JP5242015B2 - Manufacturing method of glass substrate for magnetic disk and manufacturing method of magnetic disk - Google Patents

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 has a correlation with the surface roughness of the surface of the magnetic disk, and when the flying height of the magnetic head is reduced, the possibility that the magnetic head contacts the surface of the magnetic disk increases. 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 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 tempered 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 disk 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 using a polishing liquid containing colloidal silica abrasive grains as described in Patent Document 1 as a polishing liquid used in such a polishing process.

  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 the magnetic disk, it is necessary to reduce defects such as residues of abrasive grains on the surface of the magnetic disk. In order to reduce such defects on the surface of the magnetic disk, ultrasonic cleaning using water or an aqueous alkali solution is performed as cleaning after the polishing process.

  In addition, in order to supply a large amount of low-priced magnetic disks, it is necessary to reduce the manufacturing cost. For this reason, the polishing liquid used in the polishing process is collected and recycled through a filter. Yes.

JP 2003-173518 A

  By the way, for a glass substrate for a magnetic disk polished using a polishing liquid containing colloidal silica abrasive grains, ultrasonic cleaning using water or an alkaline aqueous solution is performed after the polishing process. In such a case, the colloidal silica abrasive grains cannot be sufficiently removed, and the abrasive grains may remain on the glass substrate.

  Further, when cleaning with an alkaline aqueous solution (for example, concentration 6 wt%, pH 12.5) is performed, the colloidal silica abrasive grains are dissolved and removed and do not remain on the magnetic disk glass substrate. However, if the cleaning conditions are increased, such as increasing the concentration of the alkaline aqueous solution to ensure the removal of the abrasive grains, the glass substrate may be damaged by the aqueous alkaline solution (concave defect) or the surface roughness of the glass substrate will increase. There is a problem of doing.

  Further, when the polishing liquid containing the abrasive grains is circulated and reused, there is a problem that the temperature of the polishing liquid increases with the lapse of the polishing time. When the temperature of the polishing liquid rises, the surface energy of the glass substrate for magnetic disks becomes highly active, and the abrasive grains contained in the polishing liquid re-adhere to the surface of the glass substrate after exerting a mechanical polishing action. There is a fear. Further, when the temperature of the polishing liquid rises, the surface of the magnetic disk glass substrate after the polishing process is dried quickly, and the abrasive grains may adhere to this surface.

  In addition, there exists a subject that colloidal silica abrasive grain tends to adhere to a glass substrate. Silica contained as a main component in the colloidal silica abrasive is the main component of the glass substrate. Once the colloidal silica abrasive grains adhere to the glass substrate, it is difficult to remove.

  Further, in the polishing step, colloidal silica abrasive grains are pressed against the surface of the glass substrate, so that they are more likely to adhere more firmly.

  Therefore, when colloidal silica polishing abrasive grains are used for mirror polishing of a glass substrate, a smooth mirror surface can be obtained, while convex foreign matters that are thought to be adhered residues of colloidal silica are likely to be generated. Therefore, there is a problem that it is difficult to reduce the flying height of the magnetic head as expected.

  As described above, if the foreign matter is chemically removed using a cleaning solution or the like, the smooth state of the glass substrate surface is disturbed, and even if it is removed by mechanical treatment, the degree of fixation is strong. It cannot be sufficiently removed from the surface of the glass substrate. Moreover, when it tries to remove mechanically, the residue of a colloidal silica abrasive grain will be pressed on a glass substrate, and as a result, a cleaning action may be inhibited.

  In the case of a glass substrate mainly composed of silica, it is difficult to create a smooth mirror surface and a surface free from convex foreign matter even if colloidal silica abrasive grains are used for mirror polishing. .

  Therefore, the present invention has been proposed in view of the above-described circumstances, and the first object thereof is to generate residues of polishing abrasive grains and concave defects after the polishing process of the main surface of the magnetic disk glass substrate. It is an object of the present invention to provide a method for producing a glass substrate for a magnetic disk, which can prevent the occurrence of the problem and can produce a highly smooth glass substrate for a magnetic disk.

  A second object of the present invention is to provide a stable and high quality glass substrate for magnetic disk and a large amount of magnetic disk at 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.

  With respect to the above problems, it is difficult to achieve a sufficient effect by using only a solution for removing polishing abrasive grains adhering to the surface of the glass substrate after the polishing step.

  The present inventor has completed a means for suppressing polishing grains from adhering to the surface of the glass substrate in the polishing step.

