JP2007090452A - Manufacturing method of glass substrate for magnetic disc and manufacturing method of magnetic disc - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a large amount of glass substrates for magnetic discs and magnetic discs having stable quality inexpensively by providing a manufacturing method of the glass substrate for the magnetic disc, which may simply polish the principal plane of the glass substrate to have a very smooth surface. <P>SOLUTION: In grinding using a planetary gear mechanism, a part of a glass disc 7 held on a carrier 13 is relatively moved to a lower surface plate 3 and an upper surface plate 4, and in that process, at least a part of the surface is passed on the outer peripheral side from the outer edges of the respective surface plates 3, 4. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a glass substrate for a magnetic disk used for a magnetic disk serving as a recording medium in an information recording apparatus such as a hard disk drive (HDD), and a method for manufacturing a magnetic disk using the glass substrate for a magnetic disk.

  In recent years, various information processing apparatuses have been proposed with the advancement of the information society, and information recording apparatuses such as hard disk drives (HDD) used in these information processing apparatuses have been proposed. In such an information recording apparatus, in order to reduce the size and performance of the information processing apparatus, an increase in information recording capacity and an increase in recording density are required.

  In a hard disk drive, in order to increase the information recording density, it is necessary to reduce so-called spacing loss, and the flying height (glide height) of the magnetic head that performs recording and reproduction on the magnetic disk as the recording medium Need to be reduced.

  When the flying height of the magnetic head is reduced, the magnetic disk rotates at a high speed during recording and reproduction, so that there is a high possibility that the magnetic head contacts the surface of the magnetic disk and is destroyed (crash). In order to prevent such destruction of the magnetic head, it is necessary to finish the main surface of the magnetic disk as a very smooth surface.

  In order to realize such smoothness of the main surface of the magnetic disk, a glass substrate is used as the disk substrate instead of the conventionally widely used aluminum substrate. This is because the glass substrate is superior in the flatness of the main surface and the substrate strength as compared with the aluminum substrate. As such a glass substrate, a chemically strengthened glass substrate or a crystallized glass substrate whose substrate strength is increased by crystallization is used in order to increase the substrate strength. Such a glass base sheet is manufactured by performing grinding (lapping) treatment and polishing treatment on the surface thereof.

  Incidentally, as a magnetic head in a hard disk drive, a magnetoresistive head using a magnetoresistive element (MR element) instead of a thin film head that has been widely used in the past in order to improve the signal intensity during recording and reproduction. (MR heads) and large magnetoresistive heads (GMR heads) have been widely used.

  In a magnetoresistive head using such a magnetoresistive effect element, if there are minute irregularities on the surface of the magnetic disk, a thermal asperity failure will occur, causing a malfunction in playback or failure in playback. May be possible. The cause of this thermal asperity failure is that the convex part formed on the surface of the magnetic disk by the foreign matter on the glass substrate causes adiabatic compression and adiabatic expansion of the air in the vicinity of the magnetoresistive head due to the high-speed rotation of the magnetic disk. The resistance type head generates heat and the resistance value of the magnetoresistive effect element fluctuates, and electromagnetic conversion is adversely affected. That is, such a thermal asperity failure can occur even when the magnetic head does not contact the magnetic disk. In order to prevent such a thermal asperity failure, the main surface of the magnetic disk needs to be finished to a very smooth surface free from foreign matter.

  For the purpose of finishing the main surface of such a disk substrate to be a smooth surface, the applicant of the present application previously described between the upper and lower surface plates to which a polishing cloth of a soft polisher was attached as described in Patent Document 1. In a method for manufacturing a glass substrate for a magnetic disk, which has a polishing step in which a glass disk is set on the surface and the polishing cloth and the glass disk are relatively slid using a planetary gear mechanism to polish both main surfaces of the glass disk. A method for appropriately selecting the surface roughness of the polishing cloth is proposed. Such a planetary gear mechanism is also used for grinding.

  In this planetary gear mechanism, the glass disk is sandwiched between the upper and lower surface plates, and the plate thickness is reduced while performing relative movement with respect to the surface plates. In this process, the glass disk is reduced to a predetermined plate thickness and the surface is finished to a predetermined flat surface and a smooth surface.

JP 2000-288919 A

  Incidentally, as described above, the planetary gear mechanism is used to slide the upper and lower surface plates, or the sliding contact surfaces of a pair of upper and lower polishing cloths against the two main surface portions of the glass disk, When polishing is performed, the surface of the surface plate or the polishing cloth is gradually worn away, and the parallelism between the upper and lower surface plates or the upper and lower polishing cloths is distorted. In particular, in the grinding process, since the amount of reduction in the thickness of the glass substrate is large, the wear amount of the surface plate is also large. When the grinding or polishing process is continued using such a surface plate or polishing cloth, the shape of the glass disk after the grinding or polishing process is also distorted.

By the way, in recent years, it has become possible to realize an information recording surface density of 60 gigabits per square inch (60 Gbit / inch ² ) or more in a magnetic disk of a hard disk drive. Since such high information recording surface density can be realized, the hard disk drive can be downsized per information recording capacity. Therefore, the hard disk drive is used not only for mounting on a conventional computer device (personal computer or server) but also for a so-called MP3 player, a mobile phone device, a car navigation system, a PDA (Personal). Digital Assistance (personal digital assistants) and other portable devices and in-vehicle devices.

