JP4905238B2 - Polishing method of glass substrate for magnetic recording medium - Google Patents

Description

The present invention relates to a polishing how the glass substrate for a magnetic recording medium for use in the substrate of a magnetic disk recording apparatus.

  An aluminum alloy or glass disk is used as a substrate in a magnetic disk recording device used in a computer or the like, for example, a hard disk. A metal magnetic thin film is formed on this substrate, and information is recorded by magnetizing the metal magnetic thin film with a magnetic head.

  Conventionally, aluminum alloys have been mainly used as substrates for magnetic recording media. However, in recent years, magnetic disk recording devices have also been adopted in portable terminals such as notebook computers, and in order to increase the response speed of magnetic disk recording devices, magnetic recording media can be used at 10,000 [rpm] or more. Need to rotate at high speed. For this reason, a substrate for a high-strength magnetic recording medium has been required, and a glass substrate has been used to satisfy these needs. As this glass substrate, an amorphous glass substrate, a crystallized glass substrate, or a chemically strengthened glass substrate is used.

  Here, the manufacturing method of the glass substrate for magnetic recording media which concerns on a prior art (for example, patent document 1) is demonstrated. First, a method for manufacturing an amorphous glass substrate will be described.

  First, a glass material is melted (glass melting step), the molten glass is poured into a planar mold, and the molten glass is sandwiched between the molds to be press-molded to produce a disk-shaped glass substrate (press molding) Process). A glass substrate of a semi-finished product that is produced by this press molding process and subjected to the grinding / polishing process described below is referred to as a “blank material”. A circular through hole is formed in the center of the surface of the blank material using a diamond core drill to produce a donut-shaped glass substrate (perforated blank material) (coring step).

  Thereafter, the doughnut-shaped glass substrate (perforated blanks material) is ground by a double-side polishing machine holding a plate on which diamond pellets are attached (first lapping step). In this first lapping step, both surfaces of the perforated blanks are ground and the parallelism, flatness and thickness of the glass substrate are preliminarily adjusted.

  The glass substrate whose parallelism is preliminarily adjusted is ground and chamfered on the outer peripheral end surface and the inner peripheral end surface of the hole, and the outer diameter and roundness of the glass substrate, the inner diameter of the hole, and the like are finely adjusted. (End grinding process).

  The glass substrate whose outer diameter is finely adjusted has its inner peripheral end surface and outer peripheral end surface polished, and the end surface is mirrored (end surface polishing step). For example, the end surface is polished by supplying an abrasive to the glass substrate and pressing the end surface of the glass substrate with a predetermined pressure while rotating the nylon brush. By this polishing step, the damage generated by the processing on the inner peripheral end face and the outer peripheral end face is removed, and the inner peripheral end face and the outer peripheral end face are mirror-finished.

  The glass substrate whose end face is polished is ground again on both surfaces, and the parallelism, flatness, and thickness of the glass substrate are finely adjusted (second lapping step). The glass substrate with the finely adjusted parallelism or the like is polished on both surfaces to make the surface unevenness uniform (polishing step). The polished glass substrate is cleaned (cleaning step), further inspected, and a glass substrate that passes the test is used as a substrate for a magnetic recording medium.

  Moreover, when producing a crystallized glass substrate, after an above-mentioned press molding process, an amorphous glass substrate (blanks material) is pinched | interposed with the board | plates made from a ceramic, and it is made to crystallize (crystallization process). After the annealing process, the above-described coring process to polishing process are performed.

  Moreover, when producing a chemically strengthened glass substrate, the glass substrate (blanks material) obtained by melting and pressing is subjected to the treatment up to the polishing step, and then mixed with sodium nitrate, potassium nitrate, and the like. By immersing in molten salt, a compressive stress layer is formed on the surface to increase the fracture strength. Thereafter, the cleaning process is performed.

  A magnetic recording medium is produced by laminating a magnetic layer or the like on the surface of the glass substrate produced as described above.

