JP2001172656A - Lubricating oil composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a lubricating oil composition of high lubricity excellent in evaporation characteristics, high in rust prevention, wide in service temperature range and having long service life. SOLUTION: This lubricating oil composition is obtained by incorporating, as base oil, a mixed oil comprising poly-α-olefin hydrides which is predominant in 20-36C fraction and contains <0.1 wt.% of <=12C fraction and an ester in the weight ratio of (95:5) to (50:50) with, as a thickening agent, a polymer >=10 cst in dynamic viscosity at 40 deg.C selected from poly-α-olefin hydrides, ethylene-α- olefin copolymer hydrides and polymethacrylate. By the way, this composition may be formulated with such additive(s) as bodying agent, anti-abrasive agent, metal deactivator, antirust agent, evaporation inhibitor and/or antioxidant. This lubricating oil composition is suitable for spindle motor sliding bearings.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a sintered oil-impregnated bearing having a self-lubricating function by impregnating a porous body made of sintered metal or the like with lubricating oil or lubricating grease, or provided on a bearing surface. The present invention relates to a lubricating oil composition used for a hydrodynamic type porous oil-impregnated bearing or the like in which a sliding surface of a rotating shaft is levitated and supported by a lubricating oil film formed by a dynamic pressure effect of a dynamic pressure groove, and particularly to a polygon of a laser beam printer (LBP). Models such as scanner motors and spindle motors for magnetic disk drive devices (HDD) that require high rotational accuracy at high speed, optical disk devices such as DVD-ROM and DVD-RAM, and magneto-optical disk devices such as MO Such as spindle motors used for high-speed driving under conditions where a large unbalance load is applied by the loading of a disk. A lubricating oil composition for use in the bearing or the like.

[0002]

2. Description of the Related Art In such small spindle motors related to information equipment, further improvement in rotational performance and reduction in cost are required, and as a means for this, the bearing portion of the spindle is moved from a rolling bearing to a porous one. Replacement with oil-impregnated bearings, especially sintered oil-impregnated bearings, is being considered. But,
Because ordinary sintered oil-impregnated bearings are a type of perfect circular bearing, unstable vibration is likely to occur where the shaft eccentricity is small,
There is a drawback that so-called whirling, which oscillates at half the rotation speed, is likely to occur. When unstable vibration occurs, the rotational accuracy is impaired.Therefore, a dynamic pressure groove such as a herringbone type or spiral type is provided on the bearing surface to improve the bearing function such as radial rigidity by the dynamic pressure effect accompanying the rotation of the shaft, Attempts have been made to eliminate unstable vibrations. This is called a dynamic pressure type porous oil-impregnated bearing.

On the other hand, as an impregnating oil for a sintered oil-impregnated bearing, the generation of sludge during use is small, the operating temperature range is wide,
Because of its excellent lubricity and long life, for example, poly-α as disclosed in Japanese Patent Application Laid-open No.
-A mixture of olefin-based synthetic lubricating oil and various additives is used. This lubricating oil is a special impregnating oil for sintered oil-impregnated bearings and has excellent characteristics such as low initial torque and good durability and good durability. (Lubricity, high temperature stability,
Oxidation stability, low torque, metal resistance, resin resistance, etc.) could not be satisfied.

In recent years, compatibility with sintered materials and rubber or plastic materials used in the periphery thereof has been required, and the demand for impregnated bearing oils has been increasing. In particular, when driving at a high speed of tens of thousands of revolutions such as a polygon scanner motor of a laser beam printer (LBP), a low torque is required. Therefore, a lubricant having a low viscosity is used. The olefinic synthetic lubricating oil has a large evaporation amount, and this tendency is remarkable in a low-viscosity oil containing C10, and a long-term durability life cannot be satisfied in a high-speed and high-temperature atmosphere.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lubricating oil composition for improving lubrication, thermal / oxidative stability and rotational performance of an industrially used impregnated bearing and extending the life of the bearing. Is to provide.

