JPWO2007145305A1 - Method for preventing deterioration of lubricant, lubricant, and hydrodynamic bearing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress oxidative deterioration of a lubricant. In addition, an object of the present invention is to provide a fluid dynamic bearing device having a long life by extending the time until the lubricating function of the lubricant is impaired due to oxidative degradation. An ester-based lubricating oil is used as a lubricant while continuously or intermittently contacting an ionic compound or an ionic compound solution obtained by dissolving an ionic compound in a solvent. Further, in the hydrodynamic bearing device, an ionic compound is disposed on a part of the bearing or the shaft member and is brought into contact with the lubricating oil. Here, however, the ionic compound or ionic compound solution is substantially insoluble in the ester-based lubricating oil. [Selection] Figure 2

Description

  The present invention relates to a method for preventing deterioration of a lubricant mainly used for lubrication of a bearing device, a lubricant, and a hydrodynamic bearing device using the lubricant.

  The bearing mechanism is usually lubricated with a lubricant. While the lubricant lubricates the parts constituting the bearing mechanism, it gradually deteriorates due to oxidation or the like. In particular, in a hydrodynamic bearing mechanism used in a spindle motor for a hard disk drive, the temperature during use rises to about 60 degrees and is used for a long period of time.

  As a method for preventing such deterioration of the lubricant, particularly oxidation deterioration, for example, a lubricant containing a hindered phenol antioxidant and a benzotriazole derivative based on a fatty acid triester of trimethylolpropane (Patent Document 1) Reference), a lubricant containing a specific hindered phenolic antioxidant and an aromatic amine antioxidant in a specific ratio (see Patent Document 2), a carbonate ester as a base oil, and a sulfur-containing phenolic antioxidant And a lubricant containing a zinc-based extreme pressure agent (see Patent Document 3), a lubricant using a phenol-based antioxidant in a base oil mainly composed of a carbonate (see Patent Document 4), and the like.

JP-A-1-188592 JP-A-1-225697 JP-A-8-34987 Japanese Patent Laid-Open No. 10-183159

  The conventionally known lubricants to which amine-based antioxidants or phenol-based antioxidants are added are less deteriorated than those to which lubricants are not added. However, when used in a high temperature environment for a long time, deterioration due to oxidation is not sufficiently suppressed.

  Although the period during which deterioration is suppressed can be extended by increasing the amount added, significant improvement is difficult. Although the period during which deterioration is suppressed can be extended to some extent by increasing the amount added, if it exceeds a certain amount, the suppression period will not increase no matter how much it is increased.

  The present invention has been made in view of such problems, and an object of the present invention is to make it possible to suppress deterioration, particularly oxidation deterioration, over a long period of time with respect to a lubricant used for lubricating a bearing device or the like. To do.

  In the present invention, a deterioration inhibitor selected from an ionic compound that hardly dissolves in an ester-based lubricant is prepared, and this is brought into contact with the ester-based lubricant. The object is lubricated with the ester-based lubricating oil in this state.

  At this time, the lubricating oil need not always be in contact with the deterioration preventing agent. Usually, the lubricating oil for lubricating the bearing device or the like circulates inside the bearing device as the components slide, and the deterioration preventing agent may be touched in the course of the circulation.

  In addition, when the device to be lubricated includes a container for storing lubricating oil, the deterioration preventing agent particles may be placed in the container. In the present invention, since a deterioration preventing agent that hardly dissolves in the lubricating oil is used, even if such a deterioration preventing agent is added, it is separated or precipitated. However, since the lubricant can be brought into contact with the deterioration preventing agent, the deterioration of the lubricant can be prevented.

In the present invention, the ionic compound refers to a substance that forms a molecule or a crystal by binding a cation and an anion mainly by ionic bonds. Such substances are generally difficult to dissolve in oil.

  The following effects can be obtained by using an anti-degradation agent that does not dissolve in the lubricating oil, or that dissolves only slightly, in contact with the lubricating oil. In other words, during use, impurities that dissolve in the lubricating oil from the surroundings are absorbed by the deterioration preventing agent, thereby preventing changes in the characteristics of the lubricating oil. In addition, since a deterioration preventing agent that is only slightly dissolved in the lubricating oil can always be supplied, the state in which the lubricating oil contains a small amount of the deterioration preventing agent can be maintained for a long period of time. Moreover, since it hardly dissolves in the lubricating oil, the physical properties of the lubricating oil, such as viscosity, do not change even when a deterioration inhibitor is present.

  The deterioration preventing agent to be used may be selected from salts having a structure in which atoms constituting the acid molecule are substituted with hydrogen atom metal ions released as hydrogen cations upon ionization. These substances often have low solubility in ester-based lubricating oils.

  Among the salts, substances that exhibit an excellent deterioration preventing effect are found, such as alkali metal carbonates, alkali metal hydrogencarbonates, and alkali metal carboxylates that show alkalinity when made into an aqueous solution.

  In addition, the deterioration preventing agent does not need to be solid. An ionic compound may be dissolved in a solvent such as water to form a solution. In any case, there is an interface where the degradation inhibitor and the lubricating oil come into contact. The interface refers to a boundary that appears at a contact portion when things that do not mix with each other such as water and oil come into contact with each other. Not only the liquids but also the part where the solid and the liquid are in contact is called an interface.

  When the lubricating oil of the present invention is applied to a hydrodynamic bearing device, the deterioration preventing agent is held at any part of the shaft or the bearing, and the surface thereof is brought into contact with the lubricating liquid. As a place to hold, a depression, a groove, a hole, etc. can be used. Moreover, you may pack in the inside of the void | holes of sintered members, such as a metal sintered compact.

