JPH08259977A - Lubricating fluid composition for dynamic pressure bearing - Google Patents

Abstract

PURPOSE: To obtain a lubricating fluid compsn. which is used for a dynamic pressure bearing and excellent in lubricity, sealing properties, and reliability of life by using a specific dialkyl carbonate as the base oil solvent. CONSTITUTION: This compsn., used for lubricating a dynamic pressure bearing which supports a shaft by dynamic pressure, is prepd. by dispersing magnetic particles in a base oil solvent contg. a dialkyl carbonate represented by the fromula: ROCOOR (wherein R is 5-20C alkyl). The base oil solvent is prepd. by mixing the carbonate with a hydrogenated α-olefin. If necessary the compsn. further contains a gelation inhibitor (e. g. an antioxidant), a viscosity index improver, a metal deactivator, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lubricating fluid composition for a dynamic pressure bearing, which is used as a lubricating fluid for a dynamic pressure bearing that supports a shaft by dynamic pressure and uses its magnetic characteristics for a sealing action. .

[0002]

2. Description of the Related Art In recent years, a dynamic pressure bearing using a magnetic lubricating fluid has been proposed for various devices, particularly for devices such as a motor for driving various rotary plates such as a polygon mirror, a magnetic disk and an optical disk at high speed. . That is, a magnetic fluid is a colloidal solution in which ferromagnetic fine particles are stably dispersed in a liquid dispersion solvent, and because the liquid itself has apparently strong magnetism, it is usually used as a sealing in combination with a ball bearing. However, a dynamic pressure bearing using a magnetic lubricating fluid is considered to be promising because it is superior to the ball bearing in high-speed rotation stability and quietness. The proposal of a dynamic pressure bearing using a magnetic fluid has been made under such a background, for example, Japanese Patent Laid-Open No. 60-88223.
The publication discloses a device in which one fluid is used as both a lubricating fluid for generating a dynamic pressure and a magnetic fluid for magnetic sealing.

However, in such a device,
The magnetic fluid composition is required to have both a low evaporation property as a seal and a low viscosity property for reducing a bearing loss. Therefore, it is necessary to actually obtain a characteristic of the magnetic fluid composition that can be adapted to it. The current situation is that it is not possible. That is, the bearing portion receives a much larger shearing force than the seal portion and is exposed to a high temperature, and at the time of starting and stopping, the metals may come into contact with each other and wear to contact the active metal surface.
Although the magnetic fluid composition is used with the greatest advantage that "high airtightness can be obtained even at high speed (-10-6 Toor)", it functions as a lubricating fluid (low wear characteristics) and life characteristics (low wear characteristics). Those having both sufficient evaporating property and high temperature resistance) have not yet been developed (from PETROTECH Vol. 13, No. 12 (1989)). As described above, there is a demand for a lubricating fluid composition for a dynamic pressure bearing that covers not only the sealing property but also the lubricity and life characteristics.

[0004]

More specifically, the characteristics that the lubricating fluid composition should have in order to use both the lubricating fluid for generating dynamic pressure and the fluid for magnetic sealing as one fluid are as follows: 1) It has a low viscosity of 100 CP or less (27 ° C.), 2) it has a saturation magnetization of 50 Gauss or more, 3) it has a low evaporation property that can maintain the sealing property, and 4) there is no high temperature gelation or oxidation. In addition, it has stability that can suppress it, 5) suppresses the activity of metal generated by contact and wear, etc., but a magnetic fluid satisfying such good characteristics has not yet been obtained. . Above all, like 4) above,
The phenomenon of so-called gelation, in which fluidity is lost as a life characteristic of the magnetic lubricating fluid, is particularly likely to occur during high temperature use, and has become an important issue to be solved.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a lubricating fluid composition for a dynamic pressure bearing, which satisfies the above-mentioned respective characteristics and has lubricity, sealability and life reliability.

[0006]

In order to achieve the above object, the dynamic pressure bearing lubricating fluid composition according to claim 1 is a fluid in which magnetic fine particles are dispersed in a base oil solvent, wherein the base oil solvent is: Carbonic acid dialkyl ester (ROCOOR)
[R is a C5 to C20 alkyl group].

