EP4663722A1

EP4663722A1 - Lubricant base oil

Info

Publication number: EP4663722A1
Application number: EP24753163.5A
Authority: EP
Inventors: Kazushige Matsubara
Original assignee: Idemitsu Kosan Co Ltd
Current assignee: Idemitsu Kosan Co Ltd
Priority date: 2023-02-09
Filing date: 2024-01-29
Publication date: 2025-12-17
Also published as: CN120584169A; JPWO2024166719A1; WO2024166719A1

Abstract

Provided is a lubricant base oil having a natural origin content (ISO 16128) of 90 to 100%, and including a monoester-based compound (A) and a hydrocarbon-based compound (B).

Description

Technical Field

The present invention relates to a lubricant base oil, and a lubricating oil composition containing the lubricant base oil.

Background Art

In recent years, lubricating oil compositions used in automobiles have been developed in consideration of environmental impact. For example, Patent Literature 1 discloses a lubricating oil composition in which the structure and content of polymer components, the evaporation loss according to NOACK, and the content of fraction with a boiling point in the range of 350 to 400°C are adjusted, for the purpose of reducing fuel consumption in order to reduce carbon dioxide emissions.

Citation List

Patent Literature

Patent Literature 1: JP-A-2021-25025

Summary of Invention

Technical Problem

Meanwhile, it is becoming necessary to consider the environmental impact of lubricating oil compositions not only upon application but also upon disposal from the viewpoint of life cycle assessment. Therefore, there is a demand for a lubricant base oil that can be used to prepare a lubricating oil composition that is excellent in various properties such as rubber swelling resistance and handling properties, for example, while reducing the environmental impact upon disposal.

Solution to Problem

The present invention provides a lubricant base oil having a natural origin content (ISO 16128) of 90 to 100%, comprising a monoester-based compound and a hydrocarbon-based compound, and a lubricating oil composition comprising the lubricant base oil.
Specifically, provided are the lubricant base oil and lubricating oil composition according to the aspects [1] to [15] below.

[1] A lubricant base oil having a natural origin content (ISO 16128) of 90 to 100%, comprising a monoester-based compound (A) and a hydrocarbon-based compound (B).
[2] The lubricant base oil according to [1] above, wherein the hydrocarbon-based compound (B) has 18 or more carbon atoms.
[3] The lubricant base oil according to [1] above, wherein the hydrocarbon-based compound (B) has 20 or more carbon atoms.
[4] The lubricant base oil according to any one of [1] to [3] above, wherein the monoester-based compound (A) has 18 or more carbon atoms.
[5] The lubricant base oil according to any one of [1] to [4] above, wherein the monoester-based compound (A) comprises a monoester compound having one or more branched structures.
[6] The lubricant base oil according to any one of [1] to [5] above, wherein the monoester-based compound (A) comprises a saturated monoester compound.
[7] The lubricant base oil according to any one of [1] to [6] above, wherein the monoester-based compound (A) is a compound represented by the general formula (1) below: wherein R¹ and R² are each independently a hydrocarbon group, at least one of R¹ and R² is a branched hydrocarbon group, and the total number of carbon atoms of R¹ and R² is 17 or more.
[8] The lubricant base oil according to [7] above, wherein, in the general formula (1), R¹ and R² are each independently a saturated hydrocarbon group, and at least one of R¹ and R² is a saturated branched hydrocarbon group.
[9] The lubricant base oil according to [7] or [8] above, wherein, in the general formula (1), R¹ is an alkyl group having 8 or more carbon atoms, R² is an alkyl group having 5 or more carbon atoms, and at least one of R¹ and R² is a branched alkyl group.
[10] The lubricant base oil according to any one of [1] to [9] above, wherein the pour point of the lubricant base oil is 0°C or less.
[11] The lubricant base oil according to any one of [1] to [10] above, wherein the volume change rate of a nitrile rubber for test, as measured by immersing the nitrile rubber for test in the lubricant base oil under conditions at 150°C for 72 hours in accordance with JIS K6258, is less than 6%.
[12] The lubricant base oil according to any one of [1] to [11] above, having a flash point of 154°C or more.
[13] The lubricant base oil according to any one of [1] to [12] above, wherein the content ratio [(A)/(B)] between the component (A) and the component (B) is 5/95 or more and 95/5 or less in terms of mass ratio.
[14] A lubricating oil composition comprising the lubricant base oil according to any one of [1] to [13] above.
[15] The lubricating oil composition according to [14] above, further comprising one or more additives for lubricating oil selected from a pour point depressant, a viscosity index improver, an antioxidant, an extreme pressure agent, a metallic detergent, an ashless dispersant, a metal deactivator, a friction modifier, a rust inhibitor, and a defoamer.

Advantageous Effects of Invention

The lubricant base oil according to a preferable aspect of the present invention allows a lubricating oil composition that is excellent in various properties such as rubber swelling resistance and handling properties to be prepared, while reducing the environmental impact upon disposal.

Description of Embodiments

For the numerical ranges described herein, any upper limit and lower limit can be combined. For example, in the case where "preferably 30 to 100, more preferably 40 to 80" is described as numerical ranges, the range of "30 to 80" and the range of "40 to 100" are also included in the numerical ranges disclosed in this description. Further, for example, in the case where "preferably 30 or more, more preferably 40 or more, further preferably 100 or less, more preferably 80 or less" is described as numerical ranges, the range of "30 to 80" and the range of "40 to 100" are also included in the numerical ranges disclosed in this description.
In addition, the description "60 to 100" as a numerical range disclosed in this description, for example, means the range of "60 or more (60 or more than 60) and 100 or less (100 or less than 100)".
As used herein, kinematic viscosity and viscosity index mean values measured or calculated in accordance with JIS K2283:2000.

[Configuration of lubricant base oil]

The lubricant base oil according to an aspect of the present invention has a natural origin content (ISO 16128) of 90 to 100% and comprises a monoester-based compound (A) and a hydrocarbon-based compound (B).
As used herein, the natural origin content is a value calculated in accordance with ISO 16128 and indicates a percentage of natural raw materials derived from plants, animals, algae, microorganisms such as bacteria and fungi, and minerals in the raw materials used for the production of the lubricant base oil.
That is, since the lubricant base oil according to an aspect of the present invention has a natural origin content of 90 to 100% calculated in accordance with ISO 16128, 90% or more of the raw materials are derived from natural raw materials.
For example, in the automotive industry, lubricating oil compositions are required to reduce the environmental impact upon disposal from the viewpoint of life cycle assessment.
The lubricant base oil according to an aspect of the present invention is composed of raw materials so that the natural origin content (ISO 16128) is 90% to 100%, for reducing the environmental impact upon disposal.
When the lubricant base oil according to an aspect of the present invention is composed of raw materials derived from plants, even if carbon dioxide is generated by combustion upon disposal, the carbon dioxide in the atmosphere does not increase over the entire life cycle, since the plants constituting the raw materials absorb carbon dioxide during the growth process, so that the balance of carbon dioxide emissions can be suppressed. When the lubricant base oil has a natural origin content of 100%, carbon dioxide emissions will be treated as "carbon neutral", meaning substantially zero.
The natural origin content calculated in accordance with ISO 16128 of the lubricant base oil according to an aspect of the present invention may be 91 to 100%, 92 to 100%, 93 to 100%, 94 to 100%, 95 to 100%, 96 to 100%, 97 to 100%, 98 to 100%, 99 to 100%, or 100%.
The lubricant base oil according to an aspect of the present invention comprises the monoester-based compound (A) and the hydrocarbon-based compound (B). The lubricant base oil comprising the component (A) and the component (B) is excellent in viscometric properties, low-temperature viscometric properties, insulation properties, safety due to a high flash point, and rubber swelling resistance, and can be used to prepare a lubricating oil composition excellent in these characteristics.
The lubricant base oil according to an aspect of the present invention may further contain an additional base oil other than the components (A) and (B), as long as the natural origin content falls within the range of 90 to 100%, and the effects of the present invention are not impaired.
In the lubricant base oil according to an aspect of the present invention, the total content of the components (A) and (B) is 60 to 100 mass%, 70 to 100 mass%, 80 to 100 mass%, 90 to 100 mass%, 95 to 100 mass%, 97 to 100 mass%, 98 to 100 mass%, 99 to 100 mass%, or 100 mass%, based on the total amount (100 mass%) of the lubricant base oil.
The components (A) and (B) included in the lubricant base oil according to an aspect of the present invention will be described below.