  In addition, although the deterioration preventing agent used conventionally melt | dissolves in lubricating oil, such a deterioration preventing agent can also be used together with the deterioration preventing agent which does not melt | dissolve in the lubricating oil characterized by this invention. By using together, deterioration is further suppressed.

  According to the present invention, it is possible to obtain a lubricating oil that has good characteristics as a lubricating oil and can be used for a long period of time. Further, by using this lubricating oil, it is possible to obtain a highly reliable dynamic pressure bearing device that exhibits stable performance over a long period of time.

It is a longitudinal cross-sectional view which shows a recording disk drive device It is a longitudinal cross-sectional view which shows the spindle motor carrying the hydrodynamic bearing apparatus of this invention. It is the figure which showed the production rate of the oxidation degradation thing with respect to the base oil of an alkali carbonate It is the figure which showed the addition amount with respect to the base oil of sodium carbonate, and the generation rate of the oxidation degradation thing

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Base 17 Stator 21 Sleeve 30 Rotor 31 Hub 32 Rotating shaft part 34 Rotor magnet 42,43 Radial dynamic pressure bearing part 44 Thrust dynamic pressure bearing part

(1) Lubricating oil to which a solid ionic compound is added (1-1) Base oil The base oil used in the lubricating oil of the present invention is an ester oil. Specific examples include monoesters, diesters, polyol esters (trimethylolpropane, pentaerythritol, dipentaerythritol, neopentyldiol ester, complex ester), polyglycol esters, glycerin esters, aromatic esters, and the like.

  Furthermore, to these ester-based lubricating oils, ether oils such as alkylated diphenyl ether, alkylated triphenyl ether, alkylated tetraphenyl ether, alkylated polyphenyl ether, various poly-α-olefins, various silicone oils, or various types Fluorine oil or the like may be added.

  Monoesters include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, ricinoleic acid, linoleic acid, linolenic acid, arachidonic acid, icosapentaenoic acid, erucic acid, docosahexaene. Any one of organic acids such as acid and lignoceric acid, methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol, tridecanol, tetradecanol, pentadecanol And monoesters consisting of any one of monohydric alcohols such as

  Diesters include malonic acid, methyl malonic acid, succinic acid, methyl succinic acid, dimethyl malonic acid, ethyl malonic acid, glutamic acid, adipic acid, dimethyl succinic acid, pimelic acid, tetramethyl succinic acid, suberic acid, azelaic acid, sebacic acid Any one of organic acids having two carboxy groups such as acid and brassic acid, and methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol, tridecanol, tetradecanol And diesters composed of two molecules of the same kind or two different kinds of monovalent alcohols such as pentadecanol.

  As the polyol ester, any of trimethylolethane, trimethylolpropane, pentaerythritol, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, ricinoleic acid, linoleic acid And polyol esters composed of any one of linolenic acid, arachidonic acid, icosapentaenoic acid, erucic acid, docosahexaenoic acid, and lignoceric acid.

  Polyglycol esters include caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, ricinoleic acid, linoleic acid, linolenic acid, arachidonic acid, icosapentaenoic acid, erucic acid, docosahexaenoic acid And glycol esters composed of any of lignoceric acid and polyglycol.

  Examples of the glycerin ester include mono-fatty acid glycerin ester, di-fatty acid glycerin ester, and tri-fatty acid glycerin ester. Fatty acids bound to glycerin are caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, ricinoleic acid, linoleic acid, linolenic acid, arachidonic acid, icosapentaenoic acid, erucic acid , Docosahexaenoic acid, or lignoceric acid.

  The polyphenyl ether may have no alkyl group, or may have a linear or branched alkyl group. Specific examples of the alkyl group include, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, 2-methylbutyl, n-hexyl and isohexyl. 3-methylpentyl, ethylbutyl, n-heptyl, 2-methylhexyl, n-octyl, 2-ethylhexyl, 3-methylheptyl, n-nonyl, methyloctyl, ethylpeptyl, n-decyl, n-undecyl, n-dodecyl , N-tetradecyl and the like.

  As the base oil of the lubricating oil of the present invention, a diester oil is used, but it is also possible to use a mixture of the above base oils. Two or more kinds of oils can be mixed by a conventionally known mixing method.

(1-2) Deterioration inhibitor In the present invention, a deterioration inhibitor selected from ionic compounds is added to the base oil of the lubricating oil. Here, the ionic compound refers to a substance in which a cation and an anion are combined mainly by an ionic bond to form a molecule or a crystal. Such ionic compounds generally have low oil solubility. In the present invention, such a substance that hardly dissolves in the base oil is used as a deterioration preventing agent.

  In order to prevent oxidative degradation, alkali metal carbonates, alkali metal hydrogen carbonates, and alkali metal carboxylates are particularly suitable. However, as will be described later, among these lithium salts, the effect of preventing oxidative degradation is weak. These metal carbonates may be used alone or in combination of two or more. When an alkali metal carbonate, an alkali metal hydrogen carbonate, or an alkali metal carboxylate is used as an aqueous solution, the solution exhibits alkalinity. The acid dissociation constant pKa of these materials is approximately in the range of 9-11.

