JP2014019867A - Lubricating oil composition for fluid dynamic pressure bearing and motor for hdd using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a lubricating oil composition for a fluid dynamic pressure bearing with low viscosity, low evaporation loss, and improved oxidation stability at operating temperature; and a motor for an HDD containing the lubricating oil composition with improved reliability and quality.SOLUTION: The lubricating oil composition for a fluid dynamic pressure bearing includes, as a base oil, an aliphatic monocarboxylic acid ester specified in the figure having 16 to 46 carbon atoms in total, obtained by an esterification reaction of a specific carboxylic acid and a primary or secondary alcohol having 8 to 38 carbon atoms. The composition exhibits low viscosity, low evaporation loss, and improved oxidation stability at operating temperature.

Description

The present invention relates to a lubricating oil composition for a fluid dynamic pressure bearing having a low viscosity, low evaporation loss, and improved oxidation stability, and an HDD motor using the same.

A hard disk drive (HDD; Hard Disk Drive), which is one of information storage devices, reproduces data stored on a disk using a recording / playback head (read / write head) and records data on the disk It is.

Such a hard disk drive requires a disk drive for driving the disk, and a small spindle motor is used for the disk drive.

A fluid dynamic pressure bearing assembly is used for such a small spindle motor, and a lubricating fluid is interposed between the shaft and the sleeve of the fluid dynamic pressure bearing assembly, and the shaft is driven by the fluid pressure generated from the lubricating fluid. Support.

If the lubricating fluid has a high viscosity at a low temperature when the spindle motor rotates, the viscous resistance of the lubricating fluid to the power generation groove generated during the rotation of the motor increases, and as a result, the power loss of the motor increases.

On the other hand, if the thermal expansion and viscosity of the lubricating fluid are reduced in the high temperature region during the rotation of the motor, there is a problem that the support function cannot be sufficiently exhibited.

For this reason, the lubricating fluid needs to have a behavior characteristic of contradictory viscosity that maintains a low viscosity in the low temperature region and does not decrease in the high temperature region.

In order to satisfy such viscosity characteristics, various developments such as addition of substances such as antioxidants and extreme pressure additives to base oils mainly composed of specific ester (Ester) compounds have been conducted. .

However, although the lubricating fluids using the various additives described above are effective at the beginning, the lubricant evaporates and the viscosity characteristics change when used over a long period of time, so it is difficult to maintain such effects. .

In addition, as motors become smaller, more accurate, faster rotated, and consume less power, lubricating fluids are also required to have characteristics such as heat resistance, oxidation stability, low evaporation, and wear resistance.

On the other hand, since the base oil tends to increase the evaporation loss when the bottom viscosity is increased, the base oil is required to have a bottom viscosity at a practical temperature and to suppress the evaporation loss.

Although the grease composition containing 2-ethylhexanoic acid is disclosed in the following prior art documents, the effect of suppressing evaporation loss as well as the bottom viscosity at the practical temperature is not great.

JP 2007-154032 A

The present invention relates to a lubricating oil composition for a fluid dynamic pressure bearing having a low viscosity, low evaporation loss, and improved oxidation stability, and an HDD motor using the same.

A lubricating oil composition for a fluid dynamic bearing according to an embodiment of the present invention includes a carboxylic acid represented by the following formula 1, and a primary alcohol or secondary alcohol (alcohol) having 8 to 38 carbon atoms. An aliphatic monocarboxylic acid ester having a total carbon number of 16 to 46 obtained by the esterification reaction can be contained as a base oil.

式１

Formula 1

The aliphatic monocarboxylic acid ester may be palmityl ethylhexanoate (Calethyl Ethylhexanoate) or cetyl ethylhexanoate (Cetyl Ethylhexanoate).

The lubricating oil composition for a fluid dynamic bearing may further include 0.01 to 2 parts by weight of an oil antioxidant, and the oil antioxidant may contain 2,2′-methylene-bis (4 -Methyl-6-tert-butylphenol) (2,2'-methylene-bis (4-methyl-6-tert-butylphenol)).

The lubricating oil composition for a fluid dynamic bearing may further include 0.01 to 2 parts by weight of a metal antioxidant, and the metal antioxidant may include barium diphenylamine-4. -Sulfonate).

