U.S. patent application number 13/893785 was filed with the patent office on 2014-01-16 for lubricating oil composition for fluid dynamic bearing and motor for hdd fabricated using the same.
This patent application is currently assigned to SAMSUNG ELECTRO-MECHANICS CO., LTD.. The applicant listed for this patent is SAMSUNG ELECTRO-MECHANICS CO., LTD.. Invention is credited to Ha Yong Jung, Hyung Kyu KIM.
Application Number | 20140018270 13/893785 |
Document ID | / |
Family ID | 49914477 |
Filed Date | 2014-01-16 |
United States Patent
Application |
20140018270 |
Kind Code |
A1 |
KIM; Hyung Kyu ; et
al. |
January 16, 2014 |
LUBRICATING OIL COMPOSITION FOR FLUID DYNAMIC BEARING AND MOTOR FOR
HDD FABRICATED USING THE SAME
Abstract
There are provided a lubricating oil composition for a fluid
dynamic bearing and a motor for a hard disk drive (HDD), the
lubricating oil composition including, as a base oil, an aliphatic
monocarboxylic acid ester having a total of between 16 to 46 carbon
atoms, obtained by an esterification reaction of carboxylic acid
represented by Chemical Formula 1 below and a primary or a
secondary alcohol having between 8 to 38 carbon atoms, ##STR00001##
and thus, the motor for an HDD is fabricated using the lubricating
oil composition for a fluid dynamic bearing having low viscosity,
low evaporation loss, and improved oxidation stability at a
practicable temperature, thereby preventing a deterioration in
product reliability due to long-time use of the motor.
Inventors: |
KIM; Hyung Kyu; (Suwon,
KR) ; Jung; Ha Yong; (Suwon, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SAMSUNG ELECTRO-MECHANICS CO., LTD. |
Suwon |
|
KR |
|
|
Assignee: |
SAMSUNG ELECTRO-MECHANICS CO.,
LTD.
Suwon
KR
|
Family ID: |
49914477 |
Appl. No.: |
13/893785 |
Filed: |
May 14, 2013 |
Current U.S.
Class: |
508/409 ;
508/442; 508/463; 560/265 |
Current CPC
Class: |
C10M 141/10 20130101;
C10M 2219/044 20130101; C10M 105/34 20130101; C10N 2040/02
20130101; C10M 2207/026 20130101; C10M 169/04 20130101; C10N
2020/071 20200501; C10N 2030/10 20130101; C10M 2223/041 20130101;
C10N 2030/02 20130101; C10M 2207/2815 20130101; C10N 2010/04
20130101; C10N 2030/74 20200501; C10N 2040/18 20130101; C10M
2207/2825 20130101 |
Class at
Publication: |
508/409 ;
508/463; 508/442; 560/265 |
International
Class: |
C10M 141/10 20060101
C10M141/10; C10M 105/34 20060101 C10M105/34 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 12, 2012 |
KR |
10-2012-0076020 |
Claims
1. A lubricating oil composition for a fluid dynamic bearing, the
lubricating oil composition comprising, as a base oil, an aliphatic
monocarboxylic acid ester having a total of between 16 to 46 carbon
atoms, obtained by an esterification reaction of carboxylic acid
represented by Chemical Formula 1 below and a primary or a
secondary alcohol having between 8 to 38 carbon atoms.
##STR00009##
2. The lubricating oil composition of claim 1, wherein the
aliphatic monocarboxylic acid ester is palmityl ethylhexanoate or
cetyl ethylhexanoate.
3. The lubricating oil composition of claim 1, further comprising
0.01 to 2 parts by weight of an oil antioxidant.
4. The lubricating oil composition of claim 3, wherein the oil
antioxidant is 2,2'-methylene-bis(4-methyl-6-tert-butylphenol).
5. The lubricating oil composition of claim 1, further comprising
0.01 to 2 parts by weight of a metal antioxidant.
6. The lubricating oil composition of claim 5, wherein the metal
antioxidant is barium diphenylamine-4-sulfonate.
