JP5991728B2 - Manufacturing method of glass substrate for magnetic disk and manufacturing method of magnetic disk - Google Patents

Description

  The present invention relates to a magnetic disk mounted on a magnetic recording device such as a hard disk drive (HDD), and more specifically, a method of manufacturing a glass substrate for a magnetic disk having a step of processing an end surface of the glass substrate for a magnetic disk, and a magnetic disk It relates to a manufacturing method.

  Today, information recording technology, particularly magnetic recording technology, is required to undergo dramatic technological innovation with the rapid development of IT industry. In a magnetic disk that is a recording medium mounted on an information recording apparatus such as a hard disk drive (HDD), the demand for higher capacity is increasing.

  By the way, as an information recording medium substrate such as a magnetic disk, conventionally, an aluminum-based alloy substrate has been widely used. Recently, however, a ratio of a glass substrate as a magnetic disk substrate suitable for high recording density has been increased. It is getting higher gradually. Since the glass substrate has higher rigidity than the aluminum-based alloy substrate, it is suitable for high-speed rotation of the magnetic disk device, and a smooth surface can be obtained, so that it is easy to reduce the flying height of the magnetic head, and recording This is preferable because the S / N ratio of the signal can be improved.

In addition, in order to increase the recording density of the magnetic disk, high processing accuracy is required for the glass substrate, which is the same not only for the main surface of the glass substrate but also for the end face shape.
A glass substrate for a magnetic disk is usually produced by sequentially performing steps such as grinding, polishing, and chemical strengthening on a glass substrate formed into a disk shape.

  As a conventional method for grinding the end surface of a glass substrate, grinding is performed by rotating a grinding wheel in contact with the outer peripheral side end surface and the inner peripheral side end surface of the glass substrate while supplying a grinding liquid to the end surface portion of the glass substrate formed into a disk shape. Processing was performed, and predetermined chamfering was performed on the outer peripheral side end surface and the inner peripheral side end surface of the glass substrate. For example, as shown in FIG. 4, a grinding wheel 40 used for grinding a conventional glass substrate end surface has a groove shape, and the groove includes, for example, a side wall surface of an outer peripheral side end surface of the glass substrate 10 and the glass. It is formed so that both the main surface of the substrate and the chamfered surface between the side wall surfaces can be simultaneously ground. Specifically, the side wall portion (side wall surface grinding portion) 40a and both sides thereof are formed. The groove shape which consists of the existing chamfering part (chamfering surface grinding process part) 40b and 40b is provided. And while making the surface direction of the glass substrate 10 and the groove direction of the groove shape formed in the grinding wheel 40 coincide with each other, the glass grinding wheel 40 is brought into contact with, for example, the outer peripheral side end surface 12 of the glass substrate 10, Grinding was performed by rotating both the substrate 10 and the grinding wheel 40.

  Patent Document 1 discloses a method for grinding a glass substrate end face using the conventional general grindstone as described above.

Japanese Patent No. 3061605

With the progress of the information society, demands for higher recording density and lower prices of magnetic disks are increasing day by day. Also in the end face shape of a magnetic disk, further smoothing, improvement in processing accuracy, reduction in processing time, and improvement in the life of auxiliary materials have been demanded.
Further, the hard disk drive described above is not only mounted on a conventional personal computer or the like, but in recent years, its capacity has been increased as a recording medium for car navigation, home video recorders and video cameras. Therefore, since it is necessary to dramatically increase the recording density of the magnetic disk, an inexpensive and high-performance magnetic recording medium has been demanded.

There is a need for such a low-cost magnetic recording medium that can achieve high recording density. To that end, for example, the accuracy of the inner diameter dimension to obtain the positioning accuracy of the read / write head, the occurrence of corrosion on the main surface of the medium, etc. It is required to achieve high quality of the outer diameter end face based on the request to reduce the contamination factor.
However, in the current end face machining process using the grinding wheel as shown in FIG. 4 described above, since the damage to the substrate that occurs during grinding is large and the cracks are deep, there is a lot of polishing allowance in the next polishing step. Therefore, there are problems with the process that the dimensional accuracy is difficult to stabilize and the residual cracks are likely to remain on the end face. That is, the conventional chamfering of the end surface of the glass substrate for magnetic disks is performed by a grinding method similar to intermittent creep grinding in order to process predetermined dimensions with high efficiency. Therefore, conventionally, by using a grindstone having a coarse particle size (large particle size), a large cutting amount (grindability) for ensuring a necessary removal speed is obtained. However, such a large depth of cut becomes a grinding process in a brittle fracture mode, and it is difficult to obtain a good ground surface quality (mirror surface quality) by a grinding process mainly based on a plastic mode. Conventionally, the end surface is ground and then the end surface is subjected to a mirror polishing process to obtain mirror surface quality. However, if the depth of cut is large, the grinding surface processing distortion becomes deeper and mirror polishing is performed. However, distortion and streaks may remain and high quality may not be obtained. In order to obtain good ground surface quality, for example, it is conceivable to use a grindstone having a fine particle size (small particle size or fine particle size).

  As described above, in the conventional grinding process, grinding was performed by rotating the outer peripheral side of the cylindrical grinding wheel as shown in FIG. 4 to the outer peripheral side end face of the glass substrate. Since the contact state with the substrate is a line contact in the substrate thickness direction between the outer diameter arc of the grindstone and the outer diameter arc of the substrate, for example, grinding was performed using a fine abrasive wheel that is advantageous for processing surface quality. In this case, the load per abrasive grain becomes large, and as described above, the current cutting amount giving priority to the processing efficiency cannot follow the removal efficiency required for the abrasive grains, causing crushing or clogging for a short time. With this, grinding becomes impossible. In addition, since the abrasive grains that are cutting edges always receive grinding resistance from the same vector direction intermittently, the abrasive grains are severely damaged per unit time. Further, when the end shape to be manufactured is changed, it is necessary to manufacture a new grindstone according to the shape.

