JP2007186710A - Lubricant for fluid bearing, fluid bearing and motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lubricant for a fluid bearing, having low viscosity in a low temperature range, hardly reducing the viscosity even in a high temperature range, and hardly causing change of viscosity characteristics with time. <P>SOLUTION: The lubricant for the fluid bearing is obtained by mixing two or more kinds of oils regulated so that the difference between the maximum value and the minimum value of the evaporation rates of the mixed oils may be ≤0.5×10<SP>-2</SP>mg/(mm<SP>2</SP>×hr). The viscosity of the lubricant is preferably within the range of 15-25 mPa s. The lubricant obtained by mixing dioctyl pimelate, diisononyl adipate, dioctyl sebacate, glycol esters or the like is preferable as the lubricant for the fluid bearing, and the evaporation rate of the oil to be mixed is preferably ≤7.0×10<SP>-2</SP>mg/(mm<SP>2</SP>×hr). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fluid bearing lubricant (hereinafter sometimes simply referred to as a “lubricant”), and more particularly to a fluid bearing lubricant with little change in viscosity characteristics even when used for a long period of time.

  Conventionally, ball bearings and roller bearings have been used as bearings for motors used in hard disk drives and the like, but fluid bearings are being developed and put into practical use in recent years due to demands for motor miniaturization, low vibration and low noise. FIG. 1 shows a partial cross-sectional view of a fluid dynamic bearing. The fixed shaft 1 has a structure in which a lower end portion of the shaft portion 11 is fixed to the base member 4 and a disk-like thrust plate 12 is extended in the radial direction on the upper portion of the shaft portion 11. The rotating sleeve body 2 is rotatably fitted to the fixed shaft 1 as described above, and the lubricant 3 is held in the minute gap between the fixed shaft 1 and the rotating sleeve body 2 by utilizing capillary action. A pair of dynamic pressure generating grooves (for example, herring bones) 22 are formed in the inner peripheral surface of the sleeve portion 21 of the rotary sleeve body 2 so as to be separated from each other in the axial direction, and between the shaft portion 11 and the sleeve portion 21. A pair of radial bearing portions is configured. In addition, dynamic pressure generating grooves 13 are formed on the upper and lower surfaces of the thrust plate 12, and a pair of thrust bearing portions are formed between the thrust plate 12 and the rotating sleeve body 2.

  In the fluid bearing having such a configuration, when the rotating sleeve body 2 rotates, the lubricant 3 held in the gap between the rotating sleeve body 2 and the fixed shaft 1 follows the groove pattern of the dynamic pressure generating grooves 22 and 13. As a result, a local high pressure portion is generated in the lubricant 3 to support the radial load of the rotating sleeve body 2 in the pair of radial bearing portions, and the rotating sleeve body 2 is supported in the pair of thrust bearing portions. Supports the load in the thrust direction.

  Here, when the lubricant 3 is in a low temperature range such as when the motor is started, if the viscosity of the lubricant 3 is high, the viscous resistance of the lubricant 3 with respect to the power generating grooves 22 and 13 during rotation increases, and the power loss of the motor Becomes larger. On the other hand, when the lubricant 3 is in a high temperature range, such as when the rotary sleeve body 2 is continuously rotated, if the lubricant 3 is thermally expanded and its viscosity is reduced, the bearing rigidity is reduced and the rotary sleeve body 2 is sufficiently supported. I can't do that. For this reason, the fluid bearing lubricant is required to have seemingly contradictory viscosity characteristics that the viscosity is low at a low temperature range and does not decrease even at a high temperature range.

  In order to satisfy such viscosity characteristics, for example, as disclosed in Japanese Patent Application Laid-Open No. 11-51479, a lubricant using a base oil in which a high-viscosity oil and a low-viscosity oil are mixed; As disclosed in JP-A-8-34987, lubrication for fluid bearings that exhibits good characteristics by adding an additive such as an antioxidant or an extreme pressure additive to a base oil mainly composed of a specific carbonate compound. Agents have been proposed previously.

