EP2520637A1

EP2520637A1 - 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

Info

Publication number: EP2520637A1
Application number: EP10840849A
Authority: EP
Inventors: Toshiyuki Tsubouchi
Original assignee: Idemitsu Kosan Co Ltd
Current assignee: Idemitsu Kosan Co Ltd
Priority date: 2009-12-28
Filing date: 2010-12-06
Publication date: 2012-11-07
Also published as: EP2520637A4; WO2011080991A1; CN102695782A; KR20120112666A

Abstract

A device-cooling base oil includes 30 mass% of at least one of an oleyl ester (e.g., oleate and oleyl alcohol ester) and oleyl ether. The oleyl ester and the oleyl ether each have 23 or more of a total number of a terminal methyl group, a methylene group and an ether group in a main chain and 1 or less of a total number of a methyl branch and an ethyl branch. The base oil has a kinematic viscosity at 40 degrees C in a range of 4 mm²/s to 30 mm²/s. A device-cooling oil provided by blending the base oil is excellent in electrical insulation properties and thermal conductivity, and thus is favorably usable for cooling a motor, a battery, an inverter, an engine, an electric cell or the like in an electric vehicle, a hybrid vehicle or the like.

Description

TECHNICAL FIELD

The present invention relates to a base oil for cooling a device, a device-cooling oil using the base oil, a device to be cooled by the device-cooling oil, and a device cooling method using the device-cooling oil.

BACKGROUND ART

An improvement in the performance of electric vehicles and hybrid vehicles results in an increase in the power density and, consequently, the heat generation of a motor. Accordingly, coil, magnet and the like have been improved in heat resistance and, further, a variety of modifications in motor design have been made for, for instance, reducing the increased heat generation resulting from the improved performance of a motor.
For cooling a motor, there have been suggested three types of methods, i.e., an air-cooling method, a water-cooling method and an oil-cooling method. Among the above, the air-cooling method advantageously does not require any specific coolant to be prepared, but is unlikely to provide a large cooling capacity. The water-cooling method is excellent in cooling properties because water exhibits a high thermal conductivity. However, since a motor coil cannot be directly cooled because of the electrical conductivity of water, a cooling pipe has to be laid out, which, disadvantageously, increases the size of a cooling device.
As compared with the above cooling methods, the oil-cooling method uses oil, which is excellent in cooling efficiency and low in electrical conductivity, so that the oil-cooling method enables directly cooling a motor, resulting in a compact design. Additionally, when lubrication of a rotary member is simultaneously required, an oil for cooling the motor is usable as a dual-purpose oil not only for cooling but also for lubrication (i.e., the same packaging). For instance, hybrid vehicles in practice use a mechanism for circulating a transmission oil to simultaneously cool a motor. Some wheel-driving motors for electric vehicles have been modified in design such that a lubricating oil is circulated not only for lubricating a planetary gear but also for cooling a motor coil.
As such a dual-purpose oil usable for cooling a motor while lubricating a transmission or the like, there has been suggested, for instance, a lubricating oil composition provided by blending a low-viscosity mineral oil or synthetic oil with at least one of (A) zinc dithiophosphate containing a hydrocarbon group, (B) triaryl phosphate and (C) triaryl thiophosphate (see Patent Literature 1). Additionally, as the dual-purpose oil, there have been suggested: a lubricating oil composition using a base oil that has a urea adduct value of 4 mass% or less, a kinematic viscosity of 25 mm²/s or less at 40 degrees C and a viscosity index of 100 or more, the lubricating oil composition having a heat transfer coefficient of 720 W/m²·degrees C or more (see Patent Literature 2); and a lubricating oil composition using a base oil that contains an ester synthetic oil of 10 mass% to 100 mass% of the total amount of the base oil and has a kinematic viscosity of less than 15 mm²/s at 40 degrees C, a viscosity index of 120 or more and a density of 0.85 g/cm³ or more at 15 degrees C, the lubricating oil composition having a heat transfer coefficient of 780 W/m²·degrees C or more (see Patent Literature 3). Each of Patent Literatures 1, 2 and 3 discloses that the suggested lubricating oil composition is excellent in electrical insulation properties, cooling properties and lubricity and is favorably usable for electric motor vehicles such as electric vehicles and hybrid vehicles.

CITATION LIST

PATENT LITERATURE(S)

Patent Literature 1: WO2002/097017
Patent Literature 2: JP-A-2009-161604
Patent Literature 3: JP-A-2009-242547

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

In connection with the cooling properties of the lubricating oil composition, Patent Literature 1 does not teach anything but lowering the viscosity of the lubricating oil composition, and does not even show data on cooling properties. Additionally, neopentylglycol 2-ethyl hexanoic acid diester and alkylbenzene, which are used as base oils in Examples of Patent Literature 1, are unlikely to exhibit excellent cooling properties because of their poor thermal conductivity. Patent Literature 2 teaches in paragraph [0020] that "as an urea adduct, ... a component that deteriorates thermal conductivity... is accurately and reliably collected." In other words, contrarily to the fact, Patent Literature 2 teaches that a urea adduct component deteriorates thermal conductivity. It is probably wrong that "a component having a long paraffin main chain exhibits a poor thermal conductivity." In view of the above, it is doubtful whether or not Patent Literature 2 discloses a lubricating oil composition excellent in cooling properties. Ester compounds specifically disclosed in Patent Literature 3 are azelaic acid di-2-ethylhexyl, neopentyl glycol 2-ethylhexanoate diester and 2-ethylhexyl oleate, which unfavorably exhibit a low thermal conductivity.
An object of the invention is to provide: a base oil having excellent electrical insulation properties and thermal conductivity for cooling a device; a device-cooling oil using the base oil; a device to be cooled by the device-cooling oil; and a device cooling method using the device-cooling oil

MEANS FOR SOLVING THE PROBLEMS

As a measure of the cooling properties of a fluid, "heat transfer coefficient (heat transfer amount per unit area, unit temperature and unit time)" is usable. A fluid having a higher value of heat transfer coefficient exhibits better cooling properties. Since heat transfer coefficient is not physical properties but is variable depending on conditions such as flow rate and material type, modifications in design for increasing heat transfer coefficient have been made.
For increasing heat transfer coefficient by modifications in terms of a fluid, it should be noted that since heat transfer coefficient is variable in relation to Nusselt number, Reynolds number and Prandtl number, the cooling properties of a fluid are affected by the physical properties of the fluid such as kinematic viscosity, thermal conductivity, specific heat and density. Specifically, a fluid having smaller kinematic viscosity but larger thermal conductivity, specific heat and density exhibits better cooling properties. Accordingly, it has been considered to lower the viscosity of a fluid (e.g., a lubricating oil) for improving the cooling properties thereof. However, when the viscosity of a lubricating oil is lowered, the cooling properties are improved but a sufficient film thickness of the lubricating oil cannot be provided, thereby causing lubrication failure. In view of the above, the minimum viscosity is determined depending on conditions regarding a portion to be lubricated in a transmission or the like. Thus, among lubricating oils having the same kinematic viscosity, one having larger thermal conductivity, specific heat and density has better cooling properties. For instance, a heat transfer coefficient during forced convection of a plate having a uniform temperature is proportional to the thermal conductivity to the power of two thirds, the specific heat to the power of one third and the density to the power of one third, so that the heat transfer coefficient is the most affected by the thermal conductivity.
In view of the above, a base oil having a high thermal conductivity is favorable for a cooling oil usable in a device such as a motor. However, a correlation between the molecular structure and the thermal conductivity of a base oil has not been studied. Regarding basic low-molecular compounds, there is only a small amount of information available. Specifically, alcohols such as glycerin, ethyleneglycol and methanol are excellent in thermal conductivity as described in Kagaku Binran ("Handbook of Chemistry"). However, polar compounds such as alcohols exhibit a poor volume resistivity (poor electrical insulation properties), so that they are not usable as a cooling oil for directly cooling a device such as motor. Additionally, they are not expected to be usable as a lubricating oil because of a lack of lubricity.
As a result of concentrated studies in terms of molecular design, the inventor has found that a compound having a predetermined molecular structure is excellent in cooling properties, electrical insulation properties and lubricity.
In other words, according to the invention, there are provided: a base oil for cooling a device; a device-cooling oil using the base oil; a device to be cooled by the device-cooling oil; and a device cooling method using the device-cooling oil, as described below.

