JP2009203275A - Bearing oil composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bearing oil composition which has a lower viscosity at a practical use temperature, is little in evaporation loss, and has improved oxidation stability. <P>SOLUTION: Provided is the bearing oil composition characterized by containing a straight chain aliphatic monocarboxylate having a total carbon number of 26 to 40 obtained by esterifying a 8 to 16C straight chain aliphatic monocarboxylic acid with an alcohol represented by general formula (1), wherein, (n) is an integer of 5 to 11, as a base oil. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a bearing oil composition that can be suitably used for a hydrodynamic bearing or a sintered impregnated bearing used in a bearing portion of a rotating body such as a spindle motor.

Conventionally, a sintered impregnated bearing obtained by impregnating a porous member obtained by sintering a metal powder with a lubricating oil or grease has been used in personal computers, other peripheral devices, AV equipment, automobile electrical systems, and the like. In recent years, hydrodynamic bearings have been put to practical use in models that require high-speed and high-precision shaft rotation, such as hard disk and polygon mirror rotation motors.
As the performance required for lubricating oil for these sintered impregnated bearings and hydrodynamic bearings, as motors become smaller, more precise, and faster, heat resistance, oxidation stability, low evaporation, and wear resistance are improved. Many of them require long life because they are used without replenishment.

  Furthermore, hydrodynamic bearings are also used in portable terminals such as personal computers, AV equipment, digital cameras, and mobile phones, but these are battery-driven, so it is necessary to reduce motor power consumption and battery consumption. It is done. As means for suppressing this power consumption, means such as a low-viscosity base oil is often used as the base oil of the lubricating oil, and a means such as reducing the friction with an additive is used. However, since the base oil generally has a tendency to increase the evaporation loss when the viscosity is lowered, a base oil having a low viscosity at a practical temperature and a reduced evaporation loss is required.

As such lubricating oils for bearings, conventionally, polyα-olefins having excellent fluidity at low temperatures, aliphatic monocarboxylic acids having a specific structure, and dibasic acid diesters represented by di-2-ethylhexyl sebacate , Neopentyl glycol, trimethylolpropane fatty acid ester, and the like as base oils, and various additives have been used (see, for example, Patent Documents 1 to 3).
JP 2000-336383 A JP 2002-146374 A Japanese Patent Application Laid-Open No. 2002-338979

  The present invention has been made in recent years as bearing applications have been expanded and further increased in speed and accuracy, and has a lower viscosity at practical temperatures, less evaporation loss, and oxidation stability. An object is to provide an improved bearing oil composition.

As a result of intensive studies to solve the above problems, the present inventor has found that the following bearing oil composition according to the present invention solves the above problems, and has completed the present invention.
That is, the present invention is as follows.
<1> A linear aliphatic monocarboxylic acid having a total carbon number of 26 to 40 obtained by esterifying an alcohol represented by the following general formula (1) and a linear aliphatic monocarboxylic acid having 8 to 16 carbon atoms. A bearing oil composition comprising an acid ester as a base oil.

In general formula (1), n represents the integer of 5-11.
<2> The bearing oil composition according to <1>, containing 0.05 to 2% by mass of at least one antioxidant selected from the group consisting of amine-based antioxidants and phosphorus-based antioxidants.

<3> The bearing according to <1> or <2>, containing 0.05 to 5% by mass of at least one antiwear agent selected from the group consisting of phosphorus-based antiwear agents and polyoxyethylene sorbitol esters. Oil composition.

  According to the present invention, it is possible to provide a bearing oil composition having a lower viscosity at a practical temperature, less evaporation loss, and improved oxidation stability.

  The bearing oil composition of the present invention has a total carbon number of 26 to 40 obtained by esterifying an alcohol represented by the following general formula (1) and a linear aliphatic monocarboxylic acid having 8 to 16 carbon atoms. It is characterized by containing a linear aliphatic monocarboxylic acid ester as a base oil.

