Cooling liquid for immersion cooling system

Abstract

A cooling liquid for an immersion cooling system that is to be filled as a cooling liquid in the immersion tank of the immersion cooling system, and contains a hydrocarbon oil and one or more antioxidants selected from the group consisting of an amine-based antioxidant and a phenolic antioxidant, wherein the hydrocarbon oil is contained in an amount of 50 mass% or more relative to the total amount of the cooling liquid. This cooling liquid has a 5% distillation temperature of 320°C or higher, a %CN of 30.0 or lower, and a dynamic viscosity of 11.5 mm2 / s or higher at 40°C.

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. Hitherto, air cooling has been the mainstream method for cooling these electronic devices, but since air cooling types have limitations in cooling efficiency, 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, the polyalkylene glycol is disclosed to constitute 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] As the coolant for the liquid immersion cooling system, it is also important not to affect the electronic devices to be immersed. Specifically, in order not to affect the electronic devices to be immersed, it is required to suppress the swelling of the insulating material of the electronic devices and the elution of the metal of the electronic devices. 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 may generate an acid by hydrolysis, and the elution of the metal of the electronic devices may become a problem. In addition, as the coolant for the liquid immersion cooling system, high thermal stability is also required.

[0007] The present invention has been made in view of the above circumstances, and an object thereof is to provide a coolant for a liquid immersion cooling system having high thermal stability and more suppressed 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, containing a hydrocarbon oil and one or more antioxidants selected from the group consisting of amine-based antioxidants and phenolic antioxidants, wherein the hydrocarbon oil is contained in an amount of 50% by mass or more based on the total amount of the coolant for the liquid immersion cooling system, and the coolant for the liquid immersion cooling system has a 5% distillation temperature of 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], having a 95% distillation temperature of 430 °C or higher. [3] The content of the antioxidant is 0.01% by mass or more and 5% by mass or less based on the total amount of the coolant for the liquid immersion cooling system. The coolant for a liquid immersion cooling system according to [1] or [2].

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 thermal stability and more suppressed influence on electronic devices to be immersed.

Brief Description of the Drawings

[0010]

Figure 1

Embodiments 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 electronic devices. Examples of the electronic devices include computer servers, server motherboards, microprocessors, capacitors, and other heat-generating electronic devices.

[0012] The coolant for the immersion cooling system of this embodiment contains a hydrocarbon oil and one or more antioxidants selected from the group consisting of an amine-based antioxidant and a phenol-based antioxidant, contains the hydrocarbon oil in an amount of 50% by mass or more based on the total amount of the coolant for the immersion cooling system, and the coolant for the immersion cooling system has a 5% distillation temperature of 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.

[0013] The coolant for the 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 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] Since the coolant for the immersion cooling system of this embodiment has a kinematic viscosity at 40°C of 11.5 mm 2 / s or more, 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 the resin such as the insulating material of the electronic device. If the kinematic viscosity at 40°C of the coolant for the immersion cooling system of this embodiment is at or above the above-mentioned preferable 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 immersion cooling system of this embodiment is at or below the above-mentioned preferable upper limit value, the fluidity of the coolant for the immersion cooling system of this embodiment is improved and it becomes easier to circulate, so the cooling performance is improved. Also, the burden on the pump that delivers the coolant in the immersion cooling system can be made smaller.

[0015] For example, the coolant for the immersion cooling system of the present embodiment 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 2 / s or less, more preferably 20.0 mm 2 / s or more and 60.0 mm 2 / s or less, even more preferably 25.0 mm 2 / s or more and 50.0 mm 2 / s or less, particularly preferably.

[0016] The coolant for the immersion cooling system of the present embodiment has a kinematic viscosity at 80°C of 3.5 mm 2 / s or more and 30.0 mm 2 / s or less, preferably 4.5 mm 2 / s or more and 27.5 mm 2 / s or less, more preferably 6.0 mm 2 / s or more and 25.0 mm 2 / s or less, even more preferably.

