JP2013043897A - Lubricant base oil for fluid dynamic-pressure bearing, lubricant for fluid dynamic-pressure bearing containing the base oil, and spindle motor having the lubricant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lubricant base oil for fluid dynamic-pressure bearings, which satisfies a viscosity zone in which the fluid dynamic-pressure bearings can sufficiently support the loads of rotors in a high temperature region and controls a rise in viscosity in a low temperature region.SOLUTION: The lubricant base oil for the fluid dynamic-pressure bearings, containing the diester of an aliphatic dihydric alcohol with an aliphatic monocarboxylic acid, wherein the aliphatic dihydric alcohol is a linear ≥11C dihydric alcohol; the aliphatic monocarboxylic acid is a branched chain ≤7C aliphatic monocarboxylic acid; the kinematic viscosity of the base oil at 100°C is 2.90-3.20 mm/s; and the viscosity index of the base oil is ≥160.

Description

  The present invention relates to a lubricating base oil for fluid dynamic pressure bearings that has little viscosity change even when used in a wide temperature range, a lubricating oil for fluid dynamic pressure bearings containing the base oil, and a spindle motor equipped with the lubricating oil.

Ball bearings and fluid dynamic bearings are used as rotary bearings for hard disk drives, compact disks (CDs), and DVD motors.
Ball bearings, when used for a long time, increase the load on the bearings, and are prone to vibration and noise. On the other hand, fluid dynamic pressure bearings generate pressure by the lubrication oil flowing by the rotation of the shaft to support the rotation, and the shaft and the bearing are not in direct contact with each other, so the frictional resistance is small and low vibration and noise are also achieved. Excellent. Therefore, in recent years, fluid dynamic pressure bearings are often used.
In the case of fluid dynamic pressure bearings, when the lubricating oil is in a high temperature range, such as during continuous rotation of the motor, if the viscosity of the lubricating oil expands and its viscosity decreases, the bearing stiffness decreases and the load on the rotating body may not be sufficiently supported. There is. For this reason, the lubricating oil to be used is required to have a high viscosity in a high temperature range. On the other hand, when the lubricating oil is in a low temperature range such as when the motor is started, if the viscosity of the lubricating oil is high, the viscous resistance at the time of rotation increases and the power loss of the motor increases. For this reason, the lubricating oil used is required to have a small increase in viscosity even in the low temperature range. Therefore, the lubricating oil for fluid dynamic pressure bearings is required to have viscosity characteristics which are seemingly contradictory so that the viscosity is high at a high temperature range and does not increase even at a low temperature range.
As fluid oils for fluid dynamic bearings, di-n-octylic acid ester of 2,4-diethyl-1,5-pentanediol has been reported, such as poly-α-olefin, dioctyl sebacate, neopentyl glycol and the like. It has been reported that it is excellent in low-temperature fluidity as compared with esters with nonanoic acid and esters of pentaerythritol (Patent Document 1).
Moreover, as a lubricating oil for bearings, 3-methyl-1,5-pentanediol and n-heptanoic acid and / or a diester of n-octanoic acid have been reported to have a low viscosity in a wide temperature range ( Patent Document 2).

JP 2003-321691 A JP 2003-119482 A

In recent years, for the purpose of further reducing the power loss of a motor, a fluid dynamic bearing lubricating oil having a low viscous resistance is required. Since the conventional fluid dynamic pressure bearing lubricating oil has a large viscosity change with respect to temperature, when the viscosity in the high temperature range is increased, the viscosity in the low temperature range also increases, and the power loss of the motor increases. On the other hand, if the viscosity in the low temperature range is lowered, the viscosity in the high temperature range is also lowered, so that the load of the rotating body cannot be sufficiently supported.
Therefore, the problem to be solved by the present invention is to satisfy the viscosity region where the fluid dynamic pressure bearing can sufficiently support the load of the rotating body in the high temperature region, and to suppress the increase in the viscosity in the low temperature region.
An object of the present invention is to provide a lubricating base oil for a fluid dynamic pressure bearing that satisfies a viscosity region in which a fluid dynamic pressure bearing can sufficiently support the load of a rotating body in a high temperature region and suppresses an increase in viscosity in a low temperature region. It is to be.
Another object of the present invention is to provide a lubricating oil containing the base oil.
A further object of the present invention is to provide a spindle motor provided with the lubricating oil.

