JP2018016706A - Lubricant composition for plain bearings, and plain bearing lubrication method and plain bearing employing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lubricant composition for plain bearings having excellent heat resistance and wear resistance, and a plain bearing lubrication method and a plain bearing employing the same.SOLUTION: The present invention provides a lubricant composition for plain bearings containing a base oil, and a phosphoester selected from a phosphoric monoester and a phosphoric diester, with a content of the phosphoric diester in the phosphoester being 70 mass% or more and 100 mass% or less, and a plain bearing lubrication method and a plain bearing employing the same.SELECTED DRAWING: None

Description

  The present invention relates to a lubricating oil composition for a sliding bearing, a sliding bearing lubrication method using the same, and a sliding bearing.

  Sliding bearings are used in various devices such as engine crankshafts, suspensions, and other industrial machines used in automobiles, ships, construction machinery, agricultural machinery, and the like. For example, the shock absorber incorporated in the suspension is generally used as a cylinder structure utilizing the flow resistance of oil, and specifically, a hydraulic piston having a small hole is used. The slide bearing is employed in a form in which a bush serving as a bearing is provided at a sliding portion between the cylinder of the shock absorber and the piston rod. Since the sliding bearing of the shock absorber receives a large lateral force due to the expansion and contraction motion, the lubricating oil composition used for the sliding bearing has heat resistance against heat generated on the friction surface at that time, and the friction surface Abrasion resistance to prevent wear is required. In particular, since the shock absorber incorporated in the strut suspension receives a lateral force of 300 to 400 kgf, the lubricating oil composition to be used is required to have extremely excellent heat resistance and wear resistance.

  Conventionally, in order to obtain heat resistance of a lubricating oil composition, it has been studied to use a phosphorus-based additive such as tricresyl phosphate in the lubricating oil composition (for example, Patent Document 1). However, phosphate triesters such as tricresyl phosphate do not provide sufficient performance in terms of wear resistance.

International Publication No. 2010/027019 Pamphlet

  By the way, phosphoric acid diesters such as dialkyl or dialkenyl acid phosphate are known as additives for improving wear resistance. Commercial products of these phosphoric acid diesters, for example, commercial products of dioleyl acid phosphate, are generally sold as a mixture containing a monoester and a diester in a ratio of 1: 1. When this commercial product was used as an additive, it was confirmed that it was extremely excellent in wear resistance although sufficient performance was not obtained in terms of heat resistance. However, in a lubricating oil composition, particularly a sliding bearing lubricating composition, both heat resistance and wear resistance are particularly strongly demanded, and further studies focusing on phosphoric acid monoesters and phosphoric acid diesters, The situation is not enough.

  The present invention has been made in view of such circumstances, and provides a lubricating oil composition for a sliding bearing having excellent heat resistance and wear resistance, a lubricating method for a sliding bearing using the same, and a sliding bearing. For the purpose.

  The present inventors focused on phosphoric acid monoesters and phosphoric acid diesters, and examined whether heat resistance could be improved in addition to extremely excellent wear resistance. Phosphoric acid diesters alone or phosphoric acid diesters and phosphoric acid esters It has been found that the above-mentioned problems can be solved by using an acid monoester mixed in a predetermined ratio, and the following invention has been completed. The present invention provides the following lubricating oil composition, a lubricating method for a sliding bearing using the same, and a sliding bearing.

[1] A base oil and a phosphate ester selected from a phosphate monoester and a phosphate diester, and the content of the phosphate diester in the phosphate ester is 70% by mass or more and 100% by mass or less. Lubricating oil composition for plain bearings.
[2] A sliding bearing lubrication method using the lubricating oil composition for a sliding bearing according to [1].
[3] A sliding bearing using the lubricating oil composition for sliding bearings according to [1].

  ADVANTAGE OF THE INVENTION According to this invention, the lubricating oil composition for sliding bearings which has the outstanding heat resistance and abrasion resistance, the lubricating method of a sliding bearing using the same, and a sliding bearing can be provided.

