JP3889915B2 - Lubricating oil for fluid bearing and fluid bearing using the same - Google Patents

Description

式中、Ｒ₁は、水素原子又はメチル基を示し、Ｒ₂は、水素原子、又は窒素原子及び／又は酸素原子を含有する炭素数O〜20の基を示す。銅の耐摩耗性を向上させることから、ベンゾトリアゾール誘導体が好ましく、さらに、Ｒ₂が窒素原子を含有する炭素数10〜20の基であることが好ましい。
【００２０】
また、ベンゾトリアゾール及び／又はその誘導体は、流体軸受用潤滑油全体を基準としてO.1〜5.0質量％、さらにはO.5〜5.O質量％程度含有されるよう配合することが好ましい。添加量が少ないと、特に銅の耐摩耗の効果がなく、多すぎると、添加量に見合う効果が得られないばかりでなく、場合によってはスラッジ生成の原因となるので好ましくない。
【００２１】
フェノール系酸化防止剤としては、２，６−ジ−t−ブチルフェノール、２，６−ジ−t−ブチル−４−メチルフェノール、２，６−ジ−t−ブチル−４−エチルフェノール、２，６−ジ−t−ブチル−４-ｎブチルフェノール（エチル７４４）、４，４’メチレンビス（２，６−ジ−t−ブチルフェノール）、２，２'−チオビス（４−メチル−６-t−ブチルフェノール）等が挙げられる。また、アミン系酸化防止剤を使用してもよく、特に併用により大幅な酸化安定性の向上をはかることができる。
【００２２】
エポキシ化合物としては、フェニルグリシジルエーテル型エポキシ化合物、アルキルグリシジルエーテル型エポキシ化合物、グリシジルエステル型エポキシ化合物、脂環式エポキシ化合物、エポキシ化脂肪酸モノエステル、エポキシ化植物油などを単独で又は複数混合して使用することができる。これらのエポキシ化合物の中でも好ましいものは、アルキルグリシジルエーテル型エポキシ化合物、グリシジルエステル型エポキシ化合物、脂環式エポキシ化合物及びエポキシ化脂肪酸モノエステルである。中でもアルキルグリシジルエーテル型エポキシ化合物、グリシジルエステル型エポキシ化合物、脂環式エポキシ化合物もしくはこれらの混合物がより好ましい。これらのエポキシ化合物を添加することにより、基材の安定性、特に加水分解安定性が大幅に向上する。
【００２３】
カルボジイミド化合物は、次の一般式（２）で表される化合物である。
【化２】
Ｒ₃−Ｎ＝Ｃ＝Ｎ−Ｒ₄ （２）
式中、Ｒ₃及びＲ₄は水素又は炭化水素基、あるいは窒素及び／又は酸素を含有する炭化水素基であり、Ｒ₃及びＲ₄はそれぞれ同一であっても、異なっていてもよい。
上記一般式（２）において、好ましくは、Ｒ₃及びＲ₄が水素、炭素数１〜１２の脂肪族炭化水素基、炭素数６〜１８の芳香族炭化水素基、及び芳香−脂肪族炭化水素基の場合である。具体的には、水素、メチル、エチル、プロピル、イソプロピル、ブチル、イソブチル、ペンチル、２−メチルブチル、ヘキシル、ヘプチル、オクチル、２−エチルヘキシル、ノニル、デシル、ウンデシル、ドデシル等のアルキル基、プロペニル、ブテニル、イソブテニル、ペンテニル、２−エチルヘキセニル、オクテニル等のアルケニル基、シクロペンチル、シクロヘキシル、メチルシクロペンチル、エチルシクロペンチル等のシクロアルキル基、フェニル、ナフチル等のアリール基、トレイル、イソプロピルフェニル、ジイソプロピルフェニル、トリイソプロピルフェニル、ノニルフェニル等のアルキル置換フェニル等のアリール基、ベンジル、フェネチル等のアラルキル基等をＲ₃、Ｒ₄として含有する化合物を挙げることができる。カルボジイミド化合物は酸補足剤としての働きを有し、加水分解安定性を向上させる。
【００２４】
リン酸エステルとしては、トリクレジルホスフェート、トリフェニルホスフェート、クレジルジフェニルホスフェート、ジフェニルハイドロジェンホスフート、２−エチルヘキシルジフェニルホスフェートなどが挙げられ、トリクレジルホスフェート、トリフェニルホスフェートがより好ましい。リン酸エステルを添加することにより鉄の耐摩耗性を大幅に向上することができる。
【００２５】
フェノール系酸化防止剤、エポキシ化合物、カルボジイミド化合物及びリン酸エステルは、これらから選択される１種又は２種以上を配合することが好ましい。本発明において、特にこれらの添加剤の配合量を限定するものではないが、複数の添加剤を配合する場合にも、それぞれの添加剤について、流体軸受用潤滑油全量に対してO.05〜5.0質量％含有されるように配合すればよい。添加量が少ないと効果がなく、多すぎると基油の特性が生かされず、スラッジ生成の原因ともなるので好ましくない。
【００２６】
本発明の流体軸受は、上記の流体軸受用潤滑油を用いることを特徴とする。ボールベアリングなどの機構を有さず、スリーブと軸からなり、それらの間に収容された潤滑剤によって互いに直接接触することがないように間隔が保持される流体軸受であれば、機械的に特に限定するものではない。本発明の流体軸受は、回転軸及びスリーブの何れかに又はそれらの両方に動圧発生溝が設けられ、回転軸が動圧によって支持される流体軸受、また回転軸に垂直方向に動圧を生じるようにスラストプレートが設けられている流体軸受なども含む。
【００２７】
