JP2007039496A - Fluid dynamic bearing unit and lubricating oil composition for bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lubricating oil for bearing having excellent durability and excellent torque reducing capabilities and to provide a fluid dynamic type bearing, a porous oil-impregnated bearing, and a fluid dynamic type porous oil-impregnated bearing suited for small spindle motors related to information machines and equipment. <P>SOLUTION: The lubricating oil composition comprises (A) a major proportion of an ester synthesized from an 8C monohydric alcohol and a 6C dicarboxylic acid and (B) 1 to 5 wt.% diester having a kinematic viscosity (at 40°C) of not less than 10 mm<SP>2</SP>/s and a total carbon number of 23 to 28. The fluid dynamic type bearing unit and the porous oil-impregnated bearing unit using the lubricating oil composition are provided. A spindle motor fitted with the bearing unit is also provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a lubricating oil composition suitable as a lubricating oil for bearings, a fluid dynamic pressure bearing unit using the same, a porous oil-impregnated bearing unit, and a spindle motor using the bearing unit.

  In the fluid bearing that supports the rotating shaft by the oil film pressure of the lubricating oil interposed in the gap between the outer peripheral surface of the shaft and the inner peripheral surface of the sleeve, a dynamic pressure groove is provided on at least one of the outer peripheral surface of the shaft or the inner peripheral surface of the sleeve. Self-lubricating by impregnating a porous body composed of a fluid dynamic pressure bearing that floats and supports the sliding surface of the rotating shaft with a lubricating oil film formed by the dynamic pressure effect, or sintered metal, with lubricating oil or lubricating grease A porous oil-impregnated bearing having a function and supporting a rotating shaft, and a dynamic pressure type porous oil-impregnated bearing in which a dynamic pressure groove is provided on a bearing surface of the porous oil-impregnated bearing are known. These include models that require high rotational accuracy at high speeds, such as polygon scanner motors for laser beam printers (LBP) and spindle motors for magnetic disk drive devices (HDD), DVD-ROMs, DVD-RAMs, etc. It is suitable for a device that is driven at a high speed under a condition in which an unbalance load is applied when the disk is mounted, such as a spindle motor for an optical disk apparatus or a magneto-optical disk apparatus such as MO.

  Lubricating oils with relatively low viscosity and low evaporability in fluid dynamic pressure bearings, porous oil-impregnated bearings, dynamic pressure-type porous oil-impregnated bearings, etc. to meet the demand for lower torque of small spindle motor bearings related to information equipment Is selected. As lubricating oils used for such applications, Patent Document 1 discloses hydrocarbons such as PAO (poly-α-olefin), Patent Document 2 discloses diesters, Patent Document 3 includes polyol esters, and Patent Documents. 4 has been proposed as monoester.

Japanese Patent No. 2676767 JP-A-4-357318 JP 2001-316687 JP 2000-63860 Japanese Patent Laid-Open No. 2003-193075

  With the high performance of AV and OA equipment, small spindle motors used in these rotating parts are strongly demanded for high speed and low power consumption. Therefore, the bearings used for rotating support parts always have low torque. There is a demand for conversion. In recent years, in particular, performance that can be applied to various environments (temperatures) is demanded in consideration of use as a mobile device. Factors affecting bearing torque include bearing clearance and shaft diameter, but the viscosity of lubricating oil is one major factor in low temperature environments.

  Lubricating oil generally tends to evaporate as the viscosity becomes lower. If the lubricating oil is reduced by evaporation or the like, an appropriate oil film pressure cannot be obtained, and the rotational accuracy is remarkably lowered and regarded as the service life. Therefore, the evaporation characteristic of the lubricating oil is an important characteristic that affects the durability of the bearing. Therefore, for lubrication of sliding bearings such as fluid dynamic pressure bearings, porous oil-impregnated bearings, and dynamic pressure-type porous oil-impregnated bearings, select a lubricating oil that has low viscosity and does not have an extremely high viscosity increase even in a low temperature range and has relatively excellent evaporation characteristics. There is a need to. In many cases, ester-based lubricating oil is used.

