Lubricating oil composition

Abstract

The present invention has addressed the problem of providing a lubricating oil composition that has ensured electrically insulating properties and a high flash point while having excellent cooling performance. Moreover, the problem has been solved by a lubricating oil composition comprising a base oil (A), wherein: the base oil (A) contains an ester-based synthetic oil (A1); the content of the ester-based synthetic oil (A1) is 30-100 mass% with respect to the total amount of the base oil (A); the ester-based synthetic oil (A1) is at least one selected from the group consisting of an ester (A1-1) of a monohydric alcohol with a monobasic acid and an ester (A1-2) of a monohydric alcohol with a polybasic acid; and the base oil (A) satisfies the following requirements (1)-(3). ∙ Requirement (1): The kinematic viscosity at 40ºC is 2.00 mm2 / s to 4.00 mm2 / s. ∙ Requirement (2): The specific heat at 20ºC is at most 1.75 kJ / (kg∙K). ∙ Requirement (3): The density at 20ºC is at least 0.850 g / cm3.

Description

Technical Field

[0001] The present invention relates to a lubricating oil composition, for example, a lubricating oil composition used for cooling electric vehicle equipment.

Background Art

[0002] In recent years, reduction of carbon dioxide emissions has been strongly demanded from the viewpoint of global environmental protection. In the field of automobiles as well, efforts have been made to develop fuel-saving technologies, and the spread of hybrid vehicles and electric vehicles (hereinafter also referred to as "electric vehicles"), which are automobiles with excellent fuel efficiency and environmental performance, has been promoted. Cooling oil with excellent cooling performance and electrical insulation is required for electric vehicle equipment in electric vehicles. In addition, since some electric vehicles have a form with a gear reducer, these cooling oils are also required to have lubricity in addition to the above performance.

[0003] As cooling oil for electric vehicle equipment, lubricating oil compositions such as existing automatic transmission fluids (hereinafter also referred to as "ATF") and continuously variable transmission fluids (hereinafter also referred to as "CVTF") are mainly used, but the development of various alternative cooling oils is also underway.

[0004] For example, in Patent Document 1, a lubricating oil composition (automobile transmission oil composition) containing 10% by mass to 100% by mass of an ester-based synthetic oil based on the total amount of base oil and having the kinematic viscosity at 40°C, viscosity index, and density at 15°C adjusted to a predetermined range has been proposed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In recent years, in view of further progress in the popularization of electric vehicles and further improvement in the performance of electric vehicles, etc., the lubricating oil composition used as a cooling oil is required to further improve its cooling performance. Further, from the viewpoint of safety, the lubricating oil composition used as a cooling oil is also required to have a high flash point. By the way, in order to improve the cooling performance of the lubricating oil composition used as a cooling oil, it is effective to reduce the viscosity and increase the density of the lubricating oil composition. However, when the viscosity of the lubricating oil composition is reduced, the flash point of the lubricating oil composition tends to decrease. Therefore, there has been a problem that improving the cooling performance and increasing the flash point of the lubricating oil composition used as a cooling oil are in a trade-off relationship and it is difficult to achieve both.

[0007] The present invention has been made in view of the performance required for the lubricating oil composition used as a cooling oil and the above problems, and an object thereof is to provide a lubricating oil composition having excellent cooling performance, ensuring electrical insulation, and having a high flash point.

Means for Solving the Problems

[0008] The present inventors have intensively studied to solve the above problems and have completed the following invention. That is, the present invention relates to the following [1] to [3]. [1] A lubricating oil composition containing a base oil (A), the base oil (A) includes an ester-based synthetic oil (A1), the content of the ester-based synthetic oil (A1) is 30% by mass to 100% by mass based on the total amount of the base oil (A), the ester-based synthetic oil (A1) is one or more selected from the group consisting of an ester (A1-1) of a monohydric alcohol and a monobasic acid and an ester (A1-2) of a monohydric alcohol and a polybasic acid, the base oil (A) satisfies the following requirements (1) to (3), a lubricating oil composition. · Requirement (1): The kinematic viscosity at 40 ° C is 2.00 mm 2 / s to 4.00 mm 2 / s. ·Requirement (2): The specific heat at 20°C is 1.75 kJ / (kg·K) or less. ·Requirement (3): The density at 20°C is 0.850 g / cm 3 or more. [2] A method of using the lubricating oil composition according to [1] for cooling an electric vehicle device. [3] A cooling system for cooling an electric vehicle device, comprising the lubricating oil composition according to [1].

Advantages of the Invention

[0009] According to the present invention, it is possible to provide a lubricating oil composition that has excellent cooling performance, ensures electrical insulation, and has a high flash point.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described in detail. It should be noted that the present invention is not limited to the following embodiments, and can be arbitrarily modified and implemented without departing from the gist thereof. The upper and lower limit values of the numerical ranges described in this specification can be arbitrarily combined. For example, when "A~B" and "C~D" are described, the ranges of "A~D" and "C~B" are also included in the scope of the present invention as numerical ranges. In addition, the numerical range "lower limit value~upper limit value" described in this specification means that it is not less than the lower limit value and not more than the upper limit value unless otherwise specified. Also, in this specification, the numerical values in the examples are numerical values that can be used as the upper limit value or the lower limit value.

[0011] [Aspects of the Lubricating Oil Composition] The lubricating oil composition of the present invention is a lubricating oil composition containing a base oil (A), wherein the base oil (A) includes an ester-based synthetic oil (A1), and the content of the ester-based synthetic oil (A1) is 30% by mass to 100% by mass based on the total amount of the base oil (A), The ester-based synthetic oil (A1) is at least one selected from the group consisting of an ester (A1-1) of a monohydric alcohol and a monobasic acid and an ester (A1-2) of a monohydric alcohol and a polybasic acid, The base oil (A) is a lubricating oil composition that satisfies the following requirements (1) to (3). · Requirement (1): The kinematic viscosity at 40 °C is 2.00 mm 2 / s to 4.00 mm 2 / s. · Requirement (2): The specific heat at 20 °C is 1.75 kJ / (kg·K) or less. · Requirement (3): The density at 20 °C is 0.850 g / cm 3 or more.

[0012] The present inventors have intensively studied to provide a lubricating oil composition that has excellent cooling performance, ensures electrical insulation, and has a high flash point. First, the present inventors considered reducing the viscosity of the base oil in order to improve the cooling performance of the lubricating oil composition. However, as described above, when the viscosity of the base oil is reduced, the flash point decreases, and it is considered that the safety of the lubricating oil composition cannot be ensured. However, as a result of various studies by the present inventors, it has been found that a base oil containing a specific amount of an ester-based synthetic oil and satisfying the above requirements (1) and (2), and further the above requirement (3), although it is a low-viscosity base oil as shown in the above requirement (1), ensures electrical insulation and has a high flash point. Based on such findings, the present inventors have further intensively studied and completed the present invention.

