JP6008060B1 - Glass substrate for magnetic recording medium, magnetic recording medium, method for manufacturing glass substrate for magnetic recording medium, and glass substrate manufacturing apparatus for magnetic recording medium - Google Patents

Abstract

To provide a glass substrate for a magnetic recording medium in which fine wrinkles between a main surface and an outer peripheral chamfered portion are suppressed. A glass substrate for a magnetic recording medium having a donut shape and having a pair of main surfaces, an outer peripheral end surface, and an inner peripheral end surface, wherein the outer peripheral end surface is an outer peripheral side surface portion and a pair of outer peripheral chamfered portions. And when the chamfer width of at least one outer peripheral chamfered portion of the pair of outer peripheral chamfered portions is measured at a plurality of measurement points, the difference between the maximum value and the minimum value is 10 μm or less. A glass substrate for a magnetic recording medium is provided. [Selection] Figure 2

Description

  The present invention relates to a glass substrate for a magnetic recording medium, a magnetic recording medium, a method for manufacturing a glass substrate for a magnetic recording medium, and a glass substrate manufacturing apparatus for a magnetic recording medium.

  Conventionally, aluminum alloy substrates have been used as substrates for magnetic recording media used in magnetic disk recording devices and the like. However, in recent years, with the demand for higher recording density, glass substrates that are harder than aluminum alloy substrates and excellent in flatness and smoothness have become mainstream.

  The glass substrate for a magnetic recording medium has a donut shape having a concentric opening at the center, and the outer peripheral end surface and the inner peripheral end surface are a side surface portion that is substantially perpendicular to the main surface, and the side surface portion and the main surface. And a chamfered portion provided between the two.

  Various studies have been made on the shape of the outer peripheral chamfered portion provided on the outer peripheral end surface of the magnetic recording medium glass substrate and the inner peripheral chamfered portion provided on the inner peripheral end surface.

  For example, in Patent Document 1, for the purpose of providing a glass substrate for a magnetic recording medium with high mounting reliability, a chamfered portion is formed between the main surface and the side surface, and the main surface and the surface. A method for manufacturing a glass substrate for a magnetic recording medium is disclosed in which a curved surface having a radius of 0.003 mm or more and less than 0.2 mm is formed between at least one of a portion between a chamfered portion and between a side surface and a chamfered portion.

  When manufacturing a glass substrate for a magnetic recording medium, for example, a step of processing from a glass base plate into a donut shape, a chamfering step of forming the above-mentioned chamfered portion on the end surface, a main surface polishing step of polishing the main surface, and polishing the end surface It is processed into a desired shape by performing an end face polishing process or the like.

  Then, when the main surface polishing step is performed after the chamfering step for forming the chamfered portion on the end surface, fine wrinkles are generated between the main surface and the outer peripheral chamfered portion, and the obtained glass substrate for magnetic recording medium In some cases, such spiders were included. Such wrinkles are fine and have not been considered a problem in the past.

Japanese Patent No. 4184384

  However, in recent years, the recording density of magnetic recording media has been increased, and the occupied area per bit of data to be recorded has been reduced. Information is written to the vicinity of the outer peripheral end face of the magnetic recording medium.

  For this reason, even if the size of the wrinkles is fine and the recording density is increased even in the vicinity of the outer peripheral end face, an error occurs depending on the density of the wrinkles in the magnetic recording medium in which writing is performed up to the vicinity of the outer peripheral end face. Cause. Therefore, in the glass substrate for magnetic recording media, it is required to reduce and suppress fine wrinkles between the main surface and the outer peripheral chamfered portion.

  In view of the problems of the above-described conventional technology, an object of one aspect of the present invention is to provide a glass substrate for a magnetic recording medium in which fine wrinkles between a main surface and an outer peripheral chamfered portion are suppressed.

In order to solve the above problems, in one aspect of the present invention, a glass substrate for a magnetic recording medium having a donut shape and having a pair of main surfaces, an outer peripheral end surface, and an inner peripheral end surface, the outer peripheral end surface is It has an outer peripheral side part and a pair of outer peripheral chamfered parts,
When the chamfer width of at least one outer peripheral chamfered portion of the pair of outer peripheral chamfered portions is measured at a plurality of measurement points, the difference between the maximum measured value and the minimum value is 9.8 μm or less. A glass substrate for a recording medium is provided.

  According to one aspect of the glass substrate for a magnetic recording medium of the present invention, it is possible to provide a glass substrate for a magnetic recording medium that suppresses fine wrinkles between the main surface and the outer peripheral chamfered portion.

Explanatory drawing of the glass substrate for magnetic recording media which concerns on embodiment of this invention. Explanatory drawing of the glass substrate manufacturing apparatus for magnetic recording media which concerns on embodiment of this invention. The flowchart of the manufacturing method of the glass substrate for magnetic recording media which concerns on embodiment of this invention. The flowchart of the manufacturing method of the glass substrate for magnetic recording media which concerns on embodiment of this invention.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments, and the following embodiments are not departed from the scope of the present invention. Various modifications and substitutions can be made.
(Glass substrate for magnetic recording media)
One structural example of the glass substrate for magnetic recording media of this embodiment is demonstrated.

  The glass substrate for a magnetic recording medium of the present embodiment is a glass substrate for a magnetic recording medium having a donut shape and having a pair of main surfaces, an outer peripheral end surface, and an inner peripheral end surface, and the outer peripheral end surface is an outer peripheral side surface. And a pair of outer peripheral chamfers. And when the chamfering width of at least one outer peripheral chamfered portion of the pair of outer peripheral chamfered portions is measured at a plurality of measurement points, the difference between the maximum value and the minimum value of the measured value can be 10 μm or less. .

  First, the structure of the glass substrate for magnetic recording media of this embodiment will be described with reference to FIG.

  FIG. 1A schematically shows a perspective sectional view of a glass substrate for a magnetic recording medium according to the present embodiment. FIG. 1A is a perspective cross-sectional view including a cross section in a plane that passes through the center of the glass substrate 10 for magnetic recording medium and is perpendicular to the main surfaces 121 and 122. That is, FIG. 1A shows a half of the glass substrate for a magnetic recording medium of this embodiment and a cross-sectional view.

  FIG. 1B is a view for explaining the chamfering width of the glass substrate for magnetic recording medium of the present embodiment, and schematically shows a top view of the glass substrate for magnetic recording medium of the present embodiment. Show. In the figure, the chamfer width is shown larger than the actual width.

  As can be understood from FIGS. 1A and 1B, the glass substrate 10 for magnetic recording medium has a circular outer periphery, and a circular opening (central opening) so as to be concentric with the outer periphery in the central portion. Part) 11 having a disk shape, that is, a donut shape.

  The upper and lower surfaces are main surfaces 121 and 122. Moreover, the glass substrate 10 for magnetic recording media has the outer peripheral end surface 13 located in an outer periphery, and the inner peripheral end surface 14 located in an inner periphery.

  The outer peripheral end surface 13 and the inner peripheral end surface 14 can have chamfered portions on the main surfaces 121 and 122 side, respectively. That is, the outer peripheral end surface 13 and the inner peripheral end surface 14 can each have a pair of chamfered portions. Specifically, the outer peripheral end surface 13 can have outer peripheral chamfered portions 131 and 133, and the inner peripheral end surface 14 can have inner peripheral chamfered portions 141 and 143, respectively.

  Further, a side surface portion can be formed between the chamfered portions, the outer peripheral end surface 13 can have an outer peripheral side surface portion 132, and the inner peripheral end surface 14 can have an inner peripheral side surface portion 142. The outer peripheral side surface portion 132 and the inner peripheral side surface portion 142 can be formed so as to be substantially perpendicular to the main surfaces 121 and 122, respectively.

  As described above, the outer peripheral end surface 13 can include the outer peripheral side surface portion 132 and the outer peripheral chamfered portions 131 and 133, and the inner peripheral end surface 14 can include the inner peripheral side surface portion 142 and the inner peripheral chamfered portions 141 and 143.

  In addition, the size of the glass substrate for magnetic recording media of this embodiment is not particularly limited, and can be arbitrarily selected according to the specifications of the glass substrate for magnetic recording media. The diameter of the glass substrate for magnetic recording media of the present embodiment can be set to a size according to specifications required for the glass substrate for magnetic recording media, such as 48 mm, 65 mm, or 95 mm. In particular, the diameter of the glass substrate for a magnetic recording medium of the present embodiment is preferably 65 mm or more, for which demand is increasing in recent years.

  As described above, in the main surface polishing step for polishing the main surface of the glass substrate for magnetic recording medium, fine wrinkles are formed between the main surface and the end surface, for example, between the main surface 121 and the outer peripheral chamfer 131. May occur. Even in the vicinity of the outer peripheral end face, the size of the wrinkles is fine, and the recording density is increasing, and the magnetic recording medium in which writing is performed up to the vicinity of the outer peripheral end face may cause errors depending on the density of the wrinkles. Become. Accordingly, there has been a demand for suppressing the occurrence of such fine wrinkles in a glass substrate for a magnetic recording medium. Therefore, first, the inventors of the present invention examined the cause of such fine wrinkles.

  The main surface polishing step is usually performed after the chamfering step of forming a chamfered portion on the end surface of the glass substrate that is shaped into a donut shape. In the chamfering process, conventionally, for example, the chamfering width of the outer peripheral chamfered part is measured at an arbitrary point and if it is within the allowable range, it is used as the acceptable product for the main surface polishing process.

  And the grinding | polishing of the main surface of a glass substrate is normally implemented using a double-side polish apparatus. Specifically, in a state where the polishing pad is pressed against both main surfaces of the glass substrate set in the double-side polishing apparatus, while supplying the polishing slurry between the glass substrate and the polishing pad, the glass substrate and the polishing are supplied. This can be done by rotating the pad.

  As described above, in the past, for example, for the outer peripheral chamfered portion, whether the chamfering width is appropriate or not is determined by only measuring the outer peripheral chamfered portion at one point. No particular attention was paid to the variation. However, the present inventors have found that there is a correlation between the fine wrinkles between the main surface and the outer peripheral chamfered portion and the variation in the width of the outer peripheral chamfered portion. More specifically, the inventors of the present invention have found that a slight variation in the chamfer width of the chamfered portion, which has not been a problem in the past, may occur between the main surface and the chamfered portion in the subsequent main surface polishing step. Has been found to cause fine wrinkles.

  According to the study of the inventors of the present invention, when the variation of the chamfer width of the chamfered portion is large, the amount of the slurry entering the surface becomes unstable because the slurry is accumulated in the portion where the chamfer width is large. It is presumed to cause wrinkles due to large grains in the inside, or to prevent rotation of the glass substrate for magnetic recording medium in the double-side polishing apparatus.

  Therefore, the glass substrate for a magnetic recording medium of the present embodiment has a maximum value and a minimum value when the chamfer width of at least one outer peripheral chamfered portion of the pair of outer peripheral chamfered portions is measured at a plurality of measurement points. The difference from the value is preferably 10 μm or less. In particular, when the chamfer width of at least one outer peripheral chamfered portion is measured at a plurality of measurement points, the difference between the maximum value and the minimum value is more preferably 8 μm or less, and preferably 5 μm or less. Further preferred.

  According to the study of the inventors of the present invention, the difference between the maximum value and the minimum value when measuring the chamfer width of at least one outer peripheral chamfer at a plurality of measurement points is 10 μm or less. After the main surface polishing step, it is possible to suppress the generation of fine wrinkles between the main surface and the outer peripheral chamfered portion that are particularly required to suppress the generation of fine wrinkles. For this reason, the yield of the glass substrate for magnetic recording media used for the magnetic recording medium whose recording density has been increased can be improved, and productivity can be increased. Further, when the magnetic recording medium is used, the error occurrence rate can be suppressed.

  As described above, the glass substrate for magnetic recording medium 10 can have a pair of outer peripheral chamfered portions 131 and 133.

  As described above, when the glass substrate for magnetic recording medium has a pair of outer peripheral chamfered portions, as described above, when the chamfer width of the outer peripheral chamfered portion is measured at a plurality of measurement points, the measured value is measured. It is preferable that the difference between the maximum value and the minimum value satisfies the above range. That is, for example, for one outer peripheral chamfer 131, the difference between the maximum value and the minimum value when the chamfer width is measured at a plurality of arbitrary measurement points selected along the outer periphery may be 10 μm or less. preferable.

  This is because the pair of outer peripheral chamfered portions are formed simultaneously by the outer peripheral end surface grinding grindstone, and the maximum and minimum values of the chamfer width of the pair of outer peripheral chamfered portions included in the same glass substrate for magnetic recording medium. This is because the difference is usually similar.

