Rolling bearing, pivot assembly bearing, and disk drive device

Abstract

To provide a roller bearing with a specific grease composition sealed therein, a pivot assembly bearing device incorporated with the roller bearing, capable of preventing a volatile component from sticking to a magnetic disk or the like and further capable of preventing errors in reading / writing by an HDD from occurring, even when the grease composition sealed in the bearing is evaporated, and a disk driver comprising the same.SOLUTION: There are provided: a roller bearing including a grease composition, the grease composition including base oil, i.e., an ether compound with at least one group bonded to an ether bond (-O-) being a branched alkyl group including a 12 to 16C main chain, and a thickener; a pivot assembly bearing device comprising the roller bearing; and a disk driver comprising the pivot assembly bearing device.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a rolling bearing in which a grease composition is sealed, a pivot assembly bearing device including the rolling bearing, and a disk drive device including the pivot assembly bearing device. [Background technology]

[0002] Various lubricants such as grease and oil are used in the pivot assemblies used in the fulcrum of the actuator of a disk drive (HDD) and in the bearings built into the spindle motor to ensure smooth operation of these parts and the drive of the device. For example, in the case of a rolling bearing incorporated in an actuator of a disk drive device, there has been proposed a rolling bearing filled with grease made by blending a diurea compound having at least one of an alicyclic hydrocarbon group and an aliphatic hydrocarbon group in the skeleton as a thickener with a base oil containing an aromatic ester oil (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-236410 Summary of the Invention [Problem to be solved by the invention]

[0004] One cause of read / write errors in HDDs is the evaporation of base oil, a component of the lubricant sealed in the bearings built into the actuator and spindle motor. When the evaporated base oil cools and condenses on the surface of the magnetic disk or magnetic head, adhering to these surfaces as a liquid or solid, the magnetic disk and magnetic head may stick together, preventing normal reading and writing, which is thought to be one of the causes of read / write errors. Even if attempts are made to reduce the amount of volatilization of the lubricant base oil that occurs as the temperature rises during HDD operation, for example by selecting a low-volatility base oil, it is difficult to completely eliminate the volatilization of the components.

[0005] The present invention aims to provide a rolling bearing in which a specific grease composition is sealed, and to provide a pivot assembly bearing device and a disk drive device equipped with the same, which, by incorporating the bearing into a pivot assembly bearing device, can prevent the adhesion of volatilized base oil components to recording disks, etc., even if the grease composition sealed in the bearing volatilizes, thereby preventing read / write errors in HDDs. [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 peripheral 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, wherein the grease composition comprises a base oil containing an ether compound in which at least one group bonded to an ether bond (—O—) is a branched alkyl group containing a main chain having from 12 to 16 carbon atoms; and a thickener. Regarding rolling bearings. The present invention also relates to a pivot assembly bearing device equipped with the rolling bearing. The present invention also relates to a disk drive device equipped with the pivot assembly bearing device. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a schematic diagram illustrating an example of the structure of a rolling bearing according to the present invention. [Figure 2] 1 is a schematic diagram illustrating an example of the structure of a disk drive device according to the present invention; [Figure 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 view showing a crown cage used in the pivot assembly bearing (rolling bearing) of the present invention. FIG. [Figure 5] 10 is a photograph of a ball after a high-speed Grade 4 test for evaluating sludge generation. DETAILED DESCRIPTION OF THE INVENTION

[0008] As mentioned above, for the lubricants used in HDD actuators and spindle motors, proposals have been made to suppress the volatilization of lubricant components (such as outgassing), which is thought to be one of the causes of HDD read / write errors. Even if the volatilization of commonly used lubricants is suppressed, it is not possible to eliminate the volatilization itself. In conventional disk drives, the fly height (the distance between the magnetic head and the disk) was sufficiently large. Therefore, suppressing volatile components could prevent read / write errors. However, with increasing recording density, the fly height has been reduced to a few nanometers. In this case, a negative pressure is created between the magnetic head and the disk. This causes the surrounding gas to move toward the gap between the magnetic head and the disk and compress. This causes the gas to condense, potentially liquefying even traces of volatile components. Furthermore, with the recent increase in storage capacity per HDD, the number of disks per drive has increased, and disk drives with nine or more 3.5-inch disks are now on the market. In these drives, the internal volume of the drive is becoming even smaller. In such a small volume environment, even a small amount of contamination can lead to read / write errors in an environment with a fly height on the order of a few nanometers. Disk drives whose internal space is filled with a gas less dense than air (such as helium) are also becoming more common. In such disk drives, the internal pressure can be less than 1 atmosphere. In this case, it becomes even more difficult to prevent the volatilization of lubricant components. Furthermore, in HDDs that use the next-generation recording technology, heat-assisted magnetic recording (HAMR), the temperature of the actuator head can reach temperatures as high as 400°C in some places. This increases the internal temperature of the HDD, and even when a low-volatility base oil is used, it may not be possible to reduce the volatilization of lubricant components. As described above, with the volatilization of lubricant components becoming an increasingly serious problem, the present inventors have taken a step further in addressing the conventional challenge of reducing the volatility of lubricant components. The present inventors have continued to study lubricant components based on the new idea that even if volatilization occurs, the volatile components should be less likely to adhere to disks, etc. (Even if they do adhere, they do not remain). They then used an ether compound with an alkyl chain length bonded to an ether bond (oxygen atom) of at least a certain length as the base oil, and discovered that a grease composition that realizes this idea can be obtained.

