JP6754565B2 - Grease, rolling bearings, rolling bearing devices and information recording / playback devices - Google Patents

Description

The present invention relates to grease, rolling bearings, rolling bearing devices, and information recording / reproducing devices.

An information recording / playback device such as a hard disk drive (HDD) is known as a device that magnetically or optically records and reproduces various types of information on a disk. The information recording / reproducing device generally includes a swing arm provided with a head gimbal assembly (magnetic head) for recording / reproducing a signal on a disk at the tip, a rolling bearing device serving as a fulcrum for rotation of the swing arm, and a swing arm. It is provided with a rotating actuator. Signals can be recorded and played back by rotating the swing arm to move 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 rolling of the plurality of rolling elements causes the outer ring to rotate around the axis of the shaft, and the swing arm connected to the outer ring rotates accordingly. 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 element between the inner ring and the outer ring.

The grease for rolling bearings of information recording / playback equipment can reduce the torque of rolling bearings and obtain excellent torque smoothness (property that the torque is uniform in the rotation direction of rolling bearings), and further roll. It is required that the durability of the bearing can be improved. Further, if the 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 device. Therefore, it is important that the amount of outgas in the grease for rolling bearings is small.

Greases for rolling bearings of information recording / reproduction equipment include, for example, mineral oil, base oil containing poly-α-olefin (hereinafter referred to as “PAO”), thickener (urea compound, etc.), and extreme pressure agent. Those containing (organic phosphorus compounds, etc.) are known (Patent Document 1). The grease has a relatively small amount of outgas, and can make the rolling bearing low in torque, excellent in torque smoothness, and excellent in durability. However, in recent years, as the density of HDDs has increased and the demand for server applications has increased, the distance between the disk and the magnetic head has become nano-order, so further reduction in the amount of outgas and improvement in durability are required. There is.

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

Japanese Unexamined Patent Publication No. 2003-239954 Japanese Unexamined Patent Publication No. 2013-174334

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 ensured, 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 to 100% by mass of the base oil is 10 to 40% by mass, and the mineral oil. The kinematic viscosity ν ₁ at 40 ° C. is higher than the kinematic viscosity ν ₂ of the PAO at 40 ° C.

In the grease of the present invention, it is preferable that the ratio of the PAO is larger than the ratio 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 of the base oil at 40 ° C. is preferably 25 to 45 mm ² / s.
In the grease of the present invention, the base oil contains refined mineral oil classified into 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, preferably 250. More preferably, it is above ° C.
The poly-α-olefin preferably contains a mixture of 3 to pentamers of α-olefin having 8 to 12 carbon atoms.
The thickener is preferably a urea compound.

The rolling bearing of the present invention comprises 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 device of the present invention includes the rolling bearing device of the present invention.

The grease of the present invention has a sufficiently reduced amount of outgas, and can ensure excellent durability of the applied device.
Further, the rolling bearing, the rolling bearing device and the information recording / reproducing device of the present invention have a sufficiently reduced amount of outgas from grease and are excellent in durability.

It is a perspective view which showed an example of the information recording / reproduction apparatus of this invention. It is a vertical cross-sectional view which showed the periphery of the rolling bearing apparatus in the information recording reproduction apparatus of FIG. It is sectional drawing which showed the rolling bearing apparatus of FIG. It is a top view which showed the rolling bearing in the rolling bearing apparatus of FIG. FIG. 6 is a sectional view taken along the line AA of the rolling bearing of FIG. It is a perspective view which showed the retainer of the rolling bearing of FIG. It is a graph which showed the relationship between the standing time and evaporation loss when the grease was left standing at 85 degreeC. It is a graph which showed the relationship between the standing time and evaporation loss when the grease was left standing at 100 degreeC. It is a graph which showed the relationship between the standing time and evaporation loss when the grease was left standing at 130 degreeC.

