U.S. patent application number 13/441606 was filed with the patent office on 2013-06-27 for lubricating oil composition for fluid dynamic bearing and hdd motor fabricated using the same.
This patent application is currently assigned to SAMSUNG ELECTRO-MECHANICS CO., LTD.. The applicant listed for this patent is Ha Yong Jung, Hyung Kyu Kim. Invention is credited to Ha Yong Jung, Hyung Kyu Kim.
Application Number | 20130165356 13/441606 |
Document ID | / |
Family ID | 48633467 |
Filed Date | 2013-06-27 |
United States Patent
Application |
20130165356 |
Kind Code |
A1 |
Jung; Ha Yong ; et
al. |
June 27, 2013 |
LUBRICATING OIL COMPOSITION FOR FLUID DYNAMIC BEARING AND HDD MOTOR
FABRICATED USING THE SAME
Abstract
There are provided a lubricating oil composition for a fluid
dynamic bearing, and a HDD motor fabricated using the same. The
lubricating oil composition includes an ester base oil and 0.01 to
3.00 parts by weight of an additive relative to 100 parts by weight
of the base oil and has a density of 0.900 g/cm.sup.3 or less at
15.degree. C. and a kinetic viscosity of 9.50 cSt or less at
40.degree. C. According to the present invention, the HDD motor is
fabricated by using a lubricating oil composition for a fluid
dynamic bearing, the lubricating oil composition having advantages
such as low viscosity at practical temperature, reduced evaporation
loss and enhanced oxidation stability, thereby improving impact
resistance and low temperature operational stability of a fluid
dynamic motor.
Inventors: |
Jung; Ha Yong; (Suwon,
KR) ; Kim; Hyung Kyu; (Daejeon, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Jung; Ha Yong
Kim; Hyung Kyu |
Suwon
Daejeon |
|
KR
KR |
|
|
Assignee: |
SAMSUNG ELECTRO-MECHANICS CO.,
LTD.
|
Family ID: |
48633467 |
Appl. No.: |
13/441606 |
Filed: |
April 6, 2012 |
Current U.S.
Class: |
508/439 ;
508/465 |
Current CPC
Class: |
C10N 2010/04 20130101;
C10M 2219/044 20130101; C10M 2207/2825 20130101; C10N 2030/02
20130101; C10M 2223/041 20130101; C10M 2207/026 20130101; C10M
2207/2805 20130101; C10M 169/04 20130101; C10M 2215/064 20130101;
C10N 2040/18 20130101; C10N 2040/02 20130101 |
Class at
Publication: |
508/439 ;
508/465 |
International
Class: |
C10M 169/04 20060101
C10M169/04 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 22, 2011 |
KR |
10-2011-0140025 |
Claims
1. A lubricating oil composition for a fluid dynamic bearing,
comprising: an ester base oil; and 0.01 to 3.00 parts by weight of
an additive with respect to 100 parts by weight of the base oil,
wherein the lubricating oil composition has a density of 0.900 g/cm
or less at 15.degree. C. and a kinetic viscosity of 9.50 cSt or
less at 40.degree. C.
2. The lubricating oil composition of claim 1, wherein the density
of the lubricating oil composition ranges from 0.866 g/cm.sup.3 to
0.900 g/cm.sup.3 at 15.degree. C.
3. The lubricating oil composition of claim 1, wherein the base oil
has a viscosity of 2.30 cP or less at 100.degree. C.
4. The lubricating oil composition of claim 1, wherein the additive
includes at least one selected from the group consisting of an
antioxidant, an abrasion inhibitor, a corrosion inhibitor, an
extreme pressure additive, a viscosity modifier, an antistatic
agent and a deactivating agent.
5. The lubricating oil composition of claim 1, wherein the additive
includes 2,2'-methylene-bis(4-methyl-6-tert-butylphenol) as an
antioxidant.
6. The lubricating oil composition of claim 1, wherein the additive
includes barium diphenylamine-4-sulfonate as a metal
antioxidant.
7. The lubricating oil composition of claim 1, wherein the additive
includes tricresyl phosphate as an internal pressure inhibitor.
