Lubricant composition

Abstract

To provide a lubricant composition with excellent cooling and insulation properties.SOLUTION: The lubricant composition comprises base oil (A), solid particles (B) of an average primary particle diameter of 500 nm or less, and a dispersant (C), with the content of the solid particles (B) being 0.1 to 30 mass% on the basis of the total amount of the lubricant composition, and the content of the dispersant (C) being 0.1 to 20 mass% on the basis of the total amount of the lubricant composition.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a lubricating oil composition, a method for using and producing the lubricating oil composition, and a cooling system. [Background technology]

[0002] In recent years, there has been a strong demand for reducing CO2 emissions from the viewpoint of protecting the global environment, and therefore, in the field of automobiles, efforts have been focused on developing technologies for fuel saving. Hybrid cars and electric cars are mainstream technologies for such fuel saving, and are expected to become widespread rapidly in the future. Hybrid cars and electric cars are equipped with electric motors and generators, and when these are cooled by oil cooling, existing automatic transmission fluids (ATF) and continuously variable transmission fluids (CVTF) are mainly used as lubricating oil compositions.

[0003] These lubricating oil compositions are required to have excellent cooling properties as well as electrical insulation properties in order to maintain reliability over a long period of time in terms of the insulation properties of electric motors. For example, Patent Document 1 discloses a coolant as such a lubricating oil composition, which contains a base liquid and porous fine particles having a predetermined structure. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-113242 Summary of the Invention [Problem to be solved by the invention]

[0005] Under these circumstances, there is a demand for lubricating oil compositions that are excellent in cooling properties and insulating properties. [Means for solving the problem]

[0006] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by a lubricating oil composition comprising a base oil containing specific amounts of solid particles having an average primary particle size of 500 nm or less and a dispersant, and have thus completed the present invention. That is, the present invention provides the following aspects [1] to

[15] . [1] A lubricating oil composition comprising a base oil (A), solid particles (B) having an average primary particle diameter of 500 nm or less, and a dispersant (C), wherein the content of the solid particles (B) is 0.1 to 30 mass%, based on the total amount of the lubricating oil composition, and the content of the dispersant (C) is 0.1 to 20 mass%, based on the total amount of the lubricating oil composition. [2] The lubricating oil composition according to [1], wherein the content ratio of the solid particles (B) to the dispersant (C) [(B) / (C)], in terms of mass ratio, is 0.05 or more and less than 3. [3] The lubricating oil composition according to [1] or [2], wherein the average primary particle size of the solid particles (B) is 100 nm or less. [4] The lubricating oil composition according to any one of claims 1 to 3, wherein the solid particles (B) are selected from the group consisting of SiO2, Al2O3, AlN, TiO2, ZrO2, Y2O3, WO3, Ta2O5, V2O5, Nb2O5, CeO2, B4C, Al2TiO5, BN, MoSi2, SiC, Si3N4, TiC, TiN, ZrB2, CaO, SrO, BaO, clay minerals, mixtures thereof, and thermally stable carbonates or sulfates thereof. [5] The lubricating oil composition according to any one of [1] to [4], wherein the base oil (A) comprises at least a mineral oil (A1). [6] The kinetic viscosity of the base oil (A) at 40°C is 10mm 2 The lubricating oil composition according to any one of [1] to [5], wherein the lubricating oil composition has a viscosity of 100:1 or less. [7] The volume resistivity of the base oil (A) is 8.0×10 10 The lubricating oil composition according to any one of [1] to [6], having a viscosity of Ω·m or more. [8] The lubricating oil composition according to any one of [1] to [7], which is substantially free of water. [9] The kinematic viscosity of the lubricating oil composition at 40°C is 20mm 2The lubricating oil composition according to any one of [1] to [8], wherein the lubricating oil composition has a viscosity of 100:1 or less.

[10] The volume resistivity of the lubricating oil composition is 1.0 × 10 8 The lubricating oil composition according to any one of [1] to [9], having a viscosity of Ω·m or more.

[11] The lubricating oil composition according to any one of [1] to

[10] , which is used for cooling an electrical device.

[12] The lubricating oil composition according to

[11] , wherein the electrical equipment is a motor, a battery, an inverter, or an engine.

[13] A cooling device for cooling an electric device, which is filled with the lubricating oil composition according to any one of [1] to

[12] .

[14] A method for using the lubricating oil composition according to any one of [1] to

[12] , which comprises applying the lubricating oil composition to cooling an electric device.

