JP5298903B2 - Hydrodynamic bearing device - Google Patents

Description

  The present invention relates to a hydrodynamic bearing device.

  In recent years, a recording / reproducing apparatus such as a hard disk drive that performs recording and reproduction by rotating a recording medium is required to increase the rotation speed, improve the rotation accuracy, reduce the size, and reduce the power consumption. For this reason, in a spindle motor used in a hard disk drive, replacement of a bearing portion with a hydrodynamic bearing is being promoted.

  However, in such a hard disk drive, static electricity is accumulated by the rotation of the spindle motor, and this static electricity may cause problems such as head damage and an increased error rate.

Therefore, conventionally, it has been proposed to prevent accumulation of static electricity by blending an additive that imparts conductivity to the lubricant of the bearing (for example, Patent Document 1).
JP 2001-115180 A

  The conventional lubricant containing the additive has a problem that the durability is lowered as compared with that before adding the additive.

Therefore, in order to solve the above problems, the present invention provides
(1) A base oil filled with a sleeve having a bearing hole, a shaft disposed in the bearing hole of the sleeve so as to rotate relative to the sleeve, and a gap between the sleeve and the shaft. A hydrodynamic bearing device comprising: an ester oil as a base material; and a lubricant composition containing 0.01 to 3% by weight of a polyoxyethylene sorbitan fatty acid ester compound with respect to the entire lubricant composition;

  (2) The hydrodynamic bearing device according to (1), wherein the lubricant composition contains 0.01 to 1% by weight of a polyoxyethylene sorbitan fatty acid ester compound relative to the entire lubricant composition;

  (3) The hydrodynamic bearing device according to (1), wherein the lubricant composition contains 0.05 to 0.3% by weight of a polyoxyethylene sorbitan fatty acid ester compound with respect to the entire lubricant composition; as well as

(4) The hydrodynamic bearing device according to any one of (1) to (3), wherein the polyoxyethylene sorbitan fatty acid ester compound is polyoxyethylene sorbitan trioleate.

  The hydrodynamic bearing device of the present invention has an effect that it is possible to achieve both prevention of static electricity accumulation and good durability by having the above-described configuration of the lubricant composition.

[1] First Embodiment (1-1) Spindle Motor As an example of the hydrodynamic bearing device of the present invention, a hydrodynamic bearing device in a spindle motor for a hard disk drive will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of a spindle motor 1 according to this embodiment.

[Configuration of spindle motor 1]
As shown in FIG. 1, the spindle motor 1 of the present embodiment is a device for rotationally driving a disk-shaped magnetic recording disk 151, and mainly includes a hydrodynamic bearing device 10, a base 18, a stator core 19, And a rotor magnet 20.

  The hydrodynamic bearing device 10 smoothly rotates the rotating side member including the rotor hub 15 around the shaft 12 in a non-contact state with respect to the fixed side member such as the sleeve 11. Since the magnetic recording disk 151 is mounted on the rotor hub 15, the magnetic recording disk 151 rotates about the shaft 12. The configuration of the hydrodynamic bearing device 10 will be described later.

  The base 18 forms a base portion of the hydrodynamic bearing device 10 and the stator core 19. The base 18 is made of a non-magnetic aluminum-based metal material (for example, ADC 12) or a magnetic iron-based metal material (for example, SPCC, SPCD). A sleeve 11 and a stator core 19 are attached to the base 18.

  The stator core 19 is fixed to the base 18, and the outer peripheral portion thereof is disposed at a position facing the inner peripheral portion of the rotor magnet 20 with a predetermined gap. The stator core 19 has a plurality of salient poles formed toward the outer periphery, and coils are wound around the salient poles.

  The rotor magnet 20 has an annular shape, is fixed to the inner peripheral surface of the hanging cylindrical portion from the flange portion of the rotor hub 15, and constitutes a magnetic circuit together with the stator core 19 around which the coil is wound.

[Configuration of Fluid Bearing Device 10]
As shown in FIG. 2, the hydrodynamic bearing device 10 according to the present embodiment includes a sleeve 11, a shaft 12, a flange 13, a thrust plate 14, a rotor hub 15, a sleeve cap 16, and a lubricating fluid 17. I have.