[0006]

According to the present invention, a poly-α-olefin hydride containing not more than 0.1% by weight of C12 or less and having a main component of C20-36 and an ester in a weight ratio of 95: 5. To 50:50 as a base oil, and as a thickener, a kinematic viscosity at 40 ° C. of 1
A lubricating oil composition comprising a polymer selected from a hydride of poly-α-olefin of 0 cSt or more, a hydride of ethylene-α-olefin copolymer, and polymethacrylate. Here, the ester is preferably a diester or a polyol ester. Also, the present invention is a thickener, antiwear agent,
The above lubricating oil composition comprising one or more additives selected from the group consisting of a metal deactivator, a rust inhibitor, an evaporation inhibitor and an antioxidant. Further, the present invention is a lubricating oil composition used for a plain bearing of a spindle motor.

First, the poly-α-olefin hydride (hereinafter abbreviated as PAO) used as a component of the base oil used in the present invention has an average molecular weight of 250 to 500, preferably 28.
0 to 350, and is generally obtained by hydrogenating a polymer obtained by polymerizing an α-olefin such as decene-1 or dodecene-1 with a Lewis acid complex or an aluminum oxide catalyst. Since the PAO used in the present invention is made from 1-dodecene or dodecene-1, etc., it can be a low-viscosity oil having C20 to C36 as a main component, containing almost no C12 or less, and having excellent evaporability. .

Esters which are components of another base oil include a monoester (an ester of a monohydric alcohol and a monohydric fatty acid), a diester (an ester of a monohydric alcohol and a dihydric fatty acid), and a polyol ester (having a neopentyl skeleton). Ester of alcohol and monovalent fatty acid), complex ester (oligomer ester obtained by adding polyol and using polyol as raw material to crosslink polyol)
Any known ester-based synthetic lubricating oils may be used, but a diester such as a polyol ester or dioctyl sebacate having excellent compatibility, low viscosity and excellent evaporation characteristics is preferable. .
By using an ester, the solubility which is a drawback of PAO can be overcome, and the evaporation characteristics, lubricity, and whirl can be improved. The generation of whirl is considered to be because the generation of bubbles from the poly-α-olefin is suppressed by mixing the ester-based synthetic lubricating oil, or the bubbles disappear immediately after they are generated. The mixing amount of the ester-based synthetic lubricating oil is desirably 5% by weight or more. If the content is less than 5% by weight, generation of whirl cannot be completely prevented. The upper limit is about 50% by weight.

Examples of the thickener used in the present invention include ethylene-α-olefin copolymers, hydrides thereof, and polymethacrylate polymers. The ethylene-α-olefin copolymer or its hydride is
For example, it can be obtained by hydrogenating a polymer obtained by polymerizing ethylene, 1-decene, isobutene and the like with a catalyst such as a Lewis acid. These have a number average molecular weight (GPC method) of 5
Some have a number average molecular weight of 1,
450 or more are preferred. The average molecular weight of the polymethacrylate is about 20,000 to 1,500,000. The average molecular weight is 20,0 from the relation with the shear stability.
00 to 50,000 is preferred. The average molecular weight of the polybutene is preferably about 5,000 to 300,000.
The thickener used in the present invention has a kinematic viscosity at 40 ° C. of 1
It is necessary to be 0 cSt or more, and the compounding ratio is in the range of 1 to 30% by weight, preferably 1 to 5% by weight based on the base oil. By using such a thickener, lubricating oil accumulated in a space functioning as an oil retaining portion from the upper portion of the bearing can be sent to the upper portion again by its unique Weissenberg effect.

The lubricating oil composition of the present invention may be any one as long as it contains at least the above-mentioned thickener in a base oil comprising PAO and ester, and may further contain various additives.
Suitable additives include one or more additives selected from the group consisting of thickeners, antiwear agents, metal deactivators, rust inhibitors, evaporation inhibitors and antioxidants.