[15] A method for producing the lubricating oil composition according to any one of [1] to

[12] , comprising a step of stirring at 10,000 rpm or more. Effect of the Invention

[0007] The lubricating oil composition according to a preferred embodiment of the present invention has excellent cooling and insulating properties and can therefore be suitably used for cooling electrical equipment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The upper and lower limit values ​​of the numerical ranges described in this specification can be arbitrarily combined. For example, when the numerical range is described as "preferably 30 to 100, more preferably 40 to 80", the ranges "30 to 80" and "40 to 100" are also included in the numerical ranges described in this specification. In addition, when the numerical range is described as "preferably 30 or more, more preferably 40 or more, and preferably 100 or less, more preferably 80 or less", the ranges "30 to 80" and "40 to 100" are also included in the numerical ranges described in this specification. In addition, as a numerical range described in this specification, for example, "60 to 100" means a range of "60 or more and 100 or less." Furthermore, in defining the upper and lower limits described in this specification, a numerical range from the lower limit to the upper limit can be defined by appropriately selecting from the respective options and combining them in any desired manner. In addition, various features described as preferred embodiments in this specification may be combined in multiple ways.

[0009] [Constitution of lubricating oil composition] One embodiment of the present invention is a lubricating oil composition comprising a base oil (A) (hereinafter also referred to as "component (A)"), solid particles (B) (hereinafter also referred to as "component (B)") having an average primary particle diameter of 500 nm or less, and a dispersant (C) (hereinafter also referred to as "component (C)"), wherein the content of the solid particles (B) is 0.1 to 30 mass % based on the total amount of the lubricating oil composition, and the content of the dispersant (C) is 0.1 to 20 mass % based on the total amount of the lubricating oil composition. In order to improve the insulating properties, it is preferable to blend a base oil (A) into a lubricating oil composition used for cooling electrical equipment. On the other hand, there has been a demand for improved cooling properties in lubricating oil compositions blended with a base oil (A). A lubricating oil composition containing solid particles (B) can improve the cooling properties, but it has been necessary to add a dispersant to uniformly disperse the solid particles (B). However, the viscosity of the lubricating oil composition tends to increase when the amount of dispersant added increases, and it has been difficult to adjust the viscosity of the lubricating oil composition to an appropriate range while exhibiting excellent cooling properties. In response to these problems, the present inventors discovered that by adjusting the contents of components (B) and (C) within respective prescribed ranges, it is possible to obtain a lubricating oil composition that can exhibit excellent cooling and insulating properties while maintaining a low viscosity of the lubricating oil composition, and thus completed the present invention.

[0010] The lubricating oil composition according to one embodiment of the present invention preferably has a kinematic viscosity at 40°C of 20mm 2 / s or less, preferably 19 mm 2 / s or less, more preferably 18 mm 2 / s or less, and even more preferably 17 mm 2 / s or less, and even more preferably 16 mm 2 / s or less, particularly preferably 15 mm 2 / s or less.

[0011] The viscosity index of the lubricating oil composition of one embodiment of the present invention is preferably 70 or greater, more preferably 80 or greater, even more preferably 90 or greater, and even more preferably 100 or greater.

[0012] The lubricating oil composition of one embodiment of the present invention is substantially free of water. "Substantially free of water" means that lubricating oil compositions that are intentionally blended with water and a mixed solvent containing water are excluded. However, the lubricating oil composition of one embodiment of the present invention does not exclude embodiments in which water is inevitably blended, but from the viewpoint of obtaining a lubricating oil composition with high insulating properties, it is preferable that the content of such water is as small as possible. Specifically, the content of water that is inevitably mixed in is preferably less than 0.05 mass%, more preferably less than 0.03 mass%, even more preferably less than 0.01 mass%, and particularly preferably less than 0.001 mass%, based on the total amount (100 mass%) of the lubricating oil composition.

[0013] The lubricating oil composition of one embodiment of the present invention may further contain other lubricating oil additives in addition to components (B) and (C).

[0014] In the lubricating oil composition of one embodiment of the present invention, the total content of components (A) and (B) is, based on the total amount (100 mass%) of the lubricating oil composition, preferably 50 mass% or more, more preferably 60 mass% or more, more preferably 70 mass% or more, even more preferably 80 mass% or more, and particularly preferably 90 mass% or more, and may be 100 mass% or less, 99.0 mass% or less, 98.0 mass% or less, 97.0 mass% or less, 96.0 mass% or less, or 95.0 mass% or less.

[0015] In the lubricating oil composition of one embodiment of the present invention, the total content of components (A) and (C) is, based on the total amount (100 mass%) of the lubricating oil composition, preferably 50 mass% or more, more preferably 60 mass% or more, more preferably 70 mass% or more, even more preferably 80 mass% or more, and particularly preferably 90 mass% or more, and may be 100 mass% or less, 99.5 mass% or less, or 99.0 mass% or less.

