U.S. patent application number 11/658444 was filed with the patent office on 2008-12-11 for lithium grease composition sealed in a small motor bearing to reduce noise.
Invention is credited to Motoharu Akiyama, Hiroki Iwamatsu, Yasuhiro Miyamoto, Seiji Okamura.
Application Number | 20080305973 11/658444 |
Document ID | / |
Family ID | 35787470 |
Filed Date | 2008-12-11 |
United States Patent
Application |
20080305973 |
Kind Code |
A1 |
Iwamatsu; Hiroki ; et
al. |
December 11, 2008 |
Lithium Grease Composition Sealed in a Small Motor Bearing to
Reduce Noise
Abstract
A lithium grease composition which can be sealed in a small
motor bearing to reduce noise, composed of 5-20% by weight of a
thickener and 95-80% by weight of a base oil, wherein said grease
composition adopts lithium soap as the thickener, which is
synthesized from lithium hydroxide and a higher fatty acid with 10
to 20 carbon atoms and/or a higher hydroxyfatty acid with one or
more hydroxyl groups and 10 or more carbon atoms, and the base oil
includes, as a main component, a polymer ester oil (A) in which 8
or more ester groups are arranged in a comb tooth form on one side
of chain molecules constituted by eight or more carbon atoms which
is expressed by general formula 1: (In the formula, each of
R.sub.1, R.sub.2, R.sub.3 and R.sub.4 is an alkyl group, where x is
an integer and x.gtoreq.2, and y is an integer and y.gtoreq.2.) and
the base oil (40 C) has a viscosity of 25 to 80 mm.sup.2/s.
##STR00001##
Inventors: |
Iwamatsu; Hiroki; (Hyogo,
JP) ; Akiyama; Motoharu; (Nagano, JP) ;
Miyamoto; Yasuhiro; (Hyogo, JP) ; Okamura; Seiji;
(Osaka, JP) |
Correspondence
Address: |
James A Quinton
551 Fifth Ave, Suite 1210
New York
NY
10176
US
|
Family ID: |
35787470 |
Appl. No.: |
11/658444 |
Filed: |
July 29, 2005 |
PCT Filed: |
July 29, 2005 |
PCT NO: |
PCT/US05/27331 |
371 Date: |
January 26, 2007 |
Current U.S.
Class: |
508/469 |
Current CPC
Class: |
C10M 2219/044 20130101;
C10M 2209/06 20130101; C10N 2040/02 20130101; C10M 2207/283
20130101; F16C 2380/26 20130101; C10M 2215/064 20130101; C10M
2205/0285 20130101; C10M 2207/1265 20130101; C10M 169/02 20130101;
C10M 2207/1285 20130101; C10M 2207/0406 20130101; C10M 2205/028
20130101; C10M 2207/2825 20130101; C10N 2030/76 20200501; C10M
2207/282 20130101; C10M 2209/0606 20130101; C10M 2207/04 20130101;
C10M 2207/2835 20130101 |
Class at
Publication: |
508/469 |
International
Class: |
C10M 145/16 20060101
C10M145/16 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 30, 2004 |
JP |
2004-224885 |
Claims
1. A lithium grease composition sealed in a small motor bearing to
reduce noise comprising: a) more than 5% to less than 20% by weight
of a lithium soap thickener; b) said thickener synthesized from
lithium hydroxide and i) a higher fatty acid with 10 to 20 carbon
atoms or ii) a higher hydroxyfatty acid with one or more hydroxyl
groups and 10 or more carbon atoms, or iii) both i and ii; c) 95 to
80% by weight of a base oil; d) said base oil including a polymer
ester oil in which 8 or more ester groups are arranged in a comb
tooth form on one side of chain molecules which is expressed by
Formula 1 ##STR00005## (where each of R.sub.1, R.sub.2, R.sub.3 and
R.sub.4 represents an alkyl group, x is an integer satisfying
x.gtoreq.2, and y is an integer satisfying y.gtoreq.2) and said
base oil having a viscosity (40.degree. C.) of 25 to 80
mm.sup.2/s.
2. The lithium grease composition sealed in a small motor bearing
to reduce noise according to claim 1, further comprising said base
oil including a synthetic ester oil.
3. The lithium grease composition sealed in a small motor bearing
to reduce noise according to claim 1, further comprising said base
oil including a synthetic hydrocarbon oil.
4. The lithium grease composition sealed in a small motor bearing
to reduce noise according to claim 1, further comprising said base
oil including a synthetic ether oil.
5. The lithium grease composition sealed in a small motor bearing
to reduce noise according to claim 2 further comprising said base
oil including a synthetic ether oil.
