EP4610338A1

EP4610338A1 - Lubricating oil composition

Info

Publication number: EP4610338A1
Application number: EP23882605.1A
Authority: EP
Inventors: Shizuka AGANO
Original assignee: Idemitsu Kosan Co Ltd
Current assignee: Idemitsu Kosan Co Ltd
Priority date: 2022-10-25
Filing date: 2023-10-24
Publication date: 2025-09-03
Also published as: EP4610338A4; JP2024062827A; CN120092070A; WO2024090400A1

Abstract

Provided is a lubricating oil composition, including: a base oil (A) containing an ester oil (A1); a phenothiazine-based compound (B); and a non-metal thiophosphoric acid ester-based compound (C). The ester oil (A1) preferably contains a diester oil (A11).

Description

Technical Field

The present invention relates to a lubricating oil composition.

Background Art

In recent years, an oil-impregnated bearing formed by sintering metal powder has been widely used as a bearing incorporated into equipment, such as automobile electrical equipment, a home appliance, and OA office equipment.
In general, the oil-impregnated bearing is usually produced by forming metal powder serving as a raw material into a porous metal body through steps, such as mixing, molding, sintering, and sizing, and subsequently vacuum-impregnating the metal body with a lubricating oil through use of an impregnation device, and is a slide bearing used in a self-lubricating state.
The oil-impregnated bearing lubricates by supplying a lubricating oil composition with which the porous metal body has been impregnated, to a sliding surface between a rotation shaft and a bearing inner surface through a pumping action caused by rotation of the rotation shaft, and offers not only the advantage of excellent durability and rigidity but also the advantage that production costs are kept low.
As a base oil of the lubricating oil composition with which the oil-impregnated bearing is impregnated, various base oils, such as a mineral oil, a hydrocarbon-based synthetic oil, an ether oil, an ester oil, a fluorinated oil, and a silicone oil, are each used. In PTL 1, there is a proposal of a lubricating oil composition for an oil-impregnated bearing using an ester oil as a base oil (see, for example, PTL 1).

Citation List

Patent Literature

PTL 1: JP 2019-210443 A

Summary of Invention

Technical Problem

Incidentally, the oil-impregnated bearing is generally used without additional lubrication. Accordingly, when the amount of the lubricating oil composition with which the oil-impregnated bearing is impregnated easily decreases over time, the lifetime of the oil-impregnated bearing is liable to be shortened.
In view of the foregoing, in order to create a lubricating oil composition for an oil-impregnated bearing that is less liable to evaporate, the inventor of the present invention has conducted intensive investigations on the formulation thereof. As a result, the inventor has found a formulation enabling a lubricating oil composition for an oil-impregnated bearing using an ester oil as a base oil to have a lower evaporation tendency and excellent evaporation characteristics and to also have excellent wear resistance.
A lubricating oil composition excellent in evaporation characteristics and wear resistance may be required not only for oil-impregnated bearing applications but also for various other applications.
An object of the present invention is to provide a lubricating oil composition excellent in evaporation characteristics and wear resistance.

Solution to Problem

According to the present invention, there are provided the following items [1] to [5].

[1] A lubricating oil composition, comprising: a base oil (A) containing an ester oil (A1); a phenothiazine-based compound (B); and a non-metal thiophosphoric acid ester-based compound (C).
[2] The lubricating oil composition according to the above-mentioned item [1], wherein the lubricating oil composition is used as an oil for an oil-impregnated bearing.
[3] A method of using the lubricating oil composition of the above-mentioned item [1], the method comprising using the lubricating oil composition as an oil for an oil-impregnated bearing.
[4] An oil-impregnated bearing impregnated with the lubricating oil composition of the above-mentioned item [1].
[5] A method of producing a lubricating oil composition, comprising a step of mixing a base oil (A) containing an ester oil (A1), a phenothiazine-based compound (B), and a non-metal thiophosphoric acid ester-based compound (C).

Advantageous Effects of Invention

According to the present invention, the lubricating oil composition excellent in evaporation characteristics and wear resistance can be provided.

Description of Embodiments

The upper limit values and lower limit values of numerical ranges described herein may be arbitrarily combined. For example, when the range of "from A to B" and the range of "from C to D" are described as numerical ranges, the numerical range of "from A to D" and the numerical range of "from C to B" are also included in the scope of the present invention.
In addition, the numerical range of "from a lower limit value to an upper limit value" described herein means that a physical property value is the lower limit value or more and the upper limit value or less unless otherwise stated.
In addition, in this description, the numerical values of Examples are numerical values that may each be used as an upper limit value or a lower limit value.

[Aspect of Lubricating Oil Composition]

A lubricating oil composition according to an embodiment of the present invention comprises: a base oil (A) containing an ester oil (A1); a phenothiazine-based compound (B); and a non-metal thiophosphoric acid ester-based compound (C).
The inventor of the present invention has conducted extensive investigations in order to solve the above-mentioned problem.
As a result, the inventor has obtained a novel finding that a phenothiazine-based compound has a suppressing action on evaporation of an ester oil.
The inventor has further conducted extensive investigations based on such finding, and as a result, has come up with a finding that the use of the non-metal thiophosphoric acid ester-based compound can impart wear resistance to a lubricating oil composition without impairing the suppressing action of the phenothiazine-based compound on the evaporation of the ester oil.
The inventor has further conducted various investigations based on those findings and completed the present invention.
In the following description, the "base oil (A)," the "phenothiazine-based compound (B)," and the "non-metal thiophosphoric acid ester-based compound (C)" are also referred to as "component (A)," "component (B)," and "component (C)," respectively.
The lubricating oil composition of this embodiment may be formed only of the component (A), the component (B), and the component (C), but may further comprise any other component in addition to the component (A), the component (B), and the component (C).
The total content of the component (A), the component (B), and the component (C) in the lubricating oil composition of this embodiment is preferably 50 mass% or more, more preferably 60 mass% or more, still more preferably 70 mass% or more, still further more preferably 75 mass% or more, yet still further more preferably 80 mass% or more with respect to the total amount of the lubricating oil composition.
The respective components in the lubricating oil composition of this embodiment are described in detail below.

The lubricating oil composition of this embodiment comprises the base oil (A) containing the ester oil (A1).
The lubricating oil composition of this embodiment comprises the phenothiazine-based compound (B), and hence evaporation characteristics of the ester oil (A1) improve, and evaporation characteristics of the lubricating oil composition can be made excellent.
The content of the ester oil (A1) in the base oil (A) is preferably from 50 mass% to 100 mass%, more preferably from 60 mass% to 100 mass%, still more preferably from 70 mass% to 100 mass%, still further more preferably from 80 mass% to 100 mass%, yet still further more preferably from 90 mass% to 100 mass%, even more preferably from 95 mass% to 100 mass% with respect to the total amount of the base oil (A) from the viewpoint of more easily achieving the effects of the present invention.
The kinematic viscosity at 100°C of the base oil (A) is preferably from 2.0 mm²/s to 30.0 mm²/s, more preferably from 2.5 mm²/s to 25.0 mm²/s, still more preferably from 3.0 mm²/s to 22.0 mm²/s.
In addition, the viscosity index of the base oil (A) is preferably 65 or more.
When a mixed oil in which two or more kinds of base oils are combined is used as the base oil (A), it is preferred that the kinematic viscosity and viscosity index of the mixed oil fall within the above-mentioned ranges.
The kinematic viscosity and viscosity index of the base oil (A) mean values measured and calculated in conformity with JIS K2283:2000.
In the lubricating oil composition of this embodiment, the content of the base oil (A) is preferably 60 mass% or more, more preferably 70 mass% or more, still more preferably 75 mass% or more, still further more preferably 80 mass% or more, and is preferably 99.5 mass% or less, more preferably 99.0 mass% or less, still more preferably 98.0 mass% or less with respect to the total amount of the lubricating oil composition.

