JP4874475B2 - Abrasion resistant member for electronic equipment, method for producing the same, and bearing for electronic equipment using the same - Google Patents

Description

【００６２】
上述した実施例１〜１７および比較例１〜６による各ベアリングボールについて、電気抵抗値、焼結助剤成分の偏析部の最大径、単位面積1000×1000μm当りに存在する焼結助剤成分の偏析部の数、Ｆｅ成分の含有量（ＩＣＰ発光分析法）を、それぞれ前述した方法にしたがって測定した。これらの測定結果を表２に示す。なお、焼結助剤成分の偏析部の測定は単位面積を任意に3箇所選び、それらの測定値の平均値で示した。
【００６３】
【表２】

【００６４】
次に、実施例１〜１７および比較例１〜６による各ベアリングボールをそれぞれ10個一組としてベアリングを作製した。ボール受け部などの他のベアリング部材には軸受鋼SUJ2材を使用した。これらのベアリングをそれぞれスピンドルモータに組込み、ＨＤＤ用モータとして使用した。これらのスピンドルモータを回転速度7200rpmおよび10000rpmでそれぞれ1000時間稼動させ、ベアリングの摺動音の変化率、ベアリングボールの耐久性、ＨＤＤの静電気による不具合の有無をそれぞれ調査した。これらの評価結果を表３に示す。
【００６５】
なお、ベアリングの摺動音の変化率は、10時間稼動後の摺動音Ｎ₁₀と1000時間稼動後の摺動音Ｎ₁₀₀₀を測定し、［（Ｎ₁₀₀₀−Ｎ₁₀）／Ｎ₁₀］×100（％）に基づいて求めた。ベアリングボールの耐久性は1000時間稼動後のベアリングボール表面を調べ、表面にクラックや剥がれなどが生じていないものを「良好」、表面にクラックや剥がれなどが生じていたものを「不良」とした。
【００６６】
【表３】

【００６７】
表２および表３から明らかなように、実施例１〜１７の各ベアリングボールは、いずれも回転速度が8000rpm以下のＨＤＤ用スピンドルモータであれば実用性を満足するものであることが分かる。また、適量の導電性付与粒子を含有する窒化珪素焼結体からなるベアリングボール（実施例４〜１７）は1〜10⁶Ω・mの範囲の電気抵抗値を有しており、ＨＤＤ用スピンドルモータに求められる耐久性を有するだけでなく、静電気による不具合を解消できることが分かる。なお、実施例１〜３と同様にして作製したベアリングをそれぞれファンモータに組込み、パソコン用ファンモータ（回転速度1500rpm）として使用したところ、いずれも良好な摺動特性（耐久性）を有していることが確認された。
【００６８】
実施例１８、参考例１
実施例１と同様の組成および製造方法によって、直径3mmのベアリングボール（実施例１８）と直径3mmのベアリングボール（参考例１）を、それぞれ100個ずつ作製し、これら各ベアリングボールにおける焼結助剤成分の偏析部の最大径を実施例１と同様にして測定した。その結果、実施例１８では100個全ての偏析部の最大径が150μm以下であったのに対して、参考例１では100個中23個は偏析部の最大径が150μmを超えていることが確認された。この結果からベアリングボールの直径が3mmを超えると、焼結助剤成分の偏析部の制御が難しくなることが分かる。
【００６９】
実施例１９、参考例２
実施例１４と同様の組成および製造方法によって、直径3mmのベアリングボール（実施例１９）と直径3mmのベアリングボール（参考例２）を、それぞれ100個ずつ作製し、これら各ベアリングボールにおける焼結助剤成分の偏析部の最大径を実施例１４と同様にして測定した。その結果、実施例１９では100個全ての偏析部の最大径が150μm以下であったのに対して、参考例２では100個中8個は偏析部の最大径が150μmを超えていることが確認された。この結果からベアリングボールの直径が3mmを超えると、焼結助剤成分の偏析部の制御が難しくなることが分かる。
【００７０】
【発明の効果】
以上説明したように、本発明によれば例えば電子機器用ベアリングなどの高速回転を安定に実現し得る電子機器用耐摩耗性部材を安価に提供することができる。従って、各種電子機器に窒化珪素製の耐摩耗性部材を幅広く適用することが可能となる。また、このような電子機器用耐摩耗性部材からなるベアリングボールを具備するベアリングを使用することによって、各種電子機器の信頼性や性能などを高めることが可能となる。
【図面の簡単な説明】
【図１】 本発明の一実施形態によるベアリングボールの概略構成を一部断面で示す図である。
【符号の説明】
１……ベアリング，２……ベアリングボール，３……内輪，４……外輪[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wear-resistant member used in various electronic devices, a method for manufacturing the same, and a bearing for electronic devices using the same.
[0002]
[Prior art]
In recent years, there have been remarkable developments in magnetic recording devices such as hard disk drives (HDD) and floppy disk drives (FDD), optical disk devices such as CD-ROM and DVD, and various game devices. In these electronic devices, a rotating shaft is usually rotated at a high speed by a rotary drive device such as a spindle motor, and various disks mounted on the rotating shaft are functioned. In addition, projectors such as LCD projectors and OHPs, personal computers, and the like have built-in cooling fans for removing the heat inside the devices. In such cases, a rotational drive device such as a fan motor is used. ing.
[0003]
Conventionally, metal materials such as bearing steel have been mainly used for bearing members, particularly bearing balls, that support the rotating shaft of the electronic apparatus rotary drive device as described above. However, since metal materials such as bearing steel have insufficient wear resistance, reliability is increased by increasing the variation in life in fields where high-speed rotation of 4000 rpm or more is required, such as electronic equipment. There is a problem that some rotational drive cannot be provided.
[0004]
In order to solve such problems, ceramic materials such as a silicon nitride sintered body have recently been used for bearing balls (see, for example, JP 2000-314426 A). A silicon nitride sintered body is excellent in sliding characteristics among ceramic materials and has good wear resistance. Therefore, even when high-speed rotation is performed, it is possible to provide a mechanically reliable rotational drive.