(1) A base oil for cooling a device includes 30 mass% or more of at least one of an oleyl ester (oleate and an oleyl alcohol ester) and an oleyl ether, in which the oleyl ester and the oleyl ether each have 23 or more of a total number of a terminal methyl group, a methylene group and an ether group in a main chain, the oleyl ester and the oleyl ether each have 1 or less of a total number of a methyl branch and an ethyl branch, and the base oil has a kinematic viscosity in a range of 4 mm²/s to 30 mm²/s.
(2) In the above base oil, the oleyl ester and the oleyl ether are contained at 50 mass% or more.
(3) A base oil for cooling a device contains 30 mass% or more of at least one of an aliphatic monoester and an aliphatic monoether, in which the aliphatic monoester and the aliphatic monoether each have 18 or more of a total number of a terminal methyl group, a methylene group and an ether group in a main chain, the aliphatic monoester and the aliphatic monoether each have 2 or less of a total number of a methyl branch and an ethyl branch, and the base oil has a kinematic viscosity in a range of 4 mm²/s to 30 mm²/s.
(4) In the above base oil, at least one of the aliphatic monoester and the aliphatic monoether has a chain structure.
(5) A base oil for cooling a device contains 30 mass% or more of at least one of an aliphatic diester and an aliphatic diether, in which the aliphatic diester and the aliphatic diether each have 20 or more of a total number of a terminal methyl group, a methylene group and an ether group in a main chain, the aliphatic diester and the aliphatic diether each have 2 or less of a total number of a methyl branch and an ethyl branch, and the base oil has a kinematic viscosity in a range of 4 mm²/s to 30 mm²/s.
(6) A base oil for cooling a device contains 30 mass% or more of at least one of an aliphatic triester, an aliphatic triether, an aliphatic tri(etherester), an aliphatic tetraester, an aliphatic tetraether, an aliphatic tetra(etherester), an aromatic diester, an aromatic diether and an aromatic di(etherester), wherein each of the esters, the ethers and the etheresters has 18 or more of a total number of a terminal methyl group, a methylene group and an ether group in a main chain and 1 or less of a total number of a methyl branch and an ethyl branch, and the base oil has a kinematic viscosity in a range of 4 mm²/s to 30 mm²/s.
(7) In the above base oil, a thermal conductivity of the base oil at 25 degrees C is 0.142 W/(m·K) or more.
(8) In the above base oil, a volume resistivity of the base oil at 25 degrees C is 10¹⁰Ω·cm or more.
(9) A device-cooling oil contains the above base oil.
(10) A device is configured to be cooled by the device-cooling oil.
(11) The above device is usable for an electric vehicle or a hybrid vehicle.
(12) The device is at least one of a motor, a battery, an inverter, an engine and an electric cell.
(13) A device cooling method uses the device-cooling oil.

A device-cooling oil provided by blending a base oil for cooling a device according to the invention is excellent in electrical insulation properties and thermal conductivity, and thus is favorably usable for cooling a motor, a battery, an inverter, an engine, an electric cell or the like in an electric vehicle, a hybrid vehicle or the like.

DESCRIPTION OF EMBODIMENT(S)

A device-cooling base oil, a device-cooling oil containing the device-cooling base oil, a device to be cooled by the device-cooling oil, and a device cooling method using the device-cooling oil according to exemplary embodiments of the invention will be described below.

First Exemplary Embodiment

A device-cooling base oil in a first exemplary embodiment of the invention (hereinafter referred to as a "base oil") contains at least one of an oleyl ester (i.e., an oleate, an oleyl alcohol ester) and an oleyl ether as a basic component.
The oleyl ester and the oleyl ether each have 23 or more of a total number of a terminal methyl group, a methylene group and an ether group in a main chain and 1 or less of a total number of a methyl branch and an ethyl branch in a molecule. The "main chain" herein means a portion having the longest chain structure in the molecule.
The first exemplary embodiment will be described in detail below.
For improving the thermal conductivity of liquid molecules, it is important to accelerate the transfer of thermal vibration energy resulting from collision between the molecules and to design the molecules such that the vibration energy is not dispersed in the molecules. In order to increase the frequency of collision between the molecules, it is effective to elongate the main chain of each molecule, thereby increasing the movable range of the molecule end based on a rotation around at a carbon-carbon bond. Specifically, in order to keep the vibration energy being concentrated in the main chain of each molecule without dispersing in the molecule, methyl branch and ethyl branch, which are short in length and cause dispersion of the vibration energy, are decreased in number. Additionally, the methyl group and the ethyl group are not favorable for collision with the adjacent molecules (energy transfer) because of a small movable range thereof. Esters and ethers having a long chain structure are recognized as a molecule having such a structure.
Accordingly, in the exemplary embodiment, a main component of a base oil is provided by an oleyl ester or an oleyl ether in which the total number of a terminal methyl group(s), a methylene group(s) and an ether group(s) in the main chain is 23 or more and the total number of a methyl branch and an ethyl branch in the molecule is 1 or less. The number of the methylene group in the oleyl ester and the oleyl ether is preferably 22 or more, more preferably 24 or more in terms of an enhancement of cooling properties.
Each entire structure of the oleyl ester and the oleyl ether is preferably a chain structure, more preferably a straight-chain structure, in terms of an enhancement of the cooling properties of the base oil.
Such an oleyl ester is obtainable by typically known methods of manufacturing esters. A method of manufacturing the oleyl ester is subject to no limitation. For instance, the oleyl ester is obtainable by: a dehydration condensation reaction between oleic acid and alcohol or a dehydration condensation reaction between carboxylic acid and oleyl alcohol; a condensation reaction between oleic acid halides and alcohol or a condensation reaction between carboxylic acid halides and oleyl alcohol; and an ester exchange reaction. For instance, alcohol (the starting material) having a long linear alkyl chain and carboxylic acid (the starting material) having a long linear alkyl chain are preferably used for synthetic reaction such that the total number of the terminal methyl group, the methylene group and the ether group in the main chain (i.e., the longest chain in a molecule) is 23 or more and the total number of a short alkyl side chain in the molecule (i.e., the methyl branch and the ethyl branch) is 1 or less.
Examples of the carboxylic acid (the starting material) include monocarboxylic acids such as oleic acid, n-hexanoic acid, n-heptanoic acid, n-octanoic acid, n-nonanoic acid, n-decanoic acid, n-undecanoic acid, n-dodecanoic acid, n-tridecanoic acid, n-tetradecanoic acid, ethylhexanoate, butyl octanoic acid, pentyl nonanoic acid, hexyl decanoic acid, heptyl undecanoic acid, octyldodecanoic acid, methyl heptadecanoic acid and benzoic acid.
Examples of the alcohol (the starting material) include oleyl alcohol, n-hexanol, n-heptanol, n-octanol, n-nonanol, n-decanol, n-undecanol, n-dodecanol, n-tridecanol, n-tetradecanol, ethylhexanol, butyloctanol, pentylnonanol, hexyldecanol, heptylundecanol, octyldodecanol, methylheptadecanol, benzyl alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether and triethylene glycol monobutyl ether.
A catalyst such as titanium tetraisopropoxide may be used an esterification catalyst, or no catalyst may be used.
The above oleyl ether may be manufactured by a typical ether manufacturing method such as the Williamson ether synthetic method, but the manufacturing method of the oleyl ether is subject to no limitation.
The base oil of the exemplary embodiment contains 30 mass% or more of at least one of the ester and the ether described above, preferably 50 mass% or more, more preferably 60 mass% or more, further preferably 70 mass% or more, particularly preferably 80 mass% or more. When the base oil contains the ester and the ether at less than 30 mass%, the base oil may not exhibit a sufficient cooling properties. It should be noted that a base oil for cooling a device may be provided only by the base oil of the exemplary embodiment (at 100 mass%).
The base oil of the exemplary embodiment has a kinematic viscosity at 40 degrees C in a range from 4 mm²/s to 30 mm²/s, preferably from 4 mm²/s to 20 mm²/s. If the kinematic viscosity of the base oil at 40 degrees C is less than 4 mm²/s, for instance, when the base oil is used as a dual-purpose oil not only for a motor but also for a transmission or the like, the base oil may exhibit an insufficient lubricity. On the other hand, if the kinematic viscosity of the base oil at 40 degrees C exceeds 30 mm²/s, the cooling properties may be insufficient. Additionally, when such a base oil is used as a cooling oil for a motor or the like, the cooling oil is unlikely to smoothly circulate within a system or the like.
The base oil of the exemplary embodiment preferably has a thermal conductivity at 25 degrees C of 0.142 W/(m·K) or more, more preferably 0.144 W/(m·K) or more, in terms of the cooling properties.
The base oil of the exemplary embodiment preferably has a volume resistivity at 25 degrees C of 10¹⁰ Ω·cm or more, more preferably 10¹¹ Ω·cm or more, further preferably 10¹² Ω·cm or more, particularly preferably 10¹³ Ω·cm or more.
The base oil of the exemplary embodiment may be provided by blending the above-mentioned ester and ether with an additional component (base oil). In this case, the additional component is not particularly limited in type. However, even after blending the additional component, the viscosity range, the cooling properties, the insulation properties and the lubricity should be maintained as described above and the advantages of the invention should be achieved.
Preferable examples of the additional component are a mineral oil and a synthetic oil. Examples of the mineral oil are a naphthenic mineral oil, a paraffinic mineral oil, a GTL mineral oil and a WAX-isomerized mineral oil. Specifically, the mineral oil is exemplified by a light neutral oil, a medium neutral oil, a heavy neutral oil and a bright stock, which are provided by solvent refining or hydrogenation refining.
Examples of the synthetic oil are polybutene and a hydrogenated product thereof, poly-alpha-olefin (e.g., 1-octene oligomer and 1-decene oligomer) and a hydrogenated product thereof, alpha-olefin copolymer, alkylbenzene, polyol ester, dibasic acid ester, polyoxyalkylene glycol, polyoxyalkylene glycol ester, polyoxyalkylene glycol ether, hindered ester, and silicone oil.
A device-cooling oil containing the base oil of the exemplary embodiment is favorably usable for cooling a motor, a battery, an inverter, an engine and an electric cell or the like in an electric vehicle, a hybrid vehicle or the like. Since the viscosity of the base oil at 40 degrees C is in the above predetermined range, the device-cooling oil is excellent in lubricity, and thus is favorably usable as a dual-purpose oil not only for cooling but also for lubricating a planetary gear, a transmission or the like.
A variety of additives may be blended in the device-cooling oil of the exemplary embodiment as long as an object of the invention is attainable. For instance, a viscosity index improver, an antioxidant, a detergent dispersant, a friction modifier (e.g., an oiliness agent and an extreme pressure agent), an antiwear agent, a metal deactivator, a pour point depressant, and an antifoaming agent can be blended as needed. It should be noted that when the device-cooling oil is used as a dual-purpose oil, the respective blending ratios of the additives should be determined such that the device-cooling oil can exhibit lubricating properties while maintaining electrical insulation properties. In view of the above, the respective blending ratios are preferably determined such that the device-cooling oil has a thermal conductivity at 25 degrees C of 0.142 W/(m·K) or more, a volume resistivity at 25 degrees C of 10¹⁰Ω·m or more, and a kinematic viscosity at 40 degrees C of 4 mm²/s to 30 mm²/s.
Examples of the viscosity index improver are a non-dispersive polymethacrylate, a dispersive polymethacrylate, an olefin copolymer (e.g., an ethylene-propylene copolymer), a dispersive olefin copolymer, and a styrene copolymer (e.g., a styrene-diene copolymer hydride). When the dispersive or non-dispersive polymethacrylate is used as the viscosity index improver, the mass average molecular weight of the viscosity index improver is preferably in a range from 5,000 to 300,000. When the olefin copolymer is used, the mass average molecular weight is preferably in a range from 800 to 100,000. One of these viscosity index improvers may be singularly blended or a combination thereof may be blended. The content of the viscosity index improver(s) is preferably in a range from 0.1 mass% to 20 mass% of the total amount of the cooling oil.
Examples of the antioxidant are: amine antioxidants such as alkylated diphenylamine, phenyl-alpha-naphthylamine, and alkylated phenyl-alpha-naphthylamine; phenol antioxidants such as 2,6-di-t-butylphenol, 4,4'-methylenebis(2,6-di-t-butylphenol), isooctyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, and n-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate; sulfur-based antioxidants such as dilauryl-3,3'-thiodipropionate; phosphorus-based antioxidants such as phosphite; and molybdenum-based antioxidants. One of these antioxidants may be singularly blended or a combination thereof may be blended. Preferably, two or more of these antioxidants are blended in combination and the content thereof is in a range from 0.01 mass% to 5 mass% of the total amount of the cooling oil.
Examples of the detergent dispersant are: metal-based cleaners such as alkaline earth metal sulfonate, alkaline earth metal phenate, alkaline earth metal salicylate, and alkaline earth metal phosphonate; and ashless dispersants such as alkenyl succinimide, benzylamine, alkylpolyamine, and alkenyl succinimide ester. One of these detergent dispersants may be singularly blended or a combination of two or more thereof may be blended. The content of the detergent dispersant(s) is preferably in a range from 0.1 mass% to 30 mass% of the total amount of the cooling oil.
Examples of the friction modifier or the antiwear agent are: sulfur compounds such as olefin sulfide, dialkyl polysulfide, diarylalkyl polysulfide, and diaryl polysulfide; phosphorus compounds such as phosphate, thiophosphate, phosphite, alkyl hydrogen phosphite, phosphate amine salt, and phosphite amine salt; chloride compounds such as chlorinated fat and oil, chlorinated paraffin, chlorinated fatty acid ester, and chlorinated fatty acid; ester compounds such as alkyl or alkenyl maleate, and alkyl or alkenyl succinate; organic acid compounds such as alkyl or alkenyl maleic acid, and alkyl or alkenyl succinic acid; and organic metal compounds such as naphthenic acid salt, zinc dithiophosphate (ZnDTP), zinc dithiocarbamate (ZnDTC), sulfurized oxymolybdenum organophosphorodithioate (MoDTP), and sulfurized oxymolybdenum dithiocarbamate (MoDTC). The content of the friction modifier or the antiwear agent is preferably in a range from 0.1 mass% to 5 mass% of the total amount of the cooling oil.
Examples of the metal deactivator are benzotriazole, triazole derivative, benzotriazole derivative, and thiadiazole derivative. The content of the metal deactivator is preferably in a range from 0.01 mass% to 3 mass%.
Examples of the pour point depressant are an ethylene-vinyl acetate copolymer, a condensate of chlorinated paraffin and naphthalene, a condensate of chlorinated paraffin and phenol, polymethacrylate, and polyalkylstyrene, among which polymethacrylate is preferably usable. The content of the pour point depressant is preferably in a range from 0.01 mass% to 5 mass% of the total amount of the cooling oil.
As the antifoaming agent, a liquid silicone is suitable and, specifically, methylsilicone, fluorosilicone, polyacrylate and the like are preferably usable. The content of the antifoaming agent is preferably in a range from 0.0005 mass% to 0.01 mass% of the total amount of the cooling oil.