[0013] The lubricating oil composition according to one aspect of the present invention is preferably composed only of the base oil (A), but may contain other components other than the base oil (A) as long as the effects of the present invention are not impaired. Specifically, in the lubricating oil composition of one aspect of the present invention, from the viewpoint of making it easier to exhibit the effects of the present invention, based on the total amount of the lubricating oil composition, the content of the base oil (A) is preferably 30% by mass to 100% by mass, more preferably 50% by mass to 100% by mass, still more preferably 60% by mass to 100% by mass, even more preferably 70% by mass to 100% by mass, yet still more preferably 80% by mass to 100% by mass, even more preferably 90% by mass to 100% by mass, still more preferably 95% by mass to 100% by mass, and even more preferably 99% by mass to 100% by mass. In addition, when the lubricating oil composition of one aspect of the present invention is composed only of the base oil (A), the lubricating oil composition is also referred to as "lubricating oil base oil". Hereinafter, the base oil (A) will be described in detail.

[0014] <<Base oil (A)>> The lubricating oil composition of the present invention contains a base oil (A). The base oil (A) includes an ester-based synthetic oil (A1). And the content of the ester-based synthetic oil (A1) is 30% by mass to 100% by mass based on the total amount of the base oil (A). When the content of the ester-based synthetic oil (A1) is less than 30% by mass based on the total amount of the base oil (A), at least one of the cooling performance, electrical insulation property, and flash point of the base oil (A) is inferior, and the effects of the present invention cannot be achieved. Here, from the viewpoint of making it easier to exhibit the effects of the present invention, the content of the ester-based synthetic oil (A1) is preferably 40% by mass to 100% by mass, more preferably 50% by mass to 100% by mass based on the total amount of the base oil (A). Also, from the viewpoint of making it easier to exhibit the effects of the present invention, the content of the ester-based synthetic oil (A1) is preferably 30% by mass to 100% by mass, more preferably 40% by mass to 100% by mass, still more preferably 50% by mass to 100% by mass based on the total amount of the lubricating oil composition.

[0015] In the lubricating oil composition of the present invention, the ester-based synthetic oil (A1) is at least one selected from the group consisting of esters (A1-1) of monohydric alcohols and monobasic acids and esters (A1-2) of monohydric alcohols and polybasic acids. That is, the ester-based synthetic oil (A1) may be at least one selected from esters (A1-1) of monohydric alcohols and monobasic acids, may be at least one selected from esters (A1-2) of monohydric alcohols and polybasic acids, or may be a combination of at least one selected from esters (A1-1) of monohydric alcohols and monobasic acids and at least one selected from esters (A1-2) of monohydric alcohols and polybasic acids. Here, from the viewpoint of more easily exhibiting the effects of the present invention, the ester-based synthetic oil (A1) is preferably at least one selected from esters (A1-2) of monohydric alcohols and polybasic acids.

[0016] And in the lubricating oil composition of the present invention, the base oil (A) satisfies the following requirements (1) to (3). · Requirement (1): The kinematic viscosity at 40°C is 2.00 mm 2 / s to 4.00 mm 2 / s. · Requirement (2): The specific heat at 20°C is 1.75 kJ / (kg·K) or less. · Requirement (3): The density at 20°C is 0.850 g / cm 3 or more. The base oil (A) satisfying the above requirements (1) to (3) can be prepared, for example, by selecting the type and adjusting the content of the ester-based synthetic oil (A1). Hereinafter, requirements (1) to (3) will be described in detail.

[0017] <Requirement (1)> In requirement (1), it is defined that the kinematic viscosity at 40°C of the base oil (A) is 2.00 mm 2 / s to 4.00 mm 2 / s. The lubricating oil composition of the present invention satisfies requirements (2) and (3) despite the extremely low kinematic viscosity of base oil (A) at 40°C (hereinafter also referred to as "40°C kinematic viscosity"). Moreover, by having a specific amount of ester-based synthetic oil (A1), while increasing the flash point of base oil (A), the cooling performance of base oil (A) is made excellent. In addition, the electrical insulation of base oil (A) is also ensured. Incidentally, when the kinematic viscosity of base oil (A) at 40°C is less than 2.00 mm 2 / s, the flash point of base oil (A) cannot be made sufficiently high. Also, when the kinematic viscosity at 40°C exceeds 4.00 mm 2 / s, the cooling performance of base oil (A) cannot be sufficiently improved.

[0018] Here, from the viewpoint of making it easier to exhibit the effects of the present invention, the kinematic viscosity of base oil (A) defined in requirement (1) at 40°C is preferably 2.00 mm 2 / s to 3.50 mm 2 / s, more preferably 2.00 mm 2 / s to 3.00 mm 2 / s, still more preferably 2.00 mm 2 / s to 2.50 mm 2 / s, even more preferably 2.00 mm 2 / s to 2.30 mm 2 / s.

[0019] Also, from the viewpoint of making it easier to exhibit the effects of the present invention, in requirement (1), in addition to the kinematic viscosity of base oil (A) at 40°C, it is preferable that the kinematic viscosity of base oil (A) at 20°C (hereinafter also referred to as "20°C kinematic viscosity") is within a predetermined range. Specifically, it is preferably 3.00 mm 2 / s or more, more preferably 3.10 mm 2 / s or more, still more preferably 3.20 mm 2 / s or more, even more preferably 3.30 mm 2 / s or more. Also, it is preferably 5.50 mm 2 / s or less, more preferably 5.00 mm 2 / s or less, still more preferably 4.50 mm 2 / s or less, even more preferably 4.00 mm2 is less than or equal to / s. The upper and lower limit values of these numerical ranges can be arbitrarily combined. Specifically, preferably 3.00 mm 2 / s to 5.50 mm 2 / s, more preferably 3.10 mm 2 / s to 5.00 mm 2 / s, still more preferably 3.20 mm 2 / s to 4.50 mm 2 / s, even more preferably 3.30 mm 2 / s to 4.00 mm 2 / s.

[0020] In addition, in this specification, the kinematic viscosity at 40°C and the kinematic viscosity at 20°C of the base oil (A) are values measured or calculated in accordance with JIS K2283:2000.

[0021] <Requirement (2)> Requirement (2) stipulates that the specific heat of the base oil (A) at 20°C is 1.75 kJ / (kg·K) or less. "Specific heat" means the amount of heat required to raise the temperature of 1 g of a substance by 1°C (K), and it can be said that the higher the value, the higher the cooling performance. Therefore, the stipulation of Requirement (2) is a disadvantageous stipulation for improving the cooling performance. However, in the base oil (A) containing the ester-based synthetic oil (A1), those that satisfy the above Requirement (1) tend to satisfy Requirement (2). And even when satisfying the said Requirement (2), the base oil (A) exhibits an unexpected effect of exhibiting excellent cooling efficiency. Moreover, the electrical insulation of the base oil (A) is also ensured, and the base oil (A) has a high flash point. As described above, in the base oil (A) containing the ester-based synthetic oil (A1), those that satisfy the above Requirement (1) tend to satisfy Requirement (2). Therefore, it is difficult to prepare a base oil (A) that satisfies Requirement (1) but does not satisfy Requirement (2).

