JP2006068870A - Method of manufacturing glass substrate for magnetic disk, method of manufacturing magnetic disk, and polishing cloth - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a glass substrate for a magnetic disk capable of easily polishing a main surface of the glass substrate to be the smooth surface; and to provide a large quantity of glass substrate for the magnetic disk and the magnetic disk with stable quality at a low price. <P>SOLUTION: This method of manufacturing the glass substrate for the magnetic disk includes a polishing process for polishing a surface of a glass disk 7 by supplying a polishing liquid and relatively sliding polishing clothes 5 and 6 and the glass disk 7, the ones having a groove 9 as a passage for the polishing liquid on a sliding surface with respect to the glass disk 7 are used for the polishing clothes 5 and 6, and the relative sliding direction of the polishing clothes 5 and 6 and the glass disk 7 is the direction crossing the groove 9 in all the polishing processes. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method of 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), a method of manufacturing a magnetic disk using the glass substrate for a magnetic disk, and the aforementioned The present invention relates to a polishing cloth used in the manufacture of a 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.

  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 the method of manufacturing a glass substrate for a magnetic disk having a polishing step in which a glass substrate is set on the substrate and the polishing cloth and the glass substrate are relatively slid to polish both main surfaces of the glass substrate, the surface of the polishing cloth It proposes a method to select the roughness appropriately.

  Patent Document 2 describes the configuration of a polishing cloth for polishing a glass substrate by being attached to an upper and lower surface plate in the manufacture of a glass substrate for a magnetic disk. In this polishing cloth, a groove serving as a flow path for the polishing liquid is provided on a sliding contact surface slid on the glass substrate. Such a groove of the polishing cloth is useful for effectively supplying the polishing liquid when polishing with a large machining allowance is performed using a polishing liquid containing polishing grains having a large particle diameter.

JP 2002-92867 A Japanese Patent Laid-Open No. 10-249737

  By the way, as described above, when a glass substrate is polished using a polishing cloth in which a groove serving as a flow path for the polishing liquid is provided on a sliding surface that slides on the glass substrate, the glass substrate is polished. On the main surface of the glass substrate, a slight protrusion (surface waviness) may be formed at a location where the groove of the polishing cloth is slid in the groove direction, with a width substantially corresponding to the width of the groove. There is.

  If such protrusions are formed on the main surface of the glass substrate, the magnetic head may be destroyed or a thermal asperity failure may occur in a hard disk drive having a magnetic disk made using the glass substrate. There is. In particular, when the flying height of the magnetic head is 10 nm or less, these failures are likely to occur.

In recent years, it has become possible to realize an information recording surface density of 40 gigabits per square inch (40 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 car navigation system, a personal digital assistance (PDA), a mobile phone, etc. The company intends to expand its use to in-vehicle devices and portable devices. For use in in-vehicle devices and portable devices, they are carried (carried) or used in in-vehicle environments, so the hard disk drive housing is reduced in size and weight, and the magnetic disk is also reduced in diameter. Will be.

  For the use of the hard disk drive thus miniaturized, there is a strong demand for cost reduction and mass production, and it is necessary to supply a large amount of disk substrates and magnetic disks at a low price. However, particularly when the diameter of the disk substrate is reduced, it becomes difficult to ensure the smoothness of the main surface of a large number of disk substrates, and it becomes difficult to stably supply a large number of magnetic disks.

  Therefore, the present invention is proposed in view of the above-mentioned circumstances, and a first object thereof is a magnetic disk capable of easily and easily polishing the main surface of a glass substrate to an extremely smooth surface. By providing a glass substrate manufacturing method, it is possible to provide a stable and high quality glass substrate and magnetic disk for a magnetic disk at low cost and in large quantities.

  The second object of the present invention is to provide a magnetic disk glass capable of stably polishing the main surface 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 substrate 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 an increase in the information recording surface density in the magnetic disk. It is in.

  A third object of the present invention is to prevent the occurrence of head crashes and thermal asperity failures even when the flying height of a magnetic head is 10 nm or less in a hard disk drive. .