In order to solve this problem, the present inventors are composed of a specific aliphatic dihydric alcohol and a specific aliphatic monocarboxylic acid, and have a kinematic viscosity at 100 ° C. of 2.90 to 3.20 mm ² / s, The above problem was solved by using a diester having an index of 160 or more.
That is, according to the present invention, there are provided the following lubricating base oil for fluid dynamic pressure bearings, lubricating fluid for fluid dynamic pressure bearings containing the base oil, and a spindle motor provided with the lubricating oil:
1. A lubricating base oil for fluid dynamic pressure bearings containing a diester of an aliphatic dihydric alcohol and an aliphatic monocarboxylic acid,
The aliphatic dihydric alcohol is a linear dihydric alcohol having 11 or more carbon atoms, and the aliphatic monocarboxylic acid is a branched aliphatic monocarboxylic acid having 7 or less carbon atoms,
The base oil has a kinematic viscosity at 100 ° C. of 2.90 to 3.20 mm ² / s,
The base oil has a viscosity index of 160 or more,
Lubricating base oil for fluid dynamic bearings.
2. 2. The lubricant base oil for fluid dynamic pressure bearing according to claim 1, wherein the aliphatic monocarboxylic acid is selected from the group consisting of 2-methylpentanoic acid, 2-ethylbutanoic acid, and a mixture thereof.
3. The lubricating base oil for fluid dynamic pressure bearings according to 1 or 2 above, wherein the aliphatic dihydric alcohol is linear 1,12-dodecanediol.
4). The aliphatic dihydric alcohol is linear 1,12-dodecanediol, and the aliphatic monocarboxylic acid is 2-methylpentanoic acid or a mixture of 2-methylpentanoic acid and 2-ethylbutanoic acid. 4. The lubricating base oil for fluid dynamic bearings according to any one of 3 above.
5. A lubricating oil for fluid dynamic pressure bearings, comprising the lubricating base oil for fluid dynamic pressure bearings according to any one of claims 1 to 4.
6). Furthermore, the lubricating oil for fluid dynamic pressure bearings of the said 5 containing 0.01-5 mass% of amine-type antioxidants, and 0.01-5 mass% of phenol-type antioxidants.
7). The lubricating oil for fluid dynamic pressure bearings according to 5 or 6 above, further comprising 0.01 to 0.1% by mass of an antistatic agent.
8). A stationary part having a stator;
A rotating part having a rotor magnet;
A fluid dynamic bearing that rotatably supports the rotating part with respect to the stationary part;
The fluid dynamic bearing lubricating oil according to any one of 5 to 7,
With spindle motor.

  ADVANTAGE OF THE INVENTION According to this invention, the fluid dynamic pressure bearing can satisfy | fill the viscosity area | region which can fully support the load of a rotary body in a high temperature area, and can suppress the raise of the viscosity in a low temperature area.

It is a longitudinal cross-sectional view which shows the structure of a spindle motor.

[Base oil]
The lubricating base oil for fluid dynamic pressure bearings of the present invention is a diester of an aliphatic dihydric alcohol and a monocarboxylic acid.
The aliphatic dihydric alcohol is a linear aliphatic dihydric alcohol having 11 or more carbon atoms. A linear dihydric alcohol having 11 to 14 carbon atoms is preferred. Specific examples of the aliphatic dihydric alcohol include 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, 1,14-tetradecanediol, and the like. Of these, 1,12-dodecanediol and 1,13-tridecanediol are preferable. In particular, 1,12-dodecanediol is preferred. The aliphatic dihydric alcohols can be used alone or in combination of two or more.
The aliphatic monocarboxylic acid is a branched aliphatic monocarboxylic acid having 7 or less carbon atoms. Branched saturated aliphatic monocarboxylic acids are preferred. A branched saturated aliphatic monocarboxylic acid having 6 to 7 carbon atoms is more preferred. Specific examples of the branched aliphatic monocarboxylic acid include 2-methylpentanoic acid, 2-ethylbutanoic acid, isoheptanoic acid and the like. Of these, 2-methylpentanoic acid, 2-ethylbutanoic acid and mixtures thereof are preferred. Among these, 2-methylpentanoic acid and a mixture of 2-methylpentanoic acid and 2-ethylbutanoic acid are particularly preferable. Aliphatic monocarboxylic acids can be used alone or in admixture of two or more.
In particular, a diester composed of 1,12-dodecanediol and 2-methylpentanoic acid or a mixture of 2-methylpentanoic acid and 2-ethylbutanoic acid is preferable.