8. A HDD motor including a lubricating oil composition for a fluid
dynamic bearing, the lubricating oil composition including an ester
base oil and 0.01 to 3.00 parts by weight of an additive with
respect to 100 parts by weight of the base oil and having a density
of 0.900 g/cm or less at 15.degree. C. and a kinetic viscosity of
9.50 cSt or less at 40.degree. C.
9. The HDD motor of claim 8, wherein the density of the lubricating
oil composition ranges from 0.866 g/cm.sup.3 to 0.900 g/cm.sup.3 at
15.degree. C.
10. The HDD motor of claim 8, wherein the base oil has a viscosity
of 2.30 cP or less at 100.degree. C.
11. The HDD motor of claim 8, wherein the additive includes at
least one selected from the group consisting of an antioxidant, an
abrasion inhibitor, a corrosion inhibitor, an extreme pressure
additive, a viscosity modifier, an antistatic agent and a
deactivating agent.
12. The HDD motor of claim 8, wherein the additive includes
2,2'-methylene-bis(4-methyl-6-tert-butylphenol) as an
antioxidant.
13. The HDD motor of claim 8, wherein the additive includes barium
diphenylamine-4-sulfonate as a metal antioxidant.
14. The HDD motor of claim 8, wherein the additive includes
tricresyl phosphate as an internal pressure inhibitor.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the priority of Korean Patent
Application No. 10-2011-0140025 filed on Dec. 22, 2011, 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 low density lubricating
oil composition for a fluid dynamic bearing, enabling a fluid
dynamic bearing motor to have superior impact resistance and
operational stability at a low temperature, and a hard disk drive
(HDD) motor fabricated using the same.
[0004] 2. Description of the Related Art
[0005] A hard disk drive (HDD), as an information storage device,
uses a read/write head to read data stored in a disk or record
(write) data to the disk.
[0006] Such a HDD requires a disk driver to drive the disk and the
disk driver may be provided with a small spindle motor.
[0007] The small spindle motor may include a fluid dynamic bearing
assembly having lubricating fluid interposed between a shaft and a
sleeve thereof, in order to support the shaft using fluid pressure
generated in the lubricating fluid.
[0008] In a case in which viscosity of the lubricating fluid is
increased at a low temperature during the rotation of the spindle
motor, viscosity resistance of the lubricating fluid against a
dynamic pressure generating groove formed during the rotation of
the motor may be higher. Consequently, power loss may be incurred
in the motor.
[0009] On the contrary, when the lubricating fluid undergoes
respective decreases in thermal expansion and viscosity during the
rotation of the motor in a high temperature range, the lubricating
fluid does not sufficiently serve as a support.
[0010] For such reasons, the lubricating fluid requires contrary
viscosity behavior characteristics, in which it maintains a
relatively low viscosity in a low temperature range while the
viscosity is not decreased in a high temperature range.
[0011] In order to satisfy the foregoing viscosity characteristics,
for example, adding additive substance(s) such as an antioxidant,
an extreme pressure additive or the like to a base oil including a
specific ester compound as a main component have been developed and
further research with regard thereto is currently being
undertaken.
[0012] However, even in the case that the lubricating fluid
including the foregoing various additives exhibits initial positive
effects, while the lubricating fluid is used for an extended period
time, the lubricating fluid may be evaporated and viscosity
characteristics thereof may be varied, thus causing difficulties in
retaining desired effects.
[0013] Meanwhile, with a growing trend towards the compactness,
high precision, high rotational speed and low power dissipation of
the motor, the lubricating fluid needs thermal resistance,
oxidation stability, low evaporation, abrasion resistance, and the
like.
[0014] Furthermore, there is a need for a lubricating fluid capable
of improving the impact resistance of a fluid dynamic motor.
RELATED ART DOCUMENT
[0015] (Patent Document 1) Japanese Patent Laid-Open Publication
No. 2011-111463
SUMMARY OF THE INVENTION
[0016] An aspect of the present invention provides a low density
lubricating oil composition for a fluid dynamic bearing, enabling a
fluid dynamic bearing motor to have superior impact resistance and
operational stability at a low temperature, and a hard disk drive
(HDD) motor fabricated using the same.