The monoester-based compound (A) (hereinafter, also referred to as "component (A)") included in the lubricant base oil according to an aspect of the present invention can be generated through an ester reaction between a monocarboxylic acid component and an alcohol component.
2-Ethylhexyl palmitate, which is described in Patent Literature 1 and the like and is generally known as a lubricating base oil, is produced by an ester reaction between palmitic acid and 2-ethylhexanol, but 2-ethylhexanol is a raw material derived from petroleum and does not correspond to the natural raw material specified in ISO 16128. Therefore, the natural origin content of 2-ethylhexyl palmitate is not 100%.
Meanwhile, since the lubricant base oil according to an aspect of the present invention has a natural origin content (ISO 16128) of 90 to 100%, the monocarboxylic acid component and the alcohol component as raw materials of the component (A) used in an aspect of the present invention are preferably derived from natural raw materials. A lubricant base oil with reduced environmental impact upon disposal can be obtained by comprising, as the component (A), a monoester-based compound obtained from a monocarboxylic acid component and an alcohol component that are derived from natural raw materials.
Further, for making the lubricant base oil treated as carbon neutral, the component (A) used in an aspect of the present invention is preferably composed only of a monoester-based compound produced from a monocarboxylic acid component and an alcohol component that are derived from natural raw materials.
The natural raw materials for the monocarboxylic acid component and the alcohol component as the raw materials for the component (A) are preferably plant raw materials.
The natural origin content calculated in accordance with ISO 16128 of the component (A) used in an aspect of the present invention may be 90 to 100%, 91 to 100%, 92 to 100%, 93 to 100%, 94 to 100%, 95 to 100%, 96 to 100%, 97 to 100%, 98 to 100%, 99 to 100%, or 100%.
In the lubricant base oil according to an aspect of the present invention, by comprising the component (A), the lubricant base oil with various good properties (such as viscometric property, pour point, volume resistivity, flash point, and rubber swelling resistance), in particular, good rubber swelling resistance, a high flash point, and excellent handling properties can be obtained. On the other hand, for example, a diester compound having a natural origin content of 90 to 100% has a high flash point but is inferior in rubber swelling resistance.
Further, the component (A) used in an aspect of the present invention preferably includes a monoester compound having one or more branched structures, and more preferably includes a monoester compound having one or more branched structures and having 18 or more carbon atoms. The lubricant base oil can be excellent in various properties (such as viscometric property, pour point, volume resistivity, flash point, and rubber swelling resistance) by including the monoester compound having one or more branched structures. Therefore, the lubricating oil composition can be excellent in various lubricating properties by using the lubricant base oil.
In addition, from the same viewpoint as described above, the component (A) used in an aspect of the present invention preferably includes a saturated monoester compound, more preferably includes a saturated monoester compound having one or more branched structures, further preferably includes a saturated monoester compound having one or more branched structures and having 18 or more carbon atoms, and still further preferably includes: a saturated monoester compound having one branched structure and having 18 or more carbon atoms; or a saturated monoester compound having two branched structures and having 18 or more carbon atoms.
In the lubricant base oil according to an aspect of the present invention, the content ratio of the saturated monoester compound in the component (A) is preferably 50 to 100 mass%, 60 to 100 mass%, 70 to 100 mass%, 80 to 100 mass%, 90 to 100 mass%, 95 to 100 mass%, 98 to 100 mass%, 99 to 100 mass%, or 100 mass%, based on the total amount of the component (A) contained in the lubricant base oil taken as 100 mass%.
In the lubricant base oil according to an aspect of the present invention, the content ratio of an unsaturated monoester compound in the component (A) is preferably less than 50 mass%, less than 40 mass%, less than 30 mass%, less than 20 mass%, less than 10 mass%, less than 5.0 mass%, less than 3.0 mass%, less than 2.0 mass%, less than 1.0 mass%, less than 0.1 mass%, less than 0.01 mass%, less than 0.001 mass%, or less than 0.0001 mass%, based on the total amount (100 mass%) of the lubricant base oil.
In the lubricant base oil according to an aspect of the present invention, for achieving a lubricant base oil with a higher viscosity, a higher flash point, and further improved rubber swelling resistance, the number of carbon atoms of the monoester compound may be preferably 18 or more, more preferably 20 or more, more preferably 21 or more, further preferably 22 or more, furthermore preferably 23 or more, particularly preferably 24 or more, further be 25 or more or 26 or more, and 70 or less, 65 or less, 60 or less, 55 or less, 50 or less, 48 or less, 46 or less, 45 or less, 44 or less, 42 or less, 40 or less, 38 or less, 37 or less, 36 or less, 35 or less, 34 or less, 33 or less, 32 or less, 31 or less, 30 or less, 29 or less, 28 or less, 27 or less, 26 or less, or 25 or less.
For achieving a lubricant base oil that is excellent in various properties (such as viscometric property, pour point, flash point, and rubber swelling resistance), the component (A) used in an aspect of the present invention is preferably a compound represented by the general formula (1) below.
In the general formula (1) above, R¹ and R² are each independently a hydrocarbon group, and at least one of R¹ and R² is a branched hydrocarbon group.
The branched hydrocarbon group may be a group having one or more branching points, preferably a group having one or two branching points, more preferably a group having one branching point.
Further, for achieving a lubricant base oil with a higher viscosity, a higher flash point, and further improved rubber swelling resistance, the total number of carbon atoms of R¹ and R² may be preferably 17 or more, more preferably 19 or more, more preferably 20 or more, further preferably 21 or more, furthermore preferably 22 or more, particularly preferably 23 or more, further be 24 or more or 25 or more, and 70 or less, 65 or less, 60 or less, 55 or less, 50 or less, 48 or less, 46 or less, 45 or less, 44 or less, 42 or less, 40 or less, 38 or less, 37 or less, 36 or less, 35 or less, 34 or less, 33 or less, 32 or less, 31 or less, 30 or less, 29 or less, 28 or less, 27 or less, 26 or less, 25 or less, or 24 or less.
