JP2004091524A - Lubricating oil for fluid bearing and fluid bearing using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lubricating oil for a fluid bearing which exhibits well-balanced performance of the saving energy, low evaporation, heat resistance and low temperature characteristics. <P>SOLUTION: The lubricating oil for a liquid bearing is an ester of trimethylolpropane with a mixed acid of at least two 4-8C monovavlent fatty acids, and has a viscosity index of ≥100, a total acid value of ≤1 mgKOH/g, and a hydroxy number of ≤20 mgKOH/g. The mixed acid preferably contains at least one straight chain monovalent fatty acid, and a mixed acid of n-hexane and n-heptane is particularly preferred. <P>COPYRIGHT: (C)2004,JPO

Description

式中、Ｒ_１は、水素原子又はメチル基を示し、Ｒ_２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、Ｒ_２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。
【００３０】
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０．１〜５重量％、さらには０．５〜５重量％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。
【００３１】
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図ることができる。
【００３２】
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。
【００３３】
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】
Ｒ_３−Ｎ＝Ｃ＝Ｎ−Ｒ_４　　　　　　　　（２）
式中、Ｒ_３及びＲ_４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、Ｒ_３及びＲ_４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、Ｒ_３及びＲ_４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Ｒ_３、Ｒ_４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。
【００３４】
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。
【００３５】
アルキルベンゼンスルホン酸塩としては、炭素数１〜２０のアルキル基を置換基として持つアルキルベンゼンスルホン酸と炭素数１〜２０のアルキルアミンの中和塩などが挙げられる。このイオン系帯電防止剤は、エステル基油に対して親和力があり、静電気を逃がすのに十分な導電性を発揮させることができる。
【００３６】
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、リン酸エステル及びアルキルアリルスルホン酸塩は、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０．０５〜５重量％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。
【００３７】
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。
【００３８】
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き付きを起こすことがある。しかし、優れた省エネルギー性、耐熱性及び低温特性を有する本発明の流体軸受用潤滑油を用いることによって、長期に亘り高速回転安定性、耐久性が保持される。特に高速において優れた省エネルギー性を示す。
【００３９】
図１に、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。この図１は、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。
【００４０】
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。
【００４１】
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。
【００４２】
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。
【００４３】
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る。さらに、本発明にかかる流体軸受用潤滑油を用いることにより、優れた省エネルギー性及び耐久性を伴いながら、一層高速で安定した回転を実現できる。
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、耐久性が保持され、かつ優れた省エネルギー性、長寿命化が得られる。
【００４４】
【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。
各種の流体軸受用潤滑油を試作し、潤滑油性能を評価した。
【００４５】
流体軸受用潤滑油のべ一ス基材として次に示す本発明のエステル（Ａ〜Ｄ）、及び比較例としてのエステル（Ｅ〜Ｈ）を使用した。
Ａ：トリメチロールプロパン（ＴＭＰ）と、ｎ−Ｃ_６酸（４０　ｍｏｌ％）とｎ−Ｃ_７酸（６０　ｍｏｌ％）の混合酸とのエステル
Ｂ：ＴＭＰと、ｎ−Ｃ_５酸（２０　ｍｏｌ％）とｎ−Ｃ_７酸（８０　ｍｏｌ％）の混合酸とのエスアル
Ｃ：ＴＭＰと、ｎ−Ｃ_６酸（８０　ｍｏｌ％）とｎ−Ｃ_７酸（２０　ｍｏｌ％）の混合酸とのエステル
Ｄ：ＴＭＰと、ｎ−Ｃ_６酸（７０　ｍｏｌ％）と２−エチルヘキサン酸（３０　ｍｏｌ％）の混合酸とのエステル
【００４６】
Ｅ：ＴＭＰとｎ−Ｃ_６酸とのエステル
Ｆ：ＴＭＰとｎ−Ｃ_７酸とのエステル
Ｇ：ＴＭＰと２−エチルヘキサン酸とのエステル
Ｈ：ペンタエリスリトール（ＰＥ）とｎ−Ｃ_５酸とのエステル
【００４７】
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
【００４８】
エステル基材（Ａ〜Ｈ）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１〜１０）を調製した。実施例１〜４の油は添加剤を含有せず、実施例５〜１０は、表１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、Ｅ〜Ｈのエステル基材を用いて比較例の流体軸受用潤滑油（比較例１〜４）を調製した。なお、比較例１〜４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。
【００４９】
【表１】

【００５０】
調製した実施例１〜１０及び比較例１〜４の油について、それぞれの物性を測定して、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。
【００５１】
（１）　　蒸発量：熱重量分析法（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て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）　　低温流動性：５０　ｍｌのサンプル瓶に油を２０　ｍｌ入れて−４０℃で２日間静置し、油の流動性（固化状況）を観察した。評価は、２日間静置後に取り出したサンプル瓶を逆さにし、１分以内に流動しないものを固化とした。
（６）　　熱安定性：内径７０　ｍｍのシャーレに油を２０　ｍｌ入れて１４０℃で２週間エージングして強制的に劣化させ、劣化油の全酸価（ＪＩＳ　Ｋ　２５１４）を測定した。
【００５２】
物性測定、低温流動性及び熱安定性の評価試験の結果を表２に示す。
【００５３】
【表２】

【００５４】
表２から、実施例１〜１０の潤滑油は、いずれも蒸発量が少なく、−４０℃において流動性を有し、劣化後の全酸価は３　ｍｇＫＯＨ／ｇ以下と熱安定性にも優れ、その他の物性を含めてバランスの良い性能を示している。したがって、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１〜４の潤滑油は、流体軸受用潤滑油としての物性や性能で劣るものがあり、実用的に用いることはできない。すなわち、比較例１は蒸発量が多い。比較例２は−４０℃において固化し、かつ粘度が流体軸受用潤滑油としての適正粘度を超えている。比較例３は、比較例２よりも高粘度であり、かつ粘度指数が１００以下であり、省エネルギー性に劣ると推察される。比較例４の潤滑油は、粘度指数が小さく、蒸発量が多く、熱安定性も悪い。
