WO2014208718A1 - 磁気ディスク用ガラス基板の製造方法、磁気ディスクの製造方法、研削砥石 - Google Patents
磁気ディスク用ガラス基板の製造方法、磁気ディスクの製造方法、研削砥石 Download PDFInfo
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- WO2014208718A1 WO2014208718A1 PCT/JP2014/067139 JP2014067139W WO2014208718A1 WO 2014208718 A1 WO2014208718 A1 WO 2014208718A1 JP 2014067139 W JP2014067139 W JP 2014067139W WO 2014208718 A1 WO2014208718 A1 WO 2014208718A1
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- WIPO (PCT)
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- glass substrate
- grinding
- chamfered
- grinding wheel
- magnetic disk
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/84—Processes or apparatus specially adapted for manufacturing record carriers
- G11B5/8404—Processes or apparatus specially adapted for manufacturing record carriers manufacturing base layers
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C3/00—Glass compositions
- C03C3/04—Glass compositions containing silica
- C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
- C03C3/083—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound
- C03C3/085—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound containing an oxide of a divalent metal
- C03C3/087—Glass compositions containing silica with 40% to 90% silica, by weight containing aluminium oxide or an iron compound containing an oxide of a divalent metal containing calcium oxide, e.g. common sheet or container glass
Definitions
- the present invention relates to a method for manufacturing a glass substrate for a magnetic disk and a magnetic disk.
- a personal computer or a DVD (Digital Versatile Disc) recording device has a built-in hard disk device (HDD: Hard Disk Drive) for data recording.
- HDD Hard Disk Drive
- a hard disk device used in a portable computer such as a notebook personal computer
- a magnetic disk in which a magnetic layer is provided on a glass substrate is used, and the magnetic head slightly floats above the surface of the magnetic disk.
- magnetic recording information is recorded on or read from the magnetic layer.
- a glass substrate is preferably used because it has a property that it is less likely to be plastically deformed than a metal substrate (aluminum substrate) or the like.
- the density of magnetic recording has been increased.
- the magnetic recording information area (recording bit) is miniaturized by using a perpendicular magnetic recording method in which the magnetization direction in the magnetic layer is perpendicular to the surface of the substrate.
- the storage capacity of one disk substrate can be increased.
- the distance from the magnetic recording layer is extremely shortened by further protruding the recording / reproducing element portion of the magnetic head, thereby further improving the accuracy of information recording / reproducing (S / N). To improve the ratio).
- Such control of the recording / reproducing element portion of the magnetic head is called a DFH (Dynamic Flying Height) control mechanism, and a magnetic head equipped with this control mechanism is called a DFH head.
- the main surface of the magnetic disk glass substrate used in the HDD in combination with such a DFH head is an extremely smooth surface in order to avoid collision and contact with the magnetic head and the recording / reproducing element portion further protruding therefrom. It is produced to become.
- chamfering is performed on an inner peripheral end and an outer peripheral end of a disk-shaped glass substrate having an inner hole. That is, a chamfered surface interposed between the main surface of the glass substrate and the side wall surface is formed.
- a chamfered surface By forming the chamfered surface, generation of foreign matters from the glass substrate can be prevented, and problems such as a head crash failure and a thermal asperity failure when the manufactured magnetic disk is incorporated in the HDD can be suppressed.
- a grindstone having a groove formed on the outer peripheral portion is rotationally driven around a rotation axis inclined with respect to the rotation axis of a rotating workpiece, and the grindstone groove is covered.
- a method is known in which end surface grinding of the outer peripheral portion or inner peripheral portion of the workpiece is performed by pressing the outer peripheral portion or inner peripheral portion of the workpiece (Patent Document 1 below).
- Patent Document 1 Japanese Patent Document 1 below.
- the end surface is ground in the state of surface contact, and the contact with the outer peripheral portion or inner peripheral portion of the work piece is shocked, so that good surface quality is efficiently obtained. It is supposed to be obtained.
- the chamfer angles of the pair of chamfered surfaces of the glass substrate for magnetic disk are different, it is preferable to cause fluttering due to turbulence of the air flow in the HDD housing when the magnetic disk is installed in the HDD and rotated. Absent.
- the gripping cannot be accurately performed. As a result, the accuracy of film thickness control may be reduced.
- the present invention makes the chamfer angles of a pair of chamfered surfaces the same while ensuring good end surface quality when grinding the end surface of a disk-shaped glass substrate in the process of manufacturing a glass substrate for a magnetic disk.
- An object of the present invention is to provide a method for producing a glass substrate for a magnetic disk, a method for producing a magnetic disk, and a grinding wheel that make it possible.
- the inventors of the present application rotate the grindstone formed with the groove around the rotation axis inclined with respect to the rotation axis of the glass substrate, and press the groove of the grindstone against the outer peripheral portion or the inner peripheral portion of the glass substrate.
- the action of the abrasive grains during processing differs between one chamfered surface and the other chamfered surface. It was found that the chamfer angles after processing were not the same.
- a circular hole is formed at the center, and the end surface of a disk-shaped glass substrate having a side wall surface and a chamfered surface formed between the main surface and the side wall surface is rotated.
- a pair of chamfered surfaces of a glass substrate are ground simultaneously by inclining a rotation axis of a grinding wheel with respect to an axis orthogonal to the main surface of the substrate.
- the grinding wheel has a groove shape having a pair of chamfered surfaces for grinding the chamfered surface of the glass substrate.
- a pair of chamfered surface grinding regions is defined as a front side (individual abrasive grains) in the rotation direction of the grinding wheel with reference to a contact point between the glass substrate and the grinding wheel positioned on a straight line connecting the center of the glass substrate and the rotation axis of the grinding wheel.
- the groove shape of the grinding wheel further includes a side wall surface grinding region for grinding the side wall surface of the glass substrate, and the end surface grinding treatment is performed in a pair with the side wall surface of the glass substrate.
- the chamfered surface may be ground simultaneously.