JP 2003-63831 A

  By the way, in the end surface polishing step in the manufacturing method of the glass substrate for magnetic recording media according to the prior art, one polishing step is applied to each of the inner peripheral end surface and the outer peripheral end surface, and the inner peripheral end surface and the outer peripheral end surface are respectively polished. . By polishing the inner peripheral end face, the life of the inner peripheral holder used in the step of forming the magnetic film is extended. With respect to the outer peripheral end surface, the amount of film formation on the end surface is reduced due to limitations on the film forming apparatus when the magnetic film is formed. For this reason, if the surface of the outer peripheral end surface is rough, a glass surface on which no film is formed appears, and ion components contained in the glass are eluted. For this reason, the surface state of the outer peripheral end surface is required to have a level equivalent to that of the recording surface. However, in one polishing process for the outer peripheral end face, it has been difficult to remove the damage generated when the outer peripheral end face is processed and to finish the outer peripheral end face into a mirror surface.

  When emphasizing the removal of damage caused by end face processing, supply abrasive material with large particle size, use a hard and thick nylon brush, press the nylon brush against the outer peripheral end face of the glass substrate, and polish the outer peripheral end face To do. By polishing the outer peripheral end surface under these conditions, the processing time required for polishing can be shortened, but there is a problem that processing damage corresponding to brush scratches remains on the outer peripheral end surface after polishing.

  On the other hand, when emphasizing finishing the end surface to a mirror surface, supply an abrasive with a small particle size, use a thin and long nylon brush, and press the nylon brush against the outer peripheral end surface of the glass substrate to polish the outer peripheral end surface . In this case, brush scratches do not remain on the outer peripheral end surface after polishing, but there is a problem that the processing time required for polishing becomes long and productivity is greatly impaired.

  By using a polishing material having a large particle size and using a thick and short nylon brush, the outer peripheral end face can be polished at a speed of about 1 [μm / min], for example. Under these conditions, polishing of about 40 [μm] can be performed in about 40 minutes. On the other hand, in the case of using an abrasive having a small particle diameter and a thin and long nylon brush, it takes 90 to 120 minutes to polish a thickness of about 40 [μm]. As described above, when the end face of the glass substrate is polished under conditions suitable for mirroring, the time required for polishing becomes long, and the productivity is deteriorated.

The present invention has been made to solve the above problems, while forming a brush wound small end face, to provide a polishing how the magnetic recording medium glass substrate which can shorten the time required for the polishing of the end face With the goal.

In the present invention, the polishing step of polishing the end surface of the glass substrate using a polishing brush is divided into a first polishing step and a second polishing step, and the end surface of the glass substrate is polished under different polishing conditions. For example, the second polishing brush used in the second polishing step is made less rigid than the first polishing brush used in the first polishing step, or supplied in the second polishing step. By reducing the particle size of the first polishing material smaller than the particle size of the first abrasive supplied in the first polishing step, in the first polishing step, the damage caused by the end face processing is reduced while shortening the polishing time. In the second polishing step, it is possible to remove brush scratches on the end surface and form an end surface with few brush scratches.
Specifically, a first aspect of the present invention is a method for polishing a glass substrate for a magnetic recording medium, wherein the end surface of a disk-shaped glass substrate having an end surface around the surface and the surface is polished. A first polishing step in which the polishing blade is pressed against the end surface while rotating, and the end surface is polished; and after the first polishing step, a second lower rigidity than the first polishing brush. pressing a polishing brush to the end face while rotating, and a second polishing step of polishing the end face, viewing including the by performing the first polishing step and the second polishing step, the end face A method for polishing a glass substrate for a magnetic recording medium , wherein the surface roughness Ra is 0.5 to 1 [nm] .
According to a second aspect of the present invention, there is provided a method for polishing a glass substrate for a magnetic recording medium according to the first aspect. In the first polishing step, a first abrasive having a predetermined particle size is used. While supplying the glass substrate, the first polishing brush is pressed against the end surface to polish the end surface, and in the second polishing step, a second particle size smaller than that of the first abrasive is used. While supplying the abrasive to the glass substrate, the end surface is polished by pushing the second polishing brush against the end surface.
According to a third aspect of the present invention, there is provided a method for polishing a glass substrate for a magnetic recording medium according to the second aspect, wherein the first polishing brush and the second polishing brush include a third polishing. Material is included.
According to a fourth aspect of the present invention, there is provided a method for polishing a glass substrate for a magnetic recording medium according to any one of the first to third aspects, wherein the length of the first polishing brush is 25 [ mm] to 30 [mm], and the length of the second polishing brush is 28 [mm] to 38 [mm].