[0017] According to an aspect of the present invention, there is
provided a lubricating oil composition for a fluid dynamic bearing,
including: an ester base oil; and 0.01 to 3.00 parts by weight of
an additive with respect to 100 parts by weight of the base oil,
wherein the lubricating oil composition has a density of 0.900 g/cm
or less at 15.degree. C. and a kinetic viscosity of 9.50 cSt or
less at 40.degree. C.
[0018] The density of the lubricating oil composition may range
from 0.866 g/cm.sup.3 to 0.900 g/cm.sup.3 at 15.degree. C.
[0019] The base oil may have a viscosity of 2.30 cP or less at
100.degree. C.
[0020] The additive may include at least one selected from the
group consisting of an antioxidant, an abrasion inhibitor, a
corrosion inhibitor, an extreme pressure additive, a viscosity
modifier, an antistatic agent and a deactivating agent.
[0021] The additive may include
2,2'-methylene-bis(4-methyl-6-tert-butylphenol) as an
antioxidant.
[0022] The additive may include barium diphenylamine-4-sulfonate as
a metal antioxidant.
[0023] The additive may include tricresyl phosphate as an internal
pressure inhibitor.
[0024] According to another aspect of the present invention, there
is provided a HDD motor including a lubricating oil composition for
a fluid dynamic bearing, the lubricating oil composition including
an ester base oil and 0.01 to 3.00 parts by weight of an additive
to 100 parts by weight of the base oil and having a density of
0.900 g/cm.sup.3 or less at 15.degree. C. and a kinetic viscosity
of 9.50 cSt or less at 40.degree. C.
[0025] The density of the lubricating oil composition may range
from 0.866 g/cm.sup.3 to 0.900 g/cm.sup.3 at 15.degree. C.
[0026] The base oil may have a viscosity of 2.30 cP or less at
100.degree. C.
[0027] The additive may include at least one selected from the
group consisting of an antioxidant, an abrasion inhibitor, a
corrosion inhibitor, an extreme pressure additive, a viscosity
modifier, an antistatic agent and a deactivating agent.
[0028] The additive may include
2,2'-methylene-bis(4-methyl-6-tert-butylphenol) as an
antioxidant.
[0029] The additive may include barium diphenylamine-4-sulfonate as
a metal antioxidant.
[0030] The additive may include tricresyl phosphate as an internal
pressure inhibitor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] 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 drawing, in which:
[0032] FIG. 1 is a schematic cross-sectional view illustrating a
hard disk drive (HDD) motor having a fluid dynamic bearing assembly
according to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0033] Exemplary embodiments of the present invention will now 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. In the
drawings, the shapes and dimensions of components may be
exaggerated for clarity, and the same reference numerals will be
used throughout to designate the same or like components.
[0034] Hereinafter, embodiments of the present invention will be
described in detail with reference to the accompanying
drawings.
[0035] A lubricating oil composition for a fluid dynamic bearing
according to an embodiment of the present invention includes: an
ester base oil; and 0.01 to 3.00 parts by weight of an additive
with respect to 100 parts by weight of the base oil, wherein the
lubricating oil composition has a density of 0.900 g/cm.sup.3 or
less at 15.degree. C. and a kinetic viscosity of 9.50 cSt or less
at 40.degree. C.
[0036] A detailed description thereof will be provided below.
[0037] The lubricating oil composition for a fluid dynamic bearing
may include an ester base oil.
[0038] The base oil is not particularly limited so long as it maybe
usable for a fluid dynamic bearing. For example, an ester based
compound may be used therefor.
[0039] According to the embodiment of the invention, the
lubricating oil composition for a fluid dynamic bearing may include
0.01 to 3.00 parts by weight of an additive with respect to 100
parts by weight of the base oil.
[0040] The additive may include at least one selected from the
group consisting of an antioxidant, an abrasion inhibitor, a
corrosion inhibitor, an extreme pressure additive, a viscosity
modifier, an antistatic agent and a deactivating agent, without
being limited thereto. That is, a variety of additives may be
used.
[0041] A very small amount of additive may be added to the
lubricating oil for a fluid dynamic bearing, thereby improving a
long-term high temperature reliability of the lubricating oil.