(Ester Oil (A1))

An example of the ester oil (A1) is a compound having an ester bond.
Specific examples thereof include a diester oil (A11), a polyol ester oil (A12), and an aromatic ester oil (A13).
The ester oils (A1) may be used alone or in combination thereof.

-Diester oil (A11)-

The diester oil (A11) is an ester of a dibasic acid and an alcohol, and is preferably a compound represented by the following general formula (a-1).
In the general formula (a-1), R^a1 and R^a2 each independently represent an alkyl group having 2 to 20 carbon atoms or an alkenyl group having 2 to 20 carbon atoms. In addition, R^a3 represents an alkylene group having 2 to 20 carbon atoms.
Examples of the alkyl group that may be selected as each of R^a1 and R^a2 include an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a n-hexyl group, a n-octyl group, a 2-ethylhexyl group, a n-nonyl group, a 3,3,5-trimethylhexyl group, a n-decyl group, a dimethyloctyl group, an isodecyl group, a n-undecyl group, a n-dodecyl group, a n-tridecyl group, a n-tetradecyl group, a n-hexadecyl group, n-octadecyl group, and a n-icosyl group.
In addition, examples of the alkenyl group that may be selected as each of R^a1 and R^a2 include an ethenyl group, a n-propenyl group, a n-butenyl group, a n-hexenyl group, a n-octenyl group, a 2-ethylhexenyl group, a n-nonenyl group, a 3,3,5-trimethylhexenyl group, a n-decenyl group, a dimethyloctenyl group, an isodecenyl group, a n-undecenyl group, a n-dodecenyl group, a n-tridecenyl group, a n-tetradecenyl group, a n-pentadecenyl group, a n-hexadecenyl group, a n-octadecenyl group, and a n-icosenyl group.
The alkyl group or the alkenyl group may be linear or branched.
In addition, the number of carbon atoms of the alkyl group or the alkenyl group is preferably from 4 to 16, more preferably from 5 to 14, still more preferably from 6 to 12 from, for example, the viewpoint of improving the effects of the present invention.
In addition, examples of the alkylene group that may be selected as R^a3 include an ethylene group, a n-propylene group, an isopropylene group, a n-butylene group, an isobutylene group, a n-pentylene group, a n-hexylene group, a n-heptylene group, a n-octylene group, a 2-ethylhexylene group, a n-nonylene group, a n-decylene group, a n-undecylene group, a n-tridecylene group, a n-hexadecylene group, a n-octadecylene group, and a n-icosylene group.
The alkylene group may be linear or branched.
In addition, the number of carbon atoms of the alkylene group is preferably from 4 to 16, more preferably from 6 to 13, still more preferably from 8 to 12 from, for example, the viewpoint of improving the effects of the present invention.
The diester oils (A11) may be used alone or in combination thereof.

-Polyol Ester Oil (A12)-

The polyol ester oil (A12) is an ester that is a condensation product of a polyol with a fatty acid.
The number of carbon atoms of the polyol for forming the polyol ester oil (A12) is preferably from 2 to 20, more preferably from 2 to 15, still more preferably from 2 to 12 from the viewpoint of, for example, improving heat resistance.
The number of carbon atoms of the fatty acid for forming the polyol ester oil (A12) is preferably from 2 to 20, more preferably from 2 to 18, still more preferably from 2 to 16 from the viewpoint of, for example, improving heat resistance.
Specific examples of the polyol for forming the polyol ester oil (A12) include: diols, such as ethylene glycol, 1,3-propanediol, propylene glycol, 1,4-butanediol, 1,2-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 2-ethyl-2-methyl-1,3-propanediol, 1,7-heptanediol, 2-methyl-2-propyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, and 1,12-dodecanediol; polyhydric alcohols, such as trimethylolethane, trimethylolpropane, trimethylolbutane, ditrimethylolpropane, pentaerythritol, dipentaerythritol, glycerin, a glycerin dimer, 1,3,5-pentanetriol, sorbitol, sorbitan, adonitol, arabitol, xylitol, and mannitol; and sugars, such as xylose, arabinose, ribose, rhamnose, glucose, fructose, galactose, mannose, and sorbose.
Among them, trimethylolpropane, glycerin, pentaerythritol, and dipentaerythritol are preferred from the viewpoint of, for example, improving heat resistance.
Specific examples of the fatty acid for forming the polyol ester oil (A12) include propionic acid, n-butanoic acid, n-pentanoic acid (valeric acid), isopentanoic acid (isovaleric acid), n-hexanoic acid (caproic acid), n-heptanoic acid, isoheptanoic acid, n-octanoic acid (caprylic acid), 2-ethylhexanoic acid, isooctanoic acid, n-nonanoic acid (pelargonic acid), isononanoic acid, n-decanoic acid (capric acid), isodecanoic acid, n-undecanoic acid, isoundecanoic acid, n-dodecanoic acid (lauric acid), isododecanoic acid, n-tridecanoic acid, isotridecanoic acid, n-tetradecanoic acid (myristic acid), n-hexadecanoic acid (palmitic acid), n-octadecanoic acid (stearic acid), isostearic acid, n-eicosanoic acid (arachic acid), 10-undecenoic acid, oleic acid, elaidic acid, linoleic acid, and linolenic acid, and gadoleic acid.
Those fatty acids may be linear or branched.
In addition, those fatty acids may be saturated fatty acids or unsaturated fatty acids.
The polyol ester oils (A12) may be used alone or in combination thereof.

-Aromatic Ester Oil (A13)-

The aromatic ester oil (A13) is an ester in which one or more ester groups are bonded to an aromatic ring, and is preferably a compound represented by the following general formula (a-3).
In the general formula (a-3), "m" represents an integer of from 1 to 5, preferably an integer of from 2 to 4, more preferably an integer of 3 or 4.
R^a31 represents an alkyl group having 2 to 20 carbon atoms or an alkenyl group having 2 to 20 carbon atoms. A plurality of R^a31s may be identical to or different from each other.
Examples of the alkyl group that may be selected as R^a31 include the alkyl groups shown as examples of R^a11 and R^a12.
Examples of the alkenyl group that may be selected as R^a31 include the alkenyl groups shown as examples of R^a11 and R^a12.
The alkyl group and the alkenyl group may be linear or branched.
The number of carbon atoms of each of the alkyl group and the alkenyl group is preferably from 4 to 16, more preferably from 6 to 13, still more preferably from 8 to 12 from, for example, the viewpoint of improving heat resistance.
The aromatic ester oils (A13) may be used alone or in combination thereof.

(Preferred Mode of Ester Oil (A1))

In the lubricating oil composition of this embodiment, it is preferred that the ester oil (A1) contain the diester oil (A11).
In general, an ester in which a hydrogen atom is bonded to a carbon atom at the β-position on the alcohol side of an ester bond is easily decomposed when heated (NPL 1: Tribology Series 8: Lubricating Grease and Synthetic Lubricating Oil, Saiwai Shobo Co., Ltd., first edition, first printing issued on December 25, 1983).
According to the investigations made by the inventor of the present invention, it has been recognized that evaporation characteristics can be improved by the action of the phenothiazine-based compound (B) even in a case of the ester in which a hydrogen atom is bonded to a carbon atom at the β-position on the alcohol side of an ester bond.
Accordingly, according to the formulation described in this embodiment, the evaporation characteristics of the lubricating oil composition can be made excellent even when the ester oil (A1) contains the ester in which a hydrogen atom is bonded to a carbon atom at the β-position on the alcohol side of an ester bond.
The diester oil (A11) often has a hydrogen atom bonded to a carbon atom at the β-position on the alcohol side of an ester bond. Accordingly, evaporation characteristics thereof are often poor.
Accordingly, the formulation (that is, the lubricating oil composition of this embodiment) described in this embodiment is suitable for a case in which the ester oil (A1) contains the diester oil (A11).
In addition, the formulation described in this embodiment is more suitable for a case in which the diester oil (A11) is a diester oil (A11x) in which a hydrogen atom is bonded to a carbon atom at the β-position on the alcohol side of an ester bond.
The content of the diester oil (A11) in the ester oil (A1) is preferably from 50 mass% to 100 mass%, more preferably from 60 mass% to 100 mass%, still more preferably from 70 mass% to 100 mass%, still further more preferably from 80 mass% to 100 mass%, yet still further more preferably from 90 mass% to 100 mass%, even more preferably from 95 mass% to 100 mass% with respect to the total amount of the ester oil (A1) from the viewpoint of more easily achieving the effects of the present invention.
In addition, the content of the diester oil (A11x) in the ester oil (A1) is preferably from 50 mass% to 100 mass%, more preferably from 60 mass% to 100 mass%, still more preferably from 70 mass% to 100 mass%, still further more preferably from 80 mass% to 100 mass%, yet still further more preferably from 90 mass% to 100 mass%, even more preferably from 95 mass% to 100 mass% with respect to the total amount of the ester oil (A1) from the viewpoint of further easily achieving the effects of the present invention.