流体軸受は、非回転時には動圧が生じないためにスリーブと回転軸あるいはスリーブとスラストプレートが部分的あるいは全面接触しており、回転により動圧が生じて非接触状態となる。こうしたことから接触、非接触を繰り返し、スリーブ、回転軸あるいはスリーブとスラストプレートの金属摩耗が、また回転中の一時的な接触により焼付きが起こることがあるが、前記潤滑油の有する優れた安定性、潤滑性、防食性、スラッジ生成耐性によって、長期に亘り高速回転安定性、静寂性（耐久性）を保持するものであり、特に高速において優れた省エネルギー性を示す。したがって、本発明の流体軸受はより高速化及び省エネルギー性によって消費電力の低減を可能にすることから、この流体軸受を装備するＯＡ機器などは、高速回転安定性、静寂性に加えて、より小型なものにできるか、さもなければ長寿命が付与される。
【００２８】
さらに、本発明は、前記流体軸受を上記に規定した流体軸受用潤滑油で潤滑する流体軸受の潤滑方法である。既に記したように、前記流体軸受用潤滑油を流体軸受に充填して潤滑することにより、長期に亘り高速回転安定性、静寂性を保持され、かつ優れた省エネルギー性、長寿命化を果すことができる。
【００２９】
【実施例】
以下、実施例に基づいて、本発明をさらに詳細に説明する。なお、本発明は、以下の実施例によって何ら制限されるものではない。
【００３０】
（実施例I）
図１は、本発明の流体軸受用潤滑油を装填して用いるために好ましい流体軸受の一具体例を示すものであり、該潤滑油を用いる記録ディスク駆動用の流体軸受を装備したモータの概略構成を模式的に示す断面図である。この図１において、モータ１は、ブラケット２と、このブラケット２の中央開口部に一方の端部が外嵌固定されるシャフト４、このシャフト４に対して相対的に回転自在に保持されたロータ６とを備える。ブラケット２にはステータ１２が固定され、これに対向してロータ６に設けられたロータマグネット１０との間で、回転駆動力を生ずる。
【００３１】
シャフト４の上部及び下部には、半径方向外方に突出する円盤状の上部スラストプレート４ａと下部スラストプレート４ｂがあり、これらのスラストプレート間のシャフト外側面には、気体介在部２２が形成されている。一方ロータ６は、その外周部に記録ディスクＤが載置されるロータハブ６ａとロータ６の内周側に位置し潤滑油８が保持される微小間隙を介してシャフト４に支持されるスリーブ６ｂとを備えている。さらにスリーブ６ｂには、上部及び下部スラストプレートの外側に蓋をする形で、上部カウンタプレート７ａ及び下部カウンタプレート７ｂが設けられている。
【００３２】
シャフト４の中央部に設けられた気体介在部２２の上部に隣接するシャフト４の外周部から、上部スラストプレートの下面、外周面及び上面外周部に至る部分には、対向するスリーブ６ｂの内周部貫通孔６cの上部から上部カウンタプレート７ａの下面に至る部分との間に、微小間隙が形成され、潤滑油８が保持されている。そして上部スラストプレート４ａの下面には、ロータ６の回転にともない潤滑油８中に動圧を発生するスパイラル溝１４が形成されており、モータ回転時にロータ部を軸線方向に保持する支持力を発生すると同時に、潤滑油８を矢印Ａの方向に押し戻す。さらにスリーブ６ｂの内周部貫通孔６c上部内面の潤滑油保持部には、アンバランスなヘリンボーン状溝２４が形成され、モータ回転時にロータ部を半径方向に保持する支持力を発生すると同時に、潤滑油８を矢印Ｂの方向に押し上げる。
【００３３】
これらの溝により生じる潤滑油８の動圧により、微小間隙内の潤滑油８に生じる圧力分布は、上部スラストプレート４ａの下面内周部Ｐで最も高くなっている。その結果、仮に潤滑油８内に溶け込んだ空気が気泡化しても、その気泡は前記内周部Ｐの外側に拡散排除され、下方の気体介在部２２空隙部又は上方の上部カウンタプレート７ａ下面空隙部に至る。そしてこれらの空隙部は、直接又は外気連通孔２０により大気に解放されており、前記気泡は外気に解放され、潤滑油漏れがなくかつ支持力の高い流体軸受構造を実現している。
【００３４】
同様の微小間隙、溝、潤滑油保持部の構造が、シャフト４の中央部に設けられた気体介在部２２の下部から下部スラストプレート４ｂ及び下部カウンタプレート７ｂに、上下逆配置で形成されており、この下部動圧軸受部によりロータ部は一層安定に支持される。
また、本構造の流体軸受は、毎分２万回転前後の高速回転においても、回転遠心力による潤滑油８の外周方向への発散が、上部及び下部カウンタプレート７ａ、７ｂにより効果的に防止され、本発明にかかる流体軸受用潤滑油を用いることにより、一層高速で安定した回転を実現する。
【００３５】
（実施例II）
各種の流体軸受用潤滑油を試作し、図１に示す上記流体軸受構造を有するモータに充填して実際に駆動し、以下のようにして試験し、潤滑油性能を評価した。
【００３６】
流体軸受用潤滑油のべ一ス基材として次に示すエステル（Ａ〜Ｅ及びＨ）、鉱油（Ｆ）、アルキルベンゼン（Ｇ）を使用した。
Ａ：ネオペンチルグリコール（ＮＰＧ）とｎ-Ｃ₉酸とのエステル
Ｂ：ＮＰＧと、ｎ-Ｃ₉酸（50 mol％）とｎ-Ｃ₁₀酸（50 mol％）の混合酸とのエスアル
Ｃ：ＮＰＧと、ｎ-Ｃ₁₀酸（95 mol％）とｎ-Ｃ₁₂酸（5 mol％）の混合酸とのエステル
Ｄ：ペンタエリスリトールとｎ-Ｃ₅酸とのエステル
Ｅ：トリメチロールプロパンと２−エチルヘキサン酸とのエステル
Ｆ：パラフィン系鉱油
Ｇ：アルキルベンゼン
Ｈ：ＮＰＧと２−エチルヘキサン酸とのエステル72質量％と、ペンタエリスリトールと２−エチルヘキサン酸とのエステル28質量％の混合エステル
【００３７】
また、添加剤としては、次のものを用いた。
Ｉ：グリセリンモノオレイルエーテル
Ｊ：次の一般式（３）で表されるベンゾトリアゾール誘導体
【化３】

Ｋ：２，６−ジ−t−ブチル−４−メチルフェノール
Ｌ：２−エチルヘキシルグリシジルエーテル
Ｍ：トリクレジルホスフェート
Ｎ：ビス（ジイソプロピルフェニル）カルボジイミド
【００３８】
