JP5310671B2 - Glass substrate for magnetic recording medium and method for manufacturing the same - Google Patents

Description

  The present invention relates to a method for manufacturing a glass substrate for a magnetic recording medium, in which at least one of an inner peripheral side surface and an outer peripheral side surface of a glass substrate is ground with a grindstone.

  With the recent increase in recording density of magnetic disks, the required characteristics for glass substrates for magnetic recording media are becoming more and more severe year by year. In order to achieve a higher recording density of a magnetic disk, it is required to reduce foreign matter defects on the main surface of the glass substrate and improve the smoothness of the main surface. Moreover, in order to improve the reliability as an information recording medium, it is required to increase the mechanical strength of the glass substrate.

  Finishing the side surface of the glass substrate for magnetic recording media with high smoothness improves the mechanical strength of the glass substrate, reduces foreign matter trapped by the unevenness of the side surface, and the unevenness of the side surface scrapes the resin member of the cassette. This is important for improving the recording density and reliability of the magnetic disk.

  The side surface of the glass substrate for magnetic recording media is smoothened by grinding at least one of the inner or outer peripheral surface of the glass substrate with a grindstone in the end surface grinding process and then polishing the side surface of the glass substrate in the end surface polishing process. It is done. However, if a deep crack (hereinafter referred to as a work-affected layer) occurs in the end surface grinding process, the work-affected layer cannot be sufficiently removed in the next end face polishing process, and the work deterioration is caused on the side surface of the glass substrate for magnetic recording media. The layer remains and does not have a smooth side.

  As an end face grinding method for smoothly finishing the side surface portion of the glass substrate for magnetic recording media, the temperature of the coolant supplied to the side surface portion of the glass substrate to be ground is adjusted to 28 ° C. or less, and the abrasive grains fall off from the grindstone during grinding. A method of grinding a side surface portion of a glass substrate while suppressing this is proposed (Patent Document 1). However, in the grinding method of Patent Document 1, when there is a factor that causes a deep work-affected layer on the grindstone, it is difficult to suppress the generation of the deep work-affected layer even if the coolant temperature is 28 ° C. or lower, and a smooth side surface cannot be obtained. There is a fear.

JP 2007-98483 A

  An object of this invention is to provide the glass substrate for magnetic recording media which is excellent in the smoothness of a side part or a chamfer part. Further, an end surface grinding method for grinding a glass substrate for magnetic recording medium having excellent smoothness of a side surface portion or a chamfered portion with high productivity, and manufacture of a glass substrate for magnetic recording medium having an end surface polishing step using the end surface grinding method The purpose is to provide a method.

The present invention relates to a method of manufacturing a disk substrate for a magnetic recording medium having a circular hole in a central portion including a main plane, an inner peripheral side surface, and an outer peripheral side surface, and the manufacturing of the glass substrate for a magnetic recording medium The method includes a shape imparting step of a glass substrate having a plate shape, an end surface grinding step of grinding at least one of an inner peripheral side surface or an outer peripheral side surface of the glass substrate with a grindstone, and at least an inner peripheral side surface or an outer peripheral side surface of the glass substrate. An end surface polishing step for polishing one side, a polishing step for the main plane of the glass substrate, and a cleaning step for the glass substrate, wherein the end surface grinding step is at least one of an inner peripheral side surface or an outer peripheral side surface of the glass substrate. In addition to supplying the grinding fluid to the glass substrate, the grindstone and the glass substrate are moved relatively, and the grinding surface of the grindstone is brought into contact with at least one of the inner peripheral side surface or the outer peripheral side surface of the glass substrate for grinding. Ri, the grinding wheel is a grinding wheel made of are joined by abrasive grain binder, the abrasive grains and the maximum particle diameter dmax and the minimum diameter dmin of the particle diameter measured using a particle size distribution measuring device of laser diffraction scattering method a difference abrasive grain size distribution width △ d (= dmax-dmin) is Ri der less 23 .mu.m, and a method of manufacturing a glass substrate for a magnetic recording medium having an average particle diameter and wherein 10μm~40μm der Rukoto provide.

