Rolling bearing, pivot assy bearing, and disk drive device

Abstract

To provide a rolling bearing containing a specific grease composition, and a pivot assy bearing device in which dust generation is suppressed in the grease composition sealed in the bearing by incorporating the bearing into the pivot assy bearing device, and the occurrence of read / write errors in an HDD can be suppressed, and a disk drive device equipped with the same.SOLUTION: A rolling bearing includes a grease composition. The grease composition includes a base oil and a thickener. The base oil includes an aromatic ester based oil. The thickener includes a urea-based thickener. The grease composition has a storage modulus of 1,200 to 3,000 Pa at 80°C measured at a film thickness of 1 mm and a shear strain of 1%, an amount of oil separation at 25°C is 200 to 270 mm2 / mg. A pivot assy bearing device comprises the rolling bearing. A disk drive device comprises the pivot assy bearing device.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a rolling bearing filled with a grease composition, and a pivot assembly bearing device provided with the rolling bearing, and further to a disk drive device provided with the pivot assembly bearing device. [Background technology]

[0002] The magnetic head used to read and write data recorded in a disk drive (HDD) is generally attached to the end of a swing arm that is supported for rocking motion by a rolling bearing filled with grease, and the bearing device that supports this swing arm for rocking motion is called the pivot assembly bearing device. For example, as a rolling bearing to be incorporated in a swing arm, there has been proposed a rolling bearing filled with grease made by blending a diurea compound having at least one type of alicyclic hydrocarbon group and aliphatic hydrocarbon group in the skeleton as a thickening agent with a base oil containing an aromatic ester oil with low outgassing properties (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2006-236410 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the rolling bearing mounted in the pivot assembly bearing device, if the grease sealed in the bearing gets caught in the rolling groove of the rolling bearing, it may lead to an increase in torque and dust generation. In particular, in a disk drive device, if dust particles generated from the rolling bearing adhere to the recording disk or read / write head, it may lead to read / write errors. Previously, studies have been conducted on preventing read / write errors in HDDs by using aromatic ester base oils with low outgassing (see Patent Document 1). However, in recent years, as HDDs have become larger in capacity and higher in density to store information and their processing speeds have increased, the distance between the magnetic head and the magnetic disk has become narrower to around several nm, raising concerns about problems that may result from dust generation and volatilization of grease and the resulting adhesion.

[0005] The present invention aims to provide a rolling bearing filled with a specific grease composition, and to provide a pivot assembly bearing device and a disk drive device equipped with the same, in which, by incorporating the bearing into a pivot assembly bearing device, dust generation in the grease composition filled in the bearing is suppressed, thereby suppressing the occurrence of read / write errors in the HDD. [Means for solving the problem]

[0006] One aspect of the present invention is a rolling bearing comprising an inner ring, an outer ring arranged coaxially with the inner ring on the outer circumferential side of the inner ring, a plurality of rolling elements arranged between the inner ring and the outer ring, a cage that holds the rolling elements, and a grease composition held between the inner ring and the outer ring, the grease composition including a base oil and a thickener, The thickener contains a urea-based thickener composed of a diurea compound represented by formula (1), R1-NHCONH-R2-HNOCHN-R3...Formula (1) (In formula (1), R1 and R3 each represent a monovalent alicyclic hydrocarbon group or a monovalent aliphatic hydrocarbon group, and the molar ratio of the alicyclic hydrocarbon group to the aliphatic hydrocarbon group is 6:4 to 8:2; R2 represents a divalent aromatic hydrocarbon group. The grease composition comprises The storage modulus at 25°C measured under the condition of a film thickness of 1 mm and a shear strain of 1% is 1,200 to 3,000 Pa. Oil separation amount at 80℃ is 200-270mm 2 / mg Concerning rolling bearings. The present invention also relates to a pivot assembly bearing device equipped with the above-mentioned rolling bearing. The present invention further relates to a disk drive device including the pivot assembly bearing device. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of the structure of a rolling bearing according to the present invention. [Diagram 2] 1 is a schematic diagram illustrating an example of a structure of a disk drive device according to the present invention; [Diagram 3] 1 is a schematic diagram illustrating an example of the structure of a pivot assembly bearing device of the present invention. [Figure 4] 1 is a diagram showing a crown cage used in the pivot assembly bearing (rolling bearing) of the present invention. FIG. [Diagram 5] 1 is a photograph of a ball after a high-speed Grade 4 test for evaluating sludge generation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The grease composition (hereinafter simply referred to as "grease composition") filled in the rolling bearing according to the present invention is characterized by being blended with a specific urea-based thickener as described below, and further characterized by being blended with a specific aromatic ester-based base oil. The blending of this grease composition realizes low dust generation, and further has the property that the volatile components are unlikely to adhere even at high temperatures when the components volatilize. If the components contained in the dust particles and the volatile components of the grease have a tendency to easily adhere to recording disks, etc. (easily wet and spread), the components may be fixed on the surface of the recording disk when dust generation or volatilization occurs, leading to read / write errors. The grease composition used in the present invention can contribute to suppressing the occurrence of read / write errors in HDDs caused by dust generation and volatile components. The details are explained below.

[0009] [Rolling bearings] First, preferred embodiments of the rolling bearing according to the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments.