ＮＰＧエステル基材（Ａ〜Ｃ）及び添加剤を表１に示すように配合して本発明の流体軸受用潤滑油（実施例１〜８）を調製した。実施例１及び２の油は添加剤を含有せず、実施例３〜８は、表１の添加剤の列に示すように、上記Ｉ〜Ｎの添加剤を括弧内の数量含有されるよう配合した。また、Ｄ〜Ｈの基材を用いて比較例の流体軸受用潤滑油（比較例１〜５）を調製した。なお、比較例の流体軸受用潤滑油にはいずれも添加剤を配合していない。
【００３９】
【表１】

【００４０】
調製した実施例１〜８及び比較例１〜４の油について、それぞれの物性を測定するとともに、流体軸受の実機に装填して加速試験を行い、実用性能を評価した。物性測定及び性能評価試験は、次の方法で行った。
【００４１】
(1) 蒸発量：熟重量分析法（ＴＧ法）により、120℃に12時間保持したときの重量減少量から求めた。
(2) 動粘度、粘度指数：JIS K 2283に準じ、キャノン−フェンスケ粘度計を用い動粘度を測定するとともに粘度指数を算出した。
(3) 水酸基価：JIS K 0070に準じて測定した。
(4) 全酸価：JIS K 2514に準じて測定した。
(5) 水分：JIS K 2275のカールフィッシャー式電量滴定法に準じて測定した。
(6) 灰分：JIS K 2272に準じて測定した。但し、ppmの単位まで測定できるものとした。
【００４２】
(7) ＮＲＲＯテスト不良率（耐久性）：
各試料について、図１の流体軸受構造を有するモータ5台に装填し、80℃の温度条件下に、モータの駆動／停止を繰り返す間欠運転による加速試験を行い、回転非同期振れ（non repeatable run out、以下、ＮＲＲＯという。）を測定し、耐久性に及ぼす潤滑油の効果を評価した。このとき、モータの駆動／停止は、図２に示すように、モータを駆動（ON）し、規定回転数（例えば、10,OOO rpm）に達したらそれを保持した後、駆動開始（0N）から30秒後にモータを停止（OFF）し、その30秒後に再びモータを駆動（0N）する動作を繰り返した。
また、評価は、ＮＲＲＯ値を間欠回数1万回及び２万回の時点で測定し、ＮＲＲＯ値が0.05μmを超えた場合を不良とし、不良と判定されたモータの台数を、その試料油に使用したモータの全台数（5台）に対する割合で表した。なお、明らかに、O.05μmを超える兆候を示した場合は、１万回又は２万回に達しない時点でも測定し、O.05μmを超えた場合も不良とした。
【００４３】
(8) 省エネルギー性：
ＮＲＲＯテスト不良率（耐久性）の評価に用いたものと同じモータを使用し、モータに流れる電流を測定して省エネルギー性を評価した。すなわち、前記実施例１〜５、比較例２及び５の潤滑油を前記モータの流体軸受部に装填し、直流電源とモータとの間にセットした電流計で電流の値を測定した。また、モータ回転数10,000 rpm、無負荷、モータ外気温O℃及び40℃の条件下にて行った。
【００４４】
物性測定及び耐久性評価の試験結果を表２に示し、省エネルギー性評価の試験結果を表３に示す。
【００４５】
【表２】

【００４６】
表２から、実施例１〜８の潤滑油は、蒸発量が小さく、ＮＲＲＯテストの不良率も問題とならない程度であり、流体軸受用潤滑油として有効に使用できるものであることがわかる。一方、比較例１及び２は、蒸発量は小さいけれども、ＮＲＲＯテストの不良率が大きく、また、比較例３〜５は、蒸発量が大きすぎて実用的に用いることはできない。
【００４７】
【表３】

【００４８】
表３から、実施例の潤滑油は、0℃及び40℃のいずれの場合も電流の値が小さく（特に実施例２の潤滑油は比較例５より高い粘度であるが電流の値は小さい。）、直流回路ではモータを回す力は電流に比例するので、消費電力が少なく、省エネルギー性が高いといえる。また、実施例４、５は実施例１よりも粘度が高いにもかかわらず、電流値が低く添加剤の効果がうかがわれる。
【００４９】
【発明の効果】
本発明は、ネオペンチルグリコールと炭素数6〜12の１価脂肪酸とから得られる粘度指数100以上、全酸価O.5 mgKOH/g以下、及び水酸基価20 mgKOH/g以下の
エステルからなることを特徴とする流体軸受用潤滑油であり、また、該流体軸受用潤滑油を用いる流体軸受及び該流体軸受の潤滑方法であることから、優れた省エネルギー性及び耐久性を示し、特に高速化、コンパクト化が進む電子機器の回転装置に好適に利用することができる。
【図面の簡単な説明】
【図１】流体軸受を装備したモータの概略構成を模式的に示す断面図。
【図２】流体軸受用潤滑油の実用性能を評価する加速試験でモータの間欠運転における駆動／停止パターンを模式的に示すチャート。
【符号の説明】
１ モータ
４ シャフト（軸）
４ａ 上部スラストプレート
４ｂ 下部スラストプレート
６ｂ スリーブ[0001]
[Industrial application fields]
The present invention relates to a lubricating oil for a fluid bearing, a fluid bearing using the fluid, and a lubrication method for the fluid bearing, and in particular, a fluid bearing excellent in energy saving and durability and suitable for a compact fluid bearing used at high speed rotation. It relates to lubricating oil.