  In applications such as mounting on portable devices and in-vehicle devices, the hard disk drive housing has been reduced in size and weight to be carried (carried) or used in an on-vehicle environment. The magnetic disk is also reduced in diameter to, for example, 1 inch or less. As for the use of such a miniaturized magnetic disk, the market has rapidly expanded and mass production of more than 100 million discs has been required annually, and there is a strong demand for cost reduction and mass production. It is necessary to supply a large amount of disks at a low price.

  That is, the magnetic disk glass substrate used for such a magnetic disk is not limited to having excellent shape accuracy for each individual product, and even when a glass substrate for a magnetic disk of the same specification is mass-produced. Therefore, it is necessary to construct a stable production process that does not cause variation in quality by preventing distortion of the shape of the glass disk after grinding or polishing.

  Recently, a load / unload type (LUL type) hard disk drive has been put into practical use for the purpose of expanding the information recording / reproducing area on the surface of the magnetic disk or reducing the flying height of the magnetic head. ing. For example, in the LUL type hard disk drive, the flying height of the magnetic head can be reduced to 8 nm or less. In this case, the surface shape of the magnetic disk must be finished as a smooth surface so precise that it cannot be compared with a silicon wafer or an optical disk.

  In the LUL type hard disk drive, when the drive is stopped, the magnetic head is retracted outside the magnetic disk. When starting the drive, the magnetic head that has been retracted outside the magnetic disk is slid onto the main surface of the magnetic disk via the outer peripheral end (or inner peripheral end) of the magnetic disk. Later, information is recorded and reproduced. When stopping the activated hard disk drive, the magnetic head on the main surface of the magnetic disk is retracted to the outside of the magnetic disk via the outer peripheral edge (or inner peripheral edge) of the magnetic disk. Let The operation of reciprocating the magnetic head over the inside and outside of the magnetic disk through the end of the magnetic disk in this way is called a load / unload operation.

  In the magnetic disk for the LUL system, it is necessary to prevent a failure such as a crash even if the magnetic head frequently repeats the load / unload operation via the end of the magnetic disk. Therefore, in the LUL type magnetic disk, and in turn, the glass substrate for the magnetic disk, it is an important problem to determine the shape of the end portion.

  Therefore, the present invention is proposed in view of the above circumstances, and the first object thereof is to grind or polish the main surface of the glass disk to a very smooth surface easily and quickly. An object of the present invention is to provide a glass substrate for a magnetic disk and a magnetic disk having a stable quality in a large amount at a low cost by providing a method for manufacturing a glass substrate for a magnetic disk.

  The second object of the present invention is to stably grind or polish both main surface portions of the magnetic disk glass substrate to a very smooth surface even when the diameter of the magnetic disk glass substrate is reduced. By providing a method for manufacturing a magnetic disk glass substrate that can be used, the thermal asperity failure and head crash in a magnetic disk using the magnetic disk glass substrate can be prevented, and the information recording surface density of the magnetic disk can be reduced. It is to contribute to higher density.

  A third object of the present invention is to prevent the occurrence of head crashes and thermal asperity failures in a hard disk drive even when the flying height of the magnetic head is less than 8 nm.

  A fourth object of the present invention is to provide a glass substrate for a magnetic disk having a particularly preferable end shape as a glass substrate for a magnetic disk for producing a magnetic disk of the LUL method. It is to be able to provide a large amount of magnetic disks at low cost.

  As a result of researches to solve the above problems, the present inventor has made at least a part of the locus of the glass disk in the double-sided grinding using the planetary gear mechanism in the manufacturing process of the glass substrate for magnetic disks or the double-sided polishing process. However, it has been found that the above problem can be solved by performing so-called “overhang rotation” in which the outer surface of the surface plate is protruded beyond the outer edge of the surface plate.

  That is, the present invention includes any one of the following configurations.

[Configuration 1]
Using a pair of surface plates having sliding surfaces, the sliding surfaces of these surface plates are slid relative to both surfaces of the glass disk to grind or polish the surface of the glass disk. A method for manufacturing a glass substrate for a magnetic disk, comprising: a lower surface plate and a sun gear provided at the center of the lower surface plate and the lower side in at least one of a grinding step and a polishing step An inner gear provided on the outer edge of the surface plate, a disk-shaped carrier having a tooth portion meshing with the sun gear and the inner gear on the outer peripheral portion and holding a glass disk, and an upper surface plate facing the lower surface plate The carrier is used to hold the glass disk, the teeth on the outer periphery of the carrier are engaged with the sun gear and the internal gear, and at least one of the sun gear and the internal gear is driven to rotate. A process of relatively sliding the held glass disk is performed, and at least a part of the glass disk held by the carrier is in the process of relative movement with respect to the lower surface plate and the upper surface plate. The outer peripheral side is allowed to pass through the outer edge portions of the lower surface plate and the upper surface plate.

[Configuration 2]
A method for manufacturing a magnetic disk, wherein at least a magnetic layer is formed on a main surface of a glass substrate for a magnetic disk manufactured by the method for manufacturing a glass substrate for a magnetic disk having Configuration 1. .