[0010] 1 is a radial cross-sectional view of a rolling bearing 10 according to a preferred embodiment of the present invention. The rolling bearing 10 has a basic structure similar to that of a rolling bearing of the prior art, and includes an annular inner ring 11, an outer ring 12, a plurality of rolling elements 13, a cage 14, and a seal member 15. The inner ring 11 is a cylindrical structure installed coaxially with the center axis of a shaft (not shown) on the outer periphery side of the shaft. The outer ring 12 is a cylindrical structure arranged coaxially with the inner ring 11 on the outer periphery side of the inner ring 11. Each of the multiple rolling elements 13 is a ball arranged in a raceway in an annular bearing space 16 formed between the inner ring 11 and the outer ring 12. That is, the rolling bearing 10 in this embodiment is a ball bearing. The cage 14 is disposed in the raceway and holds a plurality of rolling elements 13. The cage 14 is an annular body that is installed coaxially with the central axis of the shaft, and has a structure in which a plurality of pockets for holding the rolling elements 13 are provided on one side in the direction of the central axis, and the rolling elements 13 are accommodated in each pocket. The rolling elements 13 are held at a predetermined interval in the circumferential direction of the inner ring 11 and the outer ring 12 by the cage 14, and the falling off of the rolling elements 13 and the contact between adjacent rolling elements 13 are suppressed. The shape (crown shape, corrugated shape, etc.) and material (steel plate, resin, etc.) of the cage 14 are arbitrary, but in the rolling bearing according to the present invention, a cage having a grease pocket (crown shape, etc.) is preferable from the viewpoint of suppressing dust generation. An example of a crown-shaped cage is shown in FIG. 4. As shown in FIG. 4, the crown-shaped cage 60 has a cylindrical annular member 61 centered on the central axis (rotation axis) of the rolling bearing 10 (not shown). The annular member 61 has an outer peripheral surface and an inner peripheral surface, and an outer peripheral surface and an outer peripheral surface are connected to each other. The annular member 60 has two end faces 61a. On one end face 61a of the annular member 61, a plurality of ball pockets (recesses) 62 for rotatably accommodating balls (rolling elements 13, not shown) are formed at predetermined intervals along the circumferential direction. Furthermore, the annular member 60 has a pair of claws 63 (63a, 63b) extending from the one end face 61a at both ends of each ball pocket 62. The pair of claws 63 are curved to approach each other so as to follow the curved surface of the ball accommodated in each ball pocket 62, thereby preventing the balls accommodated in each ball pocket 62 from falling out. In addition, a grease pocket 64 is formed between the two ball pockets 62 due to the presence of the claws 63. A grease composition G (not shown), which will be described later, is accommodated in the grease pocket 64 and contributes to lubrication between the ball pocket 62 and the balls (rolling elements 13) accommodated therein. The seal member 15 is fixed to the inner peripheral surface of the outer ring 12 and extends toward the inner ring 11 to seal the bearing space 16. The grease composition G is enclosed in the bearing space 16 sealed by the seal member 15. That is, the grease composition G is held between the inner ring 11 and the outer ring 12. The grease composition G to be described later is used. The amount of the grease composition G enclosed in the bearing space 16 is, for example, 2% to 30% of the volume. In particular, in a pivot assembly bearing device to be described later that requires low torque, 3% to 10% is more preferable. By setting the amount of the grease composition G to be enclosed in this range, the grease composition G can sufficiently lubricate the rolling elements 13, the inner ring 11, and the outer ring 12 in the bearing space 16 of the rolling bearing 10, reducing frictional resistance and reducing frictional torque. The seal member 15 is formed, for example, from a steel plate or rubber, and examples thereof include a steel plate shield that does not contact the outer periphery of the inner ring 11, and a non-contact rubber seal that does not contact the outer periphery of the inner ring 11. Either of the above-mentioned steel plate shields or non-contact rubber seals can be used in the present invention. From the viewpoint of suppressing outgassing, it is preferable to use a steel plate shield. Note that while this drawing shows an embodiment equipped with the seal member 15, the rolling bearing of the present invention also covers an embodiment of a rolling bearing that does not have a seal member. In the rolling bearing 10 having the above configuration, the grease composition G acts to reduce friction between the rolling elements 13 and the cage 14, and between the rolling elements 13 and the inner ring 11 or the outer ring 12. The reduction in friction reduces friction torque and suppresses the generation of frictional heat, promoting smooth rotation of the inner ring 11 and the outer ring 12. As can be seen from the configuration shown in Fig. 1, the grease composition G sealed in the rolling bearing 10 lubricates between the rolling elements 13 and the inner ring 11 or the outer ring 12 when the rolling bearing 10 rotates.

[0011] The rolling bearing 10 of this embodiment can be used as a rolling bearing provided in a pivot assembly bearing device. The rolling bearing 10 of this embodiment has the advantage that dust generation during operation is suppressed by using a specific grease composition described later, and the occurrence of read / write errors in a magnetic disk, which is partly caused by the adhesion of dust, can be suppressed. The rolling bearing 10 of this embodiment is suitable for use in a pivot assembly bearing device, but its uses are not limited to this and it can be used, for example, as a rolling bearing for small motors (e.g., brushless motors, stepping motors, fan motors) used in automobiles, home appliances, information devices, etc.

[0012] [Pivot assembly bearing device and disk drive device] A pivot assembly bearing device including the rolling bearing of the above embodiment and a disk drive device including the pivot assembly bearing device will be described below with reference to the accompanying drawings. Note that the present invention is not limited to the following embodiments.

[0013] FIG. 2 is a perspective view showing the overall configuration of a disk drive device 20 according to a preferred embodiment of the present invention. As shown in FIG. 2, the disk drive device 20 of this embodiment includes a substantially rectangular box-shaped base plate 21, a spindle motor 22 mounted on the base plate 21, and a drive unit 23 for driving the spindle motor 22. The magnetic disk 23 is rotated by a swing motor 22, a swing arm 24 having a magnetic head 25 that writes information to a predetermined position on the magnetic disk 23 and reads information from any position, a pivot assembly bearing device 30 that supports the swing arm 24 so that it can swing, an actuator 26 that drives the swing arm 24, and a control unit 27 that controls these devices.

[0014] The disk drive device of the present invention may be, for example, a disk drive device equipped with nine or more magnetic disks having a diameter of 3.5 inches. In a device having such a large number of disks, the spatial volume within the device is further reduced. The disk drive device may have an internal space filled with a gas having a density lower than air. In a disk drive device whose internal space is filled with such a low-density gas, the air pressure within the device may be less than 1 atmosphere. The disk drive device may also employ a thermally assisted magnetic recording (HAMR) method as a recording method. In a disk drive device employing a thermally assisted magnetic recording (HAMR) method, the temperature of the head portion of the actuator may locally reach a high temperature of 400°C.

[0015] FIG. 3 is a cross-sectional view of a pivot assembly bearing device 30 according to a preferred embodiment of the present invention. The pivot assembly bearing device 30 of this embodiment is mainly composed of a shaft (axis) 31, a first bearing 40 and a second bearing 50 which are two rolling bearings fitted onto the shaft 31 with a predetermined length of space S between them, and a sleeve 32 (outer peripheral member) which exteriorly covers the two rolling bearings 40, 50. The sleeve 32 has a spacer portion 32a provided for arranging the two rolling bearings 40, 50 with a predetermined length of space S in the axial direction. In this manner, the shaft 31 is supported in a freely rotatable state by the first bearing 40 and the second bearing 50 . The spacer portion 32a is not limited to being integrally formed with the sleeve 32 as in the embodiment shown in FIG. 3, and the sleeve and the spacer may be formed as separate parts.

[0016] For the first bearing 40 and the second bearing 50, the rolling bearing 10 according to the embodiment of the present invention described above is used. The first bearing 40 is mainly composed of a first inner ring 41, a first outer ring 42, balls 43 which are multiple rolling elements arranged in a raceway formed between the first inner ring 41 and the first outer ring 42, a retainer 44 arranged in the raceway and holding the balls 43, a sealing member 45 which isolates the raceway from the outside world, and a grease composition (not shown) used in the present invention which is sealed in the raceway. Similarly, the second bearing 50 is mainly composed of a second inner ring 51, a second outer ring 52, balls 53 which are multiple rolling elements arranged in a raceway formed between the second inner ring 51 and the second outer ring 52, a retainer 54 arranged in the raceway and holding the balls 53, a sealing member 55 which isolates the raceway from the outside world, and a grease composition (not shown) used in the present invention which is sealed in the raceway. The shaft 31 has a cylindrical shaft body 31a and a flange portion 31b formed on one end side of the shaft body 31a, and is attached to the base 21 with the flange portion 31b positioned on the base 21 (see FIG. 2) side of the disk drive device 20. One end of the second inner ring 51 of the second bearing is in contact with the flange portion 31b of the shaft.

