Cooling liquid for liquid immersion cooling system

Abstract

A cooling liquid for a liquid immersion cooling system used to fill a liquid immersion tank of the liquid immersion cooling system as a cooling liquid, wherein the cooling liquid for a liquid immersion cooling system contains 50 mass% or more of a hydrocarbon oil with respect to the total amount thereof and contains no amine antioxidants or, when the cooling liquid for a liquid immersion cooling system additionally contains any of the aforementioned antioxidants, the content thereof is less than 0.01 mass% with respect to the total amount of the cooling liquid for a liquid immersion cooling system, the 5% distillation temperature is 320℃ or more, %CN is 30.0 or less, and the kinematic viscosity at 40℃ is 11.5 mm2 / s or more.

Description

Technical Field

[0001] The present invention relates to a coolant for a liquid immersion cooling system. This application claims priority based on Japanese Patent Application No. 2022-113248 filed in Japan on July 14, 2022, and incorporates its content herein by reference.

Background Art

[0002] With the rapid increase in data transmission and reception volume, the loads on supercomputers and data servers have increased, and the amount of heat generated by these electronic devices has also increased. Conventionally, air cooling has been the mainstream method for cooling these electronic devices, but air-cooled types have limitations in cooling efficiency, so liquid immersion types with higher cooling efficiency have attracted attention.

[0003] A basic configuration example of a liquid immersion cooling system is shown in FIG. 1. The liquid immersion cooling system 10 includes a liquid immersion tank 1, a heat exchanger 3, a pump 5, and a cooling device 7. The liquid immersion tank 1 is filled with a coolant for the liquid immersion cooling system. The electronic device is cooled inside the liquid immersion tank 1. The coolant for the liquid immersion cooling system heated by the exhaust heat of the electronic device is pumped up by the pump 5 and heat-exchanged with the cold water created by the cooling device 7 in the heat exchanger 3. The coolant for the liquid immersion cooling system cooled by the heat exchange is circulated back to the liquid immersion tank 1 again. By using the liquid immersion cooling system 10, it is possible to continuously maintain a safe temperature at a constant level even when the electronic device is used under a high load condition.

[0004] Specifically, as a liquid immersion cooling system, Patent Document 1 discloses an apparatus including (a) an electronic hardware device and (b) a liquid cooling medium. The liquid cooling medium is (i) a mixture of a synthetic ester and a saturated medium-chain triglyceride, where the synthetic ester has a viscosity of 28 to 38 cSt at 40°C as determined according to ASTM D445, or (ii) contains a polyalkylene glycol, and when the liquid cooling medium contains a polyalkylene glycol, it is disclosed that the polyalkylene glycol constitutes at least 70% by weight of the liquid cooling medium.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Regarding the coolant for the liquid immersion cooling system, it is also important not to affect the electronic devices to be immersed. Specifically, it is required to suppress the swelling of the insulating material of the electronic device and the elution of the metal of the electronic device. The liquid cooling medium described in Patent Document 1 takes into account the balance between the flash point and the viscosity, but does not consider the influence on the electronic devices to be immersed. The ester contained in the liquid cooling medium of Patent Document 1 generates an acid by hydrolysis, and there is a possibility that the elution of the metal of the electronic device becomes a problem. Also, from the viewpoint of maintaining high visibility inside the liquid immersion cooling system, the coolant for the liquid immersion cooling system is also required to have high light resistance.

[0007] In view of the above circumstances, the present invention has been made, and an object thereof is to provide a coolant for a liquid immersion cooling system that has high light resistance and suppresses the influence on electronic devices to be immersed.

Means for Solving the Problems

[0008] In order to solve the above problems, the present invention adopts the following configuration. [1] A coolant for a liquid immersion cooling system filled as a coolant in a liquid immersion tank of a liquid immersion cooling system, comprising hydrocarbon oil in an amount of 50% by mass or more based on the total amount of the coolant for the liquid immersion cooling system, not containing an amine-based antioxidant, or, when further containing the amine-based antioxidant, the content of the amine-based antioxidant is less than 0.01% by mass based on the total amount of the coolant for the liquid immersion cooling system, the 5% distillation temperature is 320 °C or higher, and %C N is 30.0 or less, and the kinematic viscosity at 40 °C is 11.5 mm 2 / s or more, a coolant for a liquid immersion cooling system. [2] The coolant for a liquid immersion cooling system according to [1], wherein the 95% distillation temperature is 430 °C or higher.

Advantages of the Invention

[0009] According to the present invention, it is possible to provide a coolant for a liquid immersion cooling system having high light resistance and more suppressed influence on an electronic device to be immersed.

Brief Description of the Drawings

[0010]

Figure 1

Modes for Carrying Out the Invention

[0011] (Coolant for Liquid Immersion Cooling System) The coolant for a liquid immersion cooling system of the present embodiment is a coolant for a liquid immersion cooling system filled as a coolant in a liquid immersion tank of a liquid immersion cooling system. The coolant for a liquid immersion cooling system of the present embodiment is used for cooling an electronic device. Examples of the electronic device include a computer server, a server motherboard, a microprocessor, a capacitor, and other heat-generating electronic devices.