[0009] Furthermore, the inventors have noticed that in rolling bearings mounted in pivot assembly bearing devices, if the grease sealed in the bearing gets caught in the rolling grooves of the rolling bearing, it can lead to increased torque and dust generation. In particular, in disk drive devices, if dust particles from the rolling bearing adhere to the recording disk or read / write head, they can lead to read / write errors, just like the volatile components. As mentioned above, the distance between the magnetic head and the magnetic disk has narrowed to just a few nanometers, and there is growing concern about problems that can be caused by grease dust generation and the resulting adhesion. To address the dust generation problem that is believed to occur when the grease enclosed in the bearing becomes caught in the rolling grooves of the rolling bearing, the inventors focused on the shape of the grease enclosed in the rolling bearing, and came to adopt a specific urea-based thickener, described below, as a configuration for suppressing the movement of the grease body into the rolling grooves by maintaining the grease shape and suppressing the generation of dust from the grease that may occur in the rolling grooves. This will be explained in detail below.

[0010] [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, although the present invention is not limited to the following embodiments.

[0011] 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 the same basic structure as rolling bearings of the prior art, and comprises 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 that is installed coaxially with the center axis of a shaft (not shown) on the outer periphery of the shaft. The outer ring 12 is a cylindrical structure that is installed coaxially with the inner ring 11 on the outer periphery of the inner ring 11. Each of the multiple rolling elements 13 is a ball that is arranged in a raceway within an annular bearing space 16 formed between the inner ring 11 and the outer ring 12. In other words, the rolling bearing 10 in this embodiment is a ball bearing. The cage 14 is disposed within the raceway and holds multiple rolling elements 13. The cage 14 is an annular body installed coaxially with the central axis of the shaft. It has multiple pockets on one side in the direction of the central axis for holding the rolling elements 13, with the rolling elements 13 accommodated in each pocket. The cage 14 holds the rolling elements 13 at predetermined intervals around the circumferential direction of the inner ring 11 and the outer ring 12, thereby preventing the rolling elements 13 from falling off and preventing contact between adjacent rolling elements 13. The cage 14 may have any shape (crown-shaped, corrugated, etc.) and be made of any material (steel plate, resin, etc.). However, a crown-shaped cage (see FIG. 4) is preferably used in the rolling bearing according to the present invention. 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 circumferential surface, an inner circumferential surface, and two end faces 61a connecting the outer circumferential surface and the outer circumferential surface. One end face 61a of the annular member 61 has a plurality of ball pockets (recesses) 62 formed at predetermined intervals along the circumferential direction to rotatably accommodate balls (rolling elements 13, not shown). Furthermore, the annular member 60 has a pair of claws 63 (63a, 63b) extending from the end face 61a at both ends of each ball pocket 62. The pair of claws 63 are curved to approach each other and conform to the curved surface of the ball accommodated in each ball pocket 62, thereby preventing the ball accommodated in each ball pocket 62 from falling out. Furthermore, the presence of the claws 63 forms a grease pocket 64 between the two ball pockets 62. A grease composition G (not shown), described below, is accommodated in the grease pocket 64 and contributes to lubrication between the ball pockets 62 and the balls (rolling elements 13) accommodated therein. The seal member 15 is fixed to the inner circumferential surface of the outer ring 12 and extends toward the inner ring 11, sealing the bearing space 16. A 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. A grease composition described below is used as the grease composition G. The amount of grease composition G enclosed within the bearing space 16 is, for example, 2% to 30% of its volume. In the pivot assembly bearing device described below, which requires particularly low torque, 3% to 10% is more preferable. By ensuring that the amount of grease composition G enclosed within this range, the grease composition G can sufficiently lubricate the rolling elements 13, inner ring 11, and outer ring 12 within the bearing space 16 of the rolling bearing 10, reducing frictional resistance and reducing friction torque. The sealing member 15 is formed, for example, from 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 the steel plate shield or the non-contact rubber seal can be used in the present invention. From the perspective of suppressing outgassing, it is preferable to use a steel plate shield. Note that while this drawing shows an embodiment that includes the sealing member 15, the rolling bearing of the present invention also covers embodiments of a rolling bearing that does not include a sealing member. In the rolling bearing 10 having the above-described 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 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 outer ring 12. As can be seen from the configuration shown in FIG. In this way, the grease composition G enclosed in the rolling bearing 10 lubricates the spaces between the rolling elements 13 and the inner ring 11 or outer ring 12 when the rolling bearing 10 rotates.

[0012] 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 uses a specific grease composition described below, which makes it difficult for volatile components to adhere to the disk even if they are generated during operation, and has the advantage of being able to suppress the occurrence of magnetic disk read / write errors which are partly caused by the adhesion of volatile components. 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.

[0013] [Pivot assembly bearing device and disk drive device] A pivot assembly bearing device including the rolling bearing of the above-described 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.

[0014] 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 Figure 2, the disk drive device 20 of this embodiment includes a substantially rectangular box-shaped base (base plate) 21, a spindle motor 22 mounted on the base 21, a magnetic disk 23 rotated by the spindle 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.

[0015] The disk drive device of the present invention may be, for example, a disk drive device equipped with nine or more 3.5-inch diameter magnetic disks. In a device with such a large number of disks, the spatial volume within the device is further reduced. The disk drive device may have its internal space filled with a gas having a density lower than that of 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 lower than 1 atmosphere. The disk drive device may also employ a thermally assisted magnetic recording (HAMR) method as its recording method. In a disk drive device employing a thermally assisted magnetic recording (HAMR) method, the temperature of the actuator head may locally reach a high temperature of 400°C.