  Hereinafter, an embodiment of the present invention (hereinafter may be referred to as “this embodiment”) will be described in more detail.

[Lubricating oil composition for sliding bearings]
The lubricating oil composition for plain bearings of this embodiment contains a base oil and a phosphate ester selected from a phosphate monoester and a phosphate diester, and the phosphate diester content in the phosphate ester is 70. It is said that they are mass% or more and 100 mass% or less.

(Base oil)
There is no restriction | limiting in particular as base oil contained in this embodiment, Mineral oil may be sufficient and synthetic oil may be sufficient.
Mineral oil includes atmospheric residual oil obtained by atmospheric distillation of paraffinic, naphthenic and intermediate-based crude oil; distillate obtained by vacuum distillation of the atmospheric residual oil; Mineral oil refined by subjecting the oil to one or more of solvent removal, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, etc., for example, light neutral oil, medium neutral oil Oil, heavy neutral oil, bright stock and the like. Moreover, the mineral oil obtained by isomerizing the wax (GTL wax) manufactured by a Fischer-Tropsch method etc. is also mentioned.

  Synthetic oils include, for example, polyα-olefins such as polybutene, ethylene-α-olefin copolymers, α-olefin homopolymers or copolymers; various esters such as polyol esters, dibasic acid esters, and phosphate esters. Various ethers such as polyphenyl ether; polyglycol; alkylbenzene; alkylnaphthalene and the like.

  As the base oil, the above-described mineral oils may be used alone or in combination of plural kinds, and synthetic oils may be used alone or in combination of plural kinds. Further, one or more mineral oils and one or more synthetic oils may be combined and used as a mixed oil.

The viscosity of the base oil is not particularly limited, but the kinematic viscosity at 100 ° C. is preferably 1.5 mm ² / s or more, more preferably 1.7 mm ² / s or more, and further preferably 2 mm ² / s or more. The upper limit is preferably 5 mm ² / s or less, more preferably 4 mm ² / s or less, and still more preferably 3 mm ² / s or less. Further, 40 ° C. kinematic viscosity of the base oil is preferably at least ^{2 mm} 2 / s, more preferably at least ^{5 mm} 2 / s, more preferably not less than ^{7 mm} 2 / s, preferably 15 mm ² / s or less as the upper limit, 9 mm ² / S or less is more preferable, 8 mm ² / s or less is more preferable, and less than 8 mm ² / s is particularly preferable. When the base oil having a kinematic viscosity within the above range is used, heat resistance and wear resistance are improved, and handling for a sliding bearing becomes easier.
From the same viewpoint, the viscosity index of the base oil is preferably 75 or more, more preferably 78 or more, and still more preferably 80 or more. In this specification, kinematic viscosity and viscosity index are values measured using a glass capillary viscometer in accordance with JIS K 2283: 2000.

  The content of the base oil based on the total amount of the lubricating oil composition is usually 50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, and still more preferably 85% by mass or more. Moreover, 99.5 mass% or less is preferable, as for an upper limit, 99 mass% or less is more preferable, and 98.5 mass% or less is still more preferable. By setting the content of the base oil in the above range, heat resistance and wear resistance are improved.

(Phosphate ester)
The phosphoric acid ester contained in this embodiment is selected from phosphoric acid monoesters and phosphoric acid diesters, and the phosphoric acid diester content in the phosphoric acid esters is 70% by mass or more and 100% by mass or less. That is, the phosphate ester may be a mixture of a phosphate monoester and a phosphate diester or a phosphate diester alone as long as the content of the phosphate diester is within the above range. Moreover, as for phosphoric acid monoester and phosphoric acid diester, all may be single 1 type, and may be used in combination of multiple types.