[0016] In the lubricating oil composition of one embodiment of the present invention, the total content of components (B) and (C) is, based on the total amount (100 mass%) of the lubricating oil composition, preferably 0.2 mass% or more, more preferably 0.5 mass% or more, even more preferably 1.0 mass% or more, still more preferably 3.0 mass% or more, still more preferably 5.0 mass% or more, still more preferably 8.0 mass% or more, particularly preferably 10 mass% or more, and is preferably 50 mass% or less, more preferably 45 mass% or less, even more preferably 40 mass% or less, still more preferably 35 mass% or less, still more preferably 30 mass% or less, still more preferably 25 mass% or less, and particularly preferably 20 mass% or less.

[0017] Each component contained in the lubricating oil composition according to one embodiment of the present invention will now be described in detail.

[0018] <Base oil (A)> The base oil contained in the lubricating oil composition of one embodiment of the present invention may be a mineral oil, a synthetic oil, or a mixture of a mineral oil and a synthetic oil. Examples of mineral oils include atmospheric residual oils obtained by atmospheric distillation of crude oils such as paraffinic crude oil, intermediate base crude oil, and naphthenic crude oil; distillate oils obtained by vacuum distillation of these atmospheric residual oils; and refined oils obtained by subjecting the distillate oils to one or more refining treatments such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining.

[0019] Examples of synthetic oils include poly-α-olefins such as α-olefins, homopolymers thereof, or α-olefin copolymers (for example, α-olefin copolymers having 8 to 14 carbon atoms, such as ethylene-α-olefin copolymers); isoparaffins; monoester oils such as phosphoric acid monoesters; ether oils such as polyphenyl ether; alkylbenzenes; alkylnaphthalenes; synthetic oils (GTL) obtained by isomerizing wax produced from natural gas by the Fischer-Tropsch process or the like (GTL wax (Gas To Liquids WAX)); synthetic oils (CTL) obtained by isomerizing wax produced from coal by the Fischer-Tropsch process or the like (CTL wax (Coal To Liquids WAX)); and synthetic oils (BTL) obtained by isomerizing wax produced from biomass by the Fischer-Tropsch process or the like (BTL wax (Biomass To Liquids WAX)).

[0020] Among these, the base oil used in one embodiment of the present invention preferably contains at least one selected from mineral oils classified into Group 2 and Group 3 of the API (American Petroleum Institute) base oil category and synthetic oils. In one embodiment of the present invention, these base oils may be used alone or in combination of two or more.

[0021] From the viewpoint of obtaining a lubricating oil composition having high insulating properties, the lubricating oil composition of one embodiment of the present invention preferably contains at least a mineral oil (A1). From the same viewpoint as above, the lubricating oil composition of another embodiment of the present invention preferably contains a mixed base oil of a mineral oil (A1) and one or more synthetic oils (A2) selected from the group consisting of naphthenic oils, poly-α-olefins, aromatic oils, and ether oils, and the synthetic oils (A2) are more preferably naphthenic oils and poly-α-olefins.

[0022] In another embodiment of the lubricating oil composition of the present invention, from the viewpoint of obtaining a lubricating oil composition having high insulating properties, it is preferable that the base oil (A) does not substantially contain highly polar components. Specifically, for example, it is preferable that the base oil (A) does not substantially contain alcohols (primary alcohols, secondary alcohols, tertiary alcohols, etc.) or ester compounds other than monoester compounds (diester compounds, triester compounds, etc.). "Substantially does not contain ester compounds other than alcohols or monoester compounds" means excluding lubricating oil compositions in which these are intentionally blended, and does not exclude embodiments in which these are inevitably blended, but from the same viewpoint as above, it is preferable that the content of such alcohols or ester compounds other than monoester compounds is as small as possible. Specifically, the content of ester compounds other than alcohols or monoester compounds that are inevitably mixed in is preferably less than 0.05 mass%, more preferably less than 0.03 mass%, even more preferably less than 0.01 mass%, and particularly preferably less than 0.001 mass%, based on the total amount (100 mass%) of the lubricating oil composition. The lubricating oil composition of one embodiment of the present invention may contain a monoester compound as the base oil (A).

[0023] From the viewpoint of obtaining a lubricating oil composition having high insulating properties, the lubricating oil composition of one embodiment of the present invention preferably does not substantially contain vegetable oils such as soybean oil, palm oil, palm kernel oil, sunflower oil, rapeseed oil, etc. as the base oil (A). "Substantially does not contain vegetable oils" means excluding lubricating oil compositions in which these are intentionally blended, and does not exclude embodiments in which these are unavoidably blended, but from the same viewpoint as above, it is preferable that the content of such vegetable oils is as small as possible. Specifically, the content of vegetable oil, which is inevitably mixed in, is preferably less than 0.05 mass%, more preferably less than 0.03 mass%, even more preferably less than 0.01 mass%, and particularly preferably less than 0.001 mass%, based on the total amount (100 mass%) of the lubricating oil composition.