  In the method for manufacturing a glass substrate for a magnetic disk according to the present invention having Configuration 1, at least in either the grinding process or the polishing process, the upper and lower surface plates and the glass disk are relatively moved using a planetary gear mechanism. In performing the sliding process, at least a part of the glass disk held by the carrier is in the process of relative movement with respect to the lower surface plate and the upper surface plate. Since the outer peripheral portion is passed through the outer edge portion, uneven wear at the outer peripheral portion of each surface plate is prevented, and the parallelism between these surface plates is prevented from being distorted.

  Therefore, in this method of manufacturing a glass substrate for a magnetic disk, the main surface of the glass disk is easily and well ground while preventing distortion of the shape of the glass disk after grinding or polishing. Or it can be polished and finished to a very smooth surface. That is, in this method for manufacturing a magnetic disk glass substrate, a stable quality glass substrate for a magnetic disk can be manufactured and supplied in large quantities.

  In the method for manufacturing a magnetic disk according to the present invention having the configuration 2, at least the magnetic layer is formed on the main surface of the glass substrate for magnetic disk manufactured by the method for manufacturing the glass substrate for magnetic disk described above. It is possible to manufacture a magnetic disk in which problems due to waviness of the main surface of the disk glass substrate, that is, head crashes and thermal asperity failures are reliably prevented.

  That is, the present invention provides stable quality by providing a method for producing a glass substrate for a magnetic disk that can easily or quickly grind or polish the main surface of a glass disk to an extremely smooth surface. The glass substrate for magnetic disk and the magnetic disk can be provided in large quantities at a low cost.

  Further, the present invention provides a glass substrate for magnetic disk that can stably grind or polish the main surface of the glass substrate for magnetic disk to a very smooth surface even when the diameter of the glass substrate for magnetic disk is reduced. By providing this manufacturing method, it is possible to prevent thermal asperity failure and head crash in a magnetic disk using the magnetic disk glass substrate, thereby contributing to increase in the information recording surface density in the magnetic disk. It can be done.

  Furthermore, the present invention is capable of stably grinding or polishing both main surface portions of the magnetic disk glass substrate to a very smooth surface even when the diameter of the magnetic disk glass substrate is reduced. Even when the flying height of the head is less than 8 nm, it is possible to prevent the occurrence of a head crash or thermal asperity failure.

  The present invention provides a glass substrate for a magnetic disk having a particularly preferable end shape as a glass substrate for a magnetic disk for producing an LUL type magnetic disk, and makes a stable quality LUL type magnetic disk inexpensive. It can be provided in large quantities.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  The method for manufacturing a glass substrate for magnetic disk according to the present invention is for manufacturing a glass substrate for magnetic disk used as a disk substrate of a magnetic disk mounted on, for example, a hard disk drive (HDD). This magnetic disk is a recording medium capable of performing high-density information signal recording and reproduction by an in-plane magnetic recording system or a perpendicular magnetic recording system.

  FIG. 1 is a perspective view showing a configuration of a glass substrate for magnetic disk manufactured by the method for manufacturing a glass substrate for magnetic disk according to the present invention.

  As shown in FIG. 1, the glass substrate for a magnetic disk has an outer diameter of 15 to 30 mm, an inner diameter of 5 to 12 mm, and a plate thickness of 0.35 to 0.5 mm. Predetermined diameters such as “disk” (inner diameter 6 mm, outer diameter 21.6 mm, plate thickness 0.381 mm), “1.0 inch type magnetic disk” (inner diameter 7 mm, outer diameter 27.4 mm, plate thickness 0.381 mm), etc. It is manufactured as a magnetic disk. Further, it may be manufactured as a magnetic disk such as a “2.5 inch magnetic disk” or a “3.5 inch magnetic disk”. Here, the “inner diameter” is the inner diameter of the center hole 2 of the glass substrate 1 for magnetic disks.

  Since the glass substrate 1 for magnetic disks is made of glass, it can realize excellent smoothness by mirror polishing, has high hardness, and high rigidity, and thus has excellent impact resistance. In particular, a magnetic disk used for a hard disk drive mounted on a portable (carried) or in-vehicle information device is required to have high impact resistance. Usefulness is high. The surface roughness of the main surface of the glass substrate is preferably 0.1 nm to 0.7 in terms of Ra.

  Although glass is a brittle material, the fracture strength can be improved by a strengthening treatment such as chemical strengthening or air cooling strengthening or by means of crystallization. A preferable example of the material for the glass substrate 1 for magnetic disks is aluminosilicate glass. This is because the aluminosilicate glass can realize an excellent smooth mirror surface and can increase the breaking strength by, for example, chemical strengthening.

The aluminosilicate _{glass, SiO} 2: 62 to 75 _wt%, Al _{2 O} 3: 5 to 15 wt%, _Li 2 O: 4 to 10 wt%, _Na 2 O: 4 to 12 wt%, _ZrO 2: 5 0.5 to 15 wt% as a main component, the weight ratio of Na ₂ O to ZrO ₂ is 0.5 to 2.0, and the weight ratio of Al ₂ O ₃ to ZrO ₂ is 0.4 to 2 A glass for chemical strengthening of .5 is preferred.

Further, in such a glass substrate, in order to eliminate the protrusion of the glass substrate surface undissolved product of ZrO ₂ occurs causes a SiO ₂ 57 to 74 mol%, a ZrO ₂ 0 to 2.8 mol%, Al ₂ It is preferable to use a chemically strengthening glass containing ₃ to 15 mol% of O ₃ , 7 to 16 mol% of LiO ₂ and 4 to 14 mol% of Na ₂ O. The aluminosilicate glass having such a composition has an increased bending strength, a deep compressive stress layer, and an excellent Knoop hardness when chemically strengthened.

