JP2002339994A - Rolling bearing for hard disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rolling bearing for a hard disk of low torque. SOLUTION: An inner ring 2 having an inner ring raceway surface 1 on an outer circumferential surface and an outer ring 4 having an outer ring raceway surface 3 on an inner circumferential surface are concentrically disposed, and a plurality of rolling bodies 5 are held between the inner ring raceway surface 1 and the outer ring raceway surface 3 by a holder 7 in a rolling manner. This rolling bearing for the hard disk is sealed with grease composition containing metallic soap thickener containing long fiber-like stuff of at least 3 μm in the length of a long diameter part in a base oil formed of mixed oil of a lubricating oil having a polar group in the molecular structure and a non- polar lubricating oil with the kinematic viscosity at 40 deg.C being 18-100 mm<2> /s.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling bearing for a hard disk drive (hereinafter referred to as "HDD"), and more particularly, to a rolling bearing for an HDD suitable for a high-speed rotating motion part such as a spindle motor and reducing the torque. .

[0002]

2. Description of the Related Art In the computer-related industry, the speed of technological innovation is high. In particular, HDDs have a short life span of one type, and new models (high-speed rotation, power saving,
High responsiveness, high accuracy, compactness, etc.) are being developed one after another. In particular, rolling bearings used in high-speed rotating motion parts such as spindle motors require low torque to achieve high-speed rotation and power saving.

[0003] Therefore, in conventional rolling bearings for HDDs, an ester oil is used as a base oil and a lithium soap / ester oil-based grease in which lithium soap is blended as a thickener, or a mixture of an ester oil and an ether oil as a base oil. Lithium soap using oil as a thickener with lithium soap
Rolling bearings containing ester / ether oil-based grease are widely used. These greases generally have a base oil kinematic viscosity of 26 to 53 mm ² / s (40 ° C.) and a consistency of about 240 to 260.

[0004]

The torque of a rolling bearing is generated by friction due to minute sliding of a rolling contact surface, sliding friction at a sliding contact portion in a bearing, and viscous resistance of grease. It is known that the viscosity resistance of grease is affected by the kinematic viscosity of the base oil and the consistency of the grease, and a decrease in the kinematic viscosity of the base oil and an increase in the consistency cause a decrease in the viscosity resistance of the grease. It is valid.

[0005] However, when the kinematic viscosity of the base oil is reduced, the oil film thickness on the lubricating surface is reduced, which may cause a problem in lubrication performance. In addition, base oils having a low kinematic viscosity generally have low heat resistance, which causes a problem in durability.

[0006] Further, although reducing the amount of grease enclosed is also effective in reducing torque, it may cause poor lubrication.

In recent years, miniaturization of HDDs has been progressing, and
Rolling bearings having an outer diameter of 15 mm or less and an outer diameter of 15 mm or less are also used. In such small rolling bearings, low torque is particularly required for high-speed rotation.

The present invention has been made in view of such circumstances, and has as its object to provide a low torque HDD rolling bearing.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, have found a thickener having a specific shape and a base oil to be combined therewith, and have completed the present invention. Reached.

That is, an object of the present invention is to provide an inner ring having an inner ring raceway surface on an outer peripheral surface and an outer ring having an outer ring raceway surface on an inner peripheral surface concentrically. A plurality of rolling elements are rollably held by a retainer between
And a mixed oil of a lubricating oil having a polar group in its molecular structure and a non-polar lubricating oil, and having a kinematic viscosity at 40 ° C of 18 to 1
An HDD comprising a base oil of 00 mm ² / s and a grease composition containing a metal soap-based thickener containing a long fibrous material having a major axis of at least 3 μm in length. This is achieved by using rolling bearings.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings.

The structure of the rolling bearing for HDD of the present invention is not particularly limited. For example, a ball bearing shown in a sectional view in FIG. 1 can be exemplified. That is, an inner race 2 having an inner raceway surface 1 on the outer peripheral surface and an outer race 4 having an outer raceway surface 3 on the inner peripheral surface are arranged concentrically.
A plurality of balls 5, which are rolling elements, are held between the outer raceway surface 3 and the outer raceway surface 3 by a retainer 7, and a grease composition (not shown) described later is sealed by a seal member 6. It is schematically configured. Further, the seal member 6 prevents foreign matter from entering from outside.

