JPWO2013100154A1 - Manufacturing method of glass substrate for magnetic disk - Google Patents

Abstract

When producing a glass substrate for magnetic disk by polishing using zirconia abrasive as an abrasive for loose abrasive grains, it is possible to produce a glass substrate for magnetic disk that is less prone to problems such as head crash failure and thermal asperity failure. A method for manufacturing a glass substrate for a magnetic disk is provided. This method is a method for manufacturing a glass substrate for a magnetic disk having a pair of main surfaces and a side wall surface orthogonal to the pair of main surfaces, the disk-shaped glass base plate being held by a carrier, and the glass The main surface of the base plate is sandwiched between polishing pads, and a polishing liquid having zirconia particles as abrasive grains is supplied between the glass base plate and the polishing pad to relatively move the polishing pad and the glass base plate. In the polishing step of polishing the main surface of the glass base plate, and after the polishing step, when the side wall surface or main surface of the glass base plate is polished, the side wall surface of the glass base plate and the glass substrate And a removal step of physically removing the zirconia particles adhering to the side wall surface of the glass base plate due to rubbing between the side wall surface of the carrier and the end surface of the opposite carrier.

Description

  The present invention relates to a method for manufacturing a glass substrate for a magnetic disk.

  2. Description of the Related Art Today, a personal computer, a DVD (Digital Versatile Disc) recording device, or the like has a built-in hard disk device (HDD: Hard Disk Drive) for data recording. In particular, in a hard disk device used in a portable computer such as a notebook personal computer, a magnetic disk in which a magnetic layer is provided on a glass substrate is used, and the magnetic head slightly floats above the surface of the magnetic disk. Thus, magnetic recording information is recorded on or read from the magnetic layer. As a substrate for this magnetic disk, a glass substrate is preferably used because it has a property that it is less likely to be plastically deformed than a metal substrate (aluminum substrate) or the like.

  Further, in response to a request for an increase in storage capacity in a hard disk device, the density of magnetic recording has been increased. For example, the magnetic recording information area (recording bit) is miniaturized by using a perpendicular magnetic recording method in which the magnetization direction in the magnetic layer is perpendicular to the surface of the substrate. Thereby, the storage capacity of one disk substrate can be increased. Furthermore, in order to further increase the storage capacity, the distance from the magnetic recording layer is extremely shortened by further protruding the recording / reproducing element portion of the magnetic head, thereby further improving the accuracy of information recording / reproducing (S / N). To improve the ratio). Such control of the recording / reproducing element portion of the magnetic head is called a DFH (Dynamic Flying Height) control mechanism, and a magnetic head equipped with this control mechanism is called a DFH head. In a substrate for a magnetic disk used in an HDD in combination with such a DFH head, the surface irregularity of the substrate is extremely small in order to avoid collision and contact with the magnetic head and the recording / reproducing element portion protruding further therefrom. It is made to be smaller.

The process for producing the glass substrate for magnetic disks includes a grinding process in which the main surface of the glass base plate that has become flat after press molding is ground with fixed abrasive grains, and scratches remaining on the main surface by this grinding process. The main surface polishing step is included for the purpose of removing strain.
Conventionally, in the polishing process of the main surface, a method for manufacturing a glass substrate for a magnetic disk using cerium oxide (cerium dioxide) abrasive grains as an abrasive is known (Patent Document 1).
In this method, after the grinding step, after polishing the end face of the glass base plate, the main surface is polished (first polishing) using cerium oxide as free abrasive grains, and then the glass base plate is chemically strengthened. .

JP 2008-254166 A

On the other hand, it is conceivable to use zirconia (zirconium dioxide), which is relatively easy to obtain and is conventionally known as an abrasive in glass products, as an alternative to a rare metal cerium oxide abrasive that is relatively difficult to obtain.
However, when a magnetic disk is produced by forming a magnetic layer on a glass substrate produced by using the above zirconia as a polishing material for free abrasive grains of a glass base plate, compared with a glass substrate produced by using cerium oxide as an abrasive. In a long-time LUL test using a magnetic head, it has been found that problems such as a head crash failure and a thermal asperity failure are relatively frequent.

  Accordingly, the present invention provides a magnetic disk glass that is less prone to problems such as head crash failure and thermal asperity failure when a glass substrate for magnetic disk is produced by polishing using zirconia abrasive as an abrasive for loose abrasive grains. It aims at providing the manufacturing method of the glass substrate for magnetic discs which can manufacture a board | substrate.

  The inventors of the present application are to investigate the cause of problems such as head crash failure and thermal asperity failure in a glass substrate for magnetic disk produced by polishing using zirconia abrasive as an abrasive for loose abrasive. We have made an intensive study. As a result, the main surface of the glass substrate has zirconia particles adhering to the main surface when the magnetic layer is formed, even after the main surface is sufficiently cleaned and the particles are removed after polishing with a mirror finish. I found out that there was a case. In this case, a magnetic layer is laminated above the zirconia particles, and minute irregularities are formed on the surface of the magnetic layer. The minute irregularities cause problems such as a head crash failure and a thermal asperity failure. Furthermore, the zirconia particles adhering to the main surface of the glass substrate are part of the zirconia abrasive grains used for polishing and are likely to adhere to the outer peripheral surface and inner peripheral surface of the glass substrate. I understand. Such a problem did not occur when other abrasive grains such as cerium oxide and silica were used as an abrasive, but came to occur when zirconia abrasive grains were used. In addition, the washing | cleaning method which removes effectively the zirconia particle adhering to the glass substrate is not established. In the present specification, “adhering” means, for example, that zirconia particles are stuck and fixed to the side wall surface of the glass base plate. In this specification, the term “attach” means, for example, that the zirconia particles simply remain on the main surface of the glass base plate, and that the zirconium particles adhere to the side wall surface of the glass base plate. It may be understood to mean.

The inventors of the present application consider the reason why zirconia particles may adhere to the main surface when the magnetic layer is formed even if the main surface is sufficiently washed and particles are removed. Yes. In other words, even if zirconia particles remain on the glass base plate by main surface polishing with zirconia abrasive grains, the zirconia particles remaining on the main surface are removed by final polishing on the main surface, but on the side wall surface of the glass base plate. Residual or adhered zirconia particles are not removed by subsequent cleaning of the glass base plate. In particular, in the main surface polishing with zirconia abrasive grains, when the glass base plate is held on a carrier, the zirconia particles adhere to the side wall surface of the glass base plate by the glass base plate contacting the carrier during polishing. Conceivable.
When the main surface polishing is performed by holding the glass base plate on the carrier in this way, the zirconia particles are fixed as a cause for the zirconia particles to adhere to the glass base plate. Compared to the case, the polishing pad is pressed against the glass base plate with a much stronger force, and the surface plate and carrier are rotated (relative to the polishing pad at a higher rotational speed than when cerium oxide is used). It may be possible to move the When zirconia abrasive grains are used, the reason for performing main surface polishing under such severe conditions is that the cerium oxide abrasive grains were used under the same conditions as when cerium oxide abrasive grains were used. This is because the processing rate is significantly reduced.

And in the process after the main surface grinding | polishing by a zirconia abrasive grain, it is guessed that the zirconia particle adhering to the side wall surface will detach | leave and adhere to the main surface of a glass base plate or the glass substrate for magnetic discs. For example, after polishing the main surface of the glass base plate, the side wall surface of the glass base plate or the magnetic disk glass substrate is gripped in the process so as not to deteriorate the surface properties of the main surface. It is considered that the particles are detached. When there is a step of attaching a plurality of glass base plates or magnetic disk glass substrates to a holder and immersing them in a cleaning tank or a chemical strengthening liquid tank, the side wall surface comes into contact with the cassette and the zirconia particles are detached, Therefore, it is considered that zirconia particles adhere to the main surface.
In view of the above-mentioned points, the inventors of the present application have come up with the invention of the aspect described below.