  Moreover, there are various carboxylic acids constituting the carboxylic acid metal salt, and examples thereof include aliphatic saturated monocarboxylic acids, aliphatic unsaturated carboxylic acids, aliphatic dicarboxylic acids, and aromatic carboxylic acids. Specific examples of aliphatic saturated monocarboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid , Linear saturated acids such as cerotic acid, laccelic acid, or isopropionic acid, isobutanoic acid, isopentanoic acid, 2-methylpentanoic acid, 2-methylbutanoic acid, 2,2-dimethylbutanoic acid, 2-methylhexanoic acid, 5 -Methylhexanoic acid, 2,2-dimethylheptanoic acid, 2-ethyl-2-methylbutanoic acid, 2-ethylhexanoic acid, dimethylhexanoic acid, 2-n-propyl-pentanoic acid, 3,5,5-trimethylhexanoic acid , Dimethyloctanoic acid, isotridecanoic acid, isomyristic acid, isostearic acid isoarachidic acid, isohexanoic acid Branched fatty acids such as phosphate and the like. Further, examples of the unsaturated carboxylic acid include lumitreic acid, oleic acid, elaidic acid, linoleic acid, linolenic acid and the like, and unsaturated hydroxy acids such as ricinoleic acid. Examples of the aliphatic dicarboxylic acid include adipic acid, azelaic acid, and sebacic acid, and examples of the aromatic carboxylic acid include benzoic acid, phthalic acid, trimellitic acid, and pyrometic acid. Also, alicyclic fatty acids such as naphthenic acid can be used. Two or more of the above carboxylic acids may be used in combination.

  The number of metal elements combined per one carboxylic acid is not limited to one, and may be two or more. Moreover, you may use not only 1 type but 2 or more types of metal carbonate and carboxylic acid metal salt.

  In addition to the above ionic compounds, the use of an existing antioxidant such as a phenol-based antioxidant or an amine-based antioxidant can prevent oxidative deterioration more reliably.

  Examples of phenolic antioxidants include 4,4′-methylenebis (2,6-di-tert-butylphenol), 4,4′-bis (2,6-di-tert-butylphenol), 4,4 ′. -Bis (2-methyl-6-tert-butylphenol), 2,2'-methylenebis (4-ethyl-6-tert-butylphenol), 2,2'-methylenebis (4-methyl-6-tert-butylphenol), 4,4′-butylidenebis (3-methyl-6-tert-butylphenol), 4,4′-isopropylidenebis (2,6-di-tert-butylphenol), 2,2′-methylenebis (4-methyl-6) -Nonylphenol), 2,2'-isobutylidenebis (4,6-dimethylphenol), 2,2'-methylenebis (4-methyl) 6-cyclohexylphenol), 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol, 2,4-dimethyl-6-tert-butylphenol, 2, 6-di-tert-α-dimethylamino-p-cresol, 2,6-di-tert-butyl-4 (N, N′-dimethylaminomethylphenol), 4,4′-thiobis (2-methyl-6) -Tert-butylphenol), 4,4'-thiobis (3-methyl-6-tert-butylphenol), 2,2'-thiobis (4-methyl-6-tert-butylphenol), bis (3-methyl-4- Hydroxy-5-tert-butylbenzyl) sulfide, bis (3,5-di-tert-butyl-4-hydroxybenzyl) sulfide 2,2′-thio-diethylenebis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], tridecyl-3- (3,5-di-tert-butyl-4-hydroxy Phenyl) propionate, pentaerythrityl-tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) ) Propionate, 3-methyl-5-tert-butyl-4-hydroxyphenyl substituted fatty acid esters and the like can be mentioned as preferred examples. A mixture of two or more of these can also be used as a deterioration inhibitor.

  Examples of amine-based antioxidants include monoalkyl diphenylamines such as monooctyl diphenylamine and monononyl diphenylamine, 4,4′-dibutyldiphenylamine, 4,4′-dipentyldiphenylamine, 4,4′-dihexyldiphenylamine, Polyalkyls such as 4,4'-diheptyldiphenylamine, 4,4'-dioctyldiphenylamine, dialkyldiphenylamines such as 4,4'-dinonyldiphenylamine, tetrabutyldiphenylamine, tetrahexyldiphenylamine, tetraoctyldiphenylamine, tetranonyldiphenylamine Diphenylamine, α-naphthylamine, phenyl-α-naphthylamine, butylphenyl-α-naphthylamine, pentylphenyl-α-naphthy Amine, hexyl phenyl -α- naphthylamine, heptylphenyl -α- naphthylamine, octylphenyl -α- naphthylamine can include naphthylamine, such as nonylphenyl -α- naphthylamine. A mixture of two or more of these amino acid antioxidants can also be used as a deterioration inhibitor.

  You may mix | blend the said phenolic antioxidant and amine antioxidant in combination.

  In the lubricating oil for a hydrodynamic bearing device of the present invention, when a phenol-based antioxidant or an amine-based antioxidant is contained, the content is usually 5.0% by weight or less with respect to the entire lubricant. There is a need. Preferably it is 3.0 weight% or less, More preferably, it is 1.0 weight% or less. When the content exceeds 5.0% by weight, it is not preferable because sufficient antioxidant properties corresponding to the blending amount cannot be obtained. On the other hand, in order to obtain the antioxidant effect, it is necessary to contain 0.1% by weight or more with respect to the entire lubricant.

  At this time, various other conventionally known additives such as a viscosity index improver, a pour point depressant, a metal deactivator, a surfactant, a rust inhibitor, and a corrosion inhibitor are further utilized as necessary. You may mix | blend.

(1-3) Description of Lubricant Hereinafter, the composition of the 12 types of lubricants according to the present invention and the 7 types of lubricants of Comparative Examples will be described. In addition, the base oil used for embodiment mentioned below is a diester.

(1-3-1) Composition of lubricant according to an embodiment of the present invention Embodiment 1: 1 wt% sodium carbonate is added to 100 parts by weight of base oil. Embodiment 2: 100 parts by weight of base oil With respect to 1% by weight of sodium carbonate and 0.2% by weight of a mixture of 2,6-di-tert-butyl-4-ethylphenol and 4,4′-dibutyldiphenylamine. 1% by weight of sodium bicarbonate and 0.2% by weight of a mixture of 2,6-di-tert-butyl-4-ethylphenol and 4,4′-dibutyldiphenylamine are added to 100 parts by weight of oil. thing.