The base oil of the grease composition to be encapsulated is a mixed oil of a lubricating oil having a polar group in its molecular structure (hereinafter referred to as "polar group-containing lubricating oil") and a non-polar lubricating oil. As the polar group-containing lubricating oil, a lubricating oil having an ester structure or a lubricating oil having an ether structure is preferable.

The lubricating oil having an ester structure is not particularly limited, but is obtained from a diester oil or a carbonate ester oil obtained from a reaction between a dibasic acid and a branched alcohol, and a lubricating oil obtained from a reaction between an aromatic tribasic acid and a branched alcohol. Aromatic ester oils, polyol ester oils obtained from the reaction between monobasic acids and polyhydric alcohols, and the like.
These may be used alone or in combination of two or more. less than,
Illustrate each preferred specific example

As diester oils, dioctyl adipate (DOA), diisobutyl adipate (DIB)
A), dibutyl adipate (DBA), dioctyl adipate (DOZ), dibutyl sebacate (DBS), dioctyl sebacate (DOS), methyl acetyl ricinoleate (MAR-N) and the like.

Examples of the aromatic ester oil include toluoctyl trimellitate (TOTM), tridecyl trimellitate, tetraoctyl pyromellitate and the like.

Examples of the polyol ester oil include those obtained by appropriately reacting a polyhydric alcohol shown below with a monobasic acid. The monobasic acid reacted with the polyhydric alcohol may be used alone or in combination. Further, it may be used as a complex ester which is an oligoester of a polyhydric alcohol and a mixed fatty acid of dibasic acid / monobasic acid. Examples of the polyhydric alcohol include trimethylolpropane (TMP), pentaerythritol (PE), dipentaerythritol (DPE), neopentyl prechol (NPG), and 2-methyl-2-propyl-1,3-
And propanediol (MPPD). As the monobasic acid, mainly univalent fatty acid C ₄ -C ₁₆ are used. Specifically, butyric acid, valeric acid, caproic acid,
Caprylic acid, enanthic acid, pelargonic acid, capric acid,
Undecanoic acid, lauric acid, mysteric acid, palmitic acid, tallow fatty acid, sialic acid, caproleic acid, palmitoleic acid, petroselinic acid, oleic acid, elaidic acid, asclepinic acid, vaccenic acid, sorbic acid, linoleic acid, linolenic acid, avininic acid And ricinoleic acid.

As the carbonate oil, those having a straight-chain or branched alkyl group having 6 to 30 carbon atoms are preferred.

Further, as a lubricating oil having an ether structure, for example, (di) alkyldiphenyl ether oil,
(Di) alkyl polyphenyl ether oil, polyalkylene glycol oil, and the like.

The above polar group-containing lubricating oils may be used alone or in combination. Further, in consideration of torque characteristics and acoustic durability, polyol ester oils and aromatic ester oils are particularly preferable.

On the other hand, as the nonpolar lubricating oil, mineral oil, synthetic hydrocarbon oil or a mixed oil thereof can be used. Specifically, mineral oils include paraffinic mineral oils and naphthenic mineral oils, and synthetic hydrocarbon oils include poly-α-olefin oils. Among them, a synthetic hydrocarbon oil is preferable in consideration of acoustic durability.

The above-mentioned polar group-containing lubricating oil and non-polar lubricating oil are preferably blended so that the polar group-containing lubricating oil accounts for 5 to 70% by weight, especially 10 to 70% by weight of the total amount of the base oil. If the content of the polar group-containing lubricating oil is less than 5% by mass,
A sufficient effect on acoustic durability and torque reduction cannot be obtained. As described later, in the grease composition of the present invention, upon its production, a metal soap-based thickener containing long fibrous materials is synthesized in advance in a non-polar lubricating oil, and after dissolving, a gel body is produced. The gel body and the lubricating oil containing a polar group are mixed. Therefore, when the amount of the polar group-containing lubricating oil exceeds 70% by mass, the amount of the non-polar lubricating oil is too small, which adversely affects the synthesis of the metal soap-based thickener.