  That is, one aspect of the present invention is a method of manufacturing a glass substrate for a magnetic disk having a pair of main surfaces and a side wall surface orthogonal to the pair of main surfaces, and the disk-shaped glass base plate is held by a carrier The main surface of the glass base plate is sandwiched between polishing pads, a polishing liquid having zirconia particles as abrasive grains is supplied between the glass base plate and the polishing pad, and the polishing pad and the glass base plate are relative to each other. Polishing the main surface of the glass base plate, and after the polishing step, when the side wall surface or main surface of the glass base plate is polished, the side of the glass base plate A removing step of physically removing the zirconia particles adhering to the side wall surface of the glass base plate by rubbing the wall surface and the end surface of the carrier facing the side wall surface of the glass substrate.

  Another aspect of the present invention is a method of manufacturing a glass substrate for a magnetic disk having a pair of main surfaces and a side wall surface orthogonal to the pair of main surfaces, the disk-shaped glass base plate being held by a carrier The main surface of the glass base plate is sandwiched between polishing pads, a polishing liquid having zirconia particles as abrasive grains is supplied between the glass base plate and the polishing pad, and the polishing pad and the glass base plate are relative to each other. The main surface polishing step for polishing the main surface of the glass base plate, and after the main surface polishing step, the glass base plate in contact with the end face of the carrier in the main surface polishing step. And an end surface polishing step for polishing the side wall surface.

  Yet another aspect of the present invention is a method of manufacturing a glass substrate for a magnetic disk comprising a pair of main surfaces and a side wall surface orthogonal to the pair of main surfaces, wherein the disk-shaped glass base plate is used as a carrier. Holding the main surface of the glass base plate with a polishing pad, supplying a polishing liquid having zirconia particles as abrasive grains between the glass base plate and the polishing pad, and attaching the polishing pad and the glass base plate By relatively moving, the first polishing step of polishing the main surface of the glass base plate, the glass base plate is held by the carrier, the main surface of the glass base plate is sandwiched between the polishing pads, A polishing liquid having abrasive grains other than zirconia particles as abrasive grains is supplied between the glass base plate and the polishing pad, and between the side wall surface of the glass base plate and the end face of the carrier. Relative to the base plate Be to moving includes a second polishing step of polishing the main surface of the glass workpiece, the.

  In the second polishing step of the method for manufacturing the glass substrate for magnetic disk, the maximum gap between the glass base plate and the carrier is preferably 0.5 mm or more.

  In the method for manufacturing the glass substrate for magnetic disk, it is preferable that the surface roughness of the end surface of the carrier that contacts the side wall surface of the glass base plate is 5 μm or less.

  In the method for manufacturing a glass substrate for a magnetic disk, the surface roughness of the side wall surface of the glass base plate before being polished using the polishing liquid having zirconia particles is 0.1 μm or less in terms of arithmetic average roughness Ra. It is preferable.

  The method for manufacturing a glass substrate for a magnetic disk is preferably performed when the glass substrate for a magnetic disk has a diameter larger than 2.5 inches and a plate thickness of 0.6 mm or less.

  In the method for manufacturing a glass substrate for a magnetic disk, it is preferable to polish using a fixed abrasive when the side wall surface of the glass base plate is polished.

  In the method for producing a glass substrate for a magnetic disk, when the side wall surface of the glass base plate is polished, it may be polished using free abrasive grains. In that case, the size of the free abrasive grains is zirconia. It is preferable that it is smaller than the grain size.

  In the method for manufacturing a glass substrate for a magnetic disk, it is preferable to chemically strengthen the glass base plate after polishing the side wall surface of the glass base plate.

  It is preferable to polish the side wall surface of the glass base plate before the first polishing step of the method for manufacturing the magnetic disk glass substrate.

  It is preferable to chemically strengthen the glass base plate after the second polishing step of the method for producing the glass substrate for magnetic disk.

  According to the above-described method for manufacturing a glass substrate for magnetic disk, when manufacturing a glass substrate for magnetic disk by polishing using zirconia abrasive grains as a polishing material for loose abrasive grains, head crash failure, thermal asperity failure, etc. It is possible to manufacture a glass substrate for a magnetic disk that hardly causes a problem.

The figure which shows an example of the flow of the manufacturing method of the glass substrate of 1st Embodiment. The disassembled perspective view of the grinding | polishing apparatus (double-side polish apparatus) used at a 1st grinding | polishing process. Sectional drawing of the polisher (double-side polish apparatus) used at a 1st grinding | polishing process. The figure which shows an example of the flow of the manufacturing method of the glass substrate of 2nd Embodiment. The figure which shows the clearance gap between a carrier and the glass substrate in grinding | polishing.

Hereinafter, the manufacturing method of the glass substrate for magnetic disks of this invention is demonstrated in detail.
(1) 1st Embodiment First, the manufacturing method of the glass substrate for magnetic discs of 1st Embodiment is demonstrated.

[Magnetic disk glass substrate]
Aluminosilicate glass, soda lime glass, borosilicate glass, or the like can be used as the material for the magnetic disk glass substrate in the present embodiment. In particular, aluminosilicate glass can be suitably used in that it can be chemically strengthened and a glass substrate for a magnetic disk excellent in the flatness of the main surface and the strength of the substrate can be produced.

Although the composition of the glass substrate for a magnetic disk of this embodiment is not limited, the glass substrate of this embodiment is preferably converted to an oxide standard and expressed in mol%, SiO ₂ is 50 to 75%, Al _{2 to} O ₃ is selected from 1 to 15%, at least one component selected from Li ₂ O, Na ₂ O and K ₂ O in total 5 to 35%, selected from MgO, CaO, SrO, BaO and ZnO 0-20% in total of at least one component, as well as _{ZrO 2, TiO 2, La 2} O 3, Y 2 O 3, Ta 2 O 5, Nb 2 O 5 and at least one selected from HfO ₂ It is an aluminosilicate glass having a composition having 0 to 10% in total.

  The glass substrate for a magnetic disk in the present embodiment is an annular thin glass substrate. Although the size of the glass substrate for magnetic disks is not ask | required, for example, it is suitable as a glass substrate for magnetic disks with a nominal diameter of 2.5 inches.

[Method of manufacturing glass substrate for magnetic disk]
Hereinafter, the manufacturing method of the glass substrate for magnetic disks of 1st Embodiment is demonstrated for every process shown in FIG. However, the order of each step may be changed as appropriate.

(1) Molding of glass base plate (S10) and lapping step (S12)
For example, in a glass base plate forming step by a float method, first, a glass sheet is obtained by continuously pouring molten glass having the above-described composition into a bath filled with molten metal such as tin. The molten glass flows along the traveling direction in a bathtub that has been subjected to a strict temperature operation, and finally a plate-like glass adjusted to a desired thickness and width is formed. From this plate glass, a glass base plate having a predetermined shape as a base of the glass substrate for a magnetic disk is cut out. Since the surface of the molten tin in the bath is horizontal, the flatness of the surface of the glass base plate obtained by the float process is sufficiently high.
For example, in a glass base plate molding process by a press molding method, a glass gob made of molten glass is supplied onto a lower mold that is a receiving gob forming mold, and an upper mold that is a lower mold and an opposing gob forming mold is used. Glass gob is press molded. More specifically, after a glass gob made of molten glass is supplied onto the lower mold, the lower surface of the upper mold cylinder and the upper surface of the lower mold cylinder are brought into contact with each other, and the upper mold and the upper mold mold are slid. Form a thin glass blank forming space outside the moving surface and the sliding surface of the lower mold and the lower mold body, and lower the upper mold to perform press molding. To rise. Thereby, the glass base plate used as the origin of the glass substrate for magnetic discs is shape | molded.
In addition, a glass base plate can be manufactured not only using the method mentioned above but using well-known manufacturing methods, such as a downdraw method, a redraw method, and a fusion method.