[0017] The pivot assembly bearing device 30 of this embodiment uses first and second bearings 40, 50, which are rolling bearings filled with a grease composition, which will be described later. A typical rolling bearing rotates continuously in one direction, but the pivot assembly bearing device 30 performs a high-speed oscillating motion that repeats forward and reverse rotations at a small angle in order to move the magnetic head 25 of the disk drive device 20 above the magnetic disk 23. It is necessary to move the magnetic head 25 to an accurate position with high response speed.

[0018] The grease composition used in this embodiment can achieve an appropriate range of oil separation amount and exhibits excellent grease shape stability. Therefore, it is possible to prevent insufficient supply of lubricant and oil leakage. As a result, the disk drive device 20 of this embodiment can stably drive the rolling bearings (first and second bearings 40, 50) for a long period of time. This leads to suppression of read / write errors in the disk drive device and enables the pivot assembly bearing device and the disk drive device to have a longer life. Furthermore, with the grease composition used in this embodiment, even if the base oil volatilizes at high temperatures, the volatilized base oil is less likely to adhere to magnetic disks, etc., making it possible to suppress read / write errors in disk drive devices.

[0019] [Grease composition] The inventors focused on the shape of the grease enclosed in the rolling bearing to prevent dust generation that is believed to occur when the grease enclosed in the bearing is caught in the rolling groove of the rolling bearing, and came to adopt a specific urea-based thickener as a configuration for suppressing the movement of the grease body into the rolling groove by maintaining the grease shape and suppressing dust generation from the grease that may occur from the rolling groove. Furthermore, the present inventors have investigated the components based on the new idea that even if dust is generated or the components of the grease volatilize, these components are unlikely to adhere to the disk, etc. (Even if they do adhere, they do not remain there).Then, by adopting an aromatic ester compound having an alkyl chain length of a certain length or more as the base oil, they found that a grease composition that realizes the above idea can be obtained. The grease composition packed in the rolling bearing of the present invention will now be described.

[0020] <Base oil> In the grease composition packed in the rolling bearing according to this embodiment, an aromatic ester-based base oil is used.

[0021] The aromatic ester base oil used in the present invention is characterized in that it is an aromatic ester compound having an ester group as a substituent on a ring and an alkyl group having a total of 8 or more carbon atoms bonded to the oxygen atom of the ester group. By using an aromatic ester compound having the above structure as a base oil, a grease composition can be obtained which has the property that even when the base oil is exposed to high temperatures and volatilizes, the volatilized base oil is less likely to adhere to the surfaces of magnetic disks and the like.

[0022] The aromatic ester compounds mentioned above are compounds in which an alkyl group having a total of 8 or more carbon atoms is bonded to an aromatic ring via an ester group *-(CO)O- (* is the bond site with the aromatic ring). In other words, they are compounds in which the hydrogen atoms on the aromatic ring are substituted with alkyl ester groups having 8 or more carbon atoms (the number of carbon atoms here refers to the number of carbon atoms in the alkyl group portion). Examples of the aromatic ring include a benzene ring and a naphthalene ring, and particularly, a benzene ring. The number of alkyl ester groups substituted on the aromatic ring is not particularly limited, and examples thereof include compounds substituted with 1 to 3 alkyl ester groups. When the aromatic ester compound is a compound substituted with two or more alkyl ester groups, the alkyl ester groups may be the same or different. When the aromatic ester compound is a compound substituted with two or more alkyl ester groups, it is preferable that at least one of the alkyl ester groups has 8 or more carbon atoms, and all of the alkyl ester groups have 8 or more carbon atoms (the number of carbon atoms here refers to the number of carbon atoms in the alkyl group portion) (the same applies to the examples of linear and branched alkyl groups described later, and when the aromatic ester compound has two or more alkyl ester groups, at least one alkyl ester group The alkyl groups in the above formula (I) have the groups exemplified above, and preferably the alkyl groups in all the alkyl ester groups have the groups exemplified above).

[0023] The alkyl group having a total of 8 or more carbon atoms may be linear or branched. A branched alkyl group may have a plurality of branched chains, and the branching positions are not particularly limited.

[0024] In the aromatic ester compound, the linear alkyl group having a total of 8 or more carbon atoms may be, for example, a linear alkyl group having 8 to 11 carbon atoms, or alternatively, a linear alkyl group having 9 to 11 carbon atoms. Additionally, a branched alkyl group having a total of 8 or more carbon atoms can have a total of 9 or more and 16 or less carbon atoms, for example, a total of 11 or more and 16 or less carbon atoms. The branched alkyl group having a total of 8 or more carbon atoms may be, for example, a branched alkyl group formed by bonding a branched chain to a linear alkyl group having 8 to 11 carbon atoms. The branched alkyl group is an alkyl group having a longest carbon chain with 8 to 11 carbon atoms, counting from the carbon atom bonded to the oxygen atom of the ester group. The branched alkyl group may be, for example, a branched alkyl group formed by bonding a plurality of branched chains to a linear alkyl group having 6 to 11 carbon atoms, so long as the total number of carbon atoms is 8 or more. In the above aromatic ester compound, the embodiment in which the alkyl group having a total of 8 or more carbon atoms is a linear alkyl group having the above-mentioned specific total number of carbon atoms, or the embodiment in which the alkyl group having a total of 8 or more carbon atoms is a branched alkyl group having the above-mentioned specific total number of carbon atoms means that the aromatic ester compound essentially contains the linear alkyl group or branched alkyl group as the alkyl group bonded to the oxygen atom of the ester group *-(CO)O-. In other words, for example, when an aromatic ester compound is substituted with two or more alkyl ester groups, the alkyl group of at least one of the alkyl ester groups may be the above-mentioned specific linear alkyl group or specific branched alkyl group, and it is not excluded that the alkyl group of the remaining alkyl ester group may be another alkyl group, and it is not intended to particularly exclude the use of aromatic ester compounds having other alkyl groups having a total of 8 or more carbon atoms as a base oil. In short, in the above aromatic ester compound, for example, the embodiment in which "the branched alkyl group having a total number of 8 or more carbon atoms is a branched alkyl group having a total number of 9 or more and 16 or less carbon atoms" can include any of the following embodiments in which the aromatic ester base oil consists only of aromatic ester compounds containing only the branched alkyl group as the alkyl group bonded to the oxygen atom of the ester group; the aromatic ester base oil consists only of aromatic ester compounds containing the branched alkyl group and another alkyl group (for example, a linear alkyl group having a total number of 8 or more and 11 or less carbon atoms) as the alkyl group bonded to the oxygen atom of the ester group; and the aromatic ester base oil contains one or both of these aromatic ester compounds and an aromatic ester compound containing an alkyl group other than the branched alkyl group as the alkyl group bonded to the oxygen atom of the ester group (for example, an aromatic ester compound containing a linear alkyl group having a total number of 8 or more and 11 or less carbon atoms). In one embodiment of the present invention, the base oil is selected from aromatic ester compounds in which at least one branched alkyl group having a total carbon atom number of 9 to 16 is bonded to the oxygen atom of the ester group. That is, in this embodiment, when the aromatic ester compound has two or more ester groups, at least one of the alkyl groups bonded to the oxygen atom of the ester group may be a branched alkyl group having a total carbon atom number of 9 to 16, and the remaining alkyl groups are not limited to the branched alkyl group having a total carbon atom number of 9 to 16. In another embodiment, the branched alkyl group having a total carbon atom number of 9 to 16 may be a branched alkyl group having a total carbon atom number of 11 to 16, and even in this embodiment, when the aromatic ester compound has two or more ester groups, at least one of the alkyl groups bonded to the oxygen atom of the ester group may be a branched alkyl group having a total carbon atom number of 11 to 16. However, the remaining alkyl groups are not limited to the branched alkyl groups having a total of 11 to 16 carbon atoms.

