Lubricating oil 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 of using the lubricating oil composition, a method of manufacturing the lubricating oil composition, and a cooling device. [Background technology] 【0002】 In recent years, there has been a strong demand for CO2 reduction from the perspective of protecting the global environment, and therefore, efforts are being made in the automotive sector to develop technologies for fuel efficiency. Hybrid vehicles and electric vehicles are the mainstream technologies for such fuel efficiency, and are predicted to spread rapidly in the future. Hybrid vehicles and electric vehicles are equipped with electric motors and generators, and when these are cooled using an oil cooling system, existing automatic transmission fluid (ATF) and continuously variable transmission fluid (CVTF) are mainly used as the lubricating oil composition. 【0003】 These lubricating oil compositions require not only excellent cooling properties but also electrical insulation to maintain long-term reliability in terms of the insulation of electric motors. As such a lubricating oil composition, for example, Patent Document 1 discloses a coolant comprising a base liquid and porous fine particles having a predetermined configuration. [Prior art documents] [Patent Documents] 【0004】 [Patent Document 1] Japanese Patent Publication No. 2021-113242 [Overview of the Initiative] [Problems that the invention aims to solve] 【0005】 Under these circumstances, there is a need for a lubricating oil composition that offers excellent cooling and insulating properties. [Means for solving the problem] 【0006】 As a result of diligent research, the inventors of the present invention have found that a lubricating oil composition containing a specific amount of solid particles with an average primary particle diameter of 500 nm or less and a dispersant in a base oil can solve the above problems, and have completed the present invention. In other words, the present invention provides the following embodiments [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 solid particles (B) is 0.1 to 30% by mass on a basis of the total amount of the lubricating oil composition, and the content of dispersant (C) is 0.1 to 20% by mass on a basis of the total amount of the lubricating oil composition. [2] The lubricating oil composition according to [1], wherein the content ratio of solid particles (B) to dispersant (C) [(B) / (C)] is 0.05 or more and less than 3 by mass ratio. [3] The lubricating oil composition according to [1] or [2], wherein the average primary particle diameter 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, and mixtures thereof, as well as thermally stable carbonates or sulfates thereof. [5] A lubricating oil composition according to any one of [1] to [4], wherein the base oil (A) comprises at least mineral oil (A1). [6] The kinematic viscosity of base oil (A) at 40°C is 10 mm 2 A lubricating oil composition according to any one of items [1] to [5], wherein the s is less than or equal to / s. [7] The volume resistivity of the base oil (A) is 8.0 × 10 10 A lubricating oil composition according to any one of items [1] to [6], wherein the m content is Ω·m or greater. [8] A 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 20 mm 2The lubricating oil composition according to any one of [1] to [8], which is below / s.

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

[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 device is a motor, a battery, an inverter, and an engine.

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

[12] .

[14] A method of using a lubricating oil composition, which applies the lubricating oil composition according to any one of [1] to

[12] to cooling an electrical device.

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

[12] , which includes 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 properties and insulation properties. Therefore, the lubricating oil composition according to one embodiment of the present invention can be suitably used for cooling an electrical device. [Embodiment for Carrying out the Invention] 【0008】 Regarding the numerical ranges described in this specification, the upper limit value and the lower limit value can be arbitrarily combined. For example, when the numerical range is described as "preferably 30 to 100, more preferably 40 to 80", the ranges of "30 to 80" and "40 to 100" are also included in the numerical ranges described in this specification. Also, for example, 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 of "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 the provisions for upper and lower limits described herein, the numerical range from the lower limit to the upper limit can be defined by appropriately selecting and combining options from each set of choices as appropriate. In addition, several of the requirements described as preferred embodiments in this specification can be combined. 