  Next, lapping processing using alumina-based loose abrasive grains is performed on both main surfaces of the glass base plate cut into a predetermined shape, if necessary. Specifically, the lapping platen is pressed on both sides of the glass base plate from above and below, a grinding liquid (slurry) containing free abrasive grains is supplied onto the main surface of the glass base plate, and these are moved relatively. Perform lapping. In addition, when a glass base plate is shape | molded with the float glass process, since the precision of the roughness of the main surface after shaping | molding is high, you may abbreviate | omit this lapping process.

(2) Coring step (S14)
Using a cylindrical diamond drill, an inner hole is formed in the center of the glass base plate to obtain an annular glass base plate.

(3) Chamfering process (S16)
After the coring step, a chamfering step for forming a chamfered portion at the ends (outer peripheral end and inner peripheral end) is performed. In the chamfering step, the outer peripheral end and the inner peripheral end of the annular glass base plate are chamfered with, for example, a metal bond grindstone using diamond abrasive grains to form a chamfered portion.

(4) Grinding process with fixed abrasive (S18)
In the grinding process using fixed abrasive grains, grinding is performed on the main surface of the annular glass base plate using a double-side grinding apparatus equipped with a planetary gear mechanism. The machining allowance by grinding is, for example, about several μm to 100 μm. The double-sided grinding apparatus has a pair of upper and lower surface plates (upper surface plate and lower surface plate), and an annular glass base plate is sandwiched between the upper surface plate and the lower surface plate. Then, by moving both the upper surface plate and the lower surface plate, or both of them, the main surface of the glass base plate is ground by relatively moving the glass base plate and each surface plate. be able to.

(5) First polishing (main surface polishing) step (S20)
Next, 1st grinding | polishing is given to the main surface of the ground glass base plate. The machining allowance by the first polishing is, for example, about several μm to 50 μm. The purpose of the first polishing is to remove scratches, distortion, waviness, and fine waviness remaining on the main surface by grinding with fixed abrasive grains. In addition, the surface roughness (Ra) of the side wall surface of the glass base plate before the first polishing is preferably 0.1 μm or less, and more preferably 0.05 μm or less. The surface roughness (Ra) here can be measured with a stylus roughness meter. Since the surface roughness of the side wall surface of the glass base plate is so small, the contact area with the carrier can be increased, so that the number of abrasive grains intercalated increases and the force is distributed to more abrasive grains. Therefore, the ZrO ₂ particles are less likely to pierce. Also, if the roughness is small, scratches caused by the carrier are less likely to enter when coming into contact with the carrier, so the probability of piercing the side wall surface of the glass base plate is indirectly reduced by reducing the number of ZrO ₂ abrasive grains captured by the scratch. It can be made even smaller. Therefore, it is difficult for zirconia abrasive grains to stick to the side wall surface of the glass base plate during the first polishing.
[Polishing equipment]
A polishing apparatus used in the first polishing step will be described with reference to FIGS. FIG. 2 is an exploded perspective view of a polishing apparatus (double-side polishing apparatus) used in the first polishing step. FIG. 3 is a cross-sectional view of a polishing apparatus (double-side polishing apparatus) used in the first polishing process. Note that the same configuration as this polishing apparatus can be applied to a grinding apparatus used in the above-described grinding process.

  As shown in FIG. 2, the polishing apparatus has a pair of upper and lower surface plates, that is, an upper surface plate 40 and a lower surface plate 50. An annular glass base plate G is sandwiched between the upper surface plate 40 and the lower surface plate 50, and either one or both of the upper surface plate 40 and the lower surface plate 50 are moved to operate the glass base plate G. By moving the surface plates relative to each other, both main surfaces of the glass base plate G can be polished.

The configuration of the polishing apparatus will be described more specifically with reference to FIGS.
In the polishing apparatus, an annular flat polishing pad 10 is attached to the upper surface of the lower platen 50 and the bottom surface of the upper platen 40 as a whole. The carrier 30 (holding member) includes a tooth portion 31 provided on the outer peripheral portion and meshing with the sun gear 61 and the internal gear 62, and one or a plurality of hole portions 31 for receiving and holding the glass base plate G. . The surface roughness of the end surface of the hole portion 31 that contacts the side wall surface of the glass base plate (the wall surface facing the side wall surface of the glass base plate) is 5 μm or less, preferably 3 μm or less. The surface roughness (Ra) here can be measured by moving the needle in the circumferential direction with respect to the end face of the hole 31 using a stylus type roughness meter. Since the surface roughness of the end face of the hole portion 31 of the carrier is so small, the contact area with the glass base plate can be increased, so that the number of abrasive grains entering between them increases, and more abrasive grains are obtained. Since the force is dispersed, the ZrO ₂ particles are hardly stuck. In addition, if the roughness is small, scratches are less likely to enter the glass base plate when it comes into contact with the glass base plate, so that the ZrO ₂ abrasive grains captured by the scratches are reduced, and the glass base plate is pierced. Probability can also be reduced indirectly. During the first polishing, the side wall surface of the glass base plate is prevented from being excessively roughened, and zirconia abrasive grains are difficult to adhere to the side wall surface.
The sun gear 61, the internal gear 62 provided on the outer edge, and the disk-shaped carrier 30 constitute a planetary gear mechanism centered on the central axis CTR as a whole. The disc-shaped carrier 30 meshes with the sun gear 61 on the inner peripheral side and meshes with the internal gear 62 on the outer peripheral side, and accommodates and holds one or more glass base plates G (workpieces). On the lower surface plate 50, the carrier 30 revolves while rotating as a planetary gear, and the glass base plate G and the lower surface plate 50 are relatively moved. For example, if the sun gear 61 rotates in the CCW (counterclockwise) direction, the carrier 30 rotates in the CW (clockwise) direction, and the internal gear 62 rotates in the CCW direction. As a result, relative movement occurs between the polishing pad 10 and the glass base plate G. Similarly, the glass base plate G and the upper surface plate 40 may be relatively moved.

  During the operation of the relative movement, the upper surface plate 40 is pressed against the glass base plate G (that is, in the vertical direction) with a predetermined load, and the polishing pad 10 is pressed against the glass base plate G. A polishing liquid (slurry) is supplied between the glass base plate G and the polishing pad 10 from the polishing liquid supply tank 71 via one or a plurality of pipes 72 by a pump (not shown). The main surface of the glass base plate G is polished by the abrasive contained in the polishing liquid. Here, it is preferable that the polishing liquid used for polishing the glass base plate G is discharged from the upper and lower surface plates, returned to the polishing liquid supply tank 71 by a filter and a return pipe (not shown), and reused.

In this polishing apparatus, it is preferable that the load of the upper surface plate 40 applied to the glass base plate G is adjusted for the purpose of setting a desired polishing load on the glass base plate G. The load is preferably 50 g / cm ² or more, more preferably 70 g / cm ² or more, and still more preferably 90 g / cm ² or more from the viewpoint of achieving a high polishing rate and suppressing scratches on the glass base plate. Further, from the viewpoint of reducing scratches and stabilizing the quality, the polishing load is preferably 180 g / cm ² or less, more preferably 160 g / cm ² or less, and even more preferably 140 g / cm ² or less. That is, the load is ^{preferably 50g / cm 2 ~180g / cm 2} , more preferably ^{70g / cm 2 ~160g / cm 2} , 90g / cm 2 ~140g / cm 2 is more preferred. Further, in this polishing apparatus, the load of the upper surface plate 40 applied to the glass base plate G may be adjusted for the purpose of achieving a processing rate equal to or higher than that in the case of polishing using cerium oxide abrasive grains. . Load, 120 g / cm ² or more is preferred from the viewpoint of high polishing rate achieved, more preferably from 130 g / cm ² or more, more preferably 150 g / cm ² or more. Further, from the viewpoint of achieving a high polishing rate, the platen rotational speed is preferably 35 rpm or more, more preferably 50 rpm or more. Moreover, 1 rpm or more is preferable and, as for the rotational speed of the sun gear 61, 2 rpm or more is more preferable.