  In addition, the material which comprises the glass substrate 1 for magnetic discs manufactured in this invention is not necessarily limited to what was mentioned above. That is, as a material of the glass substrate 1 for magnetic disks, in addition to the aluminosilicate glass described above, for example, soda lime glass, soda aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, quartz glass, chain silicate glass, or And glass ceramics such as crystallized glass.

  In the present invention, it is preferable that the magnetic disk glass substrate 1 has chamfered ridges on both sides of the end surface. This is because the glass substrate 1 for a magnetic disk has a high crushing strength due to the chamfered edge portion of the end surface.

  Hereinafter, the manufacturing method of the glass substrate for magnetic disks which concerns on this invention is demonstrated in order of a process.

(1) Shape processing process In the manufacturing method of the glass substrate for magnetic discs concerning this invention, a disk-shaped glass disc is formed first. As described above, the glass disk is preferably made of aluminosilicate glass. The glass disk is formed to have a diameter slightly larger than the diameter of the magnetic disk glass substrate 1 to be manufactured, for example, from a molten glass base material by a pressing method or the like.

  Next, a center hole of a predetermined size is formed at the center of the glass disk. This central hole is the central hole 2 in the magnetic disk glass substrate 1 and is formed as a hole having an inner diameter slightly smaller than the inner diameter of the central hole 2. Further, in this step, chamfering is performed on the outer peripheral side end surface portion and the inner peripheral side end surface portion of the glass disk.

(2) Grinding (lapping) step In this step, the shape of the glass disk is adjusted and the main surface is ground. In grinding processing, processing is performed using a double-sided grinding device and alumina abrasive grains, and the dimensional accuracy and shape accuracy of the glass disk are set to predetermined values.

  FIG. 2 is a perspective view showing a configuration of a planetary gear mechanism serving as a double-side grinding apparatus.

  In this grinding process, as shown in FIG. 2, a planetary gear mechanism serving as a double-side grinding apparatus is used. This planetary gear mechanism has a pair of upper and lower surface plates 3, 4 as shown in FIG. These surface plates 3 and 4 are formed in a flat plate shape from spheroidal graphite-containing cast iron. A plurality of grooves 9 for supplying an abrasive is formed in a lattice shape on the surface portions of the surface plates 3 and 4. In this grinding step, the slidable contact surface of the surface plate may be composed of a material containing spherical graphite, or the material forming the slidable contact surface of the surface plate may be a material containing diamond abrasive grains. Good.

  In this double-side grinding apparatus, a glass disk 7 is installed between the surface plates 3 and 4, and either or both of the surface plates 3 and 4 are moved to operate the glass disk 7 and the surface plates. Both main surfaces of the glass disk 7 can be ground by bringing 3 and 4 into sliding contact with each other.

  That is, the planetary gear mechanism includes a lower surface plate 3, a sun gear 11 provided at the center of the lower surface plate 3, an internal gear 12 provided at the outer edge of the lower surface plate 3, And a disk-shaped carrier 13 for holding the glass disk 7. The carrier 13 has a tooth portion 14 that meshes with the sun gear 11 and the internal gear 12 on the outer peripheral portion. The carrier 13 is formed in a disk shape that is slightly thinner than the glass disk 7, and has at least one circular through-hole portion 15 having an inner diameter slightly larger than the outer diameter of the glass disk 7. The carrier 13 holds the glass disk 7 by positioning the glass disk 7 in the through hole portion 15. The planetary gear mechanism has an upper surface plate 4 that faces the lower surface plate 3.

  In this planetary gear mechanism, the tooth portion 14 on the outer peripheral portion of the carrier 13 is engaged with the sun gear 11 and the internal gear 12 with the glass disk 7 held in the through-hole portion 15 of the carrier 13. Then, by sandwiching the carrier 13 and the glass disk 7 by the respective surface plates 3, 4, the glass disk 7 is held at the main surfaces on both sides by the surface plates 3, 4, and the peripheral portion is a through hole of the carrier 13. It becomes the state hold | maintained at the inner edge part of the part 15.

  And in this planetary gear mechanism, while supplying a grinding fluid between each surface plate 3 and 4 and the main surface of the glass disk 7, either or both of the sun gear 11 and the internal gear 12 are rotationally driven. By doing so, each surface plate 3 and 4 and the main surface of the glass disc 7 are slid relatively, and the main surface of this glass disc 7 is ground. At this time, it is preferable that both or one of the surface plates 3 and 4 is rotationally driven.

  FIG. 3 is a side view showing the positional relationship between the glass disk and each surface plate in the planetary gear mechanism.

  In this grinding process, a part of the glass disk 7 held by the carrier 13 is at least partially in the process of relative movement with respect to the lower surface plate 3 and the upper surface plate 4 as shown in FIG. The so-called “overhang rotation” is performed in which the outer peripheral side of the lower surface plate 3 and the upper surface plate 4 is passed through the outer peripheral side.

