JP4789447B2 - Lubricating oil for fluid bearing and fluid bearing using the same - Google Patents

Description

The present invention relates to a lubricating oil for hydrodynamic bearings comprising a lubricating oil containing a dicarboxylic acid diester having excellent low temperature fluidity and a high viscosity index.

  Furthermore, the present invention relates to a fluid bearing lubricating oil used for a bearing portion of a rotating body such as a motor, a fluid bearing using the same, and a fluid bearing lubricating method.

  Lubricating oils are widely used in various industrial fields, and their use is mainly to reduce friction and wear on the contact surface during contact sliding between metals. The physical properties required for the lubricating oil vary depending on the application field, but generally include lubricity, oxidation stability, thermal stability, low temperature fluidity, viscosity characteristics, and the like.

  In order to satisfy the above-described performance, various natural products and synthetic products have been used as base oils and additives of various lubricating oil compositions. Specifically, natural products include mineral oil, animals and plants. Fatty acids derived from fats and oils and animal and vegetable oils are used, and synthetic products include α-olefin oligomers, polyalkylene glycols, fatty acid monoesters and diesters, polyol (hindered) esters, phosphate esters, silicate esters, silanes, silicones, poly Phenyl ethers and fluorocarbons are used. And the lubricating oil composition which has the target performance is utilized by using these individually or in combination.

  On the other hand, with the diversification and sophistication of the industrial field in recent years, it has become difficult to sufficiently satisfy the performance required for conventional synthetic lubricating oils while the usage conditions of lubricating oils become more severe. Specifically, the use conditions are becoming severe, such as a very low temperature range of −30 ° C. or lower and a high temperature range exceeding 150 ° C. due to heating, sliding with metal, and the like. In recent years, there has been a demand for a lubricating oil that can be used for a long time even under such conditions. Good lubricating properties, heat resistance, oxidation stability, low-temperature fluidity, and high viscosity index are particularly important as lubricating oil performance. It is said that. As such a lubricating oil, a lubricating oil based on a dicarboxylic acid ester, an ether composed of a polyoxyalkylene glycol and an alcohol, or an ester composed of a polyoxyalkylene glycol and an aliphatic monovalent carboxylic acid (see Patent Document 1). Has been proposed. However, the lubricating oil cannot satisfy various performances required for recent synthetic lubricating oils used under severe conditions.

  On the other hand, there have been remarkable progresses in reducing the size and weight of video / audio equipment, personal computers, etc., increasing capacity, and speeding up information processing. These electronic devices use various rotating devices such as rotating devices that drive magnetic disks and optical disks such as FD, MO, zip, mini disk, compact disk (CD), DVD, hard disk, etc. Improvements in bearings, which are indispensable for rotating devices, have greatly contributed to the reduction in size, weight, capacity, and speed of electronic equipment. A fluid bearing consisting of a sleeve and a rotating shaft facing each other through a lubricating oil does not have a ball bearing, so it is suitable for reduction in size and weight, and is excellent in quietness, economy, etc. Its application has been expanded to audio equipment, visual equipment and car navigation.

  In addition, the lubricating oil or bearing fluid used in the hydrodynamic bearing includes one or more of olefin, diester or neopentyl polyol ester synthetic oil, squalane and naphthenic mineral oil, and urea compound thickener grease. (See Patent Document 2), trimethylolpropane fatty acid triester as a base oil, containing a hindered phenolic antioxidant and a benzotriazole derivative (see Patent Document 3), a specific polymer hindered phenol Base oils containing a specific antioxidant and an aromatic amine antioxidant (see Patent Document 4), a specific monocarboxylic acid ester having a phenyl group and / or a specific dicarboxylic acid diester One (see Patent Document 5), one based on a single composition (see Patent Document 6), charcoal An ester as a base oil, containing a sulfur-containing phenolic antioxidant and a zinc-based extreme pressure agent (see Patent Document 7), containing a magnetic fluid (see Patent Documents 8, 9, and 10), a specific carbonic acid An ester as a base oil and containing a phenolic antioxidant (see Patent Document 11), an ester of trimethylolpropane and a monovalent fatty acid having 4 to 8 carbon atoms as a base oil (see Patent Document 12) Etc. have been proposed.

