JP2002241178A - Electrically conductive ceramic bearing ball, ball bearing, motor provided with the same bering, hard disk device, and polygon scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrically conductive ceramic bearing ball which has excellent wear resistance and is hardly electrified and in which no abnormal sound and vibration are caused even when used for a device operated at a high rotational speed, such as a hard disk drive. SOLUTION: The ceramic bearing ball is produced by forming a powdery raw material containing silicon nitride powder and titanium nitride powder into a spherical green body, sintering the green body to obtain a spherical sintered body and subjecting the sintered body to outer surface polishing and has such a structure that a titanium nitride phase derived from the above titanium nitride powder is dispersed in a silicon nitride matrix derived from the above silicon nitride powder, wherein: the silicon nitride powder has a <=0.8 μm 50% particle size measured with a laser diffraction particle size meter and a 10-13 m2/g BET specific surface area; and the titanium nitride powder has a <=3.0 mass % oxygen content, a <=0.3 mass % iron content and a <=3.0 μm 50% particle size measured with the laser diffraction particle size meter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a conductive ceramic bearing ball, a ball bearing using the conductive ceramic bearing ball, a motor with a bearing using the ball bearing, a hard disk drive, and a polygon scanner.

[0002]

2. Description of the Related Art In general, bearing balls are made of metal such as bearing steel. However, in order to impart more wear resistance, those using ceramic bearing balls have begun to spread. I have. The ceramic used is, for example, a silicon nitride ceramic, an alumina ceramic or a zirconia ceramic.

[0003]

The above-mentioned bearing balls are all insulators, and have the property of being easily charged by static electricity generated by friction while rotating as a bearing rolling element. If such charging occurs excessively, for example, in the case of a small-diameter ball or the like, a smooth process progress is hindered, for example, the ball adheres to an apparatus (for example, a container) or the like during production, or dust adheres to the ball. There are cases.

Further, bearing balls used as bearings for precision electronic equipment, for example, computer hard disk drives, are used at high speeds. Therefore, if foreign matter such as dust adheres to the balls, the inner ring or the outer ring due to static electricity, a different kind is obtained. It often causes sound and vibration.

[0005] As for bearing balls used in such precision electronic equipment, there has been an attempt to produce a conductive ceramic bearing ball having a structure in which conductive ceramic is dispersed in an insulating ceramic substrate. If a large amount of the conductive ceramic phase is contained for improvement, the strength and wear resistance of the bearing ball may be insufficient. Also, depending on the type of impurities in the raw materials used, when applied to high-speed rotating precision electronic equipment such as a hard disk drive for computers and a polygon scanner, defects that cause abnormal noise and vibration may occur. .

SUMMARY OF THE INVENTION An object of the present invention is to prevent the ball from being easily charged and, consequently, to reduce the flow of the product in the manufacturing process and to cause problems such as generation of abnormal noise and vibration due to adhesion of foreign matter even when applied to a high-speed rotating bearing. A conductive ceramic bearing ball which is difficult and has sufficient strength and wear resistance for practical use, a ball bearing using the same, a motor with a bearing using the ball bearing, a hard disk drive using the motor with the bearing, and To provide a polygon scanner.

[0007]

In order to solve the above-mentioned problems, a conductive ceramic bearing ball of the present invention is a composite having a structure in which a titanium nitride-based phase is dispersed in a silicon nitride substrate. Composed of ceramic, the composite ceramic having an oxygen content of 3.0% by mass or less,
The iron content is 0.2% by mass or less, and the surface electrical resistivity is 10 ⁶ Ω · cm or less.

[0008] Silicon nitride ceramics are lighter in weight and superior in abrasion resistance than other ceramic materials, and are well-balanced in mechanical strength and toughness. Therefore, it is widely used as a structural material for various sliding parts, cutting tools, and bearing balls. However, since it is a ceramic having a very high insulating property, there is an aspect in which the above-mentioned charging problem is likely to occur when applied to a bearing ball. Therefore, in the present invention, the ball is formed of a composite ceramic having a structure in which a titanium nitride-based phase having excellent conductivity and hardly causing a decrease in the strength of the entire ceramic when dispersed in a silicon nitride substrate is dispersed. Titanium nitride alone is inferior to silicon nitride in strength and abrasion resistance, but since it has relatively high lattice matching with the silicon nitride-based phase, it can improve conductivity if it is dispersed to some extent. Therefore, even if a considerable amount is blended in the silicon nitride substrate, the ceramic has a characteristic that the strength and wear resistance of the whole ceramic are hardly reduced by the dispersion strengthening action.

The present inventors have studied and found that, depending on the content of specific impurities, specifically iron, in the composite ceramic, the strength and wear resistance of the finally obtained bearing ball or the bearing A considerable difference occurs in the vibration and acoustic characteristics when used as, and the content of the impurities is kept at a certain level or less, while ensuring good conductivity, strength and wear resistance, and vibration and The present inventors have found that a conductive ceramic bearing ball having excellent acoustic characteristics can be obtained, and have completed the present invention.

When the iron content in the composite ceramic exceeds 0.2% by mass, the content of iron-based inclusions in the ceramic balls increases, and the inclusions exposed on the polished surface cause the inclusions to be used as bearings. Abnormal noise and vibration are likely to occur when used. The content of iron in the composite ceramic is preferably set to 0.05% by mass or less, more preferably,
As far as no problem arises in cost, it is preferable that it is not contained as much as possible (thus containing 0% by mass). On the other hand, when the oxygen content exceeds 3.0%, it is difficult to secure the conductivity of the obtained ceramic ball. However, it is difficult to completely remove oxygen unavoidably mixed from the raw material,
At least about 2% by mass may be contained.