[0017] The coolant for the immersion cooling system of the present embodiment has a kinematic viscosity at 100°C of 2.5 mm 2 / s or more and 20.0 mm 2 / s or less, preferably 3.0 mm 2 / s or more and 17.5 mm 2 / s or less, more preferably 4.0 mm 2 / s or more and 15.0 mm 2 / s or less, even more preferably.

[0018] The kinematic viscosities at 40°C, 80°C, and 10°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 immersion cooling system of the present 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 immersion cooling system is preferably 600°C or lower, more preferably 550°C or lower, and even more preferably 520°C or lower.

[0020] When the 5% distillation temperature of the coolant for the 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 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 immersion cooling system is at or above the above-preferred lower limit, swelling of the insulating material of the electronic device can be more effectively suppressed. If the 5% distillation temperature of the coolant for the immersion cooling system is at or below the above-preferred upper limit, the fluidity of the coolant for the immersion cooling system is improved and it becomes easier to circulate, so the cooling performance is improved. Also, the burden on the pump that delivers the coolant in the immersion cooling system can be made smaller.

[0021] For example, the 5% distillation temperature of 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, even 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 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 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.

[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. Also, 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, for the coolant for the liquid immersion cooling system of the present embodiment, the 5% distillation temperature is preferably 320°C or higher and 600°C or lower, and the 95% distillation temperature is preferably 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-mentioned preferable ranges, it is possible to improve the cooling performance while further suppressing swelling of the insulating material of the electronic device.

[0026] In this specification, the 5% distillation temperature and the 95% distillation temperature mean 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 (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 rising rate: 10 °C / min Injection volume: 0.5 μL (carbon disulfide solution) (2) When the end point (100% distillation 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 the present 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 preferable upper limit value, swelling of the insulating material of the electronic device can be more suppressed. %C of the coolant for the liquid immersion cooling system N If it is above the above preferable lower limit value, the solubility of the additive is improved.

[0030] For example, the %C of the coolant for the immersion cooling system of the present 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] The %C of the coolant for the immersion cooling system of the present embodiment P is preferably 99.5 or less, more preferably 98.5 or less, and even more preferably 97.5 or less. Also, the %C of the coolant for the 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] When the %C of the coolant for the immersion cooling system P is below the above-preferred upper limit value, the solubility of the additive is further improved. When the %C of the coolant for the immersion cooling system P is above the above-preferred lower limit value, the swelling of the insulating material of the electronic device can be further suppressed.

[0033] For example, the %C of the coolant for the 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] The %C of the coolant for the 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] When the %C of the coolant for the immersion cooling system A is below the above-preferred upper limit value, it is less likely to affect the electronic device.

[0036] In this specification, %C N , %CP and %C A are determined by the method (n-d-M ring analysis) conforming to ASTM D 3238-85, respectively. %C N means the percentage (mass ratio) of the total carbon number of naphthenic carbon number to the total carbon number. %C P means the percentage (mass ratio) of the total carbon number of paraffinic carbon number to the total carbon number. %C A means the percentage of the total carbon number of aromatic carbon number to the total carbon number. The above-mentioned %C N , %C P and %C A The preferred ranges are based on the values obtained by the above method. Even for a mineral oil-based base oil containing no naphthene component, the %C N obtained by the above method may show a value exceeding 0.

[0037] <Hydrocarbon oil> The coolant for the liquid immersion cooling system of this embodiment contains a 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 paraffinic hydrocarbon) or a branched-chain saturated hydrocarbon oil (isoparaffinic 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. Further, a distillate obtained by vacuum distillation of this distillate and a lubricating oil fraction purified by various purification processes can also be used. As the purification processes, hydrorefining, solvent extraction, solvent dewaxing, hydrodewaxing, sulfuric acid washing, clay treatment, etc. can be appropriately combined. By combining these purification processes in an appropriate order and treating them, 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 method (FT method), or slack wax obtained by solvent dewaxing, etc. into a lubricating oil fraction. Note that GTL wax is wax synthesized by the FT method using natural gas as a raw material, and CTL wax is wax synthesized by the FT method 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 with 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 with 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 with 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 with 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 and alkylbenzenes.