  In the future, demands for high-speed processing of large-capacity information and further downsizing of devices are expected to become stronger. Conventionally, power consumption of audio equipment, personal computers, etc. has not been attracting attention because it is not so large, but the demand for energy saving remains because the equipment can be downsized by extending the life of the built-in battery or reducing the capacity. There is something strong. Thus, with the demand for high-speed processing of large-capacity information and downsizing of devices, fluid bearings are required to rotate at higher speed. However, the energy loss in the bearing increases as the speed increases.

  Therefore, in addition to basic performance such as lubricity, deterioration stability (life), sludge generation prevention, wear prevention, corrosion prevention, etc., it has energy saving performance and evaporability In order to meet demands for high-speed processing of information, compactness, and the like, a lubricating oil having a low volume resistivity for preventing electrification is demanded.

  Furthermore, the use of the above information processing devices is also increasing in harsh environments as the devices become popular. In particular, a device such as a car navigation system that is mounted on a car and used must be able to withstand use from a cold region to a hot weather in consideration of the use environment of the car. Therefore, it is required that the lubricating oil for bearings used in in-vehicle devices can be used without any problem in a wide temperature range of -40 to 80 ° C. Therefore, a lubricating oil having a low pour point and a high viscosity index is particularly required.

JP 62-263288 A Japanese Patent Laid-Open No. 01-279117 Japanese Patent Laid-Open No. 01-185852 Japanese Patent Publication No. 01-225697 Japanese Patent Laid-Open No. 04-357318 Japanese Patent No. 2621329 Japanese Patent Application Laid-Open No. 08-34987 Japanese Patent Laid-Open No. 08-259977 JP 08-259982 A Japanese Patent Laid-Open No. 08-259985 Japanese Patent Laid-Open No. 10-183159 JP 2004-91524 A

  Accordingly, an object of the present invention is to provide a lubricating oil that is excellent not only in lubricity but also in performance such as energy saving, low evaporation and heat resistance, in particular, low temperature characteristics and antistatic performance. Another object of the present invention is to provide a fluid bearing lubricant using such a lubricant, a fluid bearing using the lubricant, and a method of lubricating the fluid bearing.

  As a result of intensive investigations to achieve the above object, the present inventors have a specific dicarboxylic acid diester compound as a main component, and a lubricating oil having a specific range of kinematic viscosity, total acid value and hydroxyl value is energy saving, The present inventors have found that it is excellent in low evaporation, heat resistance, low temperature characteristics and antistatic performance, and completed the present invention.

That is, the lubricating oil for fluid bearings of the present invention has the following general formula (1):
R ¹ O— (A ¹ O) —OC—R ³ —CO— (OA ² ) —OR ² (1)
[Wherein, R ¹ and R ² are each independently an alkyl group having 1 to 20 carbon atoms or an aryl group having 6 to 20 carbon atoms, and A ¹ O and OA ² are each independently a single type or two or more types. And a main component is a compound having a kinematic viscosity at 40 ° C. of 5 to 5 and a mono or polyoxyalkylene group composed of alkylene having 2 to 4 carbon atoms, and R ³ is an alkylene group having 2 to 15 carbon atoms. It is characterized by comprising a lubricating oil having a total acid value of 5 mgKOH / g or less and a hydroxyl value of 20 mgKOH / g or less at 100 mm ² / s, and the lubricating oil preferably has a kinematic viscosity of 40 ° C. 5 to 70 mm ² / s, viscosity index is 100 or more, total acid value is 1 mgKOH / g or less, pour point is -30 ° C or less, and volume resistivity is 1 × 10 ¹³ Ω · cm or less is there. The lubricating oil is mainly composed of a compound in which R ¹ and R ² are each independently an alkyl group having 1 to 20 carbon atoms and R ³ is an alkylene group having 4 to 8 carbon atoms in the general formula (1). It is particularly preferable that

Further, the lubricating oil, in addition to the compound represented by the general formula (1), (a) a polyhydric alcohol partial ester compound having at least one ester bond and at least two hydroxyl groups and / or at least two It is preferable to contain 0.1 to 5% by weight of a polyhydric alcohol partial ether compound having a hydroxyl group and at least one ether bond, and / or (b) 0.1 to 5% by weight of benzotriazole and / or a derivative thereof, It is more preferable to contain 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 ester and an alkylbenzene sulfonate.

Furthermore , the present invention is a fluid dynamic bearing comprising a shaft and a sleeve, which is filled with the fluid bearing lubricating oil, and further lubricates the fluid bearing using the fluid bearing lubricating oil. Lubrication method.

