JP2003105369A - Lubricant for hydrodynamic bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lubricant for a hydrodynamic bearing having excellent long-term reliability by enabling a suitable base oil to be selected by judging the high-quality base oil satisfying the evaluation of heat resistance required for the hydrodynamic bearing based on initial data. SOLUTION: This lubricant for the hydrodynamic bearing is obtained by selecting and preparing the base oil and the lubricant having a little change of the viscosity at a low vaporized amount by the control of the initial purity of the base oil. As a result, the cost and a test period for selecting the base oil and the lubricant can be extremely reduced, and the selection can be precisely carried out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lubricating oil for a dynamic pressure bearing used in a dynamic pressure bearing device used for bearings of rotating parts such as hard disk drives and polygon mirrors.

[0002]

2. Description of the Related Art In the field of spindle motors used for hard disk drives, polygon mirrors, etc.
Due to the demand for high speed and high capacity, a high speed and high precision spindle motor is required, and various spindle motors employing a dynamic pressure bearing structure have been proposed accordingly. The lubricant used for the dynamic pressure bearing portion of those spindle motors is used without replacement for a long period of time, and therefore a lubricant having a low evaporation property, a small change in viscosity and a long-term reliability is required.

To meet those requirements, poly-α-
Synthetic oils such as olefins, monoesters, diesters, polyolesters, polyglycols, polyphenylethers, and fluorinated oils are used as base oils, and additives such as antioxidants and antiwear agents are required. It was added and used accordingly. The long-term reliability of a lubricating oil can be further improved by using additives, but it goes without saying that the selection of a high-quality base oil is a prerequisite, and the quality of the base oil must also be adjusted in order to use an appropriate amount of additives. Is important to manage and use.

Generally, when selecting a base oil, the viscosity and type of the base oil are selected in consideration of bearing rigidity, current consumption, temperature characteristics, bearing material, and the like. When selecting a base oil with even better long-term reliability, select a base oil with the highest possible viscosity and a low total acid value within the usable viscosity range, or display the evaporative test results. If so, the base oil with the smaller value was selected.

[0005]

In a dynamic pressure bearing using a lubricating oil, long-term reliability of the lubricating oil is a very important problem. When the lubricating oil deteriorates and the viscosity increases, the consumption current increases. In addition, when the lubricating oil gels or the lubricating oil evaporates, causing insufficient oil or running out of oil in the bearing,
This may cause a decrease in the value related to the rotation characteristics such as the NRRO value or, in some cases, seizure of the bearing portion. When the lubricating oil evaporates in the dynamic pressure bearing used for the hard disk drive, it also causes a problem such as contamination of the recording medium. Not only for spindle motors used in hard disk drives and polygon mirrors, but for checking the long-term reliability of general consumer electrical equipment, 70 ℃ to 100 ℃
Since the durability test for 10,000 hours or more is performed at around 0 ° C. to confirm whether the quality is deteriorated or deteriorated, the lubricating oil is required to have reliability under the same conditions.

However, at around 70 to 100 ° C., 10,000
There is no lubricating oil or base oil that guarantees the change in viscosity or the amount of evaporation after a lapse of time. The evaporative and thermal stability test of lubricating oil or base oil is 10 to 1 at around 150 to 200 ° C.
In most cases, the evaluation result of about 00 hours is displayed. This is mainly because the quality of petroleum products is displayed based on JIS test conditions. JIS tests are conducted for engine oil for automobiles, airplanes, and ships, large-scale machinery such as generator turbines and compressors. There are many tests targeting lubricants used under severe temperature conditions. Lubricating oil used for bearings of large machines as described above is used on the premise of proper quality control and regular replacement corresponding to it.
Naturally, the required quality and test conditions are different from the lubricating oil that is used for a long time without replacement, such as a dynamic bearing for a spindle motor used for a hard disk or the like.

Therefore, a base oil having a measured evaporation value, a thermal stability test result, and good initial total acid value data under a temperature condition in a region different from the actually required test condition has been selected. However, since the initial quality data cannot determine the evaporability and viscosity stability of the base oil under the actual evaluation conditions, the base oil was selected from the attached quality data and the actual temperature was 100 ° C.
When a durability test was carried out in the vicinity, there was a difference between the rank of superiority and inferiority at the time of selection and the ranking of actual evaporation amount and viscosity change. Therefore, in actuality, in the initial selection, a plurality of base oils having a viscosity and a viscosity index suitable for the bearing conditions are selected,
The fact is that the base oil that can be used for the bearing is selected after the test for more than 10000 hours at around 100 ° C, which not only requires a great deal of cost and time, but also the quality of the quality that can be used after the evaluation. When the base oil could not be obtained, the base oil was re-examined and the design of the bearing part was changed according to other usable base oils.