[0005]
[Problems to be solved by the invention]
However, a silicon nitride bearing ball is more expensive than a metal bearing ball, and has a drawback that its range of use (applicable device) is limited. In particular, electronic devices such as HDDs are being rotated at a high speed, and metal bearing balls have problems such as increased noise due to insufficient rigidity and insufficient durability. For this reason, it is strongly sought to enable the application of silicon nitride bearing balls to various electronic devices by reducing the manufacturing cost of high-stiffness silicon nitride bearing balls compared to metal balls. It has been.
[0006]
Here, as one of the cost reduction measures for a silicon nitride bearing ball, it is conceivable to use an inexpensive silicon nitride powder containing a relatively large amount of impurities such as oxygen and Fe as a raw material. However, when a sintered body is produced using a silicon nitride raw material having a large amount of impurities, the sintering aid component is easily segregated due to impurities such as oxygen and Fe. In particular, in applications where a high-density sintered body such as a bearing ball is required, the HIP treatment is generally applied. Therefore, a segregation portion of the sintering aid component grows during the HIP treatment, and the grown sintering aid is grown. There arises a problem that rigidity and durability as a bearing ball or the like are lowered based on the segregated portion of the agent component.
[0007]
Furthermore, since silicon nitride bearing balls are electrically insulating, there is a problem that static electricity generated during high-speed rotation cannot be released well to a rotating shaft or ball receiving part made of a metal material. Resulting in. If the bearings and peripheral components are charged more than necessary, a recording apparatus using a magnetic signal such as an HDD will adversely affect the recording medium. As a result, there is a concern that the recorded content in the HDD may be lost, or that the electronic device itself such as the HDD may be destroyed. For these reasons, there is a need for a bearing ball made of silicon nitride that prevents the accumulation of static electricity more than necessary in the rotational drive part of some electronic devices.
[0008]
Electric resistance value is 10^-FiveConductive silicon nitride sintered bodies of about Ω · m have been known for some time (see Japanese Patent Publication No. 2-43699) and are used as materials for producing turbine engine blades and nozzles by electric discharge machining. ing. In such a conductive silicon nitride sintered body, a large amount of a conductivity-imparting material such as metal carbide or metal nitride is added in order to realize low electrical resistance, which causes the sliding characteristics to deteriorate. It has become. The above publication does not assume any application of the conductive silicon nitride sintered body to the sliding member, and merely provides conductivity in order to use electric discharge machining or the like.
[0009]
Silicon nitride sintered bodies containing conductive compounds such as metal carbides and metal nitrides are also described in Japanese Patent Publication No. 7-29855, Japanese Patent No. 2566580, Japanese Patent Application Laid-Open No. 6-227870, and the like. However, the techniques described in these publications do not necessarily provide a silicon nitride sintered body (composite sintered body) that is inexpensive and has excellent sliding characteristics and suitable electrical conductivity.
[0010]
In addition, since conductivity imparting materials such as metal carbide and metal nitride become a factor that inhibits the sintering of silicon nitride, it is necessary to add a sintering aid more frequently than ordinary silicon nitride sintered bodies. Arise. Thus, when a comparatively large amount of sintering aid is added, segregation of the sintering aid component is promoted, and for example, the rigidity and durability of a silicon nitride bearing ball are more likely to be lowered.
[0011]
The present invention has been made in order to cope with such problems, and is capable of realizing stable high-speed rotation when applied to a bearing ball or the like, and is a wear-resistant member for electronic equipment that can reduce manufacturing costs. It is another object of the present invention to provide a wear-resistant member for electronic equipment that prevents accumulation of static electricity more than necessary. Also, by using such wear-resistant members for electronic devices, high reliability and high performance of electronic devices such as projectors and personal computers with cooling devices, magnetic recording devices, optical disk devices, game devices, etc. It aims at providing the bearing for electronic devices which can implement | achieve.
[0012]
[Means for Solving the Problems]
In order to achieve the above-described object, the present inventors have repeatedly conducted various studies and experiments on a silicon nitride sintered body for electronic equipment. As a result, the silicon nitride sintered body has been used as a wear-resistant member such as a bearing for electronic equipment. Is applied, for example, a silicon nitride sintered body produced using a raw material powder (such as silicon nitride powder) having a relatively high impurity concentration, that is, a nitridation in which the sintering aid component segregates to a certain size and amount. It was found that even a silicon sintered body can be used.
[0013]
This is because a bearing applied to electronic equipment or the like has a relatively small load applied during operation, and mainly requires a high-speed sliding characteristic rather than a load bearing characteristic. In such applications, even a silicon nitride sintered body in which a silicon nitride powder having a relatively high impurity concentration, that is, an inexpensive silicon nitride powder is used as a raw material and the sintering aid component segregates in a certain size and amount. In addition, it is possible to reduce the manufacturing cost of the silicon nitride sintered body, and thus the wear-resistant member for electronic equipment using the same, based on the reduction of the raw material cost.
[0014]
Furthermore, when the silicon nitride sintered body is produced using the silicon nitride powder having a relatively high impurity concentration as described above, the segregation part of the sintering aid component is likely to grow, which makes the bearing Although the rigidity and durability as a wear-resistant member such as a ball are likely to decrease, in the present invention, by controlling the HIP processing conditions, the segregation portion of the sintering aid component in such a silicon nitride sintered body grows. Is suppressed. This makes it possible to obtain a silicon nitride sintered body that satisfies the characteristics required of a wear-resistant member for electronic equipment with good reproducibility.
[0015]
  The present invention has been made based on such findings. That is, the wear-resistant member for electronic equipment of the present invention contains a sintering aid component in a range of 5 to 20 parts by mass with respect to 100 parts by mass of silicon nitride, and an Fe component as an impurity in a range of 30 to 600 ppm. Comprising a silicon nitride sintered body containing,Used for rotational drive units with a rotational speed of 8000 rpm or less,A wear-resistant member for electronic equipment, which is a bearing ball having a diameter of 3 mm or less, wherein the silicon nitride sintered body has a segregation portion of the sintering aid component, and the segregation portion has a maximum diameter of 10 to 150 μm. And in the range of 2 or more and 10 or less per unit area of 1000 × 1000 μm in the silicon nitride sintered body.