  The supply rate of the polishing liquid during polishing varies depending on the polishing pad 10, the composition and concentration of the polishing liquid, and the size of the glass base plate G. From the viewpoint of suppressing scratches on the glass base plate while improving the polishing rate, 500 -5000 ml / min are preferable, More preferably, it is 1000-4500 ml / min, More preferably, it is 1500-4000 ml / min.

The polishing liquid used in the polishing apparatus of FIG. 1 contains zirconia (ZrO ₂ ) abrasive grains as an abrasive.
The average particle diameter (D50) of the zirconia abrasive grains is preferably 0.10 to 0.60 μm and more preferably 0.2 to 0.4 μm from the viewpoint of improving the polishing rate. Here, the average particle size (D50) means a particle size at which the cumulative volume frequency calculated by the volume fraction is 50% calculated from the smaller particle size. Similarly, from the viewpoint of improving the polishing rate by effectively utilizing the total number of abrasive grains, it is desirable to make the grain diameters of the abrasive grains uniform, and the standard deviation (SD) of the zirconia abrasive grains in the polishing liquid is 1 μm or less. Preferably, it is 0.5 μm or less, more preferably 0.2 μm or less.

In the first polishing step, the surface irregularities of the main surface of the glass base plate are polished so that the roughness (Ra) is 0.5 nm or less and the micro waveness (MW-Rq) is 0.5 nm or less. . Here, the micro waveness can be expressed by an RMS (Rq) value calculated as a roughness of a wavelength band of 100 to 500 μm in an area of a radius of 14.0 to 31.5 mm on the entire main surface. It can measure using Model 4224 made from.
The roughness of the main surface is represented by the arithmetic average roughness Ra defined by JIS B0601: 2001. When the roughness is 0.006 μm or more and 200 μm or less, for example, the roughness is measured with a Mitutoyo Corporation roughness measuring machine SV-3100, It can be calculated by a method defined in JIS B0633: 2001. As a result, when the roughness is 0.03 μm or less, for example, it is measured with a scanning probe microscope (atomic force microscope; AFM) nanoscope manufactured by Japan Veeco, and calculated by the method defined in JIS R1683: 2007. it can. In the present application, the arithmetic average roughness Ra when measured at a resolution of 512 × 512 pixels in a 1 μm × 1 μm square measurement area can be used.

(6) End face polishing step (S22)
Next, end face polishing (edge polishing) of the annular glass base plate is performed.
In the end surface polishing, the end surface polishing is performed on the inner peripheral side wall surface (end surface) and the outer peripheral side wall surface (end surface) of the glass base plate. By performing end surface polishing, removal of contamination such as dust on the side wall surface of the glass base plate, damage or scratches, etc., preventing the occurrence of thermal asperity, corrosion of sodium and potassium, etc. It is possible to prevent the occurrence of ion precipitation that is a cause. Furthermore, by performing end face polishing, it is possible to physically remove zirconia particles that can adhere to the side wall surface of the glass base plate G in the first polishing step described above (removal step). In addition, the aspect which removes a zirconia particle from a glass base plate by an etching process, scrub washing | cleaning, etc. is not included in removing the zirconia particle physically mentioned in this specification.
The machining allowance of the side wall surface of the glass base plate by end face polishing is 30 μm or more, preferably 50 μm or more. Thereby, the zirconia particle adhering to the side wall surface of a glass base plate can be removed reliably.

  In order to remove the zirconia particles adhering to the side wall surface of the glass base plate G by polishing, either polishing using fixed abrasive grains or polishing using free abrasive grains may be used, but fixed abrasive grains are preferred. . This is due to the following reason. For example, when end face polishing is performed on a laminated body in which glass base plates are laminated with a spacer interposed therebetween, the spacers are considered in consideration of a shift at the time of stacking individual glass substrates in a direction parallel to the main surface of the glass base plate. Is dimensioned so as to be located on the inner side (center side of the glass base plate) than the side wall surface of the glass base plate. Therefore, when the glass base plates are laminated, the outer peripheral edge portion of the main surface of each glass base plate is slightly but exposed. In this state, when the end surface polishing using the free abrasive grains is performed on the laminate, the free abrasive grains may enter the outer peripheral edge portion of the exposed main surface of the glass base plate to roughen (damage) the surface. Therefore, in end face polishing, polishing using fixed abrasive grains that do not roughen the outer peripheral edge portion of the main surface with abrasive grains is preferable to polishing using loose abrasive grains.

  In polishing using fixed abrasive grains, for example, a fixed urethane grain containing an abrasive other than zirconia such as cerium with respect to a hard urethane pad (JIS-A hardness: 60 to 95) may be used. preferable. Since it is the side wall surface of the glass base plate that the zirconia particles adhere in the first polishing step of the previous step, when polishing the laminated body of the glass base plate, depending on the side wall surface of each glass base plate What is necessary is just to grind | polish with the urethane pad etc. which were provided with the surface parallel to the side surface of the laminated body comprised.

  On the other hand, when performing end face polishing using loose abrasive grains, for example, brush polishing using a slurry (polishing liquid) containing fine particles such as cerium oxide as loose abrasive grains may be used. At this time, it is preferable that the size of the loose abrasive used in the end face polishing is smaller than the size of the zirconia abrasive used in the first polishing. This is because even when free abrasive grains enter the main surface of the glass base plate during end surface polishing, since the free abrasive grains are smaller than the zirconia particles, the surface properties obtained in the first polishing step are This is because it does not worsen. For example, the average value (D50) of the particle size of the free abrasive grains is 0.3 to 1.0 μm.

(7) Chemical strengthening step (S24)
Next, the glass base plate after the first polishing is chemically strengthened.
As the chemical strengthening solution, for example, a mixed solution of potassium nitrate (60% by weight) and sodium sulfate (40% by weight) can be used. In the chemical strengthening, the chemical strengthening liquid is heated to, for example, 300 ° C. to 400 ° C., and the cleaned glass base plate is preheated to, for example, 200 ° C. to 300 ° C. Soak for 5 hours. The immersion is preferably performed in a state of being housed in a holder so that the plurality of glass base plates are held by the side wall surfaces so that the entire main surfaces of both glass base plates are chemically strengthened.
In this way, by immersing the glass base plate in the chemical strengthening solution, lithium ions and sodium ions on the surface layer of the glass base plate are replaced with sodium ions and potassium ions having a relatively large ion radius in the chemical strengthening solution, respectively. The glass base plate is strengthened. The chemically strengthened glass base plate is washed. For example, after washing with sulfuric acid, it is washed with pure water or the like.

(8) Second polishing (final polishing) step (S26)
Next, final polishing is performed on the chemically strengthened and sufficiently cleaned glass base plate. The machining allowance by the final polishing is 5 μm or less. The second polishing is intended for mirror polishing of the main surface. In the final polishing, for example, the polishing apparatus used in the first polishing is used. At this time, the difference from the first polishing is that the type and particle size of the free abrasive grains are different and the hardness of the resin polisher is different. As the free abrasive grains used in the second polishing, for example, fine particles (particle size: diameter of about 10 to 50 nm) such as colloidal silica made turbid in the slurry are used.
A glass substrate for a magnetic disk can be obtained by washing the polished glass base plate with a neutral detergent, pure water, IPA or the like.

As mentioned above, although the manufacturing method of the glass substrate for magnetic discs of this embodiment was demonstrated for every process, the order of a process is not restricted to the order mentioned above. The end face polishing step may be performed after the first polishing step using zirconia abrasive grains, and the other order may be changed as appropriate. For example, the chemical strengthening step may be performed before the first polishing step.
According to the method for manufacturing a glass substrate for a magnetic disk of the present embodiment, after the first polishing step of polishing the main surface of the glass base plate using a polishing liquid containing zirconia as polishing abrasive grains, the glass in the end face polishing step. In order to polish the side wall surface of the base plate, the zirconia particles attached to the side wall surface of the glass base plate in the first polishing step are removed in the subsequent end surface polishing step.

