US20260022306A1 - Fluid dynamic bearing, spindle motor, and disk drive device - Google Patents

Fluid dynamic bearing, spindle motor, and disk drive device

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Publication number
US20260022306A1
US20260022306A1 US18/997,140 US202318997140A US2026022306A1 US 20260022306 A1 US20260022306 A1 US 20260022306A1 US 202318997140 A US202318997140 A US 202318997140A US 2026022306 A1 US2026022306 A1 US 2026022306A1
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Prior art keywords
formula
group
carbon atoms
branched alkyl
fluid dynamic
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US18/997,140
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English (en)
Inventor
Takuya KITAJIMA
Jun HATCHO
Shintaro TAKATA
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MinebeaMitsumi Inc
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MinebeaMitsumi Inc
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Publication of US20260022306A1 publication Critical patent/US20260022306A1/en
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    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M169/00—Lubricating compositions characterised by containing as components a mixture of at least two types of ingredient selected from base-materials, thickeners or additives, covered by the preceding groups, each of these compounds being essential
    • C10M169/04—Mixtures of base-materials and additives
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M105/00—Lubricating compositions characterised by the base-material being a non-macromolecular organic compound
    • C10M105/78—Lubricating compositions characterised by the base-material being a non-macromolecular organic compound containing boron
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M105/00—Lubricating compositions characterised by the base-material being a non-macromolecular organic compound
    • C10M105/08—Lubricating compositions characterised by the base-material being a non-macromolecular organic compound containing oxygen
    • C10M105/32—Esters
    • C10M105/34—Esters of monocarboxylic acids
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M105/00—Lubricating compositions characterised by the base-material being a non-macromolecular organic compound
    • C10M105/08—Lubricating compositions characterised by the base-material being a non-macromolecular organic compound containing oxygen
    • C10M105/32—Esters
    • C10M105/36—Esters of polycarboxylic acids
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M139/00—Lubricating compositions characterised by the additive being an organic non-macromolecular compound containing atoms of elements not provided for in groups C10M127/00 - C10M137/00
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
    • F16C17/00—Sliding-contact bearings for exclusively rotary movement
    • F16C17/02—Sliding-contact bearings for exclusively rotary movement for radial load only
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
    • F16C17/00—Sliding-contact bearings for exclusively rotary movement
    • F16C17/04—Sliding-contact bearings for exclusively rotary movement for axial load only
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B19/00—Driving, starting, stopping record carriers not specifically of filamentary or web form, or of supports therefor; Control thereof; Control of operating function ; Driving both disc and head
    • G11B19/20—Driving; Starting; Stopping; Control thereof
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B33/00—Constructional parts, details or accessories not provided for in the other groups of this subclass
    • G11B33/12—Disposition of constructional parts in the apparatus, e.g. of power supply, of modules
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M2207/00—Organic non-macromolecular hydrocarbon compounds containing hydrogen, carbon and oxygen as ingredients in lubricant compositions
    • C10M2207/28—Esters
    • C10M2207/281—Esters of (cyclo)aliphatic monocarboxylic acids
    • C10M2207/2815—Esters of (cyclo)aliphatic monocarboxylic acids used as base material
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M2207/00—Organic non-macromolecular hydrocarbon compounds containing hydrogen, carbon and oxygen as ingredients in lubricant compositions
    • C10M2207/28—Esters
    • C10M2207/282—Esters of (cyclo)aliphatic oolycarboxylic acids
    • C10M2207/2825—Esters of (cyclo)aliphatic oolycarboxylic acids used as base material
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M2215/00—Organic non-macromolecular compounds containing nitrogen as ingredients in lubricant Compositions
    • C10M2215/02—Amines, e.g. polyalkylene polyamines; Quaternary amines
