JP2003231893A - Grease composition, rolling bearing and spindle motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a grease composition which has especially excellent low torque performance, anti-fretting performance and low outgas performance in comparison with conventional greases, and to provide a rolling bearing and a spindle motor. <P>SOLUTION: This grease composition comprises a thickener comprising a specific alkali metal salt or alkaline earth metal salt, a base oil comprising two carbonic esters having different kinematic viscosities, and an organic sulfonate. A rolling bearing filled with the grease composition. A spindle motor equipped with the rolling bearing. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a grease composition,
The present invention relates to a rolling bearing containing the grease composition, and further to a spindle motor using the rolling bearing. In particular, the present invention relates to the grease composition, rolling bearing, and spindle motor, which are suitable for applications in which relatively small rolling bearings are used, such as small motors for information equipment and small motors for household appliances.

[0002]

2. Description of the Related Art As a grease filled in a ball bearing of a spindle motor of a recording device such as a hard disk of a computer or a CD-R, which is one of the objects of the present invention, for example, a low friction coefficient and extension of acoustic life are provided. For the purpose, a lubricating grease composition has been proposed in which 50 to 100% by mass of the base oil is composed of a carbonate compound and the thickener is composed of lithium soap and the like (Japanese Patent Laid-Open No. 2000-26875).
Issue). In addition, there is little dust generation (scattering), small torque, excellent acoustic characteristics, and for the purpose of extending the life, carbonic acid ester compounds, alkali metal hydroxides or alkaline earth metal hydroxides, and carbon. Lubricating grease compositions containing a thickener synthesized from a higher fatty acid having a number of 10 or more or a higher hydroxy fatty acid having a carbon number of 10 or more and having one or more hydroxyl groups are also known (JP-A 2000-6).
3874 publication).

Generally, a storage device such as an HDD (hard disk drive) or FDD (floppy (registered trademark) disk drive) of a computer, a CDD (compact disk drive), a MOD (optical disk drive), a VTR (video tape recorder), etc. The required performances of the bearings used around the information equipment include low torque, excellent acoustic performance, long life, and less grease dust (scattering). In particular, in these information devices used in a clean atmosphere, minute particles of gaseous oil and grease that scatter from the inside of the bearing during rotation contaminate the surface of the disk and cause malfunctions. It is important to suppress the amount of scattering, and the present inventors have conducted various studies. Furthermore,
Recently, especially in rolling devices such as rolling ball bearings and roller bearings incorporated in information equipment, when the information equipment is carried out or carried in, or when the information equipment is carried, 5-1
A phenomenon called "fretting", in which a race surface with a ball or a roller in a bearing is damaged and deteriorated by vibration of a low frequency of about 0 hertz, has become an important problem. When fretting occurs, not only the acoustic characteristics of rolling ball bearings or roller bearings deteriorate, but also the performance of information equipment itself is adversely affected.

Further, in the conventional bearings for electric motors such as household electric appliances, various studies have been conducted in order to develop bearings having a small loss due to friction, a small noise, and a long life. In recent years, especially global environmental issues have been highlighted, and developed countries are obliged to make efforts to reduce wasteful energy consumption as much as possible. Various proposals have been made for bearings used in all fields and improvements have been made, but there is still room for improvement in order to reduce energy loss.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has heretofore been widely used in HDDs and air conditioner motors. It is an object of the present invention to provide a grease composition, a rolling bearing, and a spindle motor, which are particularly excellent in low torque performance, fretting resistance performance, and low outgas performance, as compared with the grease as exemplified above.

[0006]

In order to achieve the above object, the present invention provides (A) an alkali metal hydroxide or an alkaline earth metal hydroxide and a higher fatty acid having 10 or more carbon atoms or 1. Alkali metal salt or alkaline earth metal salt synthesized from higher fatty acid having 10 or more hydroxyl groups and 10 or more carbon atoms, (B) general formula: R ¹ -O- (CO) -OR ² (R
¹ , R ² is a hydrocarbon group having 13 to 15 carbon atoms and may be the same or different, and has a kinematic viscosity at 40 ° C. of 16 to ²⁰ mm ² / s, a carbonate compound (C).
General ^{formula: R 3 -O-CO-R} 4 (R 3, R 4 is 17 carbon atoms
20 hydrocarbon groups, which may be the same or different) and have a kinematic viscosity at 40 ° C. of 24 to 36 mm.
A grease composition comprising a carbonic acid ester compound of ² / s, (D) an organic sulfonic acid metal salt having an alkali metal, an alkaline earth metal or zinc as a metal species. The grease composition described above is encapsulated. Rolling bearings characterized by the above-mentioned rolling bearings.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to the drawings.

