JP2018145400A - Lubricating oil for hydrodynamic pressure bearing, hydrodynamic pressure bearing, spindle motor and disk driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lubricating oil for a hydrodynamic pressure bearing, which can reduce generation of an electric potential difference between a stationary portion and a rotating portion of the hydrodynamic pressure bearing, and a hydrodynamic pressure bearing, a spindle motor and a disk driving device, which use the same.SOLUTION: The disk driving device has a spindle motor 10, the spindle motor 10 has a stationary portion 2 and a rotating portion 3 and a hydrodynamic pressure bearing 4 has a lubricating oil 50 for the hydrodynamic pressure bearing. The lubricating oil 50 for the hydrodynamic pressure bearing has a metal salt or an ionic liquid which is an anion having C1-8 perfluoroalkyl group, where the anion is a compound having predominantly the nitrogen anion or the carbanion.EFFECT: The lubricating oil 50 for the hydrodynamic pressure bearing to which the metal salt or the ionic liquid is added can reduce an occurrence of the electric potential difference between the stationary portion 2 and the rotating portion 3 of the hydrodynamic pressure bearing 4 under a high temperature or a high humidity environment.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a lubricant for a fluid dynamic pressure bearing, a fluid dynamic pressure bearing, a spindle motor, and a disk drive device.

  A conventional lubricating oil for fluid dynamic bearings is disclosed in Patent Document 1. The fluid dynamic pressure bearing lubricant is filled between the shaft portion and the sleeve portion of the fluid dynamic pressure bearing. A fluid dynamic pressure bearing is used as a bearing of a spindle motor that rotationally drives a disk that is a recording medium of a disk drive device.

  With the rotation of the spindle motor, dynamic pressure is generated in the fluid dynamic bearing lubricating oil, and contact between the shaft portion and the sleeve portion is prevented. Thereby, a sleeve part rotates smoothly with respect to a shaft part.

JP 2014-209030 A

  However, according to the conventional fluid dynamic pressure bearing lubricant, the fluid dynamic pressure bearing is reduced in size and thickness with the downsizing of the disk drive device and the spindle motor, and the flying distance between the recording medium and the head is increased. Get smaller. For this reason, there has been a problem that a read / write error to the disk occurs due to a minute potential difference generated between the stationary part and the rotating part when the spindle motor is driven in a high temperature or high humidity environment.

  The present invention provides a fluid dynamic pressure bearing lubricant capable of reducing the occurrence of a potential difference between a stationary portion and a rotating portion of a fluid dynamic pressure bearing, and a fluid dynamic pressure bearing, a spindle motor, and a disk drive device using the same. For the purpose.

  The lubricating oil for fluid dynamic pressure bearings of the present invention has an antistatic agent containing a metal salt or ionic liquid added to the fluid dynamic pressure bearing lubricating oil of the fluid dynamic pressure bearing.

  According to the exemplary present invention, occurrence of a potential difference between a stationary part and a rotating part of a fluid dynamic pressure bearing can be reduced under a high temperature or high humidity environment.

FIG. 1 is a longitudinal sectional view of a disk drive device according to an embodiment of the present invention. FIG. 2 is a longitudinal sectional view of the spindle motor according to the embodiment of the present invention.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. In this 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”. Note that the vertical direction does not indicate the positional relationship or direction when incorporated in an actual device. A direction parallel to or approximately parallel to the central axis is called an “axial direction”, a radial direction centered on the central axis is simply “radial direction”, and a circumferential direction centered on the central axis is “circumferential direction”. And

(1. Overall configuration of disk drive)
A disk drive apparatus according to an exemplary embodiment of the present invention will be described below. FIG. 1 is a longitudinal sectional view of a disk drive device 100 according to the first embodiment. The disk drive device 100 is a so-called hard disk drive device. The disk drive device 100 includes a spindle motor 10, four disks 20, an access unit 30, and a housing 40.

  The spindle motor 10, the disk 20, and the access unit 30 are accommodated in the housing 40. In the housing 40, dust and dust are extremely small, and a clean space is formed.