As the antiwear agent, known ones can be used, but those having excellent wear resistance and thermal stability are preferable, and (RO) ₃ PO (where R may be the same or different) A hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an alkylene group or an alkoxy-substituted alkyl group, or a carbon atom having 6 to 12 carbon atoms;
Shows 12 aryl or alkyl-substituted aryl groups, but not all R may be hydrogen atoms. It is preferable to mix the phosphate represented by the formula (1). Examples of the phosphate include acid phosphates such as triester phosphate such as trioctyl phosphate and tricresyl phosphate, monooctyl phosphate, and dioctyl phosphate; and amine salts of alkyl phosphate esters (partially amine salts). ), Phosphite, and the like, with preference given to phosphoric acid triester. By using an antiwear agent such as a phosphate ester, the ability to form an oil film can be increased. When a phosphate ester is used as the antiwear agent, its compounding ratio with respect to the base oil is 0.1 to 10% by weight, preferably 0.5 to 3% by weight.
It is. If this compounding ratio is less than 0.1% by weight, the wear resistance cannot be improved, and even if it is added in excess of 10% by weight, no significant improvement in the wear resistance ability is observed.

The lubricating oil composition of the present invention may be grease. In this case, the thickening agent used may be either a soap-based or non-soap-based thickener. It is preferable to use an agent. Since urea has a strong interaction force between molecules, it has excellent shear stability and is easily adsorbed on a metal surface, and has an effect of enhancing a lubricating effect. The urea compound is represented by —NHCON
It has H- and includes, for example, monourea, diurea, and triurea. Monourea is obtained by the reaction of monoamine and monoisocyanate, diurea is obtained by the reaction of monoamine and diisocyanate, and triurea is obtained by the reaction of monoamine, tolylene diisocyanate and water. Among the urea compounds, diurea represented by the following formula is preferred from the viewpoint of availability of raw materials and productivity. R ₁ -NHCONH-R ₂ -NHCONH-R ₃ (however,
R _{1 to} R ₃ represent a hydrocarbon group. )

R ₁ and R ₃ of the urea compound represented by the above formula
0-100 mol% of aromatic hydrocarbon group
The micelle structure can be freely changed by adjusting between the values. In the case of dynamic pressure type porous bearings, it was mentioned earlier that pressure drop and heat generation can be suppressed by adjusting the porosity, etc. In order to obtain it, if the micelle structure of the lubricating grease can be freely changed, the durability can be further improved. In order to suppress shaft runout and oil leakage, it is possible to respond by increasing the proportion of aromatic hydrocarbon groups in R ₁ and R ₃ . The higher the proportion of aromatic hydrocarbon groups, the thicker and shorter the urea micelles. Therefore, compared with other thickeners having the same viscosity, the amount of the thickener is increased, and shaft runout and durability can be improved. On the other hand, when low current performance is required, short fiber / thick micelles have an adverse effect and may cause heat generation. In such a case, the amount of the thickener can be reduced by reducing the molar percentage of the aromatic hydrocarbon groups of R ₁ and R ₃ , so that it is possible to cope with a lower current value. Therefore, by using the urea compound for the dynamic pressure-type porous grease bearing, a wide range of required performance can be satisfied. Further, needless to say, the aromatic hydrocarbon groups contained in R ₁ and R ₃ can be adjusted according to the use in which the dynamic pressure-type porous grease bearing is used.

The urea compound is obtained by a reaction between an isocyanate and a monoamine. Examples of the isocyanate used include 2,4-tolylene diisocyanate and
2,6-tolylene diisocyanate, diphenylmethane-4,4'-diisocyanate, naphthylene-1,5-
Examples include aromatic diisocyanates such as diisocyanate, tolylene diisocyanate, triazine-derived groups, and mixtures thereof. Monoamines include aromatic amines such as aniline, benzylamine, toluidine, and chloroaniline, and octylamine, nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine, tetradecylamine, pentadecylamine, and hexadecylamine. And aliphatic amines such as heptadecylamine, octadecylamine, nonadecylamine and eicodecylamine, and cyclohexylamine.

The rust preventive used in the present invention may be any one known as a rust preventive, but a carboxylate is preferred.
Although there is no particular limitation, an ester of an aliphatic carboxylic acid having an amino group is preferable. For example, aminosuccinates and derivatives thereof are suitable. This carboxylic acid ester exhibits sufficient rust prevention without inhibiting the wear resistance of the lubricating oil. Other rust preventives include zinc organic sulfonates and the like, for example, zinc dinonylnaphthalenesulfonate is preferred. When using a rust inhibitor, a carrier may be used, but if mineral oil is used as the carrier, a large amount of sludge is generated or the lubricating performance is reduced.In the present invention, a poly-α-olefin is used as the carrier. Good. As a specific rust inhibitor, NA-SU manufactured by King Industries Co., Ltd.
LZS / PAO and the like. The amount of the rust inhibitor added to the base oil is 0.01 to 3.0% by weight, preferably 0.01 to 0.1% by weight. The amount of rust inhibitor added is 0.
If less than 01% by weight, there is no rust-preventive effect and 3.0% by weight
Exceeding the range causes turbidity and poor quality.

