JP2012031359A - Base oil for cooling of device, device-cooling oil containing the base oil, device to be cooled by the cooling oil, and device cooling method using the cooling oil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a base oil for cooling a device, having excellent electrical insulation properties and excellent thermal conductivity, a device-cooling oil containing the base oil, a device to be cooled by the cooling oil, and a device cooling method using the cooling oil.SOLUTION: There is disclosed a base oil for cooling a device which contains 30 mass% or more at least one member selected from an aliphatic diester and an aliphatic diether, wherein the total number of terminal methyl groups, methylene groups and ether groups in the main chains of the aliphatic diester and the aliphatic diether is 20 or more, the total number of methyl branches and ethyl branches in the aliphatic diester and the aliphatic diether is 2 or less, and the kinematic viscosity of the base oil is 4 to 30 mm/s at 40°C. A machine cooling oil containing the base oil has excellent electrical insulation properties and excellent thermal conductivity and is therefore suitable for cooling a motor, a battery, an inverter, an engine, an electric cell or the like in an electrically powered car or a hybrid car.

Description

  The present invention relates to an equipment cooling base oil, equipment cooling oil obtained by blending the base oil, equipment cooled by the cooling oil, and equipment cooling method using the cooling oil.

Due to the high performance of electric and hybrid vehicles, the output density of motors has increased and the amount of heat generated has also increased. For this reason, various designs have been made in the motor design, such as not only improving the heat resistance of coils and magnets, but also reducing the amount of heat generated by increasing the efficiency of the motor.
Motor cooling methods can be broadly divided into air cooling, water cooling and oil cooling. Among these, the air cooling method is excellent in that it is not necessary to prepare a cooling medium, but it is difficult to ensure a large cooling capacity. The water-cooling method is excellent in cooling because of the high thermal conductivity of water, but because of the conductivity, the motor coil cannot be directly cooled, and the necessity to stretch the cooling pipes arises, so the cooling device becomes large There is.
In contrast to these cooling systems, the oil cooling system has excellent cooling efficiency and low electrical conductivity, so that the motor can be directly cooled and a compact design can be achieved. Therefore, if it is necessary to lubricate the rotating member at the same time, the motor cooling oil can be used as the dual-purpose oil by forming the same package. For example, in a hybrid vehicle, a mechanism for circulating a transmission oil and simultaneously cooling a motor has been put into practical use. In addition, the wheel drive motor of an electric vehicle has been devised in a design that serves as both lubrication of a planetary gear and motor coil cooling by circulating lubricating oil.

As the dual-purpose oil that simultaneously performs lubrication of the transmission and the motor cooling as described above, for example, (A) a hydrocarbon group-containing zinc dithiophosphate, (B) a triaryl phosphate, and ( C) A lubricating oil composition comprising at least one of triarylthiophosphates has been proposed (see Patent Document 1). The heat transfer coefficient using a lubricating base oil having a urea adduct value of 4% by mass or less, a kinematic viscosity at 40 ° C. of 25 mm ² / s or less, and a viscosity index of 100 or more is 720 W / m ^2. A lubricating oil composition (see Patent Document 2) having a temperature of ℃ or higher or an ester-based synthetic oil in an amount of 10% by mass to 100% by mass based on the total amount of the base oil, a kinematic viscosity at 40 ° C of less than 15 mm ² / s, a viscosity The same applies to a lubricating oil composition (see Patent Document 3) having a heat transfer coefficient of 780 W / m ² · ° C. or higher using a lubricating base oil having an index of 120 or higher and a density of 0.85 g / cm ³ or higher at 15 ° C. It has been proposed as a combined oil. In each of the above-mentioned documents, it is described that the proposed lubricating oil composition is excellent in electric insulation, cooling and lubricity, and can be suitably used for an electric motor-equipped vehicle such as an electric vehicle or a hybrid vehicle. is there.