  In this embodiment, when the content of the phosphoric acid diester with respect to the total amount of the phosphoric acid monoester and the phosphoric acid diester is less than 70% by mass, excellent heat resistance and wear resistance cannot be obtained. Further, from the viewpoint of improving heat resistance and wear resistance, the content of the phosphoric acid diester is preferably larger with respect to the total amount of the phosphoric acid monoester and the phosphoric acid diester, specifically, 75% by mass or more is preferable. 80 mass% or more is more preferable, 90 mass% or more is still more preferable, and it is especially preferable that it is 100 mass%.

  Phosphoric acid monoesters and phosphoric acid diesters are phosphoric additives commonly used in lubricating oils. For example, phosphoric acid esters and acidic phosphoric acid esters can be appropriately selected and used. From the viewpoint of further improving the wear resistance, a compound represented by the following general formula (1), that is, an acidic phosphoric acid monoester and an acidic phosphoric acid diester are preferably exemplified.

In General Formula (1), R ¹ is a hydrocarbon group having 2 to 28 carbon atoms, and n is 1 or 2. When n is 2, the plurality of R ¹ may be the same as or different from each other.
Examples of the hydrocarbon group include linear, branched, or cyclic alkyl groups, alkenyl groups, and aryl groups. Among these, from the viewpoint of improving heat resistance and wear resistance, an alkyl group and an alkenyl group are preferable, and an alkenyl group is more preferable. From the same viewpoint, the number of carbon atoms is preferably 8 or more, more preferably 12 or more, still more preferably 16 or more, more preferably 28 or less, more preferably 24 or less, and still more preferably 20 or less.

More specifically, examples of the alkyl group include various octyl groups, various nonyl groups, various decyl groups, various undecyl groups, various dodecyl groups, various tridecyl groups, various tetradecyl groups, various pentadecyl groups, various hexadecyl groups, and various types. Examples include heptadecyl group, various octadecyl groups, various nonadecyl groups, various icosyl groups, various heicosyl groups, various docosyl groups, various tricosyl groups, various tetracosyl groups, and the like. Here, “various” means to include a functional group having a predetermined number of carbon atoms including linear, branched, cyclic, and isomers thereof.
Examples of the alkenyl group include various octenyl groups, various nonenyl groups, various decenyl groups, various undecenyl groups, various dodecenyl groups, various tridecenyl groups, various tetradecenyl groups, various pentadecenyl groups, various hexadecenyl groups, various heptadecenyl groups, and various octadecenyl groups. And various nonadecenyl groups, various icosenyl groups, various heicocosenyl groups, various dococenyl groups, various tricocenyl groups, various tetracocenyl groups, and the like.

n is 1 or 2. When n is 2, that is, a phosphoric acid diester, a plurality of R ¹ may be the same as or different from each other. In the present embodiment, as described above, the phosphate ester is preferably a phosphate diester, that is, n is preferably 2.

Specific examples of the phosphate ester represented by the general formula (1) include phosphorus such as monolauryl acid phosphate, monomyristyl acid phosphate, monopalmityl acid phosphate, monostearyl acid phosphate, monooleyl acid phosphate, and the like. Acid monoesters; phosphoric acid diesters such as dilauryl acid phosphate, dimyristyl acid phosphate, dipalmityl acid phosphate, distearyl acid phosphate, dioleyl acid phosphate and the like.
In the present embodiment, the phosphate ester is preferably a phosphate diester in which R ¹ in the general formula (1) is an alkenyl group having 16 to 20 carbon atoms and n is 2, and among these, The phosphoric acid diester is preferably dioleyl acid phosphate.