7. The lubricating oil composition of claim 1, further comprising
0.01 to 2 parts by weight of an internal pressure inhibitor.
8. The lubricating oil composition of claim 7, wherein the internal
pressure inhibitor is tricresyl phosphate.
9. A motor for a hard disk drive (HDD), the motor comprising a
lubricating oil composition for a fluid dynamic bearing, including,
as a base oil, an aliphatic monocarboxylic acid ester having a
total of between 16 to 46 carbon atoms, obtained by an
esterification reaction of carboxylic acid represented by Chemical
Formula 1 below and a primary or a secondary alcohol having between
8 to 38 carbon atoms. ##STR00010##
10. The motor of claim 9, wherein the aliphatic monocarboxylic acid
ester is hexadecan-7-yl-ethylhexanoate.
11. The motor of claim 9, wherein the lubricating oil composition
for a fluid dynamic bearing further includes 0.01 to 2 parts by
weight of an oil antioxidant.
12. The motor of claim 11, wherein the oil antioxidant is
2,2'-methylene-bis(4-methyl-6-tert-butylphenol).
13. The motor of claim 9, wherein the lubricating oil composition
for a fluid dynamic bearing further includes 0.01 to 2 parts by
weight of a metal antioxidant.
14. The motor of claim 13, wherein the metal antioxidant is barium
diphenylamine-4-sulfonate.
15. The motor of claim 9, wherein the lubricating oil composition
for a fluid dynamic bearing further includes 0.01 to 2 parts by
weight of an internal pressure inhibitor.
16. The motor of claim 15, wherein the internal pressure inhibitor
is tricresyl phosphate.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the priority of Korean Patent
Application No. 10-2012-0076020 filed on Jul. 12, 2012, in the
Korean Intellectual Property Office, the disclosure of which is
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a lubricating oil
composition for a fluid dynamic bearing having low viscosity, low
evaporation loss, and improved oxidation stability, and a motor for
a hard disk drive (HDD) fabricated using the same.
[0004] 2. Description of the Related Art
[0005] A hard disk drive (HDD), an information storage device,
reads data stored on a disk or writes data to a disk using a
read/write head.
[0006] A HDD requires a disk driving device capable of driving a
disk, and the disk driving device employs a small-sized spindle
motor.
[0007] In this small-sized spindle motor, a fluid dynamic bearing
assembly is used. A lubricating fluid is interposed between a shaft
and a sleeve of the fluid dynamic bearing assembly so that the
shaft is supported by fluid pressure generated in the lubricating
fluid.
[0008] In the case in which the viscosity of the lubricating fluid
is high at a low temperature during rotation of the spindle motor,
there is increased viscous resistance to a dynamic power generating
groove in the lubricating fluid, generated during rotation of the
motor, resulting in increased power loss in the motor.
[0009] On the other hand, in the case in which the lubricating
fluid is thermally expanded and the viscosity thereof is decreased
in a high temperature region during rotation of the motor, the
lubricating fluid may not sufficiently perform a supporting
role.
[0010] Due to this reason, the lubricating fluid is required to
have conflicting viscosity behavior characteristics in which low
viscosity is maintained in a low temperature region and viscosity
is not decreased in a high temperature region.
[0011] In order to satisfy these viscosity characteristics,
technologies, such as adding a material such as an anti-oxidant or
an extreme-pressure additive to a base oil containing a specific
ester compound as a main component, have been developed.
[0012] A lubricating fluid containing the above-mentioned additives
exhibits a desired effect at the start of a motor lifespan, but
when the lubricating fluid is used over an extended period of time,
a lubricating agent may be evaporated and viscosity characteristics
thereof may be changed, and thus, it may be difficult to
continuously maintain the desired effect.
[0013] In addition, with the trend for miniaturization, high
precision, high speed rotation, and low power consumption in disk
driving device motors, the lubricating fluid is required to have
characteristics such as heat resistance, oxidation stability, low
evaporation, and abrasion prevention.
[0014] Meanwhile, in the case in which the viscosity of the base
oil is reduced, the evaporation loss thereof tends to increase.