For achieving a lubricant base oil with a higher viscosity, a higher flash point, and further improved rubber swelling resistance, the number of carbon atoms of R¹ in the general formula (1) above may be preferably 3 or more, more preferably 4 or more, further preferably 5 or more, furthermore preferably 6 or more, particularly preferably 7 or more, further be 8 or more, 10 or more, 12 or more, 13 or more, 14 or more, 15 or more, or 16 or more, and 40 or less, 35 or less, 30 or less, 28 or less, 26 or less, 25 or less, 24 or less, 22 or less, 20 or less, 18 or less, 16 or less, 14 or less, 12 or less, or 10 or less.
For achieving a lubricant base oil with a higher viscosity, a higher flash point, and further improved rubber swelling resistance, the number of carbon atoms of R² in the general formula (1) above may be preferably 3 or more, more preferably 4 or more, further preferably 5 or more, furthermore preferably 6 or more, particularly preferably 7 or more, further be 8 or more, 10 or more, 12 or more, 13 or more, 14 or more, 15 or more, or 16 or more, and 30 or less, 25 or less, 22 or less, 20 or less, 18 or less, 16 or less, 14 or less, 12 or less, or 10 or less.
Examples of the hydrocarbon group that can be selected as R¹ and R² include an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, an alkylaryl group, and an arylalkyl group.
Examples of the alkyl group include a linear alkyl group or a branched alkyl group such as a methyl group, an ethyl group, a propyl group (a n-propyl group and an isopropyl group), a butyl group (a n-butyl group, a s-butyl group, a t-butyl group, and an isobutyl group), a pentyl group, a hexyl group, a heptyl group, an octyl group, a 2-ethylhexyl group, a 1-methylheptyl group, nonyl group, a 1-methyloctyl group, a 1,1-dimethylheptyl group, a decyl group, a 1-methylheptyl group, an undecyl group, a 1-methyldecyl group, a dodecyl group, a 1-methylundecyl group, a tridecyl group, a 1-methyldodecyl group, a tetradecyl group, a 1-methyltridecyl group, a pentadecyl group, a 1-methyltetradecyl group, a hexadecyl group, a 1-methylpentadecyl group, a 2-hexyldecyl group, a heptadecyl group, a 1-methylhexadecyl group, an octadecyl group, a 1-methylheptadecyl group, a nonadecyl group, and a 1-methyloctadecyl group.
Examples of the alkenyl group include linear alkenyl groups or branched alkenyl groups such as an ethenyl group, a propenyl group, a butenyl group, a pentenyl group, a hexenyl group, a heptenyl group, an octenyl group, a methylheptenyl group, a nonyl group, a methyloctenyl group, a decenyl group, a methylnonyl group, an undecenyl group, a methyldecenyl group, a dodecenyl group, a methylundecenyl group, a tridecenyl group, a methyldodecenyl group, a tetradecenyl group, a methyltridecenyl group, a pentadecenyl group, a methyltetradecenyl group, a hexadecenyl group, a methylpentadecenyl group, a heptadecenyl group, a methylhexadecenyl group, an octadecenyl group, a methylheptadecenyl group, a nonadecenyl group, and a methyloctadecenyl group.
Examples of the cycloalkyl group include a cycloalkyl group that may have an alkyl group such as a cyclohexyl group, a dimethylcyclohexyl group, an ethylcyclohexyl group, a propylcyclohexyl group, a butylcyclohexyl group, and a heptylcyclohexyl group.
Examples of the aryl group include a phenyl group, a naphthyl group, an anthracenyl group, a biphenyl group, and a tarphenyl group.
Examples of the alkylaryl group include a tolyl group, a dimethylphenyl group, a butylphenyl group, a nonylphenyl group, a methylbenzyl group, and a dimethylnaphthyl group.
Examples of the arylalkyl group include a phenylmethyl group, a phenylethyl group, and a diphenylmethyl group.
Among these, for achieving a lubricant base oil that is superior in various properties (such as viscometric property, pour point, volume resistivity, flash point, and rubber swelling resistance), it is preferable that, in the general formula (1) above, R¹ and R² are each independently an alkyl group or alkenyl group, and at least one of R¹ and R² is a branched alkyl group or a branched alkenyl group, and it is more preferable that R¹ and R² are each independently an alkyl group, and at least one of R¹ and R² is a branched alkyl group, and it is further preferable that R¹ is a linear alkyl group and R² is a branched alkyl group, or R¹ and R² are each independently a branched alkyl group.
Further, in the lubricant base oil according to an aspect of the present invention, for achieving a lubricant base oil that is superior in various properties (particularly, viscometric property, pour point, volume resistivity, flash point, and rubber swelling resistance), it is preferable that, in the general formula (1) above, R¹ and R² are each independently a saturated hydrocarbon group, and at least one of R¹ and R² is a saturated branched hydrocarbon group, and it is more preferable that R¹ is an alkyl group having 5 or more (preferably 8 or more) carbon atoms, R² is an alkyl group having 5 or more carbon atoms, and at least one of R¹ and R² is a branched alkyl group.
From the above viewpoint, it is preferable that, in the general formula (1) above, R¹ is a linear alkyl having 5 or more (preferably 6 or more or 7 or more, and preferably 29 or less, 27 or less, 25 or less, 23 or less, 21 or less, 20 or less, 18 or less, 16 or less, 12 or less, 10 or less, 8 or less, or 7 or less) carbon atoms, and R² is a branched alkyl group having 5 or more (preferably 6 or more, 8 or more, 10 or more, 12 or more, 14 or more, 15 or more, or 16 or more, and preferably 29 or less, 27 or less, 25 or less, 23 or less, 21 or less, 20 or less, 19 or less, 18 or less, or 17 or less) carbon atoms.
In addition, from the above viewpoint, it is preferable that, in the general formula (1) above, R¹ is a branched alkyl having 5 or more (preferably 6 or more, 8 or more, 10 or more, 12 or more, 14 or more, 15 or more, 16 or more, or 17 or more, and preferably 29 or less, 27 or less, 25 or less, 23 or less, 21 or less, 20 or less, 19 or less, or 18 or less) carbon atoms, and R² is a branched alkyl group having 5 or more (preferably 6 or more, 7 or more, or 8 or more, and preferably 29 or less, 27 or less, 25 or less, 23 or less, 21 or less, 20 or less, 18 or less, 16 or less, 12 or less, or 10 or less) carbon atoms.
For achieving a lubricant base oil with various good properties and a higher flash point, resulting in further excellent handling properties, in the lubricant base oil according to an aspect of the present invention, the content of the component (A) is preferably 3 mass% or more, 5 mass% or more, 10 mass% or more, 15 mass% or more, 20 mass% or more, 25 mass% or more, 30 mass% or more, 35 mass% or more, or 40 mass% or more; further, for achieving a lubricant base oil with further improved rubber swelling resistance, while ensuring the content of the component (B), the content of the component (A) is preferably 97 mass% or less, 95 mass% or less, 90 mass% or less, 85 mass% or less, 80 mass% or less, 75 mass% or less, 70 mass% or less, or 65 mass% or less, based on the total amount (100 mass%) of the lubricant base oil.

