ / s, more preferably 25 mm ２ / s ~ 50 mm ２ / s, more preferably 30 mm ２ / s ~ 45mm ２ / s. The viscosity index of the hydrocarbon synthetic oil (X1) is preferably 100 or more, more preferably 110 or more, and even more preferably 115 or more. The kinematic viscosity and viscosity index of the base oil are values ​​measured or calculated in accordance with JIS K2283:2000. The hydrocarbon synthetic oil (X1) may be used alone or in combination of two or more.

[0017] In the lubricating oil composition of this embodiment, the hydrocarbon synthetic oil (X1) has a kinematic viscosity at 100°C of 1.5 mmHg, from the viewpoint of improving the wear resistance and ensuring the low-temperature properties of the lubricating oil composition. ２ / s ~ 11.0 mm ２ / s, and a low-viscosity hydrocarbon-based synthetic oil (X11) having a kinematic viscosity of 50.0 mm ２ / s ~ 350.0 mm ２ 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 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, even more preferably 70% by mass to 100% by mass, still more preferably 80% by mass to 100% by mass, even more preferably 90% by mass to 100% by mass, and even more preferably 95% by mass to 100% by mass, based on the total amount of the hydrocarbon-based synthetic oil (X1).

[0018] (Low-Viscosity Hydrocarbon-Based Synthetic Oil (X11)) The low-viscosity hydrocarbon-based synthetic oil (X11) contributes to ensuring the low-temperature properties of the lubricating oil composition. In the lubricating oil composition of this embodiment, the 100°C kinematic viscosity of the low-viscosity hydrocarbon-based synthetic oil (X11) is preferably 1.5 mmHg, from the viewpoint of improving the low-temperature properties of the lubricating oil composition. ２ / s ~ 11.0 mm ２ / s, more preferably 2.0 mm ２ / s ~ 9.0 mm ２ / s, more preferably 3.0 mm ２ / s ~ 5.0 mm ２ / s.

[0019] Specific examples of the low-viscosity hydrocarbon synthetic oil (X11) include those listed as specific examples of the hydrocarbon synthetic oil (X1), which have a 100°C kinematic viscosity within the range specified above for the low-viscosity hydrocarbon synthetic oil (X11). Among these, PAOs having a 100°C kinematic viscosity within the range specified above for the low-viscosity hydrocarbon synthetic oil (X11) are preferred. Specific examples of PAOs are as described above. The low-viscosity hydrocarbon synthetic oil (X11) may be used alone or in combination of two or more.

[0020] In the lubricating oil composition of this embodiment, from the viewpoint of ensuring the low-temperature properties of the lubricating oil composition and suppressing a decrease in flash point, the content of the low-viscosity hydrocarbon synthetic oil (X11) is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 18% by mass or more, based on the total amount of the lubricating oil composition. Also, it is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less.

[0021] (High-Viscosity Hydrocarbon-Based Synthetic Oil (X12)) The high-viscosity hydrocarbon-based synthetic oil (X12) contributes to improving the wear resistance, fatigue life, etc. of the lubricating oil composition by maintaining a high kinematic viscosity of the base oil (A). In the lubricating oil composition of this embodiment, the 100°C kinematic viscosity of the high-viscosity hydrocarbon-based synthetic oil (X12) is preferably 50.0 mmHg, from the viewpoint of further improving the wear resistance, fatigue life, etc. of the lubricating oil composition. ２ / s ~ 350.0 mm ２ / s, more preferably 100.0 mm ２ / s to 300.0 mm ２ / s, more preferably 120.0 mm ２ / s to 200.0 mm ２ / s.

[0022] Specific examples of the high-viscosity hydrocarbon synthetic oil (X12) include those listed as specific examples of the hydrocarbon synthetic oil (X1), which have a 100°C kinematic viscosity within the range specified above for the high-viscosity hydrocarbon synthetic oil (X12). Among these, PAOs having a 100°C kinematic viscosity within the range specified above for the high-viscosity hydrocarbon synthetic oil (X12) are preferred. Specific examples of PAOs are as described above. The high-viscosity hydrocarbon synthetic oil (X12) may be used alone or in combination of two or more.

[0023] From the viewpoint of further increasing the viscosity index of the lubricating oil composition, the high-viscosity hydrocarbon-based synthetic oil (X12) is preferably a poly-α-olefin (hereinafter also referred to as "mPAO") obtained using a metallocene catalyst. mPAO has a higher viscosity index than PAOs produced using non-metallocene catalysts (such as Ziegler catalysts), and therefore has the effect of increasing the viscosity index of the lubricating oil composition.

[0024] mPAO is a poly-α-olefin or hydrogenated product thereof obtained by producing (polymerizing) a raw material, preferably an α-olefin having 8 to 12 carbon atoms, either alone or in combination with two or more thereof, in the presence of a metallocene catalyst. The α-olefin having 8 to 12 carbon atoms used as the raw material for mPAO may be linear or branched, but linear α-olefins are preferred. Examples of α-olefins having 8 to 12 carbon atoms used as the raw material for mPAO include 1-octene, 1-nonene, 1-decene, 1-undecene, and 1-dodecene. Among these, decene oligomers obtained by polymerization using 1-decene as the raw material are preferred.

[0025] The metallocene catalyst used as a polymerization catalyst for producing mPAO can be a complex having a five-membered conjugated carbon ring containing a Group 4 element of the periodic table, i.e., a combination of a metallocene complex and an oxygen-containing organoaluminum compound. The Group 4 element in the metallocene complex can be one or more elements selected from titanium, zirconium, and hafnium, with zirconium being preferred. Furthermore, the complex having a five-membered conjugated carbon ring is generally a complex having a substituted or unsubstituted cyclopentadienyl ligand. Examples of suitable metallocene complexes 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, etc. One type of metallocene complex may be used alone, or two or more types may be used in combination. Examples of oxygen-containing organoaluminum compounds include methylaluminoxane, ethylaluminoxane, and isobutylaluminoxane. One type of oxygen-containing organoaluminum compound may be used alone, or two or more types may be used in combination.

[0026] The mPAO may be used alone or in combination of two or more.

[0027] In the lubricating oil composition of this embodiment, from the viewpoint of maintaining a high kinematic viscosity of the lubricating oil composition and facilitating the preparation of a lubricating oil composition excellent in wear resistance and fatigue life resistance, the content of the high-viscosity hydrocarbon synthetic oil (X12) is preferably 50% by mass or more, more preferably 55% by mass or more, and even more preferably 60% by mass or more, based on the total amount of the lubricating oil composition, and is preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less.

[0028] <Ester-based synthetic oil (X2)> The lubricating oil composition of this embodiment contains an ester-based synthetic oil (X2) as a base oil. The inclusion of the ester-based synthetic oil (X2) in the lubricating oil composition contributes to improving the detergency and dispersancy action of the lubricating oil composition and improving the thermal stability, etc. As the ester-based synthetic oil (X2), any ester-based synthetic oil generally used as a base oil constituting a lubricating oil composition can be used without particular limitation. Specific examples of the ester-based synthetic oil (X2) include diesters, aromatic esters, polyol esters, and complex esters. Among these, polyol esters are preferred. One type of ester-based synthetic oil (X2) may be used alone, or two or more types may be used in combination. The 100°C kinematic viscosity of the ester-based synthetic oil (X2) is preferably 2 mm ２ / s ~ 15 mm ２ / s, more preferably 3 mm ２ / s ~ 10mm ２ / s, more preferably 4 mm ２ / s ~ 7mm ２ The viscosity index of the ester-based synthetic oil (X2) is preferably 70 or more, more preferably 80 or more, and even more preferably 90 or more. The kinematic viscosity and viscosity index of the base oil are values ​​measured or calculated in accordance with JIS K2283:2000.

