Lubricating oil composition

Abstract

There has been a demand for the development of a lubricating oil composition having an improved flash point.　This lubricating oil composition comprises: base oils (A) including a base oil (A1) and a base oil (A2) having a kinematic viscosity lower than that of the base oil (A1) at 100°C; a silicone-based compound (B); and an antioxidant (C).

Description

lubricating oil composition

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

[0002] In recent years, the increased heat generated by servers due to their high performance has led to a demand for improved cooling efficiency. Known methods for cooling servers include air conditioning to cool the entire server room, cooling with cooling water flowing through pipes connected to the servers, and immersion cooling, which involves immersing equipment such as servers in a refrigerant and cooling and circulating the refrigerant. Among these, immersion cooling, which has high cooling efficiency, has attracted attention.

[0003] Refrigerants used in immersion cooling are required to have cooling properties and insulating properties. Lubricating oil compositions are suitable as refrigerants due to their high insulating properties, and are also used to cool automobile motors and the like (see, for example, Patent Document 1). However, since lubricating oil compositions are flammable, a high flash point is desirable from the standpoint of safety.

[0004] Japanese Patent Application Laid-Open No. 2023-055627

[0005] Under these circumstances, there has been a demand for the development of lubricating oil compositions with improved flash points.

[0006] As a result of extensive research, the present inventors discovered that the above-mentioned problems could be solved by using two base oils with different kinematic viscosities at 100°C (hereinafter also referred to as "100°C kinematic viscosity") in combination with a silicone compound and an antioxidant, and completed the present invention. The present invention provides the following lubricating oil composition: [1] A lubricating oil composition comprising a base oil (A) containing a base oil (A1) and a base oil (A2) having a kinematic viscosity at 100°C lower than that of the base oil (A1), a silicone compound (B), and an antioxidant (C).

[0007] A preferred embodiment of the present invention provides a lubricating oil composition having an improved flash point, reduced oxidative degradation, and a low kinematic viscosity at 100°C while having a high flash point.

[0008] Regarding the numerical ranges described herein, the upper and lower limits can be arbitrarily combined. For example, when a 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 herein. Furthermore, when a 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 herein. Furthermore, as a numerical range described herein, for example, "60 to 100" means a range of "60 or more (greater than 60) and 100 or less (less than 100)." Furthermore, when specifying the upper and lower limits described herein, the numerical range from the lower limit to the upper limit can be specified by appropriately selecting from the respective options and combining them arbitrarily. In addition, multiple combinations of the various requirements described as preferred aspects of the present specification can be used.

[0009] [Constitution of Lubricating Oil Composition] The lubricating oil composition of the present invention comprises a base oil (A) (hereinafter also referred to as "component (A)") containing a base oil (A1) and a base oil (A2) having a kinematic viscosity at 100°C lower than that of the base oil (A1), a silicone-based compound (B) (hereinafter also referred to as "component (B)"), and an antioxidant (C) (hereinafter also referred to as "component (C)"). Generally, the lower the kinematic viscosity at 100°C of a lubricating oil composition, the better the cooling properties. However, it is known that lubricating oil compositions with low kinematic viscosity at 100°C also tend to have low flash points. However, in the present invention, by using a combination of base oils (A1) and (A2) with different kinematic viscosities at 100°C, the 100°C kinematic viscosity of the lubricating oil composition can be maintained low, while the flash point of the lubricating oil composition can be significantly improved compared to when a silicone-based compound and an antioxidant are added to a lubricating oil composition containing a single base oil. Therefore, the lubricating oil composition of one embodiment of the present invention is particularly suitable for cooling applications (particularly for cooling server equipment).

[0010] In one embodiment of the lubricating oil composition of the present invention, the content of additives other than components (A), (B), and (C) may be limited in order to provide a lubricating oil composition suitable for cooling server equipment. That is, the lubricating oil composition of one embodiment of the present invention may comprise a base oil (A) containing a base oil (A1) and a base oil (A2) having a kinematic viscosity at 100°C lower than that of the base oil (A1), a silicone compound (B), and an antioxidant (C). The lubricating oil composition of this embodiment is substantially free of components other than the base oil (A), the silicone compound (B), and the antioxidant (C). In this specification, "substantially free" means that the content of a certain component is less than 0.5 mass%, less than 0.1 mass%, or less than 0.01 mass%, based on the total amount (100 mass%) of the lubricating oil composition.

