Patent Application
20090029881
The present invention relates to a heat resistant grease composition for motor bearings for small motors, particularly home electric appliances such as an air conditioner, motor bearings for imaging equipment such as blower fan and the like, and more specifically to a heat resistant, noise reduction grease sealed in a bearing for a small motor to reduce the rotation noise of the motor.
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. To solve a problem of a unique whistle-like noise that is generated when used in cold climates, the grease is used.
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.
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.
According to the invention, a heat resistant and noise-reduction grease composition that is desirably used in a bearing for a small motor is provided. In another aspect of the invention, a sealed bearing containing the grease composition is provided which is desirably installed in small motor to reduce the rotation noise of the motor in use.
According to the invention a heat resistant noise reduction lithium grease composition is provided which has 5 to 20% preferably greater than 5% and less than 20% by weight of a lithium soap thickener. 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. The lithium soap thickener is composed of a long-chain fatty acid lithium soap with 26 to 32 carbon atoms. The lithium soap thickener also includes a higher fatty acid lithium soap with 10 to 20 carbon atoms and/or a higher hydroxyfatty acid lithium soap with one or more hydroxyl groups and 10 or more carbon atoms.
The lithium grease composition also includes 95 to 80% by weight of a base oil. The base oil contains 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
(where each of R1, R2, R3 and R4 represents an alkyl group, x is an integer satisfying x≧2, and y is an integer satisfying y≧2). The base oil has a viscosity (40° C.) of 30 to 100 mm2/s.
The polymer ester oil which is preferably present in the base oil in a significant amount preferably in an amount 20% by weight or higher preferably 20% to 50% by weight of the base oil.
Desirably, the base oil includes, in addition to polymer ester oil of Formula 1 (A), one or more of synthetic ester oil (B), synthetic hydrocarbon oil (C), synthetic ether oil (D) and mineral oil (E). Desirably the polymer ester oil (A) accounts for 20 to 50% by weight of the total of the grease composition, synthetic hydrocarbon oil (C) accounts for 10 to 40% by weight of the total of the grease composition, and mineral oil (E) accounts for 10 to 40% by weight of the total of the grease composition. Optionally according to the invention, the polymer ester oil (A) accounts for 20 to 50% by weight of the total of the grease composition, the synthetic ester oil (B) accounts for 10 to 40% by weight of the total of the grease composition, and the synthetic hydrocarbon oil (C) accounts for 10 to 40% by weight of the total of the grease composition. Advantageously, according to the present invention, the polymer ester oil (A) accounts for 20 to 50% by weight of the total of the grease composition, the synthetic ester oil (B) accounts for 10 to 30% by weight of the total of the grease composition, the synthetic hydrocarbon oil (C) accounts for 2 to 10% by weight of the total of the grease composition, and synthetic ether oil (D) accounts for 10 to 30% by weight of the total of the grease composition.
Preferably the lithium soap thickener includes the long-chain fatty acid lithium soap with 26 to 32 carbon atoms in an amount of 0.1 to 10.0% by weight of the total of the grease composition, 12-hydroxystearic acid lithium soap lithium soap in an amount for 1.5 to 10.5% by weight of the total of the grease composition, and straight-chain fatty acid lithium soap with 10 to 20 carbon atoms in an amount of 0.5 to 5.0% by weight of the total of the grease composition.
Desirably an antioxidant, anticorrosive agent and the like may be added as additives to the heat-resistant lithium grease composition.
The heat-resistant lithium grease composition is desirably sealed in a small motor bearing to reduce noise. The resulting composition has superior attachment to a metal surface. As a result in use, a protective film forms quickly and evenly on the bearing metal surfaces. The protective film can be maintained at a high temperature, which contributes to a longer operating life of the bearing. Furthermore, the composition has an advantageous dispersibility and resolvability of the additives in the base oil which keeps the noise low during operation of a motor using the sealed bearing according to the invention.
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.
According to the invention, a heat resistant and noise reducing grease composition that is desirably used in a bearing for a small motor is provided. The grease filled bearing according to the invention is desirably used in a motor of imaging equipment such as a blower fan, a bearing of a motor of home electronic appliances such as an air conditioner. In another aspect of the invention, a sealed bearing containing the composition is provided which is desirably installed in a small motor to reduce the rotation noise of the motor in use.