(Base Oil (A2) other than Ester-based Oil (A1))

The lubricating oil composition of this embodiment may comprise, as the base oil (A), one or more kinds of base oils (A2) selected from synthetic oils and mineral oils other than the ester oil (A1).
Examples of the synthetic oils other than the ester oil (A1) include: polyolefins, such as an α-olefin homopolymer and an α-olefin copolymer (e.g., an α-olefin copolymer having 8 to 14 carbon atoms such as an ethylene-α-olefin copolymer); isoparaffins; various ethers, such as polyalkylene glycols and polyphenyl ethers; alkylbenzenes; alkylnaphthalenes; and a base oil (gas to liquids (GTL)) obtained by isomerizing a wax (GTL wax) produced from natural gas using the Fischer-Tropsch process or the like.
Those synthetic oils may be used alone or in combination thereof.
Examples of the mineral oils include: atmospheric residues obtained by atmospheric distillation of a crude oil, such as a paraffin-base crude oil, an intermediate-base crude oil, or a naphthene-base crude oil; distillates obtained by vacuum distillation of those atmospheric residues; and mineral oils obtained by subjecting the distillates to one or more refining processes, such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, and hydrorefining.
Those mineral oils may be used alone or in combination thereof.

<Phenothiazine-based Compound (B)>

The lubricating oil composition of this embodiment comprises the phenothiazine-based compound (B).
The phenothiazine-based compound (B) has an improving action on the evaporation characteristics of the ester oil (A1). The action is fully exhibited even when the non-metal thiophosphoric acid ester-based compound (C) is blended into the lubricating oil composition.
The term "phenothiazine-based compound (B)" as used herein means one or more kinds selected from the group consisting of: a phenothiazine (B1); and a phenothiazine derivative (B2).

(Phenothiazine (B1))

The phenothiazine (B1) is unsubstituted phenothiazine represented by the following structural formula (b-1).

(Phenothiazine Derivative (B2))

The phenothiazine derivative (B2) is a compound in which at least one hydrogen atom of unsubstituted phenothiazine represented by the structural formula (b-1) is substituted with a substituent, and a preferred example thereof is a compound represented by the following general formula (b-2).
In the general formula (b-2), R^b1, R^b2, and R^b3 each independently represent a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 5 to 11 carbon atoms, an aryl group having 6 to 12 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an acyl group having 1 to 10 carbon atoms, a hydroxyl group, a sulfone group, a nitro group, an amino group, a carboxyl group, or a halogen.
In the general formula (b-2), p1 and p2 each independently represent an integer of from 0 to 4.
When p1 represents 2 or more, a plurality of R^b1s may be identical to or different from each other.
In addition, when p2 represents 2 or more, a plurality of R^b2s may be identical to or different from each other.
The phenothiazine derivatives (B2) may be used alone or in combination thereof.

(Preferred Modes of Phenothiazine Derivative (B2))

It is preferred that the phenothiazine derivative (B2) satisfy one or more requirements selected from the following requirements 1 to 4.

-Requirement 1-

R^b1, R^b2, and R^b3 each represent an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 5 to 11 carbon atoms, an aryl group having 6 to 12 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, or an acyl group having 1 to 10 carbon atoms from the viewpoint of improving the solubility of the phenothiazine derivative (B2) in the base oil (A).

-Requirement 2-

When R^b1, R^b2, and R^b3 each represent an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, or an acyl group having 1 to 10 carbon atoms, the number of carbon atoms of each of substituents thereof is preferably from 4 to 10, more preferably from 6 to 10 from, for example, the viewpoint of improving the solubility of the phenothiazine derivative (B2) in the base oil (A) and the viewpoint of suppressing sludge precipitation.

-Requirement 3-

Any of the substituents described above as examples of R^b1, R^b2, and R^b3 is introduced into one of the 3-position and 7-position of phenothiazine, preferably both thereof from the viewpoint of suppressing oxidation of the phenothiazine derivative (B2) itself.

- Requirement 4 -

An acyl group having 1 to 10 carbon atoms is introduced into one of the 1-position and 2-position of phenothiazine, preferably both thereof from the viewpoint of suppressing oxidation of the phenothiazine derivative (B2) itself.

(Content of Phenothiazine-based Compound (B))

The content of the phenothiazine-based compound (B) in the lubricating oil composition of this embodiment is preferably 0.01 mass% or more, more preferably 0.05 mass% or more, still more preferably 0.08 mass% or more with respect to the total amount of the lubricating oil composition from the viewpoint of more easily improving the evaporation characteristics of the lubricating oil composition. In addition, the content of the phenothiazine-based compound (B) is preferably 5.0 mass% or less, more preferably 3.0 mass% or less, still more preferably 2.5 mass% or less from the viewpoint of balancing the content of the phenothiazine-based compound (B) and the evaporation characteristic-improving effect thereof.
The upper limit values and lower limit values of those numerical ranges may be arbitrary combined. Specifically, the content is preferably from 0.01 mass% to 5.0 mass%, more preferably from 0.05 mass% to 3.0 mass%, still more preferably from 0.08 mass% to 2.5 mass%.

<Non-metal Thiophosphoric Acid Ester-based Compound (C)>

The lubricating oil composition of this embodiment comprises the non-metal thiophosphoric acid ester-based compound (C).
The non-metal thiophosphoric acid ester-based compound (C) can impart wear resistance to the lubricating oil composition while fully exhibiting the improving effect of the phenothiazine-based compound (B) on the evaporation characteristics of the ester oil (A1).
An example of the non-metal thiophosphoric acid ester-based compound (C) is a compound containing no metal atom as a constituent atom and containing a phosphorus atom and a sulfur atom as constituent atoms. Examples of such compound include one or more kinds selected from thiophosphoric acid esters and thiophosphorous acid esters, and amine salts thereof.
Among them, a thiophosphoric acid ester (C1) is preferably incorporated into the non-metal thiophosphoric acid ester-based compound (C) from the viewpoint of improving the effects of the present invention.
Examples of the thiophosphoric acid ester (C1) include one or more kinds selected from monothiophosphoric acid esters, dithiophosphoric acid esters, and trithiophosphoric acid esters.
Among them, one or more kinds selected from monothiophosphoric acid esters and dithiophosphoric acid esters are preferred.
The content of the thiophosphoric acid ester (C1) is preferably from 50 mass% to 100 mass%, more preferably from 60 mass% to 100 mass%, still more preferably from 70 mass% to 100 mass%, still further more preferably from 80 mass% to 100 mass%, yet still further more preferably from 90 mass% to 100 mass%, even more preferably from 95 mass% to 100 mass% with respect to the total amount of the non-metal thiophosphoric acid ester-based compound (C).
The term "monothiophosphoric acid ester" as used herein means a thiophosphoric acid ester in which the number of sulfur atoms bonded to a phosphorus atom is one, or a derivative thereof.
In addition, the term "dithiophosphoric acid ester" means a thiophosphoric acid ester in which the number of sulfur atoms bonded to a phosphorus atom is two, or a derivative thereof.
In addition, the term "trithiophosphoric acid ester" means a thiophosphoric acid ester in which the number of sulfur atoms bonded to a phosphorus atom is three, or a derivative thereof.