[0002]
[Prior art]
The progress of miniaturization, lightening, and increasing capacity of audio equipment and personal computers is remarkable. These electronic devices use various rotating devices, for example, rotating devices that drive magnetic disks, optical disks, FDs, mini disks, hard disks, compact disks, DVDs, etc., making them smaller, lighter, and larger in capacity. Is largely due to these improvements, or improvements to the bearings that are essential for rotating devices.
Fluid bearings consisting of a sleeve and a rotating shaft that face each other with lubricating oil do not have ball bearings, so they are excellent in size, weight reduction, quietness, and economy, and can be used for audio equipment and personal computers. It is coming.
[0003]
The lubricating oil or bearing fluid used for fluid bearings is composed of neopentyl polyol ester, squalane and / or naphthenic mineral oil and urea compound thickener grease (JP-A-1-279117), Base oil of fatty acid triester of trimethylolpropane, containing hindered phenolic antioxidant and benzotriazole derivative (Japanese Patent Laid-Open No. 1-188592), specific hindered phenolic antioxidant and aromatic amine Containing a specific amount of an antioxidant (Japanese Patent Laid-Open No. 1-225697), a specific monocarboxylic acid ester having a phenyl group and / or a specific dicarboxylic acid ester as a base oil -357318), a base composition using a base composition (Patent No. 2621329), a carbonate ester base oil, containing sulfur Those containing an enol-based antioxidant and a zinc-based extreme pressure agent (JP-A-8-34987), those using a magnetic fluid (JP-A-8-259977, 8-259982, 8-259985), carbonate ester There have been proposed those using a phenolic antioxidant as a base oil mainly composed of (Japanese Patent Laid-Open No. 10-183159).
[0004]
[Problems to be solved by the invention]
In the future, it is expected that the desire and demand for high-speed processing of large-capacity information or further downsizing of equipment will increase. Conventionally, power consumption of audio equipment and personal computers has not been attracting attention because it is not so large, but there is a demand for energy saving because the built-in battery has a longer life or the capacity can be reduced. There is still something strong. As described above, fluid bearings are required to rotate at a higher speed in accordance with a desire for high-speed processing of information or downsizing of equipment. The energy loss in the bearing increases as the speed increases. However, the various proposed lubricating oils or bearing fluids have high viscosity and have not been evaluated from the viewpoint of energy saving performance in bearings. Lubricating oils for hydrodynamic bearings have basic performances such as lubricity, deterioration stability (lifetime), sludge generation prevention, wear prevention, and corrosion prevention, as well as energy saving performance and low evaporation. Oil is demanded to meet demands for high-speed processing of information, compactness, and the like. Further, as the device becomes more compact, the durability of the device itself may be sacrificed, and the durability to which the lubricant is applied may be affected.
[0005]
The present invention solves the above-described problems, and provides a lubricating oil for a fluid bearing that has low evaporative properties and excellent performance such as energy saving and durability as well as lubricity and deterioration stability. Is an issue. Another object of the present invention is to provide a fluid dynamic bearing using the fluid lubricant for the fluid dynamic bearing and a method for lubricating the fluid dynamic bearing.
[0006]
[Means for Solving the Problems]
The present invention relates to neopentyl glycol and at least one carbon number.9 , Ten Or12'sLinear saturationA lubricating oil for fluid bearings comprising an ester having a viscosity index of 100 or more, a total acid value of 0.5 mgKOH / g or less, and a hydroxyl value of 20 mgKOH / g or less obtained from a monovalent fatty acid. Here, the at least one monovalent fatty acid is preferably two or more monovalent fatty acids.
[0007]
Furthermore, the lubricating oil for fluid bearings preferably contains 0.1 to 5.O% by mass of a polyhydric alcohol partial ester compound, a polyhydric alcohol partial ether compound, or a mixture thereof, and the ester compound or ether compound is at least 2 A compound having one hydroxyl group is preferred. Furthermore, it is preferable that the lubricating oil for a hydrodynamic bearing contains benzotriazole and / or a derivative thereof, a phenolic antioxidant, an epoxy compound, a carbodiimide compound, and / or a phosphoric ester in an amount of O.05 to 5.O% by mass. .
[0008]
Further, the present invention is a fluid dynamic bearing comprising a shaft and a sleeve, wherein the fluid bearing is filled with the fluid bearing lubricating oil, and the fluid bearing comprising the shaft and the sleeve is lubricated with the fluid bearing lubricating oil. Lubrication method.
[0009]
[Preferred embodiments]
The fluid bearing lubricating oil of the present invention includes neopentyl glycol and 9 carbon atoms., Ten OrThe ester obtained by reaction with 12 monovalent fatty acids is used as the base oil. As the monovalent fatty acid, a saturated fatty acid not containing an unsaturated bond is used in terms of chemical stability and heat resistance. Esters with monovalent fatty acids having 5 or less carbon atoms have low viscosity, and it is difficult to obtain sufficient rigidity to support the fluid bearing portion, which is not preferable for durability. On the other hand, an ester with a monovalent fatty acid having 13 or more carbon atoms has a high viscosity, and the resistance during rotation is increased, so that a good energy-saving property cannot be obtained.
[0010]
Moreover, as a fatty acid, both a branched fatty acid and a linear fatty acid can be used. Regarding the lubricating oil for fluid bearings of the present invention, diesters consisting of branched fatty acids are preferred for hydrolysis, while diesters of linear fatty acids are more preferred because they have good lubricity and high viscosity index. Of course, a diester of neopentyl glycol having both acyl groups from a branched fatty acid and a linear fatty acid having both of these properties can also be preferably used. Moreover, although saturated fatty acid and unsaturated fatty acid can be used as fatty acid, saturated fatty acid is preferable from the viewpoint of stability.