  In particular, for both outer peripheral chamfered portions 131 and 133, the measured value of the chamfered width at each outer peripheral chamfered portion when the chamfered width is measured at a plurality of arbitrary measurement points selected along the outer periphery at each outer peripheral chamfered portion. More preferably, the difference between the maximum value and the minimum value satisfies the above range.

  In addition, after the chamfering process, even when performing various polishing processes such as the main surface polishing process, the maximum value of the measured value when measuring the chamfer width of at least one outer peripheral chamfered portion at a plurality of measurement points, The difference from the minimum value hardly changes. For this reason, both the glass substrate having a donut shape on which the outer peripheral chamfered portion is provided for the main surface polishing step and the glass substrate for magnetic recording medium subjected to various polishing steps and the like have a chamfer width of at least one outer peripheral chamfered portion. It is preferable that the difference between the maximum value and the minimum value of the measurement values measured at a plurality of measurement points satisfies the above range.

Here, the chamfered width of the outer peripheral chamfered portion means the length of the chamfered portion in the horizontal direction, that is, the length in the direction parallel to the main surface, and in FIGS. 1 (A) and 1 (B) The length is shown as L _OD . The chamfering width L _OD of the outer peripheral chamfered portion is measured on a line passing through the center O of the magnetic recording medium glass substrate 10 as shown in FIG.

  The chamfer width of the outer peripheral chamfered portion may be measured at a plurality of measurement points along the outer periphery of the magnetic recording medium glass substrate as described above, that is, for example, at two or more points. It is not limited. However, it is preferable to select the number of measurement points within a range that does not impair the productivity so that the variation in chamfer width can be sufficiently evaluated.

  The number of measurement points when measuring the chamfer width is, for example, preferably 4 points or more, and more preferably 20 points or more.

  However, from the viewpoint of productivity, the number of measurement points when measuring the chamfer width is preferably 360 points or less, and more preferably 180 points or less.

  Note that the number of measurement points here means the number of measurement points when measuring the chamfer width of one outer peripheral chamfer.

  The distance between measurement points when measuring the chamfer width is preferably constant. For this reason, for example, the angle formed by one measurement point, the center of the glass substrate for magnetic recording media, and the measurement point adjacent to the one measurement point is a value obtained by dividing 360 ° by the number of measurement points. It is preferable.

The length of the chamfering width L _OD of the outer peripheral chamfered portion is not particularly limited, and can be selected according to specifications required for the glass substrate for a magnetic recording medium. However, if the chamfering width L _OD of the outer peripheral chamfered portion is too long, the area of the main surface may be reduced. For this reason, it is preferable that the chamfering width L _OD of the outer peripheral chamfered portion is 200 μm or less. The lower limit of the chamfer width L _OD of the peripheral chamfered portion is not particularly limited, it can be, for example, 50μm or more.

  In the glass substrate for magnetic recording media, it is particularly required to reduce fine wrinkles between the main surface and the outer peripheral chamfered portion, but also reduce fine wrinkles between the main surface and the inner peripheral chamfered portion. Thus, the occurrence of errors can be suppressed when the magnetic recording medium is used. And also about the fine wrinkles between the main surface and the inner peripheral chamfered portion, according to the study of the inventors of the present invention, for the same reason as the fine wrinkles between the main surface and the outer peripheral chamfered portion. It is thought that it has occurred.

  For this reason, the glass substrate for a magnetic recording medium of the present embodiment has an inner peripheral end surface having an inner peripheral side surface portion and a pair of inner peripheral chamfered portions, and at least one of the pair of inner peripheral chamfered portions. When the chamfering width of the peripheral chamfered portion is measured at a plurality of measurement points, the difference between the maximum value and the minimum value is preferably 10 μm or less. When the chamfer width of at least one inner peripheral chamfer is measured at a plurality of measurement points, the difference between the maximum value and the minimum value is more preferably 8 μm or less, and 5 μm or less. Is more preferable.

  According to the study by the inventors of the present invention, when the chamfer width of at least one inner peripheral chamfered portion is measured at a plurality of measurement points, the difference between the maximum value and the minimum value of the measured value is 10 μm or less. Thereby, it can suppress that a fine wrinkle generate | occur | produces between a main surface and an internal peripheral chamfering part after a main surface grinding | polishing process. For this reason, it is possible to improve the yield of a glass substrate for a magnetic recording medium used for a magnetic recording medium whose recording density has been increased, and to improve productivity. In addition, the error rate can be suppressed when the magnetic recording medium is used.

  As described above, the glass substrate 10 for a magnetic recording medium can have a pair of inner peripheral chamfered portions 141 and 143.

  Thus, when the glass substrate for magnetic recording media has a pair of inner peripheral chamfered portions, when the chamfer width of the inner peripheral chamfered portion is measured at a plurality of measurement points with respect to at least one inner peripheral chamfered portion as described above. The difference between the maximum value and the minimum value of the measured values preferably satisfies the above range. That is, for example, for one inner peripheral chamfer 141, the difference between the maximum value and the minimum value when the chamfer width is measured at a plurality of measurement points selected along the inner periphery is 10 μm or less. It is preferable.

  This is because the pair of inner peripheral chamfered portions are simultaneously formed by the inner peripheral end face grinding grindstone, and the maximum and minimum chamfer widths of the pair of inner peripheral chamfered portions included in the same glass substrate for magnetic recording medium. This is because the difference from the value is usually the same.

  In particular, for both inner peripheral chamfered portions 141 and 143, the chamfered width of each inner peripheral chamfered portion when the chamfered width is measured at a plurality of measurement points selected along the inner periphery in each inner peripheral chamfered portion. More preferably, the difference between the maximum value and the minimum value of the measured values satisfies the above range.

  In addition, after the chamfering process, even if various polishing processes such as the main surface polishing process are performed, the maximum value of the measured value when the chamfer width of at least one inner peripheral chamfered part is measured at a plurality of measurement points The difference from the minimum value hardly changes. For this reason, both the glass substrate having a donut shape in which the inner peripheral chamfered portion used for the main surface polishing step and the glass substrate for magnetic recording medium subjected to various polishing steps are chamfered at least one of the inner peripheral chamfered portions. It is preferable that the difference between the maximum value and the minimum value when the width is measured at a plurality of measurement points satisfies the above range.

Here, the chamfered width of the inner peripheral chamfered portion means the length of the chamfered portion in the horizontal direction, that is, the length parallel to the main surface, and is shown in FIGS. 1 (A) and 1 (B). Is the length indicated as L _ID . Note that the chamfering width L _ID of the inner peripheral chamfered portion is also measured on a line passing through the center O of the glass substrate 10 for magnetic recording medium, as shown in FIG.

  The number of measurement points of the chamfer width of the inner peripheral chamfered portion may be a plurality of measurement points, that is, two or more as in the case of measurement of the chamfer width of the outer peripheral chamfered portion. It is not limited. However, it is preferable to select the number of measurement points within a range that does not impair the productivity so that the variation in chamfer width can be sufficiently evaluated.

  The number of measurement points when measuring the chamfer width is, for example, preferably 4 points or more, and more preferably 20 points or more.

  However, from the viewpoint of productivity, the number of measurement points when measuring the chamfer width is preferably 360 points or less, and more preferably 180 points or less.

  Here, the number of measurement points means the number of measurement points when measuring the chamfer width of one inner peripheral chamfer.

  The distance between measurement points when measuring the chamfer width is preferably constant. For this reason, for example, the angle formed by one measurement point, the center of the glass substrate for magnetic recording media, and the measurement point adjacent to the one measurement point is a value obtained by dividing 360 ° by the number of measurement points. It is preferable.

The length of the chamfering width L _ID of the inner peripheral chamfered portion is not particularly limited, and can be selected according to specifications required for the glass substrate for a magnetic recording medium. However, if the chamfering width L _ID of the inner peripheral chamfered portion is too long, the area of the main surface may be reduced. For this reason, it is preferable that the chamfering width L _ID of the inner peripheral chamfered portion is 200 μm or less. The lower limit value of the chamfering width L _ID of the inner peripheral chamfered portion is not particularly limited, but may be, for example, 50 μm or more.

In the glass substrate for a magnetic recording medium of the present embodiment described above, the difference between the maximum value and the minimum value when the chamfer width of the outer peripheral chamfered portion is measured at a plurality of measurement points is suppressed. . For this reason, it is possible to suppress the occurrence of fine wrinkles between the main surface and the outer peripheral chamfered portion when subjected to the main surface polishing step, and to suppress the fine wrinkles between the main surface and the outer peripheral chamfered portion. It can be set as the glass substrate for recording media.
[Method for producing glass substrate for magnetic recording medium]
Next, a configuration example of the method for manufacturing the glass substrate for a magnetic recording medium according to the present embodiment will be described.

  In addition, according to the manufacturing method of the glass substrate for magnetic recording media of this embodiment, the glass substrate for magnetic recording media as stated above can be manufactured. For this reason, some description is abbreviate | omitted about the part which overlaps with the content demonstrated in the glass substrate for magnetic recording media.

  The manufacturing method of the glass substrate for magnetic recording media of this embodiment can have the following processes.

  Prepare a glass substrate for trial grinding having a donut shape, a pair of main surfaces, an outer peripheral end surface, and an inner peripheral end surface, and grind the outer peripheral end surface of the test grinding glass substrate with an outer peripheral end surface grinding wheel, A trial grinding process for forming a pair of outer peripheral chamfers.

  An outer peripheral chamfered portion evaluation step of measuring a chamfer width of at least one outer peripheral chamfered portion of a pair of peripheral chamfered portions of the glass substrate for trial grinding at a plurality of measurement points.

  A grindstone position correcting step for outer peripheral end face grinding that corrects the position of the outer peripheral end face grinding grindstone based on the result of the outer peripheral chamfered portion evaluation step.

  A glass substrate having a donut shape and having a pair of main surfaces, an outer peripheral end surface, and an inner peripheral end surface is prepared. After the outer peripheral end surface grinding wheel position correcting step, the outer peripheral end surface grinding wheel is used to An outer peripheral chamfering step of forming a pair of outer peripheral chamfered portions on the outer peripheral end surface.

  Here, first, a configuration example of a glass substrate manufacturing apparatus for a magnetic recording medium that can be used when forming an outer peripheral chamfered portion on a test grinding glass substrate or an outer peripheral end surface of the glass substrate in the trial grinding step and the outer peripheral chamfering step. Will be described with reference to FIG.

  FIG. 2 schematically shows a chamfered portion forming apparatus capable of forming chamfered portions on the outer peripheral end surface and the inner peripheral end surface, which is a glass substrate manufacturing apparatus for a magnetic recording medium.

  As shown in FIG. 2, the chamfered portion forming apparatus 20 can include a table 22 that holds a glass substrate 21 having a donut shape that forms an outer peripheral chamfered portion, and a grindstone 23 for outer peripheral end surface grinding. Moreover, it can also have the grindstone 24 for inner peripheral end surface grinding.

  Then, the outer peripheral end surface of the glass substrate 21 having a donut shape placed and held on the table 22 can be chamfered by grinding with the outer peripheral end surface grinding wheel 23. Further, the inner peripheral end surface of the glass substrate 21 having a donut shape placed and held on the table 22 can be chamfered by grinding with the inner peripheral end surface grinding wheel 24.

  The table 22 can adsorb and hold the glass substrate 21 having a donut shape placed on the upper surface. The table 22 is rotatably provided, and the glass substrate 21 having a donut shape to be held can be rotated by rotating the table 22.

  Note that the glass substrate 21 having a donut shape is not limited to the method of being held only by the table 22. For example, a cylindrical upper holder may be provided on the upper portion of the table 22 so as to face the table 22, and a glass substrate 21 having a donut shape may be sandwiched and fixed between the table 22 and the upper holder. it can.

  The outer peripheral end face grinding wheel 23 has a substantially cylindrical shape, and can be provided so that the central axis is substantially orthogonal to the main surface of the glass substrate 21 having a donut shape. Abrasive grains are fixed to the outer peripheral surface of the outer peripheral end surface grinding wheel 23, and a plurality of annular groove-shaped grinding surfaces 231 orthogonal to the central axis can be provided along the central axis direction.

  The outer peripheral end grinding wheel 23 is rotatably provided with the central axis as the rotation axis R, and has an outer periphery in the direction of the block arrow 23A that is the rotation axis direction and in the direction of the block arrow 23B that is orthogonal to the rotation axis direction. The end face grinding wheel moving means 232 is provided so as to be movable.

  The outer peripheral end surface grinding wheel 23 moves to a position where any one of the grinding surfaces 231 comes into contact with the outer peripheral end surface of the glass substrate 21 having a donut shape, and rotates around the outer periphery of the glass substrate 21 having a donut shape rotating together with the table 22. The end face can be ground and chamfered. For this reason, the annular groove-shaped grinding surface 231 passes through the central axis of the outer peripheral end surface grinding wheel 23 and has a cross-sectional shape parallel to the central axis to the shape of the outer peripheral end surface after chamfering the glass substrate 21 having a donut shape. It can have a corresponding shape.

