Lubricating oil composition

Abstract

To develop a lubricating oil composition having an improved flash point.SOLUTION: The lubricating oil composition comprises a base oil (A), which includes a base oil (A1) and a base oil (A2) having a lower kinematic viscosity at 100°C than the base oil (A1), a silicone-based compound (B), and an antioxidant (C).SELECTED DRAWING: None

Description

[Technical Field]

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

[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 (for example, Patent Document 1). However, since lubricating oil compositions are flammable, a high flash point is desirable from the viewpoint of safety. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-055627 Summary of the Invention [Problem to be solved by the invention]

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

[0006] As a result of extensive research, the present inventors have discovered that the above-mentioned problems can be solved by using two types of 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 have 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-based compound (B); and an antioxidant (C). [Effects of the Invention]

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

[0008] Regarding the numerical ranges described herein, the upper and lower limits can be combined in any combination. 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. In addition, as a numerical range described in this specification, for example, "60 to 100" means a range of "60 or more (60 or more) to 100 or less (100 or less)." Furthermore, in defining the upper and lower limits described in this specification, the numerical range from the lower limit to the upper limit can be defined by appropriately selecting from the respective options and combining them arbitrarily. In addition, the various features described as preferred embodiments in this specification can be combined in multiple ways.

[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)") comprising 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)"). In general, it is known that the lower the kinematic viscosity at 100°C of a lubricating oil composition, the better the cooling properties, but lubricating oil compositions with low kinematic viscosity at 100°C also tend to have a low flash point. However, in the present invention, by using a base oil (A1) and a base oil (A2) having different kinematic viscosities at 100°C in combination, 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 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 (especially 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 consist of 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 contains substantially no components other than the base oil (A), the silicone compound (B), and the antioxidant (C). As used herein, "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] Furthermore, 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 component (A), component (B), and component (C), and the total content of component (A), component (B), and component (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. The total content of component (A), component (B), and component (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), base oil (A1) and base oil (A2) having a kinematic viscosity at 100° C. lower than that of base oil (A1). The combination of base oil (A1) and base oil (A2) may be a combination of mineral oils, a combination of synthetic oils, or a combination of mineral oil and synthetic oil.

[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 processes 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, their homopolymers, and α-olefin copolymers (e.g., 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 feedstock. These synthetic oils may also 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, 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 may be used.

[0018] In one embodiment of the present invention, the content ratio of the base oil (A1) to the 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 or less from the viewpoint of improving the flash point of the lubricating oil composition. 2 / s or 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 the cooling performance, it is preferably 15 mm 2 / s or less, 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 mmHg or less from the viewpoint of improving the flash point of the lubricating oil composition. 2 / s or 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 the cooling performance, it is preferably 6.0 mm 2 / s or less, 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, the viscosity index of the base oil (A1) and the base oil (A2) is preferably 80 or more, more preferably 90 or more, even more preferably 100 or more, and still more preferably 110 or more, from the viewpoint of suppressing viscosity changes due to temperature changes and improving cooling properties. 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 compound (B) is one or more silicone compounds selected from the group consisting of alkylsilicone compounds (B1) and fluorosilicone compounds (B2).

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

[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, and more preferably a methyl group. a is preferably an integer of 200 to 1,500.

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

[0029] The dimethylpolysiloxane (b1) (b=0) and fluorine-modified dimethylpolysiloxane (b2) (b≧1) represented by the general formula (1) above may be obtained from commercially available silicone oils with the desired polymerization degree and used, 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 amine-based antioxidants (C1) and phenol-based antioxidants (C2).

[0033] Specific examples of the amine-based antioxidant (C1) include alkylated diphenylamine, phenylnaphthylamine, and alkylated phenylnaphthylamine. Specific examples of the phenolic 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, and n-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate.

[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% by mass or more, more preferably 0.30% by mass or more, and even more preferably 0.50% by mass or more, based on the total amount (100% by mass) of the lubricating oil composition; and the upper limit is not particularly limited, but may be, for example, 5.0% by mass or less, 4.0% by mass or less, 3.0% by mass or less, 2.0% by mass or less, or 1.0% by mass or less.

[0035] <Various additives> The lubricating oil composition of one embodiment of the present invention may contain various additives as needed, provided that the effects of the present invention are not impaired. Examples of the various additives include viscosity index improvers, pour point depressants, metallic detergents, ashless dispersants, antiwear 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 depressants] 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 detergents] Examples of metal detergents include metal salts such as metal sulfonates, metal salicylates, and metal phenates. The metal atoms constituting the metal salts include metal atoms selected from alkali metals and alkaline earth metals. From the viewpoint of providing a lubricating oil composition that can be suitably used for cooling server equipment, the content of the metal-based detergent 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.