The sleeve 11 has a bearing hole 11a and a communication passage 11b that communicates the open end side and the closed end side of the bearing hole 11a. Details of the sleeve 11 will be described later.
As shown in FIG. 2, the shaft 12 is rotatable in the bearing hole 11 a of the sleeve 11 so as to form a first gap G <b> 1 between the inner peripheral surface of the bearing hole 11 a and the outer peripheral surface of the shaft 12. It is inserted in the state. Dynamic pressure generating grooves 11 c and 11 d are formed on at least one of the outer peripheral surface of the shaft 12 or the inner peripheral surface of the bearing hole 11 a of the sleeve 11. A flange 13 is fixed to the lower end portion of the shaft 12 at a substantially right angle with high accuracy.

  The flange 13 is disposed at the lower end portion of the shaft 12 so that the angle formed by the shaft 12 and the flange 13 is substantially perpendicular and the upper end surface of the flange 13 faces the sleeve 11. Further, the flange 13 is disposed so as to form a gap between the sleeve 11 and the flange 13, and this gap is continuous from the first gap G1 described above.

  Further, the flange 13 is arranged so that the lower end surface thereof faces the thrust plate 14 and forms a gap between the flange 13 and the thrust plate 14. The gap is formed between the sleeve 11 and the flange described above. It continues from the gap between 13. Further, the gap between the flange 13 and the thrust plate 14 continues to the communication path 11b.

  A dynamic pressure generating groove 11e is formed on at least one of the surface of the sleeve 11 facing the flange 13 and the surface of the flange 13 facing the sleeve 11. Further, a dynamic pressure generating groove 14 a is formed on at least one of the surface of the flange 13 facing the thrust plate 14 and the surface of the thrust plate 14 facing the flange 13. Only one of the dynamic pressure generating grooves 11e and 14a may be provided.

  A rotor magnet 20 (described later) is fixed to the rotor hub 15 at a position facing the stator core 19, and a magnetic recording disk 151 such as a magnetic disk or an optical disk is attached as necessary. The rotor hub 15 includes a boss portion 15 a that protrudes toward the sleeve 11.

  The sleeve cap 16 has a central hole 16 a and is fixed to the upper end surface of the sleeve 11. The sleeve cap 16 is disposed so as to form a second gap G <b> 2 between the upper surface of the sleeve 11. The second gap G2 is continuous from the first gap G1 to the communication path 11b. The above-described boss portion 15a and shaft 12 have outer peripheral surfaces facing the inner peripheral surface of the central hole 16a, and a third gap G3 is formed between the outer peripheral surface and the inner peripheral surface of the central hole 16a. To be arranged. The third gap G3 communicates with the first gap G1 and the second gap G2. Although the third gap G3 is open to the atmosphere, the lubricating fluid 17 is held in the hydrodynamic bearing device 10 by its own surface tension.

  The lubricating fluid 17 is filled in the bearing gap including the first to third gaps G1 to G3 shown in FIG. When rotation of the rotating side member including the shaft 12 is started, the lubricating fluid 17 flows into the dynamic pressure generating grooves 11c, 11d, 11e and the like to generate dynamic pressure, and the dynamic pressure generating groove on the radial side. Circulation force is generated by 11c and 11d being formed asymmetrically and circulates in the hydrodynamic bearing device 10 along the direction of the arrow in the figure.

  Stainless steel is the most suitable material for the shaft 12. Stainless steel is effective because it has higher hardness and can suppress the amount of wear compared to other metals. More preferably, it is martensitic stainless steel.

  The sleeve 11 is preferably made of a material such as copper alloy, iron alloy, stainless steel, ceramics, or resin. Furthermore, copper alloy, iron alloy, and stainless steel, which have higher wear resistance and workability and are low in cost, are more preferable. Surface modification may be performed on a part or all of the sleeve material by plating, physical vapor deposition, chemical vapor deposition, diffusion coating, ion implantation, or the like. In addition, from the viewpoint of cost, a metal sintered body containing iron, copper or the like can be used as the sleeve material.

[Lubricating fluid 17]
As the lubricating fluid 17, a lubricant composition containing a base oil and an additive is used.
<Base oil>
The “base oil” means a substance that is a main component of the lubricant composition and imparts lubricity to the lubricant composition. Therefore, generally, the content of the base oil in the entire lubricant composition is set to 50% by weight or more. In particular, the content of the base oil in the entire lubricant composition can be set to 80% by weight or more, 90% by weight or more, or 94% by weight or more. It can be said that the content of the base oil is an amount obtained by removing additives described later from the lubricant composition.

