JP2014216043A - Manufacturing method of magnetic disk glass substrate, and manufacturing method of magnetic disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a magnetic disk glass substrate composed of a crystallized glass having small strength variations between substrates.SOLUTION: The manufacturing method of a magnetic disk glass substrate includes: end face shape processing of performing a step of fabricating a disk-shaped amorphous glass substrate having a hole in the centre, and shape processing including chamfering an end face of the fabricated amorphous glass substrate; and end face polishing processing that is performed after the end face shape processing and polishes the end face. Crystallization processing of crystallizing the amorphous glass substrate is performed at least after the end face shape processing.

Description

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

One of information recording media mounted on a magnetic recording device such as an HDD is a magnetic disk. A magnetic disk is configured by forming a thin film such as a magnetic layer on a substrate, and an aluminum substrate has been conventionally used as the substrate. However, recently, in response to the pursuit of higher recording density, the ratio of the glass substrate capable of narrowing the distance between the magnetic head and the magnetic disk as compared with the aluminum substrate is gradually increasing. Further, the surface of the glass substrate is polished with high accuracy so as to increase the recording density so that the flying height of the magnetic head can be reduced as much as possible. In recent years, demands for further increase in recording capacity of HDDs are increasing, and in order to realize this, it is necessary to further improve the quality of glass substrates for magnetic disks.

Examples of the material of such a glass substrate include aluminosilicate glass, soda lime glass, aluminoporosilicate glass, or glass ceramic such as crystallized glass.
Patent Document 1 discloses a method for producing a glass substrate for an information recording medium including forming a disk-shaped glass material from molten glass, and the glass material is further heat-treated to obtain crystallized glass. It is described that it can be.

JP 2008-169061 A

  For example, a disk-shaped glass material is obtained by press-molding molten glass, a hole is made in the center of the disk-shaped glass material, and then inner and outer peripheral end faces, main surface polishing, etc. are performed to obtain a magnetic disk Although the glass substrate for manufacture is manufactured, the said patent document 1 describes that crystallization of a glass raw material can be performed either before or after perforating for obtaining a disk.

  However, according to the study of the present inventor, as described in Patent Document 1, the glass material is crystallized either before or after drilling, and then the inner and outer peripheral end faces such as chamfering are processed. When the glass substrate for a magnetic disk was manufactured by polishing the main surface, etc., there was a problem that the variation in strength between the obtained glass substrates for the magnetic disk was large.

The present invention has been made to solve such a conventional problem, and an object of the present invention is to provide a method for manufacturing a glass substrate for a magnetic disk made of crystallized glass, which can reduce variation in strength of the substrate. is there.

The inventor has analyzed the reason why the variation in strength of the glass substrate manufactured according to the manufacturing method disclosed in Patent Document 1 is large. As a result, if the glass material is crystallized and then machined such as chamfering of the end face, latent (internal) cracks formed during the chamfering process remain, and finally the cracks cannot be removed sufficiently. I found that there is a possibility.

In addition, the present inventor has conducted further investigation focusing on the timing of crystallization in order to obtain a glass substrate made of crystallized glass with small strength variation. It has been found that there is a difference in the intensity variation of the finally obtained glass substrate depending on which stage of crystallization is performed.
Therefore, the present inventor has found that the above problems can be solved according to the invention having the following configuration based on the obtained knowledge, and has completed the present invention.

That is, this invention has the following structures in order to achieve the said subject.
(Configuration 1)
End surface shape processing for forming a side wall surface and a chamfering surface interposed between the main surface and the side wall surface by machining an end surface of a disk-shaped amorphous glass substrate having a circular hole in the center; and the end surface An end surface polishing process that is performed after the shape processing and mirrors the side wall surface and the chamfered surface, and a crystallization process for crystallizing the glass constituting the glass substrate is performed after the end surface polishing process. A method for producing a glass substrate for a magnetic disk.