[0017]
  In the wear resistant member for electronic equipment of the present invention,NitroConductivity-imparting particles are contained in the silicon carbide sintered body, and the electric resistance value is 1 to 10⁶A silicon nitride sintered body having a range of Ω · m can also be used. In the case of using such a silicon nitride sintered body, as conductivity imparting particlesIs an exampleFor example, at least one selected from a group 4A element, a group 5A element, a group 6A element, a group 7A element, silicon, boron carbide and nitride is used.
[0018]
  The wear-resistant member for electronic equipment of the present invention isAs mentioned aboveIt is suitably used as a bearing ball having a diameter of 3 mm or less. Such a wear-resistant member for electronic equipment of the present invention is, for example,ColdIt is suitably used for a rotation drive unit of a projection device with a rejection device, a personal computer, a magnetic recording device such as HDD or FDD, an optical disk device such as a CD-ROM or DVD, and various game devices.
[0019]
  BookThe manufacturing method of the wear-resistant member for electronic equipment of the invention isA method for producing the wear-resistant member for electronic equipment according to the present invention described above,A silicon nitride powder containing 1 to 1.8% by mass of oxygen as impurities and 30 to 700 ppm of Fe component and 5 to 20 parts by mass of sintering aid powder with respect to 100 parts by mass of the silicon nitride powder are mixed. A step of molding the mixture into a desired shape, a primary sintering step of sintering the molded body obtained by the molding step at a temperature in the range of 1700 to 1850 ° C., and a primary firing obtained by the primary sintering step. A secondary sintering step in which the bonded body is subjected to HIP treatment at a temperature lower by 200 ° C. or more than the sintering temperature of the primary sintering step;Used for rotational drive units with a rotational speed of 8000 rpm or less,It is characterized by producing bearing balls with a diameter of 3mm or less.
[0020]
  The electronic device bearing of the present invention is,UpIt is characterized by comprising a bearing ball made of the wear-resistant member for electronic equipment according to the present invention described above. Such a bearing for an electronic device is suitably used for the above-described projection device with a cooling device, a fan motor of a personal computer, or a spindle motor used in a magnetic recording device, an optical disk device, a game device, or the like.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, modes for carrying out the present invention will be described.
The wear-resistant member for electronic equipment according to the present invention includes, for example, a rare earth element oxide or an alkaline earth element oxide as a sintering aid component, and a part of such a sintering aid component is the maximum. It consists of a silicon nitride sintered body that exists by forming a segregation part having a diameter of 150 μm or less.
[0022]
In the wear resistant member for electronic equipment according to the present invention, the raw material powder of the silicon nitride sintered body may be, for example, a silicon nitride powder containing oxygen as an impurity in an amount of 1 to 1.8 mass% and an Fe component in a range of 30 to 700 ppm. it can. Here, the Fe component refers to a component containing all iron (Fe), such as an Fe element simple substance, and an Fe compound such as iron nitride or iron oxide. Since silicon nitride powder containing a relatively large amount of impurities is less expensive than high-purity silicon nitride powder, the manufacturing cost of wear-resistant members (sliding members) for electronic devices such as bearing balls is reduced. Contribute to. The same applies to the sintering aid powder and the conductivity imparting material powder.
[0023]
With silicon nitride powder having a low oxygen content and a low content of Fe component, the effect of reducing the manufacturing cost of the silicon nitride sintered body based on the reduction of raw material costs cannot be obtained sufficiently. However, if the amount of oxygen and the amount of Fe component in the silicon nitride powder is too large, degranulation is likely to occur when the obtained silicon nitride sintered body is polished (surface processing), which causes surface defects. As a result, the crushing strength and the like are greatly deteriorated, and the characteristics as the wear-resistant member, for example, the sliding characteristics cannot be maintained even for the electronic device. For this reason, the oxygen content in the silicon nitride powder as a raw material is preferably in the range of 1 to 1.8% by mass, and the Fe component content is preferably in the range of 30 to 700 ppm.
[0024]
In the wear resistant member for electronic equipment of the present invention, it is preferable to apply a silicon nitride sintered body containing, for example, an Fe component as an impurity in the range of 30 to 600 ppm based on the silicon nitride raw material as described above. The amount of Fe component in the silicon nitride sintered body is more preferably in the range of 100 to 400 ppm. By applying such a silicon nitride sintered body, it is possible to reduce the manufacturing cost of the wear resistant member for electronic equipment as described above. Moreover, the silicon nitride sintered body containing an appropriate amount of Fe component has high workability, and the cost required for processing can be reduced. Also from this point, the silicon nitride sintered body appropriately containing the Fe component contributes to the reduction of the manufacturing cost of the wear resistant member for electronic equipment. In addition, although the Fe component in the present invention is mainly contained as an impurity in the silicon nitride raw material, the Fe component mixed during the manufacturing process of the sintered body, and further, the Fe component actively added as necessary Including ingredients.
[0025]
In addition, the content of the Fe component of the silicon nitride sintered body in the present invention indicates a value obtained as follows. First, after the silicon nitride sintered body is finely pulverized and powdered, hydrofluoric acid or the like is added and heated to about 180 ° C. in a pressure vessel to form a solution. Next, after rinsing off hydrofluoric acid with sulfuric acid, the solution is subjected to ICP emission analysis to determine the content of Fe component. Thus, the total amount of Fe in the silicon nitride sintered body is taken as the content of the Fe component.