    • C10M2215/04—Amines, e.g. polyalkylene polyamines; Quaternary amines having amino groups bound to acyclic or cycloaliphatic carbon atoms
    • C10M2215/041—Amines, e.g. polyalkylene polyamines; Quaternary amines having amino groups bound to acyclic or cycloaliphatic carbon atoms used as base material
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M2227/00—Organic non-macromolecular compounds containing atoms of elements not provided for in groups C10M2203/00, C10M2207/00, C10M2211/00, C10M2215/00, C10M2219/00 or C10M2223/00 as ingredients in lubricant compositions
    • C10M2227/06—Organic compounds derived from inorganic acids or metal salts
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
    • C10M2227/00—Organic non-macromolecular compounds containing atoms of elements not provided for in groups C10M2203/00, C10M2207/00, C10M2211/00, C10M2215/00, C10M2219/00 or C10M2223/00 as ingredients in lubricant compositions
    • C10M2227/06—Organic compounds derived from inorganic acids or metal salts
    • C10M2227/061—Esters derived from boron
    • C10M2227/0615—Esters derived from boron used as base material
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10N—INDEXING SCHEME ASSOCIATED WITH SUBCLASS C10M RELATING TO LUBRICATING COMPOSITIONS
    • C10N2020/00—Specified physical or chemical properties or characteristics, i.e. function, of component of lubricating compositions
    • C10N2020/01—Physico-chemical properties
    • C10N2020/077—Ionic Liquids
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10N—INDEXING SCHEME ASSOCIATED WITH SUBCLASS C10M RELATING TO LUBRICATING COMPOSITIONS
    • C10N2030/00—Specified physical or chemical properties which is improved by the additive characterising the lubricating composition, e.g. multifunctional additives
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10N—INDEXING SCHEME ASSOCIATED WITH SUBCLASS C10M RELATING TO LUBRICATING COMPOSITIONS
    • C10N2040/00—Specified use or application for which the lubricating composition is intended
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10N—INDEXING SCHEME ASSOCIATED WITH SUBCLASS C10M RELATING TO LUBRICATING COMPOSITIONS
    • C10N2040/00—Specified use or application for which the lubricating composition is intended
    • C10N2040/02—Bearings
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10N—INDEXING SCHEME ASSOCIATED WITH SUBCLASS C10M RELATING TO LUBRICATING COMPOSITIONS
    • C10N2040/00—Specified use or application for which the lubricating composition is intended
    • C10N2040/14—Electric or magnetic purposes
    • C10N2040/18—Electric or magnetic purposes in connection with recordings on magnetic tape or disc

Definitions

  • the present invention relates to a fluid dynamic bearing filled with a lubricating oil composition containing an ionic liquid with Read-Write Error hardly generated, and to a spindle motor including the fluid dynamic bearing. Moreover, the present invention relates to a disk drive device including the spindle motor.
  • Various lubricants such as grease and oil are used for pivot assemblies to be used in fulcrum parts of actuators of hard disk drives (HDDs) and bearings incorporated in spindle motors for smooth operation of these components and smooth driving of these devices.
  • HDDs hard disk drives
  • a rolling bearing to be incorporated in an actuator of a hard disk drive has been proposed, the rolling bearing filled with grease formed by compounding, as a thickener, a diurea compound having at least one of an alicyclic hydrocarbon group or an aliphatic hydrocarbon group in the skeleton into a base oil containing an aromatic ester oil (Patent Document 1).
  • An ionic liquid is a salt in a liquid state including only ions (anions, cations). Since ionic liquids have characteristics such as low vapor pressure (nonvolatile), high thermal stability, flame retardancy, low viscosity, and high ionic conductivity and can design various physical properties by a combination of a cation and an anion, ionic liquids are expected to be applied to various technical fields including electrolytic solutions and solvents.
  • Patent Document 2 From the characteristics including the low vapor pressure, the high thermal stability, and the low viscosity described above, application to the above-described lubricant has also been studied, and for example, there is a proposal of a lubricant composition with an ionic liquid added for the purpose of maintaining low friction property for a long time under a high load condition (Patent Document 2).
  • Patent Document 1 JP 2006-236410 A
  • Patent Document 2 JP 2019-065256 A
  • One of the causes of the occurrence of read-write errors in HDDs is volatilization and evaporation of a lubricant component filled in the bearing incorporated in the actuator or spindle motor.
