JP2016138244A - Grease, rolling bearing, rolling bearing device and information recording and reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rolling bearing sufficiently reducing out gas amount from grease and having excellent durability.SOLUTION: There is provided grease containing a base oil and a thickener, where the base oil contains a mineral oil and poly-α-olefin, percentage of the mineral oil to 100 mass% of the base oil is 10 to 40 mass%, kinetic viscosity νat 40°C of the mineral oil is higher than kinetic viscosity νat 40°C of the poly-α-olefin. There are provided a rolling bearing, a rolling bearing device 6 and an information recording and reproducing device 1 having the grease.SELECTED DRAWING: Figure 1

Description

  The present invention relates to grease, a rolling bearing, a rolling bearing device, and an information recording / reproducing device.

  2. Description of the Related Art An information recording / reproducing apparatus such as a hard disk drive (HDD) is known as a device for recording and reproducing various types of information magnetically or optically on a disk. The information recording / reproducing apparatus generally includes a swing arm provided with a head gimbal assembly (magnetic head) for recording / reproducing a signal on a disk at a tip, a rolling bearing device serving as a fulcrum of rotation of the swing arm, and a swing arm. And an actuator to be rotated. Signals can be recorded and reproduced by rotating the swing arm and moving the magnetic head to a predetermined position on the disk.

  A rolling bearing device generally includes two rolling bearings in which a plurality of spherical rolling elements are provided between an inner ring and an outer ring, and a shaft inserted inside the rolling bearing. The outer ring rotates around the shaft axis by the rolling of the plurality of rolling elements, and accordingly, the swing arm connected to the outer ring rotates. Since the rolling bearing is required to operate stably for a long period of time, grease is used for the purpose of smoothing the movement of the rolling elements between the inner ring and the outer ring.

  The rolling bearing grease of the information recording / reproducing apparatus can reduce the torque of the rolling bearing and can provide excellent torque smoothness (property that the torque is uniform in the rotation direction of the rolling bearing). It is required to increase the durability of the bearing. In addition, if outgas from the grease accumulates in the gap between the magnetic head and the disk, a problem occurs in reading and writing of the information recording / reproducing apparatus. Therefore, it is also important that the rolling bearing grease has a small outgas amount.

  Examples of grease for rolling bearings of information recording / reproducing apparatuses include base oils containing mineral oil and poly-α-olefin (hereinafter referred to as “PAO”), thickeners (such as urea compounds), and extreme pressure agents. (Organic phosphorus compound etc.) is known (patent document 1). The grease has a relatively small outgas amount, and can make the rolling bearing low in torque, excellent in torque smoothness, and excellent in durability. However, in recent years, with the increase in the density of HDDs and the increasing demand for server applications, the distance between the disk and the magnetic head has become nano-order, so further reduction of the outgas amount and improvement in durability are required. Yes.

  As grease that can reduce the amount of outgas, there has been proposed a rolling bearing grease that uses only PAO as a base oil without using mineral oil having a larger amount of outgas than PAO (Patent Document 2). However, with this grease, although the amount of outgas is small, it is difficult to obtain a rolling bearing having sufficient durability.

Japanese Patent Application Laid-Open No. 2003-239954 JP 2013-174334 A

  An object of the present invention is to provide a grease in which the amount of outgas is sufficiently reduced and the excellent durability of the applied device can be secured, and a rolling bearing, a rolling bearing device and an information recording / reproducing device using the grease. To do.

The grease of the present invention contains a base oil and a thickener, the base oil contains mineral oil and PAO, and the ratio of the mineral oil is 10 to 40% by mass with respect to 100% by mass of the base oil. The kinematic viscosity ν ₁ at 40 ° C. of the PAO is higher than the kinematic viscosity ν ₂ at 40 ° C. of the PAO.

In the grease of the present invention, it is preferable that the proportion of the PAO is larger than the proportion of the mineral oil in the base oil.
Further, it is preferable that the kinematic viscosity [nu ₁ ratio ν ₁ / ν ₂ with respect to the kinematic viscosity [nu ₂ is 1.3 or more.
The kinematic viscosity ν ₁ is preferably 40 mm ² / s or more.
The kinematic viscosity ν ₂ is preferably 20 mm ² / s or more.
The kinematic viscosity ν at 40 ° C. of the base oil is preferably 25 to 45 mm ² / s.
In the grease of the present invention, the base oil preferably contains a refined mineral oil classified as Group III in the base oil category defined by the American Petroleum Institute, and the flash point of the refined mineral oil is preferably 240 ° C. or higher. More preferably, the temperature is higher than or equal to ° C.
The poly-α-olefin preferably contains a mixture of 3 to 5 monomers of an α-olefin having 8 to 12 carbon atoms.
The thickener is preferably a urea compound.

The rolling bearing of the present invention includes the grease of the present invention.
The rolling bearing device of the present invention includes a shaft and the rolling bearing of the present invention.
The information recording / reproducing apparatus of the present invention includes the rolling bearing device of the present invention.

In the grease of the present invention, the outgas amount is sufficiently reduced, and the excellent durability of the applied apparatus can be ensured.
Further, the rolling bearing, the rolling bearing device and the information recording / reproducing device of the present invention have a sufficiently reduced outgas amount from the grease and are excellent in durability.

It is the perspective view which showed an example of the information recording / reproducing apparatus of this invention. It is the longitudinal cross-sectional view which showed the rolling bearing apparatus periphery in the information recording / reproducing apparatus of FIG. It is sectional drawing which showed the rolling bearing apparatus of FIG. It is the top view which showed the rolling bearing in the rolling bearing apparatus of FIG. It is AA sectional drawing of the rolling bearing of FIG. It is the perspective view which showed the retainer of the rolling bearing of FIG. It is the graph which showed the relationship between standing time when a grease was left still at 85 degreeC, and evaporation loss. It is the graph which showed the relationship between standing time when a grease was left still at 100 degreeC, and evaporation loss. It is the graph which showed the relationship between standing time when a grease was left still at 130 degreeC, and evaporation loss.

