Fluid dynamic bearing, spindle motor, and disk drive device

Abstract

Provided are a fluid dynamic bearing in which a lubricating oil composition containing a base oil and an ionic liquid is sealed, a spindle motor in which evaporation of the lubricating oil composition provided in the fluid dynamic bearing can be suppressed by incorporating the fluid dynamic bearing in the spindle motor, and a disk drive device provided with the spindle motor. And the read-write error of the HDD can be inhibited. A fluid dynamic pressure bearing in which a lubricating oil composition containing a base oil and an ionic liquid having: at least one cation selected from the group consisting of tetraalkylammonium cations; and at least one anion selected from the group consisting of borate anions represented by formulae (C-1) to (C-3). (In the formula, R9 to R12 each independently represent a linear or branched alkyl group). # imgabs0 #

Description

Technical Field

[0001] The present invention relates to a fluid dynamic pressure bearing and a spindle motor having the fluid dynamic pressure bearing, wherein the fluid dynamic pressure bearing is filled with a lubricating oil composition containing an ionic liquid that is less likely to cause a read-write error. The present invention also relates to a disk drive device having the spindle motor. Background Art

[0002] Various lubricants such as grease and oil are used in the bearings of the pivot assembly and spindle motor used in the fulcrum part of the actuator of the HDD (Hard Disk Drive) to ensure smooth operation of these parts and drive of the device.

[0003] For example, in a rolling bearing installed in a hard disk drive actuator, there is a proposal for a rolling bearing that is enclosed in a grease formed by adding a diurea compound as a thickener to a base oil containing an aromatic ester oil, wherein the diurea compound has at least one of an alicyclic hydrocarbon group and an aliphatic hydrocarbon group in its skeleton (Patent Document 1).

[0004] Ionic liquids are salts in a liquid state composed only of ions (anions and cations). Ionic liquids have characteristics such as low vapor pressure (non-volatility), high thermal stability, flame retardancy, low viscosity, and high ionic conductivity. In addition, various physical properties can be designed by combining cations and anions, so they are expected to be applied to various technical fields such as electrolytes and solvents.

[0005] Based on the above-mentioned characteristics such as low vapor pressure, high thermal stability and low viscosity, applications to the above-mentioned lubricants have also been studied. For example, there is a proposal for a lubricant composition to which an ionic liquid is added for the purpose of maintaining low friction for a long time under high load conditions (Patent Document 2).

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2006-236410

[0009] Patent Document 2: Japanese Patent Application Publication No. 2019-065256 Summary of the invention

[0010] Problems to be solved by the invention

[0011] One of the causes of HDD read / write errors is the volatilization and evaporation of lubricant components sealed in the bearings of the actuator and spindle motor. The volatilized or evaporated lubricant components cool and condense on the disk surface and the magnetic head, and change into a liquid or solid phase. As a result, the disk and the magnetic head will be adsorbed, and normal reading and writing cannot be performed. This can be considered as a cause of read / write errors. For such volatilization and evaporation of lubricant components accompanied by the temperature rise when the HDD is driven, for example, it is considered to suppress the volatilization / evaporation amount by selecting components such as low-volatility base oil, but it is difficult to completely eliminate the volatilization and evaporation of the components themselves.

[0012] Furthermore, in conventional lubricants to which an ionic liquid is added, including the lubricant composition described in Patent Document 2, there has been no proposal so far that takes into account the evaporation of components contained in the lubricant, such as base oil.

[0013] An object of the present invention is to provide a fluid dynamic pressure bearing in which a lubricating oil composition containing a base oil and a specific ionic liquid is sealed, and to provide a spindle motor and a disk drive device equipped with the spindle motor. By installing the fluid dynamic pressure bearing in the spindle motor, evaporation of the lubricating oil composition equipped in the fluid dynamic pressure bearing can be suppressed. Furthermore, even if the components of the lubricating oil composition evaporate or volatilize, the evaporated / volatile components are suppressed from adhering to a magnetic disk, etc., and even the occurrence of read and write errors of the HDD can be suppressed.

[0014] Solutions for solving problems

[0015] One embodiment of the present invention is a fluid dynamic pressure bearing, in which a lubricating oil composition comprising a base oil and an ionic liquid is enclosed, wherein the ionic liquid has: at least one cation selected from the group consisting of tetraalkylammonium cations represented by the following formula (B); and at least one anion selected from the group consisting of borate anions represented by the following formula (C-1), borate anions represented by the following formula (C-2), and borate anions represented by the following formula (C-3).

[0016]

[0017] (In formula (B), R 5 , R 6 , R 7 and R 8 Each independently represents a linear or branched alkyl group having 1 to 18 carbon atoms)

[0018]

[0019] (In formula (C-1), R 9 , R 10 , R11 and R 12 Each independently represents a linear or branched alkyl group having 1 to 22 carbon atoms.

[0020] The present invention also relates to a spindle motor having a fluid dynamic pressure bearing.

[0021] Furthermore, the present invention relates to a disk drive device equipped with a spindle motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a conceptual diagram for explaining an example of the structure of the main part of the spindle motor of the present invention.

[0023] Figure 2 This is a schematic diagram for explaining an example of the structure of the drive device (disk drive device) of the present invention. DETAILED DESCRIPTION

[0024] As described above, when the components contained in the volatilizing / evaporating components of the lubricant composition adhere to the recording disk or the like, it may cause reading and writing errors. Therefore, it is desirable to suppress the volatilization / evaporation of the lubricant components as much as possible.