  The disk 20 is a disk-shaped information recording medium having a hole in the center. The respective disks 20 are mounted on the spindle motor 10 and are arranged in parallel with each other at regular intervals via spacers 22.

  The access unit 30 includes a head 31, an arm 32, and a head moving mechanism 33. The head 31 is close to the disk 20 and magnetically reads and writes information. The arm 32 supports the head 31. The head moving mechanism 33 moves the arm 31 relative to the disk 20 by moving the arm 32.

  Head 31 accesses close to rotating disk 20. The number of disks 20 is not limited to four, but may be three or less or five or more.

(2. Configuration of spindle motor)
FIG. 2 is a longitudinal sectional view of the spindle motor 10. The spindle motor 10 is an outer rotor type motor. The spindle motor 10 has a stationary part 2 and a rotating part 3. The stationary part 2 is fixed to the housing 40. The rotating part 3 is mounted so as to be rotatable with respect to the stationary part 2 around the central axis L via a fluid dynamic bearing oil 50 (hereinafter abbreviated as lubricating oil) with the disk 20 mounted thereon. Further, a conical fluid dynamic bearing 4 is constituted by a part of the stationary part 2 and a part of the rotating part 3.

(2-1. Configuration of stationary part)
The stationary part 2 includes a base part 17, a shaft part 11, annular members 12 a and 12 b, a stator core 18, and a coil 15. The base portion 17 is formed of a metal material such as aluminum and is screwed to the housing 40. Note that the base portion 17 and the housing 40 may be separate members or may be integrally formed with a single member.

  A through hole 17 a is formed along the central axis L at the center of the base portion 17. A substantially cylindrical holder portion 17b that protrudes in the axial direction is formed on the outer peripheral side of the through hole 17a.

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

  The annular members 12 a and 12 b protrude outward in the radial direction from the outer peripheral surface of the shaft portion 11. The annular members 12a and 12b are fixed vertically on the outer peripheral surface of the shaft portion 11 with an interval in the axial direction. The annular members 12a and 12b may be integrally formed with the shaft portion 11.

  In the case of the conical fluid dynamic pressure bearing 4, the annular members 12 a and 12 b have a substantially conical shape, and the upper and lower surfaces of the annular members 12 a and 12 b are gradually formed with a smaller diameter.

  The stator core 18 has a core back 18a and 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 protrude radially outward from the core back 18a.

  The coil 15 is formed of a conductive 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, a radial magnetic flux is generated in the teeth 18b.

(2-2. Configuration of rotating unit)
The rotating part 3 includes a sleeve part 14, a holding member 13, a magnet 16 and a seal part 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 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 14 b 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. 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 cylindrical 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 protruding outward in the radial direction is formed at the lower end. A hole formed in the central portion of the disk 20 (see FIG. 1) is fitted to the outer peripheral surface of the holding member 13. At this time, the disk 20 is placed on the upper surface of the flange portion 13b.

  A plurality of magnets 16 are arranged in the circumferential direction and attached to the yoke 16a. The magnet 16 is held by the holding member 13 by pressing the yoke 16a into the recess 13a. The inner peripheral surface of the magnet 16 is a magnetic pole surface and faces the outer peripheral surface 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 encloses the lubricating oil 50 in the minute gap S between the annular members 12 a and 12 b and the sleeve portion 14.

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

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

  A dynamic pressure groove (not shown) is formed in the opposing first inner peripheral surface 14a and the lower surface of the annular member 12a. In addition, a dynamic pressure groove (not shown) is formed on the opposing third inner peripheral surface 14c and the upper surface of the annular member 12b. The dynamic pressure groove induces fluid dynamic pressure in the lubricating oil 50 when the rotating unit 3 rotates. A dynamic pressure groove may be formed on one of the first inner peripheral surface 14a and the lower surface of the annular member 12a, or a dynamic pressure groove may be formed on one of the third inner peripheral surface 14c and the upper surface of the annular member 12b. Good.