  Therefore, there is a need for a grinding process that can reduce damage compared to the conventional end face grinding process. From the standpoint of further increasing information recording density, the quality requirements for glass substrates for magnetic disks, such as the dimensional accuracy of the end face of the glass substrate and the finished surface quality of the chamfering process, are increasing more than before. When a large number of glass substrates for magnetic disks are manufactured using a grinding method or a polishing method, there is a problem that it is becoming increasingly difficult to stably meet the increasing quality requirements of glass substrates, and rework is possible. Although the substrate can be reworked, there is a problem that the cost becomes high.

  Therefore, the present invention, in particular from the viewpoint of meeting the demand for higher recording density and lower price of magnetic disks, which is urgently required to ensure reliability for higher recording density, It is a first object of the present invention to provide a method for manufacturing a glass substrate for a magnetic disk that enables stable grinding that can finish the end surface on the inner peripheral side efficiently and with high quality at low cost. It is a second object of the present invention to provide a method of manufacturing a magnetic disk using a magnetic disk glass substrate according to such a manufacturing method.

As described above, when chamfering of the end surfaces of a large number of glass substrates for magnetic disks is performed using a conventional grinding method, the side wall surface orthogonal to the main surface of the glass substrate, for example, the outer peripheral side end surface of the glass substrate In addition, it is possible to stably meet the increasing quality requirements of glass substrates such as the dimensional accuracy of the two chamfered surfaces formed between the side wall surface and the main surface of the front and back surfaces and the finished surface quality of the chamfering process. It has become increasingly difficult.
In addition, the end face of the glass substrate for magnetic disks is a chamfered shape with a chamfer surface, and the tolerance accuracy requirements including the inner and outer diameter tolerances are also included in each shape. In order to ensure the dimensional shape accuracy by processing, it is necessary to maintain the sharpness while suppressing wear of the grindstone (while maintaining the shape) and to ensure stable grindability.

Therefore, as a result of intensive studies to solve the above-mentioned problems, the present inventors have completed the present invention having the following configuration.
That is, the present invention has the following configuration in order to solve the above problems.
(Configuration 1)
A glass substrate for a magnetic disk having a step of processing a shape of an end surface of the glass substrate by supplying a grinding liquid to the end surface portion of the disk-shaped glass substrate and grinding by bringing a grindstone into contact with the end surface of the glass substrate. In the manufacturing method, the grindstone is a disc-shaped rotary grindstone that is formed in a disc shape having an end surface portion and is configured to be rotatable about a center thereof as a rotation axis, and the moving direction of the grindstone and the The movement direction of the glass substrate intersects at these contact points, the end surface portion of the grindstone is brought into contact with the end surface of the glass substrate, and the glass substrate and the grindstone are moved relatively. A method for producing a glass substrate for a magnetic disk, comprising: shaping an end surface of a glass substrate.

(Configuration 2)
2. The method of manufacturing a glass substrate for a magnetic disk according to Configuration 1, wherein the shape processing is performed by rotating both the glass substrate and the grindstone.
(Configuration 3)
3. A method of manufacturing a glass substrate for a magnetic disk according to Configuration 1 or 2, wherein a grindstone that shapes the side wall surface of the end surface of the glass substrate and a grindstone that shapes the chamfered surface of the end surface are used at the same time. .
(Configuration 4)
4. The method for manufacturing a glass substrate for a magnetic disk according to any one of configurations 1 to 3, wherein the end surface of the glass substrate is shaped and then mirror-polished using a polishing brush.

(Configuration 5)
5. The method for manufacturing a glass substrate for a magnetic disk according to Configuration 4, wherein the processing direction is varied by approximately 90 degrees between the shape processing using the grindstone and the subsequent mirror polishing using a polishing brush.
(Configuration 6)
6. The method of manufacturing a glass substrate for a magnetic disk according to any one of configurations 1 to 5, wherein an end surface of the glass substrate to be processed is an outer peripheral side end surface.
(Configuration 7)
7. The glass substrate for a magnetic disk according to any one of configurations 1 to 6, wherein at least a chamfered surface of an end surface on the outer peripheral side and / or inner peripheral side after the shape processing of the glass substrate is concave. Manufacturing method.

(Configuration 8)
8. The manufacturing method of a glass substrate for a magnetic disk according to any one of the constitutions 1 to 7, wherein the outer peripheral side and / or the inner peripheral side end surface of the glass substrate are processed to have a concave shape. Method.
(Configuration 9)
A magnetic disk manufacturing method comprising: forming at least a magnetic layer on a main surface of a magnetic disk glass substrate manufactured by the magnetic disk glass substrate manufacturing method according to any one of Structures 1 to 8.

(Configuration 10)
A glass substrate for a magnetic disk obtained by processing the shape of the end surface of the glass substrate by supplying a grinding liquid to the end surface portion of the disk-shaped glass substrate and grinding by bringing a grindstone into contact with the end surface of the glass substrate. The grindstone is a disc-shaped rotary grindstone that is formed in a disc shape having an end surface portion and is rotatable about its center as a rotation axis, and the grindstone The moving direction of the glass substrate and the moving direction of the glass substrate intersect at these contact points so that the end surface portion of the grindstone contacts the end surface of the glass substrate and the glass substrate and the grindstone move relatively. By doing so, shape processing of the end surface of the glass substrate is performed, and at least the chamfered surface of the end surface on the outer peripheral side and / or inner peripheral side after the shape processing of the glass substrate is concave. Glass substrate, characterized that it is Jo.