  According to this invention, the step of polishing the end surface of the glass substrate is divided into a first polishing step and a second polishing step, and by polishing the end surface under different conditions, forming an end surface with less brush scratches, It becomes possible to shorten the processing time of end face polishing.

  For example, the rigidity of the second polishing brush is made lower than the rigidity of the first polishing brush, or the particle diameter of the second abrasive supplied in the second polishing process is supplied in the first polishing process. In the first polishing step, it is possible to remove the end face damage while shortening the polishing time, and in the second polishing step, the brush scratches are removed in the first polishing step. It is possible to form an end face with few brush scratches.

  Hereinafter, a method for polishing a glass substrate for a magnetic recording medium according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a flowchart showing in sequence the steps of polishing a glass substrate for a magnetic recording medium according to an embodiment of the present invention.

  First, a glass material is melted (S01: glass melting step), the melted glass is poured into a planar mold, and the molten glass is sandwiched between the molds and press-molded to produce a disk-shaped glass substrate ( S02: Press molding process). The blank material which is a semi-finished glass substrate is produced by this press molding process. And a through-hole is formed in the center part of the blanks material using a diamond core drill, and a doughnut-shaped glass substrate (perforated blanks material) is produced (step S03: coring process).

  Next, a first lapping step is performed on the perforated blanks material. Specifically, the blanks material is ground by a double-side polishing machine holding a plate on which diamond pellets are attached (step S04: first lapping step). In this first lapping step, both sides of the blanks material are ground and the parallelism, flatness, and thickness of the glass substrate are preliminarily adjusted.

  The glass substrate whose parallelism and the like are preliminarily adjusted is ground and chamfered on the outer peripheral end surface and the inner peripheral end surface of the hole, so that the outer diameter and roundness of the glass substrate, the inner diameter of the hole, etc. are fine. It is adjusted (step S05: end face grinding step).

  Thereafter, the glass substrate with finely adjusted outer diameter dimensions and the like is polished at the inner peripheral end face of the hole (steps S06, S07: inner peripheral end face polishing step), and further, the outer peripheral end face is polished (steps S08, S09: Peripheral edge polishing step). In these polishing steps, the inner peripheral end face and the outer peripheral end face of the glass substrate are polished to remove fine scratches and the inner peripheral end face and the outer peripheral end face of the glass substrate are mirror-finished.

  Specifically, in the inner peripheral end face polishing step and the outer peripheral end face polishing step, the inner peripheral end face and the outer peripheral end face are polished using a polishing brush and an abrasive, respectively. For example, cerium oxide, silicon carbide, zirconia, silica, or the like is used as the abrasive. Moreover, for example, a nylon brush containing alumina particles is used as the polishing brush. For the polishing brush, polypropylene, polyethylene, polyester, polycarbonate, or the like is used. Then, the inner peripheral end surface and the outer peripheral end surface are each polished by supplying an abrasive to the glass substrate and pressing it against the inner peripheral end surface and the outer peripheral end surface of the glass substrate with a predetermined pressure while rotating the polishing brush.

  In this embodiment, the process of polishing the outer peripheral end face is divided into two processes. That is, the process of polishing the outer peripheral end face is divided into a first polishing process and a second polishing process, and the outer peripheral end face is polished under different polishing conditions in the first polishing process and the second polishing process.

  Here, a polishing apparatus used in the outer peripheral end surface polishing step will be described with reference to FIGS. FIG. 2 is a sectional view of the polishing apparatus according to the embodiment of the present invention as seen from the front. FIG. 3 is a plan view of the polishing apparatus according to the embodiment of the present invention as viewed from above.

