JP2010138316A - Bearing lubricant, bearing and disc driving unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique capable of further improving the performance of a bearing such as a possibility of using the bearing in a broad temperature range. <P>SOLUTION: The bearing lubricant includes a base oil containing 2-ethyl-2-methyl-1,3-propanediol and an ester compound composed of one or more 5-12C carboxylic acids represented by formula (1) (wherein R<SB>1</SB>and R<SB>2</SB>are each a 4-11C hydrocarbon group) and having a kinematic viscosity at 40°C of 7-15 mPa and a pour point of not higher than -60°C. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a bearing lubricant, a bearing using the same, and a disk drive device including the bearing.

  Miniaturization and reduction in power consumption in electronic devices such as personal computers and portable recording devices are progressing year by year. In addition, the usable temperature range of these electronic devices is expanding year by year. Accordingly, spindle motors equipped with fluid dynamic pressure bearings, impregnated bearings, and the like have been used in high-speed small rotating recording media used in these electronic devices, such as disk drives using magnetic disks. It was. The downsizing, low power consumption, and expansion of the usable temperature range of these electronic devices are largely due to the improvement in motor performance.

  Under such circumstances, there has been an increasing demand in recent years for high-speed processing, miniaturization, low power consumption, long life, or expansion of the usable temperature range of electronic devices. On the other hand, there is a need to expand the use of devices equipped with disk drive devices to mobile devices, etc., motors and their devices can withstand use in harsh environments, and have a long service life. It has come to be required. In other words, there is a strong demand for both the expansion of the usable temperature range of the motor and its equipment and the long life.

One of the means to improve the performance of motors and their equipment is to improve the performance of bearings such as fluid dynamic bearings mounted on motors. Lubricants have been proposed (see, for example, Patent Documents 1 to 3).
JP 2006-83321 A International Publication No. 2004/018595 Pamphlet JP 2008-7741 A

  In order to improve the performance of the bearing, it is conceivable to extend the life of the bearing lubricant by reducing the evaporation loss of the bearing lubricant used. Generally, in order to reduce the evaporation loss of the bearing lubricant, it is necessary to increase the molecular weight of the base oil contained in the bearing lubricant. However, when the molecular weight of the base oil is increased, the viscosity of the lubricant for the bearing is increased, the energy loss at the bearing is increased, and the power consumption is increased. Conversely, if the molecular weight of the base oil is reduced in order to reduce the viscosity of the bearing lubricant and reduce the energy loss in the bearing, the evaporation loss of the bearing lubricant increases. In addition, since the life of fluid dynamic pressure bearings depends on the amount of bearing lubricant retained inside, an increase in the evaporation loss of bearing lubricant significantly shortens the life of fluid dynamic pressure bearings. End up.

  Furthermore, the disk drive device provided with the fluid dynamic pressure bearing is assembled with extremely high accuracy. Therefore, it is almost impossible to repair the bearing mounted inside the disk drive device. For this reason, the disk drive device whose bearing has reached the end of its life must be discarded and replaced with a new disk drive device even when members other than the bearing can sufficiently withstand use. As described above, the situation in which other members must be discarded for one bearing that has reached the end of its life is undesirable from the viewpoint of environmental resources and the like.

  In addition, the rigidity of the fluid dynamic pressure bearing (hereinafter sometimes referred to as “bearing rigidity” as appropriate) depends on the viscosity of the bearing lubricant. Therefore, when the molecular weight of the base oil is reduced, the viscosity of the bearing lubricant is lowered, but on the other hand, there is a problem that the bearing rigidity is extremely lowered under a high temperature environment. In particular, in a disk drive device equipped with a magnetic disk having a large inertia and mass, a large stress is applied to the shaft when subjected to acceleration such as vibration or impact, so that the metal between the shaft and the bearing can be easily obtained when the bearing rigidity is lowered. Contact occurs, resulting in malfunction of the disk drive.

  On the other hand, when the molecular weight of the base oil is increased, there is a problem that the viscosity of the bearing lubricant is increased and the bearing rigidity is unnecessarily increased in a low temperature environment. In particular, in the disk drive device provided with the above-described magnetic disk or the like, a large drive current flows at the time of start-up. Therefore, an increase in load under a low temperature environment causes an increase in current consumption. Becomes extremely short.