WO2002 / 097017 JP 2009-161604 A JP 2009-242547 A

  However, Patent Document 1 only mentions that the viscosity of the lubricating oil composition is low, and does not disclose any data regarding the cooling performance. Further, neopentyl glycol 2-ethylhexanoic acid diester and alkylbenzene described as base oils in the examples cannot be said to have low heat conductivity and good cooling properties. Patent Document 2 describes in paragraph [0020] of the specification that “as a urea adduct, a component that deteriorates thermal conductivity is collected accurately and reliably”. . That is, although the urea adduct component is mentioned as a component that deteriorates the thermal conductivity, it is the opposite from the actual thermal conductivity side, and “a component with a long paraffin main chain has poor thermal conductivity”. This view seems to be wrong. Therefore, it remains doubtful whether Patent Document 2 discloses a lubricating oil composition having excellent cooling performance. Further, the ester compounds specifically disclosed in Patent Document 3 are azelaic acid di-2-ethylhexyl, neopentyl glycol 2-ethylhexanoic acid diester, and oleic acid 2-ethylhexyl, which are not preferable because of low thermal conductivity. .

  Therefore, an object of the present invention is to provide a base oil for equipment cooling excellent in electrical insulation and thermal conductivity, equipment cooling oil blended with the base oil, equipment cooled by the cooling oil, and equipment using the cooling oil It is to provide a cooling method.

There is a “heat transfer coefficient (unit area, unit temperature, amount of heat transfer per unit time)” as a scale indicating the cooling performance by the fluid, and the larger this value, the better the cooling performance. However, since the heat transfer coefficient is not a physical property value but a value that changes depending on conditions such as a flow velocity and a material, a design device has been devised to increase this value.
On the other hand, in order to increase the heat transfer coefficient with a device on the fluid side, the Nusselt number, Reynolds number, and Prandtl number are related, so the physical properties of the fluid are kinematic viscosity, thermal conductivity, specific heat, and density. Affect. Specifically, the smaller the kinematic viscosity, the greater the thermal conductivity, specific heat, and density, and the better the cooling performance as a fluid. Therefore, conventionally, it has been studied to improve the cooling performance by reducing the viscosity of the fluid (lubricating oil or the like). However, in the case of lubricating oil, the cooling performance improves when the viscosity is lowered, but a sufficient oil film thickness cannot be secured, resulting in poor lubrication. Therefore, the necessary minimum limit viscosity is determined by the condition of the lubrication part such as a transmission. Therefore, even with the same kinematic viscosity, a lubricating oil with higher thermal conductivity, specific heat, and density has better cooling performance. For example, the heat transfer coefficient due to forced convection of a plate with uniform temperature is proportional to the thermal conductivity of 2/3, specific heat of 1/3, and density of 1/3. Is the largest.

Therefore, a base oil with high thermal conductivity is desired as a cooling oil used in equipment such as motors. However, there have been no studies or knowledge on the correlation between the molecular structure of the base oil and the thermal conductivity. It was. Basic low molecular weight compounds are listed in the chemical handbook, that is, are known to have high thermal conductivity of alcohols such as glycerin, ethylene glycol, and methanol. However, polar compounds such as alcohol have a low volume resistivity (poor electrical insulation) and cannot be used as a cooling oil for directly cooling devices such as motors. Also, lubricity as a lubricating oil cannot be expected.
On the other hand, the present inventor has intensively studied from the viewpoint of molecular design, and found that a compound having a predetermined molecular structure is excellent in cooling property, electrical insulation property and lubricity.
That is, the present invention provides the following equipment cooling base oil, equipment cooling oil obtained by blending the base oil, equipment cooled by the cooling oil, and equipment cooling method using the cooling oil.

(1) A base oil for equipment cooling containing 30% by mass or more of at least one of an aliphatic diester and an aliphatic diether, wherein the terminal methyl group in the main chain in the aliphatic diester and the aliphatic diether, The total number of methylene groups and ether groups is 20 or more, the total number of methyl branches and ethyl branches in the aliphatic diester and aliphatic diether is 2 or less, and the 40 ° C. kinematic viscosity of the base oil is 4 mm ² / s or more, A base oil for equipment cooling, which is 30 mm ² / s or less.
(2) The base oil for equipment cooling as described in (1) above, wherein the thermal conductivity at 25 ° C. is 0.142 W / (m · K) or more.
(3) A base oil for equipment cooling according to the above (1) or (2), wherein the volume resistivity at 25 ° C. is 10 ¹⁰ Ω · cm or more.
(4) An equipment cooling oil comprising the equipment cooling base oil according to any one of (1) to (3) above.
(5) A device that is cooled by the device cooling oil described in (4) above.
(6) The device described in (5) above is for an electric vehicle or a hybrid vehicle.
(7) The device described in (5) or (6) above is at least one of a motor, a battery, an inverter, an engine, and a battery.
(8) A device cooling method using the device cooling oil according to (4) above.