(3) End surface partial mirror polishing step Next, the end surfaces of the inner and outer circumferences of the glass disk are polished and mirror-finished. Polishing in this step is performed with a brush or the like using an abrasive. The abrasive grains contained in the abrasive used in this step can be used without particular limitation as long as they are abrasive grains that exhibit a polishing ability with respect to a glass disk. Examples thereof include cerium oxide (CeO ₂ ) abrasive grains, colloidal silica abrasive grains, alumina abrasive grains, and diamond abrasive grains, and cerium oxide abrasive grains are particularly preferable. The particle size of the abrasive grains can be selected as appropriate, but is preferably about 0.5 μm to 3 μm, for example. In addition, it is preferable that the abrasive is used as a slurry by adding a liquid such as water (pure water) to the abrasive containing abrasive grains.

  In addition, this end surface partial mirror polishing step is performed before the first polishing step, which will be described later, or in the second polishing, in order to avoid scratches or the like on the main surface of the glass substrate when end surfaces are polished by overlapping the glass substrates. It is preferable to carry out before and after the process. By this end surface partial mirror polishing step, the surface roughness of the inner and outer peripheral end surfaces of the glass disk is a mirror surface with Ra of 0.1 μm or less and Rmax of 1 μm or less.

(4) 1st grinding | polishing process Next, a 1st grinding | polishing process is given as a main surface grinding | polishing process. This first polishing step is mainly intended to remove scratches and distortions remaining on the main surface in the above-described grinding step. This step is performed using a double-side polishing apparatus and the polishing cloth (a polishing pad of a hard resin polisher) according to the present invention.

  As the double-side polishing apparatus, the planetary gear mechanism described above is used. In the first polishing step, a pair of polishing cloths (a polishing pad of a hard resin polisher) is applied to the main surface portions of the upper and lower surface plates 3 and 4 facing each other. In this double-side polishing apparatus, a glass disk 7 is installed between polishing cloths attached to the surface plates 3 and 4, and either one or both of the surface plates 3 and 4 are moved to operate glass. The disk 7 and the surface plates 3 and 4 are brought into sliding contact with each other, and both main surfaces of the glass disk 7 are polished. In the first polishing step, the glass disk can be so-called “overhang rotated” as in the above-described grinding step.

  As the polishing cloth, it is possible to use a polishing pad formed into a circular shape by impregnating a non-woven fiber base material with a polyurethane resin and wet coagulating it. The hardness of the polishing cloth is preferably about 60 to 80 in terms of Asker A hardness. As this polishing cloth, one having a groove which becomes a flow path of the polishing liquid is formed on the sliding surface with respect to the glass disk.

As the abrasive grains contained in the abrasive used in the first polishing process, any abrasive grains capable of polishing the glass disk 7 can be used without particular limitation. Examples thereof include cerium oxide (CeO ₂ ) abrasive grains, colloidal silica abrasive grains, alumina abrasive grains, and diamond abrasive grains. Among them, cerium oxide abrasive grains are preferable.

  The particle size of the abrasive grains can be selected as appropriate, but is preferably about 1.5 μm to 5 μm, for example.

  In this planetary gear mechanism, the abrasive is efficiently supplied to the entire polishing area of the polishing cloth, using the inside of the groove provided in the polishing cloth as a flow path. Further, in this planetary gear mechanism, the polishing allowance can be adjusted by adjusting the pressure at which the surface plates 3 and 4 hold the glass disk 7. In this first polishing step, it is desirable to increase the polishing allowance and increase the polishing efficiency as compared to the second polishing step described later. By using the planetary gear mechanism, it is possible to efficiently polish a large number of glass disks 7 at a time.

  When performing the first polishing using this planetary gear mechanism, the glass disk 7 is moved relative to the polishing cloth in a state where both main surface portions are sandwiched between the polishing cloths. In this planetary gear mechanism, the movement trajectory of the glass disk 7 with respect to the polishing cloth is a cycloid curve or a curve obtained by combining a cycloid curve and an arc. This movement trajectory changes depending on the ratio of the rotational direction and rotational speed of the sun gear 11, the internal gear 12, and the surface plates 3 and 4, and the ratio of the diameters of the sun gear 11 and the carrier 13.

  Considering the polishing efficiency and the uniformity of the polishing allowance, by making the rotational speeds of both the surface plates 3 and 4 or either one sufficiently faster than the rotational speeds of the sun gear 11 and the internal gear 12, It is preferable that the movement trajectory of the glass disk 7 with respect to the polishing cloth is dominated by the circumferential component of the polishing cloth.

(5) Second Polishing Step Next, a second polishing step is performed as a mirror polishing step for the main surface. The purpose of this second polishing step is to finish the main surface into a mirror surface. Similar to the first polishing step, the second polishing step can be performed using a double-side polishing apparatus and a polishing cloth (soft foam resin polisher), and is also performed using the planetary gear mechanism as described above. You can also

  In the second polishing step, a polishing cloth (soft foam resin polisher) having a flat sliding surface with respect to the glass disk, that is, a state having no groove is used. Further, the polishing cloth in the second polishing process is made of a soft material as compared with the polishing cloth used in the first polishing process.

  Accordingly, in this second polishing step, the polishing allowance is small and higher-level mirror finishing is performed as compared with the first polishing step described above.

  As a polishing agent used in the second polishing step, it is preferable to use fine cerium oxide abrasive grains as compared with the cerium oxide abrasive grains used in the first polishing step. The particle diameter of the cerium oxide abrasive grains can be set to, for example, about 0.1 μm to 1 μm.