[0012] The coolant for a liquid immersion cooling system of the present embodiment contains hydrocarbon oil in an amount of 50% by mass or more based on the total amount of the coolant for the liquid immersion cooling system, the 5% distillation temperature is 320 °C or higher, and %CN is 30.0 or less, and the kinematic viscosity at 40°C is 11.5 mm 2 / s or more.

[0013] The coolant for the liquid immersion cooling system of this embodiment has a kinematic viscosity at 40°C of 11.5 mm 2 / s or more, preferably 15.0 mm 2 / s or more, more preferably 20.0 mm 2 / s or more, and even more preferably 25.0 mm 2 / s or more. Also, the coolant for the liquid immersion cooling system of this embodiment preferably has a kinematic viscosity at 40°C of 70.0 mm 2 / s or less, more preferably 60.0 mm 2 / s or less, and even more preferably 50.0 mm 2 / s or less.

[0014] The coolant for the liquid immersion cooling system of this embodiment has a kinematic viscosity at 40°C of 11.� mm 2 / s or more, so that swelling of the insulating material of the electronic device can be suppressed. This is presumably due to the fact that higher viscosity components (for example, compounds with long carbon chains) are less likely to be incorporated into resins such as the insulating material of electronic devices. If the kinematic viscosity at 40°C of the coolant for the liquid immersion cooling system of this embodiment is at or above the above-mentioned preferred lower limit value, swelling of the insulating material of the electronic device can be more effectively suppressed. If the kinematic viscosity at 40°C of the coolant for the liquid immersion cooling system of this embodiment is at or below the above-mentioned preferred upper limit value, the fluidity of the coolant for the liquid immersion cooling system of this embodiment is improved, making it easier to circulate, and thus the cooling performance is improved. Also, the burden on the pump that delivers the coolant in the liquid immersion cooling system can be made smaller.

[0015] For example, the coolant for the liquid immersion cooling system of this embodiment preferably has a kinematic viscosity at 40°C of 11.5 mm 2 / s or more and 70.0 mm 2 / s or less, preferably 15.0 mm 2 / s or more and 60.0 mm 2More preferably, it is below / s, and 20.0 mm 2 / s or more and 60.0 mm 2 Even more preferably, it is below / s, and 25.0 mm 2 / s or more and 50.0 mm 2 Particularly preferably, it is below / s.

[0016] The coolant for the liquid immersion cooling system of this embodiment has a kinematic viscosity at 80 °C of 3.5 mm 2 / s or more and 30.0 mm 2 Preferably, it is below / s, and 4.5 mm 2 / s or more and 27.5 mm 2 More preferably, it is below / s, and 5.5 mm 2 / s or more and 25.0 mm 2 Even more preferably, it is below / s.

[0017] The coolant for the liquid immersion cooling system of this embodiment has a kinematic viscosity at 100 °C of 2.5 mm 2 / s or more and 20.0 mm 2 Preferably, it is below / s, and 3.0 mm 2 / s or more and 17.5 mm 2 More preferably, it is below / s, and 3.5 mm 2 / s or more and 15.0 mm 2 Even more preferably, it is below / s.

[0018] The kinematic viscosities at 40 °C, 80 °C, and 100 °C in this specification mean the kinematic viscosities at 40 °C, 80 °C, and 100 °C measured in accordance with JIS K2283:2000.

[0019] The 5% distillation temperature of the coolant for the liquid immersion cooling system of this embodiment is 320 °C or higher, preferably 330 °C or higher, more preferably 350 °C or higher, and even more preferably 370 °C or higher. Also, the 5% distillation temperature of the coolant for the liquid immersion cooling system is preferably 600 °C or lower, more preferably 550 °C or lower, and even more preferably 520 °C or lower.

[0020] Since the 5% distillation temperature of the coolant for the liquid immersion cooling system is 320°C or higher, swelling of the insulating material of the electronic device can be suppressed. This is presumably due to the fact that higher boiling point components are less likely to be incorporated into the resin such as the insulating material of the electronic device. If the 5% distillation temperature of the coolant for the liquid immersion cooling system is at or above the above-mentioned preferable lower limit value, swelling of the insulating material of the electronic device can be further suppressed. If the 5% distillation temperature of the coolant for the liquid immersion cooling system is at or below the above-mentioned preferable upper limit value, the fluidity of the coolant for the liquid immersion cooling system is improved and it becomes easier to circulate, so the cooling performance is improved. In addition, the burden on the pump that delivers the coolant in the liquid immersion cooling system can be made smaller.

[0021] For example, the 5% distillation temperature of the coolant for the liquid immersion cooling system of the present embodiment is preferably 320°C or higher and 600°C or lower, more preferably 330°C or higher and 550°C or lower, still more preferably 350°C or higher and 550°C or lower, and particularly preferably 370°C or higher and 520°C or lower.

[0022] The 95% distillation temperature of 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 still more preferably 500°C or higher. Also, the 95% distillation temperature of the coolant for the liquid immersion cooling system is preferably 800°C or lower, more preferably 750°C or lower, and still more preferably 700°C or lower.