  As a result of conducting research to solve the above problems, the present inventor can solve the above problems by controlling the temperature of the polishing liquid below a predetermined temperature in the polishing process in the manufacturing process of the glass substrate for magnetic disks. And gained knowledge.

  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 according to the present invention comprises: a polishing liquid containing abrasive grains after grinding the surface of a disk-shaped glass disk ; and a foamed resin polisher affixed to a pair of surface plates facing each other. , The polishing liquid is supplied between the pair of surface plates and the glass disk, the pair of surface plates and the glass disk are brought into sliding contact with each other, and both main surfaces of the glass disk are polished by a planetary gear mechanism. A method of manufacturing a glass substrate for a magnetic disk including a polishing step in which the roughness of the main surface is a mirror surface with a Ra of 0.1 nm to 0.7 nm and an Rmax of 3 nm or less , wherein aluminosilicate glass is used as the material of the glass disk A polishing liquid containing colloidal silica abrasive grains is used as the abrasive grains, and the polishing liquid is circulated between the storage tank and the surface of the glass disk. On the circulation path, the polishing liquid is cooled by heat exchanging means , and the temperature of the polishing liquid when supplying the polishing liquid to the surface of the glass disk is set to an ambient temperature or lower and 20 ° C. or lower, and the polishing step is performed. The temperature of the surface of the glass disk when it is finished is not more than the ambient temperature and not more than 30 ° C.

The material of the glass disk used in the present invention is not particularly limited, and examples thereof include quartz glass, soda lime glass, aluminosilicate glass, borosilicate glass, aluminoborosilicate glass, and alkali-free glass crystallized glass.
The average particle size of the colloidal silica abrasive grains can be appropriately adjusted depending on the smoothness (surface roughness) of the glass substrate realized by the polishing step, and is set to 0.01 to 0.5 μm, for example. In order to obtain a glass substrate that is sufficiently smooth to support a magnetic disk capable of high-density recording / reproduction in recent years, for example, a glass substrate having a surface roughness Rmax of 3 nm or less, the average particle diameter of colloidal silica is: It is desirable that the thickness be 0.5 μm or less.
Further, the concentration of the colloidal silica abrasive grains can be appropriately adjusted according to the processing speed and the surface roughness of the glass substrate. For example, it is preferably 5 to 35 wt% in consideration of the processing speed. As the concentration of the polishing agent is increased, the surface of the glass substrate after the polishing step becomes rough.

[Configuration 2]
The present invention provides a method of manufacturing a glass substrate for a magnetic disk having the configuration 1, the load at the time of each other sliding contact with the pair of platen glass disk, and characterized by a 30 g / cm ² to 120 g / cm ² To do.
[Configuration 3]
The present invention relates to a method for producing a glass substrate for a magnetic disk having Configuration 1 or Configuration 2, wherein the polishing liquid contains 5 to 32 wt% of abrasive grains, and the colloidal silica contained in the abrasive grains The average grain size of the abrasive grains is 0.01 μm to 0.1 μm.
[Configuration 4]
The present invention is a method of manufacturing a glass substrate for a magnetic disk having any one of Configurations 1 to 3, wherein the foamed resin polisher is a soft foamed resin polisher.

[Configuration 5 ]
The present invention relates to a method of manufacturing a glass substrate for a magnetic disk having any one of Configurations 1 to 4, and a cooling device having a cooling pipe in which a coolant is circulated and wound in a coil shape as heat exchange means It is characterized by using.

[Configuration 6 ]
According to the present invention, in the method for manufacturing a glass substrate for a magnetic disk having the configuration 5, as a cooling device, a detecting means for detecting the temperature and flow rate of the cooling liquid flowing in the cooling pipe and the temperature of the polishing liquid, and detection by this detecting means What is provided with the display means which displays a result is used, It is characterized by the above-mentioned.

[Configuration 7 ]
According to the present invention, in the method for manufacturing a glass substrate for a magnetic disk having the configuration 5, as a cooling device, the flow rate of the cooling liquid in the cooling pipe is controlled based on the detection result of the cooling liquid temperature and the polishing liquid temperature by the detecting means. What has a function is used.