  Due to such problems, at present, the mounting of the disk drive device to a mobile device that may be used in a wide temperature range, such as a mobile device used outdoors, is limited.

  In order to improve the performance of the bearing, it is conceivable to secure the fluidity of the bearing lubricant used in a wide temperature range. In order to meet the demand for higher performance of electronic devices as described above, for example, a bearing lubricant having a pour point of −60 ° C. or lower is expected.

  The present invention has been made based on such recognition by the inventor, and an object thereof is to provide a technique capable of further improving the performance of the bearing.

（式中、Ｒ_１、Ｒ_２は、炭素数４から１１の炭化水素基を表す） An embodiment of the present invention relates to a bearing lubricant. This bearing lubricant is an ester compound represented by the following formula (1) consisting of 2-ethyl-2-methyl-1,3-propanediol and one or more carboxylic acids having 5 to 12 carbon atoms. And a base oil having a kinematic viscosity at 40 ° C. of 7 to 15 mPa and a pour point of −60 ° C. or less.

(Wherein R ₁ and R ₂ represent a hydrocarbon group having 4 to 11 carbon atoms)

  According to this aspect, it is possible to further improve the performance of the bearing.

  It should be noted that any combination of the above-described constituent elements, and those obtained by mutually replacing constituent elements and expressions of the present invention among methods, apparatuses, systems, etc. are also effective as an aspect of the present invention.

  According to the present invention, it is possible to further improve the performance of the bearing.

  Hereinafter, the present invention will be described based on preferred embodiments. The embodiments do not limit the invention but are exemplifications, and all features and combinations described in the embodiments are not necessarily essential to the invention. Further, it will be understood by those skilled in the art that various modifications can be made to the combination of each component, and such modifications are also within the scope of the present invention.

(Embodiment)
The bearing lubricant according to the present embodiment is suitably used for a bearing such as a fluid dynamic pressure bearing. Hereinafter, the composition of the bearing lubricant of this embodiment will be described in detail.

  The bearing lubricant according to the present embodiment contains a base oil containing an ester compound represented by the following formula (1).

（式中、Ｒ_１、Ｒ_２は、炭素数４から１１の炭化水素基を表す）

(Wherein R ₁ and R ₂ represent a hydrocarbon group having 4 to 11 carbon atoms)

That is, the base oil is mainly composed of a fatty acid diol ester composed of 2-ethyl-2-methyl-1,3-propanediol as a diol and one or more carboxylic acids having 5 to 12 carbon atoms. . The base oil may be composed only of a fatty acid diol ester. In the formula (1), R ₁ and R ₂ derived from the carboxylic acid are hydrocarbon groups having 4 to 11 carbon atoms, and the carbon number is preferably 7 to 10, more preferably 7 or 8. This hydrocarbon group is an aliphatic hydrocarbon which is saturated or unsaturated and contains a linear, branched or cyclic structure. R ₁ and R ₂ may be the same or different.

Here, when the hydrocarbon groups R ₁ and R ₂ are branched, generally the pour point of the bearing lubricant can be lowered, but the viscosity may increase. On the other hand, when the hydrocarbon groups R ₁ and R ₂ are linear, the viscosity generally does not increase, but it is difficult to lower the pour point. On the other hand, in particular, by using a linear saturated aliphatic carboxylic acid having 8 or 9 carbon atoms, the pour point can be more suitably lowered without increasing the viscosity of the bearing lubricant. Therefore, the carboxylic acid constituting the ester compound is preferably a straight-chain saturated aliphatic carboxylic acid having 8 or 9 carbon atoms, and more preferably a straight-chain saturated aliphatic carboxylic acid having 9 carbon atoms. preferable. In general, as the carbon number of the carboxylic acid decreases, the kinematic viscosity decreases and the evaporation loss increases. As the carbon number of the carboxylic acid increases, the kinematic viscosity increases and the evaporation loss decreases.