- the thickness of the magnetic disk glass substrate may be smaller than 0.635 mm.
- the glass substrate for magnetic disk is preferably crystallized glass.
- a magnetic disk comprising a process for forming a magnetic layer on a main surface of a glass substrate for a magnetic disk manufactured by a method for manufacturing a glass substrate for a magnetic disk. It is a manufacturing method.
- a third aspect of the present invention is an end surface grinding process for an end surface of a disk-shaped glass substrate having a circular hole at the center and having a side wall surface and a chamfered surface formed between the main surface and the side wall surface. It is a grinding wheel used by rotating.
- This grinding wheel is composed of a cylindrical or columnar rotating body, and a groove is formed on the circumference of the rotating body.
- the groove has a side wall surface ground surface that contacts the side wall surface of the glass substrate and a chamfer surface that contacts one of the chamfered surfaces across the side wall surface of the glass substrate in a cross-sectional view of the surface including the rotation axis of the rotating body.
- the side wall surface of the chamfered surface ground surface (A) and the chamfered surface ground surface (B) comprising a ground surface (A) and a chamfered surface ground surface (B) in contact with the other chamfered surface.
- the opening angle from is different.
- the method for manufacturing a magnetic disk glass substrate when grinding the end surface of a disk-shaped glass substrate in the process of manufacturing the magnetic disk glass substrate, the chamfer angles of the pair of chamfered surfaces can be made the same while ensuring the end surface quality.
- Aluminosilicate glass, soda lime glass, borosilicate glass, or the like can be used as the material for the magnetic disk glass substrate in the present embodiment.
- aluminosilicate glass can be suitably used in that it can be chemically strengthened and a glass substrate for a magnetic disk excellent in flatness of the main surface and strength of the substrate can be produced.
- the glass substrate of the present embodiment is preferably composed of SiO 2 , Li 2 O, Na 2 O, and And at least one alkaline earth metal oxide selected from the group consisting of MgO, CaO, SrO and BaO, and the molar ratio of the content of CaO to the total content of MgO, CaO, SrO and BaO (CaO / (MgO + CaO + SrO + BaO )) Is 0.20 or less, and an amorphous aluminosilicate glass having a glass transition temperature of 650 ° C. or more may be used.
- FIG. 1A shows the appearance of the magnetic disk glass substrate of the embodiment.
- the glass substrate for a magnetic disk in the present embodiment is a donut-shaped thin glass substrate in which an inner hole 2 is formed.
- the size of the glass substrate for magnetic disks is not ask
- FIG. 1B is an enlarged view showing a cross section of an end portion on the outer peripheral side of the glass substrate for magnetic disk of the embodiment.
- the magnetic disk glass substrate includes a pair of main surfaces 1p, side wall surfaces 1t arranged along a direction orthogonal to the pair of main surfaces 1p, and a pair of main surfaces 1p and sides.
- each chamfered surface 1c has a pair of chamfered surfaces 1c arranged between the wall surface 1t.
- a side wall surface and a chamfered surface are similarly formed on the inner peripheral side end of the magnetic disk glass substrate.
- the angle (chamfer angle) formed by each chamfered surface 1c with respect to the side wall surface 1t is basically the same, and is preferably 15 to 75 degrees, for example. By making it within this range, it is preferable to prevent the edge of the substrate from being scratched or chipped in the process of manufacturing the magnetic disk glass substrate and the subsequent process of manufacturing the magnetic disk or HDD. can do.
- the chamfer angle is typically 45 degrees as shown. Note that the chamfered surface may be formed in an arc shape in a sectional view.
- the thickness of the magnetic disk glass substrate of the present embodiment is not particularly limited.
- the thickness in the case of a magnetic disk glass substrate having a nominal size of 2.5 inches, the thickness is 0.8 mm or 0.635 mm, for example.
- a glass substrate for a nominal 3.5 inch magnetic disk for example, it is 0.5 mm.
- the thinner the plate thickness the more easily flutters during rotation, and fluttering tends to occur.
- the thickness of the magnetic disk glass substrate of the present embodiment is preferably smaller than 0.635 mm, more preferably 0.5 mm or less.
- a glass base plate having a predetermined shape that is a base of a glass substrate for a magnetic disk is cut out from the plate glass.
- the glass base plate may be formed by press molding using an upper mold and a lower mold, for example.
- a glass base plate can also be manufactured not only using these methods but using well-known manufacturing methods, such as a downdraw method, a redraw method, and a fusion method.
- shape processing processing is performed.
- a circular hole is formed using a known processing method, thereby obtaining a disk-shaped glass substrate having a circular hole.
- an end surface grinding process of the glass substrate is performed to form a chamfered surface having a desired shape. That is, a chamfered surface connecting the side wall surface and the main surface is formed at the end of the glass substrate.
- FIG. 2 is a diagram showing a grinding process for the inner peripheral end face of the glass substrate G.
- FIG. 3 is a diagram illustrating a contact surface between the glass substrate G and the grinding stone 5 during the grinding process of the inner peripheral end surface of the glass substrate G.
- the grinding wheel 5 used for grinding the inner peripheral end face of the glass substrate G is entirely composed of a cylindrical rotating body, and a groove 50 is formed on the outer periphery.
- the groove 50 is formed so that the inner peripheral side wall surface and the chamfered surfaces C1 and C2 of the glass substrate G can be ground simultaneously.
- the groove 50 includes the side wall surface grinding region 50t and both sides thereof.
- Chamfered surface grinding regions 50a and 50b are provided in the circumferential direction.
- the glass substrate G is inclined with respect to the groove direction of the groove 50 formed in the grinding wheel 5, that is, the rotation axis of the glass substrate G with respect to the rotation axis L 5 of the grinding wheel 5.