(6) 1st washing process The glass substrate which finished the 2nd polishing process, neutral detergent (1), pure water (1), neutral detergent (2), pure water (2), IPA (isopropyl alcohol), Immerse in each washing tank of IPA (steam drying) and wash. In addition, it is preferable to apply an ultrasonic wave to each washing tank.

(7) Chemical Strengthening Step Next, chemical strengthening is performed on the glass disk after the above-described grinding and polishing steps. For chemical strengthening, for example, a chemical strengthening solution prepared by mixing potassium nitrate (60%) and sodium nitrate (40%) is prepared, and this chemical strengthening solution is heated to about 400 ° C and preheated to 300 ° C. The glass disk is immersed for about 3 hours. In this immersion, in order to chemically strengthen the entire surface of the glass disk, it is preferable to carry out in a state in which the plurality of glass disks are housed in a holder so as to be held by the end surfaces.

  Thus, by immersing in a chemical strengthening solution, the lithium ion and sodium ion of a glass disk surface layer are each substituted by the sodium ion and potassium ion in a chemical strengthening solution, and a glass disk is strengthened.

(8) Second cleaning step The glass disk that has been subjected to the chemical strengthening treatment is cleaned by immersing it in concentrated sulfuric acid heated to about 40 ° C. Further, the glass disk that has been cleaned with sulfuric acid is purified with pure water (1) Then, it is cleaned by immersing in pure water (2), IPA (isopropyl alcohol), and IPA (steam-dried) cleaning baths. In addition, it is preferable to apply an ultrasonic wave to each washing tank.

  In addition, the material which comprises the glass substrate used in this invention is not necessarily limited to what was mentioned above. That is, as the material of the glass substrate, in addition to the aluminosilicate glass described above, for example, soda lime glass, soda aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, quartz glass, chain silicate glass, or crystallized glass Examples thereof include glass ceramics.

(9) Manufacturing process of magnetic disk By using the glass substrate for magnetic disk thus prepared, at least a magnetic layer is formed on the main surface portion of the glass substrate for magnetic disk. It is possible to configure a magnetic disk in which the parity failure is prevented.

  As the magnetic layer, a Co—Pt alloy magnetic layer having a high anisotropic magnetic field (Hk) is preferable. In addition, an underlayer may be appropriately formed between the magnetic disk glass substrate and the magnetic layer from the viewpoint of achieving crystal orientation of the magnetic layer and making the grains uniform and fine. As a method for forming these underlayer and magnetic layer, for example, a DC magnetron sputtering method can be used.

  Moreover, it is preferable to provide a protective layer for protecting the magnetic layer on the magnetic layer. Examples of the material for the protective layer include a carbon-based protective layer. As the carbon-based protective layer, hydrogenated carbon or nitrogenated carbon can be used. For the formation of this protective layer, plasma CVD or DC magnetron sputtering can be used.

  Furthermore, it is preferable to form a lubricating layer for reducing the impact from the magnetic head on the protective layer. An example of the lubricating layer is a perfluoropolyether lubricating layer. In particular, an alcohol-modified perfluoropolyether lubricating layer having a hydroxyl group having excellent affinity with the protective layer is preferable. This lubricating layer can be formed using a dip method.

  Examples of the present invention will be described in detail below.

[Example 1]
In Example 1, a magnetic disk glass substrate was manufactured through the following steps.

(1) Shape processing step The molten aluminosilicate glass was molded into a disk shape by press working to obtain a glass disk. As the aluminosilicate glass, SiO ₂ is 57 to 74 mol%, ZrO ₂ is 0 to 2.8 mol%, Al ₂ O ₃ is 3 to 15 mol%, LiO ₂ is 7 to 16 mol%, and Na ₂ O is 4 to 4%. A chemically strengthened glass containing 14 mol% as a main component was used.

  Next, a circular hole was formed at the center of the glass disk by grinding with a grindstone, and predetermined chamfering was performed on the outer peripheral side end surface and the inner peripheral side end surface.

(2) Grinding process Next, the main surface of the obtained glass disk was ground. In the grinding process, a planetary gear mechanism was used as a double-side grinding apparatus, and the grinding process was performed using a grinding liquid containing alumina abrasive grains, and the dimensional accuracy and shape accuracy of the glass disk were set to be predetermined. The upper and lower surface plates of the planetary gear mechanism were made of cast iron containing spheroidal graphite.

  In this grinding step, the glass disk held at the outer peripheral side position of the carrier in the planetary gear mechanism moves a part of the surface of the glass disk to the lower side in the process of relative movement with respect to the lower surface plate and the upper surface plate. The so-called “overhang rotation” is performed in which the outer peripheral side of the surface plate and the upper surface plate is passed through the outer peripheral side.

  The obtained glass disk had an inner diameter of 20 mm, an outer diameter of 65 mm, a plate thickness of 0.635 mm, and was confirmed to be a predetermined size of a glass substrate for a 2.5 inch magnetic disk.

  When the surface shape of the glass disk was observed, the surface roughness of the main surface was about 2 μm in Rmax and about 0.3 μm in Ra. When the surface roughness of the end face was observed, both the side surface portion and the chamfered surface were 14 μm in Rmax and 0.5 μm in Ra.