Ester oil also tends to have poor evaporation characteristics as the viscosity becomes lower, as with other lubricating oils. Therefore, simply selecting an ester oil having a lower viscosity than the current one in order to reduce the torque of the bearing will impair the evaporation characteristics and reduce the durability of the bearing. Further, even if the viscosity is low at room temperature, if the viscosity suddenly rises in the low temperature range or loses fluidity, it will lead to a sudden increase in torque or equipment shutdown. For example, in a lubricating oil composition consisting only of a low viscosity oil such as a monoester having a viscosity of less than 8 mm ² / s at 40 ° C., the amount of evaporation increases as the molecular weight decreases, and the evaporation is almost uniform due to the uniform molecular weight. As a result, the durability is drastically reduced at certain conditions.

Moreover, since the lubricating oil based on dioctyl sebacate described in Patent Document 5 has a viscosity at 40 ° C. of about 11 to 12 mm ² / s and low evaporation, it is excellent as a lubricating oil for fluid dynamic pressure bearings. It is known. However, since the viscosity in the low temperature region is relatively high, it is difficult to satisfy the required performance as a mobile-mounted spindle motor where torque in the low temperature region is regarded as important.

  The present invention provides a lubricating oil that has a low viscosity at room temperature and does not have an excessive increase in viscosity even in a low temperature range, and has a relatively excellent evaporation characteristic, and also provides a bearing device that uses this and has a low torque and a long life. This is the issue.

In order to solve the above problems, the main component is an ester composed of a monohydric alcohol having 8 carbon atoms and a divalent carboxylic acid having 6 carbon atoms, the kinematic viscosity at 40 ° C. is 10 mm ² / s or more, and the total number of carbon atoms in the molecule. Was found to be excellent in a lubricating oil composition having a diester of 23 to 28 as a minor component.

The present invention comprises (A) an ester synthesized from a monohydric alcohol having 8 carbon atoms and a divalent carboxylic acid having 6 carbon atoms as a main component, and (B) a kinematic viscosity at 40 ° C. of 10 mm, excluding the main component. A lubricating oil composition comprising 1 to 5% by weight of a diester having a molecular weight of 23 to 28 and a molecular weight of ² / s or more. Here, as said monohydric alcohol, isooctyl alcohol is illustrated preferably.

  Furthermore, the present invention is a fluid dynamic pressure bearing unit characterized in that a dynamic pressure generating groove is provided on either one of the outer peripheral surface of the shaft and the inner peripheral surface of the sleeve, and the lubricating oil composition is used as a lubricant. . The present invention also provides a porous oil-impregnated bearing unit or a porous oil-impregnated bearing impregnated with the lubricating oil composition. Here, the porous oil-impregnated bearing is preferably exemplified by a dynamic pressure type porous oil-impregnated bearing. Moreover, this invention is a spindle motor provided with the said bearing unit.

Hereinafter, the lubricating oil composition of the present invention will be described.
The main component of the lubricating oil composition is an ester synthesized from a monohydric alcohol having 8 carbon atoms and a divalent carboxylic acid having 6 carbon atoms (component A). An ester synthesized from a monohydric alcohol with 9 or more carbon atoms and a divalent carboxylic acid with 6 carbon atoms or an ester synthesized from a divalent carboxylic acid with 7 or more carbon atoms increases the torque during rotation and obtains the required performance. I can't. On the other hand, in the ester synthesized from a monohydric alcohol having 7 or less carbon atoms or the ester synthesized from a divalent carboxylic acid having 6 or less carbon atoms, the amount of evaporation increases rapidly and the life of the spindle motor cannot be extended. Therefore, it is necessary to have an ester synthesized from a monohydric alcohol having 8 carbon atoms and a divalent carboxylic acid having 6 carbon atoms as a main component. As the monohydric alcohol having 8 carbon atoms, isooctyl alcohol is preferred.
Since the above ester is a diester of a divalent carboxylic acid, it is relatively linear and does not have large branches like a polyol ester, so it has a high viscosity index, a high flash point, and excellent low temperature fluidity. Yes.