[0024] In one embodiment of the lubricating oil composition of the present invention, from the viewpoint of providing a lubricating oil composition having high insulating properties, the content of an ester compound other than an alcohol or a monoester compound per 100 parts by mass of the mineral oil (A1) is preferably 0 to 0.1 parts by mass, more preferably 0 to 0.01 parts by mass, and even more preferably 0 to 0.001 parts by mass. In a lubricating oil composition according to another embodiment of the present invention, the content of the alcohol or ester compound per 100 parts by mass of the mineral oil (A1) is preferably 0 to 0.1 parts by mass, more preferably 0 to 0.01 parts by mass, and even more preferably 0 to 0.001 parts by mass, from the viewpoint of providing a lubricating oil composition having high insulating properties. In a lubricating oil composition according to still another embodiment of the present invention, the content of the vegetable oil per 100 parts by mass of the mineral oil (A1) is preferably 0 to 0.1 parts by mass, more preferably 0 to 0.01 parts by mass, and even more preferably 0 to 0.001 parts by mass, from the viewpoint of providing a lubricating oil composition having high insulating properties.

[0025] The base oil (A) used in one embodiment of the present invention preferably has a kinematic viscosity at 40° C. of 10 mm 2 / s or less, preferably 9.5 mm 2 / s or less, more preferably 9.0 mm 2 / s or less, and especially preferably 8.5 mm 2 / s or less, and preferably 1.0 mm 2 / s or more, preferably 2.0 mm 2 / s or more, more preferably 2.5 mm 2 / s or more, and even more preferably 3.0 mm 2 / s or more. The 40°C kinematic viscosity of the base oil is 10mm 2 If the kinematic viscosity of the base oil at 40°C is 1.0 mm / s or less, the viscosity of the lubricating oil composition can be kept low, and high cooling properties can be obtained, which is preferable. 2 / s or more is preferable for maintaining the oil film.

[0026] The viscosity index of the base oil (A) used in one embodiment of the present invention is preferably 70 or more, more preferably 80 or more, even more preferably 90 or more, and still more preferably 100 or more, from the viewpoint of suppressing viscosity change due to temperature change and improving cooling performance. In this specification, the kinematic viscosity and viscosity index refer to values ​​measured or calculated in accordance with JIS K2283:2000.

[0027] The volume resistivity of the base oil (A) used in one embodiment of the present invention is preferably 8.0×10 10 Ω·m or more, preferably 1.0×10 11 Ω·m or more, more preferably 1.0×10 12 Ω·m or more, and even more preferably 5.0×10 12 Ω·m or more, especially 15×10 12 The volume resistivity of the base oil (A) is 8.0×10 10 If the resistivity is Ω·m or more, a lubricating oil composition with high insulating properties can be obtained. In this specification, the volume resistivity is measured in accordance with JIS C2101 at a measurement temperature of 80°C and an applied voltage of 250V.

[0028] In the lubricating oil composition of one embodiment of the present invention, the content of base oil (A), based on the total amount (100 mass%) of the lubricating oil composition, is usually 55 mass% or more, preferably 60 mass% or more, more preferably 65 mass% or more, even more preferably 70 mass% or more, still more preferably 75 mass% or more, particularly preferably 80 mass% or more, and is preferably 99.9 mass% or less, more preferably 98 mass% or less, and even more preferably 95 mass% or less.

[0029] <Solid particles (B)> The lubricating oil composition of one embodiment of the present invention contains solid particles (B) having an average primary particle size of 500 nm or less. By including the solid particles (B), the cooling property of the lubricating oil composition can be improved. Examples of the solid particles (B) include silicon dioxide (SiO2), aluminum oxide (Al2O3), aluminum nitride (AlN), titanium oxide (TiO2), zirconium oxide (ZrO2), yttrium oxide (Y2O3), tungsten oxide (WO3), tantalum pentoxide (Ta2O5), vanadium pentoxide (V2O5), niobium pentoxide (Nb2O5), cerium oxide (CeO2), boron carbide (B4C), aluminum titanate (Al2TiO5), boron nitride (BN), molybdenum disilicide (MoSi2), silicon carbide (SiC), silicon nitride (Si3N4), titanium carbide (TiC), titanium nitride (TiN), zirconium boride (ZrB2), calcium oxide (CaO), strontium oxide (SrO), barium oxide (BaO), and clay minerals. The solid particles (B) may be a mixture of the above-mentioned materials, as well as thermally stable carbonates or sulfates. Among these, silicon dioxide is particularly preferred as the solid particles (B). In one embodiment of the present invention, these solid particles may be used alone or in combination of two or more kinds.