  The inner peripheral end face grinding wheel 24 can be provided so as to have a substantially cylindrical shape and a central axis substantially orthogonal to the main surface of the glass substrate 21 having a donut shape. Abrasive grains are fixed to the outer peripheral surface of the inner peripheral end face grinding grindstone 24, and a plurality of annular groove-shaped grinding surfaces 241 orthogonal to the central axis can be provided along the central axis direction.

  The inner peripheral end face grinding wheel 24 is rotatably provided with the central axis as the rotation axis R, and in the direction of the block arrow 24A that is the rotation axis direction and the direction of the block arrow 24B that is the direction orthogonal to the rotation axis direction. The inner peripheral end face grinding wheel moving means 242 is provided so as to be movable. The grinding wheel 24 for inner peripheral end surface grinding moves to a position where any one of the grinding surfaces 241 contacts the inner peripheral end surface of the glass substrate 21 having a donut shape, rotates, and rotates with the table 22. Chamfering can be performed by grinding the inner peripheral end face of the steel. For this reason, the annular groove-shaped grinding surface 241 passes through the central axis of the inner peripheral end surface grinding wheel 24 and has a cross section parallel to the central axis of the inner peripheral end surface after chamfering the glass substrate 21 having a donut shape. It can have a shape corresponding to the shape.

  The chamfered portion forming apparatus 20 can have various members as necessary in addition to the above-described members, and can include, for example, a grinding fluid supply nozzle 25 that supplies a grinding fluid. The grinding liquid supply nozzle 25 can supply, for example, a grinding liquid between the glass substrate 21 having a donut shape, the outer peripheral end surface grinding wheel 23, and the inner peripheral end surface grinding wheel 24.

  Further, it is possible to have the grindstone position control means 26 for controlling the position of each grindstone by controlling the outer peripheral end face grinding grindstone moving means 232 and the inner peripheral end face grinding grindstone moving means 242 described above.

  The outer peripheral end face grinding grindstone 23 and the inner peripheral end face grinding grindstone 24 do not interfere with the conveyance path of the doughnut-shaped glass substrate when the glass substrate 21 having the donut shape is carried in and out of the table 22. It can be moved to a different location than during grinding. For this reason, the grindstone position control means 26 can also have a memory | storage means to memorize | store the positional information etc. of the grindstone 23 for outer peripheral end surface grinding, the grindstone 24 for inner peripheral end surface grinding | polishing in the inside or the exterior.

  In the method for manufacturing a glass substrate for a magnetic recording medium of the present embodiment, the difference between the maximum value and the minimum value when the chamfer width of at least one outer peripheral chamfer is measured at a plurality of measurement points is 10 μm or less. It is possible to produce a glass substrate for a magnetic recording medium.

  And in order to make the difference between the maximum value and the minimum value of the measured value when measuring the chamfer width of at least one outer peripheral chamfered portion at a plurality of measurement points to 10 μm or less, the outer peripheral chamfering step It is preferable that the glass substrate 21 having a donut shape and the outer peripheral edge grinding wheel 23 are appropriately arranged.

  Therefore, the method for manufacturing the glass substrate for a magnetic recording medium of the present embodiment can be carried out according to the flowchart shown in FIG.

  First, the trial grinding step S31 can be performed before the outer peripheral chamfering step is performed. In the trial grinding step S31, a glass substrate for trial grinding having a donut shape and having a pair of main surfaces, an outer peripheral end surface, and an inner peripheral end surface is used in the outer peripheral chamfering step. Can be used to form a pair of outer peripheral chamfers.

  In addition, it is preferable that the glass substrate for trial grinding has the same size, shape, and material as the glass substrate used for an outer peripheral chamfering process in order to manufacture the glass substrate for magnetic recording media.

  Further, as described with reference to FIG. 1A, in the glass substrate for a magnetic recording medium, a chamfered portion can also be formed on the inner peripheral end surface. For this reason, in trial grinding process S31, when forming an outer peripheral chamfered part, an inner peripheral chamfered part can also be formed. Since the method for forming the outer peripheral chamfered portion and the inner peripheral chamfered portion by the chamfered portion forming apparatus 20 has already been described, the description thereof is omitted here.

  Next, as the outer peripheral chamfered portion evaluation step S32, the distribution of the chamfer width of at least one outer peripheral chamfered portion of the pair of outer peripheral chamfered portions of the obtained glass substrate for trial grinding can be evaluated. The means for evaluating the chamfer width at this time is not particularly limited, and may be any means that can measure the chamfer width of the outer peripheral chamfered portion at a plurality of measurement points, for example.

  As for the glass substrate for trial grinding, as in the case of the glass substrate for magnetic recording medium described with reference to FIG. 1 (A), the outer peripheral chamfering is performed on one main surface side and the other main surface side, respectively. A part can be provided and it can have a pair of peripheral chamfers. However, when the glass substrate for trial grinding has a pair of outer peripheral chamfered portions, the pair of outer peripheral chamfered portions are simultaneously formed by the outer peripheral end surface grinding grindstone, and therefore the distribution of the chamfer widths is almost the same.

  For this reason, in the outer peripheral chamfered portion evaluation step, the chamfer width of at least one outer peripheral chamfered portion may be measured at a plurality of measurement points as described above. That is, for example, for one outer peripheral chamfer, the chamfer width can be measured at a plurality of arbitrary measurement points selected along the outer periphery. In particular, in order to more accurately measure the distribution of the chamfer width, it is more preferable to measure the chamfer width at any of a plurality of measurement points selected along the outer periphery of each of the outer peripheral chamfered portions.

  In the outer peripheral chamfered portion evaluation step S32, the number of measurement points for measuring the chamfer width of the outer peripheral chamfered portion is not particularly limited. For example, the number of measurement points is preferably four or more, and more than twenty. More preferably.

  However, from the viewpoint of productivity, the number of measurement points for measuring the chamfer width of the outer peripheral chamfered portion is preferably 360 points or less, and more preferably 180 points or less.

  Note that the number of measurement points here means the number of measurement points when measuring the chamfer width of one outer peripheral chamfer.

  Moreover, it is preferable that the distance between measurement points is constant. For this reason, for example, the angle formed by one measurement point, the center of the glass substrate for trial grinding, and the measurement point adjacent to the one measurement point is a value obtained by dividing 360 ° by the number of measurement points. Preferably it is.

  Next, in the outer peripheral edge grinding wheel position correcting step S33, the position of the outer peripheral edge grinding wheel 23 can be corrected based on the evaluation result in the outer peripheral chamfered portion evaluation step S32.

  The outer peripheral edge grinding wheel 23 is different from the outer peripheral chamfering step so as not to interfere with the conveyance path of the glass substrate 21 having a donut shape when the glass substrate 21 having a donut shape is carried in and out of the table 22. Moved to position. For this reason, in the outer peripheral end face grinding wheel position correcting step S33, an appropriate position of the outer peripheral end face grinding wheel in the outer peripheral chamfering step is calculated, and the result, that is, the position information of the appropriate position of the end face grinding grindstone is stored in the storage means. It can be memorized.

  In the outer peripheral edge grinding wheel position correcting step S33, first, from the evaluation result in the outer peripheral chamfered portion evaluation step S32, for example, position information of an appropriate position is calculated for the vertical position of the outer peripheral edge grinding wheel 23 in the outer peripheral chamfering step S35. can do.

  This is because the vertical position of the outer peripheral edge grinding wheel 23 relative to the glass substrate 21 having a donut shape, specifically, the vertical position of the grinding surface 231 is shifted, and the chamfer width of the outer peripheral chamfered portion is measured in a plurality of ways. This is because the difference between the maximum value and the minimum value of the measured value when measured at a point is the main cause.

  Here, the vertical direction means a direction perpendicular to the main surface of the glass substrate 21 having a donut shape held on the table 22.

  Further, the position information of the appropriate position in the vertical direction of the outer peripheral end surface grinding wheel 23 in the outer peripheral chamfering step S35 is the maximum value of the measured value when the chamfer width of at least one outer peripheral chamfered portion is measured at a plurality of measurement points. It is preferable to calculate so that the difference between the value and the minimum value is 10 μm or less. In particular, the calculation is more preferably 8 μm or less, and further preferably 5 μm or less.

  The calculated position information of the appropriate position of the outer peripheral end face grinding wheel is updated as the appropriate position of the outer peripheral end face grinding wheel in the outer peripheral chamfering step S35, for example, storage means provided inside or outside the grindstone position control means 26 Can be memorized. In the outer peripheral chamfering step S35, which will be described later, the grindstone position control means 26 moves the outer peripheral end face grinding grindstone 23 by the outer peripheral end face grinding grindstone moving means 232 based on the updated position information, thereby performing chamfering. it can.

  An example of calculating and storing an appropriate vertical position of the outer peripheral end surface grinding wheel 23 in the outer peripheral chamfering step S35 from the evaluation result in the outer peripheral chamfered portion evaluation step S32 in the outer peripheral end surface grinding wheel position correcting step S33. However, the present invention is not limited to such a form. In addition to or in place of the appropriate vertical position of the outer peripheral end face grinding wheel 23 in the outer peripheral chamfering step S35, an appropriate angle of the rotation axis R of the outer peripheral end face grinding grindstone 23 in the outer peripheral chamfering step S35 is calculated and stored. The angle information may be stored.

  In this case, in the outer peripheral chamfering step S35 described later, the grindstone position control means 26 uses the outer peripheral end face grinding grindstone moving means 232 based on the position information and / or angle information stored in the storage means. The chamfering can be performed by moving.

  Moreover, as shown in FIG. 3, in addition to or instead of the outer peripheral end face grinding wheel position correcting step S33, a table position correcting step S33 ′ for correcting the position of the table 22 may be performed. In the table position correction step S33 ′, for example, an appropriate position of the table 22 and / or an appropriate angle of the rotating shaft in the outer peripheral chamfering step S35 can be calculated from the evaluation result in the outer peripheral chamfered portion evaluation step S32.

  And it can correct | amend so that the position of the table 22 may become an appropriate position, and / or the rotation axis of the table 22 may become an appropriate angle.

  The calculated appropriate position of the table 22 and / or the appropriate angle of the rotation axis is updated as information on the appropriate position of the table 22 and / or the angle of the rotation axis in the outer peripheral chamfering step S35, and table position control (not shown) is performed. You may memorize | store in the memory | storage means which a means etc. have. In the outer peripheral chamfering step S35, the table 22 can be moved by a table moving means (not shown) based on the updated position information or the like to perform chamfering.

  After the outer peripheral end surface grinding wheel position correcting step S33 and / or the table position correcting step S33 'is completed, for example, an outer peripheral end surface grinding wheel position checking step S34 may be performed. In the outer peripheral end surface grinding wheel position confirmation step S34, a pair of outer peripheral chamfered portions can be formed on the glass substrate for confirmation, for example, in the same manner as the aforementioned trial grinding step S31 and outer peripheral chamfered portion evaluation step S32. Then, the chamfer width of at least one of the outer peripheral chamfers is measured at a plurality of measurement points, and the difference between the maximum value and the minimum value of the measurement values can be evaluated.

  In this step, when the outer peripheral chamfered portion is formed on the glass substrate for confirmation, the position of the outer peripheral end surface grinding wheel 23 and / or the table 22 and / or the angle of the rotating shaft is changed to the outer peripheral end surface grinding wheel position correcting step. It can be implemented in a state corrected based on the position information and angle information calculated in S33 and / or the table position correction step S33 ′. Moreover, as a glass substrate for confirmation, the glass substrate of the same size, shape, and material as the glass substrate for trial grinding mentioned above, for example can be used.

  And from the result, it can confirm whether the position of the grindstone 23 for outer periphery end surface grinding after correction | amendment with respect to the glass substrate 21 which has the donut shape on the table 22 is appropriate. That is, if the difference between the maximum value and the minimum value of the chamfered width of the measured peripheral chamfered portion is within a predetermined range, the peripheral end surface grinding for the glass substrate 21 having a donut shape on the table 22 is performed. It can be confirmed that the corrected position of the grinding wheel 23 is appropriate.

  When the position of the grindstone 23 for outer peripheral end surface grinding with respect to the glass substrate having a donut shape is not appropriate, the grinding can be performed again from the trial grinding step S31.

  In addition, as shown with the broken line in FIG. 3, outer peripheral chamfering process S35 can also be implemented, without implementing outer peripheral end surface grinding wheel position confirmation process S34.

  Next, the outer peripheral chamfering step S35 can be performed.