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

(Base oil)
Base oils include mineral oils and PAOs.
As the mineral oil, a known mineral oil used as a base oil can be used, and examples thereof include naphthenic mineral oil, paraffin mineral oil, hydrogenated mineral oil, solvent refined mineral oil, and highly refined mineral oil.
As the mineral oil, one type may be used alone, or two or more types may be used in combination. For example, a plurality of mineral oils having different kinematic viscosities may be mixed and adjusted to the desired kinematic viscosity (average kinematic viscosity).

As a mineral oil, it is classified into Group III (GrIII) in the API (American Petroleum Institute) base oil category because it can obtain grease with less outgassing amount, excellent heat resistance, and excellent low temperature characteristics. The refined mineral oil produced is preferable. Examples of the refined mineral oil include paraffin-based mineral oil obtained by further 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 refining, and the amount of outgas can be further reduced. It is presumed that the reason for this is that the low molecular weight components that cause outgas are reduced.

As the PAO, known PAOs used as base oils can be used without limitation, and for example, α-olefins (1-octene, 1-nonene, 1-decene, 1-dodecene, 1-tridecene, 1-tetradecene, 1- Examples thereof include 3 to pentamers of pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonenecene, 1-eicosene, 1-dodecene, etc.). Among them, as PAO, 1 of 3 to 5 isomers of α-olefin having 8 to 12 carbon atoms is obtained from the viewpoint that the amount of outgas and evaporation loss are reduced, the oxidative deterioration resistance is excellent, and an appropriate viscosity can be obtained. It is preferable to use the seeds alone or in combination of two or more.
As the PAO, one type may be used alone, or two or more types may be used in combination. For example, a plurality of PAOs having different kinematic viscosities may be mixed and adjusted to the desired kinematic viscosity (average kinematic viscosity). It is particularly preferable to use a mixture of 3 to 5 mer of α-olefin having 8 to 12 carbon atoms because the amount of outgas and long-term evaporation loss are small and the oxidative deterioration resistance is excellent.

In addition to mineral oil and PAO, the base oil may contain other oil components other than mineral oil and PAO. Examples of other oil components include synthetic oils such as ester oils.
As other oil components, one type may be used alone, or two or more types may be used in combination.

<Kinematic viscosity>
In the grease of the present invention, the kinematic viscosity ν ₁ of the mineral oil at 40 ° C. is made higher than the kinematic viscosity ν ₂ of PAO at 40 ° C. Since the kinematic viscosity ν ₁ of the mineral oil is higher than the kinematic viscosity ν _{2 of the} PAO, the heat resistance of the mineral oil is 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, by combining PAOs having a kinematic viscosity ν ₂ lower than the kinematic viscosity ν _{1 of the} mineral oil, the kinematic viscosity ν of the base oil becomes sufficiently low. Therefore, the grease is sufficiently supplied to the portion requiring grease such as the portion where the rolling element of the rolling bearing is rolling, and the lubricating effect of the grease can be sufficiently obtained.
The kinematic viscosity of the oil in the present invention means a value measured at 40 ° C. in accordance with JIS K2283.
When a plurality of similar base oils having different kinematic viscosities are mixed, the kinematic viscosity of the mixture is considered as the kinematic viscosity of the base oil.

The ratio of the kinematic viscosity ν ₁ of the mineral oil to the kinematic viscosity ν _{2 of} PAO ν ₁ / ν ₂ is preferably 1.3 or more, and more preferably 1.5 or more, from the viewpoint of easily reducing the amount of outgas. 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, and 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 such as a rolling surface of a rolling bearing that requires grease. Is more preferable.

The kinematic viscosity ν _{2 of} PAO is preferably 20 mm ² / s or more, and more preferably 30 mm ² / s or more, from the viewpoint of easily reducing the amount of outgas. Further, the kinematic viscosity ν _{2 of} PAO is 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 such as a rolling surface of a rolling bearing that requires grease. 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. When the kinematic viscosity ν of the base oil is at least the above lower limit value, it is easy to reduce the amount of outgas. When the kinematic viscosity ν of the base oil is not more than the upper limit value, the grease or the base oil is likely to be supplied to the rolling surface of the rolling bearing or the like where grease is required. In addition, it can operate with low torque 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.). In particular, when the ratio of mineral oil to 100% by mass of base oil is 30% by mass or less, the amount of outgas is smaller when the kinematic viscosity ν of the base oil at 40 ° C. is 25 mm ² / s or more.