In the present invention of the above configuration 1, the grindstone used for processing is a disc-shaped rotary grindstone that is formed in a disc shape having an end surface portion and is rotatable about its center as a rotation axis. The moving surface and the moving direction of the glass substrate intersect (or are orthogonal) so that the end surface portion of the grindstone is in contact with the outer peripheral side end surface of the glass substrate and the glass substrate and the grindstone are relatively moved. By doing so, the shape processing of the end surface of the glass substrate is performed. Therefore, in this case, the contact state between the grindstone and the glass substrate is such that the outer peripheral end surface of the grindstone and the end surface of the substrate intersect and are in a point contact state, and the contact area between the grindstone and the substrate is reduced. Therefore, grinding efficiency can be improved. In addition, since the moving direction of the grindstone and the glass substrate intersects at these contact points, grinding traces hardly remain on the ground surface. That is, in the prior art, the movement direction of the grindstone and the glass substrate does not intersect with each other, so the circumferential streak tends to remain, and the streak can be completely removed in the subsequent polishing process (for example, simultaneous polishing of the end face and the chamfered surface with a brush). There was no case. This may have a small polishing force by the brush, but also has an influence that the moving direction of the brush and the moving direction of the glass substrate are the same in the polishing portion (where the brush and the substrate are in contact). On the other hand, in the present invention, not only is the streak difficult to enter in the first place, but even if a streak is entered, the direction of the streak can be shifted from the circumferential direction by controlling the rotation speed of the grindstone. By doing so, even if mirror polishing is subsequently performed by the brush polishing process, the movement direction of the brush can be made orthogonal to the streak direction, so it can be easily erased with a small amount of streak Become. Moreover, since a disk-shaped grindstone is used in the present invention, the processed surface is concave and the end of the processed surface tends to be sharp. On the contrary, in general mirror polishing using a polishing brush, the boundary between the chamfered surface and the end surface, and the boundary portion between the main surface and the chamfered surface are easily polished, so that the chamfered surface after the polishing process has a convex shape, At the boundary, the locality radius tends to increase. This tendency becomes more prominent as the allowance for polishing increases. Therefore, conventionally, there is a problem that the dimensional shape accuracy deteriorates when the amount of polishing processing is increased in order to remove the streak. In the present invention, not only can the margin for brush polishing be reduced, but also the effect of canceling the irregularities can be obtained by applying a convex shape to the concave surface, so that good dimensional accuracy is easily achieved. can do.
Therefore, even when grinding is performed using a fine abrasive wheel, stable grindability can be ensured, and good grinding surface quality (mirror surface quality) can be stably obtained. In addition, even when fine abrasive grains are used, the sharpness of the grindstone is maintained and the grindability is stably ensured, thereby ensuring good dimensional shape accuracy by chamfering the end face of the glass substrate.

  According to the method for manufacturing a glass substrate for a magnetic disk according to the present invention, it is possible to ensure the dimensional shape accuracy of the outer peripheral side end surface of the glass substrate for a magnetic disk from the viewpoint of meeting the demand for higher recording density and lower price of the magnetic disk. Stable shape grinding that enables efficient and high-quality finishing at low cost is possible, and it is possible to stably provide a large amount of glass substrates for magnetic disks with high-quality substrate end faces at low cost. It becomes possible.

  Furthermore, according to the magnetic disk manufacturing method using the magnetic disk glass substrate manufactured by this method of manufacturing a magnetic disk glass substrate, the end surface of the substrate can be finished with high quality, and the end surface of the substrate can be protected against corrosion. It is possible to provide a magnetic disk capable of preventing the occurrence of a failure due to the surface state and realizing further higher recording density.

1 shows a glass substrate for a magnetic disk according to the present invention, in which (A) is a side view showing a part of the glass substrate and (B) is a plan view thereof. It is a schematic perspective view which shows the structure of one embodiment in this invention. It is a schematic plan view which shows the structure of one embodiment in this invention. It is a block diagram for demonstrating the conventional grinding method of the substrate end surface.

Hereinafter, embodiments for carrying out the present invention will be described in detail.
FIG. 1 is an overall view of a glass substrate 1 for a magnetic disk to which the present invention is applied, in which (A) is a side view showing a part of the glass substrate in cross section, and (B) is a plan view thereof. The The glass substrate 1 is formed in a disc (disc) shape as a whole with a circular hole at the center, and the front and back main surfaces 11 and 11 and the end face on the outer peripheral side formed between the main surfaces 11 and 11. 12 and an end face 13 on the inner peripheral side.
The end surface 12 on the outer peripheral side of the glass substrate 1 has a side wall surface 12a orthogonal to the main surface 11 and two chamfered surfaces formed between the side wall surface 12a and the front and back main surfaces 11 and 11, respectively. (Chamfered surfaces) 12b and 12b are formed in a shape. The end surface 13 on the inner peripheral side of the glass substrate 1 is also formed between the side wall surface 13a orthogonal to the main surface 11 and between the side wall surface 13a and the main surfaces 11 and 11 on the front and back sides, respectively. Two chamfered surfaces (chamfered surfaces) 13b and 13b are formed.