【００５５】
【発明の効果】
本発明の流体軸受用潤滑油は、トリメチロールプロパンと、特定の混合酸とから合成される粘度指数１００以上、全酸価１　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から、優れた省エネルギー性、低蒸発性、耐熱性及び低温特性などのバランスの良い性能を示し、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。
【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
８　　　　潤滑油[0001]
[Industrial applications]
The present invention relates to a lubricating oil for a fluid bearing, a fluid bearing using the same, and a method of lubricating the fluid bearing, and in particular, is suitable for a compact fluid bearing which is excellent in energy saving, heat resistance and low temperature characteristics and is used at high speed rotation. Related to lubricating oils for fluid bearings.
[0002]
[Prior art]
There have been remarkable progresses in reducing the size, weight, and capacity of video / audio equipment, personal computers, and the like, and increasing the speed of information processing. These electronic devices use various types of rotating devices, for example, rotating devices that drive magnetic disks or optical disks such as FDs, MOs, zips, mini disks, compact disks (CDs), DVDs, and hard disks. -The weight reduction, large capacity, and high speed are largely due to these improvements or the improvement of the bearings which are indispensable for the rotating device. Fluid bearings consisting of a sleeve and a rotating shaft that face each other via lubricating oil are suitable for miniaturization and weight reduction because they do not have ball bearings, and are excellent in quietness, economy, etc. Its applications are expanding to visual equipment and car navigation.
[0003]
Examples of the lubricating oil or bearing fluid used in the fluid bearing include neopentyl polyol ester, squalane and / or a grease of a naphthenic mineral oil and a urea compound thickener (Japanese Patent Laid-Open No. 1-279117); Those containing a fatty acid triester of trimethylolpropane as a base oil and containing a hindered phenolic antioxidant and a benzotriazole derivative (JP-A-1-188592), a specific hindered phenolic antioxidant and an aromatic amine (Japanese Patent Application Laid-Open (JP-A) No. 1-225697) and those containing a specific monocarboxylic acid ester having a phenyl group and / or a specific dicarboxylic acid ester as a base oil (Japanese Patent Application Laid-Open No. H4-22597). -357318), using a simple composition as a base oil (Patent No. 26) No. 1329), those using a carbonate ester as a base oil and containing a sulfur-containing phenolic antioxidant and a zinc-based extreme pressure agent (JP-A-8-34987), and those using a magnetic fluid (JP-A-8-259977). JP-A-10-183159, and JP-A-10-183159, which use a phenolic antioxidant in a base oil containing a carbonate ester as a main component.
[0004]
It is expected that demands and demands for high-speed processing of large-volume information and further downsizing of devices will increase in the future. Conventionally, the power consumption of audio equipment and personal computers has not been noticed because it is not very large.However, the demand for energy saving is increasing because the equipment life can be extended or the size of the equipment can be reduced by reducing the capacity. There are still strong ones. As described above, with the desire for high-speed processing of information and miniaturization of equipment, higher speed rotation of the fluid bearing is required. And the energy loss in a bearing becomes so large that it becomes high speed.
[0005]
However, the various lubricating oils or bearing fluids proposed above have high viscosities and have not been evaluated from the viewpoint of energy saving in bearings. Lubricating oils for hydrodynamic bearings include lubrication, deterioration stability (lifetime), sludge formation prevention, wear prevention, and corrosion prevention, as well as energy-saving performance and lubricity with low evaporative properties. Oil is required to meet the demands for high-speed processing of information, compactness, and the like. In addition, as the size of the device is reduced, the durability of the device itself may be sacrificed, and the durability of the device may be affected.