The kinematic viscosity of a base oil obtained by blending a polar group-containing lubricating oil and a non-polar lubricating oil is 18 to 100 mm ² /
s (40 ° C.), especially 18 to 80 mm ² / s
(40 ° C.) is preferable. In order to smoothly carry out the above-mentioned production method, the polar group-containing lubricating oil should be 200 to 50.
It is preferable to use one having a kinematic viscosity of 00 mm ² / s (40 ° C.).

The thickener compounded in the base oil has a long diameter.
Soap containing long fibrous material whose part is at least 3 μm
It is. In particular, the type of metal soap is monovalent or
// Divalent organic fatty acids or organic hydroxy fatty acids
And organic fatty acid metal obtained by synthesizing metal hydroxide
Salts or metal salts of organic hydroxy fatty acids are preferred. Organic
The fatty acid is not particularly limited, but may be lauric acid (C
₁₂), Myristic acid (C ₁₄), Palmitic acid (C₁₆),
Margaric acid (C₁₇), Stearic acid (C₁₈), Arakiji
Acid (C₂₀), Behenic acid (C_{twenty two}), Lignoceric acid (C
_{twenty four}), Tallow fatty acid and the like. Also, organic hydro
9-hydroxystearic acid, 1
0-hydroxystearic acid, 12-hydroxystearic
Phosphoric acid, 9,10-dihydroxystearic acid, ricino
And ricinoleic acid and the like. on the other hand,
Aluminum, barium, calcium
Hydroxides such as sodium, lithium and sodium
It is.

The combination of the above-mentioned organic fatty acid or organic hydroxy fatty acid with a metal hydroxide is not particularly limited. However, stearic acid, tallow fatty acid or hydroxystearic acid (particularly, 12-hydroxystearic acid), The combination with lithium oxide is preferable because of excellent bearing performance. Further, if necessary, a plurality of types can be used in combination.

In order to obtain a metal soap-based thickener containing a long fibrous material having a long diameter of at least 3 μm, the above organic fatty acid or organic hydroxy fatty acid and a metal hydroxide are mixed with a non-polar non-polar base oil component. React in lubricating oil. The conditions for producing long fibrous materials are not particularly limited, but the following production method is mentioned as an example.

That is, hydroxystearic acid is dissolved in a synthetic hydrocarbon oil and reacted with lithium hydroxide to produce lithium soap. Then, add this lithium soap to 2
Heat above 10 ° C and dissolve in base oil. After cooling, the temperature is once held at 200 ° C. for about 60 minutes, and then slowly cooled to 140 ° C. at a rate of 1 ° C./min. And 140 ° C
At this point, additional base oil heated to 140 ° C. is added, and a three-stage roll mill is applied to obtain a grease containing the intended long-fiber thickener. The amount of the thickener may be 5 to 20% by mass as in the case of the conventional grease composition, and the amount of the organic fatty acid or hydroxy fatty acid or metal hydroxide is appropriately selected.

The obtained metal soap has a long diameter part of 3 μm.
Although the above-mentioned long fibrous materials are contained, the proportion thereof preferably accounts for 30% by mass or more of the total amount of the thickener, and if it is less than that, a sufficient effect for reducing the bearing torque cannot be obtained. Further, it is preferable that the long diameter portion of the long fibrous material is 3 μm or more. However, if the long diameter portion of the long fibrous material is too long, the vibration when entering the contact surface of the rolling bearing during rotation becomes large, and particularly has an adverse effect on the initial acoustic characteristics. Therefore, the upper limit of the long diameter portion is 10 μm or less. Is preferred. The minor diameter portion is not particularly limited, but is less than 1 μm. The proportion of these long fibrous materials,
The dimensions of the major axis and the minor axis can be controlled by appropriately selecting the above reaction conditions.

In order to measure the major axis and the minor axis of the metal soap-based thickener synthesized as described above, the dispersion is diluted with a solvent such as hexane and adhered to a copper mesh on which a collodion film is adhered. Then, observation may be performed with a transmission electron microscope at a magnification of about 6000 to 20,000 times.