[0026]
As a sintering aid, various metal compounds can be applied in the same manner as a general silicon nitride sintered body, and in particular, oxides and alkaline earths of rare earth elements (lanthanoid elements including yttrium). It is preferable to use at least one selected from elemental oxides. These oxides effectively act to increase the density of the silicon nitride sintered body. As the rare earth element oxide, an oxide such as yttrium (Y), ytterbium (Yb), or erbium (Er) is preferably used. These are constituents of the grain boundary phase. Further, it is preferable to use an oxide of magnesium or calcium as the oxide of the alkaline earth element. In addition, you may use the compound (carbonate etc.) of the rare earth element and alkaline-earth element which become an oxide at the time of sintering as a compound as a sintering auxiliary agent.
[0027]
In addition to the oxides of rare earth elements and alkaline earth elements described above, aluminum compounds such as aluminum nitride and aluminum oxide, and oxides and nitrides such as titanium, zirconium, and hafnium are used as part of the sintering aid. It is also effective to use as The aluminum compound contributes to strengthening the bonding force between the silicon nitride crystal grains. These compounds may be added as oxides or nitrides, or compounds that become oxides or nitrides during sintering may be added.
[0028]
The sintering aid as described above is preferably contained in the range of 5 to 20 parts by mass with respect to 100 parts by mass of silicon nitride. If the amount of the sintering aid is less than 5 parts by mass, the silicon nitride sintered body may not be sufficiently densified. On the other hand, if the amount of sintering aid exceeds 20 parts by mass, the amount of segregation part of the grain boundary phase and the sintering aid component increases more than necessary, which results in the wear resistance and strength of the silicon nitride sintered body. There is a risk of lowering. Among the sintering aids described above, the rare earth oxide content is preferably in the range of 5 to 15 parts by mass, and the alkaline earth oxide content is preferably in the range of 0.5 to 5 parts by mass. preferable. Furthermore, in addition to these, it is preferable to contain an aluminum compound such as aluminum nitride or aluminum oxide in the range of 1 to 7 parts by mass.
[0029]
In the wear resistant member for electronic equipment of the present invention, as described later in detail, conductivity imparting particles such as 4A group element, 5A group element, 6A group element, 7A group element, silicon, Conductivity-imparting particles comprising at least one selected from boron carbide and nitride can be contained. In such a case, the conductivity imparting particles are in the range of 15 to 40% by volume in the silicon nitride sintered body (converted assuming that the volume of the silicon nitride sintered body containing the conductivity imparting particles is 100% by volume) It is preferable to use the silicon nitride sintered body contained in (1).
[0030]
The electrical conductivity value of the silicon nitride sintered body is 1 to 10 for the content of the conductivity-imparting particles described above.⁶It is adjusted appropriately so as to be in the range of Ω · m. Specifically, the conductivity-imparting particles are preferably contained in the range of 15% by volume to 40% by volume. If the content of the conductivity imparting particles is less than 15% by volume, the electrical resistance value of the silicon nitride sintered body may not be sufficiently reduced. On the other hand, if the content of the metal carbide or metal nitride exceeds 40% by volume, the electrical resistance value of the silicon nitride sintered body itself is lowered, but the original characteristics of the silicon nitride sintered body may be deteriorated.
[0031]
The silicon nitride sintered body constituting the wear resistant member for electronic equipment of the present invention has a segregation part of the sintering aid component as described above, and further has a maximum diameter of the segregation part of the sintering aid component. Is controlled to 150 μm or less. The reason why it is possible to use a silicon nitride sintered body having a segregation part of such a sintering aid component is that a wear-resistant member such as a bearing ball used for a bearing for an electronic device (e.g. This is because the wearable member) has a relatively small load applied during operation, and mainly requires a high-speed sliding characteristic rather than a load bearing characteristic.
[0032]
That is, in a silicon nitride sintered body produced using a silicon nitride powder containing a relatively large amount of impurities as described above, the sintering aid component tends to segregate due to impurities such as oxygen and Fe components. . In particular, when a metal carbide or the like is used as the conductivity-imparting particles, the conductivity-imparting particles act as a factor inhibiting the sinterability of silicon nitride, so a sintering aid is added more frequently than usual. For this reason, the sintering aid component is more easily segregated. Such segregation parts of the sintering aid component cause deterioration of bearing characteristics (such as repeated fatigue) and load bearing characteristics (such as crushing strength) of the silicon nitride sintered body, but are not suitable for wear-resistant members for electronic devices. The applied load is small compared to wear-resistant members used in, for example, gas turbines, automobile parts, machine tools, etc., so even a silicon nitride sintered body with relatively low repeated fatigue characteristics can be used sufficiently be able to.
[0033]
However, if the maximum diameter of the segregation part of the sintering aid component is too large, breakage starting from it tends to occur. Therefore, in the silicon nitride sintered body applied to the wear-resistant member for electronic equipment of the present invention, Defines the size of the segregation part of the sintering aid component as a maximum diameter of 150 μm or less. The maximum diameter of the segregation part of the sintering aid component is more preferably 100 μm or less. In the present invention, the segregation part of the sintering aid component refers to an aggregate (aggregate) of the sintering aid component having a maximum diameter of 10 μm or more.
[0034]
Although the HIP process is effective for increasing the density of the silicon nitride sintered body, if the HIP process is applied when producing the silicon nitride sintered body using the silicon nitride powder having a relatively high impurity concentration, the HIP process The segregation part of the sintering aid component grows, and even if it is for electronic equipment, the deterioration of the characteristics of the wear-resistant member is inevitable. Therefore, in the present invention, the growth of the segregation part of the sintering aid component in such a silicon nitride sintered body is suppressed by controlling the HIP processing conditions. Specifically, the maximum diameter of the segregation part of the sintering aid component is set to 150 μm or less, which makes it possible to satisfy the reproducibility of the sliding characteristics required for bearing balls for electronic devices.
[0035]
  As described above, the silicon nitride sintered body constituting the wear-resistant member for electronic equipment of the present invention has a maximum diameter.ButIt has a segregation part of the sintering aid component in the range of 10 to 150 μm. It is preferable that two or more segregation portions of such sintering aid components exist per unit area of 1000 × 1000 μm in the silicon nitride sintered body. If the number of segregation parts of the sintering aid component is too small, the sintering aid component tends to form a larger segregation part, so that the maximum diameter of the segregation part is 150 μm or less. It is preferable that a plurality of segregation parts are present per unit area. However, if the number of segregation parts of the sintering aid component is too large, the mechanical strength of the silicon nitride sintered body tends to decrease, so the number of segregation parts is 10 or less per unit area of 1000 × 1000 μm. Preferably.