- Grinding is performed by rotating both the glass substrate G and the grinding wheel 5 while contacting the groove 50 of the grinding wheel 5 with the inner peripheral end surface of the glass substrate G in a state where L1 is inclined by an angle ⁇ ( ⁇ > 0). Do. That is, grinding is performed by inclining the grinding wheel 5 with respect to the glass substrate G so that the groove 50 of the grinding wheel 5 and the glass substrate G have a twisted positional relationship. Accordingly, the locus of the groove 50 of the grinding wheel 5 that contacts the inner peripheral end surface of the glass substrate G does not become constant, and the abrasive grains of the grinding wheel 5 contact and act on the substrate end surface at random positions.
- the side wall surface and the two chamfered surfaces of the glass substrate G are ground simultaneously.
- the regions where the side wall surface grinding region 50t and the chamfered surface grinding regions 50a, 50b of the grinding wheel 5 are in contact with the end surface of the glass substrate G are the region T and the regions Ca, Cb. That is, during the grinding process, the groove 50 of the grinding wheel 5 and the end face of the glass substrate G are in surface contact. Therefore, the contact length (cutting edge length) of the grinding wheel 5 with respect to the glass substrate G can be extended to maintain the sharpness of the abrasive grains.
- the inclination angle ⁇ of the glass substrate G with respect to the groove direction of the grinding wheel 5 described above can be arbitrarily set. However, in order to better exhibit the above-described effects, it is set within a range of, for example, 1 to 15 degrees. Is preferred.
- a so-called electrodeposited bond grindstone in which diamond abrasive grains, which are high-rigidity grindstones are hardened by electrodeposition bond, is suitable for rough grinding.
- a resin bond grindstone in which the binder for bonding abrasive grains is a resin material such as phenol resin, urethane resin, polyimide resin, polyester resin, fluororesin, or the binder is copper-based, for example.
- a metal bond grindstone that is a metallic binder such as an alloy, cast iron alloy, or titanium alloy, and a vitrified grindstone whose binder is a vitreous binder are suitable.
- a resin bond grindstone in which the adjustment of the hardness of the grindstone is relatively easy is particularly suitable.
- abrasive grains having an average grain diameter of 30 ⁇ m or less are suitable in order to maintain the grinding performance over the life of the grinding wheel while maintaining the roughness.
- Abrasive grains having an average particle diameter of 3 to 15 ⁇ m are preferred.
- a diamond abrasive grain is suitable, for example.
- the particle size of the abrasive grains can be measured by, for example, an electrical resistance test method.
- a preferable example of the peripheral speed of the grinding wheel 5 is 500 to 3000 m / min, and the peripheral speed of the glass substrate G is about 1 to 30 m / min.
- the ratio of the peripheral speed of the grinding wheel 5 to the peripheral speed of the glass substrate G is preferably in the range of 50 to 300.
- FIG. 4 is a diagram for explaining the opening angle of the groove 50 of the grinding wheel 5, and shows an enlarged portion A of the grinding wheel 5 shown in FIG. 3.
- the shape shown in FIG. 4 is the same as the shape at the time of enlarging the groove
- FIG. 4 when the opening angles of the chamfered surface grinding regions 50a and 50b are ⁇ 1 and ⁇ 2, respectively, with reference to a surface orthogonal to the side wall surface grinding region 50t, the rotation direction of the grinding wheel shown in FIG. In the case of the inclination angle ⁇ of the rotation axis L1 of the glass substrate G shown in FIG. 3 ( ⁇ > 0 in FIG. 3), ⁇ 1> ⁇ 2.
- ⁇ 1> ⁇ 2 is as follows.
- the chamfered surface grinding region 50a is based on the contact point between the glass substrate G and the grinding wheel 5 positioned on a straight line connecting the center of the glass substrate G and the rotation axis L5 of the grinding wheel 5.
- the chamfered surface of the glass substrate G is brought into contact with the rear side in the rotational direction of the grinding wheel 5.
- the chamfered surface grinding region 50b is in contact with the chamfered surface of the glass substrate G on the front side in the rotation direction of the grinding wheel 5 with the contact as a reference. That is, in this example, the chamfered surface grinding region (A) of the present invention corresponds to the chamfered surface grinding region 50b, and the chamfered surface grinding region (B) of the present invention corresponds to the chamfered surface grinding region 50a.
- the grindstone 5 is strong so that the abrasive grains bite into the chamfered surface C1 of the glass substrate G processed on the front side in the rotation direction of the grinding wheel 5 (that is, in the contact region Cb of the chamfered chamfered region 50b in FIG. 3).
- the chamfering angle of the chamfered surface C1 is an angle exceeding the opening angle ⁇ 2 of the chamfered surface grinding region 50b.
- the abrasive grains are relatively smooth on the chamfered surface C2 of the glass substrate G processed on the rear side in the rotation direction of the grinding wheel 5 (that is, in the contact area Ca of the chamfered surface grinding area 50a in FIG. 3).
- the chamfer angle of the chamfered surface C2 is an angle at which the opening angle ⁇ 1 of the chamfered surface grinding region 50a is transferred (that is, the same angle as ⁇ 1). Therefore, by setting the opening angle of the groove 50 of the grinding wheel 5 to ⁇ 1> ⁇ 2, the chamfering angles of the chamfered surfaces C1 and C2 of the glass substrate G after the end surface grinding process can be matched.
- the difference between the opening angles ⁇ 1 and ⁇ 2 is that the chamfering angles of the chamfered surfaces C1 and C2 after processing are the same based on factors such as the inclination angle ⁇ of the rotation axis L1 of the glass substrate G and the diameter of the grinding wheel 5. It can be determined as appropriate.
- the relationship between the opening angle ⁇ 1 of the chamfered surface grinding region 50a and the opening angle ⁇ 2 of the chamfered surface grinding region 50b is ⁇ 1> ⁇ 2 in the rotational direction of the grinding wheel shown in FIG. This is a case where the inclination angle ⁇ of the rotation axis L1 of the glass substrate G shown ( ⁇ > 0 in FIG. 3).