(Monothiophosphoric Acid Triester (C1x))

It is preferred that the thiophosphoric acid ester (C1) contain, as a monothiophosphoric acid ester, one or more kinds selected from a monothiophosphoric acid triester (C1x) represented by the following general formula (c-1x) from the viewpoint of improving the hydrolysis resistance of the ester oil (A1): wherein
in the general formula (c-1x), respective symbols represent the following:
R^c1, R^c2, and R^c3 each independently represent a saturated or unsaturated aliphatic hydrocarbon group having 1 to 18 carbon atoms, a saturated or unsaturated alicyclic hydrocarbon group having 5 to 18 carbon atoms that may have a substituent, or an aromatic hydrocarbon group having 5 to 18 carbon atoms that may have a substituent.
In the general formula (c-1x), the number of carbon atoms of the saturated or unsaturated aliphatic hydrocarbon group that may be selected as each of R^c1, R^c2, and R^c3 is more preferably from 5 to 18.
Specific examples of the saturated aliphatic hydrocarbon group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, a octyl group, a nonyl group, a decyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, and an octadecyl group.
Those groups may be linear or branched.
Examples of the unsaturated aliphatic hydrocarbon group may include groups in which the above-mentioned specific saturated aliphatic hydrocarbon groups except the methyl group each have at least one unsaturated bond, such as an ethylene group and a propylene group.
In the general formula (c-1x), specific examples of the saturated alicyclic hydrocarbon group that may be selected as each of R^c1, R^c2, and R^c3 include a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclononyl group, and a cyclodecyl group.
Examples of the unsaturated alicyclic hydrocarbon group may include groups in which the above-mentioned saturated alicyclic hydrocarbon groups each have at least one unsaturated bond, such as a cyclopentenyl group and a cyclohexenyl group.
In the general formula (c-1x), specific examples of the aromatic hydrocarbon group that may be selected as each of R^c1, R^c2, and R^c3 include aryl groups, such as a phenyl group and a naphthyl group.
Examples of the substituent include a C₁ to C₆ alkyl group, a C₁ to C₆ alkoxy group, and a C₆ to C₁₄ aryl group.
Specific examples of the monothiophosphoric acid triester (C1x) may include tributyl phosphorothioate, tripentyl phosphorothioate, trihexyl phosphorothioate, triheptyl phosphorothioate, trioctyl phosphorothioate, trinonyl phosphorothioate, tridecyl phosphorothioate, triundecyl phosphorothioate, tridodecyl phosphorothioate, tritridecyl phosphorothioate, tritetradecyl phosphorothioate, tripentadecyl phosphorothioate, trihexadecyl phosphorothioate, triheptadecyl phosphorothioate, trioctadecyl phosphorothioate, trioleyl phosphorothioate, triphenyl phosphorothioate, tricresyl phosphorothioate, trixylenyl phosphorothioate, cresyl diphenyl phosphorothioate, xylenyl diphenyl phosphorothioate, tris(n-propylphenyl) phosphorothioate, tris(isopropylphenyl) phosphorothioate, tris(n-butylphenyl) phosphorothioate, tris(isobutylphenyl) phosphorothioate, tris(sec-butylphenyl) phosphorothioate, and tris(tert-butylphenyl) phosphorothioate.
The content of the monothiophosphoric acid triester (C1x) is preferably from 50 mass% to 100 mass%, more preferably from 60 mass% to 100 mass%, still more preferably from 70 mass% to 100 mass%, still further more preferably from 80 mass% to 100 mass%, yet still further more preferably from 90 mass% to 100 mass%, even more preferably from 95 mass% to 100 mass% with respect to the total amount of the thiophosphoric acid ester (C1) from the viewpoint of improving the effects of the present invention and the viewpoint of improving the hydrolysis resistance of the ester oil (A1).
The monothiophosphoric acid triesters (C1x) may be used alone or in combination thereof.

(Monothiophosphoric Acid Triaryl Ester (C11x))

It is preferred that the monothiophosphoric acid triester (C1x) contain one or more kinds selected from a monothiophosphoric acid triaryl ester (C11x) represented by the following general formula (c-11x) from the viewpoint of improving the effects of the present invention and the viewpoint of improving the hydrolysis resistance of the ester oil (A1): wherein
in the general formula (c-11x), respective symbols represent the following:

R^c11, R^c12, and R^c13 each independently represent an alkyl group having 1 to 3 carbon atoms; and
n1, n2, and n3 each independently represent an integer of from 0 to 5.

In the general formula (c-11x), R^c11, R^c12, and R^c13 each independently represent an alkyl group having 1 to 3 carbon atoms. Examples of the alkyl group having 1 to 3 carbon atoms include a methyl group, an ethyl group, a n-propyl group, and an isopropyl group.
n1, n2, and n3 each independently represent preferably from 0 to 2, more preferably 0 or 1, still more preferably 0.
Specific examples of the monothiophosphoric acid triaryl ester (C11x) represented by the general formula (c-11x) include tricresyl thiophosphate and triphenyl phosphorothioate.
The content of the monothiophosphoric acid triaryl ester (C11x) is preferably from 50 mass% to 100 mass%, more preferably from 60 mass% to 100 mass%, still more preferably from 70 mass% to 100 mass%, still further more preferably from 80 mass% to 100 mass%, yet still further more preferably from 90 mass% to 100 mass%, even more preferably from 95 mass% to 100 mass% with respect to the total amount of the monothiophosphoric acid triester (C1x) from the viewpoint of improving the effects of the present invention and the viewpoint of improving the hydrolysis resistance of the ester oil (A1).
The monothiophosphoric acid triaryl esters (C11x) may be used alone or in combination thereof.

(Dithiophosphoric Acid Ester (C1y) having Carboxyl Group at Terminal thereof)

The thiophosphoric acid ester (C1) preferably contains, as a dithiophosphoric acid ester, a dithiophosphoric acid ester (C1y) having a carboxyl group at a terminal thereof from the viewpoint of providing satisfactory wear resistance.
A specific example of the dithiophosphoric acid ester having a carboxyl group at a terminal thereof is a compound represented by the following general formula (c-1y).
In the general formula (c-1y), R^c21 represents a linear or branched alkylene group having 1 to 8 carbon atoms. R^c22 and R^c23 each independently represent a hydrocarbon group having 3 to 20 carbon atoms.
In the general formula (c-1y), R^c21 represents preferably a linear or branched alkylene group having 1 to 8 carbon atoms, more preferably a linear or branched alkylene group having 2 to 4 carbon atoms, still more preferably a branched alkylene group having 2 to 4 carbon atoms from the viewpoint of providing satisfactory solubility in the base oil (A).
In addition, R^c22 and R^c23 each represent preferably a linear or branched alkyl group having 3 to 8 carbon atoms, more preferably a linear or branched alkyl group having 4 to 6 carbon atoms from the viewpoint of providing satisfactory solubility in the base oil (A) and the viewpoint of improving wear resistance. Specific examples thereof include a propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a tert-butyl group, a n-pentyl group, an isopentyl group, a n-hexyl group, a 2-ethylbutyl group, a 1-methylpentyl group, a 1,3-dimethylbutyl group, and a 2-ethylhexyl group. Among them, an isobutyl group and a tert-butyl group are preferred.
The content of the dithiophosphoric acid ester (C1y) having a carboxyl group at a terminal thereof is preferably from 50 mass% to 100 mass%, more preferably from 60 mass% to 100 mass%, still more preferably from 70 mass% to 100 mass%, still further more preferably from 80 mass% to 100 mass%, yet still further more preferably from 90 mass% to 100 mass%, even more preferably from 95 mass% to 100 mass% with respect to the total amount of the thiophosphoric acid ester (C1) from the viewpoint of improving the effects of the present invention.
The dithiophosphoric acid esters (C1y) each having a carboxyl group at a terminal thereof may be used alone or in combination thereof.