[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 the method for manufacturing a glass substrate for a magnetic disk according to the present invention having Configuration 1, a polishing liquid containing a colloidal silica abrasive as the abrasive is used, and the polishing liquid is stored on the surface of the storage tank and the glass disk. The temperature of the polishing liquid when the polishing liquid is cooled on the circulation path by the heat exchange means and the polishing liquid is supplied to the surface of the glass disk is equal to or lower than the ambient temperature, and 20 Since the temperature of the surface of the glass disk when the polishing process is completed is set to be equal to or lower than ° C and the atmospheric temperature is equal to or lower than 30 ° C, the evaporation of the polishing liquid after the polishing process is suppressed and the surface of the glass substrate is suppressed. It is possible to prevent the abrasive grains from adhering to the surface.
In addition, since aluminosilicate glass is used as the material of the glass disk and a material containing colloidal silica abrasive grains as the abrasive grains is used as the polishing liquid, the main surface of the glass disk can be polished to a good smooth surface.
Further, the polishing liquid is circulated between the storage tank and the surface of the glass disk, and the polishing liquid is cooled by the heat exchanging means on this circulation path, so that the temperature of the polishing liquid supplied to the surface of the glass disk is lowered. After the polishing process, it is possible to prevent the polishing liquid from evaporating to prevent the surface of the glass substrate from being dried and to reduce the surface energy of the glass substrate for magnetic disk to a low activity state, thereby polishing abrasive grains contained in the polishing liquid. Can be prevented from reattaching and adhering to the surface of the glass substrate.
In addition, after the polishing step, the surface energy of the magnetic disk glass substrate can be set to a low activity state, and the abrasive grains contained in the polishing liquid can be prevented from reattaching to the surface of the glass substrate. That is, since the abrasive grains after the polishing process can be easily removed from the surface of the glass substrate, it is possible to prevent the abrasive grains from remaining in ultrasonic cleaning using water or an alkaline aqueous solution after the polishing process. In addition, since it is not necessary to increase the cleaning conditions such as increasing the concentration of the aqueous alkali solution, it is possible to produce a glass substrate for magnetic disk having high smoothness without a concave defect.

In the method for manufacturing a glass substrate for a magnetic disk according to the present invention having the configuration 5 , a cooling device having a cooling pipe in which a cooling liquid is circulated and wound in a coil shape is used as a heat exchange means. The temperature of the polishing liquid supplied to the surface can be lowered efficiently.

In the method for manufacturing a glass substrate for a magnetic disk according to the present invention having the configuration 6, as a cooling device, a detecting means for detecting the temperature and flow rate of the cooling liquid flowing in the cooling pipe and the temperature of the polishing liquid, and a detection result by the detecting means Therefore, the temperature of the polishing liquid supplied to the surface of the glass disk can be accurately controlled.

In the method for manufacturing a magnetic disk glass substrate according to the present invention having the configuration 7 , the flow rate of the cooling liquid in the cooling pipe is controlled based on the detection result of the temperature of the cooling liquid and the temperature of the polishing liquid by the detecting means as the cooling device. Since one having a function is used, the temperature of the polishing liquid supplied to the surface of the glass disk can be accurately controlled.

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. , Manufactures magnetic disks that reliably prevent problems such as head crush and thermal asperity failure due to residual abrasive grains, defects (concave defects), and surface roughness degradation on the main surface of the glass substrate for magnetic disks can do.

  That is, the present invention provides a magnetic disk glass substrate that can prevent the generation of residual abrasive grains or concave defects after the polishing process of the main surface of the magnetic disk glass substrate, thereby producing a highly smooth glass substrate for magnetic disks. This manufacturing method can be provided.

  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.

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

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

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

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

  Since the glass substrate 1 for magnetic disks is made of glass, it can realize excellent smoothness by mirror polishing, has high hardness, and high rigidity, and thus has excellent impact resistance. In particular, a magnetic disk used for a hard disk drive mounted on a portable (carried) or in-vehicle information device is required to have high impact resistance. Usefulness is high. The surface roughness of the main surface of the glass substrate is preferably 0.1 nm to 0.7 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 the material of the magnetic disk glass substrate 1, in addition to the aluminosilicate glass described above, for example, soda lime glass, soda aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, quartz glass, chain silicate glass, or And glass ceramics such as crystallized glass.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

  As a polishing agent used in the second polishing step, it is preferable to use fine colloidal silica 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 0.5 μm or less, for example.

  FIG. 3 is a block diagram showing an apparatus for circulating the polishing liquid.

  In this second polishing step, as shown in FIG. 3, the polishing liquid containing colloidal silica abrasive grains is recycled and supplied to the planetary gear mechanism, and the temperature of this polishing liquid is controlled to a predetermined temperature or lower. .

  That is, in this second polishing step, the polishing liquid 21 stored in the storage tank 20 is transferred from the storage tank 20 through the transfer pipe 23 by the pump 22 and supplied to the planetary gear mechanism 25 through the filter 24. The polishing liquid that has polished the glass disk in the planetary gear mechanism 25 is discharged from the planetary gear mechanism 25 and returns to the storage tank 20.

