JP2007294073A - Method for manufacturing glass substrate for magnetic disk and method for manufacturing magnetic disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent polish abrasive grains from remaining on a glass substrate after a mirror polish process, to manufacture a glass substrate for a magnetic disk with high smoothness and to provide the glass substrate for magnetic disk and the large number of magnetic disks of stable quality at low costs, in a method for manufacturing the glass substrate for magnetic disk including the mirror polish process of supplying polish liquid containing the polish abrasive grains on the surface of the glass substrate to polish the surface of the glass substrate to a mirror surface, a storage process of the glass substrate for storing the glass substrate after the mirror polish process by bringing it into contact with storage liquid or a conveyance process of the glass substrate of conveying the glass substrate after the mirror polish process to a post process while being in contact with the storage liquid. <P>SOLUTION: The liquid adjusted to liquidity for suppressing aggregation of the polish abrasive grains adhering to the glass substrate in the mirror polish process is used as the storage liquid used in the storage process or the conveyance process. <P>COPYRIGHT: (C)2008,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.

  The flying height of the magnetic head correlates with the surface roughness of the surface of the magnetic disk. If the flying height of the magnetic head is reduced, the magnetic disk rotates at a high speed during recording and reproduction. There is a greater risk of touching. In order to reduce the flying height of the magnetic head while preventing such contact of the magnetic head, it is necessary to finish the main surface of the magnetic disk as a very smooth surface.

  In addition, as a magnetic head in a hard disk drive, a magnetoresistive head using a magnetoresistive element (MR element) instead of a conventionally used thin film head in order to improve signal strength 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.

  In the manufacturing process of a magnetic disk, a multilayer film of several nanometers is formed on the surface of a disk substrate, and recording and reproduction tracks are formed on the multilayer film. Therefore, in order to realize the smoothness of the main surface of the magnetic disk, it is important to keep the surface of the disk substrate extremely flat. In order to realize such smoothness of the main surface of the magnetic disk, a glass substrate is used instead of an aluminum substrate that has been widely used as a disk 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.

  For the purpose of finishing the main surface of such a glass substrate to a smooth surface, the applicant of the present application first sets a glass disk between upper and lower surface plates to which a polishing cloth of a soft polisher is attached, and sets the planetary gear mechanism. The manufacturing method of the glass substrate for magnetic discs which has the grinding | polishing process which grind | polishes both the main surfaces of a glass disc by making these abrasive cloths and a glass disc slide relatively using is proposed. In addition, the applicant of the present application has proposed that a polishing liquid containing colloidal silica abrasive grains is used as a polishing liquid used in such a polishing process, as described in Patent Document 1. In the planetary gear mechanism, the glass disk is sandwiched between 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.

  On the other hand, in order to achieve high-density recording on a magnetic disk, it is necessary to reduce contamination and defects including residues of abrasive grains on the surface of the glass substrate. Among these types of contamination, particulate contamination, in particular, causes convex defects on the surface after film formation, which is an impediment to high-density recording on magnetic disks. Therefore, it is necessary to remove it in the glass substrate manufacturing process. is there.

  In order to remove abrasive grains adhering to the glass substrate in the polishing process, surface cleaning with a cleaning liquid is performed. In general, for cleaning fine particles adhering to the surface of a glass substrate with a relatively weak force such as electrostatic adsorption, a cleaning liquid in which a surfactant is added to an acid or alkali solution is used. In order to promote the cleaning action, scrubbing and ultrasonic waves are also used in combination.

  On the other hand, a cleaning liquid that lifts off the glass substrate by etching the glass substrate is also used for foreign matters that are strongly adhered to the surface of the glass substrate. As such a cleaning solution, a fluorine-based chemical solution, for example, a dilute solution such as hydrofluoric acid, hydrofluoric acid, or ammonium fluoride is used. Further, a cleaning solution that dissolves the deposit itself is also used.

JP 2003-173518 A

  By the way, the residual state of the colloidal silica abrasive grains on the glass substrate after the polishing process using the polishing liquid containing the colloidal silica abrasive grains, that is, the difference in the adsorption of particles and the adhesion form is washed after the polishing process. It is known that it is greatly influenced by the management status until. That is, when the glass substrate dries in the transport process during the transition from the polishing process to the cleaning process, the colloidal silica abrasive grains have an aggregating action, and the affinity between the abrasive grains and the glass substrate. Because the mosquitoes become stronger, they are firmly connected.

  In order to prevent such drying of the glass substrate, the glass substrate is immersed in water in the transporting process, but in water, the composition of the colloidal silica polishing abrasive grains changes to change the agglomeration action, and the aggregation Progresses, and the suction power to the glass substrate may increase.

  The abrasive grains fixed and adsorbed on the glass substrate in this manner are difficult to remove by alkali cleaning or acid cleaning generally used for cleaning particle contamination.

