JP7286622B2 - lubricating oil composition - Google Patents

Description

The present invention relates to lubricating oil compositions.

The rotating part of the machine tool is preferably one that can rotate at high speed even when a high load is applied, in order to improve machining efficiency. Generally, grease is often used as a lubricating oil for rolling bearings.
However, when the rotation speed of the spindle becomes high, the supply of grease becomes insufficient, so oil-air lubrication is the mainstream.

In oil-air lubrication, which is used to lubricate the rotating parts of machine tools, lubricating oil intermittently supplied from a mixing valve is discharged into the piping and then atomized by the flow of compressed air that is continuously supplied to the inside of the piping. It adheres to the surface inside the pipe in the form of oil droplets.
Lubricating oils used for oil-air lubrication are required to have properties such as being able to form a strong oil film on the surface inside the pipes and having small changes in viscosity due to the temperature inside the pipes.
For example, Patent Document 1 discloses a lubricating oil composition used for oil-air lubrication, containing 20 to 80% by mass of ester oil and poly-α-olefin or ether oil.

JP 2014-84429 A

By the way, lubricating oil compositions are required not only for lubricating properties but also for economic aspects such as cost reduction. For example, the lubricating oil composition described in Patent Document 1 uses expensive synthetic oils such as ester oils, poly-α-olefins and ether oils, and improvements are being sought from the viewpoint of cost reduction.
From the viewpoint of cost reduction, mineral oil is used instead of synthetic oil, and among mineral oils, deasphalting treatment, dewaxing treatment, hydrorefining treatment, etc. are applied to residual oil after distillation of crude oil under reduced pressure. There is a demand for the use of bright stock, which is a highly viscous mineral oil obtained by application.
When mineral oil containing such bright stock is used, there is an advantage in terms of cost reduction, but there is a problem that it is inferior to a lubricating oil composition using synthetic oil in terms of temperature dependence and lubricating properties. be.
Therefore, even when mineral oil containing bright stock is used, there is a demand for the development of a lubricating oil composition which has similar properties to those when synthetic oil is used.

An object of the present invention is to provide a lubricating oil composition that has low temperature dependence and good lubricating properties even when a mineral oil containing bright stock is used.

The inventors of the present invention have found that the above problems can be solved by adjusting the contents of the synthetic oil and the phosphate ester in a predetermined range in a lubricating oil composition containing 30% by mass or more of a mineral oil containing bright stock. He found this and completed the present invention.

That is, the present invention provides the following [1] to [12].
[1] A lubricating oil composition containing 30% by mass or more of mineral oil (A) containing bright stock (A1) based on the total amount of the lubricating oil composition,
Further containing synthetic oil (B) and phosphate ester (C),
The content of the synthetic oil (B) is less than 70% by mass based on the total amount of the lubricating oil composition,
A lubricating oil composition in which the content of the phosphate ester (C) in terms of phosphorus atoms is 0.050 to 0.200% by mass based on the total amount of the lubricating oil composition, and the viscosity index is 150 or more. .
[2] The lubricating oil composition according to [1], wherein the bright stock (A1) has a kinematic viscosity at 100°C of 28.0 mm ² /s or more.
[3] The lubricating oil composition according to [1] or [2], wherein the content of bright stock (A1) in mineral oil (A) is 5 to 70% by mass based on the total amount of mineral oil (A).
[4] The lubricating oil composition according to any one of [1] to [3], wherein the content of the synthetic oil (B) is 10% by mass or more and less than 70% by mass based on the total amount of the lubricating oil composition. .
[5] The lubricating oil composition according to any one of [1] to [4], wherein the synthetic oil (B) has a viscosity index of 130 or more.
[6] The lubricating oil composition according to any one of [1] to [5], wherein the synthetic oil (B) has a kinematic viscosity at 100°C of 80 to 180 mm ² /s.
[7] The lubricating oil composition according to any one of [1] to [6], wherein the synthetic oil (B) contains a poly-α-olefin (B1).
[8] The lubricating oil composition according to any one of [1] to [7], wherein the phosphoric acid ester (C) comprises a compound (C1) selected from an acidic phosphoric acid ester and an amine salt of an acidic phosphoric acid ester. .
[9] Phosphate ester (C) comprises a compound (C1) selected from an acidic phosphate ester and an amine salt of an acidic phosphate ester, and a neutral phosphate ester (C2) [1] to [8 ] Lubricating oil composition according to any one of.
[10] The lubrication according to [9], wherein the content ratio [(C2)/(C1)] of the neutral phosphate ester (C2) to the compound (C1) is 2.0 to 40 in mass ratio. oil composition.
[11] Further containing a sulfur atom-containing extreme pressure agent,
The lubricating oil according to any one of [1] to [10], wherein the content of the sulfur atom-containing extreme pressure agent in terms of sulfur atoms is less than 0.12% by mass based on the total amount of the lubricating oil composition. Composition.
[12] The lubricating oil composition according to any one of [1] to [11], which is used in an oil-air lubrication system.