【0009】 [Composition of the lubricating oil composition] One aspect 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 solid particles (B) is 0.1 to 30% by mass on a basis of the total amount of the lubricating oil composition, and the content of dispersant (C) is 0.1 to 20% by mass on a basis of the total amount of the lubricating oil composition. Lubricating oil compositions used for cooling electrical equipment preferably contain a base oil (A) to enhance insulation properties. However, lubricating oil compositions containing base oil (A) also required improved cooling performance. Lubricating oil compositions containing solid particles (B) can improve cooling performance, but the addition of a dispersant was necessary to uniformly disperse the solid particles (B). However, increasing the amount of dispersant tended to increase the viscosity of the lubricating oil composition, making it difficult to adjust the viscosity of the lubricating oil composition to an appropriate range while exhibiting excellent cooling performance. To address these problems, the inventors have discovered that by adjusting the content of component (B) and component (C) to predetermined ranges, it is possible to obtain a lubricating oil composition that exhibits excellent cooling and insulating properties while maintaining a low viscosity, thus completing the present invention. 【0010】 The kinematic viscosity of a lubricating oil composition according to one embodiment of the present invention at 40°C is preferably 20 mm². 2 / s or less, more preferably 19 mm 2 / s or less, more preferably 18 mm 2 / s or less, even more preferably 17 mm 2 / s or less, 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 aspect of the present invention is preferably 70 or more, more preferably 80 or more, still more preferably 90 or more, and even more preferably 100 or more. 【0012】 The lubricating oil composition of one aspect of the present invention substantially does not contain water. "Substantially does not contain water" means excluding a lubricating oil composition intentionally formulated with water and a mixed solvent containing water. However, the lubricating oil composition of one aspect of the present invention does not exclude the case where water is inevitably incorporated, but from the viewpoint of obtaining a lubricating oil composition having 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 is preferably less than 0.05% by mass, more preferably less than 0.03% by mass, still more preferably less than 0.01% by mass, and particularly preferably less than 0.001% by mass based on the total amount (100% by mass) of the lubricating oil composition. 【0013】 The lubricating oil composition of one aspect of the present invention may further contain other additives for lubricating oil other than components (B) and (C). 【0014】 In the lubricating oil composition of one aspect of the present invention, the total content of components (A) and (B) is preferably 50% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more, even more preferably 80% by mass or more, particularly preferably 90% by mass or more, and may be 100% by mass or less, 99.0% by mass or less, 98.0% by mass or less, 97.0% by mass or less, 96.0% by mass or less, or 95.0% by mass or less based on the total amount (100% by mass) of the lubricating oil composition. 【0015】 In a lubricating oil composition according to one aspect of the present invention, the total content of components (A) and (C) is preferably 50% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more, based on the total amount (100% by mass) of the lubricating oil composition, and may also be 100% by mass or less, 99.5% by mass or less, or 99.0% by mass or less. 【0016】 In a lubricating oil composition according to one embodiment of the present invention, the total content of components (B) and (C) is preferably 0.2% by mass or more, more preferably 0.5% by mass or more, even more preferably 1.0% by mass or more, even more preferably 3.0% by mass or more, even more preferably 5.0% by mass or more, even more preferably 8.0% by mass or more, particularly preferably 10% by mass or more, and also preferably 50% by mass or less, more preferably 45% by mass or less, even more preferably 40% by mass or less, even more preferably 35% by mass or less, even more preferably 30% by mass or less, even more preferably 25% by mass or less, particularly preferably 20% by mass or less. 【0017】 The details of each component contained in a lubricating oil composition according to one embodiment of the present invention will be described below. 【0018】 <Base oil (A)> The base oil contained in the lubricating oil composition according to one embodiment of the present invention may be mineral oil, synthetic oil, or a mixture of mineral oil and synthetic oil. Examples of mineral oils include atmospheric residues obtained by atmospheric distillation of crude oils such as paraffinic crude oil, intermediate crude oil, and naphthenic crude oil; distillates obtained by vacuum distillation of these atmospheric residues; and refined oils obtained by subjecting the distillates to one or more refining processes such as solvent delamination, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining. 