  As a result of conducting research to solve the above problems, the present inventor is provided on the sliding surface of the polishing cloth with respect to the glass substrate in the step of polishing the main surface of the glass substrate in the manufacturing process of the glass substrate for magnetic disks. It has been found that the above-mentioned problems can be solved by appropriately setting the groove direction of the groove that becomes the flow path of the polishing liquid.

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

[Configuration 1]
A method for producing a glass substrate for a magnetic disk, comprising a polishing step of supplying a polishing liquid and polishing the surface of a glass disk by sliding the polishing cloth and the glass disk relative to each other. A surface having a groove that becomes a flow path for the polishing liquid is used, and the relative sliding direction of the polishing cloth and the glass disk is set to a direction intersecting the groove in the entire polishing process. It is what.

[Configuration 2]
In the method for manufacturing a glass substrate for a magnetic disk having the configuration 1, a circular polishing cloth is used as the polishing cloth, the polishing cloth is attached to a polishing surface plate, and the polishing surface plate is driven to rotate. The polishing step is performed by sliding the glass disk relatively.

[Configuration 3]
In the manufacturing method of the glass substrate for magnetic disks which has the structure 1 or the structure 2, the polishing surface plate provided with the sun gear in the center part, the internal gear provided in the outer edge of this polishing surface plate, and the outer peripheral part Using a disk-shaped carrier having a tooth portion meshing with the sun gear and the internal gear and holding the glass disk, the polishing cloth is attached to the polishing surface plate, and the carrier is made to hold the glass disk. The teeth of the outer peripheral portion are meshed with the sun gear and the internal gear, and at least one of the sun gear and the internal gear is driven to rotate, whereby the abrasive cloth and the glass disk held by the carrier are relatively slid. Then, the polishing step is performed.

[Configuration 4]
A magnetic disk that executes a second polishing step of performing mirror polishing of the surface of the glass disk after executing the polishing step in the method for manufacturing a glass substrate for a magnetic disk having any one of Configurations 1 to 3 as the first polishing step In the second polishing process, a polishing cloth that is softer than the polishing cloth used in the first polishing process and that has a flat sliding contact surface with respect to the glass disk is used. It is what.

[Configuration 5]
A magnetic disk manufacturing method, wherein at least a magnetic layer is formed on a main surface of a magnetic disk glass substrate manufactured by the method for manufacturing a magnetic disk glass substrate having any one of configurations 1 to 4. It is characterized by.

[Configuration 6]
In order to produce a glass substrate for a magnetic disk by being brought into sliding contact with the surface of a glass disk and manufacturing a glass substrate for a magnetic disk, it is a polishing cloth formed in a circular shape or a circular shape by arranging a plurality of polishing cloth pieces. The surface of the glass disk has a plurality of grooves on the slidable contact surface, and the plurality of grooves have a groove direction at an arbitrary position of the grooves, and a straight line connecting the center of the polishing cloth and the arbitrary position. It is characterized by crossing the line.

[Configuration 7]
In order to produce a glass substrate for a magnetic disk by being brought into sliding contact with the surface of a glass disk and manufacturing a glass substrate for a magnetic disk, a polishing cloth in which a plurality of polishing cloth pieces are arranged to be circular, each polishing cloth piece, It has grooves formed in a grid pattern on the sliding surface with respect to the surface of the glass disk, and the groove direction of each groove is a direction intersecting the circumferential direction of the polishing cloth. is there.

[Configuration 8]
A method of manufacturing a glass substrate for a magnetic disk, comprising the steps of relatively sliding a polishing cloth having Configuration 7 or Configuration 8 and a glass disk and polishing the surface of the glass disk. It is what.

[Configuration 9]
A method for manufacturing a magnetic disk, characterized in that 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 8. .

  In each configuration described above, the main surface portion of the polishing pad can be a polishing pad. This polishing pad can be formed, for example, by impregnating a nonwoven fabric fiber base material with a polyurethane resin and wet coagulating it. Further, the plurality of grooves in the polishing cloth have a width of 1 mm to 3 mm, respectively, and can be formed with an interval equal to or smaller than the diameter of the glass disk, for example, an interval of 10 mm to 30 mm.