The diester (component B) blended with the main component ester is a subcomponent of the lubricating oil composition, and its role is to improve evaporation characteristics that cannot be satisfied by the component A alone. This diester is a diester having a kinematic viscosity at 40 ° C. of 10 mm ² / s or more and a total carbon number of 23 to 28 in the molecule, but different from the component A. Mixing with a viscosity of less than 10 mm ² / s at 40 ° C. does not contribute to the improvement of the evaporation characteristics of the main component, but tends to increase the evaporation amount. The same is true for diesters with less than 23 total carbons in the molecule. In addition, when diester having a total carbon number of 29 or more in the molecule is mixed, the torque characteristics of the bearing cannot be reduced at low temperatures.

That is, it is desirable that the B component used as an auxiliary component is highly compatible with the main component A component, has excellent low-temperature fluidity, and exhibits low evaporation. In other words, it is desirable that the B component has a larger carbon number (molecular weight) than the A component, is difficult to evaporate, and has a high viscosity. While specifically a range viscosity of 8.5 to 9.5 mm ² / s of the A component, diesters viscosity of component B is in the range of 10 to 20 mm ² / s is more preferable. Examples of the diester used as the B component having such characteristics include DOZ (dioctyl azelate), DOS (dioctyl sebacate), and DIDA (diisodecyl adipate).

Further, the constituent ratio of the A component as the main component and the B component as the subcomponent must be in the range of 1 to 5% by weight of the B component with respect to the entire lubricating oil composition. When the content ratio of the B component exceeds 5% by weight, the influence of the B component is strong, and the characteristics such as the low viscosity and low temperature fluidity of the A component are lost, and the bearing torque increases. Furthermore, when the content ratio of the B component is less than 1% by weight, a remarkable mixing effect cannot be obtained for improving the evaporation property of the A component.
That is, the present invention achieves both low viscosity and low evaporability by mixing an optimal amount of the diester as the accessory component with the ester as the main component. In addition, the mixing maintains the good performance of the main component while realizing low oil evaporation and low torque of the bearing, thereby extending the life of the spindle motor. The ester of component A as the main component and the diester of component B as the auxiliary component constitute a lubricating base oil.

  The lubricating oil composition of the present invention may be mixed with known additives such as antioxidants, extreme pressure agents, antiwear agents, rust inhibitors, metal deactivators, oiliness improvers as necessary. it can.

  The lubricating oil composition of the present invention can be suitably used for hydrodynamic sintered oil-impregnated bearing oils, fluid dynamic pressure bearings, porous oil-impregnated bearings, and dynamic pressure-type porous oil-impregnated bearings.

  By using the lubricating oil composition of the present invention for fluid dynamic pressure bearings, porous oil-impregnated bearings, dynamic pressure-type porous oil-impregnated bearings, etc., the durability of small spindle motor bearings related to information equipment can be reduced. Torque can be realized.

The form which applies the lubricating oil composition of this invention is demonstrated in detail with reference to drawings.
2 and 3 are sectional views of the sintered oil-impregnated bearing device and the hydrodynamic sintered oil-impregnated bearing device, in which 1 is a seal, 2 is a porous oil-impregnated bearing, 3 is a radial bearing, 4 is a shaft, 5 is a housing, 6 is a seal gap, 7 is a flange shaft, 8 is a thrust bearing portion, 9 is a housing cylindrical portion, and 10 is a housing thrust receiving portion.