【0019】 Examples of synthetic oils include poly-α-olefins such as α-olefins and their homopolymers, or α-olefin copolymers (e.g., 8-14 carbon olefin copolymers such as ethylene-α-olefin copolymers); isoparaffins; monoester oils such as phosphate monoesters; ether oils such as polyphenyl ethers; alkylbenzenes; alkylnaphthalenes; synthetic oils (GTL) obtained by isomerizing wax produced from natural gas by the Fischer-Tropsch process, etc. (GTL wax (Gas To Liquids Wax)); synthetic oils (CTL) obtained by isomerizing wax produced from coal by the Fischer-Tropsch process, etc. (CTL wax (Coal To Liquids Wax)); and synthetic oils (BTL) obtained by isomerizing wax produced from biomass by the Fischer-Tropsch process, etc. (BTL wax (Biomass To Liquids Wax)). 【0020】 Among these, the base oil used in one aspect of the present invention preferably includes at least one selected from mineral oils classified in groups 2 and 3 of the API (American Petroleum Institute) base oil categories, and synthetic oils. In one aspect of the present invention, these base oils may be used individually or in combination of two or more. 【0021】 In one aspect of the present invention, the lubricating oil composition preferably contains at least mineral oil (A1) from the viewpoint of providing a lubricating oil composition with high insulating properties. In another aspect of the present invention, the lubricating oil composition preferably contains a mixed base oil of 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-based oils, from the same viewpoint as above, and naphthenic oils and poly-α-olefins are more preferred as synthetic oils (A2). 【0022】 In yet another embodiment of the present invention, from the viewpoint of providing a lubricating oil composition with high insulating properties, it is preferable that the base oil (A) substantially does not contain highly polar components. Specifically, for example, it is preferable that it substantially does not contain alcohols (primary alcohols, secondary alcohols, tertiary alcohols, etc.) or ester compounds other than monoester compounds (diester compounds, triester compounds, etc.). "Substantially free of alcohols or ester compounds other than monoester compounds" means excluding lubricating oil compositions that intentionally contain these, and does not exclude embodiments in which these are inevitably included. However, from the same viewpoint as above, it is preferable that the content of such alcohols or ester compounds other than monoester compounds is as low as possible. Specifically, the content of ester compounds other than alcohol or monoester compounds that inevitably become mixed in is preferably less than 0.05% by mass, more preferably less than 0.03% by mass, even more preferably less than 0.01% by mass, and particularly preferably less than 0.001% by mass, based on the total amount (100% by mass) of the lubricating oil composition. In addition, a lubricating oil composition according to one embodiment of the present invention may contain a monoester compound as the base oil (A). 【0023】 In one embodiment of the present invention, from the viewpoint of providing a lubricating oil composition with high insulating properties, it is preferable that the base oil (A) substantially does not contain vegetable oils such as soybean oil, palm oil, palm kernel oil, sunflower oil, and rapeseed oil. "Substantially free of vegetable oils" means excluding lubricating oil compositions that intentionally contain these oils, and does not exclude embodiments in which these oils are inevitably included. However, from the same viewpoint as above, it is preferable that the content of such vegetable oils be as low as possible. Specifically, the amount of vegetable oil that inevitably gets mixed in is preferably less than 0.05% by mass, more preferably less than 0.03% by mass, even more preferably less than 0.01% by mass, and particularly preferably less than 0.001% by mass, based on the total amount (100% by mass) of the lubricating oil composition. 【0024】 In one embodiment of the present invention, from the viewpoint of providing a lubricating oil composition with high insulating properties, the content of an ester compound other than an alcohol or monoester compound per 100 parts by mass of 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. Another embodiment of the present invention provides a lubricating oil composition with high insulating properties, wherein the content of the alcohol or ester compound per 100 parts by mass of 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 yet another embodiment of the present invention, from the viewpoint of providing a lubricating oil composition with high insulating properties, the content of vegetable oil per 100 parts by mass of 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. 【0025】 The kinematic viscosity of the base oil (A) used in one aspect of the present invention at 40°C is preferably 10 mm². 2 / s or less, more preferably 9.5 mm 2 / s or less, more preferably 9.0 mm 2 / s or less, particularly preferably 8.5 mm 2 The interval is less than or equal to / s, and preferably 1.0 mm. 2 / s or more, more preferably 2.0 mm 2 / s or more, more preferably 2.5 mm 2 / s or more, more preferably 3.0 mm 2 The kinematic viscosity of the base oil at 40°C is 10 mm² or higher. 