[0025] An example of the aromatic ester compound is a triester of trimellitic acid (1,2,4-benzenetricarboxylic acid).

[0026] A preferred aromatic ester compound is a triester compound of trimellitic acid represented by the following formula: [ka] In the formula, R is each independently a linear or branched alkyl group having a total of 8 or more carbon atoms, for example, a linear alkyl group having from 8 to 11 carbon atoms, a branched alkyl group having from 8 to 11 carbon atoms to which a branched chain is bonded, or a branched alkyl group having from 6 to 11 carbon atoms to which two or more branched chains are bonded, and the total number of carbon atoms in the branched alkyl group can be, for example, 9 to 16.

[0027] The aromatic ester-based base oil used in the present invention has a kinetic viscosity at 40° C. of, for example, 40 to 130 mm 2 / s range, especially 50-80 mm 2 An aromatic ester compound having a molecular weight in the range of 1 / s can be used. The aromatic ester base oil having a kinematic viscosity within the above-mentioned specified range is not particularly limited, but examples thereof include aromatic ester compounds having an ester group as a substituent on the ring described above, in which an alkyl group having a total of 8 or more carbon atoms is bonded to the oxygen atom of the ester group.

[0028] The above-mentioned base oil can be contained in a proportion of, for example, 80 mass % or more based on the total mass of the grease composition used in the present invention, and for example, the above-mentioned base oil is contained in a proportion of 80 mass % to 98 mass % based on the total mass of the grease composition.

[0029] <Thickener> Urea compounds have excellent heat resistance and water resistance, and are particularly stable at high temperatures, and therefore are suitably used as thickeners in applications where the application is in a high-temperature environment. The grease composition used in the present invention uses a urea compound, specifically an alicyclic aliphatic diurea compound, as a thickening agent. The alicyclic aliphatic diurea compound may be a diurea compound represented by the following formula (1). R1-NHCONH-R2-NHCONH-R3...Formula (1) (In formula (1), R1 and R3 each represent a monovalent alicyclic hydrocarbon group or a monovalent aliphatic hydrocarbon group, and the molar ratio of the alicyclic hydrocarbon group to the aliphatic hydrocarbon group is 6:4 to 8:2; R2 represents a divalent aromatic hydrocarbon group.

[0030] The above R1 and R3 may be the same, i.e., both may be monovalent alicyclic hydrocarbon groups or monovalent aliphatic hydrocarbon groups, or one may be a monovalent alicyclic hydrocarbon group and the other may be a monovalent aliphatic hydrocarbon group. In the present invention, in the diurea compound represented by formula (1), an alicyclic hydrocarbon group and an aliphatic The diurea compound is characterized in that the molar ratio of the hydrocarbon groups is in the range of 6:4 to 8:2. By setting the molar ratio of the alicyclic hydrocarbon group to the aliphatic hydrocarbon group in the above range, the storage modulus and the amount of oil separation of the grease composition containing the diurea compound can be set within a predetermined range. As described below, by employing a diurea compound in consideration of the storage modulus and amount of oil separation of the grease composition, when the grease composition is enclosed in a rolling bearing and the rolling bearing is operated, the shape of the enclosed grease composition is maintained and an appropriate amount of oil (base oil) is supplied to the rolling elements, resulting in a grease composition that has appropriate lubricating performance while suppressing dust generation.

[0031] The monovalent alicyclic hydrocarbon group includes, for example, an alicyclic hydrocarbon group having 5 to 12 carbon atoms. Examples of the monovalent aliphatic hydrocarbon group include linear or branched, saturated or unsaturated aliphatic hydrocarbon groups having 6 to 26 carbon atoms. The divalent aromatic hydrocarbon group may, for example, be a divalent aromatic hydrocarbon group having 6 to 20 carbon atoms.

[0032] The alicyclic aliphatic diurea compound used in the present invention can be synthesized using an amine compound and an isocyanate compound. For example, an alicyclic amine and an aliphatic amine are used as amine raw materials, and the compound is synthesized and obtained using the amine raw materials and an aromatic diisocyanate. The alicyclic amine and aliphatic amine, which are amine raw materials, are charged in an amount of, for example, alicyclic amine:aliphatic amine=6:4 to 8:2, and reacted with an aromatic diisocyanate to obtain a compound in which the molar ratio of alicyclic hydrocarbon group:aliphatic hydrocarbon group in the total amount of the diurea compound is 6:4 to 8:2. Examples of the amine compound include aliphatic amines such as hexylamine, octylamine, dodecylamine, hexadecylamine, octadecylamine (stearylamine), behenylamine, and oleylamine, as well as alicyclic amines such as cyclohexylamine. As the isocyanate compound, aromatic diisocyanates such as phenylene diisocyanate, tolylene diisocyanate (TDI), diphenyl diisocyanate, diphenylmethane diisocyanate (MDI), dimethylbiphenyl diisocyanate (TODI) and the like are used.

[0033] The thickener is contained in a proportion of, for example, 10% to 15% by mass based on the total mass of the grease composition used in the present invention. If the thickener is used in an amount exceeding 15% by mass, the amount of oil separation from the grease composition is too small, which may lead to poor lubrication. On the other hand, if the thickener is used in an amount less than 10% by mass, the amount of oil separation is too large, which may lead to contamination of the device, and may also lead to the grease flowing out of the grease pockets of the cage and being caught between the rolling elements and races of the bearing, which may increase the rotational torque. Among these, from the viewpoint of obtaining a grease composition having an appropriate amount of oil separation and particularly excellent flow properties and life properties, it is preferable to contain a thickener in a proportion of, for example, 10% by mass to 13% by mass.

[0034] <Other additives> In addition to the above essential components, the grease composition may contain additives that are usually used in grease compositions, if necessary, within the range that does not impair the effects of the present invention. Examples of such additives include antioxidants, rust inhibitors, extreme pressure additives (extreme pressure agents), metal deactivators, antifriction agents (antiwear agents), oiliness improvers, viscosity index improvers, and thickeners. When these other additives are contained, the amount (total amount) of them added is usually 0.1 to 10 mass % based on the total amount of the grease composition.