[0029] The polyol ester may be a partial ester or a complete ester of a polyol, but it is preferable to use a complete ester of a polyol from the viewpoint of improving the defoaming performance.

[0030] The polyol used as a raw material for the polyol ester is not particularly limited, but is preferably an aliphatic polyol, and examples thereof 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 these, trimethylolpropane and pentaerythritol are preferred, and pentaerythritol is more preferred.

[0031] The fatty acid constituting the polyol ester is preferably a saturated or unsaturated fatty acid having 4 to 20 carbon atoms, more preferably a saturated or unsaturated fatty acid having 4 to 16 carbon atoms, even more preferably a saturated or unsaturated fatty acid having 4 to 12 carbon atoms, even more preferably a saturated or unsaturated fatty acid having 4 to 11 carbon atoms, and even more preferably a saturated or unsaturated fatty acid having 5 to 9 carbon atoms. In particular, when the fatty acid constituting the polyol ester is a saturated or unsaturated fatty acid having 4 to 11 carbon atoms (preferably 5 to 9), the defoaming performance of the lubricating oil composition is more likely to be exhibited over a long period of time. Furthermore, when the fatty acid constituting the polyol ester is a saturated or unsaturated fatty acid having 4 to 11 carbon atoms, and the polyol constituting the polyol ester is pentaerythritol, the effect of the lubricating oil composition being more likely to exhibit the defoaming performance over a long period of time is more easily obtained. Therefore, the ester base oil (X2) preferably contains an ester of pentaerythritol and a fatty acid having 4 to 11 carbon atoms, more preferably contains an ester of pentaerythritol and a fatty acid having 5 to 10 carbon atoms, and even more preferably contains an ester of pentaerythritol and a fatty acid having 8 to 10 carbon atoms. The fatty acid constituting the polyol ester may be linear or branched, but is preferably linear.

[0032] In the lubricating oil composition of this embodiment, from the viewpoint of improving the detergent-dispersant effect and thermal stability of the lubricating oil composition, the content of the ester-based synthetic oil (X2) is preferably 0.5 mass% or more, more preferably 1.0 mass% or more, even more preferably 1.5 mass% or more, still more preferably 3.0 mass% or more, even more preferably 5.0 mass% or more, and even more preferably 7.0 mass% or more, based on the total amount of the lubricating oil composition. Also, it is preferably 15 mass% or less, more preferably 13 mass% or less, and even more preferably 12 mass% or less.

[0033] <Total Content of Hydrocarbon-Based Synthetic Oil (X1) and Ester-Based Synthetic Oil (X2)> 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% by mass or more, more preferably 78% by mass or more, and even more preferably 80% by mass or more, based on the total amount of the lubricating oil composition. It is also preferably 99.9% by mass or less. The total content of component (X1) and component (X2) is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, even more preferably 70% by mass to 100% by mass, even more preferably 80% by mass to 100% by mass, even more preferably 90% by mass to 100% by mass, and even more preferably 95% by mass to 100% by mass, based on the total amount of base oil in the lubricating oil composition.

[0034] <Ratio of hydrocarbon synthetic oil (X1) and ester synthetic oil (X2)> In the lubricating oil composition of this embodiment, the ratio of the hydrocarbon synthetic oil (X1) to the ester synthetic oil (X2) [(X1) / (X2)], expressed as a mass ratio, is preferably 5.0 to 50.0, more preferably 6.0 to 45.0, and even more preferably 7.0 to 40.0.

[0035] <Content Ratio of Low-Viscosity Hydrocarbon-Based Synthetic Oil (X11) and High-Viscosity Hydrocarbon-Based Synthetic Oil (X12)> In the lubricating oil composition of this embodiment, when the hydrocarbon-based synthetic oil (X1) comprises a low-viscosity hydrocarbon-based synthetic oil (X11) and a high-viscosity hydrocarbon-based synthetic oil (X12), the content ratio of the low-viscosity hydrocarbon-based synthetic oil (X11) to the high-viscosity hydrocarbon-based synthetic oil (X12) [(X11) / (X12)] is preferably 0.10 to 0.80, more preferably 0.15 to 0.70, and even more preferably 0.20 to 0.50 by mass.

[0036] <Other Base Oils> The lubricating oil composition of this embodiment may contain base oils other than component (X1) and component (X2). Examples of other base oils include mineral oils and synthetic oils other than component (X1) and component (X2). Examples of mineral oils include atmospheric residues obtained by atmospheric distillation of crude oils such as paraffinic crude oil, intermediate crude oil, or naphthenic crude oil; distillates obtained by vacuum distillation of these atmospheric residues; and mineral oils obtained by subjecting the distillates to one or more refining processes such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining. Examples of synthetic oils other than component (X1) and component (X2) include various ethers such as polyphenyl ether; polyalkylene glycols; alkylbenzenes; alkylnaphthalenes; and the like. One mineral oil may be used alone, or two or more mineral oils may be used in combination. The synthetic oils other than component (X1) and component (X2) may be used singly or in combination of two or more. Also, one or more mineral oils may be used in combination with one or more synthetic oils other than component (X1) and component (X2).

[0037] <Phosphorus-Containing Copolymer (Y)> The lubricating oil composition of this embodiment contains a phosphorus-containing copolymer (Y). The phosphorus-containing copolymer (Y) includes a structural unit (a) derived from an alkyl (meth)acrylate (A) represented by the following general formula (a-1), a structural unit (b) derived from a hydroxyl group-containing (meth)acrylate (B) represented by the following general formula (b-1), and a structural unit (c) derived from a phosphorus-containing (meth)acrylate (C) represented by the following general formula (c-1). [In the above general formula (a-1), Rａ１ is a hydrogen atom or a methyl group. ａ２ represents an alkyl group having 8 to 20 carbon atoms. [In the above general formula (b-1), R ｂ１ is a hydrogen atom or a methyl group. ｂ２ represents an alkylene group having 2 to 4 carbon atoms. m1 represents an integer of 1 to 10. When m1 is an integer of 2 or more, a plurality of R ｂ２ may be the same or different. [In the above general formula (c-1), R ｃ１ is a hydrogen atom or a methyl group. ｃ２ represents an ethylene group. m2 represents an integer of 1 to 6. When m2 is an integer of 2 or more, a plurality of R ｃ２ may be the same or different. n represents an integer of 1 or 2. When n=1, R ｃ３ is a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms. ｃ３ When n=2, at least one of R ｃ３ is a hydrogen atom.]

[0038] In the following description, the alkyl (meth)acrylate (A), the hydroxyl group-containing (meth)acrylate (B), and the phosphorus-containing (meth)acrylate (C) will also be referred to as "monomer (A)," "monomer (B)," and "monomer (C)," respectively.

[0039] In this embodiment, the phosphorus-containing copolymer (Y) may be composed only of the structural unit (a) derived from the monomer (A), the structural unit (b) derived from the monomer (B), and the structural unit (c) derived from the monomer (C), but may also contain structural units other than the structural units (a), (b), and (c) as long as the effects of the present invention are not impaired. In this embodiment, the total content of the structural units (a), (b), and (c) in the phosphorus-containing copolymer (Y) is preferably 70 mol% to 100 mol%, more preferably 80 mol% to 100 mol%, and even more preferably 90 mol% to 100 mol%, based on the total structural units of the phosphorus-containing copolymer (Y).