  The equipment cooling oil obtained by blending the equipment cooling base oil of the present invention is excellent in electrical insulation and thermal conductivity, so that motors, batteries, inverters, engines, batteries, etc. mounted on electric cars, hybrid cars, etc. Suitable for cooling.

The base oil for equipment cooling of the present invention (hereinafter, also simply referred to as “base oil”) is at least one of aliphatic dihydric carboxylic acid diester, aliphatic dihydric alcohol diester, and diether of aliphatic dihydric alcohol. A seed is a basic ingredient. The total number of terminal methyl groups, methylene groups and ether groups in the main chain in the aliphatic diester and aliphatic diether is 20 or more, and the total number of methyl branches and ethyl branches in the aliphatic diester and aliphatic diether is 2 It is as follows. Here, the main chain refers to the longest chain structure in the molecule.
The present invention is described in detail below.

  In order to improve the thermal conductivity of liquid molecules, it is important to improve the transfer of thermal vibration energy due to collision between molecules and to design the molecule so that the vibration energy does not diffuse within the molecule. In order to increase the collision frequency between molecules, it is effective to lengthen the main chain of the molecule and widen the movable range of the molecule end by the rotational motion between carbon-carbon bonds. Specifically, short methyl branches and ethyl branches that diffuse vibrational energy are reduced so that vibrational energy is not diffused in the molecule and remains concentrated in the molecular main chain. The methyl group and ethyl group are also disadvantageous for collision (energy transfer) with adjacent molecules because of their small movable range. As a molecule having such a structure, an ester or ether having a long chain molecule can be considered.

Therefore, in the present invention, the total number of terminal methyl groups, methylene groups, and ether groups in the main chain is 20 or more, and aliphatic diesters and aliphatic diethers in which the total number of methyl branches and ethyl branches in the molecule is 2 or less. At least one of them is used as the main component of the base oil. Further, from the viewpoint of improving the cooling performance, the number of methylene groups in the above-mentioned diester or diether is preferably 18 or more, and more preferably 19 or more.
Furthermore, the above-mentioned diesters and diethers are preferably linear from the viewpoint of improving the cooling performance as a base oil.

  Such an aliphatic diester can be obtained by a generally known ester production method and is not particularly limited. For example, a dehydration condensation reaction between a divalent carboxylic acid and an alcohol, a dehydration condensation reaction between a dihydric alcohol and a carboxylic acid, a condensation reaction between a divalent carboxylic acid dihalide and an alcohol, or a dihydric alcohol and a carboxylic acid halide. A condensation reaction, a transesterification reaction, etc. are mentioned. For example, using a raw material with a long linear alkyl chain, the total number of terminal methyl groups, methylene groups and ether groups in the main chain, which is the longest chain part of the molecule, is 20 or more, and short alkyl side chains (methyl) It is preferable to synthesize by reacting so that the total number of branches and ethyl branches is 2 or less.

  Examples of the raw material carboxylic acid include dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and 1,10-decamethylene dicarboxylic acid, n-butanoic acid, n-pentanoic acid, n-hexanoic acid, n-heptanoic acid, and n-octanoic acid. , N-nonanoic acid, n-decanoic acid, n-undecanoic acid, n-dodecanoic acid, n-tridecanoic acid, n-tetradecanoic acid, ethylhexanoic acid, butyloctanoic acid and the like. Moreover, as raw materials for ester production, carboxylic acid esters and carboxylic acid chlorides which are derivatives of these carboxylic acids can also be used.

As the raw material alcohol, for example, n hexanol, n heptanol, n octanol, n nonanol, n decanol, n undecanol, n dodecanol, n tridecanol, n tetradecanol, oleyl alcohol, ethyl hexanol, butyl octanol, pentyl nonanol, Monols such as hexyl decanol, heptyl undecanol, octyl dodecanol, and methyl heptadecanol, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexane Examples include diols such as diol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, and polytetramethylene glycol.
As the esterification catalyst, a catalyst such as titanium tetraisopropoxide may be used, or no catalyst may be used.
Moreover, the above-mentioned diether may be produced by a general ether production method such as a usual Williamson ether synthesis method, and is not particularly limited.