  The substrate holding unit 2 holds a number of glass substrates 1 in a stacked manner. The rotation holding table 3 holds the substrate holding unit 2 rotatably. The polishing brush 4 is installed in contact with the outer peripheral end surface portion of the glass substrate 1 stacked in large numbers. Hereinafter, each part will be described in detail.

  The substrate holding unit 2 receives the glass substrate 1 inserted into the shaft 21 with the receiving member 22, and tightens the glass substrate 1 laminated with the tightening jig 24 through the collar 23 from the upper part in the axial direction. The glass substrate 1 is held without being displaced by the rotation of the substrate holding part 2 or the rotation of the polishing brush 4 due to the friction coefficient between the main surfaces of the two.

  The rotation holding table 3 is coupled to a rotation shaft 31 and can be rotated in both forward and reverse directions by a rotation drive device (not shown) that rotationally drives the rotation shaft 31. The rotation drive device can change the rotation speed, and can select an appropriate rotation speed according to the purpose of polishing.

  The polishing brush 4 is connected to a rotation shaft 41 of a rotation drive device (not shown), and is configured to be rotatable in both forward and reverse directions. The polishing brush 4 is configured to move in the direction of arrow A when the substrate is set and when the substrate is taken out, and can be retracted to the position shown in FIG. Further, the polishing brush 4 moves in the direction of arrow B shown in FIG. 3 at the time of polishing, so that the contact length of the bristles 43 to the glass substrate 1 is adjusted. It is configured to be adjustable. The polishing brush 4 is configured to reciprocate along the rotation axis direction (the direction of arrow C) of the polishing brush 4 by a cam mechanism (not shown). The range of the reciprocating motion of the polishing brush 4 is set such that the range from the lowermost part to the uppermost part of the set glass substrate 1 is within the range of the brush hairs of the polishing brush 4.

  The polishing brush 4 is obtained by, for example, planting brush hairs in a strip shape and a spiral shape in a cylindrical body portion. Further, as the polishing brush 4, a brush body in which brush hairs are scattered in a cylindrical body portion may be used. The above-described nylon brush or the like is used for the polishing brush 4.

  The polishing liquid supply unit 5 includes a polishing liquid supply nozzle 51 and a polishing liquid supply pipe 52, and a large number of glass substrates 1 are laminated to supply the polishing liquid to the laminated glass substrate 10. The polishing liquid supply unit 6 includes a polishing liquid supply port 61 and a polishing liquid supply pipe 62 and supplies the polishing liquid to the laminated glass substrate 10. As the abrasive used in the polishing liquid, the above-described cerium oxide or the like is used.

  The polishing apparatus according to this embodiment includes a polishing liquid recovery unit that recovers the polishing liquid supplied from the polishing liquid supply units 5 and 6 from a recovery port provided on the bottom surface of the polishing chamber 7, and cleans the recovered polishing liquid. In addition, a circulation mechanism that circulates again to the polishing liquid supply units 5 and 6 is provided.

  The polishing chamber 7 has a bottom surface, a side surface, and an upper surface. The upper surface of the polishing chamber 7 does not hinder the rotation of the polishing brush or the like, the reciprocating motion of the rotating shaft 41 in the C direction, and the movement in the A direction. Thus, an opening 71 is provided.

  The water supply unit 8 supplies water 80 from two directions to the laminated glass substrate 10 when viewed from the lamination direction of the laminated glass substrate 10.

  Then, with the glass substrate 1 and the polishing brush 4 rotated in opposite directions, polishing is performed by supplying a polishing liquid to the outer peripheral end surface of the glass substrate 1. Next, the retraction of the polishing brush 4 is started, and when the bristle 43 of the polishing brush 4 is separated from the outer peripheral end surface of the glass substrate 1, the supply of the polishing liquid is stopped, and the water supply unit 8 moves to the outer peripheral end surface of the glass substrate 1. Supply water towards.

