JP2002323037A - Fluid bearing unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluid bearing unit capable of achieving stable rotation by reducing the seizure of a bearing and the leakage of lubricant. SOLUTION: A lubricant 10 is filled between a shaft 2 and a bearing body which is rotatably supported by the shaft 2. A membrane 12a is formed on the inside of a hub 5 contacting with the lubricant 10 in order to suppress the wear of the bearing body. The difference between the surface tension of a fluorine lubricant and the critical surface tension of the membrane 12a is made to be less than 5 mN/m by using the fluorine lubricant as the lubricant 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrodynamic bearing device used for a spindle motor of a magnetic disk drive.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional hydrodynamic bearing device. One end of a fixed shaft 2 having dynamic pressure generating grooves 4a and 4b formed on its outer peripheral surface is press-fitted into a base 1, and a thrust plate 3 is fixed to the other end to form a shaft portion. A sleeve 5 is press-fitted on the inner peripheral surface of a hub 6 for mounting a magnetic disk or the like, and a thrust flange 11 is attached to one end of the sleeve 5.
Are attached to form a bearing body. Then, the sleeve 5 is mounted on the fixed shaft 2 so that the thrust flange 11 and the thrust plate 3 face each other, and the gap between the shaft portion and the bearing body is filled with the lubricant 10.

A stator coil 9 is provided on a wall 1 a formed on the base 1, and a rotor magnet 7 is mounted on an inner peripheral surface of a hub 6 facing the stator coil 9 via a rotor yoke 8. Is configured.

When the sleeve 5 and the hub 6 are driven to rotate by the motor driving section, a dynamic pressure is generated in the lubricant 10 by the pumping action of the dynamic pressure generating grooves 4a and 4b formed in the fixed shaft 2, and the bearing body is rotated. The shaft portion and the bearing body are rotatably supported in a non-contact manner.

[0005]

In the hydrodynamic bearing device configured as described above, the gap between the fixed shaft 2 and the inner peripheral surface of the sleeve 5 and the gap between the sleeve 5 and the thrust flange 11 and the thrust plate 3 are filled. As the lubricant 10 to be used, it is desired to use a fluorine-based lubricant having high heat resistance and high chemical stability due to an increase in frictional heat and heat generation of the motor part due to recent high-speed rotation of the bearing.

However, fluorine-based lubricants have poor adsorbability and reactivity on the bearing surface and have low boundary lubricity. Therefore, when starting or stopping the rotation in which sufficient dynamic pressure is not generated, the sleeve 5 and the thrust flange 11 come into contact with the fixed shaft 2 and the thrust plate 3 to be easily worn, and there is a problem that the rotational accuracy of the bearing is reduced. Was.

Therefore, Japanese Patent Publication No. Hei 8-30490 discloses that
A method has been proposed in which a fluorine-based film such as a polyfluoroalkyl polymer or a fluoropolyether polymer is formed on the inner surface of a bearing body to reduce wear of the shaft portion and the bearing body.

However, since a fluorine-based film having a low surface energy tends to repel the lubricant, it is difficult to inject the lubricant 10 into the gap between the shaft portion and the bearing body when assembling the bearing. However, there is a problem that the bearing performance is not stable due to the variation in the injection amount of the alloy.

When the hydrodynamic bearing device is rotated,
Since the wettability between the film and the lubricant is low, there is a possibility that the seizure of the bearing due to the oil film breakage may occur, or bubbles may be generated inside the bearing, and the lubricant may easily leak from the bearing due to thermal expansion of the bubbles.

An object of the present invention is to solve the above-mentioned problems and to provide a hydrodynamic bearing device capable of realizing stable rotation by reducing seizure of a bearing and leakage of a lubricant.

[0011]

The hydrodynamic bearing device according to the present invention is characterized in that the difference between the surface tension of the fluorine-based lubricant and the critical surface tension of the film is set within an appropriate range.

According to the present invention, since the wettability between the film and the lubricant is improved, the lubricant can be uniformly filled in the bearing,
It is possible to perform stable rotation by reducing seizure of the bearing and leakage of the lubricant from the bearing, and to realize a highly reliable hydrodynamic bearing device.

Further, the hydrodynamic bearing device of the present invention is characterized in that the critical surface tension of the film is set to be higher on the inner side of the bearing than on the gas-liquid interface side of the lubricant. According to the present invention, since the lubricant is attracted to the inside of the bearing, leakage of the lubricant from the bearing can be reduced.