Embodiment 4: 1% by weight of lithium carbonate and 0.2% of a mixture of 2,6-di-tert-butyl-4-ethylphenol and 4,4′-dibutyldiphenylamine with respect to 100 parts by weight of base oil % Input.

Embodiment 5: 1% by weight of potassium carbonate and 0.2% of a mixture of 2,6-di-tert-butyl-4-ethylphenol and 4,4′-dibutyldiphenylamine with respect to 100 parts by weight of base oil % Input.

Embodiment 6: 1% by weight of rubidium carbonate and 0.2% of a mixture of 2,6-di-tert-butyl-4-ethylphenol and 4,4′-dibutyldiphenylamine with respect to 100 parts by weight of the base oil % Input.

Embodiment 7: Based on 100 parts by weight of base oil, 1% by weight of cesium carbonate and 0.2% of a mixture of 2,6-di-tert-butyl-4-ethylphenol and 4,4′-dibutyldiphenylamine % Input.

Embodiment 8: 1% by weight of sodium formate and 0.2% of a mixture of 2,6-di-tert-butyl-4-ethylphenol and 4,4′-dibutyldiphenylamine with respect to 100 parts by weight of base oil % Input.

Embodiment 9: 1% by weight of sodium acetate and 0.2% of a mixture of 2,6-di-tert-butyl-4-ethylphenol and 4,4′-dibutyldiphenylamine per 100 parts by weight of base oil % Input.

Embodiment 10: 1% by weight of ethylenediaminetetraacetic acid-4sodium (EDTA-4Na) and 2,6-di-tert-butyl-4-ethylphenol and 4,4′-to 100 parts by weight of base oil A 0.2% by weight mixture of dibutyldiphenylamine is added.

Embodiment 11: To 100 parts by weight of base oil, 0.5% by weight of sodium carbonate, and a mixture of 2,6-di-tert-butyl-4-ethylphenol and 4,4′-dibutyldiphenylamine was added in an amount of 0. 2% by weight input.

Embodiment 12: To 100 parts by weight of base oil, 0.25% by weight of sodium carbonate, and a mixture of 2,6-di-tert-butyl-4-ethylphenol and 4,4′-dibutyldiphenylamine was added in an amount of 0.1%. 2% by weight input.

  In addition, when preparing the lubricant according to the above-described embodiments 1 to 12, the additive was added to the base oil, followed by stirring. Additives other than salt were dissolved in the base oil by stirring, but most of the input salt was precipitated without dissolving.

(1-3-2) Comparative Example Comparative Example 1: Base oil only.

Comparative Example 2: With respect to 100 parts by weight of the base oil, 0.2% by weight of an antioxidant obtained by mixing 2,6-di-tert-butyl-4-ethylphenol and 4,4′-dibutyldiphenylamine was added. thing.

Comparative Example 3: 1% by weight of calcium carbonate and 0.2% of a mixture of 2,6-di-tert-butyl-4-ethylphenol and 4,4′-dibutyldiphenylamine with respect to 100 parts by weight of the base oil % Input.

Comparative Example 4: 1% by weight of barium carbonate and 0.2% of a mixture of 2,6-di-tert-butyl-4-ethylphenol and 4,4′-dibutyldiphenylamine with respect to 100 parts by weight of the base oil % Input.

Comparative Example 5: 1% by weight of diethyl carbonate and 0.2% of a mixture of 2,6-di-tert-butyl-4-ethylphenol and 4,4′-dibutyldiphenylamine with respect to 100 parts by weight of the base oil % Input.

Comparative Example 6: 1% by weight of sodium sulfate and 0.2% of a mixture of 2,6-di-tert-butyl-4-ethylphenol and 4,4′-dibutyldiphenylamine with respect to 100 parts by weight of the base oil % Input.

Comparative Example 7: Based on 100 parts by weight of base oil, 0.3% by weight of sodium hydroxide and 0.2% of a mixture of 2,6-di-tert-butyl-4-ethylphenol and 4,4′-dibutyldiphenylamine % By weight.

  When preparing the lubricants of Comparative Examples 1 to 7 above, the additives were added to the base oil and then stirred. Additives other than salt and sodium hydroxide were dissolved in the base oil by stirring.

(1-4) High-pressure oxygen test The following high-pressure oxygen tests were performed on the lubricants of Embodiments 1 to 10 and Comparative Examples 1 to 7, and the oxidation deterioration of the lubricating oil was investigated.

(1-4-1) Test conditions The lubricant was held in a thermostatic bath at 150 ° C. for 60 hours under oxygen filling (0.9 MPa) (8 hours for Embodiment 1 and Comparative Example 1), and then the deterioration rate of the lubricating oil Was measured.

  Liquid chromatography was used to measure the deterioration rate. At this time, the peak of the base oil and the peak of the polymer or low-molecular oxidation degradation product are detected, and the area ratio (%) of the polymer and low-molecular oxidation degradation product peak to the total peak area is calculated, respectively. The polymer degradation rate and the low molecule degradation rate were used. The results are shown in Table 1.

(1-4-2) Test results

表１の実施形態１と比較例１の分析値を対比すると、実施形態１では、高分子酸化劣化率が著しく低いことが明白である。すなわち、炭酸ナトリウムの投入により、高分子酸化劣化が著しく抑制されている。

When the analysis values of Embodiment 1 and Comparative Example 1 in Table 1 are compared, it is clear that Embodiment 1 has a significantly low polymer oxidative degradation rate. That is, polymer oxidative degradation is remarkably suppressed by adding sodium carbonate.