2 A viscosity of 1.0 mm² or less is preferable because it allows the viscosity of the lubricating oil composition to be kept low, resulting in high cooling performance. On the other hand, a kinematic viscosity of 1.0 mm² at 40°C for the base oil is preferable. 2 A value of / s or higher is preferable for maintaining the oil film. 【0026】 Furthermore, the viscosity index of the base oil (A) used in one aspect of the present invention is preferably 70 or higher, more preferably 80 or higher, even more preferably 90 or higher, and even more preferably 100 or higher, from the viewpoint of suppressing viscosity changes due to temperature changes and improving cooling performance. In this specification, 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 aspect of the present invention is preferably 8.0 × 10⁻⁶. 10 Ω·m or greater, more preferably 1.0 × 10 11 Ω·m or greater, more preferably 1.0 × 10⁻⁶ 12 Ω·m or greater, more preferably 5.0 × 10 12 Ω·m or greater, particularly preferably 15 × 10 12 It is greater than or equal to Ω·m. The volume resistivity of base oil (A) is 8.0 × 10 10 If the resistivity is Ω·m or greater, a highly insulating lubricating oil composition can be obtained. In this specification, the volume resistivity is measured in accordance with JIS C2101, under conditions of a measurement temperature of 80°C and an applied voltage of 250V. 【0028】 In a lubricating oil composition according to one aspect of the present invention, the base oil (A) content is typically 55% by mass or more, preferably 60% by mass or more, more preferably 65% ​​by mass or more, even more preferably 70% by mass or more, even more preferably 75% by mass or more, particularly preferably 80% by mass or more, based on the total amount (100% by mass) of the lubricating oil composition, and also preferably 99.9% by mass or less, more preferably 98% by mass or less, and even more preferably 95% by mass or less. 【0029】 <Solid particles (B)> A lubricating oil composition according to one aspect of the present invention contains solid particles (B) having an average primary particle diameter of 500 nm or less. By including these solid particles (B), the cooling performance of the lubricating oil composition can be improved. Examples of 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 disilicate (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. Furthermore, the solid particles (B) may be a mixture of those listed above, or a thermally stable carbonate or sulfate. 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 individually or in combination of two or more types. 【0030】 The average primary particle diameter of the solid particles (B) used in one aspect of the present invention is 500 nm or less. However, 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, and particularly preferably 100 nm or less. It 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 for example, it may be 1 nm or more, 3 nm or more, or 5 nm or more. In this specification, the average primary particle diameter of solid particles (B) refers to a value obtained by calculating the average of the equivalent circular diameters of 100 or more randomly selected primary particles using a scanning electron microscope (SEM). Furthermore, solid particles (B) may or may not form secondary particles. 【0031】 The solid particles (B) used in one aspect 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 further improved, and a lubricating oil composition with high cooling performance can be obtained. Examples of surface treatment agents include silane coupling agents and silicone oils. 【0032】 Examples of silane coupling agents 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 Examples include sisilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, tris-(trimethoxysilylpropyl)isocyanurate, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-isocyanatetopropyltriethoxysilane, and 3-trimethoxysilylpropyl succinic 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, methacrylic-modified polysiloxane, and alkyl-modified polysiloxane. 【0034】 The solid particles (B) used in one aspect of the present invention may be porous, having pores on their surface, or non-porous, not having pores. From the viewpoint of providing 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 aspect of the present invention. 【0035】 In a lubricating oil composition according to one embodiment of the present invention, the content of solid particles (B) is 0.1 to 30% by mass based on the total amount (100% by mass) of the lubricating oil composition, but from the viewpoint of obtaining a lubricating oil composition with high cooling properties, it is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, even more preferably 3.0% by mass or more, even more preferably 5.0% by mass or more, and particularly preferably 10% by mass or more, and from the viewpoint of improving the dispersibility of solid particles (B), it is preferably 25% by mass or less, more preferably 20% by mass or less, even more preferably 18% by mass or less, and particularly preferably 15% by mass or less. Note that the content of solid particles (B) refers to the content on a solid content basis. Furthermore, if surface-treated solid particles are used, the amount of the surface treatment agent is also included in the content of solid particles (B). 