[0030] The average primary particle diameter of the solid particles (B) used in one embodiment of the present invention is 500 nm or less, but from the viewpoint of obtaining a lubricating oil composition with good dispersibility of the solid particles (B) and high cooling performance, it is preferably 400 nm or less, more preferably 300 nm or less, even more preferably 200 nm or less, particularly preferably 100 nm or less, and may also be 90 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, 50 nm or less, 40 nm or less, 30 nm or less, 20 nm or less, or 10 nm or less. The lower limit of the average primary particle diameter of the solid particles (B) is not particularly limited, but may be, for example, 1 nm or more, 3 nm or more, or 5 nm or more. In this specification, the average primary particle diameter of the solid particles (B) means a value obtained by calculating the average circle equivalent diameter of 100 or more randomly selected primary particles using a scanning electron microscope (SEM). The solid particles (B) may or may not form secondary particles.

[0031] The solid particles (B) used in one embodiment of the present invention may be surface-treated with a surface treatment agent, or may not be surface-treated. By using surface-treated solid particles, the dispersibility of the solid particles is improved, and a lubricating oil composition with high cooling properties can be obtained. Examples of surface treatment agents include silane coupling agents and silicone oils.

[0032] Examples of the silane coupling agent include vinyltrimethoxysilane, vinyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, silane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, tris-(trimethoxysilylpropyl)isocyanurate, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, and 3-trimethoxysilylpropylsuccinic anhydride.

[0033] Examples of silicone oils include so-called straight silicone oils such as dimethylpolysiloxane, methylphenylpolysiloxane, and methylhydrogenpolysiloxane; and so-called modified silicone oils such as polyether-modified polysiloxane, amino-modified polysiloxane, epoxy-modified polysiloxane, polyether-modified polysiloxane, phenol-modified polysiloxane, carboxy-modified polysiloxane, mercapto-modified polysiloxane, acrylic-modified polysiloxane, methacryl-modified polysiloxane, and alkyl-modified polysiloxane.

[0034] The solid particles (B) used in one embodiment of the present invention may be porous having pores (porosity) on the surface, or may be non-porous having no pores. From the viewpoint of obtaining a lubricating oil composition with high cooling properties, it is preferable to use non-porous solid particles (B) in the lubricating oil composition of one embodiment of the present invention.

[0035] In the lubricating oil composition of one embodiment of the present invention, the content of the solid particles (B) is 0.1 to 30 mass% based on the total amount (100 mass%) of the lubricating oil composition, but from the viewpoint of obtaining a lubricating oil composition with excellent cooling properties, it is preferably 0.5 mass% or more, more preferably 1.0 mass% or more, even more preferably 3.0 mass% or more, still more preferably 5.0 mass% or more, and particularly preferably 10 mass% or more, and from the viewpoint of improving the dispersibility of the solid particles (B), it is preferably 25 mass% or less, more preferably 20 mass% or less, even more preferably 18 mass% or less, and particularly preferably 15 mass% or less. The content of the solid particles (B) means the content calculated as the solid content. When surface-treated solid particles are used, the content of the solid particles (B) also includes the amount of the surface treatment agent.

[0036] <Dispersant (C)> The lubricating oil composition of one embodiment of the present invention contains a dispersant (C). By containing the dispersant (C), the solid particles (B) can be uniformly dispersed in the lubricating oil composition, and the lubricating oil composition can have high cooling properties. Examples of the dispersant (C) that can be used include succinimide dispersants, vinylpyrrolidone (VP) / hexadecene copolymers, benzylamines, boron-containing benzylamines, succinic acid esters, fatty acids, and ashless dispersants such as mono- or di-carboxylic acid amides represented by succinic acid. Among these, succinimide dispersants and VP / hexadecene copolymers are preferred. The succinimide-based dispersant is preferably an alkenyl succinimide, and may be a modified alkenyl succinimide reacted with one or more selected from a boron compound, an alcohol, an aldehyde, a ketone, an alkylphenol, a cyclic carbonate, an epoxy compound, and an organic acid. In one embodiment of the present invention, these dispersants may be used alone or in combination of two or more.

[0037] In the lubricating oil composition of one embodiment of the present invention, the content of the dispersant (C) is 0.1 to 20 mass% based on the total amount (100 mass%) of the lubricating oil composition, but from the viewpoint of improving the dispersibility of solid particles, it is preferably 0.5 mass% or more, more preferably 1.0 mass% or more, even more preferably 1.5 mass% or more, and particularly preferably 2.0 mass% or more, and from the viewpoint of maintaining a low viscosity of the lubricating oil composition, it is preferably 20 mass% or less, more preferably 15 mass% or less, even more preferably 12 mass% or less, and even more preferably 10 mass% or less. The content of the dispersant (C) means the content calculated as the solid content.