The lubricating oil composition for a fluid dynamic pressure bearing may further include 0.01 to 2 parts by weight of an internal pressure inhibitor, and the internal pressure inhibitor may be tricresyl phosphate.

The HDD motor according to another embodiment of the present invention is obtained by an esterification reaction between a carboxylic acid represented by the following formula 1 and a primary alcohol or secondary alcohol (alcohol) having 8 to 38 carbon atoms. A lubricating oil composition for fluid dynamic pressure bearings containing an aliphatic monocarboxylic acid ester having a total carbon number of 16 to 46 as a base oil can be included.

式１

Formula 1

The aliphatic monocarboxylic acid ester may be palmityl ethylhexanoate (Calethyl Ethylhexanoate) or cetyl ethylhexanoate (Cetyl Ethylhexanoate).

The lubricating oil composition for a fluid dynamic bearing may further include 0.01 to 2 parts by weight of an oil antioxidant, and the oil antioxidant may contain 2,2′-methylene-bis (4 -Methyl-6-tert-butylphenol) (2,2'-methylene-bis (4-methyl-6-tert-butylphenol)).

The lubricating oil composition for a fluid dynamic bearing may further include 0.01 to 2 parts by weight of a metal antioxidant, and the metal antioxidant may include barium diphenylamine-4. -Sulfonate).

The lubricating oil composition for a fluid dynamic pressure bearing may further include 0.01 to 2 parts by weight of an internal pressure inhibitor, and the internal pressure inhibitor may be tricresyl phosphate.

According to the present invention, by manufacturing a motor for HDD containing a lubricating oil composition for fluid dynamic pressure bearings having low viscosity at practical temperature, low evaporation loss, and improved oxidation stability, the motor can be used for a long time. Reliability quality can be improved.

1 is a schematic cross-sectional view illustrating an HDD motor including a fluid dynamic bearing assembly according to an embodiment of the present invention.

The embodiments of the present invention can be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. Also, the embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art. Accordingly, the shape and size of elements in the drawings may be exaggerated for a clearer description, and elements denoted by the same reference numerals in the drawings are the same elements.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a schematic cross-sectional view illustrating a HDD motor including a fluid dynamic bearing assembly according to an embodiment of the present invention.

Referring to FIG. 1, a lubricating oil composition 170 for a fluid dynamic bearing according to an embodiment of the present invention includes a carboxylic acid represented by the following formula 1 and a primary alcohol or a second alcohol having 8 to 38 carbon atoms. An aliphatic monocarboxylic acid ester having a total carbon number of 16 to 46 obtained by an esterification reaction with a secondary alcohol (alcohol) can be contained as a base oil.

式１

Formula 1

Hereinafter, the above configuration will be described in detail.

The carboxylic acid represented by Formula 1 may be 2-ethylhexanoic acid (2-Ethyl Hexanoic Acid).

On the other hand, according to one embodiment of the present invention, the alcohol used for the esterification reaction with the carboxylic acid represented by the above formula 1 may be a primary alcohol having 8 to 38 carbon atoms or a second alcohol. Examples include, but are not limited to, grade alcohol (alcohol).

A lubricating oil composition 170 for a fluid dynamic bearing according to an embodiment of the present invention includes a carboxylic acid represented by the above formula 1 and a primary or secondary alcohol (alcohol) having 8 to 38 carbon atoms. An aliphatic monocarboxylic acid ester obtained by the esterification reaction with can be contained as a base oil.

Although the said aliphatic monocarboxylic acid ester is not restrict | limited in particular, For example, a total carbon number can be 16-46.

The aliphatic monocarboxylic acid ester is not particularly limited, and examples thereof include palmityl ethylhexanoate (palmityl ethylhexanoate) and cetyl ethylhexanoate (cetyl ethylhexanoate), which can be represented by the following formulas 2 and 3.

式２

Formula 2

式３

Formula 3

Specifically, the above formula 2 represents palmityl ethylhexanoate (palmityl ethylhexanoate), and the above formula 3 represents a formula representing cetyl ethylhexanoate (cetyl ethylhexanoate).

The lubricating oil composition 170 for a fluid dynamic bearing according to an embodiment of the present invention includes the 2-ethylhexanoic acid (2-Ethyl Hexanoic Acid) and the primary alcohol or the secondary alcohol having 8 to 38 carbon atoms. By containing an aliphatic monocarboxylic acid ester obtained by esterification with alcohol as a base oil, the viscosity is low, evaporation loss is small, and oxidation stability is excellent.