  In the outer peripheral chamfering step S35, the glass substrate 21 having a donut shape is placed on the table 22, calculated in the outer peripheral end surface grinding wheel position correcting step S33, and stored in the storage means included in the grinding wheel position control means 26 and the like. Based on the information and / or the angle information, the outer peripheral end surface grinding wheel 23 can be moved. Then, the table 22 and the outer peripheral end surface grinding wheel 23 are rotated along the rotation axis in a state where the outer peripheral end surface of the glass substrate 21 having a donut shape is in contact with the grinding surface 231 of the outer peripheral end surface grinding wheel 23. Then, chamfering can be performed.

  When the table position correction step S33 ′ is performed as described above, the table position and / or the rotation axis angle calculated in the table position correction step S33 ′ are set before chamfering. The table 22 can also be moved.

  In this way, the outer peripheral chamfering step can be carried out after correcting the glass substrate having a donut shape to be used for the outer peripheral chamfering step and the outer peripheral end surface grinding grindstone to have an appropriate arrangement. Thereby, the glass for the magnetic recording medium in which the difference between the maximum value and the minimum value of the measured value when measuring the chamfer width of the outer peripheral chamfered portion at a plurality of measurement points, that is, the variation in the chamfer width of the outer peripheral chamfered portion is suppressed. A substrate can be obtained.

  When a plurality of glass substrates for magnetic recording media are manufactured, the steps from the trial grinding step S31 to the grinding wheel position correcting step S33 for outer peripheral end surface grinding are performed every time the outer peripheral chamfered portion of the glass substrate for magnetic recording medium is formed. do not have to. In the trial grinding step S31, for example, when the manufactured glass substrate for magnetic recording medium is evaluated, when the variation in the chamfer width of the outer peripheral chamfered portion becomes large, or when the manufacturing conditions are changed, the magnetic recording medium It can be carried out at the start of operation of the glass substrate manufacturing apparatus.

  For this reason, after the trial grinding step S31 to the outer peripheral end surface grinding wheel position correcting step S33 and the outer peripheral end surface grinding wheel position confirmation step S34, etc., as necessary, only the outer peripheral chamfering step S35 is repeated. Can be implemented.

  Further, in the glass substrate for magnetic recording medium described above, the maximum value of the measured value when measuring the chamfer width of at least one inner peripheral chamfered portion at a plurality of measurement points among the pair of inner peripheral chamfered portions, The difference from the minimum value is also preferably 10 μm or less.

  In order to set the difference between the maximum value and the minimum value when measuring the chamfer width of at least one inner peripheral chamfered portion at a plurality of measurement points to 10 μm or less, in the inner peripheral chamfering process, It is preferable that the glass substrate 21 having a donut shape to be provided and the inner peripheral edge grinding wheel 24 are appropriately arranged.

  Therefore, the method for manufacturing a glass substrate for a magnetic recording medium according to this embodiment can be carried out according to the flowchart shown in FIG.

  First, in the above-described trial grinding step, the inner peripheral end face of the glass substrate for trial grinding can be further ground with an inner peripheral end face grinding grindstone to form a pair of inner peripheral chamfered portions. And it can also have the following processes further.

  An inner peripheral chamfer evaluation step of measuring a chamfer width of at least one inner peripheral chamfered portion at a plurality of measurement points, out of the pair of inner peripheral chamfered portions of the glass substrate for trial grinding.

  A grindstone position correcting step for grinding the inner peripheral end face for correcting the position of the grinding wheel for inner peripheral end face grinding for grinding the inner peripheral end face based on the result of the inner peripheral chamfered portion evaluation step.

  An inner peripheral chamfering step of forming a pair of inner peripheral chamfered portions on the inner peripheral end surface of the glass substrate by the inner peripheral end surface grinding wheel after the inner peripheral end surface grinding wheel position correcting step.

  In the trial grinding step S31, a glass substrate for trial grinding having a donut shape and having a pair of main surfaces, an outer peripheral end surface, and an inner peripheral end surface is used in the outer peripheral chamfering step. In addition to the outer peripheral chamfered portion, an inner peripheral chamfered portion can be formed.

  In addition, it is preferable that the glass substrate for trial grinding has the same size, shape, and material as the glass substrate used for an outer peripheral chamfering process and an inner peripheral chamfering process in order to manufacture the glass substrate for magnetic recording media.

  In the trial grinding step S31, when the outer peripheral chamfered portion and the inner peripheral chamfered portion are formed, the obtained glass substrate for trial grinding is the outer peripheral chamfered portion evaluation step S32 described above and the inner peripheral chamfered portion described in detail below. It can supply to evaluation process S42.

  Next, as the inner peripheral chamfered portion evaluation step S42, the distribution of the chamfer width of the inner peripheral chamfered portion of the obtained glass substrate for trial grinding can be evaluated. The means for evaluating the chamfer width at this time is not particularly limited, and for example, any means that can measure the chamfer width of at least one inner peripheral chamfer at a plurality of measurement points may be used.

  As for the glass substrate for trial grinding, as in the case of the glass substrate for magnetic recording medium described with reference to FIG. 1 (A), the inner circumference is provided on one main surface side and the other main surface side, respectively. A chamfered portion can be provided, and a pair of inner peripheral chamfered portions can be provided. However, when the glass substrate for trial grinding has a pair of inner peripheral chamfered portions, the pair of inner peripheral chamfered portions are simultaneously formed by the inner peripheral end surface grinding grindstone, and therefore the distribution of the chamfer width is substantially the same. Become.

  For this reason, in the inner peripheral chamfered portion evaluation step, the chamfer width of at least one inner peripheral chamfered portion may be measured at a plurality of measurement points as described above. That is, for example, for one inner peripheral chamfer, the chamfer width can be measured at a plurality of arbitrary measurement points selected along the inner periphery. In particular, in order to measure the distribution of chamfer width more accurately, it is more possible to measure the chamfer width at any of a plurality of measurement points selected along the inner circumference in each inner chamfered portion for both inner chamfered portions. preferable.

  In the inner peripheral chamfered portion evaluation step S42, the number of measurement points for measuring the chamfer width of the inner peripheral chamfered portion is not particularly limited. For example, the number of measurement points is preferably 4 points or more, and 20 points. More preferably.

  However, from the viewpoint of productivity, the number of measurement points for measuring the chamfer width of the inner peripheral chamfered portion is preferably 360 points or less, and more preferably 180 points or less.

  Here, the number of measurement points means the number of measurement points when measuring the chamfer width of one inner peripheral chamfer.

  The distance between the measurement points is preferably constant. For this reason, for example, the angle formed by one measurement point, the center of the glass substrate for trial grinding, and the measurement point adjacent to the one measurement point is a value obtained by dividing 360 ° by the number of measurement points. Preferably it is.

  Next, in the inner peripheral edge grinding wheel position correction step S43, the position of the inner peripheral edge grinding wheel 24 can be corrected based on the evaluation result in the inner peripheral chamfer evaluation step S42.

  The inner peripheral end face grinding grindstone 24 does not interfere with the conveyance path of the glass substrate 21 having the donut shape when the glass substrate 21 having the donut shape is carried in and out of the table 22. It has moved to a different position. For this reason, in the inner peripheral end face grinding wheel position correcting step S43, an appropriate position of the inner peripheral end face grinding wheel in the inner peripheral chamfering step is calculated, and as a result, that is, an appropriate position of the inner peripheral end face grinding wheel is calculated. The position information is stored in the storage means.

  In the inner peripheral edge grinding wheel position correcting step S43, first, an appropriate position is calculated for the vertical position of the inner peripheral edge grinding wheel 24 in the inner circumferential chamfering step S45 from the evaluation result in the inner circumferential chamfer evaluation step S42. can do.

  This is because the position of the inner peripheral end face grinding wheel 24 in the vertical direction with respect to the glass substrate 21 having a donut shape, specifically, the shift in the vertical direction of the grinding surface 241 increases the chamfer width of the inner peripheral chamfered portion. This is because the difference between the maximum value and the minimum value when measured at the measurement point is the main cause.

  Here, the vertical direction means a direction perpendicular to the main surface of the glass substrate 21 having a donut shape held on the table 22.

  Further, the position information of the appropriate position in the vertical direction of the inner peripheral end face grinding wheel 24 in the inner peripheral chamfering step S35 is measured when the chamfer width of at least one inner peripheral chamfered portion is measured at a plurality of measurement points. It is preferable that the difference between the maximum value and the minimum value be selected so as to be 10 μm or less. In particular, the selection is more preferably 8 μm or less, and further preferably 5 μm or less.

  The calculated information on the appropriate position of the inner peripheral end face grinding wheel is updated as the appropriate position of the inner peripheral end face grinding grindstone 24 in the inner peripheral chamfering step S45, and provided, for example, inside or outside the grindstone position control means 26. Can be stored in the storage means. Then, in the inner peripheral chamfering step S45 described later, the inner peripheral end face grinding grindstone 24 can be moved by the inner peripheral end face grinding grindstone moving means 242 to perform chamfering based on the updated position information.

  In the inner peripheral edge grinding wheel position correction step S43, an appropriate vertical position of the inner peripheral edge grinding wheel 24 in the inner circumferential chamfering step S45 is calculated from the evaluation result in the inner circumferential chamfer evaluation step S42. However, the present invention is not limited to such an embodiment. In addition to or in place of the appropriate vertical position of the inner peripheral end face grinding grindstone 24 in the inner peripheral chamfering step S45, an appropriate angle of the rotation axis of the inner peripheral end face grinding grindstone 24 in the inner peripheral chamfering step S45 is calculated. The angle information may be stored in the storage means.

  In this case, in the inner peripheral chamfering step S45 described later, the grindstone position control means 26 uses the inner peripheral end face grinding grindstone 24 based on the position information and / or angle information stored in the storage means. Chamfering can be performed by moving the moving means 242.

  Moreover, as shown in FIG. 4, in addition to or instead of the inner peripheral edge grinding grinding wheel position correcting step S43, a table position correcting step S43 ′ for correcting the position of the table 22 may be performed. In the table position correction step S43 ′, for example, an appropriate position of the table 22 and / or an appropriate inclination of the rotating shaft in the inner peripheral chamfering step S45 can be calculated from the evaluation result in the inner peripheral chamfer evaluation step S42.

  And it can correct | amend so that the position of the table 22 may become an appropriate position, and / or the rotation axis of the table 22 may become an appropriate angle.

  The calculated appropriate position of the table 22 and / or the appropriate inclination of the rotation axis is updated as information on the appropriate position of the table 22 and / or the angle of the rotation axis in the inner peripheral chamfering step S45, and the table position (not shown) You may memorize | store in the memory | storage means which a control means etc. have. In the inner peripheral chamfering step S45, the chamfering can be performed by moving the table 22 by a table moving means (not shown) based on the updated position information and the like.

  However, when performing table position correction process S33 'for outer periphery chamfering process S35, and table position correction process S43' for inner periphery chamfering process S45, it is preferable to implement only one. This is because the control content for the table position may not match.

  For example, when the table position correcting step S33 ′ is performed for the outer peripheral chamfering step S35, it is preferable to perform the inner peripheral end surface grinding wheel position correcting step S43 so as to correspond to the corrected table position. In addition, when the table position correcting step S43 ′ is performed for the inner peripheral chamfering step S45, it is preferable to perform the outer peripheral end surface grinding wheel position correcting step S33 so as to correspond to the corrected table position.

  After finishing the inner peripheral end surface grinding wheel position correcting step S43 and / or the table position correcting step S43 ', for example, an inner peripheral end surface grinding wheel position checking step S44 may be performed. In the inner peripheral end face grinding wheel position confirmation step S44, for example, a pair of inner peripheral chamfered portions is first formed on the glass substrate for confirmation, as in the above-described trial grinding step S31 and inner peripheral chamfered portion evaluation step S42. it can. Then, the chamfer width of at least one of the inner peripheral chamfers is measured at a plurality of measurement points, and the difference between the maximum value and the minimum value of the measurement values can be evaluated.

  In this step, when the inner peripheral chamfered portion is formed on the glass substrate for confirmation, the position of the inner peripheral end surface grinding wheel 24 and / or the table 22 and / or the angle of the rotating shaft is changed to the inner peripheral end surface grinding wheel. The correction can be performed in a corrected state based on the position information and the angle information calculated in the position correction step S43 and / or the table position correction step S43 ′. Moreover, as a glass substrate for confirmation, the glass substrate of the same size, shape, and material as the glass substrate for trial grinding mentioned above, for example can be used.

  Then, from the result, it can be confirmed whether the position of the corrected grinding wheel 24 for inner peripheral end face with respect to the glass substrate having a donut shape on the table 22 is appropriate. That is, if the difference between the maximum value and the minimum value of the chamfered width of the measured inner peripheral chamfered portion is within a predetermined range, the inner periphery relative to the glass substrate 21 having a donut shape on the table 22 It can be confirmed that the corrected position of the grindstone 24 for end face grinding is appropriate.