  As the abrasive grains contained in the abrasive, cerium oxide abrasive grains are preferable. In addition, it is preferable that the abrasive is a slurry obtained by adding a liquid and the abrasive grains are free abrasive grains.

  In the method for manufacturing a glass substrate for a magnetic disk according to the present invention having the configuration 1, the polishing cloth is formed by forming a groove serving as a polishing fluid channel on the sliding surface of the glass disk, and the entire process of the polishing process. Since the relative sliding direction of the polishing cloth and the glass disk is the direction intersecting the groove, the main surface of the glass disk can be satisfactorily polished and finished to a very smooth surface. Therefore, in this method of manufacturing a magnetic disk glass substrate, problems due to the undulation of the main surface of the magnetic disk glass substrate, that is, head crashes and thermal asperity failures can be prevented.

  In the manufacturing method of the glass substrate for a magnetic disk according to the present invention having the configuration 2, a circular polishing cloth is used as the polishing cloth, the polishing cloth is attached to the polishing surface plate, and the polishing surface plate is driven to rotate. Since the polishing cloth and the glass disk are relatively slid, the main surface of the glass disk can be easily and satisfactorily polished and finished to an extremely smooth surface. Therefore, in this method for producing a magnetic disk glass substrate, a stable quality glass substrate for magnetic disk can be produced and supplied in large quantities.

  In the method for manufacturing a glass substrate for a magnetic disk according to the present invention having Configuration 3, at least one of the sun gear provided at the center of the polishing surface plate and the internal gear provided at the outer edge of the polishing surface plate is rotated. Drive and relatively slide the polishing cloth affixed to the polishing surface plate and the glass disk held by the carrier, so that the main surface of the glass disk can be polished easily and satisfactorily, An extremely smooth surface can be finished. Therefore, in this method for producing a magnetic disk glass substrate, a stable quality glass substrate for magnetic disk can be produced and supplied in large quantities.

  In the method for manufacturing a glass substrate for a magnetic disk according to the present invention having the configuration 4, the second polishing step of performing the mirror polishing of the surface of the glass disk is performed after the above-described polishing step is performed as the first polishing step. In the second polishing step, a polishing cloth that is softer than the polishing cloth used in the first polishing step and has a flat sliding contact surface with respect to the glass disk is used, so that the main surface of the glass disk has a good mirror surface shape. Can be polished to a very smooth surface.

  In the method for manufacturing a magnetic disk according to the present invention having Configuration 5, at least the magnetic layer is formed on the main surface of the glass substrate for magnetic disk manufactured by the method for manufacturing a 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.

  In the polishing cloth according to the present invention having the configuration 6, a plurality of grooves are provided on the sliding contact surface with respect to the surface of the glass disk, and the groove directions at arbitrary positions of these grooves are the center of the polishing cloth and the arbitrary positions. Therefore, if this abrasive cloth is used, the main surface of the glass disk can be satisfactorily polished and finished to a very smooth surface.

  In the polishing cloth according to the present invention having the structure 7, each polishing cloth piece arranged in a circular shape has grooves formed in a lattice shape on the sliding surface with respect to the surface of the glass disk. Since the direction is a direction intersecting the circumferential direction of the polishing cloth, the main surface of the glass disk can be satisfactorily polished and finished to a very smooth surface by using this polishing cloth. Moreover, this abrasive cloth is easy to manufacture.

  In the method for manufacturing a glass substrate for a magnetic disk according to the present invention having the configuration 8, the surface of the glass disk is polished by relatively sliding the above-described polishing cloth and the glass disk. The surface can be polished well and finished to a very smooth surface.

  In the method for manufacturing a magnetic disk according to the present invention having the structure 9, at least a magnetic layer is formed on the main surface of the glass substrate for magnetic disk manufactured by the method for manufacturing a 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 a glass substrate for a magnetic disk with stable quality by providing a method for producing a glass substrate for a magnetic disk that can easily and smoothly polish the main surface of the glass substrate to a very smooth surface. In addition, the magnetic disk can be provided in large quantities at a low cost.

  Further, the present invention provides a method for producing a glass substrate for magnetic disk, which can stably 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, thermal asperity failure and head crash in a magnetic disk using the glass substrate for magnetic disk can be prevented, and the information recording surface density in the magnetic disk can be increased. .