[0025] In particular, with the increase in the capacity and density of recorded information and the increase in processing speed of HDD in recent years, the flying height (the distance between the head and the magnetic disk) of the disk drive device has been narrowed to about a few nm, and concerns about the evaporation of lubricant components and the adverse conditions that may be caused by the adhesion thereof have increased. As the flying height becomes smaller, the space between the head and the disk may become a negative pressure state. In this case, the surrounding gas is compressed / condensed toward the space between the head and the disk, so that even a small amount of evaporated / volatile components may liquefy and adhere to the disk, etc. In addition, in recent years, with the increase in the recording capacity of each HDD, the number of disks in the device has increased, and disk drives with more than 9 disks with a diameter of 3.5 inches have also begun to be sold. In such a device, the space volume in the device is further reduced. In this way, in an environment with a small space volume and a flying height of a few nm, even a small amount of contaminants may cause read and write errors.

[0026] In addition, disk drives whose internal space is filled with a gas with a density lower than that of air (such as helium) are becoming popular. In such disk drives, the air pressure inside the device is sometimes less than 1 atmosphere. In this case, it is more difficult to suppress the evaporation / volatization of lubricant components. Moreover, in the case of HDDs that use heat-assisted magnetic recording (HAMR) as a next-generation recording technology, the temperature of the actuator head may locally reach a high temperature of 400°C. As a result, the internal temperature of the HDD rises, and the evaporation and volatilization of lubricant components are more likely to occur than before, increasing the possibility of causing adverse conditions related to disk reading and writing.

[0027] The lubricating oil composition used in the fluid dynamic pressure bearing of the present invention is characterized in that a specific ionic liquid is blended as described below. The blending of the lubricating oil composition can be expected to suppress the evaporation amount of the composition even when used in a higher temperature environment such as a disk drive device using a heat-assisted magnetic recording method, and even when the components evaporate or volatilize, it can be expected to suppress the adhesion of these components to the magnetic disk, etc., which can help suppress the occurrence of HDD read and write errors caused by evaporating components.

[0028] The following is a specific description.

[0029] [Fluid Dynamic Bearings]

[0030] First, preferred embodiments of a fluid dynamic pressure bearing according to the present invention will be described in detail below with reference to the drawings.

[0031] Figure 1 This is a schematic diagram for explaining a fluid dynamic pressure bearing and a spindle motor including the fluid dynamic pressure bearing as one embodiment of the present invention. It should be noted that the embodiment described below is an exemplary embodiment of the present invention, and the present invention is not limited thereto.

[0032] like Figure 1 As shown, the spindle motor 1 is used as a motor for driving a data storage device, which has a magnetic disk, an optical disk, etc. used in a computer. The whole is composed of a stator assembly 2 and a rotor assembly 3. It should be noted that Figure 1 The spindle motor 1 is a shaft-rotating type motor, but the present invention can also be applied to a shaft-fixed type motor.

[0033] The stator assembly 2 is fixed to a cylindrical portion 5 provided to protrude upward from a shell 4 (bottom plate) constituting a housing of the data storage device. A stator core 8 having a stator coil 9 wound therearound is fitted on the outer periphery of the cylindrical portion 5 .

[0034] The rotor assembly 3 includes a rotor hub 10, which is fixed to the upper end of the shaft portion 11 and rotates together with the shaft portion 11. The shaft portion 11 is inserted into a sleeve 7 as a bearing member and is rotatably supported by the sleeve 7. The sleeve 7 is embedded and fixed inside the cylindrical portion 5. The lower cylindrical portion 10a of the rotor hub 10 rotates inside the shell 4, and a back yoke 13 is attached to the inner circumferential surface of the lower cylindrical portion 10a. A rotor magnet 14 is embedded and fixed inside the back yoke 13, and is magnetized to multiple poles of N poles and S poles.

[0035] When the stator coil 9 is energized, a magnetic field is formed by the stator core 8, and the magnetic field acts on the rotor magnet 14 disposed in the magnetic field, so that the rotor assembly 3 rotates. A recording disk, such as a magnetic disk (not shown), constituting a storage unit of a data storage device is attached to the outer peripheral surface of the intermediate cylindrical portion 15 of the rotor hub 10 of the rotor assembly 3, and is rotated or stopped by the operation of the spindle motor 1, and information is written / data processed by a recording head (not shown).

[0036] In the spindle motor 1 of such an embodiment, the fluid dynamic pressure bearing 6 is provided at a portion where the sleeve 7 rotatably supports the shaft portion 11 .

[0037] A first recessed portion 16 with a large diameter and opening downward is formed at the lower end of the sleeve 7, and a second recessed portion 17 with a small diameter is formed on the top surface of the first recessed portion 16. A counterplate (thrust bearing plate) 18 is fitted into the first recessed portion 16 with a large diameter and fixed thereto by welding / adhesion or the like, so that the inside of the sleeve 7 becomes airtight.

[0038] A thrust washer 19 is fitted, pressed and fixed to the lower end of the shaft 11 . The thrust washer 19 is arranged in the second recess 17 of the sleeve 7 , facing the counter plate 18 and the top surface of the second recess 17 , and rotates together with the shaft 11 .