The carbonic acid dialkyl ester (ROCOO
Examples of R) include dimethyl carbonate [(CH
₃ O) ₂ CO] and C5 to C20 monohydric alcohol (RO
Those obtained by transesterification with H) are adopted. The viscosity characteristics are 6.3 to 17.5 cst (40
C.) (manufactured by Mitex Co., Ltd .; trade name DIALCARB H2, DIALCARB SR10)
00 / R, etc. is adopted, but it is necessary to have good evaporation property.

The invention according to claim 2 is the above-mentioned claim 1.
Carbonic acid dialkyl ester of the invention according to (ROCOO
R) is mixed with a poly-α-olefin hydride. This poly-α-olefin hydride can be obtained, for example, by hydrogenating a polymer obtained by polymerizing 1-decene, isobutylene or the like with a Lewis acid or the like. These have a number average molecular weight of 200 to 1600.
Some have a number average molecular weight of 400 due to evaporation characteristics.
Something is preferable. Although the hydrogenation does not have to be performed completely, it is likely to deteriorate when the degree of hydrogenation is low.

Further, the invention according to claim 3 is configured such that an anti-gelling agent is added to the base oil solvent according to claim 1 or 2.

As the gelling inhibitor, for example, an antioxidant is used as in claim 4, and in the case of the antioxidant, a phenol type, amine type or peroxide which functions as a free radical chain reaction terminator is used. One or more antioxidants selected from the group consisting of sulfur-based antioxidants that act as decomposers can be used as a mixture, and amine-based and phenol-based antioxidants are preferably used in combination. It is preferable. Considering the solubility in the base oil solvent, etc., the compounding amount thereof is preferably 1 to 10 parts by weight of the amine-based antioxidant and 1 to 10 parts by weight of the phenol-based antioxidant with respect to 100 parts by weight of the base oil solvent. When used alone, 1 to 10 parts by weight of amine antioxidant is suitable. Phenolic antioxidants are effective only when used in combination.

As the phenolic antioxidant,
2,6-di-t-butyl-phenol (trade name; ethyl 701, Irganox L108 etc.), 4,4'-methylenebis (2,6-di-t-butyl-phenol) (trade name; ethyl 702, Irganox L109 etc.),
2,6-di-t-butyl-4-ethylphenol (trade name: ethyl 724, etc.) and 2,6-di-t-4-n-butylphenol (trade name: ethyl 744, etc.) are adopted. . From the viewpoint of evaporation characteristics and compatibility with the base material,
4,4'-methylenebis (2,6-di-t-butylphenol) is preferred.

Alkyldiphenylamine (trade name; Irganox L01,
L57, L06 etc.) and phenyl-α-naphthylamine (trade name; Irganox L05 etc.) are adopted. From the viewpoint of evaporation properties and compatibility with the base material, alkyldiphenylamine is preferable.

Furthermore, the invention of claim 5 is such that a viscosity temperature index improver is added to the base oil solvent according to claim 1 or claim 2.

As the viscosity temperature index improver, there is a polymethacrylate type compound having the following composition.

Embedded image The average molecular weight of this product is 20,000-1,500,
However, in view of the relationship between the effect of improving the viscosity index and the shear stability, those having an average molecular weight of 20,000 to 50,000 are preferable. In addition, since these polymers are difficult to handle in manufacturing and compounding, generally,
Although dilution is carried out with a low-viscosity mineral oil, poly-α-olefin hydride is preferably used as a diluent because low-viscosity mineral oil has problems in evaporability and dispersion stability.

Further, as the viscosity temperature index improver,
There is a polybutene type (polyisobutylene type) having the following composition.

Embedded image Although the average molecular weight of this product is 5,000 to 300,000, it is preferable to use a poly-α-olefin hydride as the diluent for the same reason as above.

On the other hand, the invention of claim 6 is such that a metal deactivator is added to the fluid according to claim 1 or claim 2.

Typical examples of the metal deactivator are benzotriazole and its derivatives, but there are also imidazoline and pyrimidine derivatives. Many of these are effective in compounds having at least an N-CN bond, and have an action of forming an inactive film on the metal surface and an antioxidant action.

Other than this, there are compounds having an N—C—S bond, but from the viewpoint of solubility and volatility in a substrate, a benzotriazole derivative (for example, Rhemet 3).
8, 39, SBT) is used.

