JP7523319B2 - Lubricating Oil Composition - Google Patents

Description

The present invention relates to a lubricating oil composition, and more specifically, to a lubricating oil composition that can be suitably used to lubricate electric motors.

In recent years, from the standpoint of energy efficiency and environmental compatibility, electric vehicles that use electric motors as a power source for running, and hybrid vehicles that use both an electric motor and an internal combustion engine as a power source for running, have been attracting attention. Electric motors generate heat when they are in operation, and the motors contain components that are sensitive to heat, such as coils and magnets. For this reason, when an electric motor is used as a power source for running, a means for cooling the electric motor is generally also used.

Air-cooling, water-cooling, and oil-cooling are known methods for cooling electric motors. Among these, the oil-cooling method is a method that can achieve a high cooling effect by circulating oil inside the electric motor, bringing the heat-generating parts inside the electric motor (e.g., coils, cores, magnets, etc.) into direct contact with the cooling medium (oil). When using the oil-cooling method, the oil circulating inside the motor simultaneously cools and lubricates the electric motor. Therefore, the oil used in the oil-cooling method (oil circulated inside the electric motor: electric motor oil) is required to have high electrical insulation so as not to impede the function of the electric motor when cooling and lubricating.

In addition, automobiles that use electric motors as a power source for running are usually equipped with a transmission that has a gear mechanism. And the lubricating oil used to lubricate the gear mechanism is usually required to be wear-resistant.

Until now, electric motors and transmissions (gear mechanisms) have generally been lubricated with different lubricants. In contrast, if it were possible to lubricate the electric motor and transmission with the same lubricant, it would be possible to simplify the lubricant circulation mechanism, and so in recent years, there has been a desire to lubricate the electric motor and transmission with the same lubricant. Recently, electric drive modules have been proposed that integrate the electric motor and transmission into a single device (package), and in such electric drive modules, it is particularly necessary to lubricate the electric motor and transmission with the same lubricant from the perspective of making the device smaller and lighter.

On the other hand, in the field of lubricating oils, various lubricating oil compositions have been proposed. For example, JP 2005-307203 A (Patent Document 1) discloses a lubricating oil composition containing a base oil and a phosphorus-containing carboxylic acid compound, and in the examples section of the publication, a lubricating oil composition is disclosed in which a base oil is combined with β-dithiophosphorylated propionic acid or β-dithiophosphorylated propionic acid ethyl ester. In addition, JP 10-67993 A (Patent Document 2) discloses a composition containing a lubricant such as a mineral oil-based oil and a compound represented by a specific formula, and in the examples section of the publication, a composition containing a base agent and β-dithiophosphorylated propionic acid, and a composition containing a base agent and ethyl-3-[(bisisopropyloxyphosphinothioyl)thio]propionate (manufactured by BASF, trade name: Irgalube 63) are disclosed. Furthermore, International Publication No. 2013/137160 (Patent Document 3) discloses a lubricating oil composition comprising a specific base oil and a sulfur compound represented by a specific formula, and in the Examples section, a lubricating oil composition containing a base oil and a dithiophosphate compound (manufactured by BASF, trade name: Irgalube 63) as a sulfur compound is disclosed. However, none of the conventional lubricating oil compositions described in Patent Documents 1 to 3 were necessarily sufficient in terms of achieving both a sufficiently high level of electrical insulation and excellent wear resistance.

JP 2005-307203 A Japanese Patent Application Publication No. 10-67993 International Publication No. WO 2013/137160

The present invention was made in consideration of the problems associated with the above-mentioned conventional technology, and aims to provide a lubricating oil composition that can achieve both a sufficiently high level of electrical insulation and excellent wear resistance.

As a result of intensive research conducted by the inventors to achieve the above object, they discovered that it is possible to achieve both a sufficiently high level of electrical insulation and excellent wear resistance by forming a lubricating oil composition containing the following components (A), (B1), and (B2) and satisfying the condition represented by the following formula (I), and thus completed the present invention.

That is, the lubricating oil composition of the present invention has
(A) a lubricating base oil;
(B1) a dithiophosphorylated fatty acid ester having a content of 0.01 mass % or more and 0.50 mass % or less based on the total mass of the lubricating oil composition;
(B2) a dithiophosphorylated fatty acid in an amount of 0.005 mass % or more and 0.15 mass % or less based on the total mass of the lubricating oil composition;
and the following formula (I):
0.30≦[M _(B1) / (M _(B1) + M _(B2) )]≦0.95 (I)
[In formula (I), M _(B1) represents the content of component (B1) based on the total mass of the lubricating oil composition, and M _(B2) represents the content of component (B2) based on the total mass of the lubricating oil composition.]
The present invention is characterized in that it satisfies the condition expressed by the following formula:

In the lubricating oil composition of the present invention, the (B1) component is represented by the following general formula (1):

[In formula (1), ^R1 and ^R2 each independently represent a linear or branched alkyl group having 1 to 18 carbon atoms, ^R3 represents a linear or branched alkylene group having 1 to 10 carbon atoms, and ^R4 represents a linear or branched alkyl group having 1 to 18 carbon atoms.]
It is preferable that the compound (X) is a compound represented by the following formula (hereinafter, sometimes simply referred to as "compound (X)").

In the lubricating oil composition of the present invention, the (B2) component is represented by the following general formula (2):

[In formula (2), ^R5 and ^R6 each independently represent a linear or branched alkyl group having 1 to 18 carbon atoms, and ^R7 represents a linear or branched alkylene group having 1 to 10 carbon atoms.]
It is preferable that the compound (Y) is a compound represented by the following formula (hereinafter, sometimes simply referred to as "compound (Y)").

