Abstract:
In spindle motors journaled on fluid-dynamic-pressure bearings, especially in such spindle motors employed in recording-disk drives in implementations that subject the drives to vibration and shock, sealing performance of a capillary seal formed between motor rotor-side and stator-side bearing surfaces, cohesiveness of oil-repellant on rotor-side/stator-side dry-area surfaces adjoining the capillary seal section, and motor inter-component adhesive strength are improved. The capillary-seal-constituting rotor-side/stator-side surface(s) are exposed to a plasma or to ultraviolet rays under predetermined conditions to improve the wettability of the surface(s) for the bearing fluid. The dry-area surface(s) are similarly irradiated so as to improve their wettability for the oil-repellant. Adhesively bonded component surfaces are likewise irradiated so as to improve their wettability for the adhesive, enhancing adhesive strength. Exposed surfaces may be constituted of a synthetic resin to enhance their wettability further, or may be made of metal, to yield a cleaning efficacy from the plasma/UV exposure.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Technical Field  
         [0002]     The present invention relates to fluid-dynamic-pressure bearing manufacturing methods, to spindle motor manufacturing methods, and to spindle motors and recording-disk drives.  
         [0003]     2. Description of the Related Art  
         [0004]     In recent years, the amount of information that is recorded per unit area on discoid recording media in hard-disk and like recording-disk drives has been increasing, and the information density has been on the rise. The increasing recording density has led to calls for stably supporting the discoid recording media under high-speed rotation.  
         [0005]     Recording-disk drives, meanwhile, are finding applications other than in stationary computers, such as desk-top and server machines, in which the drives have been traditionally employed, and are being used in vehicular devices, portable devices, and other mobile devices. Such mobile applications have led to rising demands for impact resistance and longevity-demands without precedent in implementations in which the drives are employed under environments, as has conventionally been the case, that do not subject the drives to vibration and shock.  
         [0006]     Against this backdrop, the development of bearings for stably supporting disk-drive rotor units under high-speed rotation has been ongoing.  
         [0007]     In order that the bearings meet this demand, considerations of paramount importance are: 
    (A) Improvement in the sealing performance of the bearing&#39;s capillary seal section;     (B) Improvement in the ability to prevent wetting diffusion along the surfaces in the vicinity of the capillary seal; and     (C) Improvement in the joint strength of the components that constitute the dynamic-pressure bearing and the spindle motor.    
 
         [0011]     Consideration (A)  
         [0012]     Fluid-dynamic-pressure bearings are composed of a journal unit and a journal-support unit, between which is formed a narrowed micro-gap. A lubricating fluid such as oil is retained within the gap. An oil sealing mechanism referred to as a capillary seal section is provided in the part of the bearing in which the micro-gap is open to the external atmosphere. The capillary seal section is of a form in which the gap between the journal and, opposing the journal, seal surfaces on the bearing&#39;s journal-support side gradually flares going axially upward. A boundary surface between the oil and the external atmosphere forms in the capillary seal section.  
         [0013]     If the lubricating fluid is not sealed in by the capillary seal section, the fluid ends up leaking out to the exterior. As a consequence, the lubricating fluid retained in the micro-gap runs short, ultimately curtailing the lifespan of the bearing. In bearing implementations in miniature spindle motors in particular, since the gross amount of oil retained inside the bearing is very little, if even a slight amount of the lubricating fluid manages to leak out, an oil shortfall is liable to occur. Furthermore, the problem of weak sealing performance in capillary seals can allow shock or other impact on the bearing to disturb the integrity of the seal boundary surface.  
         [0014]     Keeping the angle of contact between the oil and the components that constitute the capillary seal section small is crucial to enhancing the strength of capillary seals.  
         [0015]     Consideration (B)  
         [0016]     Oil repellant is applied to the surfaces of the components that constitute the outer side of the capillary seal section. Applying oil repellant prevents lubricating fluid from the capillary seal section from migrating along the bearing component surfaces to the bearing exterior by wetting-diffusion.  
         [0017]     The way oil repellants are applied is to spread repellant that has been dissolved in a solvent onto the component surfaces, and vaporize the solvent to get the oil repellant to adhere to the surfaces.  
         [0018]     Nevertheless, the wettability of the oil repellant for the seal component surfaces is poor, which has meant that the repellant-to-surface adhesiveness has not been satisfactory. Consequently, oil mop-up or associated concluding operations in manufacturing dynamic-pressure bearings cause the oil repellant to peel off easily. Although processes such as striating the components or spreading the oil repellant on thickly have been implemented to date on account of the behavior of the repellant, such processes elevate the component cost, and, moreover, have not amounted to a fundamental solution.  
         [0019]     Consideration (C)  
         [0020]     Spindle motors for hard-disk drives are furnished with a base component and, anchored to the base component, a cylindrical sleeve housing that serves as a stator-side bearing component. The outer circumferential surface of the sleeve housing is, by an interposed adhesive, fixed to the inner circumferential surface of a mounting hole formed in the base component.  
         [0021]     The slightest warpage or deformation in spindle-motor bearing components becomes a problem particularly in fluid-dynamic-pressure bearings, in that the bearing gaps are extraordinarily narrow. On that account, in the plurality of inter-component junctions, adhesive anchoring by means of an adhesive agent is often employed instead of welding, in which thermal deformation is liable to occur.  
         [0022]     Especially under environments, such as in mobile and vehicular devices, that place vibration and shock on the bearings, particularly large loads are placed on the joints between components. More particularly, the ability to withstand serious shock—in excess of 1000 Gs—can be mandatory in situations in which there is a likelihood of the devices being dropped. Consequent on the scaling down of spindle motors, however, is an abridgement of the inter-component binding length, which has made improving the binding strength a challenge.  
       BRIEF SUMMARY OF THE INVENTION  
       [0023]     A first object of the present invention is to make available a manufacturing method that enables the adhesive strength in spindle motors to be improved.  