[0011] In addition, from the viewpoint of making the lubricating oil composition suitable for cooling server equipment, it is preferable that the lubricating oil composition of one embodiment of the present invention has a limited content of additives other than components (A), (B), and (C), and the total content of components (A), (B), and (C) is preferably 97.00 mass% or more, 99.00 mass% or more, 99.50 mass% or more, or 100 mass% based on the total amount (100 mass%) of the lubricating oil composition. Furthermore, the total content of components (A), (B), and (C) may be 99.99 mass% or less, 99.90 mass% or less, or 99.80 mass% or less based on the total amount (100 mass%) of the lubricating oil composition.

[0012] The various components that may be contained in the lubricating oil composition of one embodiment of the present invention will be described below.

[0013] <Component (A): Base Oil> The lubricating oil composition of the present invention uses, as base oil (A), a base oil (A1) and a base oil (A2) having a kinematic viscosity at 100° C. lower than that of base oil (A1). Examples of combinations of base oil (A1) and base oil (A2) include combinations of mineral oils, combinations of synthetic oils, and combinations of mineral oils and synthetic oils.

[0014] 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 treatments such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining.

[0015] 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; polyalkylene glycols; ether oils such as polyphenyl ethers; ester oils such as polyol esters, dibasic acid esters, and monoesters; alkylbenzenes; alkylnaphthalenes; synthetic oils (GTL) obtained by isomerizing wax produced from natural gas by the Fischer-Tropsch process (GTL wax (Gas To Liquids WAX)), and synthetic oils (Ethylene To Liquid (ETL)) obtained by oligomerizing olefins produced using gas as a raw material. These synthetic oils may be produced from renewable resources.

[0016] Among these, the base oil (A1) and the base oil (A2) used in one embodiment of the present invention preferably contain 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.

[0017] In one embodiment of the present invention, the difference in kinematic viscosity at 100°C between the base oil (A1) and the base oil (A2) is preferably 2.0 mmHg from the viewpoint of improving the flash point of the lubricating oil composition. ２ / s or more, more preferably 2.5 mm ２ / s or more, more preferably 3.0 mm ２ / s or more, and 15 mm ２ / s or less, 10mm ２ / s or less, 8.0mm ２ / s or less, 6.0mm ２ / s or less.

[0018] In one embodiment of the present invention, the content ratio of base oil (A1) to base oil (A2) [(A1) / (A2)] may be, in mass ratio, 90 / 10 to 10 / 90, 80 / 20 to 20 / 80, 70 / 30 to 30 / 70, or 65 / 35 to 35 / 65, from the viewpoint of improving the flash point of the lubricating oil composition.

[0019] In one embodiment of the present invention, the kinematic viscosity at 100°C of the base oil (A1) is preferably 6.0 mmHg from the viewpoint of improving the flash point of the lubricating oil composition. ２ / s or more, more preferably 6.5 mm ２ / s or more, more preferably 7.0 mm ２ / s or more, particularly preferably 7.5 mm ２ / s or more, and from the viewpoint of improving cooling performance, it is preferably 15 mm ２ / s or less, more preferably 12 mm ２ / s or less, more preferably 10 mm ２ / s or less, particularly preferably 8.0 mm ２ / s or less.

[0020] In one embodiment of the present invention, the kinematic viscosity at 100°C of the base oil (A2) is preferably 1.0 mm ２ / s or more, more preferably 2.0 mm ２ / s or more, more preferably 3.0 mm ２ / s or more, particularly preferably 3.5 mm ２ / s or more, and from the viewpoint of improving cooling performance, it is preferably 6.0 mm ２ / s or less, more preferably 5.5 mm ２ / s or less, more preferably 5.0 mm ２ / s or less, particularly preferably 4.5 mm ２ / s or less.

[0021] In one embodiment of the present invention, the flash point of the base oil (A1) may be 230°C or higher, 240°C or higher, 250°C or higher, or 260°C or higher, and may be 290°C or lower, 285°C or lower, 280°C or lower, or 275°C or lower.