(In general formula (1), n represents an integer of 5 to 11)

(A) Base oil The base oil used in the bearing oil composition of the present invention is obtained by esterification of the alcohol represented by the general formula (1) and a linear aliphatic monocarboxylic acid having 8 to 16 carbon atoms. It is a straight chain aliphatic monocarboxylic acid ester having a total carbon number of 26 to 40.
In the said General formula (1), n is an integer of 5-11, Preferably n is an integer of 6-8, Most preferably, n is an integer of 7. When n is 4 or less, the base oil is likely to evaporate, and when n is 12 or more, the viscosity of the base oil increases.

  Specific examples of the alcohol represented by the general formula (1) include 2-butyloctanol, 2-pentylnonanol, 2-hexyldecanol, 2-heptylundecanol, 2-octyldodecanol, and 2-nonyltridecane. And 2-pentylnonanol, 2-hexyldecanol and 2-heptylundecanol are preferred, and 2-hexyldecanol is most preferred.

On the other hand, the linear aliphatic monocarboxylic acid having 8 to 16 carbon atoms is preferably a linear aliphatic monocarboxylic acid having 9 to 15 carbon atoms, and the linear aliphatic monocarboxylic acid having 10 to 14 carbon atoms is Most preferred. When the carbon number is less than 8, the viscosity of the base oil becomes very low and the evaporation amount becomes large. Moreover, since the viscosity of a base oil will become high when this carbon number exceeds 16, it is unpreferable.
Specific examples of the linear aliphatic monocarboxylic acid having 8 to 16 carbon atoms include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, and capric acid, lauric acid, and myristic acid are preferable.

  If the structure of the monocarboxylic acid is a branched chain structure, the viscosity index is lowered, which is not preferable. The straight chain aliphatic monocarboxylic acid may be a straight chain saturated aliphatic monocarboxylic acid or a straight chain unsaturated aliphatic monocarboxylic acid, but may be a straight chain saturated aliphatic monocarboxylic acid. More preferred.

  The base oil used in the bearing oil composition of the present invention is a linear aliphatic monocarboxylic ester obtained by esterifying the alcohol represented by the general formula (1) and a linear aliphatic carboxylic acid. The total carbon number is 26-40. The total carbon number is preferably 26 to 34, more preferably 26 to 30. When the total carbon number is 25 or less, evaporation loss increases, and when the total carbon number is 41 or more, the viscosity increases.

  In the bearing oil composition of the present invention, as long as the performance of the bearing oil composition is not reduced, the base oil may be a lubricant base oil other than the linear aliphatic monocarboxylic acid ester, for example, a mineral oil base lubricant or a synthetic base A lubricating base oil or the like may be mixed. Examples of the mineral oil base oil include base oil obtained by refining a lubricating oil fraction of crude oil by an appropriate combination such as solvent refining and hydrorefining. Examples of the synthetic lubricating base oil include poly-α-olefins, polyol esters, alkylbenzenes, polyglycols, phenyl ethers, and the like. However, in order to obtain a bearing oil composition excellent in low viscosity and low evaporability, the ester base oil is preferably contained in an amount of 40 to 100% by mass, and 60 to 100% by mass, based on the total amount of the base oil. It is more preferable to contain 70-100 mass%, and it is especially preferable not to contain other base oil substantially.

(B) Antioxidant The bearing oil composition of the present invention can be blended with an antioxidant in order to improve oxidation stability. In that case, a group consisting of an amine-based antioxidant and a phosphorus-based antioxidant. It is preferable to contain at least one antioxidant selected from Furthermore, in order to further improve the oxidative stability, diphenylamines of the general formula (2) and alkylated phenyl-α-naphthylamines of the general formula (3), which are amine antioxidants described later, and phosphorus series It is preferable to contain both phosphites of general formula (4) which are antioxidants. Since the effect of suppressing the evaporation loss can be expected by improving the oxidation stability, it is preferable to contain the amine-based antioxidant and the phosphorus-based antioxidant from the viewpoint of suppressing the evaporation loss. As the oxidative deterioration progresses, the acid value may increase over a long period of use, but this may cause the evaporation loss due to the hydrolysis of the ester base oil.