On the other hand, if the electric resistivity exceeds 10 ⁶ Ω · cm, the ball is likely to be charged when the ball is used by being incorporated in a bearing. When the electrical measurement is performed through the above-described bearing ball, the electrical resistivity of the ceramic constituting the ball is slightly reduced, for example, to 10 ⁵ Ω ·
cm or less. In this specification, the electrical resistivity refers to an electrical resistivity measured by a four-probe method by bringing a probe into contact with the surface of a ball formed of constituent ceramics.

Next, the conductive ceramic bearing ball of the present invention has a 50%
A silicon nitride powder having a particle diameter of 0.8 μm or less and a BET specific surface area of 10 to 13 m ² / g, an oxygen content of 3.0 mass% or less, and an iron content of 0.3 mass%
A step of sintering a spherical compact of a raw material powder containing titanium nitride powder having a 50% particle size of 3.0 μm or less and a 50% particle diameter measured by a laser diffraction type particle sizer; And a step of polishing the outer surface.

The inventors of the present invention have studied that when a conductive ceramic bearing ball provided with conductivity by using a silicon nitride powder and a titanium nitride powder is produced, the finally obtained bearing is obtained due to a difference in raw material powder. It has been found that considerable differences occur in the strength and wear resistance of the ball, or in the vibration and acoustic characteristics when used as a bearing. Further, as a result of further intensive studies, it was found that the factors such as the particle size and BET of the silicon nitride powder as the substrate
The specific surface area value, the particle diameter of the titanium nitride powder to be dispersed, the impurity concentration contained and the fact that the respective parameters of inclusions were closely involved were determined, and the purity, particle size or specific surface area value of the raw material powder was described above. By adjusting the value in the numerical range, it has been found that a conductive ceramic bearing ball having excellent strength, abrasion resistance, vibration, and acoustic characteristics while maintaining good conductivity can be obtained.

In this specification, as shown in FIG. 8, the relative cumulative frequency of the particles from the small particle size side is such that the particles to be evaluated are arranged in the order of the particle size, and When counting the frequency of particles from the particle size side, the cumulative frequency up to the particle size of interest is Nc, and the total frequency of the particles to be evaluated is No.
Means a relative frequency nrc expressed by nrc = (Nc / No) × 100 (%). And the X% particle size is
It means the particle size corresponding to nrc = X (%) in the above arrangement. For example, a 50% particle size is nrc = 50
(%).

Although the principle of measurement of a laser diffraction type particle sizer is well known, in brief, a sample powder is irradiated with laser light, the diffracted light by the powder particles is detected by a photodetector, and the detection information is obtained. The particle diameter can be known from the scattering angle and intensity of the diffracted light obtained from the above. As shown schematically in FIG. 7, the ceramic raw material powder has a plurality of primary particles aggregated to form secondary particles due to various factors such as the action of the added organic binder and the action of electrostatic force. Often. In this case, the measurement by the laser diffraction particle sizer does not cause a large difference between the diffraction behavior of the incident laser light by the aggregated particles and the diffraction behavior by the isolated primary particles. It cannot be distinguished from each other whether it is the particle size of the particles or the particle size of the aggregated secondary particles. That is, the particle diameter measured by this method is a value reflecting the secondary particle diameter D in FIG. 7 (in this case, isolated primary particles that do not cause aggregation are also regarded as secondary particles in a broad sense). Also, the average particle diameter calculated based on this or 50
The% particle diameter reflects the average particle diameter or the 50% particle diameter of the secondary particles. In the case of adjusting the molding base powder for rolling granulation described below, the particle size of the powder means a numerical value in a stage before adjustment to the molding base powder.

On the other hand, the specific surface area of the molding base powder is measured by an adsorption method. Specifically, the specific surface area can be determined from the amount of gas adsorbed on the powder surface. In general, an adsorption curve showing the relationship between the pressure of a measurement gas and the amount of adsorption is measured, and a known BET formula (collection of the inventors, Brunauer, Emmett, Teller) for multi-molecule adsorption is obtained. By applying, the adsorption amount vm when the monomolecular layer is completed is obtained, and the BET specific surface area value calculated from the adsorption amount vm is used. However, when approximately equivalent results are obtained, a simple method that does not use the BET equation,
For example, a method of directly reading the adsorption amount vm of the monolayer from the adsorption curve may be adopted. For example, when a section in which the adsorption amount is substantially proportional to the gas pressure appears in the adsorption curve, there is a method of reading the adsorption amount corresponding to the end point on the low pressure side of the section as vm (The Journal of American Chemical Society, 57
Volume (1935), p. 1754, Brunauer and Emet
t). In any case, in the specific surface area value measurement by the adsorption method, the gas molecules to be adsorbed also penetrate into the secondary particles and cover the surface of the individual primary particles constituting the secondary particles, and as a result, the specific surface area value is It reflects the specific surface area of the primary particles, and thus the average value of the primary particle diameter d in FIG. It should be noted that the specific surface area value measured by such an adsorption method does not naturally fluctuate greatly before and after adjusting to a molding base powder for rolling granulation described later.

Further, in the present specification, "main component"
The term “subject” or “mainly” means that the content of the component in the substance of interest is 50% by weight or more, unless otherwise specified. The titanium nitride-based phase is a phase containing titanium nitride as a main component.

The titanium nitride powder 50 used as a raw material
If the% particle size is larger than 3.0 μm, a considerably large void is formed when crystal grains of the titanium nitride-based phase appearing on the polished surface of the bearing ball are dropped off, causing abnormal noise and vibration when used as a bearing. It will be easier. In addition, reducing the particle size more than necessary, such as lengthening of the pulverization time, causes a rise in the cost of preparing the raw material powder,
The particle size is adjusted in such a range that such a problem does not occur. The 50% particle diameter of the titanium nitride powder is more desirably adjusted in the range of 0.9 to 1.5 μm.