  The lubricating base oil for fluid dynamic pressure bearings of the present invention is within a range that does not deteriorate its performance, that is, other lubricating base oils, that is, mineral oil, poly α-olefin, polybutene, alkylbenzene, animal and vegetable oils, organic acid esters, One or more selected from the group consisting of polyalkylene glycol, polyvinyl ether, polyphenyl ether, alkylphenyl ether, and silicone can be used in combination. The amount of the other base oil used in combination is preferably 0 to 50% by mass with respect to the lubricating base oil for fluid dynamic pressure bearings of the present invention. In order not to impair the low temperature property, the lubricating oil for fluid dynamic pressure bearings of the present invention It is preferable that it is 0-20 mass% with respect to base oil. That is, the base oil of the present invention comprises a diester of a linear aliphatic dihydric alcohol having 11 or more carbon atoms and a branched aliphatic monocarboxylic acid having 7 or less carbon atoms. Most preferably, it does not contain a base oil.

The esterification reaction between the aliphatic dihydric alcohol and the aliphatic monocarboxylic acid can be performed by a method known in the art. Usually, it is carried out at 150 to 300 ° C, preferably 200 to 250 ° C. The reaction time is not particularly limited because it varies depending on the scale of the reaction, but is preferably 1 to 10 hours. The pressure is carried out at normal pressure or reduced pressure. The ester of the aliphatic dihydric alcohol and the aliphatic monocarboxylic acid is preferably a full ester. If hydroxyl groups remain in the ester, the thermal stability decreases, so the reaction conditions are selected so as to prevent the formation of monoesters. For this reason, the charged molar ratio of the aliphatic dihydric alcohol and the aliphatic monocarboxylic acid is preferably 1.0: 1.5 to 3.0, more preferably 1.0: 1.8 to 2.0. It is desirable to do.
In the esterification reaction, a catalyst may be used. In this case, the amount of the catalyst used is preferably 0.01 to 0.5% by mass of the raw material charge. Examples of the catalyst in this case include sulfuric acid, p-toluenesulfonic acid, tin oxide, alkyl titanate and the like.

The kinematic viscosity at 100 ° C. of the lubricating base oil for fluid dynamic bearings of the present invention is 2.90 to 3.20 mm ² / s, preferably 2.90 to 3.10 mm ² / s. If the lubricating oil expands thermally and becomes less than 2.90 mm ² / s, the bearing rigidity decreases, and there is a risk that the load of the rotating body cannot be sufficiently supported.
The viscosity index of the lubricating base oil for fluid dynamic bearings of the present invention is 160 or more, preferably 160 to 180, from the viewpoint of suppressing an increase in viscosity in a low temperature range. The viscosity index is an experimentally obtained index indicating a change in the viscosity of the lubricating oil accompanying a change in temperature. In general, the larger the viscosity index, the smaller the change in viscosity with temperature change, and the smaller the viscosity index, the greater the change in viscosity with temperature change.
The pour point of the lubricating base oil for fluid dynamic bearings of the present invention is preferably −20 ° C. or lower.

〔Additive〕
The base oil of the present invention can be used as a lubricating oil. In order to improve the performance of the lubricating oil of the present invention, an antioxidant, an antistatic agent, and the like can be included as necessary.
As the antioxidant, it is preferable to add an amine-based antioxidant and / or a phenol-based antioxidant in combination. In particular, it is preferable to add a combination of an amine-based antioxidant and a phenol-based antioxidant. Addition of an amine-based antioxidant and a phenol-based antioxidant in combination can impart low volatility to the lubricating oil over a long period of time under high-temperature conditions as compared to the case where it is used alone. The content of the amine-based antioxidant is preferably 0.01 to 5% by mass with respect to the fluid dynamic bearing oil. The content of the phenol-based antioxidant is preferably 0.01 to 5% by mass with respect to the fluid dynamic pressure bearing lubricant.
The antistatic agent is preferably added in an amount of 0.01 to 0.1% by mass with respect to the fluid dynamic bearing oil.

Hereinafter, preferred embodiments will be described with reference to the drawings.
FIG. 1 is a longitudinal sectional view showing the configuration of the spindle motor. The spindle motor has a stationary part 2 and a rotating part 4. The rotating part 4 is supported rotatably with respect to the stationary part 2 by the fluid dynamic pressure bearing 3 of the present embodiment. In the description of the preferred embodiment, when describing the positional relationship and direction of each member in the upper, lower, left, and right directions, the positional relationship and direction in the drawings are only shown, and the positional relationship and direction when incorporated in an actual device are shown. It is not shown.
The base plate 10 includes a flat portion 11 provided at the center of the base plate 10 and a boss portion 13 provided at the center of the flat portion 11. Between the boss | hub part 13 and the cyclic | annular step part 14 provided in the outer peripheral part of the flat part 11, it is a cyclic | annular recessed part. A stator 17 fixed to the flat portion 11 and a rotor magnet 34 fixed to a hub 31 described later are disposed in an annular recess. A stator 17 is disposed outside the boss portion 13 in the radial direction.