[0016] 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, two rolling bearings, a first bearing 40 and a second bearing 50, fitted onto the shaft 31 with a predetermined length of space S between them, and a sleeve 32 (outer peripheral member) that exteriorly houses 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 way, the shaft 31 is held 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 separate components.

[0017] The first bearing 40 and the second bearing 50 are the rolling bearings 10 according to the embodiment of the present invention described above. Use. 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 to hold the balls 43, a sealing member 45 that isolates the raceway from the outside world, and a grease composition (not shown) used in the present invention that 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 to hold the balls 53, a sealing member 55 that isolates the raceway from the outside world, and a grease composition (not shown) used in the present invention that 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 (see FIG. 2) with the flange portion 31b positioned on the base 21 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.

[0018] 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. While a typical rolling bearing rotates continuously in one direction, 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 over the magnetic disk 23. It is also necessary to move the magnetic head 25 to an accurate position with high response speed.

[0019] The grease composition used in this embodiment is such that even when the base oil volatilizes at high temperatures, the volatilized base oil adheres less to magnetic disks and the like, making it possible to suppress disk read / write errors in disk drive devices. The grease composition used in this embodiment also achieves an appropriate range of oil separation and exhibits excellent grease shape stability. This prevents lubricant supply shortages 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 long periods of time. This reduces disk 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.

[0020] [Grease composition] The grease composition (hereinafter simply referred to as "grease composition") enclosed in the rolling bearing according to the present invention is characterized by containing a specific ether-based base oil. As mentioned above, the formulation of this grease composition achieves low volatility, and furthermore, the volatile components have the property of being less likely to adhere to disks and the like. The grease composition packed in the rolling bearing of the present invention will now be described.

[0021] <Base oil> In the grease composition packed in the rolling bearing according to this embodiment, an ether-based base oil having a specific structure is used as the base oil. By using an ether compound having a specific structure as the base oil, as described below, it is possible to obtain a grease composition having the property that even if the base oil is exposed to high temperatures and volatilizes, the volatilized base oil is less likely to adhere to the surface of a magnetic disk or the like.

[0022] The ether-based base oil used as the base oil in the present invention is an ether compound (hereinafter also referred to as ether compound A) in which at least one group bonded to an ether bond (-O-) is a branched alkyl group having a main chain containing 12 to 16 carbon atoms, i.e., -OR X base( R X The base oil is not particularly limited as long as it contains an ether compound A containing (represents a branched alkyl group having a main chain having from 12 to 16 carbon atoms). The number of ether bonds (—O—) in the ether compound A is not particularly limited, and may be various, for example, a monoether, or a polyether such as a diether, triether, or tetraether. In one embodiment, the ether compound A may be a diether. In the branched alkyl group having a main chain of 12 to 16 carbon atoms, the position of the branched chain bonded to the main chain and the number of branched chains are not particularly limited. In the branched alkyl group, the term "main chain having 12 to 16 carbon atoms" means that the longest carbon chain, counting from the carbon atom bonded to the oxygen atom of the ether bond, has 12 to 16 carbon atoms, and the number of carbon atoms in the branched chain bonded to the main chain can be, for example, about 1 to 12, such as 4 to 12, or 8 to 12. The total number of carbon atoms in the branched alkyl group having a main chain of 12 to 16 carbon atoms bonded to an ether bond can be, for example, about 13 to 30, such as 16 to 28, or 20 to 28. The main chain of the branched alkyl group having from 12 to 16 carbon atoms can be, for example, a main chain having from 14 to 16 carbon atoms, a main chain having from 12 to 14 carbon atoms, or a main chain having 14 carbon atoms.

[0023] In an embodiment of the present invention, the base oil may consist solely of an ether-based base oil, that is, the base oil may consist solely of ether compounds including an ether compound A in which at least one group bonded to the ether bond (—O—) is a branched alkyl group containing a main chain having from 12 to 16 carbon atoms. The ether compound is not particularly limited as long as it contains an ether compound A in which at least one group bonded to the ether bond (—O—) is a branched alkyl group containing a main chain having from 12 to 16 carbon atoms, and an ether compound that is typically used as a base oil for lubricants can be suitably used. For example, grease compositions using alkylated diphenyl ethers as ether compounds may be hard and have low oil separation depending on the type of alkylated diphenyl ether, so care must be taken when using large amounts, and consideration should be given to using only small amounts as the base oil for the grease composition.

[0024] In an embodiment of the present invention, the ether compound A in which at least one group bonded to the ether bond (-O-) is a branched alkyl group containing a main chain having from 12 to 16 carbon atoms may be an aliphatic ether compound (hereinafter also referred to as ether compound A1) in which at least one group bonded to the ether bond (-O-) is a branched alkyl group containing a main chain having from 12 to 16 carbon atoms. In this aliphatic ether compound (ether compound A1), the main chain of the branched alkyl group having from 12 to 16 carbon atoms can be, for example, a main chain having from 14 to 16 carbon atoms, a main chain having from 12 to 14 carbon atoms, or a main chain having 14 carbon atoms. This aliphatic ether compound (ether compound A1) can be in the form of an aliphatic diether. When ether compound A1 is in the form of an aliphatic diether, both of the alkyl groups bonded to the ether bond (i.e., the alkyl groups at both ends of the compound) can be in the form of a branched alkyl group containing a main chain having from 12 to 16 carbon atoms, and the main chain can be, for example, a main chain having from 14 to 16 carbon atoms, a main chain having from 12 to 14 carbon atoms, or a main chain having 14 carbon atoms. When the ether compound A1 is an aliphatic diether, the type of linking group connecting the ether bonds is not particularly limited, and examples thereof include a divalent hydrocarbon group having 1 to 30 carbon atoms. In one embodiment, the linking group can be an alkylene group, The alkylene group may have 1 to 30, 2 to 20, 2 to 10, 5 to 10, 5 to 7, or 6 carbon atoms, for example.