[Grease]
The grease of the present invention contains a base oil and a thickener.

(Base oil)
Base oils include mineral oil and PAO.
As mineral oil, well-known mineral oil used as base oil can be used, for example, naphthenic mineral oil, paraffinic mineral oil, hydrogenated mineral oil, solvent refined mineral oil, highly refined mineral oil, etc. are mentioned.
As mineral oil, 1 type may be used independently and 2 or more types may be used together. For example, you may use what mixed several mineral oil from which dynamic viscosity differs, and adjusted to the target dynamic viscosity (average dynamic viscosity).

  Mineral oil is classified into Group III (GrIII) in the API (American Petroleum Institute, American Petroleum Institute) base oil category because it has less outgas, better heat resistance, and excellent low-temperature properties. Refined mineral oils are preferred. Examples of the refined mineral oil include paraffinic mineral oil obtained by further highly hydrorefining a lubricating oil fraction obtained by atmospheric distillation of crude oil. The refined mineral oil classified into Group III preferably has a flash point of 240 ° C. or higher, and more preferably 250 ° C. or higher. Such refined mineral oil has a high degree of purification and can further reduce the amount of outgas. As this reason, it is estimated that the low molecular weight component which causes an outgas is reduced.

As the PAO, known PAO used as a base oil can be used without limitation. For example, α-olefins (1-octene, 1-nonene, 1-decene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-octene, Pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, 1-eicocene, 1-docosene and the like. Among them, as PAO, from the viewpoint that the outgas amount and the evaporation loss are reduced, the oxidation deterioration deterioration characteristics are excellent, and an appropriate viscosity is obtained, 1 to 3 of 1 to 5 mer of α-olefin having 8 to 12 carbon atoms. It is preferable to use seeds alone or in combination of two or more.
As PAO, 1 type may be used independently and 2 or more types may be used together. For example, a mixture of a plurality of PAOs having different kinematic viscosities and adjusted to the target kinematic viscosity (average kinematic viscosity) may be used. It is particularly preferable to use a mixture of 3 to 5 monomers of an α-olefin having 8 to 12 carbon atoms from the viewpoint that the amount of outgas and long-term evaporation loss are small and the oxidation deterioration resistance is excellent.

The base oil may contain other oil components other than mineral oil and PAO in addition to mineral oil and PAO. Examples of other oil components include synthetic oils such as ester oils.
As another oil component, 1 type may be used independently and 2 or more types may be used together.

<Kinematic viscosity>
In the grease of the present invention, the kinematic viscosity ν ₁ of mineral oil at 40 ° C. is higher than the kinematic viscosity ν ₂ of PAO at 40 ° C. When the kinematic viscosity ν ₁ of the mineral oil is higher than the kinematic viscosity ν _{2 of} PAO, the heat resistance of the mineral oil becomes excellent. As a result, the amount of outgas from the mineral oil is reduced, and as a result, the amount of outgas from the base oil is sufficiently reduced. Further, the PAO having a kinematic viscosity ν ₂ lower than the kinematic viscosity ν _{1 of the} mineral oil is combined, so that the kinematic viscosity ν of the base oil becomes sufficiently low. Therefore, a sufficient amount of grease is supplied to a portion requiring the grease, such as a portion where the rolling element of the rolling bearing is rolling, and a lubricating effect by the grease is sufficiently obtained.
The kinematic viscosity of the oil in the present invention means a value measured at 40 ° C. according to JIS K2283.
When a plurality of base oils of the same kind having different kinematic viscosities are mixed, the kinematic viscosity of the mixture is considered as the kinematic viscosity of the base oil.

The ratio ν ₁ / ν ₂ of the kinematic viscosity [nu ₁ of mineral oil on the kinematic viscosity [nu ₂ of the PAO, from the standpoint of easily reducing the outgassing amount is preferably 1.3 or more, more preferably 1.5 or more. Further, the ratio ν ₁ / ν ₂ is preferably 4 or less, and more preferably 2 or less, from the viewpoint of reducing the torque of the rolling bearing.

The kinematic viscosity ν _{1 of the} mineral oil is preferably 40 mm ² / s or more, more preferably 45 mm ² / s or more, from the viewpoint of easily reducing the amount of outgas. Further, the kinematic viscosity ν _{1 of the} mineral oil is preferably 80 mm ² / s or less, preferably 60 mm ² / s or less, from the viewpoint that grease or base oil is easily supplied to a surface that requires grease such as a rolling surface of a rolling bearing. Is more preferable.

The kinematic viscosity ν _{2 of} PAO is preferably 20 mm ² / s or more, more preferably 30 mm ² / s or more, from the viewpoint of easily reducing the amount of outgas. Further, PAO has a kinematic viscosity ν ₂ of preferably 60 mm ² / s or less, preferably 40 mm ² / s or less, from the viewpoint that grease or base oil is easily supplied to a part requiring grease such as a rolling surface of a rolling bearing. Is more preferable.

Kinematic viscosity ν at 40 ° C. of the base oil is preferably ^{25~45mm 2 / s, 30~40mm 2 /} s is more preferable. If the kinematic viscosity ν of the base oil is equal to or higher than the lower limit, the outgas amount can be easily reduced. If the kinematic viscosity ν of the base oil is not more than the above upper limit value, the grease or the base oil is likely to be supplied to a portion that requires grease, such as the rolling surface of the rolling bearing. Further, even in applications that require stable operation at low temperatures (for example, in-vehicle applications that require stable operation even at low temperatures of −30 ° C.), operation can be performed with low torque. In particular, when the ratio of mineral oil to 100% by mass of the base oil is 30% by mass or less, if the kinematic viscosity ν at 40 ° C. of the base oil is 25 mm ² / s or more, the outgas amount is smaller.