The lubricating oil composition of the present invention may contain a metal deactivator. Representative examples of the metal deactivator include benzotriazole and its derivatives, and other examples include imidazoline and pyridine derivatives. Many of these compounds are effective at least in compounds having an N—C—N bond, and have an effect of forming an inert film on the metal surface and an antioxidant effect. Otherwise, N-
Some compounds have a CS bond, but benzotriazole derivatives are effective because of their solubility in base oil and volatility. The mixing ratio of the metal deactivator is preferably in the range of 0.01 to 5% by weight based on the base oil.

Further, an antioxidant can be added to the lubricating oil composition of the present invention. As the antioxidant, one or two or more antioxidants selected from the group consisting of phenol-based, amine-based, and sulfur-based antioxidants that act as peroxide decomposers that act as free-radical chain reaction terminators are used alone. Alternatively, they can be used as a mixture, but it is preferable to use an amine type and a phenol type together as a suitable antioxidant. Examples of phenolic antioxidants include 2,6-di-t-butylphenol, 4,4′-methylenebis (2,6-di-t-butylphenol), 2,6
-Di-t-butyl-4-ethylphenol and 2,6-di-t-butyl-4-n-butylphenol.
4,4′-methylenebis (2,6-di-t-butylphenol) is preferred from the viewpoint of evaporation characteristics and compatibility with the base oil. In addition, as amine-based antioxidants, p, p'-
Dioctyl diphenylamine and phenyl-α-naphthylamine are exemplified. The antioxidant preferably has a function as an evaporation inhibitor, and p, p'-dioctyldiphenylamine is preferred from the viewpoint of its evaporation characteristics and compatibility with the base oil. The compounding amount is 0.1 to 5% by weight of the amine-based antioxidant and 0.1 to 5% by weight of the phenol-based antioxidant with respect to the base oil in consideration of the solubility in the base oil.
% By weight is preferred. When used alone, the amine-based antioxidant is preferably 0.1 to 5% by weight.

The lubricating oil composition of the present invention may further contain, if necessary, other various additives in addition to the above-mentioned additives. For example, the lubricating oil composition of the present invention may contain a pour point depressant, an ashless dispersant, a metal detergent, an oily agent, and a surfactant, as long as the object of the present invention is not impaired. , An antifoaming agent, a friction modifier and the like can be blended according to the application.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The lubricating oil composition of the present invention is a sintered oil-impregnated bearing having a self-lubricating function obtained by impregnating a porous body made of a sintered metal or the like with lubricating oil or lubricating grease, It can be suitably used for a dynamic pressure type porous oil-impregnated bearing that floats and supports a sliding surface of a rotating shaft by a lubricating oil film formed by a dynamic pressure effect of a dynamic pressure groove provided on a bearing surface. Suitable for plain bearings. The lubricating oil composition of the present invention can be used by impregnating these bearings and the like.

[0020]

EXAMPLES Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. Abbreviations of the components used in the examples and comparative examples are as follows. In addition, the compounding ratio is shown in% by weight. % Is% by weight. C10 means that the carbon number is 10. PAO3: Poly-α-olefin hydride (manufactured by Oronite Japan Co., Ltd .: PAO3, C20: 97%, C30: 3%) PAO2: Poly-α-olefin hydride (manufactured by Oronite Japan Co., Ltd .: PAO2, C10: 0. 2%, C20: 96.5%, C30: 3.3%) PMMA (kinematic viscosity at 50 ° C .: 18930 mm ² / s) RC: Ethylene-α-olefin copolymer hydride (40
℃ kinematic viscosity: 1000mm ² / s) TP: tricresyl phosphate (antiwear agent) TA: phosphite (antiwear agent) L57: p, p'- dioctyldiphenylamine (antioxidant) DOS: diester (Hatco Corporation Manufacture: H3110) Zn: zinc dinonylnaphthalene sulfonate (rust inhibitor) BTA: benzotriazole derivative (metal deactivator) DU: diurea compound (thickener)