Furthermore, in the lubricating oil composition of the present invention, the component (A) is preferably a lubricating base oil having a kinetic viscosity at 40° C. of 5.0 to 20.0 mm ² /s.

The present invention makes it possible to provide a lubricating oil composition that can simultaneously achieve a sufficiently high level of electrical insulation and excellent wear resistance.

The present invention will be described in detail below with reference to preferred embodiments. In this specification, unless otherwise specified, the notation "P to Q" for the numerical values P and Q means "greater than or equal to P and less than or equal to Q." In such notations, when a unit is added only to the numerical value Q, the unit is also applied to the numerical value P.

The lubricating oil composition of the present invention comprises
(A) a lubricating base oil;
(B1) a dithiophosphorylated fatty acid ester having a content of 0.01 mass % or more and 0.50 mass % or less based on the total mass of the lubricating oil composition;
(B2) a dithiophosphorylated fatty acid in an amount of 0.005 mass % or more and 0.15 mass % or less based on the total mass of the lubricating oil composition;
and the following formula (I):
0.30≦[M _(B1) / (M _(B1) + M _(B2) )]≦0.95 (I)
[In formula (I), M _(B1) represents the content of component (B1) based on the total mass of the lubricating oil composition, and M _(B2) represents the content of component (B2) based on the total mass of the lubricating oil composition.]
The present invention is characterized in that it satisfies the condition expressed by the following formula:

<(A) Component: Lubricating base oil>
The lubricating base oil used as component (A) in the present invention is not particularly limited, and any known base oil available in the field of lubricating oils can be appropriately used. For example, one or more mineral base oils, One or more synthetic base oils or mixtures thereof may be used. The lubricating base oil may be, among others, a Group II lubricating base oil according to the classification of base oils by the American Petroleum Institute (API). A base oil of Group III, a base oil of Group IV, a base oil of Group V, or a mixture of two or more of these base oils (mixed base oil) can be suitably used (hereinafter Here, API Group II base oils have a sulfur content of 0.03 mass % or less, a saturate content of 90 mass % or more, and a viscosity index of The mineral oil base oil has a molecular weight of 80 or more and less than 120. API Group III base oils are mineral base oils having a sulfur content of 0.03 mass% or less, a saturates content of 90 mass% or more, and a viscosity index of 120 or more. API Group IV base oils are: The base oil of API Group V is a base oil other than those of API Groups I to IV, and a preferred example of the base oil is an ester-based base oil.

Examples of mineral oil base oils include paraffinic or naphthenic mineral oil base oils obtained by applying one or more refining methods, such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfuric acid washing, and clay treatment, to the lubricating oil fraction obtained by atmospheric and vacuum distillation of crude oil. API Group II base oils and Group III base oils are usually produced through a hydrocracking process. Wax isomerized base oils and base oils produced by isomerizing GTL wax (gas-to-liquid wax) can also be used.

Examples of API Group IV base oils include ethylene-propylene copolymers, polybutene, 1-octene oligomers, 1-decene oligomers, and hydrogenated versions of these.

Examples of API Group V base oils include monoesters (e.g., butyl stearate, octyl laurate, 2-ethylhexyl oleate, etc.); diesters (e.g., ditridecyl glutarate, bis(2-ethylhexyl) adipate, diisodecyl adipate, ditridecyl adipate, bis(2-ethylhexyl) sebacate, etc.); polyesters (e.g., trimellitic acid esters, etc.); polyol esters (e.g., trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol 2-ethylhexanoate, pentaerythritol pelargonate, etc.).

The lubricating base oil (component (A)) may consist of one type of base oil, or may be a mixed base oil containing two or more types of base oils. In a mixed base oil containing two or more types of base oils, the API classifications of the base oils may be the same or different from each other. However, the content of API Group V base oil is preferably 0 to 20 mass% (more preferably 0 to 15 mass%, and even more preferably 0 to 10 mass%) based on the total amount of the lubricating base oil. By setting the content of ester-based base oil, which is a type of API Group V base oil, to the above upper limit or less, it is possible to further improve the oxidation stability and electrical insulation of the lubricating oil composition.

The (A) component is preferably a lubricating base oil having a kinetic viscosity at 100°C of 1.8 to 4.5 ^mm2 /s (more preferably 2.1 to 4.5 ^mm2 /s, particularly preferably 2.3 to 4.2 ^mm2 /s). When the kinetic viscosity at 100°C of the lubricating base oil is equal to or less than the upper limit, it is possible to improve fuel economy compared to when the kinetic viscosity exceeds the upper limit. When the kinetic viscosity at 100°C of the lubricating base oil is equal to or more than the lower limit, it is possible to improve wear resistance, fatigue resistance, and electrical insulation compared to when the kinetic viscosity is less than the lower limit. In this specification, the term "kinetic viscosity at 100°C" refers to the kinetic viscosity at 100°C measured in accordance with JIS K 2283-2000 using an automatic viscometer (trade name "CAV-2100", manufactured by Cannon Instrument Co., Ltd.) as a measuring device.

The (A) component is preferably a lubricating base oil having a kinetic viscosity at 40°C of 5.0 to 20.0 ^mm2 /s (more preferably 7.0 to 20.0 ^mm2 /s, particularly preferably 7.7 to 19.5 ^mm2 /s). When the kinetic viscosity of the lubricating base oil at 40°C is equal to or less than the upper limit, it is possible to further improve fuel economy compared to when the kinetic viscosity exceeds the upper limit. When the kinetic viscosity of the lubricating base oil at 40°C is equal to or more than the lower limit, it is possible to further improve wear resistance, fatigue resistance and electrical insulation compared to when the kinetic viscosity is less than the lower limit. In this specification, the term "kinetic viscosity at 40°C" refers to the kinetic viscosity at 40°C measured in accordance with JIS K 2283-2000 using an automatic viscometer (product name "CAV-2100", manufactured by Cannon Instrument Co., Ltd.) as a measuring device.