(Grease Composition) In the grease composition of the present invention, the above-mentioned component (A) is a thickening agent, and comprises an alkali metal hydroxide or an alkaline earth metal hydroxide and a carbon number of 10 or more. It is obtained by synthesizing a higher fatty acid or a higher fatty acid having 10 or more hydroxyl groups and having 10 or more carbon atoms. Specifically, undecanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, montanic acid, saturated fatty acids such as melissic acid, decenoic acid, undecenoic acid, dodecenoic acid. Unsaturated fatty acids such as tetradecenoic acid, hexadecenoic acid, octadecenoic acid, eicosenoic acid, docosenoic acid, tetracosenoic acid, hexacosenoic acid, and triacontenoic acid, naphthenic acid, or hydrocarbon chains of the above fatty acids such as 12-hydroxystearic acid. Examples thereof include a metal soap obtained by a saponification reaction of a fatty acid having a hydroxyl group and a metal hydroxide. As the metal, alkali metals such as lithium, sodium and potassium, and alkaline earth metals such as magnesium, calcium, strontium and barium are used. Above all, it is preferable to use lithium 12-hydroxystearate or lithium stearate alone or in combination, whereby the acoustic characteristics can be improved, the torque can be reduced, and the dropping point can be increased.

The compounding amount of the component (A) is preferably 5 to 25 mass% with respect to the total amount of grease. If it is less than 5% by mass, the grease is too soft and there is a problem such as leakage, which is not suitable for bearing encapsulation. On the other hand, if it exceeds 25% by mass, it becomes too hard, which makes it difficult to fill a certain amount in the bearing and causes an increase in torque.

In the present invention, the above components (B) and (C) are mixed to form a base oil. The component (B) is a carbonate compound represented by the general formula: R ¹ —O— (CO) —O—R ^2, where R ¹ and R ² have 13 to 15 carbon atoms.
Hydrocarbon groups, which may be the same or different. Moreover, the kinematic viscosity at 40 ° C. of the component (B) alone is 1
It is 6 to ²⁰ mm ² / s, preferably 17 to 19 mm ² / s.

On the other hand, the component (C) has the general formula: R ¹ --O--
It is a carbonic acid ester compound represented by (CO) -OR ² and R ³ and R ⁴ in the formula are hydrocarbon groups having 17 to 21 carbon atoms and may be the same or different. Also, this (C)
The kinematic viscosity of the components alone at 40 ° C is 24-36 mm ² /
s, preferably 28 to 32 mm ² / s.

The blending amounts of the component (B) and the component (C) are preferably 7 to 40% by mass of the component (B) and 40 to 70% by mass of the component (C) in the total amount of grease. Also,
The mixing ratio of the component (B) and the component (C) is (B):
(C) = 1: 9 to 5: 5, particularly preferably 3: 7 to 2: 8. In this mixing ratio, as the amount of the component (B) increases, the base oil as a whole is more likely to volatilize, and outgas may increase. Further, as the amount of the component (B) decreases, the fretting resistance tends to decrease.

In the present invention, the above-mentioned component (D) is an essential additive and has the function of enhancing the adhesion of grease.
Therefore, the grease holding performance on the rolling element surface and the raceway surface is improved, and the fretting resistance and durability are improved.
Examples of the component (D) include the following general formulas (1) to
The organic sulfonate represented by (3) is preferable.

[0014]

[Chemical 1]

Here, R, R ¹ and R ² may be the same or different and each is a hydrocarbon group having 1 to 24 carbon atoms or a hydrogen atom. Me represents an alkali metal, an alkaline earth metal, or zinc.

Among these, metal salts of dialkylnaphthalenesulfonic acid represented by the above general formula (3), in which R ¹ and R ² have 8 to 10 carbon atoms and Me is barium, calcium or zinc, are preferable. . Particularly, the barium salt, calcium salt, and zinc salt of dinonylnaphthalenesulfonic acid having 9 carbon atoms are most suitable.

