JP2014216042A - Method of manufacturing glass substrate for magnetic disk, and magnetic disk manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a glass substrate for a magnetic disk that enables end faces of the glass substrate to be finished in high quality and thereby achieving stable grinding processing for obtaining both the surface quality and processing accuracy.SOLUTION: In an end face working process of working on an end face part of a disk-shaped glass substrate by grinding with a grinding wheel brought into contact with it while supplying the end face part with grinding fluid, a grinding wheel having a groove shape in a face coming into contact with the end face of the glass substrate is used to bring the grinding wheel into contact with the end face in a state in which a rotating axis of the grinding wheel is inclined relative to an axis orthogonal to a main surface of the glass substrate, and, after grinding a side wall face and a chamfered face of the substrate at the same time, the end face of the glass substrate is polished with a brush.

Description

  The present invention relates to a method for manufacturing a glass substrate for a magnetic disk used for manufacturing a magnetic disk mounted on a magnetic recording apparatus such as a hard disk drive (hereinafter abbreviated as “HDD”), and a glass substrate by this manufacturing method. The present invention relates to a method of manufacturing a magnetic disk to be used.

  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 which is a recording medium mounted on a magnetic recording apparatus such as an HDD, a technology capable of realizing an information recording density of 750 GB or more per magnetic disk is required due to a demand for higher capacity.

  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's getting higher. 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 processing method of the 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, a grinding wheel is contacted and rotated on the outer peripheral side end surface and the inner peripheral side end surface of the glass substrate. Grinding 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 (Patent Document 1, etc.). In this case, the grindstone is generally called a general grindstone, and has a groove shape for forming the end face shape of the glass substrate. The grindstone is processed by contacting with the end face of the glass substrate. Thus, the shape of the groove of the grindstone is transferred to the end surface of the glass substrate. Further, after this chamfering process, brush polishing has been performed in order to process the end surface of the glass substrate into a mirror surface.

JP-A-11-28649

With the development of the information society, the demand for higher recording density of magnetic disks is only increasing. In the end face shape of a glass substrate for a magnetic disk, further improvement in surface quality (smoothing etc.) and improvement in processing accuracy (form accuracy etc.) have been demanded.
The reason for this is, for example, the high quality of the outer diameter end face based on the demand for reduction of contamination factors such as the accuracy of the inner diameter dimension to obtain the positioning accuracy of the magnetic head when mounted on the HDD and the occurrence of corrosion on the main surface of the medium. This is because the achievement of the conversion is required.

However, there are the following problems in the combination of the above-described grinding with a general grinding wheel and the end mirroring by brush polishing.
That is, if it is going to attach importance to shape accuracy, the allowance for brush polishing is reduced, and the grinding streaks formed by grinding with a general-purpose grindstone cannot be completely removed and the roughness tends to increase. On the other hand, if it is going to attach importance to the surface quality after a process, as a result of the machining allowance in brush polishing increasing, the shape precision formed by the grinding process by a general-purpose grindstone will deteriorate. Therefore, if you try to obtain both surface quality and shape accuracy with less allowance for brush polishing, the production efficiency is as low as possible in order to finish the above grinding conditions as well as possible. It is necessary to adopt processing conditions that sacrifice sacrificing.
In short, in manufacturing a glass substrate for a magnetic disk on the premise of mass production processing, it is difficult to achieve both processing accuracy and surface quality at the inner and outer diameter end portions of the glass substrate with a conventional processing method.

  Conventionally, the user's requirement was satisfied by placing importance on either processing accuracy or surface quality, so there was no problem, but as mentioned above, in recent years, even higher recording density of magnetic disks In response to the demands for manufacturing, the surface shape of glass substrates for magnetic disks is also required to improve surface quality and processing accuracy. It is an urgent need to achieve both surface quality and processing accuracy. Yes.