[0040] The alkyl (meth)acrylate (A), the hydroxyl group-containing (meth)acrylate (B), and the phosphorus-containing (meth)acrylate (C) will be described in detail below.

[0041] <<Alkyl(meth)acrylate (A)>> The alkyl(meth)acrylate (A) used in this embodiment is represented by the following general formula (a-1).

[0042] The structural unit (a) derived from alkyl (meth)acrylate (A) mainly plays a role in exerting oil solubility in the phosphorus-containing copolymer (Y).In addition, it is presumed that the structural unit (a) exerts defoaming performance for a long period of time in the lubricating oil composition by controlling the surface tension of the foam surface.In addition, the alkyl (meth)acrylate (A) may be used alone or in combination of two or more.Therefore, the phosphorus-containing copolymer (Y) may contain one structural unit (a) derived from alkyl (meth)acrylate (A) alone or two or more.

[0043] In the above general formula (a-1), R ａ１ is 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. ａ１ In this embodiment, from the viewpoint of facilitating the adjustment of the molecular weight of the phosphorus-containing copolymer (Y), a monomer in which R ａ１ is preferably a hydrogen atom. That is, the alkyl(meth)acrylate (A) preferably has an acryloyl group as the polymerizable functional group.

[0044] In the above general formula (a-1), R ａ２ represents an alkyl group having a carbon number of 8 to 20. When the number of carbon atoms of the alkyl group is within the above range, the oil solubility of the phosphorus-containing copolymer (Y) can be easily ensured.

[0045] R ａ２Examples of alkyl groups having 8 to 20 carbon atoms that can be selected as aryl include chain alkyl groups such as octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, and icosyl. These may be linear or branched.

[0046] Here, from the viewpoint of more easily ensuring the oil solubility of the phosphorus-containing copolymer (Y), the alkyl group preferably has 10 to 18 carbon atoms, more preferably 10 to 16 carbon atoms, and even more preferably 10 to 14 carbon atoms.

[0047] <<Hydroxyl Group-Containing (Meth)acrylate (B)>> The hydroxyl group-containing (meth)acrylate (B) used in this embodiment is represented by the following general formula (b-1).

[0048] The structural unit (b) derived from the hydroxyl group-containing (meth)acrylate (B) is presumed to have the function of making the phosphorus-containing copolymer (Y) a multipoint adsorption type copolymer, thereby contributing to the improvement of wear resistance and extreme pressure properties. Furthermore, it is presumed that the structural unit (b) is responsible for the defoaming performance by controlling the surface tension of the foam surface, so that the lubricating oil composition can exhibit defoaming performance over a long period of time. The hydroxyl group-containing (meth)acrylate (B) may be used alone or in combination of two or more. Therefore, the phosphorus-containing copolymer (Y) may contain one structural unit (b) derived from the hydroxyl group-containing (meth)acrylate (B) alone, or may contain two or more structural units.

[0049] In the above general formula (b-1), R ｂ１ is a hydrogen atom or a methyl group. That is, the hydroxyl group-containing (meth)acrylate (B) has an acryloyl group or a methacryloyl group as a polymerizable functional group. ｂ１ In this embodiment, from the viewpoint of facilitating the adjustment of the molecular weight of the phosphorus-containing copolymer (Y), a monomer in which R ｂ１is preferably a hydrogen atom. That is, the hydroxyl group-containing (meth)acrylate (B) preferably has an acryloyl group as the polymerizable functional group.

[0050] In the above general formula (b-1), R ｂ２ represents an alkylene group having 2 to 4 carbon atoms. When the number of carbon atoms in the alkylene group is within the above range, good oil solubility can be achieved, and good adsorption to metals can also be achieved. Here, from the viewpoint of easily ensuring appropriate oil solubility and appropriate adsorption to metals, the number of carbon atoms in the alkylene group is preferably 2 to 3, and more preferably 2.

[0051] m1 represents an integer of 1 to 10. When m1 is an integer of 2 or more, a plurality of R ｂ２ may be the same or different. ｂ２ ) ｍ１ The bonding mode between the moieties represented by may be a random bond or a block bond, but from the viewpoint of ease of polymerization, a random bond is preferred. When m1 is in the above range, appropriate oil solubility can be easily ensured. Here, from the viewpoint of more easily ensuring appropriate oil solubility, m1 is preferably 1 to 6, more preferably 1 to 4, even more preferably 1 to 2, and even more preferably 1.

[0052] <<Phosphorus-Containing (Meth)acrylate (C)>> The phosphorus-containing (meth)acrylate (C) used in this embodiment is represented by the following general formula (c-1).

[0053] It is presumed that the structural unit (c) derived from the phosphorus-containing (meth)acrylate (C) plays a role in improving wear resistance and extreme pressure properties by introducing a phosphate group or a group derived from an acidic phosphate ester into the side chain of the phosphorus-containing copolymer (Y). Here, phosphorus is an element that causes a decrease in thermal stability, so it is an element that is not generally introduced from the viewpoint of ensuring thermal stability. However, by introducing the structural unit (c) derived from the phosphorus-containing (meth)acrylate (C) into a copolymer in which the structural unit (a) derived from the alkyl (meth)acrylate (A) and the structural unit (b) derived from the hydroxyl group-containing (meth)acrylate (B) are combined, the problem of the decrease in thermal stability caused by the introduction of phosphorus is alleviated, and the phosphorus-containing copolymer (Y) as a whole has excellent thermal stability and is also excellent in wear resistance and extreme pressure properties.

[0054] The phosphorus-containing (meth)acrylate (C) may be used singly or in combination of two or more. Thus, the phosphorus-containing copolymer (Y) may contain either one type or two or more types of the structural unit (c) derived from the phosphorus-containing (meth)acrylate (C).

[0055] In the above general formula (c-1), R ｃ１ is 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. ｃ１ In this embodiment, from the viewpoint of facilitating the adjustment of the molecular weight of the phosphorus-containing copolymer (Y), a monomer in which R ｃ１ is preferably a hydrogen atom. That is, the phosphorus-containing (meth)acrylate (C) preferably has an acryloyl group as the polymerizable functional group.

[0056] In the above general formula (c-1), R ｃ２ represents an ethylene group. ｃ２ By having an ethylene group, the oil solubility can be improved and the adsorption onto metals can also be improved.

[0057] m2 represents an integer of 1 to 6. When m2 is an integer of 2 or more, a plurality of R ｃ２ may be the same or different. ｃ２ ) ｍ２ The bonding mode between the moieties represented by may be a random bond or a block bond, but from the viewpoint of ease of polymerization, a random bond is preferred. When m2 is in the above range, appropriate oil solubility can be easily ensured. Here, from the viewpoint of easily ensuring appropriate oil solubility, m2 is preferably 1 to 4, more preferably 1 to 2, and even more preferably 1.

