JP6888500B2 - Lubricating oil for fluid dynamic bearings, fluid dynamic bearings and spindle motors - Google Patents

Description

The present invention relates to a lubricating oil for a fluid dynamic bearing, a fluid dynamic bearing, and a spindle motor.

A conventional lubricating oil for hydrodynamic bearings is disclosed in Patent Document 1. The lubricating oil for the fluid dynamic bearing is filled between the shaft portion and the sleeve portion of the fluid dynamic bearing. Fluid dynamic bearings are used as bearings for spindle motors.

Dynamic pressure is generated in the lubricating oil for fluid dynamic bearings as the spindle motor rotates, and contact between the shaft portion and the sleeve portion is prevented. As a result, the sleeve portion rotates smoothly with respect to the shaft portion.

Fluid dynamic bearing lubricating oil contains an aliphatic carboxylic acid ester. By reducing the molecular weight of the aliphatic carboxylic acid ester, the fluid dynamic pressure bearing lubricating oil has a low viscosity and an improved fluidity. As a result, the energy loss due to viscous friction can be reduced and the power consumption of the spindle motor can be reduced.

Japanese Unexamined Patent Publication No. 2016-74816

However, according to the above-mentioned conventional lubricating oil for fluid dynamic bearings, there is a problem that the lubricating oil for fluid dynamic bearings easily evaporates in a high temperature environment when the molecular weight of the aliphatic carboxylic acid ester is reduced.

An object of the present invention is to provide a lubricating oil for a fluid dynamic bearing that is difficult to evaporate in a high temperature environment, a fluid dynamic bearing using the same, and a spindle motor while reducing a decrease in fluidity.

The lubricating oil for a fluid dynamic bearing of an exemplary fluid dynamic bearing of the present invention is
It contains an aliphatic carboxylic acid monoester represented by any of the following formulas (1) to (3).

The exemplary fluid dynamic bearing of the present invention is filled with a lubricating oil for a fluid dynamic bearing having the above configuration.

An exemplary spindle motor of the present invention comprises a fluid dynamic bearing having the above configuration.

According to an exemplary invention, it is possible to provide a lubricating oil for a fluid dynamic bearing, a fluid dynamic bearing and a spindle motor which are difficult to evaporate in a high temperature environment while reducing a decrease in fluidity.

FIG. 1 is a vertical sectional view of a spindle motor according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. In the present specification, the upper side in the central axis direction of the motor is referred to as "upper side", and the lower side is referred to as "lower side". The vertical direction does not indicate the positional relationship or direction when the device is incorporated into an actual device. In addition, the direction parallel to or substantially parallel to the central axis is called "axial direction", the radial direction centered on the central axis is simply "diametrical direction", and the circumferential direction centered on the central axis is "circumferential direction". And.

(1. Spindle motor configuration)
FIG. 1 shows a vertical cross-sectional view of the spindle motor 1. The spindle motor 1 is an outer rotor type motor. The spindle motor 1 has a stationary portion 2 and a rotating portion 3. The rotating portion 3 is rotatably supported with respect to the stationary portion 2 about the central axis L via a lubricating oil 50 for a fluid dynamic bearing (hereinafter, abbreviated as lubricating oil). Further, a conical type fluid dynamic bearing 4 is formed by a part of the stationary portion 2 and a part of the rotating portion 3.

(2-1. Configuration of stationary part)
The stationary portion 2 includes a base portion 17, a shaft portion 11, annular members 12a and 12b, a stator core 18, and a coil 15.

A through hole 17a is formed in the central portion of the base portion 17 along the central axis L. Further, a substantially cylindrical holder portion 17b protruding in the axial direction is formed on the outer peripheral side of the through hole 17a.

The shaft portion 11 is a substantially cylindrical member extending along the central axis L. The shaft portion 11 is fixed to the base portion 17 by press-fitting the lower end portion into the through hole 17a.