  When a drive current is applied to the coil 15 of the spindle motor 10, a radial magnetic flux is generated in the coil 15. Torque is generated by the action of magnetic flux between the coil 15 and the magnet 16, and the rotating part 3 rotates about the central axis L with respect to the stationary part 2.

  When the sleeve portion 14 is rotationally driven with respect to the annular members 12a and 12b, the dynamic pressure groove induces fluid dynamic pressure in the lubricating oil 50 filled in the minute gap S by the pumping action. Accordingly, the sleeve portion 14 is supported in the radial direction and the axial direction 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)
As the lubricating oil 50, for example, an oil mainly composed of an ester such as a polyol ester oil, a diester oil, or a monoester oil is used as the base oil. The oil mainly composed of ester is suitable as the lubricating oil 50 for the fluid dynamic pressure bearing 4 because it is excellent in wear resistance, thermal stability, and fluidity.

  Further, an antistatic agent containing a metal salt or an ionic liquid is added to the lubricating oil 50. By adding the antistatic agent to the lubricating oil 50, the potential difference generated between the annular portions 12a and 12b and the sleeve portion 14 that are opposed to each other through the lubricating oil 50 can be reduced.

  Thereby, when the spindle motor 10 is driven in a high-temperature environment or a high-humidity environment, it is possible to prevent occurrence of a read / write error to the disk 20 due to a minute potential difference generated between the stationary part 2 and the rotating part 3. .

  The lubricating oil 50 preferably contains 0.01 wt% or more and 5 wt% or less of a metal salt or ionic liquid.

  The metal salt or ionic liquid anion contained in the antistatic agent preferably has a perfluoroalkyl group having 1 to 8 carbon atoms.

Since the perfluoroalkyl group has a CF ₃ group, it is highly hydrophobic even if it has 1 to 8 carbon atoms. In addition, when the carbon number of the perfluoroalkyl group is larger than 9, both hydrophobicity and hydrophilicity are lowered. Further, since the perfluoroalkyl group has a C—F bond, the bond energy is large and the heat resistance and shear resistance are high.

Therefore, by adding an anion having a perfluoroalkyl group to the antistatic agent, the antistatic agent is easily dissolved in the lubricating oil 50, and the heat resistance and shear resistance of the lubricating oil 50 are high (50 ° C). ˜150 ° C.) or high humidity (82 g / m ³ or more).

  Specific examples of the anion having a perfluoroalkyl group having 1 to 8 carbon atoms are represented by the following formulas (1) to (10).

（１）
［式中、ｎ＝０〜８］

(1)
[Where n = 0 to 8]

（２）
［式中、ｐ≠ｑ、ｐ＝０〜８、ｑ＝０〜８］

(2)
[Wherein p ≠ q, p = 0-8, q = 0-8]

（３）
［式中、ｍ＝０〜８］

(3)
[Where m = 0 to 8]

（４）
［式中、ｎ＝０〜８］

(4)
[Where n = 0 to 8]

（５）
［式中、ｐ≠ｑ、ｐ＝０〜８、ｑ＝０〜８］

(5)
[Wherein p ≠ q, p = 0-8, q = 0-8]

（６）
［式中、ｎ＝０〜８］

(6)
[Where n = 0 to 8]

（７）
［式中、ｐ≠ｑ、ｐ＝０〜８、ｑ＝０〜８］

(7)
[Wherein p ≠ q, p = 0-8, q = 0-8]

（８）
［式中、ｎ＝０〜８］

(8)
[Where n = 0 to 8]

（９）
［式中、ｐ≠ｑ、ｐ＝０〜８、ｑ＝０〜８］

(9)
[Wherein p ≠ q, p = 0-8, q = 0-8]

（１０）
［式中、ｌ≠ｍ≠ｎ、ｌ＝０〜８、ｍ＝０〜８、ｎ＝０〜８］

(10)
[Wherein l ≠ m ≠ n, l = 0-8, m = 0-8, n = 0-8]

（１１）
［式中、ｎ＝０〜８］

(11)
[Where n = 0 to 8]

  Moreover, you may use the anion represented by following formula (12) for the anion of the metal salt or ionic liquid contained in an antistatic agent.