In the durability test of the base oil at about 100 ° C., evaporation and viscosity increase occur with the passage of time, and the time until the phenomenon occurs depends on the quality of the base oil. What is common to both base oils is that the evaporation and the viscosity increase proceed in parallel, and the viscosity increase further increases as the evaporation amount increases. Moreover, when the relationship between the evaporation amount of the base oil and the total acid value was investigated, an increase in the evaporation amount also caused an increase in the total acid value. Therefore, the evaporation phenomenon of the base oil near 100 ° C. is not a phenomenon in which a part of the base oil evaporates depending on the relationship between temperature, vapor pressure and time, and the weight is simply reduced,
It can be inferred that the evaporative component is generated along with the deterioration of the base oil, and at the same time, the high viscosity component is generated due to the reaction between the deteriorated component and the base oil. Such a phenomenon is similar to the natural deterioration phenomenon of oil in an environment at room temperature, and it is considered that the base oil is oxidized and deteriorated, radical cleavage in the molecular structure and a chain reaction caused by generated radicals, and the like are considered. On the other hand, in the measurement of the evaporation amount at 150 to 200 ° C., since the temperature is close to the boiling point of the base oil, most of the evaporation depends on the vapor pressure of the base oil.

Further, according to JIS, petroleum products and lubricating oil-neutralization value test method, K2501, the total acid value is 1 g of sample.
The number of milligrams (mg) of potassium hydroxide required to neutralize all the acidic components contained therein, which specification can be used to indicate the relative change in oil oxidation state during use. , Is described. In the remarks column, weakly acidic components with dissociation constants in water ^exceeding 10 ^-9 are not measured, and the absolute value of acidity for predicting the performance of oil in use is not measured. It is also described. Therefore, it is impossible to know the true value of the total amount of acidic substances by the total acid value, and at the same time,
Long-term reliability cannot be judged.

As a more specific problem, even when the same base oil is compared, there is a difference in quality depending on the product, and there is also a problem that a specific base oil cannot be simply selected. FIG. 3 is a diagram in which bis (2-ethylhexyl) sebacate (DOS), which is a general diester base oil, is obtained from various manufacturers and the time-dependent change in the evaporation amount at 100 ° C. is measured. All of the DOS-1 to DOS-4 in FIG. 3 have a total acid value of 0.1 mgKOH / g or less and are generally good quality base oils, but have a large difference in evaporability. Was there.

The present invention is intended to solve the above-mentioned problems, and an object thereof is to determine a high-quality base oil satisfying the heat resistance evaluation required for a dynamic pressure bearing from the initial data and to make it appropriate. It is to provide a lubricating oil for a dynamic pressure bearing that has excellent long-term reliability.

[0012]

SUMMARY OF THE INVENTION The present invention is characterized in that a base oil is selected and used as a lubricating oil under the following initial conditions in order to provide a lubricating oil for a dynamic pressure bearing excellent in long-term reliability. To do.

The lubricating oil for a dynamic pressure bearing according to claim 1 of the present invention is characterized by using a base oil having a purity of 95% by weight or more, or a mixed base oil of a base oil having a purity of 95% by weight or more. To do.

The lubricating oil for a dynamic pressure bearing according to claim 2 of the present invention is the lubricating oil for a dynamic pressure bearing according to claim 1, more preferably a base oil having a purity of 98% by weight or more, or a purity of 9%.
A mixed base oil of 8% by weight or more is used.

According to a third aspect of the present invention, there is provided the dynamic pressure bearing lubricating oil according to the first or second aspect, wherein the base oil is an ester oil or at least one of the base oils. One is an ester oil.

According to a fourth aspect of the present invention, the lubricating oil for a dynamic pressure bearing is the ester type oil in the lubricating oil for a dynamic pressure bearing according to the third aspect, wherein the base oil has a purity of 99% by weight or more, and
The content of carboxylic acid as a synthetic raw material of the base oil is 0.
It is characterized by being 1% by weight or less.