  An ester oil is used as the base oil. Examples of ester oils include aromatic esters such as trioctyl trimellitate, tridecyl trimellitate, tetraoctyl pyromellitate; hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecane Aliphatic monocarboxylic acids such as acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid or octadecanoic acid, and hexanol, 2-ethylhexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol, tridecanol, Monoesters such as esters with monohydric alcohols such as tetradecanol, pentadecanol, or hexadecanol; dioctyl sebacate (DOS), dioctyl azelate (DOZ), dioctyl adipate (DOA), diesters (dibasic acid esters) such as diisononyl adipate and diisodecyl adipate; and neopentyl glycol, polyglycol, 3-methyl-1,5-pentanediol, 2,4-dimethyl-1,5- Examples include polyol esters such as esters of alcohols such as pentanediol, 2,4-diethyl-1,5-pentanediol, trimethylolethane, trimethylolpropane, pentaerythritol, and fatty acids having 5 to 12 carbon atoms.

<Additives>
(Polyoxyethylene sorbitan fatty acid ester compound)
Examples of the additive include polyoxyethylene sorbitan fatty acid ester compounds. The polyoxyethylene sorbitan fatty acid ester compound is obtained by adding ethylene oxide to a sorbitan fatty acid ester. Specifically, polyoxyethylene (6) sorbitan monolaurate, polyoxyethylene (20) sorbitan monopalmitate, polyoxyethylene (6) sorbitan monostearate, polyoxyethylene (20) sorbitan monostearate, poly Oxyethylene (20) sorbitan tristearate, polyoxyethylene (6) sorbitan monooleate, polyoxyethylene (20) sorbitan monooleate, polyoxyethylene (20) sorbitan trioleate, polyoxyethylene (20) sorbitan mono Examples include isostearate, polyoxyethylene (160) sorbitan triisostearate, polyoxyethylene (20) sorbitan monococonut fatty acid ester, and the like. In addition, although the numerical value in () shows the average addition mole number of an oxyethylene group, an average addition mole number is not specifically limited.

  In addition, the polyoxyethylene sorbitan fatty acid ester compound has a melting point of 40 ° C. or lower, preferably 20 ° C. or lower, more preferably 0 ° C. or lower, from the viewpoint of compatibility with the base oil and storage stability at low temperatures.

  In addition, the viscosity of the polyoxyethylene sorbitan fatty acid ester-based compound measured according to JIS Z8803 is preferably 300 mPa · s or less, preferably 200 mPa · s or less at 40 ° C., in terms of suppressing the thickening of the lubricant.

  From these viewpoints, polyoxyethylene sorbitan monolaurates, polyoxyethylene sorbitan monooleates, and polyoxyethylene sorbitan trioleates are preferable. Furthermore, polyoxyethylene sorbitan monooleates and polyoxyethylene sorbitan trioleates are preferred.

  In terms of the effect of imparting conductivity, the polyoxyethylene sorbitan fatty acid ester compound is preferably a diester compound, further a triester compound or a tetraester compound.

These polyoxyethylene sorbitan fatty acid ester compounds may be used alone or in combination of two or more.
By containing the polyoxyethylene sorbitan fatty acid ester compound, the lubricant composition has electrical conductivity, so that accumulation of static electricity generated by the rotation of the shaft 12 can be prevented.

  Further, the content of the polyoxyethylene sorbitan fatty acid ester compound is 0.01 to 3% by weight, preferably 0.01 to 1% by weight, more preferably 0.01 to 0.1% by weight based on the entire lubricant composition. It is 0.3% by weight, more preferably 0.05 to 0.3% by weight.

  Since the content of the polyoxyethylene sorbitan fatty acid ester compound is within this range, the lubricant composition has conductivity, so that accumulation of static electricity is prevented and relatively good oxidation stability is exhibited. Good durability is achieved. Moreover, since an effect can be exhibited with a small amount, an increase in the viscosity of the lubricant composition can also be suppressed. Further, the oil film breakage of the bearing device due to the influence of moisture can be suppressed even when left in a hot and humid environment by the emulsification / dispersion action. And, if the content of the polyoxyethylene sorbitan fatty acid ester compound is within the above range, the suspension and precipitation due to the compound hardly occur even at a low temperature of −20 ° C. or even −40 ° C. or lower. The influence of the environment on the generation of dynamic pressure in the bearing device is reduced, and stable rotation characteristics can be obtained.