Examples of First Exemplary Embodiment

Next, the first exemplary embodiment will be further described in detail based on Examples, which by no means limit the first exemplary embodiment.
Specifically, base oils shown in Table 1 were prepared and various evaluations thereof were conducted. A preparation method and an evaluation method (a physical properties measuring method) for the base oils are as follows.

Table 1

	Example 1	Example 2	Example 3	Example 4	Example 5	Example 6	Exemple 7	Comp. 1	Comp. 2
Base Oil (Compound Name)	oleyl oleate	n-dodecyl oleate	n-octyl oleate	16-methylheptadecyl oleate	n-octanoic acid oleyl	n-octyloleyl ether	butoxyethyl oleate	2-ethylhexyl oleate	group-II purified mineral oil
Total of terminal methyl, methylene and ether in main chain	32	28	24	31	24	24	23	21	mixture of plural kinds
Total of methyl and ethyl branches in molecule	0	0	0	1	0	0	0	1	mixture of plural kinds
Thermal Conductivity (25°C) W/m·K	0.153	0.149	0.146	0.149	0.146	0.147	0.146	0.140	0.130
Volume Resistivity (25°C) Ω·cm	4.4E+11	3.6E+12	1.6E+11	1.5E+13	2.2E+11	2.4E+12	1.4E+10	2.9E+12	1.2E+15
Kinematic Viscosity (40°C) mm²/s	18.00	12.60	8.552	20.93	9.308	8.862	7.316	8.331	9.898
Kinematic Viscosity (100°C) mm2/s	5.018	3.765	2.837	5.284	3.002	2.871	2.491	2.705	2.722
Viscosity Index	232	213	209	204	205	199	196	188	116
Density (15°C) g/cm³	0.8707	0.8661	0.8682	0.8693	0.8682	0.8419	0.8928	0.8690	0.8265

Example 1

To a four-necked flask (500 mL) provided with a Dean-Stark apparatus, oleic acid (127 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.), oleyl alcohol (145 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.), mixed xylene (100 mL, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.), and titanium tetraisopropoxide (0.1 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) were put. A reaction was conducted at 140 degrees C for two hours while water was distilled away under nitrogen stream with stirring. Subsequently, the reaction product was washed with saturated saline three times and with 0.1 N aqueous sodium hydroxide three times and was then dried with anhydrous magnesium sulfate (a reagent manufactured by Tokyo Chemical Industry Co., Ltd.). After filtration of magnesium sulfate, excessive alcohol (the starting material) was distilled away to obtain oleyl oleate (215 g). This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density). The results are shown in Table 1. The results of the following Examples and Comparatives are also shown in Table 1.

Example 2

Example 2 was performed in the same manner as in Example 1 except that n-dodecyl alcohol (101 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) was used in place of 145 g of oleyl alcohol, so that 184 g of n-dodecyl oleate was obtained. This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Example 3

Example 3 was performed in the same manner as in Example 1 except that n-octyl alcohol (71g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) was used in place of 145 g of oleyl alcohol, so that 162g of n-octyl oleate was obtained. This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Example 4

Example 4 was performed in the same manner as in Example 1 except that 16-methylheptadecanol (147g, product name: Isostearyl Alcohol EX, manufactured by KOKYU ALCOHOL KOGYO CO., LTD) was used in place of 145 g of oleyl alcohol, so that 16-methylheptadecyl oleate (212g) was obtained. This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Example 5

Example 5 was performed in the same manner as in Example 1 except that n-octanoic acid (65g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) and 107 g of oleyl alcohol were used in place of 127 g of oleic acid and 145 g of oleyl alcohol, so that n-octanoic acid oleyl (143g) was obtained. This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Example 6

To a 1-L glass flask, oleyl alcohol (107 g), 1-bromooctane (120 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.), tetrabutyl ammonium bromide (10 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.), and an aqueous sodium hydroxide (200 g, obtained by dissolving 60 g of sodium hydroxide in 140 g of water). A mixture was reacted at 70 degrees C for 20 hours with stirring. After the reaction, the reaction mixture was transferred to a separating funnel. An organic phase was washed five times with water (300 mL). Subsequently, the organic phase was distilled, so that n-octyl oleyl ether (103 g) was obtained. This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Example 7

Example 7 was performed in the same manner as in Example 1 except that ethylene glycol monobutyl ether (65g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) was used in place of 145 g of oleyl alcohol, so that butoxyethyl oleate (158g) was obtained. This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Comparative 1

Comparative 1 was performed in the same manner as in Example 1 except that 2-ethylhexanol (71g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) was used in place of 145 g of oleyl alcohol, so that 2-ethylhexyl oleate (161g) was obtained. The obtained compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, kinematic viscosity, viscosity index, density and volume resistivity).

Comparative 2

A purified mineral oil of Group II (manufactured by Idemitsu Kosan Co., Ltd.) was measured in terms of the physical properties thereof (i.e., thermal conductivity, kinematic viscosity, viscosity index, density and volume resistivity).