The content of phosphoric acid ester in terms of phosphorus atom is 0.01 on the basis of the total amount of the lubricating oil composition, considering the viewpoint of efficiently improving heat resistance and wear resistance, and the solubility of the phosphoric acid ester in the base oil. % By mass or more is preferable, 0.03% by mass or more is more preferable, and 0.05% by mass or more is more preferable. Moreover, 0.5 mass% or less is preferable, 0.4 mass% or less is more preferable, and 0.3 mass% or less is still more preferable.
Further, from the same viewpoint, the content of the phosphate ester based on the total amount of the lubricating oil composition is preferably 0.5% by mass or more, more preferably 1% by mass or more, and further preferably 1.5% by mass or more. . Moreover, 5 mass% or less is preferable, 4 mass% or less is more preferable, and 3 mass% or less is still more preferable.

(Optional additive)
The lubricating oil composition of the present embodiment includes, for example, viscosity index improvers, antioxidants, metal detergents, dispersants, friction modifiers, antiwear agents, extreme pressure agents, pour point depressants as optional additional components. Other additives such as a metal deactivator, a rust inhibitor, and an antifoaming agent can be appropriately selected and blended. These additives can be used alone or in combination of two or more.
The total content of these additives is not particularly limited as long as it does not contradict the effects of the present invention, but considering the effect of adding the additives, 0.1 to 20% by mass based on the total amount of the composition Is preferable, 1-15 mass% is more preferable, and 3-15 mass% is still more preferable.

  As the viscosity index improver, for example, polymethacrylate, dispersed polymethacrylate, olefin copolymer (for example, ethylene-propylene copolymer), dispersed olefin copolymer, styrene copolymer (for example, Styrene-diene hydrogenated copolymer) and the like, and polymethacrylates are preferred.

  Antioxidants include monocyclic phenolic antioxidants such as 2,6-di-tert-butyl-p-cresol and 2,6-di-tert-butyl-4-ethylphenol; 4,4′-methylenebis Polycyclic phenolic antioxidants such as (2,6-di-tert-butylphenol) and 2,2′-methylenebis (4-ethyl-6-tert-butylphenol); 2,6-di-tert-butyl-4 -(4,6-bis (octylthio) -1,3,5-triazin-2-ylamino) phenol, thioterpene compounds such as a reaction product of phosphorus pentasulfide and pinene; dilaurylthiodipropionate, distearylthio And sulfur-based antioxidants such as dialkylthiodipropionates such as dipropionate.

Examples of the metal detergent include neutral metal sulfonates, neutral metal phenates, neutral metal salicylates, neutral metal phosphonates, basic metal sulfonates, basic metals containing alkaline earth metals such as calcium as metal species. Examples include phenates, basic metal salicylates, basic metal phosphonates, overbased metal sulfonates, overbased metal phenates, overbased metal salicylates, and overbased metal phosphonates.
As the dispersant, for example, monovalent or bivalent typified by boron-free succinimides, boron-containing succinimides, benzylamines, boron-containing benzylamines, succinates, fatty acids or succinic acid. Ashless dispersants such as polycarboxylic acid amides.

Examples of the friction modifier include fatty acid esters and fatty acid amides having at least one alkyl group or alkenyl group having 6 to 30 carbon atoms, particularly a linear alkyl group or linear alkenyl group having 6 to 30 carbon atoms in the molecule. Ashless friction modifiers such as fatty acids, fatty alcohols, and fatty acid ethers; molybdenum friction modifiers such as molybdenum dithiocarbamate (MoDTC), molybdenum dithiophosphate (MoDTP), and amine salts of molybdic acid.
Examples of the antiwear agent include zinc dialkyldithiophosphate (ZnDTP), zinc phosphate, zinc dithiocarbamate, molybdenum dithiocarbamate, molybdenum dithiophosphate, disulfides, sulfurized olefins, sulfurized fats and oils, sulfurized esters, and thiocarbonates. Sulfur-containing compounds such as thiocarbamates and polysulfides; for example, phosphites such as triethyl phosphite and tricresyl phosphite, tributyl phosphate, tristearyl phosphate, trioleyl phosphate, ethyl Phosphoric esters such as phenyl diphenyl phosphate, phosphoric esters such as phosphonates, and phosphorus-containing compounds such as amine salts or metal salts thereof; thiophosphites, thiophosphate esters S, thiophosphoric acid esters, and sulfur and phosphorus-containing antiwear agents, such as those amine salts or metal salts.