  A cooling pipe 26 wound in a coil shape serving as a heat exchange means is inserted into the storage tank 20 and is immersed in the polishing liquid 21 stored in the storage tank 20. In the cooling pipe 26, the coolant circulates and circulates with the coolant cooler 27. The cooling pipe 26 and the cooling liquid cooling device 27 constitute a cooling device. That is, the cooling liquid is cooled in the cooling liquid cooling device 27 and supplied into the cooling pipe 26. After the temperature is raised by cooling the surroundings in the cooling pipe 26, the cooling liquid returns to the cooling liquid cooling apparatus 27. Then, it is cooled again in the coolant cooling device 27 and supplied into the cooling pipe 26.

  Further, the storage tank 20 is provided with a temperature sensor 28 serving as a detecting means for detecting the temperature of the polishing liquid 21 stored in the storage tank 20. The detection result by the temperature sensor 28 is sent to a computer device 29 serving as display means for displaying the detection result. The computer device 29 displays the temperature of the polishing liquid 21 stored in the storage tank 20 detected by the temperature sensor 28, and the flow rate of the cooling liquid in the cooling pipe 26 according to the temperature of the polishing liquid 21. Control. That is, a flow rate control valve 30 is provided in the flow path between the cooling pipe 26 and the coolant cooling device 27, and the flow rate control valve 30 is controlled by the computer device 29. When the temperature of the polishing liquid 21 in the storage tank 20 is higher than a predetermined temperature, the computer device 29 increases the flow rate of the cooling liquid in the cooling pipe 26 and decreases the temperature of the polishing liquid 21. Further, when the temperature of the polishing liquid 21 in the storage tank 20 is lower than a predetermined temperature, the computer device 29 reduces the flow rate of the cooling liquid in the cooling pipe 26 to further reduce the temperature of the polishing liquid 21. Do not.

  In the second polishing step, the temperature of the polishing liquid 21 when the polishing liquid 21 is supplied to the surface of the glass disk in the planetary gear mechanism 25 is preferably set to the ambient temperature or lower. Furthermore, the temperature of the polishing liquid 21 when it is supplied to the surface of the glass disk is preferably 20 ° C. or less.

  Alternatively, in this second polishing step, it is preferable to control the temperature of the polishing liquid 21 so that the temperature of the surface of the glass disk when the second polishing step is finished is equal to or lower than the ambient temperature. Furthermore, it is preferable to control the temperature of the polishing liquid 21 so that the temperature of the surface of the glass disk when the second polishing step is finished is 30 ° C. or less.

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

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

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

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

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

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

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

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

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

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

〔Example〕
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 for chemical strengthening 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 with an atomic force microscope (AFM) (Digital Instruments Nanoscope), and the flatness is measured with 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 an abrasive | polishing agent, what consists of a cerium oxide abrasive grain (average particle diameter: 1.5 micrometers) and water was 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 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, colloidal silica abrasive finer than the cerium oxide abrasive used in the first polishing step was used.

As polishing conditions, a polishing liquid containing 5 wt% to 32 wt% of colloidal silica 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.

  In the second polishing step, as described above, the temperature of the polishing liquid supplied to the glass disk was controlled to be 20 ° C. or lower.

(7) 1st washing | cleaning process The glass substrate which finished the 2nd grinding | polishing process was immersed in KOH aqueous solution with a density | concentration of 5 wt% thru | or 7 wt%, and alkali cleaning was performed. Cleaning was performed by applying ultrasonic waves. Furthermore, it was immersed in each washing tank of neutral detergent, pure water (1), pure water (2), IPA (isopropyl alcohol), and IPA (steam-dried), and washed.

(8) 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.

(9) 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.

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

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

[Comparative Example]
In this comparative example, the polishing liquid was not cooled in the second polishing step. And about the other process, it carried out similarly to the above-mentioned Example, and created the glass substrate for magnetic discs. In addition, a magnetic disk was prepared by using the magnetic disk glass substrate by the same process as in the previous example.

[Contrast between each example and each comparative example]
(Comparison as glass substrate for magnetic disk)
FIG. 4 is a graph showing the relationship between the presence or absence of cooling of the polishing liquid and the number of detected convex defects in the second polishing step.