6. The lithium grease composition sealed in a small motor bearing
to reduce noise according to claim 3 further comprising said base
oil including a synthetic ether oil.
7. The lithium grease composition sealed in a small motor bearing
to reduce noise according to claim 3 further comprising said base
oil including a synthetic ester oil.
8. The lithium grease composition sealed in a small motor bearing
to reduce noise according to claim 1 further comprising said base
oil including a synthetic ester oil, a synthetic hydrocarbon oil
and a synthetic ether oil.
9. The lithium grease composition sealed in a small motor bearing
to reduce noise according to claim 1 wherein the base oil includes
one or more of the oils selected from the group of a synthetic
ester oil, a synthetic hydrocarbon oil and synthetic ether oil.
10. The lithium grease composition sealed in a small motor bearing
to reduce noise according to claims 8 wherein polymer ester oil
accounts for 20 to 50% by weight of the total of the grease
composition, synthetic ester oil accounts for 10 to 45% by weight
of the total of the grease composition, and synthetic ether oil
accounts for 10 to 45% by weight of the total of the grease
composition.
11. The lithium grease composition sealed in a small motor bearing
to reduce noise according to claims 8 or 9 wherein polymer ester
oil accounts for 20 to 50% by weight of the total of the grease
composition, synthetic ester oil accounts for 10 to 45% by weight
of the total of the grease composition, and synthetic hydrocarbon
oil accounts for 5 to 45% by weight of the total of the grease
composition.
12. The lithium grease composition sealed in a small motor bearing
to reduce noise according to claims 8 or 9 wherein said polymer
ester oil accounts for 20 to 50% by weight of the total of the
grease composition, said synthetic ester oil accounts for 10 to 45%
by weight of the total of the grease composition, said synthetic
hydrocarbon oil accounts for 5 to 15% by weight of the total of the
grease composition, and said synthetic ether oil accounts for 10 to
30% by weight of the total of the grease composition.
13. The lithium grease composition sealed in a small motor bearing
to reduce noise according to claims 1 to 9 wherein said lithium
soap is a mixture of a 12-hydroxystearic acid lithium soap and a
straight-chain fatty acid lithium soap (with 10 to 20 carbon
atoms), said 12-hydroxystearic acid lithium soap accounts for 2.5
to 10% by weight of the total of the grease composition, and said
straight-chain fatty acid lithium soap (with 10 to 20 carbon atoms)
accounts for 2.5 to 10% by weight of the total of the grease
composition.
14. The lithium grease composition sealed in a small-motor bearing
to reduce noise according to any one of claims 1 to 9 further
comprising said grease composition includes an antioxidant or an
anticorrosive agent or both an antioxidant and an anticorrosive
agent.
15. The lithium grease composition sealed in a small motor bearing
to reduce noise according to any one of claims 1 to 9 wherein said
polymer ester oil is present in an amount of 20 to 50% by weight of
said grease.
16. The lithium grease composition sealed in a small motor bearing
to reduce noise according to claims 1 to 9 wherein in d) said
polymer ester oil is present in a significant amount of 20% or
greater by weight of said base oil.
17. The lithium grease composition sealed in a small motor bearing
to reduce noise according to claims 1 to 9 wherein in d) said
polymer ester oil has a molecular weight of 1000 to 3000 and a
viscosity (40.degree. C.) of 100 to 245 mm.sup.2/s.
18. The lithium grease composition sealed in a small motor bearing
to reduce noise according to claim 9 wherein said synthetic ester
oil is a) a synthetic diester oil having the formula:
RCOOH(CH.sub.2).sub.nCOOR' (where R and R' represent alkyl groups
with 3 to 18 carbon atoms, and can be identical or different from
each other, and n is 3 to 12.); b) a synthetic trimester oil having
the formula R(CH.sub.2COO R').sub.3 (where R and R' represent alkyl
groups with 3 to 10 carbon atoms); c) a synthetic tetraester oil
having the formula R(CH.sub.2COOR').sub.4 (where R and R' represent
alkyl groups with 3 to 10 carbon atoms); or d) a synthetic
neopentyl polyol ester oil.
19. The lithium grease composition sealed in a small motor bearing
to reduce noise according to claim 9 wherein said synthetic
hydrocarbon oil is a poly-.alpha.-olefin oil or a polybutene and
olefin copolymer, that has a viscosity (40.degree. C.) of 20 to 100
mm.sup.2/s.
20. The lithium grease composition sealed in a small motor bearing
to reduce noise according to claim 9 wherein said synthetic ether
oil (D) is an alkyl diphenyl ether.