A bearing stationary portion 20 that constitutes a part of the fluid dynamic pressure bearing 3 is disposed inside the boss portion 13 in the radial direction. The bearing stationary portion 20 includes a substantially cylindrical sleeve 21 and a counter plate 22 that closes the lower end opening of the sleeve 21.
The rotating unit 4 includes a cup-shaped hub 31 and a shaft 32 disposed at the rotation center position of the hub 31.
A cylindrical portion 31 b is disposed outside the disc portion 31 a of the hub 31. A flange portion 31c extending radially outward is disposed at the lower end of the cylindrical portion 31b. An annular wall 31d is disposed inside the cylindrical portion 31b.
The outer peripheral surface of the shaft 32 and the inner peripheral surface of the sleeve 21 are opposed to each other in the radial direction through a minute gap.
An annular member 33 is fixed to the lower end of the shaft 32. The outer diameter of the annular member 33 is larger than the outer diameter of the shaft 32.

An annular rotor magnet 34 having a plurality of magnetic poles arranged in the circumferential direction is disposed inside the cylindrical portion 31b of the hub 31. The rotor magnet 34 is disposed at a position surrounding the stator 17 from the outer periphery.
One or a plurality of disc-shaped recording disks are placed on the flange portion 31 c of the hub 31. In this embodiment, a hard disk is used as the recording disk.
Minute gaps are formed between the sleeve 21 and the counter plate 22 and the shaft 32 and the annular member 33, and between the lower surface of the disk portion 31 a of the hub 31 and the upper end surface of the sleeve 21. The minute gap is filled with the lubricating oil 40.
Lubricating oil 40 is in contact with the outside air at a capillary seal portion 41 formed by the inner peripheral surface of the annular wall 31d and the outer peripheral surface of the sleeve 21 that is radially opposed to the inner peripheral surface. A meniscus gas-liquid interface in the lubricating oil 40 is located in the capillary seal portion 41. The capillary seal portion 41 has a tapered shape in which the gap is reduced as it advances upward.

Between the inner peripheral surface of the sleeve 21 and the outer peripheral surface of the shaft 32, a pair of radial dynamic pressure bearings 42 and 43 having a herringbone-shaped dynamic pressure generating groove array are formed. The radial dynamic pressure generating groove array generates a supporting force that supports the shaft 32 in the radial direction when the spindle motor rotates in a predetermined direction. A thrust dynamic pressure bearing portion 44 having a spiral thrust dynamic pressure generating groove array is formed between the upper end surface of the sleeve 21 and the lower surface of the disc portion 31a. When the spindle motor rotates in a predetermined direction, the thrust dynamic pressure groove array increases the pressure of the lubricating oil radially inward from the region where the thrust dynamic pressure generating groove array is disposed. In addition, a support force that causes the hub 31 to float upward in the axial direction is generated.
In the present embodiment, the shaft rotation type spindle motor in which the shaft 32 rotates has been described. However, the present invention is not limited to this. For example, the present invention can be suitably applied to a fixed shaft type spindle motor in which the shaft does not rotate.
Further, the present invention can be suitably applied to various industrial motors using fluid dynamic pressure bearings.

[Example 1]
A 3 L four-necked flask equipped with a stirrer, a thermometer, a nitrogen blowing tube, and a dehydrating tube equipped with a condenser was prepared, and 1,12-dodecanediol (809.3 g) (4 mol) and 2-methylpentane An acid (1393.9 g) (12 mol) was charged and reacted at 200 ° C. for 8 hours at normal pressure. Excess fatty acid was distilled off under reduced pressure (3 mmHg), followed by washing with a 20% aqueous sodium hydroxide solution (630 g) (80 ° C.), further washing with 1 L of water four times, and dehydration under reduced pressure (less than 275 ° C.) 4 mmHg or less) for 2 hours. Further, the desired diester was obtained from the above residue at 280 to 283 ° C. under reduced pressure of 4 mmHg.

[Example 2, Comparative Examples 1-8]
The diesters of Example 2 and Comparative Examples 1 to 8 were obtained in the same manner as in Example 1 except that the aliphatic dihydric alcohol and the aliphatic monocarboxylic acid shown in Table 1 were used. Comparative Example 2 corresponds to Example 1 described in Patent Document 1. Comparative Examples 6 to 8 correspond to Examples 1 to 3 described in JP 2008-69234 A.