The lubricating oil composition of the present invention uses a mineral oil containing bright stock, and is superior in terms of cost reduction, has low temperature dependence, and has good lubricating properties.

[Lubricating oil composition]
The lubricating oil composition of the present invention contains mineral oil (A) containing bright stock (A1), synthetic oil (B), and phosphate ester (C), and is prepared to have a viscosity index of 150 or more. is.
If the viscosity index is less than 150, for example, when used for oil-air lubrication, depending on the temperature inside the pipe, it may be difficult to form a firm oil film on the surface inside the pipe.
In order to avoid the above problems, the viscosity index of the lubricating oil composition of the present invention is 150 or more, preferably 151 or more, more preferably 153 or more.

In addition, the kinematic viscosity at 100° C. of the lubricating oil composition of one embodiment of the present invention is preferably 30.0 to 60.0 mm ² /s, more preferably 35.0 to 55.0 mm ² /s, still more preferably is 40.0 to 52.0 mm ² /s.
In addition, in this specification, a kinematic viscosity and a viscosity index mean the value measured and calculated based on JISK2283:2000.

The lubricating oil composition of one aspect of the present invention preferably further contains an antioxidant (D).
In addition, the lubricating oil composition of one aspect of the present invention may further contain lubricating oil additives other than components (C) and (D) within a range that does not impair the effects of the present invention.

In the lubricating oil composition of one aspect of the present invention, the total content of component (A), component (B), and component (C) is based on the total amount (100% by mass) of the lubricating oil composition, preferably 70 to 100% by mass, more preferably 75 to 100% by mass, still more preferably 80 to 100% by mass, still more preferably 90 to 100% by mass.

Further, in the lubricating oil composition of one aspect of the present invention, the total content of the component (A) and the component (B) is based on the total amount (100% by mass) of the lubricating oil composition, preferably 65% by mass or more , More preferably 71% by mass or more, more preferably 76% by mass or more, still more preferably 81% by mass or more, still more preferably 86% by mass or more, and preferably 99.9% by mass or less, more preferably It is 99.5% by mass or less, more preferably 99.0% by mass or less.

Details of each component contained in the lubricating oil composition of the present invention are described below.

<Mineral oil (A)>
The mineral oil (A) contained in the lubricating oil composition of the present invention includes, for example, atmospheric residual oil obtained by atmospheric distillation of crude oil such as paraffinic crude oil, intermediate crude oil, naphthenic crude oil; Distillate obtained by vacuum distillation of pressure residue; the distillate is subjected to one or more treatments such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, etc. and mineral oil (GTL) obtained by isomerizing wax (GTL wax (Gas To Liquids WAX)) produced from natural gas by the Fischer-Tropsch process or the like.
These mineral oils (A) may be used alone or in combination of two or more.