The lubricating oil used for the fluid bearing lubricating oil of the present invention is composed mainly of the compound represented by the above general formula (1), has a kinematic viscosity at 40 ° C. of 5 to 100 mm ² / s, and a total acid value of 5 mgKOH. Since the hydroxyl value is 20 mgKOH / g or less at / g or less, it is excellent in energy saving, low evaporation, heat resistance, low temperature characteristics, antistatic performance, etc., and its balance is good, especially at high speed It is excellent as a lubricating oil for rotating devices of electronic devices that are becoming more compact.

The lubricating oil used for the fluid bearing lubricating oil of the present invention contains the compound represented by the general formula (1) as a main component. The alkyl group having 1 to 20 carbon atoms in R ¹ and R ² in the general formula (1), a methyl group, an ethyl group, a propyl group, an isopropyl group, butyl group, isobutyl group, amyl group, isoamyl group, Hexyl, cyclohexyl, methylhexyl, heptyl, methylheptyl, octyl, 2-ethylhexyl, nonyl, isononyl, 3,5,5-trimethylhexyl, decyl, isodecyl, lauryl , Tridecyl group, myristyl group, isomyristyl group, cetyl group, stearyl group, isostearyl group, and the like. As the aryl group having 6 to 20 carbon atoms, phenyl group, tolyl group, ethylphenyl group, dimethylphenyl group, A trimethylphenyl group, a naphthyl group, a methylnaphthyl group, etc. are mentioned. As the R ¹ and R ^2, preferably an alkyl group having 1 to 20 carbon atoms, more preferably an alkyl group having 1 to 7 carbon atoms.

Examples of mono- or polyoxyalkylene groups composed of alkylene having 2 to 4 carbon atoms in A ¹ O and OA ² of the general formula (1) include monooxyalkylenes such as oxyethylene groups, various oxypropylene groups, and various oxybutylene groups. And a polyoxyalkylene group such as a polyoxyethylene group, a polyoxypropylene group, or a polyoxybutylene group in which these monooxyalkylene groups are preferably repeated 2 to 5, more preferably 2 to 3 are mentioned. .

In addition, as the alkylene group having 2 to 15 carbon atoms in R ³ of the general formula (1), ethylene group, trimethylene group, tetramethylene group, pentamethylene group, hexamethylene group, heptamethylene group, octamethylene group, nonamethylene Group, decamethylene group, undecamethylene group, dodecamethylene group, tridecamethylene group and other linear alkylene groups, methylethylene group, dimethylethylene group, methylethylethylene group, ethylethylene group, diethylethylene group, methyl Examples thereof include branched alkylene groups such as trimethylene group, dimethyltrimethylene group, methylethyltrimethylene group, ethyltrimethylene group, diethyltrimethylene group, and 1,1-dimethyltrimethylene group. In addition, as R < ³ >, a C2-C11 alkylene group is preferable and a C2-C8 alkylene group is still more preferable.

The compound represented by the general formula (1), which is the main component of the lubricating oil used for the fluid bearing lubricating oil of the present invention, has 4 to 17 carbon atoms, preferably 4 to 13 carbon atoms, more preferably 6 to carbon atoms. 10 linear or branched aliphatic dibasic acids, alkylene glycols having linear or branched alkylenes having 2 to 4 carbon atoms, or polyoxyalkylene glycols that are polymers thereof, and 1 to 20 carbon atoms, Preferably, it is obtained by esterifying an oxyalkylene alcohol having 3 to 30 carbon atoms, preferably 3 to 10 carbon atoms, obtained by condensation with 1 to 7 alcohols.

  Examples of the linear aliphatic dibasic acid include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, brassic acid, tetradecanedioic acid, pentadecane. A diacid etc. can be mentioned. Examples of the branched aliphatic dibasic acid include methyl succinic acid, dimethyl succinic acid, methyl ethyl succinic acid, ethyl succinic acid, diethyl succinic acid, methyl glutaric acid, dimethyl glutaric acid, methyl ethyl glutaric acid, ethyl glutaric acid, Examples include diethyl glutaric acid, 1,1-dimethyl-1,3-dicarboxypropane, and the like. Among these, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid are preferable. These aliphatic dibasic acids may be used alone or in combination of two or more.

