U.S. patent application number 10/477627 was filed with the patent office on 2004-09-09 for lubricant composition and analysis method for same.
Invention is credited to Matsuoka, Kaoru, Tojou, Fumiyo.
Application Number | 20040176261 10/477627 |
Document ID | / |
Family ID | 27482273 |
Filed Date | 2004-09-09 |
United States Patent
Application |
20040176261 |
Kind Code |
A1 |
Tojou, Fumiyo ; et
al. |
September 9, 2004 |
Lubricant composition and analysis method for same
Abstract
A lubricant composition is provided, wherein a base oil of the
lubricant is a single ester having a chemical structure of
(chemical formula 15) where an integer n is any of 7, 8 or 9,
wherein at least one antioxidant of hindered phenol-based
antioxidants, including at least one
(3,5-di-tert-butyl-4-hydroxyphenyl), and hindered amine based
antioxidants is included, wherein a triglyceride represented by the
structure of (chemical formula 16) where R1, R2 and R3 are
unsaturated or saturated straight chain structures or branched
structures formed of CxHyOz is included and wherein the viscosity
characteristics are no greater than 48 mPa.multidot.s at 40.degree.
C. 1
Inventors: |
Tojou, Fumiyo; (Gose-shi,
JP) ; Matsuoka, Kaoru; (Osaka-shi, JP) |
Correspondence
Address: |
McDermott Will & Emery
600 13th Street NW
Washington
DC
20005-3096
US
|
Family ID: |
27482273 |
Appl. No.: |
10/477627 |
Filed: |
November 14, 2003 |
PCT Filed: |
May 15, 2002 |
PCT NO: |
PCT/JP02/04679 |
Current U.S.
Class: |
508/485 ;
508/486; 508/487 |
Current CPC
Class: |
C10M 2215/02 20130101;
C10N 2040/34 20130101; C10N 2040/16 20130101; C10N 2040/40
20200501; C10N 2040/50 20200501; C10M 169/04 20130101; C10N 2040/30
20130101; F16C 33/109 20130101; C10N 2040/36 20130101; F16C 17/045
20130101; C10M 2207/023 20130101; C10N 2030/10 20130101; C10N
2040/44 20200501; C10N 2040/00 20130101; F16C 2370/12 20130101;
G01N 33/2888 20130101; C10M 2207/283 20130101; C10N 2040/42
20200501; C10M 2207/026 20130101; C10M 2207/027 20130101; C10M
129/10 20130101; C10N 2030/02 20130101; C10M 105/38 20130101; C10N
2040/18 20130101; C10N 2040/08 20130101; C10M 2207/2835 20130101;
C10N 2040/32 20130101; C10N 2040/02 20130101; F16C 17/102 20130101;
C10M 2207/40 20130101; C10N 2040/17 20200501; C10N 2040/38
20200501; C10M 2207/2835 20130101; C10M 2207/2835 20130101 |
Class at
Publication: |
508/485 ;
508/486; 508/487 |
International
Class: |
C10M 15/38 |
Foreign Application Data
Date |
Code |
Application Number |
May 15, 2001 |
JP |
P2001-144405 |
May 15, 2001 |
JP |
P2001-144406 |
Nov 5, 2001 |
JP |
P2001-339115 |
Nov 5, 2001 |
JP |
P2001-339116 |
Claims
1. A lubricant composition comprising a base oil which is a single
ester having the following chemical structure of: 15wherein n is
any of 7, 8 or 9 and the viscosity characteristics thereof are no
greater than 48 mPa.multidot.s at 0.degree. C. and no greater than
12 mPa.multidot.s at 40.degree. C.
2. A lubricant composition according to claim 1, further comprising
at least one antioxidant of hindered phenol-based antioxidants and
hindered amine-based antioxidants
3. A lubricant composition according to claim 2, wherein said
hindered phenol-based antioxidants include at least one
(3,5-di-tert-butyl-4-hydro- xyphenyl) in the structure thereof.
4. A lubricant composition comprising a base oil which is a single
ester having the following chemical structure of: 16wherein n is
any of 7, 8 or 9, and wherein at least one antioxidant of hindered
phenol-based antioxidants including at least one
(3,5-di-tert-butyl-4-hydroxyphenyl) and hindered amine-based
antioxidants is further included, and wherein a triglyceride
represented by the following chemical structure of: 17is further
included; where R1, R2 and R3 are unsaturated or saturated straight
chain structures or branched structures formed of CxHyOz.
5. A lubricant composition comprising a base oil which is a single
ester having the following chemical structure of: 18and a mixed
antioxidant formed of a hindered phenol-based antioxidant including
at least one (3,5-di-tert-butyl-4-hydroxyphenyl) and a hindered
amine-based antioxidant
6. A lubricant composition, wherein the secondary ion intensity has
peaks at "127," "213" and "357" of the mass numbers of positive
secondary ions per unit charge when a base oil included in the
lubricant is analyzed by means of secondary ion mass
spectrometry.
7. A lubricant composition, wherein the secondary ion intensity has
peaks at "141," "227" and "385" of the mass numbers of positive
secondary ions per unit charge when a base oil included in the
lubricant is analyzed by means of secondary ion mass
spectrometry.
8. A lubricant composition, wherein the secondary ion intensity has
peaks at "155," "241" and "413" of the mass numbers of positive
secondary ions per unit charge when a base oil included in the
lubricant is analyzed by means of secondary ion mass
spectrometry.
9. A lubricant composition according to any of claims 1 and 5 to 8,
wherein a triglyceride represented by the following chemical
structure of: 19is further included.
10. A lubricant composition according to claim 9, wherein CxHyOz
that are R1, R2 and R3 of the triglyceride represented by said the
chemical formula of: 20have respective integer values of x in a
range of from 15 to 21, y in a range of from 29 to 43 and z in a
range of from 0 to 1.
11. A lubricant composition according to any of claims 2 and 4 to
8, wherein the content of said antioxidant is no less than 0.1 wt.
%.
12. A lubricant composition according to claim 11, wherein the
content of said mixed antioxidant is no less than 0.1 wt. % and no
greater than 8 wt. %.
13. A lubricant composition according to any of claims 4 to 8,
wherein the content of said triglyceride is no greater than 5 wt.
%, preferably no greater than 3 wt. %.
14. A lubricant composition according to claim 5, wherein said
hindered phenol-based antioxidant and said hindered amine-based
antioxidant are included in approximately the equal amounts.
15. A lubricant composition according to any of claims 1 and 4 to
8, wherein the viscosity characteristics are no greater than 48
mPa.multidot.s at 0.degree. C. and no greater than 10
mPa.multidot.s at 40.degree. C.
16. A lubricant composition according to any of claims 1 and 4 to
8, wherein the viscosity characteristics are no greater than 38
mPa.multidot.s at 0.degree. C. and no greater than 8 mPa.multidot.s
at 40.degree. C.
17. A lubricant composition according to any of claims 1 and 4 to
8, which is filled into a gap between the surfaces facing each
other of two members that shift in relation to each other.
18. A lubricant composition according to any of claims 1 and 4 to
8, which is filled into a gap between the surfaces facing each
other of a rotational axis part and a bearing part in a dynamic
pressure hydraulic bearing wherein said rotational axis part is
engaged with said bearing part so as to be freely rotatable and
wherein a dynamic pressure generation trench is created in at least
one of the two surfaces facing each other of said rotational axis
part and said bearing part.
19. An analysis method of a lubricant composition for analyzing a
base oil included in a lubricant by means of secondary ion mass
spectrometry for determining whether or not a peak of the secondary
ion intensity exists at "127," "213" and "357" of the mass numbers
of positive secondary ions per unit charge in a mass spectrum and
for identifying a lubricant wherein the peak exists at said mass
numbers as a lubricant having a single ester having the following
chemical structure: 21as a base oil.
20. An analysis method of a lubricant composition for analyzing a
base oil included in a lubricant by means of secondary ion mass
spectrometry, for determining whether or not a peak of the
secondary ion intensity exists at "141," "227" and "385" of the
mass numbers of positive secondary ions per unit charge in a mass
spectrum and for identifying a lubricant wherein the peak exists at
said mass numbers as a lubricant having a single ester having the
following chemical structure: 22as a base oil.
21. An analysis method of a lubricant composition for analyzing a
base oil included in a lubricant by means of secondary ion mass
spectrometry, for determining whether or not a peak of the
secondary ion intensity exists at "155," "241" and "413" of the
mass numbers of positive secondary ions per unit charge in a mass
spectrum and for identifying a lubricant wherein the peak exists at
said mass numbers as a lubricant having a single ester having the
following chemical structure: 23as a base oil.
22. A deterioration analysis method for a lubricant composition,
wherein a lubricant composition in an initial condition is analyzed
by means of secondary ion mass spectrometry so as to find the
secondary ion intensities at "127," "213" and "357" of the mass
numbers of positive secondary ions per unit charge in a mass
spectrum and the lubricant composition after the utilization for a
predetermined period of time is analyzed in the same manner so as
to find the secondary ion intensities at the same mass numbers and
wherein a ratio of a secondary ion intensity of said initial
condition to a secondary ion intensity after said utilization is
found so as to evaluate a deterioration condition of said lubricant
composition.
23. A deterioration analysis method for a lubricant composition,
wherein a lubricant composition in an initial condition is analyzed
by means of secondary ion mass spectrometry so as to find the
secondary ion intensities at "141," "227" and "385" of the mass
numbers of positive secondary ions per unit charge in a mass
spectrum and the lubricant composition after the utilization for a
predetermined period of time is analyzed in the same manner so as
to find the secondary ion intensities at the same mass numbers and
wherein a ratio of a secondary ion intensity of said initial
condition to a secondary ion intensity after said utilization is
found so as to evaluate a deterioration condition of said lubricant
composition.
24. A deterioration analysis method for a lubricant composition,
wherein a lubricant composition in an initial condition is analyzed
by means of secondary ion mass spectrometry so as to find the
secondary ion intensities at "155," "241" and "413" of the mass
numbers of positive secondary ions per unit charge in a mass
spectrum and the lubricant composition after the utilization for a
predetermined period of time is analyzed in the same manner so as
to find the secondary ion intensities at the same mass numbers and
wherein a ratio of a secondary ion intensity of said initial
condition to a secondary ion intensity after said utilization is
found so as to evaluate a deterioration condition of said lubricant
composition.
25. A dynamic pressure hydraulic bearing, comprising: a bearing
part and a rotational axis part engaged with each other so as to be
freely rotatable; a dynamic pressure generation trench created in
at least one of the two surfaces facing each other that form a gap
between said bearing part and said rotational axis part; and a
lubricant composition filled in said gap, wherein a lubricant
composition according to any of claims 1-8 and 14 is used as said
lubricant composition.
26. A motor, comprising: a base part; a stator for generating a
magnetic field secured to said base part; a rotor having a
rotational magnet opposed to said stator; a rotational axis part
provided in said rotor; a bearing part which is provided in said
base part and to which said rotational axis part is engaged so as
to be freely rotatable; a dynamic pressure generation trench
created in at least one of the two surfaces facing each other that
form a gap between said baring part and said rotational axis part;
and a lubricant composition filled into said gap, wherein a
lubricant composition according to any of claims 1-8 and 14 is used
as said lubricant composition.
27. A motor according to claim 26, wherein said bearing part on the
base part side is of a cylindrical form and said rotational axis
part on the rotor side is engaged with the inside of said bearing
part.
28. A motor according to claim 26, wherein said rotational axis
part on the rotor side is of a cylindrical form and said rotational
axis part is engaged with the outside of said bearing part on the
base part side.
29. A motor according to claim 26, which has a radial bearing part
wherein said bearing part and said rotational axis part face each
other in the radial direction and said lubricant composition is
filled in into a gap between said bearing part and said rotational
axis part and wherein a dynamic pressure generation trench is
created in at least one of the two faces that form the gap in said
radial bearing part.
30. A motor according to claim 26, which has a thrust bearing part
wherein said bearing part and said rotational axis part face each
other in the axis direction and said lubricant composition is
filled in into a gap between said bearing part and said rotational
axis part and wherein a dynamic pressure generation trench is
created in at least one of the two faces that form the gap in said
thrust bearing part.
31. A motor according to claim 27, wherein a thrust bearing part is
formed of an end surface on the side having an opening of said
cylindrical bearing part and of an annular region in said rotor
that is opposed to the end surface on the side having the opening
of said bearing part and wherein a dynamic pressure generation
trench is created in at least one of said end surface on the side
having the opening and said annular region opposed to this end
surface in said thrust bearing part.
32. A motor according to claim 28, wherein a thrust bearing part is
formed of an end surface on the side having an opening of said
cylindrical rotational axis part and of an annular region in said
base part that is opposed to the end surface on the side having the
opening of said rotational axis part and wherein a dynamic pressure
generation trench is created in at least one of said end surface on
the side having the opening and said annular region opposed to this
end surface in said thrust bearing part.
33. A motor according to claim 26, wherein nickel phosphorous
plating film is formed on the two surfaces facing each other that
form the gap between said bearing part and said rotational axis
part.
34. A motor according to claim 33, wherein said nickel phosphorous
plating film is an electroless plating film of which the
phosphorous concentration is no greater than 15 wt. %.
35. A motor integrated device to which a motor according to claim
26 is mounted.
Description
FIELD OF THE INVENTION
[0001] The present invention primarily relates to a lubricant
composition used for lubricating parts that slide in relation to
each other in a mechanical system, in particular, to a lubricant
composition (hereinafter referred to as simply lubricant, if
necessary) suitable for a dynamic pressure hydraulic bearing such
as in a spindle motor.
BACKGROUND OF THE INVENTION
[0002] At present, a spindle motor used in an information recording
and reproduction device, such as a hard disk device, has a
rotational speed of approximately 10,000 rpm and is targeted to
have a rotational speed of 15,000 rpm at the next stage. Under the
conditions for such a high-speed rotational operation, the motor is
expected to produce quite a large amount of heat. When an
simulation is actually carried out, the result is gained that the
temperature of the motor exceeds 100.degree. C. Then, a dynamic
pressure hydraulic bearing tends to be used. The characteristics of
the lubricant have a great influence on the bearing performance of
a dynamic pressure hydraulic bearing. It is required to restrict
metal contact between the rotational axis part and the bearing part
immediately after the startup or immediately before the stoppage of
the motor. In addition, at the time of continuous operation, stable
hydraulic lubricant characteristics having little deterioration,
such as oxidation, decomposition and vaporization of the lubricant,
are required in spite of the great generation of heat due to
rotation. Furthermore, a lubricant of a low viscosity, of which the
friction coefficient is low, is required in order to reduce the
driving power. The lowering of the torque can be implemented by
lowering the viscosity of the lubricant while the problem wherein
the lowering of the viscosity allows the deterioration of the heat
resistance and of the vaporization characteristics must be
solved.
[0003] The lubricants that have conventionally been used with
dynamic pressure hydraulic bearings include di-esters represented
by DOS (sebacic acid di-2-ethylhexyl) and tri-esters of
trimethylolpropane and monovalent fatty acids. In addition, there
are lubricants of which the base oil is a mixed ester of a capryl
acid of neopentylglycol and capric acid.
[0004] When the viscosity of a di-ester is lowered, the heat
resistance and vaporization characteristics deteriorate and
hydrolysis more easily occurs. A mixed ester has a property wherein
its characteristics may vary after utilization for a long period of
time under high temperature and high-speed conditions and wherein
viscosity becomes higher through polymerization. As the rotational
speed of a spindle motor becomes higher, the amount of heat
generation increases and, in some cases, the temperature of the
bearing part exceeds 100.degree. C. When a lubricant including a
di-ester or a tri-ester is used under such temperature conditions,
hydrolysis or polymerization of the lubricant is promoted and,
therefore, a dynamic pressure hydraulic bearing cannot be stably
utilized for a long period of time under high-speed rotational
conditions as described above.
[0005] On the other hand, as for a lubricant wherein a mixed ester
of capryl acid of neopentylglycol and a capric acid is used as a
base oil, overall deterioration of the lubricant advances due to
the decomposition of the low viscosity ester component so that
change in viscosity occurs. As a result an abnormal rotation of the
motor or an increase in torque occurs and, therefore, not only is
reliability lowered but, also, a reduction in power consumption
cannot be implemented.
[0006] Bearing loss increases at low temperatures wherein the
viscosity increases and the lubricant film breaks down at high
temperatures wherein viscosity decreases so that seizure, or the
like, easily occurs due to metal contact caused by breakdown of the
lubricant film. Under conditions wherein temperature variation is
great, such as utilization outdoors during the cold season and in
after being left in a car during the hot season, the attainment of
a stable rotational performance is required.
SUMMARY OF THE INVENTION
[0007] Accordingly, a major object of the present invention is to
provide a lubricant having a low viscosity even at low temperatures
and having a small variation in viscosity and a small vaporization
loss wherein oxidation and decomposition are restricted even at
high temperatures and of which the characteristics are stable.
[0008] Other objects, characteristics and benefits of the present
invention will become clear from the descriptions below.
[0009] In order to achieve the above described object, the present
invention provides, as the first means for solving the problem, a
lubricant composition comprising a base oil which is a single ester
of which the chemical structure is (chemical formula 1), (here n is
any of 7, 8 or 9), wherein the viscosity characteristics thereof
are 48 mPa.multidot.s or less at 0.degree. C. and 12 mPa.multidot.s
or less at 40.degree. C. 2
[0010] Here, in chemical formulas in this specification, C
indicates a carbon atom and O, an oxygen atom.
[0011] A base oil having the structure of (chemical formula 1) is a
single ester made of a polyol and a fatty acid. In regard to the
above description, it is preferable for the base oil to further
include at least one of the antioxidants from among hindered
phenol-based antioxidants and hindered amine-based antioxidants.
Furthermore, the above described hindered phenol-based antioxidants
preferably include at least one (3,5-di-tert-butyl-4-hydroxyphenyl)
in the structures thereof. "tert" indicates the third class.
[0012] A hindered phenol-based antioxidant or hindered amine-based
antioxidant has the function of a radical scavenger and has the
nature of prevention of oxidation of the base oil through
self-oxidation when heated. Accordingly, even in the case that the
lubricant becomes of a high temperature due to the heating of the
dynamic pressure hydraulic bearing at the time of high-speed
rotation, oxidation is not allowed to occur so that deterioration
of the characteristics of the lubricant can be prevented.
[0013] According to the above description the viscosity
characteristics required in the case wherein the lubricant is used
with a dynamic pressure hydraulic bearing, that is to say, a
viscosity of 48 mPa.multidot.s or less at 0.degree. C. and of 12
mPa.multidot.s or less at 40.degree. C. can be secured. In
particular, the lubricant is suitable for a dynamic pressure
hydraulic bearing in a spindle motor for rotationally driving, at a
high-speed, an information recording medium that is mounted to an
information recording and reproduction device, such as a magnetic
disk device, an optical disk device and an optical magnetic disk
device. In addition, the lubricant is suitable for a dynamic
pressure hydraulic bearing in a motor that rotationally drives, at
a high speed, a polygonal mirror for a scanner of an LBP (laser
beam printer).