[0035] Examples of the antioxidant include octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-t-butylanilino)-1,3,5-triazine, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, triethylene glycol-bis[3- hindered phenolic antioxidants such as N,N'-hexamethylenebis(3,5-di-t-butyl-4-hydroxy-hydrocinnamate), octyl-3,5-di-tert-butyl-4-hydroxy-hydrocinnamic acid, 1,6-hexanediol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 1,6-hexanediol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 2,2-thio-diethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], N,N'-hexamethylenebis(3,5-di-t-butyl-4-hydroxy-hydrocinnamate), and octyl-3,5-di-tert-butyl-4-hydroxy-hydrocinnamic acid; Other phenolic antioxidants such as 2,6-di-t-butyl-4-methylphenol, and 4,4-methylenebis(2,6-di-t-butylphenol); Examples of the antioxidant include amine-based antioxidants such as diphenylamine, alkylated diphenylamine, triphenylamine, hindered amine, phenyl-α-naphthylamine, alkylated phenyl-α-naphthylamine, phenothiazine, and alkylated phenothiazine. Among these, from the viewpoint of disk adhesion, phenol-based antioxidants, particularly octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-t-butylanilino)-1,3,5-triazine, triethylene glycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate], 2,2-thio-diethylene bis[3-(3,5-di-t-butyl and octyl-3,5-di-tert-butyl-4-hydroxy-3,5-dipropionate, and octyl-3,5-di-tert-butyl-4-hydroxy-hydrocinnamic acid; and amine-based antioxidants such as diarylamine compounds, e.g., diphenylamine, alkylated diphenylamine, phenyl-α-naphthylamine, and alkylated phenyl-α-naphthylamine. From the viewpoint of sludge inhibition, the above-mentioned hindered phenol-based antioxidants are further preferred.

[0036] Examples of the extreme pressure additive include phosphorus-based compounds, chlorine-based compounds, and polymer esters. Among these, phosphate compounds such as phosphate esters, phosphites, and amine salts of phosphate esters, that is, phosphorus compounds, can be preferably used. Suitable phosphoric acid ester compounds include, for example, phosphoric acid triesters such as tricresyl phosphate (CAS No. 1330-78-5), triphenyl phosphate, tributyl phosphate, trioctyl phosphate, and trioleyl phosphate; dilauryl hydrogen phosphite (CAS No. 21302-09-0), tricresyl phosphite (CAS No. 25586-42-9), tris(2-ethylhexyl)phosphite (CAS No. 301-13-3), triisodecyl phosphite (CAS No. 25448-25-3), trilauryl phosphite (CAS No. 3076-63-9), tris(triisodecyl)phosphite (CAS No. 77745-66-5), trioleyl phosphite (CAS and phosphoric acid monoesters and / or phosphoric acid diesters (acid phosphoric acid esters) such as 2-ethylhexyl acid phosphate (CAS No. 12645-31-7), alkyl (C12, C14, C16, C18) acid phosphate, isotridecyl acid phosphate (CAS No. 52933-07-0), and oleyl acid phosphate (CAS No. 37310-83-1). These are also available as commercial products. Among these, from the viewpoint of sludge suppression, the above-mentioned phosphate triesters and phosphate monoesters are preferred. Among them, phosphate triesters are preferred. Specific examples thereof include at least one selected from the group consisting of tricresyl phosphate (CAS No. 1330-78-5), triphenyl phosphate, tributyl phosphate, trioctyl phosphate, trioleyl phosphate, 2-ethylhexyl acid phosphate (CAS No. 12645-31-7), alkyl (C12, C14, C16, C18) acid phosphate, isotridecyl acid phosphate (CAS No. 52933-07-0), and oleyl acid phosphate (CAS No. 37310-83-1). Particularly from the viewpoint of corrosion inhibition, one selected from the group consisting of tricresyl phosphate (CAS No. 1330-78-5), triphenyl phosphate, tributyl phosphate, trioctyl phosphate, and trioleyl phosphate is preferred, and among these, tricresyl phosphate is preferred. From the viewpoint of suppressing sludge, it is desirable to avoid the use of sulfur-containing additives that have conventionally been used as extreme pressure additives, such as metal salts of sulfur-based compounds (e.g., calcium sulfonate) and thiophosphate triesters such as triphenoxyphosphine sulfide (TPPS), which can also be classified as phosphorus-based compounds.

[0037] Examples of the metal deactivator include benzotriazole and sodium nitrite.

[0038] Anti-wear agents include tricresyl phosphate and polymer esters. Examples of the polymer ester include esters of aliphatic monovalent carboxylic acids and divalent carboxylic acids with polyhydric alcohols. Specific examples of the polymer ester include, but are not limited to, the PRIOLUBE (registered trademark) series manufactured by Croda Japan.

[0039] The grease composition used in the present invention can be obtained by blending the aromatic ester base oil, the thickener, and, if desired, other additives. Furthermore, for example, a urea-based grease (base grease) consisting of the aromatic ester-based base oil and the urea-based thickener may be blended with other additives as desired to obtain a grease composition. Typically, the content of the thickener in the base grease is about 10 to 30 mass %, and for example, the content of the diurea compound (urea-based thickener) in the above-mentioned urea-based grease can be, for example, about 10 to 25 mass %, or about 10 to 20 mass %.

[0040] <Storage modulus> The grease composition used in the present invention preferably has a storage modulus in an appropriate range, i.e., a storage modulus of 1,200 to 3,000 Pa at 25°C measured under conditions of a film thickness of 1 mm and a shear strain of 1%.

[0041] The storage modulus is a value that indicates the shape stability of a grease, and is an effective parameter for understanding the shape stability of a grease immediately after the grease is packed into a bearing device or when the bearing device is oscillating. For example, in a pivot assembly bearing device, grease is filled only in the grease pockets of the crown retainer, so if the shape of the grease changes from the shape at the time of filling, the grease will get tangled with the balls (rolling elements), etc., which not only leads to increased torque and torque fluctuations in the rolling bearing, but can also be a cause of dust generation. Therefore, the shape retention ability (shape stability) of the grease is an important factor in preventing initial and long-term torque stability and dust generation. From the viewpoint of the shape stability of the grease, it is preferable that the storage modulus of the grease composition used in the present invention at 25°C under the above measurement conditions (film thickness 1 mm, shear strain 1%) is 1,200 Pa or more. However, if the storage modulus is too high, the grease composition may fall out of the grease pockets of the crown retainer while maintaining its shape. In this case, since the grease is located on the orbit of the rolling elements, the resistance increases when the ball passes over the grease, and there is a concern that the torque will increase. Therefore, it is desirable to set the storage modulus to a value not exceeding 3,000 Pa.

[0042] <About oil separation amount> The grease composition used in the present invention has an oil separation amount in the appropriate range, i.e., an oil separation amount of 200 to 270 mm at 80°C. 2 / mg is preferred.