In the case of a magnetic disk, for example, a 2.5 inch disk, the glass substrate 1 is finished to have an outer diameter of 65 mm and an inner diameter of 20 mm. Here, the inner diameter is the inner diameter of a circular hole in the center of the glass substrate 1.
Further, the main surface 11, the outer peripheral side end face 12, and the inner peripheral side end face 13 of the magnetic disk glass substrate 1 are polished (mirror polished) so as to have a predetermined surface roughness. Both the outer peripheral side end surface 12 and the inner peripheral side end surface 13 are finished to the end face shape as described above, and the surface roughness is finished to a mirror surface state with, for example, Rmax of 1 μm or less and Ra of 0.1 μm or less. Is usually required.

The glass substrate 1 for a magnetic disk is usually a glass substrate (glass disk) 10 formed into a predetermined disk shape by, for example, direct pressing, etc., and sequentially performs processes such as end face grinding, polishing, main surface mirror polishing, and chemical strengthening. Manufactured.
First, the grinding process of the end surface of the glass substrate (glass disk) 10 will be described.

  The method for manufacturing a glass substrate for a magnetic disk according to the present invention is characterized in that a grinding liquid is supplied to an end surface portion of a disk-shaped glass substrate and a grindstone is brought into contact with the end surface of the glass substrate to perform grinding. A method of manufacturing a glass substrate for a magnetic disk having a step of shaping an end face, wherein the grindstone is formed in a disc shape having an end face portion and is configured to be rotatable about its center as a rotation axis. It is a disk-shaped rotary grindstone, and the movement direction of the grindstone and the movement direction of the glass substrate intersect at these contact points so that the end surface portion of the grindstone contacts the end surface of the glass substrate and the glass substrate The end surface of the glass substrate is shaped by moving the whetstone and the grindstone relatively.

FIG. 2 is a schematic perspective view showing the configuration of an embodiment of the present invention, and FIG. 3 is a schematic plan view thereof.
In the present embodiment, the glass substrate 10 is disposed so that the substrate surface is horizontal, and is set on a driving unit 26 that rotationally drives the glass substrate 10.
The upper outer diameter chamfering grindstone 20, the lower outer diameter chamfering grindstone 22, and the outer diameter side wall chamfering grindstone 24 are all formed in a disk shape having an end surface portion and the center thereof. It is a disk-shaped rotating grindstone configured to be rotatable about a rotating shaft. The upper outer diameter chamfering grindstone 20 is rotated in a predetermined direction by a drive unit 21, the lower outer diameter chamfering grindstone 22 is rotated by a drive unit 23, and the outer diameter side wall chamfering grindstone 24 is rotated in a predetermined direction by a drive unit 25. Driven.

The outer diameter side surface chamfering grindstone 24 can be processed on the outer peripheral end surface of the glass substrate 10 so that the side wall surfaces perpendicular to the upper and lower main surfaces can be processed. The lower outer diameter chamfering grindstone 22 is formed between the side wall surface and the lower main surface so that the chamfered surface formed between the side wall surface and the upper main surface can be processed. Each chamfered surface is disposed at a predetermined position so that it can be processed. Note that “upper” and “lower” are positional relationships for convenience in FIG.
The arrangement relationship of the upper outer diameter chamfering grindstone 20, the lower outer diameter chamfering grindstone 22 and the outer diameter side wall chamfering grindstone 24 with respect to the glass substrate 10 shown in FIG. 2 is an example. Thus, the present invention is not limited to this.

  In the present invention, as described above, the upper outer diameter chamfering grindstone 20, the lower outer diameter chamfering grindstone 22, and the outer diameter side wall chamfering grindstone 24 all have their moving directions and the glass. The movement direction of the substrate 10 intersects at these contact points so that the end surface portions of the respective grindstones are brought into contact with the end surfaces of the glass substrate 10 and the glass substrate 10 and the respective grindstones are relatively moved. Thus, the end surface of the glass substrate 10 is processed. The movement in this case is a rotational movement.

  In the present embodiment, as shown in FIGS. 2 and 3, all of the upper outer diameter chamfering grindstone 20, the lower outer diameter chamfering grindstone 22, and the outer diameter sidewall chamfering grindstone 24 are all. The rotation direction and the rotation direction of the glass substrate 10 intersect each other substantially perpendicularly. The angle at which the rotation direction of each of the grinding stones and the rotation direction of the glass substrate 10 (direction of the substrate surface) intersect is not limited to being substantially vertical, but the operational effects of the present invention are better exhibited. Is preferably in the range of 60 to 90 degrees at the smaller angle, for example.

  The operation will be specifically described. The upper outer diameter chamfering grindstone 20, the lower outer diameter chamfering grindstone 22, and the outer diameter side wall chamfering grindstone 24 each have a predetermined shape as shown in FIG. The glass substrate 10 is not in contact with the end surface of the glass substrate 10 at this time. After the glass substrate 10 is rotated at a predetermined rotation speed, the upper outer diameter chamfering grindstone 20, the lower outer diameter chamfering grindstone 22, and the outer diameter side wall chamfering grindstone 24 are rotated. The grindstone is fed at an optimum speed toward the glass substrate 10 that is a workpiece (the feed mechanism is not shown), and the end face portion of each grindstone is moved to the outer peripheral side of the glass substrate 10. The end surface of the glass substrate 10 is shaped by contacting the end surface and relatively rotating the glass substrate 10 and the grindstones.