Example 3
The lubricating oil of Example 3 was prepared by adding an amine antioxidant and an antistatic agent to the lubricating base oil prepared in Example 1.
Example 4
The lubricating oil of Example 5 was prepared by adding an amine antioxidant, a phenolic antioxidant, and an antistatic agent to the lubricating base oil prepared in Example 1.
Example 5
The lubricating oil of Example 5 was prepared by adding an amine-based antioxidant and an antistatic agent to the lubricating base oil prepared in Example 2.
<Test method>
・ Kinematic viscosity and viscosity index The kinematic viscosity at 100 ° C. and 40 ° C. is measured using a precision thermostat for kinematic viscosity measurement (Cata. (40 ° C)) using JIS K 2283. : Measured according to 1983. The viscosity index is JIS K 2283 based on the measured kinematic viscosity. : Calculated according to 1983.
-Pour point The pour point was measured in accordance with the provisions of JIS K 2269: 1987, using a pour point tester (manufactured by Kogaisha, Cat. No. 520R, 14L).

<Evaluation criteria>
・ Kinematic viscosity (100 ℃)
× <2.90mm ² / s
2.90mm ² / s ≤ ○ ≤ 3.20mm ² / s
3. 20mm ² / s <×
・ Viscosity index 160 ≦ ○
× <160

In the table, the unit “%” of the additive is based on the total mass of the ester obtained above, the amine-based antioxidant, the phenol-based antioxidant, and the antistatic agent. Examples 1 and 2 and Comparative Examples 1 to 8 represent the kinematic viscosity and viscosity index of the base oil, and Examples 3 to 5 represent the kinematic viscosity and viscosity index of the lubricating oil.
As is apparent from Tables 1 and 2, the lubricating base oil and the lubricating oil for fluid dynamic pressure bearings of the present invention satisfy a viscosity region in which the fluid dynamic pressure bearing can sufficiently support the load of the rotating body at a high temperature range, In addition, it exhibits excellent viscosity characteristics with a small increase in viscosity at low temperatures. Therefore, the present invention is suitable as a lubricating base oil and lubricating oil for fluid dynamic pressure bearings.

2 stationary part 3 fluid dynamic pressure bearing 4 rotating part 10 base plate 11 flat part 13 boss part 14 annular step part 17 stator 20 bearing stationary part 21 sleeve 22 counter plate 31 hub 31a disc part 31b cylindrical part 31c flange part 31d annular wall 32 Shaft 33 Annular member 34 Rotor magnet 40 Lubricating oil 41 Capillary seal portion 42, 43 Radial dynamic pressure bearing 44 Thrust dynamic pressure bearing portion

Claims (8)

A lubricating base oil for fluid dynamic pressure bearings containing a diester of an aliphatic dihydric alcohol and an aliphatic monocarboxylic acid,
The aliphatic dihydric alcohol is a linear dihydric alcohol having 11 or more carbon atoms, and the aliphatic monocarboxylic acid is a branched aliphatic monocarboxylic acid having 7 or less carbon atoms,
The base oil has a kinematic viscosity at 100 ° C. of 2.90 to 3.20 mm ² / s,
The base oil has a viscosity index of 160 or more,
Lubricating base oil for fluid dynamic bearings.   The lubricating base oil for fluid dynamic bearings according to claim 1, wherein the aliphatic monocarboxylic acid is selected from the group consisting of 2-methylpentanoic acid, 2-ethylbutanoic acid, and mixtures thereof.   The lubricating base oil for fluid dynamic pressure bearing according to claim 1 or 2, wherein the aliphatic dihydric alcohol is linear 1,12-dodecanediol.   The aliphatic dihydric alcohol is linear 1,12-dodecanediol, and the aliphatic monocarboxylic acid is 2-methylpentanoic acid or a mixture of 2-methylpentanoic acid and 2-ethylbutanoic acid. The lubricating base oil for fluid dynamic pressure bearings according to any one of?   A lubricating oil for fluid dynamic pressure bearings, comprising the lubricating base oil for fluid dynamic pressure bearings according to any one of claims 1 to 4.   Furthermore, the lubricating oil for fluid dynamic pressure bearings of Claim 5 which contains 0.01-5 mass% of amine antioxidants and / or 0.01-5 mass% of phenolic antioxidants.   Furthermore, the lubricating oil for fluid dynamic pressure bearings of Claim 5 or 6 which contains 0.01-0.1 mass% of antistatic agents. A stationary part having a stator;
A rotating part having a rotor magnet;
A fluid dynamic bearing that rotatably supports the rotating part with respect to the stationary part;
Lubricating oil for fluid dynamic pressure bearing according to any one of claims 5 to 7,
With spindle motor.

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