[0014] According to the experiments of the present inventors, 46.7
mPa.multidot.s was gained (in the case wherein R=C.sub.9H.sub.19)
as a high value of viscosity at 0.degree. C., which makes possible
the implementation of 48 mPa.multidot.s or less including a margin
in accordance with empirical observation. In addition, 9.50
mPa.multidot.s was gained (in the case wherein R=C.sub.9H.sub.19)
as a high value of viscosity at 40.degree. C., which makes possible
the implementation of 12 mPa.multidot.s or less, and, more
preferably, 10 mPa.multidot.s or less, including a margin in
accordance with empirical observation.
[0015] In addition, according to the experiments of the present
inventors, 36.1 mPa.multidot.s was gained (in the case wherein
R=C.sub.8H.sub.17) as a viscosity at 0.degree. C., which makes
possible the implementation of 38 mPa.multidot.s or less including
a margin in accordance with empirical observation. In addition, 7.7
mPa.multidot.s was gained (in the case wherein R=C.sub.8H.sub.17)
as a viscosity at 40.degree. C., which makes possible the
implementation of 10 mPa.multidot.s, and more preferably 8 to 9
mPa.multidot.s or less, including a margin in accordance with
empirical observation.
[0016] In regard to the above description, it is preferable for the
antioxidant content to be 0.1 wt. % or more. In the case that the
content is lower than this, the antioxidant effect cannot be
expected to a great degree. The optimal amount to be added differs
according to the purpose of utilization and when, at least, 0.1 wt.
% or more is added, it produces the effect of antioxidant
prevention. In addition, an excessive content allows the
performance of the base oil to deteriorate and, therefore, it is
desirable for the upper limit value of the content to be set at 10
wt. % and, moreover, it is more preferable for the upper limit
value to be set at 8 wt. % or less, because the occurrence of
deterioration of the performance of the base oil is minimal.
[0017] As the second means for solving the problem, the present
invention provides a lubricant component wherein the base oil of
the lubricant is a single ester (here n is any of 7, 8 or 9) having
the chemical structure of (chemical formula 1) and, moreover, at
least one antioxidant from among hindered phenol-based antioxidants
that include at least one (3,5-di-tert-butyl-4-hydroxyphenyl) and
hindered amine-based antioxidants is included and, moreover, a
triglyceride indicated by the structure of (chemical formula 2) is
included. 3
[0018] Here, R1, R2 and R3 are unsaturated or saturated straight
chain structures or branched structures consisting of CxHyOz.
[0019] Slidability can be increased under the metal contact
condition that occurs when the dynamic pressure becomes low
immediately after start-up or immediately before stoppage by adding
a triglyceride. Accordingly, in the case that a spindle motor is
frequently started up or stopped, such as in a hard disk device,
friction and wear of the rotational axis part and of the bearing
part can be reduced so that a dynamic pressure hydraulic bearing of
a high reliability can be implemented.
[0020] In addition, low viscosity can be maintained even in low
temperature conditions and a lubricant wherein decomposition or
oxidation does not occur, even at high temperatures, can be gained.
Bearing loss is small even at the time of utilization at low
temperatures and the bearing can be stably utilized even at the
time of high-speed rotation wherein the temperature of the
lubricant becomes high. Accordingly, a spindle motor wherein a
dynamic pressure hydraulic bearing is mounted exercises a stable
rotational performance of a high reliability even under conditions
wherein change in temperature is great, such as utilization
outdoors during the winter or utilization after being left in a car
in summer. In addition, the change in quality in the lubricant does
not easily occur in a dynamic pressure hydraulic bearing of a
copper alloy material wherein vaporization loss is small. In
particular, change in quality does not occur in a dynamic pressure
hydraulic bearing formed of a copper alloy material on which nickel
phosphorus plating has been carried out.
[0021] In the above description, it is preferable for CxHyOz, which
are R1, R2 and R3 of the triglyceride, to have an integer value of
x in the range of from 15 to 21, an integer value of y in the range
of from 29 to 43 and an integer value of z in the range of from 0
to 1, respectively.
[0022] In the case that the value of z is 0, a structure of an
unsaturated or a saturated straight chain alkyl base or a branched
alkyl base is provided. In the case that the value of z is 1, an
unsaturated or a saturated straight chain structure or a branched
structure having an OH base in the structure is provided. In the
case that the structure has an OH base, wettability with metal
forming the dynamic pressure hydraulic bearing is improved so that
the lubricant characteristics can be improved. In addition, in the
case that the values of x and y are made greater than the upper
limit of the above described ranges, the triglyceride becomes a
solid having a poor compatibility with the base oil. Furthermore,
the viscosity also becomes great. In addition, in the case that the
values of x and y are smaller than the lower limit of the above
described ranges, the lubricant characteristics at the time of
start-up are lowered. As for conditions that can obviate the above
problems, the above described values of x and y are in the desired
ranges.
[0023] In addition, in the above description, in the case that the
triglyceride content exceeds 5 wt. %, the performance of the base
oil is lowered. The allowance of the addition of triglyceride for
maintaining performance is 5 wt. % while the addition of
triglyceride can increase the slidability in the metal contact
condition that occurs when the dynamic pressure is low immediately
after start-up or immediately before stoppage. In the case that the
triglyceride content is 3 wt. % or less, the lifetime of the
lubricant can be prevented from being lowered and this is more
desirable.
[0024] As the third means for solving the problem, the present
invention provides a lubricant composition wherein the base oil of
the lubricant is a single ester having the chemical structure of
(chemical formula 3) and, furthermore, wherein a mixed antioxidant
formed of a hindered phenol-based antioxidant including, at least,
one (3,5-di-tert-butyl-4-hy- droxyphenyl) and a hindered
amine-based antioxidant is included. 4
[0025] This limits the alkyl base R=C.sub.nH.sub.2+1 to
C.sub.8H.sub.17 in the case wherein n=8 and the antioxidant is
limited to a mixed antioxidant.
[0026] In the case wherein R=C.sub.7H.sub.15, there is a
possibility that the lubricant, though having a low viscosity, may
be vaporized for a short period of time in the case of an
environment wherein the temperature is too high because the amount
of vaporization is comparatively great. It is comparatively
difficult, however, to suppress the amount of vaporization by means
of the additive.
[0027] On the other hand, in the case wherein R=C.sub.9H.sub.19,
though the amount of vaporization is small, the viscosity is
comparatively great. Since reduction in power consumption is a
primary requirement in a portable apparatus, a lubricant of a low
viscosity is necessary in the case of application in a hard disk
device. However, the amount of vaporization becomes large in the
case that an ester-based material of a low viscosity is added.
[0028] In contrast to this, when a base oil is formed of
R.dbd.C.sub.8H.sub.17, the viscosity and the amount of vaporization
are both optimized. Furthermore, fluctuation in viscosity is
recognized to be minimal in the accelerated high temperature test.
As a whole, a base oil having R=C.sub.8H.sub.17 is the most
well-balanced and a lubricant having excellent characteristics can
be gained.
[0029] In addition, though a hindered phenol-based antioxidant or a
hindered amine-based antioxidant has an antioxidant effect even in
the case that these are used alone, the addition of the two can
further increase the antioxidant effect.
[0030] As a synergetic result of the above, the lubricant has a low
viscosity over a broad range of temperatures, from low temperatures
to high temperatures, and the fluctuation in the viscosity thereof
is small and, in addition, the lubricant does not easily vaporize
so that an increase in the resistance to environmental conditions
and in the reliability of the dynamic pressure hydraulic bearing
can be implemented. In addition, not only is the rotational
precision of a motor provided with such a dynamic pressure
hydraulic bearing increased but, also, the motor is stable over a
broad range of temperatures and lowering of the power consumption
can be implemented. In particular, the power consumption can be
lowered and the reliability can be increased in a motor mounted in
a portable apparatus, or the like.
[0031] In the above description, it is preferable for the hindered
phenol-based antioxidant and hindered amine-based antioxidant of
the mixed antioxidant to be included in approximately equal amounts
with respect to a mixture ratio thereof. Thereby, heat resistance
stability can be improved without increasing the viscosity and a
dynamic pressure hydraulic bearing that is stable up to a high
temperature and of which the power consumption is low can be
implemented.
[0032] In addition, in the above description, it is preferable for
the mixed antioxidant content to be 0.1 wt. % or more and 8 wt. %
or less. Oxidation or deterioration of a base oil wherein
R=C.sub.8H.sub.17 is reduced and heat resistance stability is
improved as the mixed antioxidant content increases while an
increase in the viscosity is recognized. Contrarily, in the case
that the no antioxidant is added, deterioration occurs for a short
period of time. Though it depends on conditions of utilization of a
dynamic pressure hydraulic bearing, the addition of 0.1 wt. % or
more, of the antioxidant can secure heat resistance stability for
practical use. In addition, by adjusting the amount of the
antioxidant to 8 wt. % or less, a viscosity of 48 mPa.multidot.s or
less, at 0.degree. C. and 12 mPa.multidot.s at 40.degree. C. or
less, can be secured in the case that the lubricant is used in a
dynamic pressure hydraulic bearing. In addition, in the case that a
motor wherein a dynamic pressure hydraulic bearing is used is
mounted to a portable apparatus, there is a possibility that it may
be utilized in a low temperature condition such as outdoors and it
is important to lower the viscosity in low temperature conditions
and, in such a case, it is desirable to adjust the amount of
antioxidant to 5 wt. % or less.
[0033] It is possible to interpret, in a broad manner, each of the
above described lubricant compositions as a lubricant that is
filled into a gap between surfaces of two members, racing each
other, that shift relative to each other. It is possible to
interpret each of the above described lubricant compositions, in a
broad manner, though less broad than the above, as a lubricant that
is filled in into a gap between the two surfaces of the rotational
axis part and the bearing part in a dynamic pressure hydraulic
bearing wherein the rotational axis part is engaged with the
bearing part so as to be freely rotatable and a dynamic pressure
generation trench is created in, at least, one of the two faces
facing each other, of the rotational axis part and of the bearing
part. Dynamic pressure is generated through a shift in relation to
each other, or through a rotation in relation to each other, of the
rotational axis part and the bearing part so that the 15 rotational
axis part is supported by the bearing part in non-contact
condition.
[0034] Another aspect of the above described lubricant composition
according to the present invention can be described as follows.
[0035] This is a lubricant composition wherein peaks of the
secondary ion intensities exist at "127," "213" and "357" of the
mass numbers of positive secondary ions per unit charge when a base
oil included in the lubricant is analyzed by means of secondary ion
mass spectrometry in a manner corresponding to the case of the
lubricant including a base oil that is a single ester having the
structure of (chemical formula 1) when alkyl base
R=C.sub.1H.sub.15.
[0036] This is a single ester having the structure of (chemical
formula 1) wherein the mass numbers for specifying the base oil in
the case wherein alkyl base R=C.sub.7H.sub.15 are a combination of
"127," "213" and "357."
[0037] In addition, this is a lubricant composition wherein the
peaks of secondary ion intensities exist at "141," "227" and "385"
of the mass numbers of positive secondary ions per unit charge when
the base oil included in the lubricant is analyzed by means of
secondary ion mass spectrometry so as to correspond to the case of
a lubricant that includes a base oil of a single ester having the
structure of (chemical formula 1) in the case wherein the alkyl
base R=C.sub.8H.sub.17.
[0038] This is a single ester having the structure of (chemical
formula 1) wherein the mass numbers for identifying the base oil in
the case wherein the alkyl base R=C.sub.8H.sub.17 are a combination
of "141," "227" and "385."
[0039] Furthermore, this is a lubricant composition wherein the
peaks of secondary ion intensities exist at "155," "241" and "413"
of the mass numbers of positive secondary ions per unit charge when
the base oil included in the lubricant is analyzed by means of
secondary ion mass spectrometry so as to correspond to the case of
a lubricant that includes a base oil of a single ester having the
structure of (chemical formula 1) in the case wherein the alkyl
base R=C.sub.9H.sub.19.
[0040] This is a single ester having the structure of (chemical
formula 1) wherein the mass numbers for identifying the base oil in
the case wherein the alkyl base R=C.sub.9H.sub.19 are a combination
of "155," "241" and "413."
[0041] All of these describe one means in the case that a lubricant
composition according to the present invention is practically
specified. The grounds for the above described mass numbers will
become clear from the descriptions in from paragraph (.sctn.3) to
paragraph (.sctn.4) in the explanation in the below described third
embodiment.
[0042] It is possible to understand the present invention according
to the following expanded considerations. That is, as an invention
concerning an analysis method of a lubricant.
[0043] That is to say, in an analysis method of a lubricant
according to the present invention, a base oil included in the
lubricant is analyzed by means of secondary ion mass spectrometry
and whether or not the peaks of the secondary ion intensities exist
in the mass spectrum at "127," "213" and "357" of the mass numbers
of positive secondary ions per unit charge is determined so that a
lubricant having a base oil of single ester of (chemical formula 4)
is identified in the case that the peaks exist. 5
[0044] In addition, in another analysis method of a lubricant
according to the present invention, a base oil included in the
lubricant is analyzed by means of secondary ion mass spectrometry
and whether or not the peaks of the secondary ion intensities exist
in the mass spectrum at "141," "227" and "385" of the mass numbers
of positive secondary ions per unit charge is determined so that a
lubricant having a base oil of single ester of (chemical formula 3)
is identified in the case that the peaks exist. (chemical formula
3) is again listed. 6
[0045] Furthermore, in another analysis method of a lubricant
according to the present invention, a base oil included in the
lubricant is analyzed by means of secondary ion mass spectrometry
and whether or not the peaks of the secondary ion intensities exist
in the mass spectrum at "155," "241" and "413" of the mass numbers
of positive secondary ions per unit charge is determined so that a
lubricant having a base oil of single ester of (chemical formula 5)
is identified in the case that the peaks exist. 7
[0046] It is possible to understand the present invention according
to the following expanded considerations. That is, as an invention
concerning a deterioration analysis method of a lubricant
composition.
[0047] That is to say, in a deterioration analysis method of a
lubricant composition according to the present invention, a
lubricant composition in an initial condition is analyzed by means
of secondary ion mass spectrometry so that secondary ion
intensities at "127," "213" and "357" of the mass numbers of
positive secondary ions per unit charge in the mass spectrum are
found and the lubricant composition after utilization for a
predetermined period of time is analyzed in the same manner so that
secondary ion intensities at the same mass numbers are found. Then,
a ratio of a secondary ion intensity in the above initial condition
to a secondary ion intensity after the above described utilization
is found in order to evaluate the deterioration condition of the
above described lubricant composition.
[0048] This is effective in the deterioration analysis of a
lubricant having a base oil of a single ester of (chemical formula
4) in the case wherein the alkyl base R=C.sub.7H.sub.15.
[0049] In addition, in a deterioration analysis method of a
lubricant composition according to the present invention, a
lubricant composition in an initial condition is analyzed by means
of secondary ion mass spectrometry so that secondary ion
intensities at "141," "227" and "385" of the mass numbers of
positive secondary ions per unit charge in the mass spectrum are
found and the lubricant composition after utilization for a
predetermined period of time is analyzed in the same manner so that
secondary ion intensities at the same mass numbers are found. Then,
a ratio of a secondary ion intensity in the above initial condition
to a secondary ion intensity after the above described utilization
is found in order to evaluate the deterioration condition of the
above described lubricant composition.
[0050] This is effective in the deterioration analysis of a
lubricant having a base oil of a single ester of (chemical formula
3) in the case wherein the alkyl base R=C.sub.8H.sub.17.
[0051] Furthermore, in a deterioration analysis method of a
lubricant composition according to the present invention, a
lubricant composition in an initial condition is analyzed by means
of secondary ion mass spectrometry so that secondary ion
intensities at "155," "241" and "413" of the mass numbers of
positive secondary ions per unit charge in the mass spectrum are
found and the lubricant composition after utilization for a
predetermined period of time is analyzed in the same manner so that
secondary ion intensities at the same mass numbers are found. Then,
a ratio of a secondary ion intensity in the above initial condition
to a secondary ion intensity after the above described utilization
is found in order to evaluate the deterioration condition of the
above described lubricant composition.
[0052] This is effective in the deterioration analysis of a
lubricant having a base oil of a single ester of (chemical formula
5) in the case wherein the alkyl base R=C.sub.9H.sub.19.
[0053] In all of the above described deterioration analysis methods
of a lubricant composition, a ratio of the mass spectrum of the
lubricant before utilization to the mass spectrum of the lubricant
after utilization is gained by means of secondary ion mass
spectrometry and, thereby, the deterioration of the lubricant, even
of a sample of an extremely small amount, can be analyzed with a
high precision.
[0054] A lubricant composition gained in the above described manner
is favorably applied with the following dynamic pressure hydraulic
bearing or in the following motor.
[0055] That is to say, a dynamic pressure hydraulic bearing
according to the present invention is provided with a bearing part
and a rotational axis part engaged with each other so as to be
freely rotatable; a dynamic pressure generation trench created in,
at least, one of the two surfaces facing each other that form a gap
between the above described bearing part and the above described
rotational axis part; and a lubricant composition filled in into a
gap between the surfaces facing each other, wherein any of the
above described lubricant compositions is used as the above
described lubricant composition.
[0056] In addition, a motor according to the present invention is
provided with a base part; a stator for generating a magnetic field
secured to the above described base part; a rotor having a
rotational magnet opposed to the above described stator; a
rotational axis part provide in the above described rotor; a
bearing part provided in the above described base part and with
which the above described rotational axis part engaged so as to be
freely rotatable; a dynamic pressure generation trench created in
at least, one of the two surfaces facing each other that form a gap
between the above described bearing part and the above described
rotational axis part; and a lubricant composition filled in into a
gap between the above described surfaces facing each other, wherein
any of the above described lubricant compositions is used as the
above described lubricant composition.
[0057] There are a variety of modes, such as the following, of the
configurations of the above described motor.
[0058] A motor is provided wherein the above described bearing part
on the base part side is made in a cylindrical form and the above
described rotational axis part on the rotor side is engaged with
the inside of the above described bearing part.
[0059] In addition, a motor is provided wherein the above described
rotational axis part on the rotor side is made in a cylindrical
form and wherein the above described rotational axis part is
engaged with the outside of the above described bearing part on the
base part side.
[0060] In addition, a motor is provided so as to have a radial
bearing part wherein the above described bearing part and the above
described rotational axis part face each other in the radial
direction and the above described lubricant composition is filled
in into a gap between the above described bearing part and the
above described rotational axis part and wherein a dynamic pressure
generation trench is created in, at least, one of the two surfaces
facing each other that form the gap in the above described radial
bearing part.
[0061] In addition, a motor is provided so as to have a thrust
bearing part wherein the above described bearing part and the above
described rotational axis part face each other in the axis
direction and the above described lubricant composition is filled
in into a gap between the above described bearing part and the
above described rotational axis part and wherein a dynamic pressure
generation trench is created in, at least, one of the two surfaces
facing each other that form the gap in the above described thrust
bearing part.
[0062] In addition, a motor is provided wherein a thrust bearing
part is formed of an end surface on the side having an opening of
the above described cylindrical bearing part and of an annular
region in the above described rotor facing the above described end
surface on the side having the opening of the above described
bearing part and wherein a dynamic pressure generation trench is
formed in, at least, one of the above described end surface on the
side having the opening and the above described annular region that
faces the end surface in the above described thrust bearing
part.
[0063] In addition, a motor is provided wherein a thrust bearing
part is formed of an end surface on the side having an opening of
the above described cylindrical rotational axis part and of an
annular region in the above described base part facing the above
described end surface on the side having the opening of the above
described rotational axis part and wherein a dynamic pressure
generation trench is formed in, at least, one of the above
described end surface on the side having the opening and the above
described annular region that faces the end surface in the above
described thrust bearing part.