  The method for producing a glass substrate for a magnetic recording medium having an end surface grinding step of the present invention can produce a glass substrate for a magnetic recording medium having excellent smoothness of a side surface or a chamfered portion with high productivity. A magnetic disk manufactured by forming a thin film such as a magnetic layer on a glass substrate for a magnetic recording medium manufactured by the method for manufacturing a glass substrate for a magnetic recording medium of the present invention easily reduces the flying height of the magnetic head. In addition, since it has excellent mechanical strength, it is possible to increase the recording density and reliability of the magnetic disk.

The perspective view of the glass substrate for magnetic recording media. The cross-sectional perspective view of the glass substrate for magnetic recording media. Schematic explaining the end surface grinding process which grinds the inner peripheral side surface or outer peripheral side surface of a glass substrate with a grindstone. The expanded sectional view of the grinding surface of the grindstone whose abrasive grain size distribution width is 23 micrometers or less. The expanded sectional view of the grinding surface of the grindstone whose abrasive grain size distribution width exceeds 23 micrometers. Microscopic observation image of chamfered part (good product) without pit defects. Microscopic observation image of chamfer with pit defects. The graph which shows the particle size distribution of the abrasive grain contained in the grindstone used in Example 1. FIG. The graph which shows the particle size distribution of the abrasive grain contained in the grindstone used in Example 2. FIG. 4 is a graph showing the particle size distribution of abrasive grains contained in the grindstone used in Example 3.

  Hereinafter, although the form for implementing this invention is demonstrated, this invention is not restricted to embodiment described below.

  First, FIG. 1 shows a perspective view of a glass substrate 10 for a magnetic recording medium according to the present invention, and FIG. 2 shows a cross-sectional perspective view of the glass substrate 10 for a magnetic recording medium cut. In FIG. 1 and FIG. 2, each symbol indicates a main plane 101, an inner peripheral side surface 102, an outer peripheral side surface 103, an inner peripheral chamfered portion 104, and an outer peripheral chamfered portion 105 of the magnetic recording medium glass substrate.

  Generally, the manufacturing process of the glass substrate for magnetic recording media and the magnetic disk includes the following processes. (1) A glass base substrate molded by a float method, a fusion method, a press molding method, or the like is processed into a disk shape having a circular hole at the center. (2) Chamfering the inner peripheral side surface and the outer peripheral side surface of the glass substrate. (3) The side surfaces and chamfered portions of the glass substrate are end-polished. (4) The upper and lower main planes of the glass substrate are polished. The polishing step may be only primary polishing, primary polishing and secondary polishing may be performed, or tertiary polishing may be performed after secondary polishing. (5) The glass substrate is precisely cleaned to produce a glass substrate for a magnetic recording medium. (6) A thin film such as a magnetic layer is formed on a glass substrate for a magnetic recording medium to manufacture a magnetic disk.

  In the manufacturing process of the glass substrate for magnetic recording medium and the magnetic disk, glass substrate cleaning (inter-process cleaning) or etching of the glass substrate surface (inter-process etching) may be performed between the processes. Furthermore, when high mechanical strength is required for the glass substrate for magnetic recording media, a strengthening step (for example, a chemical strengthening step) for forming a reinforcing layer on the surface layer of the glass substrate is performed before the polishing step, after the polishing step, or the polishing step. You may carry out between.

  In the present invention, the glass substrate for a magnetic recording medium may be amorphous glass, crystallized glass, or tempered glass (for example, chemically tempered glass) having a tempered layer on the surface layer of the glass substrate. Moreover, the glass base substrate of the glass substrate of the present invention may be made by a float method, may be made by a fusion method, or may be made by a press molding method.

  The present invention relates to (2) an end surface grinding process for chamfering an inner peripheral side surface and an outer peripheral side surface of a glass substrate, and relates to an end surface grinding process of a glass substrate for a magnetic recording medium.