(Configuration 2)
The crystallization treatment is performed after the end surface polishing step in which the maximum valley depth Rv of at least one of the side wall surface and the chamfered surface of the glass substrate on which the crystallization treatment is performed is 0.3 μm or less. 2. A method for producing a glass substrate for a magnetic disk according to 1.
(Configuration 3)
Correspondence between angle (A) formed by main surface and chamfered surface before crystallization treatment and angle (B) formed by main surface and chamfered surface after crystallization treatment The magnetic field according to Configuration 1 or 2, wherein a relationship is obtained in advance, and end face shape processing and end face polishing processing are performed based on the correspondence relationship so that the angle (B) has a desired value. A method for producing a glass substrate for a disk.

(Configuration 4)
The correspondence between the diameter of the circular hole before the crystallization treatment and the diameter of the circular hole after the crystallization treatment is obtained in advance, and the diameter of the circular hole after crystallization is determined based on the correspondence. 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 shape processing is performed so as to obtain a desired value.

(Configuration 5)
A magnetic disk manufacturing method comprising forming at least a magnetic layer on a glass substrate for a magnetic disk obtained by the manufacturing method according to any one of Structures 1 to 4.

By adopting the configuration of the present invention, it is possible to manufacture a glass substrate for a magnetic disk made of crystallized glass with small variations in substrate strength (for example, bending strength) between substrates.

Hereinafter, embodiments of the present invention will be described in detail.
The present invention is a method for producing a crystallized glass for a magnetic disk, which is usually produced through a grinding step, end face shape processing, end face polishing treatment, main surface polishing step, chemical strengthening step, etc., and at least end face polishing treatment. Later, a crystallization process for crystallizing the glass is performed. In addition, processes other than the end face shape processing and the end face polishing process are examples, and are not limited to the order described here, and the process itself may not be performed.
Among these processes, the end face shape processing and the end face polishing process are processes performed on the end face (side wall face and chamfered face) of the substrate, and the grinding step and the main surface polishing step are performed on the main surface of the substrate. It is a process applied to.
Here, crystallized glass is also called glass ceramics, and is a material formed by precipitating crystals in the glass by heating the glass. That is, the glass has both a crystallized part and an amorphous part.
In the present invention, the magnetic disk glass substrate means one that has been subjected to a crystallization treatment described later. Specifically, for example, the glass substrate for a magnetic disk according to the present invention may be one immediately after the crystallization treatment is performed, or a main surface polishing process performed after the crystallization treatment, It may be in a state before post-processing such as chemical strengthening processing and before the magnetic film or the like is formed.

Here, the outline of the manufacturing method of the glass substrate for magnetic disks is demonstrated.
As a method of producing a disk-shaped amorphous glass substrate having a circular hole in the center, for example, there is a method of forming a circular hole after molding a disk-shaped glass blank disk from molten glass by direct pressing. Specifically, a disk-shaped amorphous glass having a circular hole in the center by opening a circular hole of a predetermined size in the center of a molded disk-shaped glass disk blank by using, for example, a core drill or the like. A substrate is produced. In addition to such a direct press, a disc-shaped amorphous glass substrate having a circular hole in the center can be produced by cutting out to a predetermined size from a plate glass produced by a downdraw method or a float method. .

Next, a grinding process for improving dimensional accuracy and shape accuracy is performed on the main surface of the glass substrate manufactured as described above. In this grinding process, a main surface of the glass substrate is usually ground using a double-sided lapping machine and using abrasive grains such as diamond and alumina. By grinding the main surface of the glass substrate in this way, it can be processed to a predetermined plate thickness and flatness. The grinding step may be omitted depending on the thickness and flatness of the glass substrate used.

After the grinding step, end face shape processing is performed. In this end face shape processing, the end surface of the glass substrate is machined to form a side wall surface, a main surface of the glass substrate, and a chamfered surface interposed between the side wall surfaces. This end face shape processing can be performed by machining using a rotating grindstone having a groove shape. This rotating grindstone has a side wall surface (a surface substantially orthogonal to the main surface of the substrate) and a chamfered surface (a chamfered surface formed between the side wall surface and the main surface of the front and back surfaces) on the inner and outer peripheral end surfaces of the glass substrate. It has a groove shape capable of transferring the shape of both surfaces. In other words, in the end face shape processing, the groove shape of the rotating grindstone is transferred so that the angle formed by the main surface and the chamfered surface and the angle formed by the chamfered surface and the side wall surface become a desired shape. Can be processed.