  When the position of the grinding wheel 24 for inner peripheral end face grinding with respect to the glass substrate having a donut shape is not appropriate, the grinding can be performed again from the trial grinding step S31.

  In addition, as shown with the broken line in FIG. 4, the inner peripheral chamfering step S45 can be performed without performing the inner peripheral end surface grinding wheel position confirmation step S44. Further, when the outer peripheral end surface grinding wheel position confirmation step S34 is performed, the inner peripheral end surface grinding wheel position confirmation step S44 can be simultaneously performed using the same confirmation glass substrate.

  Next, the inner peripheral chamfering step S45 can be performed.

  In the inner peripheral chamfering step S45, the glass substrate 21 having a donut shape is placed on the table 22, calculated in the inner peripheral edge grinding grinding wheel position correcting step S43, and stored in the storage means included in the grinding wheel position control means 26 or the like. On the basis of the position information and / or the angle information, the inner peripheral edge grinding wheel 24 can be moved. The table 22 and the inner peripheral end surface grinding wheel 24 are moved along the rotation axis in a state where the inner peripheral end surface of the glass substrate 21 having a donut shape is in contact with the grinding surface 241 of the inner peripheral end surface grinding wheel 24. Chamfering can be performed by rotating.

  When the table position correction step S43 ′ is performed as described above, the table position and / or the rotation axis angle calculated in the table position correction step S43 ′ is set before the chamfering is performed. The table 22 can also be moved.

  In this way, after correcting the glass substrate having a donut shape to be used for the inner peripheral chamfering step and the inner peripheral end face grinding grindstone to be appropriately arranged, the inner peripheral chamfering step can be performed. . Thereby, the magnetic recording medium in which the difference between the maximum value and the minimum value of the measured value when the chamfered width of the inner peripheral chamfered portion is measured at a plurality of measurement points, that is, the variation in the chamfered width of the inner peripheral chamfered portion is suppressed. A glass substrate can be obtained.

  When manufacturing a plurality of glass substrates for magnetic recording media, every time the inner peripheral chamfered portion of the glass substrate for magnetic recording media is formed, the process from the trial grinding step S31 to the grinding wheel position correcting step S43 for inner peripheral end surface grinding. There is no need to implement. In the trial grinding step S31, for example, when the manufactured glass substrate for magnetic recording medium is evaluated, when the variation of the chamfer width of the inner peripheral chamfered portion becomes large, or when manufacturing conditions are changed, magnetic recording is performed. It can be implemented at the start of operation of the medium glass substrate manufacturing apparatus.

  For this reason, once the process from the trial grinding step S31 to the inner peripheral end surface grinding wheel position correcting step S43 and the inner peripheral end surface grinding wheel position confirmation step S44 are performed as necessary, the inner peripheral chamfering step S45. Only can be repeated.

  Note that the outer peripheral chamfering step S35 and the inner peripheral chamfering step S45 can be performed simultaneously by, for example, the chamfered portion forming apparatus 20 shown in FIG.

  As described above, when the chamfering step includes the inner peripheral chamfering step S45 from the above-described trial grinding step S31 according to the flowchart shown in FIG. 4, the inner peripheral end face grinding grindstone has a donut shape to be used for the inner peripheral chamfering step. The position can be corrected so as to be appropriately arranged with respect to the glass substrate. For this reason, the inner peripheral chamfered portion of the obtained glass substrate for a magnetic recording medium can suppress variation in the chamfer width. And it can suppress that a fine wrinkle generate | occur | produces between a main surface and an internal peripheral chamfering part about the glass substrate for magnetic recording media obtained when it uses for a main surface grinding | polishing process after an internal peripheral chamfering process.

The manufacturing method of the glass substrate for magnetic recording media of this embodiment is not limited to the process demonstrated so far, For example, the following processes 1-process 5 can be included.
(Step 1) A shape imparting step of processing from a glass base plate into a disc-shaped glass substrate having a circular hole in the center.
(Step 2) A chamfering step for chamfering the inner surface and the outer edge of the glass substrate.
(Step 3) An end surface polishing step for polishing the end surfaces (the inner peripheral end surface and the outer peripheral end surface) of the glass substrate.
(Step 4) A main surface polishing step for polishing the main surface of the glass substrate.
(Step 5) A cleaning / drying step of cleaning and drying the glass substrate.

  It is not necessary to perform the said process in the order described, for example, you may perform a main surface polishing process before a shape provision process. Further, each step is not limited to one time, and can be performed any number of times according to the required glass substrate specifications. For example, the main surface polishing step may be performed after the shape imparting step, and then the chamfering step and the end surface polishing step may be performed, and then the main surface polishing step may be performed again.

  However, in the method for manufacturing a glass substrate for a magnetic recording medium according to the present embodiment, when the outer peripheral chamfered portion is formed in the chamfering step, variation in the chamfer width of the outer peripheral chamfered portion can be suppressed. For this reason, even when it uses for a main surface grinding | polishing process, it can suppress that a fine wrinkle arises between a main surface and an outer peripheral chamfering part. Therefore, it is preferable to perform the main surface polishing step (step 4) at least once after performing the chamfering step of (step 2).

  Here, the shape imparting step of (Step 1) is a glass-shaped glass plate formed by a float method, a fusion method, a press molding method, a down draw method or a redraw method. The substrate is processed. The glass base plate used may be amorphous glass, crystallized glass, or tempered glass having a tempered layer on the surface layer of the glass substrate.

  The chamfering step of (Step 2) can include the above-described trial grinding step S31 to the outer peripheral chamfering step S35 performed according to the flowchart shown in FIG. By carrying out the chamfering step, the outer peripheral end face of the glass substrate can be chamfered.

  The chamfering step of (Step 2) may further include the above-described trial grinding step S31 to the inner peripheral chamfering step S45 performed according to the flowchart shown in FIG. In this case, in the chamfering step of (Step 2), the inner peripheral end surface of the glass substrate can also be chamfered.

  In the end surface polishing step of (Step 3), the end surface (side surface portion and chamfered portion) of the glass substrate can be end surface polished.

  In the main surface polishing step of (Step 4), the polishing liquid is supplied to the main surface of the glass substrate having a donut shape by, for example, a double-side polishing apparatus, and the upper and lower main surfaces of the glass substrate having a donut shape can be simultaneously polished. The main surface polishing step may be only primary polishing, may be primary polishing and secondary polishing, or may be tertiary polishing after secondary polishing.

  In addition, before the main surface polishing step of (Step 4), wrapping of the main surface (for example, loose abrasive wrap, fixed abrasive wrap, etc.) may be performed. In addition, glass substrate cleaning (inter-process cleaning) and glass substrate surface etching (inter-process etching) may be performed between the processes. Here, the main surface lapping is a broad surface main surface polishing.

  The cleaning / drying step of (Step 5) is a step of cleaning and drying the polished glass substrate. A specific cleaning method is not particularly limited. For example, cleaning can be performed by scrub cleaning using a detergent, ultrasonic cleaning in a state immersed in a detergent solution, ultrasonic cleaning in a state immersed in pure water, or the like. Moreover, it does not specifically limit about the drying method, For example, it can dry with isopropyl alcohol vapor | steam.

  Further, glass substrate cleaning (inter-process cleaning) and glass substrate surface etching (inter-process etching) may be performed between the above steps. Further, when high mechanical strength is required for the glass substrate, the reinforcing step (for example, chemical strengthening step) for forming a reinforcing layer on the surface layer of the glass substrate is performed before or after the polishing step mentioned in steps 3 and 4, Or you may implement between grinding | polishing processes.

  And the glass substrate for magnetic recording media obtained by the manufacturing method including the above steps can be made into a magnetic recording medium by further performing a step of forming a thin film such as a magnetic layer on the main surface.

  According to the method for manufacturing a glass substrate for a magnetic recording medium of the present embodiment, a trial grinding step is performed in advance in the chamfering step, and the outer peripheral end surface grinding wheel is applied to the glass substrate having a donut shape to be used for the outer peripheral chamfering step. The position can be corrected for proper placement. For this reason, the outer peripheral chamfered part of the glass substrate for magnetic recording media obtained can suppress variation in the chamfer width.

And about the glass substrate for magnetic recording media obtained when it uses for a main surface grinding | polishing process after an outer periphery chamfering process, it can suppress that a fine wrinkle generate | occur | produces between a main surface and an outer periphery chamfering part.
[Glass substrate manufacturing equipment for magnetic recording media]
Next, a configuration example of the glass substrate manufacturing apparatus for a magnetic recording medium according to the present embodiment will be described.

  In addition, about the point already demonstrated about the glass substrate manufacturing apparatus for magnetic recording media of this embodiment, a part is abbreviate | omitted. Further, in the following description, a part of the description overlapping with the above-described method for manufacturing the glass substrate for a magnetic recording medium is also omitted.

  The apparatus for manufacturing a glass substrate for a magnetic recording medium according to this embodiment can include an outer peripheral end surface grinding wheel and a grinding wheel position control means.

  In addition, the grindstone for outer peripheral end surface grinding has a donut shape, and can form a pair of outer peripheral chamfered portions on the outer peripheral end surface of the glass substrate having a pair of main surfaces, an outer peripheral end surface, and an inner peripheral end surface.

  Further, the grinding wheel position control means forms a pair of outer peripheral chamfered portions on the glass substrate for trial grinding having the same shape as the glass substrate by an outer peripheral end surface grinding grindstone, and at least one outer periphery of the pair of outer peripheral chamfered portions. Based on the distribution of the chamfer width of the outer peripheral chamfered portion when the chamfered width of the chamfered portion is measured at a plurality of measurement points, the position of the outer peripheral end surface grinding wheel can be controlled.

  The glass substrate manufacturing apparatus for a magnetic recording medium of the present embodiment is, for example, the glass substrate manufacturing apparatus for a magnetic recording medium shown in FIG. It can be configured similarly.

  That is, the chamfered portion forming apparatus 20, which is a glass substrate manufacturing apparatus for a magnetic recording medium of the present embodiment, includes a table 22 that holds a glass substrate 21 having a donut shape that forms an outer peripheral chamfered portion, and an outer peripheral edge grinding wheel 23. Can have. Further, when a chamfered portion is formed on the inner peripheral end face at the same time, an inner peripheral end face grinding grindstone 24 can be provided.

  The outer peripheral end grinding wheel 23 is rotatably provided with the central axis as the rotation axis R, and has an outer periphery in the direction of the block arrow 23A that is the rotation axis direction and in the direction of the block arrow 23B that is orthogonal to the rotation axis direction. The end face grinding wheel moving means 232 is provided so as to be movable.

  In addition, a grindstone position control means 26 is connected to the outer peripheral end face grinding grindstone moving means 232, and the outer peripheral end face grinding grindstone 23 can be moved and rotated in accordance with a command from the grindstone position control means 26. .

  The grindstone position control means 26 forms a pair of outer peripheral chamfered portions on the glass substrate for trial grinding with the outer peripheral end surface grinding grindstone 23, and measures a plurality of chamfer widths of at least one outer peripheral chamfered portion of the pair of outer peripheral chamfered portions. The position of the outer peripheral end face grinding wheel can be controlled based on the distribution of the chamfer width of the outer peripheral chamfered portion when measured by a point.

  Specifically, for example, the trial grinding step S31, the outer peripheral chamfered portion evaluation step S32, and the outer peripheral end surface grinding grindstone position correcting step S33 are performed in the same manner as in the above-described method for manufacturing the glass substrate for magnetic recording medium. Can be kept. At this time, the position information of the appropriate position of the outer peripheral end surface grinding wheel 23 and / or the angle information of the rotating shaft in the outer peripheral chamfering step S35 calculated in the outer peripheral end surface grinding wheel position correcting step S33 is used as the inner position of the grinding wheel position control means 26. Or the like can be stored in a storage means.

  When the outer peripheral chamfering step S35 of the glass substrate 21 having a donut shape is performed, the outer peripheral end surface grinding is performed by the outer peripheral end surface grinding grindstone moving unit 232 based on the position information and / or the angle information stored in the storage unit. The grindstone 23 is moved. Next, the outer peripheral chamfering step S35 can be performed by rotating the table 22 and the outer peripheral end face grinding grindstone 23.

  In addition to the grindstone position control means 26, the glass substrate manufacturing apparatus for a magnetic recording medium of the present embodiment has a table moving means (not shown) that moves and controls the position of the table 22, and a table position control means that controls the table moving means. Can also be included. In this case, the table position correcting step S33 ′ can be performed, and an appropriate position of the table 22 and / or an appropriate inclination of the rotating shaft in the outer peripheral chamfering step S35 can be calculated from the evaluation result of the outer peripheral chamfered portion evaluating step S32. Further, it can be stored in storage means provided in the table position control means or the like.