         [0024]     A second object of the present invention is to afford a method of manufacturing fluid-dynamic-pressure bearings that enables the sealing performance of the capillary seal section to be improved.  
         [0025]     A third object of the present invention is to make available a method of manufacturing fluid-dynamic-pressure bearings that enables oil repellant for oil-repelling surfaces to be cohered stably to the oil-repelling surfaces.  
         [0026]     A fluid-dynamic-pressure bearing to which a fluid-dynamic-pressure bearing manufacturing method that is a first aspect of the present invention is applicable has the following configuration. Namely, the fluid-dynamic-pressure bearing comprises a stator unit and a rotor unit that is rotary with respect to the stator unit. The stator unit and the rotor unit oppose each other across a micro-gap. A lubricating fluid fills and is retained within the micro-gap.  
         [0027]     A clearance that communicates with the micro-gap is formed in between the stator unit and the rotor unit. The portion of the clearance that communicates with the micro-gap serves as the capillary seal section. A boundary surface between the lubricating fluid and the external atmosphere forms in the capillary seal section. Surfaces of the stator unit and rotor unit oppose to form the capillary seal section.  
         [0028]     The first aspect of the present invention, being a fluid-dynamic-pressure bearing manufacturing method as just set forth, includes at least the following first and second steps. In the first step, a surface-treating process consisting of at least one between plasma irradiation and ultraviolet-beam irradiation is implemented on at least one between a rotor-side surface and a stator-side surface that constitute the capillary seal section. In addition, after (which need not be directly after) the first step has been effected, the second step, in which lubricating fluid is infused into the micro-gap, is effected.  
         [0029]     The first step in the first aspect of the invention may be effected before the rotor unit and the stator unit of the fluid dynamic-pressure bearing are assembled. In particular, the respective parts of the rotor unit and the stator unit may individually undergo the surface-treating process of the first step. Likewise, the surface-treating process of the first step may be effected on both the stator unit and the rotor unit, which may be on the rotor unit and stator unit simultaneously, or not at the same time.  
         [0030]     Bearing manufacturing procedures including assembling, heating, pressurizing, and cleaning may be effected in between the first step and the second step.  
         [0031]     Embodying the first aspect of the invention improves the wettability, with respect to organic substances, of the surfaces that constitute the capillary seal section, rendering the wetting angle extremely small. The improved wettability consequently improves the sealing performance of the capillary seal. An added advantage is that ultraviolet-beam and plasma irradiation of the capillary seal section surfaces(s) decompose and clean off metal-surface clinging organic matter, which is given to deteriorating the quality of the lubricating fluid. A still further benefit is that ultraviolet-beam and plasma irradiation do not require the use of chemicals that are hazardous to the environment. What is more, compared with processing surfaces using chemicals or by machining the relevant parts, the work in carrying out ultraviolet-beam and plasma irradiation is simple and the operation time is short. Operability and productivity therefore improve.  
         [0032]     Furthermore, the second-step process of charging the bearing gap with lubricating fluid is the more advantageously effected through the capillary seal section. Charging the bearing via the surface(s) whose wettability has been improved by undergoing ultraviolet-beam or plasma irradiation keeps the lubricating fluid from incorporating air bubbles. The lubricating fluid infusion volume can therefore be adjusted more accurately.  
         [0033]     Further to the first aspect of the present invention, advantageously at least one among the stator-unit and rotor-unit surfaces that constitute the capillary seal section is formed of a resin material. Resins are activated superficially by plasma irradiation or ultraviolet-beam irradiation, and thus constituting the seal-section surface(s) from a resin material improves the wettability of the surface(s) for lubricating fluid.  
         [0034]     Still further to the first aspect of the invention, at least one among the stator-unit and rotor-unit surfaces that constitute the capillary seal section may be formed of metal. In the manufacturing method in that case, advantageously the surface-treating process, by means of at least one between plasma irradiation and ultraviolet-beam irradiation, in the first step is carried out over a broader extent on the metal components. Plasma-based cleaning or cleaning using ultraviolet beams dissolves grease and other grime clinging to the metal surfaces, and therefore are ideally suited to the cleaning of bearing components, in which a high level of cleanliness is mandatory. Effecting cleaning by means of the first step enables the cleaning process and the surface-treating process to be carried out at the same time, which makes for excellent operability of the manufacturing method.  
         [0035]     Yet further to the first aspect of the present invention, a fourteenth step may be included, in which at least one surface-treating process among the group of surface-treating processes consisting of plasma irradiation and ultraviolet-beam irradiation is implemented on at least any one surface among the stator-unit and rotor-unit surfaces that constitute the micro-gap.  
         [0036]     The surfaces of the micro-gap constitute the bearing faces of the fluid dynamic-pressure bearing. Improving the wettability of the surfaces for the lubricating fluid enhances the bearing&#39;s ability to retain lubricating fluid between the stator-unit surfaces and the rotor-unit surfaces. The heightened inter-surface lubricant retaining ability contributes to preventing the stator-unit surfaces and rotor-unit surfaces from contacting, even as the bearing withstands stronger shocks and vibrations.  
         [0037]     A fluid-dynamic-pressure bearing to which a fluid-dynamic-pressure bearing manufacturing method that is a second aspect of the present invention is applicable has the following configuration. Namely, the fluid-dynamic-pressure bearing, in a like manner as the fluid-dynamic-pressure bearing in the first aspect of the invention, comprises a stator unit and a rotor unit that is rotary with respect to the stator unit. Further, a capillary seal section is formed in the same manner as in the first aspect of the invention. A boundary surface between the lubricating fluid and the external atmosphere forms in the capillary seal section.  
         [0038]     In addition, a dry-area face adjoining the capillary seal section is provided on at least one of either of the stator unit or rotor unit. The dry-area face is formed in order for the surface to be coated with oil repellant.  