The (A) component is preferably a lubricating base oil having a viscosity index of 100 or more (more preferably 105 or more, even more preferably 110 or more, particularly preferably 120 or more, and most preferably 125 or more). When the viscosity index of the lubricating base oil is equal to or greater than the lower limit, the viscosity-temperature characteristics of the lubricating oil composition can be improved, the friction coefficient can be reduced, and the wear resistance can be further improved, compared to when the viscosity index is less than the lower limit. In this specification, the term "viscosity index" refers to a viscosity index measured in accordance with JIS K 2283-1993.

In addition, from the viewpoint of oxidation stability, the sulfur content in the lubricating base oil, which is component (A), is preferably 0.03 mass% (300 mass ppm) or less, more preferably 50 mass ppm or less, particularly preferably 10 mass ppm or less, and most preferably 1 mass ppm or less.

The above-mentioned component (A) is the main component of the lubricating oil composition of the present invention. The content of component (A) in the lubricating oil composition (when the lubricating oil base oil is a mixture of multiple base oils (mixed base oil), the proportion of the total amount) is preferably 80 mass% or more (more preferably 90 mass% or more, and even more preferably 92 mass% or more) based on the total amount of the lubricating oil composition. The content of component (A) may be 75.0 to 99.5 mass% based on the total amount of the lubricating oil composition in some cases (for example, depending on the application, the relationship with other components, etc.).

<Component (B1): Dithiophosphorylated fatty acid ester>
The dithiophosphorylated fatty acid ester used as the component (B1) in the present invention is not particularly limited, and known dithiophosphorylated fatty acid ester compounds (for example, esters of phosphorylated carboxylic acids described in JP-A-2010-150562 and JP-A-2010-138416) can be appropriately used.

The (B1) component is represented by the following general formula (1):

[In formula (1), R ¹ and R ² each independently represent a hydrocarbon group having 1 to 30 carbon atoms, R ³ represents an alkylene group having 1 to 20 carbon atoms, and R ⁴ represents a hydrocarbon group having 1 to 30 carbon atoms.]
It is preferable that the compound is represented by the following formula:

In general formula (1), R ¹ and R ² each independently represent a hydrocarbon group having 1 to 30 carbon atoms. Examples of the hydrocarbon group having 1 to 30 carbon atoms include a linear or branched alkyl group, a cycloalkyl group, a linear or branched alkenyl group, an alkyl-substituted cycloalkyl group, an aryl group, an alkyl-substituted aryl group, or an arylalkyl group. Among these, a linear or branched alkyl group is more preferable.

Examples of the linear or branched alkyl group that can be suitably selected as ^R1 and ^R2 include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tertiary butyl group, a pentyl group, an isopentyl group, a hexyl group, a heptyl group, a 3-heptyl group, an octyl group, a 2-ethylhexyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a 2-ethylbutyl group, a 1-methylphenyl group, a 1,3-dimethylbutyl group, a 1,1,3,3-tetramethylbutyl group, a 1-methylhexyl group, an isoheptyl group, a 1-methylheptyl group, a 1,1,3-trimethylhexyl group, and a 1-methylundecyl group.

The number of carbon atoms in the linear or branched alkyl group that can be selected as R ¹ and R ² in general formula (1) is preferably 1 to 18, more preferably 3 to 18, and even more preferably 3 to 8.

R ³ in the general formula (1) represents an alkylene group having 1 to 20 carbon atoms. The number of carbon atoms in such an alkylene group is preferably 1 to 10, more preferably 2 to 6, and even more preferably 2 to 4. The alkylene group that can be selected as R ³ includes the alkylene group represented by the following general formula (3):

[In formula (3), R ⁸ , R ⁹ , R ¹⁰ and R ¹¹ each independently represent a hydrogen atom or a hydrocarbon group having 1 to 4 carbon atoms, provided that R ⁸ , R ⁹ , R ¹⁰ and R ¹¹ satisfy the condition that the total number of carbon atoms is 6 or less.]
Preferred is an alkylene group represented by the following formula:

In addition, R ⁸ , R ⁹ , R ¹⁰ and R ¹¹ in general formula (3) are each independently a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms (more preferably 1 to 2), and in this case, it is more preferable that the total number of carbon atoms in R ⁸ , R ⁹ , R ¹⁰ and R ¹¹ satisfies the condition that it is 5 or less (more preferably 4 or less, particularly preferably 3 or less). In addition, it is preferable that R ⁸ , R ⁹ , R ¹⁰ and R ¹¹ in general formula (3) are all hydrogen atoms, or that R ⁸ and R ⁹ are both hydrogen atoms and one of R ¹⁰ and R ¹¹ is a hydrogen atom and the other is a methyl group.

^R4 in general formula (1) represents a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms. Such a hydrocarbon group has the same meaning as the hydrocarbon group having 1 to 30 carbon atoms described for ^R1 and ^R2 (basically, the preferred ones also have the same meaning). Among them, ^R4 in general formula (1) is particularly preferably a linear alkyl group having 1 to 8 carbon atoms (most preferably 1 to 4 carbon atoms), and is most preferably an ethyl group.