21. The lithium grease composition sealed in a small motor bearing
to reduce noise according to claim 20 wherein said synthetic ether
oil (D) is dialkyl diphenyl ether, monoalkyl diphenyl ether, or a
mixture thereof.
22. The lithium grease composition sealed in a small motor bearing
to reduce noise according to any one of claims 1 to 10 wherein the
lithium soap thickener is about 7.5% to about 17.5% by wt.
23. The lithium grease composition sealed in a small motor bearing
to reduce noise according to any one of claims 1 to 10 wherein the
lithium soap thickener is about 10% to about 15% by wt.
24. The lithium grease composition sealed in a small motor bearing
to reduce noise according to claim 11 wherein the lithium soap
thickener is about 7.5% to about 17.5% by wt.
25. The lithium grease composition sealed in a small motor bearing
to reduce noise according to claim 11 wherein the lithium soap
thickener is about 10% to about 15% by wt.
26. The lithium grease composition sealed in a small motor bearing
to reduce noise according to claim 12 wherein the lithium soap
thickener is about 7.5% to about 17.5% by wt.
27. The lithium grease composition sealed in a small motor bearing
to reduce noise according to claim 12 wherein the lithium soap
thickener is about 10% to about 15% by wt.
28. The lithium grease composition sealed in a small motor bearing
to reduce noise according to claim 24 wherein in d) said polymer
ester oil has a molecular weight of 1000 to 3000 and a viscosity
(40.degree. C.) of 100 to 245 mm.sup.2/s.
29. The lithium grease composition sealed in a small motor bearing
to reduce noise according to claim 26 wherein in d) said polymer
ester oil has a molecular weight of 1000 to 3000 and a viscosity
(40.degree. C.) of 100 to 245 mm.sup.2/s.
30. A lithium grease composition comprising: a) more than 5% to
less than 20% by weight of a lithium soap thickener; b) said
thickener synthesized from lithium hydroxide and i) a higher fatty
acid with 10 to 20 carbon atoms or ii) a higher hydroxyfatty acid
with one or more hydroxyl groups and 10 or more carbon atoms, or
iii) both i and ii; c) 95 to 80% by weight of a base oil; d) said
base oil including a polymer ester oil in which 8 or more ester
groups are arranged in a comb tooth form on one side of chain
molecules which is expressed by Formula 1 ##STR00006## (where each
of R.sub.1, R.sub.2, R.sub.3 and R.sub.4 represents an alkyl group,
x is an integer satisfying x.gtoreq.2, and y is an integer
satisfying y.gtoreq.2) and said base oil having a viscosity
(40.degree. C.) of 25 to 80 mm.sup.2/s.
31. The lithium grease composition according to claim 30 further
comprising said base oil including a synthetic ester oil.
32. The lithium grease composition according to claim 30 further
comprising said base oil including a synthetic hydrocarbon oil.
33. The lithium grease composition according to claim 30 further
comprising said base oil including a synthetic ether oil.
34. The lithium grease composition according to claim 31 further
comprising said base oil including a synthetic ether oil.
35. The lithium grease composition according to claim 32 further
comprising said base oil including a synthetic ether oil.
36. The lithium grease composition according to claim 32 further
comprising said base oil including a synthetic ester oil.
37. The lithium grease composition according to claim 30 further
comprising said base oil including a synthetic ester oil, a
synthetic hydrocarbon oil and a synthetic ether oil.
38. The lithium grease composition according to claim 30 wherein
the base oil includes one or more of the oils selected from the
group of a synthetic ester oil, a synthetic hydrocarbon oil and
synthetic ether oil.
39. The lithium grease composition according to claim 37 wherein
polymer ester oil accounts for 20 to 50% by weight of the total of
the grease composition, synthetic ester oil accounts for 10 to 45%
by weight of the total of the grease composition, and synthetic
ether oil accounts for 10 to 45% by weight of the total of the
grease composition.
40. The lithium grease composition according to claims 37 or 38
wherein polymer ester oil accounts for 20 to 50% by weight of the
total of the grease composition, synthetic ester oil accounts for
10 to 45% by weight of the total of the grease composition, and
synthetic hydrocarbon oil accounts for 5 to 45% by weight of the
total of the grease composition.
41. The lithium grease composition according to claims 37 or 38
wherein said polymer ester oil accounts for 20 to 50% by weight of
the total of the grease composition, said synthetic ester oil
accounts for 10 to 45% by weight of the total of the grease
composition, said synthetic hydrocarbon oil accounts for 5 to 15%
by weight of the total of the grease composition, and said
synthetic ether oil accounts for 10 to 30% by weight of the total
of the grease composition.