  In such a case, if a cleaning liquid that lifts off the deposits by etching the glass substrate is used, the glass substrate itself is etched, which increases the surface roughness of the glass substrate. Even when a cleaning liquid that dissolves the deposit itself is used, it is difficult to selectively dissolve only the deposit if the main constituent elements of the glass substrate and the adhered particles are the same.

  Japanese Patent Laid-Open No. 2003-141717 discloses a technique for moistening a glass substrate with a liquid or transporting it to a subsequent process while reducing the affinity of an adherent to the surface of the glass substrate. Are listed. However, although this technique can cope with problems caused by drying of the glass substrate, it cannot cope with problems caused by instability such as a change in the composition of the abrasive grains.

  Therefore, the present invention is proposed in view of the above circumstances, and the first object of the present invention is that the surface of the glass substrate is not corroded after the polishing process of the main surface of the glass substrate for magnetic disks. By controlling the agglomeration action of the agglomerated particles such as colloidal silica abrasive grains adhering to the surface of the glass substrate, the removal action in the cleaning process is improved and the residual abrasive grains are prevented, and the magnetic disk with high smoothness An object of the present invention is to provide a method for producing a glass substrate for a magnetic disk capable of producing a glass substrate for a magnetic disk.

  A second object of the present invention is to make it possible to provide a stable and high-quality glass substrate for magnetic disk and a magnetic disk in large quantities at a low cost.

  Furthermore, a third object of the present invention is to provide a magnetic disk using a glass substrate for a magnetic disk so that thermal asperity failure and head crash can be prevented even if the flying height of the magnetic head is narrowed. This contributes to an increase in information recording surface density.

  As a result of researches to solve the above-mentioned problems, the present inventor has developed a storage solution to be brought into contact with the glass substrate in the storage process after the polishing process in the manufacturing process of the magnetic disk glass substrate or in the transport process. The knowledge that the said subject can be solved by adjusting liquidity was acquired.

  First, this inventor examined the storage liquid which adjusted pH using many types of organic acid, carbonate, an inorganic acid, and an inorganic alkali. As a result, by immersing the glass substrate on which the colloidal silica abrasive grains are adhered in a storage liquid adjusted to a pH substantially equal to the pH of the polishing liquid containing the colloidal silica abrasive grains used in the polishing process, It was found that agglomeration is suppressed and the cleaning action in the cleaning step, which is a subsequent step, is improved.

  Colloidal silica abrasive grains can be used in acidic to alkaline polishing liquids having a pH of about 1.10. However, the polishing liquid contains an additive having a dispersing effect and a component that keeps the pH constant so that the colloidal silica abrasive grains remain stable for a long period of time. Is controlled.

  When the polishing liquid in such a state comes into contact with solutions having greatly different pHs, the instability of colloidal particles in the polishing liquid increases, and it is considered that aggregation and gelation occur. Therefore, by bringing the glass substrate into contact with the storage liquid adjusted to a pH approximately equal to the pH of the polishing liquid as described above, the colloidal silica abrasive grains adhering to the glass substrate are prevented from further agglomerating or gelling. It is thought that it was made.

  By suppressing the aggregation and gelation of colloidal silica abrasive grains in this way, there is no need to use a strong chemical that increases the surface roughness of the glass substrate in the cleaning process, and a glass substrate with good surface roughness can be obtained. It can be produced.

  That is, by adjusting the liquidity of the storage liquid to be in contact with the glass substrate in the storage process or the transporting process after the polishing process to a liquidity that can suppress aggregation and gelation of the abrasive grains. It is considered that the above problems can be solved.

  Accordingly, the present invention includes any one of the following configurations.

[Configuration 1]
Mirror polishing process for supplying a polishing liquid containing abrasive grains to the surface of the glass substrate and polishing the surface of the glass substrate to a mirror surface, and storing the glass substrate after contact with the storage liquid after the mirror polishing process A glass substrate for a magnetic disk comprising a step of transporting a glass substrate after the step or the mirror polishing step to a subsequent step while bringing the glass substrate into contact with the storage solution, and the storage liquid is glass in the mirror polishing step. The liquidity is adjusted to suppress aggregation of abrasive grains adhering to the substrate.

[Configuration 2]
Mirror polishing process for supplying a polishing liquid containing abrasive grains to the surface of the glass substrate and polishing the surface of the glass substrate to a mirror surface, and storing the glass substrate after contact with the storage liquid after the mirror polishing process A glass substrate for a magnetic disk comprising a step of transporting a glass substrate to a subsequent step while contacting the glass substrate after the step or the mirror polishing step with the storage solution, wherein the storage solution is a hydrogen ion of the polishing solution It is characterized by being adjusted to a hydrogen ion concentration substantially equal to the concentration.

[Configuration 3]
In the method for producing a glass substrate for a magnetic disk having Configuration 1 or Configuration 2, the storage liquid is adjusted to a pH within ± 2 with respect to the pH of the polishing liquid.