  As described above, from the viewpoint of increasing the recording density, the quality requirements for the glass substrate for magnetic disks, such as the dimensional accuracy of the end surface of the glass substrate and the finished surface quality of the chamfering process, are increasing more than before, When a glass substrate for a magnetic disk is manufactured using a grinding method or a polishing method, it has become difficult to stably meet the increasing quality requirements of the glass substrate.

  Therefore, the present invention can efficiently finish the end surface of a magnetic disk glass substrate with high quality from the viewpoint of meeting the demand for higher recording density of a magnetic disk, which is urgently required to ensure reliability. It is a first object to provide a method for producing a glass substrate. A second object of the present invention is to provide a method of manufacturing a magnetic disk using a glass substrate by such a manufacturing method.

Therefore, as a result of intensive studies to solve the above-mentioned problems, the present inventors have completed the present invention.
That is, the present invention has the following configuration in order to solve the above problems.

(Configuration 1)
Grinding liquid is supplied to the end surface portion of the disk-shaped glass substrate having a circular hole in the center, and a grindstone is placed on the side wall surface that is the end surface of the glass substrate, the main surface of the glass substrate, and the chamfered surface that interposes the side wall surface. A method of manufacturing a glass substrate for a magnetic disk including an end face processing for processing an end face of the glass substrate by contacting and grinding, wherein the end face processing is performed with respect to an axis orthogonal to the main surface of the glass substrate. A first processing step of grinding the side wall surface and the chamfered surface of the glass substrate at the same time by bringing the rotating grindstone into contact with the end surface of the glass substrate in a state where the rotation axis of the rotating grindstone is inclined; A second processing step that is performed after the first processing step and polishes the side wall surface and the chamfered surface of the glass substrate processed by the first processing step by bringing a brush having a rotating shaft into contact therewith. Method of manufacturing a glass substrate for a magnetic disk, wherein.

(Configuration 2)
2. The method for manufacturing a glass substrate for a magnetic disk according to Configuration 1, wherein a processing locus by the first processing step and a processing locus by the second processing step do not overlap with each other on an end surface of the glass substrate.
(Configuration 3)
In the first processing step, the angle between the axis orthogonal to the main surface of the glass substrate and the rotation axis of the rotating grindstone is in the range of 2 degrees to 30 degrees. The manufacturing method of the glass substrate for magnetic disks of description.

(Configuration 4)
In the second processing step, using a brush in which the flocking angle of the brush bristles is inclined with respect to the rotation axis of the brush, the axis orthogonal to the main surface of the glass substrate and the rotation axis of the brush are parallel to each other. And the angle between the flocking angle of the brush and the main surface of the glass substrate and the rotating surface of the rotating grindstone in the first processing step is different from each other. The manufacturing method of the glass substrate for magnetic discs in any one of 1-3.
(Configuration 5)
The first processing step is performed on the glass substrate on which both the side wall surface of the end surface of the glass substrate and the chamfered surface between the main surface and the side wall surface of the glass substrate are formed. The manufacturing method of the glass substrate for magnetic discs in any one of the structures 1 thru | or 4.

(Configuration 6)
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 method for manufacturing a magnetic disk glass substrate according to any one of Structures 1 to 5.

According to the method for manufacturing a glass substrate for magnetic disk according to the present invention, the end surface of the glass substrate for magnetic disk can be finished efficiently and with high quality, and stable grinding that achieves both surface quality and processing accuracy is possible. .
Further, 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 surface quality of the end face of the substrate and the processing accuracy can be made compatible and finished with high quality. In addition, it is possible to provide a highly reliable magnetic disk capable of preventing the occurrence of failures due to the surface state of the substrate end face and the processing accuracy and realizing a further higher recording density.