The blending amount of the component (D) is 0.5 to 10% by mass, preferably 1 to 8% by mass based on the total amount of the grease.
If the content of the component (D) is less than 0.5% by mass, the predetermined effect cannot be obtained, and even if it is added in an amount of more than 10% by mass, the fretting resistance and durability are not further improved and the torque and the outgas performance are adversely affected. Exert. From the balance of fretting resistance, torque and outgassing performance, the blending amount of component (D) is 1-
8 mass% is more desirable.

By adding an organic fatty acid derivative containing no metal having 10 or more carbon atoms to the grease composition of the present invention, vibration resistance can be improved without impairing other performances. . Specifically, undecanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, serotic acid, montanic acid, saturated fatty acids such as melicinic acid, decenoic acid, undecenoic acid, dodecenoic acid. , Tetradecenoic acid,
Unsaturated fatty acids such as hexadecenoic acid, octadecenoic acid, eicosenoic acid, docosenoic acid, tetracosenoic acid, hexacosenoic acid and triacontenoic acid, naphthenic acid, esters of 12-hydroxystearic acid and alkenylsuccinic acid with alcohols, or these Anhydrides, imides and the like can be preferably used. Among them, it is preferable to use an alkenylsuccinic acid ester or anhydride, or a derivative of a higher fatty acid having about 18 carbon atoms, alone or in a mixture.

The preferred amount of the organic fatty acid derivative added is 0.1 to 10% by mass based on the total amount of grease. 0.
If it is less than 1% by mass, the effect by addition is not obtained, and if it is added in excess of 10% by mass, no further effect is obtained.

Furthermore, in the grease composition of the present invention, as other components, an antioxidant, a copper corrosion inhibitor, an extreme pressure agent,
A rust preventive agent or the like can be added. Any of these may be known ones, and the addition amount thereof can be appropriately selected within a range that does not impair the effects of the present invention.

Although the consistency of the grease varies depending on the use, it is in the range of 150 to 350 when it is used for rolling bearings, and 180 to 300 is particularly preferable when it is used for rolling bearings of spindle motors.

(Rolling Bearing) The present invention also provides a rolling bearing containing the above grease composition. There is no limitation on the rolling bearing itself, and a ball bearing as shown in FIG. 1 can be exemplified. The illustrated ball bearing 1 includes a plurality of balls 1 with a cage 12 between an inner ring 10 and an outer ring 11.
3 is rotatably held, and the above grease composition is further enclosed in the bearing internal space S and sealed with a seal member 14 to have a schematic configuration.

In the present invention, it is preferable that the amount of the grease composition enclosed is an amount that occupies 5 to 35% of the bearing internal space S. If it is less than 5%, the durability may be shortened, and if it exceeds 35%, the stirring resistance of the grease is increased, and the low torque property may be impaired.

(Spindle Motor) The present invention further provides a spindle motor provided with the above-mentioned rolling bearing. There are no restrictions on the type of spindle motor, and although not shown in the drawings, for example, the above-mentioned HDD, FDD, CD-RC
A spindle motor incorporated in a DD, MOD, VTR or the like can be exemplified.

[0025]

EXAMPLES The present invention will be further described below with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

(Preparation of Test Grease) The composition of each test grease of Examples 1 to 7 and Comparative Examples 1 to 5 is as shown in Table 1. Incidentally, lithium stearate and lithium 12-hydroxystearate as the component (A), a carbonic acid ester having 13 to 15 carbon atoms as the component (B) (kinematic viscosity at 40 ° C. of 18 mm ² / s), and carbon as the component (C). The number is 1
7 to 20 carbonic acid ester (Kinematic viscosity at 40 ° C. 32 m
m ² / s), NA-SUL of King as component (D)
A series of sulfonates and alkylated diphenylamine (liquid) as antioxidant were used. Regarding the grease of Comparative Example 1, polyol ester oil was also used as the base oil.

In the preparation, first, the predetermined amounts (parts by weight) of the components (A), (B) and (C) are weighed,
The mixture was heated to 200 to 218 [deg.] C. with stirring and liquefied.
Then, the liquid material is poured into a stainless steel container so as to have a thickness of about 5 mm and cooled, and then the component (D), and further Table 1 are used.
Each of the organic fatty acid derivatives shown in (4) was added in a predetermined amount and kneaded so as to be uniform with a kneader. Then, the kneaded product was passed through a three-stage roll mill three times to homogenize it and then defoamed to obtain a test grease.

As a reference example, a commercially available grease 1,
I prepared 2. In Table 1, "+" indicates that the component is contained.