[0022] Here, from the viewpoint of more easily exerting the effects of the present invention, the specific heat of the base oil (A) defined in requirement (2) at 20°C is preferably 1.50 kJ / (kg·K) or more, more preferably 1.53 kJ / (kg·K) or more, still more preferably 1.55 kJ / (kg·K) or more, and even more preferably 1.57 kJ / (kg·K) or more. Also, it is preferably 1.75 kJ / (kg·K) or less, more preferably 1.72 kJ / (kg·K) or less, still more preferably 1.68 kJ / (kg·K) or less, and even more preferably 1.64 kJ / (kg·K) or less. The upper and lower limit values of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 1.50 kJ / (kg·K) to 1.75 kJ / (kg·K), more preferably 1.53 kJ / (kg·K) to 1.72 kJ / (kg·K), still more preferably 1.55 kJ / (kg·K) to 1.68 kJ / (kg·K), and even more preferably 1.57 kJ / (kg·K) to 1.64 kJ / (kg·K).

[0023] In addition, in this specification, the specific heat of the base oil (A) at 20°C means a value calculated by the following formula (f1) using the thermal conductivity measurement value and the thermal diffusivity measurement value measured by a thermal conductivity measurement device and the density at 20°C measured by the method described later. (Specific heat at 20°C) = (Thermal diffusivity at 20°C) 2 / {(Thermal conductivity at 20°C) × (Density at 20°C)} ···· (f1)

[0024] <Requirement (3)> In requirement (3), it is defined that the density of the base oil (A) at 20°C is 0.850 g / cm 3 or more. The higher the density, the more densely packed the molecules constituting the base oil (A) are, and it can be said that it is easier to improve the cooling performance of the base oil (A). Here, generally, substances with low viscosity tend to have low density. However, among the base oils (A) containing the ester-based synthetic oil (A1), those that satisfy the above requirement (1) tend to satisfy requirement (3), which contributes to the improvement of cooling performance. That is, in the present invention, by satisfying the mutually contradictory requirements (1) and (3), an unexpected effect of exhibiting excellent cooling performance is achieved. Moreover, the electrical insulation of the base oil (A) is ensured, and the base oil (A) has a high flash point. In addition, when the density of the base oil (A) at 20°C is less than 0.850 g / cm 3 it is impossible to sufficiently improve the cooling performance of the base oil (A).

[0025] Here, from the viewpoint of more easily exerting the effects of the present invention, the density of the base oil (A) at 20°C defined in requirement (3) is preferably 0.850 g / cm 3 or more, more preferably 0.860 g / cm 3 or more, still more preferably 0.900 g / cm 3 or more, even more preferably 0.940 g / cm 3 or more, yet even more preferably 0.970 g / cm 3 or more, still even more preferably 0.990 g / cm 3 or more. Also, it is preferably 1.20 g / cm 3 or less, more preferably 1.15 g / cm 3 or less, still more preferably 1.12 g / cm 3 or less, even more preferably 1.10 g / cm 3 or less, yet even more preferably 1.08 g / cm 3 or less, still even more preferably 1.06 g / cm 3 or less. The upper and lower limit values of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 0.850 g / cm 3 to 1.20 g / cm 3 , more preferably 0.860 g / cm 3 to 1.15 g / cm 3 , still more preferably 0.900 g / cm 3 to 1.12 g / cm 3 , even more preferably 0.940 g / cm3 ~1.10 g / cm 3 、 and more preferably 0.970 g / cm 3 ~1.08 g / cm 3 、 still more preferably 0.990 g / cm 3 ~1.06 g / cm 3 is required.

[0026] In this specification, the density of base oil (A) at 20°C means a value measured in accordance with JIS K 2249-1:2011 (Crude oil and petroleum products - Method for determination of density - Part 1: Vibration method).

[0027] <Requirement (4) to (7)> In one aspect of the lubricating oil composition of the present invention, it is preferable that base oil (A) satisfies one or more selected from Requirements (4) to (7), more preferably satisfies two or more, still more preferably satisfies three or more, and even more preferably satisfies all four. Among these, it is particularly preferable to satisfy the requirement of the relative heat transfer coefficient defined in Requirement (5). Base oil (A) that satisfies the above Requirements (4) to (7) can be prepared, for example, by selecting the type and adjusting the content of ester synthetic oil (A1). Hereinafter, Requirements (4) to (7) will be described in detail.

[0028] (Requirement (4)) Requirement (4) stipulates that the thermal conductivity of base oil (A) at 20°C is 0.140 W / (m·K) or more. Thermal conductivity is an index of how heat is transferred within the same substance (i.e., within base oil (A)). The larger the thermal conductivity defined in Requirement (4), the easier it is to improve the cooling performance of base oil (A). When the thermal conductivity of base oil (A) at 20°C is 0.140 W / (m·K) or more, it is easier to make the cooling performance of base oil (A) more excellent. Here, from the viewpoint of more easily exerting the effects of the present invention, the thermal conductivity of the base oil (A) defined in requirement (4) at 20°C is preferably 0.140 W / (m·K) or more, more preferably 0.143 W / (m·K) or more, still more preferably 0.148 W / (m·K) or more, even more preferably 0.152 W / (m·K) or more, yet even more preferably 0.154 W / (m·K) or more, and still more preferably 0.156 W / (m·K) or more. Also, it is preferably 0.170 W / (m·K) or less, more preferably 0.165 W / (m·K) or less, still more preferably 0.163 W / (m·K) or less, even more preferably 0.162 W / (m·K) or less, yet even more preferably 0.161 W / (m·K) or less, and still more preferably 0.160 W / (m·K) or less. The upper and lower limit values of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 0.140 W / (m·K) to 0.170 W / (m·K), more preferably 0.143 W / (m·K) to 0.165 W / (m·K), still more preferably 0.148 W / (m·K) to 0.163 W / (m·K), even more preferably 0.152 W / (m·K) to 0.162 W / (m·K), yet even more preferably 0.154 W / (m·K) to 0.161 W / (m·K), and still more preferably 0.156 W / (m·K) to 0.160 W / (m·K).

[0029] In addition, in this specification, the thermal conductivity of the base oil (A) at 20°C means the thermal conductivity measured by a thermal conductivity measuring device.

