JP2000204387A - Lubricating oil, its production, hydrodynamic lubrication bearing, spindle motor and rotor apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a lubricating oil containing solid particles dispersed in high dispersibility and free from the problems of precipitation, deposition, etc., in a hydrodynamic pressure generating part of a hydrodynamic lubrication bearing without lowering the characteristics of a base oil by dispersing porous inorganic particles in a base oil. SOLUTION: The objective lubricating oil is produced by dispersing (A) porous inorganic particles in (B) a base oil. A mineral oil, a synthetic oil, etc., is used as the component B owing to the low volatility and small viscosity, surface tension and frictional coefficient and concrete examples of the oil are ester-type mineral oil, ether-type mineral oil, fluorine-based synthetic oil, etc. The component A acts as a friction decreasing agent in the lubricating oil and is preferably porous quartz bead, porous glass bead, etc. The difference between the apparent specific gravity of the component A and the specific gravity of the component B is preferably within ±20%, more preferably within ±5%, further preferably both specific gravity values are nearly equal to each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lubricating oil used for a bearing for holding a member rotating at a high speed through a lubricating material to a fixed member, and more particularly to a dynamic pressure for holding a rotating member in a non-contact manner. The present invention relates to a bearing, a spindle motor using the dynamic pressure bearing, and a rotating device including the spindle motor as a driving source of a rotating body.

[0002]

2. Description of the Related Art Rotating devices such as a magnetic disk device, an optical disk device, and a scanner including a polygon mirror include:
2. Description of the Related Art A spindle motor having a dynamic pressure bearing, which is a non-contact bearing, is widely used as a drive source of a rotating body such as a magnetic disk, an optical disk, and a polygon mirror. Since the dynamic pressure bearing rotates in a non-contact manner during the rated rotation, the dynamic pressure bearing does not have rotation unevenness or vibration caused by the bearing, and has excellent characteristics of high-speed durability.

[0003] The dynamic pressure bearings are roughly classified into air dynamic pressure bearings and liquid dynamic pressure bearings. Since the air dynamic pressure bearing does not use lubricant such as oil, the surface of the rotating body such as a magnetic disk can be kept clean from oil contamination, etc.
It is widely used in rotating devices for rotating these magnetic disks and the like. However, the air dynamic pressure bearing has extremely low bearing stiffness and the clearance between the bearings is on the order of several microns. Also, it is difficult to obtain a sufficient air dynamic pressure in a low speed rotation range. On the other hand, the liquid dynamic pressure bearing has a high bearing rigidity and is relatively easy to manufacture. In particular, a sufficient dynamic pressure can be obtained at a low speed of about several thousand rotations.

[0004] The liquid dynamic pressure bearing comprises a shaft-like member and a cylindrical member into which the shaft-like member is fitted. A minute gap is provided between the shaft member and the cylindrical member, and the gap is filled with lubricating oil to generate liquid dynamic pressure on the gap side surface of the shaft member or the cylindrical member. (Dynamic pressure groove) is provided and formed as a liquid dynamic pressure generating portion. When the liquid dynamic pressure bearing rotates, the lubricating oil flows along a groove formed in the shaft member or the cylindrical member to generate a liquid dynamic pressure. Can rotate in contact.

[0005]

However, when the liquid dynamic pressure bearing is stationary, the shaft member and the cylindrical member are partially in contact with each other, and the liquid dynamic pressure bearing is started in a state in which both members are in contact with each other. The coefficient of friction between the cylinder and the cylindrical member becomes a problem. If the coefficient of friction between the shaft member and the cylindrical member is large,
The power consumption of the device in which the liquid dynamic pressure bearing is incorporated increases, or the dynamic pressure groove formed in the shaft member or the cylindrical member is broken. Attempts have been made to improve the lubricating oil filled in the liquid dynamic pressure generating portion in order to reduce the friction coefficient at the contact portion between the shaft member and the cylindrical member when the liquid dynamic pressure bearing is started.