(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 urea compounds, lithium soap and the like. Among them, 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 having an aliphatic group at the end, an alicyclic diurea compound having an alicyclic group at the end, and an aromatic diurea compound having an aromatic group at the end.
Specific examples of the diurea compound include compounds obtained by reacting diisocyanate (phenylenediocyanate, tolylene diisocyanate, etc.) with monoamine (octylamine, dodecylamine, stearylamine, aniline, p-toluidine, etc.).

Examples of the lithium soap include lithium stearate, lithium 12-hydroxystearate and the like.
As the thickener, one type may be used alone, or two or more types may be used in combination.

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

Examples of extreme pressure agents include organic molybdenum compounds (molybdenum dithiocarbamate, molybdenum dithiophosphate, etc.), organic fatty acid compounds (oleic acid, naphthenic acid, succinic acid, etc.), and organophosphorus compounds (trioctyl phosphate, triphenyl phosphate, etc.). , Triethyl phosphate, etc.), phosphate ester, etc. Further, as the extreme pressure agent, zinc dithiocarbamate, antimony dithiocarbamate and the like may be used.
As the extreme pressure agent, one type may be used alone, or two or more types may be used in combination.

Examples of the antioxidant include a phenolic antioxidant (2,6-di-t-butyl-4-methylphenol, etc.), an amine-based antioxidant (p, p'-dioctyldiphenylamine, etc.) and the like. .. As the antioxidant, one type may be used alone, or two or more types may be used in combination. When the grease of the present invention contains an antioxidant, it is preferable to use a phenolic antioxidant and an amine antioxidant in combination. 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 of organic sulfonic acids or alkaline earth metal salts (calcium sulphonate, magnesium sulphonate, barium sulphonate, etc.) and polyhydric alcohols (sorbitan monooleate, etc.). Partial ester and the like can be mentioned.
As the rust preventive, one type may be used alone, or two or more types may be used in combination.

(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, more preferably 80 to 90% by mass. When the ratio of the base oil is equal to or higher than the lower limit value, the grease or the base oil is likely to be supplied to a surface such as a rolling surface of a rolling bearing that requires grease. When the ratio of the base oil is not more than the above upper limit value, the grease is in a semi-solid state and is hard to leak and scatter.

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

The ratio of PAO to 100% by mass of the base oil is preferably 50 to 90% by mass, more preferably 60 to 80% by mass. When the ratio of PAO is at least the above lower limit value, it is easy to obtain grease in which the amount of outgas is sufficiently reduced. When the ratio of PAO is not more than the above upper limit value, a grease having a good balance between excellent 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. When the total ratio of mineral oil and PAO is at least the above lower limit value, 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 ratio of PAO is larger than the ratio 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 the mineral oil in the base oil (PAO / mineral oil) is preferably 1.25 to 9, and more preferably 1.5 to 4. When the mass ratio is at least the lower limit value, the amount of outgas can be sufficiently reduced. When the mass ratio is not more than the upper limit value, excellent durability and torque smoothness can be easily obtained.

The ratio of the thickener to 100% by mass of the grease of the present invention is preferably 7 to 20% by mass, more preferably 10 to 15% by mass. When the ratio of the thickener is equal to or higher than the lower limit, the grease is in a semi-solid state and is less likely to leak or scatter. When the ratio of the thickener is not more than the above upper limit value, grease or base oil is likely to be supplied to a surface such as a rolling surface of a rolling bearing that requires grease.

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, 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, more preferably 0.2 to 2% by mass.
The ratio of the rust preventive to 100% by mass of the grease of the present invention is preferably 0.2 to 4% by mass, more preferably 0.5 to 2% by mass.