[Configuration 4]
In the method of manufacturing a magnetic disk glass substrate having any one of Configurations 1 to 3, the storage solution is a buffer solution.

  Thus, by using the storage solution as a buffer solution, it is possible to prevent the pH of the storage solution from fluctuating when mass-producing a large number of glass substrates for magnetic disks.

[Configuration 5]
The present invention is characterized in that, in the method for manufacturing a glass substrate for a magnetic disk having any one of Configurations 1 to 4, a polishing liquid containing colloidal silica abrasive grains is used.

[Configuration 6]
In the method for manufacturing a glass substrate for a magnetic disk having any one of configurations 1 to 5, the storage solution is adjusted to a liquid property that suppresses aggregation of colloidal silica abrasive grains. .

  In a strongly alkaline solution having a pH of 11 or more, colloidal silica abrasive grains dissolve little by little from the surface and the concentration of silicic acid increases, so that the state of the solution becomes unstable and the aggregating action increases. In addition, in the neutral region, the surface of the colloidal silica polishing abrasive grains is easily affected by electric potential, so that instability increases.

[Configuration 7]
In the method for manufacturing a glass substrate for a magnetic disk having any one of Configurations 1 to 6, after the glass substrate is brought into contact with a storage solution, a cleaning process is performed to remove abrasive grains remaining on the surface of the glass substrate. It is characterized by this.

[Configuration 8]
According to the magnetic disk manufacturing method of the present invention, at least a magnetic layer is formed on the main surface of the magnetic disk glass substrate manufactured by the magnetic disk glass substrate manufacturing method having any one of configurations 1 to 7. It is characterized by doing.

  In addition, when using a polishing liquid containing colloidal silica abrasive grains as a polishing liquid for polishing the surface of a glass substrate to a mirror surface, the present inventor uses acidic colloidal silica abrasive grains instead of alkaline colloidal silica abrasive grains. It has been found that there is a possibility of further flattening the surface of the glass substrate by using it.

  FIG. 1 is a graph showing the number of foreign matters on a glass substrate after cleaning when an acidic colloidal silica abrasive is used. Moreover, FIG. 2 is a graph which shows the number of the foreign material on the glass substrate after washing | cleaning at the time of using an alkaline colloidal silica abrasive | polishing agent. 1 and 2, the horizontal axis represents the pH of the storage liquid, and the vertical axis represents the number of foreign substances per unit area on the glass substrate.

  That is, as shown in FIG. 1 and FIG. 2, a glass in which a colloidal silica abrasive is adhered to a storage liquid that is polished using an acidic colloidal silica abrasive and adjusted to the same pH region as the pH of the acidic colloidal silica abrasive. It was found that by immersing the substrate, the aggregation of the abrasive was suppressed, and the cleaning property was improved in the cleaning step which is a subsequent step. Accordingly, the present invention includes any one of the following configurations.

[Configuration 9]
In the method for producing a glass substrate for a magnetic disk having Configuration 2, the storage liquid is an aqueous solution whose hydrogen ion concentration is adjusted to the acidic side.

[Configuration 10]
In the method for producing a glass substrate for a magnetic disk having the structure 9, the storage solution contains at least one substance of organic acid species having a linear number of 2 to 4 and having a carboxyl group or an aldehyde group as a terminal group, and having a pH It is a liquid having an adjusting action.

[Configuration 11]
In the method for manufacturing a magnetic disk having the configuration 8, a magnetic disk corresponding to information recording / reproducing by a magnetic head including a magnetoresistive effect reproducing element is manufactured.

[Configuration 12]
In the method of manufacturing a magnetic disk having the configuration 8 or the configuration 11, a magnetic disk mounted on a hard disk drive that performs a start / stop operation by a load / unload method is manufactured.

  In the method for manufacturing a glass substrate for a magnetic disk according to the present invention having Configuration 1, the storage liquid brought into contact with the glass substrate after the mirror polishing step suppresses aggregation of abrasive grains adhering to the glass substrate in the mirror polishing step. Since the liquidity is adjusted, it is possible to prevent the abrasive grains adhering to the glass substrate from being aggregated or gelled.

  In the method for manufacturing a magnetic disk glass substrate according to the present invention having Configuration 2, the storage liquid brought into contact with the glass substrate after the mirror polishing step is adjusted to a hydrogen ion concentration substantially equal to the hydrogen ion concentration of the polishing liquid. Therefore, it is possible to prevent the abrasive grains adhering to the glass substrate from being aggregated or gelled.

  In the method for producing a magnetic disk glass substrate according to the present invention having the configuration 3, the pH of the storage liquid is adjusted to within ± 2 with respect to the pH of the polishing liquid, so that the abrasive grains adhering to the glass substrate are aggregated. Or gelation can be reliably prevented.