The kinematic viscosity of the aliphatic monocarboxylic acid ester according to one embodiment of the present invention can be measured at -20 ° C, 25 ° C and 85 ° C.

The viscosity can be measured using a Brookfield DB-III Rheometer, and each component is divided into three temperature intervals (−20 ° C., 25 ° C.) in order to confirm the tendency due to temperature. ° C and 85 ° C).

Of the above three temperatures, −20 ° C. corresponds to a low temperature storage temperature in a normal motor reliability test, 25 ° C. corresponds to a normal operating temperature of the motor, and 85 ° C. corresponds to a high operating temperature of the motor. Can be equivalent.

According to one embodiment of the present invention, the aliphatic monocarboxylic acid ester may be a dioctyl adipate (DOA), dioctyl sebacate (DOS), or dioctyl azelate (DOZ). The viscosity is lower than that of the aliphatic monocarboxylic acid ester, and the amount of high-temperature evaporation can be reduced.

Therefore, when the above aliphatic monocarboxylic acid ester is used as a base oil, it has a low viscosity, can reduce friction loss of the apparatus more effectively, has a small amount of evaporation, and has excellent stability at high temperatures. Can have.

The lubricating oil composition containing the aliphatic monocarboxylic acid ester as a base oil is not particularly limited, but is suitable for use as, for example, a fluid bearing of a motor for a hard disk drive (HDD).

In the case of a small hard disk drive, power consumption needs to be low, and stability at high temperatures can be a very important factor due to the high speed rotation of the motor.

The lubricating oil composition according to an embodiment of the present invention can satisfy the above-mentioned conditions for a small hard disk by having a low friction loss and stability at a high temperature.

The lubricating oil composition for a fluid dynamic bearing may further include 0.01 to 2 parts by weight of an oil antioxidant, and the oil antioxidant is not particularly limited. For example, 2, 2 ′ -Methylene-bis (4-methyl-6-tert-butylphenol) (2,2'-methylene-bis (4-methyl-6-tert-butylphenol)).

The oil antioxidant may contain 0.01 to 2 parts by weight within a range not deteriorating the performance of the lubricating oil composition. When the amount is less than 0.01 parts by weight, an antioxidant is added. The effect may not be sufficiently exhibited, and if it exceeds 2 parts by weight, the performance of the lubricating oil composition may be deteriorated.

The lubricating oil composition for fluid dynamic pressure bearings may further include 0.01 to 2 parts by weight of a metal antioxidant, and the metal antioxidant is not particularly limited. For example, diphenylamine-4- A barium sulfonate (Barium diphenylamine-4-sulfonate) is mentioned.

When the added amount of the metal antioxidant is less than 0.01 parts by weight, the effect of oxidation stability may not be sufficiently exhibited. When the added amount exceeds 2 parts by weight, the performance of the lubricating oil composition is deteriorated. Therefore, the amount added is preferably in the range of 0.01 to 2 parts by weight.

The lubricating oil composition for a fluid dynamic pressure bearing may further include 0.01 to 2 parts by weight of an internal pressure inhibitor, and the internal pressure inhibitor is not particularly limited, and examples thereof include tricresyl phosphate (Tricresyl Phosphate). It is done.

When the added amount of the internal pressure inhibitor is less than 0.01 parts by weight, the effect of preventing the internal pressure may not be sufficiently exhibited. When the added amount exceeds 2 parts by weight, the performance of the lubricating oil composition is deteriorated. Therefore, the amount added is preferably in the range of 0.01 to 2 parts by weight.

The HDD motor according to another embodiment of the present invention is obtained by an esterification reaction between a carboxylic acid represented by the following formula 1 and a primary alcohol or secondary alcohol (alcohol) having 8 to 38 carbon atoms. A lubricating oil composition for fluid dynamic pressure bearings containing an aliphatic monocarboxylic acid ester having a total carbon number of 16 to 46 as a base oil can be included.

式１

Formula 1

Hereinafter, the HDD motor according to another embodiment of the present invention will be described in detail, but the description overlapping with the description of the above-described embodiment of the present invention will be omitted.