[0043] Conventionally, there is an oil separation measurement test as a method for evaluating the amount of oil (base oil and additives) that seeps out from grease. Since the life of the grease changes depending on the amount of oil separation, understanding the amount of oil separation is not only important for understanding the life characteristics of the grease, but also important for obtaining appropriate lubrication performance. For example, in a pivot assembly bearing device in which grease is applied to the grease pockets between the ball pockets of a crown-shaped retainer, if the amount of oil separation is too small, the lubricating components (base oil and additives) supplied to the balls (rolling elements) will be insufficient over time, which may lead to torque roughness and seizure. On the other hand, if the amount of oil separation is too large, there is also the problem that contamination due to oil leakage is more likely to occur.

[0044] Greases containing the urea-based thickener used in the present invention generally have a low amount of oil separation, so when the amount of oil separation is measured using an oil separation measurement method according to a publicly known standard such as JIS K2220, which specifies the method for measuring the degree of oil separation, it may be difficult to see a clear difference in the measurement results. For this reason, in the present invention, a unique method was adopted that makes the difference in the amount of oil separation clearer. Specifically, 9 mg of the grease composition was placed in a cylindrical shape with a diameter of 3 mm on the side of the medicine wrapping paper on which the medicine is placed, and after leaving it in an environment of 80°C for 24 hours, the area of ​​the oil-stained part (stained base oil) that occurred on the medicine wrapping paper was measured. The area of ​​the oil-stained part per mass of grease was then calculated as the amount of oil separation (mm 2 In this test, the drug packaging paper used was "Pure White Imitation (Medium)" (size: 105 mm × 105 mm, thickness: 42 μm, basis weight: 30 g / m2 ) and the grease composition was placed on the side (glossy side) on which the medicine was to be placed, as described above. Based on the above definition, when conventional greases that did not experience poor lubrication were evaluated using this unique method, the amount of oil separation was approximately 230 to 280 mm 2 It was confirmed that the amount of oil separation was about 200 mm 2 With conventional greases with a grease content of less than 1 / mg, seizure due to poor lubrication was confirmed. Also, considering that too much oil separation can cause oil leakage, the upper limit was set at 300 mm 2 / mg.

[0045] Based on the above results, for the grease composition used in the present invention, 9 mg of the grease composition was placed in a cylindrical shape with a diameter of 3 mm on a medicine wrapping paper and left for 24 hours in an environment of 80°C. At that point, the area of ​​the oil-stained part on the medicine wrapping paper was measured, and the amount of oil separation, which is the area of ​​the oil-stained part per mass of the grease composition, was determined to be 200 mm 2 / mg~270mm 2 / mg is evaluated as being suitable.

[0046] As described above, by setting the storage modulus of the grease composition used in the present embodiment within a predetermined range, the shape of the grease composition enclosed in the ball pockets (grease pockets) of the retainer (cage) is not easily distorted, and by having an appropriate amount of oil separation, the grease composition itself will not fall from the ball pockets (grease pockets) onto the raceway surfaces of the rolling bearing, and it is expected that dust generation that causes particle generation will be suppressed. In addition, by using an aromatic ester compound having an alkyl group with a predetermined number of carbon atoms or more as the base oil, even if the above-mentioned dust generation or volatilization of the base oil occurs during operation in a high-temperature environment, it is possible to suppress the adhesion of dust components and volatile components to magnetic disks, etc. The above configuration makes it possible to suppress disk read / write errors in disk drive devices, which are partly caused by dust and volatile components.

[0047] The present invention is not limited to the embodiments and specific examples described in this specification, and various changes and modifications are possible within the scope of the technical ideas described in the claims. EXAMPLES

[0048] The present invention will be described in more detail below with reference to examples, although the present invention is not limited thereto.

[0049] Grease compositions used in Examples 1 to 5 and Comparative Examples 1 to 5 were prepared in the amounts shown in the following tables. Note that "hardening treatment" in Tables 1 and 2 below refers to a treatment in which the prepared grease composition was allowed to stand for 5 hours at 75°C and 40% RH. This treatment was performed in consideration of the possibility that the properties may be the same as after the hardening treatment depending on the grease compounding conditions, or in the case where a harder grease is required. Details of the components used in the preparation of the grease compositions of the Examples and Comparative Examples and their abbreviations are as follows: <Thickener> Alicyclic aliphatic diurea compound:alicyclic hydrocarbon group:aliphatic hydrocarbon group molar ratio is 5:5 to 8:2 (see Tables 1 and 2) <Base oil> Aromatic esters (trimellitic esters): Number of carbon atoms: 9 carbon atom alkyl ester of trimellitic acid (compound in the following formula [A] where R is represented by K1) Carbon atom number 11: C11 alkyl ester of trimellitic acid (compound in the following formula [A] where R is represented by K2) Number of carbon atoms: 8 carbon atom alkyl ester of trimellitic acid (compound in the following formula [A] where R is represented by K3) Mineral oil + PAO: A mixture of mineral oil and polyalphaolefin oil [ka] <Additives> Antioxidants: Phenol-based: Hindered phenol-based antioxidant (2,2-thio-diethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], product name "Irganox L115", BASF Japan Ltd.) Amine type: Hindered amine type antioxidant (bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, product name "ADEKA STAB LA-72", ADEKA Corporation) Extreme pressure additives: Phosphate ester-based extreme pressure additive Fujifilm Wako Pure Chemical Industries, Ltd., product name "Tritolyle phosphate"

[0050] The storage modulus, oil separation amount, particle number (amount of dust) and disk adhesion of the base oil for the obtained grease compositions were evaluated using the following procedures. In addition, the worked penetration of each grease composition was measured. The obtained results are shown in Tables 1 and 2.

[0051] <(1) Measurement and evaluation of storage modulus (unit: Pa)> The storage modulus G' of each grease composition was measured using a rotational viscometer manufactured by Anton Paar. The measurement mode was strain dispersion method (strain variable from 100% to 0.01%), the jig was parallel plate φ25mm (PP25), the plate gap was 1mm, and the temperature was 25°C. The measured value at a strain of 1% was taken as the storage modulus G' (Pa), and the storage modulus (average value of N=3) was evaluated according to the following criteria. <Judgment criteria> N: Storage modulus less than 1,200 Pa A: Storage modulus is 1,200 Pa or more and 3,000 Pa or less N: Storage modulus exceeds 3,000 Pa

[0052] <(2) Amount of oil separated (unit: mm 2 / mg) Measurement and Evaluation> 9 mg of each grease composition prepared was placed in a cylindrical shape of φ3 mm on the side of the medicine-wrapping paper on which the medicine was placed, and left for 24 hours in an environment of 80°C. After 24 hours, the area of ​​the oil-stained part on the medicine-wrapping paper was measured. The area of ​​the oil-stained part per mass of the grease composition was defined as the amount of oil separation (mm 2 The amount of oil separation (average value of N=3) was evaluated according to the following criteria. In this test, the medicine wrapping paper used was "Pure White Imitation (Medium)" (size: 105 mm x 105 mm, thickness: 42 μm, basis weight: 30 g / m 2 ) and the grease composition was allowed to stand on the side (glossy side) on which the medicine was to be placed, as described above. <Judgment criteria> N: Oil separation amount is 200mm 2 / mg A: Oil separation amount is 200 mm 2 / mg or more 270mm 2 / mg or less N: Oil separation amount is 270mm 2 / mg super