[0023] If the 95% distillation temperature of the coolant for the liquid immersion cooling system is at or above the above-mentioned preferable lower limit value, swelling of the insulating material of the electronic device can be further suppressed. If the 95% distillation temperature of the coolant for the liquid immersion cooling system is at or below the above-mentioned preferable upper limit value, the fluidity of the coolant for the liquid immersion cooling system is improved and it becomes easier to circulate, so the cooling performance is improved. In addition, the burden on the pump that delivers the coolant in the liquid immersion cooling system can be made smaller.

[0024] For example, the 95% distillation temperature of the coolant for the liquid immersion cooling system of the present embodiment is preferably 430°C or higher and 800°C or lower, more preferably 450°C or higher and 750°C or lower, and even more preferably 500°C or higher and 700°C or lower.

[0025] For example, among the above, the coolant for the liquid immersion cooling system of the present embodiment preferably has a 5% distillation temperature of 320°C or higher and 600°C or lower, and a 95% distillation temperature of 430°C or higher and 800°C or lower. More preferably, the 5% distillation temperature is 330°C or higher and 550°C or lower, and the 95% distillation temperature is 450°C or higher and 750°C or lower. Even more preferably, the 5% distillation temperature is 350°C or higher and 550°C or lower, and the 95% distillation temperature is 450°C or higher and 750°C or lower. Particularly preferably, the 5% distillation temperature is 370°C or higher and 520°C or lower, and the 95% distillation temperature is 500°C or higher and 700°C or lower. If the 5% distillation temperature and the 95% distillation temperature of the coolant for the liquid immersion cooling system of the present embodiment are within the above-preferred ranges, it is possible to improve the cooling performance while further suppressing the swelling of the insulating material of the electronic device.

[0026] In this specification, the 5% distillation temperature and the 95% distillation temperature mean the values in gas chromatographic distillation measured in accordance with JIS K2254:2018.

[0027] The measurement conditions for gas chromatographic distillation in this specification are as follows. (1) When the end point (100% distillation temperature) is 600°C or higher Apparatus: GC-2030 manufactured by Shimadzu Corporation Column: UA-1HT (30m × 0.5mm I.D. × 0.10μm) Carrier gas: Helium 15 mL / min Detector: FID Detector temperature: 400°C Inlet temperature: PTV 40~380°C Column temperature: 40~380°C (6 min) Temperature rising rate: 10°C / min Injection volume: 0.5 μL (carbon disulfide solution) (2) When the end point (100% retention temperature) is less than 600 °C Apparatus: GC-2010plus manufactured by Shimadzu Corporation Column: UA-1HT (30 m × 0.5 mm I.D. × 0.10 μm) Carrier gas: Helium 15 mL / min Detector: FID Detector temperature: 360 °C Inlet temperature: PTV 40 - 380 °C Column temperature: 40 - 350 °C (6 min) Temperature rising rate: 10 °C / min Injection volume: 0.5 μL (carbon disulfide solution)

[0028] %C of the coolant for the liquid immersion cooling system of this embodiment N is 30.0 or less, preferably 27.5 or less, and more preferably 25.0 or less. Also, %C of the coolant for the liquid immersion cooling system N is preferably 0.5 or more, more preferably 1.5 or more, and even more preferably 2.5 or more.

[0029] %C of the coolant for the liquid immersion cooling system N If it is 30.0 or less, swelling of the insulating material of the electronic device can be suppressed. If it is below the above preferred upper limit value, swelling of the insulating material of the electronic device can be more effectively suppressed. %C of the coolant for the liquid immersion cooling system N If it is above the above preferred lower limit value, the solubility of the additive is improved.

[0030] For example, %C of the coolant for the liquid immersion cooling system of this embodiment N is preferably 0.5 or more and 30.0 or less, more preferably 1.5 or more and 27.5 or less, and even more preferably 2.5 or more and 25.0 or less.

[0031] %C of the coolant for the liquid immersion cooling system of this embodiment Pis preferably 99.5 or less, more preferably 98.5 or less, and even more preferably 97.5 or less. In addition, %C of the coolant for the liquid immersion cooling system P is preferably 70.0 or more, more preferably 72.5 or more, and even more preferably 75.0 or more.

[0032] %C of the coolant for the liquid immersion cooling system P If it is below the above-mentioned preferable upper limit value, the solubility of the additive is further improved. %C of the coolant for the liquid immersion cooling system P If it is above the above-mentioned preferable lower limit value, swelling of the insulating material of the electronic device can be further suppressed.

[0033] For example, %C of the coolant for the liquid immersion cooling system of the present embodiment P is preferably 70.0 or more and 99.5 or less, more preferably 72.5 or more and 98.5 or less, and even more preferably 75.0 or more and 97.5 or less.

[0034] %C of the coolant for the liquid immersion cooling system of the present embodiment A is preferably 5.0 or less, more preferably 3.0 or less, and even more preferably 0.

[0035] %C of the coolant for the liquid immersion cooling system A If it is below the above-mentioned preferable upper limit value, it is less likely to affect the electronic device.