(Other additives)
The lubricant composition may contain further additives. Examples of such additives include antioxidants, rust inhibitors, metal deactivators, metal corrosion inhibitors, oil agents, extreme pressure agents, friction modifiers, antiwear agents, viscosity index improvers, pour points. Examples include a depressant, a defoaming agent, a hydrolysis inhibitor, a conductivity imparting agent, and a cleaning dispersant.

  In the lubricant composition of the present invention, the additive amount of the additive is not particularly limited, but is, for example, 10% by weight or less, preferably 5% by weight or less, more preferably, based on the entire lubricant composition. May be 3 wt% or less.

<Characteristics of entire lubricant composition>
The lubricant composition preferably has the following physicochemical properties.
The oxidation stability (RBOT value) measured according to JIS K2514 is 400 minutes or more, preferably 500 minutes or more, and more preferably 600 minutes or more.

The volume resistivity at 25 ° C. and 5 V, measured in accordance with JIS C2101, is 5 × 10 ¹¹ Ω · cm or less, preferably 1 × 10 ¹¹ Ω · cm or less, more preferably 1 × 10 ¹⁰ Ω · cm or less.

The viscosity index calculated according to JIS K2283 is 100 or more, preferably 120 or more, more preferably 140 or more.
The amount of evaporation measured according to JIS C2101 is 5% by weight or less, preferably 4% by weight or less, more preferably 3% by weight or less.

  The pour point measured according to JIS K2269 is −20 ° C. or lower, preferably −30 ° C. or lower, more preferably −40 ° C. or lower. The low-temperature solidification temperature is −20 ° C. or lower, preferably −30 ° C. or lower, more preferably −40 ° C. or lower. However, the low-temperature solidification temperature in this case is a temperature different from the pour point. The low temperature solidification temperature is a temperature at which a part or all of the lubricant is solidified when collected in a temperature vessel for 2 days after collecting the lubricant in a sample bottle. is there.

  The kinematic viscosity measured according to JIS K2283 and the viscosity determined from the density measured according to JIS K2249 are 70 to 200 mPa · s at −20 ° C., more preferably 70 to 150 mPa · s, and 5 to 35 mPa · s at 20 ° C. s, more preferably 10 to 25 mPa · s, and at 80 ° C., 2 to 5 mPa · s, more preferably 3 to 4 mPa · s.

<Manufacture of lubricant composition>
The lubricant composition of the present invention can be produced by mixing the base oil and the additive by a conventional method.

  The lubricant composition is preferably subjected to pressure filtration or vacuum filtration with a filter having a pore diameter equal to or smaller than the minimum gap formed between the sleeve and the shaft structure before filling the hydrodynamic bearing device. As a result, the foreign matter is removed, and rotation problems caused by the foreign matter can be suppressed. In addition, the pore diameter of a specific filter is 0.5 μm or less, preferably 0.2 μm or less, and more preferably 0.1 μm or less.

(1-2) Operation of Spindle Motor 1 As shown in FIG. 1, when the stator core 19 is energized, a rotating magnetic field is generated between the rotor magnet 20 and the stator core 19, and the rotor magnet 20 is connected to the shaft 12. , The rotation is started together with the flange 13 and the rotor hub 15. When the shaft 12 starts rotating, the lubricating fluid 17 gathers in the dynamic pressure generating grooves 11c to 11e and 14a, so that the shaft 12 rotates in a non-contact manner with respect to the sleeve 11 while floating in the lubricating fluid 17. The lubricating fluid 17 circulates between the communication path 11b and the gaps G1 and G2.

  As is clear from the above description, the sleeve 11 is a stationary member, and the shaft 12 and the flange 13 are rotating members.

(1-3) Magnetic Recording / Reproducing Device The spindle motor 1 described above can be applied to a magnetic recording / reproducing device. FIG. 3 is a cross-sectional view showing a configuration of the magnetic recording / reproducing apparatus 150 according to the present embodiment.

As shown in FIG. 3, the magnetic recording / reproducing apparatus 150 includes a spindle motor 1, a recording disk 151, and a recording head 152.
The magnetic recording disk 151 is mounted on a disk mounting portion of the rotor hub 15. For example, a disk-shaped clamper having spring property in the axial direction (not shown) is set on a tapping screw (not shown), and the central portion of the shaft 12 is set. By screwing the tapping screw into the provided screw tap portion, the tapping screw is pressed down in the axial direction and is held between the clamper and the disk mounting portion of the rotor hub 15.