[0030] (Requirement (5)) Requirement (5) stipulates that the relative heat transfer rate of the base oil (A) at 20°C is 1.05 or more. The relative heat transfer rate is the heat transfer rate of the base oil (A) when the heat transfer rate of the mineral oil (α) satisfying the following requirements (α1) to (α4) at 20°C is set to 1.00. · Requirement (α1): The kinematic viscosity at 20°C is 7.06 mm 2 / s. · Requirement (α2): The specific heat at 20°C is 1.67 kJ / (kg·K). ·Requirement (α3): The density at 20°C is 0.857 g / cm 3 . ·Requirement (α4): The thermal conductivity at 20°C is 0.141 W / (m·K).

[0031] The heat transfer rate is an index of the ease of heat transfer between two substances (i.e., base oil (A) and the object to be cooled). In Requirement (5), the heat transfer rate of base oil (A) is defined as the relative heat transfer rate with respect to the heat transfer rate of mineral oil (α). The higher the relative heat transfer rate defined in Requirement (5), the better the cooling performance can be said. The thermal conductivity of the fluid at 20°C (A α , unit: W / (m 2 ·K)) can be calculated from the following formula (I). [Number] In the above formula (I), A D20 is the density of the fluid at 20°C (unit: g / cm 3 ). A C20 is the specific heat of the fluid at 20°C (unit: kJ / (kg·K)). A HC20 is the thermal conductivity of the fluid at 20°C (unit: W / (m·K)). A KV20 is the kinematic viscosity of the fluid at 20°C (unit: mm 2 / s).

[0032] Here, from the viewpoint of making it easier to exhibit the effects of the present invention, the relative heat transfer rate of base oil (A) at 20°C defined in Requirement (5) is preferably 1.10 or more, more preferably 1.15 or more, and still more preferably 1.20 or more. Also, usually, it is 1.60 or less.

[0033] (Requirement (6)) In Requirement (6), it is defined that the flash point of base oil (A) is 105°C or higher. By having a flash point of 105°C or higher, it is easy to improve the safety by making it difficult to ignite base oil (A). The base oil (A) contained in the lubricating oil composition of the present invention satisfies the above requirements (1) to (3), and further has a specific amount of an ester-based synthetic oil (A1). Therefore, the flash point of the base oil (A) is high, and it is easy to prepare the base oil (A) that satisfies the requirement (6).

[0034] Here, the flash point defined in the requirement (6) is preferably 109 °C or higher, more preferably 112 °C or higher, and still more preferably 115 °C or higher. The base oil (A) that satisfies the above requirements (1) to (3) and further has a specific amount of the ester-based synthetic oil (A1) usually has a flash point of 200 °C or lower.

[0035] In this specification, the flash point of the base oil (A) means a value measured by the Cleveland Open Cup method (COC method) in accordance with JIS K 2265-4:2007.

[0036] (Requirement (7)) In the requirement (7), it is defined that the volume resistivity of the base oil (A) at 25 °C is 0.03×10 7 Ω·m or more. The higher the volume resistivity, the better the electrical insulation property. The base oil (A) contained in the lubricating oil composition of the present invention satisfies the above requirements (1) to (3), and further has a specific amount of the ester-based synthetic oil (A1). Therefore, the electrical insulation property of the base oil (A) is high, and it is easy to prepare the base oil (A) that satisfies the requirement (7).

[0037] Here, the volume resistivity at 25 °C defined in the requirement (7) is preferably 0.05×10 7 Ω·m or more, more preferably 0.1×10 7 Ω·m or more, still more preferably 0.5×10 7 Ω·m or more, even more preferably 1.0×10 7 Ω·m or more, still even more preferably 4.0×10 7 Ω·m or more, even more preferably 4.2×10 7 Ω·m or more, still even more preferably 4.4×10 7 Ω·m or more, still even more preferably 4.5×10 7is 1.0×10 or more Ω·m. The base oil (A) that satisfies the above requirements (1) to (3) and further has a specific amount of the ester-based synthetic oil (A1) has a volume resistivity at 25°C of usually 1.0×10 10 Ω·m or less.

[0038] In this specification, the volume resistivity of the base oil (A) at 25°C means a value measured under the conditions of a measurement temperature of 25°C and an applied voltage of 250V in accordance with JIS C2101:1999.

[0039] <Ester-based synthetic oil (A1)> In the lubricating oil composition of the present invention, as the ester-based synthetic oil (A1), one or more selected from the group consisting of an ester (A1-1) of a monohydric alcohol and a monobasic acid and an ester (A1-2) of a monohydric alcohol and a polybasic acid are used. Hereinafter, from the viewpoint of preparing the base oil (A) that satisfies the above requirements (1) to (3) and further the above requirements (4) to (7), the ester (A1-1) of a monohydric alcohol and a monobasic acid and the ester (A1-2) of a monohydric alcohol and a polybasic acid will be described in detail.

[0040] (Ester (A1-1) of a monohydric alcohol and a monobasic acid) The monohydric alcohol constituting the ester (A1-1) preferably has 1 to 24 carbon atoms, more preferably 1 to 12 carbon atoms, and still more preferably 1 to 10 carbon atoms from the viewpoint of facilitating the preparation of the base oil (A) that satisfies the above requirements (1) to (3) and further the above requirements (4) to (7). The monohydric alcohol may be linear or branched, and may be saturated or unsaturated, but is preferably branched from the viewpoint of improving the low-temperature characteristics by making the fluidity good.

[0041] Specific examples of the monohydric alcohol constituting the ester (A1-1) include methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol, tridecanol, tetradecanol, pentadecanol, hexadecanol, heptadecanol, octadecanol, nonadecanol, icosanol, heneicosanol, docosanol, tricosanol, and tetracosanol, as well as butenol, pentenol, hexenol, heptenol, octenol, nonenol, decenol, undecenol, dodecenol, tridecenol, tetradecenol, pentadecenol, hexadecenol, heptadecenol, octadecenol, nonadecenol, icosanol, heneicosanol, docosanol, tricosanol, and tetracosanol. These may be linear or branched-chain.

[0042] Further, as the monobasic acid constituting the ester (A1-1), from the viewpoint of facilitating the preparation of the base oil (A) that satisfies the above requirements (1) to (3), and further the above requirements (4) to (7), fatty acids having 2 to 16 carbon atoms are preferable, fatty acids having 4 to 14 carbon atoms are more preferable, fatty acids having 5 to 12 carbon atoms are still more preferable, and fatty acids having 6 to 10 carbon atoms are even more preferable. The fatty acid may be linear or branched-chain, and may be saturated or unsaturated.

[0043] Specific examples of the monobasic acid constituting the ester (A1-1) include acetic acid, propionic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid (caprylic acid), nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, and hexadecanoic acid, as well as acrylic acid, butenoic acid, pentenoic acid, hexenoic acid, heptenoic acid, octenoic acid, nonenoic acid, decenoic acid, undecenoic acid, dodecenic acid, tridecenic acid, tetradecenic acid, pentadecenic acid, and hexadecenic acid.