  The diol of the ester compound is 2-ethyl-2-methyl-1,3-propanediol. A methyl group and an ethyl group are bonded to the 2-position carbon of 1,3-propanediol, so that the ester compound may contain an enantiomer. Thereby, the pour point of the lubricant for bearings can be lowered. In addition, the freezing point of the bearing lubricant can be lowered. In the case of a structure in which a methyl group and an ethyl group are bonded to the carbon at the 2-position (hereinafter sometimes referred to as ethylmethyl), a structure in which a propyl group and a methyl group are bonded to the carbon at the 2-position (hereinafter referred to as propylmethyl). The pour point can be lowered with a relatively high viscosity index of the bearing lubricant. On the other hand, in the case of a structure in which two methyl groups are bonded to carbon at the 2-position (hereinafter sometimes referred to as dimethyl), the viscosity index is comparable to that of ethylmethyl, that is, relatively high compared to propylmethyl. The point gets higher. In the case of propylmethyl, the pour point can be lowered, but the viscosity index becomes lower than that of ethylmethyl and dimethyl.

  The base oil has a kinematic viscosity at 40 ° C. of 5 to 20 mPa, preferably 7 to 15 mPa. Since the base oil has the kinematic viscosity as described above, it is suitably used for a bearing such as a fluid dynamic pressure bearing. Alternatively, the kinematic viscosity at 40 ° C. of the fatty acid diol ester represented by the formula (1) may be 5 to 20 mPa, preferably 7 to 15 mPa. Further, the base oil has a pour point of −40 ° C. or lower, preferably −60 ° C. or lower, so that the bearing can rotatably support the rotating body even under low temperature conditions.

  The bearing lubricant according to the present embodiment may contain an antioxidant including at least one of a hindered phenol-based antioxidant and a hindered amine-based antioxidant. For example, the antioxidant is included in the bearing lubricant so as to be 0.05% by weight or more and 10.0% by weight or less with respect to the total weight of the bearing lubricant. For example, the antioxidant is included in the bearing lubricant so as to be 0.1% by weight or more based on the total weight of the bearing lubricant.

  Examples of hindered phenol antioxidants include 2,6-di-tert-butyl-4-hydroxytoluene and n-octadecyl-3- (3 ′, 5′-di-tert-butyl-4′-hydroxyphenyl). ) Monophenols such as propionate, diphenols such as 4,4′-butylidenebis (3-methyl-6-tert-butylphenol), 4,4′-methylenebis (4-methyl-6-tert-butylphenol), or And phenolic antioxidants having three or more 2,6-di-tert-butyl-4-hydroxy structures. These phenolic antioxidants may be used alone or in combination of two or more. The hindered phenol-based antioxidant is preferably a phenol-based antioxidant having three or more 2,6-di-tert-butyl-4-hydroxy structures, and is preferably based on the total weight of the bearing lubricant. Is included in the bearing lubricant so as to be in the range of 0 to 10.0% by weight.

  Examples of the hindered amine antioxidant include dialkylated diphenylamine, dioctyl diphenylamine, and 4,4′-bis (α, α-dimethylbenzyl) diphenylamine. These amine-based antioxidants may be used alone or in combination of two or more. The hindered amine antioxidant is preferably dioctyl diphenylamine or 4,4′-bis (α, α-dimethylbenzyl) diphenylamine, and preferably 0 to 10.0 weight based on the total weight of the bearing lubricant. % Is included in the bearing lubricant.

  Further, the bearing lubricant according to the present embodiment may include at least one of phosphate esters and phosphites. In this embodiment, phosphate esters and phosphites are added as wear modifiers.

  Phosphate esters as wear modifiers, that is, phosphate ester-based wear modifiers include, for example, trialkyl phosphates such as tributyl phosphate and trioctyl phosphate, or triphenyl phosphate and tricresyl phosphate. And triallyl phosphates such as trisnonylphenyl phosphate. These phosphate ester type wear control agents are preferably included in the bearing lubricant so as to be in the range of 0.01 to 5.0% by weight based on the total weight of the bearing lubricant.

  Phosphites as wear modifiers, that is, phosphite-based wear modifiers include alkoxide phosphites such as tributyl phosphite and trioctyl phosphite, triphenyl phosphite, tri (octylphenyl) Examples thereof include phenoxide-type phosphites such as phosphite or a composite type of these phosphites. These phosphite ester wear modifiers are preferably included in the bearing lubricant so as to be in the range of 0.01 to 5% by weight based on the total weight of the bearing lubricant.

  Further, the bearing lubricant according to the present embodiment may include a phosphorus-based extreme pressure additive.