[0038] In the lubricating oil composition of one embodiment of the present invention, the content ratio of the solid particles (B) to the dispersant (C) [(B) / (C)], in mass ratio, is at least 0.05 and less than 3; from the viewpoint of improving the dispersibility of the solid particles (B), it is preferably at least 0.06, more preferably at least 0.07, even more preferably at least 0.08, still more preferably at least 0.09, and particularly preferably at least 0.1; and from the viewpoint of improving the cooling ability and maintaining a low viscosity of the lubricating oil composition, it is preferably at most 3, more preferably at most 2.5, even more preferably at most 2, still more preferably at most 1.5, and particularly preferably at most 1.

[0039] <Various additives> The lubricating oil composition according to one embodiment of the present invention may contain various additives as required, provided that the effects of the present invention are not impaired. Examples of such various additives include viscosity index improvers, pour point depressants, antioxidants, metal detergents, anti-wear agents, rust inhibitors, anti-foaming agents, extreme pressure additives, and the like. These lubricating oil additives may be used alone, or two or more of them may be used in combination.

[0040] The content of each of these various additives can be appropriately adjusted within a range that does not impair the effects of the present invention, but is usually 0.001 to 15 mass%, preferably 0.005 to 10 mass%, and more preferably 0.01 to 5 mass%, for each additive independently, based on the total amount (100 mass%) of the lubricating oil composition.

[0041] Furthermore, as the additive, a commercially available additive package containing a plurality of additives may be used. Furthermore, a compound having multiple functions as the above-mentioned additives (for example, a compound having functions as an antiwear agent and an extreme pressure additive) may be used. Furthermore, each of these lubricating oil additives may be used alone, or two or more of them may be used in combination.

[0042] [Viscosity index improver] The lubricating oil composition of one embodiment of the present invention may further contain a viscosity index improver. The viscosity index improvers may be used alone or in combination of two or more kinds. Examples of viscosity index improvers used in one embodiment of the present invention include polymethacrylates, dispersion-type polymethacrylates, olefin copolymers (e.g., ethylene-propylene copolymers, etc.), dispersion-type olefin copolymers, and styrene copolymers (e.g., styrene-diene copolymers, styrene-isoprene copolymers, etc.).

[0043] [Pour point depressants] The lubricating oil composition of one embodiment of the present invention may further contain a pour point depressant. The pour point depressants may be used alone or in combination of two or more kinds. Examples of pour point depressants used in one embodiment of the present invention include ethylene-vinyl acetate copolymers, condensates of chlorinated paraffin and naphthalene, condensates of chlorinated paraffin and phenol, polymethacrylates, and polyalkylstyrenes.

[0044] [Antioxidants] The lubricating oil composition of one embodiment of the present invention may further contain an antioxidant. The antioxidants may be used alone or in combination of two or more kinds. Examples of the antioxidant used in one embodiment of the present invention include amine-based antioxidants such as alkylated diphenylamine, phenylnaphthylamine, and alkylated phenylnaphthylamine; phenol-based antioxidants such as 2,6-di-t-butylphenol, 4,4'-methylenebis(2,6-di-t-butylphenol), isooctyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, and n-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate; and sulfur-based antioxidants such as phenothiazine, dioctadecyl sulfide, dilauryl-3,3'-thiodipropionate, and 2-mercaptobenzimidazole.

[0045] [Metal-based cleaning agents] The lubricating oil composition of one embodiment of the present invention may further contain a metallic detergent. The metallic detergent may be used alone or in combination of two or more kinds. The metal-based detergent used in one embodiment of the present invention includes metal salts such as metal sulfonates, metal salicylates, and metal phenates. The metal atom constituting the metal salt is preferably a metal atom selected from alkali metals and alkaline earth metals, more preferably sodium, calcium, magnesium, or barium, and even more preferably calcium.

[0046] [Anti-wear agent] The lubricating oil composition of one embodiment of the present invention may further contain an anti-wear agent. The anti-wear agents may be used alone or in combination of two or more kinds. Examples of anti-wear agents used in one embodiment of the present invention include sulfur-containing compounds such as zinc dialkyldithiophosphate (ZnDTP), zinc phosphate, zinc dithiocarbamate, molybdenum dithiocarbamate, molybdenum dithiophosphate, disulfides, sulfurized olefins, sulfurized oils and fats, sulfurized esters, thiocarbonates, thiocarbamates, and polysulfides; phosphorus-containing compounds such as phosphites, phosphates, phosphonates, and amine salts or metal salts thereof; and sulfur- and phosphorus-containing anti-wear agents such as thiophosphites, thiophosphates, thiophosphonates, and amine salts or metal salts thereof.