An embodiment of the 1st processing process in the present invention is shown, (a) is a perspective view and (b) is a front view which changed direction from (a). The other embodiment of the 1st processing process in this invention is shown, (a) is a perspective view, (b) is the front view which changed direction from (a). It is a figure which shows typically an example of the processing locus by the 1st processing process in the present invention, and the processing locus by the 2nd processing process. It is sectional drawing which shows an example of the groove shape of the grindstone used for the 1st processing process in this invention. It is sectional drawing which shows an example of the end surface shape of a glass substrate.

Hereinafter, embodiments for carrying out the present invention will be described in detail.
FIG. 5 is a cross-sectional view of the outer peripheral end of the magnetic disk glass substrate 1 to which the present invention is applied. Although the glass substrate 1 is not shown in FIG. 5, the whole having a circular hole 4 at the center is formed in a disc shape (see FIG. 1 and the like), and main surfaces 1a and 1a on the front and back sides thereof, It has an outer peripheral end face and an inner peripheral end face formed between the main surfaces 1a and 1a.
The outer peripheral end surface of the glass substrate 1 has a side wall surface 1b orthogonal to the main surface 1a, and two chamfered surfaces (chamfered surfaces) formed between the side wall surface 1b and the front and back main surfaces 1a and 1a. Surface) 1c, 1c. Moreover, although it does not show in figure about the end surface of the inner peripheral side of the said glass substrate 1, like the said outer peripheral side end surface, the side wall surface orthogonal to the main surface 1a, and this side wall surface and main surface 1a, 1a of the front and back Are formed in a shape composed of two chamfered surfaces (chamfered surfaces) formed between the two.

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.

  The main surface 1a, the outer peripheral side end surface, and the inner peripheral side end surface of the glass substrate 1 for magnetic disk are all polished (mirror polished) so as to finally have a predetermined surface roughness. Both the outer peripheral side end face and the inner peripheral side end face of the glass substrate 1 are finished in the end face shape as described above, and the surface roughness is finished in a mirror surface state with Rmax of 1 μm or less and Ra of 0.1 μm or less, for example. It is usually sought to be.

The glass substrate 1 for a magnetic disk is usually subjected to processes such as end face grinding, polishing, main surface mirror polishing, and chemical strengthening on a glass substrate (glass disk) 1 formed into a predetermined disk shape by, for example, direct pressing. Manufactured sequentially.
First, the grinding / polishing process of the end face of the glass substrate 1 will be described.
In the present specification, for convenience of explanation, from a glass disk molded into a predetermined disk shape by direct press or the like to a final product glass substrate produced by processing, processing, etc. on this glass disk. These are all referred to as glass substrates or magnetic disk glass substrates.

In the method for manufacturing a glass substrate for a magnetic disk according to the present invention, the grinding liquid is supplied to an end surface portion of a disk-shaped glass substrate having a circular hole at the center, as in Configuration 1, and the end surface of the glass substrate is used. A method of manufacturing a glass substrate for a magnetic disk, comprising: an end face processing for processing an end face of the glass substrate by grinding a contact with a grindstone in contact with a certain side wall surface, a main surface of the glass substrate, and a chamfered surface interposing the side wall surface In the end face processing, the rotating grindstone is brought into contact with the end face of the glass substrate in a state where the rotating shaft of the rotating grindstone is inclined with respect to an axis orthogonal to the main surface of the glass substrate. A first processing step for simultaneously grinding the side wall surface and the chamfered surface of the substrate, and the side wall surface and the chamfered surface of the glass substrate that are performed after the first processing step and processed by the first processing step. A configuration and a second processing step of brushing.
In other words, the method for manufacturing a glass substrate for a magnetic disk according to the present invention is performed by supplying a grinding liquid to an end surface portion of a disk-shaped glass substrate and grinding by bringing a grindstone into contact with the end surface of the glass substrate. A method of manufacturing a glass substrate for a magnetic disk including an end face processing for processing an end face of a glass substrate, wherein the end face processing is performed using a grindstone having a groove shape on a surface in contact with the end face of the glass substrate. The end face of the glass substrate and the grindstone are brought into contact with each other and the glass substrate and the grindstone are relatively moved so that the trajectory of the grindstone contacting the end face of the glass substrate is not constant. A first processing step for processing the end surface, and a second process that is performed after the first processing step and brushes the end surface of the glass substrate processed by the first processing step. It has a configuration and a step.