  When the outer peripheral chamfering step S35 is performed, the table 22 is moved to the predetermined position and / or the rotation axis of the table 22 by the table moving means based on the information stored in the storage means provided in the table position control means or the like. Can be moved at a predetermined angle. Further, as described above, the outer peripheral end surface grinding wheel 23 can be moved to a predetermined position by the outer peripheral end surface grinding wheel moving means 232.

  Next, the outer peripheral chamfering step S35 can be performed by rotating the table 22 and the outer peripheral end face grinding grindstone 23.

  According to the glass substrate manufacturing apparatus for a magnetic recording medium of the present embodiment described above, when the outer peripheral chamfered portion is formed on the outer peripheral end surface of the glass substrate having a donut shape placed on the table, the doughnut shape is formed. The glass substrate and the outer peripheral end surface grinding wheel can be arranged at appropriate positions. For this reason, the glass substrate for magnetic recording media which suppressed the dispersion | variation in the chamfering width | variety of an outer peripheral chamfering part can be manufactured.

  Moreover, the glass substrate manufacturing apparatus for magnetic recording media of this embodiment can also have the grindstone 24 for internal peripheral end surface grinding further as mentioned above.

  The grinding wheel for inner peripheral end face grinding has a donut shape and forms a pair of inner peripheral chamfered portions on the inner peripheral end face of the glass substrate having a pair of main surfaces, an outer peripheral end face, and an inner peripheral end face. Can do.

  Further, the grinding wheel position control means forms a pair of inner peripheral chamfered portions with a grinding wheel for inner peripheral end surface grinding on a glass substrate for trial grinding having the same shape as the glass substrate, and at least of the pair of inner peripheral chamfered portions. Based on the distribution of the chamfer width of the inner peripheral chamfered portion when the chamfered width of one inner peripheral chamfered portion is measured at a plurality of measurement points, the position of the inner peripheral end face grinding grindstone can be controlled.

  The inner peripheral end face grinding wheel 24 is rotatably provided with the central axis as the rotation axis R, and in the direction of the block arrow 24A that is the rotation axis direction and the direction of the block arrow 24B that is the direction orthogonal to the rotation axis direction. The inner peripheral end face grinding wheel moving means 242 is provided so as to be movable.

  Further, a grindstone position control means 26 is connected to the inner peripheral end face grinding grindstone moving means 242, and the inner peripheral end face grinding grindstone 24 is moved and rotated in accordance with a command from the grindstone position control means 26. Can do.

  The grindstone position control means 26 forms a pair of inner peripheral chamfered portions on the glass substrate for trial grinding with an inner peripheral end face grinding grindstone, and sets the chamfer width of at least one inner peripheral chamfered portion of the pair of inner peripheral chamfered portions. The position of the grindstone for inner peripheral end face grinding can be controlled based on the distribution of the chamfer width of the inner peripheral chamfered portion when measured at a plurality of measurement points.

  Specifically, for example, in the same manner as in the above-described method for manufacturing a glass substrate for magnetic recording medium, a trial grinding step S31, an inner peripheral chamfered portion evaluation step S42, and an inner peripheral end face grinding grindstone position correcting step S43 are performed in advance. Can be implemented. At this time, the position information of the appropriate position of the grinding wheel for inner peripheral end face grinding in the inner peripheral chamfering step S45 and / or the angle information of the rotating shaft calculated in the grinding wheel position correction process S43 for inner peripheral end face grinding is used as the grinding wheel position control means. 26 can be stored in storage means provided in the interior of the apparatus.

  Then, when the inner peripheral chamfering step S45 of the glass substrate 21 having a donut shape is performed, the inner peripheral end surface grinding grindstone moving means 242 uses the inner peripheral end surface grinding grindstone moving means 242 based on the position information and / or angle information stored in the storage means. The peripheral edge grinding wheel 24 is moved. Next, the inner peripheral chamfering step S45 can be performed by rotating the table 22 and the inner peripheral end face grinding wheel 24.

  Thus, when forming the inner peripheral chamfered portion on the inner peripheral end surface of the glass substrate having a donut shape placed on the table by providing the inner peripheral end surface grinding grindstone and the grindstone position control means, The glass substrate having a donut shape and the grinding wheel for inner peripheral end face grinding can be arranged at appropriate positions. For this reason, the glass substrate for magnetic recording media which suppressed the dispersion | variation in the chamfering width | variety of an inner peripheral chamfer part can also be manufactured.

  In addition to the grindstone position control unit 26, the glass substrate manufacturing apparatus for a magnetic recording medium according to the present embodiment includes a table moving unit (not shown) that controls the position of the table 22, and a table position control unit that controls the table moving unit. You can also. In this case, the table position correction step S43 ′ is performed, and an appropriate position of the table 22 and / or an appropriate inclination of the rotating shaft in the inner peripheral chamfering step S45 is calculated from the evaluation result of the inner peripheral chamfer evaluation step S42. it can. Further, it can be stored in storage means provided in the table position control means or the like.

  When performing the inner peripheral chamfering step S45, the table 22 is moved to a predetermined position and / or rotated by the table moving means based on the information stored in the storage means provided in the table position control means or the like. The shaft is moved to a predetermined angle. Further, as described above, the inner peripheral end face grinding grindstone moving means 242 moves the inner peripheral end face grinding grindstone 24 to a predetermined position.

  Next, the inner peripheral chamfering step S45 can be performed by rotating the table 22 and the inner peripheral end face grinding wheel 24.

Also in this case, when forming the inner peripheral chamfered portion on the inner peripheral end face of the glass substrate having a donut shape placed on the table, the glass substrate having the donut shape and an inner peripheral end face grinding grindstone are appropriately combined. Can be placed in position. For this reason, the glass substrate for magnetic recording media which suppressed the dispersion | variation in the chamfering width | variety of an inner peripheral chamfer part can also be manufactured.
[Magnetic recording medium]
Next, a configuration example of the magnetic recording medium of this embodiment will be described.

  The magnetic recording medium of this embodiment can include the glass substrate for magnetic recording medium described above.

  The configuration of the magnetic recording medium of the present embodiment is not limited as long as it includes the glass substrate for magnetic recording medium described above. For example, a magnetic layer is formed on the surface of the glass substrate for magnetic recording medium. , A protective layer, and a lubricating layer.

  The magnetic recording medium includes a horizontal magnetic recording method and a vertical magnetic recording method. Here, a specific manufacturing method will be described below by taking the case of the vertical magnetic recording method as an example.

  The magnetic recording medium can have a magnetic layer, a protective layer, and a lubricating layer on the surface of the magnetic recording medium glass substrate as described above. In the case of the perpendicular magnetic recording system, a soft magnetic underlayer made of a soft magnetic material that plays a role of circulating a recording magnetic field from a magnetic head is generally provided. For this reason, for example, a soft magnetic underlayer, a nonmagnetic intermediate layer, a perpendicular recording magnetic layer, a protective layer, and a lubricating layer can be stacked in this order from the surface of the magnetic recording medium glass substrate.

  Each layer will be described below.

  As the soft magnetic underlayer, for example, CoNiFe, FeCoB, CoCuFe, NiFe, FeAlSi, FeTaN, FeN, FeTaC, CoFeB, CoZrN, or the like can be used.

  The nonmagnetic intermediate layer is made of Ru, Ru alloy or the like. This nonmagnetic intermediate layer has a function for facilitating the epitaxial growth of the perpendicular recording magnetic layer and a function for breaking the magnetic exchange coupling between the soft magnetic underlayer and the perpendicular recording magnetic layer.

The perpendicular recording magnetic layer is a magnetic film having an easy axis of magnetization oriented in a direction perpendicular to the substrate surface, and can contain at least Co and Pt. In order to reduce intergranular exchange coupling that causes high intrinsic medium noise, a well-isolated fine particle structure (granular structure) is preferable. Specifically, an oxide (SiO ₂ , SiO, Cr ₂ O ₃ , CoO, Ta ₂ O ₃ , TiO _2, etc.), Cr, B, Cu, Ta, Zr or the like added to a CoPt alloy or the like Should be used.

  The soft magnetic underlayer, nonmagnetic intermediate layer, and perpendicular recording magnetic layer described so far can be continuously manufactured by an in-line sputtering method, a DC magnetron sputtering method, or the like.

Next, the protective layer is provided to prevent corrosion of the perpendicular recording magnetic layer and to prevent damage to the surface of the medium even when the magnetic head comes into contact with the medium, and is provided on the perpendicular recording magnetic layer. . As the protective layer, a material containing C, ZrO ₂ , SiO ₂ or the like can be used.

  As the formation method, for example, an in-line sputtering method, a CVD method, a spin coating method, or the like can be used.

  A lubricating layer is formed on the surface of the protective layer in order to reduce friction between the magnetic head and the recording medium (magnetic disk). For the lubricating layer, for example, perfluoropolyether, fluorinated alcohol, fluorinated carboxylic acid, or the like can be used. The lubricating layer can be formed by a dip method, a spray method, or the like.

  The magnetic recording medium of this embodiment described above includes the glass substrate for magnetic recording medium described above. That is, a glass substrate for a magnetic recording medium with few fine wrinkles is used between the main surface and the peripheral chamfered portion. For this reason, it is possible to suppress the occurrence of errors even when incorporated in a magnetic recording device such as a hard disk drive.

  Specific examples will be described below, but the present invention is not limited to these examples.

  First, the evaluation method of the glass substrate for magnetic recording media in the following examples and comparative examples will be described.

(1) Chamfering width, mounting runout of outer peripheral (inner peripheral) end face grinding wheel The outer peripheral chamfered portion of the glass substrate for trial grinding, the glass substrate for confirmation and the glass substrate for magnetic recording medium produced in the following examples and comparative examples, And about an internal peripheral chamfering part, a chamfering width | variety is measured using an image dimension measuring device and a projector (Keyence Co., Ltd. make: model IM6120).

  In measurement, the measurement points are determined so that the central angle of the sector formed by the adjacent measurement point and the center of the glass substrate for magnetic recording medium is 5.625 ° in each of the outer peripheral chamfered portion and the inner peripheral chamfered portion. The chamfer width is measured for each measurement point. That is, the chamfer width is measured at 64 measurement points for each of the outer peripheral chamfered portion and the inner peripheral chamfered portion.

  In addition, as demonstrated using FIG. 1 (A), the glass substrate for trial grinding, the glass substrate for confirmation, and the glass substrate for magnetic recording media produced in the following examples and comparative examples have an outer peripheral chamfered portion, One inner chamfered portion is formed on each of the upper and lower portions. However, in the glass substrate for trial grinding, the glass substrate for confirmation, and the glass substrate for magnetic recording media produced in the following examples and comparative examples, the outer peripheral chamfered portion and the inner peripheral chamfered portion have a distribution of the chamfer width, respectively. The upper and lower chamfers are the same.

  For this reason, about the glass substrate for trial grinding, the distribution of the chamfering width is measured for one of the two chamfered portions on the outer peripheral chamfered portion and the inner peripheral chamfered portion.

  In addition, the glass substrate for confirmation, and the glass substrate for magnetic recording medium produced in the following examples and comparative examples are the outer chamfered portion and the inner peripheral chamfered portion, one of the chamfered portions of the upper and lower chamfered portions. The difference between the maximum value and the minimum value of the chamfer width is calculated.

  In each of the following Examples and Comparative Examples, a plurality of glass substrates for magnetic recording media were produced under the same conditions, and the chamfer width was measured as described above for any five sheets. Then, the difference between the maximum value and the minimum value is calculated from the measurement result of the chamfer width for each glass substrate for magnetic recording medium, and the measured value of the chamfer width of the measured five glass substrates for magnetic recording medium Table 1 shows the largest value (maximum value) of the difference between the maximum value and the minimum value. Table 1 also shows the standard deviation and the average value of the difference between the maximum value and the minimum value of the measured values of the chamfer width of the five glass substrates for magnetic recording media.

Further, in each of the examples and comparative examples, the outer periphery (inner side) in the chamfering step when producing the glass substrate for a magnetic recording medium from the distribution of the chamfer width of the outer peripheral chamfered portion and the inner peripheral chamfered portion measured for the confirmation glass substrate. Circumference) The runout of the grinding wheel for end face grinding is calculated. In Tables 1 and 2, the vertical direction is the direction perpendicular to the main surface of the glass substrate having a donut shape subjected to grinding, and the horizontal direction is the main surface of the glass substrate having a donut shape subjected to grinding. Means the direction parallel to.
(2) Micro-wrinkle generation rate For the glass substrates for magnetic recording media prepared in the following examples and comparative examples, using a light scattering surface observing device (manufactured by KLA Tencor: OSA Candela 7100), the main surface and the inner peripheral chamfer The presence or absence of the occurrence of minute wrinkles is evaluated between the two parts and between the main surface and the outer peripheral chamfered part.