[0053] <(3) Particle count (amount of dust) measurement> An oscillation tester was placed in a closed space configured to prevent the intrusion of dust and the like from the outside, and a pivot assembly bearing device equipped with a ball bearing containing each grease composition was placed in the oscillation tester, and oscillated for 7 hours at an oscillation angle of 20 degrees, an oscillation frequency of 20 Hz, and a temperature of 20 to 30°C. The number of particles in the closed space during shaking was measured using an air particle counter (KC22-A, manufactured by Rion Co., Ltd.), and the total volume of the particles [μm 3 This was evaluated as the particle count (amount of dust generated: average value of N=3) for each example.

[0054] <(4) Disc Adhesion (1)> For each of the base oils used in Example 1, Example 2 (Examples 2 to 7), Comparative Example 1 (Comparative Examples 1 to 5), Comparative Example 6, and Comparative Examples 1 to 7, disk adhesion was evaluated by the following procedure. An electroless nickel-plated aluminum magnetic disk was washed twice with n-hexane and isopropyl alcohol of 99% or higher purity, and then completely dried. 5 μL of base oil (sample oil) diluted to 10 vol% with hexane was dropped onto the disk and allowed to stand for 1 hour. The state of the droplet after dropping was photographed with a camera fixed above the disk. The total area of ​​the droplet immediately after dropping (about 5 seconds later) and after leaving it for 1 hour was calculated using image analysis software, and the percentage (%) (disk adhesion) of the area value after leaving it for 1 hour to the area value immediately after dropping [area value 1 hour after dropping (final area) / area value immediately after dropping (initial area)] was calculated (when the area value before and after leaving it remains unchanged, the disk adhesion is 100%). This test was performed at a temperature of 20 to 30°C and a humidity of 30 to 70% RH, with each sample being repeated multiple times. The average value when reproducibility was obtained (area value results within ±5%, N=4 or more) was used as the test result. The results were evaluated according to the following criteria. <Disc adhesion criteria> A: Disc adhesion is less than 30% N: Disc adhesion is 30% or more

[0055] [Table 1]

[0056] [Table 2]

[0057] As shown in Table 1, the grease compositions of Examples 1 to 5 had a storage modulus (1,200 Pa or more and 3,000 Pa or less) and an amount of oil separation (200 mm 2 / mg or more 270mm 2 / mg or less) was in the preferred (A) range, and the particle count was smaller than in the comparative examples described later, indicating that dust generation was suppressed. Furthermore, the base oils used in the grease compositions of these examples were rated A for disk adhesion (difficult to adhere to disk). On the other hand, the storage modulus of all the grease compositions of Comparative Examples 1 to 5 was judged to be unsuitable (N), and the amount of oil separation was also judged to be unsuitable (N) for the grease compositions of Comparative Examples 3 and 5. As a result, the particle count values ​​were larger than those of the Examples. The base oils used in the grease compositions of Comparative Examples 4 and 5 were rated N for disk adhesion.

[0058] <(5) Disc Adhesion (2)> Using the same procedures and test procedures as those in <(4) Disc Adhesion (1)> above, the disc adhesion of the antioxidants shown in Table 3 used in the grease compositions was evaluated. The abbreviations in Table 3 are as follows. <Hindered phenol-based antioxidant> Irganox L115: 2,2-thio-diethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], BASF Japan Ltd. Irganox L135: Octyl-3,5-di-tert-butyl-4-hydroxy-hydrocinnamate Irganox 1076FD: Octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, BASF Japan Ltd. Irganox 245: Triethylene glycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate], BASF Japan Ltd. Irganox 565: 2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-t-butylanilino)-1,3,5-triazine, BASF Japan Ltd. <Amine-based antioxidants> <Diarylamine antioxidant> Irganox L57: Diphenylamine represented by the following formula [B] Irganox L67: Diphenylamine represented by the following formula [B] [ka] (In the formula, R' and R" each independently represent an octyl group, a hydrogen atom, or a tert-butyl group.) Irganox L06: Octylated phenyl-α-naphthylamine, BASF Japan Ltd. <Hindered amine antioxidants> Adeka STAB LA-72: Bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, ADEKA Corporation · Irgalube Base 10: Dodecanoic acid (2,2,6,6-tetramethyl-4-piperidyl), BASF Japan Ltd.

[0059] An electroless nickel-plated aluminum magnetic disk was washed twice with n-hexane and isopropyl alcohol, each having a purity of 99% or higher, and then completely dried. Each antioxidant shown in Table 3 was diluted to 10 vol% with an alkyl ester of trimellitic acid having 11 carbon atoms (a compound represented by K2 in the above formula [A]), and then further diluted to 10 vol% with hexane to prepare an antioxidant sample. 5 μL of this antioxidant sample was dropped onto the above washed and dried disk, and the disk was allowed to stand for 1 hour. The state of the droplet after dropping was observed in the same manner as in (4) Disc adhesion> above, and the disc adhesion [%] was calculated from the area of ​​the droplet before and after leaving it for 1 hour after dropping. The results were evaluated according to the following criteria. <Disc adhesion criteria> A: Disc adhesion is less than 30% N: Disc adhesion is 30% or more

[0060] [Table 3]

[0061] As shown in Table 3, it was confirmed that the hindered phenol-based antioxidants and diarylamine-based antioxidants are antioxidants that are less likely to adhere to the disk. On the other hand, hindered amine-based antioxidants are evaluated as being prone to adhering to disks, and it has been confirmed that they are not suitable for addition to the grease composition according to the present invention.

[0062] <(6) Sludge generation evaluation> The extreme pressure additives shown in Table 4 used in the grease composition were evaluated for sludge formation. The extreme pressure additives shown in Table 4 were each diluted with an alkyl ester of trimellitic acid having 11 carbon atoms (a compound represented by K2 in the above formula [A]) to a concentration of 1 to 2 vol %. Each of the extreme pressure additive samples was subjected to a Shell high speed class 4 test in accordance with ASTM D 4172 at a rotation speed of 1,200 rpm, a load of 392 N, a temperature of 75° C., and a time of 5 minutes.