[0042] The additive may include an antioxidant, such as
2,2'-methylene-bis(4-methyl-6-tert-butylphenol), without being
limited thereto.
[0043] The additive may further include a metal antioxidant, such
as barium diphenylamine-4-sulfonate, without being limited
thereto.
[0044] Further, the additive may include an internal pressure
inhibitor, such as tricresyl phosphate, without being limited
thereto.
[0045] 0.01 to 3.00 parts by weight of the additive may be
contained with respect to 100 parts by weight of the base oil,
thereby allowing the lubricating oil to maintain a low viscosity in
a low temperature range without a reduction of the viscosity in a
high temperature range.
[0046] In a case in which the content of the additive is less than
0.01 parts by weight with respect to 100 parts by weight of the
base oil, the effects of the additive may not be sufficiently
achieved.
[0047] On the other hand, in a case in which the content of the
additive exceeds 3.00 parts by weight with respect to 100 parts by
weight of the base oil, the lubricating oil for a fluid dynamic
bearing may encounter deterioration in physical properties.
[0048] Meanwhile, the lubricating oil composition for a fluid
dynamic bearing according to the embodiment of the invention may
have a density of 0.900 g/cm or less at 15.degree. C. and a kinetic
viscosity of 9.50 cSt or less at 40.degree. C.
[0049] According to the embodiment of the invention, the density of
the lubricating oil composition for a fluid dynamic bearing may be
adjusted to 0.900 g/cm or less at 15.degree. C., thereby improving
impact resistance of the fluid dynamic bearing motor and
operational stability thereof at a low temperature.
[0050] Although selection of the lubricating oil is usually based
on kinetic viscosity, the driving of the fluid dynamic bearing
motor is practically associated with dynamic viscosity
(hereinafter, also referred to as `viscosity`).
[0051] In this regard, since the dynamic viscosity is represented
as a function of kinetic viscosity x density, when the lubricating
oil has a low density, the dynamic viscosity thereof may be
decreased, in particular, such effects may be more remarkable in a
low temperature range in which the viscosity is rapidly
increased.
[0052] That is, the density of the lubricating oil composition for
a fluid dynamic bearing is adjusted to 0.900 g/cm.sup.3 or less at
15.degree. C., such that the lubricating oil composition may
maintain a low level of viscosity in a low temperature range to
thereby improve low temperature operational stability.
[0053] In addition, the use of the low density lubricating oil may
allow for improvements in the impact resistance of the fluid
dynamic bearing motor.
[0054] In the case in which the lubricating oil composition for a
fluid dynamic bearing has a density of more than 0.900 g/cm.sup.3
at 15.degree. C., it may be problematic in terms of low temperature
operational stability and/or impact resistance of the fluid dynamic
bearing motor.
[0055] Meanwhile, according to the embodiment of the invention, the
kinetic viscosity of the lubricating oil composition for a fluid
dynamic bearing at 40.degree. C. may be adjusted to 9.50 cSt or
less, thereby improving impact resistance of the fluid dynamic
bearing motor as well as low temperature operational stability.
[0056] In other words, the density of the lubricating oil
composition for a fluid dynamic bearing is adjusted to be 0.900
g/cm or less at 15.degree. C. while the kinetic viscosity thereof
is adjusted to be 9.50 cSt or less at 40.degree. C., whereby the
dynamic viscosity thereof may be reduced and excellent low
temperature operational stability may be attained.
[0057] In the case in which the kinetic viscosity of the
lubricating oil composition for a fluid dynamic bearing exceeds
9.50 cSt at 40.degree. C., the dynamic viscosity of the lubricating
oil composition cannot be maintained to a low level even when the
density of the lubricating oil composition is adjusted to be 0.900
g/cm.sup.3 or less, thereby causing problems in terms of low
temperature operational stability and impact resistance of the
fluid dynamic bearing motor.
[0058] The kinetic viscosity of the lubricating oil composition for
a fluid dynamic bearing according to the embodiment of the
invention may be measured at 0.degree. C., 25.degree. C.,
40.degree. C. and 100.degree. C.