[0044] Here, preferred embodiments of the combination of the monohydric alcohol and the monobasic acid constituting the ester (A1-1) are shown below. · Preferred combination: monohydric alcohol having 1 to 24 carbon atoms and fatty acid having 2 to 16 carbon atoms · More preferred combination: monohydric alcohol having 1 to 12 carbon atoms and fatty acid having 4 to 14 carbon atoms · Even more preferred combination: monohydric alcohol having 1 to 10 carbon atoms and fatty acid having 5 to 12 carbon atoms · Even more preferred combination: monohydric alcohol having 1 to 10 carbon atoms and fatty acid having 6 to 10 carbon atoms

[0045] In addition, the ester (A1-1) of the monohydric alcohol and the monobasic acid may be used alone or in combination of two or more.

[0046] (Ester (A1-2) of monohydric alcohol and polybasic acid) The monohydric alcohol constituting the ester (A1-2) has a carbon number of preferably 1 to 12, more preferably 1 to 10, even more preferably 1 to 8, even more preferably 1 to 6, and even more preferably 1 to 4, from the viewpoint of facilitating the preparation of the base oil (A) that satisfies the above requirements (1) to (3), and further the above requirements (4) to (7). The monohydric alcohol may be linear or branched, and may be saturated or unsaturated.

[0047] Specific examples of the monohydric alcohol constituting the ester (A1-2) include methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, undecanol, and dodecanol, and butenol, pentenol, hexenol, heptenol, octenol, nonenol, decenol, undecenol, and dodecenol. These may be linear or branched.

[0048] As the polybasic acid constituting the ester (A1-2), from the viewpoint of facilitating the preparation of the base oil (A) that satisfies the above requirements (1) to (3), and further the above requirements (4) to (7), dibasic acids having 2 to 8 carbon atoms are preferable, dibasic acids having 4 to 8 carbon atoms are more preferable, and dibasic acids having 5 to 7 carbon atoms are even more preferable. The dibasic acid may be linear or branched, and may be saturated or unsaturated.

[0049] Specific examples of the polybasic acid constituting the ester (A1-2) include ethanedioic acid, propanedioic acid, butanedioic acid, pentanedioic acid, hexanedioic acid (adipic acid), heptanedioic acid, and octanedioic acid, as well as butenedioic acid, pentenedioic acid, hexenedioic acid, heptenedioic acid, and octenedioic acid.

[0050] Here, preferred embodiments of the combination of the monohydric alcohol and the dibasic acid constituting the ester (A1-2) are shown below. · Preferred combination: monohydric alcohol having 1 to 12 carbon atoms and dibasic acid having 2 to 8 carbon atoms · More preferred combination: monohydric alcohol having 1 to 10 carbon atoms and dibasic acid having 4 to 8 carbon atoms · Even more preferred combination: monohydric alcohol having 1 to 8 carbon atoms and dibasic acid having 5 to 7 carbon atoms · Even more preferred combination: monohydric alcohol having 1 to 6 carbon atoms and dibasic acid having 5 to 7 carbon atoms · Even more preferred combination: monohydric alcohol having 1 to 4 carbon atoms and dibasic acid having 5 to 7 carbon atoms

[0051] Note that the ester (A1-2) of the monohydric alcohol and the polybasic acid may be used alone or in combination of two or more.

[0052] <Base oil (A2) other than the ester-based synthetic oil (A1)> In the lubricating oil composition of one embodiment of the present invention, the base oil (A) may contain a base oil (A2) other than the ester-based synthetic oil (A1) (hereinafter, also simply referred to as "other base oil (A2)"). From the viewpoint of facilitating the preparation of the base oil (A) that satisfies the above requirements (1) to (3), and further the above requirements (4) to (7), the content of the other base oil (A) is preferably 70% by mass or less, more preferably 60% by mass or less, and still more preferably 50% by mass or less based on the total amount of the base oil (A).

[0053] The other base oil (A2) is not particularly limited as long as it can prepare the base oil (A) that satisfies the above requirements (1) to (3), and further the above requirements (4) to (7), and one or more selected from the group consisting of mineral oils and synthetic oils can be used.

[0054] Examples of the mineral oil include atmospheric residue obtained by atmospheric distillation of crude oil such as paraffinic crude oil, intermediate-base crude oil, or naphthenic crude oil; distillate oil obtained by vacuum distillation of these atmospheric residues; mineral oil obtained by subjecting the distillate oil to one or more refining treatments such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining; and the like.

[0055] Examples of the synthetic oil include polyalphaolefins such as α-olefin homopolymers and α-olefin copolymers (for example, α-olefin copolymers having 8 to 14 carbon atoms such as ethylene-α-olefin copolymers); isoparaffin; various esters such as polyol esters and dibasic acid esters (excluding the above ester-based synthetic oil (A1)); various ethers such as polyphenyl ether; polyalkylene glycol; alkylbenzene; alkylnaphthalene; GTL base oil obtained by isomerizing wax (gas to liquid (GTL) wax) produced from natural gas by the Fischer-Tropsch method or the like.

[0056] The other base oil (A2) may be used alone or in combination of two or more kinds of mineral oils, or may be used alone or in combination of two or more kinds of synthetic oils. Further, one or more kinds of mineral oils and one or more kinds of synthetic oils may be used in combination. Here, as the other base oil (A2), mineral oil is preferred. By combining and using the ester-based synthetic oil (A1) and mineral oil, it is possible to further improve the electrical insulation while ensuring sufficient cooling performance without significantly degrading the cooling performance, and to prepare a lubricating oil composition with an extremely excellent balance between cooling performance and electrical insulation. From such a perspective, the content of the mineral oil is preferably 10% by mass or more, more preferably 30% by mass or more, still more preferably 40% by mass or more, based on the total amount of the base oil (A). Also, it is preferably 70% by mass or less, more preferably 60% by mass or less. The upper and lower limit values of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 10% by mass to 70% by mass, more preferably 30% by mass to 60% by mass, still more preferably 40% by mass to 60% by mass. Also, the content ratio [(ester-based synthetic oil (A1)) / (mineral oil)] of the ester-based synthetic oil (A1) and the mineral oil is preferably 30 / 70 or more, more preferably 40 / 60 or more, by mass ratio. Also, it is preferably 90 / 10 or less, more preferably 70 / 30 or less, still more preferably 60 / 40 or less. The upper and lower limit values of these numerical ranges can be arbitrarily combined. Specifically, it is preferably 30 / 70 to 90 / 10, more preferably 40 / 60 to 70 / 30, still more preferably 40 / 60 to 60 / 40.