When the oxygen content in the titanium nitride powder exceeds 3.0% by mass, a large amount of titanium oxide having poor conductivity is generated, so that it is difficult to sufficiently secure the conductivity of the bearing ball obtained. Becomes In addition, when the titanium nitride powder is covered with the titanium oxide film, diffusion during sintering is hindered and sinterability is reduced, so that a dense ceramic ball may not be obtained. The oxygen content in the titanium nitride powder is desirably 2.5% or less, and more desirably, is as low as possible within a range that does not cause a problem in cost.

Next, most of the iron components in the titanium nitride powder are iron-based contaminants that are abraded and mixed in from the pulverizer during the production of the titanium nitride powder. When the iron content in the titanium nitride powder exceeds 0.3% by mass, the content of the Fe-based inclusions derived from the iron-based contaminants increases in the obtained ceramic ball, and the polished surface Due to the effect of the exposed inclusions, abnormal noise and vibration tend to occur when used as a bearing. The iron component in the titanium nitride powder is preferably set to 0.1% by mass or less, and more desirably, is contained as little as possible within a range that does not cause a problem in cost.

Next, the silicon nitride powder used as a raw material
BET specific surface area value of 10 to 13 m ²/ G
And the silicon nitride crystal in the resulting ceramic ball
Local coarsening of particles can be suppressed, and titanium nitride-based
Since the dispersibility of the crystal particles can be increased,
Improved wear and
Generation of noise and vibration can be suppressed. BET specific surface area value is 10
m²/ G, coarse silicon nitride at the stage of the raw material powder
As the ratio of the raw powder particles increases, the resulting ceramic
Silicon balls with locally coarse silicon nitride crystal grains
Are easily formed. As a result, the polished surface is coarse
Large silicon nitride-based crystal particles
Gap is easily formed, and when used as a bearing
It may cause abnormal noise and vibrations. On the other hand, BET ratio table
Area value is 13m²/ G of silicon nitride-based powder
In addition to cost increase such as prolonged time, liquidity deteriorates
Therefore, handling during manufacture becomes difficult.

On the other hand, by setting the 50% particle diameter of the silicon nitride powder used as a raw material to 0.8 μm or less, the strength of the obtained bearing ball is improved, and furthermore, the crystal falling off on the polished surface is reduced. Since the size of the particles is generally small, it is easy to secure the accuracy of the polished surface represented by the sphericity, the irregular diameter, and the like. On the other hand, if the particle size of the silicon nitride-based powder is made smaller than necessary, the cost of preparing the raw material powder increases, such as the lengthening of the pulverization time, so the particle size is adjusted within a range that does not cause such problems. I do. The particle size of the silicon nitride powder is more desirably 0.3 to 0.6 μm.
It is better to adjust within the range.

Next, the content of the titanium nitride phase in the silicon nitride substrate in the composite ceramic is desirably 10 to 70% by volume. When the titanium nitride phase is less than 10% by volume, the conductivity of the constituent ceramics becomes insufficient (for example, it becomes impossible to secure 10 ⁶ Ω · cm or less in the electric resistivity), and the above-mentioned effect of the present invention is sufficiently achieved. May not be achieved. On the other hand, if it exceeds 70% by volume, the characteristics of the silicon nitride substrate cannot be sufficiently exhibited, and the improvement in wear resistance and the like due to the formation of a composite material cannot be expected much. The content of the titanium nitride phase is more desirably 15 to 70% by volume, and further desirably 30 to 50% by volume.

In the present invention, the composite ceramic is
As sintering aid components, 3A, 4A, 5A, 3
B (eg, Al (alumina, etc.)) and 4B (eg, S
i (silica or the like)) and at least one element selected from the group consisting of Mg and 1 to 10% by mass in terms of oxide. These exist mainly in the oxide state in the sintered body. If the sintering aid component is less than 1% by mass, it is difficult to obtain a dense sintered body. On the other hand, if it exceeds 10% by mass, insufficient strength and toughness are caused. The content of the sintering aid component is
Desirably, the content is 2 to 8% by mass.

The sintering aid component of group 3A includes S
c, Y, La, Ce, Pr, Nd, Sm, Eu, Gd,
Tb, Dy, Ho, Er, Tm, Yb, and Lu are generally used. The content of these elements R is RO only for Ce.
₂ and others are calculated using R ₂ O ₃ type oxides. Of these, oxides of heavy rare earth elements of Y, Ce, Tb, Dy, Ho, Er, Tm, and Yb are preferably used because they have the effect of improving the strength, toughness, and wear resistance of the sintered body. Is done.
In addition, magnesia spinel, zirconia and the like can also be used as a sintering aid.

The silicon nitride phase is mainly composed of Si ₃ N ₄ having a β conversion of 70% by volume or more (preferably 90% by volume or more). In this case, the silicon nitride phase is Li,
It may be a solid solution of metal atoms such as Ca, Mg, and Y. For example, it can be exemplified Sialon which is expressed by the following general formula; _{beta-sialon: Si 6-z Al z O} z N 8-z (z =
0-4.2) α-sialon: M _x (Si, Al) ₁₂ (O, N)
₁₆ (x = 0 to 2) M: Li, Mg, Ca, Y, R (R is a rare earth element excluding La and Ce).

The sintering aid component mainly constitutes a binder phase, but a part thereof may be taken into a silicon nitride-based phase or a titanium nitride-based phase. The binder phase may contain unavoidable impurities, for example, silicon oxide contained in the silicon nitride raw material powder, in addition to components intentionally added as a sintering aid.

It is desirable that the silicon nitride powder used as a raw material has an α-rate (a ratio of α-silicon nitride in the total silicon nitride) of 70% or more.
At least one element selected from the group consisting of rare earth elements, 3A, 4A, 5A, 3B, and 4B elements;
0% by mass, preferably 2 to 8% by mass.
In addition, at the time of compounding the raw materials, in addition to oxides of these elements, compounds which can be converted to oxides by sintering, for example, carbonates, hydroxides and the like may be mixed.