  The content of at least one antioxidant selected from the group consisting of the amine-based antioxidant and the phosphorus-based antioxidant is preferably 0.05 to 2% by mass, and preferably 0.1 to 1% by mass. More preferably, it is more preferable to set it as 0.1-0.5 mass%. In addition, when content of the said antioxidant exceeds 2 mass%, the effect corresponding to content may not be acquired in many cases. When the content of the antioxidant is 2% by mass or less, it is economical and a sufficient effect can be obtained. The said antioxidant may be used individually by 1 type, and may combine 2 or more types. In the case of combining two or more, the total amount is preferably within the above range.

(I) Amine-based antioxidant In the bearing oil composition of the present invention, examples of the amine-based antioxidant preferably used as the antioxidant include diphenylamines and alkylated phenyl-α-naphthylamine.
Examples of the diphenylamines include those having a structure represented by the following general formula (2).

In the said General formula (2), R < ¹ > and R < ² > represents a hydrogen atom or a C1-C16 linear or branched alkyl group. The linear or branched alkyl group is preferably a linear or branched alkyl group having 3 to 9 carbon atoms, and particularly preferably a linear or branched alkyl group having 4 to 8 carbon atoms. If the linear or branched alkyl group has more than 16 carbon atoms, the solubility in oil may decrease, which is not preferable.

Further, R ¹ and R ² are may be the same or different. Specific examples of the diphenylamines include diphenylamine, butyldiphenylamine, octyldiphenylamine, dibutyldiphenylamine, octylbutyldiphenylamine, and dioctyldiphenylamine. Diphenylamines may be used alone or in combination of two or more.

  Examples of the alkylated phenyl-α-naphthylamine include those having a structure represented by the following general formula (3).

In the general formula (3), R ³ represents a linear or branched alkyl group having 1 to 16 carbon atoms, preferably a linear or branched alkyl group having 4 to 8 carbon atoms. Specific examples of the alkylated phenyl-α-naphthylamine include n-pentylated phenyl-α-naphthylamine, 2-methylbutylated phenyl-α-naphthylamine, 2-ethylhexylated phenyl-α-naphthylamine, and n-octylated phenyl. -Α-naphthylamine, 1-methyloctylated phenyl-α-naphthylamine and the like. The alkylated phenyl-α-naphthylamine may be used alone or in combination of two or more.

(Ii) Phosphorous Antioxidant In the bearing oil composition of the present invention, a preferred specific example of the phosphorus antioxidant preferably used as an antioxidant includes phosphite.
Examples of the phosphite include those having a structure represented by the following general formula (4).

In the general formula (4), R ⁴ and R ⁵ represent a linear or branched alkyl group having 1 to 20 carbon atoms, preferably a linear or branched alkyl group having 2 to 6 carbon atoms. . These phosphites may be used alone or in combination of two or more.

(C) Antiwear agent The bearing oil composition of the present invention includes at least one antiwear agent selected from the group consisting of phosphorus antiwear agents and polyoxyethylene sorbitol esters in order to improve antiwear properties. It is preferable to contain. Furthermore, in consideration of the influence on the hydrolysis of linear aliphatic monocarboxylic acid ester and the evaporability considered to be caused by this, it is preferable to select an antiwear agent that is unlikely to be a factor in promoting hydrolysis. . From this viewpoint, as the phosphorus-based antiwear agent, at least one selected from the group consisting of alkylaryl phosphates and polyoxyethylene sorbitol esters in which R ^{6 to} R ⁸ are alkylaryl groups in the general formula (5) described later It is preferable to use polyoxyethylene sorbitol esters.