Therefore, a base oil having a low viscosity at a practical
temperature but suppressing evaporation loss is required.
[0015] The following related art document discloses a grease
composition containing 2-ethylhexanoic acid. However, while the
grease composition has low viscosity at a practical temperature,
the evaporation loss thereof is not significantly suppressed.
RELATED ART DOCUMENT
[0016] (Patent Document 1) Japanese Patent Laid-Open Publication
No. 2007-154032
SUMMARY OF THE INVENTION
[0017] An aspect of the present invention provides a lubricating
oil composition for a fluid dynamic bearing having low viscosity,
low evaporation loss, and improved oxidation stability, and a motor
for a hard disk drive (HDD) fabricated using the same.
[0018] According to an aspect of the present invention, there is
provided a lubricating oil composition for a fluid dynamic bearing,
the lubricating oil composition including, as a base oil, an
aliphatic monocarboxylic acid ester having a total of between 16 to
46 carbon atoms, obtained by an esterification reaction of
carboxylic acid represented by Chemical Formula 1 below and a
primary or a secondary alcohol having between 8 to 38 carbon
atoms.
##STR00002##
[0019] The aliphatic monocarboxylic acid ester may be palmityl
ethylhexanoate or cetyl ethylhexanoate.
[0020] The lubricating oil composition may further include 0.01 to
2 parts by weight of an oil antioxidant, and the oil antioxidant
may be 2,2'-methylene-bis(4-methyl-6-tert-butylphenol).
[0021] The lubricating oil composition may further include 0.01 to
2 parts by weight of a metal antioxidant, and the metal antioxidant
may be barium diphenylamine-4-sulfonate.
[0022] The lubricating oil composition may further include 0.01 to
2 parts by weight of an internal pressure inhibitor, and the
internal pressure inhibitor may be tricresyl phosphate.
[0023] According to another aspect of the present invention, there
is provided a motor for a hard disk drive (HDD), the motor
including a lubricating oil composition for a fluid dynamic
bearing, including, as a base oil, an aliphatic monocarboxylic acid
ester having a total of between 16 to 46 carbon atoms, obtained by
an esterification reaction of carboxylic acid represented by
Chemical Formula 1 below and a primary or a secondary alcohol
having between 8 to 38 carbon atoms.
##STR00003##
[0024] The aliphatic monocarboxylic acid ester may be
hexadecan-7-yl-ethylhexanoate.
[0025] 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 be
2,2'-methylene-bis(4-methyl-6-tert-butylphenol).
[0026] 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 be barium
diphenylamine-4-sulfonate.
[0027] The lubricating oil composition for a fluid dynamic 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The above and other aspects, features and other advantages
of the present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
[0029] FIG. 1 is a schematic cross sectional view showing a motor
for a hard disk drive (HDD), including a fluid dynamic bearing
assembly according to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0030] Hereinafter, embodiments of the present invention will be
described in detail with reference to the accompanying drawings.
The invention may, however, be embodied in many different forms and
should not be construed as being limited to the embodiments set
forth herein. Rather, these embodiments are provided so that this
disclosure will be thorough and complete, and will fully convey the
scope of the invention to those skilled in the art.
[0031] In the drawings, the shapes and dimensions of elements maybe
exaggerated for clarity, and the same reference numerals will be
used throughout to designate the same or like elements.
[0032] FIG. 1 is a schematic cross sectional view showing a motor
for a hard disk drive (HDD), including a fluid dynamic bearing
assembly according to an embodiment of the present invention.
[0033] Referring to FIG. 1, a lubricating oil composition 170 for a
fluid dynamic bearing according to an embodiment of the present
invention may include, as a base oil, an aliphatic monocarboxylic
acid ester having a total of between 16 to 46 carbon atoms,
obtained by an esterification reaction of carboxylic acid
represented by Chemical Formula 1 below and a primary or a
secondary alcohol having between 8 to 38 carbon atoms.
##STR00004##
[0034] Hereinafter, the above constitution will be described in
detail.
