U.S. patent application number 10/207096 was filed with the patent office on 2003-01-16 for bearing grease composition.
This patent application is currently assigned to Minebea Co., Ltd.. Invention is credited to Akiyama, Motoharu, Miyamoto, Yasuhiro, Okamura, Seiji.
Application Number | 20030013622 10/207096 |
Document ID | / |
Family ID | 17538935 |
Filed Date | 2003-01-16 |
United States Patent
Application |
20030013622 |
Kind Code |
A1 |
Miyamoto, Yasuhiro ; et
al. |
January 16, 2003 |
Bearing grease composition
Abstract
A bearing grease composition used under clean atmosphere, as in
a bearing of hard disc drive, which has small dust generation
(scatter), a long life, excellent acoustic performance and low
torque. It has been found that especially the bearing grease
composition comprising a carbonate having a branched alkyl group of
13 to 15 carbon atoms and a metallic soap shows remarkable
characteristics.
Inventors: |
Miyamoto, Yasuhiro;
(Kobe-shi, JP) ; Akiyama, Motoharu; (Miyota-machi,
JP) ; Okamura, Seiji; (Kobe-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. Box 19928
Alexandria
VA
22320
US
|
Assignee: |
Minebea Co., Ltd.
|
Family ID: |
17538935 |
Appl. No.: |
10/207096 |
Filed: |
July 30, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10207096 |
Jul 30, 2002 |
|
|
|
09349465 |
Jul 9, 1999 |
|
|
|
Current U.S.
Class: |
508/462 ;
508/539 |
Current CPC
Class: |
C10M 2207/1285 20130101;
C10N 2040/17 20200501; C10M 2207/125 20130101; C10M 2207/32
20130101; C10N 2040/38 20200501; C10N 2040/32 20130101; C10N
2040/40 20200501; C10M 105/48 20130101; C10N 2010/00 20130101; C10N
2040/36 20130101; C10N 2040/34 20130101; C10N 2040/14 20130101;
C10M 2207/1245 20130101; C10N 2040/16 20130101; C10N 2040/50
20200501; C10M 117/04 20130101; C10N 2040/30 20130101; C10N 2040/00
20130101; C10N 2040/18 20130101; C10N 2040/42 20200501; C10N
2040/185 20200501; C10N 2010/02 20130101; C10N 2040/175 20200501;
C10N 2040/44 20200501; C10M 169/02 20130101; C10M 2207/325
20130101; C10N 2010/04 20130101 |
Class at
Publication: |
508/462 ;
508/539 |
International
Class: |
C10M 101/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 22, 1998 |
JP |
10-274238 |
Claims
What is claimed is:
1. A grease composition for a bearing for a spindle motor
comprising: (a) a base oil including a carbonate compound
represented by the following formula (I): 10 wherein R and R',
which may be the same or different, are each represented by the
following formula (II): 11 wherein n is a number from 13 to 15 and
m is a number from 0 to 6; and (b) at least one of lithium stearate
and lithium 12-hydroxystearate, wherein said grease composition
comprises 70 to 95 parts by weight of component (a) and 5 to 30
parts by weight of component (b).
2. The grease composition of claim 1, wherein said component (a)
includes two or more carbonate compounds, each represented by said
formula (I), wherein said carbonate compounds may be the same
compound or a mixture of compounds.
3. The grease composition of claim 1, wherein said grease
composition includes a lubricant and/or additives.
4. The grease composition of claim 3, wherein said lubricant is
selected from the group consisting of a mineral oil, synthesized
hydrocarbon oil, ether oil and ester oil.
5. The grease composition of claim 3, wherein said additives are an
antioxidant and a rust inhibitor.
6. The grease composition of claim 1, wherein said component (a)
has a dynamic viscosity of 10 to 50 mm.sup.2/sec at 40.degree.
C.
7. The grease composition of claim 1, wherein said formula (II) is
12
8. The grease composition of claim 1, wherein said formula (II) is
13
9. The grease composition of claim 1, wherein said formula (II) is
14
10. The grease composition of claim 4, wherein said lubricant is
selected from alkyl diphenyl ether and polyol ester oil.
11. The grease composition of claim 1, wherein said spindle motor
is for a hard disk drive.