42. The lithium grease composition according to claims 30 to 38
wherein said lithium soap is a mixture of a 12-hydroxystearic acid
lithium soap and a straight-chain fatty acid lithium soap (with 10
to 20 carbon atoms), said 12-hydroxystearic acid lithium soap
accounts for 2.5 to 10% by weight of the total of the grease
composition, and said straight-chain fatty acid lithium soap (with
10 to 20 carbon atoms) accounts for 2.5 to 10% by weight of the
total of the grease composition.
43. The lithium grease composition according to any one of claims
30 to 38 further comprising said grease composition includes an
antioxidant or an anticorrosive agent or both an antioxidant and an
anticorrosive agent.
44. The lithium grease composition according to any one of claims
30 to 38 wherein said polymer ester oil is present in an amount of
20 to 50% by weight of said grease.
45. The lithium grease composition according to claims 30 to 38
wherein in d) said polymer ester oil is present in a significant
amount of 20% or greater by weight of said base oil.
46. The lithium grease composition according to claims 30 to 38
wherein in d) said polymer ester oil has a molecular weight of 1000
to 3000 and a viscosity (40.degree. C.) of 100 to 245
mm.sup.2/s.
47. The lithium grease composition according to claim 38 wherein
said synthetic ester oil is a) a synthetic diester oil having the
formula: RCOOH(CH.sub.2).sub.nCOOR' (where R and R' represent alkyl
groups with 3 to 18 carbon atoms, and can be identical or different
from each other, and n is 3 to 12.); b) a synthetic trimester oil
having the formula: R(CH.sub.2COOR').sub.3 (where R and R'
represent alkyl groups with 3 to 10 carbon atoms); c) a synthetic
tetraester oil having the formula: R(CH.sub.2COOR').sub.4 (where R
and R' represent alkyl groups with 3 to 10 carbon atoms); or d) a
synthetic neopentyl polyol ester oil.
48. The lithium grease composition according to claim 38 wherein
said synthetic hydrocarbon oil is a poly-.alpha.-olefin oil or a
polybutene and olefin copolymer, that has a viscosity (40.degree.
C.) of 20 to 100 mm.sup.2/s.
49. The lithium grease composition according to claim 38 wherein
said synthetic ether oil (D) is an alkyl diphenyl ether.
50. The lithium grease composition according to claim 49 wherein
said synthetic ether oil (D) is dialkyl diphenyl ether, monoalkyl
diphenyl ether, or a mixture thereof.
51. The lithium grease composition according to any one of claims
30 to 39 wherein the lithium soap thickener is about 7.5% to about
17.5% by wt.
52. The lithium grease composition according to any one of claims
30 to 39 wherein the lithium soap thickener is about 10% to about
15% by wt.
53. The lithium grease composition according to claim 40 wherein
the lithium soap thickener is about 7.5% to about 17.5% by wt.
54. The lithium grease composition according to claim 40 wherein
the lithium soap thickener is about 10% to about 15% by wt.
55. The lithium grease composition according to claim 41 wherein
the lithium soap thickener is about 7.5% to about 17.5% by wt.
56. The lithium grease composition according to claim 41 wherein
the lithium soap thickener is about 10% to about 15% by wt.
57. The lithium grease composition according to claim 53 wherein in
d) said polymer ester oil has a molecular weight of 1000 to 3000
and a viscosity (40.degree. C.) of 100 to 245 mm.sup.2/s.
58. The lithium grease composition according to claim 55 wherein in
d) said polymer ester oil has a molecular weight of 1000 to 3000
and a viscosity (40.degree. C.) of 100 to 245 mm.sup.2/s.
Description
TECHNICAL FIELD
[0001] The present invention relates to a grease composition for
motor bearings for small motors, particularly home electric
appliances such as an air conditioner, motor bearings for
information equipment such as a hard disk driver and the like, and
more specifically to a noise reduction grease sealed in a bearing
for a small motor to reduce the rotation noise of the motor.
BACKGROUND ART
[0002] Generally the use of greases sealed in a bearing is known.
The prior art shows a grease composition in which 8 or more ester
groups are arranged in a comb tooth form on one side of the chain
molecules of oil composed of 8 or more carbon atoms. The grease is
formed by adding a urea thickener to a base oil in which a
synthetic hydrocarbon oil and a synthetic ester oil are mixed in a
weight ratio of 0.65-0.75:0.35-0.25. See Japanese Patent No.
3514574 and U.S. Pat. No. 5,910,470. This grease is sealed in a
ball bearing that supports a belt driven pulley placed in the
vicinity of an automobile engine. Such devices makes a quick change
in its rotation speed. In order to solve a problem of a unique
whistle-like noise that is generated when used in cold climates,
the grease is used.