  The base oil of the present invention contains 30% by mass or more of the above-mentioned diester or diether, but the content as the base oil is preferably 50% or more, more preferably 60% by mass or more, and 70% by mass. More preferably, it is more preferably 80% by mass or more. If a base oil having a content of the above diester or diether of less than 30% by mass is used, the cooling performance may not be sufficiently exhibited. Of course, you may use the base oil of this invention independently (100 mass%) as a base oil for apparatus cooling.

The base oil of the present invention has a kinematic viscosity at 40 ° C. of 4 mm ² / s or more and 30 mm ² / s or less, preferably 4 mm ² / s or more and 20 mm ² / s or less. When the 40 ° C. kinematic viscosity is less than 4 mm ² / s, for example, when used as a combined oil for a motor and a transmission, the lubricity may be insufficient. On the other hand, if the 40 ° C. kinematic viscosity exceeds 30 mm ² / s, the cooling performance may be insufficient, and there may be a problem in the system circulation as cooling oil for motors and the like.

The base oil of the present invention preferably has a thermal conductivity at 25 ° C. of 0.142 W / (m · K) or more from the viewpoint of cooling properties, and more preferably 0.144 W / (m · K) or more. is there.
Further, the base oil of the present invention preferably has a volume resistivity of 10 ¹⁰ Ω · cm or more, more preferably 10 ¹¹ Ω · cm or more, and more preferably 10 ¹² Ω · cm or more from the viewpoint of electrical insulation. More preferably.

As a base oil of this invention, another component (base oil) can also be mixed and used for the above-mentioned compound. In that case, there are no particular limitations on the types of other components, but components that do not impair the above-described viscosity range and that do not impair the cooling performance, insulating properties, and lubricity are mixed to such an extent that the effects of the present invention are not impaired. There is a need.
Preferred examples of such other components include mineral oil and synthetic oil. Examples of the mineral oil include naphthenic mineral oil, paraffinic mineral oil, GTL mineral oil, WAX isomerized mineral oil, and the like. Specific examples include light neutral oil, medium neutral oil, heavy neutral oil, bright stock and the like by solvent refining or hydrogenation refining.
On the other hand, synthetic oils include polybutene or its hydride, poly α-olefin (1-octene oligomer, 1-decene oligomer, etc.) or its hydride, α-olefin copolymer, alkylbenzene, polyol ester, dibasic acid ester, poly Examples thereof include oxyalkylene glycol, polyoxyalkylene glycol ester, polyoxyalkylene glycol ether, hindered ester, and silicone oil.

The above-described equipment cooling oil comprising the base oil of the present invention can be suitably used for cooling motors, batteries, inverters, engines, batteries, and the like of electric vehicles and hybrid vehicles. Further, since the 40 ° C. viscosity of the base oil is also in a predetermined range, it is excellent in lubricity and is preferable as a dual-purpose oil that also lubricates planetary gears, transmissions, and the like.
In addition, various additives can be mix | blended with the apparatus cooling oil of this invention in the range which does not inhibit the objective of this invention. For example, viscosity index improvers, antioxidants, detergent dispersants, friction modifiers (oiliness agents, extreme pressure agents), antiwear agents, metal deactivators, pour point depressants, and antifoaming agents are required It can be blended accordingly. However, when equipment cooling oil is used as a dual-purpose oil, care should be taken so as to have a blended formulation that exhibits lubricating performance without impairing electrical insulation. Therefore, as equipment cooling oil, the thermal conductivity at 25 ° C. is 0.142 W / (m · K) or more, the volume resistivity at 25 ° C. is 10 ¹⁰ Ω · cm or more, and the kinematic viscosity at 40 ° C. It is desirable that the formulation is determined so that it is 4 mm ² / s or more and 30 mm ² / s or less.

  Examples of the viscosity index improver include non-dispersed polymethacrylates, dispersed polymethacrylates, olefin copolymers (for example, ethylene-propylene copolymers), dispersed olefin copolymers, styrene copolymers. (For example, styrene-diene hydrogenated copolymer). The mass average molecular weight of these viscosity index improvers is preferably 5,000 or more and 300,000 or less for, for example, dispersed and non-dispersed polymethacrylates. In the case of an olefin copolymer, about 800 or more and 100,000 or less are preferable. These viscosity index improvers can be blended singly or in any combination, but the blending amount is preferably in the range of 0.1% by mass or more and 20% by mass or less based on the total amount of cooling oil. .