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

(Mechanism of action)
In the grease of the present invention described above, in addition to PAO, mineral oil having a kinematic viscosity ν ₁ higher than the kinematic viscosity ν _{2 of} PAO is contained in a specific ratio, so that the amount of outgas can be sufficiently reduced and rolling bearings and the like can be sufficiently reduced. Excellent durability can also be ensured in equipment that requires the same grease. The factors for obtaining the above effect are considered as follows.

For example, in a rolling bearing in an information recording / reproducing device, operating conditions such as swing speed and rotation range of a swing arm are complicated and wide. It is difficult to cope with various operating conditions of rolling bearings with grease using only PAO having a narrow molecular weight distribution as a base oil as in Patent Document 2. Therefore, the movement of the swing arm cannot be made smooth enough, and it is difficult to secure excellent durability.
On the other hand, in the grease of the present invention, since mineral oil having a wider molecular weight distribution than PAO is used in combination with PAO, it is possible to cope with various operating conditions of rolling bearings. For example, even when the swing arm moves at a low speed, an oil film having a sufficient thickness is formed due to the influence of a component having a high molecular weight and a high viscosity in the mineral oil, and a sufficient lubricating effect is exhibited. Even when the swing arm moves at high speed or the swing arm moves in a minute range, grease is sufficiently supplied to the part where the rolling element rolls due to the influence of the components having a low molecular weight and low viscosity in the mineral oil. .. As described above, since it is possible to cope with a wide range of operating conditions of the rolling bearing, excellent durability can be ensured.

In addition, the mineral oil in the grease of the present invention has excellent heat resistance because the kinematic viscosity ν ₁ is higher than the kinematic viscosity ν _{2 of} PAO, and outgas is less likely to be generated as compared with the mineral oil having a low kinematic viscosity. Then, in the grease of the present invention, the ratio of the mineral oil in the base oil is controlled within a specific range. Therefore, the amount of outgas is sufficiently reduced. Further, since the kinematic viscosity ν of the base oil as a whole can be sufficiently lowered by PAO having a kinematic viscosity ν ₂ lower than that of the mineral oil, the torque of the rolling bearing and the like can be suppressed, and the grease on the rolling surface of the rolling element in the rolling bearing and the like can be suppressed. Grease is sufficiently supplied to the surface that requires. Therefore, it is possible to achieve both the effect of reducing outgas and the effect of improving durability.

In addition, since PAO does not have polarity, it has a low affinity with polar thickeners and additives, and if only PAO is used as the base oil, it is difficult to uniformly disperse the thickeners and additives, and their effects Is difficult to obtain sufficiently. However, in the grease of the present invention, when a polar mineral oil is used in combination with PAO, the affinity between the base oil and the thickener or additive is improved. As a result, variations in the size of the thickener synthesized in the base oil can be 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 the 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 may adopt known embodiments except that the grease of the present invention is used. Hereinafter, an example of the rolling bearing, the rolling bearing device, and the information recording / reproducing device of the present invention will be described.
The information recording / reproducing device 1 of the present embodiment is a device that writes to the disk (magnetic recording medium) D in a vertical recording manner, and as shown in FIG. 1, the disk D, the swing arm 2, and the optical motor. 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 (rotational drive unit) 8, a control unit 9, and a housing 10 are provided. There is.

The housing 10 accommodates each component of the information recording / reproducing device 1.
The housing 10 has a rectangular bottom portion 10a in a plan view, a peripheral wall portion (not shown) that stands up from the peripheral edge of the bottom portion 10a, and a lid that is detachably fixed to the upper portion of the peripheral wall portion and closes the opening (not shown). And. 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 body are omitted for convenience.
The material of the housing 10 is not particularly limited, and examples thereof include a metal material such as aluminum.

The spindle motor 8 is attached to the substantially center of the bottom portion 10a of the housing 10. Further, by fitting the center hole formed in the center of the disc D into the spindle motor 8, three discs D are detachably mounted. The spindle motor 8 makes it possible to rotate the disc D in a certain direction about the rotation axis L1.