[0003] A grease sealed in a similar bearing is shown in Japanese
Laid Open Patent Application Publication No. 1994-306383. There a
grease composition is sealed in a bearing. The grease composition
is formed by adding a urea thickener to a base oil in which a
synthetic hydrocarbon oil and a synthetic ester oil are mixed in a
weight ratio of 0.65-0.75:0.35-0.25.
[0004] Japanese Patent No. 3324628 shows that when noise reduction
and vibration reduction are priority issues for a grease
composition sealed in a bearing for an electronic calculator,
semiconductor manufacturing device and the like, a noise and torque
reducing grease is used. The patent shows a grease with lithium
soap as a thickener and an ester oil as a base oil. This
lithium-soap-ester grease, however, tends to spatter and has a
problem of damaging a recording medium if it is used as is. There
is still a need in the art for improved noise reducing grease
compositions sealed in a bearing for a small motor.
DISCLOSURE OF THE INVENTION
[0005] According to the invention, a noise reducing grease
composition and a sealed bearing containing the composition are
provided. The bearing is desirably used for small motors
particularly for home electronic appliances for example air
conditioners, a motor for information equipment such as a hard disk
driver and the like, and sealed in a bearing for a small motor to
reduce the rotation noise of the motor. The present invention
provides a grease composition composed of 5 to 20% preferably
greater than 5% and less than 20% by weight of a lithium soap
thickener. The thickener is synthesized from lithium hydroxide and
a higher fatty acid with 10 to 20 carbon atoms or a higher
hydroxyfatty acid with one or more hydroxyl groups and 10 or more
carbon atoms, or both. Desirably, the lithium soap thickener
accounts for about 7.5% to about 17.5% by weight of the grease
composition preferably about 10% to about 15% particularly about
12% to about 13% by weight.
[0006] The grease according to the invention also includes 95 to
80% by weight of a base oil. As a component of the ester oil is a
polymer ester oil preferably present in a significant amount,
desirably in an amount of 20% or greater by weight of the base oil.
The polymer base oil has 8 or more ester groups arranged in a comb
tooth form on one side of the chain molecules which is expressed by
a general formula
##STR00002##
where each of R.sub.1, R.sub.2, R.sub.3 and R.sub.4 represents an
alkyl group, x is an integer satisfying x.gtoreq.2, and y is an
integer satisfying y.gtoreq.2) and the base oil having a viscosity
(40 C) of 25 to 80 mm.sup.2/s. The resulting grease composition has
good affinity for the bearing member and has excellent noise
reduction properties.
[0007] In another aspect of the invention, the base oil is composed
of one or more oils in addition to the polymer ester oil. According
to the invention, the base oil includes a polymer ester oil of
Formula 1 as a significant component preferably in an amount of 20%
by weight or more of the base oil. The polymer ester oil (A) should
be included as a significant component of the base oil, and more
specifically, besides polymer ester oil (A), one or more of
synthetic ester oil (B), synthetic hydrocarbon oil (C) and
synthetic ether oil (D) may be included.
[0008] Further, according to the present invention, it is
preferable that the polymer ester oil (A) accounts for 20-50% by
weight of the total of the grease composition, the synthetic ester
oil (B) accounts for 10-45% by weight of the total of the grease
composition, and the synthetic hydrocarbon oil (C) accounts for
5-45% by weight of the total of the grease composition.
[0009] According to the present invention, the lithium soap
thickener can be a mixture of a 12-hydroxystearic acid lithium soap
and a straight-chain fatty acid lithium soap, wherein the
12-hydroxystearic acid lithium soap accounts for 2.5-10% by weight
of the total of the grease composition, and the straight-chain
fatty acid lithium soap accounts for 2.5-10% by weight of the total
of the grease composition.
[0010] Further, according to the present invention, an antioxidant,
anticorrosive agent and the like may be added to the grease
composition, as additives.
[0011] The resulting grease composition sealed in a small motor
bearing has excellent acoustic properties, torque reduction,
volatilization reduction and long life span.
[0012] The preferred embodiment of the present invention is
illustrated in the examples. However, it should be expressly
understood that the present invention should not be limited solely
to the illustrative embodiment.