12. The grease composition of claim 1, wherein said component (a)
is a carbonate represented by the following formula (VI): 15
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a bearing grease
composition for hard disc drive or the like. More particularly, the
invention relates to a bearing grease composition for spindle
motors which are used under clean environment, as in memories such
as hard disc drive (HDD) or floppy disc drive (FDD) in
computers.
BACKGROUND OF THE INVENTION
[0002] In general, performances required for a bearing grease
composition used in memories, for examples, HDD or FDD in computers
are that dust generation (scatter) is low, torque is small,
acoustic performance is excellent and life is long. In particular,
in HDD used under a clean atmosphere, fine particles of gaseous oil
or grease scattered from the inside of a bearing during revolution
contaminates the surface of a disc, resulting in cause of wrong
operation. Therefore, it is considered to be most important to
suppress the amount of scatter.
[0003] A sodium complex soap-based grease comprising a mineral oil
as a base oil or a lithium soap-based grease comprising as a base
oil, a synthetic ester (diester oil or polyol ester oil) which is a
reaction product of an organic acid and an alcohol has
conventionally been used as HDD bearing grease.
[0004] The sodium complex soap-based grease comprising a mineral
oil as a base oil has been used for a long time with appreciation
that the amount of scatter is small. However, the grease had the
problems that dispersion of a thickening agent in the grease is
poor, and it is difficult to form a homogeneous mixture, so that
acoustic and vibrating performances during evolution of the bearing
is not good; moisture absorption is high, and the grease cures with
the passage of time, so that flowability of the grease in the
bearing becomes poor, causing defective lubrication.
[0005] Further, the lithium soap-based grease comprising as a base
oil, a synthetic ester (diester or polyol ester oil) which is a
reaction product of an organic acid and an alcohol had no problem
due to that dispersibility of the lithium soap is good, and low
torque property was good.
[0006] However, the lithium soap-based grease tends to scatter, and
if the grease is used as it is, there is the great possibility to
damage a hard disc. Therefore, in order to prevent the damage, the
grease is used in combination with an expensive magnetic fluid seal
which is used in a motor. This rather results in increase of cost
of a motor and prevents the motor from being miniaturized. Further,
for example, due to the demand of high speed revolution and high
precision of the motor, this grease does not sufficiently withstand
acoustic performance and torque, disorder has sometimes occurred in
acoustic performance or torque.
SUMMARY OF THE INVENTION
[0007] As a result of extensive investigations to overcome the
above-described problems in the prior art, it has been found that
properties required for a bearing grease composition which is used
under a clean environment as in, for example, memories such as HDD
or FDD are satisfied by using a metallic soap-based grease
comprising as a base oil a carbonate containing an organic
carbonate represented by the formula (I) described hereinafter. The
present invention has been completed based on this finding.
[0008] Accordingly, an object of the present invention is to
provide a grease composition which can maintain stable low torque
property, low noise property and low scatter property even at high
speed revolution.
[0009] According to the present invention, there is provided a
bearing grease composition comprising:
[0010] (a) a carbonate compound represented by the following
formula (I) 1
[0011] wherein R and R', which may be the same or different, each
represent a branched alkyl group having 13 to 15 carbon atoms;
and
[0012] (b) a group consisting of an alkali metal salt and/or an
alkaline earth metal salt, which are synthesized from a hydroxide
of an alkali metal or an alkaline earth metal and a higher
hydroxyfatty acid having 10 or more carbon atoms or a higher
hydroxyfatty acid having at least one hydroxyl group and having 10
or more carbon atoms.
[0013] The branched alkyl group R and R' in the carbonate compound
represented by the formula (I) is represented by the following
formula (II): 2
[0014] wherein n is a number of 13 to 15 and m is a number of 0 to
6.
[0015] The representative examples of the branched alkyl group are
groups represented by the following formulae (III), (IV) and (V):
3
[0016] The bearing grease composition of the present invention
preferably comprises 70 to 95 parts by weight of component (a) of
the carbonate compound, and 5 to 30 parts by weight of component
(b) of the alkali metal salt and/or alkaline earth metal salt.
[0017] If the amount of component (b) of the alkali metal salt
and/or alkaline earth metal salt is less than 5 parts by weight, a
worked penetration becomes soft, and as a result, the grease
composition leaks or scatters during revolution of a bearing,
resulting in possibility of contaminating HDD, FDD and the
like.