According to such a configuration of the present invention, the contact state between the grindstone and the glass substrate is such that the outer peripheral end surface of the grindstone and the end surface of the substrate intersect and are in a point contact state, and the contact area between the grindstone and the substrate is reduced. Therefore, grinding efficiency can be improved. In addition, since the moving direction of the grindstone and the glass substrate intersects at these contact points, grinding traces (grinding traces) hardly remain on the ground surface. In the prior art, the direction of movement of the grindstone and the glass substrate does not intersect, so it is easy to leave circumferential lines, and these lines cannot be removed in the subsequent polishing process (for example, simultaneous polishing of the end face and chamfered surface with a brush). was there. In the present invention, not only is the streak difficult to enter in the first place, but even if a streak is entered, it is possible to shift the direction of the streak from the circumferential direction by controlling the rotational speed of the grindstone. By doing so, even if mirror polishing is subsequently performed by the brush polishing process, the movement direction of the brush can be made orthogonal to the streak direction, so it can be easily erased with a small amount of streak Become.
Moreover, since a disk-shaped grindstone is used in the present invention, the processed surface is concave and the end of the processed surface tends to be sharp. In general, in mirror polishing using a polishing brush, the boundary between the chamfered surface and the end surface and the boundary between the main surface and the chamfered surface are easily polished. Tends to have a larger radius of curvature. This tendency becomes more prominent as the allowance for polishing increases. Therefore, conventionally, there is a problem that the dimensional shape accuracy deteriorates when the amount of polishing processing is increased in order to remove the streak. In the present invention, not only can the margin for brush polishing be reduced, but also the effect of canceling the irregularities can be obtained by applying a convex shape to the concave surface, so that good dimensional accuracy is easily achieved. can do.
Therefore, even when grinding is performed using a fine abrasive wheel, stable grindability can be ensured, and good grinding surface quality (mirror surface quality) can be stably obtained. In addition, even when fine abrasive grains are used, the sharpness of the grindstone is maintained and the grindability is stably ensured, thereby ensuring good dimensional shape accuracy by chamfering the end face of the glass substrate.

  In addition, the side wall surface of the end surface of the glass substrate 10 can be obtained by simultaneously using the grindstone 24 that shapes the side wall surface of the end surface of the glass substrate 10 and the grindstones 20 and 22 that shape the chamfered surface of the end surface. However, the method is not limited to this, but the side wall surface and the chamfered surface may be processed in separate steps.

In the present invention, each size of the upper outer diameter chamfering grindstone 20, the lower outer diameter chamfering grindstone 22, and the outer diameter sidewall chamfering grindstone 24 is, for example, the outer diameter of the glass substrate 10. What is necessary is just to determine suitably in consideration.
Further, in the present invention, the rotational speeds of the respective grindstones and the glass substrate 10 do not need to be particularly limited, and may be appropriately determined in view of grindability and processing efficiency.

  As the upper outer diameter chamfering grindstone 20, the lower outer diameter chamfering grindstone 22 and the outer diameter side wall chamfering grindstone 24 used in the present invention, a resin grindstone made of abrasive grains and resin is used. Can be used. For chamfering the end face of the magnetic disk glass substrate as in the present invention, it is preferable to use a resin grindstone as a grinding grindstone. In addition, a metal grindstone composed of abrasive grains and a metal binder, a vitrified grindstone composed of abrasive grains and a vitreous binder, and a composite grindstone obtained by mixing these binders can also be used. In particular, as a resin grindstone, for example, diamond abrasive grains are added to a suitable filler as necessary, and bonded to a phenol resin, an epoxy resin, a polyethylene resin, a polystyrene resin, a polyimide resin, or the like, and formed into a predetermined shape. Things can be used. Also, alumina abrasive grains, cubic boron nitride abrasive grains, and the like can be used. As the grain size of the abrasive grains, for example, fine abrasive grains of # 1500 or smaller can be suitably used. In the case of the present invention, even when a fine abrasive wheel that is advantageous from the viewpoint of improving the quality of the processed surface is used, the sharpness of the grindstone can be maintained and stable grindability can be ensured, and the good grinding surface quality (mirror surface quality) ) And good dimensional shape accuracy can be stably obtained.

  Further, the grinding fluid (coolant) used in the present invention is not particularly limited, but a water-soluble grinding fluid having a high cooling effect and high safety at the production site is particularly suitable.

The glass type used for the magnetic disk glass substrate is not particularly limited. Examples of the glass substrate material include aluminosilicate glass, soda lime glass, soda aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, Examples thereof include glass ceramics such as quartz glass, chain silicate glass, or crystallized glass. Among these, amorphous aluminosilicate glass is particularly preferable because it is excellent in impact resistance and vibration resistance. The aluminosilicate _{glass, SiO 2: 62~75wt%, Al} 2 O 3: 5~15wt%, Li 2 O: 4~10wt%, Na 2 O: 4~12wt%, ZrO 2: the 5.5～15Wt% A glass for chemical strengthening or the like having a weight ratio of Na ₂ O / ZrO ₂ of 0.5 to 2.0 and a weight ratio of Al ₂ O ₃ / ZrO ₂ of 0.4 to 2.5 is preferable. In order to eliminate protrusions on the glass substrate surface caused by the undissolved material of ZrO ₂ , SiO ₂ is 57 to 74%, ZnO ₂ is 0 to 2.8%, and Al ₂ O ₃ is 3 in terms of mol%. It is preferable to use glass containing ˜15%, LiO ₂ ˜7-16%, Na ₂ O 4˜14%.

  In addition, although the grinding process of the outer peripheral side end surface of the glass substrate 10 is performed as described above, the present invention can be similarly applied to the grinding process of the inner peripheral side end surface. It should be noted that the present invention can be applied only to one of the outer circumference and the inner circumference, and the conventional method can be applied to the other.