(Evaluation test) Inner diameter 5 mm, outer diameter 13 mm,
Ball bearings with a width of 3 mm and a plastic cage (see Fig. 1;
A test bearing was prepared by enclosing the above test grease in a bearing number B5-39 manufactured by NSK Ltd. so as to occupy 15% by volume of the inner space of the bearing. Then, each test shown below was performed using the test bearing.

(1) Noise As shown in FIG. 2, a pair of test bearings A were mounted on the shaft 21 of the motor 23 and fixed by the casing 22. Then, at room temperature, the inner ring of the test bearing A was rotated at 5400 rpm for 2
After rotating for h, the noise at that time was measured by a microphone at a position 50 cm away from the spindle.

(2) Acoustic durability The inner ring of the test bearing A was set to 5 in an atmosphere of 60 ° C. and 90% RH.
After rotating at 400 rpm for 500 hours, noise was measured at room temperature in the same manner as (1) above.

(3) Torque and Torque Fluctuation Using the torque measuring device shown in FIG. 3, the torque and torque fluctuation of the test bearing were measured. In FIG. 3, the test bearing A has an inner ring fixed to the air spindle 31 via an arbor 32, and an outer ring fixed to an aluminum cap 34 having an air bearing 33. And the air spindle 3
When 1 is rotated, the inner ring of the test bearing A also rotates, and the torque value at that time is measured by the strain gauge 35 connected to the aluminum cap 34, and the measured value is the strain amplifier 36.
And is recorded by the recorder 38 via the low-pass filter 37. The test was conducted at room temperature with the inner ring at 5400 rpm for 2
After rotating for a period of time, it was further rotated at room temperature at 5400 rpm for 1 hour, and the fluctuation range of the torque was obtained.

(4) Grease reduction (outgas, scattering) After the acoustic durability test (2) above was completed, the weight of the test bearing A was measured to obtain the weight difference from that before the test.

(5) Anti-fretting performance The fretting resistance of the test bearing was evaluated using the fretting test device shown in FIG. The test equipment shown is
A drive mechanism 41 attached to the frame 40 and including a drive source such as an AC servomotor, a fixed shaft 42 fixed to the frame 40, and a lower end 43 of the drive shaft 4 of the drive mechanism 41.
4, and an outer cylinder 45 that is driven to rotate about the axis by the driving force of the driving mechanism 41. The fixed shaft 42 is inserted into the outer cylinder 45, and the lower end portion thereof is supported by the outer cylinder 45 via a support bearing 46. An upper end portion of the fixed shaft 42 is supported by a preload spring mechanism 47, and a bearing fixing portion 48 under test is provided at an intermediate portion between the upper end portion and the lower end portion thereof. The inner races of the plurality of test bearings A are fixed to the bearing under test fixing portion 48, and the outer races of the respective test bearings A are fixed to the outer cylinder 45. The preload spring mechanism 47 presses the fixed shaft 42 from its upper end with a predetermined pressure,
The test bearing A is configured to be preloaded. During the fretting test, the test bearing A is preloaded by the preload spring mechanism 47, and the outer cylinder 45 is driven by the drive mechanism 41.
The test bearing A is oscillated by the oscillating outer cylinder 45 by oscillating the shaft around its axis at a predetermined cycle and a predetermined number of times. As an index for evaluating the fretting resistance, the average torque before and after the fretting test and the torque fluctuation range were measured, and the measured values were compared. The test conditions are as follows.・ Frequency: 18Hz ・ Preload: 9.8N ・ Swing angle: 2 ° ・ Test time: 2 hours

In each of the above test results, the level of the commercially available grease 1 is D, and the more superior one is C (+
1), more excellent is B (+2), particularly excellent is A (+3), and inferior to D is E (-1).
Points), and these total points were calculated. The results are also shown in Table 1.

[0036]

[Table 1]

As shown in Table 1, in each of the examples according to the present invention, in addition to excellent comprehensive evaluation, generally excellent results are obtained in terms of each test item.

FIG. 5 shows the relationship between the content of the organic sulfonic acid metal salt in the grease and the anti-fretting performance, torque and outgas characteristics. In addition, when the content of the organic sulfonic acid metal salt is 2.5% by mass, anti-fretting,
The torque and outgas characteristics are set to 1 and are shown by their relative values. As shown in the drawing, with respect to anti-fretting performance, good results have been obtained when the content of the organic sulfonic acid metal salt is 0.5% by mass or more, particularly 1% by mass or more. Further, generation of outgas can be suppressed by setting the content of the organic sulfonic acid metal salt to 10% by mass or less, preferably 8% by mass or less. Regarding the torque, the content of the organic sulfonic acid metal salt is 10% by mass or less,
It can be suppressed to a small level by preferably setting it to 8% by mass or less. From these, it can be said that the content of the organic sulfonic acid metal salt is preferably 0.5 to 10% by mass, particularly preferably 1 to 8% by mass.