In the lubricating oil composition of the present invention, the content of the mineral oil (A) is 30% by mass or more based on the total amount (100% by mass) of the lubricating oil composition, from the viewpoint of cost reduction, but the synthetic oil ( B) and the phosphate ester (C) are ensured, and from the viewpoint of obtaining a lubricating oil composition having low temperature dependence and good lubricating properties, it is preferably 30 to 90% by mass, more preferably 30 to 80% by mass, more preferably 30 to 70% by mass, even more preferably 30 to 60% by mass.

The mineral oil (A) contained in the lubricating oil composition of the present invention contains bright stock (A1) from the viewpoint of cost reduction.
In the present specification, "bright stock" refers to solvent deasphalting, solvent extraction, solvent dewaxing, solvent deasphalting, solvent extraction, solvent dewaxing, and the like for residual oil after vacuum distillation of crude oil such as paraffinic crude oil, intermediate crude oil, and naphthenic crude oil. and high-viscosity mineral oil produced by a process selected from hydrorefining and the like.

The kinematic viscosity at 100° C. of Bright Stock (A1) is preferably 28.0 mm ² /s or more, more preferably 29.0 mm ² /s or more, still more preferably 30.0 mm ² /s or more, and usually 40 0 mm ² /s or less, preferably 35.0 mm ² /s or less.

The viscosity index of bright stock (A1) is preferably 80 or higher, more preferably 90 or higher, and even more preferably 100 or higher, from the viewpoint of providing a lubricating oil composition with low temperature dependence.

The paraffin content (%C _P ) of the bright stock (A1) used in one embodiment of the present invention is preferably 50-90, more preferably 60-85, and still more preferably 70-80.
The naphthene content (% C _N ) of bright stock (A1) is preferably 10-40, more preferably 15-35, still more preferably 20-30.
The aromatic content (% C _A ) of the bright stock (A1) is preferably 0-30, more preferably 0-20, still more preferably 0-10.
In this specification, the values of paraffin content (% C _P ), naphthene content (% C _N ), and aromatic content (% C _A ) are based on ASTM D-3238 ring analysis (ndM method). means the proportions (percentages) of paraffinic, naphthenic, and aromatic content as determined by .

The content of bright stock (A1) in mineral oil (A) is based on the total amount (100% by mass) of mineral oil (A), from the viewpoint of cost reduction, low temperature dependence, and good lubricating properties. From the viewpoint of a lubricating oil composition, it is preferably 5 to 70% by mass, more preferably 10 to 67% by mass, even more preferably 12 to 65% by mass, and even more preferably 14 to 62% by mass.

Mineral oil (A) used in one aspect of the present invention preferably contains mineral oil (A2) other than bright stock (A1) from the viewpoint of adjusting the viscosity to a predetermined level.
Mineral oils (A2) include those described above and are classified into groups 1 to 3 of the American Petroleum Institute (API) base oil category, and isomerizing GTL wax. can be used, but mineral oils classified as Group 1 or 2 are preferred from the viewpoint of cost reduction.
In the lubricating oil composition of the present invention, even if a mineral oil classified into Group 1 or 2 is used, it can be prepared to have low temperature dependence and good lubricating properties.

The kinematic viscosity of mineral oil (A2) at 100° C. is preferably 7.0 to 15.0 mm ² /s, more preferably 9.0 to 13.0 mm ² /s, still more preferably 10.0 to 12.0 mm. ² /s.
Also, the mineral oil (A2) has a viscosity index of preferably 80 or higher, more preferably 90 or higher, and even more preferably 100 or higher.

The paraffin content (%C _P ) of the mineral oil (A2) used in one embodiment of the present invention is preferably 50-90, more preferably 60-85, still more preferably 70-80.
The naphthene content (% C _N ) of the mineral oil (A2) is preferably 10-40, more preferably 15-35, still more preferably 20-30.
The aromatic content (% C _A ) of the mineral oil (A2) is preferably 0-20, more preferably 0-10, still more preferably 0-5.