An actuator 7 is attached to one corner of the bottom 10a of the housing 10 so as to be located outside the disc D. A swing arm 2 extending toward the disc D is connected to the actuator 7. A rolling bearing device 6 is provided at a portion on the base end side of the swing arm 2. By being driven by the actuator 7, the swing arm 2 rotates in a horizontal plane about the rotation axis L2 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 disc D. The swing arm 2 is obtained, for example, by integrally forming the base portion 2a and the arm portion 2b by machining or the like.
The base portion 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 a tapered shape that tapers from the base end portion toward the tip end portion. The arm portion 2b extends from the front surface (the surface opposite to the corner portion) 2d on the side opposite to the rear surface 2c to which the actuator 7 is attached in the base portion 2a in the surface direction (in the horizontal plane) of the upper surface of the base portion 2a. It is provided as follows.
Further, in the swing arm 2 of this example, three arm portions 2b are provided so that the disc D is sandwiched between the arm portions 2b in the height direction (vertical direction) of the base portion 2a. That is, the arm portion 2b and the disc D are arranged so as to be alternately positioned in the height direction, and the arm portion 2b moves in the direction parallel to the disc surface (surface of the disc D) D1 by the drive of the actuator 7. It is designed to do.

A head gimbal assembly 5 is provided at the tip of the arm portion 2b of the swing arm 2. A laser light source 4 is provided on the side surface of the base portion 2a of the swing arm 2. An optical waveguide 3 connecting the laser light source 4 and the head gimbal assembly 5 is provided on the base portion 2a and the arm portion 2b of the swing arm 2. As a result, light can be supplied from the laser light source 4 to the head gimbal assembly 5 via 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. When light is guided from the laser light source 4 to the slider 5b, near-field light is generated from the near-field light generating element. By using the near-field light, various information can be recorded and reproduced on the disc D.
The near-field light generating element is composed of, for example, an optical microaperture, a protrusion formed in a nanometer size, or the like.

The head gimbal assembly 5 moves in a direction parallel to the disc 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 disc D by driving the actuator 7 when the rotation of the disc D is stopped.

The control unit 9 is connected to the laser light source 4. The control unit 9 can control the luminous flux of the light supplied to the slider 5b of the head gimbal assembly 5 by the current modulated according to the information.

(Rolling bearing device)
As shown in FIGS. 2 and 3, the rolling bearing device 6 has a shaft 20, a sleeve 21 installed on the outside of the shaft 20 coaxially with the shaft 20, and 2 installed between the shaft 20 and the sleeve 21. It is provided with two rolling bearings 22.

The shaft 20 is a cylindrical rod-shaped member, and is erected from the bottom portion 10a of the housing 10. The central axis of the shaft 20 is the rotation axis L2 when the swing arm 2 rotates.
On the portion of the shaft 20 on the bottom 10a side of the housing 10, a flange portion 20b having a diameter larger than that of the main body 20a and a diameter-reduced portion 20c having a diameter smaller than that of the main body 20a are provided in order toward the base end. 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 10a of the housing 10. At this time, the lower surface of the flange portion 20b is in contact with the bottom portion 10a of the housing 10, so that the shaft 20 is positioned in the height direction.

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 the inner peripheral surface thereof is separated from the outer peripheral surface of the shaft 20 at predetermined intervals. The central axis of the shaft 20 and the central axis of the sleeve 21 are aligned with each other.
Further, the sleeve 21 is press-fitted directly into the mounting hole 2e formed in the base portion 2a of the swing arm 2, is press-fitted through an elastic body such as a metal ring formed in a wavy shape, or is adhesively fitted. By being combined, it is integrally combined with the swing arm 2.