[0039] The gap between the sleeve 7 and the shaft portion 11, the gap between the thrust washer 19 and the second recessed portion 17, and the gap between the thrust washer 19 and the shaft portion 11 and the counter plate 18 are connected to each other, and the lubricating oil composition 12 described later is sealed in the connected gaps. The lubricating oil composition 12 is injected from between the sleeve 7 and the shaft portion 11.

[0040] The first radial dynamic pressure groove 20 and the second radial dynamic pressure groove 21 for generating dynamic pressure are formed separately in the axial direction on the inner peripheral surface of the sleeve 7 opposite to the shaft portion 11. The radial dynamic pressure grooves 20 and 21 generate dynamic pressure that causes the shaft portion 11 and the sleeve 7 to be in a non-contact state in the radial direction through the rotation of the shaft portion 11. In addition, the first thrust dynamic pressure groove 22 and the second thrust dynamic pressure groove 23 are formed on the top surface of the second recess 17 opposite to the upper end surface of the thrust washer 19 and the upper end surface of the counter plate 18 opposite to the lower end surface of the thrust washer 19, respectively. The thrust dynamic pressure grooves 22 and 23 generate dynamic pressure for stably floating the shaft portion 11 in the thrust direction through the rotation of the shaft portion 11. Through the action of these dynamic pressure grooves, the shaft portion 11 can be stably rotated at high speed in a non-contact state with the sleeve 7. As the dynamic pressure groove, a well-known pattern such as a fishbone groove and a spiral groove can be used.

[0041] [Disc drive device]

[0042] Figure 2 1 is a perspective view showing the overall structure of a disk drive device 30 using the spindle motor according to the present embodiment.

[0043] like Figure 2 As shown, the disk drive device 30 of this embodiment includes: a base (bottom plate) 31 that is roughly rectangular box-shaped; a spindle motor 1 that is mounted on the base 31; a magnetic disk 32 that is rotated by the spindle motor 1; a swing arm 33 that has a magnetic head 34 that writes information to a specified position of the magnetic disk 32 and reads information from an arbitrary position; a pivot assembly bearing device 35 that supports the swing arm 33 so that it can swing; an actuator 36 that drives the swing arm 33; and a control unit 37 that controls these devices.

[0044] The disk drive device of the present invention can be made into a disk drive device with more than 9 magnetic disks with a diameter of 3.5 inches. In such a device with a large number of disks, the spatial volume within the device becomes further reduced. The internal space of the disk drive device can be filled with a gas with a density lower than that of air. In such a disk drive device whose internal space is filled with a low-density gas, the gas pressure inside the device is sometimes less than 1 atmosphere. In addition, the disk device can adopt a heat-assisted magnetic recording (HAMR) method as a recording method. In a disk drive device that adopts the heat-assisted magnetic recording (HAMR) method, the temperature of the head of the actuator may locally reach a high temperature of 400°C.

[0045] The lubricating oil composition used in the present embodiment described later uses a specific ionic liquid and further a specific base oil, thereby showing low evaporation / low volatility, and the volatilized / evaporated components show low adhesion to the disk etc. Therefore, in the fluid dynamic pressure bearing and the spindle motor using the lubricating oil composition, the evaporation of the components of the lubricating oil composition can be suppressed even during driving at high temperature, and the disk read / write error of the disk drive device caused by the adhesion of the evaporated components to the magnetic disk etc. can be suppressed.

[0046] [Lubricating oil composition]

[0047] The present inventors have focused on adding an ionic liquid to a lubricating oil composition used for a fluid dynamic bearing and have found that an ionic liquid composed of specific cations and anions can suppress the evaporation of the lubricating oil composition.

[0048] Hereinafter, the lubricating oil composition enclosed in the fluid dynamic pressure bearing of the present invention will be described.

[0049] <Ionic liquid>

[0050] The lubricating oil composition used for the fluid dynamic bearing of the present embodiment must contain a specific ionic liquid.

[0051] Conventionally, in order to release static electricity generated between parts due to rotational friction, conductivity has been imparted to lubricants as necessary, and as one of the methods, the addition of ionic liquids has been studied.

[0052] The ionic liquid used in the present invention not only imparts electrical conductivity but also plays the role of suppressing the evaporation amount of the lubricating oil composition and, when an ester oil is used as the base oil, suppressing the hydrolysis of the ester oil.

[0053] The above-mentioned ionic liquid has: at least one cation selected from the group consisting of tetraalkylammonium cations represented by the following formula (B); and at least one anion selected from the group consisting of borate anions represented by the following formula (C-1), borate anions represented by the following formula (C-2), and borate anions represented by the following formula (C-3).

[0054] <Cation>

[0055] The tetraalkylammonium cation used in the ionic liquid of the present invention is represented by formula (B).

[0056]

[0057] In the above formula (B), R 5 , R 6 , R 7 and R 8Each independently represents a linear or branched alkyl group having 1 to 18 carbon atoms.

[0058] Preferably, R 5 , R 6 , R 7 and R 8 Each independently represents a linear or branched alkyl group having 5 to 18 carbon atoms.

[0059] Examples of the alkyl group having 1 to 18 carbon atoms in the above formula (B) include methyl, ethyl, n-propyl, n-butyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl and octadecyl.