[0025] In an embodiment of the present invention, the ether-based base oil may contain an aliphatic ether compound or may consist of an aliphatic ether compound. For example, in an embodiment of the present invention, the base oil may be an aliphatic ether compound containing an aliphatic ether compound A1 in which at least one group bonded to the ether bond (—O—) is a branched alkyl group having a main chain containing 12 to 16 carbon atoms. The aliphatic ether compound is not particularly limited as long as it contains an aliphatic ether compound A1 in which at least one group bonded to the ether bond (—O—) is a branched alkyl group containing a main chain having from 12 to 16 carbon atoms, and an aliphatic ether compound that is typically used as a base oil for lubricants can be suitably used. In an embodiment of the present invention, the aliphatic ether compound may be the aliphatic ether compound A1 used alone, or may be a mixture of two or more of the aliphatic ether compound A1 and other aliphatic ether compounds.

[0026] An example of the aliphatic ether compound is an aliphatic ether compound having 8 to 300 carbon atoms in one molecule and 1 to 150 oxygen atoms in one molecule. When the number of carbon atoms and the number of oxygen atoms in one molecule are within the above ranges, a good balance of viscosity, low volatility, and low-temperature fluidity can be expected. The aliphatic ether compound may have, for example, 8 to 80 carbon atoms and 1 to 40 oxygen atoms in one molecule, or may have 8 to 60 carbon atoms and 1 to 30 oxygen atoms in one molecule.

[0027] One embodiment of the aliphatic ether compound is represented by the following formula (E1). [ka] In the above formula (E1), at least one of n1 and n4 represents an integer of 8 to 12, and for example, n1 and n4 can each independently represent an integer of 8 to 12. Alternatively, n1 and n4 can be integers whose average value is in the range of 8 to 12. In one embodiment, at least one of n1 and n4, or n1 and n4 each independently, or n1 and n4 can be 8 to 10 or 10 to 12 on average, or an embodiment in which n1 and n4 are both 10 is also possible. In the above formula (E1), at least one of n2 and n3 represents an integer of 6 to 10, and for example, n2 and n3 can each independently represent an integer of 6 to 10. Alternatively, n2 and n3 can be integers whose average value is in the range of 6 to 10. In the above formula (E1), n5 can be an integer of 1 to 2. In one embodiment, n5 is 2. It can be said that:

[0028] Another embodiment of the aliphatic ether compound is represented by the following formula (E2): That is, the aliphatic ether compound may have three or more ether bonds. [ka] In the above formula, R a and R c each independently represents an alkyl group having a total of 8 to 28 carbon atoms, and R b represents an alkylene group having 2 to 28 carbon atoms, and m represents an integer of 1 to 6 on average. b -O) may be the same group or different groups in each structural unit. In one embodiment of the compound represented by formula (E2), R a and R c At least one of the above may be a branched alkyl group containing a main chain having 12 to 16 carbon atoms. R a , R b and R cmay be linear or branched, and in one embodiment R a and R c When the chain is branched, the position of the branched chain and the number of branched chains are not particularly limited. R a and R c The alkyl group R may have, for example, 8 to 26 carbon atoms, or alternatively, 10 to 24 carbon atoms. a and R c When the branched chain is branched, the number of carbon atoms in the main chain can be, for example, 8 to 16, or 10 to 14, independently.

[0029] In addition, R a and R c When at least one of the alkyl groups represents a branched alkyl group containing a main chain having from 12 to 16 carbon atoms, the total number of carbon atoms in the branched alkyl group may be 13 to 26 or alternatively 13 to 24, and in this case the number of carbon atoms in the branched chain may be 1 to 10. Furthermore, the main chain having from 12 to 16 carbon atoms in the branched alkyl group may be, for example, a main chain having from 14 to 16 carbon atoms, a main chain having from 12 to 14 carbon atoms, or a main chain having 14 carbon atoms. Also, R b The number of carbon atoms can be, for example, 2 to 12, or alternatively, 2 to 8.

[0030] R a and R c In the case of the ether compound having 8 or more carbon atoms, that is, the terminal of the molecular structure is an alkoxy group, the separability from water can be improved. Also R b By making the number of carbon atoms 2 or more, i.e., an ether compound that does not contain an acetal structure, it is expected that the compound will have excellent moisture resistance and Lewis acid resistance, and by making the number of carbon atoms 18 or less, it is expected that the low-temperature fluidity will not be significantly impaired. A good balance of viscosity, low volatility, and low-temperature fluidity can be expected by setting m to an integer of 1 to 6 on average. For example, the average value of m can be 1 to 4, or 1 to 2.

[0031] Specific examples of the aliphatic ether compound represented by the above formula (E2) include, but are not limited to, compounds represented by the following formulas (i) to (iv). [ka]

[0032] The ether-based base oil used in the present invention has a kinematic viscosity at 40°C of, for example, 40 to 100 mm 2 / s range, especially 40-70 mm 2 Ether compounds in the range of / s can be used. The ether-based base oil having a kinematic viscosity within the above-mentioned range is not particularly limited, but examples thereof include ether compounds in which at least one group bonded to the above-mentioned ether bond (—O—) is a branched alkyl group having from 12 to 16 carbon atoms.