（１２）

(12)

When the antistatic agent contains a metal salt, the metal salt can be any of Na ⁺ , Rb ⁺ , Cs ⁺ , Li ⁺ , and K ⁺ as a counter cation of the anion represented by the above formulas (1) to (12). Have some cations.

When the counter cation of the metal salt is Li ⁺ , n = 1 in the formula (1), m = 1 in the formula (3), m = 4, and n = 1 in the formula (8) are excluded. When the counter cation of the metal salt is K ⁺ , n = 1 in the formula (1) and m = 1 in the formula (3) are excluded.

  When the antistatic agent contains an ionic liquid, the ionic liquid is represented by any one of the following formulas (13) to (21) as a counter cation of the anion represented by the above formulas (1) to (12). Having cations.

（１３）
［式中、Ｒ１、Ｒ２は、炭素数が１〜２２のアルキル基又はアルケニル基、若しくは炭素数が６〜３０のアリール基又はアルキルベンゼン基］

(13)
[Wherein R1 and R2 are alkyl groups or alkenyl groups having 1 to 22 carbon atoms, or aryl groups or alkylbenzene groups having 6 to 30 carbon atoms]

（１４）
［式中、Ｒ１、Ｒ２、Ｒ３、Ｒ４は、炭素数が１〜２２のアルキル基又はアルケニル基、若しくは炭素数が６〜３０のアリール基又はアルキルベンゼン基］

(14)
[Wherein R 1, R 2, R 3, R 4 are an alkyl group or alkenyl group having 1 to 22 carbon atoms, or an aryl group or alkyl benzene group having 6 to 30 carbon atoms]

（１５）
［式中、Ｒは、炭素数が１〜２２のアルキル基又はアルケニル基、若しくは炭素数が６〜３０のアリール基又はアルキルベンゼン基］

(15)
[Wherein, R represents an alkyl group or alkenyl group having 1 to 22 carbon atoms, or an aryl group or alkylbenzene group having 6 to 30 carbon atoms]

（１６）
［式中、Ｒ１、Ｒ２は、炭素数が１〜２２のアルキル基又はアルケニル基、若しくは炭素数が６〜３０のアリール基又はアルキルベンゼン基］

(16)
[Wherein R1 and R2 are alkyl groups or alkenyl groups having 1 to 22 carbon atoms, or aryl groups or alkylbenzene groups having 6 to 30 carbon atoms]

（１７）
［式中、Ｒ１、Ｒ２は、炭素数が１〜２２のアルキル基又はアルケニル基、若しくは炭素数が６〜３０のアリール基又はアルキルベンゼン基］

(17)
[Wherein R1 and R2 are alkyl groups or alkenyl groups having 1 to 22 carbon atoms, or aryl groups or alkylbenzene groups having 6 to 30 carbon atoms]

（１８）
［式中、Ｒ１、Ｒ２、Ｒ３、Ｒ４は、炭素数が１〜２２のアルキル基又はアルケニル基、若しくは炭素数が６〜３０のアリール基又はアルキルベンゼン基］

(18)
[Wherein R 1, R 2, R 3, R 4 are an alkyl group or alkenyl group having 1 to 22 carbon atoms, or an aryl group or alkyl benzene group having 6 to 30 carbon atoms]

（１９）
［式中、Ｒ１、Ｒ２は、炭素数が１〜２２のアルキル基又はアルケニル基、若しくは炭素数が６〜３０のアリール基又はアルキルベンゼン基］

(19)
[Wherein R1 and R2 are alkyl groups or alkenyl groups having 1 to 22 carbon atoms, or aryl groups or alkylbenzene groups having 6 to 30 carbon atoms]

（２０）
［式中、Ｒ１、Ｒ２は、炭素数が１〜２２のアルキル基又はアルケニル基、若しくは炭素数が６〜３０のアリール基又はアルキルベンゼン基］

(20)
[Wherein R1 and R2 are alkyl groups or alkenyl groups having 1 to 22 carbon atoms, or aryl groups or alkylbenzene groups having 6 to 30 carbon atoms]

（２１）

(21)

  The lubricating oil 50 contains a nonionic surfactant made of sorbitan fatty acid ester. By including a nonionic surfactant, the metal salt or ionic liquid can be dispersed in the lubricating oil 50. The lubricating oil 50 preferably contains 0.01% by weight or more and 1% by weight or less of a nonionic surfactant.