Therefore, consider a bearing device having a structure as shown in FIG. In this structure, the inner space of the housing is used in a state filled with lubricating oil.
An enlarged view of the seal portion in the steady state is shown as c-4 in FIG. The lubricating oil surface is on the inner peripheral portion of the seal, and the lubricating oil surface is always designed to be on the inner peripheral portion of the seal under the assumed conditions such as operating environment temperature and posture. If the lubricating oil surface is above the upper end surface of the seal, the lubricating oil naturally leaks outside the bearing device. In addition, when the lubricating oil surface falls below the seal lower end surface, air is mixed into the lubricating oil supplied to the bearing surface, reducing the rotational accuracy and causing the internal lubricating oil to flow outside the bearing device due to the thermal expansion of the air. This will cause the oil to leak out. The latter phenomenon occurs when the lubricating oil evaporates. Therefore, as a specific design, at the minimum operating temperature of the bearing device (that is, the state where the lubricating oil volume is the smallest and the surface position is the lowest), the lubricating oil surface position is evaporated from the state of c-4 in FIG. It is necessary to design so that the time until the state of c-5 becomes longer than the durability time required for the entire apparatus.

  Temporarily, in the environment of the minimum temperature of use of the bearing device, when the state of c-4 in FIG. Assuming that the endurance time required for the bearing device is 10000h, as shown in FIG. 5, the durability cannot be satisfied unless a lubricating oil having an evaporation rate of less than 3% by weight is selected after leaving for 10000h. Thus, there is a correlation between the evaporation characteristics of the lubricating oil and the durability of the bearing device (or the motor incorporating the same), and selecting a lubricating oil with good evaporation characteristics leads to a longer life of the bearing device. .

  On the other hand, factors affecting bearing torque include bearing clearance and shaft diameter, but the viscosity of the lubricating oil is also one major factor. By using a lower viscosity lubricating oil, the stirring resistance (viscous resistance) can be reduced, resulting in a lower torque.

FIG. 6 shows the results of preparing the lubricating oils having different kinematic viscosities and measuring the torque with the bearing device having the structure shown by c-1 in FIG. As shown in FIG. 6, there is a proportional relationship between the kinematic viscosity of the lubricating oil and the torque, and it can be seen that a reduction in the lubricating oil viscosity directly leads to a reduction in the bearing torque.
As described above, the problem of providing a bearing device having a low torque and a long service life can be solved by selecting a lubricating oil having a low viscosity and excellent evaporation characteristics.

Hereinafter, the present invention will be described with reference to examples and comparative examples.
Table 1 shows the main component (component A) and subcomponent (component B) esters. A component, B component and other additives were blended in the proportions shown in Tables 2 to 5 to obtain lubricating oil compositions. About this lubricating oil composition, the evaluation results of evaporation rate and bearing torque are shown together in Tables 2 to 5. Table 2 shows the evaluation results of the evaporation rate and bearing torque (room temperature and −20 ° C.) of the lubricating oils of Comparative Examples 1 to 10. Tables 3 to 5 show the results of evaluating the evaporation rate and the bearing torque by preparing several types of lubricating oil using diisooctyl adipate as the A component and changing the mixing ratio of the B component. In addition, in the comparative examples and examples shown in Tables 2 to 5, the same amount of alkyldiphenylamine (ADPA) which is a known antioxidant and benzotriazole (BTA) which is a metal deactivator are added. In Tables 2 to 5, the blending amount is% by weight, and the remainder indicates the remainder when the entire lubricating oil composition is 100% by weight.

The method of measuring the evaporation rate is as follows.
Container: φ37 × 50
Lubricating oil amount: 3g
Leaving temperature: 120 ° C (constant temperature bath)
Leaving time: 3000h
The weight reduction rate from the initial weight was measured, and less than 5% by weight was accepted.
Judgment criteria A: Less than 2.0% by weight (pass)
○: 2.0% by weight or more and less than 5% by weight (pass)
×: 5.0% by weight or more (failed)

Bearing torque evaluation conditions Rotational speed: 3600rpm
Ambient temperature: -20 ℃, 25 ℃
Motor posture: Upright judgment criteria ◎: -20 ℃ less than 210mA, 25 ℃ less than 25mA (pass)
○: -20 ℃ 210mA or more, less than 230mA, 25 ℃ 25mA or more, less than 30mA (pass)
×: -20 ℃ 230mA or more, 25 ℃ 30mA or more (failed)