【0036】 <Dispersant (C)> A lubricating oil composition according to one aspect of the present invention contains a dispersant (C). By including the dispersant (C), solid particles (B) can be uniformly dispersed in the lubricating oil composition, resulting in a lubricating oil composition with high cooling performance. As the dispersant (C), for example, ashless dispersants such as succinimide-based dispersants, vinylpyrrolidone (VP) / hexadecene copolymer, benzylamines, boron-containing benzylamines, succinic acid esters, and monovalent or divalent carboxylic acid amides represented by fatty acids or succinic acid can be used. Among these, succinimide-based dispersants or VP / hexadecene copolymer are preferred. Furthermore, the succinimide-based dispersant is preferably alkenyl succinimide, and may also be a modified alkenyl succinimide obtained by reacting with one or more selected from boron compounds, alcohols, aldehydes, ketones, alkylphenols, cyclic carbonates, epoxy compounds, and organic acids. In one embodiment of the present invention, these dispersants may be used individually or in combination of two or more. 【0037】 In a lubricating oil composition according to one embodiment of the present invention, the content of the dispersant (C) is 0.1 to 20% by mass based on the total amount (100% by mass) of the lubricating oil composition, but from the viewpoint of improving the dispersibility of solid particles, it is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, even more preferably 1.5% by mass or more, and particularly preferably 2.0% by mass or more, and from the viewpoint of keeping the viscosity of the lubricating oil composition low, it is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 12% by mass or less, and even more preferably 10% by mass or less. Note that the content of dispersant (C) refers to the content on a solids basis. 【0038】 In a lubricating oil composition according to one aspect of the present invention, the content ratio of solid particles (B) to dispersant (C) [(B) / (C)] is 0.05 or more and less than 3 by mass ratio, but from the viewpoint of improving the dispersibility of solid particles (B), it is preferably 0.06 or more, more preferably 0.07 or more, even more preferably 0.08 or more, even more preferably 0.09 or more, and particularly preferably 0.1 or more. Furthermore, from the viewpoint of improving cooling performance and keeping the viscosity of the lubricating oil composition low, it is preferably 3 or less, more preferably 2.5 or less, even more preferably 2 or less, even more preferably 1.5 or less, and particularly preferably 1 or less. 【0039】 <Various additives> A lubricating oil composition according to one aspect of the present invention may contain various additives as needed, as long as they do not impair the effects of the present invention. Examples of such additives include viscosity index improvers, pour point depressants, antioxidants, metal-based detergents, wear inhibitors, rust inhibitors, defoamers, and extreme pressure additives. These lubricating oil additives may be used individually or in combination of two or more types. 【0040】 The content of each of these various additives can be adjusted as appropriate within a range that does not impair the effects of the present invention, but on a basis of the total amount (100% by mass) of the lubricating oil composition, the content of each additive is usually 0.001 to 15% by mass, preferably 0.005 to 10% by mass, and more preferably 0.01 to 5% by mass for each additive independently. 【0041】 Alternatively, a commercially available additive package containing multiple additives may be used as an additive. Furthermore, compounds having multiple functions as additives (for example, compounds having functions as a wear-resistant agent and an extreme pressure additive) may be used. Furthermore, these lubricating oil additives may be used individually or in combination of two or more types. 【0042】 [Viscosity index improver] A lubricating oil composition according to one embodiment of the present invention may further contain a viscosity index improver. The viscosity index improver may be used alone or in combination of two or more types. Examples of viscosity index improvers used in one aspect of the present invention include polymethacrylate, dispersed polymethacrylate, olefin copolymers (e.g., ethylene-propylene copolymer), dispersed olefin copolymer, styrene copolymer (e.g., styrene-diene copolymer, styrene-isoprene copolymer), and the like. 【0043】 [Pour point depressant] A lubricating oil composition according to one embodiment of the present invention may further contain a pour point depressant. The pour point depressant may be used alone or in combination of two or more types. Examples of pour point depressants used in one aspect 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】 [Antioxidant] A lubricating oil composition according to one embodiment of the present invention may further contain an antioxidant. The antioxidant may be used alone or in combination of two or more types. Examples of antioxidants used in one aspect 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 agent] A lubricating oil composition according to one aspect of the present invention may further contain a metal-based detergent. The metal-based detergent may be used alone or in combination of two or more types. Examples of metal-based detergents used in one aspect of the present invention include metal salts such as metal sulfonates, metal salicylates, and metal phenates. Furthermore, the metal atoms constituting the metal salt are preferably selected from alkali metals and alkaline earth metals, more preferably sodium, calcium, magnesium, or barium, and even more preferably calcium. 