[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 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, and boron fluoride; Ziegler type catalysts such as organic aluminum chloride-titanium tetrachloride systems and organic aluminum-titanium tetrachloride systems; metallocene type catalysts such as aluminoxane-zirconocene systems and ionic compound-zirconocene systems; and Lewis acid complex type catalysts such as aluminum chloride-base systems and boron fluoride-base systems to homopolymerize or copolymerize the above olefins to produce the target polyolefins.

[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 biomass-derived carbon. Specific examples of the hydrocarbon oil having biomass-derived carbon 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 oil having biomass-derived carbon 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 preferable.

[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, thus improving the cooling performance. Also, the burden on the pump for delivering 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 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, 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 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. 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 liquid 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 that delivers the coolant in the liquid immersion cooling system can be made smaller.

[0055] For example, the 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 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 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, 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 preferable 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 obtained by gas chromatographic distillation measured for the mixture of two or more hydrocarbon oils.

[0058] ≪Antioxidant≫ The coolant for the immersion cooling system of the present embodiment contains one or more antioxidants selected from the group consisting of amine-based antioxidants and phenol-based antioxidants. The antioxidant may be used alone or in combination of two or more.

[0059] ·Amine-based antioxidant Examples of the amine-based antioxidant include aromatic amine-based antioxidants and hindered amine-based antioxidants. Examples of the aromatic amine-based antioxidant 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.

[0060] Among the above, alkylated diphenylamine, or alkylated phenyl-α-naphthylamine, or a combination thereof is preferable as the aromatic amine-based antioxidant.

[0061] Examples of the hindered amine-based antioxidant include compounds having a 2,2,6,6-tetraalkylpiperidine skeleton (2,2,6,6-tetraalkylpiperidine derivatives). As the 2,2,6,6-tetraalkylpiperidine derivative, a 2,2,6,6-tetraalkylpiperidine derivative having a substituent at the 4-position is preferable. Further, two 2,2,6,6-tetraalkylpiperidine skeletons may be bonded via the substituents at the 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 preferably a 2,2,6,6-tetramethylpiperidine skeleton.

[0062] Examples of the substituent at the 4-position of the 2,2,6,6-tetraalkylpiperidine skeleton include an acyloxy group (R 1 COO-), an alkoxy group (R 1 O-), an alkylamino group (R 1 NH-), an acylamino group (R 1 CONH-), and the like. R 1 is preferably a hydrocarbon group having 1 to 30 carbon atoms, more preferably a hydrocarbon group having 1 to 24 carbon atoms, and even more preferably a hydrocarbon group having 1 to 20 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, and the like.

[0063] Examples of the substituent when two 2,2,6,6-tetraalkylpiperidine skeletons are bonded via the substituents at the respective 4-positions include a hydrocarbylenebis(carbonyloxy) group (-OOC-R 2 -COO-), a hydrocarbylenediamino group (-HN-R 2 -NH-), a hydrocarbylenebis(carbonylamino) group (-HNCO-R 2 -CONH-), and the like. R 2 is preferably a hydrocarbylene group having 1 to 30 carbon atoms, and more preferably an alkylene group.

[0064] As the substituent at the 4-position of the 2,2,6,6-tetraalkylpiperidine skeleton, an acyloxy group is preferred. 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.

[0065] · Phenolic antioxidants 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'-butylidenebis(3-methyl-6-tert-butylphenol); 4,4'-isopropylidenebis(2,6-di-tert-butylphenol); 2,2'-methylenebis(4-methyl-6-nonylphenol); 2,2'-isobutylidenebis(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)propionic acid esters; 3-methyl-5-tert-butyl-4-hydroxyphenol fatty acid esters, and other hindered phenol compounds and bisphenol compounds, etc.

[0066] Among the above, 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid esters are preferred as phenolic antioxidants.

[0067] Examples of the 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid esters 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-diethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate], etc. Among them, octyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate is preferred.

[0068] <Optional component> The coolant for the liquid immersion cooling system of this embodiment may contain optional components other than the above-mentioned hydrocarbon oil, amine-based antioxidant, and phenolic antioxidant. Examples of the optional components include antioxidants other than amine-based antioxidants and phenolic antioxidants, metal deactivators, rust inhibitors, antifoaming agents, metal-based detergents, antiwear agents, viscosity index improvers, pour point depressants, mist inhibitors, and demulsifiers.