[0006]
Further, the places where the above-mentioned information processing devices are used are becoming popular and their use in harsh environments is expanding. In particular, a device such as a car navigation system mounted on a car must be able to withstand use from a cold region to under the scorching sun in consideration of the use environment of the vehicle. Therefore, it is required that lubricating oil for bearings used in vehicle-mounted equipment can be used without problems in a wide temperature range of -40 to 80 ° C.
[0007]
[Problems to be solved by the invention]
The present invention has been made to solve the above-described problems, and has an object to provide a lubricating oil for a fluid bearing having excellent lubricity, as well as energy saving, low evaporability, heat resistance and low-temperature characteristics. I do. Another object of the present invention is to provide a fluid bearing and a method of lubricating the fluid bearing using such a fluid bearing lubricating oil.
[0008]
[Means for Solving the Problems]
The present invention relates to an ester of trimethylolpropane and at least two kinds of mixed acids of a monovalent fatty acid having 4 to 8 carbon atoms, having a viscosity index of 100 or more, a total acid value of 1 mgKOH / g or less, and a hydroxyl value. Is a lubricating oil for hydrodynamic bearing of 20 mgKOH / g or less. Further, the mixed acid preferably contains at least one type of linear monovalent fatty acid, and is a mixed acid of n-hexanoic acid and n-hexanoic acid, and the mixing ratio (molar ratio) is 2%. : 8 to 8: 2.
[0009]
Further, the lubricating oil for a hydrodynamic bearing may comprise (a) a polyhydric alcohol partial ester compound having at least two hydroxyl groups and at least one ester bond and / or a polyhydric alcohol compound having at least two hydroxyl groups and at least one ether bond. It is preferable to contain 0.1 to 5% by weight of a partially alcoholic ether compound and / or 0.1 to 5% by weight of (b) benzotriazole and / or a derivative thereof.
[0010]
Further, it is preferable to contain 0.01 to 5% by weight of one or more selected from the group consisting of phenolic antioxidants, epoxy compounds, carbodiimide compounds, phosphates and alkylbenzene sulfonates. .
[0011]
Further, the present invention relates to a fluid bearing comprising a shaft and a sleeve, wherein the fluid bearing is filled with the fluid bearing lubricating oil, and the fluid bearing is further lubricated by using the fluid bearing lubricating oil. It is a lubrication method.
[0012]
[Preferred Embodiment]
The widespread use of video / audio equipment, personal computers, and the like requires that the general public be able to use them without special consideration, and their use environment is becoming increasingly severe. In particular, in-vehicle equipment such as a car navigation system needs to be able to be used without problems in a wide temperature range of -40 to 80 ° C. In order to enable use under such conditions, lubricating oils for hydrodynamic bearings are also required to have excellent low-temperature properties that allow sufficient fluidity to be obtained at low temperatures, and heat resistance that does not deteriorate at high temperatures.
[0013]
As described above, lubricating oils for hydrodynamic bearings include (A) energy saving (appropriate viscosity and high viscosity index), (B) low evaporability, and (C) adaptability in a wide temperature range (low temperature fluidity, heat resistance). Properties) are required. It is preferable that the viscosity is low in order to ensure the energy saving of (A). However, since the low-viscosity lubricating oil generally has a high evaporability, it is troublesome to ensure the low-evaporation of (B). In addition, ensuring the low evaporation property of (B) usually means high viscosity, and deteriorates the energy saving property of (A) and the low temperature fluidity of (C). The adaptability in a wide temperature range of (C) is a function required especially for lubricating oils for in-vehicle equipment, and has a low-temperature fluidity that does not solidify even at −40 ° C. and deteriorates even when exposed to a high temperature when exposed to hot weather. It is required to have heat resistance that is difficult to perform. Therefore, the lubricating oil for a hydrodynamic bearing is required to exhibit the above-mentioned functions in a well-balanced manner because the opposing functions are complicatedly complicated as described above.
[0014]
In the present invention, a viscosity index of 100 or more, a total acid value of 1 mg KOH / g or less, and a hydroxyl value of 20 synthesized from trimethylolpropane and a mixed acid of at least two or more monovalent fatty acids having 4 to 8 carbon atoms. Esters of up to mg KOH / g are used as base oil. By doing so, the lubricating oil for a hydrodynamic bearing of the present invention is suitable for various rotating devices in video / audio equipment, personal computers, etc., which are desired for miniaturization, weight reduction, large capacity, and high-speed processing of information. It can be used effectively as oil. That is, the lubricating oil for a hydrodynamic bearing of the present invention uses the above-identified ester to provide the above-described various properties required of (A) to (C), that is, excellent energy saving and low evaporability. , Excellent low temperature properties and heat resistance are imparted in a well-balanced manner.
[0015]
The ester used in the present invention is an ester synthesized from trimethylolpropane, a polyhydric alcohol having a neopentyl skeleton, and at least two or more mixed acids of monovalent fatty acids having 4 to 8 carbon atoms. Esters of trimethylolpropane have a neopentyl skeleton and are excellent in chemical stability and heat resistance. An ester having a neopentyl skeleton can be obtained by using neopentyl polyol or neoacid. To obtain a lubricating oil for a fluid bearing having the above-mentioned well-balanced properties, trimethylolpropane is used.