  Further, in the bearing lubricant according to this embodiment, the base oil contains 40% by weight or more of the ester compound represented by the formula (1) with respect to the total weight of the bearing lubricant, and the kinematic viscosity is 5 mPa or more. The poly α-olefin may be included.

  Further, the base oil may contain an ester compound represented by the formula (1) in an amount of 40% by weight or more based on the total weight of the bearing lubricant and a diester having a kinematic viscosity of 6 mPa or more. .

  Further, the base oil contains 40% by weight or more of the ester compound represented by the formula (1) with respect to the total weight of the bearing lubricant, and contains trimethylolpropane esters having a kinematic viscosity of 6 mPa or more. There may be.

  The bearing lubricant according to the present embodiment is suitably used for a bearing that rotatably supports a rotating body. When the bearing lubricant according to this embodiment is used for a bearing, the resistance between the rotating body and the bearing can be reduced for a longer period of time and in a lower temperature environment.

  Summarizing the effects of the bearing lubricant according to the present embodiment described above, the bearing lubricant according to the present embodiment includes 2-ethyl-2-methylpropanediol and one or more types of 5 to 12 carbon atoms. And a base oil having a kinematic viscosity at 40 ° C. of 7 to 15 mPa and a pour point of −60 ° C. or less. Thereby, a low-viscosity and low-volatility bearing lubricant can be obtained, the evaporation loss of the bearing lubricant can be reduced, and an increase in the viscosity of the bearing lubricant can be suppressed. Further, a bearing lubricant having a low pour point and a very small change in viscosity can be obtained. As a result, energy loss in the bearing can be suppressed over a long period of time. Further, the bearing can stably support the rotating body even in a low temperature environment. As a result, it is possible to reduce the power consumption, extend the service life, and expand the usable temperature range of a motor equipped with this bearing and an electronic device equipped with this motor.

  For example, when a fluid dynamic pressure bearing using the bearing lubricant according to the present embodiment is mounted on a disk drive device, the disk drive device can be used for a long time by improving the evaporation loss of the bearing lubricant. Will be able to withstand. Therefore, the frequency of replacement of the disk drive device is reduced, and the situation that many members other than the bearing must be discarded for one bearing can be reduced. As a result, wasteful consumption of limited resources can be reduced.

  On the other hand, by lowering the pour point of the lubricant for bearings, the bearing rigidity does not increase unnecessarily in a low temperature environment, so that an increase in current consumption due to an increase in load or the like can be prevented. Therefore, even when the device equipped with the disk drive device is a battery-driven type, the usage time of the device can be extended. As a result, the disk drive device can be suitably mounted on a mobile device or the like used outdoors.

  For example, according to the present invention, it is possible to improve the performance of a hard disk drive, a spindle motor, a polygon mirror scanner motor, and the like applicable to the hard disk drive.

  Further, when the carboxylic acid is a straight-chain saturated aliphatic carboxylic acid having 8 or 9 carbon atoms, the pour point can be lowered more suitably without increasing the viscosity of the bearing lubricant. In addition, by containing an antioxidant containing at least one of a hindered phenol antioxidant and a hindered amine antioxidant, the bearing lubricant is prevented from being oxidized, and the bearing lubricant has a longer life. Can be achieved. When the antioxidant is included in an amount of 0.05 wt% or more and 10.0 wt% or less with respect to the total weight of the bearing lubricant, the low viscosity, low volatility of the bearing lubricant, The influence on characteristics such as a low pour point can be suppressed. Furthermore, when at least one of phosphoric acid esters and phosphorous acid esters is included, damage due to wear of the bearing and the rotating body can be reduced, and the life of the bearing can be extended.

(Configuration of bearing and disk drive)
Subsequently, the configuration of a bearing capable of using the bearing lubricant according to the present embodiment and a disk drive device including the bearing will be described. FIG. 1 is a schematic cross-sectional view showing the configuration of the disk drive device according to the first embodiment. In the following description, for the sake of convenience, the lower part shown in the drawing is expressed as lower and the upper part is expressed as upper.

  A disk drive device 50 that drives a hard disk includes a fixed body, a radial fluid dynamic pressure bearing, a thrust fluid dynamic pressure bearing, and a rotating body. The rotational speed of the rotating body is, for example, 5400 times / minute.