The lubricating oil for a dynamic pressure bearing according to claim 5 of the present invention is the lubricating oil for a dynamic pressure bearing according to any one of claims 1 to 4, in which an additive having an antioxidant function is added to the lubricating oil. It is characterized by

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The lubricating oil for a dynamic pressure bearing of the present invention is a base oil having excellent long-term reliability of evaporation and viscosity change in a test at about 70 to 100 ° C. by controlling the base oil purity. It allows the selection, but does not prescribe the method for producing and refining the base oil. Therefore, the base oil having the corresponding purity may be selected and used at the time of acquisition, or the base oil may be refined as necessary to prepare the base oil having the desired purity.

The purity of the base oil can be measured by using the data if available from the manufacturer. If the data is not available, it can be obtained by requesting an analyst. The analysis is generally carried out using liquid chromatography, gas chromatography or the like.

If the reagent is a general reagent, the lot number is Corresponding to the above, the purity is usually controlled, and it is possible to obtain information on the purity and the amount of impurities contained by requesting. For example, bis (2-ethylhexyl) sebacate (DOS), which is commonly used as a lubricating base oil for dynamic pressure bearings.
About Wako Pure Chemical Industries, Ltd.,
It was possible to know the content of acid (sebacic acid) and the content of water. Further, it was possible to obtain information on purity, total acid value, hydroxide value, water content, and peroxide from ACROS ORGANICS.

However, in the case of a base oil for lubricating oil sold by an oil maker, the purity and details of the components of the base oil are often not disclosed even if they have not been analyzed. In that case, it is possible to know the detailed information of the contained components in the same manner as the disclosure information of the reagent manufacturer by performing the analysis as described above or by asking the analyst.

The following are examples of various embodiments of the present invention using various base oils and adjusted oils.

Example 1 Table 1 shows bis (2-ethylhexyl) sebacate which is one of diester oils.
(DOS) A table summarizing the purity of each of the base oils obtained from a reagent manufacturer or a lubricant manufacturer. DOS is one of the general base oils as a lubricant base oil for bearings, and is easily available because it is also described in the reagent catalog, and it is also available from many lubricant manufacturers, so It is a suitable base oil for comparing the ingredients and the heat resistance quality.

[0024]

[Table 1]

Samples 1 to 6 in Table 1 were put into a test at 100 ° C., and the elapsed time and the evaporation amount were investigated, and the results shown in FIG. 1 were obtained. Sample 1 has evaporated after the test was charged. Samples 2 and 3 were stable with a low evaporation amount at the beginning, but the evaporation of the base oil started at around 500 to 1000 hours. In Sample 4, the increase in the amount of evaporation started after 2000 hours. On the other hand, in Samples 5 and 6, the evaporation amount was 0.5% or less and remained extremely stable even after 10,000 hours.

Regarding the change in viscosity, in Samples 5 and 6, the increase was within 3% after 10,000 hours. In Samples 2, 3 and 4, no change in viscosity was observed when the evaporation amount was stable, but the viscosity increased as the evaporation amount increased. In Sample 1, the viscosity increased as the amount of evaporation increased, and when the amount of evaporation reached 10% or more, the viscosity doubled.

Therefore, if the operating time of the dynamic pressure bearing is short and the temperature is guaranteed to be close to room temperature, a base oil having a purity of about 95% by weight or a base oil having a purity of 98% by weight or more can be used as a lubricating oil. In addition, it is possible to add lubricants such as abrasion resistance and conductivity imparting to the base oil, whose evaporative property and viscosity change are controlled, to prepare a lubricating oil.

Example 2 Regarding Samples 1 to 6, 3 parts by weight of DBPC (2,6-di-tert-butylparacresol) was added as a general antioxidant to 100 parts by weight of the sample. , Sample names are Sample 1A to Sample 6
It was set to A. Measure the change over time in the amount of evaporation at 100 ° C,
The results are shown in Table 2.

[0029]

[Table 2]

Compared to FIG. 1, in Sample 1A, the amount of evaporation tends to be suppressed by adding the antioxidant, but the evaporation cannot be stopped. In Samples 2A and 3A, the evaporation amount could be suppressed to 0.5 to 1%, and the stable state was continued. In Samples 4A to 6A, the amount of evaporation was 0.3% or less and the more stable state was continued. Even when the amount of antioxidant added was increased, the amount of evaporation did not change and the effect was constant. However, if added in an extremely small amount, the effect of the antioxidant stops after a certain period of time, showing the results depending on the vaporization property of the base oil. Further, if the amount added is too large, not only the inherent properties of the base oil such as the viscosity are affected, but also the evaporation property of the antioxidant itself becomes a problem. Therefore, it is desirable that the addition amount of the antioxidant be within the range of 5% by weight or less and the necessary minimum amount.