[0058] n represents an integer of 1 or 2. When n=1, R ｃ３ is a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms. ｃ３ When n=2, at least one of R ｃ３ is a hydrogen atom. When n=1, multiple R ｃ３ Only one of the R ｃ３ The other of R is a hydrocarbon group having 1 to 3 carbon atoms. ｃ３ If the other of R is a hydrocarbon group having 1 to 3 carbon atoms, the hydrocarbon group is preferably a methyl group or an ethyl group. ｃ３are preferably hydrogen atoms. Here, the phosphorus-containing (meth)acrylate (C) preferably contains a phosphorus-containing (meth)acrylate (C1) where n = 1 as a main component. In this specification, the term "main component" refers to a component whose content exceeds 50% by mass. That is, the content of the phosphorus-containing (meth)acrylate (C1) where n = 1 is preferably from more than 50% by mass to 100% by mass, more preferably from 60% by mass to 100% by mass, even more preferably from 70% by mass to 100% by mass, still more preferably from 80% by mass to 100% by mass, and even more preferably from 90% by mass to 100% by mass, based on the total amount of the phosphorus-containing (meth)acrylate (C). Furthermore, the content of the structural unit (c1) derived from the phosphorus-containing (meth)acrylate (C1) where n = 1, based on the total amount of the structural unit (c) derived from the phosphorus-containing (meth)acrylate (C), is preferably from more than 50 to 100% by mass, more preferably from 60 to 100% by mass, even more preferably from 70 to 100% by mass, still more preferably from 80 to 100% by mass, and even more preferably from 90 to 100% by mass.

[0059] Furthermore, from the viewpoint of further improving the wear resistance and extreme pressure properties of the phosphorus-containing copolymer (Y), the phosphorus-containing (meth)acrylate (C) used in this embodiment preferably has an acid value of 300 mgKOH / g to 600 mgKOH / g, more preferably 350 mgKOH / g to 550 mgKOH / g. In this specification, the acid value of the phosphorus-containing (meth)acrylate (C) means a value measured by the potentiometric method specified in JIS K 2501:2003-7.

[0060] (Requirement (α): Content Ratio of Structural Unit (a) to Structural Unit (b)) From the viewpoint of solubility in the base oil, the content ratio of the structural unit (a) to the structural unit (b) [(a) / (b)] in terms of molar ratio is preferably 7 / 3 to 9 / 1, and more preferably 8 / 2.

[0061] (Requirement (β): Phosphorus Content) The phosphorus-containing copolymer (Y) has a phosphorus content of preferably 0.05% by mass to 1.0% by mass, more preferably 0.06% by mass to 0.70% by mass, even more preferably 0.07% by mass to 0.50% by mass, still more preferably 0.08% by mass to 0.40% by mass, and even more preferably 0.10% by mass to 0.30% by mass, based on the total amount of the phosphorus-containing copolymer (Y). The phosphorus content of the phosphorus-containing copolymer (Y) can be calculated based on the results of dissolving a predetermined amount of the phosphorus-containing copolymer (Y) in an organic solvent (e.g., a lubricating base oil) and then measuring the amount of phosphorus in the organic solvent in accordance with JPI-5S-38-03, and the amount of the phosphorus-containing copolymer (Y) dissolved in the organic solvent.

[0062] (Other Monomers) In addition to the above-described structural units (a), (b), and (c), the phosphorus-containing copolymer (Y) may contain structural units derived from other monomers, provided that the effects of the present invention are not significantly impaired. Examples of such other monomers include functional group-containing monomers other than the monomers (A), (B), and (C). Examples of such other functional group-containing monomers include functional group-containing (meth)acrylates other than the monomers (A), (B), and (C). However, from the viewpoint of further enhancing the effects of the present invention, the total content of the structural units (a), (b), and (c) in the phosphorus-containing copolymer (Y) is preferably greater than 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, even more preferably 70% by mass to 100% by mass, still more preferably 80% by mass to 100% by mass, and even more preferably 90% by mass to 100% by mass, based on the total structural units of the phosphorus-containing copolymer (Y). Furthermore, from the viewpoint of making it easier to improve the effects of the present invention, the content of structural units derived from functional group-containing monomers other than the monomers (A), (B), and (C) in the phosphorus-containing copolymer (Y) is preferably 50% by mass or less, more preferably less than 40% by mass, even more preferably less than 30% by mass, still more preferably less than 20% by mass, and even more preferably less than 10% by mass, based on all structural units.

[0063] (Mass Average Molecular Weight (Mw) of Phosphorus-Containing Copolymer (Y)) From the viewpoint of making it easier to exhibit the effects of the present invention and from the viewpoint of solubility in base oil, the mass average molecular weight (Mw) of the phosphorus-containing copolymer (Y) is preferably 5,000 to 100,000, more preferably 5,000 to 80,000, and even more preferably 5,000 to 60,000. The mass average molecular weight (Mw) is a value measured or calculated by the method described in the examples below.

[0064] (Polymerization mode of phosphorus-containing copolymer (Y)) 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 these, random copolymerization is preferred from the viewpoint of ease of polymerization reaction.

[0065] <Content of Phosphorus-Containing Copolymer (Y)> In the lubricating oil composition of this embodiment, the content of the phosphorus-containing copolymer (Y) (equivalent to the resin content) is preferably 0.10 mass % to 5.0 mass %, more preferably 0.15 mass % to 3.0 mass %, and even more preferably 0.20 mass % to 2.0 mass %, based on the total amount of the lubricating oil composition, from the viewpoint of improving the effects of the present invention and improving the wear resistance of the lubricating oil composition.

[0066] <<Method for Producing Phosphorus-Containing Copolymer (Y)>> The phosphorus-containing copolymer (Y) is produced by a production method including a step (S) of polymerizing an alkyl (meth)acrylate (A) represented by the above general formula (a-1), a hydroxyl group-containing (meth)acrylate (B) represented by the above general formula (b-1), and a phosphorus-containing (meth)acrylate (C) represented by the above general formula (c-1). Hereinafter, the step (S) for producing the phosphorus-containing copolymer (Y) will be described in detail.

[0067] (Step (S) of Producing (Polymerizing) Phosphorus-Containing Copolymer (Y)) The step (S) of producing the phosphorus-containing copolymer (Y) is not particularly limited, and the phosphorus-containing copolymer (Y) can be produced by applying any of known steps (S). Examples of such step (S) include emulsion polymerization, suspension polymerization, and solution polymerization. Here, it is preferable to adopt a solution polymerization method using a solvent that is soluble in a lubricating base oil as a solvent for the step (S) of producing the phosphorus-containing copolymer (Y).

[0068] (Solution Polymerization Method) The solution polymerization method is carried out, for example, by charging the monomers (A), (B), and (C), as well as a solvent and an initiator, replacing the atmosphere in the reactor with nitrogen, and then stirring and reacting the mixture at 60° C. to 100° C. for 2 to 10 hours. Monomers other than the monomers (A), (B), and (C) may also be charged into the reactor as desired.

[0069] Examples of solvents used in solution polymerization 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 oil; and synthetic oils such as poly-α-olefins, ethylene-α-olefin copolymers, alkylbenzenes, alkylnaphthalenes, polyphenyl ethers, alkyl-substituted diphenyl ethers, polyol esters, dibasic acid esters, hindered esters, monoesters, and GTL base oils. These may be used alone or in combination of two or more.

[0070] Examples of initiators used in the solution polymerization method include azo 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; and hydrogen peroxide-Fe ２＋ and other existing radical initiators.

[0071] The molecular weight of the phosphorus-containing copolymer (Y) can be controlled by a known method, for example, by adjusting the reaction temperature, reaction time, amount of initiator, amount of each monomer charged, type of solvent, use of a chain transfer agent, etc.

[0072] ((Preferred Aspect 1 in Step (S))) In the step (S), from the viewpoint of producing a phosphorus-containing copolymer (Y) that satisfies the above-mentioned requirement (α), the blending ratio [(A) / (B)] of the alkyl (meth)acrylate (A) to the hydroxyl group-containing (meth)acrylate (B) is preferably adjusted to a molar ratio of 7 / 3 to 9 / 1, and more preferably adjusted to 8 / 2.