  The process of polishing the outer peripheral end face is divided into a first polishing process (step S08) and a second polishing process (step S09), and the outer peripheral end face is polished under different polishing conditions in each polishing process. For example, in the first polishing step and the second polishing step, the outer peripheral end surface of the glass substrate is polished by using different polishing brushes or using abrasives having different particle sizes.

  For example, when changing the conditions of the polishing brush, the second polishing brush (nylon brush) used in the second polishing step (step S09) is the first polishing brush (nylon brush or nylon brush) used in the first polishing step (step S08). Use a brush with lower rigidity than abrasive nylon brushes. For example, a hard and thick brush is used as the first polishing brush, and a softer and thinner brush than the first polishing brush is used as the second polishing brush.

  For example, as the first polishing brush, it is preferable to use a polishing brush having a brush length of 25 [mm] to 30 [mm] and a brush wire diameter of 0.3 [mm]. Further, it is preferable to use a polishing brush having a brush length of 28 [mm] to 38 [mm] and a brush wire diameter of 0.1 to 0.3 [mm] as the second polishing brush.

  Further, when changing the particle size of the abrasive, in the second polishing step (step S09), an abrasive having a smaller particle size is supplied to the glass substrate than in the first polishing step (step S08). For example, in the first polishing step, cerium oxide having a particle size of 2 [μm] is used as an abrasive, and in the second polishing step, cerium oxide having a particle size of 0.8 [μm] or 0.1 [μm] or less. A silica having a particle size of 5 mm is used as an abrasive.

  A 1st grinding | polishing process is a grinding | polishing process suitable for removing the damage which generate | occur | produced by the process of an outer peripheral end surface, and a 2nd grinding | polishing process is a grinding | polishing process suitable for mirror-finishing an outer peripheral end surface. By performing the first polishing step, it is possible to remove the damage generated when the outer peripheral end surface of the glass substrate is processed. Furthermore, by performing the second polishing step, the outer peripheral end surface can be mirrored. .

  That is, in the first polishing step (step S08), damage generated when the outer peripheral end face is processed can be removed by using a hard and thick nylon brush or supplying an abrasive having a large particle diameter. . Further, by polishing under the conditions of the first polishing step, the time required for polishing can be shortened.

  In the first polishing step, a hard and thick nylon brush may be used, and an abrasive having a large particle size may be supplied to polish the outer terminal surface.

  However, by performing the first polishing process, damage corresponding to the scratches on the polishing brush remains on the outer peripheral end surface of the polished glass substrate. In order to remove the damage caused by the polishing brush, a second polishing step is performed.

  In the second polishing step (step S09), a soft and thin nylon brush is used or an abrasive having a small particle diameter is supplied to remove damage corresponding to the scratches on the polishing brush generated in the first polishing step. The outer peripheral end face can be mirrored.

  In the second polishing step, the outer end surface may be polished by using a soft and thin nylon brush and further supplying an abrasive having a small particle size.

  As described above, the damage generated when the outer peripheral end surface is processed in the first polishing step is removed, and the outer peripheral end surface is mirror-finished in the second polishing step, thereby forming the outer peripheral end surface with less brush damage. It is possible to reduce the time required for the process. As described above, since the end surface with few brush scratches can be formed, it is possible to suppress the occurrence of defects due to the scratches on the outer peripheral end surface, which are generated in the process of manufacturing the magnetic recording medium. In addition, since the time required for polishing can be shortened by performing the first polishing step, the productivity of the glass substrate for a magnetic recording medium can be improved.

  Moreover, surface roughness Ra of an outer terminal surface can be 0.5-1 [nm] by giving a 1st grinding | polishing process and a 2nd grinding | polishing process.

  The glass substrate whose inner peripheral end face and outer peripheral end face are polished is ground again on both surfaces, and the parallelism, flatness, and thickness of the glass substrate are finely adjusted (step S10: second lapping step). The glass substrate whose degree of parallelism and the like is finely adjusted has both surfaces polished to make the surface unevenness uniform (step S11: polishing step). The polished glass substrate is cleaned (step S12: cleaning process), further inspected, and a glass substrate that has passed the inspection is used as a substrate for a magnetic recording medium.