[0057] <<Additives>> The lubricating oil composition of one aspect of the present invention can be blended with additives such as an anti-wear agent, an antioxidant, a viscosity index improver, a rust inhibitor, a metal deactivator, an antifoaming agent, and a detergent-dispersant, as necessary, within a range that does not inhibit the effects of the present invention. These additives may be used singly or in combination of two or more. The total content of these additives is not particularly limited, but is, for example, about 0 to 20% by weight based on the total amount of the composition.

[0058] <Anti-wear agent> The antiwear agent is not particularly limited, and any one can be appropriately selected from the antiwear agents conventionally used in lubricating oils and used. For example, when used in combination with an electric motor and a gear reducer in a hybrid vehicle or an electric vehicle, it is preferable to use one or more selected from a neutral phosphorus-based compound, an acidic phosphite or its amine salt, and a sulfur-based compound so as not to impair the electrical insulation as much as possible. The content of the antiwear agent is not particularly limited, but is, for example, about 0.01 to 5% by weight based on the total amount of the composition.

[0059] Examples of the neutral phosphorus-based compound include aromatic neutral phosphate esters such as tricresyl phosphate, triphenyl phosphate, trixylenyl phosphate, tricresyl phenyl phosphate, tricresyl thiophosphate, and triphenyl thiophosphate; aliphatic neutral phosphate esters such as tributyl phosphate, tri-2-ethylhexyl phosphate, tributoxy phosphate, and tributyl thiophosphate; aromatic neutral phosphite esters such as triphenyl phosphite, tricresyl phosphite, trisnonylphenyl phosphite, diphenyl mono-2-ethylhexyl phosphite, diphenyl monotridecyl phosphite, tolcresyl thiophosphite, and triphenyl thiophosphite; and aliphatic neutral phosphite esters such as tributyl phosphite, trioctyl phosphite, tridecyl phosphite, tristridecyl phosphite, trioleyl phosphite, tributyl thiophosphite, and trioctyl thiophosphite. These may be used alone or in combination of two or more.

[0060] Examples of the acidic phosphite esters include aliphatic acidic phosphate ester amine salts such as di-2-ethylhexyl acid phosphate amine salt, dilauryl acid phosphate amine salt, and dioleyl acid phosphate amine salt; aliphatic acidic phosphite esters such as di-2-ethylhexyl hydrogen phosphite, dilauryl hydrogen phosphite, and dioleyl hydrogen phosphite, and amine salts thereof; aromatic acidic phosphate ester amine salts such as diphenyl acid phosphate amine salt and dicresyl acid phosphate amine salt; aromatic acidic phosphite esters such as diphenyl hydrogen phosphite and dicresyl hydrogen phosphite, and amine salts thereof; sulfur-containing acidic phosphate ester amine salts such as S-octylthioethyl acid phosphate amine salt and S-dodecylthioethyl acid phosphate amine salt; sulfur-containing acidic phosphite esters such as S-octylthioethyl hydrogen phosphite and S-dodecylthioethyl hydrogen phosphite, and amine salts thereof. These may be used alone or in combination of two or more.

[0061] As the sulfur-based compounds, various ones can be used. Specifically, examples thereof include thiadiazole-based compounds, polysulfide-based compounds, dithiocarbamate-based compounds, sulfurized oil and fat-based compounds, and sulfurized olefin-based compounds. These may be used alone or in combination of two or more.

[0062] <Antioxidant> As the antioxidant, any one can be appropriately selected from known antioxidants conventionally used as antioxidants for lubricating oils. For example, amine-based antioxidants (diphenylamines, naphthylamines), phenol-based antioxidants, molybdenum-based antioxidants, sulfur-based antioxidants, phosphorus-based antioxidants, etc. can be mentioned. The antioxidant may be used alone or in combination of two or more. The content of the antioxidant is not particularly limited, but is, for example, about 0.05 to 7% by weight based on the total amount of the composition.

[0063] <Viscosity index improver> Examples of the viscosity index improver include polymethacrylate, dispersed polymethacrylate, olefin copolymers (such as ethylene-propylene copolymer, etc.), dispersed olefin copolymers, styrene copolymers (such as styrene-diene copolymer, styrene-isoprene copolymer, etc.). The viscosity index improver may be used alone or in combination of two or more kinds. The compounding amount (in terms of resin content) of the viscosity index improver is not particularly limited, but for example, from the viewpoint of the compounding effect, it is about 0.1% by weight or more and 10% by weight or less based on the total amount of the composition.

[0064] <Rust inhibitor> Examples of the rust inhibitor include fatty acids, alkenyl succinic acid half esters, fatty acid soaps, alkyl sulfonates, polyhydric alcohol fatty acid esters, fatty acid amides, oxidized paraffin, alkyl polyoxyethylene ethers, etc. The rust inhibitor may be used alone or in combination of two or more kinds. The preferable compounding amount of the rust inhibitor is not particularly limited, but it is about 0.01% by weight or more and 3% by weight or less based on the total amount of the composition.

[0065] <Metal deactivator> Examples of the metal deactivator include benzotriazole, triazole derivatives, benzotriazole derivatives, thiadiazole derivatives. The metal deactivator may be used alone or in combination of two or more kinds. The content of the metal deactivator is not particularly limited, but preferably it is 0.01 - 5% by weight based on the total amount of the composition.

[0066] <Defoaming agent> Examples of the defoaming agent include silicone compounds such as dimethylpolysiloxane, polyacrylate, etc. The defoaming agent may be used alone or in combination of two or more kinds. The content of the defoaming agent is not particularly limited, but it is about 0.001% by weight or more and 0.5% by weight or less based on the total amount of the composition.

[0067] <Detergent-dispersant> Examples of the detergent-dispersant include succinimide compounds, boron imide compounds, acid amide compounds, etc. The detergent-dispersant may be used alone or in combination of two or more. The content of the detergent-dispersant is not particularly limited, but is preferably 0.1 to 20% by weight based on the total amount of the composition.

[0068] [Properties of Lubricating Oil Composition] The lubricating oil composition according to one aspect of the present invention preferably satisfies the above requirements (1) to (3) defined as requirements for the base oil (A). In addition to the above requirements (1) to (3), it is preferable to satisfy one or more selected from the above requirements (4) to (7), more preferably to satisfy two or more, still more preferably to satisfy three or more, and even more preferably to satisfy four. When the above requirements (1) to (7) are defined as physical property values for the lubricating oil composition according to one aspect of the present invention, the preferred conditions in these requirements (1) to (7) are as described above.