[0060] As R in the above formula (B) 5 , R 6 , R 7 and R 8 Combinations of, for example, include: R 5 is a linear or branched alkyl group having 1 to 4 carbon atoms, R 6 ~R 8 are independently a linear or branched alkyl group having 6 to 14 carbon atoms; and R 5 is a linear or branched alkyl group having 11 to 16 carbon atoms, R 6 ~R 8 A combination of each independently being a linear or branched alkyl group having 6 to 10 carbon atoms; or R 5 ~R 8 A combination of each independently being a linear or branched alkyl group having 6 to 12 carbon atoms, and the like.

[0061] In the above formula (B), R 5 , R 6 , R 7 and R 8 The total number of carbon atoms can be set to 24 to 40, for example.

[0062] Examples of the tetraalkylammonium cation represented by formula (B) include: 5 ~R 8 tetrahexylammonium cation, R 5 is methyl and R 6 ~R 8 is an octyl methyltri(octyl)ammonium cation, R 5 is tetradecyl and R 6 ~R 8 is a hexyl (tetradecyl) tri(hexyl) ammonium cation, R 5 ~R 8The tetraoctylammonium cation R 5 ~R 8 The tetradecylammonium cation which is a decyl group, etc.

[0063] <Anions>

[0064] The anion used in the ionic liquid of the present invention is selected from the group consisting of a borate anion represented by formula (C-1), a borate anion represented by formula (C-2), and a borate anion represented by formula (C-3).

[0065] From the viewpoint that control such as prohibition of use and restriction of use of fluorine-based compounds is being advanced recently, the above-mentioned borate anion can also be said to be a preferred option.

[0066]

[0067] In the above formula (C-1), R 9 , R 10 , R 11 and R 12 Each independently represents a linear or branched alkyl group having 1 to 22 carbon atoms.

[0068] In one embodiment, R in (C-1) above 9 , R 10 , R 11 and R 12 Each independently represents a linear or branched alkyl group having 1 to 22 carbon atoms, or each independently represents a linear or branched alkyl group having 1 to 10 carbon atoms, or each independently represents a linear or branched alkyl group having 6 to 10 carbon atoms, or each independently represents a linear or branched alkyl group having 1 to 8 carbon atoms, or each independently represents a linear or branched alkyl group having 1 to 6 carbon atoms, or each independently represents a linear or branched alkyl group having 1 to 2 carbon atoms.

[0069] As the above R 9 , R 10 , R 11 and R 12 The alkyl group having 1 to 22 carbon atoms in the above-mentioned group includes, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, heneicosyl, and docosyl.

[0070] As R in the above formula (C-1) 9 , R 10 , R 11 and R 12Combinations of, for example, include: R 9 ~R 12 A combination of alkyl groups each independently being a linear or branched carbon number 1 to 8; or R 9 ~R 12 A combination of all methyl groups, etc.

[0071] As the ionic liquid used in the present invention, for example, combinations of cations and anions shown in the following (a) to (k) can be used.

[0072] (a)

[0073] Selected from the group represented by the above formula (B), wherein R 5 , R 6 , R 7 and R 8 A combination of at least one cation selected from the group consisting of tetraalkylammonium cations which independently represent a linear or branched alkyl group having 5 to 18 carbon atoms; and at least one anion selected from the group consisting of the borate anion represented by the above formula (C-1), the borate anion represented by the above formula (C-2), and the borate anion represented by the above formula (C-3).

[0074] (b)

[0075] Selected from the group represented by the above formula (B), wherein R 5 , R 6 , R 7 and R 8 A combination of at least one cation selected from the group consisting of tetraalkylammonium cations which independently represent a linear or branched alkyl group having 5 to 18 carbon atoms; and at least one anion selected from the group consisting of the borate anion represented by the above formula (C-1) and the borate anion represented by the above formula (C-3).

[0076] (c)

[0077] Selected from the group represented by the above formula (B), wherein R 5 , R 6 , R 7 and R 8 At least one cation selected from the group consisting of tetraalkylammonium cations having a total carbon number of 24 to 40; and selected from the group consisting of tetraalkylammonium cations represented by the above formula (C-1), wherein R 9 , R 10 , R 11 and R 12 A combination of a methyl borate anion and at least one anion selected from the group consisting of a borate anion represented by the above formula (C-3).

[0078] (d)

[0079] The tetrahexylammonium cation and the above formula (C-1), wherein R 9 , R 10 , R 11 and R 12 A combination of a borate anion with a methyl group.

[0080] (e)

[0081] The tetraoctylammonium cation and the above formula (C-1), wherein R 9 , R 10 , R 11 and R 12 A combination of a borate anion with a methyl group.

[0082] (f)

[0083] The tetradecyl ammonium cation and the above formula (C-1), wherein R 9 , R 10 , R 11 and R 12 A combination of a borate anion with a methyl group.

[0084] (g)

[0085] A combination of a tetraoctylammonium cation and a borate anion represented by the above formula (C-2).

[0086] (h)

[0087] A combination of a tetradecylammonium cation and a borate anion represented by the above formula (C-3).

[0088] (i)

[0089] The tetrahexylammonium cation and the above formula (C-1), wherein R 9 and R 11 is methyl and R 10 and R 12 A combination of an ethyl borate anion.

[0090] (j)

[0091] The tetrahexylammonium cation and the above formula (C-1), wherein R 9 , R 10 , R 11 and R 12 A combination of an ethyl borate anion.

[0092] (k)

[0093] The tetrahexylammonium cation and the above formula (C-1), wherein R 9 , R 10, R 11 and R 12 A combination of an n-octyl borate anion.

