JP2001059082A - Oil repellent for hydrodynamic bearing and liquid dynamic pressure bearing device and spindle motor using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject oil repellent having long-term sustained oil- repelling effect by including fluorine-contg. metal alkoxide(s) and titanium oxide fine powder. SOLUTION: This oil repellent is obtained by including (A) at least one kind of fluorine-contg. metal alkoxide (the metallic element being pref. silicon, and the fluorine content being pref. >=5 atom%) and (B) titanium oxide fine powder (pref. 50-1,000 μm in average particle size). This oil repellent is served on the opposite side close to the interfacial boundary between the atmosphere and a lubricating oil held in the gap of a hydrodynamic bearing. If this oil repellent is used, there occurs neither its deterioration nor decline in its oil repellency due to contamination even after used for a long period of time, enabling lubricating oil leakages to be prevented over a long period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oil repellent used for a liquid dynamic bearing, a liquid dynamic bearing using the same, and a spindle motor.

[0002]

2. Description of the Related Art Conventionally, liquid dynamic pressure bearings have been known as being suitable as bearings for rotating devices in fields such as computers and copiers because they can rotate smoothly at high speed. The liquid dynamic pressure bearing realizes non-contact rotation by forming a high-pressure lubricating oil layer in a minute gap between the fixed side and the rotation side during normal rotation. Therefore, it is necessary to prevent the lubricating oil from leaking from the bearing gap.

[0003] Conventionally, a capillary seal has been provided to incline the wall surface near the interface boundary between the lubricating oil and the atmosphere to reduce the surface tension in which the oil repellent tends to leak, and a fluoride resin having a high oil repellency has been provided. Is applied to the wall surface near the gas-liquid interface boundary so that the surface tension acts in a direction opposite to the direction in which the lubricating oil leaks.

[0004]

However, conventional oil repellents have the problem that they deteriorate over time and become contaminated, resulting in reduced oil repellency and no longer functioning as an oil repellent. In view of such circumstances, the present invention provides an oil repellent for a liquid dynamic pressure bearing capable of maintaining an oil repellent effect for a long period of time, and a liquid dynamic pressure bearing device and a spindle motor using the same. Make it an issue.

[0005]

According to a first aspect of the present invention, there is provided a liquid dynamic pressure bearing comprising a liquid provided on an opposed surface near an interface boundary between lubricating oil held in a bearing gap and the atmosphere. An oil repellent for a fluid dynamic pressure bearing, comprising: at least one selected from the group consisting of fluorine-containing metal alkoxides; and titanium oxide fine powder.

According to a second aspect of the present invention, there is provided an oil repellent for a liquid dynamic pressure bearing according to the first aspect, wherein the fluorine-containing metal alkoxide is a fluorine-containing metal alkoxide containing silicon as a metal element. . According to a third aspect of the present invention, there is provided an oil repellent for a liquid dynamic pressure bearing according to the first or second aspect, wherein the fluorine content of the fluorine-containing metal alkoxide is 5 atomic% or more.

According to a fourth aspect of the present invention, in any one of the first to third aspects, the average particle diameter of the titanium oxide fine powder is:
An oil repellent for a liquid dynamic pressure bearing, which is in the range of 50 to 1000 μm. According to a fifth aspect of the present invention, there is provided a shaft portion and a bearing portion for supporting the shaft portion, a dynamic pressure generating groove on one of the opposing surfaces thereof, and a lubricating oil between the opposing surfaces. In the liquid dynamic pressure bearing device, at least one selected from the group consisting of fluorine-containing metal alkoxides is provided on the facing surface near the interface boundary between the lubricating oil and the atmosphere.
An oil repellent containing a seed and fine titanium oxide powder is provided in the liquid dynamic pressure bearing device.

According to a sixth aspect of the present invention, in the fifth aspect, the shaft portion has a disk-shaped thrust bearing portion at a central portion in the axial direction, and a radial bearing column portion and a support column portion on both sides thereof. A flanged cylindrical bearing member having
The bearing portion has a small-diameter cylindrical portion on the closed end side into which the radial bearing cylindrical portion of the flanged cylindrical bearing member is rotatably inserted, and a large diameter into which the disc-shaped thrust bearing portion is rotatably inserted. A liquid dynamic pressure bearing device comprising: a stepped cylindrical bearing member having a cylindrical portion on an open end side; and a disc-shaped thrust holding member sealing an open end of the stepped cylindrical bearing member. It is in.

According to a seventh aspect of the present invention, in the sixth aspect, a radial dynamic pressure generating groove is formed on one of an outer peripheral surface of the cylindrical portion for a radial bearing and an opposing surface thereof. A thrust dynamic pressure generating groove is formed on one of the surfaces on both axial sides of the bearing portion or the opposing surfaces thereof. An eighth aspect of the present invention is the liquid dynamic bearing device according to any one of the fifth to seventh aspects, wherein the oil repellent is baked after being applied to the facing surface.

