Cooling liquid for immersion liquid cooling system

Abstract

A cooling liquid for an immersion liquid cooling system, which is filled as a cooling liquid in an immersion liquid tank of the immersion liquid cooling system, and which contains a hydrocarbon oil and one or more antioxidants selected from the group consisting of amine antioxidants and phenolic antioxidants, the amount of the antioxidant being less than or equal to the amount of the hydrocarbon oil relative to the total amount of the cooling liquid for the immersion liquid cooling system, and the amount of the antioxidant being less than or equal to the amount of the phenolic antioxidants being less than or equal to the amount of the hydrocarbon oil. The hydrocarbon oil is contained in an amount of 50 mass% or more, and the coolant for an immersion cooling system has a 5% distillation temperature of 320 DEG C or more, a% CN of 30.0 or less, and a kinematic viscosity at 40 DEG C of 11.5 mm2 / s or more.

Description

Technical Field

[0001] The invention relates to a coolant for an immersion cooling system.

[0002] This application claims priority based on Japanese Patent Application No. 2022-113248 filed in Japan on July 14, 2022, and the contents are incorporated herein by reference. Background Art

[0003] As the amount of data sent and received increases dramatically, the load on supercomputers and data servers increases, and the heat generated by these electronic devices also increases. The mainstream cooling method for these electronic devices has been air cooling, but since air cooling has a limit to its cooling efficiency, the immersion type, which has a higher cooling efficiency, has attracted attention.

[0004] The basic structure of the immersion cooling system is shown in Figure 1 middle.

[0005] The immersion cooling system 10 includes an immersion tank 1, a heat exchanger 3, a pump 5, and a cooling device 7. The immersion tank 1 is filled with a coolant for the immersion cooling system.

[0006] The electronic device is cooled in the immersion tank 1. The immersion cooling system coolant heated by the exhaust heat of the electronic device is pumped up by the pump 5, and heat is exchanged with the cold water produced in the cooling device 7 by the heat exchanger 3. The immersion cooling system coolant cooled by the heat exchange is circulated again in the immersion tank 1.

[0007] By using the immersion cooling system 10 , a safe temperature can be constantly maintained even when the electronic device is continuously used under a high load condition.

[0008] Specifically, Patent Document 1 discloses a liquid immersion cooling system including (a) an electronic hardware device and (b) a liquid cooling medium.

[0009] The liquid cooling medium is disclosed to contain (i) a mixture of a synthetic ester and a saturated medium-chain triglyceride, or (ii) a polyalkylene glycol, wherein the synthetic ester has a viscosity of 28 to 38 cSt at 40° C. determined in accordance with ASTM D445, and when the liquid cooling medium contains the polyalkylene glycol, the polyalkylene glycol constitutes at least 70% by weight of the liquid cooling medium.

[0010] Prior art literature

[0011] Patent Literature

[0012] Patent Document 1: Japanese Patent No. 6282289 Summary of the invention

[0013] Problems to be solved by the invention

[0014] As a coolant for an immersion cooling system, the property of not affecting the immersed electronic device is also valued. Specifically, the property of not affecting the immersed electronic device is required to suppress swelling of the insulating material of the electronic device and elution of the metal of the electronic device.

[0015] The liquid coolant described in Patent Document 1 considers the balance between flash point and viscosity, but does not study the effect on the immersed electronic device. The ester contained in the liquid coolant of Patent Document 1 generates acid by hydrolysis, and the elution of metal from the electronic device may become a problem.

[0016] Furthermore, as a coolant for an immersion cooling system, high thermal stability is also required.

[0017] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a coolant for an immersion cooling system which has high thermal stability and further suppresses the influence on an electronic device immersed therein.

[0018] Means for solving problems

[0019] In order to solve the above-mentioned problems, the present invention adopts the following configuration.

[0020] [1] A coolant for an immersion cooling system, which is a coolant for an immersion cooling system filled in an immersion tank of an immersion cooling system, comprising a hydrocarbon oil and one or more antioxidants selected from the group consisting of an amine antioxidant and a phenolic antioxidant, wherein the hydrocarbon oil is contained in an amount of 50% by mass or more relative to the total amount of the coolant for an immersion cooling system, the 5% distillation temperature of the coolant for an immersion cooling system being 320° C. or higher, and the 5% distillation temperature of the coolant for an immersion cooling system being 320° C. or higher. N The kinematic viscosity at 40°C is 11.5 mm 2 / s or more.

[0021] [2] The coolant for an immersion cooling system according to [1], wherein the 95% distillation temperature is 430° C. or higher.

[0022] [3] The coolant for an immersion cooling system according to [1] or [2], wherein the content of the antioxidant is 0.01 mass % or more and 5 mass % or less relative to the total amount of the coolant for an immersion cooling system.

[0023] Effects of the Invention

[0024] According to the present invention, it is possible to provide a coolant for an immersion cooling system which has high thermal stability and further reduces the influence on an electronic device immersed therein. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1is a schematic diagram of the immersion cooling system. DETAILED DESCRIPTION

[0026] (Coolant for immersion cooling system)

[0027] The coolant for the immersion cooling system of the present embodiment is the coolant for the immersion cooling system which is filled as a coolant in the immersion tank of the immersion cooling system.

[0028] The liquid immersion cooling system of the present embodiment uses a coolant to cool electronic equipment.

[0029] Examples of the electronic device include a computer server, a server motherboard, a microprocessor, a capacitor, and other heat-dissipating electronic devices.

[0030] The coolant for the immersion cooling system of the present embodiment contains hydrocarbon oil and one or more antioxidants selected from the group consisting of amine antioxidants and phenolic antioxidants, and contains 50% by mass or more of the hydrocarbon oil relative to the total amount of the coolant for the immersion cooling system, and the 5% distillation temperature of the coolant for the immersion cooling system is 320° C. or higher, and the %C N The kinematic viscosity at 40°C is 11.5 mm 2 / s or more.

[0031] The kinematic viscosity of the coolant for the immersion cooling system of this embodiment at 40°C is 11.5 mm 2 / s or more, preferably 15.0 mm 2 / s or more, more preferably 20.0 mm 2 / s or more, more preferably 25.0 mm 2 / s or more.