[0039]

As described above, according to the present invention,
In particular, a grease composition excellent in low torque performance, fretting resistance performance, and low outgas performance can be obtained. Further, by enclosing the grease of the present invention, a rolling bearing excellent in low torque performance, anti-fretting performance and low outgas performance can be obtained, and further, a spindle motor having these various performances can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing a ball bearing which is an embodiment of a rolling bearing of the present invention.

FIG. 2 is a cross-sectional view showing a configuration of a motor tester used in an example.

FIG. 3 is a cross-sectional view showing a configuration of a torque measuring device used in an example.

FIG. 4 is a cross-sectional view showing a configuration of a fretting test device used in an example.

FIG. 5 is a graph showing the relationship between the content of the organic sulfonic acid metal salt obtained in the example and the anti-fretting performance, torque and outgas characteristics.

[Explanation of symbols]

1 ball bearing 10 inner ring 11 outer ring 12 cage 13 balls 14 Seal member

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F16C 33/66 F16C 33/66 Z H02K 5/173 H02K 5/173 A // C10N 10:02 C10N 10: 02 10:04 10:04 20:02 20:02 40:02 40:02 40:04 40:04 50:10 50:10 (72) Inventor Yasunobu Fujita 1-5-50 Kumeiuma Kuminuma, Fujisawa City, Kanagawa Prefecture Within Japan Seiko Co., Ltd. (72) Inventor Michiharu Naka, 1-5-50 Kumei, Kugenuma, Fujisawa-shi, Kanagawa Within Japan Seiko Co., Ltd. (72) Takehiro Kudo 1-5-50, Kumei, Kugenuma, Fujisawa-shi, Kanagawa Japan Seiko Co., Ltd. (72) Inventor Hirotoshi Miyajima 1-5-50, Kuminuma Shinmei, Fujisawa-shi, Kanagawa Nippon Seiko Co., Ltd. F-term (reference) 3J101 AA03 AA32 AA42 AA62 CA40 EA63 FA35 FA41 FA60 GA24 4H104 AA13R BB17B BB17R BB19B BB37A BG06C EA02A FA01 FA02 PA01 QA18 5H605 AA05 BB05 CC04 EB10 EB23

Claims (5)

[Claims] 1. Synthesized from (A) a hydroxide of an alkali metal or a hydroxide of an alkaline earth metal and a higher fatty acid having 10 or more carbon atoms or a higher fatty acid having 10 or more carbon atoms and having one or more hydroxyl groups. Alkali metal salt or alkaline earth metal salt, (B) General formula: R ¹ —O— (CO)
-O-R ² (R ¹ and R ² are hydrocarbon groups having 13 to 15 carbon atoms and may be the same or different),
Carbonic acid ester compound having a kinematic viscosity at 16 ° C. of 16 to ²⁰ mm ² / s, (C) General formula: R ³ —O—CO—R ⁴ (R ³ , R ⁴
Is a hydrocarbon group having 17 to 21 carbon atoms, which may be the same or different, and has a kinematic viscosity at 40 ° C. of 2
A grease composition comprising a carbonic acid ester compound of 4 to 36 mm ² / s and (D) an organic sulfonic acid metal salt having an alkali metal, an alkaline earth metal or zinc as a metal species. 2. (A) is 5 to 25 mass% in the total amount of grease, (B) is 7 to 40 mass% in the total amount of grease, and (C)
The grease composition according to claim 1, wherein is contained in an amount of 40 to 70% by mass in the total amount of grease, and (D) is included in an amount of 0.5 to 10% by mass in the total amount of grease. 3. A base oil comprising (B) :( C) in a ratio of 1: 9 to 5: 5 and a mixture of (B) and (C) having a kinematic viscosity at 40 ° C. of 20 to 35 mm. The grease composition according to claim 1 or 2, wherein the grease composition is ² / s. 4. A rolling bearing comprising the grease composition according to claim 1 enclosed therein. 5. A spindle motor comprising the rolling bearing according to claim 4.