  Furthermore, the present invention can prevent the occurrence of head crashes and thermal asperity failures even when the flying height of the magnetic head is 10 nm or less in a hard disk drive.

  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, for example, a perpendicular magnetic recording method.

  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, since 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, a glass substrate is used in such a magnetic disk. 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. This glass disk is formed to have a diameter slightly larger than the diameter of the glass substrate 1 for magnetic disk to be manufactured, for example, from a melted glass base material by a pressing method or the like.

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

  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.

(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. Moreover, it is preferable that a polishing agent adds liquid, such as water (pure water), to the polishing agent containing an abrasive grain, and uses this polishing agent as a slurry.

  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. The first polishing process is mainly intended to remove scratches and distortions remaining on the main surface in the lapping process described above. 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.

  FIG. 2 is a side view showing the configuration of the double-side polishing apparatus.

  As shown in FIG. 2, the double-side polishing apparatus has a pair of upper and lower polishing surface plates 3, 4, and a polishing cloth (a polishing pad of a hard resin polisher) is disposed on the mutually opposing main surface portions of the polishing surface plates 3, 4. ) 5 and 6 are affixed. In this double-side polishing apparatus, a glass disk 7 is installed between the polishing cloths 5 and 6 attached to the polishing surface plates 3 and 4, and one or both of the polishing surface plates 3 and 4 are moved. By doing so, the main surface of this glass disk 7 can be grind | polished by making the glass disk 7 and the polishing cloths 5 and 6 mutually slide-contact.

  FIG. 3 is a perspective view showing the shape of the polishing pad.

  As the polishing cloths 5 and 6, a polishing pad formed by impregnating a nonwoven fabric fiber base material with a polyurethane resin and wet coagulating it into a predetermined shape can be used. The hardness of the polishing cloths 5 and 6 is preferably about 60 to 80 in terms of Asker A hardness. As shown in FIG. 3, the polishing cloths 5 and 6 are formed by forming grooves 9 serving as a flow path for the polishing liquid on the sliding contact surface 8 with respect to the glass disk. The plurality of grooves 9 in the polishing cloths 5 and 6 each have a width of 1 mm to 3 mm, and are preferably formed with an interval equal to or less than the diameter of the glass disk 7, for example, an interval of 10 mm to 30 mm. .

  In the present invention, in the entire process of the first polishing step, the relative sliding direction between the polishing cloths 5 and 6 and the glass disk 7 is as shown by an arrow A in FIG. The direction intersects the direction.

  In addition, as the polishing cloths 5 and 6, those formed in a circular shape or a plurality of polishing cloth pieces arranged in a circular shape can be used. In this case, the polishing cloths 5 and 6 are affixed to a circular polishing surface plate, and the polishing surface plate is driven to rotate so that the polishing cloths 5 and 6 and the glass disk 7 are relatively slid. The main surface of the glass disk 7 can be polished.

  FIG. 4 is a plan view showing a configuration of a polishing cloth formed in a circular shape.

  In the case where the polishing cloths 5 and 6 are formed in a circular shape, as shown in FIG. 4, the plurality of grooves 9 provided in the polishing cloths 5 and 6 have a groove direction C at an arbitrary position B of the grooves 9. It is made to cross | intersect with the normal line D of the straight line which connects the center of this polishing cloth 5 and 6 and this arbitrary location B. FIG. In the polishing cloths 5 and 6, the angle formed by the groove direction C at an arbitrary position B and the normal line D connecting the center of the polishing cloth and the arbitrary position B is set in the entire region of the polishing cloths 5 and 6. When the angle is substantially constant less than 90 °, the groove 9 is formed in a spiral shape as shown in FIG.

  FIG. 5 is a plan view showing another example of the configuration of the polishing cloth formed in a circular shape.

  Further, in this polishing cloth 5, 6, the angle formed by the groove direction C at an arbitrary location B and the straight line normal line D connecting the center of the polishing cloth and the arbitrary location B is set to the entire width of the polishing cloth 5, 6. If the angle is 90 ° in the region, the groove 9 is formed in a radial shape as shown in FIG.