After the above end face shape processing, an end face polishing process is performed to mirror the side wall face and the chamfered face, which are the end faces of the glass substrate. This end surface polishing treatment is performed, for example, by brush polishing, but in addition to brush polishing, end surface polishing can also be performed using a grindstone having a small abrasive grain size or a polishing pad. By this end surface polishing treatment, the end surface of the substrate is finished to a predetermined mirror surface state. At this time, the maximum valley depth (Rv) of at least one of the chamfered surface and the side wall surface formed by the end surface polishing treatment is preferably 0.3 μm or less, more preferably 0.2 μm or less. The arithmetic average roughness (Ra) of at least one of the chamfered surface and the side wall surface is preferably 0.02 μm or less, more preferably 0.015 μm or less. Moreover, it is more preferable that both the chamfered surface and the side wall surface are within the range of the maximum valley depth and the arithmetic average roughness (Ra).

By the way, in the present invention, since a crystallized glass obtained by crystallizing amorphous glass is used as a glass substrate for a magnetic disk, a crystallization process for crystallizing amorphous glass is performed.

The manufacturing method of the glass substrate for magnetic disks of this invention is the structure which performs the crystallization process which crystallizes the glass which comprises the amorphous glass substrate after an end surface grinding | polishing process.

According to the study of the present inventor, as described in the prior art (Patent Document 1), a circular hole having a predetermined size is formed in the center of a disk-shaped glass blank formed by direct press from molten glass. In the glass substrate obtained by crystallization of the glass material either before or after the process, and then through inner and outer end face shape processing such as chamfering, main surface polishing, etc. Depending on the processing conditions, it has been found that there is a glass substrate with a large variation in strength (for example, bending strength).

Therefore, as a result of analyzing the point where the strength variation is large, the present inventor has found that the latent material formed during the chamfering process depends on the processing conditions when the glass material is crystallized and then machined such as chamfering of the end face. It was found that (internal) cracks remained, and finally the cracks could not be sufficiently removed, and that the strength variation might increase due to the cracks.

And based on this knowledge, this inventor discovered that the dispersion | variation in intensity | strength could be reduced by removing the crack which arises in an end surface before performing a crystallization process.

When the crystallization treatment is performed before the end face shape processing as in the above prior art, the chamfering process is performed after the glass is crystallized, so that the chamfering process such as the chamfering of the end face is performed. The latent (internal) cracks deeply enter during processing, and even after polishing the end face, cracks formed on the end face during chamfering processing cannot be fully removed and remain inside, resulting in reduced strength variation. It is thought to produce.

In contrast, in the present invention, the amorphous glass substrate is subjected to an end surface polishing treatment, and then a crystallization treatment is performed. After the end surface shape processing, which is a machining process, is performed, the glass is crystallized. Therefore, it is not affected by crystallization during the end face shape processing. And the crack formed in the end face at the time of end face shape processing can be sufficiently removed by the end face polishing treatment for the subsequent amorphous glass substrate, and finally the depth of the crack remaining inside is conventionally reduced. It can be reduced compared to technology. For this reason, it is possible to suppress variations in strength.

Moreover, this invention is easy to improve the surface roughness of the end surface of a glass substrate compared with a prior art by performing crystallization after an end surface grinding | polishing process. This will be described below. By performing the crystallization of the glass, the glass has both a crystallized part and a non-crystallized or amorphous part. As a result, the crystallized portion has a higher density than the amorphous portion. When this crystallized glass is polished, the amorphous part is more easily processed than the crystallized part. That is, when crystallized glass is polished, the crystallized portion is difficult to be polished, while the amorphous portion is easily polished. Therefore, it is difficult to reduce the surface roughness after polishing.
However, in the present invention, when the end surface of the glass substrate is mirror-polished in an amorphous glass state to achieve the required surface roughness as a glass substrate for a magnetic disk, polishing is not performed after crystallization. Also good. In addition, since the end surface polishing process is performed on the amorphous glass substrate, the end surface of the glass substrate can be easily mirror-finished as compared with the conventional configuration in which the end surface polishing process is performed after crystallization.
In the present invention, end face polishing may be performed before the crystallization treatment, and further end face polishing may be performed after the crystallization treatment. However, even in this case, the machining allowance in the end surface polishing after the crystallization treatment can be reduced.