The content of the antiwear agent is preferably 0.05 to 5% by mass, more preferably 0.1 to 3% by mass, further preferably 0.15 to 2% by mass, It is especially preferable that it is 0.15-1.5 mass%. When the content of the antiwear agent exceeds 5% by mass, an effect commensurate with the content is often not obtained. When the content of the antiwear agent is 5% by mass or less, it is economical and a sufficient effect can be obtained.
The said antiwear agent may be used individually by 1 type, and may combine 2 or more types. In the case of combining two or more, the total amount is preferably within the above range.

(I) Phosphorous antiwear agent Examples of the phosphorus antiwear agent include phosphates, phosphites, acid phosphates, and amine salts of acid phosphates.
Examples of the phosphate include those having a structure represented by the following general formula (5).

In the general formula (5), R ⁶ ~R ⁸ is a hydrogen atom or an alkyl group having 1 to 22 carbon atoms, an alkenyl group, an alkylaryl group or an arylalkyl group, it may be different even if the same. When R ^{6 to} R ⁸ are an alkyl group, an alkenyl group, an alkylaryl group, or an arylalkyl group, a carbon number of 3 to 9 is preferable. If the alkyl group, alkenyl group, alkylaryl group or arylalkyl group represented by R ^{6 to} R ⁸ has more than 22 carbon atoms, the solubility in the base oil may be reduced.

  Examples of the phosphate include triaryl phosphate, trialkyl phosphate, and the like. Specifically, benzyl diphenyl phosphate, allyl diphenyl phosphate, triphenyl phosphate, tricresyl phosphate, tributyl phosphate, cresyl diphenyl phosphate, dicresyl phenyl Mention may be made of compounds such as phosphate, ethylphenyldiphenylphosphate, diethylphenylphenylphosphate, propylphenyldiphenylphosphate, dipropylphenylphenylphosphate, triethylphenylphosphate, tripropylphenylphosphate and the like.

  Examples of the phosphite include those having a structure represented by the following general formula (6) or general formula (7).

In the general formula (6) and general formula (7), R ^{9 to} R ¹¹ represent an alkyl group, alkenyl group, alkylaryl group or arylalkyl group having 1 to 22 carbon atoms, which may be the same or different. Also good. R ^{9 to} R ¹¹ preferably have 8 to 18 carbon atoms. If the number of carbon atoms exceeds 22, the solubility in the base oil decreases, such being undesirable.
Specific examples of the phosphites include trialkyl phosphites such as trioctadecyl phosphite, tristearyl phosphite, triisooctyl phosphite, tris (nonylphenyl) phosphite, diphenylisodecyl phosphite, and phosphorus phosphite. Examples include acid dialkyl esters and phosphorous acid monoalkyl esters.

  As said acid phosphate, what has a structure represented by General formula (8) and General formula (9) is mentioned.

In General Formula (8) and General Formula (9), R ¹² and R ¹³ represent a hydrocarbon group having 4 or more carbon atoms, and may be the same or different. Specific examples of R ¹² and R ¹³ include a linear or branched saturated or unsaturated aliphatic hydrocarbon group having 4 to 20 carbon atoms, that is, an alkyl group and an alkenyl group, and an aromatic carbon atom having 4 to 20 carbon atoms. Examples thereof include a hydrogen group and a cycloalkyl group. When the carbon number is 4 to 20, the effect of improving the wear resistance is sufficiently exhibited. The hydrocarbon group represented by R ¹² and R ¹³ preferably has 6 to 18 carbon atoms, and more preferably 8 to 12 carbon atoms.

  Specific examples of the acid phosphate include 2-ethylhexyl acid phosphate, isodecyl acid phosphate, di (2-ethylhexyl) phosphate, and the like.

  Preferred examples of the acid phosphate amine salt include those obtained by neutralizing the above acid phosphate with an alkylamine having a structure represented by the general formula (10).