[0069] ≪Other antioxidants≫ Specific examples of antioxidants other than amine-based antioxidants and phenolic antioxidants include peroxide decomposers such as sulfur-based antioxidants and sulfur-phosphorus-based antioxidants.

[0070] The content of other antioxidants is preferably, for example, 1.0% by mass or less, more preferably 0.1% by mass or less, and even more preferably not containing other antioxidants.

[0071] ≪Metal Inactivator≫ Examples of the metal inactivator include benzotriazole-based compounds, tolyltriazole-based compounds, thiadiazole-based compounds, imidazole-based compounds, and the like.

[0072] ≪Defoaming Agent≫ Examples of the defoaming agent include silicone-based defoaming agents.

[0073] ≪Viscosity Index Improver≫ 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.

[0074] ≪Pour Point Depressant≫ Examples of the pour point depressant include polymethacrylate-based polymers compatible with the hydrocarbon oil described above.

[0075] ≪Mist Suppressant≫ Examples of the mist suppressant include ethylene-propylene copolymers, polymethacrylate, polyisobutylene, polybutene, and the like. The average molecular weight of these compounds as the mist suppressant is usually from 10,000 to 8,000,000.

[0076] The content of the hydrocarbon oil in the coolant for the liquid immersion cooling system of the present embodiment is preferably 95% by mass or more, more preferably 97% by mass or more, and still more preferably 98.5% by mass or more with respect to the total amount of the coolant for the liquid immersion cooling system. Also, the content of the hydrocarbon oil is preferably 99.99% by mass or less, more preferably 99.95% by mass or less, and still more preferably 99.92% by mass or less with respect to the total amount of the coolant for the liquid immersion cooling system. For example, the hydrocarbon oil content is preferably 95% by mass or more and 99.99% by mass or less, more preferably 97% by mass or more and 99.95% by mass or less, and even more preferably 98.5% by mass or more and 99.92% by mass or less, based on the total amount of the coolant for the liquid immersion cooling system.

[0077] The content of one or more antioxidants selected from the group consisting of amine-based antioxidants and phenolic antioxidants in the coolant for the liquid immersion cooling system is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.08% by mass or more, based on the total amount of the coolant for the liquid immersion cooling system. Also, the content of one or more antioxidants selected from the group consisting of amine-based antioxidants and phenolic antioxidants is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1.5% by mass or less, based on the total amount of the coolant for the liquid immersion cooling system. For example, the content of one or more antioxidants selected from the group consisting of amine-based antioxidants and phenolic antioxidants is preferably 0.01% by mass or more and 5% by mass or less, more preferably 0.05% by mass or more and 3% by mass or less, and even more preferably 0.08% by mass or more and 1.5% by mass or less, based on the total amount of the coolant for the liquid immersion cooling system. If the content of one or more antioxidants selected from the group consisting of amine-based antioxidants and phenolic antioxidants in the coolant for the liquid immersion cooling system is within the above-preferred range, the influence on the electronic device can be further suppressed while improving the thermal stability.

[0078] The content of one or more antioxidants selected from the group consisting of amine-based antioxidants and phenolic antioxidants in the coolant for the liquid immersion cooling system is preferably 0.01 part by mass or more, more preferably 0.05 part by mass or more, and even more preferably 0.08 part by mass or more, per 100 parts by mass of the hydrocarbon oil. In addition, the content of one or more antioxidants selected from the group consisting of amine-based 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 with respect to 100 parts by mass of the hydrocarbon oil. For example, the content of one or more antioxidants selected from the group consisting of amine-based antioxidants and phenolic antioxidants is preferably 0.01 part by mass or more and 5 parts by mass or less, more preferably 0.05 part by mass or more and 3 parts by mass or less, and even more preferably 0.08 part by mass or more and 1.5 parts by mass or less with respect to 100 parts by mass of the hydrocarbon oil.