  In the method for manufacturing a magnetic disk glass substrate according to the present invention having the configuration 4, since the storage liquid is a buffer solution, the pH of the storage liquid fluctuates even when mass-producing a large number of magnetic disk glass substrates. Can be prevented.

  In the method for manufacturing a glass substrate for a magnetic disk according to the present invention having the configuration 5, since a polishing liquid containing colloidal silica abrasive grains is used, the main surface of the glass disk can be polished to a good smooth surface. it can.

  In the method for manufacturing a glass substrate for a magnetic disk according to the present invention having the configuration 6, the storage liquid is adjusted to a liquid property that suppresses aggregation of the colloidal silica abrasive grains, so that the colloidal silica abrasive that adheres to the glass substrate It is possible to prevent the grains from aggregating or gelling.

  In the method for producing a glass substrate for a magnetic disk according to the present invention having the structure 7, after the glass substrate is brought into contact with the storage liquid, a cleaning process for removing abrasive grains remaining on the surface of the glass substrate is performed. Without using a strong chemical that increases the surface roughness of the glass substrate, a good cleaning action can be obtained, and a glass substrate with good surface roughness can be produced.

  In the method for manufacturing a magnetic disk according to the present invention having configuration 8, 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. Thus, it is possible to manufacture a magnetic disk in which problems due to residual abrasive grains and deterioration of surface roughness on the main surface of the glass substrate for magnetic disk, that is, head crash and thermal asperity failure are reliably prevented.

  That is, the present invention provides an aggregating action of agglomerated particles such as colloidal silica abrasive grains adhering to the surface of the glass substrate without corroding the surface of the glass substrate after the polishing process of the main surface of the glass substrate for magnetic disk. By controlling, it is possible to provide a method for producing a glass substrate for a magnetic disk that can improve the removal action in the cleaning process, prevent the remaining abrasive grains, and produce a glass substrate for a magnetic disk with high smoothness. It is.

  In addition, the present invention makes it possible to provide a stable and high quality glass substrate for magnetic disk and a large number of magnetic disks at low cost.

  Further, the present invention provides a magnetic disk using a magnetic disk glass substrate, so that even if the flying height of the magnetic head is narrowed, thermal asperity failure and head crash are prevented, so that the information recording surface density on the magnetic disk is reduced. It can contribute to the higher density.

  In the method for manufacturing a glass substrate for a magnetic disk according to the present invention having the configuration 9, the storage liquid is an aqueous solution in which the hydrogen ion concentration is adjusted to the acidic side, so that abrasive grains adhering to the glass substrate aggregate. Gelling can be prevented.

  That is, according to the present invention, it is possible to reduce the number of remaining foreign matters by 30% to 50% compared to the case where the polished glass substrate for magnetic disk is stored in water as in the prior art.

  In the method for producing a glass substrate for a magnetic disk according to the present invention having the constitution 10, the storage liquid is at least one of organic acid species having a linear number of 2 to 4 and having a carboxyl group or an aldehyde group as a terminal group. Since the liquid contains a substance and has a pH adjusting action, it is possible to prevent the pH of the storage liquid from fluctuating even when mass-producing a large number of glass substrates for magnetic disks.

  In the magnetic disk manufacturing method according to the present invention having the structure 11, the magnetic disk corresponding to the information recording / reproducing by the magnetic head having the magnetoresistive effect type reproducing element is manufactured, so the information recording surface density of the magnetic disk is high. Can contribute.

  In the method of manufacturing a magnetic disk according to the present invention having the configuration 12, since the magnetic disk mounted on the hard disk drive that performs the start / stop operation by the load / unload method is manufactured, the information recording surface density of the magnetic disk is high. Can contribute.

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

  As shown in FIG. 3, the glass substrate for 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 nm in Ra and 3 nm or less in Rmax.

  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. 4 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. 4, a planetary gear mechanism that is 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 a polishing liquid are 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.

(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. The polishing in this step is performed with a brush or the like using a polishing liquid. The abrasive grains contained in the polishing liquid used in this step can be used without particular limitation as long as they are abrasive grains that exhibit a polishing ability for glass disks. 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 polishing liquid is a slurry containing abrasive grains and a liquid such as water (pure water) is added to the polishing liquid and used as a slurry.

  The end surface partial mirror polishing step is performed before the first polishing step described later or the second polishing in order to avoid scratching 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.

  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 polishing liquid 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, diamond abrasive grains, etc. 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 polishing liquid is efficiently supplied to the entire polishing area of the polishing cloth, with 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 process (mirror polishing process)
Next, a second polishing process is performed as a mirror polishing process of 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 liquid used in the second polishing step, it is preferable to use a polishing liquid containing fine colloidal silica polishing abrasive grains as compared with the cerium oxide abrasive grains used in the first polishing step. The particle size of the colloidal silica abrasive is preferably, for example, 0.5 μm or less.

(6) Storage (or transport) step This storage (or transport) step is a step of immersing and storing (or transporting) the glass disk that has undergone the second polishing step in a storage solution.