Moreover, the compound represented by the general formula (1) is more preferably the compound (X). That is, as the compound represented by the general formula (1), it is more preferable that R ¹ and R ² in the general formula (1) each independently represent a linear or branched alkyl group having 1 to 18 carbon atoms (more preferably 3 to 18, particularly preferably 3 to 8), R ³ represents a linear or branched alkyl group having 1 to 10 carbon atoms (particularly preferably the alkylene group represented by the above general formula (3)), and R ⁴ represents a linear or branched alkyl group having 1 to 18 carbon atoms (particularly preferably a linear alkyl group having 1 to 8 carbon atoms, most preferably a linear alkyl group having 1 to 4 carbon atoms).

The method for producing component (B1) is not particularly limited, and any known method can be used as appropriate. In addition, a commercially available product may be used as component (B1).

<Component (B2): Dithiophosphorylated fatty acid>
The dithiophosphorylated fatty acid used as component (B2) in the present invention is not particularly limited, and known dithiophosphorylated fatty acid compounds (e.g., the phosphorylated carboxylic acids described in JP-A-2010-150562 and JP-A-2010-138416) can be used as appropriate.

The (B2) component is represented by the following general formula (2):

[In formula (2), ^R5 and ^R6 each independently represent a hydrocarbon group having 1 to 30 carbon atoms, and ^R7 represents an alkylene group having 1 to 20 carbon atoms.]
It is preferable that the compound is represented by the following formula:

The hydrocarbon group having 1 to 30 carbon atoms which can be selected as ^R5 and ^R6 in the general formula (2) has the same meaning as the hydrocarbon group having 1 to 30 carbon atoms which can be selected as ^R1 and ^R2 in the general formula (1) (preferable ones thereof also have the same meaning), and the alkylene group having 1 to 20 carbon atoms which can be selected as ^R7 in the general formula (2) has the same meaning as the alkylene group having 1 to 20 carbon atoms which can be selected as ^R3 in the general formula (1) (preferable ones thereof also have the same meaning).

The compound represented by general formula (2) is more preferably the compound (Y). That is, the compound represented by general formula (2) is more preferably a compound in which R ⁵ and R ⁶ in general formula (2) each independently represent a linear or branched alkyl group having 1 to 18 carbon atoms (more preferably 3 to 18, particularly preferably 3 to 8), and R ⁷ represents a linear or branched alkyl group having 1 to 10 carbon atoms (particularly preferably an alkylene group represented by general formula (3) above).

The method for producing component (B2) is not particularly limited, and any known method can be used as appropriate. In addition, a commercially available product may be used as component (B2).

<Contents of components (B1) and (B2)>
The content of the (B1) component is 0.01 mass% or more and 0.50 mass% or less (more preferably 0.10 mass% or more and 0.40 mass% or less) based on the total mass of the lubricating oil composition. When the content of the (B1) component is equal to or more than the lower limit, it is possible to improve the wear resistance more than when it is less than the lower limit. On the other hand, when the content of the (B1) component is equal to or less than the upper limit, it is possible to improve the wear resistance and electrical insulation more than when it exceeds the upper limit.

The content of component (B2) is 0.005 mass% or more and 0.15 mass% or less (more preferably 0.01 mass% or more and 0.10 mass% or less) based on the total mass of the lubricating oil composition. When the content of component (B2) is equal to or more than the lower limit, it is possible to improve the wear resistance more than when the content is below the lower limit. On the other hand, when the content of component (B2) is equal to or less than the upper limit, it is possible to improve the electrical insulation more than when the content exceeds the upper limit.

In the lubricating oil composition of the present invention, the content of the component (B1) and the content of the component (B2) are determined based on the following formula (I):
0.30≦[M _(B1) / (M _(B1) + M _(B2) )]≦0.95 (I)
[In formula (I), M _(B1) represents the content (mass ratio) of component (B1) based on the total mass of the lubricating oil composition, and M _(B2) represents the content (mass ratio) of component (B2) based on the total mass of the lubricating oil composition.]
It is necessary to satisfy the condition represented by the following formula. By setting the value of [M _(B1) /(M _(B1) +M _(B2) ] in the above formula (I) to a value within the above range (a value within the range of 0.30 to 0.95), it is possible to obtain a higher level of excellent abrasion resistance compared to other cases, and it is possible to achieve both a sufficiently high level of electrical insulation and excellent abrasion resistance. Furthermore, since a higher effect can be obtained from the same viewpoint, it is more preferable that the value of [M _(B1) /(M _(B1) +M _(B2) ] in the formula (I) is 0.40 or more and 0.90 or less, and particularly preferably 0.50 or more and 0.85 or less.

<Additives>
In addition to the (A), (B1) and (B2) components, the lubricating oil composition of the present invention may appropriately contain known additives that are generally used in lubricating oil compositions according to the purpose in order to further improve its performance.In addition, as the additives to be contained in the lubricating oil composition of the present invention, from the viewpoint of further improving the oxidation stability of the lubricating oil composition, (C) metal detergent, (D) ashless dispersant and (E) antioxidant are preferable.In addition, in the lubricating oil composition of the present invention, it is particularly preferable to contain the (C), (D) and (E) components in combination, since it is possible to further improve the oxidation stability of the lubricating oil composition.

<Component (C): Metal-Based Detergent>
The lubricating oil composition of the present invention can further improve wear resistance and oxidation stability, so it is preferable to further include (C) a metal-based detergent.The (C) component is not particularly limited, and a known metal-based detergent can be appropriately used, for example, a sulfonate detergent, a phenate detergent, a salicylate detergent, etc., which have an alkali metal or an alkaline earth metal as a positive component.In addition, among the (C) components, a sulfonate detergent and a salicylate detergent are preferred, because they can obtain a higher effect in terms of wear resistance and oxidation stability.