         [0039]     The second aspect of the present invention, being a fluid-dynamic-pressure bearing manufacturing method as just set forth, includes the following fourth, fifth and sixth steps. In the fourth step, a surface-treating process consisting of at least one between plasma irradiation and ultraviolet-beam irradiation is implemented on the dry-area face on at least one of either of the stator side or rotor side of the bearing. Furthermore, after (which need not be directly after) the fourth step, the fifth step, in which oil repellant is applied to the dry-area face(s), is effected. In addition, after (which need not be directly after) the fifth step, the sixth step, in which the inside of the micro-gap is charged with lubricating fluid, is effected.  
         [0040]     As is the case with the first step in the first aspect of the present invention, it does not matter whether the fourth step precedes or follows the bearing assembly process. Furthermore, in implementations in which the fourth step is effected on both the stator unit and the rotor unit, it may be so simultaneously, or not at the same time. Additionally, other procedures associated with manufacturing the bearing, including assembling, heating, pressurizing, and cleaning may as needed be effected in between the fourth step and the fifth step, or between the fifth step and the sixth step.  
         [0041]     Embodying the second aspect of the invention improves the wettability, in the dry-area face(s), between the dry-area face(s) and the oil repellant. This improved wettability prevents the oil repellant from exfoliating (peeling off). Accordingly, lubricating fluid is prevented from migrating by wetting-diffusion over the dry-area face(s) continuous with the capillary seal.  
         [0042]     Since in particular the dry-area face of the rotor unit is susceptible to wetting diffusion due to centrifugal force when the rotor unit spins, the fourth step is advantageously effected on the dry-area face of the rotor unit so that the oil repellant does not peel off.  
         [0043]     In the second aspect of the present invention, further advantageously a seventh step is included, in which a surface-treating process consisting of at least one between plasma irradiation and ultraviolet irradiation is implemented on one of either of the stator unit and rotor unit where the capillary seal section is formed.  
         [0044]     Moreover, inasmuch as the face(s) constituting the dry-area face(s), and the surfaces constituting the capillary seal section adjoin each other, carrying out the fourth step and the seventh step at the same time makes for efficient manufacturing work.  
         [0045]     The foregoing surface-treating processes improve the lubricating-fluid retaining ability of the capillary seal section and prevent the oil repellant from peeling off, which all the more effectively prevents the lubricating fluid from leaking out.  
         [0046]     Further to the second aspect of the present invention, advantageously at least one among the stator-unit and rotor-unit surfaces that constitute the capillary seal section is formed of a resin material. Resins are readily activated at the surface by plasma irradiation or ultraviolet-beam irradiation, and thus constituting the seal-section surface(s) from a resin material improves the cohesion between the surface(s) and the oil repellant.  
         [0047]     Still further to the second aspect of the invention, the dry-area face on at least one of either of the stator-unit side and the rotor-unit side of the bearing may be formed of metal. In the manufacturing method in that case, advantageously the surface-treating process, by means of at least one between plasma irradiation and ultraviolet-beam irradiation, in the fourth step is carried out over a broader extent on the metal components. Plasma-based cleaning or cleaning using ultraviolet beams dissolves grease and other grime clinging to the metal surfaces, and therefore are ideally suited to the cleaning of bearing components, in which a high level of cleanliness is mandatory. Effecting cleaning by means of the fourth step enables the cleaning process and the surface-treating process to be carried out at the same time, which makes for excellent operability of the manufacturing method.  
         [0048]     Yet further to the second aspect of the present invention, a fifteenth step may be included, in which at least one surface-treating process among the group of surface-treating processes consisting of plasma irradiation and ultraviolet-beam irradiation is implemented on at least any one surface among the stator-unit and rotor-unit surfaces that constitute the micro-gap.  
         [0049]     The surfaces of the micro-gap constitute the bearing faces of the fluid dynamic-pressure bearing. Improving the wettability of the surfaces for the lubricating fluid enhances the bearing&#39;s ability to retain lubricating fluid between the stator-unit surfaces and the rotor-unit surfaces. The heightened inter-surface lubricant retaining ability contributes to preventing the stator-unit surfaces and rotor-unit surfaces from contacting, even as the bearing withstands stronger shocks and vibrations.  
         [0050]     A spindle motor to which a spindle-motor manufacturing method that is a second aspect of the present invention is applicable has the following configuration. Namely, the spindle motor is furnished with a base component, a stator unit fixed to the base component, and a rotor unit supported to let it rotate with respect to the stator unit. The base component is the baseplate of the spindle motor. In implementations in which the spindle motor is a DC brushless motor, a stator around which coils are wound is anchored to the base component or to the stator unit.  
         [0051]     The stator unit defines an outer circumferential surface. The base component is furnished with an adhesion surface of conformation corresponding to the form of the stator-unit outer circumferential surface. The stator unit is adhesively affixed to the base component.  
         [0052]     The third aspect of the present invention, being a spindle-motor manufacturing method as just set forth, includes the following eighth through tenth steps. Namely, in the eighth step, at least one surface-treating process among the group of surface-treating processes consisting of plasma irradiation and ultraviolet-beam irradiation is implemented on at least one of either of the outer circumferential surface of the stator unit or the adhesion surface of the base component. In the ninth step, which is effected following the eighth step, an adhesive agent is applied to at least one of either of the outer circumferential surface of the stator unit or the adhesion surface of the base component. Subsequently, in the tenth step, the stator unit is inset into the base component, with the stator-unit outer circumferential surface fitting to the base-component adhesion surface, whereby the stator unit and the base component cohere via the adhesive agent. Furthermore in the tenth step, the adhesive agent is hardened to fix the stator unit to the base component. Examples of how the adhesive agent would be hardened include: by heating it, if the adhesive is thermosetting; by shielding it from the air, if the adhesive is anaerobic; by irradiating it with an ultraviolet beam if the adhesive is UV curing; and by mixing it with a hardener if the adhesive involves a two-component system.  