  According to the present embodiment, since the antistatic agent containing a metal salt or ionic liquid is added to the lubricating oil 50 of the fluid dynamic pressure bearing 4, the disk 20 due to a slight potential difference generated between the stationary part 2 and the rotating part 3. Occurrence of a write error can be prevented.

  Further, since the metal salt or ionic liquid contained in the antistatic agent contains an anion having a perfluoroalkyl group having 1 to 8 carbon atoms, the antistatic agent is easily dissolved in the lubricating oil 50 and the lubricating oil 50 Heat resistance and shear resistance can be stabilized for a long time in an environment of high temperature or high humidity.

  Further, since the metal salt or ionic liquid contained in the antistatic agent contains any one of the anions represented by the formulas (1) to (12), the lubricating oil 50 having stable heat resistance and shear resistance can be easily obtained. Can be realized.

  Moreover, since the antistatic agent contains 0.01 wt% or more and 5 wt% or less of the metal salt or ionic liquid, the lubricating oil 50 having stable heat resistance and shear resistance can be easily realized.

In addition, since the metal salt contained in the antistatic agent has a cation of Na ⁺ , Rb ⁺ , Cs ⁺ , Li ⁺ , or K ⁺ , the lubricating oil 50 having stable heat resistance and shear resistance can be easily obtained. Can be realized.

  Further, since the ionic liquid contained in the antistatic agent has any one of the cations represented by the formulas (13) to (21), it is possible to easily realize the lubricating oil 50 having stable heat resistance and shear resistance. it can.

  Moreover, since an antistatic agent contains the nonionic surfactant which consists of sorbitan fatty acid ester, a metal salt or an ionic liquid can be disperse | distributed.

  Further, since the antistatic agent contains a nonionic surfactant composed of a sorbitan fatty acid ester in an amount of 0.01% by weight to 5% by weight, the lubricating oil 50 in which a metal salt or an ionic liquid is dispersed can be realized more easily. .

  Next, the effects of the present invention will be specifically described using examples and comparative examples. In the following experiment, the potential difference between the shaft portion 11 and the sleeve portion 14 was evaluated using the lubricating oil 50 added with the antistatic agent.

  All the lubricating oils according to the following Examples 1 to 19 and Comparative Example 1 used monoester oils having a molecular weight of 420 to 480 as the base oil. Moreover, 0.05 weight% of different antistatic agents were added to the lubricating oils of Examples 1 to 19.

The antistatic agent of Example 1 contains a metal salt. The cation of this metal salt is Na ⁺ , the anion is represented by the formula (1), and n = 1.

The antistatic agent of Example 2 contains a metal salt. The cation of this metal salt is Na ⁺ , the anion is represented by the formula (1), and n = 1. Further, 0.05% by weight of a nonionic surfactant made of sorbitan sesquioleate was added to the antistatic agent.

The antistatic agent of Example 3 contains a metal salt. The cation of this metal salt is Na ⁺ , and the anion is represented by the formula (11).

The antistatic agent of Example 4 contains a metal salt. The cation of this metal salt is Li ⁺ , the anion is represented by the formula (2), and p = 1 and q = 4.

The antistatic agent of Example 5 contains a metal salt. The cation of this metal salt is Li ⁺ , and the anion is represented by the formula (12).

  The antistatic agent of Example 6 contains an ionic liquid. The cation of this ionic liquid is represented by the formula (14), and R1 = R2 = R3 = 5 and R4 = 3. The anion of the ionic liquid is represented by the formula (1), and n = 1.