[0063] Images of the balls after the high-speed four-ball test were taken with an optical microscope (magnification: 200x). As reference images, photographed images of balls that were rated E, A, and N according to the judging criteria described below are shown in Figure 5 [Figure 5(a): Rating E, Figure 5(b): Rating A, Figure 5(c): Rating N] (image analysis described below was performed based on the photographed images shown in Figure 5). The following analysis of the photographed images was performed using the image analysis software ImageJ 1.53f. The captured image was converted to 16-bit grayscale (65,536 gradations), and then converted to monochrome two-gradation, with the areas with color tones of 0 to 100 treated as black. These black areas correspond to areas where sludge has occurred. After conversion, the left and right ends of the image, where the amount of light is unstable, were each removed by 15% of the image width. The monochrome two-tone image after excluding both the left and right ends was used as the image to be analyzed, and the sum of the area of ​​the black parts of the image to be analyzed was calculated using the Analyze Particles function of the image analysis software ImageJ 1.53f. The ratio of the sum of the areas of the black parts to the total area of ​​the image to be analyzed [sum of the areas of the black parts / total area of ​​the image to be analyzed] (percentage (%)) was taken as the area rate, and was evaluated according to the following criteria. <Judgment criteria> E (Very good): Area ratio is less than 0.1% A (Good): Area ratio is 0.1% or more and less than 10% N(Not Good): Area ratio is 10% or more

[0064] [Table 4]

[0065] As shown in Table 4, the sludge rating for the phosphate triester, phosphate monoester and / or phosphate diester was E (very good), and the sludge rating for the phosphite diester and / or phosphite triester was A (good), confirming that the phosphate ester-based extreme pressure additives suppress sludge. On the other hand, the sulfur-containing additive was rated as N (not suitable) for sludge, which resulted in it being deemed unsuitable for grease compositions.

[0066] Although the best embodiment has been described in detail above, the present invention is not limited to the above embodiment, and modifications and improvements within the scope of the present invention that can achieve the object of the present invention are included in the present invention. [Explanation of symbols]

[0067] 10... rolling bearing, 11... inner ring, 12... outer ring, 13... rolling element, 14... cage, 15... seam 16...bearing space, 20... disk drive device, 21... base (base plate), 22... spindle motor, 23... magnetic disk, 24... swing arm, 25... magnetic head, 26... actuator, 27... control unit, 30... pivot assembly bearing device, 31... shaft (axis), 31a... shaft main body, 31b... flange portion, 32... sleeve (outer peripheral member), 32a... spacer portion, 40... first bearing, 41... first inner race, 42... first outer race, 43... ball (rolling element), 44... retainer, 45... seal member, 50... second bearing, 51... second inner race, 52... second outer race, 53... ball (rolling element), 54... retainer, 55... seal member, 60: crown-shaped cage; 61: annular member; 61a: end face; 62: ball pocket (recess); 63 (63a, 63b): claw; 64: grease pocket

Claims

1. A rolling bearing, With inner circle, an outer ring arranged coaxially with the inner ring on an outer peripheral side of the inner ring; a plurality of rolling elements disposed between the inner ring and the outer ring; a cage that holds the rolling elements; a grease composition held between the inner ring and the outer ring, The grease composition includes a base oil and a thickener, The thickener contains a urea-based thickener composed of a diurea compound represented by formula (1), R １ -NHCONH-R ２ -HNOCHN-R ３ ・・・Form (1) (In formula (1), R １ and R ３ represents a monovalent alicyclic hydrocarbon group or a monovalent aliphatic hydrocarbon group, and the molar ratio of the alicyclic hydrocarbon group to the aliphatic hydrocarbon group is 6:4 to 8:2; R ２ represents a divalent aromatic hydrocarbon group. The grease composition comprises The storage modulus at 25°C measured under the condition of a film thickness of 1 mm and a shear strain of 1% is 1,200 to 3,000 Pa, Oil separation amount at 80℃ is 200 to 270 mm ２ / mg, The base oil contains an aromatic ester compound. Rolling bearing.

2. The base oil is an aromatic ester compound composed of a trimellitic acid ester.

2. The rolling bearing according to claim 1.

3. The grease composition further comprises a phenolic antioxidant.

2. The rolling bearing according to claim 1.

4. The phenolic antioxidant is a hindered phenolic antioxidant.

4. The rolling bearing according to claim 3.

5. the hindered phenol antioxidant is at least one selected from the group consisting of octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-t-butylanilino)-1,3,5-triazine, triethylene glycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate], 2,2-thio-diethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], and octyl-3,5-di-tert-butyl-4-hydroxy-hydrocinnamic acid; 5. The rolling bearing according to claim 4.

6. The grease composition further contains a diarylamine-based antioxidant.

2. The rolling bearing according to claim 1.

7. The diarylamine antioxidant is at least one selected from the group consisting of diphenylamine, alkylated diphenylamine, and alkylated phenyl-α-naphthylamine.

7. The rolling bearing according to claim 6.

8. The grease composition further contains a phosphate ester-based extreme pressure additive.

2. The rolling bearing according to claim 1.

9. The phosphate ester-based extreme pressure additive is selected from the group consisting of dilauryl hydrogen phosphite (CAS No. 21302-09-0), tricresyl phosphite (CAS No. 25586-42-9), tris(2-ethylhexyl) phosphite (CAS No. 301-13-3), triisodecyl phosphite (CAS No. 25448-25-3), trilauryl phosphite (CAS No. 3076-63-9), tris(triisodecyl) phosphite (CAS No. 77745-66-5), trioleyl phosphite (CAS No. 13023-13-7), tricresyl phosphate (CAS No. No. 1330-78-5), triphenyl phosphate, tributyl phosphate, trioctyl phosphate, trioleyl phosphate, 2-ethylhexyl acid phosphate (CAS No. 12645-31-7), alkyl (C12, C14, C16, C18) acid phosphate, isotridecyl acid phosphate (CAS No. 52933-07-0), and oleyl acid phosphate (CAS No. 37310-83-1), 9. The rolling bearing according to claim 8.

10. The phosphate ester-based extreme pressure additive is at least one selected from the group consisting of tricresyl phosphate (CAS No. 1330-78-5), triphenyl phosphate, tributyl phosphate, trioctyl phosphate, trioleyl phosphate, 2-ethylhexyl acid phosphate (CAS No. 12645-31-7), alkyl (C12, C14, C16, C18) acid phosphate, isotridecyl acid phosphate (CAS No. 52933-07-0), and oleyl acid phosphate (CAS No. 37310-83-1).

10. The rolling bearing according to claim 9.

11. The phosphate ester-based extreme pressure additive is tricresyl phosphate.

11. The rolling bearing according to claim 10.

12. The grease composition contains 10% by mass to 13% by mass of the total mass of the grease composition. In this case, the thickener is contained.

2. The rolling bearing according to claim 1.

13. The grease composition has a worked penetration of 260 to 300.

2. The rolling bearing according to claim 1.

14. A pivot assembly bearing device comprising the rolling bearing according to any one of claims 1 to 13.

15. A disk drive device comprising the pivot assembly bearing device according to claim 14.

16. 16. The disk drive device according to claim 15, comprising nine or more disks each having a diameter of 3.5 inches.

17. 16. The disk drive device according to claim 15, wherein the internal space is filled with a gas having a density less than that of air.

18. 16. The disk drive device according to claim 15, wherein a heat-assisted magnetic recording method is adopted.

Images