[0094] The amount of the ionic liquid contained in the lubricating oil composition is not particularly limited and can be appropriately selected depending on the intended purpose.

[0095] For example, the content may be 0.01% by mass to 10% by mass, or 0.03% by mass to 1% by mass, or 0.03% by mass to 0.5% by mass, etc., relative to the base oil described below.

[0096] <Base oil>

[0097] In the lubricating oil composition used for the fluid dynamic bearing of this embodiment, the base oil is not particularly limited, and synthetic oils such as mineral oils, hydrocarbon synthetic oils, ester synthetic oils, and ether synthetic oils commonly used as base oils in lubricating oils can be used alone or in combination.

[0098] Among them, ester-based synthetic oils can be preferably used from the viewpoint of being able to easily dissolve the above-mentioned ionic liquids.

[0099] Examples of the ester-based synthetic oil (also simply referred to as ester oil) include monoester oil, diester oil, polyol ester oil, aromatic ester oil, and the like.

[0100] In one embodiment, the base oil used in the present embodiment contains at least one compound selected from the group consisting of aliphatic monoester compounds (monoester oils) and diester compounds (diester oils) having a specific alkyl chain length described below.

[0101] When the volatilization of the components added to the lubricating oil composition was considered to be a further problem, the inventors of the present invention went further from the conventional problem of making the components low in volatility, and studied the components based on the new idea that even if volatilization occurs, the volatile components are unlikely to adhere (or even if adhered, they do not stay) to the disk, etc. As a component to realize the above idea, an aliphatic monoester compound or diester compound having an alkyl chain length of a certain length or more was used.

[0102] In one embodiment, as the base oil used in the present embodiment, monoester oils and diester oils other than the aliphatic monoester compounds (monoester oils) and diester compounds (diester oils) having specific alkyl chain lengths listed below may be used or used in combination.

[0103] <Monoester compound (monoester oil)>

[0104] The above monoester compound is represented by formula (1).

[0105] R21 -C(=O)O-R 22 ……(1)

[0106] In the above formula (1), R 21 is a straight-chain or branched alkyl group having a total carbon number of 10 or more, preferably a total carbon number of 23 or less. 21 In the case of a branched alkyl group, the number of carbon atoms in the branch chain is 10 or more, and preferably 15 or less.

[0107] In addition, R 22 is a straight-chain or branched alkyl group having a total carbon number of 9 or more, preferably a total carbon number of 20 or less. 22 In the case of a branched alkyl group, the number of carbon atoms in the branch chain is 7 or more, and preferably 8 or less.

[0108] It should be noted that in this specification, the number of carbon atoms in the branch chain refers to the number of carbon atoms in the branched portion of the branched alkyl group, and is not the number of carbon atoms counted from the carbon atom bonded to the carbonyl group (-C(=O)-) or the oxygen atom (-O-). In addition, the branch chain refers to the branched portion from the main chain (the longest carbon chain counted from the carbon atom bonded to the carbonyl group or the oxygen atom), and the number of branches is not particularly limited.

[0109] In one embodiment, R 21 and R 22 One of them is a linear alkyl group, and the other is a branched alkyl group.

[0110] Specific examples of the monoester compound (monoester oil) include the following compounds, but are not limited thereto.

[0111]

[0112] <Diester compound (Diester oil)>

[0113] The above diester compound is represented by formula (2).

[0114] R 23 -E 1 -R 24 -E 2 -R 25 ……(2)

[0115] In formula (2), R 23 and R 25 Each independently represents a straight-chain or branched alkyl group having a total carbon number of 8 or more, preferably a total carbon number of 10 or less. 23 and R 25 When it is a branched alkyl group, 1 or E 2The number of carbon atoms in the longest carbon chain, counted from the bonded carbon atoms, is 9 or more, and preferably 9 can be the longest carbon chain.

[0116] R 24 It is a linear or branched alkylene group having a total carbon number of 4 or more and preferably a total carbon number of 6 or less.

[0117] Here, it is preferred that R 23 and R 25 are all straight-chain alkyl groups and R 24 is a branched alkylene group; or R 23 and R 25 are all branched alkyl groups and R 24 It is a straight-chain alkylene group.

[0118] E 1 and E 2 Each independently represents -C(=O)O- or -OC(=O)-.

[0119] In a preferred embodiment, R 23 and R 25 The same group may be used.

[0120] In addition, E 1 and E 2 Can be set to E 1 Indicates -C(=O)O- and E 2 Indicates -OC(=O)-; or E 1 Indicates -OC(=O)- and E 2 It represents -C(=O)O-.

[0121] For example, we can set R 23 and R 25 represents the same straight-chain alkyl group, R 24 represents a branched alkylene group, E 1 Indicates -C(=O)O- and E 2 It represents a compound of -OC(=O)-.

[0122] Alternatively, R 23 and R 25 represents the same branched alkyl group, R 24 represents a straight-chain alkylene group, E 1 Indicates -OC(=O)- and E 2 It represents -C(=O)O-.

[0123] Specific examples of the diester compound (diester oil) include the following compounds, but are not limited thereto.

[0124]

[0125] <Polyol ester oil>

[0126] Examples of the polyol ester oil include full esters of polyols [triols (eg, trimethylolpropane), tetraols (eg, pentaerythritol), hexaols (eg, dipentaerythritol), etc.] and linear and / or branched fatty acids having 4 to 22 carbon atoms.