  In each example and comparative example, 5000 glass substrates for magnetic recording media were produced under the same conditions, and the total number of substrates produced under the same conditions or the substrates were measured until there were 5 defects, and the measured magnetic properties were measured. The incidence of defective products in the glass substrate for recording media is calculated as the incidence of minute wrinkles.

  In Tables 1 and 2, the outer peripheral fine wrinkle occurrence rate means the occurrence rate of the glass substrate for magnetic recording medium including fine wrinkles between the main surface and the outer peripheral chamfered portion, and the inner peripheral fine wrinkle occurrence rate Means the occurrence rate of a glass substrate for a magnetic recording medium including minute wrinkles between the main surface and the inner peripheral chamfered portion.

  When evaluating the generation of minute wrinkles between the main surface and the inner peripheral chamfered portion, a glass substrate for a magnetic recording medium including a minute wrinkle between the main surface and the inner peripheral chamfered portion is used. Evaluate as defective.

  In addition, when evaluating the generation of minute wrinkles between the main surface and the outer peripheral chamfered portion, the glass substrate for a magnetic recording medium including the minute wrinkles between the main surface and the outer peripheral chamfered portion is regarded as defective. evaluate.

  That is, for example, in the evaluation of the generation of minute wrinkles between the main surface and the inner peripheral chamfered portion, even if the glass substrate is regarded as defective, there is no generation of minute wrinkles between the main surface and the outer peripheral chamfered portion. In the evaluation of the generation of minute wrinkles between the main surface and the outer peripheral chamfered portion, it is evaluated as a non-defective product.

  Initially, the minute wrinkle generation rate was evaluated using a disk surface inspection device (model number: NS7000, manufactured by Hitachi High-Tech Fine Systems Co., Ltd.) that is usually used in the inspection of the glass substrate for magnetic recording media. . However, since the wrinkles in question are fine, it is difficult to distinguish between noise and wrinkles. For this reason, the above-mentioned light scattering type surface observation machine is used.

Next, the manufacturing method of the glass substrate for magnetic recording media in each Example and a comparative example is demonstrated.
[Example 1]
A glass substrate for a magnetic recording medium is produced according to the following procedure.

In order to obtain 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, a glass base plate mainly composed of SiO ₂ formed by a float method has a circular hole in the center. Processing into a glass substrate having a donut shape. (Shaping process)
Chamfering is performed 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 between the inner peripheral end surface and the outer peripheral end surface of the glass substrate having the donut shape. (Chamfering process)
The chamfering process is performed using the chamfered portion forming apparatus 20 which is the glass substrate manufacturing apparatus for a magnetic recording medium shown in FIG.

  The chamfering process will be specifically described below.

  First, a glass substrate for trial grinding having the same size, shape and material as the glass substrate having the donut shape described above is prepared.

  Then, the glass substrate for trial grinding is placed on the table 22 and is sucked and held by the table 22.

  Next, the outer peripheral end face grinding grindstone 23 and the inner peripheral end face grinding grindstone 24 are moved by the outer peripheral end face grinding grindstone moving means 232 and the inner peripheral end face grinding grindstone moving means 242 according to a command from the grindstone position control means 26. Let At this time, the outer peripheral end surface and the inner peripheral end surface of the glass substrate for trial grinding are moved so as to come into contact with the grinding surface 231 of the outer peripheral end surface grinding wheel 23 and the grinding surface 241 of the inner peripheral end surface grinding wheel 24, respectively. Yes.

Then, by rotating the table 22, the outer peripheral end face grinding grindstone 23, and the inner peripheral end face grinding grindstone 24, a pair of outer peripheral chamfered portions and a pair of inner peripheral chamfered portions are formed on the glass substrate for trial grinding. (Trial grinding step S31)
After the outer peripheral chamfered portion and the inner peripheral chamfered portion are formed on the glass substrate for trial grinding, the above-described evaluation of the chamfer width, that is, the evaluation of the distribution of the chamfer width is performed. (Outer peripheral chamfered portion evaluation step S32, inner peripheral chamfered portion evaluation step S42)
Based on the evaluation results of the outer peripheral chamfered portion evaluation step S32 and the inner peripheral chamfered portion evaluation step S42, the upper and lower ends of the outer peripheral end face grinding grindstone 23 in the outer peripheral chamfering step S35 and the inner peripheral end face grinding grindstone 24 in the inner peripheral chamfered step S45. An appropriate position is calculated for the direction position.

  In calculating the appropriate vertical position of the outer peripheral end face grinding grindstone 23 and the inner peripheral end face grinding grindstone 24 in the outer peripheral chamfering step and the inner peripheral chamfering step, the chamfer widths of the outer peripheral chamfered portion and the inner peripheral chamfered portion are calculated. The difference between the maximum value and the minimum value of the measured values is calculated to be 5 μm or less.

  Further, the angle of the rotation axis of the outer peripheral end face grinding grindstone 23 in the outer peripheral chamfering step S35 and the angle of the rotation axis of the inner peripheral end face grinding grindstone 24 in the inner peripheral chamfering step S45 are calculated together with appropriate angles.

  Here, the above-described vertical position means a direction perpendicular to the main surface of the glass substrate having a donut shape held on the table 22. Also, the appropriate angle of the rotation axis of the outer peripheral end face grinding wheel 23 and the inner peripheral end face grinding wheel 24 is that each wheel is rotated and viewed along a direction perpendicular to the main surface of the glass substrate having a donut shape. Means an angle at which eccentricity can be suppressed.

The calculated information about the vertical position of the outer peripheral end face grinding wheel 23 and the inner peripheral end face grinding grindstone 24 and the appropriate angle of the rotation axis is stored in a storage means (not shown) of the grindstone position control means 26. . (Outer peripheral end grinding wheel position correcting step S33, inner peripheral end grinding wheel position correcting step S43)
Next, in order to confirm whether the calculated vertical position of the outer peripheral end face grinding wheel 23 and the inner peripheral end face grinding wheel 24 and the angle of the rotating shaft are appropriate, the outer end face grinding is performed. A grindstone position confirmation process (S34) and a grindstone position confirmation process (S44) for inner peripheral end face grinding are performed.

  Specifically, a glass substrate for confirmation of the same size, shape, and material as the trial grinding glass substrate is placed on the table 22, and is sucked and held by the table 22. Then, in accordance with a command from the grindstone position control means 26, the outer peripheral end face grinding grindstone 23 and the inner peripheral end face grinding grindstone 24 are changed by the outer peripheral end face grinding grindstone moving means 232 and the inner peripheral end face grinding grindstone moving means 242. The position is moved based on the stored position and the information on the angle of the rotation axis. Next, the table 22, the outer peripheral end face grinding grindstone 23, and the inner peripheral end face grinding grindstone 24 are rotated to form the outer peripheral chamfered portion and the inner peripheral chamfered portion on the confirmation glass substrate.

  Then, after forming a pair of outer peripheral chamfered portions and a pair of inner peripheral chamfered portions on the glass substrate for confirmation, the above-described evaluation of the chamfer width is performed, and both the outer peripheral chamfered portion and the inner peripheral chamfered portion are chamfered. It is confirmed that the difference between the maximum value and the minimum value of the measured width is 5 μm or less.

  Next, an outer peripheral chamfering step (S35) and an inner peripheral chamfering step (S45) are performed.

  Specifically, first, the glass substrate 21 having the above-described donut shape is placed on the table 22 and is sucked and held.

  Then, in accordance with a command from the grindstone position control means 26, the outer peripheral end face grinding grindstone 23 and the inner peripheral end face grinding grindstone 24 are moved by the outer peripheral end face grinding grindstone moving means 232 and the inner peripheral end face grinding grindstone moving means 242. Let At this time, the upper and lower sides of the outer peripheral end face grinding grindstone 23 and the inner peripheral end face grinding grindstone 24 stored in the storage means in the outer peripheral end face grinding grindstone position correcting process S33 and the inner peripheral end face grinding grindstone position correcting process S43 described above. It moves so that it may become the position of a direction, and the angle of a rotating shaft.

  Next, the table 22, the outer peripheral end face grinding grindstone 23, and the inner peripheral end face grinding grindstone 24 are rotated to form an outer peripheral chamfered portion and an inner peripheral chamfered portion of the glass substrate 21 having a donut shape.

  In addition, while chamfering any glass substrate, the grinding liquid is supplied from the grinding liquid supply nozzle 25 to the glass substrate 21 having a donut shape, the outer peripheral end surface grinding wheel 23, and the inner peripheral end surface grinding wheel 24. Supply continues in the meantime.

  In this embodiment, 5000 glass substrates for a magnetic recording medium are manufactured. In the second and subsequent chamfering processes, information stored in the storage means included in the grindstone position control means 26 is used to Only the chamfering process and the inner peripheral chamfering process are repeated. That is, in the chamfering process for the second and subsequent glass substrates, the trial grinding process S31 to the outer peripheral end face grinding wheel position correcting process S33 and the inner peripheral end face grinding wheel position correcting process S43 are not performed.

  After chamfering, the main surface and end face are ground and polished by the following procedure.

The upper and lower main surfaces of the obtained glass substrate are lapped using alumina abrasive grains. (Primary main surface grinding process)
The primary main surface grinding step is performed by a 16B type double-side polishing apparatus using a cast iron surface plate and a grinding liquid containing alumina abrasive grains as a polishing tool.

  Moreover, an abrasive grain is wash | cleaned and removed about the glass substrate after a primary main surface grinding process.

Next, the outer peripheral side surface portion and the outer peripheral chamfered portion of the glass substrate are polished with a polishing brush and a polishing liquid containing cerium oxide abrasive grains, and a work-affected layer (such as a scratch) on the outer peripheral side surface and the outer peripheral chamfered portion is polished. The outer peripheral end face is polished so as to be a mirror surface. (Outer peripheral edge polishing process)
The abrasive grains are washed and removed from the glass substrate after the outer peripheral end face polishing step.

After the outer peripheral end surface polishing, the inner peripheral side surface portion and the inner peripheral chamfered portion of the glass substrate for magnetic recording medium are polished with a polishing liquid containing a polishing brush and cerium oxide abrasive grains, and the inner peripheral side surface portion and the inner peripheral surface are polished. The process-affected layer (scratches, etc.) in the chamfered portion is removed, and the inner peripheral end surface is polished so as to be a mirror surface. (Inner end face polishing process)
The abrasive grains are washed and removed from the glass substrate after the inner peripheral end surface is polished.

Next, the upper and lower main surfaces of the glass substrate are lapped. (Secondary main surface grinding process)
The secondary main surface grinding step is performed by a 16B double-side polishing apparatus using a fixed abrasive tool containing diamond abrasive grains having an average particle diameter of 4 μm and a grinding fluid containing a surfactant.

  Moreover, an abrasive grain is wash | cleaned and removed about the glass substrate after completion | finish of a secondary grinding process.

Next, the upper and lower main surfaces are polished by a 16B double-side polishing apparatus using a polishing liquid containing a soft urethane polishing pad (suede polishing pad) and a cerium oxide abrasive as a polishing tool. (Primary main surface polishing process)
As the polishing liquid containing cerium oxide abrasive grains, a polishing liquid composition containing cerium oxide having an average particle diameter (hereinafter abbreviated as average particle diameter) of about 1.0 μm is used.

  Further, in the primary main surface polishing step, the upper and lower main surfaces are polished for a total thickness of 30 μm in the plate thickness direction.

  After completion of the primary main surface polishing step, the glass substrate is cleaned and removed of the cerium oxide abrasive grains.

  After completion of the primary main surface polishing step, a secondary main surface polishing step is performed on both main surfaces of the cleaned glass substrate (secondary main surface polishing step).

  In the secondary main surface polishing step, a polishing pad containing a soft urethane polishing pad and a colloidal silica abrasive having an average particle diameter of 20 nm is used as a polishing tool, and the 16B double-side polishing apparatus is used.

  Colloidal silica abrasive grains are washed and removed from the glass substrate after the completion of the secondary main surface polishing step.

The glass substrate that has been subjected to the secondary main surface polishing step is sequentially subjected to scrub cleaning, ultrasonic cleaning in a state of immersion in a detergent solution, and ultrasonic cleaning in a state of immersion in pure water (precision cleaning), and isopropyl alcohol Dry with steam. (Washing / drying process)
The difference between the maximum value and the minimum value of the chamfered width of the outer peripheral chamfered portion and the chamfered width of the inner peripheral chamfered portion of the glass substrate for magnetic recording medium obtained by the above procedure is evaluated by the above method. .