[0032] In addition, the kinematic viscosity of the coolant for the immersion cooling system of the present embodiment at 40° C. is preferably 70.0 mm 2 / s or less, more preferably 60.0 mm 2 / s or less, more preferably 50.0 mm 2 / s or less.

[0033] The coolant for the immersion cooling system of this embodiment has a kinematic viscosity of 11.5 mm at 40°C. 2 / s or more, so the swelling of the insulating material of the electronic device can be suppressed. It is speculated that this is because high-viscosity components (such as compounds with long carbon chains) are less likely to be absorbed into resins such as insulating materials of electronic devices. If the kinematic viscosity of the coolant for the immersion cooling system of this embodiment at 40°C is above the above-mentioned preferred lower limit, the swelling of the insulating material of the electronic device can be further suppressed.

[0034] If the kinematic viscosity of the coolant for the immersion cooling system of the present embodiment at 40°C is below the above-mentioned preferred upper limit, the fluidity of the coolant for the immersion cooling system of the present embodiment is improved, and it becomes easy to circulate, thereby improving the cooling performance. In addition, the burden on the pump that delivers the coolant in the immersion cooling system can be further reduced.

[0035] For example, the kinematic viscosity of the coolant for the immersion cooling system of the present embodiment at 40° C. is preferably 11.5 mm 2 / s or more and 70.0mm 2 / s or less, more preferably 15.0 mm 2 / s or more and 60.0mm 2 / s or less, more preferably 20.0 mm 2 / s or more and 60.0mm 2 / s or less, particularly preferably 25.0 mm 2 / s or more and 50.0mm 2 / s or less.

[0036] The kinematic viscosity of the coolant for the immersion cooling system of the present embodiment at 80° C. is preferably 3.5 mm 2 / s or more and 30.0mm 2 / s or less, more preferably 4.5mm 2 / s or more and 27.5mm 2 / s or less, more preferably 6.0 mm 2 / s or more and 25.0mm 2 / s or less.

[0037] The kinematic viscosity of the coolant for the immersion cooling system of the present embodiment at 100° C. is preferably 2.5 mm 2 / s or more and 20.0mm 2 / s or less, more preferably 3.0 mm 2 / s or more and 17.5mm 2 / s or less, more preferably 4.0 mm 2 / s or more and 15.0mm 2 / s or less.

[0038] The kinematic viscosity at 40° C., 80° C., and 100° C. in this specification means the kinematic viscosity at 40° C., 80° C., and 100° C. measured in accordance with JIS K2283:2000.

[0039] The 5% distillation temperature of the coolant for the immersion cooling system of the present embodiment is 320°C or higher, preferably 330°C or higher, more preferably 350°C or higher, and further preferably 370°C or higher.

[0040] Furthermore, the 5% distillation temperature of the coolant for the immersion cooling system is preferably 600° C. or lower, more preferably 550° C. or lower, and further preferably 520° C. or lower.

[0041] The swelling of the insulating material of the electronic device can be suppressed by setting the 5% distillation temperature of the coolant for the immersion cooling system to 320°C or above. It is presumed that this is because high-boiling-point components are less likely to be absorbed into the resin such as the insulating material of the electronic device. If the 5% distillation temperature of the coolant for the immersion cooling system is above the above-mentioned preferred lower limit, the swelling of the insulating material of the electronic device can be further suppressed.

[0042] If the 5% distillation temperature of the coolant for the immersion cooling system is below the above preferred upper limit, the fluidity of the coolant for the immersion cooling system is improved, and it becomes easier to circulate, thereby improving the cooling performance. In addition, the burden on the pump that delivers the coolant in the immersion cooling system can be further reduced.

[0043] For example, the 5% distillation temperature of the coolant for the immersion cooling system of the present embodiment is preferably 320°C to 600°C, more preferably 330°C to 550°C, further preferably 350°C to 550°C, particularly preferably 370°C to 520°C.

[0044] The 95% distillation temperature of the coolant for the immersion cooling system of the present embodiment is preferably 430° C. or higher, more preferably 450° C. or higher, and even more preferably 500° C. or higher.

[0045] Furthermore, the 95% distillation temperature of the coolant for the immersion cooling system is preferably 800° C. or lower, more preferably 750° C. or lower, and even more preferably 700° C. or lower.

[0046] When the 95% distillation temperature of the coolant for the immersion cooling system is equal to or higher than the above-described preferred lower limit value, swelling of the insulating material of the electronic device can be further suppressed.

[0047] If the 95% distillation temperature of the coolant for the immersion cooling system is below the above-mentioned preferred upper limit, the fluidity of the coolant for the immersion cooling system is improved, and it becomes easy to circulate, thereby improving the cooling performance. In addition, the burden on the pump that delivers the coolant in the immersion cooling system can be further reduced.

[0048] For example, the 95% distillation temperature of the coolant for the immersion cooling system of the present embodiment is preferably 430°C to 800°C, more preferably 450°C to 750°C, and even more preferably 500°C to 700°C.

[0049] For example, the coolant for the immersion cooling system of the present embodiment preferably has a 5% distillation temperature of 320°C to 600°C, and a 95% distillation temperature of 430°C to 800°C, more preferably a 5% distillation temperature of 330°C to 550°C, and a 95% distillation temperature of 450°C to 750°C, further preferably a 5% distillation temperature of 350°C to 550°C, and a 95% distillation temperature of 450°C to 750°C, particularly preferably a 5% distillation temperature of 370°C to 520°C, and a 95% distillation temperature of 500°C to 700°C.

[0050] When the 5% distillation temperature and the 95% distillation temperature of the coolant for the immersion cooling system of the present embodiment are within the above-mentioned preferred ranges, swelling of the insulating material of the electronic device can be further suppressed and cooling performance can be improved.

[0051] In this specification, the 5% distillation temperature and the 95% distillation temperature refer to the values ​​measured in gas chromatography distillation in accordance with JIS K2254:2018.

[0052] The measurement conditions of the gas chromatography distillation in this specification are as follows.