A ninth aspect of the present invention is the liquid dynamic pressure bearing according to any one of the fifth to eighth aspects, wherein the fluorine-containing metal alkoxide is a fluorine-containing metal alkoxide containing silicon as a metal element. In the device. In a tenth aspect of the present invention, in any one of the fifth to ninth aspects,
When the fluorine content of the fluorine-containing metal alkoxide is 5
Liquid dynamic pressure bearing device characterized by being at least atomic%.

An eleventh aspect of the present invention is the liquid dynamic bearing according to any one of the fifth to tenth aspects, wherein the average particle diameter of the titanium oxide fine powder is in a range of 50 to 1000 μm. In the device. A twelfth aspect of the present invention is a spindle motor using the liquid dynamic bearing device according to any one of the fifth to eleventh aspects.

As described above, the oil repellent for a liquid dynamic pressure bearing of the present invention is a mixture of at least one selected from the group consisting of fluorine-containing metal alkoxides and titanium oxide fine powder. The fluorine-containing metal alkoxide preferably contains silicon as a metal element, but is not limited to this.

The fluorine content of the fluorine-containing metal alkoxide is preferably at least 5 atomic%. This is for exhibiting a remarkable oil repellent effect. Such a fluorine-containing metal alkoxide is mixed with titanium oxide and preferably baked to form an oil-repellent film in a glassy state. Since such an oil-repellent film is in a glass state composed of a quasi-inorganic component, it is resistant to external force and corrosion, and is excellent in oil repellency, so that a liquid dynamic pressure bearing excellent in long-term reliability can be configured.

The titanium oxide is not particularly limited as long as it can be mixed with the fluorine-containing metal alkoxide, but preferably has an average particle size of 50 to 1000 μm. Further, the mixing ratio is not particularly limited as long as it is a unit in which the effect is exhibited, but is 0.3% by weight or more, preferably 0.5% by weight or more in order to achieve a remarkable effect. It should be noted that as the amount of addition increases and the particle size increases, small cracks and the like tend to occur in the oil-repellent film when fired.

The oil repellent of the present invention preferably contains 20
By firing at a low temperature of 0 ° C. or less, a glassy film is formed, and therefore, long-term reliability is excellent. When the thickness is reduced, it is not always necessary to bake. The lube repellent of the present invention may be provided in the vicinity of the gas-liquid interface boundary at the portion where the lubricating oil is retained in the gap between the shaft and the sleeve of the liquid dynamic pressure bearing. As a result, the contact angle of the lubricating oil increases, and the surface tension of the lubricating oil acts inward, making it difficult for the lubricating oil to leak. Even when used for a liquid dynamic pressure bearing provided with a capillary seal, the effects of both are combined to further prevent lubricating oil from leaking.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments. (Examples 1 to 6) C ₃ H ₈ FSiOH had an average particle size of 50 μm.
0.2% by weight, 0.5% by weight, 1.0% by weight
%, 2.0% by weight, and 3.0% by weight, respectively, to obtain an oil repellent.

Each oil repellent was applied to a stainless steel test piece by printing to a thickness of 1 μm, and baked at 150 ° C. for 1 hour to form an oil repellent layer. The test piece thus formed was allowed to stand, and the contact angle with respect to the lubricating oil was measured every day to measure the number of days maintaining 90 ° or more. The results in Table 1 below were obtained. (Comparative Example 1) An experiment was performed in the same manner as in the example except that titanium oxide was not added. The results are shown in Table 1.

[0018]

[Table 1]

(Examples 6 to 10) 0.3% by weight of titanium oxide having an average particle diameter of 50 μm was added to C ₄ H ₈ F ₃ SiOH at 0.3% by weight.
4% by weight, 1.0% by weight, 2.0% by weight, 3.0% by weight
Each was added to give an oil repellent. Each oil repellent is applied to a stainless steel test piece by printing to a thickness of 1 μm,
For 1 hour to form an oil-repellent layer.

The test piece thus formed was allowed to stand, and the contact angle with respect to the lubricating oil was measured every day to measure the number of days maintaining 90 ° or more. The results shown in Table 2 below were obtained. (Comparative Example 2) An experiment was performed in the same manner as in the example except that titanium oxide was not added. The results are shown in Table 1.

[0021]

[Table 2]

As can be seen from the results of the examples and comparative examples, the oil repellent of the present invention can maintain oil repellency for a long period of time due to the synergistic action of the fluorine-containing metal alkoxide and titanium oxide. It was confirmed that a remarkable effect was exhibited when the content was 0.3% by weight or more. Similar experiments were performed using titanium oxide having an average particle diameter of 100 μm, 500 μm, and 1000 μm instead of those described above, and almost the same effect was confirmed.