  When the analysis values of Embodiment 2 and Comparative Example 2 are compared, in Embodiment 2, the polymer oxidative degradation rate is further improved as compared to Embodiment 1, and the low molecular oxidative degradation rate is also greatly improved. . That is, it can be seen that sodium carbonate further suppresses both high-molecular oxidative degradation and low-molecular oxidative degradation in the presence of a conventional oxidative degradation inhibitor.

  Table 2 shows Embodiments 4, 2, 5, 6, and 7 extracted from the embodiments shown in Table 1. It is a table comparing the effects of alkali metal carbonates from lithium to cesium. FIG. 3 is a graph showing the results.

表２及び図３から明らかなように、ナトリウムからセシウムまでの炭酸塩は、高分子劣化率、低分子劣化率を共に大幅に改善する。最も改善効果が大きいのはカリウムの場合である。ナトリウムとルビジウムの場合は、カリウムよりもやや劣り、セシウムになると更に効果が弱くなる。しかし、これら何れの金属の炭酸塩においても、劣化が抑制されていることは明白である。

As is apparent from Table 2 and FIG. 3, the carbonates from sodium to cesium greatly improve both the high molecular deterioration rate and the low molecular deterioration rate. The most effective improvement is in the case of potassium. In the case of sodium and rubidium, it is slightly inferior to potassium. However, it is clear that the deterioration of any of these metal carbonates is suppressed.

  Among alkali metal carbonates, lithium carbonate is not so clearly suppressed in oxidative degradation. Lithium is originally a somewhat special element among alkali metals, and carbonates also have different physical properties from other alkali metal carbonates. Such a difference may be a difference in improvement.

  Table 3 shows the results of the high-temperature oxygen test for Embodiments 2, 11, 12 and Comparative Example 2. FIG. 4 summarizes this in a graph.

表３及び図４から明らかなように、炭酸ナトリウムの投入量が増えるほどに、高分子酸化劣化率、及び低分子酸化劣化率が改善している。また、投入量が０．２５wt%でも効果は見られるが、比較例との差異は小さい。図４において、高分子酸化劣化率と低分子酸化劣化率の和を２０％以下とすることを改善の最低目標とするならば、炭酸ナトリウムは、０．１重量％以上の投入が必要である。

As is clear from Table 3 and FIG. 4, the higher the amount of sodium carbonate added, the higher the polymer oxidative degradation rate and the low molecular oxidative degradation rate. In addition, the effect is seen even when the input amount is 0.25 wt%, but the difference from the comparative example is small. In FIG. 4, if the minimum goal of improvement is to set the sum of the high molecular oxidative degradation rate and the low molecular oxidative degradation rate to 20% or less, sodium carbonate needs to be introduced in an amount of 0.1% by weight or more. .

(2) Lubricating oil to which aqueous solution was added (2-1) Composition of additive Carbonated to 50 g of base oil to which a mixture of 2,6-di-tert-butyl-4-ethylphenol and 4,4′-dibutyldiphenylamine was added To a base oil to which a lubricant (Embodiment 13) charged with 1.2 mL of an aqueous metal salt solution and a mixture of 2,6-di-tert-butyl-4-ethylphenol and 4,4′-dibutyldiphenylamine were added, A lubricant (Embodiment 14) in which 1.2 mL of an aqueous solution of EDTA-4Na was added was prepared and subjected to an oxidation stability test.

(2-2) Oxidation stability test (RBOT test)
The oxidation life of the lubricating oil was measured by a method based on RBOT of the JIS standard test (JIS2514), and the RBOT value was calculated. That is, water, a copper coil, and lubricating oil are put together in the sealable container together with the aqueous solution, pressurized to 620 kPa with oxygen, the sealed container is put in a thermostatic bath at 150 degrees, and the container is placed at 30 degrees. The rotation was continued at 100 revolutions per minute while maintaining the angle. Then, the time from when the internal pressure reached the maximum until the pressure dropped to 175 kPa was measured. Moreover, the same test was done also about the lubricating oil of the said comparative example 2 which does not add the said aqueous solution. In this case, the lubricating oil was used for the test in contact with water, not an aqueous solution. The results are shown in Table 4.

表３から明らかなように、炭酸金属塩水溶液を添加した実施形態１３では、加えていない比較例２に比して、ＲＢＯＴ値が２倍以上になっている。また、ＥＤＴＡ−４Ｎａ水溶液を添加した実施形態１４では、３倍以上になっている。共に、酸化安定度が大幅に改善している。また、潤滑液に水を加えて行う試験であるＲＢＯＴ試験にて、酸化安定度が増すことは、基油の加水分解が抑制されていることを示している。

As is apparent from Table 3, in the thirteenth embodiment to which the aqueous metal carbonate solution was added, the RBOT value was more than twice that of Comparative Example 2 in which the metal carbonate aqueous solution was not added. Moreover, in Embodiment 14 which added EDTA-4Na aqueous solution, it is 3 times or more. In both cases, the oxidation stability is greatly improved. Further, in the RBOT test, which is a test performed by adding water to the lubricating liquid, an increase in oxidation stability indicates that hydrolysis of the base oil is suppressed.

(3) Hydrodynamic bearing device, spindle motor, and disk drive device (3-1) Disk drive device FIG. 1 shows the internal configuration of a disk drive device (hard disk device in this example) 60. The interior of the housing 61 of the disk drive device 60 is a clean space with extremely little dust. Inside the housing 61 are housed a spindle motor 1 for driving a disk on which a disk-shaped recording medium 62 on which information is recorded is mounted, and an access unit 63 for writing and reading information on the recording medium 62. Yes.