[0053] (1) When the final distillation point (100% distillation temperature) is 600°C or higher

[0054] Device: GC-2030 manufactured by Shimadzu Corporation

[0055] Column: UA-1HT (30m×0.5mmI.D.×0.10μm)

[0056] Carrier gas: Helium 15mL / min

[0057] Detector: FID

[0058] Detector temperature: 400°C

[0059] Inlet temperature: PTV 40~380℃

[0060] Column temperature: 40~380℃(6min)

[0061] Heating rate: 10℃ / min

[0062] Injection volume: 0.5μL (carbon disulfide solution)

[0063] (2) When the final distillation point (100% distillation temperature) is lower than 600°C

[0064] Device: GC-2010plus manufactured by Shimadzu Corporation

[0065] Column: UA-1HT (30m×0.5mmI.D.×0.10μm)

[0066] Carrier gas: Helium 15mL / min

[0067] Detector: FID

[0068] Detector temperature: 360°C

[0069] Inlet temperature: PTV 40~380℃

[0070] Column temperature: 40~350℃(6min)

[0071] Heating rate: 10℃ / min

[0072] Injection volume: 0.5μL (carbon disulfide solution)

[0073] The %C of the coolant for the immersion cooling system of this embodiment N It is 30.0 or less, preferably 27.5 or less, and more preferably 25.0 or less.

[0074] In addition, the %C of the coolant used in the immersion cooling system N It is preferably 0.5 or more, more preferably 1.5 or more, and further preferably 2.5 or more.

[0075] If the immersion cooling system uses a coolant of %C N When it is 30.0 or less, swelling of the insulating material of the electronic device can be suppressed. When it is below the above preferred upper limit, swelling of the insulating material of the electronic device can be further suppressed.

[0076] If the immersion cooling system uses a coolant of %C N When the content is at least the above-described preferred lower limit, the solubility of the additive is improved.

[0077] For example, the %C of the coolant used in the immersion cooling system of this embodiment is N It is preferably 0.5 or more and 30.0 or less, more preferably 1.5 or more and 27.5 or less, and further preferably 2.5 or more and 25.0 or less.

[0078] The %C of the coolant for the immersion cooling system of this embodiment P It is preferably 99.5 or less, more preferably 98.5 or less, and further preferably 97.5 or less.

[0079] In addition, the %C of the coolant used in the immersion cooling system P It is preferably 70.0 or more, more preferably 72.5 or more, and further preferably 75.0 or more.

[0080] If the immersion cooling system uses a coolant of %C P When the content is below the above preferred upper limit, the solubility of the additive is further improved.

[0081] If the immersion cooling system uses a coolant of %C P When the content is not less than the above-described preferred lower limit, swelling of the insulating material of the electronic device can be further suppressed.

[0082] For example, the %C of the coolant used in the immersion cooling system of this embodiment is P It is preferably 70.0 or more and 99.5 or less, more preferably 72.5 or more and 98.5 or less, and further preferably 75.0 or more and 97.5 or less.

[0083] The %C of the coolant for the immersion cooling system of this embodiment A It is preferably 5.0 or less, more preferably 3.0 or less, and still more preferably 0.

[0084] If the immersion cooling system uses a coolant of %C A When it is below the above-mentioned preferred upper limit, electronic equipment is less likely to be affected.

[0085] In this specification, %C N 、%C P and %C A Each was determined by a method (ndM ring analysis) in accordance with ASTM D3238-85.

[0086] %C N Refers to the percentage (mass ratio) of the cycloalkane carbon number relative to the total carbon number. %C P Refers to the percentage (mass ratio) of the carbon number of paraffins relative to the total carbon number. %C A It refers to the percentage of aromatic carbon number relative to the total carbon number.

[0087] The above %C N 、%C P and %C A The preferred range of %C is based on the range of values ​​obtained by the above method. For example, even if the mineral oil-based base oil does not contain cyclohexane components, the %C obtained by the above method is N Values ​​greater than 0 may also be displayed.

[0088] <Hydrocarbon Oil>

[0089] The coolant for the liquid immersion cooling system of the present embodiment contains hydrocarbon oil.

[0090] Examples of the hydrocarbon oil include aliphatic saturated hydrocarbon oils, aliphatic unsaturated hydrocarbon oils (olefinic hydrocarbons), alicyclic hydrocarbon oils (cycloparaffinic hydrocarbons), and aromatic hydrocarbon oils.

[0091] The aliphatic saturated hydrocarbon oil may be a straight-chain saturated hydrocarbon oil (normal-paraffinic hydrocarbons) or a branched-chain saturated hydrocarbon oil (isoparaffinic hydrocarbons).

[0092] Specific examples of the hydrocarbon oil in the coolant for the liquid immersion cooling system of the present embodiment include mineral oil and synthetic oil.

[0093] Mineral Oil

[0094] As the mineral oil, a distillate obtained by distilling crude oil under normal pressure can be used, or a lubricating oil fraction obtained by refining a distillate obtained by further distilling the distillate under reduced pressure through various refining processes can be used.

[0095] As the refining process, it is possible to appropriately combine hydrotreating, solvent extraction, solvent dewaxing, hydrodewaxing, sulfuric acid washing, clay treatment, etc. By combining these refining processes in an appropriate order and performing the treatment, a mineral oil can be obtained.

[0096] In addition, mineral oil also includes wax isomerized oil. Wax isomerized oil is a hydrocarbon obtained by hydrocracking and hydroisomerizing GTL wax or CTL wax synthesized by the Fischer-Tropsch process (FT process), or pine wax obtained by solvent dewaxing to make a lubricating oil fraction. It should be noted that GTL wax is a wax synthesized by the FT process using natural gas as a raw material, and CTL wax is a wax synthesized by the FT process using coal as a raw material. The hydrocarbons obtained by hydrocracking and isomerizing these waxes to make a lubricating oil fraction are generally called GTL or CTL.

[0097] As the mineral oil, a mixture of a plurality of refined oils having different properties obtained by subjecting different crude oils or distillate oils to different refining processes, or a mixture with GTL or the like may be used.

[0098] As the mineral oil, Group I base oil (hereinafter referred to as "API Group I base oil"), Group II base oil (hereinafter referred to as "API Group II base oil"), or Group III base oil (hereinafter referred to as "API Group III base oil") of the API base oil classification, or a mixed base oil thereof can be used.

[0099] API Group I base oil is a mineral oil-based base oil having a sulfur content exceeding 0.03% by mass and / or a saturated content of less than 90% by mass and a viscosity index of 80 or more and less than 120.