Japanese National Patent Publication No. 11-51479 Japanese Patent Laid-Open No. 08-034987

  However, although the conventionally proposed lubricants have the desired effects at the beginning of use, the desired effects cannot be continuously achieved because the viscosity characteristics change when used for a long time.

  The present invention has been made in view of such conventional problems, and the viscosity characteristics are not affected by the temperature and the period of use, that is, sufficient bearing rigidity is obtained even in a high temperature range while having a low viscosity in a low temperature range. It is an object of the present invention to provide a fluid bearing lubricant and fluid bearing, and a motor that can be changed and that does not change over time, such as a composition change due to long-term use, which affects viscosity characteristics. is there.

According to the present invention, it is a fluid bearing lubricant in which two or more kinds of oils are mixed, and the difference between the maximum value and the minimum value of the evaporation rate of the mixed oil is 0.5 × 10 ⁻² mg / (mm ² · hr) A lubricant for a hydrodynamic bearing is provided.

  The evaporation rate here refers to the measured value when the oil to be measured is poured into a 5 mm diameter aluminum dish using a thermogravimetric analyzer (TGA) and then heated to 120 ° C. Say.

  Here, the viscosity of the lubricant is preferably in the range of 15 to 25 mPa · s from the viewpoint of sufficiently supporting the load of the rotating body during rotation and suppressing an increase in power loss at the start of rotation of the rotating body. In addition, the viscosity said here means the measured value at 20 degreeC using the viscometer "VT501" (made by HAAKE).

The fluid bearing lubricant is preferably a mixture of dioctyl pimelate, diisonyl adipate, dioctyl sebacate, glycol ester, etc., and the evaporation rate of the oil to be mixed is 7.0 × 10 ⁻² mg / (mm ² · hr) or less. More preferably, the evaporation rate of the oil to be mixed is 5.0 × 10 ⁻² mg / (mm ² · hr) or less. The viscosity of the lubricant is preferably in the range of 15 to 25 mPa · s. The mixing ratio of two or more kinds of oils may be in the range of 2: 8 to 8: 2 by weight. It can apply to a fluid bearing and a motor using this lubricant for fluid bearings.

In the fluid bearing lubricant of the present invention, two or more kinds of oils are mixed, and the difference between the maximum value and the minimum value of the evaporation rate of the mixed oil is 0.5 × 10 ⁻² mg / (mm ² · hr) or less, an excellent characteristic is obtained in that the viscosity is low in the low temperature range, the viscosity does not decrease even in the high temperature range, and the viscosity characteristics do not change with time. Accordingly, when the lubricant of the present invention is used as a fluid bearing lubricant, the power loss when the rotating body starts rotating is reduced. Further, when the rotating body is continuously rotated, the lubricant viscosity is not easily lowered by the heat generated by the rotation, so that the bearing rigidity of the lubricant is not lowered. Furthermore, even if the temperature of the lubricant rises while the rotating body is being driven, only some of the component oil in the lubricant will not evaporate. Can be prevented.

  The inventors of the present invention have made extensive studies on whether or not a fluid bearing lubricant having a low viscosity in a low temperature range and a viscosity that does not decrease even at a high temperature range and whose viscosity characteristics do not change with time has been obtained. The viscosity characteristics of the agent change over time due to long-term use. For lubricants mixed with several types of oil, the evaporation rate of the oil to be mixed is different. It has been determined that the cause is that the compound) evaporates during use and the composition of the lubricant changes, and the present invention has been made.

A major feature of the fluid bearing lubricant of the present invention is that the difference between the maximum value and the minimum value of the evaporation rate of the oil to be mixed is 0.5 × 10 ⁻² mg / (mm ² · hr) or less. . In general, the evaporation rate of oil is related to the molecular weight. The lower the molecular weight, the higher the evaporation rate, and the higher the molecular weight, the lower the evaporation rate. For this reason, when the temperature of the lubricant rises during driving of the rotating body, oil having a small molecular weight and a high evaporation rate evaporates. As a result, the viscosity of the lubricant at a low temperature increases and the power loss at the start of rotation increases. On the other hand, in the lubricant of the present invention, the difference between the maximum value and the minimum value of the evaporation rate of the oil to be mixed is 0.5 × 10 ⁻² mg / (mm ² · hr) or less. Even when it becomes high, only the specific component oil in the lubricant does not evaporate unevenly, and even if the lubricant is used for a long time, the viscosity characteristics do not change abruptly. A more preferable difference in evaporation rate is 0.35 × 10 ⁻² mg / (mm ² · hr) or less. The evaporation rate of oil can be adjusted by the kind of oil, molecular weight, molecular weight distribution, side chain length, and the like.