Since the volume of the glass substrate is reduced by performing the crystallization treatment, the shape of the glass substrate is different before and after the crystallization treatment. In particular, since the glass substrate for magnetic disk in the present invention has a very large diameter (high aspect ratio) compared to the plate thickness, the shape change due to the crystallization treatment differs between the plate thickness direction and the main surface direction. It will be. Therefore, it is preferable to set the processing conditions for the end face shape processing and / or the end face polishing processing before the crystallization processing in consideration of the influence of the shape change that changes due to the crystallization processing.
Specifically, regarding the shape of the end face, the angle (A) formed by the main surface and the chamfered surface before the crystallization treatment, and the main surface and the chamfered surface after the crystallization treatment are performed. Is obtained in advance, and the end face shape processing and the end face polishing treatment are performed so that the angle of the angle (B) becomes a desired value based on the correspondence relation. More preferred. Thereby, the end surface shape of the glass substrate after passing through a crystallization process can be made into the end surface shape requested | required as a glass substrate for magnetic discs.
This will be described in detail. As a manufacturing process in which the shape of the chamfered surface and the side wall surface is determined, the end surface shape processing and the end surface polishing treatment are particularly affected. Then, by changing these processing conditions to create a plurality of glass substrates in which the angle between the main surface and the chamfered surface is made different in advance, after crystallizing these glass substrates, before crystallization In the same manner as described above, the angle between the main surface and the chamfered surface is obtained, and the correspondence relationship between the angles before and after the crystallization treatment is obtained. And, based on the obtained correspondence, select the processing condition that the angle formed by the main surface and the chamfered surface obtained after the crystallization process is an angle required for the glass substrate for magnetic disk, What is necessary is just to perform the said end surface shape process and an end surface grinding | polishing process. Further, in the above description, it has been described that the correspondence relationship between the angles formed by the main surface and the chamfered surface is obtained. However, the present invention is not limited to the above. The correspondence between the length of the wall surface and / or the angle between the chamfered surface and the side wall surface is obtained before and after the crystallization process, and the end face shape after the crystallization process (the chamfered surface and the side wall surface). The end face shape processing and the end face polishing process performed before the crystallization process may be performed so that the shape of the glass substrate for the magnetic disk becomes a shape required for the magnetic disk.
Further, the size of the circular hole is the same as described above. For example, the correspondence between the diameter of the circular hole before the crystallization treatment and the diameter of the circular hole after the crystallization treatment is obtained in advance. In addition, it is more preferable to perform the end face shape processing and the end face polishing treatment so that the diameter of the circular hole after crystallization becomes a desired value based on the above correspondence. Thereby, the diameter of the circular hole after a crystallization process can be made into the diameter requested | required as a glass substrate for magnetic discs.

In the present invention, the bending strength of the glass substrate after the crystallization treatment is preferably 7 kgf or more, and particularly preferably 8 kgf or more from the viewpoint of improving impact resistance.

Next, the crystallization process will be described. In the crystallization treatment, for example, crystal nuclei are generated inside the glass by heat-treating the glass. Note that large crystal grains may be obtained by growing crystal nuclei. What is necessary is just to set suitably the conditions of the heat processing in a crystallization process according to the crystallinity degree of the crystallized glass obtained.
The size of the crystal grains generated by the crystallization treatment is preferably 10 nm or less, and more preferably 5 nm or less. By making the crystal grains in the above range, it is preferable because the surface roughness required for a glass substrate for a magnetic disk, which is the final product described later, can be easily formed.
The Young's modulus of the magnetic disk glass substrate according to the present invention is preferably 100 GPa or more, more preferably 120 GPa or more. In order to increase the Young's modulus to 100 GPa or more, it is conceivable to increase the degree of crystallinity. In such a case, however, the degree of surface roughness due to etching becomes larger than that of crystallized glass having a low degree of crystallinity. Therefore, the present invention is applied to manufacture a glass substrate for a magnetic disk having a Young's modulus of 100 GPa or more and a maximum valley depth (Rv) of a side wall surface and a chamfered surface of 0.3 μm or less. Is more preferable.