(3) End surface partial mirror polishing step First, the outer peripheral side end surface of the glass disk was subjected to mirror polishing by a brush polishing method. At this time, slurry (free abrasive grains) containing cerium oxide abrasive grains was used as the abrasive grains. Next, the inner peripheral side end face was also subjected to mirror polishing by a brush polishing method. And the glass disk which finished the end surface partial mirror polishing was washed with water.

(4) 1st grinding | polishing process Next, the 1st grinding | polishing process was performed as a main surface grinding | polishing process. In the first polishing step, main surface polishing was performed by a planetary gear mechanism using a polishing cloth (a polishing pad of a hard resin polisher). As the abrasive, cerium oxide abrasive grains were used.

  The glass substrate after the first polishing step was cleaned by sequentially immersing it in each cleaning tank of pure water (1), neutral detergent, pure water, IPA (isopropyl alcohol), and IPA (steam drying).

(5) Second Polishing Step Next, a second polishing step was performed as a mirror polishing step for the main surface. In this second polishing step, mirror polishing of the main surface was performed by a planetary gear mechanism using a polishing cloth (soft foam resin polisher). As the polishing agent, fine cerium oxide abrasive grains were used as compared with the cerium oxide abrasive grains used in the first polishing step.

(6) 1st washing process The glass substrate which finished the 2nd polishing process, neutral detergent (1), pure water (1), neutral detergent (2), pure water (2), IPA (isopropyl alcohol), It was immersed in each washing tank of IPA (steam drying) in order and washed. In addition, ultrasonic waves were applied to each cleaning tank.

(7) Chemical strengthening process Next, the glass substrate which finished the above-mentioned grinding and polishing process was chemically strengthened. For chemical strengthening, a chemically strengthened solution prepared by mixing potassium nitrate (60%) and sodium nitrate (40%) is prepared, and this chemically strengthened solution is heated to 400 ° C and preheated to 300 ° C. Was immersed for about 3 hours. In this immersion, in order to chemically strengthen the entire surface of the glass substrate, the plurality of glass substrates were stored in a holder so as to be held by the end surfaces.

  Thus, by immersing in the chemical strengthening solution, the lithium ions and sodium ions on the surface of the glass substrate are replaced with sodium ions and potassium ions in the chemical strengthening solution, respectively, and the glass substrate is strengthened.

  The thickness of the compressive stress layer formed on the surface layer of the glass substrate was about 100 to 200 μm.

  The glass substrate that had been chemically strengthened was immersed in a 20 ° C. water bath for rapid cooling and maintained for about 10 minutes.

(8) 2nd washing | cleaning process The glass substrate which finished the chemical strengthening process was immersed in the concentrated sulfuric acid heated to about 40 degreeC, and was wash | cleaned. Furthermore, the glass substrate that had been subjected to the sulfuric acid cleaning was sequentially immersed in each cleaning tank of pure water, pure water, IPA (isopropyl alcohol), and IPA (steam drying) and cleaned. In addition, ultrasonic waves were applied to each cleaning tank.

  The surface roughness of the inner peripheral side end surface of the circular hole of the magnetic disk glass substrate obtained through the above-described steps was Rmax 0.4 μm and Ra 0.04 μm on the chamfered surface, and Rmax 0.4 μm and Ra 0.05 μm on the side surface. It was. The surface roughness Ra at the outer peripheral end surface was 0.04 μm at the chamfered surface and 0.07 μm at the side surface portion. As described above, it was confirmed that the inner peripheral side end face was finished in a mirror surface like the outer peripheral side end face.

  Further, the surface roughness Ra of the main surface portion of the glass substrate was 0.5 nm (measured by AFM). When the end surface was observed with an electron microscope (4000 times), the side surface and the chamfered surface were in a mirror state. Further, no foreign matter or cracks were observed on the side surface and the chamfered surface, which are the inner peripheral side end faces of the circular holes, and no foreign matter or particles causing thermal asperity were found on the surface of the glass substrate. Furthermore, when the bending strength was measured using a bending strength tester (Shimadzu Autograph DDS-2000), it was 12 to 20 kg.

(9) Film formation process Next, the magnetic disk was manufactured through the following processes.

  On both main surfaces of the glass substrate for magnetic disk obtained as described above, an Al—Ru alloy first underlayer, a Cr—Mo alloy second underlayer, Co— A Cr—Pt—B alloy magnetic layer and a hydrogenated carbon protective layer were sequentially formed. Next, an alcohol-modified perfluoropolyether lubricating layer was formed by dipping. In this way, a magnetic disk was obtained.

[Comparative example]
In this comparative example, in the grinding process, all the glass disks held by the carrier in the planetary gear mechanism are moved by the lower surface plate and the upper surface plate in the process of relative movement with respect to the lower surface plate and the upper surface plate. In order not to protrude beyond the outer edge, the so-called “overhang rotation” was not performed.

  And about the other process, it carried out similarly to the above-mentioned Example 1, and created the glass substrate for magnetic discs. Further, a magnetic disk was prepared by the same process as in Example 1 using the magnetic disk glass substrate.

[Contrast between each example and each comparative example]
(Comparison as glass substrate for magnetic disk)
As shown in the following [Table 1], the shape of the main surface portion of the large number of glass substrates for magnetic disks prepared by each example and the large number of glass substrates for magnetic disks prepared by the comparative example. The data were compared.