The lubricant base oil according to an aspect of the present invention comprises a hydrocarbon-based compound (B) (hereinafter, also referred to as "component (B)").
By comprising the component (B) together with the component (A), the lubricant base oil according to an aspect of the present invention can have various good properties (such as viscometric property, pour point, volume resistivity, flash point, and rubber swelling resistance), in particular, have further improved rubber swelling resistance.
The natural origin content calculated in accordance with ISO 16128 of the component (B) used in an aspect of the present invention may be 90 to 100%, 91 to 100%, 92 to 100%, 93 to 100%, 94 to 100%, 95 to 100%, 96 to 100%, 97 to 100%, 98 to 100%, 99 to 100%, or 100%.
The component (B) used in an aspect of the present invention includes a compound derived from a natural raw material and composed of hydrocarbon atoms and hydrogen atoms, more specifically includes a compound (B1) selected from reaction products obtained by reacting one or two or more unsaturated hydrocarbon compounds or hydrogenated products thereof, a compound (B2) selected from normal paraffins and isoparaffins, and the like.
The component (B) used in an aspect of the present invention may be used singly, or two or more kinds thereof may be used in combination.
Examples of an unsaturated hydrocarbon compound composing the component (B1) include α-olefins such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1-butene, 3-methyl-1-pentene, 3-ethyl-1-pentene, 4-methyl-1-pentene, 4-methyl-1-hexene, 4,4-dimethyl-1-hexene, 4,4-dimethyl-1-pentene, 4-ethyl-1-hexene, 3-ethyl-1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and 1-eicosene.
For achieving a lubricant base oil with various good properties and a higher flash point, resulting in further excellent handling properties, the number of carbon atoms of the unsaturated hydrocarbon compound composing the component (B1) is preferably 4 or more, more preferably 6 or more, more preferably 8 or more, further preferably 10 or more, further preferably 12 or more, furthermore preferably 14 or more, particularly preferably 16 or more, further be 18 or more, 20 or more, 22 or more, 24 or more, 26 or more, 28 or more, 30 or more, or 32 or more, and 50 or less, 45 or less, 40 or less, 38 or less, 36 or less, or 34 or less.
The component (B1) preferably has a kinematic viscosity at 100°C of 2.0 mm²/s or more, 2.2 mm²/s or more, 2.4 mm²/s or more, 2.6 mm²/s or more, 2.8 mm²/s or more, 3.0 mm²/s or more, 3.2 mm²/s or more, 3.6 mm²/s or more, 3.8 mm²/s or more, 4.0 mm²/s or more, or 4.2 mm²/s or more, and 8.0 mm²/s or less, 7.8 mm²/s or less, 7.6 mm²/s or less, 7.4 mm²/s or less, 7.2 mm²/s or less, 7.0 mm²/s or less, 6.8 mm²/s or less, 6.6 mm²/s or less, 6.4 mm²/s or less, 6.2 mm²/s or less, 6.0 mm²/s or less, 5.8 mm²/s or less, 5.6 mm²/s or less, 5.4 mm²/s or less, 5.2 mm²/s or less, 5.0 mm²/s or less, or 4.8 mm²/s or less.
For achieving a lubricant base oil with various good properties, further improved rubber swelling resistance, and a higher flash point, resulting in further excellent handling properties, the number of carbon atoms of the component (B2) may be preferably 10 or more, more preferably 12 or more, further preferably 14 or more, furthermore preferably 16 or more, particularly preferably 18 or more, and 50 or less, 45 or less, 40 or less, 38 or less, 36 or less, 34 or less, 32 or less, or 30 or less.
In an aspect of the present invention, the component (B2) used as the component (B) is preferably an isoparaffin for achieving a lubricant base oil with various good properties and superior low-temperature flowability.
For achieving a lubricant base oil with various good properties, further improved rubber swelling resistance, and a higher flash point, resulting in further excellent handling properties, the component (B) used in an aspect of the present invention preferably includes the component (B1).
In the lubricant base oil according to an aspect of the present invention, the content ratio of the component (B1) in the component (B) is preferably 50 to 100 mass%, more preferably 60 to 100 mass%, more preferably 70 to 100 mass%, further preferably 80 to 100 mass%, furthermore preferably 90 to 100 mass%, particularly preferably 95 to 100 mass%, based on the total amount (100 mass%) of the component (B) contained in the lubricant base oil.
For achieving a lubricant base oil with various good properties, further improved rubber swelling resistance, and a higher flash point, resulting in further excellent handling properties, the number of carbon atoms of the component (B) used in an aspect of the present invention is preferably 18 or more, more preferably 20 or more, more preferably 22 or more, further preferably 24 or more, further preferably 26 or more, furthermore preferably 28 or more, and particularly preferably 30 or more.
For achieving a lubricant base oil with various good properties and further improved rubber swelling resistance, in the lubricant base oil according to an aspect of the present invention, the content of the component (B) is preferably 3 mass% or more, 5 mass% or more, 10 mass% or more, 15 mass% or more, 20 mass% or more, 25 mass% or more, 30 mass% or more, 35 mass% or more, 40 mass% or more, or 45 mass% or more; further, for achieving a lubricant base oil with a higher flash point resulting in further excellent handling properties, while ensuring the content of the component (A), the content of the component (B) is preferably is preferably 97 mass% or less, 95 mass% or less, 90 mass% or less, 85 mass% or less, 80 mass% or less, 75 mass% or less, 70 mass% or less, or 65 mass% or less, based on the total amount (100 mass%) of the lubricant base oil.
For achieving a lubricant base oil with various good properties, further improved rubber swelling resistance, and a higher flash point, resulting in further excellent handling properties, in the lubricant base oil according to an aspect of the present invention, the content ratio [(A)/(B)] between the component (A) and the component (B) is preferably 5/95 or more, 10/90 or more, 15/85 or more, 20/80 or more, 25/75 or more, 30/70 or more, 35/65 or more, or 40/60 or more, and is preferably 95/5 or less, 90/10 or less, 85/15 or less, 80/20 or less, 75/25 or less, 70/30 or less, 65/35 or less, 60/40 or less, or 55/45 or less, in terms of mass ratio.