Physical Properties Measuring Method

(1) Thermal Conductivity

A thermal conductivity was measured using a single needle sensor of KD2pro thermal properties analyzer manufactured by Decagon Device, Inc. at a room temperature of 25 degrees C.

(2) Volume Resistivity

A volume resistivity was measured at a room temperature of 25 degrees C in accordance with JIS (Japanese Industrial Standards) C2101, 24 (Volume Resistivity Test).

(3) Kinematic Viscosity

A kinematic viscosity was measured according to "Test Methods for Kinematic Viscosity of Petroleum Products" defined in JIS K 2283.

(4) Viscosity Index

A viscosity index was measured according to "Test Methods for Kinematic Viscosity of Petroleum Products" defined in JIS K 2283.

(5) Density

A density was measured in accordance with JIS K2249, "Crude Oil and Petroleum Product—Density Test Method".

(6) Total Number of Terminal Methyl Group, Methylene Group and Ether Group in Main Chain and Total Number of Methyl Branch and Ethyl Branch in Molecule

After formation of a target product was confirmed by 6850 Gas Chromatograph (manufactured by Agilent Technologies) and AL-400 NMR (manufactured by JEOL Ltd.), the total number of a terminal methyl group, a methylene group and an ether group in a main chain and the total number of a methyl branch and an ethyl branch in a molecule were obtained according to a structural formula of the target product.

Evaluation Result

As understood from the results of Table 1, the base oil (a compound) according to this exemplary embodiment in each of Examples 1 to 7 was a predetermined ester or ether. Since the ester and the ether each had 23 or more of the total number of the terminal methyl group, the methylene group and the ether group in the main chain and 1 or less of the total number of the methyl branch and the ethyl branch in a molecule, the ester and the ether exhibited excellent thermal conductivity (cooling properties) and electrical insulation properties. Further, these base oils were excellent in lubricating properties because the kinematic viscosities thereof were within the predetermined range. Thus, it is understandable that a device-cooling oil using the base oil according to the invention is favorably usable as a dual-purpose oil not only for cooling a motor, a battery, an inverter, an engine, an electric cell or the like in an electric vehicle or a hybrid vehicle but also for lubricating a transmission or the like.
On the other hand, although the base oil in Comparative 1 was an ester obtained from alcohol having 8 carbon atoms in the same manner as in Example 3, the total number of a terminal methyl group, a methylene group and an ether group in a main chain was small, so that the base oil exhibited a poor thermal conductivity. In Comparative 2 in which the purified mineral oil was used, since the base oil was a mixture of many kinds of isomers, the above parameters on the main chain and the molecule were not within a predetermined range, so that the base oil exhibited a poor thermal conductivity.

Second Exemplary Embodiment

The base oil according to the first exemplary embodiment contains at least one of the oleyl ester (oleate, oleyl alcohol ester) and the oleyl ether as a fundamental component.
A device-cooling base oil according to a second exemplary embodiment of the invention contains at least one of an aliphatic monoester and an aliphatic monoether as a basic component.
The total number of a terminal methyl group, a methylene group and an ether group in a main chain of the monoester and the monoether is 18 or more. The total number of a methyl branch and an ethyl branch in a molecule of the monoester and the monoether is 2 or less. The "main chain" herein means a portion having the longest chain structure in the molecule.
The second exemplary embodiment will be described in detail below.
In describing this exemplary embodiment, what has been described in the above first exemplary embodiment will be omitted or simplified.
In this exemplary embodiment, the aliphatic monoester and the aliphatic monoether are used as main components of the base oil. The total number of the terminal methyl group, the methylene group and the ether group in the main chain in each of the ester and the ether is 18 or more in terms of an enhancement of cooling properties. Moreover, the total number of the methyl branches and the ethyl branches in a molecule of the ester and the ether is 2 or less in terms of an enhancement of cooling properties. The number of the methylene group in each of the ester and the ether is preferably 17 or more in terms of an enhancement of cooling properties. In terms of the cooling properties, the ester and the ether each preferably have a chain structure, more preferably a linear chain structure including no branch.
Such an ester is obtainable by typically known methods of manufacturing esters. A method of manufacturing the oleyl ester is subject to no limitation. For instance, the ester is obtainable by a dehydro-condensation reaction between a carboxylic acid and alcohol, a condensation reaction between a carboxylic halide or alcohol, and a transesterification. For instance, a starting material having a long linear alkyl chain is preferably used for synthetic reaction such that the total number of the terminal methyl group, the methylene group and the ether group in the main chain (i.e., the longest chain in a molecule) is 18 or more and the total number of a short alkyl side chain in the molecule (i.e., the methyl branch and the ethyl branch) is 2 or less.
Examples of the carboxylic acid (the starting material) include monocarboxylic acids such as oleic acid, n-hexanoic acid, n-heptanoic acid, n-octanoic acid, n-nonanoic acid, n-decanoic acid, n-undecanoic acid, n-dodecanoic acid, n-tridecanoic acid, n-tetradecanoic acid, ethylhexanoate, butyl octanoic acid, pentyl nonanoic acid, hexyl decanoic acid, heptyl undecanoic acid, octyldodecanoic acid, methyl heptadecanoic acid and benzoic acid. As a starting material for manufacturing esters, a carboxylic acid ester and a carboxylic acid chloride, which are derivatives of the above carboxylic acids, are usable.
Examples of the alcohol (the starting material) include a monool such as n-hexanol, n-heptanol, n-octanol, n-nonanol, n-decanol, n-undecanol, n-dodecanol, n-tridecanol, n-tetradecanol, oleyl alcohol, ethylhexanol, butyloctanol, pentylnonanol, hexyldecanol, heptylundecanol, octyldodecanol, methylheptadecanol, benzyl alcohol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether and triethylene glycol monobutyl ether.
A catalyst such as titanium tetraisopropoxide may be used as an esterification catalyst, or no catalyst may be used.
The ether may be manufactured by a typical ether manufacturing method such as the Williamson ether synthetic method, but the manufacturing method of the ether is subject to no limitation.
The base oil of the exemplary embodiment contains 30 mass% or more of the ester and the ether, preferably 50 mass% or more, more preferably 60 mass% or more, further preferably 70 mass% or more, particularly preferably 80 mass% or more. When the base oil contains the ester and the ether at less than 30 mass%, the base oil may not exhibit a sufficient cooling properties. It should be noted that a base oil for cooling a device may be provided only by the base oil of the exemplary embodiment (at 100 mass%).
The base oil of the exemplary embodiment has a kinematic viscosity at 40 degrees C in a range of 4 mm²/s to 30 mm²/s, preferably of 4 mm²/s to 20 mm²/s, in the same manner as in the above-mentioned exemplary embodiment. If the kinematic viscosity of the base oil at 40 degrees C is less than 4 mm²/s, for instance, when the base oil is used as a dual-purpose oil not only for a motor but also for a transmission or the like, the base oil may exhibit an insufficient lubricity. On the other hand, if the kinematic viscosity of the base oil at 40 degrees C exceeds 30 mm²/s, the cooling properties may be insufficient. Additionally, when such a base oil is used as a cooling oil for a motor or the like, the cooling oil is unlikely to smoothly circulate within a system or the like.
According to the exemplary embodiment, the thermal conductivity of the base oil at 25 degrees C is preferably 0.142 W/(m·K) or more, more preferably 0.144 W/(m·K) or more in terms of the cooling properties, in the same manner as in the above-mentioned exemplary embodiment.
The base oil of the exemplary embodiment preferably has a volume resistivity at 25 degrees C of 10¹⁰ Ω·cm or more, more preferably 10¹¹ Ω·cm or more, further preferably 10¹² Ω·cm or more, particularly preferably 10¹³ Ω·cm or more.
The base oil of the exemplary embodiment may be provided by blending the above-mentioned ester and ether with an additional component (base oil) that is the same as one described in the first exemplary embodiment.
The device-cooling oil containing the base oil of the exemplary embodiment is favorably usable for cooling a motor, a battery, an inverter, an engine and an electric cell or the like in an electric vehicle, a hybrid vehicle or the like, in the same manner as in the above-mentioned exemplary embodiment. Since the viscosity of the base oil at 40 degrees C is in the above predetermined range, the device-cooling oil is excellent in lubricity, and thus is favorably usable as a dual-purpose oil not only for cooling but also for lubricating a planetary gear, a transmission or the like.
The same additives as ones described in the first exemplary embodiment may be blended in the device-cooling oil of the exemplary embodiment as long as an object of the invention is attainable.

Examples of Second Exemplary Embodiment

Next, the second exemplary embodiment will be further described in detail based on Examples, which by no means limit the first exemplary embodiment.
Specifically, base oils shown in Table 2 were prepared and various evaluations thereof were conducted. Preparation methods of the base oils are described below.
Evaluation was conducted by the same method as the property measurement method in Examples of the first exemplary embodiment.