In [Table 1], the process capability index Cp for the end shape of the glass substrate for magnetic disks is a process capability index for the dub-off value, which is a standard for the end shape. The dub-off value is a straight line connecting the surface of the glass substrate at 30.4 mm from the center of the glass substrate for magnetic disk and the surface of the glass substrate at 31.9 mm from the center, and the shape line of the glass substrate surface in the meantime. It is a numerical value indicating the maximum deviation distance, and the default value is within ± 25 nm. The process capability index Cp is based on the assumption that the distribution of the dub-off value is a normal distribution. The variation (standard deviation) is σ, the upper limit (+25 nm) of the standard value is S _U , and the lower limit (−25 nm) of the standard value. ) Is a value expressed as follows, when S _L is set.
Cp = (S _U −S _L ) / 6σ

  In industrial production, the process capability index Cp is required to be 1.33 or more, and less than 1.67 is sufficient. Therefore, it is confirmed that the glass substrate for magnetic disk of the example has a sufficiently low defect rate in industrial production, while the glass substrate for magnetic disk of the comparative example has a defect rate that is too high in industrial production. confirmed.

  Moreover, the surface roughness of the glass substrate for magnetic disks of an Example and the glass substrate for magnetic disks of a comparative example was compared. The measurement was performed on a predetermined region on the main surface of the glass substrate (a rectangular minute region having a length of 5 μm and a width of 5 μm in an annular region serving as a recording region) using an atomic microscope. As a result, both the glass substrate of each example and the glass substrate of the comparative example had the same surface roughness (surface roughness Ra was about 0.5 nm).

(Comparison as a magnetic disk)
About the magnetic disk obtained by the Example, it confirmed that the defect did not generate | occur | produce in films | membranes, such as a magnetic layer, by the foreign material. In addition, when the glide test was performed, no hit (the head bited against the protrusion on the surface of the magnetic disk) or crash (the head collided with the protrusion on the surface of the magnetic disk) was not recognized. Furthermore, when a reproduction test was conducted with a magnetoresistive head, no malfunction of reproduction due to thermal asperity failure was found.

  In addition, it was confirmed that the magnetic disk obtained by the comparative example had no defects in the film such as the magnetic layer due to the foreign matter.

  Next, a load / unload (LUL) durability test was performed on the magnetic disks obtained in the examples and comparative examples. That is, the obtained magnetic disk was mounted on a hard disk drive, and the load / unload operation was repeated continuously. As a result, it was confirmed that the load and unload durability of the examples can be withstood for 600,000 times or more of load / unload operations in 100 out of 100 units, and the durability is sufficient. It was.

  On the other hand, as for the comparative example, in 45 out of 100 units, it was confirmed that a crash failure occurred in the load / unload operation less than 600,000 times, and sufficient durability was not realized.

  Therefore, it was confirmed that the present invention is particularly suitable as a magnetic disk mounted on a hard disk drive that is recorded / reproduced by the load / unload (LUL) method, or a glass substrate for the magnetic disk. Further, in a load / unload type hard disk drive, it is necessary to use a magnetic disk having a flat and smooth surface as compared with a contact start / stop (CSS) type hard disk drive. Since the magnetic disk having a touchdown height of 4 nm or less can be used, it can be preferably mounted on a load / unload type hard disk drive.

It is a perspective view which shows the structure of the glass substrate for magnetic discs manufactured by the manufacturing method of the glass substrate for magnetic discs which concerns on this invention. It is a perspective view which shows the structure of the planetary gear mechanism used as the double-sided grinding apparatus used in the manufacturing method of the said glass substrate for magnetic discs. It is a side view which shows the positional relationship of the glass disk and each surface plate in the planetary gear mechanism used in the manufacturing method of the said glass substrate for magnetic discs.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass substrate for magnetic discs 2 Center hole 3, 4 Surface plate 7 Glass disk 8 Sliding contact surface 9 Groove 11 Sun gear 12 Internal gear 13 Carrier 14 Tooth part 15 Through-hole part

Claims (2)

Using a pair of surface plates having sliding surfaces, a sliding step of sliding the surface of the surface plates relative to both surfaces of the glass disk, and grinding or polishing the surface of the glass disk; A method for producing a glass substrate for a magnetic disk including a polishing step,
At least in any one of the grinding step or the polishing step, a lower surface plate, a sun gear provided at the center of the lower surface plate, and an internal gear provided at the outer edge of the lower surface plate And a carrier having a disc shape having a tooth portion meshing with the sun gear and the internal gear on an outer peripheral portion and holding the glass disk, and an upper surface plate facing the lower surface plate, Holding the glass disk, meshing the teeth of the outer periphery of the carrier with the sun gear and the internal gear, and rotating and driving at least one of the sun gear and the internal gear. And a process of relatively sliding the glass disk held by the carrier,
A part of the glass disk held by the carrier is at least partly in the process of relative movement with respect to the lower surface plate and the upper surface plate, than the outer edge portions of the lower surface plate and the upper surface plate. A method for producing a glass substrate for a magnetic disk, wherein the outer peripheral side is passed. A method for producing a magnetic disk, comprising: forming at least a magnetic layer on a main surface of the glass substrate for a magnetic disk produced by the method for producing a glass substrate for a magnetic disk according to claim 1.