[0127] Specific examples thereof include trimethylolpropane triheptanoate, trimethylolpropane trioctanoate, trimethylolpropane trinonanoate, pentaerythritol tetraheptanoate, pentaerythritol tri(2-ethylhexanoate), pentaerythritol tetraoleate, and neopentyl polyol.

[0128] <Aromatic ester oil>

[0129] Examples of the aromatic ester oil include esters of aromatic polycarboxylic acids such as phthalic acid, trimellitic acid, and pyromellitic acid, and aliphatic monohydric alcohols having 4 to 16 carbon atoms.

[0130] Specific examples thereof include ditridecyl phthalate, trioctyl trimellitate, tri-2-ethylhexyl trimellitate, tridecyl trimellitate, tetraoctyl pyromellitate, and tetra-2-ethylhexyl pyromellitate.

[0131] The ratio of the base oil to the total amount of the lubricating oil composition used in the fluid dynamic bearing of the present invention can be set to the remainder after excluding the amount of the ionic liquid and other additives that may be added as needed.

[0132] <Additives>

[0133] The lubricating oil composition may contain, in addition to the above-mentioned essential components, additives commonly used in lubricating oil compositions as necessary within a range that does not impair the effects of the present invention.

[0134] Examples of the additives include extreme pressure additives, antioxidants, metal scavengers, oiliness agents, anti-wear agents, metal deactivators, corrosion inhibitors, rust inhibitors, viscosity index improvers, pour point depressants, conductivity imparting agents, dispersants, defoaming agents, and hydrolysis inhibitors.

[0135] When these additives are added, the amount thereof may be, for example, 0.5% to 5% by mass, or 1% to 3% by mass, based on the total amount of the additives, relative to the lubricating oil composition.

[0136] Specific examples of the additives include the following, but the additives are not limited to these examples.

[0137] As extreme pressure additives, conventionally known additives containing sulfur, chlorine, phosphorus, etc. can be used, for example: phosphorus compounds such as phosphates, phosphites, and amine salts of phosphates; sulfur compounds such as sulfides and disulfides; chlorine compounds such as chlorinated paraffins and chlorinated biphenyls; metal salts of sulfur compounds such as zinc dialkyl dithiophosphates and molybdenum dialkyl dithiocarbamates, etc.

[0138] Examples of the antioxidant include phenolic antioxidants, diphenylamines, phosphorus antioxidants, sulfur compounds such as phenothiazine, etc. These antioxidants may be used alone or in combination of two or more.

[0139] Among them, from the viewpoint of disk adhesion, phenolic antioxidants are preferred, and hindered phenolic antioxidants selected from the group consisting of octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 2,4-di(n-octylthio)-6-(4-hydroxy-3,5-di-tert-butylanilino)-1,3,5-triazine, triethylene glycol-bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl) propionate], 2,2-thio-diethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] and octyl 3,5-di-tert-butyl-4-hydroxy-hydrocinnamate are particularly preferred. In addition, from the viewpoint of disk adhesion, it is desirable to avoid the use of alkylated phenyl-α-naphthylamine.

[0140] Examples of the anti-wear agent include phosphoric acid esters, phosphites, and acidic phosphoric acid esters.

[0141] Among them, from the viewpoint of disc adhesion, it is desirable to avoid the use of amine salts of acidic phosphate esters conventionally used as anti-wear agents.

[0142] Examples of the rust inhibitor include dodecenyl succinic acid half ester and the like.

[0143] Examples of the metal deactivator include benzotriazole compounds and thiadiazole compounds.

[0144] Examples of the viscosity index improver include polyalkyl methacrylate, polyalkyl styrene, and polybutene.

[0145] Examples of the pour point depressant include the above-mentioned viscosity index improvers, such as polyalkyl methacrylate, polyalkyl styrene, and polybutene.

[0146] Examples of the conductivity-imparting agent include nonionic surfactants and benzenesulfonic acid.

[0147] Examples of the dispersant include polyalkenyl succinimide, polyalkenyl succinamide, polyalkenyl benzylamine, and polyalkenyl succinic acid esters.

[0148] Examples of the hydrolysis inhibitor include alkyl glycidyl ether epoxy compounds, glycidyl ester epoxy compounds, alicyclic epoxy compounds, and carbodiimide.

[0149] The present invention is not limited to the embodiments and specific examples described in this specification, and various changes and modifications can be made within the scope of the technical concept described in the claims.

[0150] Example

[0151] Hereinafter, the present invention will be described in further detail by way of examples, but the present invention is not limited thereto.

[0152] The read / write error occurrence test was carried out in the following order using the ionic liquids of Examples 1 to 8 and Comparative Examples 1 to 3 having cations and anions shown in Table 1 and the base oil A. In the following description, the example number of the ionic liquid is also treated as the example number of the evaluation of each test.