[0014]

A fluid bearing device according to a first aspect of the present invention is characterized in that a lubricant is filled between a bearing portion and a shaft portion, one of which is rotatably supported with respect to the other, and wherein the lubricant is filled. A fluid bearing device formed on at least one of an outer surface of the shaft portion or an inner surface of the bearing body in contact with the shaft portion and a coating that reduces wear of the bearing body, wherein the lubricant is a fluorine-based lubricant. The difference between the surface tension of the fluorine-based lubricant and the critical surface tension of the film is 5 mN / m or less.

According to this configuration, the wettability between the lubricant and the film is improved by setting the difference between the surface tension of the fluorine-based lubricant and the critical surface force of the film in an appropriate range, and the shaft portion and the bearing body are improved. In addition to stabilizing the bearing performance by injecting a certain amount of lubricant into the small gap between the bearing and the bearing, it also reduces the generation of bubbles at the interface between the film and the lubricant during rotation, and reduces the oil film. Leakage of lubricant due to burn-in or thermal expansion of bubbles can be reduced.

According to a second aspect of the present invention, there is provided a hydrodynamic bearing device.
A lubricant is filled between a shaft part and a bearing body, one of which is rotatably supported with respect to the other, and at least one of an outer surface of the shaft part or an inner surface of the bearing body in contact with the lubricant is provided on the bearing body. A fluid bearing device having a film for reducing wear of a shaft portion and a bearing body, wherein the lubricant is a fluorine-based lubricant, and a critical surface of the film formed near a gas-liquid interface of the fluorine-based lubricant. It is characterized in that the critical surface tension of the film formed on the inner side of the bearing is larger than the tension.

According to this configuration, since the lubricant is attracted toward the inside of the bearing where the surface energy of the film, that is, the critical surface tension is relatively large, leakage of the lubricant from the bearing can be reduced.

According to a third aspect of the present invention, there is provided a hydrodynamic bearing device.
A lubricant is filled between a shaft part and a bearing body, one of which is rotatably supported with respect to the other, and at least one of an outer surface of the shaft part or an inner surface of the bearing body in contact with the lubricant is provided on the bearing body. A fluid bearing device having a film for reducing wear of a shaft portion and a bearing body, wherein the lubricant is a fluorine-based lubricant, and a difference between a surface tension of the fluorine-based lubricant and a critical surface tension of the film. Is not more than 5 mN / m, and the critical surface tension of the coating formed on the inner side of the bearing is larger than the critical surface tension of the coating formed near the gas-liquid interface of the fluorine-based lubricant.

According to this structure, the wettability between the film and the lubricant is improved, and the seizure of the bearing due to the breakage of the oil film and the leakage of the lubricant due to the thermal expansion of bubbles can be more reliably reduced.

The hydrodynamic bearing device according to claim 4 of the present invention is
The film according to any one of claims 1 to 3, wherein the film is a fluorine-containing material. According to this configuration, since the film containing fluorine is a compound of the same type as the fluorine-based lubricant, the film can easily hold the lubricant by an adsorption action by affinity, and has low friction characteristics, so that lubricity can be improved.

According to a fifth aspect of the present invention, there is provided a hydrodynamic bearing device.
In claim 4, the fluorine-containing material is a resin. According to this configuration, since the resin film is formed by applying and drying a coating solution in which a resin component is dissolved, the dimensional change due to heat of the bearing base material is smaller than that of a metal or ceramic which is heated at the time of formation. It has excellent dimensional stability and can be realized at low cost.

The hydrodynamic bearing device according to claim 6 of the present invention is
In any one of the first to third aspects, the fluorine-based lubricant contains at least one of a perfluoropolyether and a perfluoropolyether derivative.

According to this structure, these are more excellent in heat resistance and chemical stability among fluorine-based lubricants and have a characteristic that kinematic viscosity has a small temperature change, so that they can withstand use in a high temperature range and torque fluctuation due to temperature. Hydrodynamic bearing device with a small size can be realized.

Hereinafter, embodiments of the present invention will be described with reference to FIGS.
This will be described with reference to FIG. Components having the same configuration as that of FIG. 4 showing a conventional example will be described using the same reference numerals.

(Embodiment 1) FIGS. 1 and 2 show Embodiment 1 of the present invention. As shown in FIG. 1, in the fluid dynamic bearing device configured in the same manner as in FIG. 4, a fluorine-based lubricant having high heat resistance and high chemical stability is used for the lubricant 10 so as to cope with high-speed rotation. . Further, since this fluorine-based lubricant has poor adsorbability and reactivity on the bearing surface and low boundary lubrication, a coating 12a is formed on the inner surface of the sleeve 5 so as to reduce wear of the shaft portion and the bearing body. ing.