(Thickener)
The thickener serves to keep the grease semi-solid.
As the thickener, a known thickener usually used for grease can be used without limitation. Specific examples of the thickener include a urea compound and lithium soap. Among these, as the thickener, a urea compound is preferable from the viewpoint of excellent heat resistance, and a diurea compound having two urea bonds in one molecule is more preferable.

Examples of the diurea compound include an aliphatic diurea compound whose end is an aliphatic group, an alicyclic diurea compound whose end is an alicyclic group, and an aromatic diurea compound whose end is an aromatic group.
Specific examples of the diurea compound include compounds obtained by reaction of diisocyanates (phenylene diisocyanate, tolylene diisocyanate, etc.) and monoamines (octylamine, dodecylamine, stearylamine, aniline, p-toluidine, etc.).

Examples of the lithium soap include lithium stearate and lithium 12-hydroxystearate.
As a thickener, 1 type may be used independently and 2 or more types may be used together.

(Other ingredients)
The grease of the present invention may contain other components other than the base oil and the thickener, if necessary, in addition to the base oil and the thickener.
As other components, known components that are usually used in grease can be used, and examples thereof include additives such as extreme pressure agents, antioxidants, rust inhibitors, oiliness improvers, and metal deactivators.

Examples of extreme pressure agents include organic molybdenum compounds (such as molybdenum dithiocarbamate and molybdenum dithiophosphate), organic fatty acid compounds (such as oleic acid, naphthenic acid, and succinic acid), and organic phosphorus compounds (such as trioctyl phosphate and triphenyl phosphate). , Triethyl phosphate, etc.), phosphate esters and the like. Further, as the extreme pressure agent, zinc dithiocarbamate, antimony dithiocarbamate, or the like may be used.
As an extreme pressure agent, 1 type may be used independently and 2 or more types may be used together.

  Examples of the antioxidant include phenolic antioxidants (2,6-di-t-butyl-4-methylphenol and the like), amine antioxidants (p, p′-dioctyldiphenylamine and the like), and the like. . As antioxidant, 1 type may be used independently and 2 or more types may be used together. When the grease of the present invention contains an antioxidant, it is preferable to use a combination of a phenolic antioxidant and an amine antioxidant. In this case, it is more preferable that the content of the amine-based antioxidant in the grease is larger than the content of the phenol-based antioxidant.

Examples of the rust preventive include alkali metal salts or alkaline earth metal salts of organic sulfonic acids (calcium sulfonate, magnesium sulfonate, barium sulfonate, etc.) and polyhydric alcohols (sorbitan monooleate, etc.). Examples include partial esters.
As a rust preventive agent, 1 type may be used independently and 2 or more types may be used together.

(Ratio of each component)
The ratio of the base oil to 100% by mass of the grease of the present invention is preferably 75 to 93% by mass, and more preferably 80 to 90% by mass. If the ratio of the base oil is equal to or higher than the lower limit value, the grease or the base oil is easily supplied to a surface that requires grease, such as a rolling surface of a rolling bearing. If the ratio of the base oil is equal to or less than the above upper limit value, the grease is semi-solid and difficult to leak and scatter.

  The ratio of the mineral oil to 100% by mass of the base oil is 10 to 40% by mass, and preferably 20 to 30% by mass. If the ratio of mineral oil is equal to or greater than the lower limit, a grease having a good balance between durability and torque smoothness can be obtained. If the ratio of mineral oil is not more than the above upper limit value, a grease with a sufficiently reduced outgas amount can be obtained.

  50-90 mass% is preferable and, as for the ratio of PAO with respect to 100 mass% of base oils, 60-80 mass% is more preferable. If the PAO ratio is equal to or greater than the lower limit, it is easy to obtain a grease with a sufficiently reduced outgas amount. When the proportion of PAO is not more than the above upper limit value, a grease having a good balance between durability and torque smoothness can be obtained.

  The total ratio of mineral oil and PAO to 100% by mass of the base oil is preferably 70% by mass or more, more preferably 80% by mass or more, and further preferably 90% by mass or more. If the total ratio of mineral oil and PAO is equal to or higher than the lower limit, a low torque grease can be easily obtained. The upper limit of the total ratio of the mineral oil and PAO is 100% by mass.

In the grease of the present invention, it is preferable that the proportion of PAO is larger than the proportion of mineral oil in the base oil because it is easy to achieve both a reduction in the amount of outgas and excellent durability.
The mass ratio of PAO to mineral oil in the base oil (PAO / mineral oil) is preferably 1.25 to 9, and more preferably 1.5 to 4. If the mass ratio is greater than or equal to the lower limit, the outgas amount can be easily reduced sufficiently. If the said mass ratio is below the said upper limit, the outstanding durability and torque smoothness will be easy to be obtained.

  The ratio of the thickener to 100% by mass of the grease of the present invention is preferably 7 to 20% by mass, and more preferably 10 to 15% by mass. If the proportion of the thickener is equal to or greater than the lower limit, the grease is semi-solid and is difficult to leak and scatter. If the ratio of the thickener is equal to or less than the upper limit value, grease or base oil is likely to be supplied to a surface that requires grease, such as a rolling surface of a rolling bearing.

The ratio of the extreme pressure agent to 100% by mass of the grease of the present invention is preferably 0.2 to 4% by mass, and more preferably 0.5 to 2% by mass.
The ratio of the antioxidant to 100% by mass of the grease of the present invention is preferably 0.05 to 4% by mass, and more preferably 0.2 to 2% by mass.
The ratio of the rust inhibitor to 100% by mass of the grease of the present invention is preferably 0.2 to 4% by mass, and more preferably 0.5 to 2% by mass.