In the general formula ^{(10), R} 14 ~R ¹⁶ represents a hydrocarbon group or a hydrogen atom monovalent 1-22 carbon ^atoms, at least one of R 14 ^{to R 16} is a hydrocarbon group. R ^{14 to} R ¹⁶ are preferably a monovalent hydrocarbon group having 4 to 18 carbon atoms or a hydrogen atom.
Specific examples of the alkylamine include dibutylamine, octylamine, dioctylamine, laurylamine, dilaurylamine, oleylamine, coconut amine, and beef tallow amine.
These phosphorus wear inhibitors may be used alone or in combination of two or more.

(Ii) Polyoxyethylene sorbitol esters The polyoxyethylene sorbitol esters are represented by the following general formula (11), and a polyoxyethylene group in which 3 to 100 moles of an oxyethylene group are polymerized to a hydroxyl group of sorbitol is bonded. It is a compound having a structure in which monocarboxylic acid is ester-bonded to oxyethylene sorbitol.

In general formula (11), a, b, c, d, e, and f are integers in which a + b + c + d + e + f is 3 to 100, and R ^{17 to} R ²² are hydrogen or a monocarboxylic acid-derived moiety having 5 to 25 carbon atoms. It is.
The monocarboxylic acid is preferably an aliphatic monocarboxylic acid having 5 to 25 carbon atoms, more preferably an aliphatic monocarboxylic acid having 8 to 22 carbon atoms, and most preferably an aliphatic monocarboxylic acid having 10 to 20 carbon atoms. The ester of sorbitol and the above monocarboxylic acid may be any of monoester, diester, triester, tetraester, pentaester, and hexaester, and may be an ester with one fatty acid or a mixed ester with two or more fatty acids. .

(D) Other additives Various additives other than the above can be blended in the bearing oil composition of the present invention, if necessary. For example, benzotriazole and derivatives thereof, rust inhibitors such as alkyl succinic acid derivatives, dispersants such as polyalkenyl succinimide and derivatives thereof, pour point depressants such as styrene-butadiene copolymers, polyisobutylene, polymethacrylate, Examples thereof include viscosity index improvers such as olefin polymers and conductivity imparting agents.

(E) Kinematic Viscosity / Viscosity Index of Composition The bearing oil composition of the present invention preferably has a kinematic viscosity at 40 ° C. of 6 to 13 mm ² / s, more preferably 8 to 12 mm ² / s. If the 40 ° C. kinematic viscosity is less than 6 mm ² / s, evaporation loss may increase. If it exceeds 13 mm ² / s, the viscosity torque when the shaft rotates increases, or the low-temperature fluidity decreases. This is not preferable.
Further, the bearing oil composition of the present invention preferably has a viscosity index of 120 or more, more preferably 130 or more. When the viscosity index is less than 120, the viscosity change with respect to the temperature change increases, and the viscosity torque at low temperature may increase, which is not preferable.

Next, the present invention will be described more specifically with reference to examples. In addition, this invention is not restrict | limited at all by these examples.
The base oil and additive components used in the preparation of the compositions in each Example and Comparative Example are as follows.
(A) Base oil (A-i) Monoester base oil A
In the general formula (1), a linear aliphatic monocarboxylic acid ester obtained by esterifying an alcohol having n of 7 and capric acid (a linear saturated aliphatic monocarboxylic acid having 10 carbon atoms) is a monoester. Base oil A was designated. The monoester base oil A has a total carbon number of 26.

(A-ii) Monoester base oil B
In the general formula (1), a linear aliphatic monocarboxylic acid ester obtained by esterifying an alcohol in which n is 7 and lauric acid (a linear saturated aliphatic monocarboxylic acid having 12 carbon atoms) is a monoester Base oil B was designated. The total number of carbon atoms of the monoester base oil B is 28.