Moreover, after performing the shape grinding process of the end surface of the glass substrate by the above-mentioned this invention, the process of mirror-polishing an end surface similarly according to the required mirror surface quality may be added. In this case, mirror polishing can be performed using a conventional polishing brush.
In the present embodiment, as described above, the upper outer diameter chamfering grindstone 20, the lower outer diameter chamfering grindstone 22, and the outer diameter side wall chamfering grindstone 24 are all in the rotational movement direction. Is processed so that the rotational movement direction of the glass substrate 10 intersects substantially perpendicularly, for example, so that the processing direction differs by approximately 90 degrees between this shape processing and the subsequent mirror polishing using a polishing brush. Is possible. According to the present invention, not only is the streak difficult to enter in the first place, but even if a streak is entered, it is possible to shift the direction of the streak from the circumferential direction by controlling the rotational speed of the grindstone. By doing so, even if mirror polishing is subsequently performed by the brush polishing process, the movement direction of the brush can be made orthogonal to the streak direction, so it can be easily erased with a small amount of streak Become.

By performing the shape grinding of the end face of the glass substrate according to the present invention described above, it is possible to stably obtain a good grinding surface quality and good dimensional shape accuracy. Further, the end face is also mirror-polished by brush polishing or the like. Even in this case, the polishing allowance is small, and the polishing process time can be as short as, for example, several tens of seconds, and the work load is reduced.
The glass substrate that has been subjected to the grinding and polishing steps of the outer peripheral side and inner peripheral side end surfaces of the substrate as described above is then subjected to a mirror polishing step, a chemical strengthening step, and the like of the main surface, as shown in FIG. Such a magnetic disk glass substrate 1 is obtained.

  According to the method for manufacturing a glass substrate for a magnetic disk according to the present invention, it is possible to ensure the dimensional shape accuracy of the outer peripheral side end surface of the glass substrate for a magnetic disk from the viewpoint of meeting the demand for higher recording density and lower price of the magnetic disk. Stable shape processing that can be finished with high quality efficiently at low cost is possible. Therefore, it is possible to stably provide a large number of glass substrates for magnetic disks whose end surfaces are finished with high quality at low cost.

According to another aspect of the present invention, there is provided a magnetic disk manufacturing method comprising: forming at least a magnetic layer on a main surface of a magnetic disk glass substrate manufactured by the above-described method for manufacturing a magnetic disk glass substrate according to the present invention. Also provide.
That is, a magnetic disk can be obtained by forming at least a magnetic layer on the glass substrate for a magnetic disk obtained by the above-described embodiment of the present invention. In general, for example, a perpendicular magnetic recording medium is preferably a magnetic disk in which an adhesion layer, a soft magnetic layer, an underlayer, a magnetic layer, a protective layer, a lubricating layer, and the like are provided on a glass substrate.
According to the method of manufacturing a magnetic disk using the glass substrate for a magnetic disk according to the present invention, the end surface of the substrate can be finished with high quality, and the occurrence of failures due to the surface state of the substrate end surface, such as anti-corrosion, is prevented. A magnetic disk capable of realizing higher recording density can be provided.

Hereinafter, the embodiment of the present invention will be described more specifically with reference to examples. In addition, this invention is not limited to a following example.
Example 1
(1) Rough lapping step (rough grinding step), (2) Fine lapping step (fine grinding step), (3) End surface grinding step (4) End surface polishing step, (5) Main surface first polishing step, ( 6) A glass substrate for a magnetic disk of this example was manufactured through a chemical strengthening step and (7) a main surface second polishing step.

(1) Coarse lapping step First, a glass substrate (glass disk) made of disc-shaped aluminosilicate glass having a diameter of 66 mmφ and a thickness of 1.0 mm is obtained from molten glass by direct pressing using an upper die, a lower die, and a barrel die. It was. In this case, in addition to the direct press, a disk-shaped glass substrate may be obtained by cutting out with a grinding wheel from a sheet glass formed by a downdraw method or a float method. As the aluminosilicate _glass, SiO 2: 58 to 75 _{wt%, Al} 2 O 3: _{5~23 wt%,} Li 2 O: _{3~10 wt%,} Na 2 O: _4~13 chemical containing wt% Tempered glass was used. Next, a lapping process was performed on the glass substrate in order to improve dimensional accuracy and shape accuracy. This lapping process was performed using a double-sided lapping machine and using abrasive grains having a particle size of # 400. Specifically, first, using alumina abrasive grains of particle size # 400, setting the load to about 100 kg and rotating the sun gear and the internal gear of the lapping device, both surfaces of the glass substrate housed in the carrier are faced. Lapping was performed with an accuracy of 0 to 1 μm and a surface roughness (Rmax) of about 6 μm.

(2) Fine lapping step Next, the grain size of the abrasive grains was changed to # 1000 and the surface of the glass substrate was lapped so that the surface roughness was about 2 μm in Rmax and about 0.2 μm in Ra. The glass substrate after the lapping process was immersed in each washing tank (applied with ultrasonic waves) in a neutral detergent and water in order to perform ultrasonic cleaning.

(3) End surface grinding step Next, a hole is made in the central portion of the glass substrate using a cylindrical grindstone, and the outer peripheral side end surface of the substrate is ground by the method shown in FIG. Then, a predetermined chamfering process was performed on the outer peripheral side end face. In this case, both the chamfering grindstone and the side wall grindstone are formed by bonding diamond abrasive grains having a particle size of # 3000 with a phenolic resin and forming them into a disk shape having an end face portion as shown in FIG. used. A water-soluble grinding fluid (temperature 20 ° C.) was used as the grinding fluid.
While the grinding liquid is supplied to the outer peripheral side end surface portion of the glass substrate, the outer peripheral side end surface of the glass substrate is rotated by bringing the grinding stone into contact with the outer peripheral side end surface of the glass substrate and rotating both the glass substrate and the grindstone. Both the wall surface and the chamfered surface were shaped. The rotational speed of the grindstone was 20000 rpm, and the rotational speed of the glass substrate was 20 rpm.