[0073] ((Preferred Aspect 2 in Step (S))) In Step (S), from the viewpoint of producing a phosphorus-containing copolymer (Y) that satisfies the above-mentioned requirement (β), it is preferable to adjust 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 hydroxyl group-containing (meth)acrylate (B) to a molar ratio of 0.1 / 100 to 10 / 100. Furthermore, from the viewpoint of making it easier to improve the wear resistance and extreme pressure properties of the phosphorus-containing copolymer (Y), [(C) / {(A)+(B)}] is more preferably 0.5 / 100 or more, and even more preferably 1.0 / 100 or more. Furthermore, from the viewpoint of making it easier to improve the thermal stability of the phosphorus-containing copolymer (Y), [(C) / {(A)+(B)}] is more preferably 5.0 / 100 or less, and even more preferably 3.0 / 100 or less. The upper and lower limits of these numerical ranges can be combined arbitrarily. Specifically, the range is more preferably 0.5 / 100 to 5.0 / 100, and even more preferably 1.0 / 100 to 3.0 / 100.

[0074] <Other Additives> The lubricating oil composition of this embodiment may contain additives other than component (Y) (hereinafter also referred to as "lubricating oil additives") to the extent that the effects of the present invention are not impaired. Examples of lubricating oil additives include antioxidants, metal deactivators, demulsifiers, detergent-dispersants, antifoaming agents, and extreme pressure agents. These lubricating oil additives may be used alone or in combination of two or more.

[0075] In this specification, the additive may be blended with other components in the form of a solution dissolved in diluent oil, taking into consideration handling and solubility in base oil. In such cases, the content of the additive in this specification is the content in terms of active ingredient (resin content) excluding diluent oil. Below, the details of each of the above lubricating oil additives will be described.

[0076] (Antioxidant) As the antioxidant, amine-based antioxidants, phenol-based antioxidants, phosphorus-based antioxidants, sulfur-based antioxidants, molybdenum amine complex-based antioxidants, etc., which are used in conventional lubricating oil compositions, can be used. One type of antioxidant may be used alone, or two or more types may be used in combination.

[0077] Examples of the amine antioxidant include monoalkyldiphenylamine compounds such as monooctyldiphenylamine and monononyldiphenylamine; dialkyldiphenylamine compounds such as 4,4'-dibutyldiphenylamine, 4,4'-dipentyldiphenylamine, 4,4'-dihexyldiphenylamine, 4,4'-diheptyldiphenylamine, 4,4'-dioctyldiphenylamine, 4,4'-dinonyldiphenylamine and monobutylphenylmonoctylphenylamine; tetrabutyldiphenylamine, and polyalkyldiphenylamine 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.

[0078] Examples of the phenolic antioxidant include monophenolic 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 diphenolic compounds such as 4,4'-methylenebis(2,6-di-tert-butylphenol) and 2,2'-methylenebis(4-ethyl-6-tert-butylphenol).

[0079] The content of the antioxidant may be the minimum amount necessary to maintain oxidation stability, and is preferably 0.01 to 1.5 mass %, more preferably 0.1 to 1.2 mass %, based on the total amount of the lubricating oil composition.

[0080] (Metal Deactivator) Examples of the metal deactivator include benzotriazole compounds, tolyltriazole compounds, thiadiazole compounds, imidazole compounds, and pyrimidine compounds. One type of metal deactivator may be used alone, or two or more types may be used in combination. From the viewpoint of the effect of addition, the content of the metal deactivator is preferably 0.01% by mass to 5.0% by mass, and more preferably 0.02% by mass to 3.0% by mass, based on the total amount of the lubricating oil composition.

[0081] (Demulsifier) ​​Examples of demulsifiers include cationic surfactants such as quaternary ammonium salts and imidazolines; polyoxyalkylene block polymers (ethylene oxide (EO)-propylene oxide (PO) block copolymers, etc.), polyoxyalkylene glycols, and polyoxyalkylene polyglycols; alkylene oxide adducts of alkylphenol-formaldehyde polycondensates, etc. One type of demulsifier may be used alone, or two or more types may be used in combination. The content of the demulsifier is preferably 0.0005 to 0.5% by mass, more preferably 0.0008 to 0.2% by mass, based on the total amount of the lubricating oil composition.

[0082] (Detergent-dispersant) Examples of detergent-dispersants include succinimides, boron-containing succinimides, benzylamines, boron-containing benzylamines, succinic acid esters, fatty acids, and mono- or di-carboxylic acid amides typified by succinic acid. One detergent-dispersant may be used alone, or two or more detergent-dispersants may be used in combination. From the viewpoint of the effect of addition, the content of the detergent-dispersant is preferably 0.01 to 5.0 mass%, more preferably 0.02 to 3.0 mass%, based on the total amount of the lubricating oil composition.

[0083] (Antifoaming Agent) Examples of antifoaming agents include silicone oil, fluorosilicone oil, fluoroalkyl ether, and acrylate compounds such as polymethacrylate. Among these, acrylate compounds such as polymethacrylate and silicone oil are preferred. One type of antifoaming agent may be used alone, or two or more types may be used in combination. The content of the antifoaming agent is preferably 0.001 mass % to 1.0 mass %, more preferably 0.002 mass % to 0.5 mass %, and even more preferably 0.003 mass % to 0.3 mass %, based on the total amount of the lubricating oil composition.

[0084] (Extreme Pressure Agent) As the extreme pressure agent, organometallic extreme pressure agents, sulfur-based extreme pressure agents, phosphorus-based extreme pressure agents, and sulfur-phosphorus-based extreme pressure agents that are used in conventional lubricating oil compositions can be used. One type of extreme pressure agent may be used alone, or two or more types may be used in combination.

[0085] Examples of organometallic extreme pressure agents include organomolybdenum compounds such as molybdenum dialkyldithiocarbamate (MoDTC) and molybdenum dialkyldithiophosphate (MoDTP), and organozinc compounds such as zinc dialkyldithiocarbamate (ZnDTC) and zinc dialkyldithiophosphate (ZnDTP).

[0086] Examples of sulfur-based extreme pressure agents include sulfurized fats and oils, sulfurized fatty acids, sulfurized esters, sulfurized olefins, monosulfides, polysulfides, dihydrocarbyl sulfides, thiadiazole compounds, alkylthiocarbamoyl compounds, thiocarbamate compounds, thioterpene compounds, and dialkylthiodipropionate compounds.

[0087] Examples of phosphorus-based extreme pressure agents include phosphoric acid esters such as aryl phosphate, alkyl phosphate, alkenyl phosphate, and alkylaryl phosphate; acidic phosphoric acid esters such as monoaryl acid phosphate, diaryl acid phosphate, monoalkyl acid phosphate, dialkyl acid phosphate, monoalkenyl acid phosphate, and dialkenyl acid phosphate; phosphite esters such as aryl hydrogen phosphite, alkyl hydrogen phosphite, aryl phosphite, alkyl phosphite, alkenyl phosphite, and aryl alkyl phosphite; acidic phosphite esters such as monoalkyl acid phosphite, dialkyl acid phosphite, monoalkenyl acid phosphite, and dialkenyl acid phosphite; and amine salts thereof.