[0022] In one embodiment of the present invention, the flash point of the base oil (A2) may be 190°C or higher, 200°C or higher, 210°C or higher, or 220°C or higher, and may be 250°C or lower, 245°C or lower, 240°C or lower, or 235°C or lower.

[0023] In one embodiment of the present invention, from the viewpoint of suppressing viscosity changes due to temperature changes and improving cooling properties, the viscosity index of the base oil (A1) and the base oil (A2) is preferably at least 80, more preferably at least 90, even more preferably at least 100, and still more preferably at least 110. In this specification, the kinematic viscosity and viscosity index refer to values ​​measured or calculated in accordance with JIS K2283:2000.

[0024] In the lubricating oil composition of one embodiment of the present invention, the content of base oil (A) may be 94.00 mass % or more, 95.00 mass % or more, or 96.00 mass % or more, based on the total amount (100 mass %) of the lubricating oil composition, and may be 99.90 mass % or less, 99.70 mass % or less, or 99.50 mass % or less.

[0025] <Component (B): Silicone-Based Compound> The lubricating oil composition of the present invention contains a silicone-based compound (B). Generally, the silicone-based compound (B) functions as an antifoaming agent. In the present invention, the silicone-based compound (B) is an essential component for improving the flash point of the lubricating oil composition. In one embodiment of the present invention, the silicone-based compound (B) is one or more silicone-based compounds selected from the group consisting of alkylsilicone-based compounds (B1) and fluorosilicone-based compounds (B2).

[0026] Specific examples of such silicone-based compounds (B) include organopolysiloxanes (b) represented by the following general formula (1): The organopolysiloxanes (b) represented by the following general formula (1) may be dimethylpolysiloxanes (b1) and fluorine-modified dimethylpolysiloxanes (b2) in some cases.

[0027] In the above general formula (1), when b = 0, each R is independently a hydrogen atom, a methyl group, an ethyl group, or a phenyl group, and a is an integer of 100 to 2000. In this case, R is preferably a methyl group or an ethyl group, more preferably a methyl group. a is preferably an integer of 200 to 1500.

[0028] In the above general formula (1), when b≧1, R is a methyl group, a is an integer from 0 to 500, b is an integer from 1 to 400, p is 1 or 2, and q is an integer from 0 to 10. In this case, a is preferably 0 or an integer from 50 to 300. b is preferably an integer from 20 to 200. q is preferably an integer from 0 to 5.

[0029] The dimethylpolysiloxane (b1) (b=0) and the fluorine-modified dimethylpolysiloxane (b2) (b≧1) represented by the general formula (1) above may be obtained from commercially available silicone oils and used to have the desired degree of polymerization, or may be synthesized by a known method.

[0030] The silicone compound (B) can be added directly to the lubricating oil composition and dissolved or dispersed using a homogenizer or the like. Alternatively, the silicone compound (B) may be dissolved in a solvent capable of dissolving the silicone compound (B) to prepare a concentrated solution in advance, and the concentrated solution may be added to the lubricating oil composition. Examples of solvents used to prepare the concentrated solution include kerosene, toluene, cyclohexanone, methyl isobutyl ketone (MIBK), etc., but are not particularly limited, and any solvent capable of dissolving the silicone compound (B) may be used.

[0031] In the lubricating oil composition of one embodiment of the present invention, the content of the silicone compound (B) including diluent oil is preferably 0.01 mass% or more, more preferably 0.03 mass% or more, and even more preferably 0.04 mass% or more, based on the total amount (100 mass%) of the lubricating oil composition, from the viewpoint of improving the flash point of the lubricating oil composition, and from the viewpoint of suppressing a decrease in transmittance due to oxidative degradation of the lubricating oil composition, it is preferably 0.4 mass% or less, more preferably 0.3 mass% or less, and even more preferably 0.1 mass% or less. If the blending amount of the silicone compound (B) exceeds 0.4 mass%, there is a risk that the lubricating oil composition will undergo oxidative degradation and the transmittance will decrease, even if a predetermined amount of antioxidant (C), described below, is blended.