From Table 2, when the carbon number of the divalent carboxylic acid part constituting the diester is 6, when the carbon number of the alcohol part is 9 or more, an increase in bearing torque is observed with an increase in viscosity at low temperature. Further, even when the carbon number of the alcohol part constituting the diester is 8, when the carbon number of the divalent carboxylic acid part becomes 6 or more, an increase in the bearing torque is recognized similarly. In addition, when the total number of carbon atoms in the molecule is small as in DBS, the polarity of the molecule increases, so that fluidity is lost in a low temperature region of −20 ° C. On the other hand, the evaporation rate of oil tends to increase abruptly when the kinematic viscosity at 40 ° C. is about 9 mm ² / s as a boundary. Therefore, in the present invention, the bearing torque at low temperature is excellent and the evaporation rate alone does not satisfy the required performance, but the kinematic viscosity at 40 ° C is around 9 mm ² / s, which is improved by mixing with other oils. An ester synthesized from a monohydric alcohol having 8 carbon atoms and a divalent carboxylic acid having 6 carbon atoms was selected as the main component. Then, by mixing the main component ester with a secondary component lubricating oil which is a lubricating oil having a higher viscosity than that of the main component ester, the evaporation rate can be further reduced while maintaining the low temperature fluidity of the main component. The alcohol component having 8 carbon atoms used for the main component divalent carboxylic acid having 6 carbon atoms may be any monovalent alcohol, but from the viewpoint of viscosity and stability, isooctyl alcohol may be used. preferable.

From Table 3, the lubricating oil used as an auxiliary component has a viscosity higher than that of the ester as the main component in order to reduce the evaporation rate of the mixed oil, specifically, the kinematic viscosity at 40 ° C. is 10 mm ² / Must be greater than or equal to s. Furthermore, in order to suppress an increase in viscosity at a low temperature, it is preferable to select one having a total carbon number in the range of 23 to 28. If the total number of carbon atoms in the molecule is 22 or less, evaporation will be promoted even if the optimum amount of mixing is performed. In addition, if the number of carbon atoms in the molecule is 29 or more, the torque of the bearing will increase due to the increase in viscosity at low or normal temperature.

From the results of Tables 4 to 5, it can be seen that the bearing torque at low temperature increases when the ratio exceeds 5% by weight, although it depends on the type of low-viscosity lubricating oil that is a subcomponent. In that case, since the component ratio of the auxiliary component lubricating oil is large, the influence appears strongly, and it is considered that the viscosity at low temperature is increased. Therefore, the component ratio of the auxiliary component lubricating oil must be 5% by weight or less. Further, when the component ratio of the auxiliary component lubricating oil is less than 1% by weight, the influence of the mixing is hardly observed, and the effect of suppressing the evaporation rate of the main component is not recognized. When the component ratio of the subcomponent lubricant is 1% by weight, there is no particular difference from the viscosity of less than 1% by weight, but there are some that satisfy the evaporation characteristics with the subcomponent lubricant to be mixed. Although it is only 1% by weight, it has a great effect of satisfying the evaporation characteristics while maintaining the low temperature characteristics of the main component diester. In particular, diesters such as DOZ, DOS, and DIDA are preferable as subcomponents from the viewpoint of low evaporation, compatibility, and lubricity.
From the above, when lubricating oil with a kinematic viscosity at 40 ° C of 10 mm ² / s or more is mixed as an auxiliary component with an ester composed of a monohydric alcohol having 8 carbon atoms and a divalent carboxylic acid having 6 carbon atoms as the main components, It is desirable that the composition ratio of the subcomponents in the entire lubricating oil is 1% by weight or more and 5% by weight or less.