Conventional lubricating oils for liquid dynamic bearings include:
An additive such as an antioxidant and a viscosity modifier is added to a base oil. As the base oil, ester-based mineral oil, ether-based mineral oil, fluoride-based synthetic oil, and the like are used. As a means for reducing the friction coefficient of lubricating oil, a method of adding solid particles such as glass beads and amorphous carbon to a base oil has been studied.

However, when solid particles are added to the base oil to reduce the coefficient of friction, the specific gravity of the solid particles differs greatly from the base oil, and the dispersibility of the solid particles in the base oil is poor. Thereafter, as time elapses, the solid particles are easily separated from the base oil, and the solid particles settle and adhere to a specific location in the bearing gap, so that the friction coefficient cannot be reduced for a long time. In order to improve the dispersibility of the solid particles in the lubricating oil, it is conceivable to use a dispersant, but the addition of the dispersant is not practical because the properties of the base oil are reduced.

The present invention solves the above-mentioned drawbacks of the prior art, in which the dispersibility of the solid particles is good without deteriorating the characteristics of the base oil, and the sedimentation in the liquid dynamic pressure generating portion of the liquid dynamic pressure bearing is reduced. It is an object of the present invention to provide a lubricating oil having a small coefficient of friction and having no problems such as adhesion.

Another object of the present invention is to provide a method for producing a lubricating oil capable of stably producing the above-mentioned lubricating oil.

Another object of the present invention is to prevent the dynamic pressure generating groove from being worn or damaged due to contact friction at the time of starting rotation or rotating at a low speed, thereby extending the life of the dynamic pressure bearing.

Another object of the present invention is to provide a spindle motor having a dynamic pressure bearing which consumes less current and has an improved service life.

Another object of the present invention is to provide a rotating body device using the spindle motor as a drive source of a rotating body such as a magnetic disk.

[0013]

The present invention provides (1) a lubricating oil characterized by dispersing porous inorganic particles in a base oil, and (2) a porous silica particle comprising porous quartz beads or The lubricating oil according to the above (1), which is a porous glass bead;
(3) The lubricating oil according to the above (1) or (2), wherein the content of the porous inorganic particles is such that the areal density in the bearing gap is 400 particles / mm ² or less, and (4) the porosity of the porous inorganic particles is The lubricating oil according to any one of the above (1) to (3), wherein the specific gravity of the porous inorganic particles is within ± 20% of the specific gravity of the base oil; (5) ultrasonic dispersion (6) A method for producing a lubricating oil comprising dispersing porous inorganic particles in a base oil using a device and then performing a decompression treatment, (6) a bearing in which a rotating member and a fixed member are combined. The gap between the rotating member and the fixed member is provided in the above (1) to (4).
(4) A dynamic pressure bearing characterized by being filled with the lubricating oil described in any one of (4) and (7) a dynamic pressure bearing described in (6) above. (8) A rotating body device including the spindle motor described in (7) above as a drive source for the rotating body.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The base oil of the lubricating oil of the present invention is difficult to evaporate and has low viscosity, surface tension, and low coefficient of friction.
Mineral oil or synthetic oil is used, and specific examples include ester-based mineral oil, ether-based mineral oil, and fluorine-based synthetic oil.

The porous inorganic particles added to the lubricating oil of the present invention function as a friction reducing agent in the lubricating oil, and it is preferable to use porous quartz beads or porous glass beads. The porous inorganic particles have a spherical or non-spherical outer shape and have continuous or discontinuous pores inside. Porous inorganic particles have a large surface area and good lipophilicity to the base oil as compared with non-porous inorganic particles whose inside is clogged, so that the dispersibility in the lubricating oil is good and the Does not settle out.

The porosity, expressed as the amount of voids in the porous inorganic particles, can be calculated from the following [Equation 1].

Porosity (%) = (W1−W2) / W1 × 100 W1 (g / cm ³ ): a weight per unit volume when the porous inorganic particles are assumed to be non-porous. Specific gravity of the constituent material itself. W2 (g / cm ³ ): Apparent specific gravity of the porous inorganic particles, which is a weight per unit volume actually measured and obtained.