  A magnetic recording medium is produced by forming a magnetic layer on the glass substrate for a magnetic recording medium produced by the above process.

  In addition, the magnitude | size of the glass substrate manufactured by the manufacturing method which concerns on this embodiment is not specifically limited. For example, the manufacturing method according to this embodiment may be applied to glass substrates of 0.85 inch, 1 inch, 2.5 inch, and 3.5 inch.

[Example]
Next, specific examples of the above embodiment will be described.

Example 1
Below, the dimension of the glass substrate (perforated blanks material) after the 1st lapping process used for Example 1 and the grinding process of an outer periphery and an inner periphery is shown.
Size: Diameter (2R) = 65.1 [mm]
Glass substrate thickness = 0.9 [mm]
Glass substrate hole diameter = 20 [mm]
In Example 1, a borosilicate glass amorphous glass substrate was used.

(Step S08: First polishing step of outer peripheral end face)
By performing the 1st grinding | polishing process of an outer peripheral end surface, the outer peripheral end surface of the glass substrate was grind | polished. The polishing conditions in the first polishing step of the outer peripheral end surface are shown below.
First polishing brush: nylon brush with a wire diameter of 0.3 mm, brush length is 30 [mm]
First abrasive: Mireiku E10, made by Mitsui Kinzoku
Polished amount: 30 [μm]

(Step S09: Second polishing step of outer peripheral end face)
The outer peripheral end surface of the glass substrate was polished by applying the second polishing step of the outer peripheral end surface to the glass substrate on which the first polishing step of the outer peripheral end surface was performed. The polishing conditions in the second polishing step of the outer peripheral end surface are shown below. In the second polishing step, the second polishing brush was made thinner and longer than the first polishing brush, and the processing conditions in the first polishing step and the particle size of the abrasive were the same.
Second polishing brush: nylon brush with a wire diameter of 0.1 mm, brush length is 30 [mm]
Second abrasive: Mitsui Metal, Milleak E10
Polished amount: 10 [μm]

(Evaluation)
The outer peripheral end face of the glass substrate was polished under the above conditions, and the time required for the polishing and the surface roughness Ra of the outer peripheral end face after polishing were measured.
Time required for polishing: First polishing: 30 minutes, Second polishing: 15 minutes Surface roughness Ra: 0.9 [nm]

(Example 2)
Next, Example 2 will be described. The dimensions and materials of the glass substrate (perforated blanks material) after completion of the first lapping process and the outer and inner peripheral grinding processes used in Example 2 are the same as the dimensions and materials of the perforated blanks material according to Example 1. Since it is the same, description is abbreviate | omitted.

(Step S08: First polishing step of outer peripheral end face)
By performing the 1st grinding | polishing process of an outer peripheral end surface, the outer peripheral end surface of the glass substrate was grind | polished. The polishing conditions in the first polishing step of the outer peripheral end surface are shown below.
First polishing brush: nylon brush with a wire diameter of 0.3 mm, brush length is 25 [mm]
First abrasive: Mireiku E10, made by Mitsui Kinzoku
Polished amount: 30 [μm]

(Step S09: Second polishing step of outer peripheral end face)
The outer peripheral end surface of the glass substrate was polished by applying the second polishing step of the outer peripheral end surface to the glass substrate on which the first polishing step of the outer peripheral end surface was performed. The polishing conditions in the second polishing step of the outer peripheral end surface are shown below. The rigidity of the polishing brush and the particle size of the abrasive were made smaller than the rigidity of the polishing brush and the particle size of the abrasive in the first polishing step.
Second polishing brush: nylon brush with a wire diameter of 0.3 mm, brush length is 28 [mm]
Second abrasive: Showa Denko, Rocks V-210
Polished amount: 10 [μm]

(Evaluation)
The outer peripheral end face of the glass substrate was polished under the above conditions, and the time required for the polishing and the surface roughness Ra of the outer peripheral end face after polishing were measured.
Time required for polishing: 1st polishing: 25 minutes, 2nd polishing: 12 minutes Surface roughness Ra: 0.95 [nm]

Example 3
Next, Example 3 will be described. The dimensions and materials of the glass substrate (perforated blanks material) after completion of the first lapping process and the outer and inner peripheral grinding processes used in Example 3 are the same as the dimensions and materials of the blanks material according to Example 1. Therefore, the description is omitted.