  As a storage solution, it does not corrode the surface of the glass disk, suppresses the aggregation of the colloidal silica abrasive grains remaining on the surface of the glass disk, and suppresses the abrasive grains from firmly adhering to the glass surface. An aqueous solution that can be used is used. That is, it is desirable that the storage liquid is adjusted to a liquid property that suppresses aggregation of abrasive grains adhering to the glass disk in the second polishing step.

  Examples of such storage liquid include those adjusted to a hydrogen ion concentration substantially equal to the hydrogen ion concentration of the polishing liquid. That is, it is desirable that the storage liquid is adjusted to a pH within ± 2 with respect to the pH of the polishing liquid. Examples of the adjusting agent for adjusting the pH of the storage liquid include a mixture of at least one of carbonates, phosphates, sulfates, inorganic acids, and organic acids.

  Although it does not specifically limit as carbonates used in a preservation | save liquid, Sodium carbonate, sodium hydrogencarbonate, potassium carbonate, calcium carbonate etc. are mentioned. The amount of carbonate added is preferably about 0.1 ppm to 10,000 ppm.

  The phosphate used in the storage solution is not particularly limited, and examples thereof include trisodium hydrogen phosphate and disodium hydrogen phosphate. The amount of phosphate added is preferably about 0.1 ppm to 10,000 ppm.

  The sulfates used in the storage solution are not particularly limited, and examples thereof include sodium sulfate, potassium sulfate, and calcium sulfate. The amount of sulfate added is preferably about 0.1 ppm to 10,000 ppm.

  Examples of the inorganic acid used in the storage liquid include hydrochloric acid and sulfuric acid.

  The organic acid used in the storage solution is not particularly limited, and examples thereof include tartaric acid, citric acid, malic acid, fumaric acid, malonic acid, maleic acid, ascorbic acid, and glyoxylic acid. The addition amount of the organic acid is preferably about 0.1 ppm to 10,000 ppm.

  As this storage solution, in addition to the pH adjusting solution, an aqueous solution in which at least one of a complexing agent (chelating agent) and a surfactant is mixed can be used. The surfactant used in the storage solution is not particularly limited, and examples thereof include ionic surfactants, nonionic surfactants, and amphoteric surfactants, such as sodium laurate, sodium dodecylbenzenesulfonate, dodecyl sulfate. Sodium, polyethylene glycol, etc. are mentioned, and the addition amount is desirably about 0.001 wt% to 5 wt%.

  Moreover, when using what contains a colloidal silica abrasive grain as a polishing liquid in a 2nd grinding | polishing process, it is desirable that the storage liquid is adjusted to the liquidity which suppresses aggregation of a colloidal silica abrasive grain. . In a strongly alkaline solution having a pH of 11 or more, colloidal silica abrasive grains dissolve little by little from the surface and the concentration of silicic acid increases, so that the state of the solution becomes unstable and the aggregating action increases. In addition, in the neutral region, the surface of the colloidal silica polishing abrasive grains is easily affected by electric potential, so that instability increases.

  Furthermore, it is desirable that the storage solution is a buffer solution having a buffering action with respect to the target pH. By using the storage solution as a buffer solution, it is possible to prevent the pH of the storage solution from fluctuating when mass-producing a large number of glass substrates for magnetic disks.

  Further, in the case where an abrasive containing acidic colloidal silica abrasive grains is used, the storage solution has a carboxyl group or an aldehyde group at the end group having 2 to 4 straight chain as an adjusting agent for pH adjustment. It may contain at least one substance of organic acids. Furthermore, as a regulator for adjusting the pH of the storage liquid, at least one of a complexing agent (chelating agent) and a surfactant can be used.

  In order to bring the storage liquid into contact with the glass disk, the storage liquid may be discharged toward the glass disk in addition to the method of immersing the glass disk in the storage liquid.

(7) 1st washing | cleaning process The washing | cleaning liquid which mixed at least 1 sort (s) among inorganic acid, inorganic alkali, organic alkali, organic acid, complexing agent, and surfactant was used for the glass disk which passed through the storage (or conveyance) process. Use to wash. In the first cleaning step, the cleaning process can be performed by bringing the glass disk into contact with the cleaning liquid by a method of immersing the glass disk in the cleaning liquid or a method of discharging the cleaning liquid onto the glass disk.

  Moreover, in this 1st washing | cleaning process, a cleaning effect can be heightened by immersing a glass disk in a washing | cleaning liquid, applying the ultrasonic wave of frequency 28kHz or more. Further, in this first cleaning step, when the cleaning liquid is brought into contact with the glass disk, the cleaning effect can be enhanced by adjusting the cleaning liquid to a temperature of 20 ° C. to 50 ° C.

  In the present invention, agglomeration of abrasive grains on the glass disk is suppressed in the storage (or transport) process, and formation of strong deposits is prevented. Obtainable.