[0069] [Use of Lubricating Oil Composition] The lubricating oil composition of the present invention has excellent cooling performance, while ensuring electrical insulation and having a high flash point. Also, lubricity is ensured. Therefore, the lubricating oil composition of the present invention can be suitably used as a cooling oil for cooling various devices. In particular, it can be suitably used as a cooling oil for cooling devices for electric vehicles possessed by electric vehicles. Specifically, for example, it can be suitably used as a cooling oil for cooling one or more devices for electric vehicles selected from the group consisting of motors, generators, capacitors, converters, inverters, engines, and transmissions. The motor may be a dedicated drive motor or a motor that also serves as a generator. The generator mentioned as a device for electric vehicles means a generator mounted separately from a motor that also serves as a generator. Examples of the capacitor include batteries and capacitors. In one aspect of the present invention, a method of using the lubricating oil composition of the present invention for cooling an electric vehicle device of an electric vehicle is provided. As described above, examples of the electric vehicle device include one or more selected from the group consisting of a motor, a generator, a battery, a converter, an inverter, an engine, and a transmission.

[0070] [Cooling System] The lubricating oil composition of the present invention has excellent cooling performance, while ensuring electrical insulation and having a high flash point. Moreover, lubricity is also ensured. Therefore, the lubricating oil composition of the present invention cools the device while lubricating the device by circulating various devices such as electric vehicle devices. Here, in one aspect of the present invention, a cooling system for cooling an electric vehicle device is provided, which includes the above-described lubricating oil composition of the present invention. As described above, examples of the electric vehicle device include one or more selected from the group consisting of a motor, a generator, a battery, a converter, an inverter, an engine, and a transmission. The cooling system includes a circulation path through which the lubricating oil composition circulates and a cooling target part. The cooling target part is the device (preferably the electric vehicle device). The cooling method in the cooling target part may be either a direct cooling method or an indirect cooling method, and is appropriately set according to the cooling method required for the device (preferably the electric vehicle device). The cooling system may further include a supply device that supplies the lubricating oil composition to the cooling target part through the circulation path. Further, a sensor part that detects the temperature of the cooling target part and a control device that controls the operation of the supply device according to the temperature detected by the sensor part may be further provided. In this specification, the "cooling system" means an "object" in which a plurality of components including at least the circulation path and the cooling target part are assembled to exhibit a function of cooling the cooling target part, and can also be paraphrased as a "device" in which a plurality of components are assembled to exhibit a function of cooling the cooling target part.

[0071] [Method for Producing Lubricating Oil Composition] The method for producing the lubricating oil composition of the present invention is not particularly limited. The method for producing the lubricating oil composition according to one embodiment includes an ester-based synthetic oil (A1), and the content of the ester-based synthetic oil (A1) is 30% by mass to 100% by mass (based on the total amount of base oil (A)), and the ester-based synthetic oil (A1) is one or more selected from the group consisting of an ester (A1-1) of a monohydric alcohol and a monobasic acid and an ester (A1-2) of a monohydric alcohol and a polybasic acid, and includes a step of preparing a base oil (A) that satisfies the following requirements (1) to (3). · Requirement (1): The kinematic viscosity at 40 °C is 2.00 mm 2 / s to 4.00 mm 2 / s. · Requirement (2): The specific heat at 20 °C is 1.75 kJ / (kg·K) or less. · Requirement (3): The density at 20 °C is 0.850 g / cm 3 or more. The base oil (A) is further prepared to satisfy preferably one or more, more preferably two or more, still more preferably three or more, and even more preferably four of the requirements selected from the above requirements (4) to (7). The preferred conditions in the above requirements (1) to (7) are as described above. Further, the method may include a step of mixing an additive with the base oil (A) as necessary. The additive may be blended by any method, and the order and method of blending are not limited.

[0072] [One Aspect of the Present Invention Provided] According to one aspect of the present invention, the following [1] to [9] are provided. [1] A lubricating oil composition containing a base oil (A), wherein the base oil (A) includes an ester-based synthetic oil (A1), the content of the ester-based synthetic oil (A1) is 30% by mass to 100% by mass based on the total amount of the base oil (A), The ester-based synthetic oil (A1) is at least one selected from the group consisting of an ester (A1-1) of a monohydric alcohol and a monobasic acid and an ester (A1-2) of a monohydric alcohol and a polybasic acid. The base oil (A) is a lubricating oil composition that satisfies the following requirements (1) to (3). · Requirement (1): The kinematic viscosity at 40°C is 2.00 mm 2 / s to 4.00 mm 2 / s. · Requirement (2): The specific heat at 20°C is 1.75 kJ / (kg·K) or less. · Requirement (3): The density at 20°C is 0.850 g / cm 3 or more. [2] The lubricating oil composition according to [1], wherein the base oil (A) further satisfies the following requirement (4). · Requirement (4): The thermal conductivity at 20°C is 0.140 W / (m·K) or more. [3] The lubricating oil composition according to [1] or [2], wherein the base oil (A) further satisfies the following requirement (6). · Requirement (6): The flash point by the Cleveland open cup method is 105°C or more. [4] The lubricating oil composition according to any one of [1] to [3], wherein the base oil (A) further satisfies the following requirement (7). · Requirement (7): The volume resistivity at 25°C is 0.03×10 7 Ω·m or more. [5] The lubricating oil composition according to any one of [1] to [4], wherein the ester-based synthetic oil (A1) is an ester (A1-2) of a monohydric alcohol and a polybasic acid. [6] The lubricating oil composition according to any one of [1] to [5], which is used for cooling electric vehicle equipment. [7] The lubricating oil composition according to [6], wherein the electric vehicle equipment is at least one selected from a motor, a battery, an inverter, an engine, and a transmission. [8] A method of using the lubricating oil composition according to any one of [1] to [7] for cooling electric vehicle equipment. [9] A cooling system for cooling the electric vehicle equipment, comprising the lubricating oil composition according to any one of [1] to [7].

Example

[0073] The present invention will be specifically described by the following examples, but the present invention is not limited to the following examples.

[0074] [Examples 1 to 4 and Comparative Examples 1 to 6] The base oils shown below were used alone or in a mixture of two as shown in Table 1 to obtain the lubricating oil compositions of Examples 1 to 4 and Comparative Examples 1 to 6. The details of the base oils used in Examples 1 to 4 and Comparative Examples 1 to 6 are as shown below.