  Antioxidants include amine-based antioxidants such as alkylated diphenylamine, phenyl-α-naphthylamine, alkylated phenyl-α-naphthylamine, 2,6-di-t-butylphenol, 4,4′-methylenebis (2, 6-di-t-butylphenol), isooctyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, n-octadecyl-3- (3,5-di-t-butyl-4- Phenol-based antioxidants such as hydroxyphenyl) propionate, sulfur-based antioxidants such as dilauryl-3,3'-thiodipropionate, phosphorus-based antioxidants such as phosphite, and molybdenum-based antioxidants. . These antioxidants can be contained alone or in any combination of two or more, but usually two or more combinations are preferable, and the blending amount is 0.01% by mass or more based on the total amount of the cooling oil. The mass% or less is preferable.

  Examples of cleaning dispersants include metal detergents such as alkaline earth metal sulfonates, alkaline earth metal phenates, alkaline earth metal salicylates, alkaline earth metal phosphonates, alkenyl succinimides, benzyl amines, alkyl polyamines, alkenyl succinates. Examples include ashless dispersants such as acid esters. These detergent dispersants may be used alone or in combination of two or more. The blending amount is preferably 0.1% by mass or more and 30% by mass or less based on the total amount of cooling oil.

  Examples of friction modifiers and antiwear agents include sulfur compounds such as sulfurized olefins, dialkyl polysulfides, diarylalkyl polysulfides, diaryl polysulfides, phosphate esters, thiophosphate esters, phosphite esters, alkyl hydrogen phosphites, phosphate esters. Phosphorus compounds such as amine salts and phosphite amine salts, chlorinated oils and fats, chlorinated paraffins, chlorinated fatty acid esters, chlorinated fatty acid and other chlorinated compounds, alkyl or alkenyl maleic acid esters, alkyl or alkenyl succinic acid esters Ester compounds such as alkyl or alkenyl maleic acid, organic acid compounds such as alkyl or alkenyl succinic acid, naphthenate, zinc dithiophosphate (ZnDTP), dithiocarbamic acid Lead (ZnDTC), sulfurized oxymolybdenum organo phosphorodithioate (MoDTP), and an organic metal-based compounds such as sulfurized oxymolybdenum dithiocarbamate (MoDTC). The blending amount is preferably 0.1% by mass or more and 5% by mass or less based on the total amount of cooling oil.

Examples of the metal deactivator include benzotriazole, triazole derivatives, benzotriazole derivatives, thiadiazole derivatives, and the like, and the blending amount is preferably 0.01% by mass or less and 3% by mass or less based on the total amount of the cooling oil.
Examples of the pour point depressant include ethylene-vinyl acetate copolymer, condensate of chlorinated paraffin and naphthalene, condensate of chlorinated paraffin and phenol, polymethacrylate, polyalkylstyrene, etc. Methacrylate is preferably used. These blending amounts are preferably 0.01% by mass or more and 5% by mass or less based on the total amount of the cooling oil.
As the antifoaming agent, liquid silicone is suitable, for example, methyl silicone, fluorosilicone, polyacrylate and the like are suitable. A preferable blending amount of these antifoaming agents is 0.0005% by mass or more and 0.01% by mass or less based on the total amount of cooling oil.

EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.
Specifically, various base oils as shown in Table 1 were prepared and subjected to various evaluations. The base oil preparation method and evaluation method (physical property measurement method) are as follows.

[Example 1]
In a 500 mL four-necked flask equipped with a Dean-Stark apparatus, 94 g of azelaic acid (reagent manufactured by Tokyo Chemical Industry Co., Ltd.), 156 g of 1-octanol (reagent manufactured by Tokyo Chemical Industry Co., Ltd.), 100 mL of mixed xylene (reagent manufactured by Tokyo Chemical Industry Co., Ltd.) ), 0.1 g of titanium tetraisopropoxide (reagent manufactured by Tokyo Chemical Industry Co., Ltd.) was added, and the mixture was reacted at 140 ° C. for 2 hours while distilling off water under stirring with a nitrogen stream. Thereafter, washing with a saturated saline solution and washing with a 0.1 N aqueous sodium hydroxide solution were performed three times each, followed by drying over anhydrous magnesium sulfate (a reagent manufactured by Tokyo Chemical Industry Co., Ltd.). After filtering the magnesium sulfate, excess raw material alcohol was distilled off to obtain 188 g of di-n-octyl azelate. Various physical properties (thermal conductivity, volume resistivity, kinematic viscosity, viscosity index, density) of this compound were measured. The results are shown in Table 1. The results are also shown in Table 1 for the following examples and comparative examples.