As a sulfonate detergent suitable for the component (C), for example, an alkali metal salt or alkaline earth metal salt of an alkyl aromatic sulfonic acid obtained by sulfonating an alkyl aromatic compound having a molecular weight of 300 to 1500 (more preferably 400 to 1300) can be mentioned. As the alkyl aromatic sulfonic acid, for example, petroleum sulfonic acid and synthetic sulfonic acid can be mentioned. Furthermore, as the petroleum sulfonic acid and synthetic sulfonic acid, known ones can be appropriately used.

As the sulfonate detergent, (C1) calcium sulfonate detergent is more preferable. Examples of the (C1) component include calcium sulfonate, which is a calcium salt of an alkyl aromatic sulfonic acid, a basic salt of the calcium sulfonate, and an overbased salt of the calcium sulfonate. There are no particular limitations on the method for preparing the basic salt or overbased salt, and known methods can be used as appropriate. As the sulfonate detergent, known ones that can be used in lubricating oil compositions (for example, those described in JP 2016-020454 A) can be used as appropriate.

The salicylate detergent suitable as the (C) component is not particularly limited, but examples thereof include alkali metal salts or alkaline earth metal salts of alkylsalicylic acid having 1 to 2 alkyl or alkenyl groups having 4 to 36 carbon atoms (more preferably 14 to 30) as a substituent, and mixtures thereof. As the salicylate detergent, (C2) calcium salicylate detergent is more preferable. In addition, as the (C2) component, for example, calcium salicylate, basic salts of calcium salicylate, and overbased salts of calcium salicylate can be used. In addition, there are no particular limitations on the method of preparing the basic salt or overbased salt, and known methods can be used as appropriate. In addition, as the (C2) component, known substances that can be used in lubricating oil compositions (for example, those described in JP 2020-076004 A and WO 2020/095970 A) can be used as appropriate.

As component (C), components (C1) and (C2) are more preferred, with component (C1) being particularly preferred, as component (C1) is even more preferred, as component (C) because they provide even greater effects in terms of wear resistance and oxidation stability. Thus, calcium sulfonate detergents are particularly preferred as component (C). Note that component (C) may be used alone or in combination of two or more types.

The base number of the metal-based detergent, component (C), is not particularly limited, but is preferably 50 to 500 mgKOH/g, more preferably 100 to 500 mgKOH/g, and particularly preferably 150 to 500 mgKOH/g. By having the base number of component (C) equal to or greater than the above lower limit, it becomes possible to further improve the electrical insulation of the composition after oxidative degradation.

The method for producing component (C) is not particularly limited, and any known production method can be used as appropriate. Note that a commercially available product may be used as component (C).

When the lubricating oil composition of the present invention contains component (C), the content of component (C) is not particularly limited, but is preferably 0.01 to 0.50 mass% (more preferably 0.05 to 0.30 mass%) based on the total amount of the lubricating oil composition. The content of component (C) is preferably an amount such that the mass of metal elements is 10 to 500 mass ppm (more preferably 50 to 300 mass ppm) based on the total amount of the lubricating oil composition. When the content of component (C) is equal to or less than the upper limit, the electrical insulation of the lubricating oil composition can be improved compared to when the content exceeds the upper limit. On the other hand, when the content of component (C) is equal to or more than the lower limit, the fatigue resistance can be improved compared to when the content is less than the lower limit.

<Component (D): Ashless Dispersant>
It is preferable that the lubricating oil composition of the present invention further contains (D) an ashless dispersant, since this makes it possible to more highly disperse metal powder generated by wear during use, thereby making it possible to further improve the wear resistance and the oxidation stability.

As the (D) component, known compounds used as ashless dispersants in the field of lubricating oil compositions (see, for example, JP 2003-155492 A, JP 2020-76004 A, WO 2013/147162, etc.) can be appropriately used. Examples of the ashless dispersant include mono- or bis-succinimide having at least one linear or branched alkyl or alkenyl group in the molecule, benzylamine having at least one alkyl or alkenyl group in the molecule, or polyamine having at least one alkyl or alkenyl group in the molecule, or products modified with boron compounds, carboxylic acids, phosphoric acids, etc. In addition, in the (D) component, the linear or branched alkyl or alkenyl group is preferably a linear or branched alkyl or alkenyl group having 40 to 400 carbon atoms (more preferably 60 to 350).

As component (D), from the viewpoint of providing better dispersibility for metal powders and the like, (D1) boronated succinimide (such as the boron-modified mono- or bis-succinimide compounds described above), (D2) non-boronated succinimide (such as the mono- or bis-succinimide compounds described above), and mixtures thereof can be suitably used.

As the (D1) and (D2) components, known boronized succinimide compounds and non-boronized succinimide compounds used as ashless dispersants can be appropriately used. As the (D1) and (D2) components, the nitrogen atom content is preferably 0.5 to 3.0 mass% based on the total amount of the (D1) and (D2) components. As the (D1) component, the boron atom content is preferably 0.1 to 5.0 mass% based on the total amount of the (D1) component. Furthermore, as the (D1) and (D2) components, the weight average molecular weight is preferably 1000 to 20000 (more preferably 2000 to 20000, and even more preferably 4000 to 15000). As the (D) component, one type may be used alone, or two or more types may be used in combination.

When the lubricating oil composition of the present invention contains component (D), the content of component (D) is not particularly limited, but is preferably 0.1 to 5.0 mass% (more preferably 0.1 to 2.5 mass%) based on the total amount of the lubricating oil composition. By keeping the content of component (D) within the above range, it is possible to further improve the electrical insulation properties.

<Component (E): Antioxidant>
The lubricating oil composition of the present invention preferably further contains an antioxidant (E) since this makes it possible to further improve the oxidation stability. The component (E) is not particularly limited, and any known antioxidant used in the field of lubricating oil compositions can be appropriately used, such as (E1) a phenol-based antioxidant (hereinafter sometimes simply referred to as "component (E1)"), (E2) an amine-based antioxidant (hereinafter sometimes simply referred to as "component (E2)"), etc.