         [0053]     Embodying the third aspect of the invention improves the wettability, with respect to organic substances, of the surfaces adhered by the adhesive agent, which therefore improves the cohesiveness between the adhesive agent and the adhering surfaces. In this way the adhesive strength when the adhesive is set improves. Moreover, the fact that the wettability of the surfaces for the adhesive agent is improved enables the adhesive to enter into the narrow gap between the stator unit and the base component to yield more powerful adhesive strength. The spindle motor is therefore made tougher, especially against disturbances such as shock and vibration, which makes for longer motor lifespan.  
         [0054]     Further to the third aspect of the present invention, advantageously at least one between the outer circumferential surface of the stator unit and the adhesion surface of the baseplate is formed of a resin material. Resins are readily activated at the surface by plasma irradiation or ultraviolet-beam irradiation, and thus constituting the stator-unit/baseplate surface(s) from a resin material improves the wettability between the surface(s) and the adhesive agent.  
         [0055]     Further yet to the third aspect of the invention, at least one of either of the outer circumferential surface of the stator unit and the adhesion surface of the baseplate may be formed of metal. In the manufacturing method in that case, advantageously the surface-treating process, by means of at least one between plasma irradiation and ultraviolet-beam irradiation, in the eighth step is carried out over a broader extent on the stator unit and the baseplate. Plasma-based cleaning or cleaning using ultraviolet beams dissolves grease and other grime clinging to the metal surfaces, and therefore are ideally suited to the cleaning of spindle motors, in which a high level of cleanliness is mandatory. Effecting cleaning by means of the eighth step enables the cleaning process and the surface-treating process to be carried out at the same time, which makes for excellent operability of the manufacturing method.  
         [0056]     The performance of the capillary seal section in a spindle motor utilizing a fluid-dynamic-pressure bearing manufactured by a manufacturing method of the first aspect of the present invention is superior, and this heightened capillary-seal performance contributes to producing spindle motors that are of extended lifespan and are tough against impact.  
         [0057]     In turn, a spindle motor utilizing a fluid-dynamic-pressure bearing manufactured by a manufacturing method of the second aspect of the invention enables the surfaces onto which the oil repellant is applied to maintain stabilized oil repellency, which, by preventing wetting diffusion of the lubricating fluid, contributes to producing spindle motors of prolonged lifespan.  
         [0058]     A recording-disk drive utilizing a spindle motor manufactured by a manufacturing method of the third aspect of the present invention especially improves the motor&#39;s longevity and resistance to impact. In implementations in which the base component constitutes part of the disk-drive case, exit/entry of air internal/external to the recording-disk drive can be prevented, which keep contaminants from entering into the interior of the case.  
         [0059]     From the following detailed description in conjunction with the accompanying drawings, the foregoing and other objects, features, aspects and advantages of the present invention will become readily apparent to those skilled in the art. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0060]      FIG. 1  is a sectional view of a recording-disk drive of the present invention;  
         [0061]      FIG. 2  is a sectional view of a fluid-dynamic-pressure bearing, and a spindle motor in which the bearing is utilized, involving a first embodiment of the present invention;  
         [0062]      FIG. 3  is a sectional view of a fluid-dynamic-pressure bearing, and a spindle motor in which the bearing is utilized, involving a second embodiment of the present invention;  
         [0063]      FIG. 4  is a sectional view of a fluid-dynamic-pressure bearing, and a spindle motor in which the bearing is utilized, involving a third embodiment of the present invention; and  
         [0064]      FIG. 5  is an enlarged fragmentary sectional view, in which a blowup of the capillary seal section is inset, illustrating key features of a fluid-dynamic-pressure bearing of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0065]     An explanation of modes of embodying the present invention will be made while referring to the drawings. It should be understood that in the description of the embodiments, when terms that indicate directions are used without special notation, the terms indicate directions represented in the drawings; consequently such noting does not limit orientations in embodying the invention.  
       First Embodiment  
       [0066]     In the present embodiment, a fluid-dynamic-pressure bearing for which a manufacturing method of the present invention is utilized is employed in a spindle motor  3  that spins discoid recording media.  
         [0067]     Hard-Disk Drive  
         [0068]     Reference is made to  FIG. 1 , which is a sectional view illustrating a hard-disk drive  1  that is a recording-disk drive device embodying the present invention. The hard-disk drive  1  is in the interior of a case  11  furnished with a spindle motor  3  that spins recording disks  12 , heads  13  that read information from and write information into the recording disks  12 , and an actuator unit  14  that shifts the heads  13  into select locations over the recording disks  12 .  
         [0069]     Spindle Motor Configurational Outline  
         [0070]     The spindle motor  3  is, as depicted in  FIG. 2 , furnished with: a rotor hub  21  having a carrying surface on which the recording disks  12  are carried; a toroidal rotor magnet  32  attached to the rotor hub  21 ; a bracket  27  that serves as the base component; a stator  31  made up of a plurality of coils; and a fluid-dynamic-pressure bearing  2  that rotatively supports the rotor hub  21  and rotor magnet  32  with respect to the bracket  27  and stator  31 . The stator  31  is fixed to the bracket  27 , radially opposing the inner circumferential surface of the rotor magnet  32 . The fluid-dynamic-pressure bearing  2  is mounted in, unitized with, the bracket  21 . It should be noted that the bracket  27  may be integrated with the case  11  to constitute the baseplate (base component).  
         [0071]     Fluid-Dynamic-Pressure Bearing Configuration  
         [0072]     The fluid-dynamic-pressure bearing  2  is furnished with: a shaft  24  fixed into the rotor hub  21 ; a sleeve  22  fit over the shaft  24 ; a substantially cup-shaped bearing housing  23  on the radially outer side of the sleeve  22 , and into which the sleeve  22  is inset; and a seal bushing  26  mounted in a location to the upper side of the sleeve  22 . The rotor hub  21  and the shaft  24  constitute the rotor unit; the bearing housing  23 , the sleeve  22 , and the seal bushing  26  constitute the stator unit.  