In the present invention, the total compounding ratio is 40 to 50 parts by weight of carbonic acid dialkyl ester, 10 to 30 parts by weight of poly-α-olefin hydride, and 10 to 20 of antioxidant.
Parts by weight, 10 to 20 parts by weight of metal deactivator, magnetic fine particles 2
It is preferable that the range is 5 to 35 parts by weight, and the viscosity is 100.
The saturation magnetization is preferably cp or less and 150 Gauss or more. When the amount of magnetic fine particles is 25 parts by weight or less, it is less than 150 gauss, and when it is 35 parts by weight or more, it affects thickening.

[0020]

According to the means according to the inventions of claims 1 and 2, a base oil satisfying physical properties such as viscosity, evaporation and high temperature gelation can be obtained. As in the invention of No. 6, by adding an anti-gelling agent (antioxidant), a viscosity temperature index improver, and a metal deactivator, particularly the high temperature gelling property and the viscosity property are further improved.

[0021]

Embodiments of the present invention will be described below. In each example of the present invention, Mn-Zn ferrite obtained by the coprecipitation method was used as the magnetic fine particles. Manganese sulfate 0.1 mol, zinc sulfate 0.4 mol, ferric sulfate 0.
Dissolve 5 mol in 1 liter of water and adjust the temperature of this water-soluble liquid to 90
While maintaining the temperature at ℃ and stirring, 6N sodium hydroxide was added dropwise to adjust the pH of the aqueous solution to 11 to generate a colloid of Mn-Zn ferrite. After cooling the solution to room temperature with the addition of 250 ml of a 10% solution of sodium acidate, 3
An aqueous hydrochloric acid solution of N was added to adjust the pH to 6. The aggregated colloidal particles were thoroughly washed with water and further dehydrated and dried to obtain Mn-Zn ferrite fine particles coated with oleic acid.

Then, the Mn coated with the above-mentioned oleic acid was used.
Taking 14.8 g of Zn ferrite, adding 15 g of the following base oil solvent and thoroughly stirring to disperse, then remove the undispersed substance by centrifugation, and further add base oil to a specific gravity of 1.16. In addition, a fluid was obtained. The thus obtained fluid had a ferrite concentration of 35 wt% and a saturation magnetization of 250 gauss.

Further, Mn-Zn as the above magnetic fine particles
As a base oil solvent for dispersing ferrite, poly-α-olefin hydride [C30 to C40] (Shinflude 401 manufactured by Nippon Steel Chemical Co., Ltd.), carbonic acid dialkyl ester (ROCOOR) [R is C5 to C20. Alkyl group] (Mitsui Petrochemical Co., Ltd .; DIALCARBS
R1000 / R), diisodecyl adipate oil (manufactured by Nippon Steel Chemical Co., Ltd .; HATCOL 2910), trioctyl ester trimellitic acid oil (manufactured by Nippon Steel Chemical Co., Ltd.);
HATCOL2920) with a mixture of antioxidants (alkyldiphenylamine / trade name; Irganox L5)
7), a viscosity index improver (manufactured by OSWARD BOLL;
OLICAT-M) and a metal deactivator (manufactured by Ciba-Geigy; Rheomet 39) were used. Then, the ratio of each element in this base oil solvent was variously changed as shown in Table 1 below to obtain Examples 1 to 5 and Comparative Example 1.
Each of the lubricating fluid compositions of ~ 4 was made.

[0024]

[Table 1] It should be noted that “Bal” in Table 1 represents that all the rest other than the numerically displayed ones are themselves.

Each of the obtained lubricating fluid compositions was put in a petri dish and the dispersion stability of the magnetic fine particles was evaluated by confirming the appearance such as precipitation, aggregation, separation, etc., and at a temperature of 80 ° C./520.
The evaporation amount was compared by the weight reduction in time, and further the gelling time when the temperature was left at 140 ° C. was compared. Regarding the viscosity, the viscosity at 25 ° C. and the viscosity temperature index were compared. Table 2 shows the evaluation results.

[0026]

[Table 2] In Table 2, in each of the samples of Examples 1 and 2 of the present invention, the properties of dispersion stability, viscosity, evaporation amount, viscosity temperature index and high temperature gelation time all show preferable values, and particularly dialkyl carbonates are used. It was found that the increased amount of the sample according to Example 1 had a very high high-temperature gelation time, and thus was excellent in high-temperature stability.