In the first embodiment, in order to improve the wettability between the film 12a and the lubricant 10, attention is paid to the critical surface tension, which is an intrinsic physical property, as an index of the wettability of the film 12a. This is different from the above conventional example in that the difference between the surface tension and the critical surface tension of the film 12a is set to an appropriate value.

Here, the critical surface tension is used as an index of the wettability of the film 12a because the surface energy of the solid at the solid-liquid interface, that is, the critical surface tension is smaller than the surface tension of the liquid. This is because they have a property that they are hardly wet by liquids, and it is difficult to measure the surface tension of solids. The critical surface tension is defined as follows: θ is the contact angle of the homologous series of the organic liquid compound on the solid surface, and γ is the surface tension of the liquid. A linear relationship is obtained between cos θ and γ. 0, that is, the value of γ corresponding to cos θ = 1.

In order to examine the relationship between the surface tension of the lubricant 10 and the critical surface tension of the film 12a, a certain amount of fluorine-based lubricant 10 is dropped on the film 12a, and the lubrication after a certain period of time has passed. The contact angle between the agent 10 and the film 12a and the difference between the surface tension of the fluorine-based lubricant 10 and the critical surface tension of the film 12a were measured in a 20 ° C. atmosphere. A fluorine-based lubricant was used for the lubricant 10, and a fluorine-based film was used for the film 12a.

FIG. 2 shows the obtained measurement results. As is clear from the graph, when the difference between the surface tension of the fluorine-based lubricant and the critical surface tension of the fluorine-based film is larger than 5 mN / m, the lubricant 10 is repelled by the film 12a, and the surface tension of the fluorine-based lubricant is reduced. The larger the difference from the critical surface tension of the fluorine-based coating, the higher the contact angle. On the other hand, when the difference between them was 5 mN / m or less, the lubricant 10 spread and spread, and did not show a contact angle. Although not shown here, when the critical surface tension of the film 12a is larger than the surface tension of the lubricant 10, that is, the difference between the surface tension of the fluorine-based lubricant and the critical surface tension of the fluorine-based film is minus. In some cases, the lubricant 10 spread out and did not show a contact angle.

The same tendency was obtained for the coating 12a other than the fluorine type, for example, the silicone type. Therefore, as a fluorine-based lubricant, the surface tension at 20 ° C. is 23 mN.
/ M of perfluoropolyether and the film 12a was formed of a commercially available fluorine resin having a critical surface tension of 19 mN / m, and the hydrodynamic bearing device shown in FIG. 1 was prepared. The film 1a is sufficiently wetted and spread on the fluororesin which is to be used as the base material 12a, and the film 1
The specified amount of the lubricant 10 could be filled without being repelled by 2a and without generating bubbles or the like in the bearing.

When the motor equipped with the hydrodynamic bearing device was continuously rotated in a high-temperature environment, stable performance was obtained, and no seizure of the bearing or leakage of the lubricant was confirmed.

The film 12a used in the first embodiment
The material is not particularly limited as long as it is a material that can reduce the wear of the bearing. Lubricity, abrasion, heat resistance, hardness, conductivity, regardless of the type of metal-containing material, ceramics, carbon material, resin, etc. , Cost and the like can be conveniently selected. Above all, a fluorine-containing substance containing a fluorine element is preferable, and a fluorine resin is more preferable, in order to have an affinity with the fluorine-based lubricant and to easily hold the lubricant 10 in the bearing by an adsorption action.

As the fluororesin, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PV
DF) polyvinyl fluoride (PVF), ethylene / tetrafluoroethylene copolymer (ETFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE), polychlorotrifluoroethylene (PCTFE), tetrafluoroethylene / perfluoroalkyl Vinyl ether copolymer (PFA), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), and the like, some of which are substituted with functional groups such as a hydroxyl group, a carboxyl group, an amino group, an isocyanate group, and an epoxy group. These may be used alone, or in a mixture or copolymer. Similar effects can be obtained by using commercially available fluorine compounds such as Florado FC manufactured by Sumitomo 3M, Sumiflunon FP manufactured by Sakata Inx, and Cytop manufactured by Asahi Glass.

A film 12a made of these fluororesins
Can be easily formed by applying a coating solution in which a fluorine-based resin is dissolved or dispersed on the surface on which the film 12a is formed, and then drying the film at room temperature or by heating, and the film can be formed at a relatively low temperature. Thus, the bearing base material is less likely to change in size due to heat than a material having a high temperature at the time of formation, has excellent dimensional stability, and can be realized at low cost, so that it can be suitably used. The method of applying the coating liquid can be arbitrarily selected according to the size and shape of the member, such as spin coating, dip coating, spray coating, transfer coating, potting coating, and brush coating.