[0059] The viscosity may be measured using a viscometer, i.e.,
Brookfield DB-III Rheometer. In order to determine
temperature-dependent tendency, the measurement may be performed in
four different temperature ranges (0.degree. C., 25.degree. C.,
40.degree. C., and 100.degree. C.), respectively.
[0060] Such lubricating oil composition for a fluid dynamic bearing
is not particularly limited and, for example, may be suitably used
for a fluid bearing of a hard disk drive (HDD) motor.
[0061] In the case of a small HDD, reduced power consumption, low
temperature operational stability and impact resistance may be very
important factors.
[0062] The lubricating oil composition according to the embodiment
of the invention shows a reduction in friction loss and improvement
in low temperature operational stability, thereby satisfying the
above-described desired conditions of the small HDD.
[0063] FIG. 1 is a schematic cross-sectional view illustrating an
HDD motor having a fluid dynamic bearing assembly according to an
embodiment of the present invention.
[0064] Referring to FIG. 1, the HDD motor according to this
embodiment of the present invention may include a lubricating oil
composition for a fluid dynamic bearing including an ester base
oil, and 0.01 to 3.0 parts by weight of an additive with respect to
100 parts by weight of the base oil, wherein the lubricating oil
composition has a density of 0.900 g/cm.sup.3 or less at 15.degree.
C. and a kinetic viscosity of 9.50 cSt or less at 40.degree. C.
[0065] Hereinafter, the HDD motor according to the embodiment of
the present invention will be described in detail, except that the
description overlapping with that of the foregoing embodiment of
the present invention will be omitted.
[0066] A motor 10 having a base assembly for a motor (hereinafter,
referred to as `base assembly`) may include a base assembly 100
having a base 110 for a motor (hereinafter, referred to as `base`),
a sleeve 220 supporting the rotation of a rotational member, and a
core 240 having a coil 230 wound thereon.
[0067] First, terms regarding directions are defined as follows: as
shown FIG. 1, an axial direction refers to a vertical direction
with respect to the shaft 210, and an outer or inner radial
direction refers to a direction towards an outer edge of a hub 250
with respect to the shaft 210 or a direction towards the center of
the shaft 210 with respect to the outer edge of the hub 250.
[0068] In addition, a circumferential direction refers to a
rotational direction of the shaft 210, that is, a direction
rotating along an outer circumferential surface of the shaft
210.
[0069] The base assembly 100 may include the base 110 and a pull
plate 120, and the base 110 may be coupled to the core 240 having
the coil 230 wound therearound.
[0070] In other words, the base 110 may be a fixed member
supporting a rotational member including the hub 250, and may be
coupled to the core 240 having the coil 230 wound therearound and
the coil 230 generating electromagnetic force having a
predetermined magnitude when power is applied thereto.
[0071] Here, the base 110 may have a protrusion 112 and a body part
114, and an inner circumferential surface of the protrusion 112 may
be bonded to an outer circumferential surface of the sleeve 220
supporting the shaft 210, thereby supporting the sleeve 220.
[0072] That is, the protrusion 112 may have a hollow and be
protruded upward in the axial direction, and the sleeve 220
supporting the shaft 210 may be inserted into the hollow and they
are combined by welding, bonding and/or press-fitting.
[0073] In addition, an outer circumferential surface of the
protrusion 112 may be bonded to the core 240 having the coil 230
wound therearound. In order to ensure desired rotational stability
of the motor 10, rigidity should be secured.
[0074] In this regard, the body part 114 of the base 110 may be
combined with the pull plate 120, and the pull plate 120 may
prevent the excessive floating of the rotational member including
the shaft 210 and the hub 250.
[0075] More particularly, the pull plate 120 may be combined with
the body part 114 corresponding to a bottom surface of a magnet 260
coupled to the hub 250by a bonding method or the like, and may have
magnetic properties such that it allows for magnetic attraction to
the magnet 260.
[0076] The shaft 210 and the hub 250 of the motor 10 according to
the embodiment of the invention need to be floated to a
predetermined height for stable rotation. However, in the case of
the excessive floating thereof beyond the predetermined height, the
performance of the rotational members may be adversely affected
thereby.
[0077] In this case, the base 112 may be combined with the pull
plate 120 in order to prevent the excessive floating of the shaft
210 and the hub 250, and magnetic attraction between the pull plate
120 and the magnet 260 may prevent the excessive floating of the
foregoing rotational members.