[0018] On the other hand, if the above amount of component (b)
exceeds 30 parts by weight, the grease composition becomes too
hard, and flowability of grease in the bearing becomes poor. As a
result, there is the possibility of causing defective
lubrication.
[0019] The bearing grease composition according to the present
invention can contain, in addition to the components (a) and (b)
described above, lubricants other than the component (a), and
various additives, as a third component.
[0020] Examples of the lubricants used in the present invention
include mineral oils, synthesized hydrocarbon oils, ether oils and
ester oils, which are generally used as a base oil of grease
compositions.
[0021] The additives used in the present invention are additives
generally used in grease composition, and the examples thereof
include antioxidants and rust inhibitors.
[0022] The grease composition of the present invention may further
contain one or more of thickening agents.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] The present invention described in detail below.
[0024] (1) According to the preferred embodiments of the present
invention, a bearing grease composition preferably comprises:
[0025] (a) a carbonate compound represented by the following
formula (I) 4
[0026] wherein R and R' which may be the same or different each
represent a branched alkyl group having 13 to 15 carbon atoms;
and
[0027] (b) a group consisting of an alkali metal salt and/or an
alkaline earth metal salt, synthesized from a hydroxide of an
alkali metal or an alkaline earth metal and a higher hydroxyfatty
acid having 10 or more carbon atoms or a higher hydroxyfatty acid
having at least one hydroxyl group and having 10 or more carbon
atoms.
[0028] (2) Preferably, the bearing grease composition
comprises:
[0029] (a) a carbonate compound -represented by the following
formula (I) 5
[0030] wherein R and R', which may be the same or different, each
represent a branched alkyl group having 13 to 15 carbon atoms,
wherein the branched alkyl group R and R' in the carbonate compound
represented by the formula (I) is represented by the following
formula (II): 6
[0031] wherein n is a number of 13 to 15 and m is a number of 0 to
6; and
[0032] (b) a group consisting of an alkali metal salt and/or an
alkaline earth metal salt, synthesized from a hydroxide of an
alkali metal or an alkaline earth metal and a higher hydroxyfatty
acid having 10 or more carbon atoms or a higher hydroxyfatty acid
having at least one hydroxyl group and having 10 or more carbon
atoms.
[0033] (3) The bearing grease composition comprises 70 to 95 parts
by weight of the carbonate compound represented by formulas (I) and
(II) and 5 to 30 parts by weight of the member selected from the
group consisting of an alkali metal salt and/or an alkaline earth
metal salt, synthesized from a hydroxide of an alkali metal or an
alkaline earth metal and a higher hydroxyfatty acid having 10 or
more carbon atoms or a higher hydroxyfatty acid having at least one
hydroxyl group and having 10 or more carbon atoms.
[0034] (4) The bearing grease composition for hard disc drive
includes preferably a plurality of carbonate compounds.
[0035] (5) The bearing grease composition for hard disc drive in
which the carbonate compound preferably has a dynamic viscosity of
10 to 50 mm.sup.2/sec at 40.degree. C.
[0036] (6) Preferably, the bearing grease composition further
comprises one or more thickening agents.
[0037] (7) The bearing grease composition as in any of the
above-described aspects (1) to (6) comprising further lubricants
and/or additives.
[0038] The carbonate compound can be used alone or as mixtures
thereof.
[0039] The present invention will now be described in more detail
below by referring to the following examples, but the invention
should not be limited thereto.
EXAMPLES 1 TO 6
[0040] Those examples are the preparation example of the typical
bearing grease composition consisting of component (a) and
component (b).
[0041] A carbonate represented by the following formula (VI): 7
[0042] that is, in the formula (I), R is the branched alkyl group
represented by the following formula (IV): 8
[0043] and R' is the branched alkyl group represented by the
following formula (V): 9
[0044] (this carbonate is hereinafter referred to as "carbonate oil
A") alone, or a mixed oil of a carbonate containing commercially
available organic carbonate having different structure of an alkyl
group (CYCRANT T-394, trade name, a product of Mitsui Petrochemical
Industries, Ltd.) (this ester is hereinafter referred to as
"carbonate ester oil B") and the carbonate ester oil A was mixed
with lithium stearate and/or lithium 12 hydroxystearate in the
proportions as shown in Table 1 such that the sum of those was 100
mass %. The resulting mixture was heated to 220-230.degree. C.
while stirring until the whole of mixture became liquid. The liquid
thus obtained was poured into a stainless steel vessel at a depth
of 3-5 mm. The liquid was cooled at 50.degree. C. or less and then
homogenized with three rollers to obtain a grease composition.