Examples of the (E1) component include 4,4'-methylenebis(2,6-di-t-butylphenol); 4,4'-bis(2,6-di-tert-butylphenol); 4,4'-bis(2-methyl-6-tert-butylphenol); 2,2'-methylenebis(4-ethyl-6-tert-butylphenol); 2,2'-methylenebis(4-methyl-6-tert-butylphenol); 4,4'-butylidenebis (3-methyl-6-tert-butylphenol); 4,4'-isopropylidenebis(2,6-di-tert-butylphenol); 2,2'-methylenebis(4-methyl-6-nonylphenol); 2,2'-isobutylidenebis(4,6-dimethylphenol); 2,2'-methylenebis(4-methyl-6-cyclohexylphenol); 2,6-di-tert-butyl-4-methylphenol; 2,6-di-t Examples of the hindered phenol compounds and bisphenol compounds include tert-butyl-4-ethylphenol; 2,4-dimethyl-6-tert-butylphenol; 2,6-di-tert-butyl-4-(N,N'-dimethylaminomethyl)phenol; 4,4'-thiobis(2-methyl-6-tert-butylphenol); 4,4'-thiobis(3-methyl-6-tert-butylphenol); 2,2'-thiobis(4-methyl-6-tert-butylphenol); bis(3-methyl-4-hydroxy-5-tert-butylbenzyl)sulfide; bis(3,5-di-tert-butyl-4-hydroxybenzyl)sulfide; 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid esters; and 3-methyl-5-tert-butyl-4-hydroxyphenol fatty acid esters. Examples of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid esters include octyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; decyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; dodecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; tetradecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate. hexadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; pentaerythritol-tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; 2,2'-thio-diethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], etc.

As the (E2) component, for example, compounds known as amine-based antioxidants such as aromatic amine-based antioxidants and hindered amine-based antioxidants (for example, compounds exemplified in WO 2020/095970) can be appropriately used. As the aromatic amine-based antioxidant, alkylated diphenylamine and alkylated phenyl-α-naphthylamine can be preferably used. As the hindered amine-based antioxidant, for example, a compound having a 2,2,6,6-tetraalkylpiperidine skeleton (2,2,6,6-tetraalkylpiperidine derivative) can be preferably used. As the amine-based antioxidant, aromatic amine-based antioxidants can be more preferably used.

The (E) component may be used alone or in combination of two or more. Furthermore, it is preferable to use a combination of the (E1) and (E2) components as the (E) component, from the viewpoint of being able to suppress oxidative deterioration of the lubricating oil composition for a long period of time.

When the lubricating oil composition of the present invention contains the component (E), the content of the component (E) is preferably 0.1 to 1.5 mass% (more preferably 0.1 to 1.0 mass%) based on the total amount of the lubricating oil composition. By setting the content of the component (E) within the above range, it is possible to further improve the oxidation stability and electrical insulation. In addition, when the lubricating oil composition of the present invention contains the component (E1), the content of the component (E1) is preferably more than 0 mass% and not more than 1.5 mass% (more preferably more than 0 mass% and not more than 1.0 mass%) based on the total amount of the lubricating oil composition (it is more preferable that the lower limit of such content is 0.1 mass% or more). By setting the content of the component (E1) within the above range, it is possible to further improve the electrical insulation. In addition, when the lubricating oil composition of the present invention contains the (E2) component, the content of the (E2) component is preferably more than 0 mass% and not more than 1.5 mass% (more preferably more than 0 mass% and not more than 1.0 mass%) based on the total amount of the lubricating oil composition (it is more preferable that the lower limit of the content is 0.005 mass% or more). In addition, when the (E2) component is contained, the content of the (E2) component is preferably an amount such that the mass of nitrogen is more than 0 mass% and not more than 0.15 mass% (more preferably more than 0 mass% and not more than 0.10 mass%) based on the total amount of the lubricating oil composition (it is more preferable that the lower limit of the mass of nitrogen is 0.0005 mass% or more). By setting the content of the (E2) component within the above range, it is possible to further improve the electrical insulation.

<Other additives>
As described above, the additives that can be suitably used in the lubricating oil composition of the present invention, namely, (C) a metal-based detergent, (D) an ashless dispersant, and (E) an antioxidant, have been described. However, the additives that can be used in the lubricating oil composition of the present invention are not limited to the above (C) to (E) components, and as described above, other known additives used in the field of lubricating oil compositions can be appropriately used. In addition, the additives other than the above (C) to (E) components are not particularly limited, but examples thereof include pour point depressants, friction modifiers, metal deactivators, rubber swelling agents, antifoaming agents, diluent oils, viscosity index improvers, rust inhibitors, antiemulsifiers, colorants, and corrosion inhibitors. In addition, such other additives are not particularly limited, and known additives (for example, those described in JP 2003-155492 A, WO 2017/073748 A, JP 2020-76004 A, WO 2020/095970 A, etc.) can be appropriately used.

<Lubricating Oil Composition>
The lubricating oil composition of the present invention is more preferably one having a kinetic viscosity at 100°C of 2.0 to 5.0 ^mm2 /s. The lubricating oil composition of the present invention is more preferably one having a kinetic viscosity at 40°C of 7.0 to 20.5 ^mm2 /s. When these kinetic viscosities are equal to or less than the upper limit values, it becomes possible to improve fuel economy more than when these kinetic viscosities exceed the upper limit values. On the other hand, when these kinetic viscosities are equal to or more than the lower limit values, it becomes possible to improve seizure resistance, wear resistance, fatigue resistance and electrical insulation more than when these kinetic viscosities are less than the lower limit values.