[0064] In addition, a motor is provided wherein nickel phosphorus
plating film is applied to the two surfaces facing each other that
form the gap between the above described bearing part and the above
described rotational axis part. It is preferable for the above
described nickel phosphorus plating film to be an electroless
plated film of which the phosphorus concentration is 15 wt. % or
less.
[0065] Thus, a motor integrated device to which any of the above
described motors is mounted is also an effective invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0066] These and other objects as well as advantages of the
invention will become clear by the following description of
preferred embodiments of the invention with reference to the
accompanying drawings, wherein:
[0067] FIG. 1 is a graph showing the result of an accelerated high
temperature test carried out on the lubricants of the examples and
of the comparative examples used with a nickel phosphorous plated
copper alloy with respect to the lubricant composition according to
the first embodiment of the present invention;
[0068] FIG. 2 is a graph showing the result of an accelerated high
temperature test carried out on the lubricants of the examples used
with a copper alloy with respect to the lubricant component
according to the first embodiment of the present invention;
[0069] FIG. 3 is a mass spectrum graph as a result of secondary ion
mass spectrometry of the lubricant of the first example with
respect to the lubricant composition according to the second
embodiment of the present invention;
[0070] FIG. 4 is a mass spectrum graph as a result of secondary ion
mass spectrometry of the lubricant of the second example with
respect to the lubricant composition according to the second
embodiment of the present invention;
[0071] FIG. 5 is a mass spectrum graph as a result of secondary ion
mass spectrometry of the lubricant of the third example with
respect to the lubricant composition according to the second
embodiment of the present invention;
[0072] FIG. 6 is a mass spectrum graph as a result of secondary ion
mass spectrometry of the lubricant of the fourth example with
respect to the lubricant composition according to the second
embodiment of the present invention;
[0073] FIG. 7 is a mass spectrum graph as a result of secondary ion
mass spectrometry of the lubricant of a comparative example with
respect to the lubricant composition according to the second
embodiment of the present invention;
[0074] FIG. 8 is a cross sectional view showing an example wherein
a motor to which a dynamic pressure hydraulic bearing according to
the fourth embodiment of the present invention is applied in a hard
disk device;
[0075] FIG. 9 is a cross sectional view of an enlarged portion in
FIG. 9;
[0076] FIG. 10 is a view showing a pattern of dynamic pressure
trench in the thrust surface of the dynamic pressure hydraulic
bearing in FIG. 9;
[0077] FIG. 11 is a graph showing the result of an accelerate high
temperature test carried out on the lubricant of an example and the
lubricants of comparative examples with respect to the lubricant
composition according to the fourth embodiment of the present
invention;
[0078] FIG. 12A is a plan view showing the configuration of the
main parts of a device in which a motor is integrated according to
the fifth embodiment of the present invention;
[0079] FIG. 12B is a cross sectional view corresponding to FIG.
12A;
[0080] FIG. 13 is a cross sectional view of the main parts of the
motor according to the fifth embodiment of the present
invention;
[0081] FIG. 14A is a plan view of a rotor of the motor according to
the fifth embodiment of the present invention;
[0082] FIG. 14B is a plan view of a rotor of another motor
according to the fifth embodiment of the present invention;
[0083] FIG. 15 is a cross sectional view showing the structure of
an outer rotor-type motor according to the sixth embodiment of the
present invention;
[0084] FIG. 16 is a cross sectional view showing the structure of
an axial gap-type motor according to the seventh embodiment of the
present invention;
[0085] FIG. 17 is a cross sectional view of main parts of a motor
according to the eighth embodiment of the present invention;
[0086] FIG. 18A is a plan view of a rotor of a motor according to
the eighth embodiment of the present invention;
[0087] FIG. 18B is a plan view of a base part of a motor according
to the eighth embodiment of the present invention;
[0088] FIG. 19 is a graph showing variations over time in viscosity
of lubricants used in a motor according to the fifth to eighth
embodiments of the present invention;
[0089] FIG. 20 is another graph showing variations over time in
viscosity of lubricants used in a motor according to the fifth to
eighth embodiments of the present invention;
[0090] FIG. 21 is a graph showing the effects of oil agents added
to a lubricant used in a motor according to the fifth to eighth
embodiments of the present invention; and
[0091] FIG. 22 is a graph showing the effects of nickel phosphorous
plating and of lubricants used with a dynamic pressure hydraulic
bearing part provided in a motor according to the fifth to eighth
embodiments of the present invention.
[0092] In all these figures, like components are indicated by the
same numerals.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0093] In the following, the present embodiments of the present
invention are described in reference to the drawings.
[0094] (First Embodiment)
[0095] Lubricant compositions (lubricant) according to the first
embodiment of the present invention include at least a base oil, an
antioxidant and an additive and is filled into the gap between two
opposing faces of two members that shift relative to each other
wherein the lubricant is composed as follows.
[0096] First, a substance having the structure of (chemical formula
6) is adopted as the base oil. 8
[0097] Here, n=7, n=8 or n=9 in (chemical formula 6). Concretely,
they are base oil (A) having the structure of (chemical formula 7),
base oil (B) having the structure of (chemical formula 8) or base
oil (C) having the structure of (chemical formula 9), all of which
are single esters. 9
[0098] Any one type from among the above three types is used as the
base oil of the lubricant. Here, all of base oils (A) to (C) are
esters made up of a polyol and a fatty acid.
[0099] In one lubricant the alkyl bases R=C.sub.nH.sub.2n+1 on both
ends of the base oil are the same. In addition, in one lubricant
the above described three types of base oils are not mixed but,
rather, the base oil is limited to any one type. In this sense, the
base oil in a lubricant of the present invention is a single ester.
Base oil (A), base oil (B) and base oil (C) have alkyl bases R on
each end that differ from each other and, due to this, these three
types of base oils have viscosities differing from each other.
Unlike the mixed ester in the case of the prior art, a plural
number of types of base oils having differing viscosities are not
mixed in the present invention. That is to say, the base oil in a
lubricant of the present invention is a single ester. Here, a
lubricant wherein the above described base oil is used, according
to the present invention, has the appropriate application object of
a dynamic pressure hydraulic bearing.
[0100] In the case that a mixed ester is used, the low viscosity
component in the mixed component decomposes earlier than the other
components when utilized for a long period of time and, due to
this, a phenomenon occurs wherein the deterioration of the
lubricant is accelerated. In contrast to this, exactly the same
alkyl base is used in the structure and, in addition, a base oil
consisting of only one type is used according to the present
invention and, thereby, the viscosity characteristics can be
adjusted to have a predetermined value, that is to say, 48
mPa.multidot.s or less at 0.degree. C. and 12 mPa.multidot.s or
less at 40.degree. C.
[0101] A lubricant having a low viscosity, even in low temperature
conditions, and of which the variation in viscosity is small in
response to change in temperature from low to high can be realized
by using a base oil having the structure represented by (chemical
formula 6) and having the above described viscosity
characteristics. In the case that this lubricant is utilized for a
dynamic pressure hydraulic bearing, bearing loss is small when
utilized at a low temperature and the bearing can be utilized
stably at a high rotation speed wherein the temperature of the
lubricant becomes high.
[0102] Here, a viscosity of 48 mPa.multidot.s or less at 0.degree.
C. is a value wherein the bearing loss is allowable and the bearing
loss can be further reduced in the case that the viscosity is 40
mPa.multidot.s or less at 0.degree. C. In addition, the viscosity
at a temperature of 40.degree. C. is 12 mPa.multidot.s or less and,
in the case that the viscosity is 48 mPa.multidot.s at 0.degree. C.
and 12 mPa.multidot.s at 40.degree. C., variation in viscosity due
to temperature fluctuation can be restricted to the range of
allowable values and, therefore, the bearing loss can be reduced
over a broad temperature range. The above has been discovered by
the present inventors.
[0103] Next, the antioxidant is described and a lubricant of the
present invention has a main body of the above described base oil
and, in addition, includes an additive of one type, at least, from
among hindered phenol-based antioxidants or hindered amine-based
antioxidants as the antioxidant. The total amount of this additive
is made to be, at least, 0.1 wt. % or more. In the case of a
hindered phenol-based antioxidant, at least one
(3,5-di-tert-butyl-4-hydroxyphenyl) is included in the structure
thereof. Here, at least one (3,5-di-tert-butyl-4-hydroxyphenyl) may
be included and two, three or four thereof may be included.
[0104] In summary, a hindered phenol-based antioxidant including
(3,5-di-tert-butyl-4-hydroxyphenyl) or a hindered amine-based
antioxidant is added or both of these antioxidants are added.
[0105] Oxidation can be prevented from occurring even when the
lubricant becomes of a high temperature so that deterioration of
the characteristics of the lubricant can be prevented by adding 0.1
wt. % or more, of a hindered phenol-based or hindered amine-based
antioxidant to the above described base oil. This hindered
phenol-based antioxidant or hindered amine-based antioxidant has
the function of radical scavenger and is of a nature that prevents
oxidation of the base oil through self-oxidation when heated. That
is to say, in the case that a lubricant is exposed to high
temperature, unstable peroxide is generated as an oxidization
product generated at the initial stage. This peroxide decomposes so
as to generate new free radicals and, thereby, the oxidation
progresses in an accelerated manner. However, a hindered
phenol-based antioxidant or a hindered amine-based antioxidant has
the effect of reacting with and deactivating these free radicals.
Accordingly, oxidation can be prevented. Though the optimal amount
of these antioxidants to be added differs depending on the purpose
of utilization, the addition of, at least, 0.1 wt. % or more, gains
an anti-oxidation effect.
[0106] Here, if the added amount is excessive, the performance of
the base oil deteriorates and, therefore, it is desirable for the
upper limit value of the added amount to be set at 10 wt. % and,
furthermore, 8 wt.% or less, is more desirable because it is in the
range wherein performance deterioration of the base oil hardly
occurs.
[0107] In addition, an additive for reduction of the friction
coefficient is required for the lubricant and a lubricant of the
present invention includes a triglyceride shown in the structure of
(chemical formula 10). 10
[0108] Here, R1, R2 and R3 are, respectively, an unsaturated or
saturated straight chain structure or branched structure consisting
of CxHyOz and, furthermore, R1, R2 and R3 preferably have the same
structure or at least one of them has a differing structure.
Moreover, it is preferable for the value of x to be an integer
value in the range of from 15 to 21, for the value of y to be an
integer value in the range of from 29 to 43 and for the value of z
to be an integer value in the range of from 0 to 1.
[0109] More concretely, when the value of z is 0, a structure of an
unsaturated or saturated straight chain alkyl base or branched
alkyl base is gained while when the value of z is 1 an unsaturated
or saturated straight chain structure or branched structure having
an OH base in the structure is gained. In the case that an OH base
is in the structure, the wettability of the bearing member vis--vis
a metal is improved so that the friction coefficient is reduced
and, therefore, the characteristics of the lubricant can be
improved.
[0110] Here, in the case that the values of x and y are greater
than the upper limit of the above described range, the triglyceride
becomes a solid and not only the miscibility with the base oil
becomes worse but, also, the viscosity becomes greater. In
addition, in the case that the values are made smaller than the
lower limit of the above described range, the characteristics of
the lubricant at the time of start up are lowered. Accordingly, the
above described values indicate desirable ranges as the conditions
for overcoming both of these limitations.
[0111] Then, the total amount of the additive, which includes, at
least, triglyceride, is made to be 5 wt. %, or less. In the case
that the amount of the triglyceride to be added is excessive, the
performance of the base oil is lowered and a limit of 5 wt. % of
additive is within the performance allowance while in the case of 3
wt. % or less, the lifetime of the lubricant can be prevented from
being lowered, which is more desirable.
[0112] A metal-contact condition occurs in the dynamic pressure
hydraulic bearing when the dynamic pressure becomes small
immediately after start up or immediately before stoppage and in
the case that a lubricant, to which 5 wt. % or less, of
triglyceride having the above described structure is added, is
used, the slidability at that time can be increased. Accordingly,
in the case that a spindle motor is frequently started up or
stopped such as in a hard disk device, the friction and wear of the
rotation axis and the bearing part can be reduced so that a dynamic
pressure hydraulic bearing of a high reliability can be
implemented.
[0113] As described above, a lubricant (lubricant compositions) of
the present embodiment is characterized in that the viscosity
characteristics are adjusted so that the viscosity at 0.degree. C.
is 48 mPa.multidot.s or less and the viscosity at 40.degree. C. is
12 mPa.multidot.s or less by adding a hindered phenol-based
antioxidant, a hindered amine-based antioxidant or both of these
and a triglyceride to a base oil of a single ester having the above
described structure of (chemical formula 7), (chemical formula 8)
or (chemical formula 9) so as to gain a substitute for DOS (sebacic
acid di-2-ethylhexyl) that is a representative example of
conventional diesters, (trimethylolpropane+monovalent fatty acid)
that is a representative example of triesters or a mixed ester of a
capryl acid of neopentylglycol and capric acid and, thereby, a
lubricant is provided wherein the low viscosity can be maintained
even in low temperature conditions and decomposition or oxidation
does not occur at a high temperature and, therefore, the friction
coefficient is low. Accordingly, in the case that the lubricant is
utilized for a dynamic pressure hydraulic bearing, bearing loss is
small at the time of low temperature utilization and, when the
temperature of the lubricant becomes high, the bearing can be
utilized stably even at high rotation speed. Furthermore, a
lubricant for a dynamic pressure hydraulic bearing can be provided,
of which the characteristics are very stable, having a small
variation in viscosity and a small vaporization loss and having
good heat resistance so that oxidation or decomposition hardly
occurs.
EXAMPLES OF FIRST EMBODIMENT
[0114] In the following, the present invention is described in
detail by using examples of the first embodiment.
First Example
[0115] A lubricant of the first example was prepared as follows.
This is a lubricant that includes a single ester base oil having
the structure shown in (chemical formula 6) wherein the alkyl base
R=C.sub.nH.sub.2n+1 is a straight chain saturated alkyl base of
C.sub.7H.sub.16 in the case of n=7. 1 wt. % of hindered
phenol-based antioxidant having four
(3,5-di-tert-butyl-4-hydroxyphenyl) was added to the above base oil
as an antioxidant.
Second Example
[0116] A lubricant of the second example was prepared as follows.
This is a lubricant that includes a single ester base oil having
the structure shown in (chemical formula 6) wherein the alkyl base
R=C.sub.nH.sub.2n+1 is a straight chain saturated alkyl base of
C.sub.8H.sub.17 in the case of n=8. 1 wt. % of hindered
phenol-based antioxidant having four
(3,5-di-tert-butyl-4-hydroxyphenyl) was added to the above base oil
as an antioxidant.
[0117] (Third Example)
[0118] A lubricant of the third example was prepared as follows.
This is a lubricant that includes a single ester base oil having
the structure shown in (chemical formula 6) wherein the alkyl base
R=C.sub.nH.sub.2n+1 is a straight chain saturated alkyl base of
C.sub.9H.sub.19 in the case of n=9. 1 wt. % of hindered
phenol-based antioxidant having four
(3,5-di-tert-butyl-4-hydroxyphenyl) was added to the above base oil
as an antioxidant.
[0119] (Fourth Example)
[0120] A lubricant of the fourth example was prepared as follows.
This is a lubricant that includes a single ester base oil having
the structure shown in (chemical formula 6) wherein the alkyl base
R=C.sub.nH.sub.2n+1 is a straight chain saturated alkyl base of
C.sub.8H.sub.17 in the case of n=8. 1 wt. % of hindered
phenol-based antioxidant having four
(3,5-di-tert-butyl-4-hydroxyphenyl) was added to the above base oil
as an antioxidant. In addition, 1 wt. % of a triglyceride shown in
(chemical formula 10) was added. Here, R1, R2 and R3 have the same
structure and have, respectively, the structure of CxHyOz wherein
the value of x is 17, the value of y is 33 and the value of z is
1.
[0121] The first example, the second example and the third example
are the same except that the structure of the alkyl base
R=CnH.sub.2n+1 in the base oil differs. The fourth example
corresponds to the case wherein a triglyceride is added in the
second example.
First Comparative Example
[0122] DOS (sebacic acid di-2-ethylhexyl), which is a lubricant
that has been used with dynamic pressure hydraulic bearings, was
used as the first comparative example.
[0123] (Second Comparative Example)
[0124] A lubricant having a mixed ester as the base oil wherein two
types of esters, an ester of neopentylglycol and capryl acid and an
ester of neopentylglycol and a capric acid, are mixed was used as
the second comparative example.
(.sctn.1)
[0125] Here, the amounts of main components of the base oils in the
lubricants of from first to fourth examples are shown in Table
1.
1TABLE 1 lubricant First Second Third Fourth component Example
Example Example Example amount of 98.5 85.3 97.7 96.7 base oil as
main component (wt. %)
[0126] As can be seen from (Table 1), the amounts of the main
components of the base oil of the lubricants of from first to
fourth examples, respectively, are 85 wt. % or more.
[0127] The results of measuring the viscosity, the stability of the
viscosity, the amount of vaporization, the antioxidation, the
stability at high temperature and the friction coefficient with
respect to the above described lubricants of the four examples and
the two comparative examples are described in the following.
[0128] Table 2 shows the viscosity at 0.degree. C. and at
40.degree. C., the rates of change according to temperature (B
value) and the amounts of vaporization.
2TABLE 2 First Second First Second Third Fourth Comparative
Comparative Example Example Example Example Example Example
Viscosity 27.3 36.13 46.71 36.52 52.72 37.39 at 0.degree. C. (mPa
.multidot. s) Viscosity 6.44 7.72 9.50 7.75 10.42 8.00 at
40.degree. C. (mPa .multidot. s) rate of 2925 2757 2960 2914 3256
2975 change according to temperature: B value amount 0.58 0.29 0.09
0.25 0.61 0.50 of vaporization (wt. %)
[0129] As for the viscosity at 0.degree. C. and the viscosity at
40.degree. C., all the lubricants of from first to fourth examples
have a viscosity lower than that of the lubricant (characterized by
DOS) of the first comparative example. In addition, all the
lubricants of the first, second and fourth examples, except for the
lubricant (characterized by C.sub.9H.sub.19) of the third example,
have a viscosity lower than that of the lubricant (characterized
the mixed ester) of the second comparative example.
[0130] The lubricant (characterized by DOS) of the first
comparative example has been conventionally utilized in spindle
motors of hard disk devices. Each example differs greatly from the
first comparative example and the following drop in viscosity was
recognized. That is to say, the results of
[0131] 48% drop at 0.degree. C. and 38% drop at 40.degree. C. in
the lubricant (characterized by C.sub.7H.sub.15) of the first
example,
[0132] 31% drop at 0.degree. C. and 26% drop at 40.degree. C. in
the lubricant (characterized by C.sub.6H.sub.17) of the second
example,
[0133] 11% drop at 0.degree. C. and 8% drop at 40.degree. C. in the
lubricant (characterized by C.sub.9H.sub.19) of the third example,
and
[0134] 31% drop at 0.degree. C. and 25% drop at 40.degree. C. in
the lubricant (characterized by C.sub.9H.sub.1. +triglyceride) of
the fourth example, are gained.