[0047] [Rust inhibitor] The lubricating oil composition of one embodiment of the present invention may further contain a rust inhibitor. The rust inhibitor may be used alone or in combination of two or more kinds. Examples of the rust inhibitor used in one embodiment of the present invention include fatty acids, alkenyl succinic acid half esters, fatty acid soaps, alkyl sulfonates, polyhydric alcohol fatty acid esters, fatty acid amines, paraffin oxide, and alkyl polyoxyethylene ethers.

[0048] [Antifoaming agent] The lubricating oil composition of one embodiment of the present invention may further contain an antifoaming agent. The antifoaming agents may be used alone or in combination of two or more kinds. Examples of the defoaming agent used in one embodiment of the present invention include alkyl silicone defoaming agents, fluoro silicone defoaming agents, and fluoroalkyl ether defoaming agents.

[0049] [Extreme pressure additives] The lubricating oil composition of one embodiment of the present invention may further contain an extreme pressure additive. The extreme pressure additives may be used alone or in combination of two or more kinds. Examples of the extreme pressure additives used in one embodiment of the present invention include chlorine-based extreme pressure additives such as chlorinated paraffin, chlorinated fatty acid, and chlorinated fatty oil; sulfur-based extreme pressure additives such as sulfurized olefin, sulfurized lard, alkyl polysulfide, and sulfurized fatty acid; and phosphorus-based extreme pressure additives such as phosphate esters, phosphites, thiophosphate esters, and salts thereof, phosphine-based, and tricresyl phosphate.

[0050] <Method of producing lubricating oil composition> The method for producing a lubricating oil composition according to one embodiment of the present invention preferably includes a step of stirring a composition containing a base oil (A), solid particles (B) and a dispersant (C) at 10,000 rpm or more. This step allows the solid particles (B) to be uniformly dispersed in the lubricating oil composition. In this step, the stirring speed may be 12,000 rpm or more, 15,000 rpm or more, 17,000 rpm or more, or 20,000 rpm or more. The method for producing a lubricating oil composition according to one embodiment of the present invention preferably includes a step of blending various other additives, as necessary, in addition to the above-mentioned components (A) to (C). The order of blending the components can be appropriately determined.

[0051] [Properties of the lubricating oil composition] The lubricating oil composition of one embodiment of the present invention preferably has a kinematic viscosity at 100°C of 0.8 mm 2 / s or more, preferably 1.0 mm 2 / s or more, more preferably 1.2 mm 2 / s or more, and preferably 4.0 mm 2 / s or less, preferably 3.5 mm 2 / s or less, more preferably 3.0 mm 2 / s or less.

[0052] The volume resistivity of the lubricating oil composition according to one embodiment of the present invention is preferably 1.0×10 8 Ω·m or more, preferably 1.3×10 8 Ω·m or more, more preferably 1.5×10 8 Ω·m or more, and even more preferably 2.0×10 8Ω·m or more, especially 2.1×10 8 It is greater than or equal to Ω·m.

[0053] The cooling property of the lubricating oil composition of one embodiment of the present invention is preferably 20.0° C. / sec or more, more preferably 22.0° C. / sec or more, even more preferably 23.0° C. / sec or more, and particularly preferably 25.0° C. / sec or more. In this specification, the cooling property means the maximum cooling rate (° C. / sec) for 12 seconds from the start of immersion in oil when a silver rod heated to 200° C. is immersed in oil controlled at 30° C. according to JIS K2242.

[0054] [Uses of the lubricating oil composition] The lubricating oil composition of the present invention has excellent cooling and insulating properties. Therefore, the lubricating oil composition of the present invention can be suitably used for cooling electrical equipment, such as motors, batteries, inverters, and engines. Therefore, the present invention also provides a cooling device as described below in [I], and a method for using the lubricating oil composition as described below in [II]. [I] A cooling device for cooling an electric device, which is filled with the lubricating oil composition according to one embodiment of the present invention described above. [II] A method for using the lubricating oil composition according to one embodiment of the present invention described above, which comprises applying the lubricating oil composition to cooling electrical equipment. EXAMPLES

[0055] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples. Various physical properties of the components used in the examples, comparative examples and reference examples and the obtained lubricating oil compositions were measured according to the following methods.