  • volatilized or evaporated lubricant component When the volatilized or evaporated lubricant component is cooled and condensed on the surface of a magnetic disk or a magnetic head and undergoes phase transition to a liquid or a solid, making the magnetic disk and the magnetic head attract to each other disabling normal reading and writing, these are considered to be a cause of the read-write error.
  • An object of the present invention is to provide a fluid dynamic bearing filled with a lubricating oil composition containing a base oil and a specific ionic liquid, and to provide a spindle motor with evaporation being suppressed in the lubricating oil composition provided in the fluid dynamic bearing by incorporating the fluid dynamic bearing in the spindle motor, even if components of the lubricating oil composition evaporate or volatilize, adhesion of the evaporation/volatile component to a magnetic disk and the like is suppressed, and thus occurrence of a read-write error in an HDD can be suppressed, and a disk drive device including the spindle motor.
  • One aspect of the present invention relates to a fluid dynamic bearing filled with a lubricating oil composition containing a base oil and an ionic liquid,
  • R 5 , R 6 , R 7 , and R 8 each independently represent a linear or branched alkyl group having from 1 to 18 carbon atoms
  • R 9 , R 10 , R 11 , and R 12 each independently represent a linear or branched alkyl group having from 1 to 22 carbon atoms.
  • the present invention also relates to a spindle motor including the fluid dynamic bearing.
  • the present invention relates to a disk drive device equipped with the spindle motor.
  • FIG. 1 is a conceptual diagram illustrating an example of a main component structure of a spindle motor of the present invention.
  • FIG. 2 is a schematic view illustrating an example of a structure of a drive device (disk drive device) of the present invention.
  • a fly height (distance between a magnetic head and a magnetic disk) of a disk drive device has narrowed to about several nm, and there is an increasing concern about defects that may be caused by evaporation of the lubricant component and adhesion associated with the evaporation. Since the fly height is reduced, a space between the magnetic head and the disk can be brought into a negative pressure state, and in this case, the surrounding gas is compressed/condensed toward the space between the magnetic head and the disk, so that even a small amount of evaporative/volatile components may be liquefied, leading to adhesion to the disk and the like.
  • a disk drive device including an internal space filled with a gas (for example, helium or the like) having a lower density than air has also started to spread.
  • the air pressure inside the device may be less than one atmosphere.
  • the temperature of a head part of an actuator can locally reach a temperature as high as 400° C.
  • evaporation and volatilization of the lubricant component are more likely to occur than before, and there is an increasing possibility of causing a defect related to disk reading and writing.
  • a lubricating oil composition applied to the fluid dynamic bearing according to the present invention is characterized in that a specific ionic liquid is blended as described later.
  • the blending of the lubricating oil composition can be expected to suppress an evaporation amount of the composition even in application in a higher temperature environment as in a disk drive device employing a thermally assisted magnetic recording system, can be expected to suppress the adhesion of the components to a magnetic disk and the like even when the components are evaporated or volatilized, and can contribute to the suppression of the occurrence of a read-write error of the HDD due to the component, such as evaporation.
  • FIG. 1 is a schematic view for illustrating a fluid dynamic bearing and a spindle motor including the fluid dynamic bearing according to an embodiment of the present invention. Note that the embodiments described below are exemplary embodiments of the present invention, and the present invention is not limited to the embodiments.
  • a spindle motor 1 is used as a motor for driving a data storage device including a magnetic disk, an optical disk, or the like used for a computer.
  • the spindle motor 1 includes a stator assembly 2 and a rotor assembly 3 .
  • the spindle motor 1 in FIG. 1 is a shaft rotating motor, the present invention is also applicable to a shaft fixed motor.
  • the stator assembly 2 is fixed to a cylindrical part 5 provided to a housing 4 (base plate) constituting a casing of the data storage device in such a manner that the cylindrical part 5 protrudes upward.
  • a stator core 8 wound around with a stator coil 9 is fitted and attached to an outer circumferential part of the cylindrical part 5 .
  • the rotor assembly 3 includes a rotor hub 10 , and the rotor hub 10 is fixed to an upper end part of a shaft part 11 and rotates together with the shaft part 11 .