(3-2) Spindle Motor FIG. 2 is a longitudinal sectional view showing the configuration of the spindle motor 1. The spindle motor 1 includes a stationary member and a rotating member. With the hydrodynamic bearing device according to the embodiment of the present invention, the rotating member is supported so as to be rotatable about the rotating shaft portion 32 with respect to the fixed member.

(3-2-1) Stationary member of spindle motor The base 10 has a flat portion 11 provided at the center thereof and an annular boss portion 13 provided at the center of the flat portion 11. An annular recess is formed between the annular boss portion 13 and the annular step portion 14 provided on the outer peripheral portion of the flat portion 11. A stator 17 fixed to the flat portion 11 and a rotor magnet 34 attached to a hub 31 to be described later are disposed in this recess. The annular boss portion 13 is provided at a position near the outer peripheral portion of the cylindrical support wall 15 protruding upward, and the stator 17 is fixed to the outer periphery thereof. The stator 17 includes an annular stator core 17a formed by laminating a plurality of electromagnetic steel plates, and a multi-phase (for example, three-phase) winding 17b wound around each tooth of the stator core 17a. The stator 17 is fixed by using a means such as press-fitting or adhesion by fitting the stator core 17a to the cylindrical support wall 15. The stator 17 is fixed to the cylindrical support wall 15. The fixing method is press-fitting, adhesion or the like.

  Inside the annular boss portion 13, a stainless steel bearing stationary portion 20 that constitutes a part of the hydrodynamic bearing device is fitted and fixed. The bearing stationary portion 20 includes a substantially cylindrical sleeve 21 and a counter plate 22 that closes the lower end opening of the sleeve 21. The inner peripheral surface of the through hole of the sleeve 21 is formed over almost the entire length of the sleeve 21, and has a small-diameter inner peripheral surface 21 a where the radial bearing portion is located and a lower portion of the sleeve 21 that is wider than the small-diameter inner peripheral surface 21 a. The diameter is divided into an inner diameter inner peripheral surface 21b and a large inner diameter inner surface 21c positioned at the lowermost end of the sleeve 21 and further expanded from the inner diameter inner peripheral surface 21b. The counter plate 22 is disposed in a space inside the large-diameter inner peripheral surface 21c, and is fixed to the sleeve 21 by a method such as press-fitting, caulking, welding, or bonding. The lower half of the outer peripheral surface of the sleeve 21 is fixed to the inner peripheral surface of the annular boss portion 13 by a method such as press fitting, bonding, or welding. A tapered surface 23 is formed on the upper outer peripheral surface of the sleeve 21 to form an inner peripheral surface of a taper seal portion described later. This taper surface 23 has a form which leaves | separates from the center axis | shaft of a bearing as it goes upwards in a figure.

(3-2) Configuration of Rotating Member and Hydrodynamic Bearing Device The rotor 30 includes an inverted cup-shaped hub 31 and a rotating shaft portion 32 disposed at the rotation center position of the hub 31. Since the rotating shaft portion 32 is supported by the bearing stationary portion 20, the rotor 30 is rotatable with respect to the flat portion 11.

  The hub 31 is made of a ferromagnetic material such as iron or stainless steel. A cylindrical portion 31b extending downward in the drawing is connected to the outer peripheral portion of the disc portion 31a constituting the top plate portion. At the lower end of the cylindrical portion 31b, there is a flange portion 31c projecting outward in the radial direction. An annular wall 31d extending downward from the disk portion 31a is disposed inside the cylindrical portion 31b. The annular wall 31 d is disposed between the sleeve 21 and the cylindrical support wall 15 and surrounds the upper outer periphery of the sleeve 21. Further, the annular wall 31 d forms a labyrinth gap constituting a labyrinth seal with the cylindrical support wall 15.

  The attachment hole 31e is formed at the center of the disk portion 31a, and the upper end portion of the rotating shaft portion 32 having a slightly smaller diameter is press-fitted therein. Thereby, the hub 31 and the rotating shaft part 32 are united. The rotating shaft portion 32 is hollow, and an internal thread 32b is formed on the inner peripheral surface over almost the entire length. The outer peripheral surface 32a of the rotating shaft part 32 and the small-diameter inner peripheral surface 21a of the sleeve 21 face each other in the radial direction (radial direction) through a slight gap.

  The tip of the rotary shaft portion 32 passed through the sleeve 21 slightly protrudes downward from the small-diameter inner peripheral surface 21a. The retaining member 33 includes a male screw portion 33 a that is screwed into the female screw 32 b of the rotating shaft portion 32, and a circular plate portion 33 b. The circular plate portion 33b has an outer diameter that is larger than the outer diameter of the rotating shaft portion 32 and smaller than the inner diameter of the medium-diameter inner peripheral surface 21b. A clearance is secured between the circular plate portion 33 b and the sleeve, and the rotation shaft portion 32 including the retaining member 33 can freely rotate with respect to the sleeve 21. When a force is applied in the direction in which the rotary shaft portion 32 is pulled out from the sleeve, the circular plate portion 32 b comes into contact with the sleeve 21, thereby preventing the rotary shaft portion 32 from being pulled out.

  An annular rotor magnet 34 having a plurality of magnetic poles arranged in the circumferential direction is disposed inside the cylindrical portion 31b of the hub 31. The rotor magnet 34 is disposed at a position surrounding the stator 17 from the outer periphery. A hub 31 made of a ferromagnetic material also serves as a back yoke of the magnet 34.

  One or a plurality of disc-shaped recording disks (hard disks) (not shown) are placed on the flange portion 31 c of the hub 31. The hard disk has a hole in the center, and the edge of the hole is in contact with the outer peripheral surface of the cylindrical wall 31b. A clamp member is attached to the hub. The clamp member comes into contact with the upper surface in the vicinity of the hole of the disk and sandwiches and fixes the disk together with the flange portion 31c.