[0035] The carboxylic acid represented by Chemical Formula 1 may be
2-ethyl hexanoic acid.
[0036] Meanwhile, according to the embodiment of the present
invention, the alcohol may be a primary or a secondary alcohol
having between 8 to 38 carbon atoms in order to perform an
esterification reaction with the carboxylic acid represented by
Chemical Formula 1, but is not limited thereto.
[0037] The lubricating oil composition 170 for a fluid dynamic
bearing according to an embodiment of the present invention may
include, as a base oil, an aliphatic monocarboxylic acid ester
obtained by an esterification reaction of the carboxylic acid
represented by Chemical Formula 1 below and the primary or the
secondary alcohol having between 8 to 38 carbon atoms.
[0038] The aliphatic monocarboxylic acid ester may have, but is not
limited to, for example, a total of between 16 to 46 carbon
atoms.
[0039] The aliphatic monocarboxylic acid ester may be, but is not
limited to, for example, palmityl ethylhexanoate or cetyl
ethylhexanoate, represented by Chemical Formula 2 or Chemical
Formula 3 below.
##STR00005##
[0040] Specifically, Chemical Formula 2 represents palmityl
ethylhexanoate, and Chemical Formula 3 represents cetyl
ethylhexanoate.
[0041] The lubricating oil composition 170 for a fluid dynamic
bearing according to the embodiment of the present invention may
have low viscosity, low evaporation loss, and excellent oxidation
stability, by including, as the base oil, the aliphatic
monocarboxylic acid ester obtained by the esterification reaction
of the 2-ethyl hexanoic acid and the primary or the secondary
alcohol having between 8 to 38 carbon atoms.
[0042] The kinematic viscosity of the aliphatic monocarboxylic acid
ester according to the embodiment of the present invention may be
measured together with viscosities at temperatures of -20.degree.
C., 25.degree. C., and 85.degree. C.
[0043] Viscosity may be measured by using the Brookfield DB-III
Rheometer Viscometer, and may be measured for respective components
at three temperature regions (-20.degree. C., 25.degree. C., and
85.degree. C.) in order to check the viscosity tendency thereof
with regard to temperature.
[0044] In a general test of motor reliability, among the three
temperatures, -20.degree. C. corresponds to a low-temperature motor
storage temperature, 25.degree. C. corresponds to a
room-temperature motor operating temperature, and 85.degree. C.
corresponds to a high-temperature motor operating temperature.
[0045] According to the embodiment of the present invention, the
aliphatic monocarboxylic acid ester may have lower viscosity and a
lower evaporation rate at high temperatures as compared to a
generally used aliphatic monocarboxylic acid ester such as dioctyl
adipate (DOA), dioctyl sebacate (DOS), or dioctyl azelate
(DOZ).
[0046] Therefore, the use of the aliphatic monocarboxylic acid
ester as a base oil can more effectively reduce friction loss in an
apparatus while inducing low viscosity, and improve stability at
high temperatures due to low evaporation thereof.
[0047] The lubricating oil composition including, as the base oil,
the aliphatic monocarboxylic acid ester, may be suitable to be used
for, but is not limited thereto, for example, a fluid dynamic
bearing of a motor for a hard disc drive (HDD).
[0048] As for a small-sized HDD, power consumption thereof needs to
be low, and stability at high temperatures may be a very important
factor due to high speed rotation of the motor.
[0049] The lubricating oil composition according to the embodiment
of the present invention has low friction loss and superior
stability at high temperatures, and thus, can satisfy the above
conditions of the small-sized HDD.
[0050] The lubricating oil composition for a fluid dynamic bearing
may further 0.01 to 2 parts by weight of an oil antioxidant, and
the oil antioxidant may be, but is not limited to,
2,2'-methylene-bis(4-methyl-6-tert-butylphenol).
[0051] The oil antioxidant may be included in a content of 0.01 to
2 parts by weight within such a range that performance of the
lubricating oil composition is not deteriorated. If the content of
the oil antioxidant is below 0.01 parts by weight, the addition of
the oil antioxidant is less effective, and if the content of the
oil antioxidant is above 2 parts by weight, the performance of the
lubricating oil composition may be deteriorated.