Examples of extreme pressure agents include sulfur-based extreme pressure agents such as sulfides, sulfoxides, sulfones, thiophosphinates, halogen-based extreme pressure agents such as chlorinated hydrocarbons, and organometallic extreme pressure agents. It is done.
Examples of the pour point depressant include ethylene-vinyl acetate copolymer, condensate of chlorinated paraffin and naphthalene, condensate of chlorinated paraffin and phenol, polymethacrylate, polyalkylstyrene, and the like.
Examples of the metal deactivator include benzotriazole, tolyltriazole, thiadiazole, and imidazole compounds.
Examples of the rust preventive include petroleum sulfonate, alkylbenzene sulfonate, dinonylnaphthalene sulfonate, alkenyl succinic acid ester, polyhydric alcohol ester and the like.
Examples of the antifoaming agent include silicone oil, fluorosilicone oil, and fluoroalkyl ether.

(Amine compound)
It is preferable that the lubricating oil composition of this embodiment does not contain an amine compound. In the present embodiment, the heat resistance and the wear resistance can be improved at the same time by using a predetermined phosphate ester, so that it is not necessary to use an amine compound for improving these performances, and fewer additives. It is possible to exert an excellent effect. Moreover, the effect by phosphate ester may fall by including an amine compound.
Here, “does not contain” means that the amine compound is not intentionally added and does not contain substantially, and the content of the amine compound based on the total amount of the lubricating oil composition is 0% by mass. It is a concept including an embodiment and an embodiment of more than 0% by mass and 0.1% by mass or less, preferably 0.05% by mass or less, more preferably 0.03% by mass or less. Even if the amine compound is contained, the effect of the phosphate ester is not lowered as long as the content is within the above range.
Moreover, said "amine compound" is an aliphatic polyamine shown by following General formula (2) used as an additive of a lubricating oil composition, for example, a friction modifier and a friction reducing agent.

In the general formula (2), ^{R 2} represents an alkyl or alkenyl group having 6 to 22 carbon atoms, ^{R 3} represents an alkylene group having 2 to 4 carbon atoms, m is an integer of 1 to 4. When m is 2 to 4, the plurality of R ³ may be the same or different.

(Various physical properties of lubricating oil composition)
100 ° C. The kinematic viscosity of the lubricating oil composition of the present embodiment is preferably at least 1.5 mm ² / s, more preferably at least 1.8 mm ² / s, more preferably more than ^{2 mm} 2 / s. Moreover, 5 mm < ² > / s or less is preferable, 4 mm < ² > / s or less is more preferable, and 3 mm < ² > / s or more is still more preferable. 40 ° C. The kinematic viscosity of the lubricating oil composition of the present embodiment is preferably at least ^{2 mm} 2 / s, more preferably at least ^{5 mm} 2 / s, more preferably not less than ^{7 mm} 2 / s, more ^{8 mm} 2 / s is particularly preferred. And is preferably 15 mm ² / s or less, more preferably 12 mm ² / s, still more preferably 10 mm ² / s or less, particularly preferably ^{9 mm} 2 / s. Further, the viscosity index of the lubricating oil composition of the present embodiment is preferably 75 or more, more preferably 78 or more, and still more preferably 80 or more. Here, the method for measuring the kinematic viscosity and the viscosity index is the same as the above base oil.
When the kinematic viscosity and viscosity index of the lubricating oil composition of the present embodiment are within the above ranges, heat resistance and wear resistance are improved, and handling for a sliding bearing becomes easier.