(Use)
The grease of the present invention is particularly useful as a grease used for rolling bearings in information recording / reproducing apparatuses and electronic equipment manufacturing apparatuses. Examples of the electronic device manufacturing apparatus include a semiconductor manufacturing apparatus, a liquid crystal manufacturing apparatus, and a printed board manufacturing apparatus. The grease of the present invention can also be used as grease sealed in a linear guide or a ball screw.

(Action mechanism)
In the grease of the present invention described above, in addition to PAO, mineral oil having a kinematic viscosity ν ₁ higher than the PAO kinematic viscosity ν ₂ is contained in a specific ratio, so that the amount of outgas can be sufficiently reduced, and a rolling bearing, etc. Excellent durability can be secured in an apparatus that requires the above grease. Factors for obtaining the effect are considered as follows.

For example, in a rolling bearing in an information recording / reproducing apparatus, operating conditions such as a swing speed and a rotation range of a swing arm are complicated and wide. With a grease using only PAO having a narrow molecular weight distribution as a base oil as in Patent Document 2, it is difficult to cope with various operating conditions of a rolling bearing. Therefore, the movement of the swing arm cannot be made sufficiently smooth, and it is difficult to ensure excellent durability.
On the other hand, in the grease of the present invention, mineral oil having a broad molecular weight distribution compared with PAO is used in combination with PAO, so that it is possible to cope with various operating conditions of the rolling bearing. For example, even when the swing arm moves at a low speed, an oil film having a sufficient thickness is formed under the influence of a component having a high molecular weight and high viscosity in mineral oil, and a sufficient lubricating effect is exhibited. Even when the swing arm moves at a high speed or when the swing arm moves in a very small range, grease is sufficiently supplied to the part where the rolling element rolls due to the low molecular weight and low viscosity component of the mineral oil. . Thus, since it can respond to the wide operating condition of a rolling bearing, the outstanding durability can be ensured.

In addition, the mineral oil in the grease of the present invention is excellent in heat resistance because the kinematic viscosity ν ₁ is higher than the kinematic viscosity ν _{2 of} PAO, and outgassing is less likely to occur than a mineral oil having a low kinematic viscosity. And in the grease of this invention, the ratio of this mineral oil in base oil is controlled by the specific range. Therefore, the amount of outgas is sufficiently reduced. Further, the PAO having a kinematic viscosity ν ₂ lower than that of the mineral oil can sufficiently reduce the kinematic viscosity ν of the base oil as a whole, so that the torque of the rolling bearing and the like can be suppressed, and grease such as the rolling surface of the rolling element in the rolling bearing can be suppressed. A sufficient amount of grease is supplied to the surface that needs to be used. Therefore, both the effect of reducing outgas and the effect of improving durability can be achieved.

  In addition, since PAO has no polarity, it has low affinity with polar thickeners and additives, and when only PAO is used as the base oil, it is difficult to disperse thickeners and additives uniformly. Is difficult to obtain. However, in the grease of the present invention, the affinity between the base oil and the thickener or additive is improved by using polar mineral oil together with PAO. Thereby, the variation in the size of the thickener synthesized in the base oil is suppressed, the size can be reduced, and the dispersibility of the thickener is excellent, so that the torque smoothness is excellent. And the effect of an additive is fully exhibited.

[Information recording / playback device]
The rolling bearing, the rolling bearing device, and the information recording / reproducing device of the present invention can adopt known modes except for using the grease of the present invention. Hereinafter, an example of the rolling bearing, the rolling bearing device, and the information recording / reproducing device of the present invention will be described.
An information recording / reproducing apparatus 1 according to the present embodiment is an apparatus that performs writing on a disk (magnetic recording medium) D by a perpendicular recording method. As shown in FIG. 1, the disk D, the swing arm 2, and the light guide A waveguide 3, a laser light source 4, a head gimbal assembly (HGA) 5, a rolling bearing device 6, an actuator 7, a spindle motor (rotation drive unit) 8, a control unit 9, and a housing 10 are provided. Yes.

The housing 10 accommodates each component in the information recording / reproducing apparatus 1.
The housing 10 has a rectangular bottom 10a in plan view, a peripheral wall (not shown) erected from the periphery of the bottom 10a, and a lid (not shown) that is detachably fixed to the top of the peripheral wall and closes the opening. And comprising. In the housing 10, each component is accommodated inside the peripheral wall portion on the bottom portion 10a. In FIG. 1, the peripheral wall portion and the lid are omitted for convenience.
The material of the housing 10 is not specifically limited, For example, metal materials, such as aluminum, are mentioned.

  A spindle motor 8 is attached to the approximate center of the bottom 10 a of the housing 10. Further, the center hole formed at the center of the disk D is fitted into the spindle motor 8 so that the three disks D are detachably mounted. The spindle motor 8 can rotate the disk D in a fixed direction around the rotation axis L1.

  An actuator 7 is attached to one corner of the bottom 10 a of the housing 10 so as to be located outside the disk D. A swing arm 2 extending toward the disk D is connected to the actuator 7. A rolling bearing device 6 is provided on the base end side portion of the swing arm 2. By driving by the actuator 7, the swing arm 2 is rotated in a horizontal plane around the rotation axis L <b> 2 of the rolling bearing device 6.

The swing arm 2 includes a base portion 2a connected to the actuator 7 and an arm portion 2b extending from the base portion 2a toward the disk D. The swing arm 2 can be obtained, for example, by integrally forming the base portion 2a and the arm portion 2b by cutting or the like.
The base 2a has a substantially rectangular parallelepiped shape, and is rotatably supported by the rolling bearing device 6 so as to surround the rolling bearing device 6.