- the rotation direction of the grinding wheel 5 when the rotation direction of the grinding wheel 5 is reversed, the anteroposterior relationship with respect to the rotation direction of the grinding wheel 5 in the contact areas Ca and Cb between the grinding wheel 5 and the glass substrate G is also reversed. It is preferable to set ⁇ 2.
- FIG. 5 is a diagram showing a grinding process of the outer peripheral end surface of the glass substrate G.
- the grinding wheel 7 used for the end face grinding process of the outer peripheral end face is made of a cylindrical rotating body, and a groove is formed on the inner circumference thereof.
- the groove of the grinding wheel 7 and the glass substrate G are in a twisted positional relationship. Grinding is performed by inclining the grinding wheel 7 with respect to the substrate G.
- the side wall surface and the two chamfered surfaces of the glass substrate G are ground at the same time as in the grinding process of the inner peripheral end surface.
- the inclination angle of the glass substrate G with respect to the groove direction of the grinding wheel 7 is preferably in the range of 1 to 15 degrees, for example, as in the grinding treatment of the inner peripheral end face.
- the opening angle of the groove of the grinding wheel 7 may be the same as that shown in FIG.
- the chamfering of the glass substrate G on the front side in the rotation direction of the grinding wheel 7 is based on the contact point between the grinding wheel 7 and the glass substrate G positioned on a straight line connecting the center of the glass substrate G and the rotation axis of the grinding wheel 7.
- the opening angle of the region (A) is set smaller than the opening angle of the chamfered surface grinding region (B).
- the grinding wheel 5 on the inner peripheral end surface has the chamfered surface grinding regions 50a and 50b and the side wall surface grinding region 50t, and the grinding wheel 5 is paired with the side wall surface on the inner peripheral end surface of the glass substrate G.
- the grinding wheel 5 may grind the pair of chamfered surfaces at the same time and not grind the side wall surfaces at that time.
- the grinding process using the grinding wheel 5 may be only grinding a pair of chamfered surfaces simultaneously.
- there is an effect of shortening the end surface grinding time there is an effect of shortening the end surface grinding time. The same can be said for the outer peripheral end face.
- the end surface polishing process is a process for performing polishing by supplying a polishing liquid containing loose abrasive grains between the polishing brush and the end surface of the glass substrate and relatively moving the polishing brush and the glass substrate.
- the inner peripheral end surface and the outer peripheral side end surface of the glass substrate are subjected to polishing, and the inner peripheral end surface and the outer peripheral side end surface are in a mirror state.
- a polishing liquid containing fine particles such as cerium oxide as free abrasive grains is used.
- the double-sided grinding apparatus has a pair of upper and lower surface plates (an upper surface plate and a lower surface plate), and a disk-shaped glass substrate mounted on a carrier is sandwiched between the upper surface plate and the lower surface plate. . Then, by moving the upper surface plate or the lower surface plate, or both of them, the main surface of the glass substrate can be ground by relatively moving the glass substrate and each surface plate. it can.
- a first polishing process is performed on the main surface of the glass substrate.
- the main surfaces on both sides of the glass substrate are polished using a double-side polishing apparatus equipped with a planetary gear mechanism.
- loose abrasive grains such as cerium oxide abrasive grains or zirconia abrasive grains and a resin polisher are used.
- the first polishing removes cracks and distortions remaining on the main surface when, for example, fine grinding is performed.
- the glass substrate can be appropriately chemically strengthened.
- the chemical strengthening liquid for example, a molten liquid obtained by heating potassium nitrate, sodium nitrate, or a mixture thereof can be used. Then, by immersing the glass substrate in the chemical strengthening solution, lithium ions and sodium ions in the glass composition on the surface of the glass substrate are converted into sodium ions and potassium ions having relatively large ionic radii in the chemical strengthening solution, respectively. By replacing each, a compressive stress layer is formed in the surface layer portion, and the glass substrate is strengthened. The timing of performing the chemical strengthening treatment can be determined as appropriate.
- the polishing treatment is performed after the chemical strengthening treatment, the foreign matter fixed to the surface of the glass substrate by the chemical strengthening treatment can be removed together with the smoothing of the surface. This is particularly preferable because it can be performed.
- the chemical strengthening treatment may be performed as necessary, and may not be performed.
- Second Polishing (Final Polishing) Process
- the second polishing is intended for mirror polishing of the main surface.
- a double-side polishing apparatus having the same configuration as the double-side polishing apparatus used for the first polishing is used.
- the free abrasive grains used for the second polishing treatment for example, fine particles such as colloidal silica are used.
- the second polishing process is not necessarily an essential process, but it is preferable that the second polishing process is performed in that the level of surface irregularities on the main surface of the glass substrate can be further improved. Thereafter, by cleaning, a glass substrate for a magnetic disk is obtained. Note that the glass substrate is polished so that the arithmetic average roughness Ra of the surface roughness of the glass substrate after the second polishing treatment is 0.15 nm or less, thereby producing a glass substrate for a magnetic disk having a small surface roughness. This is preferable.
- the crystallization process is performed in the middle of each process described above.
- a plate called a disk-shaped setter is sandwiched between the glass substrates, and heat treatment is performed in a heating furnace.
- the setter may be made of ceramics.
- the glass substrate is crystallized by holding at a nucleation temperature for a predetermined time and then holding at a crystal growth temperature for a predetermined time.
- the nucleation temperature and the crystal growth temperature and time may be appropriately set depending on the glass composition of the glass substrate.
- the presence or absence of crystallization of the crystallized glass substrate can be determined using, for example, the diffraction intensity distribution obtained by the powder X-ray diffraction method.
- the average crystal grain size exceeds 10 nm, the processing time by polishing the main surface of the glass substrate becomes long, and the surface roughness becomes a size that cannot be ignored due to the crystal phase that cannot be completely removed by polishing.
- Crystallized glass (hereinafter referred to as crystallized glass) is a material having a structure in which crystals are precipitated in glass by heating amorphous glass, and can be distinguished from amorphous glass. Crystallized glass exhibits characteristics that cannot be obtained with amorphous glass due to crystals dispersed inside.