[0032] <Component (C): Antioxidant> The lubricating oil composition of the present invention contains an antioxidant (C). The antioxidant (C) is also an essential component for improving the flash point of the lubricating oil composition. In addition, the inclusion of the antioxidant (C) can also reduce oxidative degradation of the lubricating oil composition. The antioxidant (C) used in one embodiment of the present invention may be one or more selected from an amine-based antioxidant (C1) and a phenol-based antioxidant (C2).

[0033] Specific examples of the amine-based antioxidant (C1) include alkylated diphenylamine, phenylnaphthylamine, alkylated phenylnaphthylamine, etc. Specific examples of the phenol-based antioxidant (C2) include 2,6-di-t-butylphenol, 4,4'-methylenebis(2,6-di-t-butylphenol), isooctyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, n-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, etc.

[0034] In the lubricating oil composition of one embodiment of the present invention, the content of the antioxidant (C) is, from the viewpoint of improving the flash point of the lubricating oil composition, preferably 0.10 mass % or more, more preferably 0.30 mass % or more, and even more preferably 0.50 mass % or more, based on the total amount (100 mass %) of the lubricating oil composition; and the upper limit is not particularly limited, but may be, for example, 5.0 mass % or less, 4.0 mass % or less, 3.0 mass % or less, 2.0 mass % or less, or 1.0 mass % or less.

[0035] <Various Additives> The lubricating oil composition of one embodiment of the present invention may contain various additives as needed, as long as the effects of the present invention are not impaired. Examples of various additives include viscosity index improvers, pour point depressants, metal detergents, ashless dispersants, anti-wear agents, rust inhibitors, extreme pressure additives, surfactants, etc. When these lubricating oil additives are used, they may be used alone or in combination of two or more.

[0036] When various additives are used, the content of each can be adjusted as appropriate within a range that does not impair the effects of the present invention, but may be independently 0.001 to 15 mass %, 0.005 to 10 mass %, or 0.01 to 5 mass % for each additive, based on the total amount (100 mass %) of the lubricating oil composition.

[0037] [Viscosity Index Improver] Examples of viscosity index improvers include polymethacrylate, disperse polymethacrylate, olefin copolymers (e.g., ethylene-propylene copolymers), disperse olefin copolymers, and styrene copolymers (e.g., styrene-diene copolymers, styrene-isoprene copolymers).

[0038] [Pour Point Depressant] Examples of pour point depressants include ethylene-vinyl acetate copolymers, condensates of chlorinated paraffin and naphthalene, condensates of chlorinated paraffin and phenol, polymethacrylates, and polyalkylstyrenes.

[0039] [Metallic detergent] Metallic detergent can be metal salt such as metal sulfonate, metal salicylate and metal phenate.In addition, the metal atom constituting this metal salt can be selected from alkali metal and alkaline earth metal.In order to make the lubricating oil composition suitable for use in cooling server equipment, the content of metallic detergent can be less than 1.0 mass%, less than 0.5 mass%, less than 0.1 mass%, less than 0.01 mass%, less than 0.001 mass%, less than 0.0001 mass%, or less than 0.00001 mass% based on the total amount (100 mass%) of the lubricating oil composition.

[0040] [Ashless Dispersant] Examples of the ashless dispersant include alkenyl succinimide; modified alkenyl succinimide reacted with one or more selected from boron compounds, alcohols, aldehydes, ketones, alkylphenols, cyclic carbonates, epoxy compounds, and organic acids; and the like.

[0041] [Anti-wear Agent] Examples of anti-wear agents include sulfur-containing compounds such as zinc dialkyldithiophosphate (ZnDTP), zinc phosphate, zinc dithiocarbamate, disulfides, sulfurized olefins, sulfurized fats and oils, sulfurized esters, thiocarbonates, thiocarbamates, and polysulfides; phosphorus-containing compounds such as phosphites, phosphate esters, phosphonate esters, and amine salts or metal salts thereof; and sulfur- and phosphorus-containing anti-wear agents such as thiophosphites, thiophosphate esters, thiophosphonate esters, and amine salts or metal salts thereof.

[0042] [Rust Inhibitor] Examples of the rust inhibitor include fatty acids, alkenyl succinic acid half esters, fatty acid soaps, alkyl sulfonates, polyhydric alcohol fatty acid esters, fatty acid amines, oxidized paraffins, and alkyl polyoxyethylene ethers.