MODES FOR CARRYING OUT THE INVENTION
[0013] According to the invention, a noise reducing grease
composition and a sealed bearing containing the composition are
provided. The bearing is desirably used for a motor for home
electronic appliances for example air conditioners, a motor for
information equipment such as a hard disk driver and the like, and
sealed in a bearing for a small motor to reduce the rotation noise
of the motor. The present invention provides a grease composition
composed of 5 to 20% preferably greater than 5% and less than 20%
by weight of a lithium soap thickener. The thickener is synthesized
from lithium hydroxide and a higher fatty acid with 10 to 20 carbon
atoms or a higher hydroxyfatty acid with one or more hydroxyl
groups and 10 or more carbon atoms, or both. According to the
present invention, the lithium soap desirably can desirably be a
mixture of a 12-hydroxystearic acid lithium soap and a
straight-chain fatty acid lithium soap, wherein the
12-hydroxystearic acid lithium soap accounts for 2.5-10% by weight
of the total of the grease composition, and the straight-chain
fatty add lithium soap accounts for 2.5-10% by weight of the total
of the grease composition. In the present invention, if the lithium
soap accounts less than 5% by weight of the total of the grease
composition, the grease becomes too thin, and if the lithium soap
accounts for more than 20% by weight of the total of the grease
composition, the grease becomes too thick. Desirably, the lithium
soap thickener accounts for about 7.5% to about 17.5% by weight of
the grease composition preferably about 10% to about 15% by weight
particularly about 12% to about 13% by weight of the grease
composition.
[0014] The grease also includes 95 to 80% by weight of a base oil.
A component of the base oil is a polymer ester oil preferably
present in a significant amount, desirably in an amount of 20% or
greater by weight of the base oil. The polymer base oil has 8 or
more ester groups arranged in a comb tooth form on one side of the
chain molecules which is expressed by Formula 1 below:
##STR00003##
where each of R.sub.1, R.sub.2, R.sub.3 and R.sub.4 represents an
alkyl group, x is an integer satisfying x.gtoreq.2, and y is an
integer satisfying y.gtoreq.2). The base oil preferably has a
viscosity (40 C) of 25 to 80 mm.sup.2/s. It is preferable, that
polymer ester oil component of Formula 1 has a molecular weight of
1000 to 3000 and viscosity (40 C) of 100 to 245 mm.sup.2/s. The
resulting grease composition has good affinity for the bearing
member and has excellent noise reduction properties.
[0015] In another aspect of the invention, the base oil is composed
of one or more oils in addition to the polymer ester oil. According
to the invention the base oil includes a polymer ester oil of
Formula 1 as a significant component preferably in an amount of 20%
by weight or more of the base oil.
[0016] The polymer ester oil (A) should be included as a
significant component of the base oil, and more specifically, in
addition to the polymer ester oil (A), one or more of synthetic
ester oils (B), synthetic hydrocarbon oil (C) and synthetic ether
oil (D) may be included desirably. Desirably the polymer ester oil
has a molecular weight of 1000 to 3000 and viscosity (40 C) of 100
to 245 mm.sup.2/s and the final base oil has a viscosity (40 C) of
25 to 80 mm.sup.2/s.
[0017] The synthetic ester oil (B) used in the present invention
can desirably expressed by general formulae (a), (b) or (c) shown
below.
[0018] Thus a synthetic diester oil expressed by general formula
(a) can be used as (B):
RCOOH(CH.sub.2).sub.nCOOR' (a) [0019] (where R and R' represent
alkyl groups with 3 to 18 carbon atoms, and can be identical or
different from each other, and n is 3 to 12.); [0020] a synthetic
trimester oil expressed by general formula (b) can be used as
(B):
[0020] R(CH.sub.2COO R').sub.3 (b) [0021] (where R and R' represent
alkyl groups with 3 to 10 carbon atoms); a synthetic tetraester oil
expressed by general formula (c) can be used as (B):
[0021] R(CH.sub.2COO R').sub.4 (c) [0022] (where R and R' represent
alkyl groups with 3 to 10 carbon atoms); and other synthetic
neopentyl polyol ester oils can be used.
[0023] Preferably, the synthetic ester oil (B) is present in an
amount of 10-45% by weight of the total grease composition.
[0024] The synthetic hydrocarbon oil (C) according to the invention
can be selected from a variety of hydrocarbon oils. A preferable
one is a poly-.alpha.-olefin oil or a polybutene and olefin
copolymer, that has a viscosity (40.degree. C.) of 20 to 100
mm.sup.2/s. For safety, it is preferable to employ a synthetic
hydrocarbon oil with an ignition point of 220.degree. C. or higher.
The synthetic hydrocarbon oil desirably has a structure in which
.alpha.-olefin is low-polymerized to obtain an oligomer and
hydrogen is added to its terminal double bond. A typical formula of
which may be expressed as follows:
##STR00004##
(where R represents an alkyl group, and n represents an integer of
1 to 6). Polybutene can be produced by polymerizing a starting
material mainly containing isobutylene by use of aluminum chloride
as a catalyst. Polybutene may be used as it is or by adding
hydrogen to it. Preferably the synthetic hydrocarbon oil (C) used
in the present invention preferably accounts for 5 to 45% by weight
of the total of the grease composition.