Although the lubricant base oil according to an aspect of the present invention may further comprise other base oils other than the component (A) and the component (B), the smaller the content thereof, the more preferable.
For example, in the lubricant base oil according to an aspect of the present invention, the smaller the content of mineral oil, the more preferable, and the content of mineral oil is preferably less than 10 mass%, less than 5.0 mass%, less than 3.0 mass%, less than 2.0 mass%, less than 1.0 mass%, less than 0.1 mass%, less than 0.01 mass%, or less than 0.001 mass%, based on the total amount (100 mass%) of the lubricant base oil.
Although the lubricant base oil according to an aspect of the present invention may comprise an ester-based compound (a diester compound, a triester compound, a polyester compound, or the like) other than the component (A), the smaller the content thereof, the more preferable, for achieving a lubricant base oil with further improved rubber swelling resistance.
The content of the ester-based compound other than the component (A) is preferably less than 10 mass%, less than 5.0 mass%, less than 3.0 mass%, less than 2.0 mass%, less than 1.0 mass%, less than 0.1 mass%, less than 0.01 mass%, or less than 0.001 mass%, based on the total amount (100 mass%) of the lubricant base oil.

[Properties of lubricant base oil]

The lubricant base oil according to an aspect of the present invention may have a kinematic viscosity at 40°C of 4.0 mm²/s or more, 4.2 mm²/s or more, 4.5 mm²/s or more, 4.7 mm²/s or more, 5.0 mm²/s or more, 5.2 mm²/s or more, 5.5 mm²/s or more, 5.7 mm²/s or more, 6.0 mm²/s or more, 6.2 mm²/s or more, 6.5 mm²/s or more, 6.7 mm²/s or more, 7.0 mm²/s or more, 7.5 mm²/s or more, 8.0 mm²/s or more, 8.5 mm²/s or more, 9.0 mm²/s or more, or 9.5 mm²/s or more, and 100 mm²/s or less, 90 mm²/s or less, 80 mm²/s or less, 70 mm²/s or less, 60 mm²/s or less, 50 mm²/s or less, 40 mm²/s or less, 35 mm²/s or less, 30 mm²/s or less, 25 mm²/s or less, 20 mm²/s or less, 19 mm²/s or less, 18 mm²/s or less, or 17 mm²/s or less.
The lubricant base oil according to an aspect of the present invention may have a kinematic viscosity at 100°C of 1.0 mm²/s or more, 1.2 mm²/s or more, 1.5 mm²/s or more, 1.7 mm²/s or more, 1.8 mm²/s or more, 2.0 mm²/s or more, 2.2 mm²/s or more, 2.5 mm²/s or more, 2.7 mm²/s or more, or 3.0 mm²/s or more, and 10 mm²/s or less, 9.0 mm²/s or less, 8.0 mm²/s or less, 7.0 mm²/s or less, 6.0 mm²/s or less, 5.0 mm²/s or less, 4.5 mm²/s or less, 4.2 mm²/s or less, 4.0 mm²/s or less, 3.8 mm²/s or less, or 3.5 mm²/s or less.
The lubricant base oil according to an aspect of the present invention may have a viscosity index of 70 or more, 80 or more, 85 or more, 90 or more, 95 or more, 100 or more, 105 or more, 110 or more, 115 or more, 120 or more, 125 or more, or 130 or more.
For achieving a lubricant base oil that can be easily prepared into a lubricating oil composition that can be used in a wide temperature range, the lubricant base oil according to an aspect of the present invention preferably has a pour point of 0°C or less, more preferably -10°C or less, more preferably -20°C or less, further preferably -30°C or less, further preferably - 35°C or less, furthermore preferably -37.5°C or less, furthermore preferably -40°C or less, furthermore preferably -45°C or less, particularly preferably -47.5°C or less.
As used herein, the pour point means a value measured in accordance with JIS K2269.
For achieving a lubricant base oil with excellent insulation properties, the volume resistivity measured for the lubricant base oil according to an aspect of the present invention under test conditions of a measurement temperature of 80°C, an applied voltage of 250 V, and a measurement time of one minute, in accordance with JIS C2101 is preferably 1.0 × 10⁵ Ωm or more, more preferably 5.0 × 10⁵ Ωm or more, more preferably 1.0 × 10⁶ Ωm or more, further preferably 5.0 × 10⁶ Ωm or more, further preferably 1.0 × 10⁷ Ωm or more, furthermore preferably 5.0 × 10⁷ Ωm or more, particularly preferably 1.0 × 10⁸ Ωm or more.
The lubricant base oil according to an aspect of the present invention may have a flash point of preferably 154°C or more, more preferably 160°C or more, more preferably 164°C or more, more preferably 170°C or more, further preferably 174°C or more, further preferably 180°C or more, further preferably 190°C or more, furthermore preferably 200°C or more, furthermore preferably 210°C or more, particularly preferably 220°C or more, and 400°C or less, 380°C or less, 350°C or less, 330°C or less, 320°C or less, 310°C or less, or 300°C or less.
As used herein, the flash point means a value measured by the Cleveland Open Cup method (COC method) in accordance with JIS K2265-4 (Determination of flash point- Part 4: Cleveland open cup method).
The volume change rate of a nitrile rubber for test, as measured by immersing the nitrile rubber for test in the lubricant base oil according to an aspect of the present invention under conditions at 150°C for 72 hours in accordance with JIS K6258 is preferably less than 6%, more preferably 5% or less, further preferably 4% or less, furthermore preferably 3% or less, particularly preferably 2% or less, for achieving a lubricant base oil with good rubber swelling resistance.
As used herein, the volume change rate of the nitrile rubber for test means a value measured and calculated by the method described in Examples.

[Configuration of lubricating oil composition]

The lubricating oil composition according to an aspect of the present invention comprises the lubricant base oil according to an aspect of the present invention.
The lubricating oil composition according to an aspect of the present invention may further contain additives for lubricating oil. Specifically, it may further contain one or more additives for lubricating oil selected from a pour point depressant, a viscosity index improver, an antioxidant, an extreme pressure agent, a metallic detergent, an ashless dispersant, a metal deactivator, a friction modifier, a rust inhibitor, and a defoamer.
One of these additives for lubricating oil may be used alone, or two or more of them may be used in combination.
The content of such an additive for lubricating oil can be appropriately adjusted, as long as the effects of the present invention are not impaired, but is generally 0.001 to 15 mass%, preferably 0.005 to 10 mass%, more preferably 0.01 to 5 mass%, independently for each additive, based on the total amount (100 mass%) of the lubricating oil composition.
In addition, contents of additives for lubricating oil including other additives (a surfactant, a colorant, and the like) in addition to those described above may be limited. The limited contents of additives for lubricating oil may be less than 3.0%, less than 2.0%, less than 1.0%, less than 0.1%, less than 0.01%, less than 0.001%, less than 0.0001%, or less than 0.00001%, independently for each additive, based on the total amount (100 mass%) of the lubricating oil composition.
In the lubricating oil composition according to an aspect of the present invention, the content of the lubricant base oil according to an aspect of the present invention is preferably 50 mass% or more, more preferably 60 mass% or more, further preferably 70 mass% or more, furthermore preferably 80 mass% or more, particularly preferably 90 mass% or more, based on the total amount (100 mass%) of the lubricating oil composition.

[Pour point depressant]

Examples of the pour point depressant to be used in an aspect of the present invention include ethylene-vinyl acetate copolymer, a condensate of chlorinated paraffin and naphthalene, a condensate of chlorinated paraffin and phenol, polymethacrylate, and polyalkylstyrene.
One of these pour point depressants may be used alone, or two or more of them may be used in combination.

[Viscosity index improver]

Examples of the viscosity index improver to be used in an aspect of the present invention include polymers such as non-dispersed polymethacrylates, dispersed polymethacrylates, olefin copolymers (e.g., ethylenepropylene copolymer), dispersed olefin copolymers, styrene copolymers (e.g., styrene-diene copolymer and styrene-isoprene copolymer).
One of these viscosity index improvers may be used alone, or two or more of them may be used in combination.
Further, the weight-average molecular weight (Mw) of the viscosity index improver to be used in an aspect of the present invention may be 5,000 or more, 7,000 or more, 10,000 or more, 15,000 or more, or 20,000 or more, and 1,000,000 or less, 700,000 or less, 500,000 or less, 300,000 or less, 200,000 or less, 100,000 or less, or 50,000 or less.