[0052] In addition, 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 be, but is not
limited to, for example, barium diphenylamine-4-sulfonate.
[0053] If the addition amount of the metal antioxidant is below
0.01 parts by weight, the oxidation stability effect is less
effective, but if the addition amount of the metal antioxidant is
above 2 parts by weight, the performance of the lubricating oil
composition may be deteriorated.
[0054] The lubricating oil composition for a fluid dynamic bearing
may further include 0.01 to 2 parts by weight of an internal
pressure inhibitor, and the internal pressure inhibitor may be, but
is not limited to, for example, tricresyl phosphate.
[0055] If the addition amount of the internal pressure inhibitor is
below 0.01 parts by weight, the internal pressure inhibition effect
is less effective, but if the addition amount of the internal
pressure inhibitor is above 2 parts by weight, the performance of
the lubricating oil composition may be deteriorated. Therefore, the
addition amount of the internal pressure inhibitor may be within
the range of 0.01 to 2 parts by weight.
[0056] A motor for an HDD according to another embodiment of the
present invention may include a lubricating oil composition for a
fluid dynamic bearing containing, as a base oil, an aliphatic
monocarboxylic acid ester having a total of between 16 to 46 carbon
atoms, obtained by an esterification reaction of carboxylic acid
represented by Chemical Formula 1 below and a primary or a
secondary alcohol having between 8 to 38 carbon atoms.
##STR00006##
[0057] Hereinafter, a motor for an HDD according to another
embodiment of the present invention will be described in detail,
and descriptions overlapping with those of the above-described
embodiment of the present invention will be omitted.
[0058] As for a motor 400 for an HDD, an oil sealing portion 160
may be formed between stationary members 120 and 140 and rotator
members 110, 130, and 212, and particularly, may be formed among a
sleeve 120, a thrust plate 130, and a cap 140.
[0059] The cap 140 is a member that is press-fitted from above the
thrust plate 130 so that a lubricating fluid is sealed between the
cap 140 and the thrust plate 130. A circumferential groove may be
formed in an outer diameter direction thereof so that the cap 140
is press-fitted on the thrust plate 130 and the sleeve 120.
[0060] The cap 140 may have a protrusion formed on a bottom surface
thereof in order to seal the lubricating oil, which uses a
capillary phenomenon and surface tension of the lubricating fluid
in order to prevent the lubricating fluid from being leaked to the
outside at the time of motor driving.
[0061] Meanwhile, the motor 400 for an HDD 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
sealing portion 160.
[0062] The sleeve 120 may support the shaft 110 such that an upper
end of the shaft 110 protrudes upwardly in an axial direction, and
may be formed by forging Cu or Al or sintering a Cu--Fe-based alloy
powder or an SUS-based power.
[0063] Here, the shaft 110 is inserted into a shaft hole of the
sleeve 120 such that there is a micro gap therebetween. The micro
gap is filled with the lubricating fluid and the rotation of the
rotor 200 may be more smoothly supported by a radial dynamic
pressure groove formed in at least one of an outer diameter of the
shaft 110 and an inner diameter of the sleeve 120.
[0064] The radial dynamic pressure groove may be formed in an
inside surface of the sleeve 120, an inside of the shaft hole of
the sleeve 120, and generate pressure to be biased to one side
during rotation of the shaft 110.
[0065] However, it is to be noted that the radial dynamic pressure
groove is not limited to being provided in the inside surface of
the sleeve 120, as described above, but for example, may be
provided in an outer diameter portion of the shaft 110 and the
number of radial dynamic pressure grooves is not restricted.
[0066] The sleeve 120 may have a bypass channel 125 communicating
an upper portion and a lower portion of the sleeve 120 with each
other to thereby distribute and balance the pressure of the
lubricating fluid in the fluid dynamic bearing assembly 100 and
move and exhaust bubbles or the like present in the fluid dynamic
bearing assembly 100 by circulation.