  • the shaft part 11 is inserted into a sleeve 7 being a bearing member and is rotatably supported by the sleeve 7 .
  • the sleeve 7 is fitted and fixed inside the cylindrical part 5 .
  • a lower cylindrical part 10 a of the rotor hub 10 rotates inside the housing 4 , but a back yoke 13 is mounted on an inner circumferential surface of the lower cylindrical part 10 a, and a rotor magnet 14 is further fitted and fixed inside the back yoke 13 and is magnetized to a plurality of poles of N and S poles.
  • a magnetic field is formed by the stator core 8 , and this magnetic field acts on the rotor magnet 14 disposed in the magnetic field to rotate the rotor assembly 3 .
  • a recording disk such as a magnetic disk (not illustrated), constituting a storage unit of the data storage device, is mounted, and is configured to be rotated or stopped by the operation of the spindle motor 1 , so that information writing and data processing are performed by a recording head (not illustrated).
  • a fluid dynamic bearing 6 is provided at a part where the sleeve 7 rotatably supports the shaft part 11 .
  • a large-diameter first recess part 16 opening downward is provided at a lower end part of the sleeve 7 , and a small-diameter second recess part 17 is further formed at a top surface of the first recess part 16 .
  • a counter plate (thrust receiving plate) 18 is fitted into the large-diameter first recess part 16 and fixed to the first recess part 16 by, for example, welding, bonding, or the other means, so that the inside of the sleeve 7 is in an airtight state.
  • a thrust washer 19 is fitted, press-fitted and fixed to a lower end part of the shaft part 11 , and the thrust washer 19 is disposed in the second recess part 17 of the sleeve 7 to rotate together with the shaft part 11 while opposing the counter plate 18 and a top surface of the second recess part 17 .
  • the lubricating oil composition 12 is injected from between the sleeve 7 and the shaft part 11 .
  • a first radial dynamic pressure groove 20 and a second radial dynamic pressure groove 21 for generating dynamic pressure are formed at an inner circumferential surface of the sleeve 7 opposing the shaft part 11 to be spaced apart from each other in an axial direction. Due to the rotation of the shaft part 11 , the radial dynamic pressure grooves 20 and 21 generate dynamic pressure causing the shaft part 11 and the sleeve 7 to be in a non-contact state in a radial direction.
  • a first thrust dynamic pressure groove 22 and a second thrust dynamic pressure groove 23 are formed at the top surface of the second recess part 17 opposing an upper end surface of the thrust washer 19 and an upper end surface of the counter plate 18 opposing a lower end surface of the thrust washer 19 , respectively.
  • the thrust dynamic pressure grooves 22 and 23 Due to the rotation of the shaft part 11 , the thrust dynamic pressure grooves 22 and 23 generate dynamic pressure for stably floating the shaft part 11 in a thrust direction. Due to the operation of the dynamic pressure grooves, the shaft part 11 can stably rotate at a high speed in the non-contact state with respect to the sleeve 7 .
  • the dynamic pressure grooves known patterns such as herringbone grooves and spiral grooves can be used.
  • FIG. 2 is a perspective view illustrating an overall configuration of a disk drive device 30 with the spindle motor according to the present embodiment.
  • the disk drive device 30 includes a base member (base plate) 31 having a substantially rectangular box shape, the spindle motor 1 placed on the base member 31 , a magnetic disk 32 configured to be rotated by the spindle motor 1 , a swing arm 33 having a magnetic head 34 for writing information at a predetermined position on the magnetic disk 32 and reading information from an arbitrary position on the magnetic disk 32 , a pivot assembly bearing device 35 for swingably supporting the swing arm 33 , an actuator 36 for driving the swing arm 33 , and a control unit 37 for controlling these components.
  • base member base plate
  • the spindle motor 1 placed on the base member 31
  • a magnetic disk 32 configured to be rotated by the spindle motor 1
  • a swing arm 33 having a magnetic head 34 for writing information at a predetermined position on the magnetic disk 32 and reading information from an arbitrary position on the magnetic disk 32
  • a pivot assembly bearing device 35 for swingably supporting the swing arm 33
  • an actuator 36 for driving the swing arm 33
  • a control unit 37 for controlling these components.