[0075] <Base oil (A)> (Ester synthetic oil (A1)) · Diethyl adipate (ester of adipic acid (hexanedioic acid) and ethanol) · Dimethyl adipate (ester of adipic acid (hexanedioic acid) and methanol) · 2-Ethylhexyl caprylate (ester of caprylic acid (octanoic acid) and 2-ethylhexanol) · 2-Ethylhexyl oleate (ester of oleic acid and 2-ethylhexanol) · Di(2-ethylhexyl) azelate (ester of azelaic acid and 2-ethylhexanol) Note that diethyl adipate, dimethyl adipate, and di(2-ethylhexyl) azelate are esters of a monohydric alcohol and a polybasic acid (dibasic acid). 2-Ethylhexyl caprylate and 2-ethylhexyl oleate are esters of a monohydric alcohol and a monobasic acid. · Mineral oil 1 (equivalent to VG2) · Mineral oil 2 (equivalent to VG5): Corresponding to the above-mentioned mineral oil (α). · Ethylene glycol

[0076] <Measurement methods of various physical property values> The measurements and calculations of the properties of the lubricating oil compositions of Examples 1 to 4 and Comparative Examples 1 to 6 were carried out according to the following procedures. In this example, since the study was conducted without blending additives other than the base oil, each property of the lubricating oil composition is also the property of the base oil. (1) Kinematic viscosity at 40 °C and kinematic viscosity at 100 °C Measured in accordance with JIS K2283:2000. (2) Kinematic viscosity at 20 °C Calculated in accordance with JIS K2283:2000 using the measurement results of kinematic viscosity at 40 °C and kinematic viscosity at 100 °C. (3) Density at 20 °C Measured in accordance with JIS K 2249-1:2011 (Crude oil and petroleum products - Method for determining density - Part 1: Vibration method). (4) Specific heat at 20 °C Using a thermal conductivity measuring device (TCi, manufactured by C-THERM Technology), the thermal conductivity measurement value and the thermal diffusivity measurement value were obtained, and calculated using the above formula (f1). The density at 20 °C was the value measured in (3) above. (5) Thermal conductivity at 20 °C The thermal conductivity at 20 °C was measured using a thermal conductivity measuring device (TCi, manufactured by C-THERM Technology). (6) Flash point Measured in accordance with JIS K 2265-4:2007 by the Cleveland open cup method (COC method). (7) Volume resistivity at 25 °C Measured in accordance with JIS C2101:1999 under the conditions of a measurement temperature of 25 °C and an applied voltage of 250 V.

[0077] <Calculation of relative heat transfer coefficient> From the density at 20 °C, the specific heat at 20 °C, the thermal conductivity at 20 °C, and the kinematic viscosity at 20 °C obtained by the above measurements, the heat transfer coefficients at 20 °C of the lubricating oil compositions of Examples 1 to 4 and Comparative Examples 1 to 6 were calculated using the above formula (I). Then, when the heat transfer coefficient of Comparative Example 4 (using Mineral Oil 2 corresponding to Mineral Oil (α)) was set to 1.00, the heat transfer coefficients of Examples 1 to 4, Comparative Examples 1 to 3, and Comparative Examples 5 to 6 were calculated, and this was defined as the relative heat transfer coefficient.

[0078] <Evaluation> In this Example, a lubricating oil composition (base oil) with a relative heat transfer coefficient of 1.05 or more (the above requirement (5)), a flash point of 105°C or more (the above requirement (6)), and a volume resistivity of 0.03×10 7 Ω·m or more (the above requirement (7)) was considered qualified. The results are shown in Table 1.

[0079]

Table 1

[0080] From the results shown in Table 1, the following can be understood. When an ester-based synthetic oil (A1) is contained in an amount of 30% by mass or more based on the total amount of the base oil (A) and all of the above requirements (1) to (3) are satisfied, as in the lubricating oil compositions (base oils) of Examples 1 to 4, it can be seen that all of the relative heat transfer coefficient defined by the above requirement (5), the flash point defined by the above requirement (6), and the volume resistivity defined by the above requirement (7) are satisfied. On the other hand, even when an ester-based synthetic oil (A1) is contained in an amount of 30% by mass or more based on the total amount of the base oil (A), as in the lubricating oil compositions (base oils) of Comparative Examples 1 and 2, if the above requirements (1) and (2) are not satisfied, it can be seen that the relative heat transfer coefficient defined by the above requirement (5) is not satisfied. Also, when the base oil (A) consists only of mineral oil and does not contain an ester-based synthetic oil (A1) in an amount of 30% by mass or more based on the total amount of the base oil (A), as in the lubricating oil compositions (base oils) of Comparative Examples 3 and 4, it can be seen that the flash point defined by the above requirement (6) or the relative heat transfer coefficient defined by the above requirement (5) is not satisfied. Specifically, when the above requirement (3) is not satisfied, the flash point defined by the above requirement (6) is not satisfied, and when the above requirement (1) is not satisfied, it can be seen that the relative heat transfer coefficient defined by the above requirement (5) is not satisfied. Also, as in the lubricating oil compositions (base oils) of Comparative Examples 5 and 6, when the base oil (A) consists only of ethylene glycol or a mixture of ethylene glycol and water and does not contain 30% by mass or more of the ester-based synthetic oil (A1) based on the total amount of the base oil (A), it can be seen that the volume resistivity defined in the above requirement (7) is not satisfied.

Claims

1. A lubricating oil composition used for cooling an electric vehicle device containing a base oil (A), wherein the base oil (A) contains an ester synthetic oil (A1), the content of the ester synthetic oil (A1) is 30% by mass to 100% by mass based on the total amount of the base oil (A), the ester synthetic oil (A1) is one or more selected from the group consisting of an ester (A1-1) of a monohydric alcohol having 1 to 10 carbon atoms and a monobasic acid having 6 to 10 carbon atoms and an ester (A1-2) of a monohydric alcohol having 1 to 10 carbon atoms and a dibasic acid having 4 to 8 carbon atoms, the base oil (A) satisfies the following requirements (1) to (3), and is a lubricating oil composition used for cooling an electric vehicle device. ・Requirement (1): The kinematic viscosity at 40 °C is 2.00 mm ２ / s to 4.00 mm ２ / s. - Requirement (2): The specific heat at 20°C is 1.75 kJ / (kg·K) or less. ・Requirement (3): The density at 20°C is 0.850 g / cm ３ or more.

2. The lubricating oil composition according to claim 1, wherein the base oil (A) further satisfies the following requirement (4). - Requirement (4): The thermal conductivity at 20°C is 0.140 W / (m·K) or more.

3. The lubricating oil composition according to claim 1 or 2, wherein the base oil (A) further satisfies the following requirement (6). - Requirement (6): The flash point by the Cleveland open cup method is 105°C or higher.

4. The lubricating oil composition according to any one of claims 1 to 3, wherein the base oil (A) further satisfies the following requirement (7). ・Requirement (7): The volume resistivity at 25°C is 0.03×10 ７ Ω·m or more.

5. The lubricating oil composition according to any one of claims 1 to 4, wherein the ester synthetic oil (A1) is an ester (A1-2) of a monohydric alcohol and a dibasic acid.

6. The lubricating oil composition according to any one of claims 1 to 5, wherein the electric vehicle device is one or more selected from the group consisting of a motor, a generator, a battery, a converter, an inverter, an engine, and a transmission.

7. A method of using the lubricating oil composition according to any one of claims 1 to 6 for cooling an electric vehicle device.

8. A cooling system for cooling an electric vehicle device, comprising the lubricating oil composition according to any one of claims 1 to 6.

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