  The viscosity of the fluid bearing lubricant of the present invention is preferably in the range of 15 to 25 mPa · s at 20 ° C. This is because by setting the viscosity of the lubricant in such a range, the viscosity can be lowered at a low temperature range and the decrease in viscosity can be reduced even at a high temperature range. When the viscosity of the lubricant is less than 15 mPa · s, there is a possibility that the bearing rigidity of the lubricant is lowered and the load of the rotating body cannot be sufficiently supported when the rotating body rotates. On the other hand, when the viscosity of the lubricant is higher than 25 mPa · s, the power loss at the start of rotation of the rotating body may increase. A more preferable viscosity of the lubricant is in the range of 16.5 to 22.5 mPa · s. The viscosity of the lubricant can be adjusted by the type and mixing ratio of the oil to be mixed, and the viscosity of the oil can be adjusted by its molecular weight, molecular weight distribution, and side chain length.

  The oil used as the material for the fluid bearing lubricant of the present invention is not particularly limited, and conventionally known oils can be used. Examples of such oils include polyol ester oils, diester oils, poly-α-olefin oils, mineral oils, silicone oils, and fluorine oils.

  The polyol ester-based oil has a structure obtained by esterifying a polyhydric alcohol and a saturated or unsaturated fatty acid having 5 to 20 carbon atoms. In the present invention, one or more of these are used in combination. be able to. Examples of the polyhydric alcohol include hexamethylene glycol, neopentyl glycol, decamethylene glycol, pentaerythritol, dipentaerythritol, trimethylolethane, and trimethylolpropane. Examples of the fatty acid having 5 to 20 carbon atoms include pentanoic acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, and eicosanoic acid. Specific examples of the polyol ester oil include ester oils of hexamethylene glycol and caprylic acid and nonanoic acid, and glycol esters such as caprylic acid ester of decamethylene glycol and trimethylolpropane ester of caproic acid and capric acid. .

  The diester oil has a structure in which a monovalent aliphatic alcohol and an aliphatic and aromatic dicarboxylic acid are esterified. In the present invention, one or more of these can be used in combination. . Monovalent aliphatic alcohols include carbons such as butanol, pentanol, hexanol, heptanol, octanol, isooctanol, 2-ethylhexanol, nonanol, decanol, isodecanol, dodecanol, tetradecanol, hexadecanol, octadecanol, etc. An aliphatic alcohol having a number of about 4 to 18 is mentioned. On the other hand, examples of aliphatic and aromatic dicarboxylic acids include adipic acid, sebacic acid, azelaic acid, phthalic acid, isophthalic acid, and terephthalic acid. Such a monovalent aliphatic alcohol and an aliphatic or aromatic dicarboxylic acid are used for esterification reaction to obtain a diester oil. Specifically, dioctyl adipate, diisononyl adipate, dioctyl azelate, dioctyl sebacate and the like are preferably used. The esterification groups may be the same or different. The total acid value of the diester oil is preferably 0.1 mgKOH or less, more preferably 0.05 mgKOH or less.

  The poly-α-olefin-based oil is a mixture of oligomers or polymers of α-olefin or isomerized α-olefin. Examples of the α-olefin include octene, nonene, decene, dodecene, tridecene, tetradecene, pentadecene, hexadecene, heptadecene, octadecene, nonadecene, eicosene, dococene, tetracocene and the like.

  Examples of the mineral oil include paraffinic mineral oil and naphthenic mineral oil.