  FIG. 6 is a plan view showing still another example of the configuration of the polishing cloth formed in a circular shape.

  Further, in the polishing cloths 5 and 6, the groove direction C at an arbitrary position B and the straight line normal line D connecting the center of the polishing cloth and the arbitrary position B are in the entire region of the polishing cloths 5 and 6. It is not necessary to make a certain angle, and as shown in FIG. 6, it is only necessary that the groove direction C and the normal line D intersect even if the angle is different for each arbitrary position.

  FIG. 7 is a plan view showing a configuration of an abrasive cloth in which a plurality of abrasive cloth pieces are formed in a circular shape.

  FIG. 8 is a plan view showing another example of a configuration of an abrasive cloth in which a plurality of abrasive cloth pieces are formed in a circular shape.

  And when this abrasive cloth 5 and 6 arrange | positions several abrasive cloth pieces and makes it circular, as shown in FIG.7 and FIG.8, as each abrasive cloth piece, the sliding contact surface with respect to the surface of a glass disk 8 having grooves 9 formed in a lattice shape can be used. At this time, the groove direction of each groove 9 is a direction intersecting with the circular circumferential direction formed by the polishing cloths 5 and 6. In this case, all the polishing cloth pieces may be fan-shaped as shown in FIG. 7, or may be a combination of a fan-shape and a rectangle as shown in FIG.

  FIG. 9 is a plan view showing still another example of a configuration of a polishing cloth in which a plurality of polishing cloth pieces are formed in a circular shape.

  In the case where a plurality of polishing cloth pieces are arranged to form circular polishing cloths 5 and 6, when using each of the polishing cloth pieces having grooves 9 formed in a lattice shape, the lattice shape formed by these grooves 9 is: As shown in FIG. 8, it may be an orthogonal lattice shape, or may be an oblique lattice shape as shown in FIG. Also in this case, the groove direction of each groove 9 in each polishing cloth piece is a direction intersecting the circular circumferential direction formed by the polishing cloths 5 and 6.

  In addition, as a polishing cloth piece which has the groove | channel 9 formed in the orthogonal | lattice grid | lattice shape, it can obtain by cut | disconnecting the general purpose polishing cloth formed in the elongate sheet shape suitably.

  And in this 1st grinding | polishing process, you may make it grind | polish the glass disk 7 using a planetary gear mechanism.

  FIG. 10 is a perspective view showing the configuration of the planetary gear mechanism.

  As shown in FIG. 10, the planetary gear mechanism includes a sun gear 11 provided at the center of one polishing surface plate 10, an internal gear 12 provided on the outer edge of the polishing surface plate 10, and a glass disk 7. It consists of a disk-shaped carrier 13 to be held. 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. Further, the planetary gear mechanism has the other polishing surface plate 16 facing the one polishing surface plate 10.

  In this planetary gear mechanism, first, polishing cloths 5 and 6 are attached to the main surface portions of one or both polishing surface plates 10 and 16. Then, with the glass disk 7 held in the through-hole portion 15 of the carrier 13, 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. Then, by sandwiching the carrier 13 and the glass disk 7 by the polishing surface plates 10, 16, the glass disk 7 is held on the main surfaces on both sides by the polishing surface plates 10, 16 and the peripheral portion of the carrier 13. The state is held at the inner edge of the through hole 15.

  In this planetary gear mechanism, both the sun gear 11 and the internal gear 12 are supplied while supplying an abrasive between the polishing cloths 5 and 6 affixed to the polishing surface plates 10 and 16 and the main surface of the glass disk 7. Alternatively, by rotating one of them, the polishing cloths 5 and 6 and the main surface of the glass disk 7 slide relative to each other, and the main surface of the glass disk 7 is polished. At this time, it is preferable that both or one of the polishing surface plates 10 and 16 is rotationally driven.

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 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.

  The abrasive may be dry (powder abrasive) or wet (free abrasive). From the viewpoint of preferably realizing the polishing action, wet (free abrasive grains) is preferable. In order to use the abrasive as wet (free abrasive grains), it is preferable to add a liquid such as water (pure water) to the abrasive containing magnetic particles and abrasive grains and use the abrasive as a slurry.