  • the disk drive device of the present invention can be a disk drive device including 9 or more 3.5-inch-diameter magnetic disks, for example. In such a device having a large number of disks, a spatial volume in the device is further reduced.
  • the internal space of the disk drive device may be filled with a gas having a lower density than air. In such a disk drive device with its internal space filled with such a low-density gas, the air pressure inside the device may be less than one atmosphere.
  • the disk drive device can employ a heat-assisted magnetic recording (HAMR) system as a recording system. In the disk drive device employing the heat-assisted magnetic recording (HAMR) system, the temperature of a head part of an actuator may locally reach a high temperature of 400° C.
  • HAMR heat-assisted magnetic recording
  • the lubricating oil composition used in the present embodiment described later exhibits low evaporability and low volatility by employing a specific ionic liquid and further employing a specific base oil, and the volatilized and evaporated components exhibit low adhesion to a disk and the like.
  • the evaporation and the like of the component of the lubricating oil composition are suppressed even in driving at a high temperature, and it is possible to suppress a disk read-write error of the disk drive device due to the adhesion of the component such as evaporation to the magnetic disk and the like.
  • the present inventors have focused on the addition of an ionic liquid in the lubricating oil composition applied to the fluid dynamic bearing.
  • the present inventors have found that an ionic liquid including a specific cation and a specific anion suppresses an evaporation amount of the lubricating oil composition.
  • the lubricating oil composition applied to the fluid dynamic bearing according to the present embodiment essentially contains a specific ionic liquid.
  • the ionic liquid used in the present invention plays a role of suppressing the evaporation amount of the lubricating oil composition in addition to imparting conductivity and suppressing hydrolysis of ester oil when the ester oil is used as the base oil.
  • the ionic liquid has at least one cation selected from the group consisting of tetraalkylammonium cations represented by Formula (B) described below and at least one anion 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) described below.
  • the tetraalkylammonium cations used in the ionic liquid according to the present invention are represented by Formula (B).
  • R 5 , R 6 , R 7 , and R 8 each independently represent a linear or branched alkyl group having from 1 to 18 carbon atoms.
  • R 5 , R 6 , R 7 , and R 8 each independently represent a linear or branched alkyl group having from 5 to 18 carbon atoms.
  • Examples of the alkyl group having from 1 to 18 carbon atoms in Formula (B) include a methyl group, an ethyl group, a n-propyl group, a n-butyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, and an octadecyl group.
  • Examples of the combination of R 5 , R 6 , R 7 , and R 8 in Formula (B) include a combination where R 5 is a linear or branched alkyl group having from 1 to 4 carbon atoms and R 6 to R 8 are each independently a linear or branched alkyl group having from 6 to 14 carbon atoms, a combination where R 5 is a linear or branched alkyl group having from 11 to 16 carbon atoms and R 6 to R 8 are each independently a linear or branched alkyl group having from 6 to 10 carbon atoms, and a combination where R 5 to R 8 are each independently a linear or branched alkyl group having from 6 to 12 carbon atoms.
  • the total number of carbon atoms of R 5 , R 6 , R 7 , and R 8 in Formula (B) may be, for example, 24 to 40.
  • Examples of the tetraalkylammonium cations represented by Formula (B) include a tetrahexylammonium cation where R 5 to R 8 are hexyl groups, a methyltri(octyl)ammonium cation where R 5 is a methyl group and R 6 to R 8 are octyl groups, a (tetradecyl)tri(hexyl) ammonium cation where R 5 is a tetradecyl group and R 6 to R 8 are hexyl groups, a tetraoctylammonium cation where R 5 to R 8 are octyl groups, and a tetradecylammonium cation where R 5 to R 8 are decyl groups.
  • the anion used in the ionic liquid according to 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).
  • the borate anion can be said to be a preferred aspect also from the viewpoint that recent regulations such as prohibition and restriction of use of fluorine-based compounds are in progress.
  • R 9 , R 10 , R 11 , and R 12 each independently represent a linear or branched alkyl group having from 1 to 22 carbon atoms.