[0100] The API Group II base oil is a mineral oil-based base oil having a sulfur content of 0.03 mass % or less, a saturated content of 90 mass % or more, and a viscosity index of 80 or more and less than 120.

[0101] API Group III base oil is a mineral oil-based base oil having a sulfur content of 0.03 mass % or less, a saturated content of 90 mass % or more, and a viscosity index of 120 or more.

[0102] The hydrocarbon oil may contain one mineral oil or may be a mixed base oil containing two or more mineral oils. In the mixed base oil containing two or more mineral oils, the API classifications of these mineral oils may be the same or different.

[0103] From the viewpoint of further suppressing the influence on electronic equipment, the mineral oil in the coolant for the immersion cooling system of the present embodiment preferably contains an API Group III base oil.

[0104] Synthetic Oil

[0105] Examples of the synthetic oil include polyolefins and alkylbenzenes.

[0106] Polyolefin

[0107] Examples of polyolefins include those obtained by homopolymerizing or copolymerizing olefin monomers having 2 to 16 carbon atoms, preferably 2 to 12 carbon atoms, and hydrogenated products of these polymers. The olefin monomers may be any of α-olefins, internal olefins, linear olefins, and branched olefins. Specifically, examples of such olefin monomers include ethylene, propylene, 1-butene, 2-butene, isobutylene, pentene, hexene, heptene, octene, nonene, decene, undecene, dodecene, tridecene, tetradecene, pentadecene, hexadecene, and mixtures thereof.

[0108] As the polyolefin, among the above, poly-α-olefin (PAO) is preferred from the viewpoint of viscosity characteristics and oxidation stability.

[0109] The above-mentioned polyolefin can be produced by a known method. For example, in addition to being produced by a thermal reaction without a catalyst, the target polyolefin can also be produced by homopolymerizing or copolymerizing the above-mentioned olefin using a known catalyst such as an organic peroxide catalyst such as benzoyl peroxide; a Friedel-Crafts type catalyst such as aluminum chloride, aluminum chloride-polyol system, aluminum chloride-titanium tetrachloride system, aluminum chloride-alkyl tin halide system, boron fluoride, etc.; a Ziegler type catalyst such as an organic aluminum chloride-titanium tetrachloride system, an organic aluminum-titanium tetrachloride system; a metallocene catalyst such as an aluminoxane-zirocene system, an ionic compound-zirocene system; a Lewis acid composite catalyst such as an aluminum chloride-alkali system, a boron fluoride-alkali system, etc.

[0110] ·Alkylbenzene

[0111] As the alkylbenzene, an alkylbenzene having 1 to 4 alkyl groups with a carbon number of 1 to 40 in the molecule is preferred. The alkyl group of the alkylbenzene may be linear or branched, but a branched alkyl group is preferred from the viewpoint of stability, viscosity characteristics, etc., and a branched alkyl group derived from an oligomer of an olefin such as propylene, butene, isobutylene, etc. is particularly preferred from the viewpoint of easy availability.

[0112] Among the above, the alkylbenzene in the present embodiment is most preferably an alkylbenzene having one or two alkyl groups, i.e., a monoalkylbenzene, a dialkylbenzene, or a mixture thereof, from the aspects of stability and availability. In addition, the alkylbenzene may be not only an alkylbenzene of a single structure but also a mixture of alkylbenzenes having different structures.

[0113] The alkylbenzene can be produced by a known method, for example, by using an aromatic compound as a raw material and an alkylating agent and an alkylating catalyst.

[0114] Here, specific examples of the aromatic compound used as a raw material include benzene, toluene, xylene, ethylbenzene, methylethylbenzene, diethylbenzene, and mixtures thereof.

[0115] Specific examples of the alkylating agent include linear or branched olefins having a carbon number of 6 to 40 obtained by polymerization of lower monoolefins such as ethylene, propylene, butene, isobutylene, and preferably propylene; linear or branched olefins having a carbon number of 6 to 40 obtained by thermal decomposition of wax, heavy oil, petroleum fractions, polyethylene, polypropylene, and the like; linear olefins having a carbon number of 9 to 40 obtained by separating normal paraffins from petroleum fractions such as kerosene and light oil and subjecting them to olefination using a catalyst; and mixtures thereof.

[0116] Examples of the alkylation catalyst used in the alkylation include known catalysts such as Friedel-Crafts type catalysts such as aluminum chloride and zinc chloride; and acidic catalysts such as sulfuric acid, phosphoric acid, silicotungstic acid, hydrofluoric acid, and activated clay.

[0117] The hydrocarbon oil in the coolant for the liquid immersion cooling system of the present embodiment may contain hydrocarbon oil containing biomass-derived carbon.

[0118] Specific examples of hydrocarbon oils having biomass-derived carbon include base oils synthesized from plant oils such as coconut oil, coconut oil, soybean oil, rapeseed oil, and mixtures thereof.

[0119] Examples of commercially available hydrocarbon oils containing biomass-derived carbon include SynNova TM 4Base Oil (Novvi) and SynNova TM 9Base Oil (manufactured by Novvi), etc.

[0120] The hydrocarbon oil in the coolant for the immersion cooling system of the present embodiment may be only mineral oil, only synthetic oil, or a mixture of mineral oil and synthetic oil. Among the above, API Group III base oil or poly-α-olefin is preferred.

[0121] The 5% distillation temperature of the hydrocarbon oil in the coolant for the liquid immersion cooling system of the present embodiment is preferably 320°C or higher, more preferably 330°C or higher, and even more preferably 350°C or higher.

[0122] Furthermore, the 5% distillation temperature of the hydrocarbon oil is preferably 600°C or lower, more preferably 550°C or lower, and further preferably 520°C or lower.

[0123] When the 5% distillation temperature of the hydrocarbon oil is equal to or higher than the above-described preferred lower limit value, swelling of the insulating material of the electronic device can be further suppressed.

[0124] If the 5% distillation temperature of the hydrocarbon oil is below the above preferred upper limit, the fluidity of the coolant in the immersion cooling system of this embodiment is improved and circulation is facilitated, thereby improving cooling performance. In addition, the load on the pump that delivers the coolant in the immersion cooling system can be further reduced.