Next, the present invention also provides a ball bearing in which a plurality of the above-mentioned ceramic balls are incorporated as bearing rolling elements. Such ball bearings
For example, a hard disk drive, a CD-ROM drive,
It can be effectively used as a bearing ball for a rotary drive bearing in a computer peripheral device such as an MO drive or a DVD drive, or a precision device such as a polygon scanner such as a laser printer. High-speed rotation of, for example, 8000 rpm or more (in the case where high-speed performance is required, 10,000 rpm or more and 30,000 rpm or more) is required for the bearing of the rotary drive unit in these precision instruments. Even when used, generation of abnormal noise and vibration is effectively prevented or suppressed, and exfoliation on the surface does not easily occur and is excellent in wear resistance. In recent years, the production of laser printers and computer peripherals including hard disk drives has exploded, and there has been a strong demand for a technique for producing small-diameter, high-performance ceramic bearing balls.

Therefore, as in the present invention, a part of the constituent ceramic is made of a titanium nitride phase, and by imparting appropriate conductivity to the ceramic, the charging of the bearing balls can be effectively prevented or suppressed. . Thereby, for example, in the case of a small-diameter ball or the like, a problem that the ball adheres to a device (for example, a container) due to static electricity during manufacturing and a smooth process progress is prevented is less likely to occur. Further, when used in precision electronic equipment used at high speed rotation, for example, a computer hard disk drive, the adhesion of foreign matter due to the electrification of the ball, and hence the generation of abnormal noise and vibration are effectively prevented or suppressed. For example, in such precision electronic equipment, high-speed rotation (for example,
m), the life can be ensured for a long period of time.

Also, depending on the application field of the bearing,
When the conductivity of the bearing ball is improved, the following effects different from the above-described charging due to static electricity may occur. For example, in a semiconductor wafer measuring device, for example, in a flatness measuring device, a wafer is placed on a rotation measurement table and rotated to conduct electricity between the wafer and the rotation measurement table to measure the capacitance. A method of evaluating the flatness of the wafer based on the measured value of the capacitance has been adopted, in such a case,
Normally, the rotation measurement table is energized by using the bearing and the rotating shaft of the table as conduction paths. Therefore, in order to secure a conduction path between the inner and outer races of the bearing, the bearing balls used in the above-mentioned field have conventionally been exclusively made of metal such as bearing steel. However, metal bearing balls are inferior in wear resistance to ceramics, and therefore have disadvantages such as dust generation and short life. On the other hand, if a normal insulating ceramic is used as the ball material, there is a problem that a conduction path cannot be secured.

Therefore, as in the present invention, by providing a part of the ceramic constituting the ball with a titanium nitride phase to impart conductivity, it is possible to use a ceramic having better wear resistance than metal, Conduction paths necessary for the above-described measuring device can be secured.

[0033]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 5 shows an embodiment of an apparatus used in the step of preparing a green body powder for molding. In the apparatus, the hot air flow passage 1 is formed to include a vertically arranged hot air duct 4, and a gas flow member that allows hot air to pass therethrough and does not allow the drying medium 2 to pass therethrough, in the middle of the hot air duct 4. For example, a media holding unit 5 formed of a net or a perforated plate is formed. Then, on the medium holding portion 5, the dry media 2 composed of ceramic spheres mainly composed of any one of alumina, zirconia, and their mixed ceramics are accumulated, and a layered dry media aggregate 3 is formed. .

On the other hand, as a raw material, a silicon nitride powder, a titanium nitride powder, and a sintering aid powder are mixed at a ratio of 15 to 70 (preferably 30 to 50) of a titanium nitride phase in a composite ceramic finally obtained. It is prepared in the form of a slurry obtained by blending so as to obtain a volume%, further adding an aqueous solvent, and wet-mixing (or wet-mixing / grinding) with a ball mill or an attritor. Titanium nitride powder having an oxygen content of 3.0% by mass or less, an iron content of 0.3% by mass or less, and a 50% particle size measured by a laser diffraction type particle size analyzer of 3.0 μm or less. Is used. The silicon nitride powder has a 50% particle size of 0.8 μm or less measured by a laser diffraction type particle sizer and a BET specific surface area of 1%.
Those having 0 to 13 m ² / g are used.

As shown in FIG. 5, the dry media assembly 3
On the other hand, the hot air is circulated in the hot air duct 4 so as to move upward from the lower side of the medium holding portion 5 while moving the drying medium 2 up. On the other hand, as shown in FIG.
Is pumped up from the slurry tank 20 by the pump P, and is dropped and supplied to the dry media assembly 3 from above. Thereby, as shown in FIG. 6, the slurry is dried by hot air and adheres to the surface of the drying medium 2 in the form of the powder aggregation layer PL.

Then, by the flow of hot air, the drying medium 2 repeatedly hits and falls and strikes each other, and the powder agglomeration layer PL is pulverized into base powder particles 9 for molding by the rubbing caused by the hitting. . The crushed base powder particles 9 for molding include those in the form of isolated primary particles, but are mostly secondary particles in which the primary particles are aggregated. The molding base powder particles 9 having a particle diameter of a certain size or less flow downstream along with the hot air (FIG. 6). On the other hand, the crushed particles larger than a certain size are not blown off by the hot air but fall again to the dry media assembly 3 and are further crushed between the media. In this way, the molding base powder particles 9 that have flowed to the downstream side together with the hot air are collected as the molding base powder 10 by the collection unit 21 via the cyclone S.

In FIG. 5, the diameter of the drying medium 2 is
It is set appropriately according to the flow cross-sectional area of the hot air duct 4. If the diameter is insufficient, the impact force on the powder agglomeration layer formed on the medium is insufficient, and a molding base powder having a particle diameter within an intended range may not be obtained. On the other hand, if the diameter is too large, the driving force of the drying medium 2 is less likely to occur even when hot air is circulated, so that the hitting force is also insufficient, and a molding base powder having a particle diameter within a desired range can be obtained. May not be. Note that it is desirable to use a dry medium 2 having a uniform size as much as possible in order to form an appropriate gap between the media and promote the movement of the medium during hot air circulation.