  In this planetary gear mechanism, the abrasive is efficiently supplied to the entire polishing area of the polishing cloth 5, 6 using the inside of the groove 9 provided in the polishing cloth 5, 6 as a flow path. Further, in this planetary gear mechanism, the polishing allowance can be adjusted by adjusting the pressure at which the polishing surface plates 10 and 16 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.

  In this planetary gear mechanism, the movement trajectory of the glass disk 7 with respect to the polishing cloths 5 and 6 is a cycloid curve or a curve in which a cycloid curve and an arc are combined. This movement trajectory varies depending on the ratio of the rotation direction and the rotation speed of the sun gear 11, the internal gear 12, and each polishing surface plate 10, 16 and the ratio of the diameters of the sun gear 11 and the carrier 13.

  In consideration of the polishing efficiency and the uniformity of the polishing allowance, the rotation speeds of either or both of the polishing surface plates 10 and 16 are sufficiently increased with respect to the rotation speeds of the sun gear 11 and the internal gear 12. The movement trajectory of the glass disk 7 with respect to the polishing cloths 5 and 6 is preferably such that the circumferential components of the polishing cloths 5 and 6 are dominant. In this case, when the polishing cloths 5 and 6 having the grooves 9 as described above are used, the relative sliding direction between the polishing cloths 5 and 6 and the glass disk 7 is determined in the entire process of the first polishing process. The direction intersects the groove direction of the groove 9.

(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 the 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 particles 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 | cleaning process The glass substrate which finished the 2nd grinding | polishing process is immersed in each washing tank of neutral detergent, neutral detergent, pure water, pure water, IPA (isopropyl alcohol), and IPA (steam drying) sequentially. 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 cleaned with pure water and pure water. , IPA (isopropyl alcohol) and IPA (steam-dried) are sequentially immersed in each cleaning tank for cleaning. 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.

  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.

(2) Lapping process Next, the main surface of the obtained glass disk was lapped. In the lapping process, processing is performed using a double-sided lapping apparatus and alumina abrasive grains, and the dimensional accuracy and shape accuracy of the glass disk are set to be predetermined. Next, a circular hole was formed at the center of the glass disk by grinding with a grindstone, and a predetermined chamfering process was performed on the outer peripheral side end surface and the inner peripheral side end surface.

  The obtained glass disk had an inner diameter of 7 mm, an outer diameter of 27.4 mm, a plate thickness of 0.381 mm, and was confirmed to be a predetermined size of a glass substrate for a 1.0 inch type 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 the above-described polishing cloth (polishing pad of hard resin polisher). As the abrasive, cerium oxide abrasive grains were used.

  The glass substrate after the first polishing step was sequentially immersed in each cleaning bath of neutral detergent, pure water, pure water, IPA (isopropyl alcohol), and IPA (steam drying) to be cleaned.

(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 | cleaning process The glass substrate which finished the 2nd grinding | polishing process is immersed in each washing tank of neutral detergent, neutral detergent, pure water, pure water, IPA (isopropyl alcohol), and IPA (steam drying) sequentially. 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, 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. In addition, when the bending strength was similarly measured by changing the chemical strengthening level, it was about 10 to 25 kg.

[Comparative Example 1]
In the first polishing step, polishing is performed using a circular polishing cloth in which a groove having a groove direction in the circumferential direction is formed, and the other steps are the same as in the first embodiment, and the magnetic disk is used. A glass substrate was created.

[Contrast between Example 1 and Comparative Example 1]
The data on the shape of the main surface portion of the glass substrate for magnetic disk prepared in Example 1 and the glass substrate for magnetic disk prepared in Comparative Example 1 were compared. As the shape of the main surface portion, surface waviness (Wa) was measured and compared. For the surface waviness (Wa), a value calculated according to the following definition from a value measured by a non-contact laser interferometry for a predetermined region (an annular region serving as a recording region) on the main surface of the glass substrate for a magnetic disk is used. It was.