The arm portion 2b has a flat plate shape and has a tapered shape that tapers from the base end portion toward the tip end portion. The arm portion 2b extends from the front surface (surface opposite to the corner portion) 2d opposite to the rear surface 2c to which the actuator 7 is attached in the base portion 2a in the surface direction (horizontal plane direction) of the upper surface of the base portion 2a. It is provided as follows.
In the swing arm 2 of this example, the three arm portions 2b are provided in the height direction (vertical direction) of the base portion 2a so that the disk D is sandwiched between the arm portions 2b. In other words, the arm portions 2b and the disk D are alternately arranged in the height direction, and the arm portion 2b is moved in a direction parallel to the disk surface (the surface of the disk D) D1 by driving the actuator 7. It is supposed to be.

  A head gimbal assembly 5 is provided at the tip of the arm portion 2 b in the swing arm 2. A laser light source 4 is provided on the side surface of the base 2 a of the swing arm 2. An optical waveguide 3 that connects the laser light source 4 and the head gimbal assembly 5 is provided on the base 2 a and the arm 2 b of the swing arm 2. Thus, light can be supplied from the laser light source 4 to the head gimbal assembly 5 through the optical waveguide 3.

The head gimbal assembly 5 includes a suspension 5a and a slider 5b attached to the tip of the suspension 5a.
The slider 5b has a near-field light generating element. Near-field light is generated from the near-field light generating element when light is guided from the laser light source 4 to the slider 5b. By using the near-field light, various information can be recorded on or reproduced from the disk D.
The near-field light generating element is configured by, for example, an optical minute aperture, a protrusion formed in a nanometer size, or the like.

  The head gimbal assembly 5 is moved in a direction parallel to the disk surface D1 together with the arm portion 2b of the swing arm 2 by driving the actuator 7. The swing arm 2 and the head gimbal assembly 5 are retracted from the disk D by driving the actuator 7 when the rotation of the disk D is stopped.

  The control unit 9 is connected to the laser light source 4. In the control unit 9, the light beam supplied to the slider 5 b of the head gimbal assembly 5 can be controlled by a current modulated according to information.

(Rolling bearing device)
2 and 3, the rolling bearing device 6 includes a shaft 20, a sleeve 21 installed coaxially with the shaft 20 outside the shaft 20, and 2 installed between the shaft 20 and the sleeve 21. Two rolling bearings 22.

The shaft 20 is a cylindrical rod-shaped member and is erected from the bottom 10 a of the housing 10. The central axis of the shaft 20 is the rotation axis L2 when the swing arm 2 rotates.
A flange portion 20b having a diameter larger than that of the main body portion 20a and a reduced diameter portion 20c having a diameter smaller than that of the main body portion 20a are sequentially provided toward the base end of the shaft 20 on the bottom 10a side of the housing 10. ing. A male screw 20d is formed on the outer peripheral surface of the reduced diameter portion 20c. By inserting the reduced diameter portion 20c of the shaft 20 into the hole 10b provided in the bottom portion 10a of the housing 10, and screwing the female screw 10c formed on the inner peripheral surface of the hole 10b and the male screw 20d of the reduced diameter portion 20c. The shaft 20 is erected on the bottom 10 a of the housing 10. At this time, the shaft 20 is positioned in the height direction by the lower surface of the flange portion 20 b being in contact with the bottom portion 10 a of the housing 10.

The sleeve 21 is a member formed in a cylindrical shape. The inner diameter of the sleeve 21 is substantially the same as the outer diameter of the flange portion 20b.
The sleeve 21 is installed so as to surround the shaft 20 from the outside in the radial direction, and its inner peripheral surface is separated from the outer peripheral surface of the shaft 20 at a predetermined interval. The central axis of the shaft 20 and the central axis of the sleeve 21 coincide with each other.
The sleeve 21 is directly press-fitted into the mounting hole 2e formed in the base 2a of the swing arm 2, is press-fitted through an elastic body such as a metal ring formed in a corrugated shape, or is an adhesive fit. By being combined, the swing arm 2 is combined integrally.

  A spacer portion 21 a that protrudes inward over the entire circumference in the circumferential direction is formed at the center in the height direction on the inner circumferential surface of the sleeve 21. Between the shaft 20 and the sleeve 21, two rolling bearings 22 are installed above and below the spacer portion 21a, respectively, and the distance between the two rolling bearings 22 is maintained at a predetermined distance.

<Rolling bearing>
The two rolling bearings 22 provided in the rolling bearing device 6 are the same.
As shown in FIGS. 3 to 6, the rolling bearing 22 includes an inner ring 30, an outer ring 31, a retainer 32, a plurality of rolling elements 33, and two shield plates 34.

The inner ring 30 is a cylindrical member.
The inner ring 30 has an inner diameter that allows the shaft 20 to be inserted. In the present embodiment, the inner diameter of the inner ring 30 is slightly larger than the outer diameter of the shaft 20. The shaft 20 is inserted into the inner ring 30 and the inner ring 30 is fixed to the shaft 20 with an adhesive or the like.
The inner diameter of the inner ring 30 may be the same as or slightly smaller than the outer diameter of the shaft 20 as long as it can be installed on the shaft 20. In this case, the shaft 20 is press-fitted and fixed to the inner ring 30.

In the rolling bearing 22, a so-called inner ring preload in which the inner ring 30 is fixed to the shaft 20 in a state where a preload is applied to the inner ring 30 in the axial direction relative to the shaft 20 can be employed. Thereby, the rolling bearing 22 can be made highly rigid, and the resonance frequency (resonance point) of the rolling bearing device 6 can be increased. Therefore, the rolling bearing device 6 can cope with higher speed rotation.
The rolling bearing 22 may employ so-called outer ring preload in which the outer ring 31 is fixed to the sleeve 21 in a state in which a preload is applied to the outer ring 31 in the axial direction relative to the shaft 20.

A concave inner ring rolling surface 30 a that guides the rolling of the rolling elements 33 is formed over the entire circumference of the inner ring 30 at an axial intermediate portion of the outer circumferential surface of the inner ring 30. The inner ring rolling surface 30a has an arcuate cross section when cut along a plane passing through the central axis of the inner ring 30.
Examples of the material of the inner ring 30 include metal materials such as stainless steel. The inner ring 30 can be manufactured, for example, by forging or machining.