  The antistatic agent of Example 7 contains an ionic liquid. The cation of this ionic liquid is represented by the formula (14), and R1 = R2 = R3 = 8 and R4 = 1. The anion of the ionic liquid is represented by the formula (1), and n = 1.

  The antistatic agent of Example 8 contains an ionic liquid. The cation of this ionic liquid is represented by the formula (14), and R1 = R2 = R3 = 8 and R4 = 1. Moreover, the anion of an ionic liquid is represented by Formula (2), and is p = 1 and q = 4.

  The antistatic agent of Example 9 contains an ionic liquid. The cation of this ionic liquid is represented by the formula (14), and R1 = R2 = R3 = 8 and R4 = 1. The anion of the ionic liquid is represented by the formula (3), and m = 1.

  The antistatic agent of Example 10 contains an ionic liquid. The cation of this ionic liquid is represented by the formula (14), and R1 = R2 = R3 = 8 and R4 = 1. The anion of the ionic liquid is represented by the formula (4), and n = 1.

  The antistatic agent of Example 11 contains an ionic liquid. The cation of this ionic liquid is represented by the formula (14), and R1 = R2 = R3 = 8 and R4 = 1. Moreover, the anion of an ionic liquid is represented by Formula (5), and is p = 1 and q = 2.

  The antistatic agent of Example 12 contains an ionic liquid. The cation of this ionic liquid is represented by the formula (14), and R1 = R2 = R3 = 8 and R4 = 1. Further, the anion of the ionic liquid is represented by the formula (6), and n = 1.

  The antistatic agent of Example 13 contains an ionic liquid. The cation of this ionic liquid is represented by the formula (14), and R1 = R2 = R3 = 8 and R4 = 1. Moreover, the anion of an ionic liquid is represented by Formula (7), and is p = 1 and q = 2.

  The antistatic agent of Example 14 contains an ionic liquid. The cation of this ionic liquid is represented by the formula (14), and R1 = R2 = R3 = 8 and R4 = 1. The anion of the ionic liquid is represented by the formula (8), and n = 1.

  The antistatic agent of Example 15 contains an ionic liquid. The cation of this ionic liquid is represented by the formula (14), and R1 = R2 = R3 = 8 and R4 = 1. Moreover, the anion of an ionic liquid is represented by Formula (9), and is p = 1 and q = 2.

  The antistatic agent of Example 16 contains an ionic liquid. The cation of this ionic liquid is represented by the formula (14), and R1 = R2 = R3 = 8 and R4 = 1. An anion of the ionic liquid is represented by the formula (10), where l = 1, m = 2, and n = 3.

  The antistatic agent of Example 17 contains an ionic liquid. The cation of this ionic liquid is represented by the formula (14), and R1 = R2 = R3 = 8 and R4 = 1. Moreover, the anion of an ionic liquid is represented by Formula (11).

  The antistatic agent of Example 18 contains an ionic liquid. The cation of this ionic liquid is represented by the formula (14), and R1 = R2 = R3 = 8 and R4 = 1. Moreover, the anion of an ionic liquid is represented by Formula (12).

  The antistatic agent of Example 19 contains an ionic liquid. The cation of this ionic liquid is represented by the formula (16), and R1 = 6 and R2 = 2. The anion of the ionic liquid is represented by the formula (1), and n = 1.

[Comparative example]
Instead of the antistatic agent, 0.03% by weight of quaternary ammonium ions (having 16 or more carbon atoms) and alkylnaphthalene sulfonate ions (having 16 or more carbon atoms) were added to the lubricating oil of the comparative example.

[Evaluation of potential difference]
The lubricating oils according to Examples 1 to 19 and the comparative example were heated to 90 ° C. and stirred for 1 hour, and then filled in the minute gap S of the fluid dynamic pressure bearing 4 in an environment of 0 ° C.