Since the lubricating oil composition for sliding bearings of this embodiment has excellent heat resistance and wear resistance, the crankshafts and suspensions of engines used for sliding bearings, for example, automobiles, ships, construction machinery, agricultural machinery, etc. It is used for sliding bearings used in various equipment such as other industrial machines. Especially, it is used suitably for the sliding bearing of the shock absorber integrated in a suspension. The shock absorber built into the suspension is generally of a double cylinder type or a single cylinder type, and can be used as a sliding bearing for any type of shock absorber. It can be used.
The lubricating oil composition of the present embodiment is further used for various industrial machines such as an internal combustion engine, a hydraulic machine, a turbine, a compressor, a machine tool, and a cutting machine, which require excellent heat resistance and wear resistance. In general, it can also be used for gears, rolling bearings and the like provided in these industrial machines.

[Lubrication method and sliding bearing of sliding bearing]
The sliding bearing lubrication method of the present embodiment uses the lubricating oil composition for sliding bearings of the present embodiment. As described above, the lubricating oil composition for slide bearings of this embodiment has excellent heat resistance and wear resistance. Therefore, the lubrication method of the slide bearing of the present embodiment is the lubrication of the slide bearing used in various devices such as engine crankshafts, suspensions, and other industrial machines used in automobiles, ships, construction machinery, agricultural machinery and the like. The method is preferably employed.

  Moreover, the sliding bearing of this embodiment uses the lubricating oil composition for sliding bearings of this embodiment. The slide bearing of this embodiment is suitably employed as a slide bearing used in various devices such as engine crankshafts, suspensions, and other industrial machines used in automobiles, ships, construction machines, agricultural machines, and the like.

EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.
In addition, evaluation of each physical property in this invention was performed with the following method.
[Evaluation method]
1. Measurement of kinematic viscosity The kinematic viscosity at 40 ° C and 100 ° C was measured according to JIS K 2283: 2000.
2. Measurement of viscosity index The viscosity index was measured according to JIS K 2283: 2000.
3. Measurement of phosphorus atom content Measured according to JIS-5S-38-92.
4). Evaluation of heat resistance 30 cc of a lubricating oil composition (hereinafter referred to as “sample oil”) of each example and comparative example was poured into a 50 cc bottle, to which a bronze plate and a steel (SPCC) plate (1 cm × 1 cm × 2 mm (thickness)) was put in, and a thermal stability test was performed by leaving it in an environment of 100 ° C. for 24 hours.
The appearance (color) of the test oil before and after the thermal stability test was evaluated according to the following criteria.
A. Colorless and transparent B. Pale yellow C.I. Light brown The presence or absence of corrosion of the bronze plate after the black thermal stability test was evaluated according to the following criteria.
A. No corrosion was observed.
B. Slight corrosion was confirmed.
C. Corrosion was confirmed.
The presence or absence of sludge generation after the thermal stability test was evaluated according to the following criteria.
A. No sludge was confirmed.
B. Slight sludge was confirmed.
C. Sludge was confirmed.
Moreover, about the sample oil after a thermal stability test, n-pentane insoluble matter (A method) was measured.
Appearance (color) is closer to transparency (closer to A), less bronze plate corrosion (closer to A), less sludge (closer to A), and less The smaller the dissolved content, the better the heat resistance.
5. Evaluation of wear resistance A commercially available shock absorber (“54302 KRH (product number)”, manufactured by Nissan Motor Co., Ltd.) was prepared, a slide bearing (φ20 mm) incorporated in the shock absorber, and a shaft (hard chrome-plated product, (φ20 mm) portion was used for this evaluation. After 2 cc of test oil was applied to the shaft, a load (100 kgf) was applied from above the sliding bearing at room temperature (25 ° C.), and the shaft was vibrated (stroke: ± 0.8 mm, vibration frequency: 10 Hz, test time: 120 minutes), and the wear width of the sliding bearing was measured. The smaller the wear width, the better the wear resistance.