[0040] [Ashless dispersant] Examples of ashless dispersants include alkenyl succinimides; modified alkenyl succinimides 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] [Surfactants] Examples of surfactants include anionic surfactants such as castor oil sulfate ester salts and petroleum sulfonates; cationic surfactants such as quaternary ammonium salts and imidazolines; polyalkylene glycol-based nonionic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, and polyoxyethylene alkyl naphthyl ether; polyoxyalkylene polyglycols and their dicarboxylic acid esters; and alkylene oxide adducts of alkylphenol-formaldehyde polycondensates. From the viewpoint of providing a lubricating oil composition that can be suitably used for cooling server equipment, the content of the surfactant 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 providing a lubricating oil composition that can be suitably used for cooling server equipment. Specifically, from the viewpoint of providing a lubricating oil composition that can be suitably used for cooling server equipment, the content of the sulfur 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. Furthermore, from the viewpoint of providing 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. Furthermore, from the viewpoint of providing 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, 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, 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 mmHg or less. 2 / s or more, preferably 28.0 mm 2 / s or more, and more preferably 29.0 mm 2 / s or more, and preferably 34.0 mm 2 / s or less, 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 at least 98%, more preferably at least 99%, and even more preferably 100%. If the visible light transmittance is above the above 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 the following cooling device [I] and the following method for using the lubricating oil composition [II]. [I] A cooling device filled with the lubricating oil composition according to one embodiment of the present invention. [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 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] Kinematic viscosity at 100°C is 4.0 to 10mm 2 The lubricating oil composition according to [1] or [2], wherein the total amount of the lubricating oil is 1000 mg / s. [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 the base oil (A1) to the base oil (A2) [(A1) / (A2)] is 90 / 10 to 10 / 90 in mass ratio. [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 2The lubricating oil composition according to any one of [1] to [5], wherein the lubricating oil composition has a viscosity of less than 1000 s. / s. [7] The lubricating oil composition according to any one of [1] to [7], 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 [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 [1] to [8].

[10] A method for using the lubricating oil composition according to any one of [1] to [8], which comprises applying the lubricating oil composition to cooling server equipment. [Example]

[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 Measurements and calculations were made in accordance with JIS K2283:2000. (2)Visible light transmittance The 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 The flash point was measured using the COC method in accordance with JIS K2265-4. Products with a flash point of 250°C or higher were judged to pass.

[0059] Examples 1 to 4, Comparative Examples 1 to 5 Each lubricating oil composition was prepared 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 composition are as follows:

[0060] <Component (A): Base oil> ·Base oil (1): 100N mineral oil (A2) (40℃ kinematic viscosity: 18.4mm 2 / s, 100℃ kinematic viscosity: 4.1mm 2 / s, flash point 222℃) and 220N mineral oil (A1) (40℃ kinematic viscosity 43.8mm 2 / s, 100℃ kinematic viscosity: 7.6mm 2 / s, flash point 262℃) and a mixed base oil in a ratio of 40:60 (the properties of the mixed base oil are kinematic viscosity at 40℃ of 30.5mm 2 / s, 100℃ kinematic viscosity 5.9mm 2 / s, flash point is 244°C). ·Base oil (2): 100N mineral oil (A2) (40℃ kinematic viscosity: 18.4mm 2 / s, 100℃ kinematic viscosity: 4.1mm 2 / s, flash point 222℃) and 220N mineral oil (A1) (40℃ kinematic viscosity 43.8mm 2 / s, 100℃ kinematic viscosity: 7.6mm 2 / s, flash point 262℃) and a mixed base oil in a ratio of 44:56 (the properties of the mixed base oil are kinematic viscosity at 40℃ of 29.8mm 2 / s, 100℃ kinematic viscosity is 5.8mm 2 / s, flash point is 244°C). Base oil (3): 40℃ kinematic viscosity 35.2mm 2 / s, 100℃ kinematic viscosity is 6.4mm 2 / s, mineral oil with a flash point of 232°C. <Component (B): Silicone-based compound (antifoaming agent)> Dimethyl silicone (a 100-fold dilution of dimethylpolysiloxane in the above general formula (1), where b = 0, R = methyl group, and a = an integer of 100 to 2000). <Component (C): Antioxidant> Phenolic antioxidants

[0061] [Table 1]

[0062] As shown in Table 1, the lubricating oil compositions of Examples 1 to 4 all had flash points of 250°C or higher, satisfying the pass criteria. In particular, the lubricating oil compositions of Examples 1 to 3 had a visible light transmittance of 100% and showed good reduction in oxidative degradation. On the other hand, the lubricating oil compositions of Comparative Examples 1 to 5 had flash points of 250° C. or less and did not 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. 2. The lubricating oil composition of claim 1, having a flash point of 250°C or higher.

3. Kinematic viscosity at 100°C: 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 the base oil (A1) to the base oil (A2) [(A1) / (A2)] is 90 / 10 to 10 / 90 in mass ratio.

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 7, 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, which comprises applying the lubricating oil composition to cooling server equipment.

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