[0033] In an embodiment of the present invention, the base oil comprises an ether compound A having the above-mentioned specific alkyl group, for example, an aliphatic ether compound A1 having the above-mentioned specific alkyl group. In another embodiment of the present invention, the base oil consists solely of an ether-based base oil containing the ether compound A having the specific alkyl group described above, and for example, consists solely of an aliphatic ether-based base oil containing the aliphatic ether compound A1 having the specific alkyl group described above. For example, in an embodiment of the present invention, another base oil other than the aliphatic ether-based base oil may be included, and in this case, the amount of the other base oil may be, but is not limited to, 10% by mass or less, or 5% by mass or less, based on the total amount of the base oil.

[0034] Furthermore, for example, an aromatic ester compound having an alkyl chain length of at least a certain length can be used as the base oil. The aromatic ester base oil may be, for example, 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 that 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 surface of a magnetic disk or the like.

[0035] The aromatic ester compounds described above are compounds in which an alkyl group having a total of eight or more carbon atoms is bonded to an aromatic ring via an ester group *-(CO)O- (* indicates the bond point to 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 eight or more carbon atoms (the number of carbon atoms here refers to the number of carbon atoms in the alkyl group). 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 having 1 to about 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 is an alkyl ester group having 8 or more carbon atoms, and that all of the alkyl ester groups are 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). (The same applies to the examples of linear and branched alkyl groups described below; when the aromatic ester compound has two or more alkyl ester groups, the alkyl group in at least one alkyl ester group has the exemplified group, and preferably the alkyl groups in all of the alkyl ester groups have the exemplified group.)

[0036] The alkyl group having a total of 8 or more carbon atoms may be linear or branched. A branched alkyl group may have multiple branched chains, and the branching positions are not particularly limited.

[0037] The linear alkyl group having a total of 8 or more carbon atoms in the aromatic ester compound 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. Furthermore, 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 is, for example, a group having 8 to 11 carbon atoms. The branched alkyl group may be formed by bonding a branched chain to a linear alkyl group. The branched alkyl group is an alkyl group having a carbon atom in the longest chain, counting from the carbon atom bonded to the oxygen atom of the ester group, of 8 to 11 carbon atoms. The branched alkyl group may be formed by bonding a plurality of branched chains to a linear alkyl group having 6 to 11 carbon atoms, as long as the total number of carbon atoms is 8 or more.

[0038] The aromatic ester compound may be, for example, a triester of trimellitic acid (1,2,4-benzenetricarboxylic acid).

[0039] A preferred aromatic ester compound is a triester compound of trimellitic acid represented by the following formula: [ka] In the formula, each R is 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, or 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.

[0040] The aromatic ester-based base oil has a kinematic viscosity at 40°C of, for example, 40 to 130 mm 2 / s range, especially 50-80 mm 2 An aromatic ester compound in the range of / s can be used. The aromatic ester base oil having a kinematic viscosity within the above-mentioned 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.

[0041] The base oil may 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 base oil is contained in a proportion of 80 mass % to 98 mass % based on the total mass of the grease composition.

[0042] <Thickener> The grease composition used in the present invention can preferably use a urea compound as a thickener. Urea compounds have excellent heat resistance and water resistance, and are particularly stable at high temperatures, and are therefore suitable for use as thickeners in applications that are subject to high-temperature environments. The grease composition used in the present invention is expected to achieve low dust generation by blending a specific urea-based thickener, which will be described later.

[0043] The grease composition used in the present invention can use, for example, an alicyclic aliphatic diurea compound as a urea-based thickener, and a specific example is a diurea compound represented by the following formula (1). R1-NHCONH-R2-NHCONH-R3...Formula (1) (In formula (1), R1 and R3 are monovalent alicyclic hydrocarbon groups or monovalent aliphatic hydrocarbon groups. wherein 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.

[0044] The 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. However, it is preferable to use a diurea compound represented by formula (1) (within the total amount of diurea compounds) in which the molar ratio of the alicyclic hydrocarbon group to the aliphatic hydrocarbon group 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 within the above range, the storage modulus and oil separation amount of a grease composition containing the diurea compound can be set within predetermined ranges. As will be described later, 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 driven, the shape of the enclosed grease composition is maintained and an appropriate amount of oil (base oil) is supplied to the rolling elements, making it possible to obtain a grease composition that has appropriate lubricating performance while suppressing dust generation.

[0045] The monovalent alicyclic hydrocarbon group may, for example, be 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.

[0046] The alicyclic aliphatic diurea compound used in the present invention can be synthesized using an amine compound and an isocyanate compound. For example, the compound can be obtained by synthesizing an alicyclic amine and an aliphatic amine as amine raw materials using these and an aromatic diisocyanate. The alicyclic amine and aliphatic amine as amine raw materials are charged in an amount of, for example, alicyclic amine:aliphatic amine=6:4 to 8:2, and reacting this with an aromatic diisocyanate to obtain a compound in which the molar ratio of alicyclic hydrocarbon groups to aliphatic hydrocarbon groups 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), and dimethylbiphenyl diisocyanate (TODI) are used.

[0047] 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 will be too small, which may result in poor lubrication. On the other hand, if the thickener is used in an amount less than 10% by mass, the amount of oil separation will be too large, which may not only cause contamination of the equipment but also cause the grease to leak out of the grease pockets in the cage and become caught between the rolling elements and raceways of the bearing, resulting in an increase in rotational torque. In particular, from the viewpoint of obtaining a grease composition that has an appropriate amount of oil separation and is particularly excellent in flow characteristics and life characteristics, it is preferable to contain a thickener in a proportion of, for example, 10 to 13 mass %.