[0016]
In the present invention, as an acid which forms an ester with trimethylolpropane, a mixed acid of at least two or more monovalent fatty acids having 4 to 8 carbon atoms is used. The monovalent fatty acid used here may be saturated or unsaturated, but is preferably a saturated monovalent fatty acid from the viewpoint of chemical stability and heat resistance. From the viewpoint of energy saving, the ester preferably has a low viscosity. However, since the low-viscosity ester is easily evaporated, a monovalent fatty acid having 4 or more carbon atoms is used. Esters with monovalent fatty acids having more than 8 carbon atoms are preferred from the viewpoint of high viscosity and low evaporability, but have poor energy saving properties and low-temperature fluidity.
The kinematic viscosity at 40 ° C. suitable for a lubricating oil for hydrodynamic bearing is 8 to 13 mm. ² / S, and in order to obtain such a viscosity, it is preferable to use a monovalent fatty acid having 4 to 8 carbon atoms.
[0017]
The monovalent fatty acid having 4 to 8 carbon atoms used in the present invention is preferably a saturated monovalent fatty acid, and specifically, n-butanoic acid, n-pentanoic acid, n-hexanoic acid, n-heptanoic acid and n And straight-chain monovalent fatty acids of octanoic acid, and various branched monovalent fatty acids that are isomers thereof. As branched-chain monovalent fatty acids, particularly, i-butanoic acid, 2-methylpentanoic acid, 2-ethylpentanoic acid, 2-methylhexanoic acid, 2-ethylhexanoic acid, 3-ethylhexanoic acid, 2-methylheptanoic acid And the like can be preferably used. Among these, n-pentanoic acid, n-hexanoic acid, n-heptanoic acid, 2-methylhexanoic acid and 2-ethylhexanoic acid are preferred, and n-pentanoic acid, n-hexanoic acid and n-heptanoic acid are particularly preferred. Are preferred.
[0018]
The ester used in the lubricating oil for a hydrodynamic bearing of the present invention is an ester with two or more monovalent fatty acids. Ester with only one type of monovalent fatty acid is easily crystallized, and low-temperature fluidity may be deteriorated even with low-viscosity ester, but an ester with a mixed acid of two or more types of monovalent fatty acid is used. Thereby, the low temperature fluidity is improved. The two or more kinds of mixed acids are not limited to a combination of two or more kinds of monovalent fatty acids selected from linear, branched, and saturated and unsaturated monovalent fatty acids. A combination of two or more monovalent fatty acids having different carbon numbers even in a chain, a combination of a linear monovalent fatty acid and a branched monovalent fatty acid having the same carbon number, or a branched chain fatty acid having the same carbon number. This also means a combination of a plurality of fatty acids having different substituent positions, in other words, a combination of two or more monovalent fatty acids having different molecular structures.
[0019]
In general, an ester with a linear monovalent fatty acid is inferior in low-temperature fluidity, but an ester with a mixed acid having a different molecular weight improves the low-temperature fluidity. This improvement in low-temperature fluidity is particularly effective for in-vehicle devices such as car navigation systems that require a wide operating temperature range. Straight-chain monovalent fatty acids have a high viscosity index and are relatively poor in low-temperature fluidity. However, the use of two or more mixed acids as described above significantly improves low-temperature fluidity. You. Therefore, in the present invention, the mixed acid preferably contains at least one linear monovalent fatty acid.
[0020]
In the mixed acid of two or more monovalent fatty acids, the mixing ratio is not particularly limited, but the minimum component may be contained in a ratio of 5 mol% or more, preferably 10 mol% or more, particularly 20% or more. It is preferable for lubricating oil for a fluid bearing to improve low-temperature fluidity. As the mixed acid, a combination of n-hexanoic acid and n-heptanoic acid is particularly preferable, and a combination in which the mixing ratio (molar ratio) of both is 2: 8 to 8: 2 is preferable.
[0021]
The ester used in the present invention can be easily synthesized from trimethylolpropane and a mixture of two or more monovalent fatty acids. Further, the ester of the present invention can be obtained from the ester of the above monohydric fatty acid and a lower alcohol or a derivative of the monohydric fatty acid such as an acid anhydride or chloride by a known esterification reaction or transesterification reaction. Therefore, the ester referred to in the present invention includes an ester obtained by such a method. When a derivative of a monovalent fatty acid is used, chloride produces by-products of a corrosive chlorine compound during ester synthesis, lowering the quality of the ester product, and impeding troublesome removal and purification of chlorine. It is preferable to use lower alcohol esters or acid anhydrides.