<Synthetic oil (B)>
The synthetic oil (B) contained in the lubricating oil composition of the present invention includes, for example, poly-α-olefins; isoparaffins; various esters such as polyol esters and dibasic acid esters; various ethers such as polyphenyl ethers; alkylbenzene; alkylnaphthalene; and the like.
These synthetic oils (B) may be used alone or in combination of two or more.

In the lubricating oil composition of the present invention, the content of the synthetic oil (B) is less than 70% by mass based on the total amount (100% by mass) of the lubricating oil composition from the viewpoint of cost reduction. From the viewpoint of obtaining a lubricating oil composition having low lubricity and good lubricating properties, the content is preferably 10% by mass or more and less than 70% by mass, more preferably 20% by mass or more and less than 70% by mass, still more preferably 30% by mass or more and 70% by mass. Less than mass %, more preferably 40 mass % or more and less than 65 mass %.

The kinematic viscosity at 100° C. of the synthetic oil (B) used in one aspect of the present invention is preferably 80 to 180 mm ² /s, more preferably 85 to 175 mm ² /s, still more preferably 90 to 170 mm ² /s. be.
The viscosity index of the synthetic oil (B) is preferably 130 or higher, more preferably 150 or higher, and even more preferably 170 or higher.

The synthetic oil (B) used in one embodiment of the present invention is a lubricating oil composition having low temperature dependence and good lubricating properties even when a mineral oil containing bright stock is used. It preferably contains (B1).
The poly α-olefin (B1) may be an α-olefin homopolymer or an α-olefin copolymer.
Examples of α-olefin copolymers include copolymers of ethylene and α-olefins having 8 to 20 carbon atoms (preferably 8 to 14 carbon atoms).
Poly-α-olefin (B1) may be used alone or in combination of two or more.

From the viewpoint of obtaining a lubricating oil composition having low temperature dependence and good lubricating properties even when a mineral oil containing bright stock is used, the poly-α-olefin (B1) is a raw material α-olefin. A poly-α-olefin (hereinafter also referred to as “m-PAO”) obtained by polymerization using a metallocene catalyst is preferred.

The content of the poly-α-olefin (B1) in the synthetic oil (B) is preferably 50 to 100% by mass, 65 to 100% by mass, based on the total amount (100% by mass) of the synthetic oil (B), and further It is preferably 80 to 100% by mass, more preferably 90 to 100% by mass.

<Phosphate ester (C)>
In the lubricating oil composition of the present invention, even when a mineral oil containing bright stock is used, the lubricating oil composition has improved lubricating properties, in particular, improved wear resistance and thermal stability. Contains ester (C).
Examples of the phosphate (C) include neutral phosphates such as aryl phosphates, alkyl phosphates, alkenyl phosphates and alkylaryl phosphates; monoaryl acid phosphates, diaryl acid phosphates, monoalkyl acid phosphates, dialkyl acid phosphates, mono Acidic phosphate esters such as alkenyl acid phosphates and dialkenyl acid phosphates; acidic phosphites such as acid phosphite, dialkyl acid phosphite, monoalkenyl acid phosphite, dialkenyl acid phosphite;
The above acid phosphates and acid phosphites may be amine salts.
Moreover, these phosphate esters (C) may be used alone or in combination of two or more.

In the lubricating oil composition of the present invention, from the viewpoint of improving lubricating properties, in particular, improving wear resistance and thermal stability, the content of the phosphate ester (C) in terms of phosphorus atoms is the lubricating oil composition Based on the total amount (100% by mass) of 0.050 to 0.200% by mass, preferably 0.055 to 0.150% by mass, more preferably 0.060 to 0.110% by mass, still more preferably is 0.065 to 0.100% by mass.
In this specification, the content in terms of phosphorus atoms means the value measured according to JPI-5S-38-03.

In the lubricating oil composition of one aspect of the present invention, in particular, from the viewpoint of improving the thermal stability and maintaining excellent wear resistance even when continued use in a high temperature environment, The phosphate ester (C) preferably contains a compound (C1) selected from an acidic phosphate ester and an amine salt of an acidic phosphate ester, and contains the compound (C1) and a neutral phosphate ester (C2). is more preferred.