(Content of Non-metal Thiophosphoric Acid Ester-based Compound (C))

In the lubricating oil composition of this embodiment, the content of the non-metal thiophosphoric acid ester-based compound (C) is preferably 0.10 mass% or more, more preferably 0.50 mass% or more, still more preferably 0.80 mass% or more with respect to the total amount of the lubricating oil composition from the viewpoint of more easily improving the wear resistance of the lubricating oil composition. In addition, the content of the non-metal thiophosphoric acid ester-based compound (C) is preferably 5.0 mass% or less, more preferably 3.0 mass% or less, still more preferably 2.5 mass% or less from the viewpoint of balancing the content of the non-metal thiophosphoric acid ester-based compound (C) and the wear resistance-improving effect thereof.
The upper limit values and lower limit values of those numerical ranges may be arbitrary combined. Specifically, the content is preferably from 0.10 mass% to 5.0 mass%, more preferably from 0.50 mass% to 3.0 mass%, still more preferably from 0.80 mass% to 2.5 mass%.
In the lubricating oil composition of this embodiment, the content of the dithiophosphoric acid ester (C1y) having a carboxyl group at a terminal thereof is preferably small from the viewpoint of improving the hydrolysis resistance of the ester oil (A1). Specifically, the content of the dithiophosphoric acid ester (C1y) having a carboxyl group at a terminal thereof is preferably less than 0.95 mass%, more preferably less than 0.5 mass%, still more preferably less than 0.1 mass%, still further more preferably less than 0.01 mass% with respect to the total amount of the lubricating oil composition, and it is yet still further more preferred that the lubricating oil composition be free of the dithiophosphoric acid ester (C1y) having a carboxyl group at a terminal thereof.

The content ratio [(B)/(C)] between the phenothiazine-based compound (B) and the non-metal thiophosphoric acid ester-based compound (C) is preferably from 1/10 to 10/1, more preferably from 1/8 to 8/1, still more preferably from 1/6 to 6/1 in terms of mass ratio from the viewpoint of improving the effects of the present invention.

It is preferred that the lubricating oil composition of this embodiment further comprise a metal deactivator (D) from the viewpoint of improving the hydrolysis resistance of the ester oil (A1).
In the following description, the "metal deactivator (D)" is also referred to as "component (D)."
Examples of the metal deactivator (D) include a triazole-based compound, a thiadiazole-based compound, an imidazole-based compound, and a pyrimidine-based compound.
Those compounds may be used alone or in combination thereof.

(Benzotriazole-based Compound (D 1))

The metal deactivator (D) preferably contains a triazole-based compound, and more preferably contains a benzotriazole-based compound (D1) represented by the following general formula (d-1) from the viewpoint of further improving the hydrolysis resistance of the ester oil (A1).
In the general formula (d-1), R^d1 represents an alkyl group having 1 to 4 carbon atoms. The alkyl group may be linear or branched. The number of carbon atoms of the alkyl group is preferably from 1 to 3, more preferably 1 or 2, still more preferably 1 from the viewpoint of improving the hydrolysis resistance of the ester oil (A1).
In the general formula (d-1), "q" represents an integer of from 0 to 4. When a plurality of R^d1s are present (that is, when "q" represents an integer of from 2 to 4), the plurality of R^d1s may be identical to or different from each other. "q" herein represents preferably from 0 to 3, more preferably from 0 to 2, still more preferably 1 from the viewpoint of improving the hydrolysis resistance of the ester oil (A1).
In the general formula (d-1), R^d2 represents a methylene group or an ethylene group. R^d2 herein preferably represents a methylene group from the viewpoint of improving the hydrolysis resistance of the ester oil (A1).
In the general formula (d-1), R^d3 and R^d4 each independently represent a hydrogen atom or an alkyl group having 1 to 18 carbon atoms. The alkyl group may be linear or branched, and is preferably branched from the viewpoint of improving the hydrolysis resistance of the ester oil (A1). In addition, the number of carbon atoms of the alkyl group is preferably from 2 to 14, more preferably from 4 to 12, still more preferably from 6 to 10 from the viewpoint of improving the hydrolysis resistance of the ester oil (A1).
The content of the benzotriazole-based compound (D1) in the metal deactivator (D) is preferably from 50 mass% to 100 mass%, more preferably from 60 mass% to 100 mass%, still more preferably from 70 mass% to 100 mass%, still further more preferably from 80 mass% to 100 mass%, yet still further more preferably from 90 mass% to 100 mass%, even more preferably from 95 mass% to 100 mass% with respect to the total amount of the metal deactivator (D) from the viewpoint of improving the hydrolysis resistance of the ester oil (A1).
The content of the metal deactivator (D) is preferably from 0.01 mass% to 2.0 mass%, more preferably from 0.05 mass% to 1.5 mass%, still more preferably from 0.08 mass% to 1.0 mass% with respect to the total amount of the lubricating oil composition from the viewpoint of improving the hydrolysis resistance of the ester oil (A1).

The lubricating oil composition of this embodiment may further comprise a lubricating oil additive other than the component (B), the component (C), and the component (D) as required.
Examples of such lubricating oil additive include an antioxidant (e.g., an amine-based antioxidant and a phenol-based antioxidant), a metal-based detergent, a dispersant, a friction modifier, an antiwear agent (e.g., zinc dithiophosphate) other than the non-metal thiophosphoric acid ester-based compound (C), an extreme pressure agent, a viscosity index improver, a pour point depressant, an antifoaming agent, a rust inhibitor, and an antistatic agent.
Among them, a dispersant such as a succinimide-based dispersant and a viscosity index improver such as polymethacrylate are preferably incorporated.
The lubricating oil additives may be used alone or in combination thereof.
The content of each of those lubricating oil additives may be appropriately adjusted within a range not impairing the effects of the present invention, and is typically from 0.001 mass% to 15 mass%, preferably from 0.005 mass% to 10 mass%, more preferably from 0.01 mass% to 5 mass% independently for each additive with respect to the total amount (100 mass%) of the lubricating oil composition.
It is preferred that the content of the phenol-based antioxidant in the lubricating oil composition of this embodiment be small from the viewpoint of improving the evaporation characteristics.
Examples of the phenol-based antioxidant include a monophenol-based antioxidant and a bisphenol-based antioxidant.
Examples of the monophenol-based antioxidant include: alkyl-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl) propionates (each having an alkyl group having, for example, 4 to 20 carbon atoms, preferably 8 to 18 carbon atoms), such as n-octyl-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl) propionate, 6-methylheptyl-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl) propionate and n-octadecyl-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl) propionate; 2,6-di-tert-butyl-4-alkylphenols (each having an alkyl group having 1 to 4 carbon atoms), such as 2,6-di-tert-butyl-4-methylphenol and 2,6-di-tert-butyl-4-ethylphenol; and 2,4-dimethyl-6-tertbutylphenol and 2,6-di-tert-amyl-p-cresol.
In addition, examples of the bisphenol antioxidant include 4,4'-methylenebis(2,6-di-tert-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-tertbutylphenol), 2,2'-methylenebis(4-methyl-6-nonylphenol), 2,2'-isobutylidenebis(4,6-dimethylphenol), 2,2'-methylenebis(4-methyl-6-cyclohexylphenol), 4,4'-thiobis(2-methyl-6-tert-butylphenol), 4,4'-thiobis(3-methyl-6-tert-butylphenol), 2,2'-thiobis(4-methyl-6-tertbutylphenol), bis(3-methyl-4-hydroxy-5-tert-butylbenzyl) sulfide, bis(3,5-di-tert-butyl-4-hydroxybenzyl) sulfide, and thiodiethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate].
The content of the phenol-based antioxidant is preferably less than 0.5 mass%, more preferably less than 0.1 mass%, still more preferably less than 0.01 mass% with respect to the total amount of the lubricating oil composition, and it is still further more preferred that the lubricating oil composition be free of the phenol-based antioxidant.
In addition, it is preferred that the content of a thiocarbamate-based compound, which corresponds to the antiwear agent other than the non-metal thiophosphoric acid ester-based compound (C), in the lubricating oil composition of this embodiment be small from the viewpoint of improving the hydrolysis resistance of the ester oil (A1).
Examples of the thiocarbamate-based compound include a thiocarbamate compound and a dithiocarbamate compound.
Examples of the thiocarbamate compound include diethylthiocarbamic acid, methylene diethylthiocarbamate, ethylene diethyldithiocarbamate, dipropylthiocarbamic acid, methylene dipropylthiocarbamate, ethylene dipropyldithiocarbamate, dibutyldithiocarbamic acid, methylene dibutyldithiocarbamate, ethylene dibutyldithiocarbamate, dipentyldithiocarbamic acid, methylene dipentyldithiocarbamate, ethylene dipentyldithiocarbamate, methylene dihexyldithiocarbamate, and ethylene dihexyldithiocarbamate.
Examples of the dithiocarbamate compound include methylene bis(diethylthiocarbamate), ethylene bis(diethyldithiocarbamate), methylenebis(dipropylthiocarbamate), ethylene bis(dipropyldithiocarbamate), methylene bis(dibutyldithiocarbamate), ethylene bis(dibutyldithiocarbamate), methylene bis(dipentyldithiocarbamate), ethylene bis(dipentyldithiocarbamate), methylene bis(dihexyldithiocarbamate), and ethylene bis(dihexyldithiocarbamate).
The content of the thiocarbamate-based compound is preferably less than 1.0 mass%, more preferably less than 0.1 mass%, still more preferably less than 0.01 mass% with respect to the total amount of the lubricating oil composition, and it is still further more preferred that the lubricating oil composition be free of the thiocarbamate-based compound.
In addition, it is preferred that the content of a molybdenum-based friction modifier in the lubricating oil composition of this embodiment be small.
Examples of the molybdenum-based friction modifier include molybdenum dithiocarbamate (MoDTC) and molybdenum dithiophosphate (MoDTP).
The content of the molybdenum-based friction modifier is preferably less than 0.5 mass%, more preferably less than 0.1 mass%, still more preferably less than 0.01 mass% with respect to the total amount of the lubricating oil composition, and it is still further more preferred that the lubricating oil composition be free of the molybdenum-based friction modifier.