  As the fluid bearing lubricant of the present invention, a mixture of a polyol ester oil and a diester oil among the above oils is particularly preferable from the viewpoint of wear resistance, thermal stability, and fluidity. As for the mixing ratio, (polyol ester type oil) / (diester type oil) is preferably in the range of 2/8 to 8/2 by weight. This is because if the mixing ratio is less than 2/8, there may be a problem that the thermal stability is insufficient, and if it is more than 8/2, there may be a problem that the fluidity becomes high. A more desirable mixing ratio is in the range of 4/6 to 6/4 by weight. Table 1 shows the viscosity and evaporation rate of typical polyol ester oils and diester oils.

  Two or more kinds of oils can be mixed by a conventionally known mixing method. At this time, as long as it does not impair the effects of the present invention, if necessary, antiwear agents, viscosity index improvers, pour point depressants, antioxidants, metal deactivators, surfactants, rust inhibitors, corrosion inhibitors, etc. Various additives may be blended.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited at all by these.

Comparative Example 1 Hexamethylene glycol caprylate ester (evaporation rate: 7.1 × 10 ⁻² mg / (mm ² · hr)) which is a polyol ester oil and dioctyl sebacate (evaporation rate: diester oil) 0.6 × 10 ⁻² mg / (mm ² · hr)) was mixed at a weight ratio of 3: 1 to obtain a fluid bearing lubricant. The difference in evaporation rate was 6.5 × 10 ⁻² mg / (mm ² · hr). The viscosity of the lubricant was 15.9 mPa · s (20 ° C.). The components of this lubricant were measured using gas chromatography. The measurement results are shown in FIG. Time 32.87 is the detection peak for hexamethylene glycol caprylate, and time 35.46 is the detection peak for dioctyl sebacate. Time 32.06 is an impurity detection peak. An environmental test was conducted in which 15 g of the prepared lubricant was placed in a sample bottle having a diameter of 10 mm and left at 120 ° C. for 2 months, and then the components were analyzed using gas chromatography in the same manner as described above. The results are shown in FIG. FIG. 3 shows that the amount of dioctyl sebacate at time 35.46 is increased relative to the hexamethylene glycol caprylate at time 32.87. This means that the relative component amount of dioctyl sebacate increased due to more evaporation of hexamethylene glycol caprylate. When the component ratio was calculated from FIG. 3, the weight ratio of hexamethylene glycol / caprylate ester and dioctyl sebacate was 3: 2. The viscosity of the lubricant increased to 17.9 mPa · s (20 ° C.).

Example 1 Heptamethylene glycol caprylate (evaporation rate: 5.0 × 10 ⁻² ) was used as the polyol ester oil, and dioctyl pimelate (evaporation rate: 5.0 × 10 ⁻² ) was used as the diester oil. These were mixed at a weight ratio of 5: 5 to obtain a lubricant. The difference in evaporation rate between them was zero, and the viscosity of the lubricant was 16.9 mPa · s. After conducting an environmental test in the same manner as in Comparative Example 1, the components of the lubricant were analyzed using gas chromatography. As a result, the component ratio of the lubricant was hardly changed from the initial component ratio. The viscosity was hardly changed.

Example 2 Hexamethylene glycol caprate (evaporation rate: 2.4 × 10 ⁻² ) was used as the polyol ester oil, and diisononyl adipate (evaporation rate: 2.3 × 10 ⁻² ) was used as the diester oil. These were mixed at a weight ratio of 6: 4 to obtain a lubricant. The difference in evaporation rate between them was 0.1 × 10 ⁻² mg / (mm ² · hr), and the viscosity of the lubricant was 19.9 mPa · s. After conducting an environmental test in the same manner as in Comparative Example 1, the components of the lubricant were analyzed using gas chromatography. As a result, the component ratio of the lubricant was hardly changed from the initial component ratio. The viscosity was hardly changed.