The annular members 12a and 12b project radially outward from the outer peripheral surface of the shaft portion 11. The annular members 12a and 12b are vertically fixed to the outer peripheral surface of the shaft portion 11 at intervals in the axial direction. The annular members 12a and 12b may be integrally molded with the shaft portion 11.

In the case of the conical type hydrodynamic bearing 4, the annular members 12a and 12b have a substantially conical shape, and the upper and lower surfaces of the annular members 12a and 12b are gradually formed to have smaller diameters.

The stator core 18 has a core back 18a and a teeth 18b. The core back 18a has an annular shape and is fitted to the outer peripheral surface of the holder portion 17b. A plurality of teeth 18b project radially outward from the core back 18a.

The coil 15 is formed by a conducting wire wound around each tooth 18b. The coil 15 is connected to a power supply device (not shown). When a drive current is applied to the coil 15 from the power supply device, magnetic flux is generated.

(2-2. Configuration of rotating part)
The rotating portion 3 includes a sleeve portion 14, a holding member 13, a magnet 16, and a sealing portion 19. The sleeve portion 14 is formed in a substantially cylindrical shape, and has first, second, and third inner peripheral surfaces 14a, 14b, and 14c in this order from above. The first inner peripheral surface 14a is inclined upward in a direction away from the shaft portion 11 and faces the annular member 12a.

The second inner peripheral surface 14b is formed along the central axis L and faces the outer peripheral surface of the shaft portion 11. The third inner peripheral surface 14c is inclined downward in a direction away from the shaft portion 11 and faces the upper surface of the annular member 12b. Further, the sleeve portion 14 has a minute gap S between the annular member 12a, the shaft portion 11 and the annular member 12b.

The holding member 13 is formed in a tubular shape, and the sleeve portion 14 is press-fitted. An annular recess 13a is formed on the inner surface side of the lower portion of the holding member 13, and a flange portion 13b is formed on the lower end of the holding member 13 so as to project outward in the radial direction.

A plurality of magnets 16 are arranged side by side in the circumferential direction and attached to the yoke 16a. The yoke 16a is press-fitted into the recess 13a, and the magnet 16 is held by the holding member 13. The inner peripheral surface of the magnet 16 is a magnetic pole surface, and faces the outer peripheral surfaces of the plurality of teeth 18b of the stator core 18 in the radial direction.

The seal portion 19 is attached to the upper surface and the lower surface of the sleeve portion 14, and the lubricating oil 50 is sealed in the minute gap S between the annular members 12a and 12b and the sleeve portion 14.

(3. Configuration of fluid dynamic bearing)
The fluid dynamic bearing 4 is formed of a shaft portion 11, annular members 12a and 12b, a sleeve portion 14, and a lubricating oil 50. As described above, the shaft portion 11 and the annular members 12a and 12b are a part of the stationary portion 2, and the sleeve portion 14 is a part of the rotating portion 3.

The fluid dynamic bearing 4 is a conical type, and supports radial and axial loads by a shaft portion 11, an annular member 12a, and an annular member 12b facing the sleeve portion 14.

Dynamic pressure grooves (not shown) are formed on the lower surfaces of the first inner peripheral surface 14a and the annular member 12a facing each other. Further, a dynamic pressure groove (not shown) is formed on the upper surfaces of the third inner peripheral surface 14c and the annular member 12b facing each other. The dynamic pressure groove induces fluid dynamic pressure in the lubricating oil 50 when the rotating portion 3 rotates. A dynamic groove may be formed on one of the lower surfaces of the first inner peripheral surface 14a and the annular member 12a, or a dynamic groove may be formed on one of the upper surfaces of the third inner peripheral surface 14c and the annular member 12b. Good.

When a drive current is applied to the coil 15 of the spindle motor 1, a magnetic flux is generated in the coil 15. Torque is generated by the action of the magnetic flux between the coil 15 and the magnet 16, and the rotating portion 3 rotates about the central axis L with respect to the stationary portion 2.