[0135] In addition, in comparison with the lubricant (characterized
by the mixed ester) of the second comparative example, the results
of
[0136] 26% drop at 0.degree. C. and 19% drop at 40.degree. C. in
the first example,
[0137] 3% drop at 0.degree. C. and 3% drop at 40.degree. C. in the
second example, and
[0138] 2% drop at 0.degree. C. and 3% drop at 40.degree. C. in the
fourth example, are gained.
[0139] Accordingly, in comparison with the lubricant (characterized
by DOS) of the first comparative example that has been
conventionally utilized, each of the lubricants of the present
examples has a lower viscosity, both under low temperature and
under high temperature conditions so that bearing loss of the
dynamic pressure hydraulic bearing can be reduced.
[0140] In addition, in comparison with the lubricant (characterized
by the mixed ester) of the second comparative example that is
ester-based in the same manner, the viscosity is lower in the
first, second and fourth examples so that the bearing loss can be
reduced.
[0141] It is also important for the variation in viscosity of the
lubricant to be small over a broad temperature range in order to
maintain, in a highly precise manner, the rotational speed of a
spindle motor and, therefore, this variation in viscosity is
evaluated. As for the method of evaluation, data of the viscosity
shown in Table 2 is used so as to approximate the relationship
between the viscosity Y and the reciprocal of the absolute
temperature T to an exponential function shown in (equation 1) and
the variation in viscosity is compared by using the value of a
constant B.
Y=A.multidot.e.sup.-B/T [equation 1]
[0142] In (equation 1), A and B are constants. The constant B shows
the slope of the curve which represents the variation ratio of the
viscosity according to the temperature. That is to say, the curve
represents wherein the smaller the value of the constant B is, the
smaller is the variation in viscosity of the lubricant according to
temperature. This result is shown as B values in Table 2.
[0143] The B values of the lubricants of the first to fourth
examples were smaller than the respective B values of the first
comparative example and the second comparative example so that the
result was gained that fluctuation in viscosity according to change
in temperature does not easily occur.
[0144] Large variation in viscosity means that bearing loss becomes
large on the lower temperature side wherein the viscosity becomes
high and that seizure easily occurs due to contact with metal when
the lubricant film is broken on the high temperature side wherein
the viscosity becomes low. Each of the lubricants of the present
examples has a smaller change in viscosity than that in the
comparative examples even under the conditions wherein change in
temperature is great such that an apparatus, to which a motor
wherein such a lubricant is used is mounted, is utilized outdoors
in winter or is utilized after being left in a car in summer and,
therefore, a dynamic pressure hydraulic bearing with which such a
lubricant is used or a spindle motor wherein such a dynamic
pressure hydraulic bearing is used can gain a stable rotational
performance over a broad temperature range and in a high-speed
rotation region.
[0145] Next, the results of measurements of vaporization loss are
described. As for the vaporization loss, each of the lubricants of
the first to fourth examples as well as the first and second
comparative examples is put in a glass beaker and the beaker is
left in a thermostatic bath at 100.degree. C. for 120 hours and,
after that, the amount of decrease in weight (wt. %) is found as
vapor loss. This result is shown as the amount of vaporization in
Table 2.
[0146] The results are gained that the vaporization losses of the
second, third and fourth examples are lower than the vaporization
losses of the first and second comparative examples. In particular,
the result of significantly low vaporization loss is gained in the
third example. That is to say, the lubricants of the second, third
and fourth examples have small vaporization losses so that
lubricant does not run short after a long period of operation and
the lifetime of a spindle motor can be increased. In particular,
the lubricant of the third example has a remarkable stability.
[0147] Next, heat resistance stability of a lubricant when the
lubricant contacts a rotating shaft and a metal that is a bearing
member under a high temperature for a long period of time is
evaluated according to an accelerated high temperature test. The
accelerated high temperature test is carried out according to the
following procedure by taking into consideration the condition of
the lubricant at the time of actual drive of a spindle motor and by
using an oil heating bath with a shaker.
[0148] First, each of the lubricants of the first to fourth
examples as well as the first and second comparative examples is
poured into a test tube made of stainless steel. The same metal
material as that of the rotating shaft and the bearing member is
soaked in the lubricant in each of the test tubes into which the
lubricant has been poured. As for this metal material, a columnar
rod made of a copper alloy is used that is frequently utilized as a
bearing member, on the surface of which a coating film of nickel
phosphor plating, which is generally used for the hardening of the
surface, is formed. These test tubes are soaked in the oil heating
bath with a shaker that has been heated to 150.degree. C. and are
shaken in order to carry out the accelerated high temperature test.
A test tube made of stainless steel and a copper alloy rod on which
nickel phosphorus plating is carried out are in constant contact
with each other due to oscillation by means of the shaker and,
therefore, newly created surfaces are always formed on the surfaces
of the respective metal so that the interface lubrication condition
can be implemented.
[0149] As for the evaluation method, a constant amount of each of
the lubricants is sampled and the viscosity is measured whenever a
constant period of time elapses during the above described
accelerated high temperature test and, thereby, the variation in
viscosity is evaluated and the total oxidation number after 627
hours (26 days and 3 hours) has elapsed is measured for the
evaluation. In the case of a lubricant of which the heat resistance
is inferior or in the case of a lubricant that decomposes or
deteriorates when metal works as a catalyst, the viscosity thereof
changes under high temperature conditions or due to catalysis when
a metal is added and, therefore, the heat resistance of the
lubricant can be evaluated by measuring the change in
viscosity.
[0150] Here, the total oxidation number is the amount, indicated in
milligram units, of potassium hydroxide that is required for
neutralizing the acid components included in the measured sample of
1 gram. In the case that the value of the total oxidation number is
great, it means that the lubricant is oxidized under high
temperature conditions and, furthermore, decomposition, or the
like, has progressed and, as a result, the acid components have
been generated. Accordingly, a great value for the total oxidation
number indicates that deterioration, such as oxidation or
decomposition, has occurred in the lubricant and, thereby, the heat
resistance can be evaluated.
[0151] The results of the measurement of the change in viscosity
according to the accelerated high temperature test are shown in
FIG. 1. The lateral axis shows the period of time during which high
temperature conditions are maintained and the longitudinal axis the
viscosity after every constant period of time has elapsed. Here,
the measurement of the viscosity is carried out at 40.degree. C. P1
is the lubricant of the first example, P2 is the lubricant of the
second example, P3 is the lubricant of the third example, P4 is the
lubricant of the fourth example, Q1 is the lubricant of the first
comparative example and Q2 is the lubricant of the second
comparative example.
[0152] In the case of the lubricant Q1 (characterized by DOS) of
the first comparative example, the viscosity increases in an
approximately linear manner as time elapses and is saturated at the
point in time when approximately 340 hours has elapsed.
[0153] In the case that the change in viscosity occurs in such a
manner, bearing loss becomes large under the utilization condition
wherein the bearing part becomes of a high temperature so that
utilization of the lubricant becomes difficult. In addition, the
change in viscosity has occurred after approximately 170 hours have
elapsed in the lubricant Q2 (characterized by the mixed ester) of
the second comparative example, which has a good heat resistance in
comparison with the lubricant Q1 of the first comparative example
but which, however, is recognized to have a problem of reliability
over long periods of time.
[0154] On the other hand, the change in viscosity of the lubricant
of the first to fourth examples is barely detectable as time
elapses during the accelerated high temperature test and,
therefore, it is confirmed that the heat resistance stability is
excellent.
[0155] Next, the results of the measurement of the total oxidation
numbers of the above described six types of lubricants after 627
hours has elapsed are shown in (Table 3).
3TABLE 3 First Second First Second Third Fourth Comparative
Comparative Example Example Example Example Example Example total
0.00 0.91 0.00 0.37 18.16 1.00 oxidation number (mgKOH/ g)
[0156] All of the lubricants of the first to fourth examples have
values of the total oxidation number smaller than those of the
first and second comparative examples so that a good heat
resistance is confirmed. In particular, the values of the total
oxidation number of the lubricant (characterized by
C.sub.7H.sub.15) of the first example and the lubricant
(characterized by C.sub.9H.sub.19) of the third example are 0 and
it is recognized that they are very stable lubricants wherein
decomposition does not occur even under high temperature
conditions.
[0157] On the other hand, in the case of the lubricant
(characterized by DOS) of the first comparative example, the value
of the total oxidation number is great and, therefore, it can be
seen that decomposition has occurred during the accelerated high
temperature test. That is to say, it has become clear that the
lubricant of the first comparative example has a poor heat
resistance stability and, accordingly, has a great change in
viscosity.
[0158] In addition, in the case of the lubricant (characterized by
mixed ester) of the second comparative example, the value of the
total oxidation number is slightly greater than that of the
lubricant (characterized by C.sub.8H.sub.17) of the second example
while change in viscosity is clearly greater than that of the
second example. As a result of this, it was observed that change in
viscosity occurred in the lubricant of the second comparative
example not because the mixed ester, which is a composition,
decomposed but, rather, because the mixed ester was chemically
polymerized. That is to say, a chemical polymerization occurs under
high temperature conditions in the lubricant of the second
comparative example wherein a base oil made of the mixed ester is
used while the lubricant wherein a base oil of a single ester, in
which only one type from among C.sub.7H.sub.15, C.sub.8H.sub.17 or
C.sub.9H.sub.19 is used as the alkyl base R=C.sub.nH.sub.2n+1 in
(chemical formula 6) of the present invention, was observed to be
stable even at high temperatures.
[0159] Here, when the lubricant (characterized by C.sub.8H.sub.17)
of the second example and the lubricant (characterized by
C.sub.8H.sub.17+a triglyceride) of the fourth example are compared,
the result is gained such that the value of the total oxidation
number of the lubricant of the fourth example is approximately 60%
smaller than the that of the lubricant of the second example. It
has become clear from this that the triglyceride has the effect of
suppression of the decomposition of the base oil.
[0160] Here, an accelerated high temperature test using a copper
alloy material, on which nickel phosphorus plating is not carried
out, is performed on the lubricants of the first to fourth examples
wherein change in viscosity has not occurred with respect to the
copper alloy material on which nickel phosphorus plating is carried
out. This result is shown in FIG. 2. The test conditions are
similar to the above described accelerated high temperature
test.
[0161] As can be seen from FIG. 2, it becomes clear that change in
viscosity does not occur when a copper alloy material on which
nickel phosphorus plating is not carried out is used and a good
heat resistance stability is observed.
[0162] Here, as for the metal material utilized for a rotating
shaft and for a bearing part, not only the above described copper
alloys on which nickel phosphorus plating is carried out or on
which nickel phosphorus plating is not carried out but, also, there
is a possibility that a variety of other materials may be utilized
and in such a case a coating by means of plating, or the like, may
be applied to the surface in accordance with the material or an
inhibitor for inhibiting metal corrosion or metal deactivator may
be added to the lubricant.
[0163] Next, the result of evaluation of slidability
characteristics when contact with metal has occurred. Contact with
metal occurs when the oil film is broken immediately after the
start up of, or immediately before stoppage of, the motor to which
a dynamic pressure hydraulic bearing is mounted. When contact with
metal has occurred, the friction coefficient becomes large and,
therefore, a large amount of wear is caused.
[0164] An evaluation method of the slidability characteristics when
contact with metal has occurred is carried out by measuring the
friction coefficient using a pinion disk testing apparatus. A pin
made of stainless steel generally used for a rotating shaft and a
disk made of a copper alloy on which nickel phosphorus plating
coating film is formed and which is, in some cases, utilized for a
bearing part are utilized in the pinion disk test. As for test
conditions, the speed of the disk relative to the pin is set at
0.16 m/sec and the load added to the pin is set at 624 mN. The
result of the test is shown in Table 4.
4TABLE 4 First Second First Second Third Fourth Comparative
Comparative Example Example Example Example Example Example
Friction 0.15 0.14 0.14 0.12 0.16 0.15 coefficient
[0165] The result is gained that all of the friction coefficients
of the lubricants of the first to fourth examples are smaller than
those of the lubricants of the first and second comparative
examples. Among these, the lubricant of the fourth example has the
lowest friction coefficient and the effects of the addition of
triglyceride are clearly confirmed.
[0166] The results of the comparison of the performance of
lubricants of the first to fourth examples with the lubricants of
the first and second comparative examples are summarized as
follows.
[0167] That is to say, though the lubricant (characterized by
C.sub.7H.sub.15) of the first example has a low viscosity and heat
resistance is good, the amount of vaporization is slightly greater
than that of the lubricant of the second comparative example having
the mixed ester as the base oil. However, heat generation due to
friction of the lubricant itself is small because of its low
viscosity and, therefore, the generation of heat can be restrained
in comparison with the second comparative example. Accordingly,
even in the case that the amount of vaporization is slightly
greater than that of the second comparative example, the lubricant
of the first example has an overall stability at a high temperature
in comparison with the second comparative example.
[0168] The lubricant (characterized by C.sub.8H.sub.17) of the
second example and the lubricant (C.sub.8H.sub.17+a triglyceride)
of the fourth example have better characteristics from an overall
point of view than those of the first and second comparative
examples and it can be seen that they are the lubricants having a
high heat resistance and small bearing loss.
[0169] On the other hand, the lubricant (characterized by
C.sub.9H.sub.19) of the third embodiment has a viscosity greater
than that of the lubricant made up of the mixed ester of the second
comparative example. However, the amount of vaporization is very
small and the value of the total oxidation number is 0 so that the
heat resistance is excellent. As a result of this, a dynamic
pressure hydraulic bearing of a high reliability can be gained
wherein oxidation, decomposition, or the like, does not occur even
though the viscosity is great so that the friction of the lubricant
itself easily causes heat generation.
[0170] As described above, the lubricants of the present examples
all have, overall, superior characteristics in comparison to the
comparative examples and, therefore, lubricants, having excellent
reliability at high temperature could be achieved.
[0171] Here, a variety of additives such as, for example, oil
agent, metal corrosion inhibitor or metal deactivator may further
be added in accordance with the environment or conditions wherein
the dynamic pressure hydraulic bearing will be utilized.
[0172] Moreover, the lubricant (characterized by C.sub.7H.sub.15)
of the first example has the lowest viscosity and has excellent
heat resistance and, therefore, this is appropriate as a lubricant
for, for example, a motor for driving a rotational drum-shaped head
of a video recorder in which a camera is integrated or for a
dynamic pressure hydraulic bearing of a spindle motor for a mobile
apparatus.
[0173] In addition, the lubricant (characterized by
C.sub.7H.sub.15) of the second example and the lubricant
(characterized by C.sub.8H.sub.17+a triglyceride) of the fourth
example have overall superior performance to in comparison with the
comparative examples and are well-balanced lubricants. In addition,
the lubricant of the fourth example has a small friction
coefficient and, therefore, is appropriate for the applications
wherein a motor is frequently started up or stopped.
[0174] Furthermore, though the viscosity is greater than that of
the lubricant (characterized by the mixed ester) of the second
comparative example, the lubricant (characterized by
C.sub.9H.sub.19) of the third example has a small vaporization loss
and has an excellent resistance to oxidation and decomposition and
an excellent heat resistance so that no deterioration occurs even
when the bearing part is exposed to a high temperature and,
therefore, is suitable as a lubricant for dynamic pressure
hydraulic bearings requiring a high reliability and long life.
[0175] The above described lubricant of the first embodiment can be
summarized as follows.
[0176] A base oil of a single ester having any of the structures of
(chemical formula 7), (chemical formula 8) or (chemical formula 9)
is used as the base oil and at least one type from among hindered
phenol-based antioxidants (having at least one
(3,5-di-tert-butyl-4-hydro- xyphenyl)) or hindered amine-based
antioxidants is included and, furthermore, a triglyceride is
included for the reduction of the friction coefficient in the
configuration and, thereby, the viscosity characteristics are
adjusted to be 48 mPa.multidot.s or less at 0.degree. C. and 12
mPa.multidot.s or less at 40.degree. C. in these lubricants. Then
these lubricants are mainly utilized for dynamic pressure hydraulic
bearings.
[0177] Since the lubricants have such compositions, the low
viscosity can be maintained under low temperature conditions
decomposition or oxidation does not occur at high temperatures so
that high heat resistance stability can be achieved. Furthermore,
vaporization loss is small and, at least, copper alloy materials on
which nickel phosphorus plating has been carried out, or on which
nickel phosphorus plating has not been carried out, do not cause
change in quality of the lubricant. Accordingly, the bearing loss
is small even when the lubricant is utilized at low temperatures
and the lubricant can be utilized so as to have a high reliability
even at the time of high-speed rotation wherein the temperature
becomes high and, therefore, significant effects are gained such
that a dynamic pressure hydraulic bearing that can be utilized at
the time of high-speed rotation or over a broad temperature range
can be achieved.
(.sctn.2)
[0178] Second Embodiment
[0179] The second embodiment of the present invention relates to an
analysis method of a lubricant (base oil). This analysis method of
a lubricant is a technology for identifying a lubricant, from among
other lubricants, and the like, of which the base oil is a single
ester having the above described structure of (chemical formula 6)
and having only one type of alkyl base R=C.sub.nH.sub.2n+3 wherein
n=7, n=8 or n=9.
(.sctn.3)
[0180] An analysis method of a lubricant of the present embodiment
is based on the following principle. 11
[0181] One molecule of the base oil that is a single ester molecule
having a molecular structure shown by (chemical formula 11) is
represented by the symbol S (here, S is not sulfur). An H atom is
joined to this base oil molecule S which is ionized so as to be
represented as (S+H).sup.+. In the case that the base oil molecule
S decomposes, an (a) portion is ionized or a (b) portion is
ionized. When the mass numbers are assumed such that H=1, C=12 and
O=16, the respective ass numbers of the (a) portion, the (b)
portion and the (S+).sup.+ portion are calculated.
[0182] [1] If R6=R7=C.sub.7H.sub.15,
[0183] In the (a) portion in (chemical formula 11), the number of
H, C and O are 15, 8 and 1, respectively, because R7 is
C.sub.7H.sub.15, and the mass number is
1.times.15+12.times.8+16.times.1=127.
[0184] In the (b) portion, the number of H, C, and O are 25, 13 and
2, respectively, because R6 is also C.sub.7H.sub.15 and the mass
number is
1.times.25+12.times.13+16.times.2=213.
[0185] The oil molecule S is gained by adding O(of which the number
is one) into the (a) portion and the (b) portion. One H atom is
joined to this base oil molecule S which is ionized so as to become
(S+H).sup.+. The mass number of (S+H)+becomes
127+213+16+1=357.
[0186] Accordingly, the mass number for specifying the base oil
that is a single having the structure of (chemical formula 6) in
the case of alkyl base R=C.sub.7H.sub.15 is a combination of "127,"
"213" and "357." Then, "127," "213" and "357" are assumed to be the
first group with respect to the combination of masses of positive
secondary ions per charge unit at the time of analysis by means of
a secondary ion mass spectrometer.
[0187] In the case that a peak is gained in the secondary ion
intensity at the mass numbers of "127," "213" and "357" of the
first group, a structure can be specified that corresponds to the
case wherein R6 and R7 are both the alkyl base of C.sub.7H.sub.15
in (chemical formula 11).
[0188] [2] case wherein R6=R7=C.sub.8H.sub.17
[0189] Since R7 is C.sub.8H.sub.17, the (a) portion in (chemical
formula 11) has two additional H and one additional C in comparison
with the first group according to the calculation and, therefore,
the mass number is
127+1.times.2+12.times.1=127+14=141.