First, the first processing step will be described. 1A and 1B show an embodiment of the first processing step. FIG. 1A is a perspective view, and FIG. 1B is a front view in which the direction is changed from FIG.
The center part is drilled, and the glass substrate 1 having the circular holes 4 is processed using the grindstone 2 for the outer peripheral end face and the grindstone 3 for the inner peripheral end face. The grindstone 2 is formed in a disk shape of a predetermined size as shown in the figure, and has a groove shape on the outer peripheral side thereof in contact with the end surface of the glass substrate. For example, as shown in FIG. 4, the groove shape is a concave shape 6 that is recessed inward in a cross-sectional view. Of course, the shape illustrated in FIG. 4 is an example, and the present invention is not limited to this. In addition, the grindstone 3 is formed in a cylindrical shape having a predetermined size as shown in the figure, and a groove shape (for example, a concave shape as shown in FIG. 4) is formed on the outer peripheral side of the grindstone 3 in contact with the end surface of the glass substrate. )have.

As the grindstone (rotary grindstone) 2 and grindstone (rotary grindstone) 3 used in the first processing step of the present invention, a resin grindstone in which fine-grained abrasive grains are hardened with a resin such as phenol resin and / or urethane resin is suitable. It is. In this case, the average particle diameter of the abrasive grains is preferably, for example, 65 μm or less, and particularly preferably 2 μm or more and 65 μm or less. In other words, as a grindstone used in the first processing step, it is preferable to use a grindstone having a particle size in the range of # 400 to # 8000.

In the first processing step, the processing is performed by bringing the end face of the glass substrate into contact with the grindstone so that the trajectory of the grindstone contacting the end face of the glass substrate is not constant. Specifically, the rotating grindstone 2 or the rotating grindstone 3 is inclined with respect to the direction orthogonal to the main surface of the glass substrate, in other words, the rotation of the rotating grindstone with the axis orthogonal to the main surface of the glass substrate. In a state where the shaft is in a torsional relationship, the rotating grindstone 2 or the rotating grindstone 3 and the glass substrate are brought into contact with each other, and the side wall surface and the chamfered surface of the glass substrate 1 are simultaneously ground. This will be described in detail below.
As shown in FIG. 1, the grindstone 2 for machining the outer peripheral side of the substrate is processed in a state where the plane direction of the grindstone 2 is inclined by an angle α with respect to the plane direction of the glass substrate 1. Further, the grindstone 3 for machining the inner peripheral side of the substrate is processed in a state where the rotation axis direction of the grindstone 3 is inclined by the angle β with respect to the rotation axis direction of the glass substrate 1. About the grindstone 2, it contacts with the arrow 13 direction (cutting direction) in the figure with respect to the outer peripheral side end surface of the glass substrate 1, and about the grindstone 3, the arrow 14 in the figure with respect to the inner peripheral side end surface of the glass substrate 1 is shown. Touch the direction (cutting direction). In this case, it is preferable to perform processing while rotating the grindstone 2 or the grindstone 3 and the glass substrate 1 in predetermined directions, respectively, and the peripheral speed and the peripheral speed ratio are suitable for processing the inner and outer peripheral side end faces. What is necessary is just to set suitably. In FIG. 1, the glass substrate 1 is rotated in the direction of the arrow 10, the grindstone 2 is rotated in the direction of the arrow 11, and the grindstone 3 is rotated in the direction of the arrow 12, but the rotation direction is not limited thereto. The rotation direction of the grindstone 2 or the grindstone 3 and the glass substrate 1 may be either the same direction (counter direction) or a different direction (anticounter direction).