In the HDD motor 400, an oil seal 160 may be formed between the fixing members 120 and 140 and the rotating members 110, 130, and 212. In particular, the sleeve 120 and the thrust plate may be used. ) 130 and a cap 140.

The cap 140 is a member that is press-fitted on the upper side of the thrust plate 130 so that the lubricating fluid is sealed between the cap and the thrust plate 130, and is pressed into the thrust plate 130 and the sleeve 120. In the outer diameter direction, a circumferential groove can be formed.

The cap 140 may be formed with a protrusion on a lower surface thereof to allow the lubricating fluid to be sealed, and this may cause capillary action and leakage to prevent the lubricating fluid from leaking to the outside when the motor is driven. The surface tension of the lubricating fluid is used.

Meanwhile, the HDD motor 400 according to another embodiment of the present invention may include a shaft 110, a sleeve 120, a thrust plate 130, a cap member 140, and an oil seal portion 160.

The sleeve 120 can support the shaft 110 such that the upper end of the shaft 110 protrudes upward in the axial direction, and forges Cu or Al, or burns Cu-Fe alloy powder or SUS powder. It can be formed by tying.

Here, the shaft 110 is inserted so as to have a minute gap with the shaft hole of the sleeve 120, and the minute gap is filled with a lubricating fluid. Further, the rotation of the rotor 200 can be more smoothly supported by a radial dynamic pressure groove formed in at least one of the outer diameter of the shaft 110 and the inner diameter of the sleeve 120.

The radial dynamic pressure groove is formed on the inner surface of the sleeve 120, which is the inside of the shaft hole of the sleeve 120, and can generate pressure so as to be biased to one side when the shaft 110 rotates.

However, the radial dynamic pressure grooves are not limited to being provided on the inner side surface of the sleeve 120 as described above, and can be provided on the outer diameter portion of the shaft 110, and the number is not limited. .

The sleeve 120 is provided with a bypass water passage 125 formed so as to communicate with the upper and lower portions of the sleeve 120, and the pressure of the lubricating fluid inside the fluid dynamic bearing assembly 100 can be distributed and balanced, Bubbles and the like existing in the fluid dynamic bearing assembly 100 can be moved so as to be discharged by circulation.

Here, a lower plate of the sleeve 120 may be coupled to the sleeve 120 while maintaining a gap, and a cover plate 150 containing a lubricating fluid may be coupled to the gap.

The cover plate 150 accommodates a lubricating fluid in a gap between the sleeve 120 and the cover plate 150 itself can function as a bearing that supports the lower surface of the shaft 110.

The thrust plate 130 is disposed at the upper part of the sleeve 120 in the axial direction, and has a hole corresponding to the cross section of the shaft 110 at the center, into which the shaft 110 can be inserted.

At this time, the thrust plate 130 may be separately manufactured and coupled to the shaft 110. However, the thrust plate 130 may be integrally formed with the shaft 110 from the time of manufacture. Rotating movement along.

A thrust dynamic pressure groove for providing a thrust dynamic pressure to the shaft 110 may be formed on the upper surface of the thrust plate 130.

The thrust dynamic pressure groove is not limited to being formed on the upper surface of the thrust plate 130 as described above, and may be formed on the upper surface of the sleeve 120 corresponding to the lower surface of the thrust plate 130.

The stator 300 may include a coil 320, a core 330, and a base member 310.

That is, the stator 300 is a fixed structure including a coil 320 that generates an electromagnetic force having a predetermined magnitude when power is applied, and a plurality of cores 330 around which the coil 320 is wound. Can do.

The core 330 is fixedly disposed on an upper part of a base member 310 provided with a printed circuit board (not shown) on which a pattern circuit is printed, and the upper surface of the base member 310 corresponding to the winding coil 320 is disposed on the upper surface of the base member 310. A plurality of coil holes having a predetermined size may be formed through to expose the wire coil 320 in the lower part. In addition, the winding coil 320 may be electrically connected to the printed circuit board (not shown) so that external power is supplied.

The base member 310 is press-fitted and fixed to the outer peripheral surface of the sleeve 120, and a core 330 around which the coil 320 is wound can be inserted.

In addition, the base member 310 and the sleeve 120 can be assembled to each other by applying an adhesive to the inner surface of the base member 310 or the outer surface of the sleeve 120.