A spacer portion 21a that projects inward over the entire circumference in the circumferential direction is formed at the central portion of the inner peripheral surface of the sleeve 21 in the height direction. Two rolling bearings 22 are installed above and below the spacer portion 21a between the shaft 20 and the sleeve 21, 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 diameter of the inner ring 30 is sized so that the shaft 20 can 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 inside 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 the inner ring 30 is relatively preloaded in the axial direction with respect to the shaft 20, can be adopted. As a result, the rolling bearing 22 can be made highly rigid, and the resonance frequency (resonance point) of the rolling bearing device 6 can be made high. Therefore, the rolling bearing device 6 can handle higher speed rotation.
The rolling bearing 22 may employ a so-called outer ring preload in which the outer ring 31 is fixed to the sleeve 21 in a state where the outer ring 31 is preloaded relative to the shaft 20 in the axial direction.

An axially intermediate portion of the outer peripheral surface of the inner ring 30 is formed with a concave inner ring rolling surface 30a that guides the rolling of the rolling element 33 over the entire circumference of the inner ring 30. The inner ring rolling surface 30a has an arcuate cross-sectional shape when cut in a plane passing through the central axis of the inner ring 30.
Examples of the material of the inner ring 30 include a metal material such as stainless steel. The inner ring 30 can be manufactured by, for example, forging or machining.

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

At the axially intermediate portion of the inner peripheral surface of the outer ring 31, a concave outer ring rolling surface 31a that guides the rolling of the rolling element 33 so as to face the inner ring rolling surface 30a of the inner ring 30 is formed on the outer ring 31. It is formed all around. The outer ring rolling surface 31a has an arcuate cross-sectional shape when cut in a plane passing through the central axis of the outer ring 31.
Examples of the material of the outer ring 31 include a metal material such as stainless steel. The inner ring 30 can be manufactured by, for example, forging or machining.

As shown in FIG. 6, the retainer 32 is formed from an annular main body portion 32a and an upper portion of the main body portion 32a, and has seven pairs of claw portions 32b that rise in an arc shape so as to approach each other toward the tip. , 32c. The seven pairs of claw portions 32b and 32c are provided at equal intervals in the circumferential direction of the retainer 32. A ball pocket B having a substantially circular shape in front view is formed inside each of the paired claws 32b and 32c to hold the rolling elements 33 so that they can roll.
The number of pairs of claws, that is, the number of ball pockets B is not limited to 7, and may be 6 or less, or 8 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. With the retainer 32 installed between the inner ring 30 and the outer ring 31, the rolling elements 33 are rotatably held in the respective ball pockets B. In this way, the rolling element 33 is arranged 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 while the rolling elements 33 are rotatably held in the respective ball pockets B.
The material of the retainer 32 is not particularly limited, and examples thereof include a resin such as a polyamide resin.

A grease pocket G having a shallower depth than the ball pocket B is formed between the pair of claw portions 32b and 32c on the upper portion of the retainer 32 and the pair of claw portions 32b and 32c adjacent to the pair of claw portions 32b and 32c. 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 grease of the present invention is arranged in the grease pocket G and the rolling element 33 rotates together with the retainer 32 in the state where the rolling element 33 is arranged in the ball pocket B, the grease pocket G rolls from the grease pocket G to the inner ring 30 and the outer ring 31. Grease seeps out between the moving body 33 and the lubricating effect of the grease is obtained.
By using grease for the rolling bearing 22 by utilizing 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 / writing to / from the disk D.

The rolling element 33 in this example is spherical. The rolling element 33 is arranged 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 formed on the inner ring rolling surface 30a and the outer ring rolling surface 31a. It is designed to roll along. Each rolling element 33 is evenly arranged in the circumferential direction by the retainer 32.
The number of rolling elements 33 is 7 in this example, but it may be determined according to the number of ball pockets B in the retainer 32, and may be 6 or less, or 8 or more.
Examples of the material of the rolling element 33 include a metal material such as bearing steel.

The shield plate 34 is an annular plate member that closes the top and bottom of the annular space formed between the inner ring 30 and the outer ring 31. The shield plate 34 is 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 of the shield plates 34 is fixed to the outer ring 31 in a state where the outer peripheral edge portion thereof is inserted into the engaging annular groove portion 40 formed in the outer ring 31.