Table 2

	Example 1	Example 2	Example 3	Example 4	Example 5	Example 6	Example 7	Comp 1	Comp 2	Comp 3	Comp 4
Base Oil (Compound Name)	16-methylheptadecanoic acid n-dodecyl	2-heptylundecanoic acid n-dodecyl	16-methylheptadecanoic acid 16-methylheptadecyl	n-decanoic acid n-decyl	n-octanoic acid 2-octyldodecyl	2-octyldodecyl n-octyl ether	triethylene glycol monobutyl ether n-octanoic acid ester	3,5,5-trimethylhexanoic acid 2-octyldodecyl	2,2,4,8,10,10,-hexamethyl-5-undecanoic acid 3,5,5-trimethyl hexyl	1-decanol	group-II purified mineral oil
Total of terminal methyl, methylene and ether in main chain	28	22	32	20	19	20	21	15	9	10	mixture
Total of methyl and ethyl branches in molecule	1	0	2	0	0	0	0	3	9	0	mixture of plural kinds
Thermal Conductivity (25°C) W/m·K	0.148	0.145	0.145	0142	0.142	0.144	0144	0132	0.107	0153	0.130
Volume Resistivity (25°C) Ω cm	1.1E+13	1.6E+13	1.7E+13	9 0E+12	1 3E+13	8 7E+13	5 6E+10	4.2E+13	1 1E+14	2 8E+09	1 2E+15
Kinematic Viscosity (40°C) mm²/s	15.90	1271	2297	5487	1049	9.844	5 166	13 19	2355	8371	9898
Kinematic Viscosity (100°C) mm2/s	4.146	3 367	5.080	1 980	2.973	2.830	1 859	3389	3977	1.838	2.722
Viscosity Index	176	144	157	-	145	141	-	135	27	-	116
Density (15°C) g/cm³	0.8663	0.8560	0.8644	08610	0.8587	0.8275	09527	08570	0.8578	0 8340	0.8265

Example 1

To a four-necked flask (500 mL) provided with a Dean-Stark apparatus, 16-methylheptadecanoic acid (128 g, product name: Isostearic acid EX, manufactured by KOKYU ALCOHOL KOGYO CO., LTD), 1-dodecyl alcohol (101 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.), mixed xylene (100 mL, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.), and titanium tetraisopropoxide (0.1 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) were put. A reaction was conducted at 140 degrees C for two hours while water was distilled away under nitrogen stream with stirring. Subsequently, the reaction product was washed with saturated saline three times and with 0.1 N aqueous sodium hydroxide three times and was then dried with anhydrous magnesium sulfate (a reagent manufactured by Tokyo Chemical Industry Co., Ltd.). After filtration of magnesium sulfate, excessive alcohol (the starting material) was distilled away to obtain 16-methylheptadecanoic acid n-dodecyl (182 g). This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density). The results are shown in Table 2. The results of the following Examples and Comparatives are also shown in Table 2.

Example 2

Example 2 was performed in the same manner as in Example 1 except that 2-heptyl undecanoic acid (128 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) was used in place of 16-methylheptadecanoic acid (128 g), so that 2-heptylundecanoic acid n-dodecyl (180 g) was obtained. This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Example 3

Example 3 was performed in the same manner as in Example 1 except that 16-methylheptadecaol (134 g, product name: Isostearyl Alcohol EX, KOKYU ALCOHOL KOGYO CO., LTD) was used in place of 1-dodecyl alcohol (101 g), so that 16-methylheptadecanoic acid 16-methylheptadecyl (206 g) was obtained. This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Example 4

Example 4 was performed in the same manner as in Example 1 except that n-decanoic acid (78 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) and 1-decyl alcohol (86 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) were used in place of 128 g of 16-methylheptadecanoic acid and 101 g of 1-dodecyl alcohol, so that n-decanoic acid n-dodecyl (132 g) was obtained. This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Example 5

Example 5 was performed in the same manner as in Example 1 except that n-octanoic acid (72g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) and 2-octyldodecanol (119 g, product name: NJCOL 200A, manufactured by New Japan chemical Co., Ltd.) were used in place of 128 g of 16-methylheptadecanoic acid and 1-dodecyl alcohol (101 g), so that n-octanoic acid 2-octyldodecyl (132 g) was obtained. This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Example 6

To a 2-L glass flask, 2-octyldodecanol (300 g, product name: NJCOL 200A, manufactured by New Japan chemical Co., Ltd.), 1-bromooctane (300 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.), tetrabutyl ammonium bromide (30 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.), and an aqueous sodium hydroxide (500 g, obtained by dissolving 150 g of sodium hydroxide in 350g of water). The mixture was reacted at 50 degrees C for 20 hours with stirring. After the reaction, the reaction mixture was transferred to a separating funnel. An organic phase was washed five times with water (500 mL). Subsequently, the organic phase was distilled, so that 2-octyldodecyl n-octyl ether (266 g) was obtained. This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Example 7

Example 7 was performed in the same manner as in Example 1 except that n-octanoic acid (144g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) and triethylene glycol monobutyl ether (165 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) were used in place of 128 g of 16-methylheptadecanoic acid and 101 g of 1-dodecyl alcohol, so that 188 g of n-octanoic acid ester of triethylene glycol monobutyl ether was obtained. This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Comparative 1

Comparative 1 was performed in the same manner as in Example 1 except that 3,5,5-trimethylhexanoic acid (79 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) and 2-octyldodecanol (119 g, product name: NJCOL 200A, manufactured by New Japan chemical Co., Ltd.) were used in place of 16-methylheptadecanoic acid (128 g) and 1-dodecyl alcohol (101 g), so that 139 g of 3,5,5-trimethylhexanoic acid 2-octyldodecyl was obtained. This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Comparative 2

Comparative 2 was performed in the same manner as in Example 1 except that 2,2,4,8,10,10-hexamethyl-5-undecanoic acid (114 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) and 3,5,5-trimethyl hexanol (72 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) were used in place of 16-methylheptadecanoic acid (128 g) and 1-dodecyl alcohol (101 g), so that 148 g of 2,2,4,8,10,10-hexamethyl-5-undecanoic acid 3,5,5-trimethyl hexyl was obtained. This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Comparative 3

1-decanol (a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Comparative 4

A purified mineral oil of Group II (manufactured by Idemitsu Kosan Co., Ltd.) was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index, and density).

Evaluation Result

As is obvious from the results shown in Table 2, in each of the base oils (compounds) of Examples 1 to 7 according to the exemplary embodiment, the total number of a terminal methyl group(s), a methylene group(s) and an ether group(s) in the main chain was 18 or more and the total number of a methyl branch and an ethyl branch in a molecule was 2 or less, so that these base oils were excellent in thermal conductivity (cooling properties) and electrical insulation properties. Further, these base oils were excellent in lubricating properties because the kinematic viscosities thereof were within the predetermined range. Thus, it is understandable that a device-cooling oil using the base oil according to the invention is favorably usable as a dual-purpose oil not only for cooling a motor, a battery, an inverter, an engine, an electric cell or the like in an electric vehicle or a hybrid vehicle but also for lubricating a transmission or the like.
On the other hand, although the base oil of Comparative 1 is an ester obtained from 2-octyldodecanol in the same manner as in Example 5, the base oil exhibits a poor thermal conductivity because of a large number of methyl branches. The ester of Comparative 2 exhibits an extremely poor thermal conductivity because of an extremely large number of methyl branches. The base oil of Comparative 3 is alcohol and exhibits a favorable thermal conductivity but exhibits poor electrical insulation properties. In Comparative 4 in which the purified mineral oil was used, since the base oil was a mixture of many kinds of isomers, the above parameters on the main chain and the molecule were not within a predetermined range, so that the base oil exhibited a poor thermal conductivity.