From the above viewpoint, in the lubricating oil composition of one aspect of the present invention, the content of the compound (C1) is preferably 0.010 to 0.50 based on the total amount (100% by mass) of the lubricating oil composition. % by mass, more preferably 0.015 to 0.40% by mass, still more preferably 0.020 to 0.30% by mass, and even more preferably 0.025 to 0.25% by mass.

Further, in one aspect of the present invention, when the phosphate ester (C) contains the compound (C1) and the neutral phosphate ester (C2), the content of the neutral phosphate ester (C2) relative to the compound (C1) The ratio [(C2)/(C1)] is preferably 2.0 to 40, more preferably 2.2 to 32, still more preferably 2.4 to 25, and even more preferably 2.5 in mass ratio. ~15.

As the acidic phosphate that can be selected as the compound (C1), a compound represented by the following general formula (c1) is preferable.

n is 1 or 2 in said general formula (c1). Each R ^a is independently an alkyl group having 1 to 18 (preferably 1 to 15) carbon atoms.
When n is 2, a plurality of R ^a may be the same or different from each other.

As the amine salt of an acidic phosphoric acid ester that can be selected as the compound (C1), an amine salt of the compound represented by the general formula (c1) is preferable. The amine constituting the amine salt is preferably a compound represented by the following general formula (ci).

In the general formula (ci), q represents an integer of 1-3.
Each R ^c is independently an alkyl group having 6 to 18 carbon atoms, an alkenyl group having 6 to 18 carbon atoms, an aryl group having 6 to 18 ring carbon atoms, an arylalkyl group having 7 to 18 carbon atoms, or an arylalkyl group having 7 to 18 carbon atoms. 6-18 hydroxyalkyl groups.
In addition, when a plurality of R ^c are present, the plurality of R ^c may be the same or different from each other.

As the neutral phosphate (C2), compounds represented by the following general formula (c2-1) are preferable, and compounds represented by the following general formula (c2-2) are more preferable.

In general formula (c2-1), R ¹ to R ³ are each independently an alkyl group having 1 to 12 carbon atoms, or a ring having 6 to 6 carbon atoms substituted with an alkyl group having 1 to 12 carbon atoms. 18 aryl groups.

In general formula (c2-2), R ¹¹ to R ¹³ are each independently an alkyl group having 1 to 12 carbon atoms, preferably an alkyl group having 1 to 4 carbon atoms.
p1 to p3 are each independently an integer of 1 to 5, preferably an integer of 1 to 2, and more preferably 1.

<Antioxidant (D)>
The lubricating oil composition of one aspect of the present invention preferably further contains an antioxidant (D).
In the lubricating oil composition of one aspect of the present invention, the content of the antioxidant (D) is based on the total amount (100% by mass) of the lubricating oil composition, preferably 0.1 to 7.0% by mass. , more preferably 0.2 to 5.0% by mass, still more preferably 0.3 to 3.0% by mass.

In one aspect of the present invention, the antioxidant (D) preferably contains one or more selected from phenolic antioxidants (D1) and amine antioxidants (D2), and phenolic antioxidants It is more preferable to contain both the agent (D1) and the amine antioxidant (D2).

In one aspect of the present invention, the content ratio [(D1)/(D2)] of the phenolic antioxidant (D1) and the amine antioxidant (D2) is a mass ratio, preferably from 1/5 to 5/1, more preferably 1/4 to 4/1, even more preferably 1/3 to 3/1.

Phenolic antioxidants (D1) include, for example, 2,6-di-t-butylphenol, 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butyl-4- Monophenols such as ethylphenol, isooctyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate Diphenol compounds such as 4,4'-methylenebis(2,6-di-t-butylphenol) and 2,2'-methylenebis(4-ethyl-6-t-butylphenol); Hindered phenol compounds ; and the like.