  Examples of the alkylene glycol include ethylene glycol, propylene glycol (1,2-propanediol), trimethylene glycol (1,3-propanediol), 1,2-butanediol, 1,3-butanediol, and 1,4- And monomers such as butanediol, 2,3-butanediol, and isobutylene glycol. Moreover, as said polyoxyalkylene glycol, the polymer which consists of 1 type or 2 or more types of the monomer quoted as the specific example of the said alkylene glycol, Preferably it is 2-5 pieces, Most preferably, it is 2-3. The polymer may be block or random.

  Examples of the alcohol having 1 to 20 carbon atoms include methanol, ethanol, propanol, isopropanol, butanol, isobutanol, amyl alcohol, isoamyl alcohol, hexanol, cyclohexanol, methylhexanol, heptanol, methylheptanol, octanol, and 2-ethyl. Hexanol, nonanol, isononanol, 3,5,5-trimethylhexanol, decanol, isodecanol, lauryl alcohol, tridecanol, myristyl alcohol, isomyristyl alcohol, cetanol, stearyl alcohol, isostearyl alcohol, phenol, cresol, ethylphenol, dimethylphenol, Trimethylphenol, naphthol, methylnaphthol and the like are preferred.

  These alcohols and the above alkylene glycol or polyoxyalkylene glycol are converted into the above oxyalkylene alcohol by a normal condensation reaction. These alcohols, alkylene glycols and polyoxyalkylene glycols may be used alone or in combination of two or more.

The compound represented by the general formula (1) used in the lubricating oil for fluid bearings of the present invention is an esterification reaction by the dehydration reaction between the aliphatic dibasic acid and the oxyalkylene alcohol, or a derivative of an aliphatic dibasic acid. It can be obtained by a general esterification reaction via an acid anhydride, acid chloride or the like or transesterification of each derivative.

  The compound represented by the general formula (1) obtained by the above method does not particularly limit the unreacted acid and hydroxyl group, but if the residual amount of the carboxyl group is large, the acid value becomes high. Since the hydroxyl value increases when the residual amount is large, it is preferable that the carboxyl group and the hydroxyl group remain as little as possible.

  Furthermore, the water that is mixed during esterification is a substance involved in hydrolysis, and ash can be a catalyst that promotes hydrolysis and causes sludge generation. It is preferable to adjust the amount to the smallest possible value. Specifically, 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. The moisture can be removed by, for example, heating distillation, heating vacuum distillation or blowing of 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 so, ester hydrolysis and sludge generation can be minimized, and a highly stable ester can be obtained. Therefore, the deterioration resistance and long-term stability of the lubricating oil are improved and the life is extended. be able to.

  The compound represented by the above general formula (1) may be contained as a main component of the lubricating oil, but the total required performance such as excellent energy saving, low evaporation, heat resistance, low temperature characteristics, and antistatic properties is included. From the viewpoint of more reliably and well-balanced, the compound represented by the general formula (1) is preferably contained in an amount of 50% by mass or more, more preferably 80% by mass or more based on the total amount of the lubricating oil. Preferably, it is more preferably 90% by mass or more, and most preferably 95% by mass or more.

In addition to the compound represented by the general formula (1), the lubricating oil used for the fluid bearing lubricating oil of the present invention includes mineral oil, olefin polymer, hydrocarbon oil such as alkylbenzene, polyglycol, polyvinyl ether, Oxygen-containing synthetic oils such as ketones, polyphenyl ethers, silicones, polysiloxanes, perfluoroethers, and esters and ethers other than the compound represented by the general formula (1) may be used.

The lubricating oil used in the fluid bearing lubricating oil of the present invention requires a kinematic viscosity at 40 ° C. of 5 to 100 mm ² / s in order to obtain excellent lubricating performance, energy saving, etc. It is preferably in the range of mm ² / s. In addition, the lubricating oil used for the lubricating oil for fluid bearings of the present invention requires a total acid value of 5 mgKOH / g or less in order to ensure corrosion prevention, wear resistance and stability. / g or less is preferable. Furthermore, the lubricating oil used for the lubricating oil for fluid bearings of the present invention requires a hydroxyl value of 20 mgKOH / g or less and 5 mgKOH / g or less from the viewpoint of moisture absorption resistance and stability improvement. Is preferred. The lubricating oil having such properties can be obtained by sufficiently performing the esterification reaction and then using the compound represented by the general formula (1), which is appropriately purified by a known method.