[0078] The shaft 210 may be a rotational member coupled to the hub
250 and rotating together with the hub 250, and may be supported by
the sleeve 220.
[0079] The sleeve 220 supports the rotation of the rotational
members, that is, the shaft 210 and the hub 250. More particularly,
the sleeve 220 may support the shaft 210 while allowing a top end
of the shaft 210 to be protruded upward in the axial direction, and
may be fabricated by forging Cu or Al, or sintering Cu-Fe alloy
powder or SUS powder.
[0080] In addition, the sleeve 220 may have a shaft hole, into
which the shaft 210 is inserted with a micro clearance
therebetween. The micro clearance is filled with oil O such that
the shaft 210 may be stably supported by radial dynamic pressure
through the oil O.
[0081] The hub 250 is a rotational structure provided to rotate
with respect to a fixed structure including the base 110, and may
have the ring-shaped magnet 260 facing the core 240 with a
predetermined interval therebetween.
[0082] Here, the rotational driving force of the motor 10 may be
generated by interaction between the magnet 260 and the coil 230
wound around the core 240.
[0083] A HDD motor according to another embodiment of the present
invention includes a lubricating oil composition 170 for a fluid
dynamic bearing, such that it may efficiently reduce friction loss
of the motor while having low viscosity and attain superior
operational stability at a low temperature and excellent impact
resistance.
[0084] Furthermore, since the HDD motor is fabricated using the
lubricating oil composition for a fluid dynamic bearing having
reduced viscosity at practical temperature, low evaporation loss
and improved oxidation stability, the reliability thereof when
being used for a long time may be enhanced.
[0085] A method of fabricating the HDD motor 10 may be
substantially identical to a general method, except that the
lubricating oil composition 170 for a fluid dynamic bearing is used
therein.
[0086] Hereinafter, the following examples will be given for
concretely describing the present invention; however, the present
invention is not limited thereto.
EXAMPLES 1 TO 3
[0087] In Example 1, a base oil was prepared by mixing dioctyl
adipate and 2-hexyldecyl dodecanoate in a ratio of 1:1. The base
oil was used in an amount of 97 parts by weight.
[0088] The dioctyl adipate and the 2-hexyldecyl dodecanoate were
represented by Formula 1 and 2, respectively. Here, the dioctyl
adipate had a density of 0.927 g/cm.sup.3 at 15.degree. C., while
the 2-hexyldecyl dodecanoate had a density of 0.859 g/cm.sup.3 at
15.degree. C.
##STR00001##
[0089] Then, at least one additive selected from the group
consisting of an antioxidant, an abrasion inhibitor, a corrosion
inhibitor, an extreme pressure additive, a viscosity modifier, an
antistatic agent and a deactivating agent was mixed in a ratio of 3
parts by weight with respect to total weight, thereby forming a
lubricating oil for a fluid dynamic bearing.
[0090] The lubricating oil exhibited a density of 0.895 g/cm.sup.3
at 15.degree. C.
[0091] In Example 2, a base oil was prepared by using ethylhexyl
oleate in an amount of 97 parts by weight.
[0092] The ethylhexyl oleate was represented by Formula 3 and had a
density of 0.866 g/cm.sup.3 at 15.degree. C.
##STR00002##
[0093] Also, the lubricating oil for a fluid dynamic bearing was
prepared by mixing the same additive as that used in Example 1 in a
ratio of 3 parts by weight with respect to total weight. The
prepared lubricating oil had a density of 0.870 g/cm.sup.3 at
15.degree. C.
[0094] In Example 3, a base oil was prepared by using 2-hexyldecyl
dodecanoate having a low density in an amount of 97 parts by
weight.
[0095] The 2-hexyldexyl dodecanoate may be represented by
[0096] Formula 4 and had a density of 0.859 g/cm.sup.3 at
15.degree. C.
##STR00003##
[0097] Also, the lubricating oil for a fluid dynamic bearing was
prepared by mixing the same additive as that used in Example 1 in a
ratio of 3 parts by weight with respect to total weight.