  FIG. 3 is a schematic view for explaining an end surface grinding step of grinding the outer peripheral side surface of the glass substrate with a grindstone. In FIG. 3, 20 is a grindstone, 201 is abrasive grains, 202 is a grinding surface, 205 is a base, 30 is a grinding fluid supply nozzle, and 301 is a grinding fluid. The same components as those shown in FIGS. 1 and 2 are denoted by the same reference numerals, and description thereof is omitted. The same applies to the inner peripheral side surface of the glass substrate.

  FIG. 4 is an enlarged cross-sectional view of the grinding surface of the grindstone. 4A is an enlarged cross-sectional view schematically showing a grinding surface of a grindstone having an abrasive grain size distribution width of 23 μm or less, and FIG. 4B is an enlarged cross-sectional view schematically showing a grinding surface of a grindstone having an abrasive grain size distribution width exceeding 23 μm. Respectively. 4A and 4B, 203 indicates abrasive grains having a large particle diameter, and 204 indicates a binder. Note that components having the same contents as those in FIG.

  The outer peripheral side surface 103 of the glass substrate 10 for magnetic recording medium is supplied with the grinding fluid 301 from the grinding fluid supply nozzle 30 to the grinding surface 202 using an end surface grinding device on which a grindstone 20 for grinding the side surface of the glass substrate is set. Then, the glass substrate 10 for magnetic recording medium and the grindstone 20 are relatively moved, and the outer peripheral side surface 103 and the grinding surface 202 of the glass substrate are brought into contact with each other to be ground.

  As a result of studying means for producing the glass substrate 10 for magnetic recording medium having no deep work-affected layer on the side surface portion or chamfered portion of the glass substrate with high productivity, the inventor has found that the inner peripheral side surface of the glass substrate 10 for magnetic recording medium. In an end face grinding process in which at least one of 102 or the outer peripheral side surface 103 is ground with a grindstone, it has been found that it is effective to set the abrasive grain size distribution width Δd of the abrasive grains 201 contained in the grindstone 20 to 23 μm or less.

  When the abrasive grain size distribution width Δd of the abrasive grains 201 contained in the grindstone 20 is 23 μm or less, for example, the side surface of the glass substrate is ground by the grinding surface 202 as shown in FIG. A deep work-affected layer does not occur in the chamfer. However, when the abrasive grain size distribution width Δd of the abrasive grains 201 contained in the grindstone 20 exceeds 23 μm, the grinding surface 202 on which the abrasive grains 203 having a large particle diameter as shown in FIG. Since the side surface is ground, the side surface portion or the chamfered portion of the glass substrate may be greatly damaged by the abrasive grains 203 having a large particle diameter protruding from the ground surface, thereby generating a deep work-affected layer.

  The abrasive grain size distribution width Δd of the abrasive grains 201 contained in the grindstone 20 is 23 μm or less, preferably 22 μm or less, and particularly preferably 20 μm or less.

  The average particle size of the abrasive grains contained in the grindstone 20 of the present invention is preferably 10 μm to 40 μm. When the average particle diameter of the abrasive grains is less than 10 μm, the grinding processing speed is low and the productivity may be inferior. When the average particle diameter of the abrasive grains exceeds 40 μm, the grinding processing speed is high, but a deep work-affected layer is formed in the side surface portion or chamfered portion of the glass substrate, and the side surface portion or chamfered portion having excellent smoothness is produced. There is a possibility that a glass substrate for recording medium cannot be obtained.

  The average particle diameter of the abrasive grains 201 contained in the grindstone 20 is preferably 10 μm to 40 μm, more preferably 10 μm to 35 μm, and particularly preferably 10 μm to 30 μm.

  The particle diameter of the abrasive grains is measured using a laser diffraction / scattering particle size distribution measuring apparatus.

  In the present invention, the grindstone 20 includes, as the abrasive grains 201, at least one of diamond abrasive grains, alumina abrasive grains, and silicon carbide abrasive grains. Among the abrasive grains, diamond abrasive grains are preferable because the grinding speed is high and it is difficult to generate a work-affected layer. As the binder 204 that binds the abrasive grains 201, any one or more binders of metal, resin, or vitreous (vitrified) are used.