(A-iii) Monoester base oil C
In the general formula (1), a linear aliphatic monocarboxylic acid ester obtained by esterifying an alcohol having n of 5 and myristic acid (a linear saturated aliphatic monocarboxylic acid having 14 carbon atoms) is a monoester. Base oil C was designated. The total number of carbon atoms of the monoester base oil C is 26.

(A-iv) Monoester base oil D
The monoester base oil D was isotridecyl n-dodecanoate. The total carbon number of the monoester base oil D is 25.

(Av) Monoester base oil E
In the general formula (1), a linear aliphatic monocarboxylic acid ester obtained by esterifying an alcohol having n of 5 and lauric acid (a linear saturated aliphatic monocarboxylic acid having 12 carbon atoms) is a monoester. Base oil E was designated. The total carbon number of the monoester base oil E is 24.

(A-vi) Monoester base oil F
In general formula (1), a linear aliphatic monocarboxylic acid ester obtained by esterifying an alcohol in which n is 7 and 2-butyloctanoic acid (branched saturated aliphatic monocarboxylic acid having 12 carbon atoms) Was designated as monoester base oil F. The total number of carbon atoms of the monoester base oil F is 28.

(A-vii) Monoester base oil G
In general formula (1), a linear aliphatic compound obtained by esterifying a mixture of alcohols in which n is 7 to 9 and 2-ethylhexanoic acid (a branched saturated aliphatic monocarboxylic acid having 8 carbon atoms) The monocarboxylic acid ester was designated as monoester base oil G. The total carbon number of the monoester base oil G is 24 to 28.

(A-viii) Monoester base oil H
In general formula (1), a linear aliphatic monocarboxylic acid ester obtained by esterifying alcohol having n of 9 and 2-ethylhexanoic acid (branched saturated aliphatic monocarboxylic acid having 8 carbon atoms) Was a monoester base oil H. The total carbon number of the monoester base oil H is 28.

(A-ix) Diester base oil A
In the general formula (1), a linear aliphatic dicarboxylic acid ester obtained by esterifying an alcohol having n of 3 and adipic acid (a linear saturated aliphatic dicarboxylic acid having 6 carbon atoms) is converted into a diester base oil A. It was. The total carbon number of the diester base oil A is 22.

(Ax) Diester base oil B
In the general formula (1), a linear aliphatic dicarboxylic acid ester obtained by esterifying an alcohol having n of 3 and sebacic acid (a linear saturated aliphatic dicarboxylic acid having 10 carbon atoms) is converted into a diester base oil B It was. The total carbon number of the diester base oil B is 26.

(B) Antioxidant (Bi) Diphenylamines An alkylated diphenylamine in which R ¹ and R ² are linear or branched C ₈ H ₁₇ in the general formula (2).

(B-ii) Alkylated phenyl-α-naphthylamine In the general formula (3), alkylated phenyl-α-naphthylamine in which R ³ is linear or branched C ₈ H ₁₇ .

(B-iii) Phosphorous antioxidant Phosphite in which R ⁴ and R ⁵ are t-butyl in the general formula (4).

(C) In the anti-wear agent (C-i) phosphate general formula ^(5), phosphate R 6 to R ⁸ are the same cresyl group.

(C-ii) Polyoxyethylene sorbitol ester In the general formula (11), a + b + c + d + e + f is 6, R ^{17 to} R ²⁰ are oleic acid, and R ²¹ and R ²² are hydrogen.

(C-iii) Polyoxyethylene sorbitol ester Polyoxyethylene sorbitol ester in general formula (11), wherein a + b + c + d + e + f is 30, R ^{17 to} R ²⁰ are oleic acid, and R ²¹ and R ²² are hydrogen.

(Evaluation methods)
In this example, the following evaluation methods were used to evaluate the low viscosity, low evaporation, oxidation stability, and wear resistance required as lubricating oils for impregnated bearings.
[Kinematic viscosity / viscosity index]
The kinematic viscosity at 0 ° C., 40 ° C., and 100 ° C. was measured by the kinematic viscosity test method specified in JIS K 2283, and the kinematic viscosity and the viscosity index were evaluated.