On the other hand, in Comparative Examples 1 and 2 in which the amount of the other ester was increased without using the carbonic acid dialkyl ester, the magnetic fine particles could not be dispersed. Similarly, in Comparative Examples 3 and 4 in which the amount of the other ester was reduced and the poly-α-olefin hydride was mixed without using the carbonic acid dialkyl ester, the viscosity and the evaporation amount of the poly-α-olefin that became dispersible were changed. The characteristics became poor.

Further, in the sample according to Example 3 in which the metal deactivator was removed from the sample of Example 1 described above, each property also showed good values, but the high temperature gelation time was slightly decreased. Therefore, it was revealed that the addition of the metal deactivator makes it possible to prolong the high temperature gelation time.

The samples according to Example 4 in which the viscosity temperature index improver was removed from the samples of Example 3 also showed good values for each property, but of course, the viscosity properties slightly decreased. Therefore, it was found that the viscosity characteristics can be improved by adding the viscosity temperature index improver.

On the other hand, the sample according to Example 5 in which the antioxidant was removed from the sample of Example 4 showed relatively good values, but the high-temperature gelation time was considerably reduced. From this, it was found that the addition of the antioxidant can significantly extend the high temperature gelation time.

Although the invention made according to the present invention has been specifically described based on the embodiments, the present invention is not limited to the above, and various modifications can be made without departing from the scope of the invention. There is no end. For example, as the magnetic fine particles, Ni-Zn ferrite or magnetite can be used similarly in addition to Mn-Zn ferrite.
Further, as the surfactant, any other higher fatty acid can be adopted. Further, as the gelling agent, for example, amine-based, phenol-based, or sulfur-based ones other than the antioxidant can be similarly employed.

[0032]

As described above, the first and second aspects are provided.
The lubricating fluid composition according to the invention of claim 1 uses a base oil solvent containing carbonic acid dialkyl ester (ROCOOR) [R is a C5 to C20 alkyl group],
Since it has improved physical properties such as evaporation and high temperature gelation, good properties can be obtained with a simple structure. In particular, a lubricating fluid for dynamic pressure generation and a fluid for magnetic sealing are one fluid. It is possible to improve the feasibility and reliability of the dynamic pressure bearing which is also used in the above.

Further, as in the inventions of claims 3 to 6, by adding an anti-gelling agent, a viscosity temperature index improver, and a metal deactivator, the characteristics such as viscosity and high temperature gelation are further improved. Therefore, it is possible to further improve the feasibility and reliability of the dynamic pressure bearing.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshihiro Kobayashi 5329 Shimosuwa-cho, Suwa-gun, Nagano Sankyo Seiki Co., Ltd. (72) Inventor Kazuya Shimizu 9 Kirihara-cho, Fujisawa-shi, Kanagawa Taiho Industrial Co., Ltd. Central Research Institute (72) Inventor Yusuke Matsumura 2-21-44, Takanawa, Minato-ku, Tokyo Taiho Kogyo Co., Ltd. (72) Inventor Masuhiro Onoyama 997-10 Higashi Ohtake, Isehara City, Kanagawa Prefecture (72) Inventor Katsumi Nagano Aichi Prefecture 12 4-4-4 Azajigaoka, Chita-shi

Claims (6)

[Claims] 1. A lubricating fluid composition for a dynamic pressure bearing, which is used as a lubricating fluid for a dynamic pressure bearing that supports a shaft by dynamic pressure, wherein magnetic particles are dispersed in a base oil solvent. The oil solvent is carbonic acid dialkyl ester (ROCO
OR) [R is an alkyl group of C5 to C20], and a lubricating fluid composition for a dynamic pressure bearing. 2. The base oil solvent includes carbonic acid dialkyl ester (ROCOOR) and poly-α-olefin hydride (P
AO) is mixed, and the lubricating fluid composition for dynamic pressure bearings according to claim 1. 3. A lubricating fluid composition for a dynamic pressure bearing according to claim 1, wherein a gelling inhibitor is added in a predetermined amount. 4. A lubricating fluid composition for a dynamic pressure bearing, wherein the anti-gelling agent according to claim 3 is an antioxidant. 5. The lubricating fluid composition for a dynamic pressure bearing according to claim 1, wherein a predetermined amount of a viscosity index improver is added. 6. The lubricating fluid composition for a pressure bearing according to claim 1, wherein the metal deactivator is added in a predetermined amount.