(8) 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.

(9) 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.

(10) Texture processing step Here, texture processing may be applied to the main surface and the end surface of the glass disk.

  This texture processing is performed by holding a glass disk on a rotating chucking shaft, sandwiching both main surfaces of the glass disk with a pair of polishing tapes, rotating the chucking shaft and feeding the polishing tape. Do. The chucking shaft reciprocates with a predetermined circumference and amplitude in a direction orthogonal to the axis. A polishing liquid is supplied between the glass disk and each polishing tape. As this polishing liquid, one containing diamond abrasive grains as abrasive grains can be used.

(11) 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.

[First embodiment]
In this example, a glass substrate for a magnetic disk 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, the SiO ₂ 58 to 75 wt%, the _Al 2 _{O 3} 5 to 23 wt%, the LiO ₂ 3 to 10% by weight, as a main component 4 to 13% by weight of Na ₂ O The contained glass 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-sided grinding device, and the grinding was performed using a grinding liquid containing alumina abrasive grains having a particle size of # 400, 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.

  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, it was 4 μm for Rmax and 0.5 μm for Ra for both the side surface portion and the chamfered surface.

(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. The surface roughness of the outer peripheral side of the glass disk was polished to about 1 μm for Rmax and about 0.3 μm for Ra. And the glass disk which finished the end surface partial mirror polishing was washed with water.

(4) Fine grinding step Next, the grain size of the abrasive grains was changed to # 1000, and the surface of the glass disk was ground, so that the flatness was 3 μm, the surface roughness Rmax was about 2 μm, and Ra was about 0.2 μm. Rmax and Ra are measured by an atomic force microscope (AFM) (Nanoscope manufactured by Digital Instruments), and the flatness is measured by a flatness measuring device. The highest and lowest portions of the substrate surface The distance (height difference) in the vertical direction (direction perpendicular to the surface).

  The glass substrate after the fine grinding step was cleaned by immersing it in each cleaning layer of neutral detergent and water.

(5) 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 polishing liquid, a cerium oxide abrasive grain (average particle diameter: 1.5 μm) and water were used. The removal amount (polishing allowance) in the first polishing step is about 35 μm to 45 μm.

  The glass substrate after the first polishing process was cleaned by sequentially immersing it in each cleaning tank of pure water (1), neutral detergent, pure water (2), IPA (isopropyl alcohol), and IPA (steam drying). .

(6) Second polishing step (mirror 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 liquid, colloidal silica polishing abrasive finer than the cerium oxide abrasive used in the first polishing step was used. As this polishing liquid, an alkaline (pH 10) colloidal silica polishing liquid corresponding to Test Example 1 to Test Example 5 in the following storage (or transport) step, and an acidity (pH 2) corresponding to Test Example 6 to Test Example 9 are used. ) Colloidal silica polishing liquid.

As polishing conditions, a polishing liquid containing 5 wt% to 32 wt% of colloidal silica polishing abrasive grains having an average particle diameter of 0.01 μm to 0.1 μm was used. The load in the planetary gear mechanism is 30 g / cm ^{2 to} 120 g / cm ² , and the polishing time is 5 minutes to 40 minutes. The removal amount (polishing allowance) was 0.5 μm to 8 μm.

(7) Storage (or transport) step As shown in [Table 1] below, as a storage solution for a glass disk that has been subjected to the second polishing step using an alkaline (pH 10) colloidal silica polishing solution, Tartaric acid aqueous solution (Test Example 1), phthalate aqueous solution (Test Example 2), sodium bicarbonate and sodium carbonate aqueous solution (Test Example 3), potassium hydroxide (KOH) aqueous solution (Test Example 4) and water (Test Example 5) Was used for storage (or transportation).

  Further, a tartaric acid aqueous solution (Test Example 6), a phthalate aqueous solution (Test Example 7), carbonic acid as a storage solution for a glass disk subjected to the second polishing step using an acidic (pH 2) colloidal silica polishing liquid. Storage (or conveyance) was performed using sodium hydrogen and sodium carbonate aqueous solution (Test Example 8) and water (Test Example 9).

  The storage solution in each test example was used after adjusting to predetermined pH conditions and concentration conditions shown in [Table 1].

  In each test example, the glass disk that has undergone the second polishing step is immersed in a storage solution for 1 hour, rinsed and dried, and the number of foreign matters remaining on the glass disk is measured with a laser interference type defect measuring instrument, followed by washing. The quality of the sex was confirmed.

  As shown in [Table 1], a glass disk polished with a colloidal silica polishing solution having a pH of 10 is immediately immersed in a storage solution adjusted to pH 10 after the second polishing step. It can be seen that the number of foreign matter detected in the test is the smallest and the cleaning property is the best. Further, as shown in [Table 1], in the storage (or transport) step, in the test example in which the difference in pH (absolute value) between the polishing liquid and the storage liquid was within 2, the foreign matter on the surface of the glass disk It can be seen that the number of detected foreign matters in the inspection test is 10 or less, which is a good result.