         [0073]     The shaft  24  defines a cylindrical outer circumferential surface. The sleeve  22  is formed of a sintered porous metal, and the sleeve  22  defines a cylindrical inner circumferential surface that radially opposes the outer circumferential surface of the shaft  24 . The outer circumferential surface of the sleeve  22  is adhesively affixed to the inner circumferential surface of the bearing housing  23 . The bearing housing  23  is formed of a resin such as a liquid-crystalline polymer.  
         [0074]     Radially extending and axially extending gaps between the shaft  24  and the sleeve  22  are charged with and retain a lubricating fluid  35 . An ester-based or a poly(α-olefin) based oil is, for example, utilized as the lubricating fluid  35 . It will be appreciated that for the lubricating fluid  35 , oils or other liquids appropriately selected and adjusted according to the how the lubricating fluid is to perform may be utilized.  
         [0075]     At least a portion of the outer circumferential surface of the shaft  24  and of the inner circumferential surface of the sleeve  22  radially oppose spaced apart by several μm, wherein a radial dynamic-pressure bearing  42  is formed. The shaft  24  is flanged adjacent the end on its lower side, forming a radially outward extending flange  25 , and the upper and lower surfaces of the flange  25  axially oppose the bottom surface of the bearing housing  23  and the lower endface of the sleeve  22 , wherein respective thrust dynamic-pressure bearings  43   a  and  43   b  are constituted.  
         [0076]     The radial dynamic-pressure bearing  42  and the thrust dynamic-pressure bearings  43  rotatively support the shaft  24  and the rotor hub  21  with respect to the sleeve  22 , by the force of pressure produced due to the difference in flow speed of the lubricating fluid  35  retained in the gaps in between the rotating shaft  24  and the sleeve  22  opposing the shaft. Further, dynamic-pressure grooves (not illustrated) of herringbone conformation, that when the shaft  24  rotates with respect to the sleeve  22  exert a pumping action on the lubricating fluid  35  in a direction gathering the fluid into an axial stretch of the radial dynamic-pressure bearing  42 , are formed on the radial-bearing constituting, inner-circumferential surface of the sleeve  22 .  
         [0077]     The description now turns to  FIG. 5 , which is a fragmentary view enlarged from  FIG. 2  to show key features of the seal bushing  26  and the shaft  24 . The interval between the outer circumferential surface of the shaft  24  and the inner circumferential surface of the seal bushing  26  flares as the spacing heads upward. Herein the bearing  2  is configured so that at the lower end of the seal bushing  26  the spacing is about 20 μm, and at the upper end of the seal bushing  26  it is about 300 μm. In the spacing, a boundary surface  44  between the lubricating fluid  35  and the external atmosphere forms, constituting a capillary seal  41 . The position of the boundary surface  44  is determined by the measure of surface tension acting on the interface between the lubricating fluid  35  and the external atmosphere; the stronger this surface tension is, the more stably the boundary surface  44  is maintained. The size of the spacing for the capillary seal  41 , and the size θ1 of the wetting angle between the lubricating fluid  35  and the surfaces that are constituents of the capillary seal section  41  greatly influence the strength of the surface tension.  
         [0078]     Manufacturing Method  
         [0079]     A method of manufacturing the fluid-dynamic-pressure bearing  2  is as follows.  
         [0080]     Processing &amp; Cleaning  
         [0081]     Namely, to begin with the rotor hub  21 , the sleeve  22 , the bearing housing  23 , the shaft  24 , the seal bushing  26 , and the base component  27  are respectively machined/formed. Thereafter the components are cleaned. Purified water, solvents, acidic/alkaline solutions, surface-active agents, etc. are utilized for the cleaning.  
         [0082]     Herein, cleaning by means of ultraviolet-beam irradiation or plasma, such as UV-ozone cleaning, may be carried out. Cleaning employing UV rays or plasma makes it possible to achieve highly effective cleansing on grime due to organic residues. What is more, both the liquid-based and irradiation-based cleaning processes may be carried out jointly.  
         [0083]     UV-Beam Irradiation of Sleeve Outer Circumferential Surface  
         [0084]     Next, the outer circumferential surface of the sleeve  22  is irradiated with an ultraviolet beam. The UV beam has a distinct spectrum that, for example, with a mercury lamp is 365 nm, and in an implementation in which a low-pressure mercury lamp is utilized, is 185 nm, 254 nm; and in an implementation in which an excimer lamp is utilized, the spectrum is 126 nm, 146 nm, 172 nm, 222 nm. In order to have the irradiation be UV rays in a specific bandwidth alone, the light can be put through filtering and beam-splitting as required to render single-wavelength components exclusively. The exposure duration is about 20 seconds.  
         [0085]     Subsequently the outer circumferential surface of the bearing housing  23  is irradiated with an ultraviolet beam. The UV irradiation is equivalent to that effected on the outer circumferential surface of the sleeve  22 . The exposure duration is about 20 seconds.  
         [0086]     UV-Beam Irradiation of Seal Bushing  
         [0087]     Next, the upper endface and the inner circumferential surface of the seal bushing  26  are irradiated with an ultraviolet beam. The UV beam is the same as that with which the outer circumferential surface of the sleeve  22  is irradiated, and is output from the same light source. The exposure duration is about 20 seconds, and the cumulative dose is set to be 35 kJ/m 2 . The upper endface of the seal bushing  26  serves as a stator-side oil-repellant application surface  46   a , while the inner circumferential surface of the seal bushing  26  serves as a stator-side, capillary-seal  41  constituting seal surface  45   a.    
         [0088]     It will be appreciated that these UV exposure operations enable surface-cleansing effectiveness to be achieved. Cleaning employing ultraviolet rays or plasma makes it possible to achieve highly effective cleansing on grime due organic residues.  