The crystallized glass has a lower Young's modulus than the glass before crystallization, so the processing rate is low, but as in the present invention, the glass is crystallized after end-face polishing, thereby processing the glass. Since processing can be performed on amorphous glass having a high rate, the time required for processing can be shortened.

After passing through the crystallization treatment, a main surface mirror polishing process for obtaining a highly accurate main surface is performed. As a mirror polishing method for the main surface of the glass substrate, it is preferable to use a polishing pad such as foamed polyurethane while supplying a slurry (polishing liquid) containing a metal oxide abrasive such as cerium oxide or colloidal silica. It is. Although the polishing method is not particularly limited, for example, the glass substrate and the polishing pad are brought into contact with each other, and the polishing pad and the glass substrate are relatively moved while supplying the polishing liquid containing the abrasive grains. The surface of the glass substrate may be polished in a mirror shape.

In the present invention, the glass (the glass type) constituting the glass substrate is preferably an aluminosilicate glass containing SiO2 as a main component and further containing alumina. A glass substrate using such glass can be finished to a smooth mirror surface by mirror polishing the surface, and the strength after processing is good. Further, the strength can be further increased by chemical strengthening.

In the present invention, the main surface of the glass substrate after the mirror polishing is preferably a mirror surface having an arithmetic average surface roughness Ra of 0.20 nm or less, particularly 0.15 nm or less. Furthermore, it is preferable that the mirror surface has a maximum roughness Rmax of 2.0 nm or less. In the present invention, Ra and Rmax are roughnesses calculated in accordance with Japanese Industrial Standard (JIS) B0601.
Further, in the present invention, the surface roughness (for example, the maximum roughness Rmax, the arithmetic average roughness Ra) is measured with a resolution of 256 × 256 pixels in a range of 1 μm × 1 μm using an atomic force microscope (AFM). Is the value obtained.

In the present invention, the maximum valley depth (Rz) of the end surface (at least one of the chamfered surface and the side wall surface) of the finally obtained magnetic disk glass substrate is 0.3 μm or less, more preferably 0.2 μm. The following is preferable. The arithmetic average roughness (Ra) is preferably 0.02 μm or less, more preferably 0.015 μm or less. In addition, what is necessary is just to measure the surface roughness of an end surface, for example using a laser microscope.

In the present invention, chemical strengthening treatment may be performed after the crystallization treatment and before or after the mirror polishing process of the main surface. As a method of the chemical strengthening treatment, for example, a low-temperature ion exchange method in which ion exchange is performed in a temperature range not exceeding the glass transition temperature is preferable. The chemical strengthening treatment is a process in which a molten chemical strengthening salt is brought into contact with a glass substrate, whereby an alkali metal element having a relatively large atomic radius in the chemical strengthening salt and a relatively small atomic radius in the glass substrate. This is a treatment in which an alkali metal element is ion-exchanged, an alkali metal element having a large ion radius is permeated into the surface layer of the glass substrate, and compressive stress is generated on the surface of the glass substrate. Since the chemically strengthened glass substrate is excellent in impact resistance, it is particularly preferable for mounting on a HDD for mobile use, for example.

The present invention also provides a method for producing a magnetic disk using the above glass substrate for a magnetic disk. The magnetic disk is manufactured by forming at least a magnetic layer on the magnetic disk glass substrate according to the present invention. As a material for the magnetic layer, a hexagonal CoCrPt-based or CoPt-based ferromagnetic alloy having a large anisotropic magnetic field can be used. As a method of forming the magnetic layer, it is preferable to use a method of forming a magnetic layer on a glass substrate by a sputtering method, for example, a DC magnetron sputtering method. Further, by interposing an underlayer between the glass substrate and the magnetic layer, the orientation direction of the magnetic grains of the magnetic layer and the size of the magnetic grains can be controlled. For example, by using a hexagonal underlayer containing Ru or Ti, for example, the easy magnetization direction of the magnetic layer can be oriented along the normal of the magnetic disk surface. In this case, a perpendicular magnetic recording type magnetic disk is manufactured. The underlayer can be formed by sputtering as with the magnetic layer.