The outer ring 31 is a cylindrical member that is larger in diameter than the inner ring 30 and is similar to the inner ring 30.
The outer ring 31 is fixed to the inside of the sleeve 21, and is installed outside the inner ring 30 in a state of being separated from the inner ring 30. The inner ring 30 and the outer ring 31 are installed on the same axis so that their central axes coincide with the central axis of the shaft 20.

A concave outer ring rolling surface 31 a that guides the rolling of the rolling element 33 is provided at the intermediate portion in the axial direction on the inner circumferential surface of the outer ring 31 so as to face the inner ring rolling surface 30 a of the inner ring 30. It is formed all around. The outer ring rolling surface 31a has an arcuate cross section when cut along a plane passing through the central axis of the outer ring 31.
Examples of the material of the outer ring 31 include metal materials such as stainless steel. The inner ring 30 can be manufactured, for example, by forging or machining.

As shown in FIG. 6, the retainer 32 is formed from an annular main body portion 32 a and an upper portion of the main body portion 32 a, and seven pairs of claw portions 32 b that rise in an arc shape so as to approach each other toward the tip. , 32c. The seven pairs of claw portions 32 b and 32 c are provided at equal intervals in the circumferential direction of the retainer 32. A ball pocket B having a substantially circular shape when viewed from the front is formed inside the paired claw portion 32b and claw portion 32c so as to hold the rolling element 33 in a rollable manner.
The number of pairs of claws, that is, the number of ball pockets B is not limited to seven, but may be six or less, or may be eight or more.

The inner diameter of the retainer 32 is larger than the outer diameter of the inner ring 30, and the outer diameter of the retainer 32 is smaller than the inner diameter of the outer ring 31. In a state where the retainer 32 is installed between the inner ring 30 and the outer ring 31, the rolling elements 33 are held in the respective ball pockets B so as to be able to roll. Thus, the rolling element 33 is disposed between the inner ring rolling surface 30a of the inner ring 30 and the outer ring rolling surface 31a of the outer ring 31 in a state where the inner ring 30 and the outer ring 31 and the retainer 32 do not interfere with each other.
The retainer 32 can rotate around the central axis L2 in a state where the rolling elements 33 are held in the ball pockets B so as to be able to roll.
The material of the retainer 32 is not particularly limited, and examples thereof include resins such as polyamide resin.

  A grease pocket G having a shallower depth than the ball pocket B is formed between the pair of claw portions 32 b and 32 c at the upper portion of the retainer 32 and the pair of claw portions 32 b and 32 c adjacent thereto. That is, in the retainer 32, ball pockets B and grease pockets G are alternately formed in the circumferential direction by a plurality of pairs of claw portions 32b and 32c.

When the rolling element 33 rotates together with the retainer 32 in a state where the grease of the present invention is disposed in the grease pocket G and the rolling element 33 is disposed in the ball pocket B, the inner ring 30 and the outer ring 31 are rotated from the grease pocket G. Grease oozes out between the moving body 33 and a lubricating effect by the grease is obtained.
By using the grease for the rolling bearing 22 using the grease pocket G, the amount of grease used can be reduced. As a result, it becomes easy to suppress an increase in the torque of the rolling bearing 22 due to an excessive amount of grease, and it becomes easy to obtain a sufficient cleanliness required for reading and writing to the disk D.

The rolling element 33 in this example is spherical. The rolling element 33 is disposed in the ball pocket B of the retainer 32 between the inner ring rolling surface 30a of the inner ring 30 and the outer ring rolling surface 31a of the outer ring 31, and is disposed on the inner ring rolling surface 30a and the outer ring rolling surface 31a. It is designed to roll along. The respective rolling elements 33 are evenly arranged in the circumferential direction by the retainer 32.
Although the number of rolling elements 33 is seven in this example, it may be determined according to the number of ball pockets B in the retainer 32, and may be six or less, or may be eight or more.
Examples of the material of the rolling element 33 include metal materials such as bearing steel.

  The shield plate 34 is an annular plate member that blocks the upper and lower sides of the annular space formed between the inner ring 30 and the outer ring 31. The shield plates 34 are installed above and below the retainer 32 and the plurality of rolling elements 33 between the inner ring 30 and the outer ring 31. Each shield plate 34 is fixed to the outer ring 31 in a state where the outer peripheral edge of the shield plate 34 enters the annular groove 40 for engagement formed in the outer ring 31.

(Action mechanism)
In the information recording / reproducing apparatus 1, the grease of the present invention is disposed in the grease pocket G of the retainer 32 in the rolling bearing 22. When the swing arm 2 is rotated by driving the actuator 7, the grease disposed in the grease pocket G passes through the side surfaces of the inner ring 30, the outer ring 31 and the retainer 32, and is supplied between the inner ring 30 and the outer ring 31 and the rolling element 33. The lubricating effect of grease is exhibited.
Since the information recording / reproducing apparatus 1 uses the grease of the present invention, the amount of outgas is sufficiently reduced. Therefore, outgas hardly accumulates in a gap between the head gimbal assembly and the disk D, and reading and writing can be performed stably. Further, excellent durability can be ensured, and a low torque and excellent torque smoothness can be maintained for a long period of time.

(Other embodiments)
The rolling bearing, the rolling bearing device, and the information recording / reproducing device of the present invention are not limited to those described above as long as the grease of the present invention is used.
For example, the information recording / reproducing apparatus 1 including the rolling bearing 22 and the rolling bearing device 6 uses near-field light, but a general HDD including a rolling bearing and a rolling bearing device using the grease of the present invention may be used. It may be an optical disk D device or the like.