[0025] The synthetic ether oil (D) utilized in the present
invention, preferably is an alkyl diphenyl ether, for example
dialkyl diphenyl ether, monoalkyl diphenyl ether, a mixture thereof
and the like. It is preferable that synthetic ether oil (D)
utilized in the present invention account for 10 to 45% by weight
of the total of the grease composition. The final base oil
desirably has a viscosity (40.degree. C.) of 25 to 80
mm.sup.2/s.
[0026] According to the present invention, it is preferable that
the polymer ester oil (A) accounts for 20-50% by weight of the
total of the grease composition, the synthetic ester oil (B)
accounts for 10-45% by weight of the total of the grease
composition, and the synthetic hydrocarbon oil (C) accounts for
5-45% by weight of the total of the grease composition.
[0027] Alternatively, according to the present invention, it is
desirable that polymer ester oil (A) accounts for 20-50% by weight
of the total of the grease composition, synthetic ester oil (B)
accounts for 10-45% by weight of the total of the grease
composition, synthetic hydrocarbon oil (C) accounts for 5-15% by
weight of the total of the grease composition, and synthetic ether
oil (D) accounts for 10-45% by weight of the total of the grease
composition.
[0028] The grease composition of the present invention may contain
various additives that are commonly used for greases. Such
additives include antioxidants such as
phenyl-.alpha.(.beta.)-naphtylamine, alkyl diphenylamine,
phenothiazine, t-butylphenol and the like, and anticorrosive agents
such as metal sulfonate, non-ionic anticorrosive agents, amine
anticorrosive agents an the like.
[0029] The resulting grease composition sealed in a small motor
bearing according to the present invention has excellent acoustic
properties, torque reduction, volatilization reduction and long
life span.
Specific examples will be discussed next; however, the present
invention should not be restricted by the working examples.
EXAMPLES 1-13 OF THE INVENTION
[0030] As a thickener, a lithium soap synthesized from lithium
hydroxide, stearic acid and 12-hydroxysteraric acid was
employed.
[0031] As a base oil, a polymer ester oil with a viscosity
(40.degree. C.) of approximately 140 mm.sup.2/s was used. As a
synthetic ester oil, a tetraester oil and/or diester oil were used.
DOS (di-2-ethylhexyl sebacate) was used as a diester oil, and PE
(pentaerythritol ester) was used as a tetraester oil.
[0032] As a synthetic hydrocarbon oil, poly-.alpha.-olefin oil was
used.
[0033] As a synthetic ether oil, an alkyl diphenyl ether oil was
used.
[0034] Alkyl diphenylamine was employed as an antioxidant and
calcium sulphonate was employed as an anticorrosive agent.
[0035] The components were mixed in ratios as shown in Table 1, and
heated to 220 to 230.degree. C. while being stirred until the
entire mixture became fluid. The solution was poured into a
stainless steel container so as to form a depth of 3 to 5 mm and
cooled to 50.degree. C. or lower. A grease composition was obtained
by homogenizing it using a three-roll mill. The component ratios of
the grease compositions and the results of the tests are reported
in Table 1.
TABLE-US-00001 TABLE 1 Example 1 2 3 4 5 6 7 Composition Thickener
Higher hydroxyfatty acid lithium 8.5 8.5 10.0 8.5 8.5 8.5 8.5 soap
Higher fatty acid lithium soap 3.5 3.5 2.5 3.5 3.5 3.5 3.5 Base oil
Polymer ester oil 40.0 40.0 40.0 40.0 40.0 20.0 20.0 Synthetic
hydrocarbon oil 44.0 31.5 5.5 14.5 Pentaerythritol ester oil 44.0
18.5 31.5 12.5 33.0 24.0 Diester oil Alkyl diphenyl ether oil 25.5
12.5 25.5 25.5 Additive Antioxidant 4.0 4.0 4.0 4.0 4.0 4.0 4.0
Anticorrosive Agent, etc. 185AProperty Base oil viscosity (40 C.)