The filling depth t1 of the drying medium 2 in the drying medium assembly 3 is appropriately set in accordance with the flow rate of the hot air and within a range in which the flow of the medium 2 occurs without excess or deficiency. If the filling depth t1 is too large, the flow of the drying medium 2 becomes difficult, and the impact force is insufficient, so that a molding base powder having a desired range of particle diameter may not be obtained. On the other hand, if the filling depth t1 is too small, the amount of the dry medium 2 is too small, and the frequency of impact is reduced, leading to a reduction in processing efficiency.

Next, the temperature of the hot air is appropriately set within a range in which the drying of the slurry proceeds sufficiently and no problems such as thermal deterioration occur in the powder. For example, when the solvent of the slurry is mainly water, when the hot air temperature is lower than 100 ° C., the supplied slurry does not sufficiently dry, and the moisture content of the obtained molding base powder becomes too high. Agglomeration is likely to occur, and a powder having an intended particle size may not be obtained.

Further, the flow rate of the hot air is appropriately set within a range in which the drying medium 2 is not blown to the collection section 21. If the flow velocity is too low, the flow of the drying medium 2 becomes difficult, and the impact force is insufficient, so that a molding base powder having a particle diameter within an intended range may not be obtained. On the other hand, if the flow velocity is too high, the drying medium 2 rises too high and the collision frequency is rather reduced, leading to a reduction in processing efficiency.

The molding base powder 10 thus obtained is
It can be formed into a spherical shape by the rolling granulation molding method. That is, as shown in FIG. 1, the molding base powder 10 is put into a granulation container 32, and as shown in FIG. 2, the granulation container 32 is driven to rotate at a constant peripheral speed. The granulation container 3
Water W is supplied to the molding base powder 10 in 2, for example, by spraying or the like. As shown in FIG. 3 (a), the injected molding base powder 10 is spherically aggregated while rolling on an inclined powder layer 10k formed in a rotating granulation container to form a compact 80. . The operating conditions of the tumbling granulator 30 are adjusted so that the relative density of the obtained compact 80 is 61% or more. Specifically, the rotation speed of the granulation container 32 is adjusted at 10 to 200 rpm, and the amount of water supply is such that the moisture content in the finally obtained molded body is 10 to 20 rpm.
It is adjusted so as to be mass%.

In performing the rolling granulation, as shown in FIG. 1, a molding core 50 is separately provided to promote the growth of the molding.
(Which can be produced by press-molding ceramic powder or by injection-molding with a resin binder) is desirably charged into the granulation container 32. In this way, as shown in FIG. 3A, while the molding core body 50 is rolling on the molding base powder layer 10k, as shown in FIG.
The molding base powder 10 adheres and agglomerates in a spherical shape around the molding core 50 to form a spherical molded body 80 (rolling granulation step).
By sintering the molded body 80, a bearing element ball 90 is obtained. In addition, in FIG.
0 into the granulation container 32, and agglomerates of the powder are generated by rotating the container at a lower speed than at the time of growing the compact, and when a sufficient amount and size of the aggregate are generated, By increasing the rotation speed of the container 32, the aggregates
The molded body 80 may be grown so as to be used as zero. In this case, it is not necessary to intentionally put the nucleus produced in a separate process together with the molding base powder 10 into the container 32 as described above.

The molded core body 50 can stably maintain its shape without collapse even when a slight external force acts. As a result, as shown in FIG. 3A, even when rolling on the green body powder layer for molding 10k, a reaction due to its own weight can be reliably received. Further, as shown in FIG. 3 (c), it is considered that the powder particles rolled up when rolled can be pressed firmly against the surface, so that the powder is appropriately compressed and the high-density aggregate layer 10a can be grown. . In addition, it is also possible to perform rolling granulation without using a core. In this case, as shown in FIG. 3D, the agglomerate 100 corresponding to the nucleus has a slightly low agglomeration degree at the initial stage of molding and is weak. It is advisable to drop a little.

If the compact 80 is fired, the titanium nitride phase is contained in the silicon nitride ceramic in an amount of 10 to 70% by volume (preferably 15 to 70% by volume, more preferably 3 to 70% by volume).
0-50 volume%) dispersed composite ceramic elementary sphere (hereinafter, referred to as
Simply called elementary spheres). In the present specification, the content of the titanium nitride phase by volume% is as follows:
It is considered that the area ratio of the titanium nitride phase in the polished cross section of the composite ceramic is approximately the same. The calcination may be gas pressure calcination in which the calcination is performed in an atmosphere containing at least nitrogen of 1 atm or more and 200 atm or less, or 200 to 2000
This is performed by hot isostatic pressing (HIP), which is performed in an atmosphere containing atm nitrogen. The firing temperature is, for example, 1
The temperature is preferably set in the range of 500 to 1800 ° C. If the firing temperature is lower than 1500 ° C., defects such as pores cannot be eliminated and the strength is reduced.
If it exceeds, the strength of the sintered body decreases due to grain growth, which is not preferable. This firing can also be performed by two-stage firing of primary firing and secondary firing.
For example, the primary firing is performed at 1800 ° C. or less in a non-oxidizing atmosphere at a normal pressure or gas pressure of 10 atmospheres or less containing nitrogen, and the relative density of the sintered body after the primary firing is 78% or more, preferably 90% or more. %. If the relative density of the sintered body after the primary firing is less than 78%, many defects such as pores tend to remain after the secondary firing, which is not preferable. The secondary firing can be performed at 1500 to 1800 ° C. in a non-oxidizing atmosphere by gas pressure of 200 atm or less containing nitrogen or hot isostatic firing (HIP) of 200 to 2000 atm.