  When the magnetic disk glass substrates produced in the examples and comparative examples were inspected with an optical defect inspection apparatus, as shown in FIG. 4, the magnetic disk glass substrates of the examples (with cooling of the polishing liquid) were As a result, the number of detected convex defects was low as compared with the glass substrate for magnetic disk of the comparative example (without cooling of the polishing liquid).

  Further, when the defect at the known coordinate position detected here was analyzed, the silicon (Si) element and the oxygen (O) element were detected from the surface of the glass substrate of the comparative example, whereas the example No silicon element was detected from the glass substrate. This silicon element seems to be a residue of colloidal silica abrasive grains, and the convex defects present on the surface of the glass substrate of the comparative example are considered to be residues of colloidal silica abrasive grains.

(Comparison as a magnetic disk)
Regarding the magnetic disk using the glass substrate for magnetic disk of the example, 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.

  About the magnetic disk using the glass substrate for magnetic disks of a comparative example, it confirmed that the defects, such as a magnetic layer, did not generate | occur | produce with the foreign material. In addition, when the glide test was performed, a case where a hit (the head bites a protrusion on the surface of the magnetic disk) occurred was observed.

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

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

  Therefore, it 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.

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 block diagram which shows the apparatus which circulates the polishing liquid used in the manufacturing method of the said glass substrate for magnetic discs. It is a graph which shows the relationship between the presence or absence of cooling of the polishing liquid in the 2nd grinding | polishing process of the manufacturing method of the said glass substrate for magnetic discs, and the detected number of convex defects.

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 20 Storage tank 21 Polishing liquid 22 Pump 23 Transport pipe 24 Filter 25 Planetary gear mechanism 26 Cooling Pipe 27 Coolant Cooling Device 28 Temperature Sensor 29 Computer Device 30 Flow Control Valve

Claims (8)

After grinding the surface of the disk-shaped glass disk, a polishing liquid containing polishing abrasive grains and a foamed resin polisher affixed to a pair of surface plates facing each other are used to remove the polishing liquid from the pair of surface plates and glass. The pair of surface plates and the glass disk are brought into sliding contact with each other while being supplied to the disk, and both the main surfaces of the glass disk are polished by a planetary gear mechanism so that the roughness of both the main surfaces is 0 by Ra. A method for producing a glass substrate for a magnetic disk, comprising a polishing step of making a mirror surface having a mirror surface of 1 nm to 0.7 nm and Rmax of 3 nm or less ,
Aluminosilicate glass is used as the material of the glass disk,
As the polishing liquid, use what contains colloidal silica abrasive grains as the abrasive grains,
And circulating the polishing liquid between the storage tank and the surface of the glass disk, on the circulation path, the polishing liquid is cooled by heat exchange means,
The temperature of the polishing liquid when supplying the polishing liquid to the surface of the glass disk is set to an ambient temperature or lower and 20 ° C or lower,
The temperature of the surface of the glass disk at the time of completion of the polishing process, ambient temperature or lower, and method of manufacturing a glass substrate for a magnetic disk, wherein you than 30 ° C.   The load when the pair of surface plates and the glass disk are in sliding contact with each other is 30 g / cm ² ~ 120g / cm ² Is
  The method for producing a glass substrate for a magnetic disk according to claim 1.   The polishing liquid contains 5 to 32 wt% of the polishing abrasive grains, and the average particle diameter of the colloidal silica abrasive grains contained in the polishing abrasive grains is 0.01 μm to 0.1 μm.
  The method for producing a glass substrate for a magnetic disk according to claim 1 or 2, wherein   The foamed resin polisher is a soft foamed resin polisher
  The method for producing a glass substrate for a magnetic disk according to any one of claims 1 to 3, wherein: The magnetic disk according to any one of claims 1 to 4, wherein a cooling device having a cooling pipe in which a cooling liquid is circulated and wound in a coil shape is used as the heat exchange means. A method for producing a glass substrate. As the cooling device, a device provided with a detecting means for detecting the temperature and flow rate of the coolant flowing through the cooling pipe and the temperature of the polishing liquid, and a display means for displaying the detection result by the detecting means is used. The method for producing a glass substrate for a magnetic disk according to claim 5, wherein: The cooling device having a function of controlling the flow rate of the cooling liquid in the cooling pipe based on the detection result of the temperature of the cooling liquid and the temperature of the polishing liquid by the detection unit is used. Item 6. A method for producing a glass substrate for a magnetic disk according to Item 5 . To claim 1 or on the main surface of the magnetic disk glass substrate manufactured by the manufacturing method of the glass substrate according to any one of claims 7, a magnetic disk, which comprises forming at least a magnetic layer Manufacturing method.

Images