  The clamp member is screwed to the rotary shaft portion by a screw that is screwed onto the female screw 32b of the rotary shaft portion 32 from above.

  A minute gap is secured between the small-diameter inner peripheral surface 21a of the sleeve 21 and the outer peripheral surface 32a of the rotating shaft portion 32, and between the lower surface of the disk portion 31a of the hub 31 and the upper end surface of the sleeve 21, and lubrication is performed. Filled with oil 40. To the lubricating oil 40, a mixture of 2,6-di-tert-butyl-4-ethylphenol and 4,4'-dibutyldiphenylamine is added.

  The lubricating oil 40 also fills a space surrounded by the inner diameter inner peripheral surface 21 b of the sleeve 21, the surface of the counter plate 22, and the surface of the circular plate portion 33 b of the retaining member 33. The lubricating oil 40 is in contact with the outside air at a taper seal portion 41 formed by the inner peripheral surface 31f of the annular wall 31d of the hub 31 and the tapered surface 23 on the upper outer periphery of the sleeve 21, and the liquid surface having an arc-shaped cross section is maintained. Has been. The taper seal portion 41 has a tapered shape in which the gap is reduced as it advances upward.

  On the small-diameter inner peripheral surface 21a of the sleeve 21, herringbone-shaped dynamic pressure generating grooves are formed at two locations corresponding to 42 and 43 in the drawing and separated from each other in the axial direction. The dynamic pressure generating groove generates a supporting force for holding the rotating shaft portion 32 in the radial direction when the spindle motor rotates in a predetermined direction. That is, a pair of radial dynamic pressure bearings are arranged at 42 and 43. A spiral-shaped dynamic pressure generating groove is also formed on the upper end surface of the sleeve 21 to constitute a thrust dynamic pressure bearing portion 44. The spiral groove increases the pressure of the lubricating oil inside the region where the dynamic pressure generating groove is formed when the spindle motor rotates in the predetermined direction. In addition, a support force that causes the hub 31 to float upward in the axial direction is generated.

  A communication hole 45 penetrating in the axial direction is formed in the sleeve 21, and the inside is filled with the lubricating oil 40. The through hole 45 has a lower end opened inside the inner peripheral surface 21b of the medium diameter portion, and an upper end opened toward the inner peripheral portion side of the thrust dynamic pressure bearing portion 44 in the thrust minute gap. The communication hole 45 is configured to communicate both end portions of the two radial dynamic pressure bearing portions 42 and 43, and enables the lubricating oil 40 to circulate within the bearing device.

  A recess 70 is formed on the outer peripheral portion of the inner peripheral surface 21b of the medium diameter portion. Potassium carbonate is fixed inside the recess 70 and is always in contact with the lubricating oil 40. Instead of this potassium carbonate, an aqueous solution of potassium carbonate may be disposed.

  In addition, as a raw material which comprises the sleeve 21, it can replace with stainless steel and can utilize a porous sintered metal. In this case, in a part of the sleeve, potassium carbonate or an aqueous solution thereof can be sealed inside the hole. And in the other part of a sleeve, the state which lubricating oil and potassium carbonate contacted inside the sintered compact can be created by filling the inside of a hole with lubricating oil.

  Also, potassium carbonate is disposed slightly below (71) the wall surface of the taper seal portion 41, and the lubricating oil 40 expands due to a rise in temperature so that the interface is in contact with the potassium carbonate only when the interface moves downward. You can also In this case, the lubricating oil 40 comes into contact with potassium carbonate, which is a deterioration preventing agent, only at a high temperature at which deterioration progresses quickly. The deterioration of the lubricating oil can be effectively prevented while minimizing the contact between the potassium carbonate and the lubricating oil.

  The embodiments of the lubricant, the lubricant deterioration preventing method, and the hydrodynamic bearing device according to the present invention have been described above. However, the present invention is not limited to such embodiments and does not depart from the scope of the present invention. Various modifications are possible.

  For example, in the present embodiment, the dynamic pressure bearing device has a structure including two radial dynamic pressure bearing portions and one thrust dynamic pressure bearing portion, but the structure of the dynamic pressure bearing device is not limited thereto. Further, the formation position of the dynamic pressure generating groove is not limited to the position of the above embodiment.

  Further, the ionic compound to be brought into contact with the lubricating oil is not limited to those that cause an effect of preventing oxidative degradation. For example, a material such as silica gel having hygroscopicity may be disposed in the recess 60 of FIG.

The anti-degradation agent used, of atoms constituting the molecule of acid, hydrogen atoms are released as cations hydrogen when ionizing having a substituent structure with metal ions can be selected from among the salts. These substances often have low solubility in ester-based lubricating oils.

表３及び図４から明らかなように、炭酸ナトリウムの添加量が増えるほどに、高分子酸化劣化率、及び低分子酸化劣化率が改善している。また、投入量が０．２５wt%でも効果は見られるが、比較例との差異は小さい。図４において、高分子酸化劣化率と低分子酸化劣化率の和を２０％以下とすることを改善の最低目標とするならば、炭酸ナトリウムは、０．１２５重量％以上の添加が必要である。

As is apparent from Table 3 and FIG. 4, the higher the amount of sodium carbonate added, the higher the polymer oxidative degradation rate and the low molecular oxidative degradation rate. In addition, the effect is seen even when the input amount is 0.25 wt%, but the difference from the comparative example is small. In FIG. 4, if the minimum goal of improvement is to make the sum of the high molecular oxidative degradation rate and the low molecular oxidative degradation rate 20% or less, sodium carbonate needs to be added in an amount of 0.125 % by weight or more. .