Example 3 Decamethylene glycol nonanoic acid ester (evaporation rate: 0.6 × 10 ⁻² ) was used as the polyol ester oil, and dioctyl sebacate (evaporation rate: 0.6 × 10 ⁻² ) was used as the diester oil. These were mixed at a weight ratio of 4: 6 to obtain a lubricant. The difference in evaporation rate between them was zero, and the viscosity of the lubricant was 22.0 mPa · s. After conducting an environmental test in the same manner as in Comparative Example 1, the components of the lubricant were analyzed using gas chromatography. As a result, the component ratio of the lubricant was hardly changed from the initial component ratio. The viscosity was hardly changed.

Example 4 Decamethylene glycol nonanoic acid ester (evaporation rate: 0.6 × 10 ⁻² ) was used as the polyol ester oil, and dioctyl azelate (evaporation rate: 1.0 × 10 ⁻² ) was used as the diester oil. These were mixed at a weight ratio of 4: 6 to obtain a lubricant. The difference in evaporation rate between them was 0.4 × 10 ⁻² mg / (mm ² · hr), and the viscosity of the lubricant was 21.4 mPa · s. After conducting an environmental test in the same manner as in Comparative Example 1, the components of the lubricant were analyzed using gas chromatography. As a result, the component ratio of the lubricant was hardly changed from the initial component ratio. The viscosity was hardly changed.

It is a partial cross section figure which shows the structure of a fluid bearing. It is a figure which shows the measurement result by the gas chromatography about the lubricant of the comparative example 1. It is a figure which shows the measurement result by the gas chromatography about the lubricant after the environmental test of the comparative example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fixed shaft 2 Rotating sleeve body 3 Lubricant 4 Base member 11 Shaft part 12 Thrust plate 13, 22 Dynamic pressure generating groove 21 Sleeve part

Claims (9)

A fluid bearing lubricant in which two or more types of oil are mixed,
At least one kind of oil is dioctyl pimelate, and the difference between the maximum value and the minimum value of the evaporation rate of the oil mixed with dioctyl pimelate is 0.5 × 10 ⁻² mg / (mm ² · hr) or less A lubricant for fluid bearings, characterized in that A fluid bearing lubricant in which two or more types of oil are mixed,
At least one kind of oil is diisonyl adipate, and the difference between the maximum value and the minimum value of the evaporation rate with the oil mixed with diisonyl adipate is 0.5 × 10 ⁻² mg / (mm ² · hr) or less A lubricant for fluid bearings, characterized in that A fluid bearing lubricant in which two or more types of oil are mixed,
At least one kind of oil is dioctyl sebacate, and the difference between the maximum value and the minimum value of the evaporation rate of the oil mixed with dioctyl sebacate is 0.5 × 10 ⁻² mg / (mm ² · hr) or less A lubricant for fluid bearings, characterized in that A fluid bearing lubricant in which two or more types of oil are mixed,
At least one kind of oil is a glycol ester, and the difference between the maximum value and the minimum value of the evaporation rate with the oil mixed with the glycol ester is 0.5 × 10 ⁻² mg / (mm ² · hr) or less. A fluid bearing lubricant characterized by that. A fluid bearing lubricant in which two or more types of oil are mixed,
The evaporation rate of the oil to be mixed is 7.0 × 10 ⁻² mg / (mm ² · hr) or less, and the difference between the maximum value and the minimum value of the evaporation rate of the oil to be mixed is 0.5 × 10 ⁻² A lubricant for fluid bearings, characterized in that it is not more than mg / (mm ² · hr). The fluid bearing lubricant according to any one of claims 1 to 5, wherein the viscosity of the lubricant is in a range of 15 to 25 mPa · s. The fluid bearing lubricant according to any one of claims 1 to 6, wherein a mixing ratio of the two or more kinds of oils ranges from 2: 8 to 8: 2 by weight. A fluid bearing comprising a shaft and a sleeve, wherein the fluid bearing lubricant according to any one of claims 1 to 7 is used. A bracket for holding the stator;
A rotor that rotates relative to the bracket;
A rotor magnet fixed to the rotor and generating a rotating magnetic field in cooperation with the stator;
In a motor provided with a fluid bearing that supports rotation of the rotor,
The motor according to claim 8, wherein the fluid bearing is a fluid bearing.

Images