By increasing the relative density of the compact to 61% or more by the above-mentioned tumbling granulation method, the elementary sphere obtained by sintering is further densified more remarkably, and voids and the like are formed in the surface layer of the sphere. Defects are less likely to remain. The conductive ball of the present invention is obtained by subjecting the elementary sphere to rough polishing for size adjustment and then to precision polishing using fixed abrasive grains. The conductive ceramic bearing ball is
The cumulative area ratio of defects having a dimension of 1 μm or more observed on the polished surface can be 1% or less, and the average number of defects formed per 1 mm ² can be 500 or less. In addition, the arithmetic mean roughness Ra of the polished surface can be set to 0.012 μm or less, and the sphericity can be ensured to 0.08 μm or less.
Further, the diameter difference can be secured to 0.10 μm or less.

As shown in FIG. 9, if the conductive ceramic bearing ball 43 obtained as described above is incorporated between an inner ring 42 and an outer ring 41 made of, for example, metal or ceramic, a radial type ball bearing 40 is formed. can get. The shaft SH is provided on the inner surface of the inner ring 42 of the ball bearing 40.
Is fixed, the conductive ceramic bearing balls 43
Is held rotatably or slidably with respect to the outer ring 41 or the inner ring 42. Conductive ceramic bearing ball 43
Means that the titanium nitride phase is 10% in the silicon nitride ceramic substrate.
７０70% by volume (preferably 15 to 75% by volume, more preferably 30 to 50% by volume), thereby having a relatively high electrical conductivity of 10 ⁶ Ω · cm or less. As a result, charging is effectively prevented or suppressed. For example, when handling a lot of conductive ceramic bearing balls after manufacturing, the balls are less likely to be electrostatically attached to a container or the like, and the process flow can be kept smooth. In addition, when used by being incorporated in the ball bearing 40, adhesion of foreign matter such as dust due to static electricity is unlikely to occur, and it is possible to significantly suppress the occurrence of vibration and abnormal noise even during high-speed rotation.

FIG. 10 is a longitudinal sectional view showing an example of the configuration of a hard disk drive mechanism using the above-described ball bearing. The hard disk drive mechanism 100 includes a main body case 1
In the center of the inner surface of the bottom of 02, a cylindrical shaft holding portion 108 is formed so as to rise vertically, and a cylindrical bearing holding bush 112 is coaxially fitted inside the shaft holding portion 108. The bearing holding bush 112 has a bush fixing flange 110 formed on the outer peripheral surface thereof, and is positioned in the axial direction such that the bush fixing flange 110 comes into contact with one end of the shaft holding portion 108.
Also, at both inner ends of the bearing holding bush 112,
Each of the ceramic balls 144 of the present invention is attached to the inner ring 140.
A plurality of ball bearings 116 and 118 having the same structure as that shown in FIG. Are respectively abutted and positioned.

A disk rotating shaft 146 is inserted and fixed in each of the inner rings 140 and 140 of the ball bearings 116 and 118, and is rotatably supported by the bearings 116 and 118 with respect to the bearing holding bush 112 and the main body case 102. A flat cylindrical disk fixing member (rotating member) 152 is integrated with one end of the disk rotating shaft 146, and a wall portion 154 is formed so as to extend downward along the outer peripheral edge thereof. An exciting permanent magnet 126 is attached to the inner peripheral surface of the wall 154, and a field coil 124 fixed to the outer peripheral surface of the bearing holding bush 112 has an exciting permanent magnet 126 mounted inside the wall 154.
And are arranged so as to face. The field coil 124 and the exciting permanent magnet 126 constitute a DC motor 122 for driving the rotation of the disk. Also, the disk fixing member 152
A disk fixing flange 156 protrudes from the outer peripheral surface of the wall portion 154, and the inner peripheral edge of the recording hard disk 106 is held and fixed in such a manner as to be sandwiched between the recording hard disk 106 and the holding plate 121. A fixing bolt 151 is screwed into the disk rotation shaft 146 so as to penetrate the holding plate 121.

The motor 122 operates by energizing the field coil 124 to generate a rotational driving force using the disk fixing member 152 as a rotor. As a result, the hard disk 106 fixed to the disk fixing member 152 is moved to the disk rotating shaft 14 supported by the bearings 116 and 118.
6 at a high speed of, for example, 5400 to 15000 rpm.

Next, FIG. 11 shows a structure of a hard disk drive (hereinafter abbreviated as HDD) 400 including a head arm driving portion. In this structure, the hub 4
And a rotation shaft 405 of a head arm 404 having a magnetic head (not shown) attached to the end thereof. The shafts 403 and 405 are a pair of two axially spaced ball bearings 40 of the present invention having the same structure as described above.
6,407 (bearing balls 413, 414, respectively)
(A conductive ceramic ball is used as an example.) Then, the rotating shaft 403 of the magnetic disk 402
Inner ring 408 of a set of ball bearings 406 for supporting
Is mounted so as to rotate integrally with the rotating shaft 403, and the outer ring 409 is a cylindrical stator 411 of a spindle motor (the rotating shaft 403 is an output shaft, and the bearing 406 constitutes a bearing-equipped motor of the present invention) 410. The rotary shaft 403 is fixed to the center of the deep dish type rotor 412 and the rotary shaft 403 is fixed to the spindle motor 41.
Rotated at 0.

The magnetic disk 402 rotatably supported by such a structure rotates at a high speed in accordance with the rotation speed of the spindle motor 410. At this time, a head arm 404 having a magnetic head for reading and writing magnetic recording data is mounted. Also operates appropriately. The distal end of the head arm 404 is supported on the upper part of a rotating shaft 405. The rotating shaft 405 is rotated around the axis by an actuator (not shown) such as a VCM, and the tip of the head arm 404 is turned by a required angle to mount the magnetic head. Move to the required position. As described above, the rotation operation of the rotation shaft 405 enables reading and writing of required magnetic recording data in the effective recording area of the magnetic disk 402.