Conventionally, in a method in which a glass base plate is held on a carrier and main surface polishing is performed using cerium oxide abrasive grains as an abrasive, polishing can be performed at a high processing rate even under relatively gentle processing conditions. For example, polishing could be performed under processing conditions where the processing pressure was about 100 g / cm ² and the rotation speed of the surface plate was about 10 rpm. However, in the method of polishing using zirconium abrasive grains, the processing rate becomes extremely worse if the same processing conditions as when using cerium oxide abrasive grains are applied, so that processing is severer than when cerium oxide is used. Conditions need to be applied. For example, it is necessary to perform polishing under processing conditions in which the load of the upper platen 40 applied to the glass base plate G is 120 g / cm ² or more and the platen rotation number is 35 rpm or more. Thus, since the processing conditions in the case of using zirconia abrasive grains are different from the general processing conditions in the case of using cerium oxide, zirconia abrasive grains are formed on the side wall surface of the glass base plate during main surface polishing. There is a problem that it sticks easily by sticking. However, according to the manufacturing method of the present embodiment, since the zirconia particles attached to the side wall surface of the glass base plate in the first polishing step are removed in the subsequent end surface polishing step, the zirconia particles are removed from the glass base plate in the subsequent step. It will not adhere to the main surface.

  The manufacturing method of this embodiment is suitable for manufacturing a glass substrate for a magnetic disk having a diameter larger than 2.5 inch size and a plate thickness of 0.6 mm or less. Such a glass substrate for a magnetic disk has a higher aspect ratio (diameter / plate thickness) than the conventional one. For this reason, since the plate | board thickness of a glass base plate is thin and a contact area with the end surface of a carrier is small, a glass base plate tends to contact the end surface of a carrier with a stronger force. Moreover, since the area of the main surface of a glass base plate is large and it is easy to receive a frictional force from a polishing pad, this also makes a glass base plate contact the end surface of a carrier with a stronger force. For these reasons, the zirconia particles are likely to adhere to the side wall surface of the glass base plate, and the ratio of the zirconia particles attached to the side wall surface of the glass base plate increases. However, according to the manufacturing method of this embodiment, since the zirconia particle adhering to the side wall surface of a glass base plate is removed in an end surface grinding | polishing process as mentioned above, generation | occurrence | production of such a problem can be suppressed.

  In addition, in the manufacturing method of the glass substrate for magnetic disks of this embodiment, it is preferable to perform a chemical strengthening process after end surface grinding | polishing. This is due to the following reason. That is, in the chemical strengthening step, as described above, a plurality of glass base plates are attached to a holder and immersed in a chemical strengthening liquid tank. At that time, when zirconia particles remain on the side wall surface of the glass base plate. The zirconia particles fall off when the glass base plate is gripped or the side wall surface of the glass base plate comes into contact with the holder, and the dropped zirconia particles may adhere to the main surface of the glass base plate. is there.

[Magnetic disk]
A magnetic disk is obtained as follows using a magnetic disk glass substrate.
The magnetic disk is, for example, on the main surface of a glass substrate for magnetic disk (hereinafter simply referred to as “substrate”), in order from the closest to the main surface, at least an adhesion layer, an underlayer, a magnetic layer (magnetic recording layer), and a protective layer. A layer and a lubricating layer are laminated.
For example, the substrate is introduced into a film forming apparatus that has been evacuated, and a film is sequentially formed from an adhesion layer to a magnetic layer on the main surface of the substrate in an Ar atmosphere by a DC magnetron sputtering method. For example, CrTi can be used as the adhesion layer, and CrRu can be used as the underlayer. As the magnetic layer, for example, a CoPt alloy can be used. It is also possible to form a CoPt-based alloy and FePt based alloy L ₁₀ regular structure and magnetic layer for heat-assisted magnetic recording. After the above film formation, a magnetic recording medium can be formed by forming a protective layer using, for example, C ₂ H ₄ by a CVD method and subsequently performing nitriding treatment for introducing nitrogen into the surface. Thereafter, for example, PFPE (perfluoropolyether) is applied on the protective layer by a dip coating method, whereby a lubricating layer can be formed.
The produced magnetic disk is preferably incorporated in an HDD (Hard Disk Drive) as a magnetic recording / reproducing apparatus together with a magnetic head equipped with a DFH (Dynamic Flying Height) control mechanism.

(2) Second Embodiment Next, a method for manufacturing a glass substrate for a magnetic disk according to a second embodiment will be described.
Here, a description will be given focusing on differences from the first embodiment.
In FIG. 4, an example of the flow of the manufacturing method of the glass substrate of 2nd Embodiment is shown. Hereinafter, each process shown in FIG. 4 will be described. The order of the steps shown in FIG. 4 may be changed as appropriate.

  The manufacturing method of the glass substrate of 2nd Embodiment is a glass base plate shaping | molding (S30), a lapping process (S32), a coring process (S34), a chamfering process (S36), an end surface grinding | polishing process (S38), fixed grinding | polishing. Each step includes a grinding step with grains (S40), a first polishing (main surface polishing) step (S42), a second polishing step (S44), a chemical strengthening step (S46), and a final polishing step (S48).

(1) Molding of glass base plate (S30) and lapping step (S32)
It is performed in the same manner as the glass base plate molding (S10) and the lapping step (S12) of the first embodiment.
(2) Coring step (S34)
It is performed in the same manner as the coring step (S14) of the first embodiment.
(3) Chamfering process (S36)
It is performed in the same manner as the chamfering step (S16) of the first embodiment.

(4) End face polishing step (S38)
Except for the following points, it is performed in the same manner as the end surface polishing step (S22) of the first embodiment.
In the present embodiment, in the end surface polishing, the inner peripheral side wall surface (end surface) and the outer peripheral side wall surface (end surface) of the glass base plate are mirror-finished by brush polishing. At this time, a slurry containing fine particles such as cerium oxide as free abrasive grains is used.
The end surface polishing step is performed before the first polishing step in order to smooth the end surface of the glass base plate and thereby make it difficult for the zirconia abrasive grains to adhere to the side wall surface of the glass base plate in the first polishing step of the subsequent step. It is preferable. For example, it is preferable to perform the end surface polishing so that the arithmetic average roughness Ra of the end surface of the glass base plate after the end surface polishing step is 0.1 μm or less.
In the present embodiment, in order to remove the zirconia particles adhering to the side wall surface of the glass base plate G by polishing, either polishing using fixed abrasive grains or polishing using free abrasive grains may be used.

(5) Grinding process with fixed abrasive (S40)
This is performed in the same manner as the grinding step (S16) with the fixed abrasive grains of the first embodiment.
(6) First polishing (main surface polishing) step (S42)
This is performed in the same manner as the first polishing (main surface polishing) step (S24) of the first embodiment.

(7) Second polishing step (S44)
In the second polishing step (S44), second polishing is performed on the main surface of the glass base plate that has undergone the first polishing step. The machining allowance by the second polishing is, for example, about several μm to 20 μm, preferably 30 μm or more, and more preferably 50 μm or more. Thereby, the zirconia particle adhering to the side wall surface of a glass base plate can be removed reliably. In the second polishing, the main surface is polished at a high polishing rate, and zirconia particles that can adhere to the side wall surface of the glass base plate in the first polishing step are physically removed (removal step is performed). Objective. In the second polishing step, it is preferable to use cerium oxide (cerium dioxide) abrasive grains as the abrasive.

In the second polishing, for example, the polishing apparatus used in the first polishing is used. For the purpose of polishing the main surface while supplying cerium oxide abrasive grains between the glass base plate and the carrier 30, the glass base plate G is used. A gap is provided between the carrier 30 and the carrier 30. This point will be further described with reference to FIG. FIG. 5 is a view showing a state in which the glass base plate G is accommodated in the hole 31 of the carrier 30.
As shown in FIG. 5, when the outer diameter of the glass base plate G to be polished is D1, and the diameter of the hole 31 of the carrier 30 (the diameter of the contact surface with which the glass base plate abuts) is D2, D2> D1 Is established. Thereby, abrasive grains of cerium oxide (CeO ₂ ) in the polishing liquid enter between the side wall surface Gt of the glass base plate G and the side wall surface 30t forming the hole portion 31 of the carrier 30 (that is, supply) The gap CL is provided to such an extent that it can be). In this case, the maximum value (maximum gap) of the gap CL is (D2-D1) at the maximum. The maximum value of the relative displacement amount between the glass base plate G and the carrier 30 is defined by the gap CL.