[0088] Examples of sulfur-phosphorus extreme pressure agents include alkylthiophosphate esters such as monoalkylthiophosphate, dialkyldithiophosphate, and trialkyltrithiophosphate, and amine salts thereof, as well as zinc dialkyldithiophosphate (Zn-DTP).

[0089] From the viewpoint of improving wear resistance, the lubricating oil composition of this embodiment preferably contains, as an extreme pressure agent, an amine salt of an acidic phosphoric acid ester selected from the group consisting of monoalkyl acid phosphates and dialkyl acid phosphates. The number of carbon atoms in the alkyl group of the monoalkyl acid phosphate and dialkyl acid phosphate is preferably 6 to 20, more preferably 8 to 16, and even more preferably 10 to 14. The alkyl group may be linear or branched.

[0090] From the viewpoint of the effect of addition, the content of the extreme pressure agent is preferably 0.1 to 5.0 mass %, more preferably 0.2 to 3.0 mass %, and even more preferably 0.3 to 1.0 mass %, based on the total amount of the lubricating oil composition.

[0091] From the viewpoint of improving long-term antifoaming performance, it is preferable that the content of the thiocarbamate compound is small. Examples of the thiocarbamate compound include dialkyldithiocarbamate compounds such as methylenebis(dibutyldithiocarbamate). The content of the thiocarbamate compound is preferably less than 0.01 mass%, more preferably less than 0.001 mass%, based on the total amount of the lubricating oil composition, and even more preferably, the lubricating oil composition does not contain any thiocarbamate compound.

[0092] [Physical Properties of Lubricating Oil Composition] The lubricating oil composition of this embodiment preferably satisfies the following physical properties.

[0093] <Kinematic Viscosity and Viscosity Index> The kinematic viscosity at 40°C of the lubricating oil composition of this embodiment is preferably 90 mm ２ / s~1,100mm ２ / s, more preferably 135 mm ２ / s ~ 748 mm ２ / s, more preferably 198 mm ２ / s ~ 506 mm ２ / s, and even more preferably 288 mm ２ / s ~ 352 mm ２ The viscosity index of the lubricating oil composition of this embodiment is preferably 140 or higher, more preferably 160 or higher, even more preferably 170 or higher, and even more preferably 180 or higher. The kinematic viscosity and viscosity index of the lubricating oil composition are values ​​measured or calculated in accordance with JIS K2283:2000.

[0094] <Anti-foaming performance> The lubricating oil composition of this embodiment preferably has anti-foaming performance measured by the method described in the examples below, all of which are within the following ranges.

[0095] (Defoaming Performance by Sequences I, II, and III) When evaluation 1 of defoaming performance in the examples described later is carried out, the volume of foam immediately after completion of air blowing is preferably 100 mL or less, more preferably 50 mL or less, and even more preferably 30 mL or less. Furthermore, when evaluation 1 of defoaming performance in the examples described later is carried out, the volume of foam after standing for 10 minutes from completion of air blowing is preferably 10 mL or less, and more preferably 0 mL.

[0096] (Defoaming Performance in 7-Day Continuous Foaming Test) When evaluation 2 of defoaming performance in the examples described below is carried out, the foam volume is preferably 50 mL or less, more preferably 40 mL or less, and even more preferably 30 mL or less.

[0097] (Wear Resistance) The lubricating oil composition of this embodiment preferably has an average roller wear amount measured by the method described in the Examples section below of 30 mg or less, more preferably 20 mg or less, and even more preferably 10 mg or less.

[0098] [Method for Producing Lubricating Oil Composition] The method for producing the lubricating oil composition of this embodiment is not particularly limited. For example, the method for producing the lubricating oil composition of this embodiment includes 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 structural unit (a) derived from an alkyl (meth)acrylate (A) represented by the general formula (a-1) above, a structural unit (b) derived from a hydroxyl group-containing (meth)acrylate (B) represented by the general formula (b-1) above, and a structural unit (c) derived from a phosphorus-containing (meth)acrylate (C) represented by the general formula (c-1) above.

[0099] When a lubricating oil additive is blended, the lubricating oil additive may be blended simultaneously with component (Y) or separately. Each component may be blended after being made into a solution (dispersion) by adding a diluent oil or the like. After blending each component, it is preferable to uniformly disperse the components by stirring using a known method. The preferred embodiments of each component are as described above.

[0100] [Uses of Lubricating Oil Composition] The lubricating oil composition of this embodiment can maintain excellent anti-foaming performance for a long period of time. Therefore, the lubricating oil composition of this embodiment can be widely used in lubrication applications requiring long-term anti-foaming performance. For example, the lubricating oil composition of this embodiment can be suitably used as a speed-increasing oil for wind turbines, hydraulic oil, compressor oil, gear oil, cutting oil, machine tool oil, refrigeration oil, turbine oil, internal combustion oil, transmission oil, or automotive axle unit oil, and is particularly suitably used as a speed-increasing oil for wind turbines. Therefore, this embodiment provides the following methods (1) or (2). (1) A method of using the lubricating oil composition of this embodiment as a speed-increasing oil for wind turbines, hydraulic oil, compressor oil, gear oil, cutting oil, machine tool oil, refrigeration oil, turbine oil, internal combustion oil, transmission oil, or automotive axle unit oil. (2) A method of using the lubricating oil composition of the present invention as a speed-increasing oil for wind turbines. This embodiment also provides the following method (3). (3) A method for suppressing foaming of a lubricating oil composition comprising a hydrocarbon synthetic oil (X1) and an ester synthetic oil (X2), by blending a phosphorus-containing copolymer (Y) with the lubricating oil composition.

[0101] [One Aspect of the Present Invention Provided] In one aspect of the present invention, the following items [1] to

[10] are provided: [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 structural unit (a) derived from an alkyl (meth)acrylate (A) represented by the following general formula (a-1), a structural unit (b) derived from a hydroxyl group-containing (meth)acrylate (B) represented by the following general formula (b-1), and a structural unit (c) derived from a phosphorus-containing (meth)acrylate (C) represented by the following general formula (c-1): [In the above general formula (a-1), R ａ１ is a hydrogen atom or a methyl group. ａ２ represents an alkyl group having 8 to 20 carbon atoms. [In the above general formula (b-1), R ｂ１ is a hydrogen atom or a methyl group. ｂ２ represents an alkylene group having 2 to 4 carbon atoms. m1 represents an integer of 1 to 10. When m1 is an integer of 2 or more, a plurality of Rｂ２ may be the same or different. [In the above general formula (c-1), R ｃ１ is a hydrogen atom or a methyl group. ｃ２ represents an ethylene group. m2 represents an integer of 1 to 6. When m2 is an integer of 2 or more, a plurality of R ｃ２ may be the same or different. n represents an integer of 1 or 2. When n=1, R ｃ３ is a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms. ｃ３ When n=2, at least one of R ｃ３ is a hydrogen atom.] [2] The hydrocarbon synthetic oil (X1) has a kinematic viscosity at 100°C of 20 mm ２ / s ~ 55 mm ２ [3] The lubricating oil composition according to the above [1], wherein the hydrocarbon synthetic oil (X1) has a kinematic viscosity at 100°C of 1.5 mm / s. ２ / s ~ 11.0 mm ２ / s, and a low-viscosity hydrocarbon-based synthetic oil (X11) having a kinematic viscosity of 50.0 mm ２ / s ~ 350.0 mm ２[4] The lubricating oil composition according to any one of [1] to [3] above, 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 [1] to [4] above, wherein the phosphorus-containing copolymer (Y) has a molar ratio of the structural unit (a) to the structural unit (b) [(a) / (b)] of 7 / 3 to 9 / 1. [6] The lubricating oil composition according to any one of [1] to [5] above, wherein the phosphorus-containing copolymer (Y) has a phosphorus content of 0.05 to 1.0 mass%, based on the total amount of the phosphorus-containing copolymer (Y). [7] The lubricating oil composition according to any one of [1] to [6] above, wherein the phosphorus-containing copolymer (Y) has a mass average molecular weight (Mw) of 5,000 to 100,000. [8] The lubricating oil composition according to any one of [1] to [7] above, further comprising one or more additives selected from the group consisting of antioxidants, metal deactivators, demulsifiers, detergent-dispersants, antifoaming agents, and extreme pressure agents. [9] The lubricating oil composition according to any one of [1] to [8] above, which is used as a speed increaser oil for wind turbines, hydraulic oil, compressor oil, gear oil, cutting oil, machine tool oil, refrigeration oil, turbine oil, internal combustion engine oil, transmission oil, or automotive axle unit oil.