[0036]
Here, the maximum diameter and the number per unit area (1000 × 1000 μm) of the segregation part of the sintering aid component described above are obtained as follows. That is, in the cross section of the silicon nitride sintered body, an arbitrary measurement location (area: 1000 × 1000 μm) is observed with a metal microscope (for example, 50 to 100 times magnification), and an observation field corresponding to this unit area (1000 × 1000 μm) ( Or the number of segregation parts of the sintering aid component existing in the enlarged photo), that is, the maximum diameter (the maximum diameter in this case indicates the maximum diameter of each segregation part) of 10 to 150 μm. Measure the number. Further, among the maximum diameters of these segregated portions, the maximum diameter of the largest segregated portion is defined as the maximum diameter.
[0037]
As described above, a silicon nitride sintered body having a segregation portion of a sintering aid component having a maximum diameter of 150 μm or less can be sufficiently applied to a wear-resistant member for electronic equipment. Then, by using such a wear-resistant member made of a silicon nitride sintered body as a bearing ball, for example, in a rotational drive part of various electronic devices in which an increase in noise is a problem due to high-speed rotation, for example. It is possible to apply a high-rigidity silicon nitride bearing ball.
[0038]
By the way, silicon nitride itself is essentially an insulating material, and generally the electric resistance value of a silicon nitride sintered body is 10⁹Ω · m or more. When such a ball bearing made of a silicon nitride sintered body is used for a rotation drive unit of an electronic device, static electricity generated at the time of high-speed rotation accumulates more than necessary, and a magnetic signal such as an HDD is generated. The apparatus used will adversely affect the recording medium. Therefore, the silicon nitride sintered body of the present invention contains conductivity imparting particles, for example, 1 to 10⁶It can also be used as a silicon nitride sintered body provided with an electric resistance value in the range of Ω · m.
[0039]
10 sintered silicon nitride⁶By having an electrical resistance value of Ω · m or less, when used in an electronic device such as an HDD, the static electricity generated by high-speed rotation is released to a bearing member made of a metal material such as a rotating shaft and a ball receiving portion. It becomes possible. Accordingly, it is possible to eliminate problems associated with electrostatic charging. On the other hand, even if the electrical resistance value of the silicon nitride sintered body is less than 1 Ω · m, not only a further effect is not obtained with respect to the dissipation of static electricity, but in order to obtain such an electrical resistance value, a large amount of Since it is necessary to add conductivity-imparting particles, mechanical properties such as fracture toughness and wear resistance of the silicon nitride sintered body are impaired. The electrical resistance value of the silicon nitride sintered body is 10 to 10^FiveA range of Ω · m is more preferable. In addition, the electrical resistance value of the silicon nitride sintered body basically indicates a volume specific resistance value.
[0040]
In the wear-resistant member for electronic equipment of the present invention, the conductivity imparting particles contained in the silicon nitride sintered body in order to obtain the above-described electrical resistance value are 10^-FiveIt preferably has an electric resistance value of Ω · m or less. The electrical resistance value of the conductivity-imparting particles is 10^-FiveIf it exceeds Ω · m, the compounding amount for imparting a predetermined electric resistance value to the silicon nitride sintered body increases, so that the mechanical properties of the silicon nitride sintered body may be deteriorated.
[0041]
Various materials such as carbides, nitrides, borides, metals, and the like that can control the electrical resistance value of the silicon nitride sintered body can be used for the conductivity-imparting particles. Among these, at least one selected from a group 4A element, a group 5A element, a group 6A element, a group 7A element, silicon, boron carbide and nitride is preferable. Since carbides and nitrides are chemically stable and excellent in heat resistance, they are not easily affected by heat generated when sliding a bearing ball or the like. The presence of these conductivity-imparting particles can be analyzed by EPMA or X-ray diffraction.
[0042]
As the conductivity-imparting particles, at least one carbide or nitride selected from tantalum (Ta), titanium (Ti), niobium (Nb), tungsten (W), silicon (Si), and boron (B) is used. It is preferable to use it. When the wear resistant member of the present invention is used as a bearing ball or the like, the conductivity imparting particles present on the surface of the silicon nitride sintered body are naturally slid together with the silicon nitride sintered body. Therefore, since some degree of sliding characteristics are required for the conductivity-imparting particles, it is preferable to use carbides or nitrides having excellent sliding characteristics as described above. Silicon carbide is particularly effective for improving the sliding characteristics. Moreover, in order to suppress the sinterability fall of a silicon nitride sintered compact, it is preferable to add the titanium oxide used as titanium nitride after sintering.
[0043]
The conductivity-imparting particles made of the above-described carbide or nitride preferably have a particle shape with an average particle size of 2 μm or less. Furthermore, the conductivity imparting particles preferably have a maximum diameter of 4 μm or less, more preferably 2 μm or less. By using such carbide particles or nitride particles, the conductivity imparting particles can be appropriately dispersed in the silicon nitride sintered body. On the other hand, when whiskers or fibers are used as the conductivity-imparting material, they may be present as thorn-shaped convex portions on the surface of a bearing ball or the like. If thorn-shaped convex portions exist on the surface, they tend to become a starting point for grain separation during surface processing, and may increase the attacking property against the mating member during sliding, and may become a starting point for destruction. The maximum diameter of the conductivity-imparting particles is the size of each particle, and shows the longest diagonal line of the conductivity-imparting particles when an enlarged photograph of the surface and cross section of the silicon nitride sintered body and the color map of EPMA are viewed. Shall.