[0067] Here, a cover plate 150 may be coupled with a lower portion
of the sleeve 120 such that a gap between the sleeve 120 and the
cover plate 150 is maintained, and the lubricating oil is contained
in the gap.
[0068] The cover plate 150 may serve as a bearing supporting a
lower surface of the shaft 110 since the lubricating oil is
contained in the gap between the cover plate 150 and the sleeve
120.
[0069] The thrust plate 130 is disposed upwardly of the sleeve 120
in the axial direction and includes a hole corresponding to a cross
section of the shaft 110 at the center thereof. The shaft 110 may
be inserted into the hole.
[0070] Here, the thrust plate 130 may be separately manufactured,
and then coupled to the shaft 110, but may also be formed
integrally with the shaft 110. The thrust plate 130 may be rotated
following the shaft 110 during rotation of the shaft 110.
[0071] In addition, a thrust dynamic pressure groove may be formed
in an upper surface of the thrust plate 130 to provide thrust
dynamic pressure to the shaft 110.
[0072] The thrust dynamic pressure groove is not limited to being
formed in the upper surface of the thrust plate 130 as described
above, but may be formed in the upper surface of the sleeve 120
corresponding to a lower surface of the thrust plate 130.
[0073] A stator 300 may include a coil 320, a core 330, and a base
member 310.
[0074] In other words, the stator 300 may be a fixed structure that
includes the coil 320 generating electromagnetic force having a
predetermined magnitude at the time of the application of power and
a plurality of cores 330 wound by the coil 320.
[0075] The core 330 may be fixed to an upper portion of a base
member 310 including a printed circuit board (not shown) having
circuit patterns printed thereon. A plurality of coil holes having
a predetermined size penetrate the upper surface of the base member
310 corresponding to the winding coil 320 so that the winding coil
320 is downwardly exposed. The winding coil 320 may be electrically
connected to the printed circuit board (not shown) to supply
external power thereto.
[0076] The base member 310 is press-fitted and fixed to an outer
circumferential surface of the sleeve 120 and the core 330 wound by
the coil 320 may be inserted thereinto.
[0077] In addition, the base member 310 and the sleeve 120 may be
coupled to each other by applying an adhesive to an inner surface
of the base member 310 and an outer surface of the sleeve 120.
[0078] The rotor 200, a rotational structure provided to be
rotatable with respect to the stator 300, may include a rotor case
210 having a ring-shaped magnet 220 formed on an outer
circumferential surface thereof, the magnet facing the core 330 at
a predetermined distance.
[0079] In addition, the magnet 220 may be a permanent magnet of
which an N pole and an S pole are alternately magnetized in a
circumferential direction to thereby generate magnetic force having
a predetermined magnitude.
[0080] Here, the rotor case 210 may be composed of a hub base 212
press-fitted and fixed to the upper end of the shaft 110 and a
magnet support part 212 extending from the hub base 214 in the
outer diameter direction and bent downwardly in the axial direction
to support the magnet 220.
[0081] The motor for an HDD according to another embodiment of the
present invention includes the lubricating oil composition for a
fluid dynamic bearing, thereby more effectively reducing friction
loss in the apparatus while having low viscosity and achieving
excellent stability at high temperatures due to low
evaporation.
[0082] In addition, the motor for an HDD is fabricated with a
lubricating oil composition for a fluid dynamic bearing having low
viscosity at a practicable temperature, low evaporation loss, and
improved oxidation stability, thereby preventing a deterioration in
product reliability due to long-time use of the motor.
[0083] A method of manufacturing the motor 400 for an HDD may be
the same as a general manufacturing method, except for the
inclusion of the lubricating oil composition 170 for a fluid
dynamic bearing.
[0084] Hereafter, the present invention will be described in detail
with reference to embodiments, but is not limited thereto.
INVENTIVE EXAMPLE 1
[0085] In Inventive Example 1, 2-ethyl hexanoic acid and
hexadecan-7-ol, commercially available from vendors such as
Aldrich, Merck, TCI or the like, were reacted with each other to
synthesize hexadecan-7-yl-ethylhexanoate of Chemical Formula 4
below.