The method for producing the lubricating oil composition of the present invention is not particularly limited, and any method can be appropriately adopted that allows the lubricating oil composition of the present invention to be obtained by incorporating the (A), (B1) and (B2) components such that the content of the (B1) component based on the total mass of the lubricating oil composition is 0.01 mass% or more and 0.50 mass% or less, the content of the (B2) component based on the total mass of the lubricating oil composition is 0.005 mass% or more and 0.15 mass% or less, and further, the contents of the (B1) and (B2) components satisfy the condition described in the above formula (I).

Furthermore, since the lubricating oil composition of the present invention is capable of achieving both wear resistance and electrical insulation properties at a sufficiently high level, it can be suitably used, for example, as an electric motor oil, a transmission oil, a common lubricating oil for an electric motor and a transmission (gear mechanism), a lubricating oil for an electric drive module equipped with an electric motor and a transmission (gear mechanism) (a lubricating oil for lubricating both the electric motor and the transmission), and the like.

The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

(Ingredients used in each example)
First, the lubricating base oils and additives used in the examples are shown below.

[Component (A): Lubricating base oil]
A-1: Hydrotreated mineral oil (API base oil classification: Group II, kinematic viscosity (40°C): 7.7 mm ² /s, kinematic viscosity (100°C): 2.3 mm ² /s, viscosity index: 118, Sulfur content: less than 1 mass ppm)
A-2: Hydrotreated mineral oil (API base oil classification: Group III, kinematic viscosity (40°C): 19.5 mm ² /s, kinematic viscosity (100°C): 4.2 mm ² /s, viscosity index: 125, Sulfur content: less than 1 mass ppm)
A-3: Wax isomerized base oil (API base oil classification: Group III, kinematic viscosity (40°C): 9.3 mm ² /s, kinematic viscosity (100°C): 2.7 mm ² /s, viscosity index: 125 , sulfur content: less than 1 mass ppm)
A-4: Wax isomerized base oil (API base oil classification: Group III, kinematic viscosity (40°C): 15.7 mm ² /s, kinematic viscosity (100°C): 3.8 mm ² /s, viscosity index: 143 , sulfur content: less than 1 mass ppm)
A-5: Poly-α-olefin (API base oil classification: Group IV, kinematic viscosity (40°C): 5.0 mm ² /s, kinematic viscosity (100°C): 1.7 mm ² /s)
A-6: Poly α-olefin (API base oil classification: Group IV, kinematic viscosity (40°C): 18.4 mm 2 /s, kinematic viscosity (100°C): 4.1 mm ² /s, viscosity index: 124)
A-7: Monoester base oil (API base oil classification: Group V, kinematic viscosity (40°C): 8.5 mm ² /s, kinematic viscosity (100°C): 2.7 mm ² /s, viscosity index: 177) .

[Component (B): Dithiophosphorylated fatty acid compound]
B-1: Dithiophosphorylated fatty acid ester: a compound represented by the following formula (X1) (manufactured by BASF, trade name "Irgalube 63", ethyl-3-[(bisisopropyloxyphosphinothioyl)thio]propionate)

B-2: Dithiophosphorylated fatty acid: A compound represented by the following formula (Y1) (manufactured by BASF, product name "Irgalube 353", bis(2-methylpropoxy)phosphinothiolthio-2-methyl)

[Component (C): Metal-based detergent]
C-1: Calcium sulfonate detergent (base number 300 mg KOH/g, calcium atom content: 11.6% by mass)
C-2: Calcium salicylate detergent (base number 325 mg KOH/g, calcium atom content: 11.4 mass%).

[Component (D): Ashless Dispersant]
D-1: boronized succinimide (nitrogen atom content: 0.73% by mass, boron atom content: 0.19% by mass, weight average molecular weight: 9300)
D-2: Non-boronated succinimide (nitrogen atom content: 1.5 mass%, weight average molecular weight: 4600).

[Component (E): Antioxidant]
E-1: Phenol-based antioxidant: 3-(3,5-di-tert-butyl-4-hydroxyphenyl)octyl propionate E-2: Amine-based antioxidant: monobutylphenyl monooctylphenylamine (nitrogen atom content: 4.5% by mass).

(Examples 1 to 21 and Comparative Examples 1 to 6)
The lubricating oil compositions were prepared using each of the above-mentioned components so as to have the compositions shown in Tables 1 to 4. In Tables 1 to 4, "-" indicates that the component was not used. In addition, in the following Tables 1 to 4, the unit of the content of component (A) "in mass%" represents the content (mass%) of each base oil component relative to the total amount of the lubricating base oil, and the unit of the content of components (B) to (E) "mass%" represents the content (mass%) of each additive relative to the total amount of the lubricating oil composition. In addition, Tables 1 to 4 also show the kinematic viscosity at 40 ° C. and the kinematic viscosity at 100 ° C. of component (A) (or the mixture in the case of a mixture of two types of base oils) used in each example. Tables 1 to 4 also show the value of "M _(B-1) /(M(B-1)+M _{(B-2))" for each lubricating oil composition, where the content of B-1 is M( B -1)} and the content of B-2 is M _(B-2 ).

[Method for evaluating the properties of the lubricating oil compositions obtained in each example, etc.]
<Evaluation of Electrical Insulation: Measurement of Volume Resistivity>
The volume resistivity of the lubricating oil compositions obtained in each Example was determined by measuring at an oil temperature of 80°C in accordance with the volume resistivity test specified in JIS C 2101:1999. The results (volume resistivity value [unit: 10 ¹⁰ Ω·cm]) are shown in Tables 1 to 4. In this specification, a volume resistivity of 1.0×10 ¹⁰ Ω·cm or more is evaluated as a sufficiently high level of electrical insulation.