(Mechanism of action)
In the information recording / reproducing device 1, the grease of the present invention is arranged in the grease pocket G of the retainer 32 in the rolling bearing 22. When the swing arm 2 is rotated by the drive of the actuator 7, the grease arranged 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, the outer ring 31, and the rolling element 33. And the lubrication effect of grease is exhibited.
Since the grease of the present invention is used in the information recording / reproducing device 1, the amount of outgassing is sufficiently reduced. Therefore, outgas is less likely to accumulate in the gap between the head gimbal assembly and the disc D, and stable reading and writing can be performed. In addition, excellent durability can be ensured, and a state of 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 may be any one using the grease of the present invention, and are not limited to those described above.
For example, the information recording / reproducing device 1 provided with the rolling bearing 22 and the rolling bearing device 6 uses near-field light, but a general HDD provided with the rolling bearing and the rolling bearing device using the grease of the present invention or the like. It may be an optical disk D device or the like.

Further, the rolling bearing device may not include a sleeve. Specifically, for example, between two rolling bearings arranged axially apart on the outside of the shaft, an annular spacer ring for keeping the distance between the rolling bearings at a predetermined distance is provided, and a sleeve is provided. It may be a non-rolling bearing device. In this case, the outer ring of the rolling bearing may 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.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to the following description.
[Kinematic viscosity]
The kinematic viscosities of mineral oil, PAO and base oil were measured at 40 ° C. using a Canon-Fenceke viscometer according to JIS K2283.

[Measurement of outgassing amount]
The sample grease (4.5 to 5.5 mg) was evenly applied on a 15 mm square aluminum foil with a glass rod to prepare a measurement sample. The measurement sample was heated at 85 ° C. for 3 hours in an oven together with 5 μL (100 ng) of a standard reagent (hexadecane), and the generated gas was adsorbed on a collection tube. Next, the collection tube was installed in a heat desorption device (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 holding at 40 ° C. for 2 minutes, raising the temperature to 280 ° C. over 20 minutes at 12 ° C./min, and holding at 280 ° C. for 20 minutes to obtain chromatogram data inside the GC-MS. The components were identified by the library of. The amount of outgas was calculated as a standard reagent conversion based on the chromatograph 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 placed in the grease pocket G of the retainer 32, continuous operation is performed under the following operating conditions, and continuous operation with respect to the initial torque before 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: 10 deg
Operating time: 100 hours Operating environment temperature: 80 ° C

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

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

[Example 1]
Refined mineral oil (classified in Group III in the API base oil category; kinematic viscosity ν ₁ = 47 mm ² / s (40 ° C), ignition point 250 ° C or higher) and PAO (α with 8 to 12 carbon atoms) A mixture of 3 to pentameric olefins and kinematic viscosity ν ₂ = 30 mm ² / s (40 ° C.) was mixed at a mass ratio of 3: 7 and the base oil (kinematic viscosity ν = 34 mm ² / s (40 ° C.)) was mixed. )).
Next, the base oil was greased using an alicyclic diurea compound as a thickener, and an antioxidant and a rust preventive were added and mixed. The ratio 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% by mass of rust inhibitor with respect to 100% by mass of grease. It was% by mass.

[Example 2]
The same as in Example 1 was carried out 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 an antioxidant and a rust preventive. 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% by mass of rust inhibitor with respect to 100% by mass of grease. The mass% and the extreme pressure agent were 1.0% by 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 pentamer of α-olefin with 8 to 12 carbon atoms, kinematic viscosity ν ₂ = 52 mm ² / S (40 ° C.)) was used and they 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 preventive were added and mixed.

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

[Comparative Example 3]
Same as in Example 2 except that PAO (a mixture of 3 to pentameric α-olefins having 8 to 12 carbon atoms, kinematic viscosity ν = 30 mm ² / s (40 ° C.)) was used as the base oil. Obtained grease.