Examples of the amine antioxidant (D2) include diphenylamine compounds such as alkylated diphenylamine having an alkyl group having 3 to 20 carbon atoms; α-naphthylamine, phenyl-α-naphthylamine, alkyl naphthylamine compounds such as substituted phenyl-α-naphthylamine having a group;

<Additives for lubricating oils>
The lubricating oil composition of one aspect of the present invention may contain lubricating oil additives other than the components (C) and (D) as long as the effects of the present invention are not impaired.
Such lubricating oil additives include, for example, viscosity index improvers, pour point depressants, detergents, dispersants, rust inhibitors, metal deactivators, demulsifiers, defoamers and the like.
Each of these lubricating oil additives may be used alone, or two or more of them may be used in combination.

The content of each of these lubricating oil additives can be appropriately adjusted within a range that does not impair the effects of the present invention. ~10% by mass.

In the present specification, additives such as viscosity index improvers and antifoaming agents are diluted and dissolved in a part of the above-mentioned mineral oil (A) in consideration of handling properties and solubility in mineral oil (A). It may be mixed with other ingredients in the form of a solid solution.
In such a case, in this specification, the above-mentioned content of additives such as antifoaming agents and viscosity index improvers means the content in terms of active ingredients excluding diluent oil (in terms of resin content). .

The lubricating oil composition of one aspect of the present invention may contain an extreme pressure agent other than the component (C) as long as the effect of the present invention is not impaired. It is preferable that the content of the sulfur atom-containing extreme pressure agent is as low as possible.
Examples of sulfur atom-containing extreme pressure agents include sulfur-based extreme-pressure agents such as dibenzyl disulfide; sulfur-phosphorus-based extreme pressure agents such as 0,0,0-triphenylphosphorothioate; and the like.

In the lubricating oil composition of one aspect of the present invention, the content of the sulfur atom-containing extreme pressure agent in terms of sulfur atoms is preferably 0.12% by mass based on the total amount (100% by mass) of the lubricating oil composition. less than, more preferably less than 0.07% by mass, and even more preferably less than 0.01% by mass.
In the present specification, the content in terms of sulfur atoms means a value measured according to JIS K2541-6:2013.

[Characteristics and uses of lubricating oil composition]
The lubricating oil composition of the present invention uses a mineral oil containing bright stock, and is superior in terms of cost reduction, has low temperature dependence, and has good lubricating properties, particularly wear resistance.
The lubricating oil composition of one embodiment of the present invention was subjected to a four-ball test in accordance with ASTM D4172 under the conditions of oil temperature of 60 ° C., number of rotations of 1200 rpm, load of 392 N, and test time of 60 minutes. The wear scar diameter of the stationary ball (the wear scar diameter determined by the four-ball test before the thermal stability test) is preferably 0.55 mm or less, more preferably 0.50 mm or less, and even more preferably 0.47 mm or less.

In addition, the lubricating oil composition of one aspect of the present invention was subjected to a thermal stability test at 150 ° C. for 168 hours in accordance with JIS K2540, then an oil temperature of 60 ° C., a rotation speed of 1200 rpm, a load of 392 N, and a test. The wear scar diameter of the fixed ball after the four-ball test in accordance with ASTM D4172 (abrasion scar diameter in the four-ball test after the thermal stability test) is preferably 0.5. It is 70 mm or less, more preferably 0.65 mm or less, still more preferably 0.60 mm or less.

The lubricating oil composition of the present invention can be applied to various lubricating applications, but it has good lubricating properties such as low temperature dependence and excellent wear resistance, so it is preferably used in oil-air lubrication systems.

That is, the present invention can also provide an oil-air lubrication system shown in (1) below and a method of using a lubricating oil composition shown in (2) below.
Preferred aspects of the lubricating oil composition defined in (1) and (2) below are as described above.