When the sleeve portion 14 is rotationally driven with respect to the annular members 12a and 12b, the dynamic pressure groove induces a fluid dynamic pressure in the lubricating oil 50 filled in the minute gap S by a pumping action. As a result, the sleeve portion 14 is supported in the radial and axial directions without contact with the annular members 12a and 12b, and can smoothly rotate at high speed with respect to the annular members 12a and 12b and the shaft portion 11.

(4. Composition of lubricating oil)
The lubricating oil 50 uses an aliphatic carboxylic acid monoester represented by the formulas (1) to (3) (hereinafter referred to as an ester compound) as a base oil. The ester compound is preferably 90% by mass or more, more preferably 93% by mass or more, and further preferably 95% by mass or more, based on the total mass of the lubricating oil 50.

Further, the total carbon number of the ester compounds represented by the formulas (1) to (3) is preferably 26 or more and 32 or less, and more preferably 29 or 30. The molecular weight of the ester compound is preferably 454 or more and 468 or less.

By using the ester compounds represented by the formulas (1) to (3) as the base oil in the lubricating oil 50, the lubricating oil 50 is less likely to evaporate in a high temperature environment while reducing a decrease in fluidity. Further, in a high humidity environment, it is difficult to generate a deteriorated substance having a low molecular weight due to decomposition or the like, and it is excellent in moisture resistance. Therefore, the ester compounds represented by the formulas (1) to (3) are preferably used as the lubricating oil 50 for the fluid dynamic bearing 4.

Specifically, the fluidity of the lubricating oil 50 is in the range where the absolute viscosity at 40 ° C. is 10 mPa · s or more and 12 mPa · s or less. If the absolute viscosity is less than 10 mPa · s, the sleeve portion 14 and the annular members 12a and 12b may come into contact with each other to damage the spindle motor 1. Further, when the absolute viscosity is larger than 12 mPa · s, the energy loss due to viscous friction is increased and the power consumption of the spindle motor 1 is increased.

The pour point of the lubricating oil 50 is −30 ° C. or lower, more preferably −35 ° C. or lower, as measured by the method specified in JIS K 2269: 1987. When the pour point is −30 ° C. or lower, the spindle motor 1 can be started even in a low temperature environment, and a predetermined torque can be obtained.

Further, the lubricating oil 50 has a mass change rate of 0.9% or less before and after 1000 hours have passed in a high temperature environment of 120 ° C., and is excellent in characteristics that it is difficult to evaporate (hereinafter, "low evaporation property").

Further, the lubricating oil 50 is excellent in moisture resistance because a deteriorated substance having a low molecular weight due to decomposition of an ester compound or the like is not generated for 2000 hours or more in a high humidity environment of 90% or more in humidity.

When n is 0, the carboxylic acid component of the ester compound of the formula (1) has two methyl groups branched at the α-position. When n is 1, the carboxylic acid component of the ester compound has two methyl groups branched at the β-position.

By branching two methyl groups at the α- or β-position, the α-carbon or β-carbon of the carboxylic acid component of the ester compound is a quaternary carbon that is not bonded to a proton. Therefore, low molecular weight is unlikely to occur due to oxidative deterioration. As a result, the molecular weight reduction of the ester compound is suppressed, and the low evaporation property of the lubricating oil 50 is improved.

Further, the alcohol component of the ester compound of the formula (1) has two methyl groups branched at the β-position. By branching two methyl groups at the β-position, the β-carbon of the alcohol component is a quaternary carbon that is not bonded to a proton. This prevents the ester compound from being thermally decomposed into a carboxylic acid and an alkene to reduce the molecular weight. As a result, the molecular weight reduction of the ester compound is suppressed, and the low evaporation property of the lubricating oil 50 is improved.

Further, the carboxylic acid component of the ester compound of the formula (1) has a large molecular weight due to the branching of a short methyl group at the α-position or the β-position. In addition, the alcohol component of the ester compound has a large molecular weight due to the branching of a short methyl group at the β-position. By increasing the molecular weight of the ester compound by short branching such as a methyl group, the low evaporability of the lubricating oil 50 is further improved while suppressing the increase in viscosity and pour point due to the increase in molecular weight.