Further, the rolling bearing device may not include a sleeve. Specifically, for example, an annular spacer ring is provided between two rolling bearings that are spaced apart from each other in the axial direction outside the shaft, and the sleeve is provided with an annular spacer ring that keeps the distance between the rolling bearings at a predetermined distance. There may be no rolling bearing device. In this case, the outer ring of the rolling bearing can be directly press-fitted or adhesively fitted into the mounting hole formed in the base of the swing arm.
Further, the rolling element in the rolling bearing may be a cylindrical roller.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by the following description.
[Kinematic viscosity]
The kinematic viscosities of mineral oil, PAO and base oil were measured at 40 ° C. according to JIS K2283 using a Canon-Fenske viscometer.

[Measurement of outgas amount]
A sample grease (4.5 to 5.5 mg) was evenly applied to a 15 mm square aluminum foil with a glass rod to obtain a measurement sample. The measurement sample was heated in an oven at 85 ° C. for 3 hours with 5 μL (100 ng) of a standard reagent (hexadecane), and the generated gas was adsorbed to a collection tube. Next, the collection tube was installed in a heat desorption apparatus (TD-100) and heated to 320 ° C., and the gas generated from the collection tube was sent to a gas chromatograph mass spectrometer (GC-MS). In GC-MS, chromatogram data is obtained by a temperature profile that is held at 40 ° C. for 2 minutes, heated to 280 ° C. over 20 minutes at 12 ° C./minute, and held at 280 ° C. for 20 minutes. Component identification was performed using the library. The outgas amount was calculated in terms of standard reagent based on the chromatographic peak (equivalent to 100 ng) of the standard reagent (hexadecane).

[An endurance test]
The rolling bearing device 6 illustrated in FIGS. 3 to 6 is manufactured, the grease of each example is disposed in the grease pocket G of the retainer 32, and the continuous operation is performed under the following operating conditions, and the continuous operation with respect to the initial torque before the continuous operation is performed. The torque fluctuation range (hash) was measured as the ratio of the subsequent torque.
<Operating conditions>
Operating frequency: 30Hz
Operating angle: 10deg
Operating time: 100 hours Operating environment temperature: 80 ° C

[Grease bump test]
The rolling bearing device 6 illustrated in FIGS. 3 to 6 is manufactured, the grease of each example is placed in the grease pocket G of the retainer 32, the continuous operation is performed under the following operating conditions, and the torque immediately after the continuous operation is measured. Evaluation was made according to the following criteria.
<Operating conditions>
Operating frequency: 15Hz
Operating angle: 5deg
Operating time: 50 hours Operating environment temperature: Room temperature <Evaluation criteria>
○: The torque immediately after the continuous operation hardly changes compared to the initial torque before the continuous operation.
X: The torque immediately after the continuous operation changes greatly compared to the initial torque before the continuous operation.

[Low temperature torque test]
A low temperature torque test is performed at 0 ° C. and −30 ° C. in accordance with JIS K 2220 (Low Temperature Torque Test, bearing: 6204) to determine the starting torque (initial torque) and the rotational torque after the torque is stabilized after starting. Each was measured.

[Long-term evaporation loss test]
Put 5g of grease in a petri dish with an outer diameter of 41mm, an inner diameter of 37mm, and a height of 8mm (storage height of 5mm), and place it in a constant temperature bath at 85 ° C, 100 ° C or 130 ° C with the surface smooth and flat. The grease was weighed out at regular intervals. The evaporation loss (mass%) of the grease was calculated from the change in the mass at each time with respect to the mass of the grease before standing in the thermostat.

[Example 1]
Refined mineral oil (classified as group III in the API base oil category. Kinematic viscosity ν ₁ = 47 mm ² / s (40 ° C.), flash point 250 ° C. or higher) and PAO (α having 8 to 12 carbon atoms) -Mixture of olefin 3-5 mer, kinematic viscosity ν ₂ = 30 mm ² / s (40 ° C)) at a mass ratio of 3: 7, and base oil (kinematic viscosity ν = 34 mm ² / s (40 ° C) )).
Next, the base oil was greased using an alicyclic diurea compound as a thickener, and an antioxidant and a rust inhibitor were added and mixed. The proportion of each component is 86.0% by mass of base oil, 12.5% by mass of thickener, 0.5% by mass of antioxidant, and 1.0% of rust inhibitor with respect to 100% by mass of grease. It was mass%.

[Example 2]
The same procedure as in Example 1 was repeated except that the base oil was greased using an alicyclic diurea compound as a thickener, and an extreme pressure agent was further added and mixed in addition to the antioxidant and the rust inhibitor. The ratio of each component is 85.0% by mass of base oil, 12.5% by mass of thickener, 0.5% by mass of antioxidant, and 1.0% of rust inhibitor with respect to 100% by mass of grease. The mass% and the extreme pressure agent were 1.0 mass%.

[Comparative Example 1]
Mineral oil (kinematic viscosity ν ₁ = 52 mm ² / s (40 ° C.), flash point 220 ° C. or higher), PAO (mixture of 3 to 5 carbon atoms of α-olefins having 8 to 12 carbon atoms), kinematic viscosity ν ₂ = 52 mm ² / S (40 ° C.)) were mixed at a mass ratio of 1: 1 to obtain a base oil (kinematic viscosity ν = 52 mm ² / s (40 ° C.)). Next, the base oil was greased using an alicyclic diurea compound as a thickener, and an antioxidant and a rust inhibitor were added and mixed.

[Comparative Example 2]
The same procedure as in Example 1 was performed except that PAO (mixture of 3 to 5 carbon atoms of α-olefin having 8 to 12 carbon atoms, kinematic viscosity ν = 30 mm ² / s (40 ° C.)) was used as the base oil. A grease was obtained.

[Comparative Example 3]
The same procedure as in Example 2 was performed except that PAO (a mixture of 3 to 5 monomers of α-olefin having 8 to 12 carbon atoms, kinematic viscosity ν = 30 mm ² / s (40 ° C.)) was used as the base oil. A grease was obtained.