Third Exemplary Embodiment

The base oil according to the first exemplary embodiment contains at least one of the oleyl ester (oleate, oleyl alcohol ester) and the oleyl ether as a fundamental component. The base oil according to the second exemplary embodiment contains at least one of the aliphatic monoester and the aliphatic monoether as a fundamental component.
The device-cooling base oil according to the third exemplary embodiment of the invention contains at least one of a divalent aliphatic carboxylic acid diester and a divalent aliphatic alcohol diether as a fundamental component.
The aliphatic diester and the aliphatic diether each have 20 or more of a total number of a terminal methyl group, a methylene group and an ether group in a main chain and 2 or less of a total number of a methyl branch and an ethyl branch in the aliphatic diester and the aliphatic diether. The "main chain" herein means a portion having the longest chain structure in the molecule.
The third exemplary embodiment will be described in detail below.
In describing this exemplary embodiment, what has been described in the above first and second exemplary embodiments will be omitted or simplified.
In this exemplary embodiment, at least one of the aliphatic diester and the aliphatic diether is used as main components of the base oil. The aliphatic diester and the aliphatic diether each have 20 or more of the total number of the terminal methyl group, the methylene group and the ether group in the main chain and 2 or less of the total number of the methyl branch and the ethyl branch in the molecule. The number of the methylene group in the diester and the diether is preferably 18 or more, more preferably 19 or more in terms of an enhancement of cooling properties.
The diester and the diether preferably have a linear chain structure in terms of an enhancement of the cooling properties of the base oil.
Such an aliphatic diester is obtainable by typically known methods of manufacturing esters. A method of manufacturing the aliphatic diester ester is subject to no limitation. For instance, the aliphatic diester is obtainable by: a dehydration condensation reaction between a divalent carboxylic acid and alcohol or a dehydration condensation reaction between divalent alcohol and a carboxylic acid; a condensation reaction between a divalent carboxylic acid dihalide and alcohol or a condensation reaction between divalent alcohol and a carboxylic acid halide; and a transesterification. For instance, a starting material having a long linear alkyl chain is preferably used for synthetic reaction such that the total number of the terminal methyl group, the methylene group and the ether group in the main chain (i.e., the longest chain in a molecule) is 20 or more and the total number of a short alkyl side chain in the molecule (i.e., the methyl branch and the ethyl branch) is 2 or less.
Examples of the carboxylic acid (the starting material) include: dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and 1,10-decamethylene dicarboxylic acid; monocarboxylic acids such as n-butanoic acid, n-pentanoic acid, n-hexanoic acid, n-heptanoic acid, n-octanoic acid, n-nonanoic acid, n-decanoic acid, n-undecanoic acid, n-dodecanoic acid, n-tridecanoic acid, n-tetradecanoic acid, ethylhexanoate, and butyl octanoic acid. As a starting material for manufacturing esters, a carboxylic acid ester and a carboxylic acid chloride, which are derivatives of the above carboxylic acids, are usable.
Examples of the alcohol (the starting material) include: a monool such as n-hexanol, n-heptanol, n-octanol, n-nonanol, n-decanol, n-undecanol, n-dodecanol, n-tridecanol, n-tetradecanol, oleyl alcohol, ethylhexanol, butyloctanol, pentylnonanol, hexyldecanol, heptylundecanol, octyldodecanol, and methylheptadecanol; and a diol such as ethylene glycol, 1,3-propane diol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexandiol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol and polytetramethylene glycol.
A catalyst such as titanium tetraisopropoxide may be used as an esterification catalyst, or no catalyst may be used.
The diether may be manufactured by a typical ether manufacturing method such as the Williamson ether synthetic method, but the manufacturing method of the ether is subject to no limitation.
The base oil of the exemplary embodiment contains 30 mass% or more of the diester and the diether, preferably 50 mass% or more, more preferably 60 mass% or more, further preferably 70 mass% or more, particularly preferably 80 mass% or more. When the base oil contains the diester and the diether at less than 30 mass%, the base oil may not exhibit a sufficient cooling properties. It should be noted that a base oil for cooling a device may be provided only by the base oil of the exemplary embodiment (at 100 mass%).
The base oil of the exemplary embodiment has a kinematic viscosity at 40 degrees C in a range of 4 mm²/s to 30 mm²/s, preferably of 4 mm²/s to 20 mm²/s, in the same manner as in the above-mentioned exemplary embodiment. If the kinematic viscosity of the base oil at 40 degrees C is less than 4 mm²/s, for instance, when the base oil is used as a dual-purpose oil not only for a motor but also for a transmission or the like, the base oil may exhibit an insufficient lubricity. On the other hand, if the kinematic viscosity of the base oil at 40 degrees C exceeds 30 mm²/s, the cooling properties may be insufficient. Additionally, when such a base oil is used as a cooling oil for a motor or the like, the cooling oil is unlikely to smoothly circulate within a system or the like.
According to the exemplary embodiment, the thermal conductivity of the base oil at 25 degrees C is preferably 0.142 W/(m·K) or more, more preferably 0.144 W/(m·K) or more in terms of the cooling properties, in the same manner as in the above-mentioned exemplary embodiment.
In terms of electrical insulation properties, the base oil of the exemplary embodiment preferably has a volume resistivity at 25 degrees C of 10¹⁰ Ω·cm or more, more preferably 10¹¹ Ω·cm or more, further preferably 10¹² Ω·cm or more.
The base oil of the exemplary embodiment may be provided by blending the above-mentioned ester and ether with an additional component (base oil) that is the same as one described in the first exemplary embodiment.
The device-cooling oil containing the base oil of the exemplary embodiment is favorably usable for cooling a motor, a battery, an inverter, an engine and an electric cell or the like in an electric vehicle, a hybrid vehicle or the like, in the same manner as in the above-mentioned exemplary embodiment. Since the viscosity of the base oil at 40 degrees C is in the above predetermined range, the device-cooling oil is excellent in lubricity, and thus is favorably usable as a dual-purpose oil not only for cooling but also for lubricating a planetary gear, a transmission or the like.
The same additives as ones described in the first exemplary embodiment may be blended in the device-cooling oil of the exemplary embodiment as long as an object of the invention is attainable.

Examples of Third Exemplary Embodiment

Next, the third exemplary embodiment will be further described in detail based on Examples, which by no means limit the first exemplary embodiment.
Specifically, base oils shown in Table 3 were prepared and various evaluations thereof were conducted. Preparation methods of the base oils are described below.
Evaluation was conducted by the same method as the property measurement method in Examples of the first exemplary embodiment.

Table 3

	Example 1	Example 2	Example 3	Example 4	Example 5	Example 6	Example 7	Comp. 1	Comp 2	Comp 3	Comp 4
Base Oil (Compound Name)	azelaic acid di-noctyl	azelaic acid noctyl 2-ethylhexyl	dodecanedioic acid di-2-ethylhexyl	sebacic acid n-octyl 2-ethylhexyl	bis-n-octyl 1,4-butane diether	2-ethylhexanoic acid diester of polytetrahydrofuran 250	triethylene glycol n-octanoic acid diester	azelaic acid di-2-ethylhexyl	neopentyl glycol n-octanoic acid diester	neopentyl glycol 2-ehtylhexane acid diester	group-II purified mineral oil
Total of terminal methyl, methylene and ether in main chain	25	22 (average)	22	23.3 (average)	22	27 (average)	24	19	18	12	mixture
Total of methyl and ethyl branches in molecule	0	095 (average)	2	0.9 (average)	0	2	0	2	2	4	mixture of plural kinds
Thermal Conductivity (25°C) W/m·K	0.148	0144	0.143	0.145	0142	0.146	0147	0.137	0.133	0.123	0.130
Volume Resistivity (25°C) Ω cm	1 6E+11	3 5E+11	1.7E+12	8.7E+11	26E+12	1.0E+11	1 9E+10	5.9E+11	3.4E+11	2 9E+12	1.2E+15
Kinematic Viscosity (40°C) mm²/s	1102	10 75	1409	11.67	4 809	2245	8918	10.48	7.161	7486	9.898
Kinematic Viscosity (100°C) mm2/s	3 300	3139	3 764	3353	1 88	4989	2.720	2.991	2.257	2076	2.722
Viscosity Index	188	168	168	174	-	156	158	149	133	58	116
Density (15°C) g/cm³	09167	09184	09130	09156	0.8505	09515	09740	0.9206	0 9230	09185	0 8265

Example 1

To a four-necked flask (500 mL) provided with a Dean-Stark apparatus, azelaic acid (94 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.), 1-octanol (156 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.), mixed xylene (100 mL, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.), and titanium tetraisopropoxide (0.1 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) were put. A reaction was conducted at 140 degrees C for two hours while water was distilled away under nitrogen stream with stirring. Subsequently, the reaction product was washed with saturated saline three times and with 0.1 N aqueous sodium hydroxide three times and was then dried with anhydrous magnesium sulfate (a reagent manufactured by Tokyo Chemical Industry Co., Ltd.). After filtration of magnesium sulfate, excessive alcohol (the starting material) was distilled away to obtain azelaic acid di-n-octyl (188g). This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density). The results are shown in Table 3. The results of the following Examples and Comparatives are also shown in Table 3.

Example 2

Example 2 was performed in the same manner as in Example 1 except that 75 g of azelaic acid, 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 place of 94 g of azelaic acid and 156g of 1-octanol, so that 145 g of a mixture containing 30 mass% of azelaic acid di-n-octyl, 45 mass% of azelaic acid n-octyl 2-ethylhexyl, and 25 mass% of azelaic acid di-2-ethylhexyl was obtained. This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Example 3

Dodecanedioic acid di-2-ethylhexyl (a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Example 4

Example 4 was performed in the same manner as in Example 1 except that 81g of sebacic acid, 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 place of 94g of azelaic acid and 156g of 1-octanol, so that 147g of a mixture containing 32 mass% of sebacic acid di-n-octyl, 46 mass% of sebacic acid n-octyl 2-ethylhexyl, and 22 mass% of sebacic acid di-2-ethylhexyl was obtained. This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Example 5

To a 1-L glass flask, 1,4-butanediol (27 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.), 1-bromooctane (174 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.), tetrabutyl ammonium bromide (10 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.), and an aqueous sodium hydroxide (200 g, obtained by dissolving 60 g of sodium hydroxide in 140 g of water). A mixture was reacted at 70 degrees C for 20 hours with stirring. After the reaction, the reaction mixture was transferred to a separating funnel. An organic phase was washed five times with water (300 mL). Subsequently, excessive 1-bromooctane was distilled, so that bis-n-octyl 1,4-butane diether (76g) was obtained. This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Example 6

Example 6 was performed in the same manner as in Example 1 except that 2-ethyl hexanoic acid (130 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) and polytetrahydrofuran 250 (75 g, a reagent manufactured by Sigma-Aldrich Co. LLC.) were used in place of 94 g of azelaic acid and 156 g of 1-octanol, so that 126 g of 2-ethylhexanoic acid diester of polytetrahydrofuran 250 was obtained. This ester was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Example 7

Example 7 was performed in the same manner as in Example 1 except that n-octanoic acid (180 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) and triethylene glycol (75 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) were used in place of 94 g of azelaic acid and 156 g of 1-octanol, so that 163 g of n-octanoic acid diester of triethylene glycol was obtained. This ester was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Comparative 1

Azelaic acid di-2-ethylhexyl (a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Comparative 2

Comparative 2 was performed in the same manner as in Example 1 except that n-octanoic acid (173 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) and neopentyl glycol (52 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) were used in place of 94 g of azelaic acid and 156 g of 1-octanol, so that 160 g of neopentyl glycol n-octanoic acid diester was obtained. This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Comparative 3

Comparative 3 was performed in the same manner as in Example 1 except that 2-ethylhexane acid (165 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) and neopentyl glycol (52 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) were used in place of 94 g of azelaic acid and 156 g of 1-octanol, so that 160 g of neopentyl glycol 2-ethylhexane acid diester was obtained. This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Comparative 4

Evaluation Result

As understood from the results of Table 3, the base oil (a compound) according to this exemplary embodiment in each of Examples 1 to 7 was a predetermined ester or ether. Since the ester and the ether each had 20 or more of the total number of the terminal methyl group, the methylene group and the ether group in the main chain and 2 or less of the total number of the methyl branch and the ethyl branch in a molecule, the ester and the ether exhibited excellent thermal conductivity (cooling properties) and electrical insulation properties. Further, these base oils were excellent in lubricating properties because the kinematic viscosities thereof were within the predetermined range. Thus, it is understandable that a device-cooling oil using the base oil according to the exemplary embodiment is favorably usable as a dual-purpose oil not only for cooling a motor, a battery, an inverter, an engine, an electric cell or the like in an electric vehicle or a hybrid vehicle but also for lubricating a transmission or the like.
On the other hand, the esters of Comparatives 1 and 2 had a poor thermal conductivity because of the short main chain and a small number of the methylene groups. The ester of Comparative 3 had an extremely poor thermal conductivity because of a large number of the methyl branches and the ethyl branches in addition to the short main chain and the small number of the methylene groups. In Comparative 4 in which the purified mineral oil was used, since the base oil was a mixture of many kinds of isomers, the above parameters on the main chain and the molecule were not within a predetermined range, so that the base oil exhibited a poor thermal conductivity.