[0048] <Other additives> In addition to the above essential components, the grease composition may contain additives that are commonly used in grease compositions, as needed, 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, anti-friction agents (anti-wear 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.

[0049] 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-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate], 1,6-hexanediol-bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 2,2-thio hindered phenol-based antioxidants such as diethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], N,N'-hexamethylenebis(3,5-di-t-butyl-4-hydroxy-hydrocinnamide), and octyl-3,5-di-tert-butyl-4-hydroxy-hydrocinnamic acid; other phenol-based antioxidants such as 2,6-di-t-butyl-4-methylphenol and 4,4-methylenebis(2,6-di-t-butylphenol); and 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 disc adhesion, phenolic antioxidants, especially 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 Preferred are hindered phenol-based antioxidants selected from the group consisting of octyl-3,5-di-tert-butyl-4-hydroxy-hydrocinnamic acid, 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. Furthermore, from the viewpoint of sludge suppression, the above-mentioned hindered phenol-based antioxidants are preferred.

[0050] Examples of extreme pressure additives include phosphorus compounds, chlorine 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), and trioleyl phosphite (CAS No. 13023-13-7). Examples include phosphorous diesters and / or phosphorous triesters; and phosphoric acid monoesters and / or phosphoric acid diesters (acidic 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), which are commercially available products. Among these, from the viewpoint of sludge suppression, the phosphoric acid triesters, phosphoric acid monoesters, and / or phosphoric acid diesters are preferred, and phosphoric acid triesters are particularly preferred. Specific examples 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 phosphates, 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 sludge suppression, 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.

[0051] Examples of the metal deactivator include benzotriazole and sodium nitrite.

[0052] Anti-wear agents include tricresyl phosphate and polymeric esters. Examples of the polymer ester include esters of aliphatic monocarboxylic acids and dicarboxylic 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.

[0053] The grease composition used in the present invention can be obtained by blending the base oil, the thickener, and, if desired, other additives. Furthermore, for example, a grease composition can be obtained by blending other additives, if desired, with a urea-based grease (base grease) consisting of the base oil and the urea-based thickener. 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 %.

[0054] <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%.

[0055] The storage modulus is a value that indicates the shape stability of the grease, and is an effective parameter for understanding the shape stability of the grease immediately after the grease is sealed in the bearing device or when the bearing device is vibrating. For example, in a pivot assembly bearing device, grease is sealed only in the grease pockets of the crown-shaped retainer (cage). If the shape of the grease changes from the shape at the time of sealing, the grease This can entangle the balls (rolling elements) and lead to increased torque and torque fluctuations in the rolling bearing, as well as causing dust generation. Therefore, the ability of the grease to maintain its shape (shape stability) is an important factor in maintaining initial and long-term torque stability and suppressing dust generation. From the viewpoint of the grease's shape stability, it is preferable that the grease composition used in the present invention has a storage modulus of 1,200 Pa or more at 25°C under the above-mentioned measurement conditions (film thickness 1 mm, shear strain 1%). However, if the storage modulus is too high, there is a possibility that the grease composition will fall out of the grease pocket in the crown-shaped retainer while maintaining its shape. In this case, since the grease is located on the orbital path of the rolling elements, resistance increases when the balls pass over the grease, raising concerns about an increase in torque. Therefore, it is desirable that the storage modulus not exceed 3,000 Pa.

[0056] <About oil separation amount> The grease composition used in the present invention has an oil separation rate within an appropriate range, i.e., an oil separation rate of 200 to 270 mm at 25°C. 2 / mg is preferred.

[0057] Oil separation testing has traditionally been used to evaluate the amount of oil (base oil and additives) seeping out of grease. Because the amount of oil separation affects the lifespan of a grease, understanding the amount of oil separation is important not only for understanding the life characteristics of the grease, but also for achieving 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 low, the lubricating components (base oil and additives) supplied to the balls (rolling elements) will be insufficient over time, which could lead to torque fluctuations and seizure. On the other hand, if the amount of oil separation is too high, contamination due to oil leakage becomes more likely.

[0058] Greases containing the urea-based thickener used in the present invention generally have a low amount of oil separation, and therefore, 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. Therefore, 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 φ3 mm cylindrical shape on the side of the medicine paper on which the medicine is placed, and after leaving it in an 80°C environment for 24 hours, the area of ​​the oil-smeared part (smeared base oil) that occurred on the medicine paper was measured. The area of ​​the oil-smeared part per mass of grease was then calculated as the amount of oil separation (mm 2 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. Based on the above definition, when conventional greases that did not suffer from poor lubrication were evaluated using this unique method, the amount of oil separation was found to be approximately 230 to 280 mm 2 It was confirmed that the oil separation amount was about 200 mm 2 With conventional greases with a lubrication rate of 0.1 / mg or less, seizure due to poor lubrication was confirmed. Also, considering that excessive oil separation can cause oil leakage, the upper limit was set at 300mm 2 / mg.

[0059] 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 after leaving it in an environment of 80°C for 24 hours, 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.

[0060] As described above, the grease composition used in this embodiment has a storage modulus within a predetermined range, so that the shape of the grease composition sealed in the ball pocket (grease pocket) of the retainer (cage) is not easily distorted, and the ball pocket (grease pocket) is easily separated from the grease composition by an appropriate amount of oil. The grease composition itself will not fall from the roller (the roller) onto the raceway surface of the rolling bearing, and it is expected that dust generation that causes particle generation will be suppressed. Furthermore, by using an ether compound having an alkyl group with a predetermined number of carbon atoms 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, adhesion of dust-generating components and volatile components to magnetic disks, etc. can be suppressed. The above configuration makes it possible to suppress disk read / write errors in disk drive devices that are partly caused by dust particles and volatile components.