- crystallized glass exhibits properties that cannot be realized with amorphous glass.
- crystallized glass exhibits different characteristics from ceramics having a structure in which powder is sintered. Crystallized glass has an extremely small number of pores and a dense structure as compared with ceramics.
- the Young's modulus of the glass substrate after the crystallization treatment is preferably 100 GPa or more, more preferably 120 GPa or more. By carrying out like this, it can be set as a glass substrate with high bending strength and impact resistance.
- the bending strength of the glass substrate after the crystallization treatment is preferably 7 kgf or more, particularly preferably 8 kgf or more, from the viewpoint of improving impact resistance. By doing so, a glass substrate for a magnetic disk suitable for a high-speed rotation HDD of 10,000 rpm or more can be obtained.
- a magnetic disk is obtained as follows using a magnetic disk glass substrate.
- the magnetic disk is, for example, on the main surface of a glass substrate for magnetic disk (hereinafter simply referred to as “substrate”), in order from the closest to the main surface, at least an adhesion layer, an underlayer, a magnetic layer (magnetic recording layer), and a protection A layer and a lubricating layer are laminated.
- the substrate is introduced into a film forming apparatus that has been evacuated, and a film is sequentially formed from an adhesion layer to a magnetic layer on the main surface of the substrate in an Ar atmosphere by a DC magnetron sputtering method.
- a CoPt alloy can be used as the adhesion layer
- CrRu can be used as the underlayer.
- a CoPt alloy can be used. It is also possible to form a CoPt-based alloy and FePt based alloy L 10 regular structure and magnetic layer for heat-assisted magnetic recording.
- a magnetic recording medium can be formed by forming a protective layer using, for example, C 2 H 4 by a CVD method and subsequently performing nitriding treatment for introducing nitrogen into the surface. Thereafter, for example, PFPE (perfluoropolyether) is applied on the protective layer by a dip coating method, whereby a lubricating layer can be formed.
- PFPE perfluoropolyether
- the manufactured magnetic disk is preferably a magnetic disk drive device (HDD) as a magnetic recording / reproducing device, which includes a magnetic head equipped with a DFH (Dynamic Flying Height) control mechanism and a spindle for fixing the magnetic disk. (Hard Disk Drive)).
- HDD magnetic disk drive device
- DFH Dynamic Flying Height
- the composition of the used glass is as follows.
- Glass composition In terms of mass%, SiO 2 is 65.08%, Al 2 O 3 is 15.14%, Li 2 O is 3.61%, Na 2 O is 10.68%, K 2 O is 0.35%, An amorphous aluminosilicate glass having a composition having 0.99% MgO, 2.07% CaO, 1.98% ZrO 2 and 0.10% Fe 2 O 3 , and has a glass transition temperature of 510 ° C. It is.
- Tables 1 and 2 when the glass substrates for magnetic disks of Examples and Comparative Examples are produced, the opening angles of the grooves of the grinding wheel are different.
- Table 1 shows the case of end face grinding on the inner peripheral side