Next, FIG. 12 shows an example of a polygon scanner using the above-described ball bearing ((a) is a front view, (b) is a plan view, and (c) is a longitudinal sectional view). The polygon scanner 300 is used for generating a scanning light beam in image processing such as photographing and copying, and further in a laser printer, and is a substantially cylindrical sealed case comprising a base 311 and a cover 312 for covering the base 311. A motor 314 (here, an outer rotor type) which is a motor with a bearing of the present invention is accommodated in 313, and both ends of a fixed shaft 315 are fixed to the base 311 and the cover 312, respectively. The polygon mirror 316 in which the reflecting mirror is formed on each side surface of the polygonal plate-like body is a regular octagonal plate-like body in this example, and the rotor 317 of the motor 314 is fitted in the mounting hole 316a formed in the center thereof. It is inserted and fixed to this so as to be integrally rotatable. The rotor 317 is rotatably supported by the fixed shaft 315 via the ball bearings 323 and 323 of the present invention having the same structure as in FIG. Motor 3
14 rotates at a high speed at a maximum rotation speed of, for example, 10,000 rpm or more and 30,000 rpm or more.

The polygon mirror 31 is provided on the side of the base 311.
A window 318 for inputting and outputting a light beam is provided at a position facing the window 6, and a window glass 319 is attached to the window 318. The window glass 319 is fitted into the window 318 from the outside, and is pressed and fixed by a pair of leaf springs 321. In the drawing, reference numeral 322 denotes a mounting screw for fixing the other end of the leaf spring 321 to the base 311. In addition, on the inner surface side of the base body 311, there is a protruding portion 311 a for forming the abutting surface of the window glass 319.

By driving the motor 314, the polygon mirror 316 rotates around the axis of the fixed shaft 315, and a light beam such as a laser beam is incident on the rotating polygon mirror 316 through a window 318 from a predetermined direction. You. The reflecting mirrors on each side of the polygon mirror 316 sequentially reflect the incident light beam while rotating, and the reflected light generates a scanning light beam.
Emitted from 18.

FIG. 13 shows an apparatus for measuring the flatness of a semiconductor wafer (for example, a silicon wafer). In this apparatus, while the wafer W is placed on the rotation measurement table 200 and rotated, a current is supplied between the wafer W and the rotation measurement table 200 to measure the capacitance, and the wafer is measured based on the measured value of the capacitance. This is to evaluate the flatness of W. The rotary table 200 is driven to rotate by a motor 203 via a shaft 201, and its radial bearing is formed by the ball bearing 40 described above. The rotation measurement table 200 is energized by using the bearing 40 and the shaft 201 as conduction paths and using the measurement power supply 2.
02. In this case, in order to secure conductivity for forming the same passage, the electrical resistivity of the composite ceramic constituting the ball is set to 10 ⁵ Ω · cm or less, and the content of the titanium nitride-based phase is set to 15 to 50% by volume. Is good.

[0056]

[Experimental Examples] In order to confirm the effects of the present invention, the following experiments were conducted. The following materials were prepared as silicon nitride powder to be used as raw materials and titanium nitride powder. 100 parts by volume of silicon nitride-based powder (50% particle diameter 0.5 μm, BET specific surface area value 12 m ² / g), 1.3 parts by weight of ceria powder (50% particle diameter 1.4 μm), and alumina powder (50% A blend of 1.3 parts by volume (particle size: 0.2 μm), 1.3 parts by volume of zirconia powder (50% particle size: 1.4 μm), and 1.3 parts by volume of magnesium carbonate powder. 100 parts by volume of silicon nitride-based powder (50% particle diameter 0.8 μm, BET specific surface area value 10 m ² / g), 1.3 parts by weight of ceria powder (50% particle diameter 1.4 μm), and alumina powder (50% A blend of 1.3 parts by volume (particle size: 0.2 μm), 1.3 parts by volume of zirconia powder (50% particle size: 1.4 μm), and 1.3 parts by volume of magnesium carbonate powder. 100 parts by volume of silicon nitride-based powder (50% particle diameter 1.5 μm, BET specific surface area value 8 m ² / g) and ceria powder (5
1.3 parts by volume of 0% particle diameter 1.4 μm), 1.3 parts by volume of alumina powder (50% particle diameter 0.2 μm) and 1.3 parts by volume of zirconia powder (50% particle diameter 1.4 μm). And 1.3 parts by volume of magnesium carbonate powder. Titanium nitride powder (50% particle diameter 1.1 μm, oxygen content 2.0 mass%, iron content 0.05 mass%) Titanium nitride powder (50% particle diameter 3.5 μm, oxygen content 0.8 mass%) , Iron content: 0.05% by mass) Titanium nitride powder (50% particle size: 2.0 μm, oxygen content: 4.0% by mass, iron content: 0.05% by mass) Titanium nitride powder (50% particle size: 1.0%) 1 μm, oxygen content 2.0% by mass, iron content 0.45% by mass)

Using the above silicon nitride powder as a substrate, the titanium nitride powder is blended so that the content ratio of the titanium nitride phase in the final ceramic substrate is approximately 30% by volume. 50 parts by mass of pure water as a solvent and an appropriate amount of an organic binder were added to 100 parts by mass of the mixture, and the mixture was mixed by an attritor mill for 10 hours to obtain a slurry of a base powder for molding. The slurry was made into a green body powder for molding by the apparatus shown in FIG. Table 1 shows these compounding patterns as AF. In addition, about 50% particle diameter about the base powder for shaping | molding which mix | blends AF, the laser diffraction-type particle sizer (the Horiba, Ltd. make, product number: LA-50)
0), and the BET specific surface area was measured using a BET specific surface area measuring device (manufactured by Yuasa Ionics Co., Ltd., Multi Soap 1).
Each was measured in 2). Table 1 shows the measurement results.