[0011]
Carbon number9 , Ten OrSpecific examples of the 12 saturated monovalent fatty acid include pelargonic acid, capric acid, lauric acid, or a mixed acid thereof, and those which can obtain a neopentyl glycol ester having a viscosity index of 100 or more can be mentioned. In addition, the synthesis | combination of neopentyl glycol ester can be performed by a well-known esterification reaction or transesterification reaction from neopentyl glycol and the said fatty acid.
[0012]
The environment in which fluid bearing lubricants are used with the spread of acoustic equipment, personal computers, etc. is equivalent to home appliances, and the range of use must be considered from -20 to 60 ° C. In order to enable use under such conditions, excellent low temperature characteristics are required so that sufficient fluidity can be obtained even at low temperatures. Neopentyl glycol esters are preferred because esters obtained using two or more saturated monovalent fatty acids having different chemical structures have good low temperature fluidity. For example, when two types of fatty acids are used, there are three types of esters with different chemical structures: an ester in which only one fatty acid is bonded, an ester in which only the other fatty acid is bonded, and an ester in which both fatty acids are bonded one by one. An ester mixture containing is obtained. Such an ester mixture is considered to improve the low temperature fluidity because it loses crystallinity compared to an ester having only a single chemical structure.
[0013]
The ester used in the lubricating oil of the present invention has a viscosity index of 100 or more. The viscosity index of esters tends to be higher as the acyl group is linear and the number of carbons is higher.. SpecialIf only straight chain mixed fatty acids are used, a high viscosity index and good lubricity can be ensured, and since it has a high viscosity index, low viscosity at low temperatures and energy saving are possible, and high viscosity at high temperatures. Since it can be secured, the lubricity becomes good.
[0014]
In the lubricating oil for fluid bearings of the present invention, an ester having a total acid value of 0.5 mgKOH / g or less and a hydroxyl value of 20 mgKOH / g or less is used. The total acid value is important for ensuring corrosion prevention, wear resistance and stability, and is preferably 0.3 mgKOH / g or less. The hydroxyl value is preferably 5 mgKOH / g or less from the viewpoints of moisture absorption resistance and stability. An ester having such properties can be obtained by sufficiently performing an esterification reaction and then appropriately purifying by a known method.
[0015]
Furthermore, the moisture contained in the ester is a substance involved in hydrolysis, and the ash content can be a catalyst that promotes hydrolysis and a causative substance for sludge generation. The water content is preferably 500 ppm or less, more preferably 100 ppm or less, and the ash content is preferably 10 ppm or less, more preferably 1 ppm or less. Water can be removed by, for example, heating distillation, heating under reduced pressure, or blowing an inert gas, and ash can be removed by adsorption treatment. In order to reduce the ash content, it is also effective to perform ester synthesis without a catalyst. By doing this, hydrolysis of sludge and sludge generation are suppressed to a minimum, and a highly stable ester can be obtained, so that the deterioration resistance stability of the lubricating oil for fluid bearings is improved, and long-term stability and long life are improved. Can be achieved.
[0016]
In addition to the neopentyl glycol ester as the base oil, the lubricating oil of the present invention may contain various additives in order to improve practical performance. Examples of such additives include fatty acid monoester compounds and / or monoether compounds of polyhydric alcohols, benzotriazole and / or derivatives thereof. Furthermore, it is also effective to blend one or more selected from phenolic antioxidants, epoxy compounds, carbodiimide compounds, and phosphate esters.
[0017]
Fatty acid monoesters and monoethers of polyhydric alcohols are polyhydric alcohol derivatives having two or more hydroxyl groups, and further having one or more hydrocarbon groups added by ether bonds or ester bonds, Used as This polyhydric alcohol derivative is adsorbed on one bearing metal (eg, shaft) at the hydroxyl portion, and the hydrocarbon group extending from the ether bond or ester bond prevents contact with the other bearing metal (eg, sleeve). Therefore, it is considered that the lubricating action is improved.
Such a polyhydric alcohol derivative can be obtained by a condensation reaction between a polyhydric alcohol having 3 to 6 hydroxyl groups and a monool or monovalent fatty acid having 10 to 22 carbon atoms. Here, specific examples of the polyhydric alcohol include glycerin, trimethylolpropane, diglycerin, erythritol, pentaerythritol, triglycerin, sorbitol, mannitol, and the like. In particular, trivalent alcohol is preferable, and glycerin is particularly preferable. preferable. The monovalent fatty acid that forms a partial ester with a polyhydric alcohol is more preferably one having 14 to 20 carbon atoms. Specifically, myristic acid, palmitic acid, stearic acid, isostearic acid, oleic acid, erucic acid Etc. Monools that produce polyhydric alcohols and partial ethers include monohydric alcohols corresponding to these acids. In particular, oleic acid and oleyl alcohol are preferable, and glycerol monooleate or glycerol monooleyl ether is particularly preferable as the compound of the polyhydric alcohol derivative.
[0018]
The polyhydric alcohol derivative may be appropriately blended in an effective amount that exerts an effect, and the blending amount is not particularly limited, but is 0.1 to 5.O% by mass based on the fluid bearing lubricant, It is preferable to mix | blend so that it may contain about O.5-5.0 mass%. In addition, the partial (particularly mono) ether and partial (particularly mono) ester of the polyhydric alcohol may be used singly, or a plurality of compounds may be used, or a mixture thereof may be used.
[0019]
As benzotriazole and / or a derivative thereof, a compound represented by the following general formula (1) is preferably used.
[Chemical 1]

Where R₁Represents a hydrogen atom or a methyl group, R₂Represents a hydrogen atom or a group having 0 to 20 carbon atoms containing a nitrogen atom and / or an oxygen atom. Benzotriazole derivatives are preferred because they improve the wear resistance of copper, and R₂Is preferably a group having 10 to 20 carbon atoms and containing a nitrogen atom.