[0190] Since R6 is also C.sub.8H.sub.17, the (b) portion in
(chemical formula 11) has two additional H and one additional C in
comparison with the first group according to the calculation and,
therefore, the mass number is
213+14=227.
[0191] Then, the (S+H).sup.+ portion has two additional sets of two
H and one C in comparison with the first group according to the
calculation and, therefore, the mass number becomes
357+14.times.2=385.
[0192] Accordingly, the mass number for specifying the base oil
that is a single ester having the structure of (chemical formula 6)
in the case of alkyl base R=C.sub.8H.sub.17 is a combination of
"141," "227" and "385." Then, "141," "227" and "385" are assumed to
be the second group with respect to the combination of masses of
positive secondary ions per charge unit at the time of analysis by
means of a secondary ion mass spectrometer.
[0193] In the case that a peak is gained in the secondary ion
intensity at the mass numbers of "141," "227" and "385" of the
second group, a structure can be specified that corresponds to the
case where R6 and R7 are both the alkyl base of C.sub.8H.sub.17 in
(chemical formula 11).
[0194] [3] case wherein R6=R7=C.sub.9H.sub.19
[0195] Since R7 is C.sub.9H.sub.19, the (a) portion in (chemical
formula 11) has two additional H and one additional C in comparison
with the second group according to the calculation and, therefore,
the mass number is
141+14=155.
[0196] Since R6 is also C.sub.9H.sub.19, the (b) portion in
(chemical formula 11) has two additional H and one additional C in
comparison with the second group according to the calculation and,
therefore, the mass number is
227+14=241.
[0197] Then, the (S+H).sup.+ portion has two additional sets of two
H and one C in comparison with the second group and, therefore, the
mass number becomes
385+14.times.2=413.
[0198] Accordingly, the mass number for specifying the base oil
that is a single ester having the structure of (chemical formula 6)
in the case that the alkyl base R=C.sub.9H.sub.19 is a combination
of "155," "241" and "413." Then, "155," "241" and "413" are assumed
to be the third group with respect to the combination of the masses
of the positive secondary ions per charge unit at the time of
analysis by means of a secondary ion mass spectrometer.
[0199] In the case that a peak is gained in the secondary ion
intensity at the mass numbers of "155," "241" and "413" of the
third group, a structure can be specified that corresponds to the
case wherein R6 and R7 are both the alkyl base of C.sub.9H.sub.19
in (chemical formula 11).
[0200] The above descriptions are summarized as follows. That is to
say, whether or not a peak in each of the mass numbers of "127,"
"213" and "357" of the first group is gained is determined, in an
analysis method of a lubricant according to the present invention,
with respect to the peak of the positive secondary ion intensity
per unit charge when secondary ion mass spectrometry is utilized.
In the case that this determination becomes affirmative, the
lubricant, of which the base oil is a single ester having the
structure of (chemical formula 6) wherein alkyl base
R=C.sub.7H.sub.15, can be identified.
[0201] In addition, whether or not a peak in each of the mass
numbers of "141," "227" and "385" of the second group is gained is
determined, in an analysis method of a lubricant according to
another embodiment of the present invention, with respect to the
peak of the positive secondary ion intensity per unit charge when
secondary ion mass spectrometry is utilized. In the case that this
determination becomes affirmative, the lubricant, of which the base
oil is a single ester having the structure of (chemical formula 6)
wherein alkyl base R=C.sub.9H.sub.17, can be identified.
[0202] In addition, whether or not a peak in each of the mass
numbers of "155," "241" and "413" of the third group is gained is
determined, in an analysis method of a lubricant according to still
another embodiment of the present invention, with respect to the
peak of the positive secondary ion intensity per unit charge when
secondary ion mass spectrometry is utilized. In the case that this
determination becomes affirmative, the lubricant, of which the base
oil is a single ester having the structure of (chemical formula 6)
wherein alkyl base R=C.sub.9H.sub.19, can be identified.
[0203] Here, in any case of the above described analysis method of
a lubricant, when the mass number of the base oil molecule S, which
is the object of determination, is M and the difference between the
mass number of the base oil molecule and the adjoining mass number
gained by static secondary ion mass spectrometry is .DELTA.M, an
analysis may be carried out under the conditions of (M+.alpha.) or
less, with respect to the mass number resolution represented by
M/.DELTA.M when .alpha. is a positive number.
[0204] In the case that the mass number per charge unit of the base
oil molecule S is "357," the mass number resolution may be
(357+.alpha.) or less, in order to significantly identify the mass
number of "1." In the case that the mass number per charge unit of
the base oil molecule S is "385," the mass number resolution may be
(385+.alpha.), or less. In the case that the mass number per charge
unit of the base oil molecule S is "413," the mass number
resolution may be (413+.alpha.) or less. Accordingly, the
conditions can be set such that the mass number resolution is, for
example, 500 or less.
[0205] Here, the base oil is allowed to have a peak in only one
group from among the first to third groups. In the case that the
base oil has peaks in two, or more, groups, the base oil includes a
mixed ester and, therefore, this case is excluded.
(.sctn.4)
[0206] Such a reaction of decomposition as is seen in di-esters,
represented by DOS (sebacic acid di-2-ethylhexyl) that is a
conventional base oil, does not easily occur. Di-esters,
represented by DOS, have, in general, the structure represented by
(chemical formula 12). R4 and R5, respectively, shown herein
indicate a straight chain or a branched alkyl base formed of CmHn
(m and n are integers). 12
[0207] In the case that R4 and R5 have the same structure and are
straight chain alkyl bases formed of CH.sub.2CH.sub.2R, molecular
motion of the base oil becomes violent when exposed to high
temperature so that the structure of (chemical formula 12) easily
changes to the structure of (chemical formula 13) and pseudo-bonds
1 and 2 of O--H are created. 13
[0208] That is to say, at least one of H (of which the number is 5,
6, 7 or 8) that are bonded to C (of which the number is 3) or C (of
which the number is 4) in (chemical formula 13) is shifted by means
of a given thermal energy and, thereby, a reaction as in (chemical
formula 14) occurs so that the di-ester decomposes comparatively
easily. 14
[0209] Here, (chemical formula 14) shows a case of the structure
wherein H atom 5 or H atom 7, shown in (chemical formula 13),
converts to a transition state. As described above, di-esters
having R4 and R5 as straight chain alkyl bases are poor in thermal
stability.
[0210] It is possible that at least one of H atoms 5, 6, 7 or 8
that are bonded to C atom 3 or C atom 4, shown in (chemical formula
13), is used in a branched alkyl base R4 or R5 formed of a
plurality of C atoms, such as a methyl base or an ethyl base. In
this case the reaction shown in (chemical formula 14) can be
prevented due to the three-dimensional blocking effect. However,
when such a branched alkyl base is used, the viscosity of the
lubricant becomes high. Accordingly, it is difficult for good heat
resistance and low viscosity to be simultaneously attained in a
di-ester. Thus, though the stability and the viscosity of the
lubricant are greatly restricted depending on the characteristics
of the base oil, it is difficult to easily evaluate whether or not
the base oil has a specific characteristic.
[0211] In contrast to this, by carrying out static secondary ion
mass spectrometry as in the present invention, the base oil
component, even of a microscopic amount, can be easily specified
with a high precision. The base oil identified in the above
described manner does not easily cause a reaction, as shown in
(chemical formula 14).
[0212] Then, a lubricant is prepared by using a base oil that is
determined in the above described manner. The component of this
lubricant is the same as in the case of the first embodiment. That
is to say, the above described base oil is used as the main body
and, furthermore, at least one type of antioxidant from among
hindered phenol-based antioxidants or hindered amine-based
antioxidants is included as an additive and an additive for the
reduction of the friction coefficient is required and a lubricant
of the present invention includes a triglyceride, of which the
structure is shown in (chemical formula 10), as an additive.
Qualities requirements and qualitative requirements of the above
are the same as in the case of the first embodiment.
[0213] As described above, the lubricant (lubricant composition) of
the present embodiment is characterized in that a hindered
phenol-based antioxidant or a hindered amine-based antioxidant, or
both of these, as well as a triglyceride are added to the base oil
of a single ester having the structure of (chemical formula 7),
(chemical formula 8) or (chemical formula 9) that is identified by
means of an analysis method, including the above described
secondary ion mass spectrometry, as substitutes for DOS (sebacic
acid di-2-ethylhexyl) that is a representative example of a
conventional diester, (trimethylolpropane+monovalent fatty acid)
that is a representative example of a triester or a mixed ester of
a capryl acid of neopentylglycol and capric acid and, thereby, the
viscosity characteristics are adjusted so that the viscosity at
0.degree. C. is 48 mPa.multidot.s or less and the viscosity at
40.degree. C. is 12 mPa.multidot.s or less. Thereby, the low
viscosity can be maintained even in low temperature conditions and
decomposition or oxidation does not occur at high temperatures and,
then, a lubricant of which the friction coefficient is low can be
provided. Accordingly, in the case that the lubricant is utilized
for a dynamic pressure hydraulic bearing, bearing loss is small
even when it is utilized at a low temperature and the lubricant can
be stably utilized at the time of high-speed rotation wherein the
temperature becomes high. Furthermore, a lubricant for a dynamic
pressure hydraulic bearing can be provided having very stable
characteristics wherein change in viscosity and vaporization loss
are low and heat resistance is excellent so that oxidation or
decomposition is not easily caused even at high temperatures.
EXAMPLES OF THE SECOND EMBODIMENT
[0214] In the following, the examples of the second embodiment are
used to describe the present invention in detail.
[0215] The measurement conditions in Table 5. Ga.sup.+ is used as a
primary ion, the irradiation energy is 12 keV, the polarity of the
measured secondary ion is positive and the detection region is 40
.mu.m.sup.2.
5 TABLE 5 primary ion Ga+ primary ion irradiation 12 kev energy
secondary ion polarity Positive detection region 40 .mu.m .times.
40 .mu.m
First Example
[0216] A lubricant of the first example was prepared as follows.
The following was used as the base oil. That is to say, when the
base oil is analyzed by using a secondary ion mass spectrometer,
the secondary ion intensity has peaks at, respectively, the
positions of mass numbers of "127," "213" and "357" of the first
group. This base oil is single ester having the structure of
(chemical formula 6), which corresponds to the lubricant in the
case of alkyl base R=C.sub.7H.sub.15. 1 wt. % of a hindered
phenol-based antioxidant having four (3,5-di-tert-butyl-4-hydrox-
yphenyl) is added to this base oil as an antioxidant. This is
substantially the same as (the first example) of the first
embodiment.
[0217] The measurement result with respect to the base oil is shown
in FIG. 3. (a), (b) and (S+H).sup.+ in FIG. 3 are peaks
corresponding to the fragments shown in (chemical formula 11), of
which the mass numbers are "127," "213" and "357,"
respectively.
Second Example
[0218] A lubricant of the second example was prepared as follows.
The following was used as the base oil. That is to say, when the
base oil is analyzed by using a secondary ion mass spectrometer,
the secondary ion intensity has peaks at, respectively, the
positions of mass numbers of "141," "227" and "385" of the second
group. This base oil is single ester having the structure of
(chemical formula 6), which corresponds to the lubricant in the
case of alkyl base R=C.sub.8H.sub.17. 1 wt. % of a hindered
phenol-based antioxidant having four (3,5-di-tert-butyl-4-hydrox-
yphenyl) is added to this base oil as an antioxidant. This is
substantially the same as (the second example) of the first
embodiment.
[0219] The measurement result with respect to the base oil is shown
in FIG. 4. (a), (b) and (S+H).sup.+ in FIG. 4 are peaks
corresponding to the fragments shown in (chemical formula 11), of
which the mass numbers are "141," "227" and "385,"
respectively.
(Third Example)
[0220] A lubricant of the third example was prepared as follows.
The following was used as the base oil. That is to say, when the
base oil is analyzed by using a secondary ion mass spectrometer,
the secondary ion intensity has peaks at, respectively, the
positions of mass numbers of "155," "241" and "413" of the third
group. This base oil is single ester having the structure of
(chemical formula 6), which corresponds to the lubricant in the
case of alkyl base R=C.sub.9H.sub.19. 1 wt. % of a hindered
phenol-based antioxidant having four (3,5-di-tert-butyl-4-hydrox-
yphenyl) is added to this base oil as an antioxidant. This is
substantially the same as (the third example) of the first
embodiment.
[0221] The measurement result with respect to the base oil is shown
in FIG. 5. (a), (b) and (S+H).sup.+ in FIG. 5 are peaks
corresponding to the fragments shown in (chemical formula 11), of
which the mass numbers are "155," "241" and "413,"
respectively.
Fourth Example
[0222] A lubricant of the third example was prepared as follows.
That is to say, when the base oil is analyzed by using a secondary
ion mass spectrometer, the secondary ion intensity has peaks at,
respectively, the positions of mass numbers of "141," "227" and
"385" of the second group. This base oil is single ester having the
structure of (chemical formula 6), which corresponds to the
lubricant in the case of alkyl base R C.sub.8H.sub.17. 1 wt. % of a
hindered phenol-based antioxidant having four
(3,5-di-tert-butyl-4-hydroxyphenyl) is added to this base oil as an
antioxidant. In addition to this, 1 wt. % of a triglyceride, shown
in (chemical formula 10) is added. Here, R1, R2 and R3 have the
same structure and have the structure of CxHyOz wherein the value
of x is 17, the value of In the above described aspect, is 33 and
the value of z is 1. This is substantially the same as (the fourth
example) of the first embodiment.
[0223] The measurement result with respect to the base oil is shown
in FIG. 6. (a), (b) and (S+H).sup.+ in FIG. 6 are peaks
corresponding to the fragments shown in (chemical formula 11), of
which the mass numbers are "141," "227" and "385," respectively. In
the case of the fourth example, it can be confirmed that the
composition of the base oil is of the same structure as that of the
second example by comparing the peaks in FIG. 4 and in FIG. 6.
Comparative Example
[0224] DOS (sebacic acid di-2-ethylhexyl), which is a lubricant
that has been conventionally used with dynamic pressure hydraulic
bearings, was used as a comparative example. This is substantially
the same as the first comparative example in the first embodiment.
The spectrum measured by a mass spectrometer under the conditions
described in the first example is shown in FIG. 7. Here,
CO--(CH.sub.2).sub.8--COOH in (chemical formula 12) corresponds to
the mass number "185."
[0225] The peak positions and the intensities thereof of this
comparative example are totally different from the ester-based base
oil in the first to fourth examples and the difference thereof can
be clearly determined.
[0226] The explanations in from paragraph (.sctn.1) to paragraph
(.sctn.2) in the descriptions of the above first embodiment
correspond to the descriptions of the examples in this second
embodiment. Here, the descriptions with respect to the second
comparative example are excluded because the present embodiment
does not have a portion corresponding to the second comparative
example.
[0227] (Third Embodiment)
[0228] The third embodiment of the present invention relates to a
deterioration analysis method of a lubricant.
[0229] Here, static secondary ion mass spectrometry is
described.
[0230] In secondary ion mass spectrometry, an accelerated primary
ion is irradiated into the surface of a sample so as to generate a
secondary ion and mass analysis is carried out on the generated
secondary ion by using a mass spectrometer and, thereby, an element
existing in the sample is identified. The acceleration energy for
the primary ion is from a few to several tens keV.
[0231] Static secondary ion mass spectrometry is a type of
secondary ion mass spectrometry and the total amount of radiated
primary ions is adjusted to be 10.sup.12/cm.sup.2 or less. Thereby,
the molecules existing on the surface of the sample have a portion
of their bonds cut off by the irradiated primary ions so as to be
ejected as molecular ions. These ejected molecular ions are
detected. As a result, a mass spectrum representing the
characteristics of the chemical bonds of the molecules existing on
the surface of the sample can be gained. Time of flight secondary
ion mass spectrometry (TOF-SIMS), wherein time of flight is used in
mass spectrometry, is utilized in the present embodiment.
[0232] The potential gap applied between the sample and the
detector is utilized so that the generated secondary ions fly from
the sample to the detector so as to be detected by the detector
and, thereby, mass segregation is carried out in TOF-SIMS. The
energy E given to a monovalent ion by a voltage gap is represented
by (equation 2) wherein the mass of the ion is M and the velocity
thereof is V.
E=M.multidot.V.sup.2/2 [equation 2]
[0233] When the distance between the sample and the detector is
denoted as L and the time required for the ion generated on the
surface of the sample to reach the detector is denoted as t, the
velocity V is represented by (equation 3).
V=L/t [equation 3]
[0234] (equation 4) is led out from the above (equation 2) and
(equation 3) so that the mass of an ion can be determined by
measuring the time required for the ion to reach the detector.
M=2.multidot.E.multidot.t.sup.2/L.sup.2 [equation 4]
[0235] As is seen from (equation 4), the smaller the mass of an ion
is, the sooner the ion reaches the detector. The amount of detected
ions is monitored as the secondary ion intensity.
[0236] In the case that a lubricant utilized with a dynamic
pressure hydraulic bearing is evaluated, the amount of oil used as
the lubricant is extremely small, such as approximately several
.mu.L (microliter). According to TOF-SIMS, however, the
identification of an element existing at the level of ppm and
analysis of an organic molecule can be simultaneously carried out
even in the case that the sample is of an extremely small amount.
In addition, an organic substance or an inorganic impurity at the
level of one molecular layer that exists on the surface of the
electrode can be analyzed with a high sensitivity and, in
particular, status analysis is possible. Accordingly, deterioration
of the base oil of the lubricant can be analyzed by analyzing
change in intensity of the mass spectrum. In addition, the
identification of a metal element that has been mixed into the
lubricant composition and the amount of the mixed in element can be
analyzed. Here, a general secondary ion mass spectrometer may, of
course, be used in the present invention without being limited to
TOF-SIMS.
[0237] In the following, a concrete deterioration evaluation method
is described. The intensity of secondary ions having a specific
mass number is denoted as (I.sub.R).sub.ref and the intensity of
the secondary ions having the mass number of interest is denoted as
(I.sub.n).sub.ref in the spectrum gained by carrying out a
secondary ion mass spectrometry on the lubricant in the initial
condition. In addition, the intensities of secondary ions of the
same mass number as that gained in the lubricant after utilization
for a specific period of time under specific conditions are,
respectively, denoted as (I.sub.R).sub.after and
(I.sub.n).sub.after.
[0238] The ratio of the secondary ion intensity of the mass number
of interest to the secondary ion intensity of the specific mass
number before the test is 1 IR ref = ( I n ) ref ( I R ) ref [
equation 5 ]
[0239] In addition, the ratio of the secondary ion intensity of the
mass number of interest to the secondary ion intensity of the
specific mass number after the test is 2 IR after = ( I n ) after (
I R ) after . [ equation 6 ]
[0240] A variety of combinations exist concerning which ion is
assigned as the ion (I.sub.R) of the specific mass number and which
ion is designated as the ion (I.sub.n) of the mass number of
interest. That is to say, in (equation 5) and (equation 6) any of
(a), (b) or (S+H).sup.+ in (chemical formula 11) may be placed as
denominator and any of (a), (b) or (S+H).sup.+ in (chemical formula
11) may be placed as the numerator under the condition that it is
different from the denominator.