In the lubricating oil used for the fluid bearing lubricating oil of the present invention, preferably, the viscosity index is 100 or more, more preferably 120 or more, the pour point is -30 ° C. or less, and the volume resistivity is 1 × 10 ¹³ Ω · cm or less. More preferably, by setting it to 1 × 10 ¹¹ Ω · cm or less, it is possible to achieve particularly excellent low-temperature characteristics and antistatic performance, and it is desirable for downsizing, weight reduction, large capacity, and high-speed processing of information. It can be effectively used as a fluid bearing lubricant suitable for various rotating devices in video / audio equipment, personal computers and the like.

In addition to the compound represented by the general formula (1) as a base oil, various additives may be added to the lubricating oil used for the fluid bearing lubricating oil of the present invention in order to improve practical performance. it can. Examples of 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 blend one or more selected from phenolic antioxidants, epoxy compounds, carbodiimide compounds, phosphate esters and alkylbenzene sulfonates.

  The polyhydric alcohol partial ester and the polyhydric alcohol partial ether 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 an oily agent. These polyhydric alcohol derivatives are adsorbed to the metal of one lubrication part at the hydroxyl portion, and the hydrocarbon group extending from the ether bond or ester bond prevents contact with the other metal, thereby improving the lubrication action. It is considered a thing.

  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, mannitol, and the like. Trivalent alcohol is particularly preferable, and glycerin is particularly preferable. Moreover, as monovalent fatty acid which produces | generates this polyhydric alcohol and partial ester, a C14-C20 thing is more preferable, Specifically, myristic acid, palmitic acid, stearic acid, isostearic acid, oleic acid, eruca An acid etc. are mentioned. Moreover, as monool which produces | generates the said polyhydric alcohol and partial ether, the monohydric alcohol corresponding to the said monohydric fatty acid is mentioned. Among these monovalent fatty acids and monools, oleic acid and oleyl alcohol are particularly preferable. That is, as the polyhydric alcohol derivative, glycerin monooleate and glycerin monooleyl ether are particularly preferable.

  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% by weight based on the whole lubricating oil, and further 0.5 to 5% by weight. It is preferable to blend so as to contain about%. In addition, the polyhydric alcohol partial ether and the polyhydric alcohol partial ester may be used singly, a plurality of ether compounds or ester compounds, or a mixture thereof.

式中、Ｒ⁴は、水素原子又はメチル基を示し、Ｒ⁵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０〜２０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、Ｒ⁵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。 As said benzotriazole and / or its derivative (s), it is preferable to use the compound shown by following General formula (2).

In the formula, R ⁴ represents a hydrogen atom or a methyl group, and R ⁵ represents a hydrogen atom or a group having 0 to 20 carbon atoms containing a nitrogen atom and / or an oxygen atom. From the viewpoint of improving the wear resistance of copper, a benzotriazole derivative is preferred, and R ⁵ is preferably a group having 10 to 20 carbon atoms containing a nitrogen atom.

  The benzotriazole and / or its derivative is preferably 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 whole lubricating oil. If the addition amount is small, the effect of improving the wear resistance of copper in particular is not obtained. If the addition amount is too large, not only an effect commensurate with the addition amount is obtained, but also sludge generation may occur in some cases.

  Examples of the phenolic antioxidant include 2,6-di-t-butylphenol, 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butyl-4-ethylphenol, 2 , 6-Di-t-butyl-4-n-butylphenol (ethyl 744), 4,4'-methylenebis (2,6-di-t-butylphenol), 2,2'-thiobis (4-methyl-6- t-butylphenol) and the like. An amine antioxidant may be used. In particular, the combined use of a phenolic antioxidant and an amine antioxidant can greatly improve oxidation stability.

  As said 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. alone or in combination Can be used. 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 and mixtures thereof are more preferred. By adding these epoxy compounds, the stability of the compound represented by the general formula (1), particularly the hydrolytic stability, is greatly improved.

The carbodiimide compound is a compound represented by the following general formula (3).
R ⁶ -N = C = N-R ⁷ (3)
In the formula, R ⁶ and R ⁷ are hydrogen or a hydrocarbon group, or a hydrocarbon group containing nitrogen and / or oxygen, and R ⁶ and R ⁷ may be the same or different, respectively. .