The potential difference is evaluated by measuring the initial value of the potential difference between the shaft portion 11 and the sleeve portion 14 when the spindle motor 10 is driven, and then leaving the spindle motor 10 in a high temperature environment and in a high temperature and high humidity environment. Later, measurement was performed again in an environment of 0 ° C. Specifically, in the high temperature environment, the spindle motor 10 was continuously driven for 48 hours at a rotation speed of 9000 rpm in a 120 ° C. environment. In addition, when left in a high temperature and high humidity environment, the spindle motor 10 was continuously driven at a rotation speed of 9000 rpm for 48 hours in an environment of 120 ° C. and 334 g / m ³ . These results are shown in Table 1.

  As shown in Table 1, the lubricating oils of Examples 1 to 19 to which an antistatic agent was added had a potential difference between the shaft portion 11 and the sleeve portion 14 after 48 hours had passed in a high temperature environment and a high humidity environment. Was found to be in the range of not less than -0.5V and not more than + 0.5V. Further, it was confirmed that the occurrence of a potential difference can be reduced as compared with the lubricating oil of the comparative example to which no antistatic agent is added.

In addition, although lubricating oil of Examples 6-18 is demonstrated using Formula (14) as a cation of an ionic liquid, it replaces with either Formula (13) or Formula (15)-Formula (21). However, the same effect can be confirmed. Similarly, the lubricating oils of Examples 6 to 18 have been described using Formula (14) containing an alkyl group as a cation of the ionic liquid, but may be replaced with any of an alkenyl group, an aryl group, and an alkylbenzene group. The same effect can be confirmed.

In addition, although the lubricating oil of Example 19 is demonstrated using Formula (16) as a cation of an ionic liquid, any of Formula (13)-Formula (15) or Formula (17)-Formula (21) Even if you replace it, you can see the same effect. Similarly, the lubricating oil of Example 19 has been described using Formula (16) containing an alkyl group as the cation of the ionic liquid, but it is equivalent if replaced with any of an alkenyl group, an aryl group, and an alkylbenzene group. The effect of can be confirmed.

(5. Other)
Although one embodiment of the present invention has been described above, the present invention is not limited to this embodiment. For example, although the conical fluid dynamic bearing 4 is applied in the present embodiment, the thrust fluid fluid dynamic bearing 4 may be applied, for example, without being limited to the conical fluid.

  In the present embodiment, the shaft-fixed outer rotor type spindle motor has been described. However, the present invention can also be applied to a shaft rotation type motor and an inner rotor type spindle motor.

2 ... stationary part,
3 ... rotating part,
4 ... Fluid dynamic pressure bearing,
10 ... Spindle motor,
11 ... shaft part,
12a, 12b ... annular member,
13: Holding member,
13a ... recess,
13b ... flange part,
14 ... Sleeve part,
14a ... 1st internal peripheral surface 14b ... 2nd internal peripheral surface 14c ... 3rd internal peripheral surface 15 ... Coil,
16 ... Magnet,
17 ... Base part,
17a ... through hole,
17b ... Holder part,
18 ... stator core,
18a ... Core backpack,
18b ... Teeth,
19 ... seal part,
20: Disc,
22 ... spacer,
30 ... access part,
31 ... head,
32 ... arm,
33 ... Head moving mechanism,
40 ... Housing,
50: Lubricating oil,
100: Disc drive L: central axis,
S: Micro gap

Claims (15)

In the fluid dynamic pressure bearing lubricant for the fluid dynamic pressure bearing,
A fluid dynamic bearing lubricating oil characterized by adding an antistatic agent containing a metal salt or an ionic liquid.   The fluid dynamic bearing lubricating oil according to claim 1, wherein the metal salt or the ionic liquid contains an anion having a perfluoroalkyl group having 1 to 8 carbon atoms. The fluid dynamic bearing lubricating oil according to claim 2, wherein the metal salt or the ionic liquid contains any one of anions represented by the following formulas (1) to (11).