By changing the porosity of the porous inorganic particles, the specific gravity of the particles can be arbitrarily set to reduce the difference in specific gravity with the base oil. The preferred apparent specific gravity of the porous inorganic particles is such that the difference from the specific gravity of the base oil is within ± 20%, more preferably ± 5%, of the specific gravity of the base oil used for the lubricating oil.
It is desirable to make the specific gravity within the range, more preferably the same as the specific gravity of the base oil, from the viewpoint of preventing sedimentation of the porous inorganic particles.

The porosity of the base oil having a specific gravity of 0.81 and porous glass beads made of glass having a specific gravity of 2.5 as the porous inorganic particles will be described as an example. The difference in specific gravity with the base oil within ± 20% means that the apparent specific gravity (W2) of the glass beads is 0.8%.
It is sufficient that 1 ± 20% = 0.648 to 0.972. The specific gravity assuming that there are no pores in the glass beads is 2.5 (W1) specific gravity of the glass itself. Therefore,
The porosity of the porous glass beads having a specific gravity difference from the base oil within ± 20% is from 74.08 to 61.6% according to the above [Equation 1].
Range.

As described above, since the apparent specific gravity can be changed by changing the porosity by using the porous inorganic particles, the difference in specific gravity from the base oil to which the particles are added can be reduced. In addition, it is possible to effectively prevent sedimentation of inorganic particles according to various base oils having different specific gravities.

The size of the porous inorganic particles is preferably from 0.1 to 5 μm, more preferably from 0.5 to 3 μm.
μm. Generally, the gap (bearing gap) filled with the lubricating oil serving as the dynamic pressure generating portion of the liquid dynamic pressure bearing is 3 μm or more, so that if the average particle diameter of the porous inorganic particles is 3 μm or less,
The particles enter the bearing gap and can sufficiently exert the effect of reducing the friction coefficient. The porous inorganic particles have an average particle size of 0.5 μm.
m or more can be actually manufactured, easily obtained, and practical. The effect of reducing the friction coefficient of the lubricating oil can be sufficiently obtained even with porous inorganic particles having a particle diameter of less than 0.5 μm.

The above-mentioned bearing clearance is the size of the actual clearance when the bearing is rotating. When the liquid dynamic pressure bearing is actually rotating, the rotating part rotates in an eccentric state, so that the center of the rotating shaft is slightly displaced from the designed rotation center. Therefore, when actually rotating,
The narrowest bearing clearance is smaller than the design value. Further, the bearing gap (design value) differs depending on the size of the bearing.
In the case of a bearing composed of a shaft member and a cylindrical member into which the shaft member is fitted, the diameter of the shaft member of the smallest bearing is about 3 mm, and the bearing clearance (design value) is about 7.5 μm. . Although the actual bearing gap is smaller than the designed value of 7.5 μm, a gap of 3 μm or more is secured even at the narrowest point.

The amount of the porous inorganic particles to be added is such that when the filler is filled in the bearing gap (design value), the area density, which is the number of particles per unit area when projected from one side of the gap to the other, is 400%.
The number is preferably set to be not more than the number of pieces / mm ^{2, and} more preferably in the range of 100 to 400 pieces / mm ² . If the areal density exceeds 400 / mm ² , sufficient dynamic pressure may not be generated. If the areal density is less than 100, the effect of reducing the coefficient of friction may be insufficient.

The lubricating oil of the present invention may be at least one in which the above porous inorganic particles are dispersed in a base oil, and other additives can be added as needed. Examples of the additive include an antioxidant and a viscosity modifier.