[0036] In this specification, %C N , %C P and %C A are each determined by a method (n-d-M ring analysis) conforming to ASTM D 3238-85. %C N means the percentage (mass ratio) of the number of naphthene carbon atoms to the total number of carbon atoms. %C P means the percentage (mass ratio) of the number of paraffin carbon atoms to the total number of carbon atoms. %C Ameans the percentage of the number of aromatic carbon atoms to the total number of carbon atoms. the above-mentioned %C N , %C P and %C A The preferred ranges of N are based on the values obtained by the above method. Even for a mineral oil-based base oil that does not contain naphthene, the %C

[0037] <Hydrocarbon oil> The coolant for the liquid immersion cooling system of this embodiment contains hydrocarbon oil. Examples of the hydrocarbon oil include aliphatic saturated hydrocarbon oil, aliphatic unsaturated hydrocarbon oil (olefinic hydrocarbon), alicyclic hydrocarbon oil (naphthenic hydrocarbon), and aromatic hydrocarbon oil. The aliphatic saturated hydrocarbon oil may be a straight-chain saturated hydrocarbon oil (normal paraffin-based hydrocarbon) or a branched-chain saturated hydrocarbon oil (isoparaffin-based hydrocarbon). Specific examples of the hydrocarbon oil in the coolant for the liquid immersion cooling system of this embodiment include mineral oil and synthetic oil.

[0038] ≪Mineral oil≫ As the mineral oil, a distillate obtained by atmospheric distillation of crude oil can be used. Also, a distillate obtained by further vacuum distillation of this distillate and refined into a lubricating oil fraction by various refining processes can be used. As the refining processes, hydrorefining, solvent extraction, solvent dewaxing, hydrodewaxing, sulfuric acid washing, clay treatment, etc. can be appropriately combined. By combining and treating these refining processes in an appropriate order, mineral oil can be obtained. 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 slack wax obtained by solvent dewaxing, etc., into a lubricating oil fraction. Note that GTL wax is wax synthesized by the FT process using natural gas as a raw material, and CTL wax is wax synthesized by the FT process using coal as a raw material. Hydrocarbons obtained by hydrocracking and isomerizing these waxes into a lubricating oil fraction are generally referred to as GTL or CTL. As the mineral oil, a mixture of a plurality of refined oils having different properties obtained by subjecting different crude oils or distillates to different combinations of refining processes, as well as a mixture with GTL or the like, may be used.

[0039] As the mineral oil, group I base oil of the API base oil classification (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"), or a mixed base oil thereof can be used. API group I base oil is a mineral oil-based base oil having a sulfur content of more than 0.03% by mass and / or a saturation of less than 90% by mass, and a viscosity index of 80 or more and less than 120. API group II base oil is a mineral oil-based base oil having a sulfur content of 0.03% by mass or less, a saturation of 90% by mass or more, and a viscosity index of 80 or more and less than 120. API group III base oil is a mineral oil-based base oil having a sulfur content of 0.03% by mass or less, a saturation of 90% by mass or more, and a viscosity index of 120 or more.

[0040] The hydrocarbon oil may consist of one kind of mineral oil or may be a mixed base oil containing two or more kinds of mineral oils. In a mixed base oil containing two or more kinds of mineral oils, their API classifications may be the same or may be different from each other. The mineral oil in the coolant for the liquid immersion cooling system of the present embodiment preferably contains API group III base oil from the viewpoint of further suppressing the influence on electronic devices.

[0041] ≪Synthetic Oil≫ Examples of synthetic oils include polyolefins, alkylbenzenes, etc.

[0042] · Polyolefin 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 hydrides of these polymers. The olefin monomer may be any of α-olefins, internal olefins, linear olefins, and branched olefins. Specific examples of such olefin monomers include ethylene, propylene, 1-butene, 2-butene, isobutene, pentene, hexene, heptene, octene, nonene, decene, undecene, dodecene, tridecene, tetradecene, pentadecene, hexadecene, and mixtures thereof. Among the above polyolefins, poly-α-olefin (PAO) is preferred from the viewpoints of viscosity characteristics and oxidation stability.

[0043] The above polyolefins can be produced by known methods. For example, they can be produced by a thermal reaction without a catalyst, or by using known catalysts such as organic peroxide catalysts such as benzoyl peroxide; Friedel-Crafts type catalysts such as aluminum chloride, aluminum chloride-polyhydric alcohol systems, aluminum chloride-titanium tetrachloride systems, aluminum chloride-alkyltin halide systems, boron fluoride; Ziegler type catalysts such as organic aluminum chloride-titanium tetrachloride systems, organic aluminum-titanium tetrachloride systems; metallocene type catalysts such as aluminoxane-zirconocene systems, ionic compound-zirconocene systems; Lewis acid complex type catalysts such as aluminum chloride-base systems, boron fluoride-base systems, etc., to homopolymerize or copolymerize the above olefins to produce the target polyolefin.