FIGS. 1 to 5 show an example of a liquid dynamic bearing in which such an oil repellent can be used. The liquid dynamic pressure bearing portion shown in FIG.
, A stepped cylindrical bearing member 30, and a disk-shaped thrust holding member 40. Flanged cylindrical bearing member 20
As shown in FIG. 2, a radial thrust bearing portion 21 is provided below a disc-shaped thrust bearing portion 21 at a central portion in the axial direction.
2. It has a supporting cylindrical portion 23 on the upper side. As shown in FIG. 3, the stepped cylindrical bearing member 30 includes a small-diameter cylindrical portion 31 into which the radial bearing cylindrical portion 22 of the flanged cylindrical bearing member 20 is rotatably inserted, and a disk-shaped thrust bearing portion 21. A large-diameter cylindrical portion 32 rotatably inserted. These two cylindrical portions are provided adjacent to each other coaxially, and a boundary surface 35 exists at the boundary between the two. The cylindrical portion 33 formed coaxially adjacent to the large-diameter cylindrical portion 32 includes:
The open end of the large-diameter cylindrical portion 32, and thus the stepped cylindrical bearing member 3
This is for inserting and fixing a disc-shaped thrust holding member 40 that seals the open end of the “0” with a capillary seal. Such a stepped cylindrical bearing member 30 is manufactured by forming the thrust holding member cylindrical portion 33, the large-diameter cylindrical portion 32, and the small-diameter cylindrical portion 31 in order from the top by cutting or the like. Has a small-diameter cylindrical portion 31 and a large-diameter cylindrical portion 32 formed at the open end. Note that the disc-shaped thrust holding member 40 has an oil reservoir S that forms a capillary seal.

Such a liquid dynamic bearing includes one radial dynamic pressure bearing, an upper first thrust bearing, and a lower second thrust bearing.
And a thrust bearing. The radial dynamic pressure bearing portion is a radial bearing cylindrical portion 22 of the flanged cylindrical bearing member 20.
And an inner peripheral surface of the small-diameter cylindrical portion 31 of the stepped cylindrical bearing member 30, and a radial dynamic pressure generating groove as shown in FIG. G1 is formed, and the other becomes a flat surface. The first thrust bearing portion includes an upper surface of the disk-shaped thrust bearing portion 21 and a lower surface that is a facing surface of the disk-shaped thrust holding member 40, and one of the upper surface and the lower surface is provided with, for example, FIG. The thrust dynamic pressure generating groove G2 shown in FIG. Further, the second thrust dynamic pressure bearing portion is provided between the lower surface of the disk-shaped thrust bearing portion 21 and the stepped cylindrical bearing member 3.
A thrust dynamic pressure generating groove G2 as shown in FIG. 5 is formed on one of the lower surface and the boundary surface 35, and the other is a flat surface.

FIG. 6 shows a schematic plan view and a longitudinal section of a spindle motor using such a liquid dynamic bearing. As shown in FIG. 6, a stepped cylindrical bearing member 30A of the liquid dynamic pressure bearing portion.
The disc-shaped thrust holding member 40A is formed integrally with a frame member 130 constituting the stator of the spindle motor, and the flanged cylindrical bearing member 20A is provided integrally with the rotor 120.

The stator 130 includes the stepped cylindrical bearing member 30.
A has stators 150 provided on the outer peripheral surface at substantially equal intervals in the circumferential direction. The stator 150 is formed by winding a coil 152 around a stator yoke 151 formed by laminating a plurality of soft magnetic metal plates such as a stainless steel plate and an iron plate. By passing a current through each coil 152 of the stator 150, an N-pole or S-pole magnetic field is generated.

On the other hand, the rotor 120 includes a disk-shaped disk portion 122 provided on one end side of a cylindrical bearing member 20A with a flange, and a cylindrical back yoke 123 provided on a peripheral portion of the disk portion 122. A cylindrical rotor magnet 124 is fixed to the inner peripheral surface of the back yoke 123 at a position facing the stator 150. Here, the rotor magnet 124 is formed by alternately multipolarizing the N pole and the S pole in the circumferential direction, and the rotor 120 is configured such that the rotor magnet 124 is attracted to the magnetic field generated by the stator 150. By utilizing the repulsive force and the repulsive force, the cylindrical bearing member 20A rotates around the flanged cylindrical bearing member 20A.