In the method for producing a lubricating oil according to the present invention, the porous inorganic particles are ultrasonically dispersed in the base oil using an ultrasonic dispersing device, and then subjected to a pressure reduction treatment. Ultrasonic dispersion using an ultrasonic dispersion apparatus can disperse porous inorganic particles in base oil without using a dispersant. In the decompression treatment, it is preferable to decompress the base oil containing the ultrasonically dispersed porous inorganic particles at a degree of vacuum of about 10 ⁻³ torr to 10 torr. The decompression time varies depending on the degree of vacuum, but it is sufficient that the air inside the voids of the porous inorganic particles is sufficiently defoamed. In the case where the porous inorganic particles have voids communicating with the surface and voids not communicating with the surface, air present in the voids communicating with the surface may be removed.

After the porous inorganic particles are dispersed, a reduced pressure treatment is performed to replace the air portion filled in the voids inside the porous inorganic particles with the base oil, and the specific gravity of the porous inorganic particles is reduced. Is close to the design value, the dispersion state is stable, and a good dispersion state can be maintained for a long time. After the porous inorganic particles are dispersed in the base oil by ultrasonic dispersion, the specific gravity of the porous inorganic particles is lower than a designed value due to air remaining in the voids communicating with the surface of the inside of the particles unless decompression treatment is performed. Even if the particles are uniformly dispersed immediately after the ultrasonic dispersion, the porous inorganic particles are likely to float and separate when the lubricating oil is allowed to stand for a long time.

FIG. 1 is a diagram for explaining a spindle motor according to one embodiment of the present invention. The spindle motor 1 of the present embodiment includes a disk-shaped fixed base 10 for fixing the spindle motor 1 itself and a rotating shaft part 23, and a flange part 21 which is substantially intermediate in the height direction. And a cylindrical member 30 fixed to the fixing base 10 and provided with a fitting portion 31 for fitting the shaft member, and a part of the rotor. And a closing member fixed to the shaft member.
A stator coil 70 is formed on the outer peripheral portion of the tubular member 30 and forms a part of the rotor. The rotor magnet 60 and the stator coil 70 are formed on an inner circumferential portion obtained by bending an outer edge of the closing member. Confront closely.

FIG. 2 is an enlarged sectional view of the bearing of the spindle motor shown in FIG. As shown in FIG.
0 has a flange portion 21 functioning as a thrust bearing. The flange portion 21 protrudes from the shaft portion 23 in a flange shape, and its upper surface 24 and lower surface face the inner peripheral portion of the cylindrical member 30 with a small gap. Upper and lower surfaces 24, 25 of the flange portion 21
A fluid dynamic pressure generating groove (not shown) is formed in one or both of the inner peripheral portions of the cylindrical member 30 facing the same.

A cylindrical portion 22 for a dynamic pressure bearing is formed below the flange portion 21 of the shaft member 20. The outer peripheral surface 26 of the cylindrical portion 22 for a dynamic pressure bearing has a cylindrical member 30 with a small gap.
Opposes the inner peripheral portion. Similarly, the bottom surface 27 of the dynamic pressure bearing cylindrical portion 22 faces the inner peripheral portion of the cylindrical member 30 with a small gap. Outer peripheral surfaces 26 of these cylindrical portions 22 for dynamic pressure bearings,
A fluid dynamic pressure generating groove (not shown) is formed on one or both of the opposing surfaces on the bottom surface 27 and the inner peripheral portion of the cylindrical member 30.

A minute gap formed between the shaft member 20 and the cylindrical member 30 is filled with a lubricating oil containing the porous inorganic particles of the present invention. The lubricating oil is introduced into the gap between the shaft member 20 and the cylindrical member 30 by a vacuum injection method or a dropping method. The gap between the bottom surface 27 of the dynamic pressure bearing cylindrical portion 22 and the bottom surface 32 of the fitting portion 31 of the cylindrical member 30, the outer peripheral surface 26 of the dynamic pressure bearing cylindrical portion 22, and the side surface 35 of the fitting portion 31
The lubricating oil is introduced so as to fill the gap between the upper surface 24 and the gap between the upper surface 24 of the flange portion 21 and the opposite flange upper surface 34.