[Example 2]
Example except that 94 g of azelaic acid and 75 g of azelaic acid instead of 156 g of 1-octanol, 53 g of 1-octanol (a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) and 65 g of 2-ethylhexanol (a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) were used. In the same manner as in Example 1, 145 g of a mixture composed of 30% by mass of di-n-octyl azelate, 45% by mass of n-octyl 2-ethylhexyl azelate, and 25% by mass of di-2-ethylhexyl azelate was obtained. Various physical properties (thermal conductivity, volume resistivity, kinematic viscosity, viscosity index, density) of this mixture were measured.

Example 3
Various physical properties (thermal conductivity, volume resistivity, kinematic viscosity, viscosity index, density) of dodecanedioic acid di-2-ethylhexyl (a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) were measured.

Example 4
Example except that 94 g of azelaic acid, 81 g of sebacic acid instead of 156 g of 1-octanol, 53 g of 1-octanol (reagent manufactured by Tokyo Chemical Industry Co., Ltd.) and 65 g of 2-ethylhexanol (reagent manufactured by Tokyo Chemical Industry Co., Ltd.) were used. In the same manner as in Example 1, 147 g of a mixture of 32% by mass of di-n-octyl sebacate, 46% by mass of n-octyl 2-ethylhexyl sebacate, and 22% by mass of di-ethylhexyl sebacate was obtained. Various physical properties (thermal conductivity, volume resistivity, kinematic viscosity, viscosity index, density) of this mixture were measured.

Example 5
In a 1 L glass flask, 27 g of 1,4-butanediol (reagent manufactured by Tokyo Chemical Industry Co., Ltd.), 174 g of 1-bromooctane (reagent manufactured by Tokyo Chemical Industry Co., Ltd.), tetrabutylammonium bromide (manufactured by Tokyo Chemical Industry Co., Ltd.) (Reagent) 10 g and 200 g of aqueous sodium hydroxide solution (60 g of sodium hydroxide dissolved in 140 g of water) were added and stirred at 70 ° C. for 20 hours for reaction. After completion of the reaction, the reaction mixture was transferred to a separatory funnel, and the organic phase was washed 5 times with 300 mL of water, and then excess 1-bromooctane was distilled off to obtain 76 g of bis-n-octyl 1,4-butanediether. . Various physical properties (thermal conductivity, volume resistivity, kinematic viscosity, viscosity index, density) of this compound were measured.

Example 6
Example 1 except that 94 g of azelaic acid and 130 g of 2-ethylhexanoic acid (reagent made by Tokyo Chemical Industry Co., Ltd.) and 75 g of polytetrahydrofuran 250 (reagent made by Sigma-Aldrich) were used instead of 94 g of azelaic acid and 156 g of 1-octanol. To obtain 126 g of 2-ethylhexanoic acid diester of polytetrahydrofuran 250. Various physical properties (thermal conductivity, volume resistivity, kinematic viscosity, viscosity index, density) of this ester were measured.

Example 7
The same procedure as in Example 1 was performed except that 180 g of n-octanoic acid (a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) and 75 g of triethylene glycol (a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) were used instead of 94 g of azelaic acid and 156 g of 1-octanol. As a result, 163 g of n-octanoic acid diester of triethylene glycol was obtained. Various physical properties (thermal conductivity, volume resistivity, kinematic viscosity, viscosity index, density) of this ester were measured.

[Comparative Example 1]
Various physical properties (thermal conductivity, volume resistivity, kinematic viscosity, viscosity index, density) of azelaic acid di-2-ethylhexyl (a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) were measured.

[Comparative Example 2]
In the same manner as in Example 1, except that octoleic acid (reagent manufactured by Tokyo Chemical Industry Co., Ltd.) 173 g and neopentyl glycol (reagent manufactured by Tokyo Chemical Industry Co., Ltd.) 52 g were used instead of 94 g of azelaic acid and 156 g of 1-octanol. To obtain 160 g of neopentyl glycol n-octanoic acid diester. Various physical properties (thermal conductivity, volume resistivity, kinematic viscosity, viscosity index, density) of this compound were measured.