Further, R1 of the carboxylic acid component of the ester compound of the formula (1) is a linear alkyl group having 7 to 10 carbon atoms, and R2 of the alcohol component is a linear alkyl group having 10 to 13 carbon atoms. Is more preferable. By arranging a long linear alkyl group at the position of R1 of the carboxylic acid component, the polarization of the carbon and oxygen atoms of the carbonyl group becomes small, and small molecules of the ester compound due to hydrolysis are less likely to be generated. As a result, the low evaporation property and moisture resistance of the lubricating oil 50 are further improved.

The carboxylic acid component of the ester compound of the formula (2) has an alkoxy group and has two methyl groups branched at the α-position of the alkoxy group. At this time, the α carbon of the alkoxy group is a quaternary carbon that is not bonded to a proton. Therefore, low molecular weight due to oxidative deterioration is unlikely to occur. As a result, the molecular weight reduction of the ester compound is suppressed, and the low evaporation property of the lubricating oil 50 is improved.

Further, in the formula (2), the alcohol component of the ester compound has one ethyl group branched at the β-position. Due to the binding of the ethyl group to the β-position, it is difficult to form a six-membered ring between molecules due to steric hindrance. As a result, the molecular weight reduction of the ester compound due to thermal decomposition is suppressed, and the low evaporation property of the lubricating oil 50 is further improved.

Further, the carboxylic acid component of the ester compound of the formula (2) has a large molecular weight due to the branching of a short methyl group at the α-position of the alkoxy group. By increasing the molecular weight of the ester compound by short branching such as a methyl group, the low evaporability of the lubricating oil 50 is further improved while suppressing the increase in viscosity and pour point due to the increase in molecular weight.

Further, the alcohol component of the ester compound of the formula (2) has one ethyl group branched at the β-position. By increasing the molecular weight of the ester compound by branching the ethyl group, the low evaporability of the lubricating oil 50 is further improved while suppressing the increase in viscosity and pour point due to the increase in molecular weight.

Further, the carboxylic acid component of the ester compound of the formula (2) has p of 10 or 11, and a linear carbon chain having 10 or 11 carbon atoms is arranged between the carbonyl group and the ether group. As a result, the polarization between the carbon atom and the oxygen atom of the carbonyl group is reduced, and it is difficult for the ester compound to have a low molecular weight due to hydrolysis. As a result, the molecular weight reduction of the ester compound is suppressed, and the low evaporation property and moisture resistance of the lubricating oil 50 are further improved.

Further, it is more preferable that R3 of the carboxylic acid component of the ester compound of the formula (2) is a linear alkyl group having 2 to 4 carbon atoms. As a result, the low evaporation property of the lubricating oil 50 is further improved.

When the m of the ester compound of the formula (3) is 0, the carboxylic acid component of the ester compound has two methyl groups branched at the α-position. When m is 1, the carboxylic acid component of the ester compound has two methyl groups branched at the β-position.

By branching two methyl groups at the α- or β-position, the α-carbon or β-carbon of the carboxylic acid component of the ester compound is a quaternary carbon that is not bonded to a proton. Therefore, low molecular weight due to oxidative deterioration is unlikely to occur. As a result, the molecular weight reduction of the ester compound is suppressed, and the low evaporation property of the lubricating oil 50 is further improved.

Further, in the ester compound of the formula (3), the alcohol component of the ester compound has one ethyl group branched at the β-position. Due to the binding of the ethyl group to the β-position, it is difficult to form a six-membered ring between molecules due to steric hindrance. As a result, the molecular weight reduction of the ester compound due to thermal decomposition is suppressed, and the low evaporation property of the lubricating oil 50 is further improved.

Further, the carboxylic acid component of the ester compound of the formula (3) has a large molecular weight due to the branching of a short methyl group at the α-position or the β-position. Further, the alcohol component of the ester compound has one ethyl group branched at the β-position. By branching a short methyl group at the α- or β-position of the carboxylic acid component or branching an ethyl group at the β-position of the alcohol component to increase the molecular weight of the ester compound, the viscosity and flow point increase due to the increase in molecular weight. The low evaporability of the lubricating oil 50 is further improved while suppressing it.