[0058]

[Table 1]

Next, each of the molding base powders A to F was subjected to tumbling granulation to produce a spherical molded body having a diameter of about 2.5 mm. The obtained spherical molded body was fired at a temperature of 1700 ° C. for 3 hours in an N ₂ atmosphere of 100 atm.

The surface of the fired ball has a sphericity of 0.
The powder was precisely polished so as to have a thickness of 08 μm and an arithmetic average roughness of 0.012 μm to obtain a conductive ceramic bearing ball having a diameter of 2 mm. In each case, no static electricity was charged during the production, and smooth handling was possible. A polished bearing ball was disposed between a metal outer ring and an inner ring to form a bearing as shown in FIG. Then, a microphone (pickup sensor) is attached to the outer ring,
Further, when the outer ring was fixed and the inner ring was rotated at 10,000 rpm, the presence or absence of sound generation was measured. The determination was made as abnormal noise generation (x) when the sensor output exceeded 30 dB, slight abnormal noise generation (発 生) when it was 30 to 25 dB, and normal (○) when it was less than 25 dB. After these measurements, the oxygen content (% by mass) and the iron content (% by mass) of the entire composite ceramic obtained were measured. The oxygen content was analyzed by a non-dispersive infrared absorption method using a powdered sintered body sample. The iron content was analyzed by EPMA (El
ectron Probe Micro Analysis: Characteristic X-rays were measured by a wavelength dispersion method (WDS: Wavelength Dispersive Spectrometer). Table 1 shows the above results.
Are shown together. As is apparent from the results, those satisfying the requirements of claim 1 of the present invention and those satisfying the numerical range described in claim 2 of the present invention were used as the silicon nitride raw material powder and the titanium nitride raw material powder. It can be seen that good results were obtained in the acoustic test.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a process of rolling granulation.

FIG. 2 is a process explanatory view following FIG. 1;

FIG. 3 is a view for explaining the progress of a rolling granulation forming step.

FIG. 4 is a longitudinal sectional view conceptually showing an example of an apparatus for producing a molding base powder.

FIG. 5 is a diagram for explaining the operation of the apparatus shown in FIG. 4;

FIG. 6 is an operation explanatory view following FIG. 5;

FIG. 7 is a diagram illustrating the concept of a primary particle diameter and a secondary particle diameter.

FIG. 8 is an explanatory diagram showing the concept of a relative cumulative frequency.

FIG. 9 is a schematic view of a ball bearing using the ceramic ball of the present invention.

FIG. 10 is a longitudinal sectional view showing an example of a computer hard disk drive mechanism using the ball bearing of FIG. 9;

FIG. 11 is a cross-sectional view showing an example of a computer hard disk device having a head drive mechanism.

FIG. 12 is a sectional view showing an example of a polygon scanner using the ball bearing of FIG. 9;

FIG. 13 is a schematic view showing an example of a semiconductor wafer flatness measuring apparatus using the ball bearing of FIG. 9;

[Explanation of symbols]

40, 116, 118, 406, 407 Ceramic ball bearings 43, 144, 413, 414 Conductive ceramic bearing balls 100 Hard disk drive 122, 314 Motor 300 Polygon scanner 400 Hard disk drive 404 Head arm

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H02K 5/173 C04B 35/58 102K 5H621 21/22 102Q 102X 102Y F term (Reference) 2H045 AA14 AA26 AA49 3J101 AA02 AA52 AA62 BA10 EA41 FA11 FA31 GA53 4G001 BA01 BA03 BA11 BA32 BA38 BB01 BB03 BB11 BB32 BB38 BB71 BB73 BC13 BC22 BC42 BC54 BC73 BD11 BD22 BE31 5D068 AA01 BB01 CC11 EE19 GG07 5H605 AA12 BB05 BB09 BB01 BB05 BB01 BB05 BB01 BB05 JK15 JK19

Claims (11)

[Claims] 1. A composite ceramic having a structure in which a titanium nitride-based phase is dispersed in a silicon nitride-based substrate, wherein the composite ceramic has an oxygen content of 3.0% by mass or less,
A conductive ceramic bearing ball having an iron content of 0.2% by mass or less and a surface electric resistivity of 10 ⁶ Ω · cm or less. 2. The oxygen content is 3.0% by mass or less, the iron content is 0.3% by mass or less, and the 50% particle size measured by a laser diffraction particle size analyzer is 3.0 μm or less. The titanium nitride powder and the 50% particle size measured by a laser diffraction type particle size analyzer are 0.
8 μm or less and a BET specific surface area value of 10 to 13
^{2. A} method comprising the steps of: sintering a spherical compact of raw material powder containing silicon nitride-based powder having m ² / g; and polishing the outer surface of the sintered body thereafter. A conductive ceramic bearing ball as described. 3. The content of the titanium nitride phase is 10 to 70.
3. The conductive ceramic bearing ball according to claim 1, wherein the content is% by volume. 4. 4. A ball bearing comprising a plurality of conductive ceramic bearing balls according to claim 1 incorporated as a bearing rolling element. 5. The ball bearing according to claim 4, wherein the ball bearing is used as a bearing part of a rotating main shaft part of a hard disk drive or a bearing part of a driving rotary shaft of a head arm. 6. A motor with a bearing, wherein the ball bearing according to claim 4 is used as a bearing component. 7. The motor with a bearing according to claim 6, which is used for a hard disk rotation drive section of a hard disk drive. 8. The motor with a bearing according to claim 6, which is used for a polygon mirror driving section of a polygon scanner. 9. The motor with a bearing according to claim 6, wherein the motor is a high-speed rotation motor having a maximum rotation speed of 8000 rpm or more. 10. A hard disk drive comprising the motor with a bearing according to claim 7 or 9 and a hard disk rotationally driven by the motor with a bearing. 11. A polygon scanner comprising: the motor with a bearing according to claim 8; and a polygon mirror rotationally driven by the motor with the bearing.