[Reference Example 1]
As the grease, a grease α for a rolling bearing of a commercially available information recording / reproducing apparatus was prepared. Grease α contains a urea compound as a thickener.

  Table 1 shows the results of outgas amount measurement, endurance test, and grease bump test of each example and comparative example. Table 2 shows the results of the low-temperature torque test of the greases of Example 2 and Reference Example 1, and FIGS. 7 to 9 show the results of the long-term evaporation loss test.

As shown in Tables 1 and 2, the greases of Examples 1 and 2 including the base oil using the mineral oil having a kinematic viscosity ν ₁ higher than the PAO kinematic viscosity ν _{2 in} the ratio of the present invention had a small outgas amount. . In Examples 1 and 2, the torque variation was small in both the durability test and the grease bump test, and excellent durability was exhibited. In addition, the grease of Example 2 was excellent in low temperature characteristics and had less evaporation loss than the commercially available grease α of Reference Example 1.
On the other hand, the grease of Comparative Example 1 having a large proportion of mineral oil had a large amount of outgas. Further, in Comparative Example 1, the torque fluctuation range in the durability test was large, and the durability was inferior compared to Examples 1 and 2. Furthermore, in the grease bump test, the torque after the continuous operation increased to about 6 times the torque before the continuous operation. This is considered to be caused by oxidation-degraded grease collecting at the edge of the operation range in the continuous operation to form a bump, or by intense wear at the edge of the operation range in the continuous operation.
Moreover, although the outgas amount was small in the grease of Comparative Examples 2 and 3 which did not use mineral oil, it was inferior in durability.

[Experiment 1]
The following four components A to D were measured for the amount of outgas described above.
Component A: Mixture of 3 to 5 mer of α-olefin having 10 carbon atoms (kinematic viscosity ν ₂ = 30 mm ² / s (40 ° C.), hereinafter referred to as PAO (decene)).
Component B: Mixture of 3 to 5 mer of α-olefin having 8 to 12 carbon atoms (kinematic viscosity ν ₂ = 30 mm ² / s (40 ° C.), hereinafter referred to as PAO (MIX)).
Component C: A component obtained by adding an antioxidant to PAO (decene) so that the content of the antioxidant is 0.2% by mass with respect to the total mass of PAO (decene) and antioxidant.
Component D: A component obtained by adding an antioxidant to PAO (MIX) so that the content of the antioxidant is 0.2% by mass with respect to the total mass of PAO (MIX) and the antioxidant.
The results are shown in Table 3.

  As shown in Table 3, compared with the components A and C in which PAO is a single component, the components B and D in which PAO is a mixture of 3 to 5 monomers of α-olefin having 8 to 12 carbon atoms are outgassed. The amount was small.

[Experiment 2]
The components A to D were subjected to an oxidation deterioration test. Specifically, 5 g of each component was sampled in a beaker (inching outer diameter × height: 30 mm × 40 mm) and allowed to stand in a constant temperature bath at 100 ° C. After 240 hours, the components in each beaker were measured by FT-IR every 24 hours to confirm the presence or absence of oxidative degradation. Table 4 shows the time when oxidative degradation was first confirmed.

  As shown in Table 4, compared with the components A and C in which PAO is a single component, components B and D in which PAO is a mixture of 3 to 5 monomers of α-olefins having 8 to 12 carbon atoms are Excellent deterioration.

DESCRIPTION OF SYMBOLS 1 Information recording / reproducing apparatus 2 Swing arm 3 Optical waveguide 4 Laser light source 5 Head gimbal assembly 6 Rolling bearing apparatus 7 Actuator 8 Spindle motor 9 Control part 10 Housing 20 Shaft 21 Sleeve 22 Rolling bearing 30 Inner ring 31 Outer ring 32 Retainer 33 Rolling element 34 Shield Plate B Ball pocket G Grease pocket

Claims (13)

Including base oils and thickeners,
The base oil includes mineral oil and poly-α-olefin,
The ratio of the mineral oil is 10 to 40% by mass with respect to 100% by mass of the base oil,
Kinematic viscosity [nu ₁ at 40 ° C. of the mineral oil is higher than the kinematic viscosity [nu ₂ at 40 ° C. of the poly--α- olefin grease.   The grease according to claim 1, wherein the proportion of the poly-α-olefin is greater than the proportion of the mineral oil in the base oil. Wherein a ratio [nu _{1 /} [nu ₂ of the kinematic viscosity versus kinematic viscosity [nu ₂ [nu ₁ is 1.3 or more, grease according to claim 1 or 2. The grease according to claim 1, wherein the kinematic viscosity ν ₁ is 40 mm ² / s or more. The grease according to claim 1, wherein the kinematic viscosity ν ₂ is 20 mm ² / s or more. Grease as described in any one of Claims 1-5 whose kinematic viscosity (nu) in 40 degreeC of the said base oil is 25-45 mm < ² > / s.   The said base oil contains the refined mineral oil classified into the group III by the base oil category which American Petroleum Institute establishes, and the flash point of the said refined mineral oil is 240 degreeC or more, Any one of Claims 1-6. Grease as described in.   The said base oil contains the refined mineral oil classified into the group III by the base oil category which American Petroleum Institute establishes, and the flash point of the said refined mineral oil is 250 degreeC or more, Any one of Claims 1-6. Grease as described in.   The grease according to any one of claims 1 to 8, wherein the poly-α-olefin comprises a mixture of 3 to 5 monomers of an α-olefin having 8 to 12 carbon atoms.   The grease according to any one of claims 1 to 9, wherein the thickener is a urea compound.   A rolling bearing comprising the grease according to any one of claims 1 to 10.   A rolling bearing device comprising a shaft and the rolling bearing according to claim 11.   An information recording / reproducing apparatus comprising the rolling bearing device according to claim 12.

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