<Wear resistance evaluation: high-speed four-ball test>
In a test method (high-speed four-ball test) conforming to JPI-5S-40-93, a high-speed four-ball tester was operated at a rotation speed of 1800 rpm, a load of 392 N, and an oil temperature of 80° C. for 30 minutes, and the wear scar diameter was measured for each lubricating oil composition. The results (wear scar diameter [unit: mm]) are shown in Tables 1 to 4. It can be seen that the smaller the wear scar diameter in this test, the more excellent the wear resistance. In this specification, a wear scar diameter of 0.8 mm or less is evaluated as having excellent wear resistance.

As is clear from the results shown in Tables 1 to 4, the lubricating oil compositions obtained in Examples 1 to 22 (corresponding to the lubricating oil compositions of the present invention) each containing a lubricating base oil, B-1 (dithiophosphorylated fatty acid ester) with a content of 0.01 mass% or more and 0.50 mass% or less based on the total amount of the lubricating oil composition, and B-2 (dithiophosphorylated fatty acid) with a content of 0.005 mass% or more and 0.15 mass% or less based on the total amount of the lubricating oil composition, and having a value of M _{( B-} 1)/(M(B-1 _)+M(B-2) ) within the range of 0.30 to 0.95, all had a volume resistivity of 1.0 x ¹⁰¹⁰ Ω·cm or more, and it was confirmed that the electrical insulation was at a sufficiently high level. Furthermore, it was also confirmed that all of the lubricating oil compositions obtained in Examples 1 to 22 (corresponding to the lubricating oil compositions of the present invention) had wear scar diameters of 0.80 mm or less (0.79 mm or less) when used in a high-speed four-ball test, and thus had excellent wear resistance.

On the other hand, the lubricating oil composition obtained in Comparative Example 1, which did not use B-2 (a lubricating oil composition containing less than 0.005% by mass of B-2), had a wear scar diameter of 1.68 mm when used in a high-speed four-ball test, which was not sufficient in terms of wear resistance. Also, the lubricating oil composition obtained in Comparative Example 2, which did not use B-1 (a lubricating oil composition containing less than 0.01% by mass of B-1), had a wear scar diameter of 0.90 mm when used in a high-speed four-ball test, which was not sufficient in terms of wear resistance. Furthermore, even in the case of lubricating oil compositions containing B-1 and B-2, when the value of M _(B-1) /(M _(B-1) +M _(B-2) ) was greater than 0.95 (Comparative Example 3), and when the value of M _(B-1) /(M _(B-1) +M _(B-2) ) was less than 0.30 (Comparative Example 4), the wear scar diameters were 1.25 mm (Comparative Example 3) and 0.89 mm (Comparative Example 4), respectively, when used in a high-speed four-ball test, and the wear resistance was also unsatisfactory. Furthermore, even in the case of a lubricating oil composition containing B-1 and B-2 and having a value of M _(B-1) /(M _(B-1) +M _(B-2) ) in the range of 0.30 to 0.95, when the content of B-1 exceeds 0.50 mass% (Comparative Example 5), the wear scar diameter is 0.82 mm when used in a high-speed four-ball test, which is insufficient in terms of wear resistance, and on the other hand, when the content of B-2 exceeds 0.15 mass% (Comparative Example 6), the volume resistivity is less than 1.0×10 ¹⁰ Ω·cm, which is insufficient in terms of electrical insulation.

These results demonstrate that the lubricating oil compositions of the present invention (Examples 1 to 22) can provide both excellent electrical insulation and wear resistance, making it possible to achieve both a sufficiently high level of electrical insulation and excellent wear resistance.

As described above, the present invention makes it possible to provide a lubricating oil composition that can achieve both a sufficiently high level of electrical insulation and excellent wear resistance. Therefore, the lubricating oil composition of the present invention is particularly useful as a lubricating oil used to lubricate both electric motors and transmissions.

Claims (4)

(A) a lubricating base oil;
(B1) a dithiophosphorylated fatty acid ester having a content of 0.01 mass % or more and 0.50 mass % or less based on the total mass of the lubricating oil composition;
(B2) a dithiophosphorylated fatty acid in an amount of 0.005 mass % or more and 0.15 mass % or less based on the total mass of the lubricating oil composition;
and the following formula (I):
0.30≦[M _(B1) / (M _(B1) + M _(B2) )]≦0.95 (I)
[In formula (I), M _(B1) represents the content of component (B1) based on the total mass of the lubricating oil composition, and M _(B2) represents the content of component (B2) based on the total mass of the lubricating oil composition.]
A lubricating oil composition characterized by satisfying the conditions represented by the above formula: The component (B1) is represented by the following general formula (1):
[In formula (1), ^R1 and ^R2 each independently represent a linear or branched alkyl group having 1 to 18 carbon atoms, ^R3 represents a linear or branched alkylene group having 1 to 10 carbon atoms, and ^R4 represents a linear or branched alkyl group having 1 to 18 carbon atoms.]
The lubricating oil composition according to claim 1, characterized in that the compound is represented by the formula: The component (B2) is represented by the following general formula (2):
[In formula (2), ^R5 and ^R6 each independently represent a linear or branched alkyl group having 1 to 18 carbon atoms, and ^R7 represents a linear or branched alkylene group having 1 to 10 carbon atoms.]
The lubricating oil composition according to claim 1 or 2, characterized in that the compound is represented by the formula: 4. The lubricating oil composition according to claim 1, wherein the component (A) is a lubricating base oil having a kinetic viscosity at 40° C. of 5.0 to 20.0 mm ² /s.