[0125] For example, the 5% distillation temperature of the hydrocarbon oil in the coolant for the immersion cooling system of the present embodiment is preferably 320°C to 600°C, more preferably 330°C to 550°C, and even more preferably 350°C to 520°C.

[0126] The hydrocarbon oil 95% distillation temperature of the hydrocarbon oil in the coolant for the liquid immersion cooling system of the present embodiment is preferably 430°C or higher, more preferably 450°C or higher, and even more preferably 500°C or higher.

[0127] Furthermore, the 95% distillation temperature of the hydrocarbon oil is preferably 800°C or lower, more preferably 750°C or lower, and even more preferably 700°C or lower.

[0128] When the 95% distillation temperature of the hydrocarbon oil is equal to or higher than the above-described preferred lower limit value, swelling of the insulating material of the electronic device can be further suppressed.

[0129] If the 95% distillation temperature of the hydrocarbon oil is below the above preferred upper limit, the fluidity of the coolant used in the immersion cooling system of this embodiment is improved and circulation becomes easier, thereby improving cooling performance. In addition, the load on the pump that delivers the coolant in the immersion cooling system can be further reduced.

[0130] For example, the 95% distillation temperature of the hydrocarbon oil in the coolant for the immersion cooling system of the present embodiment is preferably 430°C to 800°C, more preferably 450°C to 750°C, and further preferably 500°C to 700°C.

[0131] For example, the hydrocarbon oil in the coolant for the immersion cooling system of the present embodiment preferably has a 5% distillation temperature of 320°C to 600°C and a 95% distillation temperature of 430°C to 800°C, more preferably has a 5% distillation temperature of 330°C to 550°C and a 95% distillation temperature of 450°C to 750°C, and further preferably has a 5% distillation temperature of 350°C to 550°C and a 95% distillation temperature of 500°C to 700°C.

[0132] When the 5% distillation temperature and the 95% distillation temperature of the hydrocarbon oil in the coolant for the immersion cooling system of the present embodiment are within the above-mentioned preferred ranges, swelling of the insulating material of the electronic device can be further suppressed and cooling performance can be improved.

[0133] The hydrocarbon oil in the coolant for the liquid immersion cooling system of the present embodiment may be used alone or in combination of two or more.

[0134] When the coolant for the immersion cooling system of the present embodiment contains two or more hydrocarbon oils, the above-mentioned "5% distillation temperature" and "95% distillation temperature" refer to values ​​measured in gas chromatography distillation for a mixture of the two or more hydrocarbon oils.

[0135] Antioxidants

[0136] The coolant for the immersion cooling system of the present embodiment contains one or more antioxidants selected from the group consisting of amine antioxidants and phenolic antioxidants. The antioxidants may be used alone or in combination of two or more.

[0137] Amine antioxidants

[0138] Examples of the amine antioxidant include aromatic amine antioxidants and hindered amine antioxidants.

[0139] Examples of the aromatic amine antioxidant include aromatic primary amine compounds such as alkylated α-naphthylamine, and aromatic secondary amine compounds such as alkylated diphenylamine, phenyl-α-naphthylamine, alkylated phenyl-α-naphthylamine, and phenyl-β-naphthylamine.

[0140] As the aromatic amine antioxidant, among the above, alkylated diphenylamine, alkylated phenyl-α-naphthylamine, or a combination thereof is preferred.

[0141] Examples of hindered amine antioxidants include compounds having a 2,2,6,6-tetraalkylpiperidine skeleton (2,2,6,6-tetraalkylpiperidine derivatives).

[0142] As the 2,2,6,6-tetraalkylpiperidine derivative, a 2,2,6,6-tetraalkylpiperidine derivative having a substituent at the 4-position is preferred. In addition, two 2,2,6,6-tetraalkylpiperidine skeletons may be bonded via respective substituents at the 4-position. In addition, the N-position of the 2,2,6,6-tetraalkylpiperidine skeleton may be unsubstituted or may be substituted with an alkyl group having 1 to 4 carbon atoms.

[0143] The 2,2,6,6-tetraalkylpiperidine skeleton is preferably a 2,2,6,6-tetramethylpiperidine skeleton.

[0144] Examples of the substituent at the 4-position of the 2,2,6,6-tetraalkylpiperidine skeleton include an acyloxy group (R 1 COO-), alkoxy (R 1 O-), alkylamino (R 1 NH-), acylamino (R 1 CONH-) etc.

[0145] R 1 It is a hydrocarbon group having preferably 1 to 30 carbon atoms, more preferably 1 to 24 carbon atoms, and still more preferably 1 to 20 carbon atoms.

[0146] Examples of the hydrocarbon group include an alkyl group, an alkenyl group, a cycloalkyl group, an alkylcycloalkyl group, an aryl group, an alkylaryl group, and an arylalkyl group.

[0147] Examples of the substituent when two 2,2,6,6-tetraalkylpiperidine skeletons are bonded via the substituent at the 4-position of each 2,2,6,6-tetraalkylpiperidine skeleton include a alkylenebis(carbonyloxy) group (-OOC-R 2 -COO-), alkylene diamino (-HN-R 2 -NH-), alkylenebis(carbonylamino) (-HNCO-R 2 -CONH-) etc. 2 It is preferably a hydrocarbylene group having 1 to 30 carbon atoms, and more preferably an alkylene group.

[0148] The substituent at the 4-position of the 2,2,6,6-tetraalkylpiperidine skeleton is preferably an acyloxy group. Examples of the compound having an acyloxy group at the 4-position of the 2,2,6,6-tetraalkylpiperidine skeleton include esters of 2,2,6,6-tetramethyl-4-piperidinol and carboxylic acid.

[0149] Examples of the carboxylic acid include linear or branched aliphatic carboxylic acids having 8 to 20 carbon atoms.