  The fixed body includes a base member 5, a stator core 6 fixed to the outer peripheral surface of the cylindrical portion 5a provided on the base member 5, an annular housing member 15 fixed to the inner peripheral surface of the cylindrical portion 5a, And an annular shaft housing member 10 that is fixed to the inner circumferential surface of the housing member 15 and has a cylindrical portion inner circumferential surface 10a.

  The stator core 6 has a coil 7 wound around a plurality of salient poles (not shown) protruding outward. The shaft housing member 10 includes a cylindrical portion 10b having a cylindrical portion inner peripheral surface 10a, and a flange portion 10c coupled to one end side of the cylindrical portion 10b and extending to the outside of the cylindrical portion 10b. have. The housing member 15 includes a cylindrical portion that fits the shaft housing member 10 into the inner periphery, a bottom portion that seals one end portion of the cylindrical portion, and a surface in the axial direction (axial direction) provided at the other end of the cylindrical portion. And an upper end surface portion having a substantially cup shape.

  The rotating body includes a substantially cup-shaped hub 2, a shaft 13 fixed to the center hole 2 a of the hub 2, a ring-shaped magnet 8, and a thrust member 12. The hub 2 includes a first cylindrical portion 2c that is concentric with the center hole 2a and has a small diameter, a second cylindrical portion 2b that is disposed outside the first cylindrical portion 2c, and a hub that extends outward from the lower end of the second cylindrical portion 2b. The thrust member 12 is fixed to the inner peripheral surface of the first cylindrical portion 2c, and the ring magnet 8 is fixed to the inner peripheral surface of the second cylindrical portion 2b.

  A step portion 13 a is provided at the upper end portion of the shaft 13, and the diameter below the step portion 13 a of the shaft 13 is slightly larger than the diameter of the center hole 2 a of the hub 2. The upper diameter is substantially the same as the diameter of the center hole 2a. As for the shaft 13 and the hub 2, the shaft 13 is press-fitted into the center hole 2a of the hub 2, the outer peripheral surface of the portion above the step portion 13a of the shaft 13 is in contact with the inner peripheral surface of the center hole 2a, and the step portion 13a is By engaging with the hub 2 at the lower end of the center hole 2a, both are connected.

  The thrust member 12 has a thrust upper surface 12a and a thrust lower surface 12b. The thrust member 12 has a thin disk portion 12c in the axial direction and a drooping portion 12d which is coupled to the lower surface on the outer peripheral side of the disk portion 12c and which is long in the axial direction. . The inner peripheral surface of the hanging part 12d has a tapered shape whose radius decreases toward the tip, and together with the outer peripheral surface of the housing member 15, the lubricant filled in the gap of the hydrodynamic bearing leaks to the outside by capillary action. The capillary seal part which prevents this is configured.

  The disc portion 12c of the thrust member 12 is disposed through a narrow gap between the lower surface of the flange portion 10c of the shaft housing member 10 and the upper end surface of the housing member 15, and the outer periphery of the hanging portion 12d is the first portion of the hub 2. It is fixed to the inner peripheral surface of the cylindrical portion 2c. Thrust dynamic pressure grooves (not shown) are provided on both surfaces of the thrust upper surface 12a and the thrust lower surface 12b, thereby forming a thrust fluid dynamic pressure bearing.

  The radial fluid dynamic bearing includes a shaft 13, a shaft storage member 10 that stores the shaft 13 and rotatably supports the shaft 13, and a herring disposed on the cylindrical inner peripheral surface 10 a of the shaft storage member 10 so as to be separated in the axial direction. Bone-shaped first and second radial dynamic pressure grooves (not shown), a circumferential recess 10d disposed in the middle of the first and second radial dynamic pressure grooves, the outer peripheral surface of the shaft 13, and the shaft storage And a bearing lubricant filled in a gap between the cylindrical portion inner peripheral surface 10a of the member 10.

  In the present embodiment, the shaft housing member 10 is formed of a copper-based material, and using the fluid dynamic pressure bearing described above, the cylindrical portion 10b has an inner diameter of about 2.5 mm, and the cylindrical portion 10b is provided with a dynamic pressure groove. The wall thickness was about 0.6 mm. Further, a herringbone-shaped dynamic pressure groove was provided by forming a dynamic pressure groove having a depth of about 5 μm on the inner peripheral surface 10a of the cylindrical portion using a predetermined processing method. The rotating body is rotatably supported by a radial fluid dynamic pressure bearing and a thrust fluid dynamic pressure bearing, and is rotationally driven by the electromagnetic action of the stator core 6 and the ring magnet 8.