  Moreover, as shown in [Table 1], the glass disk polished with the colloidal silica polishing liquid having a pH of 2 was immersed in a storage liquid adjusted to pH 2 immediately after the second polishing process. It can be seen that the number of foreign matter inspections in the foreign matter inspection test is the smallest and the cleaning property is the best. Even in this case, as shown in [Table 1], in the test example in which the pH difference (absolute value) between the polishing liquid and the storage liquid was within 2 in the storage (or transport) step, a glass disk was used. It can be seen that the number of foreign matters detected in the surface foreign matter inspection test is 10 or less, which is a good result.

(8) 1st washing | cleaning process At least 1 or more types in the inorganic acid, an inorganic alkali, an organic alkali, an organic acid, a complexing agent, and surfactant in the glass disk of each test example which passed through the storage (or conveyance) process. Washing was performed using the mixed washing solution. In the first cleaning step, the glass disk was immersed in the cleaning liquid while applying an ultrasonic wave having a frequency of 28 kHz or higher. The temperature of the cleaning liquid was adjusted to 20 ° C. to 50 ° C.

(9) 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 375 ° 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.

(10) Second cleaning step The glass substrate after the chemical strengthening treatment was cleaned by immersing it in concentrated sulfuric acid heated to about 40 ° C. 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.

(11) 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.

  With respect to the magnetic disk using the glass substrate for magnetic disk of each test example prepared as described above, 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.

  Moreover, as shown in the above [Table 1], in the storage (or transport) step, in the test example in which the difference in pH (absolute value) between the polishing liquid and the storage liquid was within 2, the glide height test It was confirmed that the touchdown height (nm) in FIG.

  Next, a load / unload (LUL) durability test was performed on the magnetic disk obtained in each test example. That is, the obtained magnetic disk was mounted on a hard disk drive, and a load / unload operation was continuously repeated using a magnetic head having a flying height of 8 nm. As a result, as load / unload durability, it was confirmed that 100 out of 100 units could endure a load / unload operation of 600,000 times or more and had sufficient durability.

  Therefore, it has been confirmed that the present invention is suitable as a magnetic disk mounted on a hard disk drive that is recorded / reproduced by a load / unload (LUL) method, or as a glass substrate for this 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.

[Second Embodiment]
In this embodiment, when acidic and alkaline colloidal silica abrasive grains are used in the above-described polishing step, the cleaning property in the next cleaning step depends on the type of storage liquid in the next storage (or transport) step. I checked if it would change.

  That is, in order to confirm the detergency of the glass disk to which the abrasive is adhered, as shown in [Table 2] below, an acidic (pH 2.0) and alkaline (pH 10.0) colloidal silica polishing liquid is used. For the glass disk subjected to the second polishing step, as storage solutions, test solutions adjusted to predetermined pH conditions and concentration conditions, respectively, ie, tartaric acid aqueous solution (Execution solution 1), phthalate aqueous solution (Execution solution 2) ), Sodium hydrogen carbonate and an aqueous solution of sodium carbonate (Execution liquid 3) and water (Comparative liquid 1) were immersed in the glass substrate for 1 hour and stored (or transported).

  Thereafter, the number of foreign matters remaining on the glass disk that had been cleaned and rinsed and dried was measured by a laser interference type defect measuring device to confirm the cleaning performance. The results are shown in FIG. 1 and FIG.

  [Table 2] As shown in FIG. 1 and FIG. 2, the cleanability of the glass disk polished with an acidic colloidal silica abrasive (pH 2) was immediately immersed in a storage solution adjusted to pH 2 after polishing. The one (Execution liquid 1) was found to be the best.

[Third embodiment]
In this example, when acidic colloidal silica abrasive grains are used in the above-described polishing step and a pH 2 aqueous solution is used as a storage solution in the next storage (or transport) step, various organic acids exhibiting similar pH and In order to confirm the relationship with detergency, each storage solution shown in [Table 3], that is, glyoxylic acid (Execution solution 1, pH 2.7), malonic acid (Execution solution 2, pH 2.3), DL malic acid ( Working solution 3, pH 2.5), L (+) tartaric acid (working solution 4, pH 2.4), succinic acid (working solution 5, pH 2.8), citric acid (working solution 6, pH 2.5),
Lactic acid (Execution liquid 7, pH 2.9) and water (Comparative liquid 1) were used.

  After each storage solution was adjusted to a predetermined concentration condition, the glass disk subjected to the second polishing step using an acidic (pH 2.0) colloidal silica polishing solution was immersed for 10 minutes. Thereafter, the number of foreign matters remaining on the glass disk that had been cleaned and rinsed and dried was measured by a laser interference type defect measuring device to confirm the cleaning performance. The result is shown in FIG.