(Step S08: First polishing step of outer peripheral end face)
By performing the 1st grinding | polishing process of an outer peripheral end surface, the outer peripheral end surface of the glass substrate was grind | polished. The polishing conditions in the first polishing step of the outer peripheral end surface are shown below.
First polishing brush: nylon brush with a wire diameter of 0.3 mm, brush length is 30 [mm]
First abrasive: Mireiku E10, made by Mitsui Kinzoku
Polished amount: 30 [μm]

(Step S09: Second polishing step of outer peripheral end face)
The outer peripheral end surface of the glass substrate was polished by applying the second polishing step of the outer peripheral end surface to the glass substrate on which the first polishing step of the outer peripheral end surface was performed. The polishing conditions in the second polishing step of the outer peripheral end surface are shown below. In the second polishing step, a brush that is thinner and longer than the first polishing brush was used. Furthermore, the particle size of the second abrasive was made smaller than the particle size of the first abrasive.
Second polishing brush: nylon brush with a wire diameter of 0.1 mm, brush length is 35 [mm]
Second abrasive: Showa Denko, Rocks V-210
Polished amount: 10 [μm]

(Evaluation)
The outer peripheral end face of the glass substrate was polished under the above conditions, and the time required for the polishing and the surface roughness Ra of the outer peripheral end face after polishing were measured.
Time required for polishing: First polishing: 30 minutes, Second polishing: 20 minutes Surface roughness Ra: 0.87 [nm]

Example 4
Next, Example 4 will be described. The dimensions and materials of the glass substrate (perforated blanks material) after completion of the first lapping process and the outer and inner circumference grinding processes used in Example 4 are the same as the dimensions and materials of the blanks material according to Example 1. Therefore, the description is omitted.

(Step S08: First polishing step of outer peripheral end face)
By performing the 1st grinding | polishing process of an outer peripheral end surface, the outer peripheral end surface of the glass substrate was grind | polished. The polishing conditions in the first polishing step of the outer peripheral end surface are shown below.
First polishing brush: nylon brush with a wire diameter of 0.3 mm, brush length is 30 [mm]
First abrasive: Mireiku E10, made by Mitsui Kinzoku
Polished amount: 30 [μm]

(Step S09: Second polishing step of outer peripheral end face)
The outer peripheral end surface of the glass substrate was polished by applying the second polishing step of the outer peripheral end surface to the glass substrate on which the first polishing step of the outer peripheral end surface was performed. The polishing conditions in the second polishing step of the outer peripheral end surface are shown below. In the second polishing step, a brush that is thinner and longer than the first polishing brush was used. Furthermore, the particle size of the second abrasive was made smaller than the particle size of the first abrasive.
Second polishing brush: nylon brush with a wire diameter of 0.1 mm, brush length is 38 [mm]
Second abrasive: Fujimi Incorporated Compol 80
Polished amount: 10 [μm]

(Evaluation)
The outer peripheral end face of the glass substrate was polished under the above conditions, and the time required for the polishing and the surface roughness Ra of the outer peripheral end face after polishing were measured.
Time required for polishing: first polishing: 30 minutes, second polishing: 30 minutes Surface roughness Ra: 0.53 [nm]

(Comparative Example 1)
Next, a comparative example for Example 1 to Example 4 will be described. Below, the dimension of the glass substrate (perforated blanks material) after the 1st lapping process used for the comparative example and the grinding process of the outer periphery and the inner periphery is shown.
Size: Diameter (2R) = 65 [mm]
Glass substrate thickness = 0.9 [mm]
Glass substrate hole diameter = 20 [mm]
In addition, in the comparative example, the amorphous glass substrate of the borosilicate glass was used similarly to the Example.