[0150] Phenolic antioxidants

[0151] Examples of phenolic antioxidants include 4,4'-methylenebis(2,6-di-tert-butylphenol); 4,4'-bis(2,6-di-tert-butylphenol); 4,4'-bis(2-methyl-6-tert-butylphenol); 2,2'-methylenebis(4-ethyl-6-tert-butylphenol); 2,2'-methylenebis(4-methyl-6-tert-butylphenol); 4,4'-butylenebis(3-methyl-6-tert-butylphenol); 4,4'-isopropylidenebis(2,6-di-tert-butylphenol); 2,2'-methylenebis(4-methyl-6-nonylphenol); 2,2'-isobutylenebis(4,6-dimethylphenol); 2,2'-methylenebis(4-methyl-6-cyclohexylphenol); 2,6-di Tert-butyl-4-methylphenol; 2,6-di-tert-butyl-4-ethylphenol; 2,4-dimethyl-6-tert-butylphenol; 2,6-di-tert-butyl-4-(N,N'-dimethylaminomethyl)phenol; 4,4'-thiobis(2-methyl-6-tert-butylphenol); 4,4'-thiobis(3-methyl-6-tert-butylphenol); 2,2'-thiobis(4-methyl-6-tert-butylphenol); bis(3-methyl-4-hydroxy-5-tert-butylbenzyl) sulfide; bis(3,5-di-tert-butyl-4-hydroxybenzyl) sulfide; 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate; 3-methyl-5-tert-butyl-4-hydroxyphenol fatty acid esters and other hindered phenol compounds and bisphenol compounds, etc.

[0152] As the phenolic antioxidant, among the above, 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate is preferred.

[0153] Examples of 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionates include octyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate; decyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate; dodecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate; tetradecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate; hexadecyl-3-( 3,5-di-tert-butyl-4-hydroxyphenyl) propionate; octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate; pentaerythritol-tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate]; 2,2'-thio-diethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate], etc., preferably octyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate.

[0154] <Optional Ingredients>

[0155] The coolant for the immersion cooling system of the present embodiment may also contain optional components other than the hydrocarbon oil, amine antioxidant and phenol antioxidant described above. Examples of the optional components include antioxidants other than amine antioxidants and phenol antioxidants, metal deactivators, rust inhibitors, defoamers, metal detergents, anti-wear agents, viscosity index improvers, pour point depressants, anti-fogging agents, and demulsifiers.

[0156] Other Antioxidants

[0157] Specific examples of antioxidants other than the amine-based antioxidants and the phenol-based antioxidants include peroxide decomposers such as sulfur-based antioxidants and sulfur / phosphorus-based antioxidants.

[0158] The content of other antioxidants is, for example, preferably 1.0% by mass or less, more preferably 0.1% by mass or less, and further preferably no other antioxidants are contained.

[0159] Metal deactivator

[0160] Examples of the metal deactivator include benzotriazole compounds, tolyltriazole compounds, thiadiazole compounds, and imidazole compounds.

[0161] 《Defoaming agent》

[0162] Examples of the defoaming agent include silicone-based defoaming agents.

[0163] 《Viscosity Index Improver》

[0164] Examples of the viscosity index improver include non-dispersed or dispersed poly(meth)acrylate viscosity index improvers, non-dispersed or dispersed olefin-(meth)acrylate copolymer viscosity index improvers, styrene-maleic anhydride ester copolymer viscosity index improvers, and mixtures thereof.

[0165] 《Pour Point Depressant》

[0166] Examples of the pour point depressant include polymethacrylate-based polymers suitable for the above-mentioned hydrocarbon oils.

[0167] Anti-fog agent

[0168] Examples of the anti-fogging agent include ethylene-propylene copolymers, polymethacrylates, polyisobutylene, polybutene, etc. The average molecular weight of these compounds as the anti-fogging agent is usually 10,000 to 8,000,000.

[0169] The content of the hydrocarbon oil in the coolant for the liquid immersion cooling system of the present embodiment is preferably 95 mass % or more, more preferably 97 mass % or more, and even more preferably 98.5 mass % or more, based on the total amount of the coolant for the liquid immersion cooling system.

[0170] The content of the hydrocarbon oil is preferably 99.99% by mass or less, more preferably 99.95% by mass or less, and even more preferably 99.92% by mass or less, based on the total amount of the coolant for the immersion cooling system.

[0171] For example, the content of the hydrocarbon oil is preferably 95 mass % to 99.99 mass % based on the total amount of the coolant for the immersion cooling system, more preferably 97 mass % to 99.95 mass %, and further preferably 98.5 mass % to 99.92 mass %.

[0172] The content of one or more antioxidants selected from the group consisting of amine antioxidants and phenolic antioxidants in the coolant for the immersion cooling system is preferably 0.01 mass % or more, more preferably 0.05 mass % or more, and further preferably 0.08 mass % or more, relative to the total amount of the coolant for the immersion cooling system.

[0173] The content of one or more antioxidants selected from the group consisting of amine antioxidants and phenolic antioxidants is preferably 5 mass % or less, more preferably 3 mass % or less, and further preferably 1.5 mass % or less, based on the total amount of the coolant for the immersion cooling system.

[0174] For example, the content of one or more antioxidants selected from the group consisting of amine antioxidants and phenolic antioxidants is preferably 0.01 mass % to 5 mass % based on the total amount of the coolant for the immersion cooling system, more preferably 0.05 mass % to 3 mass %, and even more preferably 0.08 mass % to 1.5 mass %.

[0175] When the content of one or more antioxidants selected from the group consisting of amine antioxidants and phenolic antioxidants in the coolant for an immersion cooling system is within the above-mentioned preferred range, the influence on electronic equipment can be further suppressed and the thermal stability can be further improved.

[0176] The content of one or more antioxidants selected from the group consisting of amine antioxidants and phenolic antioxidants in the coolant for the immersion cooling system is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and further preferably 0.08 parts by mass or more, based on 100 parts by mass of the hydrocarbon oil.

[0177] The content of one or more antioxidants selected from the group consisting of amine antioxidants and phenolic antioxidants is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and even more preferably 1.5 parts by mass or less, based on 100 parts by mass of the hydrocarbon oil.

[0178] For example, the content of one or more antioxidants selected from the group consisting of amine antioxidants and phenolic antioxidants is preferably 0.01 parts by mass or more and 5 parts by mass or less, more preferably 0.05 parts by mass or more and 3 parts by mass or less, and further preferably 0.08 parts by mass or more and 1.5 parts by mass or less, relative to 100 parts by mass of the hydrocarbon oil.

[0179] The coolant for the immersion cooling system may also contain the above-mentioned optional components.