[0153] [Table 1]

[0154] [Table 1] Ionic liquids

[0155] cation Anions Example 1 Tetrahexylammonium cation The borate anion represented by the following formula (C-1-1) Example 2 Tetraoctylammonium cation The borate anion represented by the following formula (C-1-1) Example 3 Tetradecylammonium cation The borate anion represented by the following formula (C-1-1) Example 4 Tetraoctylammonium cation The borate anion represented by the following formula (C-2) Example 5 Tetradecylammonium cation The borate anion represented by the following formula (C-3) Example 6 Tetrahexylammonium cation The borate anion represented by the following formula (C-1-3) Example 7 Tetrahexylammonium cation The borate anion represented by the following formula (C-1-4) Example 8 Tetrahexylammonium cation The borate anion represented by the following formula (C-1-6) Comparative Example 1 Methyltri(octyl)ammonium cation Bis(trifluoromethylsulfonyl)imide anion Comparative Example 2 Tetradecyltrihexylphosphonium cation The borate anion represented by the following formula (C-4) Comparative Example 3 Tetradecyltrihexylphosphonium cation The borate anion represented by the following formula (C-3)

[0156]

[0157] Base oil A: 3-methyl-1,5-pentanediol di(n-undecanoate), CAS No.1265799-70-9.

[0158]

[0159] (1) Read and write error test

[0160] The cover of an unused disk drive device was removed, and about 20 mg of a sample oil prepared by dissolving 10 mass % of the ionic liquid of the examples or comparative examples shown in Table 1 in the base oil A was applied to the back side of the cover (the surface on the inner side of the housing, Figure 2 The control unit (not shown) Figure 2 : The upper periphery of the control unit 37) is then attached to the cover coated with the sample oil to the disk drive. The disk drive is of the same type for all samples. Two (N=2) disk drives are tested under each test condition.

[0161] Make the cover surface (surface on the outer side of the housing) around the oil coating portion Figure 2A contact heater is placed on the side (not shown) of the disk drive, and the temperature of the contact heater is maintained at 120°C for 48 hours. The heater is then turned off and maintained for 48 hours, during which the disk drive continues to operate (a total of 96 hours). During the operation, a computer is connected to the disk drive, and repeated measurements are continued using disk drive status monitoring software (such as CrystalDiskInfo, HD Tune, etc.). The stop of the operating disk drive (the time point when the software determines that the device has failed due to a read / write error) is monitored by a computer connected to the disk drive. The case where the disk drive does not stop during the 96-hour test time is considered to have passed the test. The results obtained are shown in Table 2.

[0162] <Judgment Criteria>

[0163] A: The disk drive did not stop during the 96-hour test period.

[0164] N: The disk drive stopped during the 96-hour test period.

[0165] It should be noted that, when a component volatilizes / evaporates due to a rise in ambient temperature, a part of the volatilized / evaporated component condenses when the temperature drops, and the condensed component adheres to, for example, a disk or head of a disk drive device, thereby possibly causing an error in the device. That is, although an error is likely to occur at the timing of temperature drop, on the other hand, if an error does not occur during the temperature drop time, the temperature rise level before the temperature drop can be determined to be acceptable.

[0166] In addition, in particular, in the process of removing the cover of the disk drive device and reattaching it, it is extremely important to perform it in a clean room in order to avoid contaminants from the outside. It should be noted that when performing this test, the above test was performed without applying the sample oil, and it was confirmed that the disk drive device did not stop even after the test deadline of 96 hours.

[0167] [Table 2]

[0168] [Table 2] Read error occurrence test results

[0169] determination Example 1 A Example 2 A Example 3 A Example 4 A Example 5 A Example 6 A Example 7 A Example 8 A Comparative Example 1 N (device stops at 19 hours) Comparative Example 2 N (device stops at 31 hours) Comparative Example 3 N (device stops at 23 hours)

[0170] As shown in Table 2, no read / write errors occurred in Examples 1 to 8, but the device stopped at 19 hours in Comparative Example 1, at 31 hours in Comparative Example 2, and at 23 hours in Comparative Example 3, resulting in read / write errors.

[0171] (2) Evaporation test

[0172] Lubricating oil compositions (evaporation test samples) were prepared by adding the ionic liquids of Examples 1 to 8 and Comparative Example 1 to the base oil A in such a manner that the concentration of the ionic liquid was 500 ppm. In addition, as Comparative Example 4, a lubricating oil composition (evaporation test sample) of only the base oil A (not containing the ionic liquid) was prepared. The test sample was placed in an oven maintained at 140° C. at a humidity of about 40 to 60% RH and atmospheric pressure for 2000 hours. The mass of the sample before and after the test (standing) was measured, and the mass reduction after standing was calculated.

[0173] The relative value of the mass reduction of each test sample was calculated when the mass reduction measured in Comparative Example 4 (containing no ionic liquid) was set to 100. The obtained results are shown in Table 3.

[0174] (3) Hydrolysis test

[0175] The amount of ester oil hydrolyzed is very small under normal temperature and humidity conditions, so a highly accelerated stress test (HAST test) was conducted in accordance with JIS C60068-2-66, "Environmental testing methods (Electrical / electronic, high temperature and high humidity, steady state (unsaturated pressurized steam)".

[0176] The ionic liquids of Examples 1 to 8 and Comparative Example 1 were added to the base oil A so that the concentration of the ionic liquid was 500 ppm, and a lubricating oil composition (hydrolysis test sample) was prepared. In addition, as Comparative Example 4, a lubricating oil composition (hydrolysis test sample) of only the base oil A was prepared in the same manner as described above. The test sample was placed in an oven maintained at 120° C. at a humidity of about 90% RH and 2 atmospheres for 250 hours, thereby performing an accelerated stress test. The mass of the sample before and after the test (standing) was measured, and the mass reduction after standing was calculated.