Further, the carboxylic acid component of the ester compound of the formula (3) has q of 7 to 10, and a linear carbon chain having 7 to 10 carbon atoms is arranged between the carbonyl group and the ether group. As a result, the polarization of the carbon atom and the oxygen atom of the carbonyl group is reduced, and it is difficult for the ester compound to have a low molecular weight due to hydrolysis. As a result, the molecular weight reduction of the ester compound is suppressed, and the low evaporation property and moisture resistance of the lubricating oil 50 are further improved.

Further, it is more preferable that R5 of the carboxylic acid component of the ester compound of the formula (3) is a linear alkyl group having 3 to 6 carbon atoms. As a result, the low evaporation property of the lubricating oil 50 is further improved.

Further, the ester compounds of the formulas (1) to (3) contain an oxygen atom derived from an ester bond and an ether bond. Therefore, the oxygen atoms repel each other and are difficult to crystallize. Therefore, it is considered that the lubricating oil 50 is hard to solidify even in a low temperature environment and has good fluidity.

Further, the lubricating oil 50 may contain an antioxidant. By adding an antioxidant, it is possible to prevent the ester compound from being oxidatively deteriorated and decomposed.

Antioxidants include diphenylamine compounds, alkylated phenyl-α-naphthylamines, hindered phenolic compounds, and phosphite.

Further, the lubricating oil 50 may contain a metal inactivating agent, a rust preventive agent, an abrasion inhibitor, a pour point lowering agent, a viscosity index improver, a hydrolysis inhibitor and the like, which are general lubricating oil additives. ..

Next, the effects of the present invention will be specifically described with reference to Examples and Comparative Examples. In the following experiments, the fluidity, low evaporation property, and moisture resistance of the lubricating oil 50 were evaluated.

As the lubricating oils according to Examples 1 to 8 and Comparative Examples 1 to 4 below, aliphatic carboxylic acid esters having a molecular weight of 426 or more and 468 or less were used as base oils. The base oil accounts for 98.0% by mass of the total composition of the lubricating oil 50. The lubricating oil 50 contains 1.00% by mass of an antioxidant (manufactured by BASF Japan Ltd., model number: INGANOX L57), 0.5% by mass of a hydrolysis inhibitor (carbodiimide compound), and 0. 5% by mass is added.

The lubricating oil 50 of Example 1 uses the ester compound represented by the above formula (1) as a base oil. Further, n is 0, R1 is a linear alkyl group having 8 carbon atoms, and R2 is a linear alkyl group having 12 carbon atoms. At this time, the molecular weight of the esterified compound portion is 454, and the total carbon number is 29.

The lubricating oil 50 of Example 2 has the same configuration as that of Example 1 except that R2 is different from that of the ester compound of Example 1. R2 is a linear alkyl group having 13 carbon atoms. At this time, the molecular weight of the ester compound is 468, and the total carbon number is 30.

The lubricating oil 50 of Example 3 uses the ester compound represented by the above formula (1) as a base oil. Further, n is 1, R1 is a linear alkyl group having 7 carbon atoms, and R2 is a linear alkyl group having 12 carbon atoms. At this time, the molecular weight of the esterified compound portion is 454, and the total carbon number is 29.

The lubricating oil 50 of Example 4 has the same configuration as that of Example 3 except that R2 is different from the ester compound used in Example 3. R2 is a linear alkyl group having 13 carbon atoms. At this time, the molecular weight of the ester compound is 468, and the total carbon number is 30.

The lubricating oil 50 of Example 5 uses the ester compound represented by the above formula (2) as a base oil. Further, p is 10, and R3 is a linear alkyl group having 3 carbon atoms. At this time, the molecular weight of the esterified compound portion is 454, and the total carbon number is 29.