The dispersion is cooled to about room temperature to form a gel, and the obtained gel is kneaded with a polar group-containing lubricating oil to obtain a grease composition. FIG.
FIG. 2A is an electron micrograph (600) showing the grease composition obtained in Example 1 described below and according to the above-mentioned production method, and FIG. 2B is a grease composition also obtained in Comparative Example 2.
(0 times), but it can be seen that in the grease composition shown in FIG. 2 (A), the fiber length of the thickener is significantly longer.

If necessary, the following additives known in the art can be added to the grease composition. These additives can be added to the polar group-containing lubricating oil in the above-described production process and kneaded with the gel body to be incorporated into the grease composition.

[Antioxidant] As the antioxidant, an antioxidant, an ozone deterioration inhibitor and an antioxidant to be added to rubber, plastic, lubricating oil and the like are appropriately selected and used. For example, phenyl-1-naphthylamine, phenyl-2-naphthylamine, diphenyl-p-phenylenediamine,
Dipyridylamine, phenothiazine, N-methylphenothiazine, N-ethylphenothiazine, 3,7-dioctylphenothiazine, p, p'-dioctyldiphenylamine, N, N'-diisopropyl-p-phenylenediamine, N, N'-di-sec Amine compounds such as -butyl-p-phenylenediamine, 2,6-di-tert
-Phenol compounds such as dibutyl phenol can be used.

[Rust inhibitors / metal deactivators] As rust inhibitors, for example, ammonium salts of organic sulfonic acids, alkali metals such as barium, zinc, calcium and magnesium;
Alkaline earth metal organic sulfonates, organic carboxylates, phenates, phosphonates, alkyl or alkenyl succinate esters and other alkyl, alkenyl succinic acid derivatives, polyhydric alcohol partial esters such as sorbitan monooleate, oleoyl monkey Hydroxy fatty acids such as cosin, mercapto fatty acids such as 1-mercaptostearic acid or metal salts thereof, higher fatty acids such as stearic acid, higher alcohols such as isostearyl alcohol, esters of higher alcohols and higher fatty acids,
2,5-dimercapto-1,3,4-thiadiazole,
Thiazoles such as 2-mercaptothiadiazole;
Imidazole compounds such as (decyldithio) -benzimidazole and benzimidazole, or 2,5-
A disulfide compound such as bis (dodecyldithio) benzimidazole, a phosphoric acid ester such as trisnonylphenyl phosphite, and a thiocarboxylic acid ester compound such as dilaurylthiopropionate can be used. Further, nitrite and the like can also be used.

As the metal deactivator, for example, triazole compounds such as benzotriazole and tolyltriazole can be used.

[Oily Agent] As the oil agent, for example, fatty acids such as oleic acid and stearic acid, fatty acid alcohols such as oleyl alcohol, fatty acid esters such as polyoxyethylene stearic acid ester and polyglyceryl oleate, phosphoric acid, tricresyl Phosphate such as phosphate, laurate or polyoxyethylene oleyl ether phosphoric acid can be used.

The torque reducing effect of the grease composition configured as described above is presumed to be due to the following effects.

That is, since the thickening agent contains a long fiber having a major axis of 3 μm or more, the long fiber shows an orientation by shearing during rotation of the bearing, and reduces the bearing torque.
This effect is even greater when combined with a non-polar lubricating oil. In addition, since a polar group-containing lubricating oil is blended in the base oil, the polar group-containing lubricating oil acts in the same manner as a conventional polar group-containing base oil (e.g., ester oil), and the contact surface of the bearing rotating portion To reduce the bearing torque by forming a suction film by improving the frictional characteristics. In addition, the polar group of the polar group-containing lubricating oil interacts with the micellar structure of the metallic soap, and in particular, weakens the bonding force between long fibrous objects, reduces the shear resistance of grease during bearing rotation, and reduces bearing torque. Further reduce.

Such a torque reduction effect is particularly effective in a small-sized HDD rolling bearing having an inner diameter of 6 mm or less and an outer diameter of 15 mm or less.