[0044]
Specifically, the wear-resistant member for electronic equipment of the present invention is used, for example, as a rolling element of a bearing in a rotational drive section of various electronic equipment. In particular, the wear resistant member of the present invention is suitable for a bearing ball for electronic equipment. The shape of the bearing ball is generally a true sphere, but the shape of the rolling element to which the present invention is applied is not necessarily limited to a true sphere, and may be a columnar shape or a rod shape. The present invention is applicable to various bearings such as ball bearings and roller bearings. The wear-resistant member for electronic equipment according to the present invention is not limited to a rolling element of a bearing, but can be used for all semiconductor jigs such as a positioning jig and a conveying jig in a semiconductor manufacturing apparatus. In particular, by adding conductivity imparting particles, the electrical resistance value is 1-10.⁶Those using a silicon nitride sintered body controlled to Ω · m are preferable because they can prevent electrostatic charge when used in general jigs for semiconductors.
[0045]
Although the manufacturing method of the wear-resistant member for electronic devices of this invention is not specifically limited, For example, manufacturing by the method as shown below is preferable.
First, a predetermined amount of each of silicon nitride powder, sintering aid powder, and if necessary, conductivity imparting material powder is weighed and mixed uniformly. In consideration of sliding properties, it is preferable to use particulate powder instead of whiskers or fibers for each raw material powder. The size of each raw material powder is not particularly limited, but the silicon nitride powder preferably has an average particle size in the range of 0.2 to 3 μm, and the sintering aid powder preferably has an average particle size of 2 μm or less. The average particle size of the conductivity imparting material powder is preferably 2 μm or less.
[0046]
As the silicon nitride powder, as described above, a raw material powder containing 1 to 1.8% by mass of oxygen as impurities and 30 to 700 ppm of Fe component can be used. Since silicon nitride powder containing a relatively large amount of impurities is less expensive than high-purity silicon nitride powder, the manufacturing cost of wear-resistant members (sliding members) for electronic devices such as bearing balls is reduced. Contribute to. The same applies to the sintering aid powder and the conductivity imparting material powder.
[0047]
The raw material mixed powder as described above is granulated as necessary, and then formed into a desired shape (for example, a ball shape). As for the molding method, a normal molding method can be applied. For example, when producing a bearing ball, it is preferable to produce a compact by applying a cold isostatic press (CIP). Such a molded body is first primarily sintered by atmospheric pressure sintering or atmospheric pressure sintering. The sintering temperature during the primary sintering step is preferably in the range of 1700-1850 ° C. If the primary sintering temperature is less than 1700 ° C., a sufficiently dense silicon nitride sintered body cannot be obtained even if the HIP treatment is performed thereafter. Moreover, not only the effect is not obtained even if the primary sintering temperature is set to exceed 1850 ° C., but the segregation part of the silicon nitride crystal grains and the sintering aid component becomes coarse and the sintered body becomes Mechanical strength is reduced. In addition, the consumption of the firing furnace and the like becomes severe.
[0048]
Next, HIP (hot isostatic pressing) treatment (secondary sintering step) is performed on the primary sintered body obtained by the primary sintering step to increase the density of the silicon nitride sintered body. However, since the segregation part of the sintering aid component present in the primary sintered body is likely to grow by HIP treatment, the HIP treatment temperature (secondary sintering temperature) is 200 ° C. or higher than the sintering temperature in the primary sintering step. Set to a lower temperature. That is, the primary sintering temperature is T₁(° C), HIP treatment temperature (secondary sintering temperature) T₂(° C), T₂Is T₁Temperature below -200 (℃) (T₂≦ T₁-200 (℃)). Thus, the growth of the segregation part of the sintering aid component can be suppressed by setting the HIP treatment temperature to be lower than the primary sintering temperature.
[0049]
HIP processing temperature (secondary sintering temperature) T₂Specifically, it is preferable to set in the range of 1300-1500 ° C. HIP processing temperature T₂If the temperature is less than 1300 ° C., the silicon nitride sintered body (secondary sintered body) may not be sufficiently densified. Furthermore, the applied pressure during HIP treatment is preferably 50 MPa or less. When the pressure at the time of HIP exceeds 50 MPa, the segregation part of the sintering aid component tends to grow as in the case of the HIP processing temperature. In order to effectively obtain the effect of the HIP treatment, the pressure during HIP is more preferably in the range of 20 to 50 MPa.
[0050]
By carrying out the primary sintering step and the secondary sintering step under the conditions as described above, the intended silicon nitride sintered body can be obtained. Further, when used as a bearing ball, surface polishing is performed to obtain the surface roughness defined by the JIS standard. At this time, since the silicon nitride sintered body containing a relatively large amount of impurities has good workability, the cost required for processing into a ball shape or the like can be reduced.
[0051]
The wear-resistant member for electronic equipment of the present invention is suitably used as a rotation ball for various electronic equipment as a bearing ball or the like. The present invention is particularly effective for small bearing balls having a diameter of 3 mm or less. The segregation part of the sintering aid component described above is proportional to the size of the silicon nitride sintered body (the larger the size of the sintered body, the larger the amount of sintering aid, the greater the probability that a large segregation part will be formed). If there is a large segregation part, the crushing strength of the sintered body may be reduced. Therefore, the wear resistant member for electronic equipment according to the present invention is not easily affected by the segregation part and the maximum diameter of the segregation part. Is preferably used as a small bearing ball having a diameter of 3 mm or less. The diameter of the bearing ball to which the present invention is applied is preferably 2 mm or less.
[0052]
Electronic devices to which wear-resistant members such as bearing balls as described above are applied include, for example, a projection device with a cooling device, a personal computer, a magnetic recording device such as an HDD or FDD, and an optical disk device such as a CD-ROM or DVD. And various disk-type game devices. The optical disk apparatus includes various apparatuses such as a magneto-optical recording apparatus, a phase change optical recording apparatus, and a reproduction-only optical disk apparatus. Furthermore, the present invention can be applied to various electronic devices as long as they are electronic devices having a rotation drive unit.