[0022]
The ester used for the lubricating oil of the present invention has a viscosity index of 100 or more. The viscosity index of the ester tends to increase as the acyl group is linear and the number of carbon atoms increases. Therefore, as long as necessary viscosity, low-temperature fluidity and lubricity can be ensured, a mixed fatty acid having a large number of carbon atoms and a large linear proportion is used. In particular, when only a straight-chain fatty acid is used, a high viscosity index causes a small increase in viscosity at a low temperature and can maintain energy saving. On the other hand, a high viscosity can be secured at a high temperature, so that good lubricity can be obtained. When a branched fatty acid is contained, the mixing ratio is preferably 50 mol% or less, more preferably 40% or less.
[0023]
Esters having a total acid value of 1 mgKOH / g or less and a hydroxyl value of 20 mgKOH / g or less are used in the lubricating oil for a fluid bearing of the present invention. The total acid value is important for ensuring corrosion protection, abrasion resistance and stability, and is further 0.5 mgKOH / g or less, particularly 0.3 mgKOH / g or less.
Is preferred. The hydroxyl value is 5 mgKOH / g or less from the viewpoint of improving moisture absorption resistance and stability.
Is preferred. Esters having such properties can be obtained by sufficiently performing an esterification reaction and then appropriately purifying the ester by a known method.
[0024]
Furthermore, water contained in the ester is a substance involved in hydrolysis, and ash is a catalyst that promotes hydrolysis and a substance that causes 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, heat distillation, heat vacuum distillation, or blowing of an inert gas, and ash can be removed by an adsorption treatment. In order to reduce ash, it is also effective to carry out ester synthesis without a catalyst. By doing so, ester hydrolysis and sludge generation are minimized, and highly stable esters can be obtained, so that the deterioration resistance stability of the lubricating oil for hydrodynamic bearings is improved, and long-term stability and long life are achieved. Can be achieved.
[0025]
The lubricating oil of the present invention may contain various additives in addition to the above-mentioned ester as a base oil in order to improve practical performance. Such additives include polyhydric alcohol partial ester compounds and / or polyhydric alcohol partial ether compounds, benzotriazole and / or derivatives thereof. Furthermore, it is also effective to mix one or more selected from a phenolic antioxidant, an epoxy compound, a carbodiimide compound, a phosphoric ester and an alkylallyl sulfonate.
[0026]
Polyhydric alcohol partial esters and polyhydric alcohol partial ethers are polyhydric alcohol derivatives having two or more hydroxyl groups, and further having one or more hydrocarbon groups added by an ether bond or an ester bond. Used as an agent. These polyhydric alcohol derivatives adsorb to one bearing metal (for example, a shaft) at a hydroxyl group portion, and the hydrocarbon group extending from the ether bond or ester bond prevents contact with the other bearing metal (for example, a sleeve). Thus, it is considered that the lubricating action is improved.
[0027]
The 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. Specific examples of the polyhydric alcohol include glycerin, trimethylolpropane, diglycerin, erythritol, pentaerythritol, triglycerin, sorbitol, and mannitol. Trihydric alcohols are particularly preferable, and glycerin is particularly preferable. Further, the monovalent fatty acid which 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 And the like. Examples of the monool that forms a partial ether with a polyhydric alcohol include monohydric alcohols corresponding to these acids. Among these, oleic acid and oleyl alcohol are particularly preferred, that is, glycerin monooleate and gliserin monooleyl ether are preferred as polyhydric alcohol derivatives.
[0028]
The polyhydric alcohol derivative may be appropriately mixed in an effective amount for exhibiting the effect, and the amount is not particularly limited. However, the amount is 0.1 to 5% by weight based on the lubricating oil for a fluid bearing, and furthermore, It is preferable to mix them so as to contain about 0.5 to 5% by weight. In addition, the polyhydric alcohol partial ether and the polyhydric alcohol partial ester may be used alone, a plurality of ether compounds or ester compounds may be used, or a mixture thereof may be used.
[0029]
As benzotriazole and / or a derivative thereof, a compound represented by the following general formula (1) is preferably used.
Embedded image

Where R ₁ Represents a hydrogen atom or a methyl group; ₂ Represents a group having 0 to 20 carbon atoms containing a hydrogen atom or a nitrogen atom and / or an oxygen atom. Benzotriazole derivatives are preferred because they improve the wear resistance of copper. ₂ Is preferably a group having 10 to 20 carbon atoms containing a nitrogen atom.
[0030]
It is preferable that benzotriazole and / or a derivative thereof be blended so as to be contained in an amount of about 0.1 to 5% by weight, more preferably about 0.5 to 5% by weight, based on the entire lubricating oil for a hydrodynamic bearing. If the addition amount is small, the effect of wear resistance of copper is not particularly obtained, and if it is too large, not only the effect corresponding to the addition amount is not obtained, but also sludge formation may be caused, which is not preferable.
[0031]
Examples of the 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 particularly, combined use can significantly improve oxidation stability.