At least one of the inner peripheral side surface and the outer peripheral side surface of the glass substrate for magnetic recording medium manufactured by the method for manufacturing a glass substrate for magnetic recording medium having the end surface grinding step of the present invention has a number of pit defects of 5 / mm ^2. It is as follows.

When the number of pit defects on the inner and outer peripheral sides of the glass substrate for magnetic recording media exceeds 5 / mm ² , the mechanical strength of the glass substrate for magnetic recording media decreases and information is obtained when a magnetic disk is obtained. There is a possibility that the reliability as a recording medium is inferior. In addition, foreign matter trapped in the irregularities on the side surface of the glass substrate or foreign matter generated when the irregularities on the side surface of the glass substrate scrape the resin member of the cassette adhere to the main plane of the glass substrate for magnetic recording media. When a magnetic disk is used, a surface foreign matter defect may occur, and the flying position of the magnetic head may be disturbed in an HDD (Hard Disk Drive) test of the magnetic disk, causing a failure of the magnetic head to contact the magnetic disk.

The number of pit defects on at least one of the inner peripheral side surface and the outer peripheral side surface of the glass substrate for magnetic recording media is preferably 3 / mm ² or less, more preferably 1 / mm ² or less, particularly 0 / mm ^2. preferable.

Furthermore, at least one of the inner peripheral chamfered portion and the outer peripheral chamfered portion of the glass substrate for magnetic recording medium manufactured by the method for manufacturing a glass substrate for magnetic recording medium having the edge grinding step of the present invention has 5 pit defects. Pieces / mm ² or less.

When the number of pit defects in the inner peripheral chamfered portion or outer peripheral chamfered portion of the glass substrate for magnetic recording medium exceeds 5 / mm ² , the mechanical strength of the glass substrate for magnetic recording medium decreases and the magnetic disk is obtained. In addition, the reliability as an information recording medium may be inferior. In addition, foreign matter trapped by the irregularities of the chamfered portion of the glass substrate or foreign matter generated when the irregularities of the chamfered portion of the glass substrate scrape the resin member of the cassette adhere to the main plane of the glass substrate for magnetic recording media. There is a possibility that the surface of the magnetic disk may become defective, and the flying position of the magnetic head may be disturbed in the HDD (Hard Disk Drive) test of the magnetic disk, causing a failure of the magnetic head to contact the magnetic disk.

The number of pit defects in at least one of the inner peripheral chamfered portion or the outer peripheral chamfered portion of the glass substrate for magnetic recording medium is preferably 3 pieces / mm ² or less, more preferably 1 piece / mm ² or less, and 0 pieces / mm ^2. Particularly preferred.

  The number of pit defects in the inner peripheral side surface 102, the outer peripheral side surface 103, the inner peripheral chamfered portion 104, and the outer peripheral chamfered portion 105 of the glass substrate 10 for magnetic recording medium is evaluated by the following procedure.

  The surface of the glass substrate is etched by 5 μm using an acidic etching solution containing hydrofluoric acid or nitric acid, and the work-affected layer (cracks, scratches, etc.) remaining on the side surface and the chamfered portion is isotropically etched and observed. The concave portion (pit defect 106) is easily sized. A circular or elliptical recess having a diameter (or major axis) of 10 μm or more was defined as a pit defect 106, and the number of pit defects 106 was counted using an optical microscope. The position where the pit defect 106 is evaluated may be performed in the entire area of the inner peripheral side surface 102, the outer peripheral side surface 103, the inner peripheral chamfered portion 104, and the outer peripheral chamfered portion 105 of the glass substrate, or in a selected specific region. Good.

  FIG. 5 shows a microscope observation image of the chamfered portion without the pit defect 106, and FIG. 6 shows a microscope observation image of the chamfered portion with the pit defect 106, respectively. The chamfered portion shown in FIG. 6 is a portion in which a severely damaged layer is generated in the chamfered portion of the glass substrate due to significant damage in the end surface grinding process.