         [0089]     Assembly  
         [0090]     Next, the shaft  24  is inserted into the sleeve  22 , and the sleeve-shaft assembly is inset into the bearing housing  23 . The sleeve  22  outer-circumferential surface and the bearing housing  23  inner-circumferential surface are adhesively affixed to each other. Insetting the sleeve  22  by press-fitting it into the bearing housing  23  runs the risk that warpage in the sleeve  22  will occur, but adhesive affixation enables the sleeve  22  to be bound to the bearing housing  23  without distorting the sleeve  22 . Furthermore, since the outer circumferential surface of the sleeve  22  prior to assembly has been irradiated with ultraviolet rays, the adhesive  34  coheres readily to the sleeve surface, dramatically improving the adhesive strength between the sleeve  22  and the bearing housing  23 .  
         [0091]     Subsequently the seal bushing  26  is inset into the bearing housing  23  and adhesively affixed to the housing inner-circumferential surface. The portion of the shaft  24  that opposes the inner circumferential surface of the seal bushing  26  serves as a rotor-side, capillary-seal  41  constituting seal surface  45   b.    
         [0092]     Applying Repellant  33   
         [0093]     In the next stage in the bearing  2  manufacturing process, an oil repellant  33  is applied to a rotor-side oil-repellant application surface  46   b  located to the upper side of the seal surface  45   b  of the shaft  24 . The oil repellant  33  is applied with a special dispenser for that purpose. A groove that serves to mark the location where the repellant  33  is applied is formed in the oil-repellant application surface  46   b  of the shaft.  
         [0094]     Infusing Lubricating Fluid  35   
         [0095]     Next, through the gap between the seal bushing  26  and the shaft  24 , lubricating fluid  35  is infused into the gap between the radial dynamic-pressure bearing  42  and the thrust dynamic-pressure bearings  43 . While the assembly is under a vacuum, the lubricating fluid  35  is poured in so as to conceal the gap between the seal bushing  26  and the shaft  24 ; the assembly is then gradually returned to near atmospheric pressure, whereby the lubricating fluid  35  enters into and is retained within the gaps that constitute the radial and thrust dynamic-pressure bearings. The lubricating fluid  35  is infused in an amount by which the interior of the gaps will be filled with the lubricating fluid  35 .  
         [0096]     Subsequently, whether the lubricating fluid  35  is the appropriate amount is examined by gauging the height of the boundary surface  44  between the lubricating fluid  35  and the external atmosphere. When the lubricating fluid  35  is the proper quantity, the locus of the boundary surface  44  will form in between the stator-side seal surface  45   a  and the rotor-side seal surface  45   b.    
         [0097]     By the foregoing method, a fluid dynamic-pressure bearing  2  made up of the sleeve  22 , the bearing housing  23 , the shaft  24 , the seal bushing  26 , and the lubricating fluid  35  retained in the radial fluid dynamic-pressure bearing  45  and the thrust fluid dynamic-pressure bearings  43  is completed.  
         [0098]     Mounting Rotor Hub  
         [0099]     The rotor hub  21  onto which the rotor magnet  32  has been attached is mounted onto the shaft  24  by press-fitting the hub onto the shaft upper end. As a means to improve the binding strength, as well as in order to prevent deformation of the components, the hub may be fixed to the shaft using an adhesive.  
         [0100]     Anchoring Bearing Unit To Base  
         [0101]     Next, the bearing housing  23  is adhesively affixed to the bracket  27  onto which the stator  31  has been mounted. A mounting hole  27   a  of substantially the same conformation as the outer circumferential surface of the bearing housing  23  is formed in the bracket  27 . With the adhesive  34  intervening, the outer circumferential surface of the bearing housing  23  is snugged along the inner circumferential surface constituting the mounting hole  27   a , to which the housing circumferential surface is thereby adhesively affixed. Since the outer circumferential surface of the bearing housing  23  has been irradiated with ultraviolet rays prior to fixing the housing into the bracket, the adhesive  34  coheres readily to the housing surface, dramatically improving the adhesive strength between the outer circumferential surface of the bearing housing  23  and the mounting hole  27   a  in the bracket  27 .  
         [0102]     A spindle motor  3  is manufactured through these steps.  
         [0103]     Embodiment Effects/Results  
         [0104]     The change in wetting angle in the capillary seal section  41  of a fluid-dynamic-pressure bearing  2  in the first embodiment, manufactured according to a manufacturing method of the present invention, will be given in the following. When an ester-based oil was employed as the lubricating fluid  35 , its wetting angle with the seal bushing  26  prior to being exposed to ultraviolet rays was about 60°. The wetting angle after a 20-second exposure with a UV beam having a principal wavelength of 185 nm became 20-30°. Quite clearly, then, the wetting angle was extraordinarily reduced. Moreover, even after seven days post UV-exposure the wetting angle remained essentially unchanged.  
         [0105]     Prior to implementing the UV-exposure operation in manufacturing the fluid-dynamic-pressure bearings, the oil repellant  33  was extremely prone to peeling off, making necessary manufacturing operations to discern the post-application peeling and reapply the repellant over again. In contrast, the cohesiveness of the oil repellant  33  for seal surfaces irradiated for 20 seconds with a UV beam having a principal wavelength of 185 nm was excellent, and thus in post-application inspections, there were almost no articles deemed to require reapplication of the repellant. Consequently, reapplication work was rendered practically unnecessary.  
         [0106]     The diameter of the bearing housing  23  is about 10 mm, and the length of the mating fit between the bearing housing  23  and the mounting hole in the bracket  27  is about 5 mm. Acryl-based anaerobic, UV-curing adhesive agents, and epoxy-based thermosetting adhesive agents have each been employed to date as the adhesive  34 . Prior to implementing the UV-exposure operation in manufacturing the fluid-dynamic-pressure bearings, the force required to pull the bearing housing  23  of a dynamic-pressure bearing  2  out of the bracket  27  was 30-100 kgf. In contrast, the force required to pull the bearing housing  23  of a fluid-dynamic-pressure bearing  2  out of the bracket  27  when the gluing operation is carried out under the same conditions, after the adhesion surface of the housing has been irradiated for 20 seconds with a UV beam having a principal wavelength of 185 nm, is a dramatically improved 60-120 kgf. Moreover, since the adhesive readily coheres to the component surfaces, the adhesive spreads uniformly along the joining faces. Breaches between the adhesive and the components are consequently not liable to form, which thus makes it all the more possible to keep contamination from the exterior from passing through such breaches and invading the interior of a recording-disk drive.  