According to the invention a heat resistant and noise reducing lithium grease composition is provided which has 5 to 20% preferably greater than 5% and less than 20% by weight of a lithium soap thickener. 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. The lithium soap thickener is composed of a long-chain fatty acid lithium soap with 26 to 32 carbon atoms. The lithium soap thickener also includes a higher fatty acid lithium soap with 10 to 20 carbon atoms and/or a higher hydroxyfatty acid lithium soap with one or more hydroxyl groups and 10 or more carbon atoms. Preferably the lithium soap thickener includes the long-chain fatty acid lithium soap with 26 to 32 carbon atoms in an amount of 0.1 to 10.0% by weight of the total of the grease composition, 12-hydroxystearic acid lithium soap lithium soap in an amount for 1.5 to 10.5% by weight of the total of the grease composition, and straight-chain fatty acid lithium soap with 10 to 20 carbon atoms in an amount of 0.5 to 5.0% by weight of the total of the grease composition. Advantageously, the lithium soap of long-chain fatty acid with 26 to 32 carbon atoms used in the present invention is obtained by bringing lithium hydroxide and a long-chain higher fatty acid with 26 to 32 carbon atoms to reaction to each other. The long-chain fatty acid with 26 to 32 carbon atoms may be used singly or as a mixture. It is preferable to use a mixture of long-chain fatty acid with 26 to 32 carbon atoms containing montanic acid with 28 carbon atoms, preferably as a substantial component.
Desirably the lithium soap thickener utilized in the present invention includes together with the long-chain fatty acid with 26 to 32 carbon atoms, a lithium soap synthesized from lithium hydroxide and higher fatty acid with 10 to 20 carbon atoms and/or higher hydroxyfatty acid with one or more hydroxyl groups and 10 or more carbon atoms.
In the present invention, if the lithium soap accounts for less than 5% by weight of the total of the grease composition, the grease becomes too thin, while if the lithium soap accounts for more than 20% by weight of the total of the grease composition, the grease becomes too thick.
The lithium grease composition also includes 95 to 80% by weight of a base oil. The base oil includes 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
(where each of R1, R2, R3 and R4 represents an alkyl group, x is an integer satisfying x≧2, and y is an integer satisfying y≧2).
The resulting base oil has a viscosity (40° C.) of 30 to 100 mm2/s. The polymer ester oil is preferably present in the base oil in a significant amount preferably in an amount of preferably in an amount 20% by weight or higher preferably 20% to 50% by weight of the base oil.
In addition to polymer ester oil (A), the base oil desirably includes, one or more of synthetic ester oil (B), synthetic hydrocarbon oil (C), synthetic ether oil (D) and mineral oil (E). It is preferable that the polymer ester oil has a molecular weight of 1000 to 3000 and viscosity (40° C.) of 100 to 1000 mm2/s. and the resulting base oil has a viscosity (40° C.) of 30 to 100 mm2/s.
Polymer ester oil (A) utilized in the present invention can be any polymer ester that is expressed by the general formula
(where each of R1, R2, R3 and R4 represents an alkyl group, x represents an integer satisfying x≧2, and y represents an integer satisfying y≧2). It is preferable, that the polymer ester oil of Formula 1 have a molecular weight of 1000 to 3000 and viscosity (40° C.) of 100 to 1000 mm2/s.
The synthetic ester oil (B) used in the present invention is expressed by general formulae (a), (b) or (c) shown below.
A synthetic diester oil expressed by general formula (a):
RCOOH(CH2)nCOOR′ (a)
(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);
a synthetic trimester oil expressed by general formula (b):
R(CH2COO R′)3 (b)
(where R and R′ represent alkyl groups with 3 to 10 carbon atoms);
a synthetic tetraester oil expressed by general formula (c):
R(CH2COOR′)4 (c)
(where R and R′ represent alkyl groups with 3 to 10 carbon atoms); and other synthetic neopentyl polyol ester oils can be used.
Synthetic hydrocarbon oil (C) used in the present invention is preferably a poly-α-olefin oil, polybutene and olefin copolymer, with a viscosity (40° C.) of 20 to 100 mm2/s, and for the sake of safe use, it is preferable to adopt those with an ignition point of 220° C. or higher.
These have a structure in which α-olefin is low-polymerized to obtain an oligomer and hydrogen is added to its terminal double bond, a typical formula of which may be as follows:
(where R represents an alkyl group, and n represents an integer of 1 to 6). Polybutene is one kind of poly-α-olefin and 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.
As synthetic ether oil (D) utilized in the present invention, an alkyl diphenyl ether may be employed, namely dialkyl diphenyl ether, monoalkyl diphenyl ether, a mixture thereof and the like.