Wa = (1 / N) Σ _{i = 1} ^N | Xi−X￣ |
However, in this definition, N is the number of measurement points, Xi is the measurement point value, that is, the height from the reference line to the main surface at the measurement point, and X￣ is the average value of the measurement point values. is there.

  FIG. 11 is a graph showing data of surface waviness (Wa (nm)).

  As a result, as shown in FIG. 11, in the glass substrate for magnetic disk produced by Example 1, about 20 glass substrates for magnetic disks, the average value of surface waviness (Wa) was 0.318 nm. On the other hand, in the glass substrate for magnetic disk produced by Comparative Example 1, the average value of the surface waviness (Wa) was 0.567 nm for the 20 glass substrates for magnetic disk.

  That is, it was confirmed that the glass substrate for magnetic disk produced by Example 1 had less surface waviness (Wa) than the glass substrate for magnetic disk produced by Comparative Example 1.

  In addition, the surface roughness of the glass substrate of Example 1 and the glass substrate of Comparative Example 1 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 Example 1 and the glass substrate of Comparative Example 1 had the same surface roughness (surface roughness Ra was approximately 0.5 nm). That is, the glass substrate of Example 1 and the glass substrate of Comparative Example 1 have substantially the same surface roughness, but the surface waviness of the glass substrate of Comparative Example 1 was approximately twice as large. .

  In Example 2, a magnetic disk was manufactured through the following steps.

  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—Cr— were formed using a stationary opposed DC magnetron sputtering apparatus. A 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 2]
Using the magnetic disk glass substrate prepared in Comparative Example 1 described above, a magnetic disk was prepared by the same process as in Example 2 described above.

[Contrast between Example 2 and Comparative Example 2]
With respect to the magnetic disk obtained in Example 2, it was confirmed that no defect occurred in the film such as the magnetic layer due to the foreign matter. 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 in Comparative Example 2 had no defects in the magnetic layer or the like due to foreign matter. However, when the glide test was performed, hits (the head biting on the protrusion on the magnetic disk surface) and crashes (the head hitting the protrusion on the magnetic disk surface) were recognized. Furthermore, when a reproduction test was conducted with a magnetoresistive head, a malfunction of reproduction due to a thermal asperity failure was observed.

  The above test was performed as a test method for a magnetic disk having an information recording density per square inch equivalent to 40 gigabits. Specifically, the flying height of the magnetic head was 10 nm, and in the recording / reproducing test, the information line recording density was 700 fci.

  Next, a glide test was performed on the magnetic disks of Example 2 and Comparative Example 2. In this glide test, the simulated head for flying is floated on the magnetic disk, the flying height is gradually reduced, and the flying height of the simulated head for testing when the simulated head is in contact with the magnetic disk. It is a test to measure. The flying height of the magnetic head when touched is called the touchdown height. In order to perform recording / reproduction safely with a magnetic head having a flying height of 10 nm, the touchdown height needs to be 5 nm or less at most.

  Thus, when the touchdown height of the magnetic disk of Example 2 was measured, it was 4 nm. On the other hand, when the touchdown height of the magnetic disk of Comparative Example 2 was measured, it was 7 nm. Since the surface waviness of the magnetic disk of Comparative Example 2 is larger, the touchdown height in the magnetic disk of Comparative Example 2 is about twice as large as that of the magnetic disk of Example 2.