In addition, although the inclination | tilt angle (alpha) with respect to the glass substrate 1 of the above-mentioned grindstone 2 can be set arbitrarily, in order to demonstrate the above-mentioned effect more, it is suitable to set it as the range of 2-30 degree | times, for example. It is. Moreover, although the inclination angle (beta) with respect to the glass substrate 1 of the above-mentioned grindstone 3 can also be set arbitrarily, in order to fully demonstrate the above-mentioned effect, it shall be in the range of 2-30 degree | times, for example. Is preferred.

From the viewpoint of grindability and processing efficiency, for example, the peripheral speed of the grindstone 2 is 1200 to 1700 m / min, the peripheral speed of the grindstone 3 is 300 to 700 m / min, and the peripheral speed of the glass substrate 1 is 3 to 10 m / min. It is preferable to set the degree.
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.

Next, the second processing step performed after the first processing step will be described.
The second processing step is a step of brush polishing the end surface of the glass substrate processed by the first processing step.
Although there is no restriction | limiting in particular in the structure of the brush used for the brush grinding | polishing in this invention, The brush etc. which used the linear material for the brush hair are suitable. Moreover, it is also preferable to use a brush in which the bristles are inclined with respect to the rotation axis direction. However, in the present invention, it is desirable to process the substrate end face so that the processing locus by the first processing step and the processing locus by the second brush polishing do not overlap, and this is used for brush polishing. It is preferable that the flocking angle of the brush hair to be selected is appropriately selected also from the above viewpoint.

Moreover, there is no limitation in particular in the kind of abrasive grain used at the brush grinding | polishing process of this invention. Moreover, as a particle size of an abrasive grain, the thing of the range whose average particle diameter is 0.01 micrometer-2.0 micrometers is preferable. It is because the allowance by brush polishing may be small by setting it as the said range.
From the viewpoint of processing efficiency, it is preferable that the peripheral speed of the polishing brush is 600 m / min and the peripheral speed of the glass substrate 1 is about 10 m / min.
Further, the grinding fluid (coolant) used in the brush polishing process 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.
In order to equalize the brush grinding trajectory while avoiding overlap between the grinding wheel grinding striation by the first machining step and the brush grinding trajectory by the second machining step, the axes of both the brush shaft and the work shaft are appropriately used. Oscillating motion may be applied in the parallel direction.

  In the first processing step, for example, in the present embodiment, the planar direction of the grindstone 2 is set with respect to the planar direction of the glass substrate 1 so that the trajectory of the grindstone 2 that contacts the end surface of the glass substrate 1 is not constant. Processing is performed while the outer peripheral side end face of the glass substrate 1 and the grindstone 2 are brought into contact with each other while being inclined by the angle α. As a result, the locus of the grindstone 2 that contacts the end surface of the glass substrate 1 does not become constant, and the convex portions (abrasive grains) of the grindstone 2 abut and act on the substrate end surface at random positions. The surface roughness and the in-plane variation of the ground surface are reduced, and the ground surface can be finished with a higher smoothness. Therefore, in the brush polishing step performed after the first processing step, the machining allowance can be reduced and the end face quality (mirror surface quality) can be improved.

FIG. 3 is a diagram schematically showing an example of a machining locus by the first machining process and a machining locus by the second machining process in the present invention.
In the present invention, it is desirable to process the substrate end face so that the processing locus by the rotating grindstone in the first processing step and the processing locus by the processing step by the second brush polishing do not overlap. For example, by adjusting the tilt angle of the glass substrate in the first processing step described above and the flocking angle of the brush bristles used in the second processing step, the processing locus by the first processing step, the second It is possible not to overlap the processing locus by the processing step by brush polishing. As can be seen from FIG. 3, the machining locus 16 by the first machining step and the machining locus 15 by the second machining step do not overlap each other, and a predetermined angle (for example, the angle α described above in the machining of the outer peripheral side end face). ), The machining locus 16 by the first machining process and the machining locus 15 by the second machining process do not overlap, so that the machining that has occurred in the first machining process in the second machining process. It is possible to perform mirror finishing with a small machining allowance while removing the locus (grinding marks and the like) and maintaining the shape accuracy of the end face obtained in the first machining step. That is, in the end face processing of the glass substrate, it is possible to achieve both surface quality and processing accuracy.