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

Table 1 shows the results of the outgas amount measurement, durability test, and grease bump test of each Example and Comparative Example. Table 2 shows the results of the low-temperature torque test of the grease 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 containing the base oil using the mineral oil having a kinematic viscosity ν ₁ higher than the PAO kinematic viscosity ν _{2 at} the ratio of the present invention had a small amount of outgassing. .. Further, in Examples 1 and 2, the torque fluctuation was small in both the durability test and the grease bump test, and excellent durability was shown. Further, the grease of Example 2 was superior 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 to that of Examples 1 and 2. Further, in the grease bump test, the torque after the continuous operation increased to about 6 times as much as the torque before the continuous operation. It is considered that this is because the grease that has been oxidized and deteriorated accumulates at the edge portion of the operating range in the continuous operation to form a bump, or the wear becomes severe at the edge portion of the operating range in the continuous operation.
In addition, the greases of Comparative Examples 2 and 3 that did not use mineral oil had a small amount of outgas, but were inferior in durability.

[Experimental Example 1]
The above-mentioned outgas amount was measured for the following four components A to D.
Component A: A mixture of 3 to pentamer 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: A mixture of 3 to pentameric α-olefins 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 in which an antioxidant is added 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 the 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, components B and D in which PAO is a mixture of 3 to pentameric α-olefins having 8 to 12 carbon atoms are outgass as compared with components A and C in which PAO is a single component. The amount was small.

[Experimental Example 2]
An oxidation resistance deterioration test was conducted on the components A to D. Specifically, 5 g of each component was collected in a beaker (dimension outer diameter x height: 30 mm x 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 deterioration. Table 4 shows the time when oxidative deterioration was first confirmed.

As shown in Table 4, components B and D, which are a mixture of 3 to pentameric α-olefins having 8 to 12 carbon atoms, have acid resistance as compared with components A and C, which have PAO as a single component. It was excellent in deterioration.

1 Information recording / playback device 2 Swing arm 3 Optical waveguide 4 Laser light source 5 Head gimbal assembly 6 Rolling bearing device 7 Actuator 8 Spindle motor 9 Control unit 10 Housing 20 Shaft 21 Sleeve 22 Rolling bearing 30 Inner ring 31 Outer ring 32 Retainer 33 Roller Board B Ball pocket G Grease pocket

Claims (7)

Contains base oil and thickener,
The thickener is a urea compound,
The base oil contains mineral oil and poly-α-olefin.
The poly-α-olefin is a mixture of two or more 3 to pentamers selected from α-olefins having 8 to 12 carbon atoms.
The ratio of the mineral oil to 100% by mass of the base oil is 10 to 40% by mass, the ratio of the poly-α-olefin is 50 to 90% by mass, and the ratio of the mineral oil and the poly-α-olefin is The total ratio is 80% by mass or more,
The kinematic viscosity ν ₁ of the mineral oil at 40 ° C. is 40 mm ² / s or more and 60 mm ² / s or less.
The kinematic viscosity ν ₂ of the poly-α-olefin at 40 ° C. is 20 mm ² / s or more and 40 mm ² / s or less.
The kinematic viscosity ν ₁ is higher than the kinematic viscosity ν ₂ .
A grease having a kinematic viscosity ν of the base oil at 40 ° C. of 25 to 45 mm ² / s. Wherein a ratio [nu _{1 /} [nu ₂ of the kinematic viscosity versus kinematic viscosity [nu ₂ [nu ₁ is 1.3 or more, grease of claim 1. The grease according to claim 1 or 2, wherein the base oil contains a refined mineral oil classified into Group III in the base oil category defined by the American Petroleum Institute, and the flash point of the refined mineral oil is 240 ° C. or higher. The grease according to claim 1 or 2, wherein the base oil contains a refined mineral oil classified into Group III in the base oil category defined by the American Petroleum Institute, and the flash point of the refined mineral oil is 250 ° C. or higher. A rolling bearing comprising the grease according to any one of claims 1 to 4 . A rolling bearing device including a shaft and the rolling bearing according to claim 5 . An information recording / reproducing device including the rolling bearing device according to claim 6 .

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