[0241] Then, the ratio IR (intensity ratio) of change of a fragment
in the lubricant is described by (equation 7). 3 IR = IR after IR
ref = ( I n ) after ( I R ) after ( I n ) ref ( I R ) ref [
equation 7 ]
[0242] The above described specific mass number and the mass number
of interest are concretely described below.
[0243] In the case of the first group, the mass numbers are a
combination of any of two from among the values of "127," "213" and
"357." In the case of the second group, they are a combination of
any of two from among the values of "141," "227" and "385." In the
case of the third group, they are a combination of any of two from
among the values of "155," "241" and "413."
[0244] In the case that the ratio IR of change is "1," the
fragmented ionic species of interest has not changed and,
therefore, it is shown that deterioration of the lubricant has not
occurred. In addition, in the case that the ratio IR of change is
greater than "1," it is shown that this ionic species has
increased, while in the case that the ratio IR of change is smaller
than "1," it is shown that this ionic species has decreased so that
in either case it can be determined that that greater is the
difference between the ratio IR of change and 1, the more the
deterioration of the lubricant has progressed. As described above,
deterioration of a lubricant can be analyzed from the fluctuation
of the peaks the fragmented ion of interest.
EXAMPLE OF THE THIRD EMBODIMENT
[0245] This example is a lubricant that includes a single ester
base oil having the structure shown in (chemical formula 6) wherein
alkyl base R=C.sub.nH.sub.2n+1 is a straight chain saturated alkyl
base of C.sub.8H.sub.17 in the case wherein n=8. This is a
lubricant wherein one wt. % of a hindered phenol-based antioxidant
having four (3,5-di-tert-butyl-4-hydroxyphenyl) as an antioxidant
is added to the above base oil. The result of the analysis of
deterioration at the time of the utilization of the lubricant of
this composition is described below.
[0246] A starting and stopping test of a motor having a dynamic
pressure hydraulic bearing wherein a lubricant of this example is
used is carried out for 1000 hours at room temperature. The test is
carried out on two types of motors having a bearing part wherein
brass, which is a copper alloy including zinc, is partially used
and having a bearing part wherein nickel phosphorus plating is
carried out on the surface of this brass. The lubricants after the
test are extracted so as to analyze the deterioration thereof by
means of TOF-SIMS. The analysis conditions of TOF-SIMS are the same
as the conditions described in Table 5.
[0247] A ratio of the secondary ion intensity of the peak of
(S+H).sup.+, wherein an H atom is attached to one molecule, from
among the spectrum gained by the measurement to the secondary ion
intensity of peak of (b) gained by the same measurement:
IR.sub.after=(S+H).sup.+.sub.after/(b).sub.after
[0248] is found. In addition, the same ratio with respect to the
lubricant before the test:
IR.sub.ref=(S+H).sup.+.sub.ref/(b).sub.ref
[0249] is found and, then, the ratio IR of change in the ratio of
IR.sub.after to this IR.sub.ref, that is to say,
IR=IR.sub.after/IR.sub.ref
[0250] is used to evaluate the degree of deterioration. This value
is shown in Table 6.
6 TABLE 6 Brass bearing NiP plating part bearing part
IR.sub.after/IR.sub.ref. 0.59 0.90 metal mixed into lubricant Cu
196 1 Pb 586 1 Fe 103 1
[0251] As is seen in Table 6, it is recognized that the degree of
deterioration is small in the case of the motor having the bearing
part on which nickel phosphorus plating has been carried out and
deterioration of the lubricant is great in the motor having the
bearing part wherein brass is used without change.
[0252] Table 6 shows metal components mixed into the lubricants,
which are simultaneously analyzed, in relative ratios to the
respective components in the lubricants before the test. In the
case that the relative ratio is "1," it indicates that the metal
component in the lubricant has not changed after the test in
comparison to the condition before the test. In the case that the
relative ratio is "196," for example, it indicates that an amount
of the metal component 196 times greater than in the lubricant
before the test has been extracted. In the case that brass was
used, Pb, which is an impurity component of brass, and Fe, which is
a component of stainless steel, used as the material of the bearing
part, greatly increased in the same manner as Cu. It has become
clear that when these metal components have increased,
deterioration of the lubricant has occurred.
[0253] Thus, TOF-SIMS is used and, thereby, the deterioration of
the lubricant utilized in an actual motor and the metal components
that have been mixed in can be analyzed. Furthermore, deterioration
of the lubricant used for a bearing part having even a very small
diameter can be analyzed with a high precision because the sample
amount required for measurement may be an extremely small amount,
to the degree of several .mu.L (microliters).
[0254] Here, though secondary ions having a positive polarity were
used in the static secondary ion mass spectrometry in the present
example, secondary ions having a negative polarity may be used.
Here, in this case the detected peaks differ and, therefore,
negative peaks corresponding to those of the positive case may be
used. In addition, though (S+H)+ and (b) are used as the values of
IR.sub.after and IR.sub.ref in the present example, a ratio of any
combination from among (a), (b) and (S+H).sup.+ may be used without
being limited to the above.
[0255] The above described deterioration analysis method of a
lubricant according to the third embodiment can be summarized as
follows.
[0256] The ratio IR.sub.ref of the secondary ion intensity of the
mass number of interest in the mass spectrum gained in secondary
ion mass spectrometry to the secondary ion intensity of a specific
mass number of a lubricant before utilization is found and, then,
the ratio IR.sub.after of the secondary ion intensity of the mass
number of interest to the secondary ion intensity of a specific
mass number of the lubricant that has been utilized for a
predetermined period of time in a dynamic pressure hydraulic
bearing part is found in the same manner. Furthermore, the ratio
IR=IR.sub.after/IR.sub.ref of a fragment in the lubricant, which is
a ratio of these before and after utilization, is found. The above
described mass number of interest and specific mass number are two
of any mass numbers selected from among three mass numbers in only
one of any group from among the above described three groups. The
deterioration condition of the lubricant is evaluated based on the
above described ratio IR of change. Thereby, the deterioration of
the lubricant can be analyzed with a high precision even in the
case that the sample is of an extremely small amount.
[0257] (Fourth Embodiment)
[0258] The fourth embodiment of the present invention relates to
one modification of a lubricant according to the first embodiment.
That is to say, it relates to a lubricant that includes a single
ester base oil having the structure represented by (chemical
formula 6) wherein the alkyl base R=C.sub.nH.sub.2n+1, is a
straight chain saturated alkyl base of C.sub.8H.sub.17 in the case
wherein n=8 and, furthermore, that a mixed antioxidant formed of
two types of antioxidants, that is to say, of a hindered
phenol-based antioxidant and a hindered amine-based antioxidant, is
added to the above base oil as an antioxidant. The above described
hindered phenol-based antioxidant has at least one
(3,5-di-tert-butyl-4-hydroxyphenyl).
[0259] In the above description, the ratios in the mixture of the
hindered phenol-based antioxidant and of the hindered amine-based
antioxidant to the mixed antioxidant are approximately the same.
The hindered phenol-based antioxidant or the hindered amine-based
antioxidant has the function of a radical scavenger so as to
prevent the oxidation of the base oil through self-oxidation at the
time of heating.
[0260] These two types of antioxidants have antioxidation effects
even in the case that they are used individually, such as in the
case of the first embodiment, and the antioxidation effects can be
further increased so that that a sufficient effect can be gained in
the case of the present embodiment wherein both of the antioxidants
are added.
[0261] Then, in the case that the above described two types of
antioxidants are added in approximately equal amounts to the base
oil having the structure of (chemical formula 6) wherein the alkyl
base R=C.sub.nH.sub.2n+1 is C.sub.8H.sub.17, the heat resistance
stability can be improved without increasing viscosity.
Accordingly, when the lubricant is utilized with a dynamic pressure
hydraulic bearing it is stable even at a high temperature so that a
reduction in the amount of power consumed can be implemented.
[0262] Furthermore, in the above description the mixed antioxidant
content in the lubricant is adjusted between 0.1 wt. % or more and
8 wt. % or less. The base oil having the structure of (chemical
formula 6), wherein the alkyl base R=C.sub.nH.sub.2n+1 is
C.sub.8H.sub.17, is improved in regard to oxidation and
deterioration accompanying the increase in the mixed antioxidant
content so that the heat resistance stability increases while, on
the other hand, the viscosity increases. Contrarily, in the case
that the mixed antioxidant is not added at all, deterioration
occurs for a very short period of time and the lubricant loses its
function. Though the heat resistance stability depends on the
utilization conditions of the dynamic pressure hydraulic bearing, a
level for practical used can be secured by adding 0.1 wt. % or more
of the mixed antioxidant. In addition, by adjusting the amount of
the mixed antioxidant to 8 wt. % or less, the viscosity
characteristics required for the case wherein the lubricant is used
with a dynamic pressure hydraulic bearing, that is to say, a
viscosity of 48 mPa.multidot.s or less at 0.degree. C. and a
viscosity of 12 mPa.multidot.s or less at 40.degree. C. can be
secured.
[0263] In the case that a motor wherein a dynamic pressure
hydraulic bearing is used is mounted to a portable apparatus having
a possibility of being utilized in low temperature conditions, such
as outdoors, it is important to lower the viscosity at low
temperature conditions and, in this case, it is desirable for the
added amount of the mixed antioxidant to be 5 wt. % or less.
[0264] Furthermore, it is preferable to add a triglyceride
represented by the structure of (chemical formula 10) of an amount
of 3 wt. % or less in order to reduce the friction coefficient. As
for the triglyceride, the structures R1, R2 and R3, as well as such
terms as x, y and z described in the first embodiment, are
utilized.
[0265] Next, an example of a motor with a dynamic pressure
hydraulic bearing wherein a lubricant according to the present
invention is utilized is described.
[0266] FIG. 8 is a cross sectional view showing one example wherein
the above described motor is applied in a hard disk device. FIG. 9
is an enlarged view of a portion thereof.
[0267] A sleeve member 20 formed of a bearing sleeve 8 and a thrust
support plate 9 is attached to the center portion of a housing 7
and an axis member 3 of a rotational disk 1 is mounted to the
sleeve member 20 so that it is freely rotatable. As shown in FIG.
9, lubricant 10 according to the present invention is sealed in a
microscopic gap between the sleeve member 20 and the axis member 3.
The rotational center is denoted as 4.
[0268] A stator 16 formed of a coupling part 13, an iron core 14
and a coil 15 is attached to the housing 7. On the other hand, a
rotor yoke 11 is attached to the rotational disk 1 and a rotational
magnet 12 is attached to the rotor yoke. The rotational disk 1, the
rotor yoke 11 and the rotational magnet 12 form a rotor 21.
[0269] The annular bearing sleeve 8 in the sleeve member 20 is
engaged with the center portion of the housing 7. The opening at
one end of the sleeve member 20 is sealed by the thrust support
plate 9. The annular coupling part 13 is secured to the housing 7
by being compressively inserted so as to be integrated. The coil 15
is wound around the iron core 14 extending toward the center from
the coupling part 13.
[0270] The rotational disk 1 is formed of a disk part 2 and axis
member 3 in a columnar form that is integrated with the center
portion of the disk 2. A recording medium layer 6 made of a
magnetic material is formed on the smooth main surface 5 of the
disk part 2. This recording medium layer 6 is formed as a film of
the magnetic material having a predetermined thickness by using
thin film formation technology, such as vacuum deposition or
sputtering.
[0271] The annular rotor yoke 11 in the rotor 21 is engaged and
secured to a circular step portion 2a in the disk part 2. The
annular rotational magnet 12, which has been magnetized in a
plurality of places, is secured to the rotor yoke 11 by means of
adhesive, or the like. An annular thrust suction plate 17 is
secured to the housing 7 so as to be opposed to the rotational
magnet 12.
[0272] A dynamic pressure generation trench is created on the
thrust surface 18, which is the end surface of the axis member 3
opposed to the thrust support plate 9. In addition, a dynamic
pressure generation trench (not shown) is created on the inner
surface of the bearing sleeve 8 opposed to the external surface of
the axis member 3. The form of this dynamic pressure generation
trench is in a herringbone form or in a spiral form. For example, a
trench 22 of a herringbone form may be created, or a trench of a
spiral form may be created, on the thrust surface 18 of the axis
member 3 in the thrust bearing part. FIG. 10 shows, as an example,
the trench 22 in the herringbone form created in the thrust surface
18 of axis member 3.
[0273] When the rotor 21 is rotated by activating the coil 15 in
the motor having the dynamic pressure hydraulic bearing applied in
the hard disk device, as described above, dynamic pressure is
generated by the effect of the lubricant 10 in the portion of the
dynamic pressure generation trench so that the rotor 21 smoothly
rotates.
[0274] A very thin type motor with a high rotational precision can
be realized in the motor configuration using a dynamic pressure
hydraulic bearing in such a manner. For example, a hard disk device
having a thickness of approximately 5 mm, or less, can be
implemented.
[0275] Here, the present invention is not limited to the type in
FIG. 8 but, rather, is applicable to a variety of motors. It may
also be applied to a spindle motor configuration similar to that
according to the prior art. In addition, it may also be applied to
a motor for the rotation of a polygonal mirror, or the like. It is
possible to be utilized with a dynamic pressure hydraulic bearing
used in other rotational parts.
[0276] As described above, a dynamic pressure hydraulic bearing
wherein a lubricant according to the present invention is used has
an axis member and a sleeve member that engage with each other so
as to be freely rotatable, the above described lubricant filled
into a bearing gap between the two and a rotatable member
integrally coupled to the axis member (or sleeve member) so as to
form the configuration wherein dynamic pressure is generated due to
the above described lubricant through the effect of dynamic
pressure generation trench created in the axis member or in the
sleeve member in the direction of thrust and in a radial direction
so as to support the rotational member in the non-contact
condition.
[0277] Furthermore, it is possible to form a thin type motor by
using such a dynamic pressure hydraulic bearing. That is to say,
this motor is provided with a housing, a stator secured to this
housing and that generates a magnetic field in order to provide
rotational force to a rotor, the rotor having a rotational magnet
that is magnetized to a plurality of magnetic poles and that is
secured in order to be opposed to the magnetic field generation
part of the stator and a bearing part for support of the axis of
the rotor so that it is freely rotatable and has the configuration
such that this bearing part corresponds to the above described
dynamic pressure hydraulic bearing.
[0278] A dynamic pressure hydraulic bearing or a motor formed in
such a manner can be formed not only in a thin type form but can
also be stably operated in a manner that power consumption is low
over a broad temperature range and wherein vaporization loss is
small. The vaporization of the lubricant thereof is low and the
lubricant has a low viscosity and the fluctuation of viscosity
change in temperature is small and, moreover, stabilization against
oxidation is excellent. Accordingly, a dynamic pressure hydraulic
bearing and a motor of which bearing loss is small over a range of
temperatures from low to high can be implemented.
EXAMPLES OF THE FOURTH EMBODIMENT
[0279] In the following, the present invention is described in
detail using examples of the fourth embodiment.
First Example
[0280] A lubricant of the first example is prepared as follows.
This is a lubricant that includes a single ester base oil having
the structure represented by (chemical formula 6), wherein the
alkyl base R=C.sub.nH.sub.2n+1, is a straight chain saturated alkyl
base of C.sub.8H.sub.17 in the case that wherein n=8. This base oil
is made to contain a mixed antioxidant made up of a hindered
phenol-based antioxidant and hindered amine-based antioxidant as an
antioxidant. The content of each antioxidant is 1 wt. %. The
hindered phenol-based antioxidant has four
(3,5-di-tert-butyl-4-hydroxyphenyl).
Second Example
[0281] A lubricant of the second example is prepared as follows.
The above described composition of the first example is made to
additionally contain 1 wt. % of the triglyceride represented by
(chemical formula 10). Here, R1, R2 and R3 have the same structure
and, respectively, have the structure of CxHyOz wherein the value
of x is 17, the value of y is 33 and the value of z is 1.
First Comparative Example
[0282] Two types of base oils are used in the first comparative
example wherein the carbon number n in the alkyl base
R=C.sub.nH.sub.2n+1 differ as follows in the structure represented
by (chemical formula 6). In either case, 1 wt. % of a hindered
phenol-based antioxidant having four
(3,5-di-tert-butyl-4-hydroxyphenyl) is included.
[0283] First Comparative Example A: R=C.sub.7H.sub.15
[0284] First Comparative Example B: R=C.sub.8H.sub.17
[0285] First Comparative Example C: R=C.sub.9H.sub.19
Second Comparative Example
[0286] The three types shown below are prepared as the second
comparative example in order to examine the effects due to the
hindered phenol-based antioxidant content. The base oil has the
structure represented by (chemical formula 6) wherein R is a
straight chain saturated alkyl base formed of C.sub.8H.sub.17. In
addition, a hindered phenol-based antioxidant having four
(3,5-di-tert-butyl-4-hydroxyphenyl) is used.
[0287] Second Comparative Example D: hindered phenol-based
antioxidant content: 0 wt. %
[0288] Second Comparative Example E: hindered phenol-based
antioxidant content: 2 wt. %
[0289] Here, the first comparative example B of the first
comparative example can also be utilized in the case wherein the
hindered phenol-based antioxidant content is 1 wt. %.
Third Comparative Example
[0290] A lubricant, shown in the third comparative example F, is
prepared in order to examine the effect due to the triglyceride
content.
[0291] Third Comparative Example F: the base oil has the structure
represented by (chemical formula 6) wherein R is straight chain
saturated alkyl base formed of C.sub.8H.sub.17. Furthermore, the
base oil is made to contain 1 wt. % of the hindered phenol-based
antioxidant and 1 wt. % of the triglyceride.
Fourth Comparative Example
[0292] Lubricants that have conventionally been used with dynamic
pressure hydraulic bearings are used as the fourth comparative
example.
[0293] Fourth Comparative Example G: DOS (sebacic acid
di-2-ethylhexyl)
[0294] Fourth Comparative Example H: a lubricant containing a mixed
ester made of two types of ester, ester of neopentylglycol and
capryl acid and ester of neopentylglycol and capric acid.
[0295] The viscosities at 40.degree. C. and at 0.degree. C., the
amount of vaporization, the stability at high temperatures in the
condition of contact with a metal of a bearing part and the total
oxidation number are, respectively, measured with respect to these
lubricants. These measurements and evaluations are carried out in
the same manner as in the case of the first embodiment, of which
the detailed descriptions are omitted.
[0296] The results of the measurements of the viscosities at
40.degree. C. and at 0.degree. C. and the amount of vaporization
with respect to these lubricants are shown in Table 7. In addition,
the results concerning the viscosity fluctuation in the accelerated
high temperature test are shown in FIG. 11. In addition, the
results of the measurements of the total oxidation numbers are
shown in Table 8.
7 TABLE 7 Total acid number (mgKOH/g) First Example 0.37 Second
Example 0.15 First Comparative Example A 0.00 First Comparative
Example B 0.91 First Comparative Example C 0.00 Second Comparative
Example D Measurement impossible Second Comparative Example E 0.50
Third Comparative Example F 0.37 Fourth Comparative Example G 18.16
Fourth Comparative Example H 1.00
[0297]
8TABLE 8 amount of viscosity Viscosity vaporization (0.degree. C.)