[0039]

The present invention will be further described with reference to the following examples. Example 1 78 g of 12-hydroxystearic acid and 6.2 g of lithium hydroxide were reacted in 552 g of poly-α-olefin oil (hereinafter referred to as “PAO”) to produce 80 g of lithium soap, After cooling to a gel body, the gel body was kneaded with 368 g of a polyol ester oil (hereinafter referred to as “POE”) to prepare a grease composition. This grease composition was diluted with hexane, adhered to a copper mesh on which a collodion film was adhered, and observed using a transmission electron microscope. As shown in FIG. 2A, the grease composition had a long diameter portion of 3 to 10 μm. Long fibrous material was confirmed.

Example 2 170 g of lithium soap was produced by reacting 168 g of stearic acid and 14.2 g of lithium hydroxide in 705 g of PAO, and cooled to room temperature to form a gel. Body and 125g PO
E was kneaded to prepare a grease composition. When this grease composition was observed using a transmission electron microscope in the same manner as in Example 1, a long fibrous material having a long diameter portion of 3 to 10 μm was confirmed.

Example 3 116 g of stearic acid and 9.8 g of lithium hydroxide were reacted in 528 g of PAO to produce 120 g of lithium soap, and cooled to room temperature to form a gel. Body and 26g POE
And a mixed oil of 106 g of diphenyl ether oil were kneaded to prepare a grease composition. When this grease composition was observed using a transmission electron microscope in the same manner as in Example 1, a long fibrous material having a long diameter portion of 3 to 10 μm was confirmed.

(Comparative Example 1) 110 g of stearic acid and 9.8 g of lithium hydroxide were reacted in 880 g of PAO to produce 120 g of lithium soap, and cooled to room temperature to prepare a grease composition. When this grease composition was observed using a transmission electron microscope in the same manner as in Example 1, a fibrous long fiber having a long diameter portion of 3 to 10 μm was confirmed.

Comparative Example 2 99 g of 12-hydroxystearic acid and 7.9 g of lithium hydroxide were combined with 900 g of P
Reacting in OE to produce 100 g of lithium soap,
The grease composition was prepared by cooling to room temperature. When this grease composition was observed using a transmission electron microscope in the same manner as in Example 1, as shown in FIG. 2B, all of the grease compositions were short fibrous materials having a major axis of less than 1 μm.

Comparative Example 3 136 g of stearic acid and 11.5 g of lithium hydroxide were reacted in 860 g of PAO to produce 140 g of lithium soap, and cooled to room temperature to prepare a grease composition. When this grease composition was observed using a transmission electron microscope in the same manner as in Example 1, a fibrous long fiber having a long diameter portion of 3 to 10 μm was confirmed.

Comparative Example 4 130 g of lithium soap was produced by reacting 130 g of stearic acid and 10.8 g of lithium hydroxide in 870 g of POE, and cooled to room temperature to prepare a grease composition. Observation of this grease composition using a transmission electron microscope in the same manner as in Example 1 revealed that all of the grease compositions were short fibrous materials having a major axis of less than 1 μm.

Comparative Example 5 A grease composition containing a mixed oil of POE and diester oil and lithium soap, which is widely used in conventional rolling bearings for HDDs, was prepared. When this was observed using a transmission electron microscope in the same manner as in Example 1, all of the fibers were short fibrous materials having a major axis of less than 1 μm.

Table 1 summarizes the composition of each component of the above Examples and Comparative Examples and the physical properties (base oil kinematic viscosity, mixing consistency, and fiber structure of the thickener) of the obtained grease compositions.

[0048]

[Table 1]

(Experiment 1: Torque Test) A torque test was performed using the measuring device shown in FIG. In this measuring device, a test bearing 11 is mounted on a shaft 12 connected to an air-spindle 14 via an arbor 15 and is fixed to an aluminum cap 16 on an outer ring. In addition, aluminum cap 1
An air bearing 17 is disposed above 6 and supports the whole. Then, the test bearing 11 is rotated by the air spindle 14, the torque generated at that time is detected by the strain gauge 13, and the output is recorded by a recorder via a strain amplifier and a low-pass filter.