[0043] [Extreme Pressure Additives] Examples of extreme pressure additives include sulfur-containing compounds such as zinc dialkyldithiophosphate (ZnDTP), zinc phosphate, zinc dithiocarbamate, disulfides, sulfurized olefins, sulfurized fats and oils, sulfurized esters, thiocarbonates, thiocarbamates, and polysulfides; phosphorus-containing compounds such as phosphites, phosphate esters, phosphonate esters, and amine salts or metal salts thereof; and sulfur- and phosphorus-containing antiwear agents such as thiophosphites, thiophosphate esters, thiophosphonate esters, and amine salts or metal salts thereof.

[0044] [Surfactant] Examples of surfactants include anionic surfactants such as castor oil sulfate salts and petroleum sulfonates; cationic surfactants such as quaternary ammonium salts and imidazolines; polyalkylene glycol-based nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, and polyoxyethylene alkylnaphthyl ethers; polyoxyalkylene polyglycols and esters of dicarboxylic acids thereof; alkylene oxide adducts of alkylphenol-formaldehyde polycondensates; etc. From the viewpoint of providing a lubricating oil composition that can be suitably used for cooling server equipment, the surfactant content may be less than 1.0 mass%, less than 0.5 mass%, less than 0.1 mass%, less than 0.01 mass%, less than 0.001 mass%, less than 0.0001 mass%, or less than 0.00001 mass%, based on the total amount (100 mass%) of the lubricating oil composition.

[0045] [Other Compounds] In addition to the various additives described above, the lubricating oil composition of one embodiment of the present invention may have a limited content of sulfur atom-containing compounds, phosphorus atom-containing compounds, and / or metal atom-containing compounds, from the viewpoint of making the lubricating oil composition suitable for use in cooling server equipment. Specifically, from the viewpoint of making the lubricating oil composition suitable for use in cooling server equipment, the content of the sulfur atom-containing compounds may be less than 1.0 mass%, less than 0.5 mass%, less than 0.1 mass%, less than 0.01 mass%, less than 0.001 mass%, less than 0.0001 mass%, or less than 0.00001 mass%, based on the total amount (100 mass%) of the lubricating oil composition. In addition, from the viewpoint of obtaining a lubricating oil composition that can be suitably used for cooling server equipment, the content of the phosphorus atom-containing compound may be less than 1.0 mass%, less than 0.5 mass%, less than 0.1 mass%, less than 0.01 mass%, less than 0.001 mass%, less than 0.0001 mass%, or less than 0.00001 mass%, based on the total amount (100 mass%) of the lubricating oil composition. In addition, from the viewpoint of obtaining a lubricating oil composition that can be suitably used for cooling server equipment, the content of the metal atom-containing compound may be less than 1.0 mass%, less than 0.5 mass%, less than 0.1 mass%, less than 0.01 mass%, less than 0.001 mass%, less than 0.0001 mass%, or less than 0.00001 mass%, based on the total amount (100 mass%) of the lubricating oil composition.

[0046] Furthermore, in the lubricating oil composition of one embodiment of the present invention, the water content may be less than 1.0 mass%, less than 0.5 mass%, less than 0.1 mass%, less than 0.01 mass%, less than 0.001 mass%, less than 0.0001 mass%, or less than 0.00001 mass%, based on the total amount (100 mass%) of the lubricating oil composition, from the viewpoint of making the lubricating oil composition suitable for use in cooling server equipment.

[0047] [Method for Producing Lubricating Oil Composition] The method for producing the lubricating oil composition of one embodiment of the present invention is not particularly limited, and is preferably a method comprising the steps of blending a silicone compound (B), an antioxidant (C), and, if necessary, other various additives with a base oil (A). The order of blending the components can be determined as appropriate.

[0048] [Properties of Lubricating Oil Composition] The kinematic viscosity at 100°C of the lubricating oil composition of one embodiment of the present invention is preferably 4.0 mm ２ / s or more, more preferably 4.5 mm ２ / s or more, more preferably 5.0 mm ２ / s or more, and preferably 10 mm ２ / s or less, more preferably 8.0 mm ２ / s or less, more preferably 6.0 mm ２ / s or less.