[Evaporation]
As one of the methods for evaluating the thermal stability of the lubricating oil, the evaporation loss was measured and evaluated under the following conditions by a test based on the thermal stability test established in JIS K 2540.
Test condition temperature: 120 ° C
Time: 1000hr

[Rotating cylinder oxidation stability (RBOT test)]
This evaluation is called Rotating Bomb Oxidation Test, and is abbreviated as RBOT hereinafter. Based on JIS K 2514, the time until the specified pressure drop at 150 ° C. was evaluated as the RBOT life.

[Shell four-ball test method]
This was carried out in accordance with ASTM D 2783, which is one of the methods for evaluating the wear resistance of a lubricating oil, and the wear resistance was evaluated by the wear diameter under the following conditions.
Test condition Rotation speed: 1200rpm
Load: 30kgf (294N)
Test time: 30min

<Examples 1-4, Comparative Examples 1-3>
As shown in Table 1, in each base oil, various additives are blended in the amounts shown in Table 1, and the bearing oil compositions of Examples 1 to 4 and Comparative Examples 1 to 3 are prepared. Evaluation was performed. The results are shown in Table 1. In Table 1, “◯” means that the corresponding base oil is contained, and the content of each base oil is such that the total amount with the additive is 100% by mass (see Tables 2 to 2 below). 4 is the same). In addition, a blank in the additive column means that it has not been added (the same applies to Tables 2 to 4 below).

<Examples 5 to 7, Comparative Example 4>
As shown in Table 2, various additives are blended in each base oil in the amounts shown in Table 2, and the bearing oil compositions of Examples 5 to 7 and Comparative Example 4 are prepared. Carried out. The results are shown in Table 2.

  From Tables 1 and 2, Examples 1 to 7 using monoester base oils A to C that are base oils of the bearing oil composition of the present invention are ester base oils that are base oils of the bearing oil of the present invention. Compared with Comparative Examples 1 to 4 using monoester base oils or diester base oils having different structures, the kinematic viscosity at 40 ° C. is almost the same, but it can be seen that low evaporability is exhibited.

<Comparative Example 5>
As shown in Table 3, in each base oil, various additives are blended in the amounts shown in Table 3 to prepare a bearing oil composition of Comparative Example 5, and together with the bearing oil compositions of Examples 1 and 4, The evaluation described in 3 was performed. The results are shown in Table 3.

<Comparative Examples 6 and 7>
As shown in Table 4, in each base oil, various additives are blended in the amounts shown in Table 4 to prepare bearing oil compositions of Comparative Examples 6 and 7, along with the bearing oil composition of Example 5. The evaluation described in 4 was carried out. The results are shown in Table 4.

  From Tables 3 and 4, Examples 1, 4, and 5 using monoester base oils A to C that are base oils of the bearing oil composition of the present invention are esters that are base oils of the bearing oil composition of the present invention. It can be seen that the viscosity index is higher than those of Comparative Examples 5, 6, and 7 using monoester base oils F to H having a structure different from that of the base oil.

Claims (3)

A linear aliphatic monocarboxylic acid ester having a total carbon number of 26 to 40 obtained by esterifying an alcohol represented by the following general formula (1) and a linear aliphatic monocarboxylic acid having 8 to 16 carbon atoms: A bearing oil composition comprising a base oil.

In general formula (1), n represents the integer of 5-11.   The bearing oil composition according to claim 1, comprising 0.05 to 2% by mass of at least one antioxidant selected from the group consisting of amine-based antioxidants and phosphorus-based antioxidants.   The bearing oil composition according to claim 1 or 2, comprising at least one antiwear agent selected from the group consisting of phosphorus-based antiwear agents and polyoxyethylene sorbitol esters at 0.05 to 5% by mass. object.