[0020]
Moreover, it is preferable to mix | blend benzotriazole and / or its derivative (s) so that it may contain about 0.1 to 5.0 mass% further about O.5 to 5.O mass% on the basis of the whole lubricating oil for fluid bearings. If the addition amount is small, there is not particularly an effect of wear resistance of copper, and if it is too large, not only the effect commensurate with the addition amount is obtained but also it may cause sludge formation in some cases, which is not preferable.
[0021]
Examples of phenolic antioxidants include 2,6-di-t-butylphenol, 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butyl-4-ethylphenol, 6-di-t-butyl-4-nbutylphenol (ethyl 744), 4,4'methylenebis (2,6-di-t-butylphenol), 2,2'-thiobis (4-methyl-6-t-butylphenol) ) And the like. In addition, an amine-based antioxidant may be used, and the oxidation stability can be greatly improved particularly by the combined use.
[0022]
As the epoxy compound, phenyl glycidyl ether type epoxy compound, alkyl glycidyl ether type epoxy compound, glycidyl ester type epoxy compound, alicyclic epoxy compound, epoxidized fatty acid monoester, epoxidized vegetable oil, etc. are used alone or in combination. can do. Among these epoxy compounds, alkyl glycidyl ether type epoxy compounds, glycidyl ester type epoxy compounds, alicyclic epoxy compounds and epoxidized fatty acid monoesters are preferred. Of these, alkyl glycidyl ether type epoxy compounds, glycidyl ester type epoxy compounds, alicyclic epoxy compounds or mixtures thereof are more preferred. By adding these epoxy compounds, the stability of the substrate, particularly the hydrolysis stability, is greatly improved.
[0023]
The carbodiimide compound is a compound represented by the following general formula (2).
[Chemical formula 2]
R_Three-N = C = N-R_Four                (2)
Where R_ThreeAnd R_FourIs a hydrogen or hydrocarbon group, or a hydrocarbon group containing nitrogen and / or oxygen, and R_ThreeAnd R_FourMay be the same or different.
In the general formula (2), preferably R_ThreeAnd R_FourAre hydrogen, an aliphatic hydrocarbon group having 1 to 12 carbon atoms, an aromatic hydrocarbon group having 6 to 18 carbon atoms, and an aromatic-aliphatic hydrocarbon group. Specifically, hydrogen, alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, 2-methylbutyl, hexyl, heptyl, octyl, 2-ethylhexyl, nonyl, decyl, undecyl, dodecyl, propenyl, butenyl , Alkenyl groups such as isobutenyl, pentenyl, 2-ethylhexenyl, octenyl, cycloalkyl groups such as cyclopentyl, cyclohexyl, methylcyclopentyl, ethylcyclopentyl, aryl groups such as phenyl, naphthyl, trail, isopropylphenyl, diisopropylphenyl, triisopropylphenyl Aryl groups such as alkyl-substituted phenyl such as nonylphenyl, aralkyl groups such as benzyl and phenethyl_Three, R_FourExamples of the compound to be contained are as follows. The carbodiimide compound functions as an acid scavenger and improves hydrolysis stability.
[0024]
Examples of phosphoric acid esters include tricresyl phosphate, triphenyl phosphate, cresyl diphenyl phosphate, diphenyl hydrogen phosphate, 2-ethylhexyl diphenyl phosphate, and tricresyl phosphate and triphenyl phosphate are more preferable. By adding phosphate ester, the wear resistance of iron can be greatly improved.
[0025]
The phenolic antioxidant, epoxy compound, carbodiimide compound and phosphate ester are preferably blended in one or more selected from these. In the present invention, the amount of these additives is not particularly limited, but even when a plurality of additives are blended, for each additive, O.05 to the total amount of fluid bearing lubricating oil. What is necessary is just to mix | blend so that 5.0 mass% content may be contained. If the amount added is small, the effect is not obtained. If the amount is too large, the characteristics of the base oil are not utilized, and sludge formation may be caused.
[0026]
The fluid dynamic bearing of the present invention is characterized by using the above-mentioned fluid bearing lubricating oil. Especially if it is a hydrodynamic bearing that does not have a mechanism such as a ball bearing, consists of a sleeve and a shaft, and is kept apart so as not to be in direct contact with each other by the lubricant contained between them It is not limited. The hydrodynamic bearing of the present invention is provided with a dynamic pressure generating groove in either or both of the rotating shaft and the sleeve, and the rotating shaft is supported by the dynamic pressure, and the dynamic pressure is applied in a direction perpendicular to the rotating shaft. It also includes a fluid bearing or the like provided with a thrust plate to generate.
[0027]
Since the hydrodynamic bearing does not generate dynamic pressure when not rotating, the sleeve and the rotary shaft or the sleeve and the thrust plate are in partial or full contact with each other, and dynamic pressure is generated by the rotation, resulting in a non-contact state. For this reason, contact and non-contact are repeated, and metal wear between the sleeve, the rotating shaft or the sleeve and the thrust plate may occur, and seizure may occur due to temporary contact during rotation. It retains high-speed rotational stability and quietness (durability) over a long period of time due to its properties, lubricity, anticorrosion, and sludge generation resistance, and exhibits excellent energy-saving properties especially at high speeds. Therefore, since the fluid dynamic bearing of the present invention enables reduction of power consumption by higher speed and energy saving, the OA equipment equipped with the fluid dynamic bearing is smaller in addition to high speed rotation stability and quietness. Can be made, otherwise it has a long life.
[0028]
Furthermore, the present invention is a fluid bearing lubrication method in which the fluid bearing is lubricated with the fluid bearing lubricating oil defined above. As already described, filling the fluid bearing lubricant into the fluid bearing and lubricating it will maintain high-speed rotational stability and quietness over a long period of time, and achieve excellent energy saving and long life. Can do.