[0098] The prepared lubricating oil had a density of 0.866
g/cm.sup.3 at 15.degree. C.
COMPARATIVE EXAMPLES 1 AND 2
[0099] In Comparative Example 1, a base oil was prepared by using a
neopentylglycol based ester lubricant in an amount of 97 parts by
weight.
[0100] The neopentylglycol based ester lubricant was represented by
Formula 5 and had a density of 0.939 g/cm.sup.3 at 15.degree.
C.
##STR00004##
[0101] The types and contents of additives were substantially
identical to those described in the foregoing examples. The
prepared lubricating oil for a fluid dynamic bearing had a density
of 0.944 g/cm.sup.3 at 15.degree. C.
[0102] In Comparative Example 2, a base oil was prepared by using
3-methyl-1,5-pentandiol based ester lubricant in an amount of 97
parts by weight.
[0103] The 3-methyl-1,5-pentadiol based ester lubricant was
represented by Formula 6 and had a density of 0.928 g/cm.sup.3 at
15.degree. C.
##STR00005##
[0104] The types and contents of additives were substantially
identical to those described in the foregoing examples. The
prepared lubricating oil for a fluid dynamic bearing had a density
of 0.944 g/cm.sup.3 at 15.degree. C.
[0105] The following Table 1 illustrates densities, kinetic
viscosities, (dynamic) viscosities of lubricating oil compositions
prepared in the Examples and the Comparative Examples, as well as
comparison between test results of low temperature operation and
impact resistance of the respective lubricating oil
compositions.
[0106] More particularly, the viscosity was measured using a
viscometer, i.e., Brookfield DB-III Rheometer. In order to assess
temperature-dependent tendency, respective components were measured
in four different temperature ranges (0.degree. C., 25.degree. C.,
40.degree. C. and 100.degree. C.)
[0107] The low temperature operation test was executed with
reference to 0.degree. C., and results thereof are shown in Table 1
below.
[0108] Impact resistance test was performed by applying severe
impact ranging from 350 to 1000 times of a gravitational constant
according to test methods and comparing results thereof to
determine whether features of the lubricating oil were altered or
not.
TABLE-US-00001 TABLE 1 Items Com. Ex. 1 Com. Ex. 2 Ex. 1 Ex. 2 Ex.
3 Density (g/cm.sup.3) 0.944 0.934 0.895 0.870 0.866 Kinetic
100.degree. C. 2.57 2.54 2.47 2.58 2.66 viscosity 40.degree. C.
9.56 9.54 9.04 9.47 9.17 (cSt) 25.degree. C. 14.90 14.79 15.40
15.34 15.36 0.degree. C. 48.60 47.50 51.30 49.20 51.00 Dynamic
100.degree. C. 2.43 2.37 2.21 2.24 2.30 viscosity 40.degree. C.
9.02 8.91 8.09 8.24 7.94 (cP) 25.degree. C. 14.07 13.81 13.78 13.35
13.30 0.degree. C. 45.88 44.37 45.91 42.80 44.17 Low temperature
0.degree. C. 115 112 116 107 110 operation (mA) Failure in impact
-- 16.7 13.3 3.3 0 0 resistance test (%)
[0109] Referring to Table 1, it can be seen that the lubricating
oil compositions according to Examples 1 to 3 of the present
invention exhibited superior low temperature operation and, as a
result of testing impact resistance of a motor, failures were
considerably reduced. Therefore, it was demonstrated that impact
resistance was efficiently improved.
[0110] On the contrary, in the case of Comparative Examples 1 and
2, the prepared compositions exhibited a density of more than 0.900
g/cm.sup.3 at 15.degree. C. and a kinetic viscosity of more than
9.50 cSt at 40.degree. C. and, according to test results, it was
found that the foregoing compositions had problems in terms of low
temperature operation and impact resistance.
[0111] As set forth above, according to embodiments of the present
invention, a HDD motor is fabricated to include a lubricating oil
composition for a fluid dynamic bearing having advantageous
features such as low viscosity at practical temperature, reduced
evaporation loss and improved oxidation stability, such that impact
resistance and low temperature operational stability of the fluid
dynamic bearing motor may be enhanced.
[0112] 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.
* * * * *