       Second Embodiment  
       [0107]     Spindle motor  103 , as illustrated in  FIG. 3 , is utilized as an alternative to spindle motor  3  in the first embodiment. The recording disks  12  are carried on and spun by a rotor hub  121  of the spindle motor  103 .  
         [0108]     The spindle motor  103  is, in a like manner as in the first embodiment, made up of a fluid-dynamic-pressure bearing  102 , a stator  32 , and a rotor magnet  132 . Likewise, in the spindle motor  103 , a baseplate  127  that constitutes a part of the case  11  for the recording-disk drive  1  serves as the base component.  
         [0109]     The fluid-dynamic-pressure bearing  102  includes: a columnar shaft  124  mounted in the rotational center portion of the rotor hub  121 ; a sleeve  122  having an inner circumferential surface that radially opposes the outer circumferential surface of the shaft  124 ; and the rotor hub  121 , which has an underside surface that axially opposes the upper endface of the sleeve  122 . The shaft  124  is composed of a hardened martensitic stainless steel, and the sleeve  122  is composed of a free-machining stainless steel. A cylindrical wall member  126  encompassing the sleeve  122  is attached to the rotor hub  121 . The inner circumferential surface  126   a  of the cylindrical wall member  126  diametrically opposes the outer circumferential surface of the sleeve  122 . The rotor hub  121 , the shaft  124 , and the rotor magnet  132  constitute the rotor unit of the spindle motor  103 . Meanwhile, the sleeve  122 , a stator  131 , and the baseplate  127  form the stator unit of the spindle motor  103 .  
         [0110]     At least a portion of the diametric gap between the outer circumferential surface of the shaft  124  and the inner circumferential surface of the sleeve  122  is rendered to measure some several μm. Likewise, a portion of the axial gap between the upper endface of the sleeve  122  and the underside surface of the rotor hub  121  is rendered to measure several to 20 μm or so. Lubricating fluid  35  fills and is retained by these gaps: In the diametric gap, lubricating fluid  35  is retained, forming a radial dynamic-pressure bearing  142 ; and in the axial gap, lubricating fluid  35  is retained, forming a thrust dynamic-pressure bearing  143 . Furthermore, the inner circumferential surface  126   a  of the cylindrical wall member  126  is a rotor-side seal surface  145   a . Along the outer circumferential surface of the sleeve  122 , the portion that opposes the rotor-side seal surface  145   a  is a stator-side seal surface  145   b . The diametrical clearance between the rotor-side seal surface  145   a  and the stator-side seal surface  145   b  flares going from the upper end to the lower end of the clearance. This clearance constitutes a capillary seal section  141 . In the clearance constituting the capillary seal section  141 , a boundary surface  144  between the lubricating fluid  35  and the external atmosphere forms.  
         [0111]     A method of manufacturing a fluid-dynamic-pressure bearing as set forth above is as follows.  
         [0112]     Namely, as is the case in the first embodiment, each component is machined/formed, and then the components are cleaned.  
         [0113]     Next, a plasma surface-treating process is implemented on the outer circumferential surface of the sleeve  122 . In the present embodiment, ozone cleaning is utilized for the plasma surface-treating process. Ozone cleaning is carried out by ozonizing oxygen with an ultraviolet beam and exposing the outer circumferential surface of the sleeve  122  with the resulting ozonic plasma. It will be appreciated that grease and other organic residues clinging to the component surfaces can be cleaned simultaneously with the surface treating process.  
         [0114]     Herein, the plasma surface-treating process may be implemented on the inner circumferential surface  126   a  of the cylindrical wall member  126  on the rotor hub  121 , and on the vicinity of the mounting hole in the baseplate  127 .  
         [0115]     Next, the shaft  124  is mounted into the rotor hub  121 . Then the sleeve  122  is fit over the shaft  124 , and the cylindrical wall member  126  is attached to the underside face of the rotor hub  121 . The cylindrical wall member  126  thus serves to lock the rotor hub  121  against coming out of the sleeve  122 . The lower end (bottom) of the sleeve  122  is then covered with an endplate  125 . Thus the interior of the sleeve  122  is made into a hermetic space.  
         [0116]     Subsequently, along the outer circumferential side of the sleeve  122 , in an area located to the lower side of the stator-side seal surface  145   b , oil repellant  33  is applied circuiting the circumference. The outer circumferential surface of the sleeve  122  onto which oil repellant  33  is applied serves as a stator-side oil-repellant application surface  146   a . In turn, oil repellant  33  is also applied to the lower part of the inner circumferential surface  126   a  of the cylindrical wall member  126 . The inner circumferential surface  126   a  of the cylindrical wall member  126  onto which oil repellant  33  is applied serves as a rotor-side oil-repellant application surface  146   b . The bearing-manufacturing method then continues by heating the fluid-dynamic-pressure bearing  102  to about 100° C. in order to cohere the oil repellant  33  to the oil-repellant application surfaces  146 . Regarding the efficacy of the plasma surface-treating process, it is to be noted that there was no diminishment of the resulting effectiveness even if the bearing was heated to as much as 120° C.  
         [0117]     At this point lubricating fluid  35  is passed through the capillary seal section  141  to charge the radial dynamic-pressure bearing  142  and thrust dynamic-pressure bearing  143  gaps with the fluid. Under a vacuum environment, with the sleeve  122  up and thus the rotor hub  121  down, lubricating fluid  35  is pooled in the capillary seal section  141  opening. The volume of lubricating fluid is the amount according to which the fluid-atmosphere boundary surface will form within the limits defined by the capillary seal section  141 . After the bearing has been charged with lubricating fluid  35 , a check/inspection is made as to whether the boundary surface has formed in the correct position. The bearing environment is thereafter repressurized gradually to atmospheric pressure, whereby the gaps are filled with the lubricating fluid  35 . Therein, the lubricating fluid  35  is stably retained within the bearing gaps by capillary force acting in the gaps.  