Thus, grinding was performed for about 30 seconds. The surface roughness of the outer peripheral side end surface of the glass substrate at this time was about 0.5 μm in Rmax for both the side wall surface and the chamfered surface. In general, a 2.5-inch HDD (hard disk drive) uses a magnetic disk having an outer diameter of 65 mm.
Next, the inner peripheral side end face of the substrate was ground and chamfered using a predetermined grinding wheel as in the conventional case. In addition, although the end surface processing method of the present invention can be applied to the inner peripheral side end surface, in this embodiment, as an example, the processing method of the present invention is applied only to the outer peripheral side end surface, and the inner peripheral side end surface is a conventional total type. Processing with a grindstone.

(4) End surface grinding | polishing process Then, the outer peripheral side end surface of the glass substrate was grind | polished using the grinding | polishing brush. In this case, the material of the bristle of the polishing brush was 6-6 nylon. The rotation speed of this polishing brush was 1000 rpm, and the rotation speed of the glass substrate was 50 rpm in the direction opposite to that of the polishing brush. Further, cerium oxide was used as the polishing agent, and a polishing liquid at about 30 ° C. containing this cerium oxide was supplied.

The surface roughness of the end face on the outer peripheral side of the glass substrate after finishing the 100 grinding and polishing processes in this way was finished to a mirror surface with an average value of Ra of about 0.05 μm. When the end face shape of the outer peripheral side of the polished glass substrate was measured with a tracer, the end face 12 was finished in a predetermined chamfered shape composed of two chamfered faces 12b and a side wall face 12a therebetween as shown in FIG. It was. And the variation of the angular shape of the side wall surface and the chamfered surface of the outer peripheral side end surface is within ± 2 ° with respect to 45 degrees, the variation of the outer diameter is also within 10 μm, and the dimensional shape accuracy of the outer peripheral side end surface is good. Met. Further, in the end face observation after the polishing finish, the remaining processing damage was observed on the entire outer peripheral end face using a microscope (magnification × 1000). However, the residual trace was not confirmed, and the polishing face was good. The grindstone used in the above-described shape processing did not cause problems such as clogging or crushing, and still maintained a good sharpness even after the above processing.
And the surface of the glass substrate which finished the said end surface grinding | polishing process was washed with water.

(5) Main surface first polishing step Next, a first polishing step for removing scratches and distortions of the main surface remaining in the lapping step described above was performed using a double-side polishing apparatus. In a double-side polishing apparatus, a glass substrate held by a carrier is brought into close contact with an upper and lower surface plate to which a polishing pad is attached, the carrier is engaged with a sun gear and an internal gear, and the glass substrate is sandwiched between upper and lower surface plates. Press. Thereafter, a polishing liquid is supplied and rotated between the polishing pad and the polishing surface of the glass substrate, whereby the glass substrate revolves while rotating on the surface plate to simultaneously polish both surfaces. Specifically, a polishing process was performed using a hard polisher (hard urethane foam) as a polisher. The polishing conditions were RO water in which cerium oxide (average particle size 1.3 μm) was dispersed as a polishing agent as a polishing liquid, a load: 100 g / cm ² , and a polishing time: 15 minutes. The glass substrate after the first polishing step was sequentially immersed in each cleaning bath of neutral detergent, pure water, pure water, IPA (isopropyl alcohol), and IPA (steam drying), ultrasonically cleaned, and dried. .

(6) Chemical strengthening process Next, the glass substrate which finished the said washing | cleaning was chemically strengthened. For chemical strengthening, a chemical strengthening solution in which potassium nitrate and sodium nitrate were mixed was prepared, the chemical strengthening solution was heated to 380 ° C., and the cleaned and dried glass substrate was immersed for about 4 hours to perform chemical strengthening treatment. The glass substrate after chemical strengthening was sequentially immersed in each of washing tanks of sulfuric acid, neutral detergent, pure water, pure water, IPA, and IPA (steam drying), ultrasonically cleaned, and dried.

(7) Main surface second polishing step Next, using the same type of double-side polishing apparatus as used in the first polishing step, the polisher was changed to a soft polisher (suede pad), and the second polishing step was performed. This second polishing step is intended to reduce, for example, the surface roughness Ra to about 0.1 to 0.3 nm or less while maintaining the flat surface obtained in the first polishing step described above. is there. The polishing conditions were RO water in which colloidal silica (average particle size 0.05 μm) was dispersed as a polishing liquid, a load: 100 g / cm ² , and a polishing time of 5 minutes. The glass substrate after the second polishing step was sequentially immersed in each cleaning bath of neutral detergent, pure water, pure water, IPA, and IPA (steam drying), ultrasonically cleaned, and dried.

  Next, a visual inspection of the glass substrate surface after the cleaning and an inspection by an optical inspection apparatus were performed. As a result, no defects such as protrusions and scratches due to deposits were found on the glass substrate surface. Further, when the surface roughness of the main surface of the glass substrate obtained through the above steps was measured with an atomic force microscope (AFM), a glass substrate for magnetic disk having an ultra-smooth surface with Ra = 0.20 nm was obtained. Obtained. The glass substrate had an outer diameter of 65 mm, an inner diameter of 20 mm, and a plate thickness of 0.635 mm.

  As described above, about 10,000 glass substrates for magnetic disks were manufactured and a long run test was performed. As a result, the average ratio of non-defective products that cleared the specified end face shape, dimensional accuracy, and surface roughness by the first end face grinding and polishing process is 90% or more on average. Most of them were.