In the present invention, it is preferable that the angle formed by the processing locus by the rotating grindstone in the first processing step and the processing locus by the processing step by the second brush polishing is, for example, 2 degrees or more and less than 90 degrees.

2A and 2B show another embodiment of the first processing step, wherein FIG. 2A is a perspective view and FIG. 2B is a front view in which the direction is changed from FIG.
The processing method of the inner peripheral side end surface of the glass substrate is the same as that of the embodiment shown in FIG. 1 described above, but the outer peripheral side end surface is formed in a cylindrical shape having such a size as to enclose the glass substrate. The point which processes using the grindstone 5 differs. On the inner peripheral side of the grindstone 5, a groove shape is formed on the surface that contacts the end surface of the glass substrate. The groove shape is, for example, a concave shape 6 as shown in FIG.

Also in the present embodiment, the glass substrate is in a state where the plane direction of the grindstone 5 is inclined by an angle α with respect to the plane direction of the glass substrate 1 so that the trajectory of the grindstone 5 contacting the end surface of the glass substrate 1 is not constant. The outer peripheral side end face of 1 and the inner peripheral side of the grindstone 5 are processed while being in contact with each other. Accordingly, if the brush polishing is performed so that the processing trajectory by the first processing step and the processing trajectory by the second brush polishing processing do not overlap, the first processing step is performed in the second brush polishing processing step. It is possible to remove the machining trajectory (grinding marks, etc.) generated in, and perform mirror finishing with a small machining allowance while maintaining the shape accuracy of the end face obtained in the first machining step. In end face processing of a substrate, it is possible to achieve both surface quality and processing accuracy.

In the present invention, the glass substrate on which both the side wall surface of the end surface of the glass substrate and the chamfered surface between the main surface and the side wall surface of the glass substrate are formed is the first substrate. It is a more preferred embodiment to perform the processing step. In this case, the processing load in the first processing step can be reduced, and it becomes possible to set processing conditions that place more emphasis on end face quality. The method for obtaining the glass substrate on which both the side wall surface of the end surface of the glass substrate and the chamfered surface between the main surface and the side wall surface of the glass substrate are formed is not particularly limited. Grinding using a so-called general-purpose grindstone that is advantageous in terms of efficiency is preferable.

In the end face processing in the present invention, it is preferable that the ratio of the machining allowance in the first processing step and the second processing step is 4: 1 to 10: 1. By setting it as the above range, it is preferable because the end face quality is further improved as compared with the conventional one and the accuracy of the end face shape is further improved.

The glass type used for the glass substrate for the magnetic disk is not particularly limited. Examples of the glass substrate material include aluminosilicate glass, soda lime glass, soda aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, and quartz glass. And glass ceramics such as chain silicate glass or crystallized glass. Of these, aluminosilicate glass is particularly preferable because it is excellent in impact resistance and vibration resistance.
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, etc. of the main surface, as shown in FIG. Such a magnetic disk glass substrate 1 is obtained.

The present invention also provides a magnetic disk manufacturing method in which at least a magnetic layer is formed on the main surface of the magnetic disk glass substrate manufactured by the above-described method for manufacturing a magnetic disk glass substrate according to the present invention.
That is, for example, a magnetic disk can be obtained by forming at least a magnetic layer on a glass substrate for a magnetic disk obtained by the above-described embodiment of the present invention. Usually, for example, 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 is preferable.