[0061] 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 idea described in the claims. [Example]

[0062] The present invention will be described in more detail below with reference to examples, although the present invention is not limited thereto.

[0063] The grease compositions used in the Examples, Comparative Examples, Reference Examples, and Reference Comparative Examples were prepared in the amounts shown in the tables below. Note that "hardening treatment" in Tables 1 and 2 below refers to a treatment in which the prepared grease composition was left to stand at 75°C and 40% RH for 5 hours. This treatment takes into consideration the possibility that the properties will be the same as after the hardening treatment depending on the grease compounding conditions, or that a harder grease is required. The details and abbreviations of the components used in preparing the grease compositions of the Examples, Reference Examples, Comparative Examples and Reference Comparative Examples are as follows: <Thickener> The molar ratio of alicyclic aliphatic diurea compound:alicyclic hydrocarbon group:aliphatic hydrocarbon group is 5:5 to 8:2 (see Tables 1 and 2). <Base oil> Ethers (aliphatic ether compounds): Number of carbon atoms: 8: A compound of the following formula (E1), in which n1 and n4 are 10, n2 and n3 are 8, and n5 is 2 Alkylated diphenyl ether: Product name: MORESCO Hi-Lube LB-60, MORESCO Corporation [ka] (Reference) Aromatic esters (trimellitic acid esters): Carbon atoms: 9 carbon atom alkyl ester of trimellitic acid (compound in the following formula [A] where R is represented by K1) Carbon atoms 11: C11 alkyl ester of trimellitic acid (compound in the following formula [A] where R is represented by K2) Carbon atoms: 8 carbon atoms alkyl ester of trimellitic acid (compound in the following formula [A] where R is represented by K3) (Reference) Mineral oil + PAO: A mixture of mineral oil and polyalphaolefin oil [ka] <Additives> Antioxidants: Phenolic: Hindered phenolic antioxidant (2,2-thio-diethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], product name "Irganox L115", BASF Japan Ltd.) Amine-based: Hindered amine-based antioxidant (bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, product name "ADEKA STAB LA-72", ADEKA Corporation) Extreme pressure additives: Phosphate ester extreme pressure additive Fujifilm Wako Pure Chemical Industries, Ltd., product name "Tritolyle phosphate"

[0064] The storage modulus, oil separation amount, particle count (amount of dust generated), and disk adhesion of the base oil for the obtained grease compositions were evaluated using the following procedures. The worked penetration of each grease composition was also measured. The results are shown in Tables 1 and 2.

[0065] <(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 the strain dispersion method (strain variable from 100% to 0.01%), and measurements were performed using a parallel plate φ25mm (PP25) jig with a plate gap of 1mm at a temperature of 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 greater than 3,000 Pa

[0066] <(2) Amount of oil separation (unit: mm 2 / mg) Measurement and Evaluation 9 mg of each prepared grease composition was placed in a φ3 mm cylindrical shape on the medicine-carrying side of the medicine-carrying paper and left to stand in an 80°C environment for 24 hours. After 24 hours, the area of ​​the oil-stained part on the medicine-carrying 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: 105mm x 105mm, thickness: 42μm, basis weight: 30g / 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 or less A: Oil separation amount is 200 mm 2 / mg or more 270mm2 / mg or less N: Oil separation amount is 270 mm 2 / mg super

[0067] <(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 filled with each grease composition was placed in the oscillation tester, and the device was 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 particles [μm 3 This was evaluated as the number of particles (amount of dust generated: average value of N=3) for each example.

[0068] <(4) Disc Adhesion (1)> The base oils used in the Examples, Reference Examples, Comparative Examples, and Reference Comparative Examples were evaluated for disc adhesion according to the following procedure. An electroless nickel-plated aluminum magnetic disk was washed twice with n-hexane and isopropyl alcohol (purity 99% or higher), and then completely dried. Five microliters of base oil (sample oil) diluted to 10% by volume with hexane was dropped onto the disk and allowed to stand for one 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 (approximately 5 seconds later) and after leaving it to stand for 1 hour was calculated using image analysis software, and the percentage (%) (disc adhesion) of the area value after leaving it to stand 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 (if the area value before and after leaving it to stand is the same, the disc adhesion is 100%). This test was conducted 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 of the values ​​obtained when reproducibility was achieved (area value results within ±5%, N=4 or more) was used as the test result. The results were evaluated based on the following criteria. <Disc adhesion criteria> A: Disc adhesion is less than 30% N: Disc adhesion is 30% or more

[0069] [Table 1]

[0070] [Table 2]

[0071] First, the appropriate ranges of storage modulus and oil separation amount were confirmed as follows from the Reference Examples and Reference Comparative Examples. That is, as shown in Table 1, the storage modulus (1,200 Pa or more and 3,000 Pa or less) and the oil separation amount (200 mm 2 / mg or more 270mm 2 The grease compositions of Reference Examples 1 to 5, in which the particle count (mg / mg or less) was in the preferred (A) range, had smaller particle counts than the comparative reference oils described later, and the results indicated that dust generation was suppressed. Furthermore, the base oils used in the grease compositions of these Reference Examples were rated A for disk adhesion (hard to adhere to the disk). The grease compositions of Reference Comparative Examples 1 to 5 were all judged as unacceptable (N) for storage modulus, and the grease compositions of Reference Comparative Examples 3 and 5 were also judged as unacceptable (N) for the amount of oil separation. As a result, the particle count values ​​were larger than those of the Reference Examples. Furthermore, the base oils used in the grease compositions of Reference Comparative Examples 4 and 5 were judged as unacceptable (N) for disk adhesion.