(mPa .multidot. s) (40.degree. C.) (mPa .multidot. s) (wt. %) First
Example 38.74 8.18 0.30 Second 39.16 8.21 0.26 Example First 27.30
6.44 0.58 Comparative Example A First 36.13 7.72 0.29 Comparative
Example B First 46.71 9.50 0.09 Comparative Example C Second 33.31
7.41 0.39 Comparative Example D Second 39.54 8.12 0.30 Comparative
Example E Third 36.52 7.75 0.25 Comparative Example F Fourth 52.72
10.42 0.61 Comparative Example G Fourth 37.39 8.00 0.50 Comparative
Example H
[0298] As for the results of the accelerated high temperature test
shown in FIG. 11, the lateral axis indicates a period of time
wherein the high temperature condition is maintained and the
longitudinal axis indicates the viscosity after a constant period
of time has elapsed.
[0299] First, the influence of the carbon number n of the alkyl
base R=C.sub.nH.sub.2n+1 in a single ester base oil formed of
(chemical formula 6) on the lubricant characteristics is
described.
[0300] The first comparative example A, wherein a base oil of which
the alkyl base R is formed of C.sub.7H.sub.15 is used, has a low
viscosity and its amount of vaporization is great. Here, as is seen
from FIG. 11 and Table 8, fluctuation in viscosity and the total
oxidation number are low and stable, even in the accelerated high
temperature test. Accordingly, low torque can be implemented and
lubricant deterioration in an axis member or in a sleeve member
does not occur. However, there is a possibility that the lubricant
will be vaporized in a comparatively short period of time because
the amount of vaporization is great so that the function of the
dynamic pressure hydraulic bearing may deteriorate. Since it is
comparatively difficult to control the amount of vaporization by
means of additives, utilization is limited to fields wherein low
rotation speeds are used in environments not of high
temperature.
[0301] On the other hand, in the first comparative example C
wherein a base oil, of which the R is formed of C.sub.9H.sub.19 is
used, the amount of vaporization becomes very small while the
viscosity has a high value in comparison with the fourth
comparative example H, which is a conventional lubricant. In the
accelerated high temperature test, however, the fluctuation in
viscosity and the total oxidation number both show excellent
characteristics. Since the reduction of power consumption is
strongly required in portable apparatuses, a lubricant of a low
viscosity is essential in order to mount a hard disk device in a
portable apparatus. In order to reduce the viscosity using this
base oil, an ester-based material of a lower viscosity needs to be
added. In this case, however, the amount of vaporization
increases.
[0302] The first comparative example B, wherein a base oil, of
which the R is formed of C.sub.8H.sub.17 is used, has a viscosity
and an amount of vaporization superior to the fourth comparative
example G and to the fourth comparative example H, which are both
conventional lubricants. Furthermore, though fluctuation in
viscosity in the accelerated high temperature test is barely
detectable, the total oxidation number is 0.91 and is slightly
superior to the fourth comparative example H (1.00), which is a
conventional lubricant.
[0303] According to the above results, it was found that the base
oil having the structure formed of (chemical formula 6), wherein
the alkyl base R is C.sub.8H.sub.17, is the most well-balanced from
the viewpoint of the overall characteristics. In the case that the
total oxidation number is further reduced, better characteristics
can be gained.
[0304] In addition, the hindered phenol-based antioxidant content
is described in reference to the second comparative example D, the
second comparative example E and the first comparative example
B.
[0305] As the hindered phenol-based antioxidant content increases,
the viscosity increases. Though the amount of vaporization is
somewhat great when the content is 0 wt. %, there is almost no
difference when the content is 1 wt. % or more. On the other hand,
it was found in the accelerated high temperature test that a great
fluctuation in viscosity occurred in an extremely short period of
time when the content was 0 wt. % and the heat resistance stability
increased when the content was increased and, thereby, the total
oxidation number was reduced. That is to say, the heat resistance
stability of the hindered phenol-based antioxidant increases
together with the increase in the hindered phenol-based antioxidant
content and, at the same time, the viscosity thereof also increases
to a comparatively great degree.
[0306] In contrast to this, in the case of the lubricant of the
first example, it was found that though the total of the hindered
phenol-based antioxidant content and the hindered amine-based
antioxidant content was 2 wt. %, which is the same as of the second
comparative example E, the total oxidation number was further
reduced so that the heat resistance stability was increased. In
addition, the viscosity of the first example at 0.degree. C. is
lower and, contrarily, the viscosity at 40.degree. C. is slightly
higher than of the lubricant of the second comparative example E
and, therefore, change in viscosity according to fluctuation in
temperature is rather small. Accordingly, low power consumption can
be achieved at low temperatures and fluctuation in power
consumption can be suppressed over a wide range of
temperatures.
[0307] Here, though not shown in the examples, it was found in
another test that heat resistance stability, when the hindered
phenol-based antioxidant content and the hindered amine-based
antioxidant content are approximately equal, improved to a great
degree with the content up to 0.1 wt. %, or more, and that the heat
resistance stability improved in a gradual manner when the content
was increased to 0.1 wt. % or more.
[0308] Next, the effect of the inclusion of a triglyceride is
described.
[0309] The inclusion of triglyceride slightly increases the
viscosity and slightly reduces the amount of vaporization while
greatly improving the total oxidation number judging from the
comparison of the third comparative example F with the first
comparative example B. In the same manner, as a result of the
inclusion of a triglyceride, the viscosity increased slightly while
the amount of vaporization and the total oxidation number both
improved judging from a comparison of the first example with the
second example.
[0310] Furthermore, the effects of the inclusion of triglyceride
were derived according to the friction coefficient in a pinion disk
test wherein a stainless steel pin and a disk made of a copper
alloy, on which is formed nickel phosphorus plating coating, is
used. As a result, it was found that the friction coefficient can
be reduced and heat resistance stability can also be improved by
including triglyceride.
[0311] It was found from the above results that the friction
coefficient can be reduced by adding triglyceride. Accordingly,
seizure, or the like, can be prevented from occurring even when a
drive mounted in a portable apparatus is repeatedly turned on and
off. Furthermore, the amount of vaporization and the total
oxidation number are both improved by adding triglyceride so that
the lubricant stability can be improved. The addition of
triglyceride up to 3 wt. % is allowable as is seen from the
improvement in the amount of vaporization and in the total
oxidation number, with a small increase in the viscosity, by adding
1 wt. % of triglyceride. The lower limit of the triglyceride
content is 0.1 wt. % judging not only from the experimental data
described herein but, also, from the additional experiments. In
particular, in the case that the lubricant is utilized in a
portable apparatus under the condition of frequent intermittent
operation, it is desirable for the triglyceride content to be 1 wt.
% or more.
[0312] Here, depending on the type of metal utilized for the axis
member and for the sleeve member, a case may result wherein the
surface of the metal is corroded due to reaction with the
lubricant. In such a case, a metal corrosion inhibitor or a metal
deactivator which serves to protect the metal surface may be added
in advance to a lubricant of the present example.
[0313] In addition, the components of the lubricant of the above
described example can be changed depending on the above described
spindle motor, dynamic pressure hydraulic bearing and hard disk
device. That is to say, a variety of additives, such as an oiliness
improver, a metal corrosion inhibitor, a metal deactivator, or the
like, may be utilized in accordance with the structure of the
spindle motor or the environment of utilization.
[0314] As described above, it was found that the best overall
characteristics can be gained in a lubricant having the composition
wherein a mixed antioxidant, of a hindered phenol-based antioxidant
and a hindered amine-based antioxidant, as well as a triglyceride
are added to a single ester base oil having the structure formed of
(chemical formula 6) wherein the alkyl base R is
C.sub.8H.sub.17.
[0315] (Fifth Embodiment)
[0316] FIGS. 12A and 12B show an information recording and
reproduction device (hard disk device) according to the fifth
embodiment of the present invention. FIG. 12A is a schematic plan
view of the major portion of this device and FIG. 12B is a
schematic cross sectional view along line A-O-A in FIG. 12A. The
spindle motor in this information recording and reproduction device
is an inner rotor-type A base part 33 and a cover 49 are secured to
a housing 48 of an information recording and reproduction device
100 so as to form a sealed space inside thereof. A cylindrical
bearing part 39 with a bottom is engaged and secured to the base
part 33. A rotational axis part 42, which is integrated with a disk
part 41, is inserted into the bearing part 39 and is supported so
as to freely rotate. As shown in FIG. 13, the end surface of the
rotational axis part 42 in the axis direction and the inner surface
of a thrust support part 40, which becomes the bottom of the
bearing part 39, face each other and lubricant 44 according to the
present invention is filled in into the gap between the two
surfaces and, thereby, a thrust bearing part 50 is formed. A
dynamic pressure generation trench (not shown) is created in, at
least, one of the surfaces including the end surface of the
rotational axis part 42 in the axis direction and the inner surface
of the thrust support part 40 which face each other. In addition,
the outer peripheral surface of the rotational axis part 42 and the
inner peripheral surface of the bearing part 39 face each other and
the lubricant 44 is filled in into the gap between the two surfaces
and, thereby, a radial bearing part 51 is formed. A dynamic
pressure generation trench (not shown) is created in, at least, one
of the surfaces including the example peripheral surface of the
rotational axis part 42 and the inner peripheral surface of the
bearing part 39, which face each other. Furthermore, the lubricant
44 is filled in into the gap between the end surface on the side
having an opening of the bearing part 39 and an annular region 41a
opposed to the above end surface on the side having the opening in
the rear surface of the disk part 41, which face each other. A
dynamic pressure generation trench (not shown) is created in, at
least, one of the surfaces including the end surface on the side
having the opening of the bearing part 39 and the annular region
41a of the disk part 41, which face each other.
[0317] A dynamic pressure hydraulic bearing is formed of the thrust
bearing part 50, the radial bearing part 51 and the thrust bearing
part 52. The thrust bearing part 52 may be omitted.
[0318] A stator 38 formed of an iron core 36 and a coil 37 is
attached the base part 33 by being compressively inserted or by
means of adhesive, or the like. On the other hand, a rotor yoke 34
is attached to the disk part 41 and a rotational magnet 35 is
attached to the rotor yoke 34. The rotor yoke 34 is an annular form
and the rotational magnet 35 is magnetized to have a plurality of
poles. The rotational magnet 35, the rotor yoke 34 and a portion of
the disk part 41 and the rotational axis part 42 form a rotor 32.
The spindle motor formed in such a manner has the rotor 32 inside
of the stator 38 and, thereby, becomes of the inner rotor-type.
[0319] A recording medium layer, made of a magnetic material, is
grown on the smooth main surface of the disk part 41. A magnetic
head for carrying out read-out and write-in of an information
signal is arranged so as to be opposed to the disk part 41 and a
head arm 46 to which this magnetic head 45 is attached is formed so
as to be driven by an actuator 47. A thrust suction plate 43 is
secured to the base part 33 so as to be opposed to the rotational
magnet 35.
[0320] Next, a dynamic pressure generation trench is described.
FIGS. 14A and 14B are bottom views of the lower side of the disk
part 41 as viewed in separation.
[0321] In the case of FIG. 14A, a dynamic pressure generation
trench 50a in a herringbone form is created on the end surface of
the rotational axis part 42 in the axis direction that forms the
thrust bearing part 50. In the case of FIG. 14B, a dynamic pressure
generation trench 52a in a herringbone form is created in the
annular region 41a of the disk part 41 that forms the thrust
bearing part 52. One of the dynamic pressure generation trenches of
FIG. 14A or 14B is necessary for generating a dynamic pressure in
the thrust direction and it is more preferable for both of them to
be provided.
[0322] In this spindle motor, when the rotor 32 is rotated by
activating the coil 37, a dynamic pressure is generated through the
effects of the lubricant 44 in the dynamic pressure generation
trench portions in a radial bearing part 51 and in thrust bearing
parts 50 and 52 so that the rotor 32 rotates smoothly around the
center axis 30. During rotation, the dynamic pressure of the
lubricant 44 that occurs due to rotation is balanced with the
weight of the rotor 32 itself and the magnetic suction power
between the rotational magnet 35 and the thrust suction plate 43
and, thereby, the rotor 32 smoothly rotates regardless of the
position of the information recording and reproduction device
100.
[0323] In the above description, a metal material such as stainless
steel, an aluminum alloy or a copper alloy, glass, a liquid crystal
polymer or a thermoplastic material, such as a PPS (polyphenylene
sulfide) is utilized as the material for forming the bearing part
39 and the rotational axis part 42. In the case that an aluminum
alloy or a copper alloy is utilized, it is preferable to harden the
surface by carrying out nickel phosphorus plating, for example, in
order to increase the resistance to abrasion.
[0324] Since the rotational magnet 35 and the thrust suction plate
43 mutually attract magnetically, the rotational axis part 42 is
prevented from being withdrawn. In addition, the lubricant 44 has
an intrinsic viscosity and has a surface tension and, therefore,
can be prevented from flowing out.
[0325] (Sixth Embodiment)
[0326] An example of an information recording and reproduction
device provided with an outer rotor-type spindle motor is shown in
FIG. 15. A cylindrical bearing part 65 with a bottom is engaged and
secured to a base part 71. A stator 63 formed of an iron core 61
and a coil 62 is engaged and secured to the external peripheral
surface of the bearing part 65. A rotational axis part 66 that is
integrated with a disk part 67, on the surface of which a recording
medium layer made of a magnetic material has been grown, is mounted
to the bearing part 65 so as to be freely rotatable. An annular
rotor yoke 68 is secured to the rear surface of the disk part 67 in
the vicinity of the external periphery of the disk part 67 and a
rotational magnet 69, which is magnetized to have a plurality of
poles, is attached to the inner peripheral surface of the rotor
yoke 68. The rotational magnetic 69, the rotor yoke 68, the disk
part 67 and the rotational axis part 66 form a rotor 70. The
rotational magnetic 69 and the rotor yoke 68, which are the main
parts of the rotor 70, are arranged outside of the stator 63 so as
to provide an outer rotor-type spindle motor.
[0327] The same type of trust bearing parts as those shown in FIG.
13 are denoted as 50 and 52 while the same type of radial bearing
part as that shown in FIG. 13 is denoted as 51. A lubricant 44 is
filled in, in the same manner as in FIG. 13, into gaps within the
thrust bearing parts 50 and 52 and the radial bearing part 51. In
addition, a dynamic pressure generation trench is created in the
same manner as in the above in, at least, one of the two surfaces
that face each other in each of the thrust bearing parts 50 and 52
and in the radial bearing part 51.
[0328] Here, a thrust suction plate is denoted as 72 and a center
axis is denoted as 73. The iron core 61 of the stator 63 may be
attached to the base part 71.
[0329] (Seventh Embodiment)
[0330] The spindle motors of FIGS. 12 and 15 are radial gap-type
brushless motors. However, the present invention may be applied to
an axial gap-type brushless motor in addition to the above. FIG. 16
shows a cross sectional structure of an axial gap-type brushless
motor.
[0331] A cylindrical bearing part 82 with a bottom is engaged and
secured to a base part 81. A rotational axis part 84, which is
integrated with a disk part 83 on the surface of which a recording
medium layer made of a magnetic material has been grown, is mounted
to the bearing part 82 so as to be freely rotatable. A rotor yoke
85 is secured to the rear surface of the disk part 83 through
adhesive, or the like, and an annular rotational magnet 86, which
is magnetized to have a plurality of poles, is secured to the lower
surface of the rotor yoke 85 through adhesive, or the like. A
stator 89 formed of a printed circuit board 87 and a plurality of
coils 88 is attached to the base part 81. The coils 88 are
approximately in a triangular form. The rotational magnetic 86 and
the coils 88 face each other separated by a small gap in the axis
direction. The rotational magnet 86, the rotor yoke 85, the disk
part 83 and the rotational axis part 84 form a rotor 90.
[0332] The same type of thrust bearing parts as those shown in FIG.
13 are denoted as 50 and 52 and the same type of radial bearing
part as that shown in FIG. 13 is denoted as 51. A lubricant 44 is
filled in, in the same manner as in FIG. 13, into gaps between the
two surfaces in the thrust bearing parts 50 and 52 and in the
radial bearing part 51. In addition, a dynamic pressure generation
trench is created, in the same manner as above, in, at least, one
of the two surfaces facing each other in each of the thrust bearing
parts 50 and 52 and in the radial bearing part 51.
[0333] (Eighth Embodiment)
[0334] FIG. 17 shows the structure of a motor according to the
eighth embodiment of the present invention. A bearing part 92 in a
shaft form is secured to a base part 91. On the other hand, a
cylindrical rotational axis part 94 is secured to a disk part 93 on
the surface of which an information recording layer is formed so
that the rotational axis part 94 is engaged with the bearing part
92 so as to be freely rotatable. A rotor yoke 95 is secured to the
rear surface of the disk part 93 in the vicinity of the outside of
the rotational axis part 94 and an annular rotational magnet 96
that is magnetized to have a plurality of poles is secured to the
rotor yoke 95 by means of adhesive, or the like. On the other hand,
a stator 99 formed of an iron core 97 and a coil 98 is secured to
the base part 91 by being compressively inserted, or by another
means. A lubricant 100 according to the present invention is filled
in into a gap between the surfaces of the bearing part 92 in a
shaft form and of the cylindrical rotational axis part 94, which
face each other in the radial direction and in the thrust
direction. The rotational magnet 96, the rotor yoke 95, a portion
of the disk part 93 and the cylindrical rotational axis part 94
form a rotor 101. A thrust suction plate 102 is attached to the
base part 91 so as to be opposed to the end surface of the
rotational magnet 96.
[0335] The present embodiment differs from the other embodiments in
a point that the cylindrical rotational axis part 94 is engaged
from the outside to the bearing part 92 in a shaft form. A dynamic
pressure generation trench (not shown) is created in, at least, one
of the surfaces including the upper end surface of the bearing part
92 in a shaft form and the lower surface of the disk part 93 that
is opposed to the upper end surface. In addition, the outer
peripheral surface of the bearing part 92 in a shaft form and the
inner peripheral surface of the cylindrical rotational axis part 94
face each other and a dynamic pressure generation trench (not
shown) is created in, at least, one of these surfaces, the outer
peripheral surface and the inner peripheral surface. Here, a
dynamic pressure generation trench may be created in, at least, one
of the surfaces including the end surface of the cylindrical
rotational axis part 94 in the axis direction and the upper surface
of the base part 91 that is opposed to this end surface. The
bearing part 92 is not necessarily solid but, rather, may be
hollow.
[0336] A metal material such as stainless steel, an aluminum alloy
or a copper alloy, glass, a liquid crystal polymer or a
thermoplastic material such as PPS (polyphenylene sulfide), for
example, is utilized in the disk part 93, the cylindrical
rotational axis part 94 and the bearing part 92 in a shaft form. In
the case that an aluminum alloy or a copper alloy is utilized, it
is preferable to harden the surface by applying nickel phosphorus
plating, for example, in order to increase the resistance to
abrasion.
[0337] FIG. 18A is a bottom view from below of the rotor 101
separated from the base part 91. A dynamic pressure generation
trench 103 is created in the rear surface of the disk part 93
inside of the cylindrical rotational axis part 94.
[0338] FIG. 18B is a plan view from above of the base part 91
separated from the rotor 101. A dynamic pressure generation trench
104 is created in an annular region of the base part 91 opposed to
the end surface of the cylindrical rotational axis part 94 in the
axis direction.
[0339] In summary, the rotational axis part 94 is cylindrical and
the bearing part 92 is in a shaft form in the spindle motor of FIG.