  As shown in [Table 3] and FIG. 5, the cleanability of the glass disk subjected to the second polishing step using an acidic (pH 2.0) colloidal silica polishing liquid is as a storage liquid as shown in FIG. In a glass disk immersed in a storage solution (working solution 1 to working solution 5) containing an organic acid having a linear number of 2 to 4 and a terminal functional group being a carboxyl group or an aldehyde group The properties were found to be good.

[Fourth embodiment]
In this example, in order to confirm the influence on the surface of the glass disk by immersing in an acidic storage solution, when a storage solution similar to the storage solution used in the third example is used, it is acidic (pH 2). 0.0) colloidal silica polishing liquid was used to immerse the glass disk subjected to the second polishing step for 10 minutes. Thereafter, the surface of the glass disk that had been washed and rinsed and dried was measured with a contact-type level difference measuring device, and the surface state of the glass disk was confirmed. The results are shown in [Table 4] and FIG.

  As shown in [Table 4] and FIG. 7, it was confirmed that the surface roughness of the glass disk was not increased by immersing the glass disk in the storage solution.

It is a graph which shows the number of the foreign material on the glass substrate after washing | cleaning at the time of using an acidic colloidal silica abrasive | polishing agent. It is a graph which shows the number of the foreign material on the glass substrate after washing | cleaning at the time of using an alkaline colloidal silica abrasive | polishing agent. 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 graph which shows the number of the foreign materials on the glass substrate after washing | cleaning at the time of using an acidic colloidal silica abrasive | polishing agent, Comprising: It is a graph which shows the result at the time of using various organic acids as a storage liquid. It is a chemical formula which shows the chemical structure of the various organic acids used as a storage liquid. It is a graph which shows the surface roughness of the glass substrate after washing | cleaning at the time of using an acidic colloidal silica abrasive | polishing agent, Comprising: It is a graph which shows the result at the time of using various organic acids as a storage liquid.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass substrate for magnetic disks 2 Center hole 3,4 Surface plate 7 Glass disk 11 Sun gear 12 Internal gear 13 Carrier 14 Tooth part 15 Through-hole part

Claims (12)

A mirror surface polishing step for supplying a polishing liquid containing abrasive grains to the surface of the glass substrate and polishing the surface of the glass substrate to a mirror surface, and a glass substrate for storing the glass substrate after the mirror polishing step in contact with a storage solution In the method for producing a glass substrate for a magnetic disk, including a storage step, or a glass substrate transport step for transporting the glass substrate after the mirror polishing step to a subsequent step while contacting the storage liquid,
The method for producing a glass substrate for a magnetic disk, wherein the storage liquid is adjusted to a liquid property that suppresses aggregation of abrasive grains adhering to the glass substrate in the mirror polishing step. A mirror surface polishing step for supplying a polishing liquid containing abrasive grains to the surface of the glass substrate and polishing the surface of the glass substrate to a mirror surface, and a glass substrate for storing the glass substrate after the mirror polishing step in contact with a storage solution In the method for producing a glass substrate for a magnetic disk, including a storage step, or a glass substrate transport step for transporting the glass substrate after the mirror polishing step to a subsequent step while contacting the storage liquid,
The method for producing a glass substrate for a magnetic disk, wherein the storage liquid is adjusted to a hydrogen ion concentration substantially equal to a hydrogen ion concentration of the polishing liquid. The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the storage liquid is adjusted to a pH within ± 2 with respect to the pH of the polishing liquid. The method for producing a glass substrate for a magnetic disk according to any one of claims 1 to 3, wherein the storage solution is a buffer solution. The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the polishing liquid contains colloidal silica abrasive grains. The method for producing a glass substrate for a magnetic disk according to any one of claims 1 to 5, wherein the storage liquid is adjusted to a liquid property that suppresses aggregation of colloidal silica abrasive grains. The cleaning process for removing the abrasive grains remaining on the surface of the glass substrate after the glass substrate is brought into contact with the storage liquid is performed. Of manufacturing a glass substrate for magnetic disk. A magnetic layer is formed at least on the main surface of the 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 7. Disc manufacturing method. The method for producing a glass substrate for a magnetic disk according to claim 2, wherein the storage solution is an aqueous solution whose hydrogen ion concentration is adjusted to the acidic side. The storage solution is a liquid having at least one substance selected from organic acid species having a linear number of 2 to 4 and having a carboxyl group or an aldehyde group as a terminal group, and having a pH adjusting action. Item 10. A method for producing a glass substrate for a magnetic disk according to Item 9. 9. The method of manufacturing a magnetic disk according to claim 8, wherein a magnetic disk corresponding to information recording / reproduction by a magnetic head including a magnetoresistive effect type reproducing element is manufactured. The magnetic disk manufacturing method according to claim 8 or 11, wherein a magnetic disk mounted on a hard disk drive that performs a start / stop operation by a load / unload method is manufactured.

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