As shown in FIG. 3, when the bearing is stationary, the shaft member 20 is not in the center of the fitting portion of the cylindrical member 30, but is in one-sided contact. At this time, the shaft-like member 2
The lubricating oil 40 containing the porous inorganic particles exists between the cylinder member 30 and the cylindrical member 30. When the rotation is started, the shaft-like member 20 starts rotating in a state in which a part thereof is in contact with the cylindrical member 30, but the friction coefficient is reduced by the porous inorganic particles in the lubricating oil 40, and the smooth start-up is performed. be able to. Further, in a state where sufficient liquid dynamic pressure is not generated at the time of low-speed rotation until the rotation reaches the rated rotation, the gap is filled even if the shaft-shaped member 20 rotates in contact with the cylindrical member 30. The rotation is smoothly performed by the lubricating oil 40. Then, when the rotation speed reaches the rated rotation, the lubricating oil contacts and flows along the dynamic pressure generating groove to generate liquid dynamic pressure, and as shown in FIG. Is held in non-contact with the tubular member 30.

A liquid dynamic pressure generating groove is formed in a minute gap between the shaft member 20 and the cylindrical member 30. The size of the minute gap is about 4 to 20 μm,
An appropriate size according to the diameter of the shaft-like member 20 is selected at the time of design. The liquid dynamic pressure generating groove includes a thrust dynamic pressure generating groove and a radial dynamic pressure generating groove. The thrust dynamic pressure generating groove is provided on one or both surfaces of the bottom surface 27 of the dynamic pressure bearing cylindrical portion 22 and the bottom surface 32 of the fitting portion 31 of the cylindrical member 30, and on the lower surface of the flange portion 21. 25 and one or both surfaces of a flange-facing lower surface 33 facing the same, and one or both surfaces of the upper surface 24 of the flange portion 21 and the flange-facing surface 34 facing the same. The radial dynamic pressure generating groove is formed on one or both surfaces of the outer peripheral surface 26 of the cylindrical portion for dynamic pressure bearing 22 and the side surface 35 of the fitting portion 31 facing each other.

The dynamic pressure bearing of the present invention, which rotates in a non-contact manner by the liquid dynamic pressure filled with the lubricating oil, is incorporated in the spindle motor 1 in this embodiment.
Is a closing member 50 constituting a rotor and the closing member 50
A rotor magnet 60 formed on an inner peripheral portion of the outer periphery of the rotor magnet is bent, and a stator coil 70 is provided in proximity to and facing the rotor magnet 60. That is, the spindle motor 1 of the present embodiment is a rotary shaft type spindle motor in which a rotor is supported on a stator by a liquid dynamic pressure bearing. In this spindle motor 1,
When the motor start switch is turned on, the stator coil 7
A current flows through the rotor, and the rotor rotates in a certain direction due to interference between the magnetic field generated by the current and the magnetic field of the rotor magnet.

FIG. 4 shows a rotating body device employing the spindle motor 1 of this embodiment. This rotating device is a magnetic disk device 5 in which a plurality of rotating magnetic disks 3 are attached to the above-described spindle motor 1, and each magnetic head 4 faces each magnetic disk 3. The dynamic pressure bearing of the present invention is not limited to a magnetic disk device, but can be applied to other optical disk devices, magneto-optical disk devices, polygon mirror devices, and other small precision rotating body devices. Since these rotary devices are provided with the liquid dynamic pressure bearing using the lubricating oil of the present invention, the friction coefficient at the time of startup is low, the power consumption is small, and good performance can be maintained for a long period of time.

[0034]

EXAMPLE 1 Porous quartz beads having a porosity of 60% and an average particle size of 0.5 to 1 μm were mixed with an ether base oil having a specific gravity of 0.81 and ultrasonically dispersed for 5 minutes. For 10 minutes to obtain a lubricating oil. When this lubricating oil was used by filling it into a liquid dynamic pressure bearing, the friction coefficient was reduced by about 35% as compared with a lubricating oil to which no porous quartz beads were added. Also,
No sedimentation of the beads was observed for more than 10,000 hours.