[10] A method for producing a lubricating oil composition, comprising the 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 structural unit (a) derived from an alkyl (meth)acrylate (A) represented by the following general formula (a-1), a structural unit (b) derived from a hydroxyl group-containing (meth)acrylate (B) represented by the following general formula (b-1), and a structural unit (c) derived from a phosphorus-containing (meth)acrylate (C) represented by the following general formula (c-1): [In the above general formula (a-1), R ａ１ is a hydrogen atom or a methyl group. ａ２ represents an alkyl group having 8 to 20 carbon atoms. [In the above general formula (b-1), R ｂ１ is a hydrogen atom or a methyl group. ｂ２represents an alkylene group having 2 to 4 carbon atoms. m1 represents an integer of 1 to 10. When m1 is an integer of 2 or more, a plurality of R ｂ２ may be the same or different. [In the above general formula (c-1), R ｃ１ is a hydrogen atom or a methyl group. ｃ２ represents an ethylene group. m2 represents an integer of 1 to 6. When m2 is an integer of 2 or more, a plurality of R ｃ２ may be the same or different. n represents an integer of 1 or 2. When n=1, R ｃ３ is a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms. ｃ３ When n=2, at least one of R ｃ３ is a hydrogen atom.]

[0102] The present invention will be specifically described with reference to the following examples, although the present invention is not limited to the following examples.

[0103] [Methods for Measuring Various Physical Properties] Measurements of the various properties of the raw materials used in each Example and Comparative Example and the lubricating oil compositions of each Example and Comparative Example were carried out according to the procedures set out below.

[0104] (1) Kinematic viscosity and viscosity index The 40°C kinematic viscosity and viscosity index of the lubricating oil composition were measured or calculated in accordance with JIS K2283: 2000. (2) Mass average molecular weight (Mw) One column "TSKguard column Super HZ-L" and two columns "TSKSuper Multipore HZ-M" manufactured by Tosoh Corporation were attached to a "1515 isocratic HPLC pump" and a "2414 differential refractive index (RI) detector" manufactured by Waters Corporation in this order from the upstream side, and measurements were performed under the following conditions: measurement temperature: 40°C, mobile phase: tetrahydrofuran, flow rate: 0.35 ml / min, sample concentration: 1.0 mg / ml, and the mass average molecular weight was calculated in terms of standard polystyrene.

[0105] [Examples 1 to 3, Comparative Examples 1 to 3] Lubricating oil compositions having the compositions shown in Table 1 were prepared by mixing the following components, and the evaluations described below were carried out. The numerical units for the blending compositions in Table 1 are "mass %." Details of each component used in preparing the lubricating oil compositions having the compositions shown in Table 1 are described below.

[0106] <Hydrocarbon-based synthetic oil> ・"PAO-1": kinematic viscosity at 40°C is 390 mm ２ / s, and the kinematic viscosity at 100°C is 39.7 mm ２ / s and a viscosity index of 152. It corresponds to hydrocarbon-based synthetic oil (X1). ２ / s, and the kinematic viscosity at 100°C is 3.9 mm ２ / s and a viscosity index of 119. It corresponds to a low viscosity hydrocarbon-based synthetic oil (X11). "mPAO": kinematic viscosity at 40°C of 1616 mm ２ / s, and the 100°C kinematic viscosity is 147.4 mm ２ It is a decene oligomer obtained by polymerizing 1-decene using a metallocene catalyst, and has a viscosity index of 202. It corresponds to a high viscosity hydrocarbon synthetic oil (X12).

[0107] <Ester-based synthetic oil> "Ester 1": diester of trimethylolpropane (TMP) and isostearic acid (kinematic viscosity at 100°C: 13.29 mm ２ / s, viscosity index: 124) "Ester 2": tetraester of pentaerythritol and C5-C9 fatty acid (kinematic viscosity at 100°C: 4.81 mm ２ / s, viscosity index: 101) Note that C5-C9 fatty acids consist of nonanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, and octanoic acid, and are fatty acids mainly composed of nonanoic acid.

[0108] <Phosphorus-Containing Copolymer> A phosphorus-containing copolymer produced according to the production example described below was used.

[0109] <Lubricating oil additives> "Phenol-based antioxidant": Octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate "Amine-based antioxidant": Monobutylphenylmonoctylphenylamine "Alkylthiophosphate": Tris[2,4-isoalkyl(C ９ , C １０ )phenyl]thiophosphate "Alkylthiocarbamate": methylenebis(dibutyldithiocarbamate) (S content = 30.3%) "Alkylbenzotriazole": N-dialkylaminomethylbenzotriazole (N content = 14.6%) "Amine salt of C10 isodecyl acid phosphate and trioctylamine" "Amine salt of C13 tridecyl acid phosphate and trioctylamine" "EO-PO copolymer": xylene solution of EO-PO block copolymer (50%) "Alkenyl succinimide": mixture of 50% polybutenyl succinimide, 20% polybutene, and 30% mineral oil (base number: 37 mg KOH / g) "Antifoaming agent": an acrylate compound with a component concentration of 5% by mass added to 95% by mass of light oil

[0110] <Monomers used in Production Examples> "Dodecyl acrylate": R ａ１ is a hydrogen atom, and R ａ２ is a dodecyl group (an alkyl group having 12 carbon atoms). It was used as alkyl (meth)acrylate (A). "2-hydroxyethyl acrylate": a compound represented by the general formula (b-1) above, where R ｂ１ is a hydrogen atom, and R ｂ２ is an ethylene group (an alkylene group having 2 carbon atoms), and m1=1. Used as the hydroxyl group-containing (meth)acrylate (B). "P-1A(N)": Light acrylate P-1A(N) (trade name), manufactured by Kyoeisha Chemical Co., Ltd., phosphorus content = 14.3 mass%. This is a mixture containing a compound in which n=1 in the above general formula (c-1) as the main component, and also containing a compound in which n=2. Note that both compounds have R ｃ１ is a hydrogen atom, and R ｃ２ is an ethylene group (an alkylene group having 2 carbon atoms), and m2=1. ｃ３is a hydrogen atom. It was used as the phosphorus-containing (meth)acrylate (C). The acid value of P-1A(N) (measured by the potentiometric method specified in JIS K 2501:2003-7) is 420 to 520 mgKOH / g.