[Comparative Example 3]
Example 1 except that 94 g of azelaic acid and 165 g of 2-ethylhexanoic acid (a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) and 52 g of neopentyl glycol (a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) were used instead of 156 g of azelaic acid In the same manner, 160 g of neopentyl glycol 2-ethylhexanoic acid diester was obtained. Various physical properties (thermal conductivity, volume resistivity, kinematic viscosity, viscosity index, density) of this compound were measured.

[Comparative Example 4]
Various properties (thermal conductivity, volume resistivity, kinematic viscosity, viscosity index, density) of group II refined mineral oil (manufactured by Idemitsu Kosan Co., Ltd.) were measured.

[Method of measuring physical properties]
(1) Thermal conductivity Using a thermal characteristic meter KD2pro manufactured by Decagon Co., Ltd., it was measured at room temperature of 25 ° C. with a single needle sensor.

(2) Volume resistivity Measured at room temperature of 25 ° C. in accordance with JIS C 2101 No. 24 (volume resistivity test).
(3) Kinematic viscosity It measured based on the "petroleum product kinematic viscosity test method" prescribed | regulated to JISK2283.
(4) Viscosity index It measured based on the "petroleum product kinematic viscosity test method" prescribed | regulated to JISK2283.
(5) Density Density was measured according to JIS K2249 “Crude oil and petroleum products—Density test method”.
(6) The total number of terminal methyl groups, methylene groups, and ether groups in the main chain, and the total number of methyl branches and ethyl branches in the molecule 6850 type gas chromatograph manufactured by Agilent Technologies and AL-400 type NMR manufactured by JEOL After confirming the formation of, it was obtained from the structural formula.

〔Evaluation results〕
As can be seen from the results in Table 1, the base oils (compounds) of the present invention shown in Examples 1 to 7 are predetermined esters or ethers, all of which are terminal methyl groups, methylene groups and Since the total number of ether groups is 20 or more and the total number of methyl branches and ethyl branches in the molecule is 2 or less, both the thermal conductivity (cooling property) and the electrical insulation are excellent. Furthermore, since the kinematic viscosity is within a predetermined range, the lubricating performance is excellent. Therefore, the equipment cooling oil using the base oil of the present invention is a combined oil that also serves as a lubricant for transmissions and the like for cooling members of motors, batteries, inverters, engines and batteries for electric vehicles and hybrid vehicles. It can be understood that it is also suitable.
On the other hand, the esters of Comparative Examples 1 and 2 are inferior in thermal conductivity because the main chain is short and the number of methylene groups is small. In addition, the ester of Comparative Example 3 has a short main chain and a small number of methylene groups, and is very inferior in thermal conductivity because of many methyl branches and ethyl branches. Although the comparative example 4 is a case where refined mineral oil is used, since it is a mixture of many kinds of isomers and the above-mentioned main chain and various parameters in the molecule are not within a predetermined range, it is inferior in thermal conductivity.

Claims (8)

A base oil for equipment cooling containing 30% by mass or more of at least one of an aliphatic diester and an aliphatic diether,
The total number of terminal methyl groups, methylene groups and ether groups in the main chain in the aliphatic diester and aliphatic diether is 20 or more;
The total number of methyl and ethyl branches in the aliphatic diester and aliphatic diether is 2 or less;
The base oil for equipment cooling, wherein the base oil has a kinematic viscosity at 40 ° C. of 4 mm ² / s or more and 30 mm ² / s or less. In the base oil for equipment cooling according to claim 1,
A base oil for equipment cooling having a thermal conductivity at 25 ° C of 0.142 W / (m · K) or more. In the base oil for apparatus cooling of Claim 1 or Claim 2,
The volume resistivity at 25 ° C. is 10 ¹⁰ Ω · cm or more. An equipment cooling oil comprising the equipment cooling base oil according to any one of claims 1 to 3. The equipment is cooled by the equipment cooling oil according to claim 4. The device according to claim 5 is for an electric vehicle or a hybrid vehicle. The device according to claim 5 or 6 is at least one of a motor, a battery, an inverter, an engine, and a battery. The apparatus cooling oil of Claim 4 is used. The apparatus cooling method characterized by the above-mentioned.