In the test, a ball bearing with a non-contact rubber seal having an inner diameter of 6 mm, an outer diameter of 15 mm, and a width of 5 mm equipped with an iron cage was used as the test bearing 11, and each grease composition of the examples and comparative examples was used for this. 10mg sealed, 15000r
The torque was measured by rotating the inner ring at pm. The measurement was performed for 10 minutes after the start of rotation, and the results are shown in FIG. As shown in the figure, it was confirmed that the bearing torque was significantly reduced by enclosing the grease composition of each example.

(Experiment 2: Verification of Compounding Ratio of Polar Group-Containing Lubricating Oil) A grease composition was prepared by changing the compounding ratio of POE according to Example 2, and a torque test was performed according to Experiment 1. The torque was measured 10 minutes after the start of rotation. The results are shown in FIG. 5, and it is understood that extremely good torque characteristics can be obtained by blending POE in an amount of 5% by weight or more, particularly 10% by weight or more and 70% by weight or less.

(Experiment 3: Verification of kinematic viscosity of base oil)
, The grease composition was prepared by changing the kinematic viscosity of the base oil, and a torque test was performed according to Experiment 1. The torque was measured 10 minutes after the start of rotation. Fig. 6 shows the results.
The kinematic viscosity of the base oil is 100 mm ² / s (40 ° C.)
It can be seen that by setting the following, the bearing torque is uniformly low, and extremely good torque characteristics can be obtained.

(Experiment 4; Verification of compounding ratio of long fibrous material of thickener) According to Example 2, a grease composition was prepared by changing the compounding ratio of long fibrous material of lithium soap. The test was performed. The torque was measured 10 minutes after the start of rotation. FIG. 7 shows the results. It can be seen that the bearing torque can be suppressed to a low level when the mixing ratio of the long fiber material is 30% by mass or more.

[0054]

As described above, according to the present invention,
A low-torque HDD rolling bearing is provided.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a rolling bearing for HDD according to the present invention.

FIG. 2 is an electron micrograph showing (A) a grease composition obtained in Example 1 and (B) a grease composition obtained in Comparative Example 2.

FIG. 3 is a schematic configuration diagram showing a measuring device used for performing a torque test in the example.

FIG. 4 is a graph showing a result of a torque test performed in Examples.

FIG. 5 shows an example of a polar group-containing lubricating oil (POE).
5 is a graph showing the relationship between the compounding ratio of P and bearing torque.

FIG. 6 is a graph showing a relationship between kinematic viscosity of base oil and bearing torque in Examples.

FIG. 7 is a graph showing the relationship between the blending ratio of long fibrous material of the thickener and the bearing torque in Examples.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inner ring raceway surface 2 Inner ring 3 Outer ring raceway surface 4 Outer ring 5 Ball 6 Seal member 7 Cage 11 Test bearing 12 Shaft 13 Strain gauge 14 Air spindle 15 Arbor 16 Aluminum cap 17 Air bearing

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C10M 107/34 C10M 107/34 117/02 117/02 117/04 117/04 169/02 169/02 / / C10N 10:02 C10N 10:02 10:04 10:04 10:06 10:06 20:02 20:02 20:06 20:06 B 40:02 40:02 50:10 50:10 (72) Invention Person Yasunobu Fujita 1-5-50, Kumeinuma Shinmei, Fujisawa-shi, Kanagawa F-term in NSK Ltd. (reference)

Claims (2)

[Claims] An inner ring having an inner raceway surface on an outer peripheral surface and an outer ring having an outer raceway surface on an inner peripheral surface are concentrically arranged, and a plurality of rolling elements are provided between the inner raceway surface and the outer raceway surface. A base oil having a kinematic viscosity of 18 to 100 mm ² / s at 40 ° C., which is made of a mixed oil of a lubricating oil having a polar group in its molecular structure and a non-polar lubricating oil, which is rotatably held by a cage. ,
A rolling bearing for a hard disk drive, characterized by being sealed with a grease composition containing a metal soap-based thickener containing a long fiber having a major diameter of at least 3 μm. 2. The rolling bearing for a hard disk drive according to claim 1, wherein the inner diameter is 6 mm or less and the outer diameter is 15 mm or less.