(1) containing 30% by mass or more of mineral oil (A) containing bright stock (A1),
Further containing synthetic oil (B) and phosphate ester (C),
The content of the synthetic oil (B) is less than 70% by mass,
The content of the phosphate ester (C) in terms of phosphorus atoms is 0.050 to 0.200% by mass,
An oil-air lubrication system for supplying a lubricating oil composition having a viscosity index of 150 or more into a pipe by means of compressed air.

(2) containing 30% by mass or more of mineral oil (A) containing bright stock (A1),
Further containing synthetic oil (B) and phosphate ester (C),
The content of the synthetic oil (B) is less than 70% by mass,
The content of the phosphate ester (C) in terms of phosphorus atoms is 0.050 to 0.200% by mass,
A method for using a lubricating oil composition having a viscosity index of 150 or more in an oil-air lubricating system.

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited by these examples. Each component used in Examples , Reference Examples and Comparative Examples and various properties of the obtained lubricating oil compositions were measured according to the following methods.

<Kinematic viscosity, viscosity index>
It was measured and calculated according to JIS K 2283:2000.
<Paraffin content (% C _P ), naphthene content (% C _N ), and aromatic content (% C _A )>
Measured by ASTM D-3238 ring analysis (ndM method).
<Phosphorus Atom Content>
Measured according to JPI-5S-38-03.
<Content of sulfur atom>
Measured according to JIS K2541-6:2013.

Examples 1-6 , Reference Examples , Comparative Examples 1-2
Mineral oil, synthetic oil and various additives shown below were added in the blending amounts shown in Table 1 and thoroughly mixed to prepare lubricating oil compositions.
Details of mineral oils and various additives used in Examples , Reference Examples and Comparative Examples are as follows.

<Mineral oil>
- "Bright stock": Bright stock classified as Group II in the API category, kinematic viscosity at 100°C = 30.9 mm ² /s, viscosity index = 107, % _CP = 73, % _CN = 27, % _CA = 0.
- "500N mineral oil": mineral oil classified as Group II in the API category, kinematic viscosity at 100°C = 10.9 mm ² /s, viscosity index = 107, % C _P = 72, % C _N = 28, % C _A = 0.
<Synthetic oil>
• "m-PAO": poly α-olefin obtained using a metallocene catalyst, kinematic viscosity at 100°C = 147.4 mm ² /s, viscosity index = 202.
- "PAO": poly-α-olefin, kinematic viscosity at 100°C = 100 mm ² /s, viscosity index = 170.

<Phosphate ester>
- "Amine salt of acidic phosphoric acid ester (1)": an amine salt of acidic phosphoric acid ester (1) in which R ^a is a methyl group and n is 1 or 2 in the general formula (c1).
- "Amine salt of acidic phosphate (2)": an amine of acidic phosphate (2) in which R ^a is an isotridecyl group (C13 alkyl group) and n is 1 or 2 in the general formula (c1) salt.
- "Acidic phosphate (3)": an acidic phosphate (3) in which R ^a is an octadecyl group (C18 alkyl group) and n is 1 or 2 in the general formula (c1).
- "Neutral phosphate ester (1)": tricresyl phosphate, a compound in which R ¹¹ to R ¹³ are methyl groups and p1 to p3 are 1 in the general formula (c2-2).
- "Neutral phosphate ester (2)": mono- or di-t-butyltriphenyl phosphate, R ¹¹ to R ¹³ in the general formula (c2-2) are t-butyl groups, p1 to p3 are 1 or 2.

<Extreme pressure agent other than phosphorus-based>
- "Sulfur-based extreme pressure agent": dibenzyl disulfide - "Sulfur-phosphorus-based extreme pressure agent": 0,0,0-triphenylphosphorothioate, phosphorus atom content = 8.9% by mass.
<Antioxidant>
• "Phenolic antioxidant": Octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate.
- "Amine-based antioxidant": monobutylphenylmonooctylphenylamine.
<Other additives>
• "Pour point depressants": polymethacrylates.
• "Metal deactivator": benzotriazole.
- "Rust inhibitor": an ester of alkenyl succinic acid and a polyhydric alcohol.
- "Antifoaming agent": Silicone antifoaming agent.