[0029]
【Example】
Hereinafter, the present invention will be described in more detail based on examples. In addition, this invention is not restrict | limited at all by the following examples.
[0030]
(Example I)
FIG. 1 shows a specific example of a fluid bearing preferable for loading and using the fluid bearing lubricating oil of the present invention, and an outline of a motor equipped with a fluid dynamic bearing for driving a recording disk using the lubricant. It is sectional drawing which shows a structure typically. In FIG. 1, a motor 1 includes a bracket 2, a shaft 4 whose one end is fitted and fixed to the central opening of the bracket 2, and a rotor that is rotatably held relative to the shaft 4. 6. A stator 12 is fixed to the bracket 2, and a rotational driving force is generated between the stator 12 and the rotor magnet 10 provided on the rotor 6.
[0031]
A disc-shaped upper thrust plate 4a and a lower thrust plate 4b projecting outward in the radial direction are provided at the upper and lower portions of the shaft 4, and a gas intervening portion 22 is formed on the outer surface of the shaft between the thrust plates. ing. On the other hand, the rotor 6 includes a rotor hub 6a on which the recording disk D is placed on the outer peripheral portion thereof, and a sleeve 6b that is positioned on the inner peripheral side of the rotor 6 and supported on the shaft 4 through a minute gap that holds the lubricating oil 8. It has. Further, the sleeve 6b is provided with an upper counter plate 7a and a lower counter plate 7b so as to cover the outer sides of the upper and lower thrust plates.
[0032]
The inner periphery of the opposing sleeve 6b extends from the outer periphery of the shaft 4 adjacent to the upper portion of the gas intervening portion 22 provided at the center of the shaft 4 to the lower surface, outer periphery and upper surface outer periphery of the upper thrust plate. A minute gap is formed between the upper part of the part through-hole 6c and the part from the upper counter plate 7a to the lower surface, and the lubricating oil 8 is held. A spiral groove 14 that generates dynamic pressure in the lubricating oil 8 as the rotor 6 rotates is formed on the lower surface of the upper thrust plate 4a, and generates a supporting force that holds the rotor portion in the axial direction when the motor rotates. At the same time, the lubricating oil 8 is pushed back in the direction of arrow A. Further, an unbalanced herringbone groove 24 is formed in the lubricating oil retaining portion of the upper inner surface of the inner peripheral portion through-hole 6c of the sleeve 6b to generate a supporting force for retaining the rotor portion in the radial direction when the motor rotates, and at the same time, lubricate Oil 8 is pushed up in the direction of arrow B.
[0033]
Due to the dynamic pressure of the lubricating oil 8 generated by these grooves, the pressure distribution generated in the lubricating oil 8 in the minute gap is highest at the lower surface inner peripheral portion P of the upper thrust plate 4a. As a result, even if the air dissolved in the lubricating oil 8 is bubbled, the bubbles are diffused and excluded to the outside of the inner peripheral part P, and the lower gas intervening part 22 gap or the upper counter plate 7a lower face gap. To the department. These voids are released to the atmosphere directly or through the outside air communication hole 20, and the bubbles are released to the outside air, thereby realizing a fluid bearing structure with no lubricating oil leakage and high supporting force.
[0034]
The same structure of minute gaps, grooves, and lubricating oil holding portions are formed in the lower thrust plate 4b and the lower counter plate 7b from the lower portion of the gas intervening portion 22 provided in the central portion of the shaft 4 in an upside down arrangement. The rotor portion is supported more stably by the lower dynamic pressure bearing portion.
Further, in the fluid bearing of this structure, even at a high speed of about 20,000 revolutions per minute, the upper and lower counter plates 7a and 7b can effectively prevent the lubricating oil 8 from spreading in the outer peripheral direction due to the rotational centrifugal force. By using the fluid bearing lubricating oil according to the present invention, a higher speed and more stable rotation is realized.
[0035]
Example II
Various types of fluid bearing lubricants were prototyped, filled in the motor having the fluid bearing structure shown in FIG. 1 and actually driven, and tested as follows to evaluate the lubricant performance.
[0036]
The following esters (A to E and H), mineral oil (F), and alkylbenzene (G) were used as base materials for the fluid bearing lubricating oil.
A: Neopentyl glycol (NPG) and n-C₉Esters with acids
B: NPG and n-C₉Acid (50 mol%) and n-C_TenEsal with mixed acid of acid (50 mol%)
C: NPG and n-C_TenAcid (95 mol%) and n-C₁₂Esters with acids (5 mol%) mixed acids
D: Pentaerythritol and n-C_FiveEsters with acids
E: ester of trimethylolpropane and 2-ethylhexanoic acid
F: Paraffinic mineral oil
G: Alkylbenzene
H: Mixed ester of 72% by mass of ester of NPG and 2-ethylhexanoic acid and 28% by mass of ester of pentaerythritol and 2-ethylhexanoic acid
[0037]
Moreover, the following were used as an additive.
I: Glycerol monooleyl ether
J: A benzotriazole derivative represented by the following general formula (3)
[Chemical Formula 3]

K: 2,6-di-tert-butyl-4-methylphenol
L: 2-ethylhexyl glycidyl ether
M: tricresyl phosphate
N: Bis (diisopropylphenyl) carbodiimide
[0038]
NPG ester base materials (A to C) and additives were blended as shown in Table 1 to prepare fluid bearing lubricating oils (Examples 1 to 8) of the present invention. The oils of Examples 1 and 2 do not contain additives, and Examples 3-8 contain the above I to N additives in parentheses as shown in the additive column of Table 1. Blended. Moreover, the lubricating oil for fluid bearings of Comparative Examples (Comparative Examples 1 to 5) was prepared using the D to H base materials. In addition, none of the lubricants for the hydrodynamic bearings of the comparative examples is blended.