  According to the present invention, a glass substrate for a magnetic recording medium having no pit defect 106 in at least one of a side surface portion or a chamfered portion of the glass substrate can be manufactured with high productivity.

  Examples The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited thereby.

[Shape imparting step of glass substrate for magnetic recording medium]
A disk-shaped glass substrate having a circular hole at the center of a glass substrate mainly composed of SiO ₂ formed by a float process for a glass substrate for a magnetic recording medium having an outer diameter of 65 mm, an inner diameter of 20 mm, and a plate thickness of 0.635 mm. It was processed into.

[End surface grinding process of glass substrate for magnetic recording media]
It contains diamond abrasive grains so that a glass substrate for a magnetic recording medium having a chamfering width of 0.15 mm and a chamfering angle of 45 ° is obtained on the inner and outer peripheral sides of a disk-shaped glass substrate having a circular hole in the center. Grind using a grindstone.

  Table 1 shows the results of grinding the side surface portion of the glass substrate using a grindstone having a different grain size distribution width Δd of diamond abrasive grains contained in the grindstone in the end face grinding step. In Table 1, Example 1 is an example, and Examples 2 and 3 are comparative examples.

  The glass substrate whose inner peripheral side surface and outer peripheral side surface were ground with the grindstone described in Examples 1 to 3 was processed in the end surface polishing step and the main plane polishing step described below, and then washed and dried in the cleaning step. The number of pit defects in the peripheral side surface and the inner peripheral chamfered portion and the number of pit defects in the outer peripheral side surface and the outer peripheral chamfered portion were evaluated.

  7A, 7B and 7C show the results of measuring the particle size distribution of the abrasive grains contained in the grindstone used in Examples 1 to 3 with a particle size distribution measuring apparatus of a laser diffraction / scattering type. FIG. 7A shows the results of measurement of the particle size distribution of the abrasive grains contained in the grindstone used in Example 1, FIG. 7B shows the results of Example 2, and FIG.

  The abrasive grain size distribution width Δd of the diamond abrasive grains contained in the grindstone used in Example 1 is 19 μm, the abrasive grain size distribution width Δd of the diamond abrasive grains contained in the grindstone used in Example 2 is 24 μm, The abrasive grain size distribution width Δd of the diamond abrasive grains contained in the grindstone used in Example 3 was 29 μm.

The grinding speed of the inner peripheral side surface was obtained by dividing the grinding amount of the inner peripheral side surface by the grinding time. The grinding amount of the inner peripheral side surface was measured using a high-precision two-dimensional dimension measuring machine (manufactured by Keyence Corporation, product name: VM8040). The diameter of the circular hole in the central portion of the glass substrate was measured before and after the inner peripheral side surface grinding, and the grinding amount was obtained by calculating the diameter difference between the circular holes before and after the inner peripheral side surface grinding.
(Grinding amount of inner peripheral surface) = ((diameter of circular hole in glass substrate after grinding) − (diameter of circular hole in glass substrate before grinding)) / 2.

The grinding speed of the outer peripheral side surface was obtained by dividing the grinding amount of the outer peripheral side surface by the grinding time. The grinding amount of the outer peripheral side surface was determined by measuring the outer diameter of the glass substrate with a micrometer before and after the outer peripheral side surface grinding and calculating the diameter difference between the outer diameters before and after the outer peripheral side surface grinding.
(Grinding amount of outer peripheral side surface) = ((diameter of outer diameter of glass substrate before grinding) − (diameter of outer diameter of glass substrate after grinding)) / 2.

[End surface polishing step of glass substrate for magnetic recording medium]
The inner peripheral side surface portion and the inner peripheral chamfered portion were subjected to inner peripheral end surface polishing using a polishing brush and cerium oxide abrasive grains. The inner peripheral end surface polishing was performed by setting the polishing time so that the polishing amount on the inner peripheral side surface was 7 μm. The glass substrate on which the inner peripheral end face had been polished was cleaned and removed by scrub cleaning using an alkaline detergent and ultrasonic cleaning in a state immersed in an alkaline detergent solution.