[Antioxidant]

Examples of the antioxidant to be used in an aspect of the present invention include amine antioxidants such as alkylated diphenylamine, phenylnaphthylamine, and alkylated phenylnaphthylamine; phenolic 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.
One of these antioxidants may be used alone, or two or more of them may be used in combination.
In the lubricating oil composition according to an aspect of the present invention, an amine antioxidant and a phenolic antioxidant are preferably used as antioxidants in combination.

[Extreme pressure agent (antiwear agent)]

Examples of the extreme pressure agent (antiwear agent) to be used in an aspect of the present invention include such as sulfur-containing compounds such as zinc dithiophosphate; phosphorus-containing compounds such as phosphorous acid esters, phosphoric acid esters, phosphonic acid esters, and amine salts or metal salts thereof; and sulfur- and phosphorus-containing compounds such as thiophosphorous acid esters, thiophosphoric acid esters, thiophosphonic acid esters, and amine salts or metal salts thereof.
One of these extreme pressure agents may be used alone, or two or more of them may be used in combination.

[Metallic detergent]

Examples of the metallic detergent to be used in an aspect of the present invention include metal salts such as metal sulfonates, metal salicylates, and metal phenates. Further, the metal atom constituting such a metal salt is preferably a metal atom selected from alkali metals and alkaline earth metals, more preferably sodium, calcium, magnesium, or barium, further preferably calcium.
One of these metallic detergents may be used alone, or two or more of them may be used in combination.
In the lubricating oil composition according to an aspect of the present invention, the metallic detergent preferably contains one or more selected from calcium sulfonate, calcium salicylate, and calcium phenate, more preferably calcium sulfonate.
The content ratio of calcium sulfonate is preferably 50 to 100 mass%, more preferably 60 to 100 mass%, further preferably 70 to 100 mass%, furthermore preferably 80 to 100 mass%, based on the total amount (100 mass%) of the metallic detergent contained in the lubricating oil composition.
The base number of the metallic detergent is preferably 0 to 600 mgKOH/g.
However, in the lubricating oil composition according to an aspect of the present invention, the metallic detergent is preferably an overbased metallic detergent having a base number of 100 mgKOH/g or more. The base number of the overbased metallic detergent is 100 mgKOH/g or more, preferably 150 to 500 mgKOH/g, more preferably 200 to 450 mgKOH/g.
As used herein, the "base number" means the base number measured by the perchloric acid method according to chapter 9 of "Petroleum products and lubricating oils-Neutralization value test method" of JIS K2501:2003.

[Ashless dispersant]

Examples of the ashless dispersant to be used in an aspect of the present invention include boron-free succinimides such as boron-free alkenylsuccinimide, boron-containing succinimides such as boron-containing alkenylsuccinimide, benzylamines, boron-containing benzylamines, succinic acid esters, and monovalent or divalent carboxylic acid amides typified by fatty acids or succinic acid.
One of these ashless dispersants may be used alone, or two or more of them may be used in combination.

[Metal deactivator]

Examples of the metal deactivator to be used in an aspect of the present invention include benzotriazole compounds, tolyltriazole compounds, imidazole compounds, and pyrimidine compounds.
One of these metal deactivators may be used alone, or two or more of them may be used in combination.

[Friction modifier]

Examples of the friction modifier to be used in an aspect of the present invention include molybdenum friction modifiers such as molybdenum dithiocarbamate (MoDTC), molybdenum dithiophosphate (MoDTP), and amine salt of molybdenum acid; ashless friction modifiers such as aliphatic amines, fatty acid esters, fatty acid amides, fatty acids, aliphatic alcohols, and aliphatic ethers having at least one alkyl group or alkenyl group having 6 to 30 carbon atoms in a molecule; fats and oils, amines, amides, and sulfurized esters.
One of these friction modifiers may be used alone, or two or more of them may be used in combination.

[Rust inhibitor]

Examples of the rust inhibitor to be used in an aspect of the present invention include fatty acids, alkenyl succinic acid half esters, fatty acid soaps, alkyl sulfonates, polyhydric alcohols fatty acid esters, fatty acid amines, oxidized paraffins, and alkyl polyoxyethylene ethers.
One of these rust inhibitors may be used alone, or two or more of them may be used in combination.

[Defoamer]

Examples of the defoamer to be used in an aspect of the present invention include silicone oils, fluorosilicone oils, and fluoroalkyl ethers.
One of these defoamers may be used alone, or two or more of them may be used in combination.

[Properties and characteristics of lubricating oil composition]

The lubricating oil composition according to an aspect of the present invention comprises the lubricant base oil having a natural origin content of 90% to 100% and thus can be a lubricating oil composition that reduces the environmental impact upon disposal.
The lubricating oil composition according to an aspect of the present invention may have a natural origin content of less than 90% by containing an additive for lubricating oil.
However, for achieving a lubricating oil composition that reduces the environmental impact upon disposal, the natural origin content of the lubricating oil composition according to an aspect of the present invention is preferably 70% or more, more preferably 80% or more, further preferably 85% or more, furthermore preferably 90% or more, particularly preferably 95% or more.
The kinematic viscosity at 40°C of the lubricating oil composition according to an aspect of the present invention is appropriately adjusted according to the application and may be 4.0 mm²/s or more, 4.2 mm²/s or more, 4.5 mm²/s or more, 4.7 mm²/s or more, 5.0 mm²/s or more, 5.2 mm²/s or more, 5.5 mm²/s or more, 5.7 mm²/s or more, 6.0 mm²/s or more, 6.2 mm²/s or more, 6.5 mm²/s or more, 6.7 mm²/s or more, 7.0 mm²/s or more, 7.5 mm²/s or more, 8.0 mm²/s or more, 8.5 mm²/s or more, 9.0 mm²/s or more, 9.5 mm²/s or more, or 10.0 mm²/s or more, and 100 mm²/s or less, 90 mm²/s or less, 80 mm²/s or less, 70 mm²/s or less, 60 mm²/s or less, 50 mm²/s or less, 40 mm²/s or less, 35 mm²/s or less, 30 mm²/s or less, 25 mm²/s or less, or 20 mm²/s or less.
The kinematic viscosity at 100°C of the lubricating oil composition according to an aspect of the present invention is appropriately adjusted according to the application and may be 1.0 mm²/s or more, 1.2 mm²/s or more, 1.5 mm²/s or more, 1.7 mm²/s or more, 2.0 mm²/s or more, 2.2 mm²/s or more, 2.5 mm²/s or more, 2.7 mm²/s or more, or 3.0 mm²/s or more, and 10 mm²/s or less, 9.0 mm²/s or less, 8.0 mm²/s or less, 7.0 mm²/s or less, 6.0 mm²/s or less, 5.0 mm²/s or less, 4.5 mm²/s or less, 4.2 mm²/s or less, 4.0 mm²/s or less, 3.8 mm²/s or less, or 3.5 mm²/s or less.
The viscosity index of the lubricating oil composition according to an aspect of the present invention may be 70 or more, 80 or more, 85 or more, 90 or more, 95 or more, 100 or more, 105 or more, 110 or more, 115 or more, 120 or more, 125 or more, or 130 or more.
The lubricating oil composition according to an aspect of the present invention preferably has a pour point of 0°C or less, more preferably -10°C or less, more preferably -20°C or less, further preferably -30°C or less, further preferably -35°C or less, furthermore preferably -40°C or less, furthermore preferably -45°C or less, particularly preferably -50°C or less.
The volume resistivity measured for the lubricating oil composition according to one aspect of the present invention under test conditions of a measurement temperature of 80°C, an applied voltage of 250 V, and a measurement time of one minute, in accordance with JIS C2101 is preferably 1.0 × 10⁵ Ωm or more, more preferably 5.0 × 10⁵ Ωm or more, further preferably 1.0 × 10⁶ Ωm or more, furthermore preferably 5.0 × 10⁵ Ωm or more, particularly preferably 1.0 × 10⁷ Ωm or more.
The lubricating oil composition according to an aspect of the present invention may have a flash point of preferably 154°C or more, more preferably 160°C or more, more preferably 164°C or more, more preferably 170°C or more, further preferably 174°C or more, further preferably 180°C or more, further preferably 190°C or more, furthermore preferably 200°C or more, furthermore preferably 210°C or more, particularly preferably 220°C or more, and 400°C or less, 380°C or less, 350°C or less, 330°C or less, 320°C or less, 310°C or less, or 300°C or less.
The volume change rate of a nitrile rubber for test, as measured by immersing the nitrile rubber for test in the lubricating oil composition according to an aspect of the present invention under conditions at 150°C for 72 hours in accordance with JIS K6258 is preferably less than 6%, more preferably 5% or less, further preferably 4% or less, furthermore preferably 3% or less, particularly preferably 2% or less.