[0044] · Alkylbenzene As the alkylbenzene, those having 1 to 4 alkyl groups with 1 to 40 carbon atoms in the molecule are preferred. Further, the alkyl group of the alkylbenzene may be linear or branched, but a branched alkyl group is preferred from the viewpoints of stability, viscosity characteristics, etc., and particularly from the viewpoint of easy availability, a branched alkyl group derived from oligomers of olefins such as propylene, butene, isobutylene, etc. is more preferred.

[0045] Among the above, the alkylbenzene in the present embodiment is most preferably an alkylbenzene having 1 or 2 alkyl groups, that is, a monoalkylbenzene, a dialkylbenzene, or a mixture thereof, from the viewpoints of stability and availability. Further, as the alkylbenzene, not only an alkylbenzene having a single structure but also a mixture of alkylbenzenes having different structures may be used.

[0046] The above alkylbenzene can be produced by a known method. For example, it can be produced using an aromatic compound as a raw material and an alkylating agent and an alkylation catalyst. Here, specific examples of the aromatic compound used as the raw material include benzene, toluene, xylene, ethylbenzene, methylethylbenzene, diethylbenzene, and mixtures thereof. Specific examples of the alkylating agent include lower monoolefins such as ethylene, propylene, butene, and isobutylene, preferably linear or branched olefins having 6 to 40 carbon atoms obtained by polymerization of propylene; linear or branched olefins having 6 to 40 carbon atoms obtained by thermal decomposition of wax, heavy oil, petroleum fraction, polyethylene, polypropylene, etc.; linear olefins having 9 to 40 carbon atoms obtained by separating n-paraffin from petroleum fractions such as kerosene and gas oil and olefinating this with a catalyst, and mixtures thereof. Examples of the alkylation catalyst in the alkylation include known catalysts such as Friedel-Crafts type catalysts such as aluminum chloride and zinc chloride; acidic catalysts such as sulfuric acid, phosphoric acid, silicotungstic acid, hydrofluoric acid, and activated clay.

[0047] The hydrocarbon oil in the coolant for the immersion cooling system of the present embodiment may contain a hydrocarbon oil having carbon derived from biomass. Specific examples of the hydrocarbon oil having carbon derived from biomass include base oils synthesized from vegetable oils such as palm oil, coconut oil, soybean oil, rapeseed oil, and mixtures thereof.

[0048] Examples of commercially available products of hydrocarbon oils having carbon derived from biomass include SynNova TM 4 Base Oil (manufactured by Novvi), and SynNova TM 9 Base Oil (manufactured by Novvi), etc.

[0049] 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.

[0050] The 5% distillation temperature of the hydrocarbon oil in the coolant for the 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. Also, the 5% distillation temperature of the hydrocarbon oil is preferably 600 °C or lower, more preferably 550 °C or lower, and even more preferably 520 °C or lower.

[0051] If the 5% distillation temperature of the hydrocarbon oil is at or above the above-preferred lower limit value, swelling of the insulating material of the electronic device can be more effectively suppressed. If the 5% distillation temperature of the hydrocarbon oil is at or below the above-preferred upper limit value, the fluidity of the coolant for the immersion cooling system of the present embodiment is improved, making it easier to circulate, thereby improving the cooling performance. Also, the burden on the pump that delivers the coolant in the immersion cooling system can be made smaller.

[0052] 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 or higher and 600°C or lower, more preferably 330°C or higher and 550°C or lower, and even more preferably 350°C or higher and 520°C or lower.

[0053] The 95% distillation temperature of the hydrocarbon oil in 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. Also, 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.

[0054] If the 95% distillation temperature of the hydrocarbon oil is equal to or higher than the above-preferred lower limit value, swelling of the insulating material of the electronic device can be more effectively suppressed. If the 95% distillation temperature of the hydrocarbon oil is equal to or lower than the above-preferred upper limit value, the fluidity of the coolant for the immersion cooling system of the present embodiment is improved, making it easier to circulate, thus improving the cooling performance. Also, the burden on the pump for delivering the coolant in the immersion cooling system can be made smaller.

[0055] 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 or higher and 800°C or lower, more preferably 450°C or higher and 750°C or lower, and even more preferably 500°C or higher and 700°C or lower.

[0056] For example, among the above, the hydrocarbon oil in the coolant for the immersion cooling system of the present embodiment preferably has a 5% distillation temperature of 320°C or higher and 600°C or lower, and a 95% distillation temperature of 430°C or higher and 800°C or lower; more preferably, it has a 5% distillation temperature of 330°C or higher and 550°C or lower, and a 95% distillation temperature of 450°C or higher and 750°C or lower; even more preferably, it has a 5% distillation temperature of 350°C or higher and 550°C or lower, and a 95% distillation temperature of 500°C or higher and 700°C or lower. If 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 preferred ranges, it is possible to further suppress the swelling of the insulating material of the electronic device while improving the cooling performance.

[0057] The hydrocarbon oil in the coolant for the immersion cooling system of the present embodiment may be used alone or in combination of two or more. When the coolant for the immersion cooling system of the present embodiment contains two or more hydrocarbon oils, the above "5% distillation temperature" and "95% distillation temperature" mean the values measured by gas chromatographic distillation for the mixture of two or more hydrocarbon oils.