The rotor 200 is a rotating structure provided to be rotatable with respect to the stator 300, and includes a rotor case 210 including annular ring-shaped magnets 220 corresponding to each other at a predetermined interval from the core 330 on an outer peripheral surface. Can do.

The magnet 220 may be provided as a permanent magnet that is alternately magnetized with N and S poles in the circumferential direction to generate a magnetic force with a predetermined strength.

Here, the rotor case 210 is press-fitted and fixed to the upper end of the shaft 110, and is extended from the hub base 212 in the outer diameter direction and bent downward in the axial direction to support the magnet 220. And a magnet support part 214.

The HDD motor according to another embodiment of the present invention includes the lubricating oil composition 170 for the fluid dynamic pressure bearing, thereby having a low viscosity and more effectively reducing the friction loss of the apparatus. The amount of evaporation is small, and it can have very good stability at high temperatures.

In addition, by manufacturing a motor for HDDs containing a lubricating oil composition for fluid dynamic pressure bearings that has low viscosity at practical temperatures, low evaporation loss, and improved oxidation stability, the reliability quality of the motor after long-term use Can be improved.

The manufacturing method of the HDD motor 400 is the same as a normal manufacturing method, except that the lubricating oil composition 170 for the fluid dynamic pressure bearing is included.

EXAMPLES Hereinafter, although this invention is demonstrated in detail with reference to an Example, this invention is not restrict | limited by this.

(Example)
Example 1 is an example of 2-ethylhexanoic acid and hexadecan-7-7 sold by Aldrich, Merck, and TCI. ol) and hexahexan-7-yl-ethylhexanoate was synthesized as shown in Formula 4 below.

式４

Formula 4

In the above reaction, an alcohol and an acid were charged into a reactor and reacted at 200 ° C. for 24 hours. After the reaction, purification was performed.

Hexadecan-7-yl-ethylhexanoate accounts for about 95 wt% of the total weight ratio, and the remaining 5 wt% is added with additives for improving other properties. did.

Specifically, in order to prevent oxidation of the oil, 2,2′-methylene-bis (4-methyl-6-tert-butylphenol) (2,2′-methylene-bis (4-methyl-6-tert- butylphenol) was added at 2 wt%, and tricresyl phosphate (tricresyl phosphate) was added at 2 wt% as an internal pressure inhibitor.

Moreover, in order to prevent the oxidation of the metal surface which contacts oil, 1 wt% of diphenylamine-4-sulfonate (Barium diphenylamine-4-sulfonate) was added.

(Comparative Examples 1 and 2)
Comparative Example 1 was lubricated by adding 5 wt% of additive to a mixture of 65 wt% of dioctyl sebacate (DOS) and 30 wt% of 2-ethylhexyl oleate (EHO) in the same manner as in Example 1. An oil composition was produced, and Comparative Example 2 was produced in the same manner as Example 1 except that dioctyl adipate (DOA) was used in an overall weight ratio of about 95 wt%.

The esters of Comparative Examples 1 and 2 can be represented by the following formulas 5 and 6.

式５

Formula 5

式６

Equation 6

Table 1 below shows the measured amounts of evaporation for comparing the viscosity and reliability in order to compare the performances of the lubricating oil compositions according to the above Examples and Comparative Examples.

The viscosity is measured using a Brookfield DB-III viscometer and each component is divided into three temperature intervals (−20 ° C., 25 ° C. and 85 ° C.) in order to confirm the tendency due to temperature. ).

The amount of evaporation was measured by placing 5 g of a lubricating oil composition for a fluid dynamic pressure bearing containing each component on a SUS material evaporating dish and putting it in a thermostatic bath at 100 ° C. to perform an experiment.

The above experiment was conducted for 144 hours (6 days), and the amount of evaporation was compared by measuring the initial weight when the lubricating oil composition was placed on the evaporating dish and the weight after 144 hours had passed at 100 ° C.

Referring to Table 1 above, the lubricating oil composition according to the present invention (Example 1) used a mixture of dioctyl sebacate (DOS) 65 wt% and 2-ethylhexyl oleate (EHO) 30 wt%. It can be seen that the viscosity is lower and the amount of evaporation is smaller than the lubricating oil composition (Comparative Example 1) and the lubricating oil composition (Comparative Example 2) using dioctyl azelate (DOZ).