  As shown in FIG. 5, the main surface is polished on the main surface of the glass base plate G in a state where cerium oxide abrasive grains are supplied to the gap CL between the glass base plate G and the hole 31 of the carrier 30. If it carries out, it will become possible to remove the zirconia particles adhering to the side wall surface Gt of the glass base plate G in the first polishing. This is due to the action described below. That is, during the polishing process, the glass base plate G moves in an unconstrained state in the hole 31 of the carrier 30 in a direction parallel to the main surface while being loaded by the surface plate in the thickness direction. At this time, the side wall surface Gt of the glass base plate G is brought into contact with the side wall surface 30 t forming the hole portion 31, but the cerium oxide abrasive supplied to the gap CL between the glass base plate G and the hole portion 31 of the carrier 30. The grains polish the side wall surface Gt of the glass base plate G, whereby the zirconia particles adhering to the side wall surface Gt are detached from the side wall surface Gt of the glass base plate G. The zirconia particles separated from the side wall surface Gt are discharged together with the polishing liquid. Note that the surface property of the side wall surface Gt is not deteriorated (that is, the surface is roughened) by an impact when the side wall surface Gt of the glass base plate G abuts on the side wall surface 30t of the carrier 30. An elastic member may be provided on the side wall surface 30t.

A sufficient amount of abrasive grains of cerium oxide (CeO ₂ ) is supplied between the side wall surface Gt of the glass base plate G and the side wall surface 30t forming the hole 31 of the carrier 30 to the side wall surface Gt of the glass base plate G. For the purpose of ensuring high polishing performance, the maximum value (maximum gap; D2-D1) of the gap CL between the side wall surface Gt of the glass base plate G and the side wall surface 30t of the carrier 30 is preferably 0.5 mm or more, More preferably, it is 1.0 mm or more.
In the second polishing, from the viewpoint of efficiently polishing the side wall surface Gt of the glass base plate G with cerium oxide abrasive grains and removing zirconia particles, the concentration of the cerium oxide abrasive grains in the polishing liquid is 5 to 30% by weight. It is preferable.

  In this polishing step, the abrasive supplied to the gap CL between the glass base plate G and the hole 31 of the carrier 30 is not limited to cerium oxide abrasive grains, and may be other abrasives. That is, cerium oxide abrasive grains are preferable from the viewpoint of increasing the processing rate of the main surface polishing, but the second purpose of the second polishing is to physically remove zirconia particles that can adhere to the side wall surface of the glass base plate. In some cases, the abrasive may not be cerium oxide abrasive. As other abrasives, for example, abrasive grains of alumina, diamond, titanium, and silica may be used. The average particle diameter (D50) of the abrasive grains in the polishing liquid in the second polishing is preferably equal to or smaller than the average particle diameter (D50) of the zirconia abrasive grains in the first polishing.

  In the second embodiment, in addition to the first polishing step (S42), similarly to the second polishing step (S44), the roughness (Ra) of the surface irregularities on the main surface of the glass base plate is 0.5 nm or less. In addition, polishing is performed so that the micro waveness (MW-Rq) is 0.5 nm or less.

(8) Chemical strengthening step (S46)
It is performed in the same manner as the chemical strengthening step (S24) of the first embodiment.
(9) Final polishing step (S48)
This is performed in substantially the same manner as the second polishing (final polishing) step (S26) of the first embodiment.
Also in the final polishing step (S48), as in the second polishing step (S44), the maximum value (maximum gap) of the gap between the side wall surface of the glass base plate and the side wall surface of the carrier is 0.5 mm or more. Preferably, it is 1.0 mm or more. Thereby, since the side wall surface of the glass base plate is polished also in the final polishing in addition to the second polishing, the removal performance for the zirconia particles that can adhere to the side wall surface is improved.
In the final polishing step, particles such as colloidal silica are supplied between the glass base plate and the hole of the carrier in the same manner as shown in FIG. The zirconia particles adhering to the side wall surface may be removed by polishing.
The glass substrate for magnetic disk and the magnetic disk are the same as described in the first embodiment.

[Examples and comparative examples related to the first embodiment]
In order to confirm the effect of the manufacturing method of the glass substrate of the first embodiment, a 2.5-inch magnetic disk is manufactured from the manufactured glass substrate, a LUL durability test is performed, and a head crash failure, a thermal asperity failure, etc. The presence or absence of defects was examined.
The composition of the glass of the manufactured magnetic disk glass substrate is as follows (% means mass%).
[Glass composition]
Converted to oxide standard, expressed in mol%, SiO ₂ is 50 to 75%, Al ₂ O ₃ is 1 to 15%, at least one component selected from Li ₂ O, Na ₂ O and K ₂ O 5 to 35% in total, 0 to 20% in total of at least one component selected from MgO, CaO, SrO, BaO and ZnO, and ZrO ₂ , TiO ₂ , La ₂ O ₃ and Y ₂ O ₃ , Aluminosilicate glass comprising a composition having a total of 0 to 10% of at least one component selected from Ta ₂ O ₅ , Nb ₂ O ₅ and HfO ₂

In the method for producing a glass substrate of the present embodiment, the glass base plate of (1) was formed by using a press molding method used in the method for producing a glass substrate for a magnetic disk described in JP2011-138589A. . In lapping, alumina-based free abrasive grains having an average particle diameter of 20 μm were used.
In the grinding with the fixed abrasive of (4), the diamond sheet (average particle diameter: 1 to 20 μm) was ground by using a grinding apparatus in which a diamond sheet obtained by hardening a resin bond was attached to the upper surface plate and the lower surface plate.
In the first polishing of (5), the polishing apparatus of FIGS. 2 and 3 was used for polishing for 60 minutes using zirconia abrasive grains having an average particle diameter (D50) of 1.0 μm.
In the end face polishing of (6), a plurality of glass base plates laminated with spacers sandwiched between glass base plates are polished using cerium oxide having an average particle size (D50) of 0.5 μm as free abrasive grains. Polished with a brush for 60 minutes.
In the chemical strengthening of (7), a liquid mixture of potassium nitrate (60% by weight) and sodium nitrate (40% by weight) is used as the chemical strengthening liquid, the temperature of the chemical strengthening liquid is set to 350 ° C., and preheated to 200 ° C. in advance. The glass base plate was immersed in the chemical strengthening solution for 4 hours.
In the second polishing of (8), polishing was performed for a predetermined time using colloidal silica having a particle diameter of 10 to 50 μm using a polishing apparatus similar to the polishing apparatus of FIGS. Thereby, arithmetic mean roughness Ra (JIS B0601: 2001) of the main surface was made into 0.15 nm or less. The glass base plate after the second polishing was cleaned using a neutral cleaning solution and an alkaline cleaning solution. This obtained the glass substrate for magnetic discs.
The average particle size (D50) was measured by a light scattering method using a particle size / particle size distribution measuring apparatus (Nikkiso Co., Ltd., Nanotrac UPA-EX150).

  A magnetic disk having a magnetic layer formed on the obtained glass substrate for a magnetic disk was prepared, and evaluated by performing an LUL durability test (600,000 times). The LUL endurance test is a state in which a hard disk drive (HDD) constituting a magnetic disk is placed in a constant temperature and humidity layer at a temperature of 70 ° C. and a humidity of 80% without stopping the movement of the head between the lamp and the ID stopper. It is a test to investigate the occurrence of abnormalities such as dirt and wear of the head after the test by reciprocating motion (seek operation). As a result of the LUL test of 80,000 times / day × 7.5 days = 600,000 times, the head ABS surface was magnified and visually observed with a microscope, and when adhesion, wear, or chipping of contamination was observed, it was evaluated as a failure. .