(2-2) Oxidation stability test (RBOT test)
The oxidation life of the lubricating oil was measured by a method based on RBOT in the JIS standard test (JIS K 2514), and the RBOT value was calculated. That is, water, a copper coil, and lubricating oil are put together in the sealable container together with the aqueous solution, pressurized to 620 kPa with oxygen, the sealed container is put in a thermostatic bath at 150 degrees, and the container is placed at 30 degrees. The rotation was continued at 100 revolutions per minute while maintaining the angle. Then, the time from when the internal pressure reached the maximum until the pressure dropped to 175 kPa was measured. Moreover, the same test was done also about the lubricating oil of the said comparative example 2 which does not add the said aqueous solution. In this case, the lubricating oil was used for the test in contact with water, not an aqueous solution. The results are shown in Table 4.

Claims (22)

A method for preventing deterioration of a lubricant,
An ester-based lubricating oil containing an ester as a main component,
A cation and an anion are mainly used as a lubricant while being contacted continuously or intermittently with an ionic compound constituting a molecule or a crystal by being bound by an ionic bond,
The ionic compound is substantially insoluble in the ester lubricant.
A method for preventing deterioration of a lubricant, characterized by A method for preventing deterioration of a lubricant,
An ester-based lubricating oil containing an ester as a main component,
Used as a lubricant while continuously or intermittently contacting an ionic compound solution in which a cation and anion are combined mainly by ionic bonds to form molecules or crystals and dissolved in a solvent. And
The ionic compound and the solvent are substantially insoluble in the ester lubricant.
A method for preventing deterioration of a lubricant, characterized by The ionic compound is a salt having a structure in which a hydrogen atom of an acid is substituted with a metal ion.
The method for preventing deterioration of a lubricant according to claim 1 or 2, characterized in that: The acid dissociation constant pKa of the salt is 9 or more and 11 or less.
The method for preventing deterioration of a lubricant according to claim 3, wherein: The salt is an alkali metal bicarbonate except lithium.
The method for preventing deterioration of a lubricant according to claim 3, wherein: The salt is an alkali metal carbonate excluding lithium,
The method for preventing deterioration of a lubricant according to claim 3, wherein: The salt is an alkali metal carboxylate excluding lithium,
The method for preventing deterioration of a lubricant according to claim 3, wherein: An ester-based lubricating oil containing an ester as a main component;
An ionic compound in which a cation and an anion are combined mainly by ionic bonds to form a molecule or crystal;
Consists of
The ionic compound is substantially insoluble in the ester-based lubricant, and
The ester-based lubricating oil forms an interface with the ionic compound,
Lubricant characterized by things. An ester-based lubricating oil containing an ester as a main component;
An ionic compound solution in which a cation and an anion are combined mainly by an ionic bond and an ionic compound constituting a molecule or crystal is dissolved in a solvent;
Consists of
The ionic compound is substantially insoluble in the ester-based lubricating oil, and
The ester-based lubricating oil forms an interface with the ionic compound solution,
Lubricant characterized by things. The ionic compound is a salt having a structure in which a hydrogen atom of an acid is substituted with a metal ion.
The lubricant according to claim 8 or 9, characterized in that. The acid dissociation constant pKa of the salt is 9 or more and 11 or less.
The lubricant according to claim 10, wherein The salt is an alkali metal bicarbonate except lithium.
The lubricant according to claim 10, characterized in that: The salt is an alkali metal carbonate excluding lithium,
The lubricant according to claim 10, characterized in that: The salt is an alkali metal carboxylate excluding lithium,
The lubricant according to claim 10, characterized in that: An ester-based lubricating oil containing an ester as a main component;
One member having a bearing surface;
The other bearing member having a bearing surface opposed to the bearing surface through a minute gap, the lubricating oil being held in the minute gap, and being rotatable relative to the one member;
Consists of
At least one part of the surface of the one member in contact with the lubricating oil and at least one part of the surface of the other member in contact with the lubricating oil are substituted with metal hydrogen ions of acid. Salt having the structure is arranged,
The salt is substantially insoluble in the ester lubricant.
This is a hydrodynamic bearing device. An ester-based lubricating oil containing an ester as a main component;
One member having a bearing surface;
The other bearing member having a bearing surface opposed to the bearing surface through a minute gap, the lubricating oil being held in the minute gap, and being rotatable relative to the one member;
Consists of
Any part of the surface of the one member in contact with the lubricating oil or any part of the surface of the other member in contact with the lubricating oil has a structure in which the hydrogen atom of the acid is replaced with a metal ion. A salt solution in which the salt is dissolved in a solvent is retained,
The salt is substantially insoluble in the ester lubricant.
This is a hydrodynamic bearing device. At least a part of the one member or the other member is made of a porous material,
In the pores of the porous material, the salt is filled.
The hydrodynamic bearing device according to claim 15, characterized in that: At least a part of the one member or the other member is made of a porous material,
In the pores of the porous material, the salt solution is filled,
The hydrodynamic bearing device according to claim 16, characterized in that: The acid dissociation constant pKa of the salt is 9 or more and 11 or less.
The hydrodynamic bearing device according to claim 15, wherein the hydrodynamic bearing device is characterized. The salt is an alkali metal bicarbonate except lithium.
The hydrodynamic bearing device according to claim 15, wherein the hydrodynamic bearing device is characterized by that. The salt is an alkali metal carbonate excluding lithium,
The hydrodynamic bearing device according to claim 15, wherein the hydrodynamic bearing device is characterized by that. The salt is an alkali metal carboxylate excluding lithium,
The hydrodynamic bearing device according to claim 15, wherein the hydrodynamic bearing device is characterized by that.

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