[0079] The coolant for the liquid immersion cooling system may contain any of the above-described components. When the coolant for the liquid immersion cooling system contains an optional component, the content of the optional component is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less with respect to the total amount of the coolant for the liquid immersion cooling system.

[0080] The coolant for the liquid immersion cooling system according to one embodiment is a coolant for the liquid immersion cooling system consisting only of the above-described hydrocarbon oil and one or more antioxidants selected from the group consisting of phenolic antioxidants and amine-based antioxidants.

[0081] The coolant for the liquid immersion cooling system of the present embodiment preferably has an acid value of 0.1 mgKOH / g or less, and 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-described 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 - Method for testing neutralization number".

Examples

[0082] 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.

[0083] <Formulation of coolant for liquid immersion cooling system> Coolants for liquid immersion cooling systems of Examples 1 to 10 and Comparative Examples 1 to 14 having the formulation ratios shown in Tables 1 to 5 were produced. The numerical values in Tables 1 to 5 represent mass % based on the total amount of the coolant for the liquid immersion cooling system.

[0084] Details of each component contained in the coolant for the liquid immersion cooling system are as shown below. <Hydrocarbon oil> (A-1): Mineral oil (kinematic viscosity at 40°C: 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) (A-2): 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) (A-3): 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-4): 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-5): 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, %CA :0) (A-6): 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-7): Mineral oil (kinematic viscosity at 40°C: 33.4 mm 2 / s, 5% distillation temperature: 408°C, 95% distillation temperature: 528°C, %C P : 80.4, %C N : 19.6, %C A :0) (A-8): Mineral oil (kinematic viscosity at 40°C: 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) (A-9): 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-10): 100% plant-derived hydrocarbon oil (product name "SynNova 4 Base Oils", 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-11): Mineral oil (kinematic viscosity at 40°C: 35.1 mm 2 / s, 5% distillation temperature: 424°C, 95% distillation temperature: 522°C, %C P : 85.7, %C N : 14.3, %C A :0)

[0085] (a-1): 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-2): Ester oil (a 78:22 mixed oil of trade names "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) (a-3): 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-4): Poly-α-olefin (kinematic viscosity at 40°C: 5.0 mm 2 / s, 5% distillation temperature: 308°C, 95% distillation temperature: 322°C, %C P :85.5, %C N :12.5, %C A :2)

[0086] [Antioxidant]< (B-1): Phenolic antioxidant (compound name "octyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate") (B-2): Amine antioxidant (compound name "monobutylphenylmonooctylphenylamine") (B-3): Amine antioxidant (compound name "N-dodecylphenyl-1-naphthylamine") (b-1) Sulfur and phosphorus-based antioxidant (compound name "zinc bis(2-ethylhexyl)dithiophosphate")

[0087] [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 two 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 extended after immersion at 80°C for one week was measured to evaluate the impact (swelling property) on electronic devices. The average value of the measured lengths and the results evaluated according to the following criteria are shown in Tables 1 to 5. ≪Immersion Test Criteria≫ A: The length by which the insulating material of the capacitor swells and extends is less than 0.29 mm. B: The length by which the insulating material of the capacitor swells and extends 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 extends is 0.39 mm or more.

[0088] [Evaluation of Kinematic Viscosity] Table 1 to 5 show the kinematic viscosities of the coolant for the liquid immersion cooling system of each example measured in accordance with JIS K2283:2000 at 40°C, 80°C, and 100°C.

[0089] [Evaluation of Distillation Characteristics] Table 1 to 5 show the 5% distillation temperature and 95% distillation temperature of the coolant for the liquid immersion cooling system of each example measured under the following conditions in accordance with JIS K2254:2018. ≪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 rising rate: 10°C / min Injection volume: 0.5 μL (carbon disulfide solution) (2) When the end point (100% distillation 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 at 15 mL / min Detector: FID Detector temperature: 360 °C Inlet temperature: PTV 40 - 380 °C Column temperature: 40 - 350 °C (6 min) Temperature ramp rate: 10 °C / min Injection volume: 0.5 μL (carbon disulfide solution)

[0090] [Evaluation of acid value] The acid values of the cooling liquids for the liquid immersion cooling systems of each example measured in accordance with JIS K2501:2003 are shown in Tables 1 - 5. From the perspective of further suppressing the elution of metals, a value of 0.1 or less was judged as passing.