mm.sup.2/s 56.04 54.23 71.50 61.98 55.52 51.37 51.73 and Mixture
thickness (25 C.) 258 255 250 261 256 254 258 perf1ormance Dropping
point C. 187 188 195 185 186 190 188 Bearing Acoustic properties A
A A A A A A characteristics Torque reduction A A B A A A A
Volatilization reduction B A A A B A A Long lifespan A A A A A A A
Overall evaluation B A B A B A A Example 8 9 10 11 12 13
Composition Thickener Higher hydroxyfatty acid lithium 8.5 8.5 2.5
8.5 8.5 8.5 soap Higher fatty acid lithium soap 3.5 3.5 10.0 3.5
3.5 3.5 Base oil Polymer ester oil 20.0 40.0 40.0 40.0 40.0 50.0
Synthetic hydrocarbon oil 30.0 5.5 5.5 5.5 5.5 5.5 Pentaerythritol
ester oil 26.0 13.0 6.5 16.0 Diester oil 34.0 13.0 6.5 Alkyl
diphenyl ether oil 12.5 25.5 25.5 25.5 12.5 Additive Antioxidant
4.0 4.0 4.0 4.0 4.0 4.0 Anticorrosive Agent, etc. 185AProperty Base
oil viscosity (40 C.) mm.sup.2/s 26.48 62.24 71.79 58.69 85.39
73.47 and Mixture thickness (25 C.) 253 263 280 255 261 263
perf1ormance Dropping point C. 189 190 188 185 187 189 Bearing
Acoustic properties A A A A A A characteristics Torque reduction A
A B A B B Volatilization reduction B A A B A A Long lifespan B A B
B B B Overall evaluation B A B B B B
COMPARATIVE EXAMPLES 1-6
[0036] In the same manner as in the examples 1-13 of the invention,
comparative grease compositions 1-4 were prepared by mixing
components. Moreover, two commercially available greases with known
base oils and thickeners were adopted as comparative examples 5 and
6, as shown on Table 2. On Table 2, the symbol ++ indicates a
component that is mixed in.
[0037] The mixture examples and the results of the tests are shown
on Table 2.
TABLE-US-00002 TABLE 2 Comparative Example 1 2 3 4 5 6 Composition
Thickener Higher hydroxyfatty add lithium 8.5 8.5 ++ ++ soap Higher
fatty acid lithium soap 3.5 3.5 12.0 12.0 ++ ++ Base oil Polymer
ester oil Synthetic hydrocarbon oil 25.0 Pentaerythritol ester oil
67.0 28.0 ++ Diester oil 17.0 59.0 56.0 ++ Mineral oil 84.0 ++
Additive Antioxidant Anticorrosive 4.0 4.0 4.0 4.0 ++ ++ Agent,
etc. Property and Base oil viscosity (40.degree. C.) mm.sup.2/s
99.85 25.60 15.25 15.15 94.66 26.86 performance Mixture thickness
(25.degree. C.) 259 254 288 278 280 250 Dropping point .degree. C.
187 190 184 188 185 193 Bearing Acoustic properties A A A A C A
characteristics Torque reduction D A A A D A Volatilization
reduction C B D D C B Long lifespan D C D D D C Overall evaluation
D C D D D C
[0038] The mixture thickness was obtained on the basis of JIS K2220
7, while the dropping point was obtained on the basis of JIS K2220
8. In the bearing characteristics test, grease components to be
tested were sealed in a small bearing, and their rotational torques
and acoustic properties were measured at room temperature, and also
their volatile amounts and the acoustic properties (acoustic life
duration) of the bearings were measured after 1000 hours of the
bearing rotation test at a rotation frequency of 300 rpm under an
atmosphere temperature of 100.degree. C. Regarding the acoustic
properties, the Anderon values were measured using an Anderon meter
before and after the bearing rotation test. The rotational torques
were measured using a torque tester at 3000 rpm, under a 2 kg load,
at room temperature. As for the volatile amount, the bearing was
weighed before and after the bearing rotation test, and the
difference was obtained. In relation to the evaluation results of
each, the results of judgment made in accordance with performances
required for a motor bearing grease composition are listed on Table
1 (examples) and Table 2 (comparative examples). A smaller Anderon
value indicates better acoustic properties, and a lower torque and
smaller volatile amount are better in performance. The evaluation
was made on 4-level scale. "A" is especially excellent, "B" is
excellent, "C" is average, and "D" is poor. The unit for the base
oil viscosity is mm.sup.2/s.
[0039] The lithium grease composition sealed in a small motor
bearing of the present invention contributes to a longer lifespan
of a bearing and maintains the low noise properties. As a result,
it is an eco-friendly grease, which is expected to be in high
demand and has various possibilities of industrial application.
[0040] The foregoing is considered as illustrative only to the
principles of the invention. Further, since numerous changes and
modification will occur to those skilled in the art, it is not
desired to limit the invention to the exact construction and
operation shown and described above, and accordingly all suitable
modifications and equivalents may be resorted to, falling within
the scope of the invention.
* * * * *