[0032]
As the epoxy compound, a phenyl glycidyl ether type epoxy compound, an alkyl glycidyl ether type epoxy compound, a glycidyl ester type epoxy compound, an alicyclic epoxy compound, an epoxidized fatty acid monoester, an epoxidized vegetable oil, or the like is used alone or in combination. can do. Preferred among these epoxy compounds are alkyl glycidyl ether type epoxy compounds, glycidyl ester type epoxy compounds, alicyclic epoxy compounds and epoxidized fatty acid monoesters. Among them, an alkyl glycidyl ether type epoxy compound, a glycidyl ester type epoxy compound, an alicyclic epoxy compound or a mixture thereof is more preferable. By adding these epoxy compounds, the stability of the substrate, especially the hydrolysis stability, is greatly improved.
[0033]
The carbodiimide compound is a compound represented by the following general formula (2).
Embedded image
R ₃ -N = C = NR ₄ (2)
Where R ₃ And R ₄ Is a hydrogen or hydrocarbon group, or a hydrocarbon group containing nitrogen and / or oxygen; ₃ And R ₄ May be the same or different.
In the above general formula (2), preferably, R ₃ And R ₄ Is 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, alkyl groups such as hydrogen, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, 2-methylbutyl, hexyl, heptyl, octyl, 2-ethylhexyl, nonyl, decyl, undecyl and dodecyl, propenyl, butenyl Alkenyl groups such as isobutenyl, pentenyl, 2-ethylhexenyl and octenyl, cycloalkyl groups such as cyclopentyl, cyclohexyl, methylcyclopentyl and ethylcyclopentyl, aryl groups such as phenyl and naphthyl, trail, isopropylphenyl, diisopropylphenyl and triisopropylphenyl , An aryl group such as alkyl-substituted phenyl such as nonylphenyl, an aralkyl group such as benzyl and phenethyl, ₃ , R ₄ As the compound contained. The carbodiimide compound functions as an acid scavenger and improves the hydrolytic stability.
[0034]
Examples of the phosphate ester include tricresyl phosphate, triphenyl phosphate, cresyl diphenyl phosphate, diphenyl hydrogen phosphate, 2-ethylhexyl diphenyl phosphate, and the like, and tricresyl phosphate and triphenyl phosphate are more preferable. By adding a phosphate ester, the wear resistance of iron can be significantly improved.
[0035]
Examples of the alkylbenzene sulfonate include neutralized salts of an alkylbenzenesulfonic acid having an alkyl group having 1 to 20 carbon atoms as a substituent and an alkylamine having 1 to 20 carbon atoms. The ionic antistatic agent has an affinity for the ester base oil and can exhibit sufficient conductivity to release static electricity.
[0036]
The phenolic antioxidant, the epoxy compound, the carbodiimide compound, the phosphoric acid ester, and the alkyl allyl sulfonate preferably contain one or more selected from them. In the present invention, the compounding amount of these additives is not particularly limited. However, even when a plurality of additives are compounded, for each additive, 0.05 to 0.05% based on the total amount of the fluid bearing lubricating oil. What is necessary is just to mix | blend so that it may contain 5 weight%. If the addition amount is too small, there is no effect, and if it is too large, the characteristics of the base oil are not utilized and sludge is formed, which is not preferable.
[0037]
A fluid bearing according to the present invention is characterized by using the above-described lubricating oil for a fluid bearing. Especially if it is a fluid bearing that does not have a mechanism such as a ball bearing, but consists of a sleeve and a shaft, and is maintained at a distance so that it does not directly contact each other by the lubricant contained between them, There is no limitation. In the fluid bearing of the present invention, a dynamic pressure generating groove is provided on one or both of the rotating shaft and the sleeve, and the rotating shaft is supported by dynamic pressure. It also includes fluid bearings and the like in which a thrust plate is provided to generate.
[0038]
In the fluid bearing, the sleeve and the rotating shaft or the sleeve and the thrust plate are in partial or full contact with each other because dynamic pressure is not generated during non-rotation, and the dynamic pressure is generated by rotation to be in a non-contact state. For this reason, contact and non-contact are repeated, and metal wear of the sleeve, the rotating shaft or the sleeve and the thrust plate may occur, and seizure may occur due to temporary contact during rotation. However, by using the lubricating oil for a hydrodynamic bearing of the present invention having excellent energy saving, heat resistance and low temperature characteristics, high-speed rotation stability and durability can be maintained for a long period of time. In particular, it shows excellent energy savings at high speeds.
[0039]
FIG. 1 shows a specific example of a fluid bearing which is preferable to be loaded with the lubricating oil for a fluid bearing of the present invention. FIG. 1 is a cross-sectional view schematically showing a schematic configuration of a motor equipped with a fluid bearing for driving a recording disk using the lubricating oil. In FIG. 1, a motor 1 includes a bracket 2, a shaft 4 having one end externally fixed to a central opening of the bracket 2, and a rotor rotatably held relatively to the shaft 4. 6 is provided. A stator 12 is fixed to the bracket 2, and a rotational driving force is generated between the bracket 12 and a rotor magnet 10 provided on the rotor 6 so as to face the stator 12.