For example, the magnetic layer may be, for example, an alloy having a Co-based hcp crystal structure for a perpendicular magnetic recording medium.
Moreover, as a protective layer, a carbon-type protective layer etc. are mentioned preferably, for example. Examples of the lubricant that forms the lubricating layer on the protective layer include PFPE (perfluoropolyether) compounds.
As a method for forming each of the layers on the glass substrate, a known sputtering method or the like can be used. A plasma CVD method is also preferably used for forming the carbon-based protective layer. A dipping method or the like can be used for forming the lubricating layer.

By producing a magnetic disk using the glass substrate for magnetic disk produced by the method for producing a glass substrate for magnetic disk according to the present invention, the end face of the substrate can be finished with high quality, and the surface state and shape of the substrate end face It is possible to provide a magnetic disk capable of preventing occurrence of a failure due to accuracy and realizing further higher recording density.

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
First, a glass substrate (glass disk) made of disk-shaped aluminosilicate glass having a diameter of 66 mmφ and a thickness of 1.0 mm was obtained from molten glass by direct pressing using an upper mold, a lower mold, and a body mold.

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 apparatus.

Next, a hole was made in the central portion of the glass substrate using a cylindrical grindstone, and the first processing step and the second processing step described above were performed to grind and polish the outer peripheral end surface of the substrate.
In the first processing step, a resin grindstone was used. The first processing step was performed by the positional relationship between the glass substrate and the grindstone shown in FIG. In the first processing step, the inclination angle α of the grindstone with respect to the glass substrate was set to 15 degrees. Moreover, the peripheral speed and rotation direction of each of the glass substrate and the grindstone were set as appropriate.
Further, in the second brush polishing process, a rotating brush in which brush bristles are provided around the rotating shaft so as to be inclined with respect to the rotating shaft was used. At this time, polishing was performed such that the rotation axis of the rotating brush and the axis orthogonal to the main surface of the glass substrate were parallel to each other. Moreover, it grind | polished using the rotating brush from which the inclination angle in the rotating shaft of a bristle and the inclination angle of the grindstone with respect to the glass substrate in the said 1st processing process differ mutually. Further, the peripheral speed and the rotation direction of each of the glass substrate and the polishing brush were appropriately set.

As described above, end face processing of 100 glass substrates was performed.
In order to confirm the shape accuracy of the side wall surface and the chamfered surface of the obtained 100 glass substrates, the curvature radius of the corner A (see FIG. 5) formed by the side wall surface and the chamfered surface is measured with a fine contour shape. Table 1 shows the results of average values and variations (standard deviation) of 100 substrates. Further, the surface roughness Rz of the chamfered surface was calculated based on the measured value by the roughness measuring machine, and the result is also shown in Table 1.

Moreover, as a reference example (reference example 1), instead of the first processing step of the present invention, after grinding using a conventional general-purpose grindstone, finish processing is performed by brush polishing in the same manner as described above. The end surface processing of the glass substrate of 1 sheet was performed. The method and conditions for machining the overall grinding wheel were appropriately set with reference to the conditions of known examples.
Moreover, as another reference example (reference example 2), only the first processing step similar to the above was performed, and end face processing of 100 glass substrates was performed. However, processing was performed in two stages by changing the type (hardness) of the grindstone used.

As is apparent from the results in Table 1 above, according to the end face processing method of the present invention, the variation between the substrates regarding the radius of curvature of the corner portion formed by the side wall surface and the chamfered surface is small, and the chamfered surface is finished to be a mirror surface. Both surface quality and shape accuracy are good.
On the other hand, according to the end face processing method of Reference Example 1 that combines conventional grinding wheel processing and brush polishing processing, the chamfered surface is a mirror surface because processing is performed with emphasis on the surface quality after processing. Although finished in a state, the machining allowance by brush polishing was large, and the shape accuracy deteriorated.
Moreover, according to the end surface processing method of Reference Example 2 in which the grindstone is tilted with respect to the substrate, the chamfered surface is finished in a mirror surface state when processing is performed with emphasis on the surface quality after processing. Shape accuracy was not obtained.