[Applications of lubricating oil composition]

The lubricating oil composition according to a preferable aspect of the present invention is excellent in various lubricating properties, while being a lubricating oil composition that reduces the environmental impact upon disposal.
In consideration of such properties, the lubricating oil composition according to an aspect of the present invention can be preferably used, for example, for lubrication in electric drive units, engines, transmissions, decelerators, compressors, and mechanisms such as torque converters, wet clutches, gear bearing mechanisms, oil pumps, and hydraulic control mechanisms that are incorporated in various hydraulic systems. Further, due to excellent cooling and insulation properties, it can be suitably used for cooling and insulation of motors or batteries.

Examples

Next, the present invention will be described in more detail with reference to Examples; however, the present invention is not limited in any way by these Examples. The methods for measuring or calculating various properties are as follows.

(1) Natural origin content

It was calculated in accordance with ISO 16128.

(2) Kinematic viscosity and viscosity index

They were measured and calculated in accordance with JIS K2283:2000.

(3) Pour point

It was measured in accordance with JIS K2269.

(4) Volume resistivity

It was measured under test conditions of a measurement temperature of 80°C, an applied voltage of 250 V, and a measurement time of one minute, in accordance with JIS C2101.

(5) Flash point

It was measured by the Cleveland Open Cup method (COC method) in accordance with JIS K2265-4 (Determination of flash point- Part 4: Cleveland open cup method).

(6) Volume change rate of nitrile rubber

A rubber immersion test in accordance with JIS K6258 was conducted. Specifically, it was measured by immersing a test piece of nitrile rubber for test (product name: "A305", available from NOK CORPORATION) in a lubricant base oil to be measured under conditions at an immersion temperature of 120°C for an immersion time of 72 hours. Then, the volume of the test piece was measured before and after the test, and the volume change rate was calculated from the following formula. [Volume change rate (%)] = ([Volume of test piece after test] - [Volume of test piece before test])/[Volume of test piece before test] × 100

Examples 1 to 8, Comparative Examples 1 to 4, and Reference Example 1

Lubricant base oils each formed from a monoester-based compound, a hydrocarbon-based compound, and a mineral oil according to the types and blending amounts shown in Table 1 were prepared. Then, lubricating oil compositions were prepared by adding 5.0 parts by mass of an additive mixture to 95.0 parts by mass of the respective lubricant base oils.
Various physical property values of the prepared lubricant base oils and the lubricating oil compositions were measured according to the aforementioned methods. Tables 1 and 2 show these results.
The details of each component used to prepare the lubricant base oils and the lubricating oil compositions are as follows.

<Ester-based compound>

"2-Hexyldecyl caprylate": a monoester compound having 24 carbon atoms produced from caprylic acid (derived from oil palm) and 2-hexyldecanol (derived from oil palm), in which R¹ is an n-heptyl group (C7 linear alkyl group), and R² is a 2-hexyldecyl group (C16 branched alkyl group) in the general formula (1). The natural origin content is 100%.
"Methylheptyl isostearate": a monoester compound having 26 carbon atoms produced from isostearic acid (derived from colza) and 2-octanol (derived from ricinus), in which R¹ is a C17 branched alkyl group, and R² is a methylheptyl group (C8 branched alkyl group) in the general formula (1). The natural origin content is 100%.
"Bis(2-ethylhexyl) sebacate": a diester compound having 26 carbon atoms produced from sebacic acid (derived from ricinus) and 2-ethylhexanol (derived from petroleum). The natural origin content is 39%.

<Hydrocarbon-based compound>

"Hydrogenated product of reaction product of octadecene and hexadecane": a saturated hydrocarbon-based compound having about 34 carbon atoms obtained by hydrogenating a reaction product of octadecene (derived from oil palm) and hexadecane (derived from oil palm). The natural origin content is 100%, and the kinetic viscosity at 100°C is 4.4 mm²/s.
"C18 isoparaffin": a branched hydrocarbon compound (derived from oil palm) having 18 carbon atoms. The natural origin content is 100%.

"60N mineral oil": a mineral oil with a kinetic viscosity at 40°C of 7.9 mm²/s, a kinetic viscosity at 100°C of 2.3 mm²/s, and a viscosity index of 104. The natural origin content is 0%.
"100N mineral oil": a mineral oil with a kinetic viscosity at 40°C of 19.8 mm²/s, a kinetic viscosity at 100°C of 4.3 mm²/s, and a viscosity index of 122. The natural origin content is 0%.

"Additive mixture": an additive mixture obtained by diluting, with a diluent oil, a pour point depressant, an antioxidant, a phosphorus-based extreme pressure agent, a sulfur-based extreme pressure agent, an ashless dispersant, a metallic detergent, a metal deactivator, and a defoamer.

[Table. 1]