- Table 2 shows the case of end face grinding on the outer peripheral side.
- the chamfering angle of the chamfered surface of the glass substrate to be ground in the chamfered surface grinding region (A) is ⁇ A
- the chamfering angle of the chamfered surface of the glass substrate to be ground in the chamfered surface grinding region (B) is ⁇ B.
- the chamfer angles ⁇ A and ⁇ B are values immediately after the end surface grinding.
- the glass substrate for magnetic disk As described above, the glass substrate for magnetic disk, the method for manufacturing the magnetic disk, and the grinding wheel of the present invention have been described in detail.
- the present invention is not limited to the above embodiment, and various modifications can be made without departing from the gist of the present invention. Of course, improvements and changes may be made.
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Abstract
Description
円板状のガラス基板の端面研削方法として、外周部に溝部が形成された砥石を、回転する被加工物の回転軸に対して傾斜した回転軸の回りに回転駆動し、砥石の溝部を被加工物の外周部あるいは内周部に押圧することにより、被加工物の外周部あるいは内周部の端面研削を行う方法が知られている(下記特許文献1)。この端面研削方法によれば、面接触の状態で端面の研削が行われ、衝撃的に被加工物の外周部あるいは内周部に接触するのが緩和されるので、効率良く良好な表面品質が得られる、とされている。
本実施形態における磁気ディスク用ガラス基板の材料として、アルミノシリケートガラス、ソーダライムガラス、ボロシリケートガラスなどを用いることができる。特に、化学強化を施すことができ、また主表面の平坦度および基板の強度において優れた磁気ディスク用ガラス基板を作製することができるという点で、アルミノシリケートガラスを好適に用いることができる。
また、酸化物基準の質量%で、SiO2:45.60~60%、およびAl2O3:7~20%、およびB2O3:1.00~8%未満、およびP2O5:0.50~7%、およびTiO2:1~15%、およびROの合計量:5~35%(ただしRはZnおよびMg)の各成分を含有し、CaOの含有量が3.00%以下、BaOの含有量が4%以下であり、PbO成分、As2O3成分およびSb2O3成分およびCl-、NO-、SO2-、F-成分を含有せず、主結晶相としてRAl2O4、R2TiO4、(ただしRはZn、Mgから選択される1種類以上)から選ばれる一種以上を含有し、主結晶相の結晶粒径が0.5nm~20nmの範囲であり、結晶化度が15%以下であり、比重が2.95以下であることを特徴とする結晶化ガラスであってもよい。
図1Bは、実施形態の磁気ディスク用ガラス基板の外周側の端部の断面を拡大して示す図である。図1Bに示すように、磁気ディスク用ガラス基板は、一対の主表面1pと、一対の主表面1pに対して直交する方向に沿って配置された側壁面1tと、一対の主表面1pと側壁面1tとの間に配置された一対の面取面1cとを有する。図示しないが、磁気ディスク用ガラス基板の内周側の端部についても同様に、側壁面と面取面が形成されている。側壁面1tを基準として各面取面1cのなす角度(面取り角)は基本的には同一であり、例えば15~75度とすることが好ましい。この範囲内とすることで、磁気ディスク用ガラス基板を製造する過程や、その後の磁気ディスクやHDDを製造する過程で基板の端部にキズが入ったり端部がカケたりすることを好適に防止することができる。面取り角は典型的には図示するように45度である。なお、面取面は、断面視において円弧状に形成されていてもよい。
以下、本実施形態の磁気ディスク用ガラス基板の製造方法について、処理毎に説明する。ただし、各処理の順番は適宜入れ替えてもよい。
例えばフロート法によって板状ガラスを形成した後、この板状ガラスから、磁気ディスク用ガラス基板の元となる所定形状のガラス素板が切り出される。フロート法の代わりに、例えば上型と下型を用いたプレス成形によってガラス素板を成形してもよい。なお、ガラス素板は、これらの方法に限らず、ダウンドロー法、リドロー法、フュージョン法などの公知の製造方法を用いて製造することもできる。
なお、ガラス素板の両主表面に対して、必要に応じて、粗研削処理を行ってもよい。
次に、形状加工処理が行われる。形状加工処理では、ガラスブランクの成形処理後、公知の加工方法を用いて円孔を形成することにより、円孔があいた円板状のガラス基板を得る。次いで、ガラス基板の端面研削処理を実施して所望の形状の面取面を形成する。つまり、ガラス基板の端部において、側壁面と主表面を繋ぐ面取面が形成される。
ガラス基板の内周端面の加工では、研削砥石5に形成された溝50の溝方向に対してガラス基板Gを傾けた状態、つまり研削砥石5の回転軸L5に対してガラス基板Gの回転軸L1を角度α(α>0)だけ傾けた状態で、ガラス基板Gの内周端面に研削砥石5の溝50を接触させながら、ガラス基板Gと研削砥石5の両方を回転させて研削加工を行う。すなわち、研削砥石5の溝50とガラス基板Gがねじれの位置の関係となるように、ガラス基板Gに対して研削砥石5を傾斜させて研削加工を行う。これによって、ガラス基板Gの内周端面に当接する研削砥石5の溝50の軌跡が一定とはならないで、研削砥石5の砥粒が基板端面に対してランダムな位置に当接、作用するため、深掘れなどによる基板へのダメージが少なく、研削加工面の表面粗さやその面内ばらつきも小さくなり、研削加工面をより高平滑に、すなわちより高い品質要求に応えられるレベルの品位に仕上げることができる。さらには砥石寿命の向上効果も有する。
上記端面研削加工で用いる研削砥石5としては、粗研削加工用には、例えば高剛性砥石であるダイヤモンド砥粒を電着ボンドで固めた所謂電着ボンド砥石が好適である。また、仕上げの精密研削加工用には、砥粒同士を結合するバインダーが例えばフェノール樹脂、ウレタン樹脂、ポリイミド樹脂、ポリエステル樹脂、フッ素樹脂等の樹脂材料であるレジンボンド砥石や、バインダーが例えば銅系合金、鋳鉄系合金、チタン系合金等の金属質結合剤であるメタルボンド砥石、バインダーがガラス質結合材であるビトリファイド砥石などが好適である。この中でも、砥石の硬度の調整が比較的容易なレジンボンド砥石が特に好適である。