[0049] The lubricating oil composition of one embodiment of the present invention preferably has a kinematic viscosity at 40°C of 27.0 mm ２ / s or more, more preferably 28.0 mm ２ / s or more, more preferably 29.0 mm ２ / s or more, and preferably 34.0 mm ２ / s or less, more preferably 33.0 mm ２ / s or less, more preferably 32.0 mm ２ / s or less.

[0050] The viscosity index of the lubricating oil composition of one embodiment of the present invention is preferably 110 or greater, more preferably 120 or greater, and even more preferably 130 or greater.

[0051] The flash point of the lubricating oil composition of one embodiment of the present invention is preferably 245°C or higher, more preferably 247°C or higher, and even more preferably 250°C or higher.

[0052] The lubricating oil composition of one embodiment of the present invention preferably has a visible light transmittance at 600 nm of 98% or more, more preferably 99% or more, and even more preferably 100%. If the visible light transmittance is above this range, it can be said that oxidative degradation of the lubricating oil composition is reduced.

[0053] [Uses of Lubricating Oil Composition] The lubricating oil composition of one embodiment of the present invention has excellent cooling properties and a significantly improved flash point. Furthermore, since the lubricating oil composition usually does not contain water, it also has high insulating properties. Therefore, the lubricating oil composition of one embodiment of the present invention can be suitably used for cooling server equipment. Therefore, the present invention also provides a cooling device as described below in [I] and a method of using the lubricating oil composition as described below in [II]. [I] A cooling device filled with the lubricating oil composition of one embodiment of the present invention described above. [II] A method of using the lubricating oil composition, in which the lubricating oil composition of one embodiment of the present invention described above is applied to cooling server equipment.

[0054] In the above cooling device and cooling method, the cooling method for the server equipment is immersion cooling, and the immersion cooling is of a single-phase type.

[0055] The server device is not particularly limited, and may be, for example, a device having a motherboard.

[0056] The present invention may include the following aspects. [1] A lubricating oil composition comprising a base oil (A) containing a base oil (A1) and a base oil (A2) having a kinematic viscosity at 100°C lower than that of the base oil (A1), a silicone compound (B), and an antioxidant (C). [2] The lubricating oil composition according to [1], which has a flash point of 250°C or higher. [3] A lubricating oil composition having a kinematic viscosity at 100°C of 4.0 to 10 mm ２ [4] The lubricating oil composition according to any one of [1] to [3], wherein the total content of components (A) to (C) is 97.00 mass% or more, based on the total amount of the lubricating oil composition. [5] The lubricating oil composition according to any one of [1] to [4], wherein the content ratio of base oil (A1) to base oil (A2) [(A1) / (A2)] is 90 / 10 to 10 / 90, in mass ratio. [6] The base oil (A1) has a kinematic viscosity at 100°C of 6.0 mm ２ / s or more 15mm ２ / s or less, and the kinematic viscosity of the base oil (A2) at 100 ° C. is 1.0 mm ２ / s or more 6.0mm ２The lubricating oil composition according to any one of [1] to [5], wherein the lubricating oil composition has a viscosity of less than 100% by mass / s. [7] The lubricating oil composition according to any one of [1] to [6], wherein the content of the silicone compound (B) is 0.01 to 0.4% by mass, based on the total amount (100% by mass) of the lubricating oil composition. [8] The lubricating oil composition according to any one of [1] to [7], which is used for cooling server equipment. [9] A server equipment cooling device filled with the lubricating oil composition according to any one of [1] to [8].

[10] A method for using the lubricating oil composition according to any one of [1] to [8], wherein the lubricating oil composition is applied to cooling server equipment.

[0057] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples. The physical properties of the components used in the examples and comparative examples and the resulting lubricating oil compositions were measured according to the following methods.

[0058] (1) Kinematic viscosity and viscosity index: Measured and calculated in accordance with JIS K2283:2000. (2) Visible light transmittance: Visible light transmittance at a wavelength of 600 nm was measured in accordance with JIS K0115. A transmittance of 97% or more was judged to be acceptable. (3) Flash point: Measured by the C.O.C. method in accordance with JIS K2265-4. A flash point of 250°C or more was judged to be acceptable.