Mineral oil (E) utilized in the present invention is desirably a paraffinic oil with a viscosity (40° C.) of 90 to 150 mm2/s.
Desirably the polymer ester oil (A) accounts for 20 to 50% by weight of the total of the grease composition, synthetic hydrocarbon oil (C) accounts for 10 to 40% by weight of the total of the grease composition, and mineral oil (E) accounts for 10 to 40% by weight of the total of the grease composition. Optionally according to the invention, the polymer ester oil (A) accounts for 20 to 50% by weight of the total of the grease composition, the synthetic ester oil (B) accounts for 10 to 40% by weight of the total of the grease composition, and the synthetic hydrocarbon oil (C) accounts for 10 to 40% by weight of the total of the grease composition. ester oil (B), synthetic hydrocarbon oil (C), synthetic ether oil (D) and mineral oil (E). Advantageously, according to the present invention, the polymer ester oil (A) accounts for 20 to 50% by weight of the total of the grease composition, the synthetic ester oil (B) accounts for 10 to 30% by weight of the total of the grease composition, the synthetic hydrocarbon oil (C) accounts for 2 to 10% by weight of the total of the grease composition, and synthetic ether oil (D) accounts for 10 to 30% by weight of the total of the grease composition.
The grease composition of the present invention may contain various additives that are commonly used for greases. Such additives include additives commonly used for a grease composition, namely antioxidants such as phenyl-α(β)-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.
Specific embodiments will be discussed next; however, the present invention should not be restricted by them.
As a thickener, lithium soap synthesized from lithium hydroxide, a long-chain fatty acid mixture with 26 to 32 carbon atoms containing 28-carbon-atom montanic acid as a substantial component, stearic acid and 12-hydroxystearic acid was employed.
As a base oil, polymer ester oils with a viscosity (40° C.) of approximately 800 mm2/s (Examples 1-6) and of approximately 140 mm2/s (Examples 7-10) were used. As a synthetic ester oil, a tetraester oil (pentaerythritol ester) was used.
As a synthetic hydrocarbon oil, poly-α-olefin oil was adopted.
As a synthetic ether oil, an alkyl diphenyl ether oil was adopted.
Moreover, alkyl diphenylamine was employed as an antioxidant, and calcium sulphonate was employed as an anticorrosive agent.
The components were mixed in ratios as shown in Table 1, and heated to 220 to 230° C. while agitating until the entire mixture became fluid. Each was poured into a stainless container so as to have a thickness of 3 to 5 mm and cooled to 50° C. or lower, and a grease composition was obtained by homogenizing with a three-roll mill. The component ratios of the grease compositions and the results of the tests are indicated in Table 1.
In the same manner as in the Examples 1 to 10, comparative grease compositions 1-4 were prepared by mixing various components. Two commercially available greases with known base oils and thickeners were used as comparative examples 5 and 6, as shown in Table 2. In Table 2, the symbol ++ denotes a component that is mixed in.
The results of the tests are shown in Table 2.
The base oil viscosity (40° C.) was obtained on the basis of JIS K2283, while the mixture thickness was obtained on the basis of JIS K2220 7. 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, whereupon their 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 rotation frequency of 3000 min−1 under an atmosphere temperature of 100° C. Regarding the acoustic properties, the Anderon values were measured using an Anderon meter before and after the bearing rotation test. 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 were listed in Table 1 (examples) and Table 2 (comparative examples). A smaller Anderon values indicates greater acoustic properties, and a smaller volatile amount is superior in performance.
The heat resistance test was carried out by the oil film measurement method utilizing optical interference method. A thicker oil film with a higher temperature is superior. An oil film measurement device is shown in
After applying a test grease on a disk, the measurement is carried out in a point contact state, by rotating the disk under a load from under a ball in a direction toward the bottom surface of the disk. (See Tribology Conference Abstracts for the Japanese Society of Tribologists, Tokyo 1997-5, p. 328.)
The following is the measurement conditions:
Load 20N (maximum hertz pressure 0.53 GPa, osculating circle diameter 0.27 mm)
Rotational speed 1.7 m/s (corresponding to 3000 min−1 with a Model 608 bearing) Temperature 120° C.
Ball bearing steel ball (¾ inch in diameter)
Disk chromium/silica deposition glass disk, 10 cm in diameter
The evaluation was made on 4-level scale. “A” is particularly favorable, “B” is favorable, “C” is average, and “D” is poor.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-227306 | Aug 2004 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US05/27542 | 8/1/2005 | WO | 00 | 3/16/2007 |