[0058] The content of the hydrocarbon oil in the coolant for the immersion cooling system of the present embodiment is 50% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and may be 100% by mass, based on the total amount of the coolant for the immersion cooling system.

[0059] If the content of the hydrocarbon oil in the coolant for the immersion cooling system of the present embodiment is not less than the above preferred lower limit value, the influence on the electronic device can be further suppressed.

[0060] The coolant for the immersion cooling system of the present embodiment contains the above-mentioned hydrocarbon oil and substantially does not contain an amine-based antioxidant. Here, "substantially does not contain an amine-based antioxidant" means the following two meanings. (i) Does not contain an amine-based antioxidant. (ii) When it contains an amine-based antioxidant, the total content of the amine-based antioxidant is less than 0.01% by mass based on the total amount of the coolant for the immersion cooling system.

[0061] The coolant for the immersion cooling system contains substantially no amine-based antioxidant, so it has good light resistance. The light resistance of the coolant does not pose a particular problem in other applications. On the other hand, when using an immersion cooling system, it is necessary to immerse the electronic device in the coolant for the immersion cooling system and observe the electronic device in the state of being immersed in the coolant for the immersion cooling system during maintenance. Therefore, it is important for the coolant for the immersion cooling system to maintain transparency. The coolant for the immersion cooling system contains substantially no amine-based antioxidant. Therefore, it has good light resistance, is easy to maintain transparency, and the maintainability of the electronic device immersed in the coolant for the immersion cooling system is improved.

[0062] · Amine-based antioxidant Examples of amine-based antioxidants include aromatic amine-based antioxidants and hindered amine-based antioxidants. Examples of aromatic amine-based antioxidants include primary aromatic amine compounds such as alkylated α-naphthylamine; secondary aromatic amine compounds such as alkylated diphenylamine, phenyl-α-naphthylamine, alkylated phenyl-α-naphthylamine, and phenyl-β-naphthylamine.

[0063] Examples of hindered amine-based antioxidants include compounds having a 2,2,6,6-tetraalkylpiperidine skeleton (2,2,6,6-tetraalkylpiperidine derivatives). Examples of 2,2,6,6-tetraalkylpiperidine derivatives include 2,2,6,6-tetraalkylpiperidine derivatives having a substituent at the 4-position. Also, two 2,2,6,6-tetraalkylpiperidine skeletons may be bonded via the substituents at their respective 4-positions. Further, the N-position of the 2,2,6,6-tetraalkylpiperidine skeleton may be unsubstituted, or an alkyl group having 1 to 4 carbon atoms may be substituted at the N-position. The 2,2,6,6-tetraalkylpiperidine skeleton is, for example, a 2,2,6,6-tetramethylpiperidine skeleton.

[0064] As the substituent at the 4-position of the 2,2,6,6-tetraalkylpiperidine skeleton, there may be mentioned an acyloxy group (R 1 COO-), an alkoxy group (R 1 O-), an alkylamino group (R 1 NH-), an acylamino group (R 1 CONH-), etc. R 1 is, for example, a hydrocarbon group having 1 to 30 carbon atoms. Examples of the hydrocarbon group include an alkyl group, an alkenyl group, a cycloalkyl group, an alkylcycloalkyl group, an aryl group, an alkylaryl group, an arylalkyl group, etc.

[0065] As the substituent when two 2,2,6,6-tetraalkylpiperidine skeletons are bonded via the substituents at their respective 4-positions, there may be mentioned a hydrocarbylenebis(carbonyloxy) group (-OOC-R 2 -COO-), a hydrocarbylenediamino group (-HN-R 2 -NH-), a hydrocarbylenebis(carbonylamino) group (-HNCO-R 2 -CONH-), etc. R 2 is, for example, a hydrocarbylene group having 1 to 30 carbon atoms.

[0066] As the substituent at the 4-position of the 2,2,6,6-tetraalkylpiperidine skeleton, there may be mentioned 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 acids. Examples of the carboxylic acid include linear or branched aliphatic carboxylic acids having 8 to 20 carbon atoms, etc.

[0067] The content of the hydrocarbon oil in the coolant for the liquid immersion cooling system is preferably 99.9% by mass or more, and may be 100% by mass, based on the total amount of the coolant for the liquid immersion cooling system.

[0068] The coolant for the immersion cooling system of one embodiment is the coolant for the immersion cooling system consisting only of the hydrocarbon oil described above.

[0069] The content of the amine-based antioxidant in the coolant for the immersion cooling system is less than 0.01% by mass, preferably less than 0.001% by mass, and more preferably does not contain an amine-based antioxidant, based on the total amount of the coolant for the immersion cooling system.

[0070] The coolant for the immersion cooling system may contain optional components. When the coolant for the immersion cooling system contains optional components, the content of the optional components is preferably 0.1% by mass or less based on the total amount of the coolant for the immersion cooling system.