[0111] <Production Example: Production of Phosphorus-Containing Copolymer> A 1,500 mL four-neck flask equipped with a thermometer, nitrogen inlet tube, and stirrer was charged with 191.56 g (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 as a solvent. The atmosphere in the flask was then replaced with nitrogen, and 0.8 g of 2,2'-azobis(isobutyronitrile) was added as an initiator. The temperature was slowly raised with stirring, and the mixture was refluxed at 75°C to 85°C for 4 hours. After completion of the reaction, the solvent was distilled off under reduced pressure to obtain a phosphorus-containing copolymer. The weight-average molecular weight (Mw) of the phosphorus-containing copolymer was 22,000. The phosphorus content was 0.13% by mass. The phosphorus-containing copolymer was diluted with mineral oil so that the phosphorus-containing copolymer content was 50% by mass.

[0112] <Evaluation 1: Evaluation 1 of defoaming performance> The foaming degree and foaming stability were evaluated in the following order according to JIS K 2518:2017: (1) Sequence I (24°C), (2) Sequence II (93°C), and (3) Sequence III (24°C). In the evaluation result "X-Y" in Table 1, X is the foam volume (unit: mL) immediately after the end of air blowing, and Y is the foam volume (unit: mL) after standing for 10 minutes after the end of air blowing. In this example, a foam having an X of 100 mL or less and an Y of 10 mL or less was deemed to have passed.

[0113] <Evaluation 2: Evaluation 2 of defoaming performance> Using a test container and diffuser stone conforming to JIS K 2518:2017, air blowing was started at a dry air blowing rate of 3 L / h at 60°C, and the foam volume was measured after 7 days. In this example, a foam volume of 50 mL or less was rated as passing.

[0114] <Evaluation 3: Evaluation of Transparency> The lubricating oil composition was placed in a transparent glass container, and the glass container was placed on a laboratory bench covered with white paper, and the transparency of the lubricating oil composition was evaluated. The evaluation of transparency was carried out in an environment of 20°C.

[0115] The results are shown in Table 1. The content of the phosphorus-containing copolymer in Table 1 includes the content of diluent oil. Furthermore, "C12:OH" of the phosphorus-containing copolymer in Table 1 means the molar ratio of the constitutional unit derived from dodecyl acrylate to the constitutional unit derived from 2-hydroxyethyl acrylate.

[0116] The following can be seen from Table 1. It can be seen that the lubricating oil compositions of Examples 1 to 3 all exhibit excellent defoaming performance over a long period of time. On the other hand, it can be seen that the lubricating oil compositions of Comparative Examples 1 and 2 have poor long-term defoaming performance. It can also be seen that when a low-viscosity hydrocarbon-based synthetic oil, a high-viscosity hydrocarbon-based synthetic oil, and an ester-based synthetic oil are contained without adding a phosphorus-containing copolymer, as in Comparative Example 3, the initial defoaming performance is poor. It can be seen that all of the lubricating oil compositions of Examples 1 to 3 were transparent and no cloudiness was observed.

[0117] <Evaluation 4: FE8 Bearing Wear Test> The lubricating oil compositions of Comparative Example 2 and Examples 2 and 3 were evaluated by measuring the amount of bearing wear in accordance with DIN 51819-3. (Experimental Conditions) Testing machine: FE8 (DIN 51819-1) manufactured by FAG Roller bearing material: High-strength brass Rotation speed: 7.5 rpm Load: 100 kN (2.1 GPa) Oil temperature: 80°C Test time: 80 hours x 2 (no oil change) (Evaluation method) Evaluation was based on the total amount of wear (mg) of two roller bearings. The results are the average of two experiments (n=2). In this example, roller bearings with an average amount of wear of 30 mg or less were considered to have passed.

[0118] The results are shown in Table 2. The content of the phosphorus-containing copolymer in Table 2 also includes the content of diluent oil. Furthermore, "C12:OH" of the phosphorus-containing copolymer in Table 2 means the molar ratio of the constitutional unit derived from dodecyl acrylate to the constitutional unit derived from 2-hydroxyethyl acrylate.

[0119] It can be seen from Table 2 that the lubricating oil compositions of Examples 2 and 3 all have excellent 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 structural unit (a) derived from an alkyl (meth)acrylate (A) represented by the following general formula (a-1), a structural unit (b) derived from a hydroxyl group-containing (meth)acrylate (B) represented by the following general formula (b-1), and a structural unit (c) derived from a phosphorus-containing (meth)acrylate (C) represented by the following general formula (c-1): [In the above general formula (a-1), R ａ１ is a hydrogen atom or a methyl group. ａ２ represents an alkyl group having 8 to 20 carbon atoms. [In the above general formula (b-1), R ｂ１ is a hydrogen atom or a methyl group. ｂ２ represents an alkylene group having 2 to 4 carbon atoms. m1 represents an integer of 1 to 10. When m1 is an integer of 2 or more, ｂ２ may be the same or different. [In the above general formula (c-1), R ｃ１ is a hydrogen atom or a methyl group. ｃ２ represents an ethylene group. m2 represents an integer of 1 to 6. When m2 is an integer of 2 or more, ｃ２ may be the same or different. n represents an integer of 1 or 2. When n=1, R ｃ３ is a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms. ｃ３ At least one of R represents a hydrogen atom. ｃ３ is a hydrogen atom.] 2. The hydrocarbon synthetic oil (X1) has a kinetic viscosity of 20 mm at 100°C. ２ / s ~ 55mm ２ The lubricating oil composition of claim 1, wherein 3. The hydrocarbon synthetic oil (X1) has a kinetic viscosity of 1.5 mm at 100°C. ２ / s ~ 11.0 mm ２ / s, and a low-viscosity hydrocarbon-based synthetic oil (X11) having a kinetic viscosity of 50.0 mm ２ / s ~ 350.0 mm ２ 3. The lubricating oil composition according to claim 1 or 2, further comprising a high viscosity hydrocarbon-based synthetic oil (X12) having a viscosity of 100% or more and a viscosity of 100% or less.

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

6. The lubricating oil composition according to any one of claims 1 to 5, wherein the phosphorus content in the phosphorus-containing copolymer (Y) is 0.05 mass % to 1.0 mass % based on the 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 5,000 to 100,000.

8. The lubricating oil composition according to any one of claims 1 to 7, further comprising one or more additives selected from the group consisting of antioxidants, metal deactivators, demulsifiers, detergent-dispersants, antifoaming agents, and extreme pressure agents.

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

10. A method for producing a lubricating oil composition, comprising the 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 structural unit (a) derived from an alkyl (meth)acrylate (A) represented by the following general formula (a-1), a structural unit (b) derived from a hydroxyl group-containing (meth)acrylate (B) represented by the following general formula (b-1), and a structural unit (c) derived from a phosphorus-containing (meth)acrylate (C) represented by the following general formula (c-1): [In the above general formula (a-1), R ａ１ is a hydrogen atom or a methyl group. ａ２ represents an alkyl group having 8 to 20 carbon atoms. [In the above general formula (b-1), R ｂ１ is a hydrogen atom or a methyl group. ｂ２ represents an alkylene group having 2 to 4 carbon atoms. m1 represents an integer of 1 to 10. When m1 is an integer of 2 or more, a plurality of R ｂ２ may be the same or different. [In the above general formula (c-1), R ｃ１ is a hydrogen atom or a methyl group. ｃ２ represents an ethylene group. m2 represents an integer of 1 to 6. When m2 is an integer of 2 or more, ｃ２ may be the same or different. n represents an integer of 1 or 2. When n=1, R ｃ３ is a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms. ｃ３ At least one of R represents a hydrogen atom. ｃ３ is a hydrogen atom.]

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