Therefore, according to one embodiment of the present invention, by manufacturing a HDD motor including a lubricating oil composition for a fluid dynamic pressure bearing having a low viscosity at a practical temperature, a low evaporation loss, and an improved oxidation stability. The reliability quality can be improved by long-term use of the motor.

The present invention is not limited by the above embodiments and the accompanying drawings, but is limited by the appended claims. Accordingly, it is apparent to those skilled in the art that various forms of substitution, modification, and change can be made without departing from the technical idea of the present invention described in the claims. This also belongs to the technical idea described in the appended claims.

DESCRIPTION OF SYMBOLS 100 Fluid dynamic pressure bearing assembly 110 Shaft 120 Sleeve 125 Bypass water channel 130 Thrust plate 140 Cap member 150 Cover plate 160 Oil seal part 170 Lubricating oil composition 200 Rotor 210 Rotor case 212 Hub base 214 Magnet support part 220 Magnet 300 Stator 310 Base member 320 Winding coil 330 Core 400 Motor

Claims (16)

Aliphatic monocarboxylic acid ester having a total carbon number of 16 to 46 obtained by esterification reaction of a carboxylic acid represented by the following formula 1 and a primary or secondary alcohol (alcohol) having 8 to 38 carbon atoms A lubricating oil composition for fluid dynamic pressure bearings, comprising

Formula 1 2. The lubricating oil composition for a fluid dynamic bearing according to claim 1, wherein the aliphatic monocarboxylic acid ester is palmityl ethylhexanoate (Palmityl Ethylhexanoate) or cetyl ethylhexanoate (Cetyl Ethylhexanoate). 3. The lubricating oil composition for a fluid dynamic pressure bearing according to claim 1, wherein the lubricating oil composition for a fluid dynamic pressure bearing further comprises 0.01 to 2 parts by weight of an oil antioxidant. The oil antioxidant is 2,2′-methylene-bis (4-methyl-6-tert-butylphenol) (2,2′-methylene-bis (4-methyl-6-tert-butylphenol)). The lubricating oil composition for fluid dynamic pressure bearings according to claim 3. The lubricating oil composition for a fluid dynamic pressure bearing according to claim 1, wherein the lubricating oil composition for a fluid dynamic pressure bearing further includes 0.01 to 2 parts by weight of a metal antioxidant. The lubricating oil composition for a fluid dynamic bearing according to claim 5, wherein the metal antioxidant is barium diphenylamine-4-sulfonate. The lubricating oil composition for a fluid dynamic pressure bearing according to claim 1, wherein the lubricating oil composition for a fluid dynamic pressure bearing further includes 0.01 to 2 parts by weight of an internal pressure inhibitor. The lubricating oil composition for a fluid dynamic bearing according to claim 7, wherein the internal pressure inhibitor is tricresyl phosphate. Aliphatic monocarboxylic acid ester having a total carbon number of 16 to 46 obtained by esterification reaction of a carboxylic acid represented by the following formula 1 and a primary or secondary alcohol (alcohol) having 8 to 38 carbon atoms An HDD motor comprising a lubricating oil composition for a fluid dynamic pressure bearing that contains a base oil.

Formula 1 The HDD motor according to claim 9, wherein the aliphatic monocarboxylic acid ester is Hexadecan-7-yl-Ethylhexanoate. The HDD motor according to claim 9, wherein the lubricating oil composition for a fluid dynamic pressure bearing further includes 0.01 to 2 parts by weight of an oil antioxidant. The oil antioxidant is 2,2′-methylene-bis (4-methyl-6-tert-butylphenol) (2,2′-methylene-bis (4-methyl-6-tert-butylphenol)). The HDD motor according to claim 11. The HDD motor according to claim 9, wherein the lubricating oil composition for a fluid dynamic pressure bearing further includes 0.01 to 2 parts by weight of a metal antioxidant. The HDD motor according to claim 13, wherein the metal antioxidant is barium diphenylamine-4-sulfonate. The HDD motor according to claim 9, wherein the lubricating oil composition for a fluid dynamic pressure bearing further includes 0.01 to 2 parts by weight of an internal pressure inhibitor. The HDD motor according to claim 15, wherein the internal pressure preventing agent is tricresyl phosphate.

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