Table 1 shows the 100° C. kinematic viscosity and viscosity index of the lubricating oil compositions prepared in Examples, Reference Examples and Comparative Examples.
Also, using each lubricating oil composition as a sample oil, the wear scar diameter was measured by a four-ball test before and after the thermal stability test according to the following method. These measurement results are also shown in Table 1.

[Wear scar diameter by 4-ball test before thermal stability test]
A four-ball test in accordance with ASTM D4172 was performed under the conditions of an oil temperature of 60°C, a rotation speed of 1200 rpm, a load of 392 N, and a test time of 60 minutes. It was defined as "abrasion scar diameter by four-ball test before thermal stability test".

[Wear scar diameter by four-ball test after thermal stability test]
The sample oil was subjected to a thermal stability test at 150° C. for 168 hours in accordance with JIS K2540.
Then, the sample oil after the thermal stability test was subjected to a four-ball test in accordance with ASTM D4172 under the conditions of oil temperature of 60 ° C., number of rotations of 1200 rpm, load of 392 N, and test time of 60 minutes. The wear scar diameter (mm) was measured, and the value was defined as "the wear scar diameter by the four-ball test after the thermal stability test".

According to Table 1, the lubricating oil compositions of Examples 1 to 6 and Reference Example have a high viscosity index and low temperature dependence, and compared to Comparative Examples 1 and 2, the four-ball test before the thermal stability test It can be seen that the wear scar diameter is small and the wear resistance is excellent.
In Comparative Examples 1 and 2, the value of the wear scar diameter in the four-ball test before the thermal stability test was large, resulting in poor wear resistance. The test was terminated without measuring the value of

Claims (10)

A lubricating oil composition containing 30% by mass or more of mineral oil (A) containing bright stock (A1) based on the total amount of the lubricating oil composition,
Further containing a synthetic oil (B) and a phosphate ester (C),
The content of the synthetic oil (B) is 30% by mass or more and less than 70% by mass based on the total amount of the lubricating oil composition,
The synthetic oil (B) contains 80 to 100% by mass of the poly-α-olefin (B1),
The content of the phosphate ester (C) in terms of phosphorus atoms is 0.050 to 0.200% by mass based on the total amount of the lubricating oil composition,
The content of the sulfur atom-containing extreme pressure agent in terms of sulfur atom is less than 0.07% by mass based on the total amount of the lubricating oil composition.
A viscosity index of 150 or more,
lubricating oil composition. The lubricating oil composition according to claim 1, wherein the bright stock (A1) has a kinematic viscosity at 100°C of 28.0 mm ² /s or more. The lubricating oil composition according to claim 1 or 2, wherein the content of bright stock (A1) in mineral oil (A) is 5 to 70% by mass based on the total amount of mineral oil (A). The lubricating oil composition according to any one of claims 1 to 3 , wherein the synthetic oil (B) has a viscosity index of 130 or more. The lubricating oil composition according to any one of claims 1 to 4 , wherein the synthetic oil (B) has a kinematic viscosity at 100°C of 80 to 180 mm ² /s. The lubricating oil composition according to any one of claims 1 to 5 , wherein the phosphate (C) comprises a compound (C1) selected from acidic phosphates and amine salts of acidic phosphates. 7. Any one of claims 1 to 6 , wherein the phosphate ester (C) comprises a compound (C1) selected from an acidic phosphate ester and an amine salt of an acidic phosphate ester, and a neutral phosphate ester (C2). The lubricating oil composition according to claim 1. The lubricating oil composition according to claim 7 , wherein the content ratio of the neutral phosphate (C2) to the compound (C1) [(C2)/(C1)] is 2.0 to 40 in mass ratio. . The lubricating oil composition according to any one of claims 1 to 8 , further comprising a sulfur atom-containing extreme pressure agent. The lubricating oil composition according to any one of claims 1 to 9 , which is used in an oil-air lubrication system.