(Comparative example)
This comparative example is different from the above-described embodiment in that the grinding of the outer peripheral side end surface of the glass substrate is performed using a conventional method. That is, grinding was performed by bringing the outer peripheral surface of the glass substrate into contact with the outer peripheral surface of a cylindrical grinding wheel as shown in FIG. 4 and rotating both the glass substrate and the grindstone. A diamond grindstone (or cerium oxide grindstone) having a particle size (fine abrasive grain # 500) was used as the grinding wheel. Other grinding conditions were adjusted as appropriate.
Subsequently, the outer peripheral side end surface of the glass substrate was polished using a conventional polishing brush and polishing apparatus. In this case, the material of the bristle of the polishing brush was 6-6 nylon. The polishing agent used was cerium oxide, and a polishing liquid containing about 30 ° C. containing cerium oxide was supplied. Other polishing conditions were adjusted as appropriate.

A glass substrate for a magnetic disk was manufactured in the same manner as in Example 1 except for the above points.
The surface roughness of the end face on the outer peripheral side of the glass substrate after finishing the grinding and polishing of 100 sheets in this way was an average value of Ra of about 0.1 μm, but the dimensional variation of the outer diameter was as large as about 50 μm.
When the end face shape of the outer peripheral side of the glass substrate after polishing was measured with a tracer, the whole was finished round when viewed in cross section. As shown in FIG. 1, the end face 12 had two chamfered faces 12b and a side between them. The predetermined chamfered shape consisting of the wall surface 12a was not exactly finished. In addition, for grinding of the outer peripheral side end surface, a fine abrasive wheel that is advantageous in terms of processing surface quality was used, but problems such as clogging and crushing occurred in a short time. It was necessary to set conditions, and work efficiency was reduced.

  Also in this comparative example, about 10,000 of the 2.5-inch magnetic disk glass substrate was manufactured and a long run test was performed. As a result of the first end face grinding and polishing, a predetermined end face shape and dimensions were obtained. The percentage of non-defective products that cleared the angular accuracy and surface roughness was 80% or less on average.

(Example 2)
The following film-forming process was performed on the glass substrate for magnetic disk of the present invention obtained in the above example to obtain a magnetic disk for perpendicular magnetic recording.
That is, an adhesion layer made of a Ti-based alloy thin film, a soft magnetic layer made of a CoTaZr alloy thin film, an underlayer made of a Ru thin film, a perpendicular magnetic recording layer made of a CoCrPt alloy, a carbon protective layer, and a lubricating layer are sequentially formed on the glass substrate. A film was formed. The protective layer is for preventing the magnetic recording layer from deteriorating due to contact with the magnetic head, and is made of hydrogenated carbon, and provides wear resistance. The lubricating layer was formed by dipping a liquid lubricant of alcohol-modified perfluoropolyether.
The obtained magnetic disk was installed in an HDD equipped with a DFH head, and a load / unload durability test was conducted for one month while operating the DFH function in a high temperature and high humidity environment of 80 ° C. and 80% RH. There were no particular obstacles and good results were obtained.

1 Glass substrate for magnetic disk 10 Disk-shaped glass substrate (glass disk)
DESCRIPTION OF SYMBOLS 11 Main surface 12 of glass substrate Outer peripheral side end surface 13 of glass substrate Inner peripheral side end surface 20 of glass substrate Upper, outer diameter chamfering grindstones 21, 23, 25, 26 Driving unit 22 Lower outer diameter chamfering grindstone 24 Grinding wheel for outer diameter side wall surface processing

Claims (9)

A glass substrate for a magnetic disk having a step of processing a shape of an end surface of the glass substrate by supplying a grinding liquid to the end surface portion of the disk-shaped glass substrate and grinding by bringing a grindstone into contact with the end surface of the glass substrate. A manufacturing method comprising:
The grindstone is a disc-shaped rotating grindstone that is formed in a disc shape having an end surface portion and is configured to be rotatable around its center as a rotation axis.
The moving direction of the grindstone and the moving direction of the glass substrate intersect at these contact points so that the end surface portion of the grindstone is in contact with the end surface of the glass substrate and the glass substrate and the grindstone are relative to each other. A method of manufacturing a glass substrate for a magnetic disk, wherein the shape of the end surface of the glass substrate is processed by moving the glass substrate to a position.   2. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the shape processing is performed by rotating both the glass substrate and the grindstone.   The manufacturing method of a glass substrate for a magnetic disk according to claim 1 or 2, wherein a grindstone that shapes the side wall surface of the end surface of the glass substrate and a grindstone that shapes the chamfered surface of the end surface are used simultaneously. Method.   4. The method for producing a glass substrate for a magnetic disk according to claim 1, wherein after the end surface of the glass substrate is shaped, the end surface is similarly mirror-polished using a polishing brush.   5. The method of manufacturing a glass substrate for a magnetic disk according to claim 4, wherein the processing direction is varied by approximately 90 degrees between the shape processing using the grindstone and the subsequent mirror polishing using a polishing brush.   6. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the end surface of the glass substrate to be processed is an outer peripheral side end surface.   7. The magnetic disk glass according to claim 1, wherein at least a chamfered surface of the outer peripheral side and / or the inner peripheral side end surface of the glass substrate is concave. A method for manufacturing a substrate.   The glass substrate for a magnetic disk according to any one of claims 1 to 7, wherein a side wall surface of the end surface on the outer peripheral side and / or the inner peripheral side after the shape processing of the glass substrate is concave. Production method.   A method for manufacturing a magnetic disk, comprising forming at least a magnetic layer on a main surface of the glass substrate for a magnetic disk manufactured by the method for manufacturing a glass substrate for a magnetic disk according to claim 1.

Images