  • R 9 , R 10 , R 11 , and R 12 in the above-described (C-1) each independently represent a linear or branched alkyl group having from 1 to 22 carbon atoms, or each independently represent a linear or branched alkyl group having from 1 to 10 carbon atoms, or each independently represent a linear or branched alkyl group having from 6 to 10 carbon atoms, or each independently represent a linear or branched alkyl group having from 1 to 8 carbon atoms, or each independently represent a linear or branched alkyl group having from 1 to 6 carbon atoms, or each independently represent a linear or branched alkyl group having from 1 to 2 carbon atoms.
  • Examples of the alkyl group having from 1 to 22 carbon atoms in R 9 , R 10 , R 11 , and R 12 include a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, an eicosyl group, a heneicosyl
  • Examples of the combination of R 9 , R 10 , R 11 , and R 12 in Formula (C-1) include a combination where R 9 to R 12 are each independently a linear or branched alkyl group having from 1 to 8 carbon atoms, and a combination where all of R 9 to R 12 are methyl groups.
  • ionic liquid used in the present invention for example, combinations of cations and anions shown in the following (a) to (k) can be used.
  • the blending amount of the ionic liquid in the lubricating oil composition is not particularly limited, and can be appropriately selected according to the purpose.
  • the content may be 0.01 mass % or more and 10 mass % or less, 0.03 mass % or more and 1 mass % or less, or 0.03 mass % or more and 0.5 mass % or less with respect to the base oil described later.
  • the base oil is not particularly limited.
  • a synthetic oil generally used as a base oil in a lubricating oil including a mineral oil, a hydrocarbon-based synthetic oil, an ester-based synthetic oil, or an ether-based synthetic oil, can be used alone or in combination.
  • ester-based synthetic oil can be preferably used from the viewpoint of easily dissolving an ionic liquid described above.
  • ester-based synthetic oil examples include monoester oil, diester oil, polyol ester oil, and aromatic ester oil.
  • 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 later.
  • monoester oil and diester oil other than the following aliphatic monoester compound (monoester oil) and diester compound (diester oil) having a specific alkyl chain length may be used or used in combination.
  • the monoester compound is represented by Formula (1):
  • the number of carbon atoms in the side chain is the number of carbon atoms in the side chain part(s) of a branched alkyl group, and is not the number of carbon atoms counted from a carbon atom bonded to a carbonyl group (—C( ⁇ O)—) or an oxygen atom (—O—).
  • the side chain is a branch part from the main chain (carbon chain that is the longest chain counted from the carbon atom bonded to the carbonyl group or the oxygen atom), and the number of side chains is not particularly limited.
  • one of R 21 and R 22 may be a linear alkyl group, and the other one may be a branched alkyl group.
  • monoester compound examples include, but are not limited to, the following compounds.
  • the diester compound is represented by Formula (2):
  • R 23 and R 25 be both linear alkyl groups and R 24 be a branched alkylene group, or that R 23 and R 25 be both branched alkyl groups and R 24 be a linear alkylene group.
  • E 1 and E 2 each independently represent —C( ⁇ O)O— or —OC( ⁇ O)—.
  • R 23 and R 25 may be an identical group.
  • E 1 represents —C( ⁇ O)O— and E 2 represents —OC( ⁇ O)—
  • E 1 represents —OC( ⁇ O)— and E 2 represents —C( ⁇ O)O—.
  • R 23 and R 25 represent an identical linear alkyl group
  • R 24 represents a branched alkylene group
  • E 1 represents —C( ⁇ O)O—
  • E 2 represents —OC( ⁇ O)—.
  • R 23 and R 25 represent an identical branched alkyl group
  • R 24 represents a linear alkylene group
  • E 1 represents —OC( ⁇ O)—
  • E 2 represents —C( ⁇ O)O—.
  • diester compound examples include, but are not limited to, the following compounds.
  • polyol ester oil examples include full esters of polyhydric alcohols [triols (for example, trimethylolpropane), tetraols (for example, pentaerythritol), hexaols (for example, dipentaerythritol), and the like] with linear and/or branched fatty acids having from 4 to 22 carbon atoms.