Table 1

				Example 1	Example 2	Example 3	Example 4	Example 5	Example 6	Example 7	Example 8
Lubricant base oil	Ester-based compound	2-Hexyldecyl caprylate	Parts by mass	45.0	70.0	20.0	45.0
		Methylheptyl isostearate	Parts by mass					45.0	45.0	70.0	20.0
		Bis(2-ethylhexyl) sebacate	Parts by mass
	Hydrocarbon-based compound	Hydrogenated product of reaction product of octadecene and hexadecane	Parts by mass	50.0	25.0	75.0		50.0
	Hydrocarbon-based compound	C18 isoparaffin	Parts by mass				50.0		50.0	25.0	75.0
	Mineral oil	60N mineral oil	Parts by mass
	Mineral oil	100N mineral oil	Parts by mass
Additive		Additive mixture	Parts by mass	5.0	5.0	5.0	5.0	5.0	5.0	5.0	5.0
Total			Parts by mass	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
Properties of lubricant base oil		Natural origin content	%	100	100	100	100	100	100	100	100
		Kinetic viscosity at 40°C	mm²/s	12.2	9.5	15.9	5.1	15.2	6.0	8.4	4.7
		Kinetic viscosity at 100°C	mm²/s	3.2	2.7	3.8	1.8	3.7	2.0	2.5	1.7
		Viscosity index	-	131	127	133	-	134	133	130	-
		Pour point	°C	-47.5	-47.5	-47.5	-40.0	-45.0	-37.5	-40.0	-35.0
		Volume resistivity	×10⁷Ωm	>10	>10	>10	>10	>10	>10	>10	>10
		Flash point (COC)	°C	220	220	220	162	228	164	176	156
		Volume change rate of nitrile rubber	%	0	2	-2	4	0	4	5	3
Properties of lubricating oil composition		Natural origin content	%	95	95	95	95	95	95	95	95
		Kinetic viscosity at 40°C	mm²/s	13.6	10.7	17.6	5.9	16.6	7.0	9.4	5.4
		Kinetic viscosity at 100°C	mm²/s	3.5	3.0	4.1	2.0	4.0	2.3	2.7	1.9
		Viscosity index	-	139	136	141	142	143	145	142	-
		Pour point	°C	-55.0	<-60.0	-50.0	-47.5	-57.5	-45.0	-50.0	-37.5
		Volume resistivity	×10⁷Ωm	1.5	1.0	2.9	0.97	2.3	1.2	1.2	1.2
		Flash point (COC)	°C	220	220	220	162	228	164	176	156
		Volume change rate of nitrile rubber	%	0	2	-2	4	0	4	5	3

[Table. 2]

Table 2

				Comparative Example 1	Comparative Example 2	Comparative Example 3	Comparative Example 4	Reference Example 1
Lubricant base oil	Ester-based compound	2-Hexyldecyl caprylate	Parts by mass	95.0
		Methylheptyl isostearate	Parts by mass		95.0
		Bis(2-ethylhexyl) sebacate	Parts by mass			95.0
	Hydrocarbon-based compound	Hydrogenated product of reaction product of octadecene and hexadecane	Parts by mass
	Hydrocarbon-based compound	C18 isoparaffin	Parts by mass				95.0
	Mineral oil	60N mineral oil	Parts by mass					50.0
	Mineral oil	100N mineral oil	Parts by mass					45.0
Additive		Additive mixture	Parts by mass	5.0	5.0	5.0	5.0	5.0
Total			Parts by mass	100.0	100.0	100.0	100.0	100.0
Properties of lubricant base oil		Natural origin content	%	100	100	39	100	0
		Kinetic viscosity at 40°C	mm²/s	7.5	11.4	11.6	3.9	12.9
		Kinetic viscosity at 100°C	mm²/s	2.3	3.1	3.2	1.5	3.2
		Viscosity index	-	123	133	147	-	113
		Pour point	°C	-47.5	-42.5	<-60.0	-32.5	-25.0
		Volume resistivity	×10⁷Ωm	>10	>10	>10	>10	>10
		Flash point (COC)	°C	220	232	234	152	180
		Volume change rate of nitrile rubber	%	6	6	20	2	2
Properties of lubricating oil composition		Natural origin content	%	95	95	37	95	0
		Kinetic viscosity at 40°C	mm²/s	8.6	12.9	13.1	4.5	14.1
		Kinetic viscosity at 100°C	mm²/s	2.6	3.4	3.5	1.7	3.5
		Viscosity index	-	133	142	159	-	123
		Pour point	°C	-57.5	<-60.0	<-60.0	-32.5	-50.0
		Volume resistivity	×10⁷Ωm	0.78	1.2	0.70	1.2	2.7
		Flash point (COC)	°C	220	232	234	152	180
		Volume change rate of nitrile rubber	%	6	6	20	2	2

As shown in Table 1, the lubricant base oils prepared in Examples 1 to 8 each had a natural origin content of 100% and can be said to be lubricant base oils with reduced environmental impact upon disposal. Further, it was confirmed that since the lubricating oil compositions prepared in Examples 1 to 8 each contain the monoester-based compound (A) and the hydrocarbon-based compound (B), the lubricating oil compositions prepared in Examples 1 to 8 are excellent in safety and rubber swelling resistance because of the viscometric properties, low-temperature viscometric properties, insulation properties, and high flash point thereof and have properties comparable to those of the lubricating oil composition of Reference Example 1 using mineral oils.
On the other hand, the lubricating oil compositions prepared in Comparative Examples 1 and 2 did not contain the hydrocarbon-based compound (B) and thus had poor rubber swelling resistance. In addition, the lubricating oil composition prepared in Comparative Example 3 contained a diester compound instead of the monoester-based compound (A) and did not contain the hydrocarbon-based compound (B), resulting in further inferior rubber swelling resistance. Further, the lubricating oil composition prepared in Comparative Example 4 did not contain the monoester-based compound (A), and as a result, a safety problem arose due to the low flash point thereof.

Claims

A lubricant base oil having a natural origin content (ISO 16128) of 90 to 100%, comprising a monoester-based compound (A) and a hydrocarbon-based compound (B).
The lubricant base oil according to claim 1, wherein the hydrocarbon-based compound (B) has 18 or more carbon atoms.
The lubricant base oil according to claim 1, wherein the hydrocarbon-based compound (B) has 20 or more carbon atoms.
The lubricant base oil according to any one of claims 1 to 3, wherein the monoester-based compound (A) has 18 or more carbon atoms.
The lubricant base oil according to any one of claims 1 to 4, wherein the monoester-based compound (A) comprises a monoester compound having one or more branched structures.
The lubricant base oil according to any one of claims 1 to 5, wherein the monoester-based compound (A) comprises a saturated monoester compound.
The lubricant base oil according to any one of claims 1 to 6, wherein the monoester-based compound (A) is a compound represented by the general formula (1) below: wherein R¹ and R² are each independently a hydrocarbon group, at least one of R¹ and R² is a branched hydrocarbon group, and a total number of carbon atoms of R¹ and R² is 17 or more.
The lubricant base oil according to claim 7, wherein, in the general formula (1), R¹ and R² are each independently a saturated hydrocarbon group, and at least one of R¹ and R² is a saturated branched hydrocarbon group.
The lubricant base oil according to claim 7 or 8, wherein, in the general formula (1), R¹ is an alkyl group having 8 or more carbon atoms, R² is an alkyl group having 5 or more carbon atoms, and at least one of R¹ and R² is a branched alkyl group.
The lubricant base oil according to any one of claims 1 to 9, wherein a pour point of the lubricant base oil is 0°C or less.
The lubricant base oil according to any one of claims 1 to 10, wherein a volume change rate of a nitrile rubber for test, as measured by immersing the nitrile rubber for test in the lubricant base oil under conditions at 150°C for 72 hours in accordance with JIS K6258, is less than 6%.
The lubricant base oil according to any one of claims 1 to 11, having a flash point of 154°C or more.
The lubricant base oil according to any one of claims 1 to 12, wherein a content ratio [(A)/(B)] between the component (A) and the component (B) is 5/95 or more and 95/5 or less in terms of mass ratio.
A lubricating oil composition comprising the lubricant base oil according to any one of claims 1 to 13.
The lubricating oil composition according to claim 14, further comprising one or more additives for lubricating oil selected from a pour point depressant, a viscosity index improver, an antioxidant, an extreme pressure agent, a metallic detergent, an ashless dispersant, a metal deactivator, a friction modifier, a rust inhibitor, and a defoamer.