Examples 1 to 7 and Comparative Examples 1 to 5 Examples 1 to 5 and Comparative Example 1 were prepared by blending the components shown in Table 1.
~ 6 lubricating oil compositions (hereinafter referred to as lubricating oils) were prepared. In Example 5 and Comparative Example 5, the lubricating oil additive had the same composition as in Example 1 and Comparative Example 1, but was carried out to confirm the effect of adding the thickener. In addition, “Bal” in Table 1 indicates that the rest other than the numerical value is the same as 100 as a whole.

[0022]

[Table 1]

As to these lubricating oils, ASTM D27
Evaluation was carried out using a tester described in JP-A-83-88. The test conditions were a rotational speed of 9,000 rpm and a load of 1
At 0 kg (average pressure; 14,650 kg / cm ² , sliding speed: 3.46 m / sec), the wear scar diameter (mm) was measured as a measurement item. The material of the test sphere was SUJ2 for the upper sphere, and brass was used for three of the lower spheres (evaluation time was 30 minutes). For the evaporability, the test oil was placed in an environment of 100 ° C. × 24 hours, and the amount of evaporation was measured. The rust prevention test was performed in accordance with JIS K2246 wetness test method, and the presence of rust was confirmed 300 hours after the sample was impregnated in the sintered oil-impregnated bearing. Table 2 shows the test results. The state of occurrence in Table 2 is the state of the appearance of the bearing in the wet test.
The numerical value representing the result of the wear scar diameter is 0.5 when the wear scar diameter is 0.5.
If it was not more than mm, it was determined to be acceptable. About evaporation amount, 1
0% or less was judged to be acceptable. Although the above criteria are not standardized, they are obtained from accumulated data for many years, and it has been found that those that do not pass this criteria cannot be actually used.

[0024]

[Table 2]

As shown in Examples and Comparative Examples, the wear characteristics can be improved by adding an antiwear agent. On the other hand, the lubricating oils of Comparative Examples 1 to 5 have the same additive composition as the examples, but the evaporation amount is out of the specification due to the effect of the performance of the PAO used as the base oil. By using the C20-based PAO, the evaporation, which is the biggest problem, can be suppressed to 1/4, which can contribute to extending the life of the spindle motor. It was also confirmed that the addition of the thickener did not adversely affect various performances. Note that Comparative Example 6 containing no additive could not satisfy all the performances.

[0026]

The lubricating oil composition of the present invention can suppress evaporation and improve various properties such as abrasion resistance and rust prevention performance. Therefore, good characteristics can be obtained even with a very simple structure such as a sintered oil-impregnated bearing used for a spindle motor, and the ease and reliability of the design of the sintered oil-impregnated bearing and its mounting device can be improved. Can be. Further, by adding a viscosity index improver, a metal deactivator, an antioxidant and the like to the lubricating oil composition of the present invention, the evaporation amount and the like can be further improved.

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 4H104 BA07A BA07C BA08C BB33A BB34A CA04C CA05C CB08C EA02C EB06 EB08 EB09 EB10 EB11 EB20 JA12 LA03 LA04 LA06 PA01 PA04

Claims (4)

[Claims] 1. A composition containing no more than 0.1% by weight of C12 or less,
A base oil is a mixed oil in which a poly-α-olefin hydride having a main component of C20 to 36 and an ester are blended in a weight ratio of 95: 5 to 50:50. Poly-α- having a kinematic viscosity of 10 cSt or more
A lubricating oil composition comprising a polymer selected from olefin hydride, hydrogenated ethylene-α-olefin copolymer, and polymethacrylate. 2. The lubricating oil composition according to claim 1, wherein the ester is a diester or a polyol ester. 3. Thickeners, antiwear agents, metal deactivators,
2. A composition comprising one or more additives selected from the group consisting of rust inhibitors, evaporation inhibitors and antioxidants.
Or the lubricating oil composition according to 2. 4. The lubricating oil composition according to claim 1, which is used for a sliding bearing of a spindle motor.