The following is mentioned as a bearing apparatus using the lubricating oil by this invention.
FIG. 1a is a cross-sectional view showing an example of a fluid dynamic pressure bearing. In the figure, 11 is a sleeve, and the same reference numerals are the same as those in FIGS. In this fluid dynamic pressure bearing, a dynamic pressure groove is provided on at least one of the outer peripheral surface of the shaft and the inner peripheral surface of the sleeve, and lubricating oil is injected or vacuumed into the clearance (bearing clearance) between the outer peripheral surface of the shaft and the inner peripheral surface of the sleeve. By filling by a method such as impregnation, the shaft is rotationally supported in the radial direction by the dynamic pressure of the lubricating oil generated with the rotation of the shaft. FIG. 1b is a cross-sectional view showing an example of a fluid dynamic pressure bearing of the type in which a thrust bearing portion 8 is further provided in the above a and the radial and thrust directions are rotationally supported. The thrust bearing portion is formed by a shaft flange portion 12 and a sleeve 11 and a bottom plate processed and assembled in a shape corresponding to the shaft flange portion. A dynamic pressure groove is provided on one side, and by injecting lubricating oil into both the radial and thrust bearings in the same manner as the fluid dynamic pressure bearing shown in a, the dynamic pressure effect of the lubricating oil generated as the shaft rotates The shaft can be supported in both radial and thrust directions. In addition, although a and b of FIG. 1 have provided the dynamic pressure groove, the fluid bearing which does not have a dynamic pressure groove may be sufficient.

  FIG. 2 is a sectional view showing an example of a porous oil-impregnated bearing unit. 2a is a perfect circle bearing having a perfect circular bearing surface, and b in FIG. 2, c-1, c-2 and c-3 in FIG. 3 are dynamic pressure type porous oil-impregnated bearings. FIGS. 2a and 2b are types in which the bearing surface is radial only, and these are a porous oil-impregnated bearing 2 impregnated with lubricating oil in advance in the bearing body and fixed to the housing member 5 by a method such as press-fitting, caulking, or bonding. The shaft 4 is fixed to the motor in the state of the bearing unit, and the shaft 4 to which the rotor is fixed is inserted into the bearing inner diameter portion. If necessary, an appropriate amount of lubricating oil is injected into the inner surface of the bearing before inserting the shaft. The non-rotor side of the housing member is sealed with a backup or the like to prevent oil leakage. A housing member having a cup shape at the bottom may be used in advance.

  On the other hand, c-1 and c-2 in FIG. 3 have bearings at the inner diameter surface and one end surface of the hydrodynamic sintered oil-impregnated bearing, and at the bottom of the housing, and the flanged shaft 7 is completely non-radial in the radial and axial directions. This type supports rotation by contact, and this type is used by assembling a motor by impregnating the unit with lubricating oil after assembling the shaft, bearings and seals in the housing. The unit's space is completely impregnated with lubricating oil and no air remains in the unit, so a continuous oil film is formed on the bearing during operation, maintaining high rotational accuracy and oil leakage due to thermal expansion of air. No worries. Since this type can exhibit high rotation accuracy in any use posture, it is suitable for rotation support in applications where the use posture of the spindle motor is horizontal, upside down, or not constant, such as an HDD or a handy video camera. This type of bearing unit is fixed to the motor as it is, and is used by fixing the rotor to the tip of the flanged shaft. In addition, as shown in c-2, a housing separation type in which the housing is separated into two bodies of the cylindrical portion 9 and the thrust receiving portion 10 may be used.

  Further, c-3 in FIG. 3 has bearing portions on the inner diameter surface and one end surface of the hydrodynamic sintered oil-impregnated bearing, and further on the end surface of the housing. The hub 13 is rotationally supported without contact completely in the radial and axial directions, and this type impregnates the unit with lubricating oil after assembling the shaft, bearings, hub, screws and bottom plate to the housing, Used in a motor. It should be noted that either the hub and the shaft can be processed integrally or can be assembled separately when assembled. When the hub and the shaft are separate bodies, a flanged shaft in which the shaft and the screw are integrated may be used.