[0056] <Kinematic viscosity, viscosity index> Measured and calculated in accordance with JIS K2283:2000. <Cooling property> In accordance with JIS K2242, a silver rod heated to 200°C was immersed in oil controlled at 30°C, and the maximum cooling rate (°C / sec) was measured for 12 seconds from the start of immersion in the oil. <Volume resistivity> Measured in accordance with JIS C2101 at a measurement temperature of 80°C and an applied voltage of 250V.

[0057] Examples 1 to 5, Comparative Examples 1 to 3 Components (A) to (C) shown in Table 1 were added and mixed in the amounts shown in Table 1, and stirred at 20,000 rpm for 5 minutes using a homogenizer to prepare lubricating oil compositions. The prepared lubricating oil compositions were substantially free of water. Details of each component used in the preparation of the lubricating oil compositions are as follows.

[0058] <Base oil (A)> ·Mineral oil: 40℃ kinematic viscosity=8.2mm 2 / s, viscosity index = 103, mineral oil classified as Group II in the API base oil category, volume resistivity = 18 x 10 12 Ω·m. <Solid particles (B)> ·SiO2: Average primary particle size = 10 nm, silica particles surface-treated with silicone oil. <Dispersant (C)> Succinimide (non-boron modified alkenyl succinic acid bisimide, nitrogen atom content = 1.80% by mass) Vinylpyrrolidone (VP) / Hexadecene Copolymer

[0059] For the lubricating oil compositions prepared in the Examples and Comparative Examples, various physical property values ​​were measured and calculated in accordance with the measurement methods described above. These results are shown in Table 1. In Table 1, the "dispersibility" was evaluated by visually checking the presence or absence of precipitation after leaving each prepared sample to stand for one week, with samples in which no precipitation was observed being rated as "A" and samples in which precipitation was observed being rated as "F." The 40°C kinematic viscosity of the lubricating oil compositions of the Examples, measured and calculated in accordance with the measurement methods described above, was 20 mm 2 / s or less and the viscosity index is 70 or more.

[0060] [Table 1]

[0061] As can be seen from Table 1, the lubricating oil compositions of Examples 1 to 5, which contain a base oil (A) and have solid particle (B) and dispersant (C) contents within the specified numerical ranges, have excellent cooling properties and insulating properties, and also have good dispersibility of the solid particles (B), compared to Comparative Examples 1 to 3.

Claims

1. A lubricating oil composition comprising a base oil (A), solid particles (B) having an average primary particle diameter of 500 nm or less, and a dispersant (C), wherein the content of the solid particles (B) is 0.1 to 30 mass % based on the total amount of the lubricating oil composition, and the content of the dispersant (C) is 0.1 to 20 mass % based on the total amount of the lubricating oil composition.

2. 2. The lubricating oil composition according to claim 1, wherein the content ratio of the solid particles (B) to the dispersant (C) [(B) / (C)] is 0.05 or more and less than 3, in terms of mass ratio.

3. 2. The lubricating oil composition according to claim 1, wherein the solid particles (B) have an average primary particle size of 100 nm or less.

4. 2. The lubricating oil composition of claim 1, wherein the solid particles (B) are selected from the group consisting of SiO2, Al2O3, AlN, TiO2, ZrO2, Y2O3, WO3, Ta2O5, V2O5, Nb2O5, CeO2, B4C, Al2TiO5, BN, MoSi2, SiC, Si3N4, TiC, TiN, ZrB2, CaO, SrO, BaO, clay minerals, and mixtures thereof, and thermally stable carbonates or sulfates thereof.

5. 2. The lubricating oil composition of claim 1, wherein the base oil (A) comprises at least a mineral oil (A1).

6. 2. The lubricating oil composition according to claim 1, wherein the base oil (A) has a kinematic viscosity at 40° C. of 10 mm2 / s or less.

7. 2. The lubricating oil composition according to claim 1, wherein the volume resistivity of the base oil (A) is 8.0×10 Ω·m or more.

8. 10. The lubricating oil composition of claim 1, which is substantially free of water.

9. 2. The lubricating oil composition according to claim 1, wherein the lubricating oil composition has a kinematic viscosity at 40° C. of 20 mm2 / s or less.

10. 2. The lubricating oil composition according to claim 1, wherein the lubricating oil composition has a volume resistivity of 1.0×10 Ω·m or more.

11. The lubricating oil composition according to claim 1, which is used for cooling electrical equipment.

12. The lubricating oil composition of claim 11, wherein the electrical device is a motor, a battery, an inverter, or an engine.

13. A cooling device for cooling an electric device, which is filled with the lubricating oil composition according to any one of claims 1 to 12.

14. A method for using the lubricating oil composition according to any one of claims 1 to 12, which comprises applying the lubricating oil composition to cooling an electric device.

15. A method for producing the lubricating oil composition according to any one of claims 1 to 12, comprising a step of stirring at 10,000 rpm or more.