[0053]
For example, in a projection device (LCD projector, OHP, etc.) with a cooling device, a personal computer, etc., the wear-resistant member for electronic equipment of the present invention is used as a bearing ball or the like in the rotational drive part of a cooling fan motor. The cooling fan motor is driven at a rotational speed of about several hundred to 3000 rpm, for example, depending on the voltage. The rotation drive part of such an electronic device has an insulating property (electric resistance value = 10⁹A bearing ball made of a silicon nitride sintered body (Ω · m or more) can be used. Since the bearing ball made of the silicon nitride sintered body has high rigidity, noise can be suppressed and durability can be improved.
[0054]
In a magnetic recording device, an optical disc device, a disc-type game device, etc., the wear-resistant member for electronic equipment of the present invention is used as a bearing ball or the like in the rotational drive portion of a medium driving spindle motor. In these electronic devices, the spindle motor is driven at a rotational speed of 4000 rpm or more, for example. The rotation drive part of such an electronic device has conductivity (electric resistance value = 1 to 10).⁶A bearing ball made of a silicon nitride sintered body of Ω · m) is preferably used. A bearing ball made of a silicon nitride sintered body having appropriate conductivity can achieve a stable high-speed rotation and can well release static electricity generated by the high-speed rotation. This makes it possible to eliminate problems caused by static electricity of the electronic device.
[0055]
The bearing of the present invention has a rolling element, for example, a bearing ball, made of the wear-resistant member for electronic equipment of the present invention as described above. FIG. 1 is a view showing a configuration of an embodiment of a bearing according to the present invention. A bearing 1 shown in FIG. 1 has a plurality of bearing balls 2 made of the wear-resistant member for electronic equipment of the present invention, and an inner ring 3 and an outer ring 4 that support these bearing balls 2. The inner ring 3 and the outer ring 4 are preferably formed of bearing steel such as SUJ2 defined in JIS-G-4805, and thereby, high-speed rotation with reliability can be realized. The basic configuration is the same as that of a normal bearing.
[0056]
As described above, the bearing 1 is used for a rotation drive unit of a cooling fan motor in an electronic apparatus such as a projector with a cooling device or a personal computer. Further, in electronic devices such as magnetic recording devices such as HDD and FDD, optical disk devices such as CD-ROM and DVD, and disk game devices, they are used as rotational drive units for various disks. Specifically, it is used to drive a spindle motor that rotates a disk-shaped recording medium at a high speed.
[0057]
【Example】
Next, specific examples of the present invention and evaluation results thereof will be described.
[0058]
Examples 1-17, Comparative Examples 1-6
First, a plurality of silicon nitride powders (average particle size: 0.7 μm) containing 1 to 1.8% by mass of oxygen as impurities and 30 to 700 ppm of Fe component are prepared, and 100 parts by mass of these silicon nitride powders are sintered. Yttrium oxide powder or aluminum oxide powder as a binder, and silicon carbide powder or titanium nitride powder as conductivity imparting particles were added and mixed based on the raw material composition shown in Table 1.
[0059]
Next, each of the raw material mixed powders described above is formed by the CIP forming method, further degreased, and then first, normal pressure sintering (primary sintering) at a temperature of 1700 to 1850 ° C. in an inert atmosphere, followed by HIP Sintering (secondary sintering) was performed. The conditions of primary sintering and secondary sintering (HIP) are as shown in Table 1, respectively. In this way, bearing balls each having a diameter of 2 mm made of a silicon nitride sintered body were produced. The surface of each bearing ball was polished to have a surface roughness equivalent to Grade 3 certified by JIS standards.
[0060]
In addition, for comparison with the present invention, a silicon nitride sintered body using a high-purity silicon nitride powder (oxygen content = 0.6 mass% or less, Fe component content = 10 ppm or less) with sufficiently reduced impurity content ( Comparative Example 1), silicon nitride sintered body (Comparative Example 2) in which the amount of sintering aid is set excessively, silicon nitride sintered body (Comparative Example 3) in which the amount of sintering aid is set too low, and HIP conditions The silicon nitride sintered body (Comparative Example 4) outside the scope of the present invention, the silicon nitride sintered body (Comparative Example 5) in which the amount of conductivity imparting particles was set excessively, and the HIP conditions were out of the scope of the present invention. A silicon nitride sintered body (Comparative Example 6) was prepared in the same manner as in Examples except for those conditions, and bearing balls each having a diameter of 2 mm were obtained.
[0061]
[Table 1]

[0062]
For each of the bearing balls according to Examples 1 to 17 and Comparative Examples 1 to 6, the electrical resistance value, the maximum diameter of the segregation part of the sintering aid component, and the sintering aid component existing per unit area of 1000 × 1000 μm The number of segregation parts and the content of Fe component (ICP emission analysis method) were measured according to the methods described above. These measurement results are shown in Table 2. In addition, the measurement of the segregation part of the sintering aid component was carried out by arbitrarily selecting three unit areas and showing the average value of the measured values.
[0063]
[Table 2]

[0064]
Next, a bearing was manufactured by setting 10 bearing balls according to Examples 1 to 17 and Comparative Examples 1 to 6 as a set. Bearing steel SUJ2 material was used for other bearing members such as ball receiving parts. Each of these bearings was incorporated into a spindle motor and used as an HDD motor. These spindle motors were operated for 1000 hours at rotational speeds of 7200 rpm and 10000 rpm, respectively, and the rate of change in bearing sliding noise, durability of bearing balls, and the presence or absence of defects due to static electricity in the HDD were investigated. These evaluation results are shown in Table 3.
[0065]
Note that the rate of change in the sliding noise of the bearing is the sliding noise N after 10 hours of operation._TenAnd sliding sound N after 1000 hours of operation₁₀₀₀And measure [(N₁₀₀₀-N_Ten) / N_Ten] × 100 (%). The durability of the bearing ball was determined by examining the surface of the bearing ball after 1000 hours of operation. The surface that did not have cracks or peeling on the surface was evaluated as “good” and the surface that had cracks or peeling on the surface was determined as “bad” .