Fourth Exemplary Embodiment

The base oil according to the first exemplary embodiment contains at least one of the oleyl ester (oleate, oleyl alcohol ester) and the oleyl ether as a fundamental component. The base oil according to the second exemplary embodiment contains at least one of the aliphatic monoester and the aliphatic monoether as a fundamental component. The base oil according to the third exemplary embodiment contains at least one of the divalent aliphatic carboxylic acid diester, the divalent aliphatic alcohol diester and the divalent aliphatic alcohol diether as a basic component.
The device-cooling base oil according to a fourth exemplary embodiment of the invention contains at least one of aliphatic triester, aliphatic triether, aliphatic tri(etherester), aliphatic tetraester, aliphatic tetraether, aliphatic tetra(etherester), aromatic diester, aromatic diether and aromatic di(etherester) as a main component of the base oil.
Each of molecules of the esters, the ethers and the etheresters have 18 or more of a total number of a terminal methyl group, a methylene group and an ether group in a main chain. Each of the molecules of the esters and the ethers has 1 or less of a total number of a methyl branch and an ethyl branch. Herein, the main chain refers to the longest chain, which may interpose an aromatic ring, in a molecule. The aliphatic tri(etherester) refers to a compound having three in total of an ether group and an ester group. The aliphatic tetra(etherester) refers to a compound having four in total of an ether group and an ester group. Aromatic di(etherester) refers to a compound having two in total of an ether group and an ester group.
The fourth exemplary embodiment will be described in detail below.
In describing this exemplary embodiment, what has been described in the above first to third exemplary embodiments will be omitted or simplified.
As described in the first exemplary embodiment, in order to improve thermal conductivity in liquid molecules and increase collision frequency between the molecules, the ester and the ether having a long chain structure are advantageous. Since the aromatic ring is so rigid as to hardly diffuse molecular vibrational energy, even when long chain structures are bonded to each other through the aromatic ring, a thermal conductivity is hardly reduced. Accordingly, when an aromatic compound is used in the exemplary embodiment, the longest chain interposing the aromatic ring is defined as the main chain.
In the exemplary embodiment, at least one of aliphatic triester, aliphatic triether, aliphatic tri(etherester), aliphatic tetraester, aliphatic tetraether, aliphatic tetra(etherester), aromatic diester, aromatic diether and aromatic di(etherester) is used as a main component of the base oil. The total number of the terminal methyl group, the methylene group and the ether group in the main chain in each of the ester, the ether and the etherester is 18 or more in terms of an enhancement of cooling properties. Moreover, the total number of the methyl branches and the ethyl branches in a molecule of the ester, the ether and the etherester is 1 or less in terms of an enhancement of cooling properties. The ester, the ether and the etherester preferably contain none of the above-mentioned methyl branch and ethyl branch in terms of an enhancement of cooling properties.
Such an ester is obtainable by typically known methods of manufacturing esters. A method of manufacturing the oleyl ester is subject to no limitation. For instance, the ester is obtainable by a dehydro-condensation reaction between a carboxylic acid and alcohol, a condensation reaction between a carboxylic halide or alcohol, and a transesterification. For instance, a starting material having a long linear alkyl chain may be used for synthetic reaction such that the total number of the terminal methyl group, the methylene group and the ether group in the main chain (i.e., the longest chain in a molecule) is 18 or more and the total number of a short alkyl side chain in the molecule (i.e., the methyl branch and the ethyl branch) is 1 or less.
Examples of the carboxylic acid (the starting material) include an aliphatic carboxylic acid and an aromatic carboxylic acid. Examples of the carboxylic acid include: monocarboxylic acids such n-hexanoic acid, n-heptanoic acid, n-octanoic acid, n-nonanoic acid, n-decanoic acid, n-undecanoic acid, n-dodecanoic acid, n-tridecanoic acid, n-tetradecanoic acid, oleic acid, ethylhexanoic acid, butyl octanoic acid, pentyl nonanoic acid, hexyl decanoic acid, heptyl undecanoic acid, octyldodecanoic acid, methyl heptadecanoic acid, salicylic acid, 4-hydroxybenzoic acid, benzoic acid and phenylacetic acid; and dicarboxylic acids such as phthalic acid, isophthalic acid and terephthalic acid. As a starting material for manufacturing esters, a carboxylic acid ester and a carboxylic acid chloride, which are derivatives of the above carboxylic acids, are usable.
Examples of the alcohol (the starting material) include: a monool such as n-hexanol, n-heptanol, n-octanol, n-nonanol, n-decanol, n-undecanol, n-dodecanol, n-tridecanol, n-tetradecanol, oleyl alcohol, ethylhexanol, butyloctanol, pentylnonanol, hexyldecanol, heptylundecanol, octyldodecanol, methylheptadecanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether and triethylene glycol monobutyl ether; a triol such as trimethylolpropane and trimethylolethane; and a tetraol such as pentaerythritol.
A catalyst such as titanium tetraisopropoxide may be used as an esterification catalyst, or no catalyst may be used.
The ether may be manufactured by a typical ether manufacturing method such as the Williamson ether synthetic method, but the manufacturing method of the ether is subject to no limitation.
The base oil of the exemplary embodiment contains 30 mass% or more of the ester and the ether, preferably 50 mass% or more, more preferably 60 mass% or more, further preferably 70 mass% or more, particularly preferably 80 mass% or more. When the base oil contains the ester and the ether at less than 30 mass%, the base oil may not exhibit a sufficient cooling properties. It should be noted that a base oil for cooling a device may be provided only by the base oil of the exemplary embodiment (at 100 mass%).
The base oil of the exemplary embodiment has a kinematic viscosity at 40 degrees C in a range of 4 mm²/s to 30 mm²/s, preferably of 4 mm²/s to 20 mm²/s, in the same manner as in the above-mentioned exemplary embodiment. If the kinematic viscosity of the base oil at 40 degrees C is less than 4 mm²/s, for instance, when the base oil is used as a dual-purpose oil not only for a motor but also for a transmission or the like, the base oil may exhibit an insufficient lubricity. On the other hand, if the kinematic viscosity of the base oil at 40 degrees C exceeds 30 mm²/s, the cooling properties may be insufficient. Additionally, when such a base oil is used as a cooling oil for a motor or the like, the cooling oil is unlikely to smoothly circulate within a system or the like.
According to the exemplary embodiment, the thermal conductivity of the base oil at 25 degrees C is preferably 0.142 W/(m·K) or more, more preferably 0.144 W/(m·K) or more in terms of the cooling properties, in the same manner as in the above-mentioned exemplary embodiment.
The base oil of the exemplary embodiment preferably has a volume resistivity at 25 degrees C of 10¹⁰ Ω·cm or more, more preferably 10¹¹ Ω·cm or more, further preferably 10¹² Ω·cm or more, particularly preferably 10¹³ Ω·cm or more.
The base oil of the exemplary embodiment may be provided by blending the above-mentioned ester and ether with an additional component (base oil) that is the same as one described in the first exemplary embodiment.
The device-cooling oil containing the base oil of the exemplary embodiment is favorably usable for cooling a motor, a battery, an inverter, an engine and an electric cell or the like in an electric vehicle, a hybrid vehicle or the like, in the same manner as in the above-mentioned exemplary embodiment. Since the viscosity of the base oil at 40 degrees C is in the above predetermined range, the device-cooling oil is excellent in lubricity, and thus is favorably usable as a dual-purpose oil not only for cooling but also for lubricating a planetary gear, a transmission or the like.
The same additives as ones described in the first exemplary embodiment may be blended in the device-cooling oil of the exemplary embodiment as long as an object of the invention is attainable.

Examples of Fourth Exemplary Embodiment

Next, the fourth exemplary embodiment will be further described in detail based on Examples, which by no means limit the first exemplary embodiment.
Specifically, base oils shown in Table 4 were prepared and various evaluations thereof were conducted. Preparation methods of the base oils are described below.
Evaluation was conducted by the same method as the property measurement method in Examples of the first exemplary embodiment.