[0059] Lubricating oil compositions were prepared for Examples 1 to 4 and Comparative Examples 1 to 5 by adding and mixing the various components shown in Table 1 in the amounts shown in Table 1. The amount of silicone compound in Table 1 is the amount including diluent oil. Details of each component used in preparing the lubricating oil compositions are as follows:

[0060] <Component (A): Base oil> - Base oil (1): 100N mineral oil (A2) (40°C kinematic viscosity: 18.4 mm ２ / s, 100℃ kinematic viscosity: 4.1mm ２ / s, flash point 222°C) and 220N mineral oil (A1) (kinematic viscosity at 40°C 43.8 mm ２ / s, 100℃ kinematic viscosity: 7.6mm ２ / s, flash point 262 ° C) and a mixed base oil (the properties of the mixed base oil are as follows: kinematic viscosity at 40 ° C is 30.5 mm ２ / s, 100°C kinematic viscosity is 5.9 mm ２ / s, flash point 244 ° C.) Base oil (2): 100N mineral oil (A2) (kinematic viscosity at 40 ° C.: 18.4 mm ２ / s, 100℃ kinematic viscosity: 4.1mm ２ / s, flash point 222°C) and 220N mineral oil (A1) (kinematic viscosity at 40°C 43.8 mm ２ / s, 100℃ kinematic viscosity: 7.6mm ２ / s, flash point 262 ° C) and a mixed base oil (properties of the mixed base oil are 40 ° C kinematic viscosity 29.8 mm ２ / s, 100°C kinematic viscosity is 5.8 mm ２ / s, flash point is 244 ° C.) Base oil (3): kinematic viscosity at 40 ° C is 35.2 mm ２ / s, 100°C kinematic viscosity is 6.4 mm ２ / s, mineral oil with a flash point of 232°C. <Component (B): Silicone-based compound (antifoaming agent)> Dimethyl silicone (a 100-fold diluted product of dimethylpolysiloxane in which, in the above general formula (1), b = 0, R = methyl group, and a = an integer of 100 to 2000.) <Component (C): Antioxidant> Phenol-based antioxidant

[0061]

[0062] As shown in Table 1, the lubricating oil compositions of Examples 1 to 4 all had flash points of 250°C or higher, meeting the pass criteria. In particular, the lubricating oil compositions of Examples 1 to 3 had a visible light transmittance of 100% and were excellent in reducing oxidative degradation. On the other hand, the lubricating oil compositions of Comparative Examples 1 to 5 had flash points of 250°C or lower, failing to meet the pass criteria.

Claims

1. A lubricating oil composition comprising a base oil (A) containing a base oil (A1) and a base oil (A2) having a kinematic viscosity at 100°C lower than that of the base oil (A1), a silicone compound (B), and an antioxidant (C).

2. The lubricating oil composition according to claim 1, which has a flash point of 250°C or higher.

3. Kinematic viscosity at 100°C is 4.0 to 10 mm ２ 3. The lubricating oil composition according to claim 1, wherein the total weight of the lubricating oil is 10 ...

4. The lubricating oil composition according to any one of claims 1 to 3, wherein the total content of components (A) to (C) is 97.00 mass% or more based on the total amount of the lubricating oil composition.

5. The lubricating oil composition according to any one of claims 1 to 4, wherein the content ratio of base oil (A1) to base oil (A2) [(A1) / (A2)] is 90 / 10 to 10 / 90 by mass.

6. The kinematic viscosity of the base oil (A1) at 100 ° C is 6.0 mm ２ / s or more 15mm ２ / s or less, and the kinematic viscosity of the base oil (A2) at 100 ° C. is 1.0 mm ２ / s or more 6.0mm ２ The lubricating oil composition according to any one of claims 1 to 5, wherein the viscosity is less than 1000 kJ / s.

7. The lubricating oil composition according to any one of claims 1 to 6, wherein the content of the silicone compound (B) is 0.01 to 0.4 mass % based on the total amount (100 mass %) of the lubricating oil composition.

8. The lubricating oil composition according to any one of claims 1 to 7, which is used for cooling server equipment.

9. A cooling device for server equipment, filled with the lubricating oil composition according to any one of claims 1 to 8.

10. A method for using the lubricating oil composition according to any one of claims 1 to 8 for cooling server equipment.

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