The lubricating oil 50 of Example 6 has the same configuration as that of Example 5 except that R3 is different from the ester compound used in Example 5. R3 is a linear alkyl group having 4 carbon atoms. At this time, the molecular weight of the ester compound is 468, and the total carbon number is 30.

The lubricating oil 50 of Example 7 uses the ester compound represented by the above formula (3) as a base oil. Further, m is 0 and q is 8. R5 is a linear alkyl group having 5 carbon atoms. At this time, the molecular weight of the esterified compound portion is 454, and the total carbon number is 29.

The lubricating oil 50 of Example 8 has the same configuration as that of Example 7 except that R5 is different from the ester compound used in Example 7. R5 is a linear alkyl group having 6 carbon atoms. At this time, the molecular weight of the ester compound is 468, and the total carbon number is 30.

[Comparative Example 1]
The lubricating oil of Comparative Example 1 is based on di2-ethylhexyl sebacate, which is an esterification compound represented by the formula (4). At this time, the molecular weight of the esterified compound portion is 426, and the total carbon number is 26.

The carboxylic acid component of the ester compound of the formula (4) does not have a methyl group branched at the α-position and the β-position.

[Comparative Example 2]
The lubricating oil of Comparative Example 2 uses the ester compound represented by the formula (5) as a base oil. At this time, the molecular weight of the esterified compound portion is 454, and the total carbon number is 28.

The carboxylic acid component of the ester compound of the formula (5) does not have a methyl group branched at the α-position and the β-position. Further, the alcohol component of the ester compound of the formula (5) does not have a methyl group and an ethyl group branched at the β-position.

[Comparative Example 3]
The lubricating oil of Comparative Example 3 uses the ester compound represented by the formula (6) as a base oil. At this time, the molecular weight of the esterified compound portion is 440, and the total carbon number is 27.

The carboxylic acid component of the ester compound of the formula (6) does not have a methyl group branched at the α-position and the β-position. Further, the alcohol component of the ester compound of the formula (6) does not have a methyl group and an ethyl group branched at the β-position.

[Comparative Example 4]
The lubricating oil of Comparative Example 4 is based on the ester compound represented by the formula (7). At this time, the molecular weight of the esterified compound portion is 440, and the total carbon number is 28.

The carboxylic acid component of the ester compound of the formula (7) does not have a methyl group branched at the α-position and the β-position. Further, the alcohol component of the ester compound of the formula (7) does not have a methyl group and an ethyl group branched at the β-position.

[Measurement of absolute viscosity]
The lubricating oils of Examples 1 to 8 and Comparative Examples 1 to 4 were measured for absolute viscosity (mPa · s) at 40 ° C. by the method specified in JIS Z 8803: 2011. The measurement results are shown in Table 1.

[Measurement of absolute pour point]
The pour point (° C.) of the lubricating oils according to Examples 1 to 8 and Comparative Examples 1 to 4 was measured by the method specified in JIS K 2269: 1987. The measurement results are shown in Table 1.

[Measurement of mass change rate]
The lubricating oils of Examples 1 to 8 and Comparative Examples 1 to 4 were stored in a constant temperature bath at 120 ° C. for 1000 hours, and the mass change rate of the lubricating oil before and after storage was determined to evaluate low evaporability. The evaluation results are shown in Table 1. The mass change rate is calculated by the following formula.

Rate of change (mass%) = (mass of lubricating oil before storage-mass of lubricating oil after storage) / mass of lubricating oil before storage x 100

[Measurement of moisture resistance time]
The lubricating oils of Examples 1 to 8 and Comparative Examples 1 to 4 were stored in a constant temperature bath at 110 ° C. and a humidity of 95%, and the time until a deteriorated substance was observed by liquid chromatography (moisture resistance time) was measured. The measurement results are shown in Table 1.

[Evaluation of liquidity]
As shown in Table 1, the lubricating oils 50 of Examples 1 to 8 have an absolute viscosity at 40 ° C. of 10.6 (mP · s) or more and 11.8 (mP · s) or less. From this, it was confirmed that the lubricating oil 50 of Examples 1 to 8 has excellent fluidity.