In the general formula (3), when R ⁶ and R ⁷ are 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 Is preferred. Specifically, hydrogen, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, 2-methylbutyl, hexyl, heptyl, octyl, 2-ethylhexyl, nonyl, decyl, undecyl, dodecyl and other alkyl groups, propenyl Alkenyl groups such as butenyl, isobutenyl, pentenyl, 2-ethylhexenyl, octenyl, cycloalkyl groups such as cyclopentyl, cyclohexyl, methylcyclopentyl, ethylcyclopentyl, aryl groups such as phenyl, naphthyl, trails, isopropylphenyl, diisopropylphenyl, triphenyl Examples include compounds containing, as R ⁶ and R ⁷ , aryl groups such as alkyl-substituted phenyl such as isopropylphenyl and nonylphenyl, and aralkyl groups such as benzyl and phenethyl. The carbodiimide compound has a function as an acid scavenger and can improve hydrolysis stability of the compound represented by the general formula (1).

  Examples of the phosphoric acid ester include tricresyl phosphate, triphenyl phosphate, cresyl diphenyl phosphate, diphenyl hydrogen phosphate, 2-ethylhexyl diphenyl phosphate, among these, tricresyl phosphate, triphenyl phosphate Is more preferable. By adding a phosphate ester, the wear resistance of iron can be greatly improved.

  Examples of the alkylbenzene sulfonate include neutralized salts of an alkylbenzene sulfonic acid having an alkyl group having 1 to 20 carbon atoms as a substituent and an alkylamine having 1 to 20 carbon atoms. This ionic antistatic agent has an affinity for the compound represented by the general formula (1), and can exhibit sufficient conductivity for releasing static electricity.

In the lubricating oil used for the fluid bearing lubricating oil of the present invention, one or more selected from the above-mentioned phenolic antioxidants, epoxy compounds, carbodiimide compounds, phosphate esters and alkylbenzene sulfonates are blended. Is preferred. Here, the blending amount of these additives is not particularly limited, but when blending a plurality of additives, each additive is contained in an amount of 0.05 to 5% by weight based on the total amount of the lubricating oil. It is preferable to blend as described above. If the amount added is small, the effect is not obtained. If the amount is too large, the characteristics of the lubricating oil are not utilized, and sludge formation is caused.

  The lubricating oil for fluid bearings of the present invention uses the above lubricating oil, and the fluid bearing of the present invention uses this lubricating oil for fluid bearings. The hydrodynamic bearing of the present invention does not have a mechanism such as a ball bearing, and is composed of a sleeve and a shaft, and the hydrodynamic bearing is maintained so as not to be in direct contact with each other by the lubricant contained between them. If it is, it will not be specifically limited mechanically. 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 so as to occur.

  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 may be repeated, and metal wear may occur between the sleeve and the rotating shaft or the sleeve and the thrust plate, or seizure may occur due to temporary contact during rotation. However, by using the lubricating oil for hydrodynamic bearings of the present invention having excellent energy saving properties, heat resistance and low temperature characteristics, high-speed rotational stability and durability are maintained over a long period of time, and excellent energy saving properties are exhibited particularly at high speeds. .

  FIG. 1 shows a specific example of a fluid bearing preferable for loading and using the fluid bearing lubricating oil of the present invention. FIG. 1 is a cross-sectional view schematically showing a schematic configuration of a motor equipped with a fluid dynamic 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 fitted and fixed to a 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 2 and the rotor magnet 10 provided on the rotor 6.

  Disc-shaped upper thrust plates 4a and lower thrust plates 4b projecting outward in the radial direction are disposed at the upper and lower portions of the shaft 4, and gas is disposed on the outer surface of the shaft between these thrust plates. The interposition part 22 is formed. On the other hand, the rotor 6 is a sleeve that is supported by the shaft 4 via a rotor hub 6a on which the recording disk D is placed on the outer peripheral portion, and a minute gap that is located on the inner peripheral side of the rotor 6 and holds the lubricating oil 8. 6b. 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.

  Here, there are sleeves facing each other from the outer peripheral portion of the shaft 4 adjacent to the upper portion of the gas intervening portion 22 provided in the central portion of the shaft 4 to the lower surface, outer peripheral surface, and upper peripheral portion of the upper thrust plate 4a. A minute gap is formed between the upper portion of the inner peripheral portion through-hole 6c of 6b and the lower surface of the upper counter plate 7a, 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 has a supporting force for holding 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 on the inner surface of the inner peripheral portion through hole 6c of the sleeve 6b, and at the same time as generating a supporting force for retaining the rotor portion in the radial direction when the motor rotates. Then, the lubricating oil 8 is pushed up in the direction of arrow B.