  The present invention is particularly suitable as a magnetic disk mounted on a hard disk drive that is recorded / reproduced by a load / unload (LUL) method, or a glass substrate for this magnetic disk. This is because a load / unload type hard disk drive needs to use a magnetic disk having a flat and smooth surface compared to a contact start / stop (CSS) type hard disk drive. For example, the magnetic disk according to the present invention can be a magnetic disk having a touchdown height of 4 nm or less, and 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 side view which shows the structure of the double-side polish apparatus used in the manufacturing method of the said glass substrate for magnetic discs. It is a perspective view which shows the shape of the polishing cloth used in the manufacturing method of the said glass substrate for magnetic discs. It is a top view which shows the structure of the abrasive cloth formed circularly based on this invention. It is a top view which shows the other example of a structure of the abrasive cloth formed circularly based on this invention. It is a top view which shows the further another example of the structure of the abrasive cloth formed circularly concerning this invention. It is a top view which shows the structure of the polishing cloth in which the several polishing cloth piece which concerns on this invention was formed circularly. It is a top view which shows the other example of a structure of the polishing cloth in which the several polishing cloth piece which concerns on this invention was formed circularly. It is a top view which shows the further another example of a structure of the polishing cloth in which the several polishing cloth piece which concerns on this invention was formed circularly. It is a perspective view which shows the structure of the planetary gear mechanism used in the manufacturing method of the glass substrate for magnetic discs which concerns on this invention. It is a graph which shows the data of the surface waviness (Wa) of the glass substrate for magnetic discs produced by the Example of this invention, and the glass substrate for magnetic discs produced by the comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass substrate for magnetic disks 2 Center hole 3,4 Polishing surface plate 5,6 Polishing cloth 7 Glass disk 8 Sliding contact surface 9 Groove 10,16 Polishing surface plate 11 Sun gear 12 Internal gear 13 Carrier 14 Tooth part 15 Through-hole Part

Claims (9)

A method for producing a glass substrate for a magnetic disk, comprising a polishing step of polishing the surface of the glass disk by supplying a polishing liquid and relatively sliding the polishing cloth and the glass disk,
As the polishing cloth, a sliding contact surface with respect to the glass disk is used in which a groove serving as a flow path for the polishing liquid is formed.
A method of manufacturing a glass substrate for a magnetic disk, wherein the relative sliding direction of the polishing cloth and the glass disk is a direction intersecting the groove in the entire process of the polishing process.   As the polishing cloth, a circular polishing cloth is used, the polishing cloth is attached to a polishing surface plate, and the polishing surface plate is driven to rotate, whereby the polishing cloth and the glass disk are relatively slid. The method for manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the polishing step is performed. A polishing platen provided with a sun gear at the center, an internal gear provided at the outer edge of the polishing platen, and a toothed portion that meshes with the sun gear and the internal gear on the outer periphery, and the glass disk With a disc-shaped carrier to hold,
Affixing the polishing cloth to the polishing surface plate, holding the glass disk on the carrier, meshing the teeth of the outer periphery of the carrier with the sun gear and the internal gear,
By rotating and driving at least one of the sun gear and the internal gear, the polishing process and the glass disk held by the carrier are relatively slid to execute the polishing step. A method for producing a glass substrate for a magnetic disk according to claim 1 or 2. A second polishing step of performing mirror polishing of the surface of the glass disk after executing the polishing step in the method for manufacturing a glass substrate for a magnetic disk according to any one of claims 1 to 3 as a first polishing step. A method of manufacturing a glass substrate for a magnetic disk to be executed,
In the second polishing step, a polishing cloth that is softer than the polishing cloth used in the first polishing step and that has a flat sliding contact surface with respect to the glass disk is used. Manufacturing method.   5. A magnetic disk, comprising at least a magnetic layer 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 according to any one of claims 1 to 4. Manufacturing method. In order to produce a glass substrate for a magnetic disk by being brought into sliding contact with the surface of a glass disk and manufacturing a glass substrate for a magnetic disk, it is a polishing cloth formed in a circular shape or a circular shape by arranging a plurality of polishing cloth pieces. ,
Having a plurality of grooves on the sliding surface against the surface of the glass disk;
The polishing cloth according to claim 1, wherein a groove direction at an arbitrary portion of the grooves intersects with a normal line of a straight line connecting the center of the polishing cloth and the arbitrary portion. In order to produce a glass substrate for a magnetic disk by being brought into sliding contact with the surface of the glass disk and manufacturing a glass substrate for a magnetic disk, a polishing cloth in which a plurality of polishing cloth pieces are arranged and made circular,
Each of the polishing cloth pieces has grooves formed in a lattice shape on the sliding surface with respect to the surface of the glass disk, and the groove direction of each groove is defined as a direction intersecting the circumferential direction of the polishing cloth. A polishing cloth characterized by   A process for producing a glass substrate for a magnetic disk, comprising the steps of relatively sliding the polishing cloth according to claim 7 or 8 and the glass disk, and polishing the surface of the glass disk. Method.   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 8.

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