[0072] As shown in Table 1, the grease composition of Example 1, which used a specific ether-based base oil, had a storage modulus (1,200 Pa or more and 3,000 Pa or less) and an oil separation amount (200 mm 2 / mg or more 270mm 2 / mg or less) is in the preferred (A) range, and As a result of the small number of droplets and the suppression of dust generation, the base oil used in the grease composition of Example 1 was rated A for disk adhesion (hard to adhere to disk). On the other hand, the grease composition of Comparative Example 1 shown in Table 2 was too hard and therefore unsuitable for use as a grease composition, and none of the worked penetration, storage modulus, amount of oil separation, or number of particles could be measured. Furthermore, the base oil used in the grease composition of Comparative Example 1 was rated N for disc adhesion.

[0073] <(5) Disc Adhesion (2)> Using the same procedures and test procedures as 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 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-hydrocinnamic acid 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> ADK STAB LA-72: Bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, ADEKA Corporation Irgalube Base 10: 2,2,6,6-tetramethyl-4-piperidyl dodecanoate, BASF Japan Ltd.

[0074] An electroless nickel-plated aluminum magnetic disk was washed twice with n-hexane and isopropyl alcohol, each of which had 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 where R is 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 washed and dried disk. It was left to stand for another 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 to stand for 1 hour after dropping. Based on the results obtained, evaluation was made according to the following criteria. <Disc adhesion criteria> A: Disc adhesion is less than 30% N: Disc adhesion is 30% or more

[0075] [Table 3]

[0076] 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 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 relating to the object of the present invention.

[0077] <(6) Sludge generation evaluation> The extreme pressure additives shown in Table 4 used in the grease compositions 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 in which R is 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 testing machine 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.

[0078] Images of the balls after the high-speed four-ball test were taken with an optical microscope (magnification 200x). For reference, Figure 5 shows images of balls that received an E, A, or N rating based on the evaluation criteria described below [Figure 5(a): E rating, Figure 5(b): A rating, Figure 5(c): N rating] (Image analysis, described below, was performed based on the images shown in Figure 5). The following analysis of the images was performed using the image analysis software ImageJ 1.53f. The captured image was converted to a 16-bit grayscale (65536 gradations), and then converted to a monochrome two-gradation image, with the area with a color tone of 0 to 100 being the black area. After conversion, the left and right edges of the image where the amount of light is unstable were 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 total area of ​​the black areas to the total area of ​​the image to be analyzed [total area of ​​the black areas / total area of ​​the image to be analyzed] (percentage (%)) was taken as the area ratio, 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

[0079] [Table 4]

[0080] As shown in Table 4, the sludge evaluation for the phosphate triester, phosphate monoester, and / or phosphate diester was E (very good), and the sludge evaluation for the phosphite diester and / or phosphite triester was A (good), confirming that the phosphate ester-based extreme pressure additives inhibit sludge. On the other hand, the sulfur-containing additives were judged to be N (unsuitable) for sludge, which meant that they were not suitable for grease compositions.

[0081] Although the best mode for carrying out the invention has been described in detail above, the present invention is not limited to the above mode. The present invention does not intend to limit the scope of the present invention, and any modifications and improvements that can achieve the object of the present invention are included in the present invention. [Explanation of symbols]

[0082] 10... rolling bearing, 11... inner ring, 12... outer ring, 13... rolling element, 14... cage, 15... sealing member, 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 ring (inner race), 42... First outer ring (outer race), 43... Balls (rolling elements), 44... Retainer, 45... Seal member, 50... Second bearing, 51... Second inner ring (inner race), 52... Second outer ring (outer race), 53... Balls (rolling elements), 54... Retainer, 55... Seal member, 60... Crown-shaped cage, 61... Annular member, 61a... End face, 62... Ball pocket (recess), 63 (63a, 63b)... Pawl, 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 comprises a base oil containing an ether compound in which at least one group bonded to an ether bond (—O—) is a branched alkyl group having a main chain containing 12 to 16 carbon atoms, and a thickener. Rolling bearing.

2. The grease composition comprises 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 25℃ is 200 to 270 mm ２ / mg, 2. The rolling bearing according to claim 1.

3. 2. The rolling bearing according to claim 1, wherein the base oil comprises an ether compound, including an ether compound in which at least one group bonded to the ether bond (—O—) is a branched alkyl group containing a main chain having from 12 to 16 carbon atoms.

4. 2. The rolling bearing according to claim 1, wherein the ether compound in which at least one group bonded to the ether bond (—O—) is a branched alkyl group containing a main chain having 12 to 16 carbon atoms is an aliphatic ether compound.

5. 2. The rolling bearing according to claim 1, wherein the base oil comprises an aliphatic ether compound, which contains an aliphatic ether compound in which at least one group bonded to the ether bond (—O—) is a branched alkyl group containing a main chain having from 12 to 16 carbon atoms.

6. The kinematic viscosity of the base oil at 40°C is 40 to 100 mm ２ 2. The rolling bearing according to claim 1, wherein the rolling bearing has a saturation of 0.1 / s.

7. A pivot assembly bearing device comprising the rolling bearing according to any one of claims 1 to 6.

8. A disk drive device comprising the pivot assembly bearing device according to claim 7.

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