  Moreover, about the obtained glass substrate for magnetic recording media, it evaluates about the fine wrinkle generation rate between a main surface and an inner peripheral chamfering part, and between a main surface and an outer peripheral chamfering part, respectively.

  The evaluation results are shown in Tables 1 and 2.

  Table 1 shows the evaluation results for the outer peripheral portion, and Table 2 shows the evaluation results for the inner peripheral portion.

［実施例２、実施例３］
実施例２、３では、外周端面研削用砥石位置補正工程Ｓ３３、内周端面研削用砥石位置補正工程Ｓ４３で、外周面取り部、内周面取り部の面取り幅の測定値の最大値と、最小値との差が所定の範囲となるように、外周面取り工程、内周面取り工程における外周端面研削用砥石２３、及び内周端面研削用砥石２４の上下方向の適切な位置の算出を実施している。具体的には、外周面取り部、および内周面取り部について、面取り幅の測定値の最大値と最小値との差が実施例２は８μｍ以下、実施例３は１０μｍ以下となるように、外周端面研削用砥石２３、及び内周端面研削用砥石２４の上下方向の適切な位置を算出している。

[Example 2 and Example 3]
In Examples 2 and 3, the maximum value and the minimum value of the measured values of the chamfer width of the outer peripheral chamfered portion and the inner peripheral chamfered portion in the outer peripheral end surface grinding wheel position correcting step S33 and the inner peripheral end surface grinding wheel position correcting step S43. The appropriate positions in the vertical direction of the outer peripheral end face grinding grindstone 23 and the inner peripheral end face grinding grindstone 24 in the outer peripheral chamfering step and the inner peripheral chamfering step are calculated so that the difference between them is within a predetermined range. . Specifically, for the outer peripheral chamfered portion and the inner peripheral chamfered portion, the difference between the maximum value and the minimum value of the measured value of the chamfer width is 8 μm or less in Example 2, and 10 μm or less in Example 3. Appropriate vertical positions of the end grinding wheel 23 and the inner peripheral end grinding wheel 24 are calculated.

  In Example 3, the angle of the rotation axis of the outer peripheral end face grinding grindstone 23 in the outer peripheral chamfering step S35 and the appropriate angle of the rotation axis of the inner peripheral end face grinding grindstone 24 in the inner peripheral chamfering step S45 are calculated. Not done.

  That is, in Example 3, the inclination of the rotating shaft is not controlled for both the end face grinding wheels. And about the grindstone which is not controlling about the inclination of a rotating shaft, it adjusted so that the main surface of the glass substrate 21 which has the donut shape on the table 22 at the time of grindstone attachment and the rotating shaft of the grindstone for end surface grinding might become perpendicular | vertical. Used in state.

Except for the above, a glass substrate for a magnetic recording medium was produced and evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2.
[Comparative Examples 1 and 2]
In the chamfering process, the trial grinding process S31, the outer peripheral chamfered part evaluation process S32, the inner peripheral chamfered part evaluation process S42, the outer peripheral edge grinding grinding wheel position correcting process S33, the inner peripheral end surface grinding at the time of manufacturing the glass substrate for magnetic recording media of each comparative example. The grinding wheel position correcting step S43, the outer peripheral end surface grinding wheel position confirmation step S34, and the inner peripheral end surface grinding wheel position confirmation step S44 are not performed. That is, in the chamfering process, the outer peripheral end face grinding grindstone 23 and the inner peripheral end face grinding grindstone 24 are used with their positions adjusted when the grindstone is mounted, and only the outer peripheral chamfering process S35 and the inner peripheral chamfering process S45 are performed. ing.

  Other than that, a glass substrate for a magnetic recording medium was prepared and evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2.

  In Examples 1 to 3 and Comparative Examples 1 and 2, for some glass substrates, the maximum value and the minimum value of the measured values of the chamfer width of the outer peripheral chamfered portion and the inner peripheral chamfered portion immediately after the chamfering step. The difference is measured and calculated in the same manner as in the case of the glass substrate for magnetic recording media obtained after the washing / drying process. As a result, the difference between the maximum value and the minimum value of the chamfer width measurement values for the outer and inner chamfered parts immediately after the chamfering process and after the chamfering process and after the cleaning / drying process are performed. It is confirmed that there is no change.

  According to the results shown in Tables 1 and 2, in Examples 1 to 3 where the difference between the maximum value and the minimum value of the chamfer width of the outer peripheral chamfered portion is 10 μm or less, micro wrinkles are generated in the outer peripheral portion. It can be confirmed that the rate is as small as 1.5% or less.

  In contrast, in Comparative Example 1 and Comparative Example 2 in which the difference between the maximum value and the minimum value of the chamfered width of the outer peripheral chamfered portion exceeds 10 μm, the minute wrinkle occurrence rate in the outer peripheral portion is 1.5. It can be confirmed that it is very high.

  Based on the above results, it was confirmed that there is a correlation between the difference between the maximum and minimum values of the chamfered width of the outer peripheral chamfered portion and the incidence of minute wrinkles between the main surface and the outer peripheral chamfered portion. it can. And it can confirm that the fine wrinkle generation rate between a main surface and an outer peripheral chamfering part can be suppressed by making the difference of the maximum value and minimum value of the measured value of the chamfering width of an outer peripheral chamfering part 10 micrometers or less.

  Further, the same correlation can be confirmed between the difference between the maximum value and the minimum value of the measured value of the chamfer width of the inner peripheral chamfered portion and the incidence of minute wrinkles between the main surface and the inner peripheral chamfered portion. And it can confirm that the fine wrinkle generation rate between a main surface and an internal peripheral chamfering part can be suppressed by making the difference of the measured value of the chamfering width of an internal peripheral chamfering part into 10 micrometers or less. .

  And before chamfering the glass substrate for magnetic recording media, with respect to the grindstone 23 for grinding the outer peripheral end surface, the vertical position control and the first and second embodiments in which the vertical position control and the grindstone axis tilt control are performed. In Example 3, the difference between the maximum value and the minimum value of the measured value of the chamfer width of the outer peripheral chamfered portion can be confirmed to be 10 μm or less as described above.

  On the other hand, in Comparative Examples 1 and 2 in which the vertical position control and the grinding wheel axis tilt control are not performed, it is confirmed that the difference between the maximum value and the minimum value of the outer peripheral chamfered portion greatly exceeds 10 μm. it can.

  In addition, after manufacturing the glass substrate for magnetic recording media of the comparative example 1, the glass substrate for magnetic recording media of the comparative example 2 is produced continuously. For this reason, it is thought that the deviation from the appropriate position of the grindstone for outer peripheral end face grinding and the grindstone for inner peripheral end face grinding becomes large, resulting in a difference between the results of Comparative Example 1 and Comparative Example 2.

  Further, before chamfering the glass substrate for a magnetic recording medium, the position of the inner peripheral end face grinding wheel 24 in the vertical direction and the first and second embodiments in which the vertical position control and the wheel axis tilt control are performed. In Example 3 in which the control is performed, it can be confirmed that the difference between the maximum value and the minimum value of the measured value of the chamfer width of the inner peripheral chamfered portion is 10 μm or less as described above.

  On the other hand, in Comparative Examples 1 and 2 in which the vertical position control and the grinding wheel axis tilt control are not performed, the difference between the maximum value and the minimum value of the chamfer width measurement value of the inner peripheral chamfered portion is 10 μm. It can be confirmed that it greatly exceeds.

DESCRIPTION OF SYMBOLS 10 Magnetic recording medium glass substrate 121, 122 Main surface 13 Outer peripheral end surface 131, 133 Outer peripheral chamfered portion 132 Outer peripheral side surface 14 Inner peripheral end surface 141, 143 Inner peripheral chamfered portion 142 Inner peripheral side surface 23 Outer peripheral end surface grinding wheel 24 Inner peripheral End grinding wheel 26 Grinding wheel position control means

Claims (9)

A glass substrate for a magnetic recording medium having a donut shape and having a pair of main surfaces, an outer peripheral end surface, and an inner peripheral end surface, the outer peripheral end surface having an outer peripheral side surface portion and a pair of outer peripheral chamfered portions ,
When the chamfer width of at least one outer peripheral chamfered portion of the pair of outer peripheral chamfered portions is measured at a plurality of measurement points, the difference between the maximum measured value and the minimum value is 9.8 μm or less. Glass substrate for recording media.   The difference between the maximum value and the minimum value of measured values when the chamfer width of at least one outer peripheral chamfered portion of the pair of outer peripheral chamfered portions is measured at a plurality of measurement points is 8.2 μm or less. 2. The glass substrate for magnetic recording media according to 1. The inner peripheral end surface has an inner peripheral side surface portion and a pair of inner peripheral chamfered portions,
The difference between the maximum value and the minimum value of the measured value is 10 μm or less when the chamfer width of at least one of the inner peripheral chamfered portions is measured at a plurality of measurement points. 3. The glass substrate for magnetic recording media according to 1 or 2 .   The inner peripheral end surface has an inner peripheral side surface portion and a pair of inner peripheral chamfered portions,
  When the chamfer width of at least one inner peripheral chamfered portion of the pair of inner peripheral chamfered portions is measured at a plurality of measurement points, the difference between the maximum value and the minimum value is 8.9 μm or less. The glass substrate for magnetic recording media according to claim 1 or 2. The magnetic recording medium containing the glass substrate for magnetic recording media as described in any one of Claims 1 thru | or 4 . Prepare a glass substrate for trial grinding having a donut shape and having a pair of main surfaces, an outer peripheral end surface, and an inner peripheral end surface, and grind the outer peripheral end surface of the trial grinding glass substrate with an outer peripheral end surface grinding wheel A trial grinding step for forming a pair of outer peripheral chamfers;
Of the pair of outer peripheral chamfered portions of the glass substrate for trial grinding, an outer peripheral chamfered portion evaluation step for measuring a chamfer width of at least one outer peripheral chamfered portion at a plurality of measurement points;
Based on the result of the outer peripheral chamfered portion evaluation step, the outer peripheral end surface grinding wheel position correcting step for correcting the position of the outer peripheral end surface grinding wheel,
A glass substrate having a donut shape, having a pair of main surfaces, an outer peripheral end surface, and an inner peripheral end surface is prepared, and after the outer peripheral end surface grinding wheel position correcting step, the outer peripheral end surface grinding wheel An outer peripheral chamfering step of forming a pair of outer peripheral chamfered portions on the outer peripheral end surface of the glass substrate. In the trial grinding step, further grinding the inner peripheral end face of the glass substrate for trial grinding with an inner peripheral end face grinding wheel, forming a pair of inner peripheral chamfered portions,
After the trial grinding step, among the pair of inner peripheral chamfered portions of the glass substrate for trial grinding, an inner peripheral chamfered portion evaluation step of measuring the chamfer width of at least one inner peripheral chamfered portion at a plurality of measurement points;
Based on the result of the inner peripheral chamfered portion evaluation step, the inner peripheral end surface grinding wheel position correcting step of correcting the position of the inner peripheral end surface grinding wheel,
After the inner peripheral edge surface grinding grindstone position correcting step, claim having the said inner circumferential edge surface grinding grindstone, and a circumferential chamfering step among of forming a pair of inner peripheral chamfered portion on the inner peripheral surface of the glass substrate 6 The manufacturing method of the glass substrate for magnetic recording media of description. A grinding wheel for outer peripheral end face grinding for forming a pair of outer peripheral chamfered portions on the outer peripheral end face of the glass substrate having a donut shape and having a pair of main surfaces, an outer peripheral end face, and an inner peripheral end face;
A pair of outer peripheral chamfered portions are formed on the test grinding glass substrate having the same shape as the glass substrate by the outer peripheral edge grinding wheel, and the chamfer width of at least one outer peripheral chamfered portion of the pair of outer peripheral chamfered portions is set. A glass substrate manufacturing apparatus for a magnetic recording medium, comprising: whetstone position control means for controlling the position of the outer peripheral end face grinding wheel based on the distribution of the chamfer width of the outer peripheral chamfered portion when measured at a plurality of measurement points. An inner peripheral end grinding wheel for forming a pair of inner peripheral chamfered portions on the inner peripheral end surface of the glass substrate;
The grindstone position control means further forms a pair of inner peripheral chamfered portions on the test grinding glass substrate by the inner peripheral end surface grinding grindstone, and at least one inner peripheral chamfered portion of the pair of inner peripheral chamfered portions. The magnetic recording according to claim 8 , wherein the position of the inner peripheral end face grinding wheel is controlled based on a distribution of the chamfer width of the inner peripheral chamfered portion when the chamfered width of the portion is measured at a plurality of measurement points. Glass substrate manufacturing equipment for media.

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