[0040]
A disk-shaped upper thrust plate 4a and a lower thrust plate 4b projecting radially outward 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 these thrust plates. ing. On the other hand, the rotor 6 includes a rotor hub 6a on which the recording disk D is mounted on its outer peripheral portion, and a sleeve 6b which is located on the inner peripheral side of the rotor 6 and is supported by the shaft 4 via a minute gap in which the lubricating oil 8 is held. 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.
[0041]
The inner periphery of the opposed sleeve 6b extends from the outer peripheral portion of the shaft 4 adjacent to the upper portion of the gas intervening portion 22 provided at the center portion of the shaft 4 to the lower surface, the outer peripheral surface, and the outer peripheral portion of the upper thrust plate. A minute gap is formed between the upper part of the through hole 6c and the lower surface of the upper counter plate 7a, and the lubricating oil 8 is held. A spiral groove 14 for generating a dynamic pressure in the lubricating oil 8 with the rotation of the rotor 6 is formed on the lower surface of the upper thrust plate 4a to generate a supporting force for holding the rotor portion in the axial direction when the motor rotates. At the same time, the lubricant 8 is pushed back in the direction of arrow A. Further, an unbalanced herringbone-shaped groove 24 is formed in the lubricating oil holding portion on the inner surface of the inner peripheral portion through hole 6c of the sleeve 6b to generate a supporting force for holding the rotor portion in the radial direction during rotation of the motor, and at the same time to provide lubrication. The oil 8 is pushed up in the direction of arrow B.
[0042]
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 inner peripheral portion P on the lower surface of the upper thrust plate 4a. As a result, even if the air dissolved in the lubricating oil 8 becomes air bubbles, the air bubbles are diffused out of the inner peripheral portion P and are eliminated, and the air gap between the lower gas intervening portion 22 or the lower surface of the upper counter plate 7a is formed. To the department. These voids are released to the atmosphere directly or through the outside air communication holes 20, and the air bubbles are released to the outside air, thereby realizing a fluid bearing structure without lubricating oil leakage and high supporting force.
[0043]
Similar structures of minute gaps, grooves, and lubricating oil holding portions are formed in a vertically inverted arrangement on the lower thrust plate 4b and the lower counter plate 7b from below the gas intervening portion 22 provided at the center of the shaft 4. The rotor section is more stably supported by the lower dynamic pressure bearing section. Further, in the fluid bearing of this structure, the upper and lower counter plates 7a and 7b effectively prevent the lubricating oil 8 from diverging in the outer peripheral direction due to the rotational centrifugal force even at a high speed of about 20,000 revolutions per minute. You. Further, by using the lubricating oil for a hydrodynamic bearing according to the present invention, it is possible to realize a higher-speed and more stable rotation with excellent energy saving and durability.
Further, the present invention is a method for lubricating a fluid bearing, wherein the fluid bearing is lubricated with the lubricant for a fluid bearing defined above. As described above, by filling the lubricating oil for a fluid bearing into the fluid bearing and lubricating the fluid bearing, high-speed rotation stability and durability can be maintained for a long period, and excellent energy saving and long life can be obtained. .
[0044]
【Example】
Hereinafter, the present invention will be described in more detail based on examples. The present invention is not limited by the following examples.
Various lubricating oils for hydrodynamic bearings were prototyped and the lubricating oil performance was evaluated.
[0045]
The following esters (A to D) of the present invention and esters (E to H) as comparative examples were used as base materials for lubricating oils for hydrodynamic bearings.
A: Trimethylolpropane (TMP) and nC ₆ Acid (40 mol%) and nC ₇ Ester of mixed acid (60 mol%) with acid
B: TMP and nC ₅ Acid (20 mol%) and nC ₇ Sual with acid (80 mol%) mixed acid
C: TMP and nC ₆ Acid (80 mol%) and nC ₇ Ester of mixed acid (20 mol%) with acid
D: TMP and nC ₆ Ester of mixed acid of acid (70 mol%) and 2-ethylhexanoic acid (30 mol%)
[0046]
E: TMP and nC ₆ Esters with acids
F: TMP and nC ₇ Esters with acids
G: ester of TMP and 2-ethylhexanoic acid
H: pentaerythritol (PE) and nC ₅ Esters with acids
[0047]
The following additives were used.
I: glycerin monooleyl ether
J: benzotriazole derivative represented by the following general formula (3)
Embedded image

K: 2,6-di-t-butyl-4-methylphenol
L: 2-ethylhexyl glycidyl ether
M: tricresyl phosphate
N: bis (diisopropylphenyl) carbodiimide
[0048]
Ester base materials (A to H) and additives were blended as shown in Table 1 to prepare lubricating oils for hydrodynamic bearings of the present invention (Examples 1 to 10). The oils of Examples 1 to 4 did not contain additives, and Examples 5 to 10 were blended so that the additives of the above I to N were contained in the quantities in parentheses as shown in Table 1. In addition, lubricating oils for hydrodynamic bearings of Comparative Examples (Comparative Examples 1 to 4) were prepared using E to H ester base materials. Note that none of the lubricants for hydrodynamic bearings of Comparative Examples 1 to 4 contained any additives.