[0180] When the coolant for an immersion cooling system contains an optional component, the content of the optional component is preferably 5 mass % or less, more preferably 3 mass % or less, and further preferably 1 mass % or less, based on the total amount of the coolant for an immersion cooling system.

[0181] The coolant for an immersion cooling system according to one embodiment is a coolant for an immersion cooling system containing only the above-mentioned hydrocarbon oil and one or more antioxidants selected from the group consisting of phenolic antioxidants and amine antioxidants.

[0182] The acid value of the coolant for the immersion cooling system of the present embodiment is preferably 0.1 mgKOH / g or less, and more preferably 0.05 mgKOH / g or less.

[0183] When the acid value of the coolant for the immersion cooling system of the present embodiment is equal to or lower than the above-described preferred upper limit value, the corrosion resistance with respect to the metal used in the electronic device to be immersed is further improved.

[0184] The acid value refers to the value of the total acid value measured in accordance with JISK 2501 "Petroleum products and lubricating oils-Neutralization value test method".

[0185] Example

[0186] Hereinafter, the effects of the present invention will be described in detail using Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[0187] <Coolant Mixture for Liquid Cooling System>

[0188] The coolants for immersion cooling systems of Examples 1 to 10 and Comparative Examples 1 to 14 were prepared in the blending ratios shown in Tables 1 to 5. The values ​​in Tables 1 to 5 are mass % based on the total amount of the coolants for immersion cooling systems.

[0189] The details of the components contained in the coolant for the immersion cooling system are as follows.

[0190] <Hydrocarbon Oil>

[0191] (A-1): Mineral oil (40°C kinematic viscosity: 11.9 mm 2 / s, 5% distillation temperature: 329°C, 95% distillation temperature: 432°C, %C P :72.9、%C N :27.1、%C A :0)

[0192] (A-2): Mineral oil (40°C kinematic viscosity: 34.8 mm 2 / s, 5% distillation temperature: 413°C, 95% distillation temperature: 528°C, %C P :84.3、%C N :15.7、%C A :0)

[0193] (A-3): Mineral oil (40°C kinematic viscosity: 44.9 mm 2 / s, 5% distillation temperature: 412°C, 95% distillation temperature: 554°C, %C P :80.4、%C N :19.6、%C A :0)

[0194] (A-4): Poly-α-olefin (40°C kinematic viscosity: 45.8 mm 2 / s, 5% distillation temperature: 463°C, 95% distillation temperature: 581°C, %C P :91.6、%C N :8.4、%C A :0)

[0195] (A-5): Poly-α-olefin (40°C kinematic viscosity: 48.0 mm 2 / s, 5% distillation temperature: 426℃, 95% distillation temperature: 593℃, %C P :90.9、%C N :9.1、%C A :0)

[0196] (A-6): Poly-α-olefin (40°C kinematic viscosity: 17.4 mm 2 / s, 5% distillation temperature: 412℃, 95% distillation temperature: 487℃, %C P :91.4、%C N :8.6、%C A :0)

[0197] (A-7): Mineral oil (40°C kinematic viscosity: 33.4 mm 2 / s, 5% distillation temperature: 408℃, 95% distillation temperature: 528℃, %C P :80.4、%C N :19.6、%C A :0)

[0198] (A-8): Mineral oil (40°C kinematic viscosity: 42.4 mm 2 / s, 5% distillation temperature: 377°C, 95% distillation temperature: 511°C, %C P :67.0、%C N :27.0、%C A :6.0)

[0199] (A-9): Mineral oil (40°C kinematic viscosity: 37.8 mm 2 / s, 5% distillation temperature: 377°C, 95% distillation temperature: 520°C, %C P :71.0、%C N :29.0、%C A :0)

[0200] (A-10): 100% plant-derived hydrocarbon oil (product name "SynNova 4Base Oils", manufactured by Novvi, 40°C kinematic viscosity: 19.7 mm 2 / s, 5% distillation temperature: 425℃, 95% distillation temperature: 461℃, %C P :93.1、%C N :6.9、%C A :0)

[0201] (A-11): Mineral oil (40°C kinematic viscosity: 35.1 mm 2 / s, 5% distillation temperature: 424℃, 95% distillation temperature: 522℃, %C P :85.7、%C N :14.3、%C A :0)

[0202] (a-1): Mineral oil (40°C kinematic viscosity: 8.7 mm 2 / s, 5% distillation temperature: 271°C, 95% distillation temperature: 418°C, %C P :65.3、%C N :34.7、%C A :0)

[0203] (a-2): ester oil (78:22 mixed oil of trade name "UNISTER (registered trademark) H-281R" and trade name "UNISTER (registered trademark) H-381R", both manufactured by NOF Corporation) (40°C kinematic viscosity: 28.6 mm 2 / s, 5% distillation temperature: 408℃, 95% distillation temperature: 615℃, %C P :31.6、%C N :68.4、%C A :0)

[0204] (a-3): Mineral oil (40°C kinematic viscosity: 54.8 mm 2 / s, 5% distillation temperature: 319°C, 95% distillation temperature: 438°C, %C P :38.3、%C N :49.6、%C A :12.2)

[0205] (a-4): Poly-α-olefin (40°C kinematic viscosity: 5.0 mm 2 / s, 5% distillation temperature: 308℃, 95% distillation temperature: 322℃, %C P :85.5、%C N :12.5、%C A :2)

[0206] <Antioxidants>

[0207] (B-1): Phenolic antioxidant (compound name: "octyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate")

[0208] (B-2): Amine antioxidant (compound name: monobutylphenyl monooctylphenylamine)

[0209] (B-3): Amine antioxidant (compound name: "N-dodecylphenyl-1-naphthylamine")

[0210] (b-1) Sulfur-phosphorus antioxidant (compound name: "zinc bis(2-ethylhexyl) dithiophosphate")

[0211] [Evaluation of the impact on electronic equipment]

[0212] Add 50 mL of the coolant for the immersion cooling system of each example to a 100 mL beaker, and immerse two capacitors (manufactured by AVX, SCCR20B335PRBLE) after the cover is peeled off and the terminals are cut. Measure the length (mm) of the capacitor's insulating material swelling and elongation after immersion at 80°C for one week, and evaluate the impact on the electronic device (swelling). The average value of the measured length and the results evaluated according to the following judgment criteria are shown in Tables 1 to 5.