[0177] The ester as the base oil is hydrolyzed into acid and alcohol by heat and moisture (humidity). The acid and alcohol generated by hydrolysis evaporate more easily than the ester as the hydrolysis raw material, so either or both of the acid and alcohol evaporates preferentially over the ester.

[0178] In this accelerated stress test, the mass reduction of the sample that underwent hydrolysis was more significant than that of the sample that did not undergo hydrolysis. The greater the mass reduction, the more advanced the hydrolysis. It should be noted that this accelerated test was conducted under the premise that the mass reduction of the sample was almost entirely caused by hydrolysis.

[0179] Similar to the evaporation test (2), the relative value of the mass reduction of each test sample was calculated when the mass reduction measured in Comparative Example 4 (containing no ionic liquid) was set to 100. Based on the obtained results, evaluation was performed according to the following criteria. The obtained results are shown in Table 3 together with the relative value of the mass reduction.

[0180] <Judgment Criteria>

[0181] E (excellent): The relative value of the mass reduction is less than 95.

[0182] A (acceptable): The relative value of the mass reduction is 95 or more.

[0183] In addition, the upper limit of the relative value which can be evaluated as the above-mentioned A (pass) is about 110.

[0184] [Table 3]

[0185] [Table 3]

[0186]

[0187] *1 The relative value when the measurement results are set as Comparative Example 4 as 100

[0188] *2 Evaluation (hydrolysis characteristics) E (excellent): less than 95 A (qualified): 95 or more

[0189] As shown in Table 3, the samples using the ionic liquids of Examples 1 to 8 showed excellent evaporation characteristics and also excellent hydrolysis characteristics (E evaluation).

[0190] Furthermore, the sample using the ionic liquid of Comparative Example 1 had inferior hydrolysis characteristics compared to Examples 1 to 8.

[0191] It should be noted that although the sample of Comparative Example 1 obtained the same evaporation characteristics as those of the Example, as shown in Table 2, read / write errors occurred. This is because, in the sample of the Example, not only the evaporation of the components is suppressed, but also the adhesion of these components to the magnetic disk is suppressed even when evaporation / volatization occurs, which is one reason for suppressing read / write errors.

[0192] As mentioned above, although the best mode for carrying out the invention has been described in detail, the present invention is not limited to the above-mentioned mode for carrying out the invention, and modifications and improvements within the scope that can achieve the object of the invention are included in the present invention.

[0193] Description of Reference Numerals

[0194] 1: spindle motor; 2: stator assembly; 3: rotor assembly; 4: shell; 5: cylinder; 6: fluid dynamic pressure bearing; 7: sleeve; 8: stator core; 9: stator coil; 10: rotor hub; 10a: lower cylinder; 11: shaft; 12: lubricating oil composition; 13: back yoke; 14: rotor magnet; 15: intermediate cylinder; 16: first recess; 17: second recess; 18: counter plate; 19: thrust washer; 20: first radial dynamic pressure groove; 21: second radial dynamic pressure groove; 22: first thrust dynamic pressure groove; 23: second thrust dynamic pressure groove; 30: disk drive device; 31: base (bottom plate); 32: magnetic disk; 33: swing arm; 34: magnetic head; 35: pivot assembly bearing device; 36: actuator; 37: control unit.

Claims

1. A fluid dynamic pressure bearing for a hard disk drive, wherein: A lubricating oil composition containing a base oil and an ionic liquid is enclosed, The ionic liquid has: At least one cation selected from the group consisting of tetraalkylammonium cations represented by the following formula (B); and at least one anion selected from the group consisting of a borate anion represented by the following formula (C-1), a borate anion represented by the following formula (C-2), and a borate anion represented by the following formula (C-3), In formula (B), R 5 , R 6 , R 7 and R 8 Each independently represents a linear or branched alkyl group having 1 to 18 carbon atoms, In formula (C-1), R 9 , R 10 , R 11 and R 12 Each independently represents a linear or branched alkyl group having 1 to 22 carbon atoms.

2. The fluid dynamic pressure bearing for a hard disk drive according to claim 1, wherein: The base oil contains at least one compound selected from the group consisting of a monoester compound represented by the following formula (1) and a diester compound represented by the following formula (2), R 21 -C(=O)O-R 22 ……(1) In formula (1), R 21 is a straight-chain or branched alkyl group with a total carbon number of 10 or more. 21 When it is a branched alkyl group, the number of carbon atoms in the branch chain is 10 or more. R 22 is a straight-chain or branched alkyl group with a total carbon number of 9 or more. 22 When it is a branched alkyl group, the number of carbon atoms in the branch chain is 7 or more. R 23 -E 1 -R 24 -E 2 -R 25 ……(2) In formula (2), R 23 and R 25 are each independently a linear or branched alkyl group having a total carbon number of 8 or more, When R 23 and R 25 When it is a branched alkyl group, 1 or E 2 The longest carbon chain has 9 or more carbon atoms, starting from the bonded carbon atoms. R 24 is a straight-chain or branched alkylene group having a total carbon number of 4 or more, E 1 and E 2 Each independently represents -C(=O)O- or -OC(=O)-.

3. A spindle motor, wherein: A fluid dynamic pressure bearing according to claim 1 is provided.

4. A disk drive device, wherein: The spindle motor according to claim 3 is mounted thereon.

5. A spindle motor, wherein: A fluid dynamic pressure bearing according to claim 2 is provided.

6. A disk drive device, wherein: The spindle motor according to claim 5 is mounted thereon.

Images