また、砥粒の粒径としては、粗さを維持しながら砥石寿命に亘って研削性能を維持できるためには、例えば平均粒子径30μm以下の砥粒が好適であるが、特に精密研削加工用には、平均粒子径3~15μmの範囲内の砥粒が好適である。砥粒としては、例えばダイヤモンド砥粒が好適である。砥粒の粒径は、例えば電気抵抗試験法で測定することが可能である。
研削砥石5の周速度の好ましい例は、500~3000m/分、ガラス基板Gの周速度は、1~30m/分程度である。また、ガラス基板Gの周速度に対する研削砥石5の周速度の比(周速度比)は、50~300の範囲内であることが好ましい。
研削砥石7の溝の開口角は、図4に示したものと同様でよい。すなわち、ガラス基板Gの中心と研削砥石7の回転軸とを結ぶ直線上に位置するガラス基板Gと研削砥石7の接点を基準として、研削砥石7の回転方向の前側でガラス基板Gの面取面と接触する面取面研削領域(A)と、研削砥石7の回転方向の後側でガラス基板Gの面取面と接触する面取面研削領域(B)とからなり、面取面研削領域(A)の開口角は、面取面研削領域(B)の開口角よりも小さく設定されている。それによって、端面研削処理後のガラス基板Gの外周側の一対の面取面の面取り角を一致させることができるようになる。
外周端面の場合についても同様のことが言える。
次にガラス基板の端面研磨処理が行われる。端面研磨処理は、研磨ブラシとガラス基板の端面との間に遊離砥粒を含む研磨液を供給して研磨ブラシとガラス基板とを相対的に移動させることにより研磨を行う処理である。端面研磨では、ガラス基板の内周端面および外周側端面を研磨対象とし、内周端面および外周側端面を鏡面状態にする。このとき、例えば酸化セリウム等の微粒子を遊離砥粒として含む研磨液が用いられる。端面研磨を行うことにより、ガラス基板の端面での塵等の異物粒子が付着した汚染、ダメージあるいはキズ等の損傷の除去を行うことができる。これにより、このガラス基板を用いて磁気ディスクを製造した場合であっても、サーマルアスペリティの発生を防止することができる。
精研削処理では、遊星歯車機構を備えた両面研削装置を用いて円板状のガラス基板の主表面に対して研削加工を行う。両面研削装置は、上下一対の定盤(上定盤および下定盤)を有しており、上定盤および下定盤の間に、キャリアに装着された円板状のガラス基板が狭持される。そして、上定盤または下定盤のいずれか一方、または、双方を移動操作することにより、ガラス基板と各定盤とを相対的に移動させることで、ガラス基板の両主表面を研削することができる。
次に、ガラス基板の主表面に第1研磨処理が施される。第1研磨処理では、遊星歯車機構を備えた両面研磨装置を用いてガラス基板の両側の主表面に対して研磨を行う。第1研磨処理では、例えば、酸化セリウム砥粒、あるいはジルコニア砥粒などの遊離砥粒と、樹脂ポリッシャが用いられる。第1研磨によって、例えば精研削処理を行った場合に主表面に残留したクラックや歪みを除去する。
ガラス基板は適宜化学強化することができる。化学強化液として、例えば硝酸カリウム,硝酸ナトリウム、またはそれらの混合物を加熱して得られる溶融液を用いることができる。そして、ガラス基板を化学強化液に浸漬することによって、ガラス基板の表層にあるガラス組成中のリチウムイオンやナトリウムイオンが、それぞれ化学強化液中のイオン半径が相対的に大きいナトリウムイオンやカリウムイオンにそれぞれ置換されることで表層部分に圧縮応力層が形成され、ガラス基板が強化される。
化学強化処理を行うタイミングは、適宜決定することができるが、化学強化処理の後に研磨処理を行うようにすると、表面の平滑化とともに化学強化処理によってガラス基板の表面に固着した異物を取り除くことができるので特に好ましい。また、化学強化処理は、必要に応じて行われればよく、行われなくてもよい。
次に、化学強化処理後のガラス基板に第2研磨が施される。第2研磨は、主表面の鏡面研磨を目的とする。第2研磨においても、第1研磨に用いる両面研磨装置と同様の構成を有する両面研磨装置が用いられる。第2研磨処理では、第1研磨処理よりも、遊離砥粒の粒子サイズと研磨パッドの樹脂ポリッシャの硬度を小さくすることが好ましい。このようにすることで、ガラス基板の表面粗さを極めて小さくすることができる。
第2研磨処理は、必ずしも必須な処理ではないが、ガラス基板の主表面の表面凹凸のレベルをさらに良好なものとすることができる点で実施することが好ましい。この後、洗浄を行うことによって、磁気ディスク用ガラス基板となる。
なお、第2研磨処理後のガラス基板の表面粗さの算術平均粗さRaが0.15nm以下となるようにガラス基板が研磨されることが、表面粗さの小さい磁気ディスク用ガラス基板を作製する点で好ましい。
結晶化したガラス基板は、例えば、粉末X線回折法で得られた回折強度分布を用いて結晶化の有無を判定することができる。なお、結晶相の平均結晶粒径は10nm以下の結晶を析出させることが、ガラス基板の主表面の表面粗さを小さくして主表面を鏡面化させる点で好ましい。
結晶相は硬いため、研磨では加工し難い。平均結晶粒径が10nmを超えると、ガラス基板の主表面の研磨による加工時間が長くなり、また、研磨で取りきれない結晶相により表面粗さは無視できない大きさになる。また、結晶化処理後で、第2研磨処理前のガラス基板の表面粗さの算術平均粗さRaは1nm以下であることが、第2研磨処理で取代量を小さくすることができる点で好ましい。
結晶化されたガラス(以降、結晶化ガラスという)は、非晶質のガラスを加熱することでガラス内部に結晶を析出させた構成の材料であり、非晶質のガラスとは区別され得る。結晶化ガラスは、内部に分散する結晶により、非晶質のガラスでは得られない特性を発揮する。例えば、ビッカース硬度、ヤング率、破壊靱性等の機械的強度、耐エッチング特性、熱膨張係数等の熱的特性について、結晶化ガラスは、非晶質ガラスでは実現しえない特性を発揮する。勿論、結晶化ガラスは紛体を焼結した構成のセラミックスとは異なる特性を発揮する。結晶化ガラスは、セラミックスと比較して、空孔が極めて少なく、緻密な構成を有する。
本実施形態においては、前記結晶化処理後のガラス基板のヤング率としては、100GPa以上、より好ましくは120GPa以上であることが好ましい。こうすることで、抗折強度や耐衝撃性が高いガラス基板とすることができる。前記結晶化処理後のガラス基板の抗折強度は、耐衝撃性を向上させる観点から7kgf以上であることが好ましく、特に8kgf以上であることが好ましい。こうすることで、10000rpm以上の高速回転のHDD向けとして好適な磁気ディスク用ガラス基板とすることができる。
磁気ディスクは、磁気ディスク用ガラス基板を用いて以下のようにして得られる。
磁気ディスクは、例えば磁気ディスク用ガラス基板(以下、単に「基板」という。)の主表面上に、主表面に近いほうから順に、少なくとも付着層、下地層、磁性層(磁気記録層)、保護層、潤滑層が積層された構成になっている。