  After polishing the inner peripheral end surface, the outer peripheral side surface portion and outer peripheral chamfered portion of the glass substrate were subjected to outer peripheral end surface polishing using a polishing brush and cerium oxide abrasive grains. The outer peripheral end surface polishing was performed by setting the polishing time so that the polishing amount of the outer peripheral side surface was 7 μm. The glass substrate after the outer peripheral end surface polishing is cleaned and removed by scrub cleaning using an alkaline detergent and ultrasonic cleaning in a state immersed in an alkaline detergent solution.

[Polishing process of main plane of glass substrate for magnetic recording medium]
After the end face processing, the upper and lower principal planes of the glass substrate were primarily polished by a double-side polishing apparatus using a fixed abrasive tool containing diamond abrasive grains as a polishing tool and a polishing liquid, and the polishing liquid was washed and removed.

  After primary polishing, a polishing liquid containing a hard urethane polishing pad and cerium oxide abrasive grains as a polishing tool (an average particle diameter, hereinafter abbreviated as average particle diameter, a polishing liquid mainly composed of about 1.3 μm of cerium oxide) The upper and lower principal planes of the glass substrate were secondarily polished by a double-side polishing apparatus using the composition), and the abrasive grains were washed and removed.

  Next, both surfaces using a polishing pad made of soft urethane as a polishing tool and a polishing liquid containing colloidal silica (polishing liquid composition mainly composed of colloidal silica having an average primary particle diameter of 20 to 30 nm) are used. The upper and lower main planes of the glass substrate were subjected to third polishing with a polishing apparatus.

[Cleaning process of glass substrate for magnetic recording medium]
The glass substrate whose upper and lower main surfaces are polished is sequentially subjected to scrub cleaning with an alkaline detergent, ultrasonic cleaning in a state immersed in an alkaline detergent solution, and ultrasonic cleaning in a state immersed in pure water. Dried.

  After the glass substrate was washed and dried, the work-affected layers on the side surface and the chamfered portion of the glass substrate for magnetic recording medium were evaluated. The evaluation of the work-affected layer was carried out by extracting 10 glass substrates from 1 lot (200 sheets).

  The evaluation of the work-affected layer on the side surface and chamfered portion of the glass substrate for magnetic recording media is performed by etching the surface of the glass substrate with an acidic etching solution containing hydrofluoric acid and nitric acid, and observing the work-affected layer with an optical microscope. It was carried out after making a pit defect of a size easy to do.

  The surface of the glass substrate is etched by 5 μm with an etching solution, washed and dried, then the glass substrate is cut to a size that can be easily observed with an optical microscope, and the cut glass substrate piece is fixed to a sample stage and a laser microscope (Olympus). Using a product name: EXT OLS 3500), pit defects at the side surface and the chamfered portion were observed.

  The objective lens of the laser microscope uses a 20 × magnification, and has a circular or elliptical shape with a diameter (or major axis) of 10 μm or more in an observation visual field of 635 μm × 480 μm (observation region where the lateral width 107 of the pit defect observation region is 635 μm). The number of defects 106 was counted. The count of the number of pit defects 106 is 0 °, 90 °, 180 °, 270 in the inner peripheral chamfered portion 104 and the inner peripheral side surface 102 on the upper and lower main plane side, and in the outer peripheral chamfered portion 105 and the outer peripheral side surface 103 on the upper and lower main plane side. It was carried out at the position of °.

  Table 1 shows numerical values obtained by dividing the number of pit defects 106 counted at the measurement position by the observation area. Example 1 in which the abrasive grain size distribution width Δd of the diamond abrasive grains contained in the grindstone is 23 μm or less has no pit defect 106 in the evaluation of the work-affected layer in the side surface portion and the chamfered portion of the glass substrate for magnetic recording medium, and the side surface portion It was confirmed that a glass substrate for a magnetic recording medium excellent in smoothness of the chamfered portion was obtained.