The oil reservoir S of such a liquid dynamic pressure bearing device
The oil repellent of the above-described embodiment was applied to the outer peripheral surface of the cylindrical bearing member 20A with flange and the inner peripheral surface of the disc-shaped thrust pressing member 40A, which were formed and fired to form the oil repellent film 200. Further, the oil reservoir S is filled with lubricating oil that is normally used. Such a spindle motor was operated at a rotation speed of 5000 rpm for 50,000 hours or more, but the oil repellency was not reduced.

On the other hand, for comparison, when a commercially available oil-repellent of a fluorine-substituted long-chain alcohol was used, the oil-repellent effect was almost lost after 20,000 hours of operation.

[0030]

As described above, according to the present invention,

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a liquid dynamic bearing according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a cylindrical bearing member with a flange of the liquid dynamic pressure bearing according to one embodiment.

FIG. 3 is a cross-sectional view of a stepped cylindrical bearing member of the liquid dynamic pressure bearing according to one embodiment.

FIG. 4 is a diagram illustrating an example of a radial dynamic pressure generating groove.

FIG. 5 is a diagram illustrating an example of a thrust dynamic pressure generation groove.

FIG. 6 is a plan view and a longitudinal sectional view showing an example of a spindle motor.

[Explanation of symbols]

 20, 20A Flanged cylindrical bearing member 21 Disc-shaped thrust bearing part 22 Radial bearing cylindrical part 23 Supporting bearing part 30 Stepped cylindrical bearing member 31 Small diameter cylindrical part 32 Large diameter cylindrical part 33 Cylindrical part for thrust holding member 40 , 40A Disc-shaped thrust holding member 120 Rotor 130 Stator 150 Stator 200 Water repellent film S Oil reservoir G1 Radial dynamic pressure generating groove G2 Thrust dynamic pressure generating groove

Claims (12)

[Claims] 1. An oil repellent for a liquid dynamic pressure bearing provided on a facing surface near an interface boundary between lubricating oil held in a bearing gap of the liquid dynamic pressure bearing and the atmosphere, selected from a group of fluorine-containing metal alkoxides. An oil repellent for a liquid dynamic pressure bearing, comprising at least one of the following and a fine powder of titanium oxide. 2. The oil repellent for a liquid dynamic pressure bearing according to claim 1, wherein the fluorine-containing metal alkoxide is a fluorine-containing metal alkoxide containing silicon as a metal element. 3. The oil repellent according to claim 1, wherein the fluorine-containing metal alkoxide has a fluorine content of 5 atomic% or more. 4. An oil repellent for a liquid dynamic pressure bearing according to claim 1, wherein the average particle diameter of the fine titanium oxide powder is in a range of 50 to 1000 μm. 5. A liquid having a shaft portion and a bearing portion for supporting the shaft portion, having a dynamic pressure generating groove on one of the opposing surfaces thereof, and holding a lubricating oil between the opposing surfaces. In the hydrodynamic bearing device, an oil repellent containing at least one selected from the group of fluorine-containing metal alkoxides and titanium oxide fine powder is provided on the facing surface near an interface boundary between the lubricating oil and the atmosphere. Characteristic liquid dynamic pressure bearing device. 6. The cylindrical bearing member with a flange according to claim 5, wherein the shaft portion has a disk-shaped thrust bearing portion at a central portion in the axial direction, and has a radial bearing column portion and a support column portion on both sides thereof. The bearing portion has a small-diameter cylindrical portion on the closed end side into which the radial bearing cylindrical portion of the flanged cylindrical bearing member is rotatably inserted, and the disc-shaped thrust bearing portion is rotatably inserted. A stepped cylindrical bearing member having a large-diameter cylindrical portion at the open end side, and a disk-shaped thrust holding member sealing the open end of the stepped cylindrical bearing member. Pressure bearing device. 7. The radial thrust bearing portion according to claim 6, wherein a radial dynamic pressure generating groove is formed on one of an outer peripheral surface of the cylindrical portion for the radial bearing and an opposing surface thereof, and surfaces on both axial sides of the disc-shaped thrust bearing portion. Alternatively, a thrust dynamic pressure generating groove is formed on one of the opposing surfaces thereof, and the liquid dynamic bearing device is characterized in that: 8. The liquid dynamic bearing device according to claim 5, wherein the oil repellent is baked after being applied to the facing surface. 9. The liquid dynamic bearing device according to claim 5, wherein the fluorine-containing metal alkoxide is a fluorine-containing metal alkoxide containing silicon as a metal element. 10. The liquid dynamic bearing device according to claim 5, wherein the fluorine-containing metal alkoxide has a fluorine content of 5 atomic% or more. 11. The titanium oxide fine powder according to claim 5, wherein the average particle diameter of the titanium oxide fine powder is 50 to 1000 μm.
A liquid dynamic pressure bearing device characterized by the following range. 12. A spindle motor using the liquid dynamic bearing device according to any one of claims 5 to 11.