例えば基板を、真空引きを行った成膜装置内に導入し、DCマグネトロンスパッタリング法にてAr雰囲気中で、基板の主表面上に付着層から磁性層まで順次成膜する。付着層としては例えばCrTi、下地層としては例えばCrRuを用いることができる。磁性層としては、例えばCoPt系合金を用いることができる。また、L10規則構造のCoPt系合金やFePt系合金を形成して熱アシスト磁気記録用の磁性層とすることもできる。上記成膜後、例えばCVD法によりC2H4を用いて保護層を成膜し、続いて表面に窒素を導入する窒化処理を行うことにより、磁気記録媒体を形成することができる。その後、例えばPFPE(パーフルオロポリエーテル)をディップコート法により保護層上に塗布することにより、潤滑層を形成することができる。
作製された磁気ディスクは、好ましくは、DFH(Dynamic Flying Height)コントロール機構を搭載した磁気ヘッドと、磁気ディスクを固定するためのスピンドルとを備えた、磁気記録再生装置としての磁気ディスクドライブ装置(HDD(Hard Disk Drive))に組み込まれる。
本実施形態の磁気ディスク用ガラス基板の製造方法の効果を確認した。使用したガラスの組成は、下記の通りである。
[ガラスの組成]
質量%表示で、SiO2を65.08%、Al2O3を15.14%、Li2Oを3.61%、Na2Oを10.68%、K2Oを0.35%、MgOを0.99%、CaOを2.07%、ZrO2を1.98%、Fe2O3を0.10%、有する組成からなるアモルファスのアルミノシリケートガラスであり、ガラス転移温度が510℃である。
実施例、比較例の磁気ディスク用ガラス基板については、上記製造方法の各処理を順序通りに行うことで、内径が20mm、外径が65mm、厚さが0.8mmの公称2.5インチサイズの磁気ディスク用ガラス基板を作製した。このとき、形状加工では、ガラス素板を切断し、円形の内孔(内径:20mm)と円形の外形(外径:65mm)を備えたドーナツ状の円板状ガラス基板を得た。このガラス基板の外周端部および内周端部に対して、図2~図5に示した端面研削加工を施して、外周側の面取面および内周側の面取面を形成した。このとき、内周端面の研削では、α=5度とし、外径15mmの研削砥石を使用した。外周端面の研削では、α=5度とし、外径100mmの研削砥石を使用した。内周端面の研削、外周端面の研削共に、粒度#400の電着ダイヤモンド砥石、粒度#2000のレジンボンドダイヤモンド砥石を順に用いた。側壁面研削領域50t(図4参照)の幅は、1.0mmとした。
表1、表2に示したように、実施例、比較例の磁気ディスク用ガラス基板を作製するに当たって、研削砥石の溝の開口角が異なる。なお、表1は内周側の端面研削の場合を、表2は外周側の端面研削の場合を、それぞれ示している。
表1、表2の面取り角をΘA、ΘBは、端面研削加工直後の値である。
表1、表2の各実施例が示すように、外周端面および内周端面の研削では、砥石の開口角について、開口角θAを開口角θBよりも小さくすることで、端面研削後のガラス基板の一対の面取面の面取り角ΘA,ΘBが同一となったことがわかる。
Claims (6)
- 中心に円孔が形成され、側壁面および主表面と側壁面との間に形成された面取面とを有する円板状ガラス基板の端面に対して、回転する研削砥石を用いて端面研削処理を行う磁気ディスク用ガラス基板の製造方法であって、
上記端面研削処理は、研削砥石の回転軸を、基板の主表面と直交する軸に対して傾斜させて、ガラス基板の一対の面取面を同時に研削するものであり、
上記研削砥石は、ガラス基板の面取面を研削する一対の面取面研削領域を有する溝形状を有し、
上記一対の面取面研削領域は、
ガラス基板の中心と研削砥石の回転軸とを結ぶ直線上に位置するガラス基板と研削砥石の接点を基準として、研削砥石の回転方向の前側でガラス基板の面取面と接触する面取面研削領域(A)と、研削砥石の回転方向の後側でガラス基板の面取面と接触する面取面研削領域(B)とからなり、
面取面研削領域(A)の開口角は、面取面研削領域(B)の開口角よりも小さいことを特徴とする、
磁気ディスク用ガラス基板の製造方法。 - 上記研削砥石の溝形状は、ガラス基板の側壁面を研削する側壁面研削領域をさらに有し、
上記端面研削処理は、ガラス基板の側壁面と一対の面取面とを同時に研削することを特徴とする、
請求項1に記載された磁気ディスク用ガラス基板の製造方法。 - 上記磁気ディスク用ガラス基板の板厚が0.635mmより小さいことを特徴とする、
請求項1又は2に記載された磁気ディスク用ガラス基板の製造方法。 - 上記磁気ディスク用ガラス基板は結晶化ガラスであることを特徴とする、
請求項1~3のいずれかに記載された磁気ディスク用ガラス基板の製造方法。 - 請求項1から4のいずれかに記載された磁気ディスク用ガラス基板の製造方法によって作製された磁気ディスク用ガラス基板の主表面上に、磁性層を形成する処理を備えたことを特徴とする、
磁気ディスクの製造方法。 - 中心に円孔が形成され、側壁面および主表面と側壁面との間に形成された面取面とを有する円板状ガラス基板の端面に対する端面研削処理において回転して使用される研削砥石であって、
上記研削砥石は、円筒状又は円柱状の回転体からなり、当該回転体の周上に溝が形成されており、
上記溝は、上記回転体の回転軸を含む面による断面視において、ガラス基板の側壁面と接触する側壁面研削面と、ガラス基板の側壁面を挟んで一方の面取面と接触する面取面研削面(A)と、他方の面取面と接触する面取面研削面(B)とからなり、
面取面研削面(A)と面取面研削面(B)の、側壁面研削面からの開口角が異なることを特徴とする、研削砥石。
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JP2007165712A (ja) * | 2005-12-15 | 2007-06-28 | Shin Etsu Handotai Co Ltd | 半導体ウエーハの面取り部の加工方法及び砥石の溝形状の修正方法 |
JP2010005772A (ja) * | 2008-06-30 | 2010-01-14 | Hoya Corp | 磁気ディスク用ガラス基板の加工方法、磁気ディスク用ガラス基板の製造方法、及び磁気ディスク用ガラス基板、並びに磁気ディスクの製造方法 |
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JPH03251356A (ja) * | 1990-02-28 | 1991-11-08 | Toyota Motor Corp | 溝面取り加工方法 |
JP2007165712A (ja) * | 2005-12-15 | 2007-06-28 | Shin Etsu Handotai Co Ltd | 半導体ウエーハの面取り部の加工方法及び砥石の溝形状の修正方法 |
JP2010005772A (ja) * | 2008-06-30 | 2010-01-14 | Hoya Corp | 磁気ディスク用ガラス基板の加工方法、磁気ディスク用ガラス基板の製造方法、及び磁気ディスク用ガラス基板、並びに磁気ディスクの製造方法 |
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