As shown in Table 1, the lubricating oil 50 of Examples 1 to 8 has a pour point of −30 ° C. or lower. As a result, it was confirmed that the lubricating oils 50 of Examples 1 to 8 have excellent fluidity in a low temperature environment.

[Evaluation of low evaporation]

As shown in Table 1, it was confirmed that the lubricating oils of Examples 1 to 8 had a mass change rate of 0.9% by mass or less and were excellent in low evaporation property.

[Evaluation of moisture resistance]

As shown in Table 1, it was confirmed that the lubricating oils of Examples 1 to 8 had a moisture resistance time of more than 2000 hours and were excellent in moisture resistance.

Further, as shown in Table 1, the lubricating oils of Comparative Examples 1 and 4 have the same absolute viscosity at 40 ° C. as the lubricating oils of Examples 1 to 8, but have low evaporation property and moisture resistance. Inferior. Further, the lubricating oils of Comparative Examples 2 and 3 have a low evaporation rate, but have a high pour point and low moisture resistance. Therefore, it is inferior in fluidity in a low temperature environment. Therefore, it was found that the lubricating oils of Examples 1 to 8 are difficult to evaporate in a high temperature environment and difficult to be reduced in molecular weight by decomposition or the like in a high humidity environment while reducing the decrease in fluidity.

(5. Others)
Although one embodiment of the present invention has been described above, the present invention is not limited to the present embodiment. For example, in the present embodiment, the conical type hydrodynamic bearing 4 is applied, but the conical type is not limited to the conical type, and for example, the thrust type fluid dynamic bearing 4 may be applied.

Further, in the present embodiment, the outer rotor type spindle motor has been described, but the present invention can also be applied to the inner rotor type spindle motor.

1 ... Spindle motor, 2 ... Stationary part, 3 ... Rotating part, 4 ... Fluid dynamic bearing, 11 ... Shaft part, 12a, 12b ... Annular member, 13 ... Holding member, 13a ... recess, 13b ... flange portion, 14 ... sleeve portion, 14a ... first inner peripheral surface, 14b ... second inner peripheral surface, 14c ... third inner Peripheral surface, 15 ... coil, 16 ... magnet, 17 ... base part, 17a ... through hole, 17b ... holder part, 18 ... stator core, 18a ... core back, 18b ... ... Teeth, 19 ... Seal part, 20 ... Disc, 22 ... Spacer, 30 ... Access part, 50 ... Lubricating oil, L ... Central axis, S ... Micro gap

Claims (9)

In lubricating oil for fluid dynamic bearings of fluid dynamic bearings,
Lubricating oil for fluid dynamic bearings containing an aliphatic carboxylic acid monoester represented by any of the following formulas (1) to (3).

The lubricating oil for a fluid dynamic bearing according to claim 1, wherein R1 is a linear alkyl group having 7 to 10 carbon atoms in the formula (1). The lubricating oil for a fluid dynamic bearing according to claim 1 or 2, wherein R2 is a linear alkyl group having 10 to 13 carbon atoms in the formula (1). The lubricating oil for a fluid dynamic bearing according to claim 1, wherein R3 is a linear alkyl group having 2 to 4 carbon atoms in the formula (2). The lubricating oil for a fluid dynamic bearing according to claim 1, wherein R5 is a linear alkyl group having 3 to 6 carbon atoms in the formula (3). The lubrication for a fluid dynamic bearing according to any one of claims 1 to 5, wherein the total carbon number of the aliphatic carboxylic acid monoester represented by any of the formulas (1) to (3) is 29 or 30. oil. The lubricating oil for a fluid dynamic bearing according to any one of claims 1 to 6, wherein the aliphatic carboxylic acid monoester represented by any of the formulas (1) to (3) has a molecular weight of 454 or more and 468 or less. .. The fluid dynamic bearing in which the lubricating oil for the fluid dynamic bearing according to any one of claims 1 to 7 is sealed. The spindle motor provided with the fluid dynamic bearing according to claim 8.

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