【0046】 [Abrasion-resistant agent] A lubricating oil composition according to one embodiment of the present invention may further contain an anti-wear agent. The anti-wear agent may be used alone or in combination of two or more types. Examples of wear-resistant agents used in one aspect 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 phosphite esters, phosphate esters, phosphonic acid esters, and their amine salts or metal salts; and sulfur and phosphorus-containing wear-resistant agents such as thiophosphite esters, thiophosphate esters, thiophosphonic acid esters, and their amine salts or metal salts. 【0047】 [Rust inhibitor] A lubricating oil composition according to one aspect of the present invention may further contain a rust inhibitor. The rust inhibitor may be used alone or in combination of two or more types. Examples of rust inhibitors used in one aspect of the present invention include fatty acids, alkenyl succinate half esters, fatty acid soaps, alkyl sulfonates, polyhydric alcohol fatty acid esters, fatty acid amines, oxidized paraffins, alkyl polyoxyethylene ethers, and the like. 【0048】 [Antifoaming agent] A lubricating oil composition according to one embodiment of the present invention may further contain an antifoaming agent. The antifoaming agent may be used alone or in combination of two or more types. Examples of defoaming agents used in one aspect of the present invention include alkyl silicone-based defoaming agents, fluorosilicone-based defoaming agents, and fluoroalkyl ether-based defoaming agents. 【0049】 [Extreme pressure additives] A lubricating oil composition according to one embodiment of the present invention may further contain extreme pressure additives. The extreme pressure additives may be used alone or in combination of two or more types. Examples of extreme pressure additives used in one aspect of the present invention include chlorine-based extreme pressure additives such as chlorinated paraffin, chlorinated fatty acids, and chlorinated fatty oils; sulfur-based extreme pressure additives such as sulfurized olefins, sulfurized lard, alkyl polysulfides, and sulfurized fatty acids; and phosphorus-based extreme pressure additives such as phosphate esters, phosphite esters, thiophosphate esters, and their salts, phosphine-based additives, and tricresyl phosphate. 【0050】 <Method for producing a lubricating oil composition> A method for producing a lubricating oil composition according to one aspect 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. Furthermore, a 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 needed, in addition to the components (A) to (C) described above. The order in which each component is blended can be set as appropriate. 【0051】 [Properties of the lubricating oil composition] The kinematic viscosity of a lubricating oil composition according to one embodiment of the present invention at 100°C is preferably 0.8 mm. 2 / s or more, more preferably 1.0 mm 2 / s or more, more preferably 1.2 mm 2 The value is 1 / s or more, and preferably 4.0 mm 2 / s or less, more preferably 3.5 mm 2 / s or less, more preferably 3.0 mm 2 It is less than or equal to / s. 【0052】 The volume resistivity of a lubricating oil composition according to one embodiment of the present invention is preferably 1.0 × 10⁻⁶. 8 Ω·m or greater, more preferably 1.3 × 10 8 Ω·m or greater, more preferably 1.5 × 10 8 Ω·m or greater, more preferably 2.0 × 10 8Ω·m or greater, particularly preferably 2.1 × 10⁻⁶ 8 It is greater than or equal to Ω·m. 【0053】 The cooling performance of a lubricating oil composition according to one embodiment of the present invention is preferably 20.0°C / sec or higher, more preferably 22.0°C / sec or higher, even more preferably 23.0°C / sec or higher, and particularly preferably 25.0°C / sec or higher. In this specification, cooling performance refers to the maximum cooling rate (°C / sec) for 12 seconds from the start of immersion when a silver rod heated to 200°C is immersed in oil controlled to 30°C, in accordance with JIS K2242. 【0054】 [Uses of lubricating oil compositions] 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. Examples of electrical equipment include motors, batteries, inverters, and engines. Therefore, the present invention also provides the cooling device described in [I] below, and a method for using the lubricating oil composition described in [II] below. [I] A cooling device for cooling electrical equipment, which is filled with a lubricating oil composition according to one embodiment of the present invention described above. [II] A method of using a lubricating oil composition according to one aspect of the present invention described above, for the cooling of electrical equipment. [Examples] 【0055】 Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited in any way by these examples. The various physical properties of each component used in the examples, comparative examples, and reference examples, and of the obtained lubricating oil compositions, were measured in accordance with the following methods. 