[0091] [Evaluation of thermal stability] 50 mL of the cooling liquid for the liquid immersion cooling system of each example was added to a 100 mL beaker. After preparation in accordance with JIS K2514-2 (Clause 6.2), one catalyst cut to 38.5 ± 1 cm was immersed. After standing in a constant temperature bath at 100 °C for one week, the acid value of the cooling liquid was measured to evaluate the thermal stability of the cooling liquid. The results are shown in Tables 1 - 5.

[0092] [Table 1]

[0093] [Table 2]

[0094] [Table 3]

[0095] [Table 4]

[0096]

Table 5

[0097] As shown in Tables 1 to 5, the coolant for the immersion cooling system of the examples did not swell the insulating material of the capacitor more compared to the coolant for the immersion cooling system of the comparative examples, and had high thermal stability. Therefore, the acid value was kept low over a long period of time. Therefore, it was confirmed that the influence on the electronic device to be immersed could be more suppressed.

[0098] The coolant for the immersion cooling system of the examples with a 5% distillation temperature of 320 °C or higher, %C N of 30.0 or less, and a kinematic viscosity at 40 °C of 11.5 mm 2 / s or more had a 5% distillation temperature of less than 320 °C, %C N greater than 30.0 in Comparative Example 10, or a 5% distillation temperature of less than 320 °C and a kinematic viscosity at 40 °C of less than 11.5 mm 2 / s in Comparative Examples 13 and 14. The swelling of the insulating material of the capacitor was suppressed compared to the coolants for the immersion cooling systems of Comparative Examples 10, 13, and 14. Therefore, it was confirmed that the influence of the coolant for the immersion cooling system of the examples on the electronic device to be immersed was more suppressed. 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 it maintains a high value even in the deteriorated oil after thermal stability. Therefore, it is presumed that the metal of the electronic device elutes more easily over a long period of time in the coolant for the immersion cooling system of Comparative Example 9 compared to the coolant for the immersion cooling system of the examples.

[0099] The coolant for a liquid immersion cooling system in an example containing one or more antioxidants selected from the group consisting of amine-based antioxidants and phenolic antioxidants has a lower acid value after a thermal stability test compared to the coolants for liquid immersion cooling systems in Comparative Examples 1 to 14 that do not contain one or more antioxidants selected from the group consisting of amine-based antioxidants and phenolic antioxidants, and Comparative Example 15 that does not contain one or more antioxidants selected from the group consisting of amine-based antioxidants and phenolic antioxidants but contains a sulfur-phosphorus-based antioxidant. Therefore, it is presumed that the coolant for the liquid immersion cooling system in the example suppresses the elution of metals from electronic devices over a long period compared to the coolants for the liquid immersion cooling systems in the comparative examples.

[0100] 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 above description and is limited only by the scope of the appended claims.

Description of Reference Numerals

[0101] 10: Liquid immersion cooling system, 1: Liquid immersion tank, 3: Heat exchanger, 5: Pump, 7: Cooling device

Claims

**Claim 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 a hydrocarbon oil, and one or more antioxidants selected from the group consisting of amine-based antioxidants and phenolic antioxidants, wherein the hydrocarbon oil is contained in an amount of 50% by mass or more based on the total amount of the coolant for the liquid immersion cooling system, The coolant for the liquid immersion cooling system has a 5% distillation temperature of 320 °C or higher, and the %C Ｎ is 0.5 or more and 30.0 or less, and the kinematic viscosity at 40 °C is 25.0 mm ２ / s or more, which is a coolant for a liquid immersion cooling system. **Claim 2** The coolant for a liquid immersion cooling system according to claim 1, having a 95% distillation temperature of 430°C or higher. **Claim 3** The coolant for a liquid immersion cooling system according to claim 1 or 2, wherein the content of the antioxidant is 0.01% by mass or more and 5% by mass or less based on the total amount of the coolant for the liquid immersion cooling system.

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