  The recording head 152 reads information on the magnetic recording disk 151 and writes information. The recording head 152 only needs to be capable of at least one of reading and writing.

  In addition, the magnetic recording / reproducing apparatus 150 includes an arm that supports the recording head 152, an arm driving unit that moves the arm, and arranges the recording head 152 at a predetermined position of the magnetic recording disk 151.

[2] Other Embodiments Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the scope of the invention.

(A)
In the above embodiment, the so-called flange type hydrodynamic bearing device 10 in which the flange 13 is attached to the shaft 12 has been described as an example. However, the present invention is not limited to this.
For example, in FIG. 2, the present invention may be applied to a so-called flangeless type hydrodynamic bearing device in which there is no flange 13 with respect to the shaft 12 and the lower end surface of the shaft 12 is a bearing surface.

(B)
In the above-described embodiment, the rotation-side member including the shaft 12 and the rotor hub 15 is described as an example of the shaft-rotation type hydrodynamic bearing device 10 that rotates with respect to the fixed-side member including the sleeve 11. However, the present invention is not limited to this.
For example, even if the fixed-side member including the shaft is filled with the lubricating fluid according to the embodiment of the present invention in the fixed-shaft type hydrodynamic bearing device in which the rotating-side member including the sleeve and the rotor hub rotates. Good.

(C)
In the above embodiment, the configuration of the hydrodynamic bearing device 10 that circulates the lubricating fluid 17 along the circulation path including the communication path 11b formed in the sleeve 11 has been described as an example. However, the present invention is not limited to this.
For example, a lubricating fluid according to an embodiment of the present invention may be filled into a non-circulating fluid bearing device having no communication path in the sleeve.

(D)
The hydrodynamic bearing device and the spindle motor can be applied to a magnetic recording / reproducing apparatus that records / reproduces information on / from a recording disk by the recording head 152. May be.
Furthermore, the present invention may be applied to a hydrodynamic bearing device included in a spindle motor that rotates a cooling fan mounted on a CPU as an information processing device.

EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated more concretely, this invention is not limited to a following example at all. In addition, the compounding quantity of each additive described below, ie, weight%, is a ratio with respect to the whole lubricant composition (total weight) including the base oil and the additive.
In any case of Examples and Comparative Examples, 0.5% by weight of dioctyl diphenylamine was added as an antioxidant.

(Examples 1-5)
An ester of 3-methyl-1,5-pentanediol and pelargonic acid (shown as (i) in Table 1) was used as the base oil, and polyoxyethylene (20) sorbitan trioleate (melting point − A lubricant composition was prepared by mixing a viscosity of 150 mPa · s at 20 ° C. and 40 ° C., manufactured by Kao Corporation. The addition amount (% by weight) of polyoxyethylene (20) sorbitan trioleate in Examples 1 to 5 is as shown in Table 1.

(Examples 6 to 9)
A lubricant composition was prepared by using dioctyl sebacate (DOS) (shown as (ii) in Table 1) as a base oil and mixing polyoxyethylene (20) sorbitan trioleate. The amount of polyoxyethylene (20) sorbitan trioleate added in Examples 6 to 9 is as shown in Table 1.

(Comparative Example 1)
The ester of 3-methyl-1,5-pentanediol and pelargonic acid used as the base oil in Examples 1 to 5 was used as a lubricant composition.

(Comparative Example 2)
A lubricant composition was prepared in the same manner as in Example 1 except that 0.1% by weight of Ca phenate was added to the base oil instead of polyoxyethylene (20) sorbitan trioleate.

(Comparative Example 3)
Dioctyl sebacate (DOS) used as the base oil in Examples 6 to 9 was used as the lubricant composition.

(Measurement of volume resistivity)
About each lubricant composition, the volume resistivity in 25 degreeC and 5V was measured according to JISC2101.

(RBOT test)
Each lubricant composition was subjected to RBOT (Rotating Bomb Oxidation stability Test) according to JIS K2514. Specifically, 50 g of a lubricant composition, 5 ml of water, a copper catalyst (diameter 1.6 mm, length 3000 mm), oxygen is sealed in a rotating cylinder to a specified pressure, and is forcedly deteriorated at a temperature of 150 ° C. The time from the maximum pressure after the start of the test until a sudden pressure drop of 175 kPa (1.8 kg / cm ² ) was observed was measured in minutes. It shows that oxidation stability is so high that this time is long.