(1)
[Where n = 0 to 8]

(2)
[Wherein p ≠ q, p = 0-8, q = 0-8]

(3)
[Where m = 0 to 8]

(4)
[Where n = 0 to 8]

(5)
[Wherein p ≠ q, p = 0-8, q = 0-8]

(6)
[Where n = 0 to 8]

(7)
[Wherein p ≠ q, p = 0-8, q = 0-8]

(8)
[Where n = 0 to 8]

(9)
[Wherein p ≠ q, p = 0-8, q = 0-8]

(10)
[Wherein l ≠ m ≠ n, l = 0-8, m = 0-8, n = 0-8]

(11)
[Where n = 0 to 8] The fluid dynamic pressure bearing lubricant according to claim 1, wherein the metal salt or the ionic liquid contains an anion represented by the following formula (12).

(12)   5. The fluid dynamic pressure bearing lubricant according to claim 2, wherein the metal salt or the ionic liquid is contained in an amount of 0.01 wt% to 5 wt%. 6. The fluid dynamic bearing lubricating oil according to claim 2, wherein the metal salt includes the anion and any one of Na ⁺ , Rb ⁺ , and Cs ⁺ cations. 7. The metal salt has the anion and Li ⁺ (except n = 1 in the formula (1), m = 1 in the formula (3), m = 4, and n = 1 in the formula (8)). The lubricating oil for fluid dynamic pressure bearings according to any one of claims 2 to 5. 6. The metal salt according to claim 2, wherein the metal salt has the anion and K ⁺ (except n = 1 in the formula (1) and m = 1 in the formula (3)). Lubricating oil for fluid dynamic pressure bearings. The fluid liquid pressure bearing according to any one of claims 2 to 5, wherein the ionic liquid has any one of cations represented by the following formulas (13) to (21) and the anions. Lubricant.

(13)
[Wherein R1 and R2 are alkyl groups or alkenyl groups having 1 to 22 carbon atoms, or aryl groups or alkylbenzene groups having 6 to 30 carbon atoms]

(14)
[Wherein R 1, R 2, R 3, R 4 are an alkyl group or alkenyl group having 1 to 22 carbon atoms, or an aryl group or alkyl benzene group having 6 to 30 carbon atoms]

(15)
[Wherein, R represents an alkyl group or alkenyl group having 1 to 22 carbon atoms, or an aryl group or alkylbenzene group having 6 to 30 carbon atoms]

(16)
[Wherein R1 and R2 are alkyl groups or alkenyl groups having 1 to 22 carbon atoms, or aryl groups or alkylbenzene groups having 6 to 30 carbon atoms]

(17)
[Wherein R1 and R2 are alkyl groups or alkenyl groups having 1 to 22 carbon atoms, or aryl groups or alkylbenzene groups having 6 to 30 carbon atoms]

(18)
[Wherein R 1, R 2, R 3, R 4 are an alkyl group or alkenyl group having 1 to 22 carbon atoms, or an aryl group or alkyl benzene group having 6 to 30 carbon atoms]

(19)
[Wherein R1 and R2 are alkyl groups or alkenyl groups having 1 to 22 carbon atoms, or aryl groups or alkylbenzene groups having 6 to 30 carbon atoms]

(20)
[Wherein R1 and R2 are alkyl groups or alkenyl groups having 1 to 22 carbon atoms, or aryl groups or alkylbenzene groups having 6 to 30 carbon atoms]

(21)
  The lubricating oil for fluid dynamic pressure bearings according to any one of claims 1 to 9, comprising a nonionic surfactant made of sorbitan fatty acid ester.   The lubricating oil for fluid dynamic pressure bearing according to claim 10, wherein the nonionic surfactant is contained in an amount of 0.01% by weight to 1% by weight. After a lapse of 48 hours in a high temperature environment of 50 ° C. to 150 ° C. or a high humidity environment with a humidity of 82 g / m ³ or more, the potential difference between the stationary part and the rotating part of the fluid dynamic pressure bearing was measured at 0 ° C.− The lubricating oil for fluid dynamic bearings according to any one of claims 1 to 11, wherein the lubricating oil is in a range of 0.5 V or more and +0.5 V or less.   A fluid dynamic bearing comprising the fluid dynamic bearing lubricant according to any one of claims 1 to 12.   A spindle motor comprising the fluid dynamic pressure bearing according to claim 13. A disk drive apparatus comprising the spindle motor according to claim 14.

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