[Physical Properties of Lubricating Oil Composition]

In the lubricating oil composition of this embodiment, it is preferred that an evaporation lifetime measured by a method described later in Examples become longer. Specifically, the evaporation lifetime is preferably 10 days or more, more preferably 12 days or more, still more preferably 14 days or more.

In the lubricating oil composition of this embodiment, it is preferred that a wear scar diameter measured by a method described later in Examples become smaller. Specifically, the wear scar diameter is preferably 0.90 mm or less, more preferably 0.80 mm or less, still more preferably 0.70 mm or less, still further more preferably 0.60 mm or less, yet still further more preferably 0.50 mm or less.

In the lubricating oil composition of this embodiment, it is preferred that an acid value of an oil content measured by a method described later in Examples become smaller. As the acid value decreases, the hydrolysis resistance becomes excellent. Specifically, the acid value is preferably 5.00 mg KOH/g or less, more preferably 4.00 mg KOH/g or less, still more preferably 3.70 mg KOH/g or less.
In the lubricating oil composition of this embodiment, it is preferred that a copper elution amount of an oil content measured by a method described later in Examples become smaller. As the copper elution amount decreases, the hydrolysis resistance becomes excellent. Specifically, the copper elution amount is preferably 20 ppm by mass or less, more preferably 15 pp by mass or less, still more preferably 10 ppm by mass or less.

The kinematic viscosity at 100°C of the lubricating oil composition of this embodiment is preferably from 2.0 mm²/s to 30.0 mm²/s, more preferably from 2.5 mm²/s to 25.0 mm²/s, still more preferably from 3.0 mm²/s to 22.0 mm²/s.
The viscosity index of the lubricating oil composition of this embodiment is preferably 90 or more.
The kinematic viscosity and viscosity index of the lubricating oil composition mean values measured and calculated in conformity with JIS K2283:2000.

[Method of producing Lubricating Oil Composition]

A method of producing the lubricating oil composition of this embodiment is not particularly limited.
For example, the method of producing the lubricating oil composition of this embodiment comprises a step of mixing the base oil (A) containing the ester oil (A1), the phenothiazine-based compound (B), and the non-metal thiophosphoric acid ester-based compound (C).
Although a method of mixing the base oil (A) containing the ester oil (A1), the phenothiazine-based compound (B), and the non-metal thiophosphoric acid ester-based compound (C) is not particularly limited, an example thereof is a method including blending, into the base oil (A) containing the ester oil (A1), the phenothiazine-based compound (B) and the non-metal thiophosphoric acid ester-based compound (C).
In a case where an additive other than the phenothiazine-based compound (B) and the non-metal thiophosphoric acid ester-based compound (C) is blended, the additive may be blended simultaneously with the phenothiazine-based compound (B) and the non-metal thiophosphoric acid ester-based compound (C) or may be separately blended. In addition, a diluent oil or the like may be added to each component to form a solution (dispersion), and the solution (dispersion) may be blended.
After the blending of the components, the components are preferably stirred and uniformly dispersed by using a known method.
Preferred modes of the above-mentioned components have already been described.

[Application of Lubricating Oil Composition]

The lubricating oil composition of this embodiment is excellent in evaporation characteristics and wear resistance.
Accordingly, the lubricating oil composition of this embodiment may be generally used for applications where evaporation characteristics and wear resistance are required, and may be particularly suitable for use in an oil-impregnated bearing incorporated into equipment, such as automobile electrical equipment, a home appliance, and OA office equipment.
Accordingly, according to the lubricating oil composition of this embodiment, the following items (1) to (3) are provided.

(1) The lubricating oil composition of this embodiment used as an oil for an oil-impregnated bearing.
(2) A method of using a lubricating oil composition, in which the lubricating oil composition of this embodiment is used as an oil for an oil-impregnated bearing.
(3) An oil-impregnated bearing impregnated with the lubricating oil composition of this embodiment.
In addition, in this embodiment, methods according to the following items (4) to (6) are also provided.
(4) A method of improving evaporation characteristics of the ester oil (A1) by blending the phenothiazine-based compound (B) into the ester oil (A1).
(5) A method of improving evaporation characteristics of the diester oil (A11) by blending the phenothiazine-based compound (B) into the diester oil (A11).
(6) A method of improving evaporation characteristics of the diester oil (A11) by blending the phenothiazine-based compound (B) into the diester oil, the diester oil being a diester oil in which a hydrogen atom is bonded to a carbon atom at the β-position on the alcohol side of an ester bond.

In addition, the application of the lubricating oil composition of this embodiment is not limited to oil-impregnated bearings, and the lubricating oil composition of this embodiment can also be suitably used for applications such as a fluid dynamic bearing for a spindle motor used in electronic devices such as a hard disk drive.

[One Aspect of the Present Invention to be provided]

According to one aspect of the present invention, there are provided the following items [1] to [11].