Examples In the examples, as described above, (1) glass base plate forming and lapping step, (2) coring step, (3) chamfering step, and (4) grinding with fixed abrasive grains. Step, (5) first polishing (main surface polishing) step, (6) end surface polishing step, (7) chemical strengthening step, and (8) second polishing (final) polishing step are performed in this order. It was. That is, the end face polishing step was performed after the first polishing step.

Comparative Example In the comparative example, (1) glass base plate forming and lapping step, (2) coring step, (3) chamfering step, (6) end surface polishing step, (4) fixed abrasive The grinding step with grains, the first polishing (main surface polishing) step (5), the chemical strengthening step (7), and the second polishing (final) polishing step (8) were performed in this order. That is, the end face polishing step was performed before the first polishing step.

In the LUL endurance test in the above examples and comparative examples, the examples passed and the comparative examples failed. When the cause of the comparative example which failed in the LUL endurance test was examined, particles adhered between the glass substrate and the magnetic layer, and the composition analysis of the particles revealed that the particles were zirconia particles. I understood it. That is, it was found that the residue of the zirconia abrasive grains used for the first polishing adhered to the main surface of the glass substrate was the cause of the failure of the durability test. From this, it can be seen that performing end face polishing after the first polishing step hardly causes problems such as head crash failure and thermal asperity failure.
[Examples and comparative examples related to the second embodiment]
Here, it demonstrates paying attention to the difference with the Example regarding the 1st Embodiment mentioned above, and a comparative example.

Each process of the manufacturing method of the glass substrate of 2nd Embodiment was performed in order.
here,
In the end face polishing of (4), a plurality of glass base plates laminated with a spacer interposed between the glass base plates is polished using cerium oxide having an average particle size (D50) of 1.0 μm as free abrasive grains. Polished with a brush.
In the grinding with the fixed abrasive of (5), the diamond sheet (average particle diameter: 1 to 20 μm) was ground by using a grinding apparatus in which a diamond sheet obtained by hardening a resin bond was attached to the upper surface plate and the lower surface plate.
In the first polishing of (6), polishing was performed for 60 minutes using the polishing apparatus of FIGS. Detailed polishing conditions are as shown below.
In the second polishing of (7), polishing was performed for 30 minutes using another polishing apparatus similar to that shown in FIGS. Detailed polishing conditions are as shown below. The maximum gap between the glass base plate and the carrier of the polishing apparatus is as shown in Table 2.

<Polishing conditions for first polishing>
・ Polishing pad: Hard urethane pad (JIS-A hardness: 80-100)
Polishing load: 120 g / cm ²
・ Surface plate speed: 30rpm
Polishing fluid supply flow rate: 3000 L / min
Polishing liquid: 15% by weight of zirconia (ZrO2) is contained as abrasive grains.
・ Average value of particle size (D50): 0.3 to 1.5 μm
・ Standard deviation of particle size (SD): 0.1 to 0.4 μm

<Polishing conditions for second polishing>
・ Polishing pad: Hard urethane pad (JIS-A hardness: 80-100)
Polishing load: 120 g / cm ²
・ Surface plate speed: 30rpm
Polishing fluid supply flow rate: 3000 L / min
Polishing liquid: 15% by weight of abrasive grains described in Tables 1 and 2 are contained.
・ Average value of particle size (D50): 0.8 to 1.5 μm
・ Standard deviation of particle size (SD): 0.2 to 0.8 μm

  In Table 2, as shown in FIG. 5, the maximum gap at the time of the second polishing is the outer diameter D1 of the glass base plate to be polished and the diameter D2 of the hole of the carrier accommodating the glass base plate. (= D2-D1).

  A magnetic disk having a magnetic layer formed on the obtained glass substrate for a magnetic disk was prepared, and evaluated by performing an LUL durability test (two types of 400,000 times and 600,000 times). The LUL endurance test is a state in which a hard disk drive (HDD) constituting a magnetic disk is placed in a constant temperature and humidity layer at a temperature of 70 ° C. and a humidity of 80% without stopping the movement of the head between the lamp and the ID stopper. It is a test to investigate the occurrence of abnormalities such as dirt and wear of the head after the test by reciprocating motion (seek operation). As a result of the LUL test of 80,000 times / day × 5 days = 400,000 times, the head ABS surface was magnified and visually observed with a microscope, and when adhesion, wear, or chipping of contamination was observed, it was evaluated as a failure. Moreover, as a result of the LUL test of 80,000 times / day × 7.5 days = 600,000 times, the head ABS surface was magnified and visually observed with a microscope. When adhesion, wear, or chipping was observed, it was evaluated as “good”, and when it was not observed, it was evaluated as “good”.

  In the LUL durability test (400,000 times) in the above Examples and Comparative Examples, Examples 1 to 6 were acceptable and Comparative Example 1 was unacceptable. When the cause of the comparative example which failed in the LUL endurance test (400,000 times) was examined, particles were adhered between the glass substrate and the magnetic layer. Was found to be zirconia particles. That is, it was found that the residue of the zirconia abrasive grains used for the first polishing adhered to the main surface of the glass substrate was the cause of the failure of the LUL durability test (400,000 times). From this, it can be seen that performing end face polishing after the first polishing step hardly causes problems such as head crash failure and thermal asperity failure.

In the LUL durability test (600,000 times) in Examples 1 to 6 that passed the LUL durability test (400,000 times), Examples 2, 3, 5, and 6 were “good”. It was better than 4. From the results of Examples 1 and 4, if the gap between the glass base plate and the carrier is narrow, the abrasive grains are not supplied to the gap in the second polishing, and the side wall surface of the glass base plate cannot be sufficiently polished, It turns out that the zirconia particle adhering to the side wall surface could not be removed sufficiently.
From Examples 2, 3, 5 and 6, if the maximum gap is provided at least 0.5 [mm] or more, the abrasive grains are supplied to the gap between the glass base plate and the carrier, and the side wall surface of the glass base plate It can be seen that the zirconia particles adhered to the side wall surface could be removed. Furthermore, if the maximum gap is set to 1.0 [mm] or more, the abrasive grains are sufficiently supplied to the gap between the carrier and the glass base plate, and the removal performance of zirconia particles can be sufficiently ensured.

  As mentioned above, although the manufacturing method of the glass substrate for magnetic discs of this invention was demonstrated in detail, this invention is not limited to the said embodiment, In the range which does not deviate from the main point of this invention, even if various improvement and a change are carried out. Of course it is good.

DESCRIPTION OF SYMBOLS 10 Polishing pad 30 Carrier 40 Upper surface plate 50 Lower surface plate 61 Sun gear 62 Internal gear 71 Polishing liquid supply tank 72 Piping

The polishing liquid used in the polishing apparatus of FIGS . 2 and 3 contains zirconia (ZrO ₂ ) abrasive grains as an abrasive.
The average particle diameter (D50) of the zirconia abrasive grains is preferably 0.10 to 0.60 μm and more preferably 0.2 to 0.4 μm from the viewpoint of improving the polishing rate. Here, the average particle size (D50) means a particle size at which the cumulative volume frequency calculated by the volume fraction is 50% calculated from the smaller particle size. Similarly, from the viewpoint of improving the polishing rate by effectively utilizing the total number of abrasive grains, it is desirable to make the grain diameters of the abrasive grains uniform, and the standard deviation (SD) of the zirconia abrasive grains in the polishing liquid is 1 μm or less. Preferably, it is 0.5 μm or less, more preferably 0.2 μm or less.

On the other hand, in the case of end polished using free abrasive grains may be, for example, a brush polishing with a slurry (polishing liquid) containing fine particles such as acid cerium as free abrasive grains. At this time, it is preferable that the size of the loose abrasive used in the end face polishing is smaller than the size of the zirconia abrasive used in the first polishing. This is because even when free abrasive grains enter the main surface of the glass base plate during end surface polishing, since the free abrasive grains are smaller than the zirconia particles, the surface properties obtained in the first polishing step are This is because it does not worsen. For example, the average value (D50) of the particle size of the free abrasive grains is 0.3 to 1.0 μm.