Examples 1 and 2 and Comparative Examples 1 to 3
Lubricating oil compositions were prepared with the blending amounts (mass%) shown in Table 1. The obtained lubricating oil composition was used as a test oil, and various evaluations were performed by the above methods. The evaluation results are shown in Table 1. In addition, the detail of each component shown by the 1st table | surface used by the present Example is as follows.
Mineral oil: 60 N (neutral) paraffinic mineral oil (100 ° C. kinematic viscosity: 2.17 mm ² / s, 40 ° C. kinematic viscosity: 7.12 mm ² / s, viscosity index: 109)
-Phosphate ester 1: dioleoyl acid phosphate simple substance-Phosphate ester 2: Mixture of monooleyl acid phosphate (25 mass%) and dioleyl acid phosphate (75 mass%)-Phosphate ester 3: monooleyl acid phosphate (50 (Mass%) and dioleyl acid phosphate (50 mass%) mixture (dioleyl acid phosphate commercial product)
-Phosphate ester 4: tricresyl phosphate

* In Table 1, "-" indicates that it is not blended.

  As is clear from the results of Examples 1 and 2, it was confirmed that the lubricating oil composition of the present embodiment was excellent in heat resistance and wear resistance. On the other hand, the sample oil of Comparative Example 1 to which no phosphate ester was added had a large wear width of 6.64 mm, did not exhibit wear resistance, and contained 50% by mass of monooleyl acid phosphate and dioleyl acid phosphate. Although the sample oil of Comparative Example 2 using the commercially available dioleoyl acid phosphate is excellent in wear resistance, it cannot be said to be sufficient in terms of heat resistance, and a phosphate triester is used. It was confirmed that the sample oil of Comparative Example 3 was not sufficient in terms of heat resistance and wear resistance.

  Since the lubricating oil composition for sliding bearings of the present invention has excellent heat resistance and wear resistance, it is used for sliding bearings, for example, engine crankshafts, suspensions, etc. used in automobiles, ships, construction machinery, agricultural machinery, etc. It is used for sliding bearings used in various other equipment such as industrial machines.

Claims (11)

  A base oil and a phosphate ester selected from a phosphate monoester and a phosphate diester, and the content of the phosphate diester in the phosphate ester is 70% by mass or more and 100% by mass or less. Lubricating oil composition. The lubricating oil composition for a sliding bearing according to claim 1, wherein the phosphoric acid monoester and the phosphoric acid diester are compounds represented by the following general formula (1).

(In General Formula (1), R ¹ is a hydrocarbon group having 2 to 28 carbon atoms, and n is 1 or 2. When n is 2, a plurality of R ¹ may be the same as each other. And may be different.)   The lubricating oil composition for a sliding bearing according to claim 2, wherein the hydrocarbon group is an alkyl group or an alkenyl group. The lubricating oil composition for a sliding bearing according to claim 2, wherein R ¹ is an alkyl group or an alkenyl group having 12 to 24 carbon atoms. The sliding bearing lubricating oil composition according to claim 2, wherein R ¹ is an alkenyl group having 16 to 20 carbon atoms, and n is 2. 4.   The lubricating oil composition for a sliding bearing according to any one of claims 1 to 5, wherein the phosphoric acid diester is dioleyl acid phosphate.   The sliding bearing according to any one of claims 1 to 6, wherein a content of the phosphate ester in terms of phosphorus atom is 0.01% by mass or more and 0.5% by mass or less based on the total amount of the lubricating oil composition. Lubricating oil composition. The lubricating oil composition for a sliding bearing according to any one of claims 1 to 7, wherein the kinematic viscosity at 40 ° C is 2 mm ² / s or more and 15 mm ² / s or less. The lubricating oil composition for a sliding bearing according to claim 1, wherein the base oil has a kinematic viscosity at 40 ° C. of 7 m ² / s or more and 8 mm ² / s or less.   A lubrication method for a sliding bearing using the lubricating oil composition for a sliding bearing according to any one of claims 1 to 9.   A sliding bearing using the lubricating oil composition for a sliding bearing according to any one of claims 1 to 9.