  • triols for example, trimethylolpropane
  • tetraols for example, pentaerythritol
  • hexaols for example, dipentaerythritol
  • trimethylolpropane triheptanoate trimethylolpropane tricaprylate, trimethylolpropane tripelargonate, pentaerythritol tetraheptanoate, pentaerythritol tri(2-ethylhexanoate), pentaerythritol tetraoleate, and neopentyl polyol.
  • aromatic ester oil examples include esters of aromatic polycarboxylic acids such as phthalic acid, trimellitic acid, and pyromellitic acid with aliphatic monoalcohols having from 4 to 16 carbon atoms.
  • ditridecyl phthalate trioctyl trimellitate, tri-2-ethylhexyl trimellitate, tridecyl trimellitate, tetraoctyl pyromellitate, and tetra-2-ethylhexyl pyromellitate.
  • a ratio of the base oil to a total amount of the lubricating oil composition applied to the fluid dynamic bearing of the present invention can be a balance excluding a blending amount of the ionic liquid described above and a blending amount of other additives that can be blended as necessary.
  • the lubricating oil composition can contain an additive normally used in lubricating oil compositions as necessary within a range not impairing the effects of the present invention.
  • additives examples include extreme pressure additives, antioxidants, metal cleaners, oiliness agents, anti-wear agents, metal deactivators, corrosion inhibitors, rust inhibitors, viscosity index improvers, pour point depressants, conductivity-imparting agents, dispersants, anti-foaming agents, and hydrolysis inhibitors.
  • the blending amount can be, for example, from 0.5 mass % to 5 mass %, or from 1 mass % to 3 mass % with respect to the lubricating oil composition as the total amount of the additives.
  • additives include, but are not limited to, the following.
  • extreme pressure additives can be used as the extreme pressure additives
  • examples of the extreme pressure additives include: phosphorus compounds such as phosphate esters, phosphite esters, and phosphate ester amine salts; sulfur compounds such as sulfides and disulfides; chlorine compounds such as chlorinated paraffin and chlorinated diphenyl; and metal salts of sulfur compounds such as zinc dialkyldithiophosphate and molybdenum dialkyldithiocarbamate.
  • antioxidants examples include phenolic antioxidants, diphenylamines, phosphorus-based antioxidants, and sulfur compounds such as phenothiazine. These antioxidants may be used alone or in combination of two or more.
  • a phenolic antioxidant particularly a hindered phenolic antioxidant selected from the group consisting of octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-t-butylanilino)-1,3,5-triazine, triethylene glycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate], 2,2-thio-diethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and octyl-3,5-di-t-butyl-4-hydroxy-hydrocinnamic acid is preferable from the viewpoint of disk adhesion.
  • anti-wear agent examples include phosphates, phosphites, and acid phosphates.
  • Examples of the rust inhibitor include dodecenyl succinic acid half ester.
  • metal deactivator examples include benzotriazole-based compounds and thiadiazole-based compounds.
  • viscosity index improver examples include polyalkyl methacrylates, polyalkyl styrenes, and polybutene.
  • pour point depressant examples include the aforementioned viscosity index improvers such as polyalkyl methacrylates, polyalkyl styrenes, and polybutene.
  • Examples of the conductivity-imparting agent include nonionic surfactants and phenyl sulfonic acid.
  • dispersant examples include polyalkenyl succinimides, polyalkenyl succinamides, polyalkenyl benzylamines, and polyalkenyl succinate esters.
  • hydrolysis inhibitor examples include alkyl glycidyl ether type epoxy compounds, glycidyl ester type epoxy compounds, alicyclic epoxy compounds, and carbodiimides.