Conventionally, in a method in which a glass base plate is held on a carrier and main surface polishing is performed using cerium oxide abrasive grains as an abrasive, polishing can be performed at a high processing rate even under relatively gentle processing conditions. For example, polishing could be performed under processing conditions where the processing pressure was about 100 g / cm ² and the rotation speed of the surface plate was about 10 rpm. However, in the method of polishing using zirconia abrasive grains, the processing rate becomes extremely worse if the same processing conditions as when cerium oxide abrasive grains are used are applied, so that processing is severer than when cerium oxide is used. Conditions need to be applied. For example, it is necessary to perform polishing under processing conditions in which the load of the upper platen 40 applied to the glass base plate G is 120 g / cm ² or more and the platen rotation number is 35 rpm or more. Thus, since the processing conditions in the case of using zirconia abrasive grains are different from the general processing conditions in the case of using cerium oxide, zirconia abrasive grains are formed on the side wall surface of the glass base plate during main surface polishing. There is a problem that it sticks easily by sticking. However, according to the manufacturing method of the present embodiment, since the zirconia particles attached to the side wall surface of the glass base plate in the first polishing step are removed in the subsequent end surface polishing step, the zirconia particles are removed from the glass base plate in the subsequent step. It will not adhere to the main surface.

A magnetic disk having a magnetic layer formed on the obtained glass substrate for a magnetic disk was prepared, and evaluated by performing an LUL durability test (600,000 times). The LUL endurance test is a state in which a hard disk drive (HDD) constituting a magnetic disk is placed in a constant temperature and humidity chamber at a temperature of 70 ° C. and a humidity of 80% without stopping the movement of the head between the lamp and the ID stopper. It is a test to investigate the occurrence of abnormalities such as dirt and wear of the head after the test by reciprocating motion (seek operation). As a result of the LUL test of 80,000 times / day × 7.5 days = 600,000 times, the head ABS surface was magnified and visually observed with a microscope, and when adhesion, wear, or chipping of contamination was observed, it was evaluated as a failure. .

Examples In the examples, as described above, (1) glass base plate forming and lapping step, (2) coring step, (3) chamfering step, and (4) grinding with fixed abrasive grains. Step, (5) first polishing (main surface polishing) step, (6) end surface polishing step, (7) chemical strengthening step, (8) second polishing (final polishing) step are performed in this order. It was. That is, the end face polishing step was performed after the first polishing step.

Comparative Example In the comparative example, (1) glass base plate forming and lapping step, (2) coring step, (3) chamfering step, (6) end surface polishing step, (4) fixed abrasive The grinding step with grains, the first polishing (main surface polishing) step (5), the chemical strengthening step (7), and the second polishing (final polishing) step (8) were performed in this order. That is, the end face polishing step was performed before the first polishing step.

Each process of the manufacturing method of the glass substrate of 2nd Embodiment was performed in order.
here,
In the end face polishing of (4), a plurality of glass base plates laminated with a spacer interposed between the glass base plates is polished using cerium oxide having an average particle size (D50) of 1.0 μm as free abrasive grains. Polished with a brush.
In the grinding with the fixed abrasive of (5), the diamond sheet (average particle diameter: 1 to 20 μm) was ground by using a grinding apparatus in which a diamond sheet obtained by hardening a resin bond was attached to the upper surface plate and the lower surface plate.
In the first polishing (6), it was polished for 60 minutes by using the polishing apparatus of FIGS. Detailed polishing conditions are as shown below.
(7) In the second polishing was polished for 30 minutes by using another polishing apparatus similar to FIGS. Detailed polishing conditions are as shown below. The maximum gap between the glass base plate and the carrier of the polishing apparatus is as shown in Table 2.

A magnetic disk having a magnetic layer formed on the obtained glass substrate for a magnetic disk was prepared, and evaluated by performing an LUL durability test (two types of 400,000 times and 600,000 times). The LUL endurance test is a state in which a hard disk drive (HDD) constituting a magnetic disk is placed in a constant temperature and humidity chamber at a temperature of 70 ° C. and a humidity of 80% without stopping the movement of the head between the lamp and the ID stopper. It is a test to investigate the occurrence of abnormalities such as dirt and wear of the head after the test by reciprocating motion (seek operation). As a result of the LUL test of 80,000 times / day × 5 days = 400,000 times, the head ABS surface was magnified and visually observed with a microscope, and when adhesion, wear, or chipping of contamination was observed, it was evaluated as a failure. Moreover, as a result of the LUL test of 80,000 times / day × 7.5 days = 600,000 times, the head ABS surface was magnified and visually observed with a microscope. When adhesion, wear, or chipping was observed, it was evaluated as “good”, and when it was not observed, it was evaluated as “good”.

Claims (7)

A method for producing a glass substrate for a magnetic disk comprising a pair of main surfaces and a side wall surface orthogonal to the pair of main surfaces,
Holding a disk-shaped glass base plate on a carrier, sandwiching the main surface of the glass base plate with a polishing pad, and supplying a polishing liquid having zirconia particles as abrasive grains between the glass base plate and the polishing pad A polishing process for polishing the main surface of the glass base plate by relatively moving the polishing pad and the glass base plate,
After the polishing step, when the side wall surface or main surface of the glass base plate is polished, the side wall surface of the glass base plate and the end surface of the carrier facing the side wall surface of the glass substrate rub against each other. A removal step of physically removing the zirconia particles fixed to the side wall surface of the base plate;
Of manufacturing a glass substrate for a magnetic disk. A method for producing a glass substrate for a magnetic disk comprising a pair of main surfaces and a side wall surface orthogonal to the pair of main surfaces,
Holding a disk-shaped glass base plate on a carrier, sandwiching the main surface of the glass base plate with a polishing pad, and supplying a polishing liquid having zirconia particles as abrasive grains between the glass base plate and the polishing pad A main surface polishing step of polishing the main surface of the glass base plate by relatively moving the polishing pad and the glass base plate,
After the main surface polishing step, an end surface polishing step of polishing the side wall surface of the glass base plate that has been in contact with the end surface of the carrier in the main surface polishing step;
Of manufacturing a glass substrate for a magnetic disk. A method for producing a glass substrate for a magnetic disk comprising a pair of main surfaces and a side wall surface orthogonal to the pair of main surfaces,
Holding a disk-shaped glass base plate on a carrier, sandwiching the main surface of the glass base plate with a polishing pad, and supplying a polishing liquid having zirconia particles as abrasive grains between the glass base plate and the polishing pad A first polishing step of polishing the main surface of the glass base plate by relatively moving the polishing pad and the glass base plate,
Holding the glass base plate on the carrier, sandwiching the main surface of the glass base plate with the polishing pad, between the glass base plate and the polishing pad, and between the side wall surface of the glass base plate and the end face of the carrier In the meantime, a polishing liquid having abrasive grains other than zirconia particles as the abrasive grains is supplied, and the main surface of the glass base plate is polished by moving the polishing pad and the glass base plate relatively. Polishing process;
Of manufacturing a glass substrate for a magnetic disk.   4. The method for manufacturing a glass substrate for a magnetic disk according to claim 3, wherein, in the second polishing step, a maximum gap between the glass base plate and the carrier is 0.5 mm or more.   The method for producing a glass substrate for a magnetic disk according to any one of claims 1 to 4, wherein the surface roughness of the end face of the carrier that contacts the side wall surface of the glass base plate is 5 µm or less.   The surface roughness of the side wall surface of the glass base plate before being polished with the polishing liquid having the zirconia particles is 0.1 μm or less in terms of arithmetic average roughness Ra. The manufacturing method of the glass substrate for magnetic discs described in any one of these.   The magnetic disk according to any one of claims 1 to 6, wherein the glass substrate for a magnetic disk has a diameter larger than 2.5 inch size and a plate thickness of 0.6 mm or less. Method for manufacturing glass substrate.