[1] A lubricating oil composition, comprising: a base oil (A) containing an ester oil (A1); a phenothiazine-based compound (B); and a non-metal thiophosphoric acid ester-based compound (C).
[2] The lubricating oil composition according to the above-mentioned item [1], wherein the ester oil (A1) contains a diester oil (A11).
[3] The lubricating oil composition according to the above-mentioned item [1] or [2], wherein the non-metal thiophosphoric acid ester-based compound (C) contains a thiophosphoric acid ester (C1).
[4] The lubricating oil composition according to the above-mentioned item [3], wherein the thiophosphoric acid ester (C1) contains one or more kinds selected from a monothiophosphoric acid triester (C1x) represented by the following general formula (c-1x): wherein
in the general formula (c-1x), respective symbols represent the following:
R^c1, R^c2, and R^c3 each independently represent a saturated or unsaturated aliphatic hydrocarbon group having 1 to 18 carbon atoms, a saturated or unsaturated alicyclic hydrocarbon group having 5 to 18 carbon atoms that may have a substituent, or an aromatic hydrocarbon group having 5 to 18 carbon atoms that may have a substituent.
[5] The lubricating oil composition according to the above-mentioned item [4], wherein the monothiophosphoric acid triester (C1x) contains one or more kinds selected from a monothiophosphoric acid triaryl ester (C11x) represented by the following general formula (c-11x): wherein
in the general formula (c-11x), respective symbols represent the following:
- R^c11, R^c12, and R^c13 each independently represent an alkyl group having 1 to 3 carbon atoms; and
- n1, n2, and n3 each independently represent an integer of from 0 to 5.
[6] The lubricating oil composition according to any one of the above-mentioned items [1] to [5], further comprising a metal deactivator (D).
[7] The lubricating oil composition according to any one of the above-mentioned items [1] to [6], wherein a content ratio [(B)/(C)] between the phenothiazine-based compound (B) and the non-metal thiophosphoric acid ester-based compound (C) is from 1/10 to 10/1 in terms of mass ratio.
[8] The lubricating oil composition according to any one of the above-mentioned items [1] to [7], wherein the lubricating oil composition is used as an oil for an oil-impregnated bearing.
[9] A method of using the lubricating oil composition of any one of the above-mentioned items [1] to [7], the method comprising using the lubricating oil composition as an oil for an oil-impregnated bearing.
[10] An oil-impregnated bearing impregnated with the lubricating oil composition of any one of the above-mentioned items [1] to [7].
[11] A method of producing a lubricating oil composition, comprising a step of mixing a base oil (A) containing an ester oil (A1), a phenothiazine-based compound (B), and a non-metal thiophosphoric acid ester-based compound (C).

Examples

The present invention is more specifically described by way of Examples below. However, the present invention is not limited to Examples below.

[Method of Measuring Various Physical Property Values]

Properties of raw materials used in each of Examples and Comparative Examples, and properties of a lubricating oil composition of each of Examples and Comparative Examples were measured according to the following procedures.

(1) Kinematic Viscosity and Viscosity Index

A kinematic viscosity and a viscosity index were measured and calculated in conformity with JIS K2283:2000.

[Examples 1 and 2, and Comparative Examples 1 to 5]

The components described above were mixed to prepare lubricating oil compositions each having the composition shown in Table 1, and the lubricating oil compositions were evaluated as described below.
The unit of the numerical values in the blending composition in Table 1 is "mass%".
Details of the components used for preparing the lubricating oil compositions each having the composition shown in Table 1 are described below.

Bis(2-ethylhexyl) dodecanedioate (DODN) was used.
Bis(2-ethylhexyl) dodecanedioate is a base oil corresponding to the diester oil (A11), and is a compound represented by the general formula (a-1) in which R^a1 and R^a2 each represent a 2-ethylhexyl group, and R^a3 represents a decylene group (-(CH₂)₁₀-). In this compound, a hydrogen atom is bonded to a carbon atom at the β-position on the alcohol side of an ester bond.
The kinematic viscosity at 40°C is 13.9 mm²/s, the kinematic viscosity at 100°C is 3.71 mm²/s, and the viscosity index is 163.

<Phenothiazine-based Compound (B)>

Phenothiazine was used.
Phenothiazine is unsubstituted phenothiazine corresponding to the phenothiazine (B1).

<Non-phenothiazine-based Compound (B')>

The following two compounds known as antioxidants were used for comparison to the phenothiazine-based compound (B).

·Amine-based compound: 4,4'-bis(α,α-dimethylbenzyl)diphenylamine
·Phenol-based compound: n-octadecyl-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate

<Non-metal Thiophosphoric Acid Ester-based Compound (C)>

Triphenyl phosphorothioate (TPPT) was used.
Triphenyl phosphorothioate is a compound corresponding to the monothiophosphoric acid triaryl ester (C11x), and is a compound represented by the general formula (c-11x) in which n1, n2, and n3 each represent 0.

A benzotriazole-based compound represented by the following structural formula was used.
The benzotriazole-based compound represented by the following structural formula is a compound corresponding to the benzotriazole-based compound (D1), and is a compound represented by the general formula (d-1) in which R^d1 represents a methyl group, "q" represents 1, R^d2 represents a methylene group, and R^d3 and R^d4 each represent a 2-ethylhexyl group.

·Viscosity index improver: polymethacrylate (mass average molecular weight: 300,000, resin content: 19 mass%, dilution oil: diester oil (diisodecyl sebacate))
·Dispersant: succinimide dispersant (succinimide: 53 mass%, components other than succinimide: deuterated paraffin (diluent) and polybutene)

The evaporation characteristics of each of the lubricating oil compositions of Examples 1 and 2, and Comparative Examples 1 to 5 were evaluated according to the following procedure.
A thermostatic bath equipped with a rotary plate (manufactured by Yoshida Kagaku Kikai Co. Ltd., model TST-9R) specified in Lubricating oils-Determination of thermal stability (JIS K 2540:2000) was used as a thermostatic bath.
A glass vessel having an inner diameter of 53 mm and a depth of 56 mm was used as a sample vessel.
After 2.0 g (±0.010 g) of the lubricating oil composition to be evaluated and 2.0 g (±0.010 g) of iron powder or copper powder were weighed and placed into a sample vessel, the sample vessel was allowed to stand still in the thermostatic bath heated to 150°C, and taken out at time points that were multiples of 24 hours, and its weights were measured.
An evaporation rate (wt%) was calculated from the weights before and after the test, and the time (days) until the evaporation rate began to increase sharply was defined as an evaporation lifetime. Specifically, the number of days of the test on which the determination coefficient R² became less than 0.9 when the change amount (a) of the evaporation rate (y) with respect to the number of days (x) of the test was represented by the regression line y=ax was defined as the evaporation lifetime.
As the evaporation lifetime increases, the evaporation characteristics of the lubricating oil composition become excellent. In contrast, as the evaporation lifetime decreases, the evaporation characteristics of the lubricating oil composition become poor.
In Examples, a lubricating oil composition with an evaporation lifetime of 10 days or more was determined to be acceptable.
The evaluation using the copper powder was not conducted for the lubricating oil compositions of Comparative Examples 2 to 5.

The wear resistance of each of the lubricating oil compositions of Examples 1 and 2, and Comparative Example 1 was evaluated according to the following procedure.
The Shell four-ball wear test was conducted with 0.5-inch SUJ-2 balls (grade 20) under the conditions of an oil temperature of 80°C, a rotational speed of 1,200 rpm, a load of 392 N, and a test duration of 60 minutes. The wear scar diameter (mm) of a fixed ball after the test was measured.
As the wear scar diameter decreases, the wear resistance of the lubricating oil composition becomes excellent. In contrast, as the wear scar diameter increases, the wear resistance of the lubricating oil composition becomes poor.
In Examples, a lubricating oil composition with a wear scar diameter of 0.90 mm or less was determined to be acceptable.
Results of Evaluation 1 and Evaluation 2 are shown in Table 1.
The symbol "<" in Table 1 means "more than."