[0071] <Optional component>[[ID=IS]] The coolant for the immersion cooling system of this embodiment may contain optional components other than the hydrocarbon oil described above. Examples of the optional components include antioxidants other than amine-based antioxidants, metal deactivators, rust inhibitors, defoamers, metal-based detergents, anti-wear agents, viscosity index improvers, pour point depressants, mist inhibitors, and demulsifiers.

[0072] ≪Other antioxidants≫ Specific examples of other antioxidants include peroxide decomposers such as phenolic antioxidants, sulfur-based antioxidants, and sulfur-phosphorus-based antioxidants.

[0073] ≪Metal deactivators≫ Examples of metal deactivators include benzotriazole-based compounds, tolyltriazole-based compounds, thiadiazole-based compounds, and imidazole-based compounds.

[0074] ≪Defoamers≫ Examples of defoamers include silicone-based defoamers.

[0075] ≪Viscosity index improvers≫ Examples of the viscosity index improver include non-dispersed or dispersed poly(meth)acrylate-based viscosity index improvers, non-dispersed or dispersed olefin-(meth)acrylate copolymer-based viscosity index improvers, styrene-maleic anhydride ester copolymer-based viscosity index improvers, and mixtures thereof.

[0076] ≪Pour point depressant≫ Examples of the pour point depressant include polymethacrylate-based polymers compatible with the above-described hydrocarbon oil.

[0077] ≪Mist inhibitor≫ Examples of the mist inhibitor include ethylene-propylene copolymers, polymethacrylates, polyisobutylenes, polybutenes, etc. The average molecular weight of these compounds as the mist inhibitor is usually from 10,000 to 8,000,000.

[0078] The coolant for the liquid immersion cooling system of the present embodiment preferably has an acid value of 0.1 mgKOH / g or less, more preferably 0.05 mgKOH / g or less. When the acid value of the coolant for the liquid immersion cooling system of the present embodiment is equal to or less than the above-mentioned preferable upper limit value, the corrosion prevention property against the metal used in the electronic device to be immersed is further improved. The acid value represents the value of the total acid value measured in accordance with JIS K 2501 "Petroleum products and lubricating oils - Test method for neutralization value".

Examples

[0079] 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.

[0080] <Composition of coolant for liquid immersion cooling system> Coolants for the liquid immersion cooling systems of Examples 1 to 13 and Comparative Examples 1 and 2 having the blending ratios shown in Tables 1 to 6 were produced. The numerical values in Tables 1 to 6 mean mass% based on the total amount of the coolant for the liquid immersion cooling system.

[0081] The details of each component contained in the coolant for the immersion cooling system are as follows. <Hydrocarbon oil> (A-1): Mineral oil (kinematic viscosity at 40°C: 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) (A-2): Poly-α-olefin (kinematic viscosity at 40°C: 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) (A-3): Poly-α-olefin (kinematic viscosity at 40°C: 48.0 mm 2 / s, 5% distillation temperature: 426°C, 95% distillation temperature: 593°C, %C P : 90.9, %C N : 9.1, %C A : 0) (A-4): Poly-α-olefin (kinematic viscosity at 40°C: 17.4 mm 2 / s, 5% distillation temperature: 412°C, 95% distillation temperature: 487°C, %C P : 91.4, %C N : 8.6, %C A : 0) (A-5): Mineral oil (kinematic viscosity at 40°C: 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) (A-6): Mineral oil (kinematic viscosity at 40°C: 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) (A-7): 100% plant-derived hydrocarbon oil (product name "SynNova 4 TM Base Oil", manufactured by Novvi, kinematic viscosity at 40°C: 19.7 mm 2 / s, 5% distillation temperature: 425 °C, 95% distillation temperature: 461 °C, %C P : 93.1, %C N : 6.9, %C A : 0) (A-8): Mineral oil (kinematic viscosity at 40 °C: 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)

[0082] (a-1): Mineral oil (kinematic viscosity at 40 °C: 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) (a-2): Poly-α-olefin (kinematic viscosity at 40 °C: 5.0 mm 2 / s, 5% distillation temperature: 308 °C, 95% distillation temperature: 332 °C, %C P : 85.5, %C N : 12.5, %C A : 2) (a-3): Ester oil (a 78:22 mixture of "Unister (registered trademark) H-281R" and "Unister (registered trademark) H-381R", both manufactured by NOF Corporation) (kinematic viscosity at 40 °C: 28.6 mm 2 / s, 5% distillation temperature: 408 °C, 95% distillation temperature: 615 °C, %C P : 31.6, %C N : 68.4, %C A : 0)

[0083] <Antioxidant> (B-1): Phenolic antioxidant (compound name "octyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate") (b-1): Amine antioxidant (compound name "monobutylphenylmonooctylphenylamine") (b-2): Amine antioxidant (compound name "N-dodecylphenyl-1-naphthylamine")

[0084] [Evaluation of the Impact on Electronic Devices] 50 mL of the coolant for the liquid immersion cooling system of each example was added to a 100 mL beaker, and 2 capacitors (manufactured by AVX Corporation, SCCR20B335PRBLE) with the coating peeled off and the terminals cut were immersed. The length (mm) by which the insulating material of the capacitor swelled and elongated after being immersed at 80°C for one week was measured to evaluate the impact (swelling property) on the electronic device. The average value of the measured length and the results evaluated according to the following criteria are shown in Tables 1 to 6. ≪Immersion Test Judgment Criteria≫ A: The length by which the insulating material of the capacitor swells and elongates is less than 0.29 mm. B: The length by which the insulating material of the capacitor swells and elongates is 0.29 mm or more and less than 0.39 mm. C: The length by which the insulating material of the capacitor swells and elongates is 0.39 mm or more.