  • Example 1 Tetrahexylammonium cation Borate anion represented by the following Formula (C-1-1)
  • Example 2 Tetraoctylammonium cation Borate anion represented by the following Formula (C-1-1)
  • Example 3 Tetradecylammonium cation Borate anion represented by the following Formula (C-1-1)
  • Example 4 Tetraoctylammonium cation Borate anion represented by the following Formula (C-2)
  • Example 5 Tetradecylammonium cation Borate anion represented by the following Formula (C-3)
  • Example 6 Tetrahexylammonium cation Borate anion represented by the following Formula (C-1-3)
  • Example 7 Tetrahexylammonium cation Borate anion represented by the following Formula (C-1-4)
  • Example 8 Tetrahexylammonium cation Borate anion represented by the following Formula (C-1-6) Comparative Methyl tri(octyl)ammonium Bis
  • Base Oil A 3-methyl-1,5-pentanediol di(n-undecanoate), CAS No. 1265799-70-9
  • a cover of a unused disk drive device was removed, about 20 mg of sample oil obtained by dissolving 10 mass % of the ionic liquid of the example or comparative example shown in Table 1 in the base oil A was applied to a periphery of an upper part of a control unit (control unit 37 in FIG. 2 ) on a back surface (an inner surface of the housing, not illustrated in FIG. 2 ) of the cover, and then, the cover coated with the sample oil was mounted back on the disk drive device.
  • the heater was brought into contact with a cover surface (an outer surface of the housing, not illustrated in FIG. 2 ) side around an oil application part, and the temperature of the heater brought into contact was maintained at 120° C. for 48 hours. Thereafter, the heater was turned off, and the operation of the disk drive device was continued during a 48-hour hold (96 hours in total).
  • condition monitoring software e.g., CrystalDiskInfo, HD Tune, etc.
  • the stop time point when the software determined that the device failed due to the occurrence of a read-write error
  • the results obtained are listed in Table 2 described below.
  • an error of the device can be caused due to the part of the volatilized/evaporated component being condensed when the temperature decreases, and the condensed component adheres to, for example, a disk or a head of a disk drive device. That is, it can be said that an error is likely to occur at the timing when the temperature is decreased, and on the other hand, if no error occurs during the time when the temperature is decreased, it can be determined that the temperature increase level before the temperature is decreased is acceptable.
  • 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 N (device stopped Example 1 in 19 hours) Comparative N (device stopped Example 2 in 31 hours) Comparative N (device stopped Example 3 in 23 hours)
  • the ionic liquids of Examples 1 to 8 and Comparative Example 1 were added to the base oil A so as to have a concentration of 500 ppm, thereby preparing a lubricating oil composition (evaporation amount test sample).
  • a lubricating oil composition (evaporation amount test sample) containing only the base oil A (not containing ionic liquid) was provided.
  • the test sample was left standing in an oven maintained at 140° C. for 2000 hours under atmospheric pressure at a humidity of about from 40 to 60% RH.
  • the mass of the sample before and after the test (standing) was measured, and the amount of reduction in mass after standing was calculated.
  • the ionic liquids of Examples 1 to 8 and Comparative Example 1 were added to the base oil A so as to have a concentration of 500 ppm, thereby preparing a lubricating oil composition (hydrolysis test sample).
  • a lubricating oil composition (hydrolysis test sample) containing only the base oil A was provided.
  • the accelerated life test was performed by leaving the test sample in an oven maintained at 120° C. for 250 hours under a humidity of about 90% RH and 2 atmospheres. The mass of the sample before and after the test (standing) was measured, and the amount of reduction in mass after standing was calculated.
  • Ester as the base oil is hydrolyzed into an acid and an alcohol by heat and moisture (humidity). Since an acid and an alcohol generated by hydrolysis are more likely to evaporate than an ester as a hydrolysis source, either or both of the acid and the alcohol evaporate more preferentially than the ester.
  • the upper limit of the relative value that can be evaluated as A (Acceptable) is generally about 110.

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JP2005290256A (ja) * 2004-04-01 2005-10-20 Matsushita Electric Ind Co Ltd 流体軸受装置、及びそれを用いたスピンドルモータ
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US20140314351A1 (en) * 2013-03-28 2014-10-23 Minebea Co., Ltd. Fluid dynamic pressure bearing oil, fluid dynamic pressure bearing using the same, and spindle motor
JP6075209B2 (ja) * 2013-05-23 2017-02-08 新日本理化株式会社 流体軸受用潤滑油基油及びスピンドルモータ
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