         [0118]     Next, the fluid dynamic-pressure bearing  102  is adhesively affixed into the baseplate  127 . A round mounting hole that closely matches the outer circumferential surface of the sleeve  122  is formed in the baseplate  127 . Adhesive  34  is applied to the inner circumferential surface of the mounting hole, into which the sleeve  127  is then inset.  
         [0119]     The stator  131  has in advance been mounted on the baseplate  127 , while the rotor magnet  132  has in advance been attached to the rotor hub  121 . In the foregoing way, the spindle motor  103  is completed.  
         [0120]     It was confirmed that the effect on the wetting angle of the lubricating fluid  35  in the capillary seal section  141  in the present embodiment was substantially equivalent to that when the bearing components were UV-irradiated in the implementation in which an ultraviolet beam and the same lubricating agent were utilized.  
         [0121]     Similar effectiveness in making the oil repellant  35  lees likely to peel off was also confirmed. In particular, in the bearing having been heated after application of the oil repellant, the oil-repellant application surface  146   b , which had been surface-treated with the plasma, was scrubbed several dozen times at a force of 100 gf using a rag, yet no oil repellant was observed stuck to the rag. As will be understood from these confirmations, by applying the oil repellant  33  to the stator-side oil-repellant application surface  146   a  having undergone the plasma-based superficial treating process, the cohesiveness of the oil repellant  33  is extraordinarily improved.  
         [0122]     What is more, the adhesive strength between the baseplate  127  and the sleeve  122  is also improved, being at least more than twice the binding strength compared with the situation in which the surfaces are not plasma-treated. Consequently, the durability of the assembly against shock or other impact improves dramatically.  
       Third Embodiment  
       [0123]     The description now turns to  FIG. 4 , which is a diagram illustrating a spindle motor  203  and a fluid dynamic-pressure bearing  202  in yet another embodiment of the present invention.  
         [0124]      FIG. 4  is of a fluid dynamic-pressure bearing  202  in which the shaft  224  is anchored into the bracket  227 . This fluid dynamic-pressure bearing  202  is made up of: a sleeve  222  mounted in a rotor hub  221  of the spindle motor  203 ; the shaft  224 , which is inserted into the sleeve  222 ; and a flange  225  that is mounted on the upper-end part of the shaft  224 . The gap between the sleeve  222  and the shaft  224  is charged with and retains lubricating fluid  35 . A radial dynamic-pressure bearing  242  is formed in between the outer circumferential surface of the shaft  224  and the inner circumferential surface of the sleeve  222 . Furthermore, thrust dynamic-pressure bearings  243   a  and  243   b  are formed in between the top and bottom surfaces of the flange  225 , and the sleeve  222  where it axially opposes the top/bottom surfaces.  
         [0125]     In this fluid dynamic-pressure bearing  202 , the outer circumferential surface of the sleeve  222  and the lower endface of the sleeve  222  are subjected to a plasma-based surface-treating process. It should be understood that these areas may also be irradiated with an ultraviolet beam. This surface-treating step may be either before or after assembling the fluid dynamic-pressure bearing  202 .  
         [0126]     Oil repellant  33  is applied to the lower endface of the sleeve  222 , after which the surface is heated to render a rotor-side oil-repellant application surface  246   a.    
         [0127]     Next, lubricating fluid  35  is infused into the gaps by which the radial dynamic-pressure bearing  242  and the thrust dynamic-pressure bearings  243  are formed. The lubricating-fluid  35  infusion method is the same as that of the first embodiment.  
         [0128]     The outer circumferential surface of the sleeve  222  is inset into a mounting hole  227   a  provided in the bracket  227 , with adhesive  34  intervening.  
         [0129]     A fluid dynamic-pressure bearing  202  of the third embodiment, owing to its retaining the lubricating fluid  35  stably, has a long lifespan; wherein leakage of the lubricating fluid  35  in reaction to impact is restrained. In addition, in the spindle motor  203  also, the adhesive strength between the bracket  227  and the fluid dynamic-pressure bearing  202  is tough, which lends the motor an enhanced capacity to withstand impact.  
         [0130]     It should be understood that the present invention is not limited only to the scope set forth in the embodiments, in that various modifications within a scope that does not depart from the gist of the present invention are possible. For example, substantially similar efficacy can be achieved by carrying out whichever of the surface treatments-whether it be a surface-treating process by ultraviolet-beam irradiation, or a plasma-based surface-treating process. Plasma-based surface-treating processes comprehend various sorts of cleaning devices, such as those for ion cleaning, ozone cleaning, or UV-ozone cleaning, as well as irradiation by charged-particle beams and high-energy RF radiation.  
         [0131]     Furthermore, of fluid dynamic-pressure bearings of the various structures that have been employed to date, the present invention is applicable to fluid dynamic-pressure bearings furnished with a capillary seal. Likewise, the present invention is applicable to spindle-motor implementations in which the fluid dynamic-pressure bearing and other components are joined by means of an adhesive, regardless of the form of the motor or the form of the bearing.  
         [0132]     Other modifications include that the type of adhesive agent, the type of oil repellant, the type of lubricating agent, and the materials and substances of the components that constitute the fluid dynamic-pressure bearing and the spindle motor may be varied according to use and design. Likewise, recording-disk drives of the present invention are not necessarily limited to hard-disk drives; the present invention may be utilized in various sorts of recording-disk drives, such as removable disk drives, optical disk drives, and magneto-optical disk drives. Still further, a fluid dynamic-pressure bearing manufacturing method of the present invention may be utilized in implementations in which bearings are manufactured for motors—such as motors for polygonal mirrors, and fan motors—that spin at high speed and in which a high degree of rotational precision is mandatory.