[0213] 《Immersion test judgment criteria》

[0214] A: The length of expansion caused by swelling of the capacitor's insulating material is less than 0.29 mm.

[0215] B: The length of expansion caused by swelling of the insulating material of the capacitor is 0.29 mm or more and less than 0.39 mm.

[0216] C: The insulating material of the capacitor swells and stretches to a length of 0.39 mm or more.

[0217] [Evaluation of kinematic viscosity]

[0218] Tables 1 to 5 show the kinematic viscosities of the coolants for the immersion cooling system of each example at 40° C., 80° C., and 100° C. measured in accordance with JIS K2283:2000.

[0219] [Evaluation of distillation properties]

[0220] Tables 1 to 5 show the 5% distillation temperature and 95% distillation temperature of the coolant for the immersion cooling system of each example measured under the following conditions in accordance with JIS K2254:2018.

[0221] 《Measurement conditions》

[0222] (1) When the final distillation point (100% distillation temperature) is 600°C or higher

[0223] Device: GC-2030 manufactured by Shimadzu Corporation

[0224] Column: UA-1HT (30m×0.5mmI.D.×0.10μm)

[0225] Carrier gas: Helium 15mL / min

[0226] Detector: FID

[0227] Detector temperature: 400°C

[0228] Inlet temperature: PTV 40~380℃

[0229] Column temperature: 40~380℃(6min)

[0230] Heating rate: 10℃ / min

[0231] Injection volume: 0.5μL (carbon disulfide solution)

[0232] (2) When the final distillation point (100% distillation temperature) is lower than 600°C

[0233] Device: GC-2010plus manufactured by Shimadzu Corporation

[0234] Column: UA-1HT (30m×0.5mmI.D.×0.10μm)

[0235] Carrier gas: Helium 15mL / min

[0236] Detector: FID

[0237] Detector temperature: 360°C

[0238] Inlet temperature: PTV 40~380℃

[0239] Column temperature: 40~350℃(6min)

[0240] Heating rate: 10℃ / min

[0241] Injection volume: 0.5μL (carbon disulfide solution)

[0242] [Evaluation of acid value]

[0243] Tables 1 to 5 show the acid values ​​of the coolants for the immersion cooling system of each example measured in accordance with JIS K2501:2003.

[0244] From the viewpoint of further suppressing the elution of metal, a value of 0.1 or less was judged as acceptable.

[0245] [Evaluation of thermal stability]

[0246] 50 mL of the cooling liquid for the immersion cooling system of each example was added to a 100 mL beaker, and a catalyst prepared according to JIS K2514-2 (6.2 item) and cut into 38.5 ± 1 cm was immersed. The acid value of the cooling liquid after standing in a constant temperature bath at 100°C for one week was measured to evaluate the thermal stability of the cooling liquid. The results are shown in Tables 1 to 5.

[0247]

[0248]

[0249]

[0250] Table 4

[0251]

[0252]

[0253] As shown in Tables 1 to 5, the coolant for an immersion cooling system of the example does not further swell the insulating material of the capacitor compared to the coolant for an immersion cooling system of the comparative example, and has a low acid value for a long time due to its high thermal stability.

[0254] Therefore, it was confirmed that the influence on the immersed electronic device can be further suppressed.

[0255] 5% distillation temperature is above 320℃, %C N The kinematic viscosity at 40°C is 11.5 mm 2 / s or more of the embodiment of the immersion cooling system coolant and 5% distillation temperature below 320 ° C, % C N Comparative Example 10 greater than 30.0, 5% distillation temperature less than 320°C, kinematic viscosity at 40°C less than 11.5 mm 2 The immersion cooling system of Comparative Examples 13 and 14 with a cooling liquid of 0.140 W / s suppressed the swelling of the insulating material of the capacitor.

[0256] Therefore, it was confirmed that the coolant of the immersion cooling system of the example further suppressed the influence on the immersed electronic device.

[0257] Since the coolant for the immersion cooling system of Comparative Example 9 uses ester oil instead of hydrocarbon oil, the acid value of the new oil is high and the acid value is maintained high even in the oil deteriorated after thermal stabilization.

[0258] Therefore, it is estimated that the coolant for an immersion cooling system of Comparative Example 9 is more likely to cause metal of the electronic device to be eluted over a long period of time than the coolant for an immersion cooling system of the example.

[0259] The coolant for an immersion cooling system of the embodiment containing one or more antioxidants selected from the group consisting of amine antioxidants and phenolic antioxidants has a lower acid value after the thermal stability test than the coolant for an immersion cooling system of Comparative Examples 1 to 14 not containing one or more antioxidants selected from the group consisting of amine antioxidants and phenolic antioxidants, and Comparative Example 15 not containing one or more antioxidants selected from the group consisting of amine antioxidants and phenolic antioxidants but containing a sulfur-phosphorus antioxidant. Therefore, it is estimated that the coolant for an immersion cooling system of the embodiment suppresses metal elution of electronic equipment for a long time compared with the coolant for an immersion cooling system of the above-mentioned comparative example.

[0260] The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments. Additions, omissions, substitutions and other changes to the structure can be made without departing from the scope of the present invention. The present invention is not limited by the above description, but only by the attached claims.

[0261] Explanation of symbols

[0262] 10: Immersion cooling system, 1: Immersion tank, 3: Heat exchanger, 5: Pump, 7: Cooling device.

Claims

1. A coolant for an immersion cooling system, which is a coolant for an immersion cooling system filled in an immersion tank of an immersion cooling system as a coolant, comprising: Hydrocarbon oil, and one or more antioxidants selected from the group consisting of amine antioxidants and phenolic antioxidants, The hydrocarbon oil is contained in an amount of 50% by mass or more relative to the total amount of the coolant for the immersion cooling system. The 5% distillation temperature of the cooling liquid used in the immersion cooling system is above 320°C. N The kinematic viscosity at 40°C is 11.5 mm 2 / s or more.

2. The coolant for the immersion cooling system according to claim 1, wherein: 95% distillation temperature is 430°C or higher.

3. The coolant for the immersion cooling system according to claim 1 or 2, wherein: The content of the antioxidant is 0.01 mass % or more and 5 mass % or less relative to the total amount of the coolant for the immersion cooling system.

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