In addition, a protective layer and a lubricating layer may be formed in this order on the magnetic layer. As the protective layer, an amorphous hydrogenated carbon-based protective layer is suitable. For example, the protective layer can be formed by a plasma CVD method. Further, as the lubricating layer, a lubricant having a functional group at the end of the main chain of the perfluoropolyether compound can be used. In particular, it is preferable that the main component is a perfluoropolyether compound having a terminal hydroxyl group as a polar functional group. The lubricating layer can be applied and formed by a dip method.
By using the glass substrate obtained by the present invention, a highly reliable magnetic disk can be obtained.
Furthermore, the glass substrate for magnetic disk made of crystallized glass obtained by the present invention is preferably used for an energy-assisted magnetic recording type magnetic disk. By having crystal grains in glass, it is preferable because it is difficult to be deformed even in a high-temperature environment necessary for manufacturing an energy-assisted magnetic recording type magnetic disk.

Hereinafter, embodiments of the present invention will be specifically described with reference to examples. In addition, this invention is not limited to a following example.
(Example 1, Comparative Examples 1, 2, and 3)
The following (1) glass blank preparation process, (2) grinding process, (3) pilot hole process, (4) end face shape processing, (5) end face polishing process, (6) main surface polishing process (first polishing process) (7) A glass substrate for a magnetic disk was manufactured through a chemical strengthening step and (8) a main surface polishing step (second polishing step). In addition to these steps, a crystallization treatment described later was performed.

(1) Glass blank production process First, a glass disk blank made of disc-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 trunk mold. .

(2) Grinding step Next, a grinding step was performed on the glass substrate in order to improve dimensional accuracy and shape accuracy. This grinding process was performed using a double-side grinding apparatus.
(3) Pilot hole process Next, using a cylindrical grindstone core drill, a hole was made in the center part of the glass disk blank (drilling process), and a disk-shaped amorphous glass substrate having a circular hole in the center was produced. .
(4) End face shape processing Next, predetermined chamfering was given to the outer peripheral end face and the inner peripheral end face using a cylindrical grindstone.

(5) End face polishing treatment Next, the end face (inner periphery, outer periphery) of the glass substrate was polished by brush polishing while rotating the glass substrate. And the surface of the glass substrate which finished the said end surface grinding | polishing was wash | cleaned.

(6) Main surface polishing step (first polishing step)
Next, the first polishing process was performed using a planetary gear type double-side polishing apparatus. In a double-side polishing machine, a glass substrate held by a carrier is closely attached between an upper and lower polishing surface plate to which a polishing pad is attached, and this carrier is engaged with a sun gear (sun gear) and an internal gear (internal gear). The glass substrate is sandwiched between upper and lower surface plates. 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 hard polisher was used as the polisher, and the first polishing process was performed. As the polishing liquid, cerium oxide was dispersed as an abrasive. The glass substrate after the first polishing step was washed and dried.

(7) Chemical strengthening step Next, chemical strengthening was performed on the glass substrate after the cleaning. The chemical strengthening was performed using a known method.

(8) Main surface polishing step (second polishing step)
Next, using the same double-side polishing apparatus as that used in the first polishing step, the second polishing step was performed by replacing the polisher with a polishing pad of a soft polisher. Colloidal silica was used as the abrasive grains. The glass substrate for the magnetic disk was obtained by washing and drying the glass substrate after the second polishing step. The main surface roughness (Ra) of the magnetic disk glass substrate according to Example 2 described later was 0.15 nm.