【0056】 <Kinematic viscosity, viscosity index> Measurements and calculations are performed in accordance with JIS K2283:2000. <Cooling property> In accordance with JIS K2242, the maximum cooling rate (°C / sec) was measured for 12 seconds from the start of immersion when a silver rod heated to 200°C was immersed in oil controlled at 30°C. <Volume resistivity> Measurements were taken in accordance with JIS C2101, under conditions of a measurement temperature of 80°C and an applied voltage of 250V. 【0057】 Examples 1-5, Comparative Examples 1-3 Components (A) to (C) shown in Table 1 were added and mixed in the amounts shown in Table 1, and the mixture was stirred at 20,000 rpm for 5 minutes using a homogenizer to prepare each lubricating oil composition. The prepared lubricating oil compositions are substantially water-free. 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 Mineral oil classified as Group II of the API base oil category, with viscosity index = 103, and volume resistivity = 18 × 10⁻⁶ / s, viscosity index = 103. 12 Ω·m. <Solid particles (B)> • SiO2: Silica particles with an average primary particle diameter of 10 nm, surface-treated with silicone oil. <Dispersant (C)> • Succinimide (non-boron-modified alkenyl succinic bisimide, nitrogen atom content = 1.80% by mass) Vinylpyrrolidone (VP) / Hexadecene copolymer 【0059】 The lubricating oil compositions prepared in the examples and comparative examples were measured and calculated according to the measurement method described above. These results are shown in Table 1. In Table 1, "dispersibility" was evaluated by visually checking for the presence or absence of sediment after each prepared sample was left to stand for one week; samples without sediment were rated "A," and samples with sediment were rated "F." Furthermore, the kinematic viscosity at 40°C of the lubricating oil compositions of the examples, measured and calculated according to the measurement method described above, was 20 mmHg. 2 The viscosity index is less than or equal to / s and is 70 or higher. 【0060】 [Table 1] 【0061】 Table 1 shows that the lubricating oil compositions of Examples 1 to 5, which contain a base oil (A) and have content levels of solid particles (B) and dispersant (C) within a predetermined range, exhibited superior cooling and insulating properties compared to Comparative Examples 1 to 3, and also showed good dispersibility of solid particles (B).

Claims

[Claim 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 solid particles (B) is 0.1 to 30% by mass on a basis of the total amount of the lubricating oil composition, and the content of dispersant (C) is 0.1 to 20% by mass on a basis of the total amount of the lubricating oil composition. The kinematic viscosity of base oil (A) at 40°C is 9.0 mm² / s or less. A lubricating oil composition in which the solid particles (B) are silicon dioxide (SiO₂) particles surface-treated with a silane coupling agent or silicone oil. [Claim 2] The lubricating oil composition according to claim 1, wherein the content ratio of solid particles (B) to dispersant (C) [(B) / (C)] is 0.05 or more and less than 3 by mass ratio. [Claim 3] The lubricating oil composition according to claim 1, wherein the average primary particle diameter of the solid particles (B) is 100 nm or less. [Claim 4] The lubricating oil composition according to claim 1, wherein the base oil (A) comprises at least mineral oil (A1). [Claim 5] The lubricating oil composition according to claim 1, wherein the volume resistivity of the base oil (A) is 8.0 × 10¹⁰ Ω·m or more. [Claim 6] A lubricating oil composition according to claim 1, which is substantially water-free. [Claim 7] The lubricating oil composition according to claim 1, wherein the kinematic viscosity of the lubricating oil composition at 40°C is 20 mm² / s or less. [Claim 8] The lubricating oil composition according to claim 1, wherein the volume resistivity of the lubricating oil composition is 1.0 × 10⁸ Ω·m or more. [Claim 9] A lubricating oil composition according to claim 1, used for cooling electrical equipment. [Claim 10] The lubricating oil composition according to claim 9, wherein the electrical equipment is a motor, a battery, an inverter, and an engine. [Claim 11] A cooling device for cooling electrical equipment, comprising a lubricating oil composition according to any one of claims 1 to 10. [Claim 12] A method of using a lubricating oil composition, wherein the lubricating oil composition according to any one of claims 1 to 10 is applied to the cooling of electrical equipment. [Claim 13] A method for producing a lubricating oil composition according to any one of claims 1 to 10, comprising the step of stirring at 10,000 rpm or more.

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