##STR00007##
[0086] The above alcohol and acid were put in a reactor, and the
reaction was performed at a temperature of 200.degree. C. for 24
hours. After the reaction, a purification process was
performed.
[0087] The hexadecan-7-yl-ethylhexanoate accounted for about 95 wt
% of a total weight, and additives for improving other
characteristics accounted for the other 5 wt %.
[0088] Specifically, 2 wt % of
2,2'-methylene-bis(4-methyl-6-tert-butylphenol) was added for
antioxidation of oil, and 2 wt % of tricresyl phosphate was added
as an internal pressure inhibitor.
[0089] In addition, 1 wt % of barium diphenylamine-4-sulfonate was
added for antioxidation of a metal surface contacted with oil.
COMPARATIVE EXAMPLES 1 AND 2
[0090] In Comparative Example 1, a lubricating oil composition was
prepared by adding 5 wt % of additives to a mixture of 65 wt % of
dioctyl sebacate (DOS) and 30 wt % of ethylhexyloleate (EHO), as in
Inventive Example 1. In Comparative Example 2, a lubricating oil
composition was prepared by the same method as Inventive Example 1
except that dioctyl adipate (DOA) was used in an amount of about 95
wt %, based on total weight.
[0091] Esters of Comparative Examples 1 and 2 may be represented by
Chemical Formulas 5 and 6 below:
##STR00008##
[0092] Table 1 below shows that viscosity for comparing performance
of the lubricating oil composition and a level of evaporation were
measured to compare reliability between the Inventive Example and
the Comparative Examples.
[0093] The viscosity was measured using the Brookfield DB-III
Rheometer viscometer, and was measured for respective components at
three temperature regions (-20.degree. C., 25.degree. C., and
85.degree. C.) in order to check the viscosity tendency thereof
according to temperature.
[0094] The evaporation amount was measured by an experiment where 5
g of a lubricating oil composition for a fluid dynamic bearing
containing respective components was placed on a SUS-based
evaporation dish made of an SUS material, which was then introduced
into a thermostat at 100.degree. C.
[0095] The experiment was performed for 144 hours (six days), and
the comparison of an amount of evaporation was carried out by
measuring an initial weight of the lubricating oil composition
placed on the evaporation dish and a weight of the lubricating oil
composition after 144 hours at 100.degree. C.
TABLE-US-00001 TABLE 1 Evaporation Viscosity (cP) Amount (wt %)
Classification 0.degree. C. 20.degree. C. 40.degree. C. 100.degree.
C. (100.degree. C., 144 h) Inventive 35.4 13.7 6.8 1.9 0.7 Example
1 Comparative 42.1 17.7 9.2 2.7 3.41 Example 1 Comparative 41.6
17.4 9.0 2.6 7.12 Example 2
[0096] It can be appreciated from Table 1 above that the
lubricating oil composition according to the present invention
(Inventive Example 1) had lower viscosity and a lower evaporation
amount than the lubricating oil composition using the mixture of 65
wt % of dioctyl sebacate (DOS) and 30 wt % of 2-ethylhexyloleate
(EHO) (Comparative Example 1) and the lubricating oil composition
using dioctyl adipate (DOA) (Comparative Example 2).
[0097] Hence, according to the present invention, the HDD motor is
fabricated by including the lubricating oil composition for a fluid
dynamic bearing having low viscosity, low evaporation loss, and
improved oxidation stability, at a practicable temperature, thereby
improving the reliability of the motor according to the long-time
use of the motor.
[0098] As set forth above, according to embodiments of the present
invention, a motor for an HDD is fabricated using a lubricating oil
composition for a fluid dynamic bearing having low viscosity, low
evaporation loss, and improved oxidation stability at a practicable
temperature, thereby preventing a deterioration in product
reliability due to long-time use of the motor.
[0099] While the present invention has been shown and described in
connection with the embodiments, it will be apparent to those
skilled in the art that modifications and variations can be made
without departing from the spirit and scope of the invention as
defined by the appended claims.
* * * * *