  INDUSTRIAL APPLICABILITY The present invention can be applied to a method for manufacturing a glass substrate having an end surface grinding process for grinding a side surface portion of a glass substrate having a plate shape. Specific examples of glass substrates to which the present invention can be applied include glass substrates for magnetic recording media, photomasks, displays such as liquid crystals and organic EL, and optical components such as optical pickup elements and optical filters. It is done.

10: glass substrate for magnetic recording medium, 101: main plane of glass substrate for magnetic recording medium, 102: inner peripheral side surface, 103: outer peripheral side surface, 104: inner peripheral chamfered portion, 105: outer peripheral chamfered portion, 106: pit defect, 107: width of pit defect observation area,
20: Whetstone, 201: Abrasive grain, 202: Grinding surface, 203: Abrasive grain with large particle diameter, 204: Binder, 205: Base material,
30: grinding fluid supply nozzle, 301: grinding fluid.

Claims (6)

A method for producing a disk-shaped glass substrate for a magnetic recording medium having a circular hole in a central portion comprising a main plane, an inner peripheral side surface, and an outer peripheral side surface,
The method for manufacturing a glass substrate for a magnetic recording medium includes a step of imparting a shape of a glass substrate having a plate shape, an end surface grinding step of grinding at least one of an inner peripheral side surface or an outer peripheral side surface of the glass substrate with a grindstone, and the glass substrate An end face polishing step for polishing at least one of the inner peripheral side surface or the outer peripheral side surface, a polishing step for the main plane of the glass substrate, and a cleaning step for the glass substrate,
In the end surface grinding step, the grinding liquid is supplied to at least one of the inner peripheral side surface or the outer peripheral side surface of the glass substrate, and the grindstone and the glass substrate are relatively moved, and the grinding surface of the grindstone is changed to the inner peripheral side surface or the outer peripheral side surface of the glass substrate. To grind in contact with at least one of
The grindstone is a grindstone in which abrasive grains are bonded by a binder, and the abrasive grains are the difference between the maximum particle diameter dmax and the minimum particle diameter dmin measured using a laser diffraction / scattering particle size distribution measuring apparatus. abrasive grain size distribution width △ d (= dmax-dmin) is Ri der less 23 .mu.m, and a method of manufacturing a glass substrate for a magnetic recording medium, wherein the average particle size of 10μm~40μm is. The abrasive grains, method of manufacturing a glass substrate for a magnetic recording medium according to claim 1, which is a diamond abrasive grains. At least one method of manufacturing a glass substrate for a magnetic recording medium according to claim 1 or 2 carbon pit defects is 5 / mm ² or less of the inner circumference side or the outer peripheral side surface of a glass substrate for a magnetic recording medium. The glass substrate for a magnetic recording medium is a glass substrate for a magnetic recording medium in which a chamfered portion is formed in at least one of an intersection between the inner peripheral side surface and the main plane or an intersection between the outer peripheral side surface and the main plane,
Method of manufacturing a glass substrate for a magnetic recording medium according to any one of claims 1-3 chamfer the number of pits defects is 5 / mm ² or less. In a disk-shaped glass substrate for a magnetic recording medium having a circular hole in a central portion composed of a main plane, an inner peripheral side surface, and an outer peripheral side surface, at least one of the inner peripheral side surface and the outer peripheral side surface of the glass substrate for magnetic recording medium Is a glass substrate for a magnetic recording medium, wherein the number of pit defects is 5 / mm ² or less. A disk-shaped glass substrate for a magnetic recording medium having a circular hole in a central portion comprising a main plane, an inner peripheral side surface, and an outer peripheral side surface, the glass substrate for a magnetic recording medium comprising an inner peripheral side surface and a main plane of which the chamfered portion is formed on at least one portion of the intersection of the intersection or the outer peripheral side surface and the main plane, chamfer is according to claim 5 the number of pits defects is 5 / mm ² or less Glass substrate for magnetic recording media.

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