Table 4

	Example 1	Example 2	Example 3	Example 4	Example 5	Comp. 1	Comp. 2	Comp. 3
Base Oil (Compound Name)	pentaerythritol tetra-n-octanoic acid ester	trimethylolpropane tri-n-octanoic acid ester	phthalic acid di-n-dodecyl	isophthalic acid di-n-octyl	mixture of n-octanoic acid ester/n-octyl ether of trimethlolpropane	trimethylolpropane 2-ethyl hexanoic acid triester	phthalic acid di-2-ethylhexyl	group-II purified mineral oil
Total of terminal methyl, methylene and ether in main chain	18	18	26	18	18	12	12	mixture
Total of methyl and ethyl branches in molecule	0	1	0	0	1	4	2	mixture of plural kinds
Thermal Conductivity (25°C) W/m·K	0.148	0.143	0.148	0.144	0.142	0.132	0.131	0.130
Volume Resistivity (25°C) Ω·cm	1.5E+13	1.9E+12	8.6E+11	2.3E+11	4.6E+12	1.1E+14	2.5E+11	1.2E+15
Kinematic Viscosity (40°C) mm²/s	25.81	16.77	28.46	22.13	11.43	24.11	27.08	9.898
Kinematic Viscosity (100°C) mm2/s	5.315	3.940	5.409	4.336	3.106	4.265	4.230	2.722
Viscosity Index	145	134	128	102	138	66	16	116
Density (15°C) g/cm³	0.9680	0.9519	0.9494	0.9820	0.8838	0.9484	0.9873	0.8265

Example 1

To a four-necked flask (500 mL) provided with a Dean-Stark apparatus, n-octanoic acid (173 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.), pentaerythritol (34 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.), mixed xylene (100 mL, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.), and titanium tetraisopropoxide (0.1 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) were put. A reaction was conducted at 140 degrees C for two hours while water was distilled away under nitrogen stream with stirring. Subsequently, the reaction product was washed with saturated saline three times and with 0.1 N aqueous sodium hydroxide three times and was then dried with anhydrous magnesium sulfate (a reagent manufactured by Tokyo Chemical Industry Co., Ltd.). After filtration of magnesium sulfate, excessive alcohol (the starting material) was distilled away to obtain pentaerythritol tetra-n-octanoic acid ester (148 g). This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density). The results are shown in Table 4. The results of the following Examples and Comparatives are also shown in Table 4.

Example 2

Example 2 was performed in the same manner as in Example 1 except that 159 g of n-octanoic acid and 40 g of trimethylolpropane (a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) were used in place of 173 g of n-octanoic acid and 34 g of pentaerythritol, so that 139 g of trimethylolpropane tri-n-octanoic acid ester was obtained. This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Example 3

Example 3 was performed in the same manner as in Example 1 except that phthalic anhydride (44 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) and 1-dodecanol (149 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) were used in place of 173 g of n-octanoic acid and 34 g of pentaerythritol, so that 137 g of phthalic acid di-n-dodecyl was obtained. This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Example 4

Example 4 was performed in the same manner as in Example 1 except that isophthalic acid (50 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) and 1-octanol (104 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) were used in place of 173 g of n-octanoic acid and 34 g of pentaerythritol, so that 107 g of isophthalic acid di-n-octyl was obtained. This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Example 5

To a 1-L glass flask, trimethylolpropane (34 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.), 1-bromooctane (217 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.), tetrabutyl ammonium bromide (10 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.), and an aqueous sodium hydroxide (200 g, obtained by dissolving 60 g of sodium hydroxide in 140 g of water). The mixture was reacted at 70 degrees C for 20 hours with stirring. After the reaction, the reaction mixture was transferred to a separating funnel. An organic phase was washed five times with water (300 mL), and then, excessive 1-bromooctane was distilled from the reaction mixture. To a four-necked flask (500 mL) provided with a Dean-Stark device, the reaction mixture, n-octanoic acid (50 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.), mixed xylene (100 mL, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.), and titanium tetraisopropoxide (0.1 g, a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) were put. A reaction was conducted at 140 degrees C for two hours while water was distilled away under nitrogen stream with stirring, thereby esterifying unreacted alcohol portion of trimethylolpropane. After washing with saturated saline, excessive n-octanoic acid was distilled away. The obtained product was washed with 0.1 N aqueous sodium hydroxide three times and was dried with anhydrous magnesium sulfate (a reagent manufactured by Tokyo Chemical Industry Co., Ltd.).. After filtration of magnesium sulfate, the solvent was distilled away, so that 102 g of a mixture of 24% of n-octyltriether of trimethylolpropane, 58% of n-octyldiether n-octanoic acid monoester of trimethylolpropane, and 18% of n-octylmonoether n-octanoic acid diester of trimethylolpropane. This compound was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Comparative 1

Trimethylolpropane 2-ethyl hexanoic acid triester (a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Comparative 2

Phthalic acid di-2-ethylhexyl (a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) was measured in terms of the physical properties thereof (i.e., thermal conductivity, volume resistivity, kinematic viscosity, viscosity index and density).

Comparative 3

Evaluation Result

As is obvious from the results shown in Table 4, in each of the base oils (compounds) of Examples 1 to 5 according to the exemplary embodiment, the total number of a terminal methyl group(s) and a methylene group(s) in the main chain was 18 or more and the total number of a methyl branch and an ethyl branch in the molecule was 1 or less, so that these base oils were excellent in thermal conductivity (cooling properties) and electrical insulation properties. Further, these base oils were excellent in lubricating properties because the kinematic viscosities thereof were within the predetermined range. Thus, it is understandable that a device-cooling oil using the base oil according to the invention is favorably usable as a dual-purpose oil not only for cooling a motor, a battery, an inverter, an engine, an electric cell or the like in an electric vehicle or a hybrid vehicle but also for lubricating a transmission or the like.
On the other hand, although the base oil of Comparative 1 was a triester of trimethylolpropane in the same manner as the base oil of Example 2, the base oil of Comparative 1 exhibited a poor thermal conductivity because of a short main chain and a large number of ethyl branches. Although the base oil of Comparative 2 was a phthalic acid ester in the same manner as the base oil of Example 3, the base oil of Comparative 2 exhibited a poor thermal conductivity because of a short main chain and a large number of ethyl branches. In Comparative 3 in which the purified mineral oil was used, since the base oil was a mixture of many kinds of isomers, the above parameters on the main chain and the molecule were not within a predetermined range, so that the base oil exhibited a poor thermal conductivity.

INDUSTRIAL APPLICABILITY

The invention is applicable to a base oil for cooling a device, a device-cooling oil using the base oil, a device to be cooled by the device-cooling oil, and a device cooling method using the device-cooling oil.

Claims

A base oil for cooling a device, comprising:
30 mass% or more of at least one of an oleyl ester (oleate and an oleyl alcohol ester) and an oleyl ether, wherein

the oleyl ester and the oleyl ether each have 23 or more of a total number of a terminal methyl group, a methylene group and an ether group in a main chain,

the oleyl ester and the oleyl ether each have 1 or less of a total number of a methyl branch and an ethyl branch, and

the base oil has a kinematic viscosity in a range of 4 mm²/s to 30 mm²/s.
The base oil according to claim 1, wherein the oleyl ester and the oleyl ether are contained at 50 mass% or more.
A base oil for cooling a device, comprising:
30 mass% or more of at least one of an aliphatic monoester and an aliphatic monoether, wherein

the aliphatic monoester and the aliphatic monoether each have 18 or more of a total number of a terminal methyl group, a methylene group and an ether group in a main chain,

the aliphatic monoester and the aliphatic monoether each have 2 or less of a total number of a methyl branch and an ethyl branch, and

the base oil has a kinematic viscosity in a range of 4 mm²/s to 30 mm²/s.
The base oil according to claim 3, wherein at least one of the aliphatic monoester and the aliphatic monoether has a chain structure.
A base oil for cooling a device, comprising:
30 mass% or more of at least one of an aliphatic diester and an aliphatic diether, wherein

the aliphatic diester and the aliphatic diether each have 20 or more of a total number of a terminal methyl group, a methylene group and an ether group in a main chain,

the aliphatic diester and the aliphatic diether each have 2 or less of a total number of a methyl branch and an ethyl branch, and

the base oil has a kinematic viscosity in a range of 4 mm²/s to 30 mm²/s.
A base oil for cooling a device, comprising:
30 mass% or more of at least one of an aliphatic triester, an aliphatic triether, an aliphatic tri(etherester), an aliphatic tetraester, an aliphatic tetraether, an aliphatic tetra(etherester), an aromatic diester, an aromatic diether and an aromatic di(etherester), wherein

each of the esters, the ethers and the etheresters has 18 or more of a total number of a terminal methyl group, a methylene group and an ether group in a main chain and 1 or less of a total number of a methyl branch and an ethyl branch, and

the base oil has a kinematic viscosity in a range of 4 mm²/s to 30 mm²/s.
The base oil according to any one of claims 1 to 6, wherein a thermal conductivity of the base oil at 25 degrees C is 0.142 W/(m·K) or more.
The base oil according to any one of claims 1 to 7, wherein a volume resistivity of the base oil at 25 degrees C is 10¹⁰Ω·cm or more.
A device-cooling oil comprising the base oil according to any one of claims 1 to 8.
A device configured to be cooled by the device-cooling oil according to claim 9.
The device according to claim 10, wherein the device is usable for an electric vehicle or a hybrid vehicle.
The device according to claim 10 or 11, wherein the device is at least one of a motor, a battery, an inverter, an engine and an electric cell.
A device cooling method using the device-cooling oil according to claim 9.