[0049]
[Table 1]

[0050]
The physical properties of the prepared oils of Examples 1 to 10 and Comparative Examples 1 to 4 were measured to evaluate the practical performance. Physical property measurement and performance evaluation test were performed by the following methods.
[0051]
(1) Evaporation: Determined by thermogravimetric analysis (TG method) from the amount of weight loss when kept at 120 ° C. for 12 hours.
(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 K0070.
(4) Total acid value: Measured according to JIS K2514.
(5) Low-temperature fluidity: 20 ml of oil was placed in a 50-ml sample bottle, allowed to stand at -40 ° C for 2 days, and the fluidity (solidification state) of the oil was observed. In the evaluation, the sample bottle taken out after standing for 2 days was inverted, and those that did not flow within 1 minute were solidified.
(6) Thermal stability: 20 ml of oil was placed in a petri dish having an inner diameter of 70 mm, aged at 140 ° C. for 2 weeks to forcibly deteriorate the oil, and the total acid value (JIS K 2514) of the deteriorated oil was measured.
[0052]
Table 2 shows the results of the physical property measurement, low-temperature fluidity and thermal stability evaluation tests.
[0053]
[Table 2]

[0054]
From Table 2, the lubricating oils of Examples 1 to 10 all have a small amount of evaporation, have fluidity at -40 ° C, and have an excellent total heat value of 3 mgKOH / g or less after deterioration, and have excellent thermal stability. , Indicating a well-balanced performance including other physical properties. Therefore, it can be seen that the lubricant can be effectively used as a lubricating oil for a hydrodynamic bearing.
On the other hand, the lubricating oils of Comparative Examples 1 to 4 have poor physical properties and performance as lubricating oils for hydrodynamic bearings, and cannot be used practically. That is, Comparative Example 1 has a large amount of evaporation. Comparative Example 2 solidifies at −40 ° C. and has a viscosity exceeding the proper viscosity as a lubricating oil for a hydrodynamic bearing. Comparative Example 3 has a higher viscosity than Comparative Example 2 and a viscosity index of 100 or less, which is presumed to be inferior in energy saving. The lubricating oil of Comparative Example 4 has a small viscosity index, a large amount of evaporation, and poor thermal stability.
[0055]
【The invention's effect】
The lubricating oil for a hydrodynamic bearing of the present invention comprises an ester synthesized from trimethylolpropane and a specific mixed acid and having a viscosity index of 100 or more, a total acid value of 1 mgKOH / g or less, and a hydroxyl value of 20 mgKOH / g or less. Therefore, it shows a well-balanced performance such as excellent energy saving property, low evaporation property, heat resistance, and low temperature property, and can be suitably used particularly for a rotating device of an electronic device, which is becoming faster and more 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 bearing.
[Explanation of symbols]
1 motor
4 shaft
4a Upper thrust plate
4b Lower thrust plate
6b sleeve
8 Lubricating oil

Claims (8)

An ester of trimethylolpropane and at least two kinds of mixed acids of a monovalent fatty acid having 4 to 8 carbon atoms, having a viscosity index of 100 or more, a total acid value of 1 mgKOH / g or less, and a hydroxyl value of 20 mgKOH / g. g or less. The lubricating oil for a hydrodynamic bearing according to claim 1, wherein the mixed acid contains at least one linear monovalent fatty acid. The lubricating oil for a hydrodynamic bearing according to claim 1, wherein the mixed acid is a mixed acid containing n-hexanoic acid and n-heptanoic acid. The lubricating oil for a hydrodynamic bearing according to claim 3, wherein a mixing ratio (molar ratio) of n-hexanoic acid and n-heptanoic acid in the mixed acid is from 2: 8 to 8: 2. Further, (a) a polyhydric alcohol partial ester compound having at least two hydroxyl groups and at least one ester bond and / or a polyhydric alcohol partial ether compound having at least two hydroxyl groups and at least one ether bond are The lubricating oil for a hydrodynamic bearing according to any one of claims 1 to 4, which comprises 0.1 to 5% by weight and / or 0.1 to 5% by weight of (b) benzotriazole and / or a derivative thereof. 2. The composition according to claim 1, further comprising 0.01 to 5% by weight of one or more selected from the group consisting of a phenolic antioxidant, an epoxy compound, a carbodiimide compound, a phosphate and an alkylbenzene sulfonate. A lubricating oil for a hydrodynamic bearing according to any one of claims 1 to 5. A fluid bearing comprising a shaft and a sleeve, wherein the lubricating oil according to claim 1 is used. A lubrication method for a hydrodynamic bearing, comprising: lubricating the hydrodynamic bearing according to claim 7 using the lubricating oil for a hydrodynamic bearing according to any one of claims 1 to 6.

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