(Motor characteristics)
Each lubricant composition was used as the lubricating fluid 17 of the spindle motor 1 described in the first embodiment, and the motor characteristics were measured.
As motor characteristics, the resistance value at 5 V between the rotor hub and the base during rotation at 5400 rpm at room temperature was measured.

(result)
Table 1 shows the additive content and test results for each lubricant composition.

Ｃａフェネートを添加した場合（比較例２）は、比較例１と比べて、体積抵抗率は低く良好であるものの、酸化安定性が大幅に低下した。すなわち、比較例２の潤滑剤組成物では、酸化安定性が低いために劣化しやすく、比較例１と比べて耐久性の点で劣る。

When Ca phenate was added (Comparative Example 2), the volume resistivity was low and good compared to Comparative Example 1, but the oxidation stability was greatly reduced. That is, the lubricant composition of Comparative Example 2 is easily deteriorated due to low oxidation stability, and is inferior in terms of durability as compared with Comparative Example 1.

In contrast, the lubricant compositions of Examples 1 to 9 exhibited a volume resistivity of about 2 × 10 ¹⁰ (Ω · cm) or less. Further, from the results of the lubricant compositions of Examples 2 to 9, when the amount of the additive was 1.0% by weight or less, the RBOT value was about 600 minutes or more, and the additive was not added (Comparative Example 1, The oxidation stability was comparable to that of Comparative Example 3). In addition, since Example 1 has less additive content than Example 2, it is estimated that the RBOT value is larger. That is, the lubricant compositions of Examples 1 to 9 were able to realize conductivity without significantly reducing the oxidation stability.

  Furthermore, the lubricant compositions of Examples 1 to 3 were able to reduce the current value of the motor as compared with Comparative Example 2. This is considered because the viscosity of the lubricant compositions of Examples 1 to 3 was reduced as compared with Comparative Example 2 in which the base oil was the same.

  Thus, by using the lubricant compositions of Examples 1 to 9 as the lubricating fluid, it is possible to effectively prevent the accumulation of static electricity and realize a fluid bearing device having good durability.

  The hydrodynamic bearing device of the present invention can be suitably used for a spindle motor for a hard disk drive because static electricity due to rotation is difficult to accumulate.

A sectional view of a spindle motor concerning one embodiment of the present invention. The partial expanded sectional view which shows the structure of the hydrodynamic bearing apparatus mounted in the said spindle motor. Sectional drawing which shows the structure of the magnetic recording / reproducing apparatus carrying the said hydrodynamic bearing apparatus.

DESCRIPTION OF SYMBOLS 1 Spindle motor 10 Fluid bearing apparatus 11 Sleeve 11a Bearing hole 11b Communication path 11c, 11d, 11e Dynamic pressure generating groove 12 Shaft 13 Flange 14 Thrust plate 14a Dynamic pressure generating groove 15 Rotor hub 15a Boss part 16 Sleeve cap 16a Central hole 17 Lubricating fluid 18 Base 19 Stator core 20 Rotor magnet 150 Magnetic recording / reproducing device 151 Magnetic recording disk 152 Recording heads G1 to G3 Gap

Claims (4)

A sleeve having a bearing hole;
A shaft disposed so as to rotate relative to the sleeve in the bearing hole of the sleeve, a gap between the sleeve and the shaft is filled with an ester oil as a base oil, and a lubricant composition A lubricant composition containing 0.01 to 1% by weight of a polyoxyethylene sorbitan fatty acid ester compound having a melting point of 40 ° C. or less and a viscosity at 40 ° C. of 300 mPa · s or less ,
A hydrodynamic bearing device comprising:   The hydrodynamic bearing device according to claim 1, wherein the lubricant composition contains 0.05 to 0.3% by weight of a polyoxyethylene sorbitan fatty acid ester compound with respect to the entire lubricant composition. The hydrodynamic bearing device according to claim 1 or 2 , wherein the polyoxyethylene sorbitan fatty acid ester compound is polyoxyethylene sorbitan trioleate. The hydrodynamic bearing device according to any one of claims 1 to 3, wherein the ester oil is an ester of 3-methyl-1,5-pentanediol and a fatty acid having 5 to 12 carbon atoms.

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