When the film 12a is formed of a resin containing no elemental fluorine, the film may be formed of a resin and then fluorinated by fluorination plasma treatment, fluorine ion implantation, or the like. It is preferable to use a fluororesin from the surface. In order to increase the wettability of the film, a surface modification treatment such as a plasma treatment or a corona treatment may be performed after the formation of the fluororesin.

Examples of the fluorine-based lubricant include perfluoropolyethers, perfluoropolyether derivatives, fluoroesters, etc. Among them, perfluoropolyethers having good heat resistance and a small change in kinematic viscosity with temperature or derivatives thereof. Can be preferably used. As commercial products of perfluoropolyether, Fomblin Y, M, Z manufactured by Ausimont, Demnum S manufactured by Daikin Industries, and the like are used. In addition, derivatives in which a part thereof is modified with a functional group such as a hydroxyl group, a carboxyl group, an isocyanate group, or an ester group can be used alone or in combination. Since the lubricant 10 is held in the bearing by its surface tension, it is desirable that the surface tension is higher to prevent leakage or bleeding from the bearing. For the purpose of improving or complementing the performance of the lubricant 10, a commercially available additive such as an extreme pressure agent, a rust preventive, or a charge imparting agent may be added in any combination as long as the characteristics are not impaired. .

As described above, a fluorine-based lubricant is used as the lubricant 10, and the surface tension of the fluorine-based lubricant and the film 12
a is set to 5 mN / m or less, the wettability between the lubricant 10 and the film 12a is improved, and the lubricant 10 is inserted into the gap between the shaft portion and the bearing body when assembling the bearing.
Can be easily and uniformly injected, and stable bearing performance can be obtained. In addition, seizure of the bearing due to oil film shortage can be reduced, and bubbles are less likely to be generated inside the bearing during rotation, so that leakage of lubricant from the bearing due to thermal expansion of bubbles can be reduced, realizing a highly reliable bearing device it can.

(Embodiment 2) FIG. 2 shows Embodiment 2 of the present invention. In the second embodiment, in that three films having different critical surface tensions are formed at three points in the bearing,
This is different from the above embodiment.

Specifically, in the hydrodynamic bearing device constructed in the same manner as in FIG. 1, a coating 12a is formed on the inner peripheral surface of the sleeve 5 in contact with the lubricant 10, and a coating 12b is formed on the surface of the thrust flange 11. , Film 1 on the surface of fixed shaft 2
2c is formed. The coating 12a and the coating 12c are made of a fluororesin having a critical surface tension of 19 mN / m.
2b is made of a fluorine-based resin having a critical surface tension of 25 mN / m. The fluorine-based lubricant 10a is a mixture of a perfluoropolyether and a perfluoropolyether derivative,
The surface tension at 0 ° C. is 21 mN / m.

Also in such a configuration, the difference between the surface tension of the fluorine-based lubricant and the critical surface tension of the film 12a is set to 5 mN / m or less as in the above-described embodiment. Can sufficiently spread on the fluororesin to reduce seizure of the bearing due to oil film breakage, and reduce leakage of lubricant from the bearing due to thermal expansion of bubbles and the like.

The critical surface tension of the coating 12b formed on the inner side of the bearing is set higher than the critical surface tension of the coatings 12a and 12c formed on the gas-liquid interface side of the fluorine-based lubricant. The lubricant 10 is attracted to the side of the film 12b having a high energy value, and smoother and more reliable filling of the lubricant 10 becomes possible.

When the motor of the hydrodynamic bearing device thus configured is continuously rotated under a high temperature environment, stable performance such as current consumption and rotational accuracy can be obtained, and seizure of the bearing and leakage of the lubricant have been confirmed. Was not done.

In the above description, the film is provided on both the shaft portion and the bearing body. However, the present invention is not limited to this, and one or more films may be provided according to the performance and cost. . Further, the formation place is not particularly limited.

In the above description, the critical surface tension between the film 12a and the film 12b is different between the film 12c formed on the shaft and the films 12a and 12b formed on the bearing body. A film may be formed only on the body, and the critical surface tension of the film may be larger on the inner side of the bearing than on the gas-liquid interface side of the lubricant 10. Alternatively, a difference in critical surface tension between the film formed on the shaft portion and the film formed on the bearing body may be provided.

In each of the above embodiments, the fixed shaft type fluid bearing device in which the base end of the shaft portion 2 is fixed to the base 1 has been described as an example, but the present invention is not limited to this. Instead, the present invention can be applied to a structure in which both ends of the shaft portion 2 are fixed, a shaft-rotating type hydrodynamic bearing device, a structure in which the inner diameter holes of the sleeve are opened on both sides, and a structure in which a pivot bearing is formed in the thrust direction. Similar effects can be obtained.