EXAMPLES 7 AND 8
[0045] Grease compositions were obtained in the same manner as in
Examples 1 to 6 above except that an alkyl diphenyl ether or a
polyol ester was further used as a third component other than
components (a) and (b) in the proportion as shown in Table 1.
COMPARATIVE EXAMPLES 1 AND 2
[0046] Two kinds of commercially available greases in which a base
oil and a thickening agent are known were used for the sake of
comparison. In Table 2, reference sign + means that such a compound
is contained.
COMPARATIVE EXAMPLE 3 AND 4
[0047] Grease compositions were obtained in the same manner as in
Examples 1-6 except that a base oil and a lithium soap were used in
the proportions as shown in Table 2.
[0048] The grease compositions obtained in the above Examples and
Comparative Examples were measured for a worked penetration and a
dropping point, and were subjected to motor characteristic test,
under the same conditions. The results obtained are shown in Tables
1 and 2.
[0049] The worked penetration was measured according to JIS K2220,
5.3, and the dropping point was measured according to JIS K2220,
5.4.
[0050] The motor characteristic test was conducted such that a
bearing having included therein a grease composition to be tested
was incorporated in a spindle motor, the motor was rotated at
10,000 rpm at a normal temperature, and noise generated, amount of
evaporation (scatter) and rotating torque were measured.
[0051] Noise was measured with a microphone at a place which is 30
cm apart from a hub edge of the motor during rotation of motor.
[0052] The amount of evaporation (scatter) was determined by the
difference between weight of motor before rotation and weight of
motor after rotation.
[0053] The torque was determined by measuring electric current
value at the rotation of motor with an ammeter, and the torque
stability was determined by the difference between the maximum
electric current value and the minimum electric current value.
[0054] The judgement results according to performances required for
a bearing grease composition for HDD or the like on each evaluation
item are shown in Table 1 (Examples) and Table 2 (Comparative
Examples).
[0055] The smaller the value, the better the low noise property;
the smaller the amount of evaporation (scatter), the better the low
scatter property; the lower the value, the better the low torque
property; and the smaller the fluctuation, the better the torque
stability.
[0056] The tests were evaluated with the following four grades.
[0057] A: Particularly excellent
[0058] B: Excellent
[0059] C: Moderate
[0060] D: Poor
1TABLE 1 Example 1 2 3 4 5 6 7 8 Thickening agent StLi 25 25 10 15
20 20 12OH St-Li 15 10 5 Base oil Carbonate A 75 85 38 90 90 80 70
70 Carbonate B 37 ADE 10 POE 10 Viscosity of 18 18 50 18 18 18 25
21 base oil (40.degree. C.) Worked 198 203 196 305 247 181 210 205
Penetration (25 .degree. C.) Dropping point 197 194 198 193 193 195
197 195 (.degree. C.) Motor charac- teristic Test Low noise A A B B
B A B B property Low scatter A B A B B B A A property Low torque A
A B A A A B B property Torque A A B B B A A A stability Total A A B
B B A B B evaluation Notes: StLi: Lithium stearate 12OH St-Li:
Lithium 12 hydroxystearate ADE: Alkyl diphenyl ether POE: Polyol
ester oil
[0061]
2TABLE 2 COMPARATIVE EXAMPLE 1 2 3 4 Thickening agent StLi + 25 25
12OH St-Li + Na-Complex + Base oil Carbonate ester A Carbonate
ester B 75 Diester oil + 38 POE + 37 Mineral oil + Viscosity of
base oil (40.degree. C.) 26 145 18 130 Worked penetration 250 205
197 181 Dropping point (.degree. C.) 194 >260 197 199 Motor
characteristic test Low noise property C D D B Low scatter property
B A D A Torque C B B D Torque stability D C D C Total evaluation C
C D C Notes: Na-Complex: Sodium complex soap 12OH St-Li: Lithium 12
hydroxystearate POE: Polyol ester oil Unit of base oil viscosity
shown in Tables 1 and 2 is mm.sup.2/S.
[0062] As shown in Table 1 above, the bearing grease composition of
the present invention shows low evaporation (scatter), low noise,
low torque property and stable torque.
* * * * *