Then, as an example, a glass substrate for a magnetic disk was prepared in which a crystallization process was performed between the (5) end surface polishing process and the (6) main surface polishing process. Moreover, as a comparative example, a glass blank molded by direct press is subjected to crystallization treatment, and then subjected to drilling, end face shape processing, etc., to Comparative Example 1 and glass blank. Comparative Example 2 (4) End face shape processing and (5) End face polishing treatment were performed after producing a disk-shaped glass substrate having a circular hole in the center, followed by crystallization treatment, followed by end face shape processing. A glass substrate for a magnetic disk was prepared as Comparative Example 3 in which crystallization treatment was performed in between. The crystallization treatment was performed by setting the heat treatment conditions for the glass substrate so that the average crystal grain size of the crystal grains was 10 nm or less. Here, the “average crystal grain size” is the average value of the longest distance when crystals appearing in an image obtained using a TEM (transmission electron microscope) are sandwiched between two parallel straight lines.

In each of Examples and Comparative Examples 1, 2, and 3, 100 magnetic disk glass substrates were prepared, and the bending strength was determined using a bending strength tester. And when the difference between the maximum value and the minimum value of the bending strength measured from the glass substrate for magnetic disk of Comparative Example 1 is 100%, the maximum value of the bending strength in Example 1 and Comparative Examples 2 and 3 It was evaluated how much the difference between each and the minimum value corresponds to. As a result, Example was 55%, Comparative Example 2 was 95%, and Comparative Example 3 was 84%.
That is, it can be seen that the variation in bending strength is smaller in the example than in Comparative Examples 1, 2, and 3. In other words, it is understood that the variation in the bending strength can be reduced by performing the crystallization process after removing the cracks formed by the end face shape processing. In addition, about the said Example and Comparative Examples 1, 2, and 3, the glass substrate for magnetic discs produced without performing a (7) chemical strengthening process was created, and the variation in bending strength was investigated, but it is the same as the above Showed the trend. By applying a chemical strengthening treatment to the glass substrate, the magnitude of the variation in bending strength can be reduced compared to a glass substrate not subjected to the chemical strengthening treatment, but the end surface polishing treatment is performed before the crystallization treatment. In the embodiment in which the end face of the glass substrate was mirror-finished, the variation could be particularly reduced.
Next, in Example and Comparative Example 3, the maximum valley depth (Rv) of the chamfered surface was compared. In the example and the comparative example 3, the processing conditions and machining allowances in (4) end face shape processing and (5) end face polishing processing are the same. As a result, the Rv of Example was 0.27 μm, while the Rv of Comparative Example 3 was 0.43 μm. That is, it can be seen that the end surface roughness can be lowered by performing the crystallization process after the end surface polishing process.

(Manufacture of magnetic disk)
The following film forming steps were performed on the magnetic disk glass substrate 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.

Claims (5)

End face shape processing that forms a side wall surface and a chamfered surface interposed between the main surface and the side wall surface by machining an end surface of a disk-shaped amorphous glass substrate having a circular hole in the center;
It is performed after the end surface shape processing, and includes an end surface polishing treatment for mirror polishing the side wall surface and the chamfered surface,
A method for producing a glass substrate for a magnetic disk, comprising performing a crystallization process for crystallizing the glass constituting the glass substrate after the end face polishing process.   2. The method for producing a glass substrate for a magnetic disk according to claim 1, wherein the maximum valley depth Rv of at least one of the side wall surface and the chamfered surface of the glass substrate before crystallization treatment is 0.3 [mu] m or less. .   Correspondence between angle (A) formed by main surface and chamfered surface before crystallization treatment and angle (B) formed by main surface and chamfered surface after crystallization treatment The end surface shape processing and the end surface polishing processing are performed so that the relationship is obtained in advance and the angle (B) becomes a desired value based on the correspondence relationship. Manufacturing method of glass substrate for magnetic disk.   The correspondence between the diameter of the circular hole before the crystallization treatment and the diameter of the circular hole after the crystallization treatment is obtained in advance, and the diameter of the circular hole after crystallization is determined based on the correspondence. 4. The method for manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the end surface shape processing is performed so as to obtain a desired value. 5. A method for manufacturing a magnetic disk, comprising forming at least a magnetic layer on a glass substrate for a magnetic disk obtained by the manufacturing method according to claim 1.