  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.

  Further, the same structure of minute gaps, grooves, and lubricating oil holding portions are formed in the upside down arrangement from the lower portion of the gas intervening portion 22 provided in the central portion of the shaft 4 to the lower thrust plate 4b and the lower counter plate 7b. The rotor portion is supported more stably by the lower dynamic pressure bearing portion. Further, in the fluid bearing of this structure, the upper and lower counter plates 7a and 7b can effectively prevent the lubricating oil 8 from spreading in the outer circumferential direction due to the rotational centrifugal force even at a high speed of about 20,000 revolutions per minute. The Furthermore, by using the fluid bearing lubricating oil according to the present invention, it is possible to realize stable rotation at a higher speed while being accompanied by excellent energy saving and durability.

  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 mentioned, by filling the fluid bearing lubricant into the fluid bearing and lubricating it, high-speed rotation stability and durability can be maintained over a long period of time, and excellent energy savings can be obtained, resulting in a longer life. Can be achieved.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

Various types of lubricating oils were made using the following esters and additives, and the lubricating oil performance was evaluated. As the base material of the lubricating oil, the following esters (A to D) according to the present invention and esters (E to H) as comparative examples were used.
A: adipic acid di (n-butoxypropyl) ester B: sebacic acid di (n-butoxypropyl) ester C: adipic acid di (isobutoxyethoxyethyl) ester D: adipic acid di (methoxydiethoxyethyl) ester

E: Ester of trimethylolpropane (TMP) and n-C ₇ acid F: Ester of TMP and mixed acid of n-C ₆ acid (20 mol%) and n-C ₇ acid (80 mol%) G: Neo Ester of pentyl glycol (NPG) and n-C ₁₀ acid H: ester of NPG and n-C ₉ acid

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 Moreover, the following were used as an additive.
I: Glycerin monooleyl ether J: Benzotriazole derivative represented by the following general formula (4)

K: 2,6-di-t-butyl-4-methylphenol L: 2-ethylhexyl glycidyl ether M: tricresyl phosphate N: bis (diisopropylphenyl) carbodiimide

  The above-described ester base materials A to D and additives were blended as shown in Table 1 to prepare lubricating oils of the present invention (Examples 1 to 10). The lubricating oils of Examples 1 to 4 do not contain additives, and the lubricating oils of Examples 5 to 10 contain the above-mentioned additives of I to N in parentheses as shown in Table 1. Formulated as such. Moreover, the lubricating oil (comparative examples 1-4) of the comparative example was prepared using the said E-H ester base material. In addition, the additive was not mix | blended with the lubricating oil of Comparative Examples 1-4.

  About the prepared lubricating oil of Examples 1-10 and Comparative Examples 1-4, each physical property was measured and the practical performance was evaluated. The physical property measurement and the performance evaluation test were conducted by the following methods. The results are shown in Table 2.

(1) Kinematic viscosity, viscosity index: According to JIS K 2283, kinematic viscosity was measured using a Canon-Fenske viscometer and a viscosity index was calculated.
(2) Total acid value: measured according to JIS C 2101.
(3) Hydroxyl value: Measured according to JIS K 0070.
(4) Volume resistivity test: Measured at 25 ° C. according to JIS C 2101.
(5) Evaporation amount: The amount of evaporation was determined from the weight loss when held at 120 ° C for 12 hours by thermogravimetric analysis (TG method).
(6) Pour point: Measured according to JIS K 2269.
(7) Low temperature fluidity: 20 ml of oil was placed in a 50 ml sample bottle and allowed to stand at −40 ° C. for 2 days, and the fluidity (solidification state) of the lubricating oil was observed. In the evaluation, the sample bottle taken out after standing for 2 days was inverted, and the one that did not flow within 1 minute was solidified.
(8) Thermal stability: 20 ml of lubricating oil was placed in a petri dish having an inner diameter of 70 mm and aged for 2 weeks at 140 ° C. to forcibly deteriorate, and the total acid value (JIS K 2501) of the deteriorated oil was measured.