Example 2 Porous quartz beads having a porosity of 18% and an average particle diameter of 2 to 3 μm were mixed with a fluorine-based base oil having a specific gravity of 1.82, ultrasonically dispersed for 20 minutes, and then 15 minutes with a simple vacuum pump. The lubricating oil was obtained by performing a vacuum treatment. When this lubricating oil was compared with a lubricating oil to which no porous quartz beads were added, the coefficient of friction was reduced by about 28%. No sedimentation of beads was observed for 10,000 hours or more.

[0036]

Since the lubricating oil of the present invention is obtained by dispersing porous inorganic particles in a base oil, the lubricating oil of the present invention does not cause sedimentation of particles compared to conventional lubricating oils using non-porous particles. A lubricating oil with a small coefficient of friction is obtained. Since the porous inorganic particles have good dispersibility and are unlikely to settle, the particles do not settle or adhere to a specific place in the bearing gap in the liquid dynamic pressure generating portion of the liquid dynamic pressure bearing, and are good for a long time. The effect of reducing the coefficient of friction can be exhibited. Further, there is no fear that the dynamic pressure generating groove is damaged at the time of starting.

Since the bearing using the lubricating oil of the present invention can smoothly rotate, especially at the time of startup, the equipment equipped with this bearing can reduce power consumption. Further, the bearing using the lubricating oil of the present invention can provide a large bearing rigidity because the lubricating oil supports the shaft-like member by the dynamic pressure generated from the liquid and the van der Waals force of the porous inorganic particle component. Becomes possible, and when applied to spindle motors, etc.
The design margin can be increased, and as a result, a highly reliable and inexpensive spindle motor can be provided.

The method for producing a lubricating oil of the present invention comprises dispersing porous inorganic particles in a base oil using an ultrasonic dispersion device,
By adopting the method of performing the reduced pressure treatment, the porous inorganic particles can be stably dispersed. As a result, there is no danger that the porous inorganic particles rise and separate over time,
A lubricating oil having an excellent coefficient of friction is reliably obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a spindle motor provided with a dynamic pressure bearing of the present invention.

FIG. 2 is an enlarged sectional view showing a dynamic pressure bearing portion of the spindle motor of FIG.

FIG. 3 is an enlarged sectional view showing a part of the dynamic pressure bearing portion of the spindle motor of FIG. 1 in a stationary state.

FIG. 4 is a perspective view showing a magnetic disk device which is an example of the rotating device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Spindle motor 3 Magnetic disk 4 Magnetic head 5 Magnetic disk device 10 Fixed base 20 Shaft member 21 Flange part 22 Cylindrical part for dynamic pressure bearings 23 Shaft member 24 Upper surface 25 Lower surface 30 Cylindrical member 31 Fitting part 32 Bottom surface 33 Flange portion opposition Lower surface 34 Upper surface facing flange

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) C10N 30:06 40:02 70:00

Claims (8)

[Claims] 1. A lubricating oil comprising porous inorganic particles dispersed in a base oil. 2. The lubricating oil according to claim 1, wherein the porous inorganic particles are porous quartz beads or porous glass beads. 3. The lubricating oil according to claim 1, wherein the content of the porous inorganic particles is such that the areal density in the bearing gap is 400 particles / mm ² or less. 4. The porous inorganic particle according to claim 1, wherein the porosity of the porous inorganic particle is formed so that the specific gravity of the porous inorganic particle is within ± 20% of the specific gravity of the base oil. Lubricating oil. 5. A method for producing a lubricating oil, comprising: dispersing porous inorganic particles in a base oil using an ultrasonic dispersion device; 6. A bearing in which a rotating member and a fixed member are combined, wherein a gap between the rotating member and the fixed member is filled with the lubricating oil according to any one of claims 1 to 4. A dynamic pressure bearing characterized by being made. 7. A spindle motor comprising a bearing comprising the dynamic pressure bearing according to claim 6. 8. A rotator device comprising the spindle motor according to claim 7 as a drive source for the rotator.