  Further, a magnetic disk (not shown) is placed on the outer periphery of the hub 2, and data is recorded and read by read / write means (not shown).

  When the kinematic viscosity at 40 ° C. of the conventional bearing lubricant and the bearing lubricant according to this embodiment is adjusted to about 9.5 cst, the disk drive device using the conventional bearing lubricant has a low temperature of 0. Although the drive current at 210 ° C. was 210 mA, the disk drive device using the bearing lubricant according to the present embodiment exhibited a current reduction effect of 150 mA under the same conditions.

  Examples of the present invention will be described below. However, these examples are merely examples for suitably explaining the present invention, and do not limit the present invention.

(Bearing lubricant)
(Examples 1 and 2 and Comparative Examples 1 and 2)
Base oils according to Examples 1 and 2 were prepared according to the components described in Table 1 below. The base oil of Example 1 is 2-ethyl-2-methyl-1,3-propanediol dioctyl ester, and the base oil of Example 2 is 2-ethyl-2-methyl-1,3-propanediol dinonyl. Ester. Moreover, diol ester (DOE) was prepared as Comparative Example 1, and neopentyl glycol (NPG) (2,2-dimethylpropanediol) was prepared as Comparative Example 2.

(Viscosity measurement, evaporation test, pour point measurement)
Viscosity was measured using a rotational viscometer. The measurement temperature was 40 ° C., which is generally used. In the evaporation test, the compositions of Examples 1 and 2 and Comparative Examples 1 and 2 were placed in a glass beaker, and the glass beaker was allowed to stand in a 100 ° C. forced residence type constant temperature bath for 240 hours. As weight%. Moreover, the above-mentioned viscosity measurement was implemented about each composition after an evaporation test, and the viscosity change rate before and behind an evaporation test was measured. The pour point was measured by a method based on JIS K2269.

  As a result, the base oils of Examples 1 and 2 were found to have a low viscosity as compared with Comparative Example 1, and to have high properties in terms of evaporation, viscosity change rate, and pour point. In addition, it was found that the base oils of Examples 1 and 2 had a very low viscosity change rate as compared with Comparative Example 2.

1 is a schematic cross-sectional view showing a configuration of a disk drive device according to Embodiment 1. FIG.

Explanation of symbols

  2 hub, 2a center hole, 2b 2nd cylindrical part, 2c 1st cylindrical part, 2d hub extension part, 5 base member, 5a cylindrical part, 6 stator core, 7 coil, 8 ring-shaped magnet, 10 shaft storage member, 10a cylindrical Internal peripheral surface, 10b cylindrical portion, 10c flange portion, 10d circumferential recess, 12 thrust member, 12a thrust upper surface, 12b thrust lower surface, 12c disk portion, 12d drooping portion, 13 shaft, 13a stepped portion, 15 housing member, 50 Disk drive device.

Claims (7)

It contains an ester compound represented by the following formula (1) consisting of 2-ethyl-2-methyl-1,3-propanediol and one or more carboxylic acids having 5 to 12 carbon atoms, and kinematic viscosity at 40 ° C. Containing a base oil having a pour point of −60 ° C. or lower.

(Wherein R ₁ and R ₂ represent a hydrocarbon group having 4 to 11 carbon atoms)   The bearing lubricant according to claim 1, wherein the carboxylic acid is a linear saturated aliphatic carboxylic acid having 8 or 9 carbon atoms.   The bearing lubricant according to claim 1 or 2, further comprising an antioxidant containing at least one of a hindered phenol-based antioxidant and a hindered amine-based antioxidant.   4. The bearing lubricant according to claim 3, wherein the antioxidant is contained in an amount of 0.05% by weight or more and 10.0% by weight or less based on the total weight of the bearing lubricant. .   The bearing lubricant according to any one of claims 1 to 4, comprising at least one of phosphate esters and phosphites.   A bearing that rotatably supports a rotating body, wherein the bearing lubricant according to any one of claims 1 to 5 is used.   A disk drive device comprising the bearing according to claim 6.

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