  As described above, the viscosity and evaporation characteristics of the lubricating oil are correlated with the torque and durability of the motor incorporating the bearing device using the lubricating oil, respectively. Although it is clear that the torque can be reduced and the life of the motor can be increased by using the bearing device in the bearing device, here, as a confirmation, the result of the durability test with the spindle motor using the bearing device is used. An example is shown. FIG. 7 shows an example in which a bearing device using the hydrodynamic sintered oil-impregnated bearing shown in FIG. 2b is mounted on a polygon scanner motor. FIG. 8 shows an example in which the bearing device indicated by c-1 in FIG. 3 is mounted on an HDD spindle motor. FIG. 9 shows the results of endurance testing of the polygon scanner motor shown in FIG. 7 under the following conditions.

Endurance test conditions Lubricating oil: Comparative Example 2 or Example 1
Rotation speed: 30000rpm
Ambient temperature: 60 ℃
Motor orientation: 40 ° tilt Test time: 500,000 cycles (market requirement is 300,000 cycles)
Operating conditions: ON / OFF (1 cycle 36 seconds)
As shown in FIG. 9, the lubricating oil compositions of the examples have lower torque (lower current value) than the case where the lubricating oil compositions of the comparative examples are used, and the durability sufficiently satisfies the market requirements. .

Cross section of fluid dynamic bearing device Sectional view of sintered oil-impregnated bearing device and dynamic pressure type sintered oil-impregnated bearing device Sectional view of sintered oil-impregnated bearing device and dynamic pressure type sintered oil-impregnated bearing device Sectional view of sintered oil-impregnated bearing device and dynamic pressure type sintered oil-impregnated bearing device A graph showing the relationship between evaporation characteristics and durability of lubricating oil compositions Graph showing the relationship between kinematic viscosity and torque Cross section of polygon scanner motor Cross section of HDD spindle motor Graph showing the durability test results with a polygon scanner motor

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Seal 2 Porous oil-impregnated bearing 3 Radial bearing part 4 Shaft 5 Housing 6 Seal clearance 7 Shaft with flange 8 Thrust bearing part 9 Housing cylinder 10 Housing thrust receiving part 11 Sleeve 12 Flange part 13 Hub

Claims (9)

(A) The main component is an ester synthesized from a monohydric alcohol having 8 carbon atoms and a divalent carboxylic acid having 6 carbon atoms, and (B) a diester that is different from the main component and has a kinematic viscosity at 40 ° C. of 10 mm. A lubricating oil composition comprising 1 to 5% by weight of a diester having a molecular weight of 23 to 28 and a molecular weight of ² / s or more.   The lubricating oil composition according to claim 1, wherein the monohydric alcohol having 8 carbon atoms is isooctyl alcohol.   A bearing portion that supports the rotating shaft by oil film pressure of lubricating oil interposed in a gap between the outer peripheral surface of the shaft and the inner peripheral surface of the sleeve is provided, and the lubricating oil composition according to claim 1 or 2 is used as a lubricant. Fluid bearing unit.   A fluid dynamic pressure bearing unit characterized in that a dynamic pressure generating groove is provided on one of the outer peripheral surface of the shaft and the inner peripheral surface of the sleeve, and the lubricating oil composition according to claim 1 is used as a lubricant.   A porous oil-impregnated bearing unit comprising a porous oil-impregnated bearing impregnated with the lubricating oil composition according to claim 1.   The porous oil-impregnated bearing unit according to claim 5, wherein the porous oil-impregnated bearing is a dynamic pressure type porous oil-impregnated bearing.   A porous oil-impregnated bearing impregnated with the lubricating oil composition according to claim 1.   The porous oil-impregnated bearing according to claim 7, wherein the porous oil-impregnated bearing is a dynamic pressure type porous oil-impregnated bearing.   A spindle motor comprising the bearing unit according to claim 3.

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