[0085] [Evaluation of Kinematic Viscosity] The kinematic viscosities of the coolants for the liquid immersion cooling system of each example measured in accordance with JIS K2283:2000 at 40°C, 80°C, and 100°C are shown in Tables 1 to 6.

[0086] [Evaluation of Distillation Characteristics] The 5% distillation temperature and 95% distillation temperature of the coolants for the liquid immersion cooling system of each example measured under the following conditions in accordance with JIS K2254:2018 are shown in Tables 1 to 6. ≪Measurement Conditions≫ (1) When the end point (100% distillation temperature) is 600°C or higher Apparatus: GC-2030 manufactured by Shimadzu Corporation Column: UA-1HT (30 m × 0.5 mm I.D. × 0.10 μm) Carrier gas: Helium 15 mL / min Detector: FID Detector temperature: 400°C Inlet temperature: PTV 40 - 380°C Column temperature: 40 - 380°C (6 min) Temperature increase rate: 10°C / min Injection volume: 0.5 μL (carbon disulfide solution) (2) When the end point (100% residue temperature) is less than 600 °C Apparatus: GC-2010plus manufactured by Shimadzu Corporation Column: UA-1HT (30 m × 0.5 mm I.D. × 0.10 μm) Carrier gas: Helium 15 mL / min Detector: FID Detector temperature: 360 °C Inlet temperature: PTV 40 - 380 °C Column temperature: 40 - 350 °C (6 min) Temperature rising rate: 10 °C / min Injection volume: 0.5 μL (carbon disulfide solution)

[0087] [Evaluation of acid value] The acid values of the coolant for the liquid immersion cooling system of each example measured in accordance with JIS K2501:2003 are shown in Tables 1 - 6. From the perspective of further suppressing the elution of metals, a value of 0.1 or less was judged as qualified.

[0088] [Evaluation of light resistance] 80 mL of the coolant for the liquid immersion cooling system of each example was sealed in a 100 mL screw bottle and left standing near a window for 4 days, and then the color phase was observed in accordance with JIS K2580.

[0089] [Table 1]

[0090] [Table 2]

[0091] [Table 3]

[0092] [Table 4]

[0093]

Table 5

[0094]

Table 6

[0095] As shown in Tables 1 to 6, it was confirmed that the coolant for the immersion cooling system of the examples can achieve both light resistance and the effect of suppressing the influence on the electronic devices to be immersed, as compared with the coolant for the immersion cooling system of the comparative examples.

[0096] The distillation temperature at 5% is 320 °C or higher, %C N is 30.0 or less, and the kinematic viscosity at 40 °C is 11.5 mm 2 / s or more for the coolant for the immersion cooling system of the examples. Compared with Comparative Example 1 where the distillation temperature at 5% is less than 320 °C and %C N is greater than 30.0, or Comparative Example 4 where the distillation temperature at 5% is less than 320 °C and the kinematic viscosity at 40 °C is less than 11.5 mm 2 / s, the swelling of the insulating material of the capacitor was suppressed for the coolant for the immersion cooling system of the examples. Therefore, it was confirmed that the influence of the coolant for the immersion cooling system of the examples on the electronic devices to be immersed is more suppressed. Since the coolant for the immersion cooling system of Comparative Example 5 uses ester oil instead of hydrocarbon oil, the acid value was high. Therefore, it is presumed that the metal of the electronic devices is more likely to elute for the coolant for the immersion cooling system of Comparative Example 5, as compared with the coolant for the immersion cooling system of the examples.

[0097] As described above, the preferred embodiments of the present invention have been described, but the present invention is not limited to these embodiments. Additions, omissions, substitutions, and other modifications of the configuration are possible without departing from the spirit of the present invention. The present invention is not limited by the foregoing description, but is limited only by the scope of the appended claims.

Explanation of Reference Numerals

[0098] 10: Immersion cooling system, 1: Immersion tank, 3: Heat exchanger, 5: Pump, 7: Cooling device

Claims

1. A coolant for a liquid immersion cooling system filled as a coolant in a liquid immersion tank of the liquid immersion cooling system, containing 50% by mass or more of hydrocarbon oil based on the total amount of the coolant for the liquid immersion cooling system, not containing an amine-based antioxidant, or, when further containing the amine-based antioxidant, the content of the amine-based antioxidant is less than 0.01% by mass based on the total amount of the coolant for the liquid immersion cooling system, The 5% retention temperature is 320 °C or higher, and %C Ｎ is 0.5 or more and 30.0 or less, A coolant for a liquid immersion cooling system having a kinematic viscosity at 40 °C of 25.0 mm ２ / s or more.

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

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