From Table 2, all of the lubricating oils of Examples 1 to 10 have a small amount of evaporation, have fluidity at -40 ° C., and have a low volume resistivity of 5 × 10 ¹¹ Ω · cm or less and good antistatic ability. In addition, it can be seen that after deterioration, the total acid value is 3 mg KOH / g or less, which is excellent in thermal stability and exhibits well-balanced performance including other physical properties. Therefore, it turns out that the lubricating oil of Examples 1-10 can be used effectively as a lubricating oil for fluid bearings.

  On the other hand, the lubricating oils of Comparative Examples 1 to 4 are inferior in physical properties and performance as fluid bearing lubricating oils and cannot be used practically. That is, although the lubricating oils of Comparative Examples 1 and 2 have a low pour point, they are solidified at −40 ° C. and thus lack appropriateness as lubricating oils. Further, the lubricating oil of Comparative Example 3 has a high pour point, solidifies and has a large amount of evaporation. The lubricating oil of Comparative Example 4 is easily solidified and has an extremely large evaporation amount, and is not suitable as a lubricating oil, particularly as a fluid bearing lubricating oil. Moreover, all the lubricating oils of Comparative Examples 1 to 4 have high volume resistivity and poor antistatic ability.

The lubricating oil mainly composed of the compound represented by the general formula (1) is excellent in energy saving, low evaporation, heat resistance, low temperature characteristics, antistatic performance, etc., and has a good balance of these performances. It can be used as a lubricating oil for fluid bearings and has an extremely high industrial utility value.

It is sectional drawing which shows typically schematic structure of the motor equipped with the fluid bearing.

Explanation of symbols

1 Motor 2 Bracket 4 Shaft
4a Upper thrust plate 4b Lower thrust plate 6 Rotor 6a Rotor hub 6b Sleeve 6c Inner peripheral through hole 7a Upper counter plate 7b Lower counter plate 8 Lubricating oil 10 Rotor magnet 12 Stator 14 Spiral groove 20 Outside air communication hole 22 Gas intervening portion 24 Herringbone shape Groove D Recording disk P Lower inner circumference of upper thrust plate

Claims (7)

The following general formula (1):
R ¹ O— (A ¹ O) —OC—R ³ —CO— (OA ² ) —OR ² (1)
[Wherein, R ¹ and R ² are each independently an alkyl group having 1 to 20 carbon atoms or an aryl group having 6 to 20 carbon atoms, and A ¹ O and OA ² are each independently a single type or two or more types. And a main component is a compound having a kinematic viscosity at 40 ° C. of 5 to 5 and a mono or polyoxyalkylene group composed of alkylene having 2 to 4 carbon atoms, and R ³ is an alkylene group having 2 to 15 carbon atoms. A lubricating oil for a hydrodynamic bearing comprising a lubricating oil having a total acid value of 5 mgKOH / g or less and a hydroxyl value of 20 mgKOH / g or less at 100 mm ² / s. 2. The lubricating oil for fluid bearings according to claim 1, wherein the lubricating oil has a viscosity index of 100 or more, a pour point of −30 ° C. or less, and a volume resistivity of 1 × 10 ¹³ Ω · cm or less. ^2. The fluid bearing lubrication according to claim 1, wherein, in the general formula (1), R ¹ and R ² are each independently an alkyl group having 1 to 20 carbon atoms and R ³ is an alkylene group having 4 to 8 carbon atoms. Oil . The lubricating oil further comprises (a) a polyhydric alcohol partial ester compound having at least two hydroxyl groups and at least one ester bond and / or a polyhydric alcohol having at least two hydroxyl groups and at least one ether bond. The lubricating oil for fluid bearings according to any one of claims 1 to 3, comprising 0.1 to 5% by weight of a partial ether compound and / or (b) 0.1 to 5% by weight of benzotriazole and / or a derivative thereof. The lubricating oil further contains 0.01 to 5% by weight of one or more selected from the group consisting of phenolic antioxidants, epoxy compounds, carbodiimide compounds, phosphate esters and alkylbenzene sulfonates. The lubricating oil for fluid bearings in any one of Claims 1-4. A hydrodynamic bearing comprising a shaft and a sleeve, wherein the hydrodynamic bearing lubricant according to any one of claims 1 to 5 is used. A fluid bearing lubrication method according to claim 6 , wherein the fluid bearing lubrication oil according to any one of claims 1 to 5 is lubricated.

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