17, which, furthermore, is formed of an inner rotor-type and this
spindle motor may be modified so as to be formed of an outer
rotor-type. In addition, this spindle motor may be formed of an
axial gap-type instead of a radial gap-type. In addition, a variety
of additives, such as an oil agent, a metal corrosion inhibitor or
a metal deactivator, for example, may, of course, be utilized in
accordance with the structure or the utilization environment of the
spindle motor. In any case, a very thin motor with a high
rotational precision can be implemented. For example, an
information recording and reproduction device, such as a disk
device having a thickness of, for example, approximately no greater
than 5 mm can be implemented.
[0340] Moreover, the present invention is applicable to an
information recording and reproduction device to which an optical
disk or an optical magnetic disk is mounted in addition to a hard
disk device. Utilization in a dynamic pressure hydraulic bearing
used in a motor for rotating a polygonal mirror or in other
rotational parts is also possible.
EXAMPLES OF THE FIFTH TO EIGHTH EMBODIMENTS
[0341] In the following, the examples are described wherein the
lubricants used in motors according to the fifth to eighth
embodiments are examined.
[0342] (First Example)
[0343] A lubricant of the first example is prepared as follows.
This is a lubricant that includes a single ester base oil having
the structure represented by (chemical formula 6), wherein the
alkyl base R=C.sub.nH.sub.2n+1 is a straight chain saturated alkyl
base of C.sub.7H.sub.15 in the case wherein n=7. The above
described base oil is made to include a mixed antioxidant formed of
a hindered phenol-based antioxidant and a hindered amine-based
antioxidant as an antioxidant. The content of each antioxidant is 1
wt. %. The hindered phenol-based antioxidant has four
(3,5-di-tert-butyl-4-hydroxyphenyl).
Second Example
[0344] A lubricant of the second example is prepared as follows.
The lubricant includes a single ester base oil wherein the alkyl
base R=C.sub.nH.sub.2n+1 is a straight chain saturated alkyl base
of C.sub.8H.sub.17 in the case wherein n=8 in place of
C.sub.7H.sub.15 in the case wherein n=7. The other parts are the
same as in the first example.
Third Example
[0345] A lubricant of the third example is prepared as follows. The
lubricant includes a single ester base oil wherein the alkyl base
R=C.sub.nH.sub.2n+.sub.1 is a straight chain saturated alkyl base
of C.sub.9H.sub.19 in the case wherein n=9 in place of
C.sub.7H.sub.15 in the case wherein n=7. The other parts are the
same as in the first example.
Fourth Example
[0346] A lubricant of the third example is prepared as follows. The
composition of the above described second example (n=8) is made to
additionally include 1 wt. % of triglyceride represented by
(chemical formula 10). Here, R1, R2 and R3 have the same structure
and, respectively, have the structure of CxHyOz wherein the value
of x is 17, the value of y is 33 and the value of z is 1.
First Comparative Example
[0347] DOS (sebacic acid di-2-ethylhexyl), which is a
di-ester-based lubricant conventionally used with dynamic pressure
hydraulic bearings, is used as the first comparative example.
Second Comparative Example
[0348] A lubricant of which the base oil is a mixed ester wherein
two types of esters, an ester of neopentylglycol and capryl acid
and an ester of neopentylglycol and capric acid are mixed is used
as the second comparative example.
[0349] Here, in the lubricants of from first to fourth examples,
the amount of the main component of the base oil is shown in Table
9. The main components of the base oils in the lubricants of the
examples are, respectively., 85 wt. % or more.
9TABLE 9 lubricant First Second Third Fourth component Example
Example Example Example amount of 98.5 85.3 97.7 96.7 main
component of base oil (wt. %)
[0350] The results of the measurements of the viscosity, the
stability of the viscosity, the amount of vaporization, antioxidant
properties, the stability at high temperatures and the friction
coefficient of the above described lubricants of the four examples
and of the two comparative examples are shown in Table 10 and in
FIG. 19 and are described in the following.
10TABLE 10 First Second First Second Third Fourth Comparative
Comparative Example Example Example Example Example Example
Viscosity 27.3 36.13 46.71 36.52 52.72 37.39 at 0.degree. C. (mPa
.multidot. s) Viscosity 6.44 7.72 9.50 7.75 10.42 8.00 at
40.degree. C. (mPa .multidot. s) ratio 2925 2757 2960 2914 3256
2975 of change according to temperature: B value amount 0.58 0.29
0.09 0.25 0.61 0.50 of vaporization (wt. %) total 0.00 0.91 0.00
0.37 18.16 1.00 oxidation number (mgKOH/ g) Friction 0.15 0.14 0.14
0.12 0.16 0.15 coefficient
[0351] The results of the measurement of the change in viscosity in
an accelerated high temperature test carried out in the same manner
as in the above described examples of the first embodiment are
shown in FIG. 19. The lubricant of the first example is denoted as
P11, the lubricant of the second example is denoted as P12, the
lubricant of the third example is denoted as P13, the lubricant of
the fourth example is denoted as P14, the lubricant of the first
comparative example is denoted as Q11 and the lubricant of the
second comparative example is denoted as Q12. The explanations in
from paragraph (.sctn.1) to paragraph (.sctn.2) in the descriptions
of the above first embodiment correspond to the descriptions of the
examples in this sixth embodiment.
[0352] Here, the lubricants from first to fourth examples, which
have not changed in viscosity, used with a bearing of a copper
alloy material on which nickel phosphorus plating has been carried
out also undergo an accelerated high temperature test by being used
with a bearing of copper alloy material on which nickel phosphorus
plating has not been carried out. The results thereof are shown in
FIG. 20. The test conditions are the same as in the above described
accelerated high temperature test.
[0353] Furthermore, the lubricants shown in the following examples
are prepared in order to confirm the influence, according to
amount, of antioxidants added to the lubricants.
Fifth Example
[0354] The lubricant of the fifth example is prepared as follows.
This is a lubricant that includes a single ester base oil having
the structure represented by (chemical formula 6) wherein the alkyl
base R=C.sub.nH.sub.2n+1 is a straight chain saturated alkyl base
of C.sub.7H.sub.15 in the case wherein n=7. An antioxidant has not
been added to the fifth example.
Sixth Example
[0355] The lubricant of the sixth example is prepared as follows.
This is a lubricant that includes a single ester base oil having
the structure represented by (chemical formula 6) wherein the alkyl
base R=C.sub.nH.sub.2n+1 is a straight chain saturated alkyl base
of C.sub.7H.sub.15 in the case wherein n=7. A mixed antioxidant
that includes 2 wt. % of a hindered phenol-based antioxidant having
four (3,5-di-tert-butyl-4-hydroxyphenyl) and 1 wt. % of a hindered
amine-based antioxidant is added to the above described base oil as
an antioxidant. This has an additional 1 wt. % of the hindered
phenol-based antioxidant in comparison with the first example.
[0356] The viscosity, the stability of viscosity, the amount of
vaporization and the antioxidant properties of the lubricants of
the above described fifth example and the sixth example are
measured so as to gain the results shown in Table 11.
11 TABLE 11 Fifth Example Sixth Example viscosity at 0.degree. C.
33.31 39.54 (mPa .multidot. s) viscosity at 40.degree. C. 7.41 8.12
(mPa .multidot. s) ratio of change according to temperature: B
value amount of 0.39 0.30 vaporization (wt. %) total oxidation
Measurement 0.50 number (mgKOH/g) impossible
[0357] As the amount of added hindered phenol-based antioxidant
increases, the viscosity increases. Though the amount of
vaporization is somewhat great when the content is 0 wt. %, there
is almost no difference when the content is 1 wt. % or more. On the
other hand, it was found in the accelerated high temperature test
that a great fluctuation in viscosity occurred in an extremely
short period of time when the added amount was 0 wt. % and the heat
resistance stability increased when the added amount was increased
and, thereby, the total oxidation number was reduced. That is to
say, the heat resistance stability of the hindered phenol-based
antioxidant increases together with the increase in the added
amount of the hindered phenol-based antioxidant and, at the same
time, the viscosity thereof also increases to a comparatively great
degree.
[0358] In the case of the lubricant of the fifth example to which
the hindered phenol-based antioxidant has not been added, though
the total oxidation number could not be measured, the heat
resistance stability increased and the viscosity at 0.degree. C. is
low while, in contrast, the viscosity at 40.degree. C. is somewhat
high in comparison with the lubricant of the second example to
which 2 wt. % of hindered phenol-based antioxidant was added and,
therefore, a change in viscosity due to the fluctuation in
temperature is rather small. Accordingly, a reduction in the amount
of power consumed can be implemented even at low temperatures and
the fluctuation in the amount of power consumed can be restricted
over a broad range of temperatures.
[0359] Though not concretely illustrated here, it was found from
another experiment with respect to the heat resistance stability
that the heat resistance stability is improved to a great extent by
adding 0.1 wt. % or more of the hindered phenol-based antioxidant
and the heat resistance stability was gradually improved in
accordance with the amount added.
[0360] Next, the effect of the addition of triglyceride is
described. When the lubricant of the second example is compared
with the lubricant of the fourth example, wherein triglyceride is
added to this lubricant of the second example, results are gained
wherein the viscosity slightly increases and the amount of
vaporization is slightly reduced in the lubricant of the fourth
example while the value of the total oxidation number of the
lubricant of the fourth example is approximately 60% smaller than
that of the lubricant of the second example, which indicates that
the addition of triglyceride has improved the properties of the
lubricant. It has become clear from the above that triglyceride has
the effects of suppressing the decomposition of the base oil.
[0361] A rotation start-up/stoppage cycle test of motors provided
with dynamic pressure hydraulic bearings is carried out. This
indicates the appearance of a change in a motor current with
respect to the number of start-up/stoppage cycles. FIG. 21 shows
the results of the case wherein the lubricant of the second
example, which does not include triglyceride, is used and of the
case wherein the lubricant of the fourth example, to which 1 wt. %
of triglyceride is added.
[0362] It was found that, as shown in this FIG. 21, the motor
current clearly tended to increase, after passing approximately
600,000 cycles, when the lubricant of the second example, which
does not include triglyceride, was used and the viscosity of the
lubricant increased so that the characteristics of the lubricant
deteriorated.
[0363] In addition, the results of the evaluation of the sliding
characteristics when metal contact has occurred in the hydraulic
lubricant part are described in order to confirm the results when
triglyceride is added to the lubricant. The metal contact occurs
when the lubricant film is broken immediately after start-up or
immediately before the stoppage of the motor to which the dynamic
pressure hydraulic bearing is mounted and the friction coefficient
becomes great so that, therefore, a large amount of friction
occurs. An evaluation is carried out by measuring the friction
coefficient using a pinion disk test device. In this test, a pin
made of stainless steel, which is, in general, used in the
rotational shaft, and a disk made of a copper alloy on nickel
phosphorus plating film has been formed, which is used in the
bearing part, are utilized. As for test conditions, the relative
speed between the pin and the disk is set at 0.16 m/sec and the
load added to the pin is set at 624 mN. Test results are shown in
Table 10.
[0364] As a result, a small friction coefficient was gained in the
case of the lubricant of the fourth example, to which triglyceride
was added, in comparison with the lubricants of the first to third
examples and the first and second comparative examples, to which
triglyceride was not added. Since the friction coefficient can be
reduced, seizure, or the like, can be prevented from occurring due
to the repeated turning on and off of the drive when the lubricant
is used in a portable apparatus. Furthermore, the addition of
triglyceride improves the amount of vaporization and the total
oxidation number and, thereby, stability of the lubricant can be
increased. Even in the case that 1 wt. % of triglyceride is added,
the increase in viscosity thereby caused is small and the amount of
vaporization and the total oxidation number are improved. As is
seen from the above, the addition of up to 5 wt. % of triglyceride
is considered to be allowable.
[0365] In the case that an aluminum alloy or a copper alloy is
utilized as a material of the part that forms the bearing part of a
motor provided with a dynamic pressure hydraulic bearing,
resistance to abrasion is increased by carrying out nickel
phosphorus plating, for example, on the surface so that the surface
is hardened.
[0366] Next, the relationship between nickel phosphorus plating and
the lubricant including the above described single ester base oil
is described.
[0367] In the case that an aluminum alloy or a copper alloy is
utilized as a material for forming a rotor made of a disk part and
a rotational axis part of a motor and a bearing part, nickel
phosphorus plating is carried out by means of electroless plating.
Concretely, an alloy plating bath is used and an aging process is
carried out at from 200.degree. C. to 350.degree. C. so as to gain
a nickel phosphorus film having a thickness of from approximately
10 .mu.m to 20 .mu.m and a hardness of from 5 GPa to 15 GPa. In the
experiment wherein brass, which is a type of copper alloy, was
used, it became clear that a film of a great hardness was formed
when the phosphorus composition of the nickel phosphorus film was
from 1 wt. % to 15 wt. %.
[0368] When the relationship between the phosphorus component and
hardness was examined, the hardness of the film started increasing
in tandem with the increase in the amount of the phosphorus
composition and a peak of hardness was found at 4 wt. %. The
condition wherein the hardness is the greatest continues to the
vicinity of 5 wt. % and a great hardness was indicated after
exceeding 5 wt. % up to the vicinity of 15 wt. %. Accordingly, it
is preferable for the phosphorus composition to be 5 wt. % or less
and the vicinity of 4 wt. %, wherein the value of the hardness
indicates a peak, is considered to be most desirable.
[0369] A bearing part is formed of brass, which is one type of
copper alloy. In addition, a bearing part, wherein nickel
phosphorus film is created by means of electroless plating on the
surface of the brass, is formed. The lubricants made of ester-based
base oil represented by (chemical formula 6) are utilized with the
respective dynamic pressure hydraulic bearing parts and a rotation
start-up/stoppage cycle test of motors is carried out. The
lubricants are extracted after the completion of 1,000,000 cycles
and metal components in the lubricants are measured by means of
time of flight secondary ion mass spectrometry (TOF-SIMS method).
The results are shown in FIG. 22.
[0370] After the test of the bearing part on which nickel
phosphorus plating has been carried out, the metal components in
the lubricant were found to be of a lowered amount and indicated
that the bearing part was not worn. Accordingly, in the case that a
lubricant made of a single ester base oil indicated by (chemical
formula 6) is utilized in the dynamic pressure hydraulic bearing of
a motor having a bearing part made of an aluminum alloy or a copper
alloy, the carrying out of nickel phosphorus plating has a great
effect from the point of view of resistance to abrasion.
[0371] In addition, it is known that when Cu or Pb precipitates out
of the lubricant due to wear of the axis part, they become
catalysts so that the deterioration of the lubricant is
accelerated. A lubricant of a low viscosity, in particular, easily
deteriorates. Then, the carrying out of nickel phosphorus plating
eliminates the influence of the above described catalysts and is
considered to have a great effect of prevention of deterioration of
the lubricant.
[0372] Here, though an example is shown above wherein a nickel
phosphorus film is formed by carrying out an aging process,
sufficient hardness can be gained without carrying out a heat
treatment. Hardness is increased when the microscopic
crystallization of the formed nickel phosphorus plating film has
advanced. Meticulous attention is required because heat treatment
may influence the dimensional precision of a motor. In addition,
depending on the type of metal used for the rotational axis part
and for the bearing part, the surface of the metal becomes corroded
through reaction with the lubricant component. In such a case it is
preferable to add a metal corrosion inhibitor or a metal
deactivator to the lubricant.
[0373] Based on the above described results, the results of a
comparison of the performances of the lubricants from first to
sixth examples with those of the lubricants of the first and second
comparative examples are summarized in the following.
[0374] That is to say, the lubricant of the first example having a
single ester base oil, wherein R represented by (chemical formula
6) is formed of C.sub.7H.sub.15, has a low viscosity and an
excellent heat resistance while having an amount of vaporization
slightly greater than that of the lubricant of the second
comparative example of which the base oil a mixed ester. As is seen
from FIG. 19 and Table 10, however, the fluctuation in viscosity
and the total oxidation number is small and stable even in the
accelerated high temperature test and the heat generation due to
friction of the lubricant itself is small due to its low viscosity.
Therefore, heat generation is suppressed in comparison with the
second comparative example and, therefore, the lubricant of the
first example has greater stability, as a whole, at high
temperatures than the lubricant of the second comparative example;
though having a slightly greater amount of vaporization.
Accordingly, though deterioration of the lubricant does not occur
when a low torque is implemented, utilization conditions wherein
the environments are not at very high temperatures are
preferable.
[0375] The lubricants of the second and fourth examples having
single ester base oils of which the alkyl base R, represented by
(chemical formula 6), is formed of C.sub.8H.sub.17 have
characteristics wherein viscosity and amount of vaporization are
both superior to those of the lubricants of the first and second
comparative examples, which are conventional lubricants. In
addition, they are found to be lubricants having great heat
resistance and small bearing loss. Furthermore, as shown in FIG.
19, the fluctuation in viscosity is hardly seen in the accelerated
high temperature test. The total oxidation number is 0.91 and this
is slightly superior to that of the lubricant of the second
comparative example, which is a conventional lubricant. The base
oil, of which the alkyl base R is C.sub.8H.sub.17 is the most
well-balanced from the point of view of the overall characteristics
from among the structures represented by (chemical formula 6) and,
in the case that the total oxidation number is further reduced, a
lubricant having even better characteristics can be gained.
[0376] On the other hand, the lubricant of the third example,
having a base oil of which the alkyl base R is formed of
C.sub.9H.sub.19, has a higher viscosity than that of the lubricant
of the second comparative example made of mixed ester while having
better viscosity than that of the lubricant of the first
comparative example and the fluctuation in viscosity and the total
oxidation number both indicate good characteristics in the
accelerated high temperature test. In addition, the amount of
vaporization is very small and heat resistance is considered to be
excellent because the value of total oxidation number is 0. As a
result of this, even in the case that heat generation occurs
because of friction of the lubricant itself, due to its great
viscosity, oxidation, decomposition, or the like, does not occur
and a dynamic pressure hydraulic bearing of a high reliability can
be gained.
[0377] The lubricant of the first example is favorable for a motor
for driving a rotary drum-shaped head of a type of a video recorder
in which a camera is integrated or for a spindle motor for a mobile
apparatus in the same manner as in the above description. In
addition, the lubricant of the second example or of the fourth
example is favorable for a motor utilized in a portable apparatus
that is frequently started up or stopped. The lubricant of the
third example, having a small vaporization loss and an excellent
resistance to oxidation, decomposition and heat, is favorable for a
dynamic pressure hydraulic bearing wherein high reliability and
long lifetime are required.
[0378] As described above, the lubricants of the present examples
have a low viscosity, in particular at low temperatures, have a
small fluctuation according to temperature so as to have excellent
lubricating characteristics and, thereby, have excellent
reliability at high temperatures while having a small vaporization
loss in comparison with the comparative examples, which are
conventional lubricants. Accordingly, these lubricants do not
require replenishment for a long period of time, the heat
resistance stability can be improved and the characteristics of a
dynamic pressure hydraulic bearing can be improved. Therefore, the
lubricants having a long lifetime and excellent overall
characteristics can be implemented.
[0379] Here, though the respective embodiments described above all
relates to specific devices, the present invention is not limited
to these but, rather, applications to other devices are also
possible.
[0380] While there has been described what is at present considered
to be preferred embodiments of this invention, it will be
understood that various modifications may be made therein, and it
is intended to cover in the appended claims all such modifications
as fall within the true spirit and scope of this invention.
* * * * *