[Table 1]

Table 1

			Example 1	Example 2	Comparative Example 1
Lubricating oil composition (unit: mass%)	Base oil (A)	DODN	Balance	Balance	Balance
	Phenothiazine-based compound (B)	Phenothiazine	1.0	1.0	-
	Non-phenothiazine-based compound (B')	Amine-based compound	-	-	0.5
	Non-phenothiazine-based compound (B')	Phenol-based compound	-	-	0.5
	Non-metal thiophosphoric acid ester-based compound (C)	TPPT	1.9	0.95	0.95
	Metal deactivator (D)	Benzotriazole-based compound	0.2	0.2	0.2
	Lubricating oil additive	Viscosity index improver	12.6	13.7	13.7
	Lubricating oil additive	Dispersant	0.5	0.5	0.5
	Total		100.0	100.0	100.0
Physical property value	Kinematic viscosity of lubricating oil composition at 100°C (mm²/s)		10.09	10.89	11.49
Evaluation 1	Evaporation lifetime in presence of iron catalyst (days)		14<	14<	7
Evaluation 1	Evaporation lifetime in presence of copper catalyst (days)		14<	14<	7
Evaluation 2	Four-ball wear 1,200 rpm, 80°C, 392 N, 60 min Wear scar diameter (mm)		0.47	0.86	0.81

Table 1 (continued)

			Comparative Example 2	Comparative Example 3	Comparative Example 4	Comparative Example 5
Lubricating oil composition (unit: mass%)	Base oil (A)	DODN	Balance	Balance	Balance	Balance
	Phenothiazine-based compound (B)	Phenothiazine	-	-	-	-
	Non-phenothiazine-based compound (B')	Amine-based compound	0.5	-	1.0	0.5
	Non-phenothiazine-based compound (B')	Phenol-based compound	-	0.5	0.5	0.5
	Non-metal thiophosphoric acid ester-based compound (C)	TPPT	0.95	0.95	0.95	0.95
	Metal deactivator (D)	Benzotriazole-based compound	0.2	0.2	0.2	0.2
	Lubricating oil additive	Viscosity index improver	13.7	13.7	13.7	13.7
	Lubricating oil additive	Dispersant	0.5	0.5	0.5	-
	Total		100.0	100.0	100.0	100.0
Physical property value	Kinematic viscosity of lubricating oil composition at 100°C (mm²/s)		11.28	11.20	11.51	11.01
Evaluation 1	Evaporation lifetime in presence of iron catalyst (days)		7	2	9	7
Evaluation 1	Evaporation lifetime in presence of copper catalyst (days)		-	-	-	-
Evaluation 2	Four-ball wear 1,200 rpm, 80°C, 392 N, 60 min Wear scar diameter (mm)		-	-	-	-

Table 1 shows the following findings.
It is found that the lubricating oil composition of each of Examples 1 and 2 is excellent in both of evaporation characteristics and wear resistance.
In contrast, it is found that the lubricating oil composition of Comparative Example 1 is poor in evaporation characteristics, though wear resistance can be ensured. It is found that the lubricating oil composition of each of Comparative Examples 2 to 5 is poor in evaporation characteristics.

The hydrolysis resistance of each of the lubricating oil compositions of Examples 1 and 2, and Comparative Example 1 was evaluated according to the following procedure.
The lubricating oil composition to be evaluated was tested under the following conditions with a rotating bomb oxidation stability tester (RBOT) and a sample vessel (RBOT test beaker) specified in JIS K 2514-3:2003. After the test, an oil content and a water content in the sample vessel were separated, and the acid value and copper elution amount of the oil content were evaluated. The acid value and copper elution amount of the lubricating oil composition before the test were also measured.

(Test Conditions)

·Sample oil quantity: 20 g
·Catalyst: 120 mg of copper powder
·Water: 1 mL inside the beaker and 1 mL outside the beaker
·Encapsulation: air (atmospheric pressure)
·Temperature: 150°C
·Test time: 24 hours

The acid value of the oil content was measured by a potentiometric method with TS1700 manufactured by Hiranuma Sangyo Co., Ltd. (Hiranuma Co., Ltd.) in conformity with JIS K2501:2003.
In addition, the copper elution amount of the oil content was measured by ICP emission spectroscopy with ICPS-8100 manufactured by Shimadzu Corporation.
As the acid value of the oil content decreases, the hydrolysis resistance becomes satisfactory. In contrast, as the acid value of the oil content increases, the hydrolysis resistance becomes poor.
In addition, as the copper elution amount of the oil content decreases, the hydrolysis resistance becomes satisfactory. In contrast, as the copper elution amount of the oil content increases, the hydrolysis resistance becomes poor.
In Examples, a lubricating oil composition exhibiting an acid value of the oil content of 5.00 mg KOH/g or less and a copper elution amount of the oil content of 20 ppm by mass or less after 24 hours was determined to be acceptable.
Results of Evaluation 3 are shown in Table 2.
The symbol ">" in Table 2 means "less than."

[Table 2]

Table 2

			Example 1	Example 2	Comparative Example 1
Lubricating oil composition (unit: mass%)	Base oil (A)	DODN	Balance	Balance	Balance
	Phenothiazine-based compound (B)	Phenothiazine	1.0	1.0	-
	Non-phenothiazine-based compound (B')	Amine-based compound	-	-	0.5
	Non-phenothiazine-based compound (B')	Phenol-based compound	-	-	0.5
	Non-metal thiophosphoric acid ester-based compound	TPPT	1.9	0.95	0.95
	Metal deactivator (D)	Benzotriazole-based compound	0.2	0.2	0.2
	Lubricating oil additive	Viscosity index improver	12.6	13.7	13.7
	Lubricating oil additive	Dispersant	0.5	0.5	0.5
	Total		100.0	100.0	100.0
Physical property value	Kinematic viscosity of lubricating oil composition at 100°C (mm²/s)		10.09	10.89	11.49
Evaluation 3	Initial	Acid value (mgKOH/g)	0.07	0.07	0.07
	Initial	Cu (ppm by mass)	5>	2>	2>
	After 24 hours	Acid value (mgKOH/g)	1.81	3.42	2.11
	After 24 hours	Cu (ppm by mass)	3	5	3

It is found from Table 2 that the lubricating oil composition of each of Examples 1 and 2 is excellent also in hydrolysis resistance.

Claims

A lubricating oil composition, comprising:
a base oil (A) comprising an ester oil (A1);

a phenothiazine-based compound (B); and

a non-metal thiophosphoric acid ester-based compound (C).
The lubricating oil composition according to claim 1, wherein the ester oil (A1) comprises a diester oil (A11).
The lubricating oil composition according to claim 1 or 2, wherein the non-metal thiophosphoric acid ester-based compound (C) comprises a thiophosphoric acid ester (C1).
The lubricating oil composition according to claim 3, wherein the thiophosphoric acid ester (C1) comprises one or more kinds selected from a monothiophosphoric acid triester (C1x) represented by the following general formula (c-1x): wherein
in the general formula (c-1x), respective symbols represent the following:
R^c1, R^c2, and R^c3 each independently represent a saturated or unsaturated aliphatic hydrocarbon group having 1 to 18 carbon atoms, a saturated or unsaturated alicyclic hydrocarbon group having 5 to 18 carbon atoms that may have a substituent, or an aromatic hydrocarbon group having 5 to 18 carbon atoms that may have a substituent.
The lubricating oil composition according to claim 4, wherein the monothiophosphoric acid triester (C1x) comprises one or more kinds selected from a monothiophosphoric acid triaryl ester (C11x) represented by the following general formula (c-11x): wherein
in the general formula (c-11x), respective symbols represent the following:
R^c11, R^c12, and R^c13 each independently represent an alkyl group having 1 to 3 carbon atoms; and

n1, n2, and n3 each independently represent an integer of from 0 to 5.
The lubricating oil composition according to any one of claims 1 to 5, further comprising a metal deactivator (D).
The lubricating oil composition according to any one of claims 1 to 6, wherein a content ratio [(B)/(C)] between the phenothiazine-based compound (B) and the non-metal thiophosphoric acid ester-based compound (C) is from 1/10 to 10/1 in terms of mass ratio.
The lubricating oil composition according to any one of claims 1 to 7, wherein the lubricating oil composition is used as an oil for an oil-impregnated bearing.
A method of using the lubricating oil composition of any one of claims 1 to 7, the method comprising using the lubricating oil composition as an oil for an oil-impregnated bearing.
An oil-impregnated bearing impregnated with the lubricating oil composition of any one of claims 1 to 7.
A method of producing a lubricating oil composition, comprising a step of mixing a base oil (A) comprising an ester oil (A1), a phenothiazine-based compound (B), and a non-metal thiophosphoric acid ester-based compound (C).