[0066]
[Table 3]

[0067]
As is apparent from Tables 2 and 3, it can be seen that each of the bearing balls of Examples 1 to 17 satisfies the practicality if it is a spindle motor for HDD with a rotational speed of 8000 rpm or less. Moreover, the bearing ball (Examples 4-17) which consists of a silicon nitride sintered compact containing appropriate quantity of electroconductivity provision particle | grains is 1-10.⁶It has an electric resistance value in the range of Ω · m, and not only has the durability required for HDD spindle motors, but also can eliminate problems caused by static electricity. In addition, when bearings produced in the same manner as in Examples 1 to 3 were respectively incorporated in a fan motor and used as a fan motor for a personal computer (rotation speed 1500 rpm), all had good sliding characteristics (durability). It was confirmed that
[0068]
Example 18, Reference Example 1
100 balls each having a diameter of 3 mm (Example 18) and 3 mm diameter bearing balls (Reference Example 1) were prepared by the same composition and manufacturing method as in Example 1, and sintering aids for each of these bearing balls were produced. The maximum diameter of the segregation part of the agent component was measured in the same manner as in Example 1. As a result, in Example 18, the maximum diameter of all 100 segregation parts was 150 μm or less, whereas in Reference Example 23, 23 of 100 segregation parts had a maximum diameter exceeding 150 μm. confirmed. From this result, it is understood that when the diameter of the bearing ball exceeds 3 mm, it is difficult to control the segregation part of the sintering aid component.
[0069]
Example 19, Reference Example 2
100 balls each having a diameter of 3 mm (Example 19) and 3 mm diameter bearing balls (Reference Example 2) were produced by the same composition and manufacturing method as in Example 14, and sintering aids for each of these bearing balls were produced. The maximum diameter of the segregation part of the agent component was measured in the same manner as in Example 14. As a result, in Example 19, the maximum diameter of all 100 segregation parts was 150 μm or less, whereas in Reference Example 2, 8 out of 100 segregation parts had a maximum diameter exceeding 150 μm. confirmed. From this result, it is understood that when the diameter of the bearing ball exceeds 3 mm, it is difficult to control the segregation part of the sintering aid component.
[0070]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a wear-resistant member for electronic equipment that can stably realize high-speed rotation such as a bearing for electronic equipment at a low cost. Therefore, a wide range of wear-resistant members made of silicon nitride can be applied to various electronic devices. In addition, by using a bearing having a bearing ball made of such a wear-resistant member for electronic equipment, it becomes possible to improve the reliability and performance of various electronic equipment.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional view showing a schematic configuration of a bearing ball according to an embodiment of the present invention.
[Explanation of symbols]
1 ... Bearing, 2 ... Bearing ball, 3 ... Inner ring, 4 ... Outer ring

Claims (10)

A silicon nitride sintered body containing a sintering aid component in a range of 5 to 20 parts by mass with respect to 100 parts by mass of silicon nitride and containing an Fe component as an impurity in a range of 30 to 600 ppm, and having a rotational speed. A wear-resistant member for electronic equipment, which is a bearing ball having a diameter of 3 mm or less , used for a rotational drive unit of 8000 rpm or less ,
The silicon nitride sintered body has a segregation part of the sintering aid component, and the segregation part has a maximum diameter in the range of 10 to 150 μm, and a unit area of 1000 × 1000 μm in the silicon nitride sintered body A wear-resistant member for electronic equipment, characterized by being present in the range of 2 to 10 per contact. The wear-resistant member for electronic equipment according to claim 1,
A wear-resistant member for electronic equipment, wherein the sintering aid component contains at least one selected from rare earth element oxides and alkaline earth element oxides. In the wear-resistant member for electronic devices according to claim 1 or 2,
The silicon nitride sintered body contains electrical conductivity-imparting particles and has an electric resistance value in the range of 1 to 10 ⁶ Ω · m. In the wear-resistant member for electronic devices according to claim 3,
The electrical conductivity imparting particles are composed of at least one selected from a group 4A element, a group 5A element, a group 6A element, a group 7A element, silicon, boron carbide and nitride, and wear resistance for electronic equipment Element. The wear-resistant member for electronic equipment according to any one of claims 1 to 3,
The segregation part is present in the range of 2 or more and 6 or less per unit area in the silicon nitride sintered body. In the abrasion-resistant member for electronic devices of any one of Claims 1 thru | or 5,
The bearing ball is used for a rotational drive unit of a magnetic recording device, an optical disk device, a game device, or a cooling device for electronic devices, and is a wear resistant member for electronic devices. A method of manufacturing the wear-resistant member for electronic equipment according to claim 1,
A silicon nitride powder containing 1 to 1.8% by mass of oxygen as impurities and 30 to 700 ppm of Fe component and 5 to 20 parts by mass of sintering aid powder with respect to 100 parts by mass of the silicon nitride powder are mixed. Molding the mixture into a desired shape;
A primary sintering step of sintering the molded body obtained by the molding step at a temperature in the range of 1700 to 1850 ° C .;
A secondary sintering step of subjecting the primary sintered body obtained by the primary sintering step to HIP treatment at a temperature lower by 200 ° C. or more than the sintering temperature of the primary sintering step;
A method for producing a wear-resistant member for electronic equipment, comprising producing a bearing ball having a diameter of 3 mm or less , which is used for a rotational drive unit having a rotational speed of 8000 rpm or less . In the manufacturing method of the wear-resistant member for electronic devices according to claim 7 ,
A method for producing a wear-resistant member for electronic equipment, wherein the HIP treatment in the secondary sintering step is performed at a temperature in the range of 1300 to 1500 ° C. under a pressure of 50 MPa or less. In the manufacturing method of the abrasion-resistant member for electronic devices of Claim 7 or Claim 8 ,
A method for producing a wear-resistant member for electronic equipment, wherein conductivity-imparting particles are further added to and mixed with the mixture. A bearing for electronic equipment, comprising a bearing ball comprising the wear resistant member for electronic equipment according to any one of claims 1 to 6 .

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