(Example 2)
In the above-described end face machining method according to the present invention, a glass substrate is obtained in the same manner as in Example 1 except that the machining allowance ratio in the first machining process and the second machining process is changed as shown in Table 2 below. Was made.
Dust generation from the end surface of the obtained glass substrate was evaluated by the following method, and judged according to the following criteria.
The glass substrate was immersed in water, and an ultrasonic wave (200 kHz) was added and shaken for 1 minute. After the processing, the number of dust generation is counted using LPC, and when the machining allowance ratio (first processing step: second processing step) is 6: 1 (Example 5) is set to 1, in other examples The number of dust generation was evaluated.
Moreover, Example 3 was set to 1 for the standard deviation indicating the variation in the radius of curvature of the end face shape of the glass substrate after the second processing step, that is, the corner portion A (see FIG. 5) formed by the side wall surface and the chamfered surface. When the standard deviation in other examples was evaluated. In addition, as this value, when smaller than 1, it has shown that it is improving compared with Example 3, and when larger than 1, it has deteriorated.
The results of the determination are shown in Table 2.

As is clear from the results of Table 2 above, it can be seen that the dust generation from the end surface improves as the polishing allowance increases, but on the other hand, the deterioration in shape accuracy due to variation in curvature becomes more prominent as the polishing allowance increases. It can be seen that the ratio of the polishing allowance needs to be selected appropriately. That is, it can be seen that the machining allowance ratio in the first machining step and the second machining step is preferably in the range of 4: 1 to 10: 1.

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 for magnetic disks 2, 5 Outer peripheral side end grinding wheel 3 Inner peripheral side end grinding wheel 6 Groove 1a Main surface 1b of glass substrate Side wall surface 1c Chamfer

Claims (6)

Grinding liquid is supplied to the end surface portion of the disk-shaped glass substrate having a circular hole in the center, and a grindstone is placed on the side wall surface that is the end surface of the glass substrate, the main surface of the glass substrate, and the chamfered surface that interposes the side wall surface. A method for producing a glass substrate for a magnetic disk, comprising an end face processing for processing an end face of the glass substrate by grinding by contact,
The end face processing is
The rotating grindstone is brought into contact with the end surface of the glass substrate in a state where the rotation axis of the rotating grindstone is inclined with respect to an axis orthogonal to the main surface of the glass substrate, and the side wall surface and the chamfered surface of the glass substrate are simultaneously brought into contact with each other. A first machining step for grinding;
A second processing step that is performed after the first processing step and polishes the side wall surface and the chamfered surface of the glass substrate processed by the first processing step by bringing a brush having a rotating shaft into contact therewith; The manufacturing method of the glass substrate for magnetic discs characterized by the above-mentioned.   2. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein a processing locus by the first processing step and a processing locus by the second processing step do not overlap with each other on an end surface of the glass substrate. .   The angle between the axis orthogonal to the main surface of the glass substrate and the rotation axis of the rotating grindstone in the first processing step is in the range of 2 degrees to 30 degrees. The manufacturing method of the glass substrate for magnetic discs as described in any one of.   In the second processing step, using a brush in which the flocking angle of the brush bristles is inclined with respect to the rotation axis of the brush, the axis orthogonal to the main surface of the glass substrate and the rotation axis of the brush are parallel to each other. The angle between the flocking angle of the brush and the main surface of the glass substrate and the rotating surface of the rotating grindstone in the first processing step is different from each other. Item 4. A method for producing a magnetic disk glass substrate according to any one of Items 1 to 3.   The first processing step is performed on the glass substrate on which both the side wall surface of the end surface of the glass substrate and the chamfered surface between the main surface and the side wall surface of the glass substrate are formed. A method for producing a glass substrate for a magnetic disk according to any one of claims 1 to 4. 6. 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