(Comparative Example 1)
Polishing brush: nylon brush with a wire diameter of 0.3 mm, brush length 30 [mm]
Abrasives: Mitsui Metal Mille E-20
Polishing amount: 40 [μm]

(Evaluation)
Time required for polishing: 35 minutes Surface roughness Ra: 1.53 [nm]

(Comparative Example 2)
Polishing brush: nylon brush with a wire diameter of 0.1 mm, brush length 35 [mm]
Abrasives: Mitsui Metal Mille E-20
Polishing amount: 40 [μm]

(Evaluation)
Time required for polishing: 90 minutes Surface roughness Ra: 0.95 [nm]

(Comparative Example 3)
Polishing brush: nylon brush with a wire diameter of 0.3 mm, brush length 25 [mm]
Abrasive: Showa Denko Rocks V-210
Polishing amount: 40 [μm]

(Evaluation)
Time required for polishing: 45 minutes Surface roughness Ra: 1.35 [nm]

(Comparative Example 4)
Polishing brush: nylon brush with a wire diameter of 0.1 mm, brush length 38 [mm]
Abrasive: Showa Denko Rocks V-210
Polishing amount: 40 [μm]

(Evaluation)
Time required for polishing: 120 minutes Surface roughness Ra: 0.65 [nm]

  As described above, the results of Example 1 to Example 4 and Comparative Example 1 to Comparative Example 4 are summarized. In Example 1 to Example 4, the surface of the outer peripheral end face is larger than Comparative Example 1 to Comparative Example 4. The roughness Ra can be reduced, and the time required for polishing can be shortened. As described above, since the end face with few brush scratches can be formed, it is possible to suppress the occurrence of defects due to the scratch on the end face, which occurs in the process of manufacturing the magnetic recording medium. Moreover, since the time required for polishing can be shortened, the productivity of the glass substrate for magnetic recording media can be improved.

  In addition, although the borosilicate glass was used as a kind of glass in the said Example and comparative example, even if it uses another glass substrate, the same result as the said Example and comparative example is obtained. For example, even if an aluminosilicate glass is used, the same effects as those of the above embodiment can be obtained.

It is a flowchart which shows in order the manufacturing process of the glass substrate for magnetic recording media which concerns on embodiment of this invention. It is sectional drawing which looked at the polish device concerning the embodiment of this invention from the front. It is the top view which looked at the polish device concerning the embodiment of this invention from the upper surface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Substrate holding part 3 Rotation holding stand 4 Polishing brush 5, 6 Polishing liquid supply part 7 Polishing chamber 8 Water supply part 10 Laminated glass substrate 51 Polishing liquid supply nozzle 52, 62 Polishing liquid supply pipe 61 Polishing liquid supply port

Claims (4)

A method of polishing a glass substrate for a magnetic recording medium, wherein the end surface of a disk-shaped glass substrate having an end surface around the surface and the surface is polished,
A first polishing step of pressing the end face while rotating the first polishing brush to polish the end face;
After the first polishing step, a second polishing step of pressing the end surface while rotating a second polishing brush having a rigidity lower than that of the first polishing brush to polish the end surface;
Only including,
Polishing the glass substrate for a magnetic recording medium, wherein the first polishing step and the second polishing step are performed, so that the end surface has a surface roughness Ra of 0.5 to 1 [nm]. Method. In the first polishing step, while supplying a first abrasive having a predetermined particle size to the glass substrate, the end surface is polished by pressing the first polishing brush against the end surface,
In the second polishing step, the second polishing brush is pushed up against the end surface while supplying the second abrasive having a particle size smaller than that of the first abrasive to the glass substrate, and the end surface is The method for polishing a glass substrate for a magnetic recording medium according to claim 1, wherein polishing is performed.   The method for polishing a glass substrate for a magnetic recording medium according to claim 2, wherein the first polishing brush and the second polishing brush contain a third abrasive.   The length of the first polishing brush is 25 [mm] to 30 [mm], and the length of the second polishing brush is 28 [mm] to 38 [mm]. The method for polishing a glass substrate for a magnetic recording medium according to claim 3.

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