As a result, if the base oil has a purity of 95% by weight or more, an antioxidant is added to the base oil at 100.degree.
It is possible to suppress the evaporation amount at 000 hours to 1% or less. In recent years, the upper limit of the amount of evaporation has tended to become extremely severe, especially in relation to hard disks, and by adding an antioxidant to base oil with a purity of 98% by weight or more, if necessary, it can be lowered over a longer period of time. It is possible to adjust the evaporative lubricating oil. Even if the lubricant for dynamic pressure bearing of the present embodiment is used by adding additives such as abrasion resistance and conductivity imparting as required, it can be used as a low-evaporative lubricant as well. .

The antioxidant used in the lubricating oil for a dynamic pressure bearing of the present invention can be appropriately selected and used from the additives and the like conventionally used for lubricating oil. A typical example is an antioxidant that functions to terminate a chain reaction, and as a phenolic antioxidant, DBPC (2,6-di-t
ert-butylparacresol), 4,4'methylene (2,6-di-tert-butylphenol), 4,
4 ′ thiobis (6-tert-butyl-o-cresol), 4,4 ′ bis (2,6-di-tert-butylphenol), and amine-based P, P′-dioctyldiphenylamine, phenyl-α-naphthylamine , Phenothiazine and the like. Further, as an antioxidant that functions as a peroxide decomposing agent, sulfur-based sulfurized fats and oils,
Examples include terpene sulfide, dialkyl sulfide, dibenzyl disulfide and sulfur / phosphorus compounds. However, when the dynamic pressure bearing is used for a hard disk, it is desirable to confirm the evaporating property of the additive because the additive also affects a small amount of outgas.

(Example 3) In DOS, the base oil component contains a small amount of the synthetic raw material sebacic acid, and generally, the higher the purity, the smaller the sebacic acid content. . An antioxidant was added to the base oil of which the purity and the content of sebacic acid were known, and the change with time of the evaporation amount at 100 ° C. was measured. As the antioxidant, 3 parts by weight of the antioxidant DBPC was added to 100 parts by weight of the base oil.

[0034]

[Table 3]

From the results shown in Table 3, it is found that high purity products having a purity of 99% by weight or more and sebacic acid 0.1% by weight or less have a purity of 10%.
Even after 000 hours, the amount of evaporation is 0.1% or less, and it is possible to meet the demand for a product with a lower amount of evaporation.

Not only DOS but also diester base oils use dicarboxylic acid as a synthetic raw material. The acid generated by the dissociation of the dicarboxylic acid causes oxidative deterioration. Therefore, it is possible to use a higher quality base oil by controlling not only the purity but also a small amount of the raw material acid component contained. Further, this tendency is applicable not only to the diester type, but also to the monoester and the polyol ester.

The polyol ester is synthesized by reacting a polyhydric alcohol having a carbon skeleton of neopentane such as neopentyl glycol, trimethylolpropane, pentaerythritol or dipentaerythritol with a fatty acid. Even after refining, the base oil contains a trace amount of fatty acid, and the acid generated from the fatty acid causes deterioration of the base oil. Therefore, in the ester-based base oil, it is possible to select and use a high-quality base oil having excellent long-term reliability by controlling the purity of the base oil and the content rate of the raw material carboxylic acid.

Example 4 In this example, various polyol esters were used in order to confirm the application of the present invention to other ester oils. In the case of a polyol ester, a mixed fatty acid, for example, a mixed fatty acid such as capric acid or caprylic acid may be used as a raw material. In that case, there are multiple types of synthesized esters, but by managing the amount of all types of esters that can be synthesized from polyhydric alcohols and mixed fatty acids as purity,
Similarly, the relationship between purity and evaporative property could be obtained. With respect to the following samples, changes with time of the evaporation amount at 100 ° C. were measured and shown in FIG.

Sample 12: A polyol ester base oil synthesized from neopentyl glycol and a mixed fatty acid having 8 to 10 carbon atoms. Purity 98.2% by weight. Sample 13: A polyol ester base oil synthesized from trimethylolpropane and a mixed fatty acid having 8 to 10 carbon atoms. Purity 99.2% by weight. Sample 14: A polyol ester base oil synthesized from trimethylolpropane and a mixed fatty acid having 8 to 10 carbon atoms. Purity 96.3% by weight. Sample 15; polyol ester base oil synthesized from trimethylolpropane and pelargonic acid. Purity 95.4% by weight.