[0046]

As described above, according to the hydrodynamic bearing device of the present invention, the lubricant is filled between the bearing and the shaft part, one of which is rotatably supported with respect to the other, and comes into contact with the lubricant. A fluid bearing device in which a coating that reduces wear of the shaft and the bearing is formed on at least one of an outer surface of the shaft and an inner surface of the bearing, wherein the lubricant is a fluorine-based lubricant, By making the difference between the surface tension of the fluorine-based lubricant and the critical surface tension of the film 5 mN / m or less,
Improves the wettability between the lubricant and the film, and the amount of lubricant injected into the minute gap between the shaft and the bearing body is constant, which not only stabilizes the bearing performance, but also breaks the oil film during rotation. Can reduce the seizure of the bearing, and can reduce the generation of bubbles at the interface between the film and the lubricant, so that the leakage of the lubricant due to the thermal expansion of the bubbles can be reduced.

Further, the coating is formed such that the critical surface tension of the coating formed on the inner side of the bearing is greater than the critical surface tension of the coating formed near the gas-liquid interface of the fluorine-based lubricant, Since the lubricant is attracted toward the inside of the bearing where the surface energy of the film, that is, the critical surface tension is relatively large, leakage of the lubricant from the bearing can be reduced.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a hydrodynamic bearing device according to a first embodiment of the present invention.

FIG. 2 is a measurement diagram showing a relationship between a surface tension of a lubricant and a critical surface tension of an oil-repellent film in the embodiment.

FIG. 3 is a longitudinal sectional view of a hydrodynamic bearing device according to the second embodiment of the present invention.

FIG. 4 is a longitudinal sectional view of a conventional hydrodynamic bearing device.

[Explanation of symbols]

 2 Fixed shaft 4a, 4b Dynamic pressure generating groove 5 Sleeve 10 Lubricant 12a to 12c Coating

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H02K 7/08 H02K 7/08 A // C10N 20:00 C10N 20:00 Z 30:06 30:06 40:02 40 : 02 50:08 50:08 F term (reference) 3J011 BA06 CA02 JA02 KA01 KA04 MA02 QA05 SC04 4H104 CD01A CD02A CD04A EA01A LA03 PA01 QA11 5H605 AA04 BB05 BB14 BB19 CC04 DD05 EB03 EB06 EB15 BB39 BB39 BB39 BB39 BB39 BB39 BB39 BB39 BB39 BB39 BB39 BB39 BB39 BB39 BB39 BB39 BB39 GG12 GG15 KK10

Claims (6)

[Claims] A lubricant is filled between a shaft part and a bearing body, one of which is rotatably supported with respect to the other, and at least an outer surface of the shaft part or an inner surface of the bearing body which comes into contact with the lubricant. A fluid bearing device in which a film that reduces wear of the shaft portion and the bearing body is formed on one surface, wherein the lubricant is a fluorine-based lubricant, and the surface tension of the fluorine-based lubricant and the criticality of the film are 5mN difference from surface tension
/ M or less. 2. A lubricant is filled between a shaft part and a bearing body, one of which is rotatably supported with respect to the other, and at least an outer surface of the shaft part or an inner surface of the bearing body in contact with the lubricant. A fluid bearing device in which a film that reduces wear of the shaft portion and the bearing body is formed on one surface, wherein the lubricant is a fluorine-based lubricant, and is formed near a gas-liquid interface of the fluorine-based lubricant. A hydrodynamic bearing device in which the critical surface tension of a film formed inside the bearing is greater than the critical surface tension of the film. 3. A lubricant is filled between a shaft and a bearing, one of which is rotatably supported with respect to the other, and at least an outer surface of the shaft or an inner surface of the bearing which comes into contact with the lubricant. A fluid bearing device in which a film that reduces wear of the shaft portion and the bearing body is formed on one surface, wherein the lubricant is a fluorine-based lubricant, and the surface tension of the fluorine-based lubricant and the criticality of the film are A fluid having a difference from the surface tension of 5 mN / m or less, wherein the critical surface tension of the film formed on the inner side of the bearing is larger than the critical surface tension of the film formed near the gas-liquid interface of the fluorine-based lubricant. Bearing device. 4. The hydrodynamic bearing device according to claim 1, wherein the coating is a fluorine-containing material. 5. The hydrodynamic bearing device according to claim 4, wherein said fluorine-containing material is a resin. 6. The hydrodynamic bearing device according to claim 1, wherein the fluorine-based lubricant contains at least one of a perfluoropolyether and a perfluoropolyether derivative.