[0039]
[Table 1]

[0040]
About the prepared oil of Examples 1-8 and Comparative Examples 1-4, while measuring each physical property, it loaded into the actual machine of the fluid bearing, the acceleration test was done, and the practical performance was evaluated. The physical property measurement and the performance evaluation test were performed by the following methods.
[0041]
(1) Evaporation amount: It was determined from the amount of weight loss when kept at 120 ° C. for 12 hours by a mature gravimetric analysis method (TG method).
(2) Kinematic viscosity and viscosity index: According to JIS K 2283, the kinematic viscosity was measured using a Canon-Fenske viscometer and the viscosity index was calculated.
(3) Hydroxyl value: measured according to JIS K 0070.
(4) Total acid value: measured according to JIS K 2514.
(5) Moisture: Measured according to Karl Fischer-type coulometric titration method of JIS K 2275.
(6) Ash content: Measured according to JIS K 2272. However, it can be measured to the unit of ppm.
[0042]
(7) NRRO test failure rate (durability):
Each sample is loaded into five motors having the hydrodynamic bearing structure shown in FIG. 1 and subjected to an acceleration test by intermittent operation in which the motor is driven / stopped at a temperature of 80 ° C. , Hereinafter referred to as NRRO), and the effect of lubricating oil on durability was evaluated. At this time, the motor is driven / stopped as shown in FIG. 2 by driving the motor (ON), holding it when it reaches a specified rotational speed (for example, 10, OOO rpm), and starting driving (0N). After 30 seconds, the motor was stopped (OFF), and after 30 seconds, the motor was driven again (0N).
In the evaluation, the NRRO value is measured at the time of 10,000 and 20,000 intermittent times, and the case where the NRRO value exceeds 0.05 μm is regarded as defective, and the number of motors determined to be defective is used as the sample oil. Expressed as a percentage of the total number of motors used (5). Obviously, when a sign exceeding O.05 μm was shown, it was measured even when it did not reach 10,000 times or 20,000 times, and when it exceeded O.05 μm, it was regarded as defective.
[0043]
(8) Energy saving:
The same motor as that used for evaluating the NRRO test failure rate (durability) was used, and the current flowing through the motor was measured to evaluate the energy saving property. That is, the lubricating oils of Examples 1 to 5 and Comparative Examples 2 and 5 were loaded into the fluid bearing portion of the motor, and the current value was measured with an ammeter set between the DC power source and the motor. Moreover, it carried out on the conditions of motor rotation speed 10,000rpm, no load, motor outside temperature O degreeC, and 40 degreeC.
[0044]
The test results of physical property measurement and durability evaluation are shown in Table 2, and the test results of energy saving evaluation are shown in Table 3.
[0045]
[Table 2]

[0046]
From Table 2, it can be seen that the lubricating oils of Examples 1 to 8 have a small amount of evaporation and the defective rate of the NRRO test is not a problem, and can be effectively used as a lubricating oil for fluid bearings. On the other hand, although the comparative examples 1 and 2 have a small evaporation amount, the defective rate of the NRRO test is large, and the comparative examples 3 to 5 cannot be practically used because the evaporation amount is too large.
[0047]
[Table 3]

[0048]
From Table 3, the lubricating oil of the example has a small current value at both 0 ° C. and 40 ° C. (particularly, the lubricating oil of the example 2 has a higher viscosity than the comparative example 5, but the current value is small). ) In the DC circuit, the power to rotate the motor is proportional to the current, so it can be said that the power consumption is low and the energy saving is high. In addition, although Examples 4 and 5 have a higher viscosity than Example 1, the current value is low and the effect of the additive is observed.
[0049]
【The invention's effect】
The present invention has a viscosity index of 100 or more obtained from neopentyl glycol and a monovalent fatty acid having 6 to 12 carbon atoms, a total acid value of 0.5 mgKOH / g or less, and a hydroxyl value of 20 mgKOH / g or less.
It is a fluid bearing lubricant characterized by comprising an ester, and since it is a fluid bearing using the fluid bearing lubricant and a lubrication method of the fluid bearing, it exhibits excellent energy saving and durability, In particular, it can be suitably used for a rotating device of an electronic device whose speed and size are becoming increasingly compact.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing a schematic configuration of a motor equipped with a fluid dynamic bearing.
FIG. 2 is a chart schematically showing a drive / stop pattern in intermittent motor operation in an acceleration test for evaluating the practical performance of a fluid bearing lubricant.
[Explanation of symbols]
1 Motor
4 Shaft
4a Upper thrust plate
4b Lower thrust plate
6b sleeve

Claims (6)

Esters having a viscosity index of 100 or more, total acid value of 0.5 mgKOH / g or less, and hydroxyl value of 20 mgKOH / g or less obtained from neopentyl glycol and at least one linear saturated monovalent fatty acid having 9 , 10, or 12 carbon atoms A lubricating oil for fluid bearings, comprising: The lubricating oil for fluid bearings according to claim 1, wherein at least one monovalent fatty acid is two or more monovalent fatty acids. And (a) a polyhydric alcohol partial ester compound having at least two hydroxyl groups and at least one ester bond, or a polyhydric alcohol partial ether compound having at least two hydroxyl groups and at least one ether bond, or a mixture thereof. The lubricating oil for hydrodynamic bearings according to claim 1 or 2 , wherein 0.1 to 5.0% by mass and / or (b) 0.1 to 5.0% by mass of benzotriazole and / or a derivative thereof are contained. The hydrodynamic bearing according to any one of claims 1 to 3 , further comprising 0.05 to 5.0 wt% of one or more selected from a phenol-based antioxidant, an epoxy compound, a carbodiimide compound, and a phosphate ester. Lubricating oil. A hydrodynamic bearing comprising a shaft and a sleeve, wherein the lubricating oil according to any one of claims 1 to 4 is used. A hydrodynamic bearing lubrication method according to claim 5 , wherein the hydrodynamic bearing lubrication oil according to any one of claims 1 to 4 is lubricated.

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