From FIG. 2, it can be seen that Sample 14 and Sample 15 having a purity of 95% by weight to 98% by weight start to evaporate in 500 to 1000 hours, and have the same tendency as in Example 1, Sample 2 and Sample 3 in FIG. there were. Sample 12 having a purity of 98.2% by weight is 30
There was evaporation after 00 hours, and the tendency was similar to that of the sample 4 in Example 1 and FIG. In addition, the highest purity sample 13
The amount of evaporation was 0.5% or less after 10,000 hours, showing the same tendency as Sample 5 and Sample 6 in FIG.

As described above, the long-term reliability of heat resistance of all ester base oils can be grasped by controlling the purity. When an antioxidant was added to Samples 12 to 14, the same tendency of evaporation as in Example 2 was exhibited, and although it is not shown in the figure or table, it was a base oil with a purity of 99% by weight or more, If the content is 0.1% or less, the same tendency as in Example 3 can be obtained. INDUSTRIAL APPLICABILITY The present invention is applicable to all ester systems, and it is also possible to mix and use a plurality of types of base oils whose purity is controlled in order to adjust the viscosity and the viscosity index as necessary.

Further, according to the lubricant for a dynamic pressure bearing of the present invention, the purity control of the base oil is applied to the base oil such as poly-α-olefin type, polyglycol type, polyphenyl ether type and fluorine type oil. Even in such a case, it is possible to obtain the same effect, and it is also possible to obtain reliability for a longer period by adding an antioxidant. Further, it is clear that controlling the content of the acidic substance in each base oil synthesis raw material enhances reliability.

[0043]

As is apparent from the above embodiments,
According to the lubricating oil for a dynamic pressure bearing of the present invention, the purity is 95% by weight.
By controlling the amount above or 98% by weight or more, it becomes possible to select a base oil having excellent long-term reliability of heat resistance. Further, by adding an additive having an antioxidant function to a base oil having a purity of 95% by weight or more, it becomes possible to suppress the evaporation amount and the viscosity change in the heat resistance long-term reliability test to be small.

Further, in the ester base oil, the carboxylic acid content of the base oil raw material which is contained together with the purity of 99% by weight or more is controlled to be 0.1% by weight or less, whereby the long-term reliability of heat resistance is excellent. It became possible to select a base oil.

Therefore, in the present invention, as a method for selecting a lubricating oil for a dynamic pressure bearing having a low evaporation amount and a small viscosity change in a long-term reliability test at around 70 ° C. to 100 ° C., it is used by controlling the initial base oil purity. The available base oil was selected and the lubricating oil could be adjusted. As a result, the cost and test time required for selecting the base oil and the lubricating oil can be significantly reduced, and moreover, it is possible to reliably select the base oil.

[Brief description of drawings]

FIG. 1 is a diagram showing a comparison of evaporative properties of base oils used in the lubricating oil for a dynamic pressure bearing of the present invention.

FIG. 2 is a diagram showing a comparison of evaporative properties of base oil used in the lubricating oil for a dynamic pressure bearing of the present invention.

[Fig. 3] Lubricating base oil (DO
The figure of S) evaporative comparison.

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Claims (5)

[Claims] 1. A base oil having a purity of 95% by weight or more, or
A lubricating oil for a dynamic pressure bearing, characterized by using a mixed base oil having a purity of 95% by weight or more. 2. The lubricating oil for a dynamic pressure bearing is more preferably a base oil having a purity of 98% by weight or more, or a purity of 9%.
The lubricating oil for dynamic pressure bearings according to claim 1, wherein a mixed base oil of 8% by weight or more is used. 3. The hydrodynamic bearing lubricating oil according to claim 1, wherein the base oil is an ester oil, or at least one of the base oils is an ester oil. Lubricating oil. 4. The ester oil in the dynamic pressure bearing lubricating oil according to claim 3, wherein the base oil has a purity of 99% by weight or more, and the content of carboxylic acid as a synthetic raw material of the base oil is in the base oil. Lubricating oil for hydrodynamic bearings, characterized in that it is 0.1% by weight or less. 5. The lubricating oil for a dynamic pressure bearing according to any one of claims 1 to 4, wherein an additive having an antioxidant function is added to the lubricating oil.