JP5306758B2 - Manufacturing method of glass substrate for magnetic disk and manufacturing method of magnetic disk - Google Patents

Description

  The present invention relates to a method for manufacturing a magnetic disk mounted on a magnetic disk device such as an HDD (hard disk drive), and a method for manufacturing a glass substrate for a magnetic disk.

Today, information recording technology, particularly magnetic recording technology, is required to undergo dramatic technological innovation with the rapid development of IT industry. For magnetic disks mounted on HDDs and the like, a technology capable of realizing an information recording density of 40 Gbit / inch ² (1 inch is 25.4 mm) or more is required due to a demand for higher capacity.
Recently, a glass substrate has attracted attention as a magnetic disk substrate suitable for increasing the recording density. Since the glass substrate has higher rigidity than the metal substrate, it is suitable for high-speed rotation of the magnetic disk device, and since a smooth and flat surface is obtained, it is easy to reduce the flying height of the magnetic head. It is suitable for improving the S / N ratio of the recording signal and increasing the recording density.

  Usually, a glass substrate for a magnetic disk is manufactured by grinding and polishing the surface of a glass disk formed in a predetermined size. Here, as a method of forming a glass disk having a predetermined size, for example, there is a method of cutting a glass disk from a sheet glass formed into a plate shape by a float process. The following Patent Document 1 describes a glass substrate for a disk obtained by forming a cut line on a glass plate using a cutter and separating it from the glass plate.

JP-A-7-223828

  However, if a glass disk is cut out by heating after forming a cut line perpendicular to the main surface of the plate glass, the glass disk cannot be separated from the plate glass or the end face of the cut glass disk In many cases, chipping, scratches, cracks, etc. are generated, resulting in defective products, and the yield is low. Therefore, Patent Document 1 describes a method of cutting a glass disk by forming a cut line obliquely with respect to the main surface of the sheet glass and then heating it.

  However, it is difficult to completely prevent the occurrence of chipping, scratches, cracks, etc. on the cut end surface of the glass disk by the method of cutting the glass disk by forming a cut line obliquely with respect to the main surface of the plate glass. is there. In addition, since the end face is cut obliquely, the end face using a polishing brush for removing the chamfered surface by the rotating grindstone, the chamfering process of the side wall surface, the surface roughness due to the chamfering process, and the processing cracks is obtained. A polishing process is required, and the processing burden is large. Also, chamfering with a rotating grindstone causes processing cracks, so if there are remaining processing cracks that could not be removed in the subsequent end face polishing step, chipping, cracking, etc. are likely to occur during subsequent processing. There is also a problem.

In recent HDDs, the start / stop operation is performed by a load unload (hereinafter referred to as LUL) method. Compared with the conventional CSS (Contact Start and Stop) HDD, the LUL HDD does not need to have a concave / convex shape for CSS on the magnetic disk surface, making the magnetic disk surface extremely smooth. As a result, the flying height of the magnetic head can be greatly reduced. For example, the flying height of the magnetic head is 10 nm or less. In such a LUL system, the flying height of the magnetic head is significantly narrower than before, so it seems that the magnetic disk mounted on the HDD or the glass substrate for the magnetic disk has been conventionally allowed. Even if there are undue cracks, scratches, and other defects, serious failures (eg, thermal asperity failures) are likely to occur.

In the manufacture of glass substrates for magnetic disks, the glass disk is cut out from the sheet glass and then subjected to predetermined grinding and polishing processes to remove scratches and cracks, but these must be completely removed. It is difficult. Therefore, at the stage of cutting out the glass disk, it is necessary to reduce as much as possible scratches, cracks, etc. that cause HDD failure. However, as described above, in the conventional method of manufacturing a glass substrate for magnetic disk, Defects such as scratches and cracks are likely to occur at the stage of cutting out the disk, and in particular, it has been difficult to stably produce a high-quality glass substrate for a magnetic disk mounted on an LUL type HDD at a high yield.

  Accordingly, an object of the present invention is to produce a glass substrate for magnetic disk that can improve the processing quality of the end face when cutting a glass disk from plate-like glass to produce a glass substrate for magnetic disk, and increase the yield. And a method of manufacturing a magnetic disk using the glass substrate for a magnetic disk.

As a result of earnest research to solve the above-mentioned problems, the present inventor made a predetermined cut line on a sheet glass, then advanced the cut line, and then with a solution having an etching action on the glass. By etching, the plate glass is divided along the cut line, and by cutting out the disk-shaped glass substrate, it is possible to stably produce a good glass substrate for magnetic disk with high end surface quality. It has been found that the yield when cutting out and manufacturing a glass substrate for a magnetic disk can be increased.
That is, the present invention has the following configuration.

(Configuration 1) A method for producing a glass substrate for a magnetic disk, comprising a step of cutting out a disk-shaped glass substrate from a plate-shaped glass formed on a molten metal, the main surface on one side of the plate-shaped glass On the other hand, a cut line that draws a curve that forms a substantially peripheral edge of a region to be a glass substrate for a magnetic disk is formed substantially straight in the thickness direction of the sheet glass, and then the cut line is advanced, A method for producing a glass substrate for a magnetic disk, comprising: cutting a plate-shaped glass substrate along the cut line using a solution having an etching action, and cutting out a disk-shaped glass substrate.

(Configuration 2) After the cut line formed on the sheet glass is advanced, the sheet glass is immersed in a solution having an etching action on the glass, thereby making the sheet glass into the cut line. The method for manufacturing a glass substrate for a magnetic disk according to Configuration 1, wherein the glass substrate is divided along the line.
(Configuration 3) After forming the cut line on the main surface on one side of the plate glass, the plate glass is heated as a whole, and the cut line is directed to the main surface on the other side of the plate glass. The manufacturing method of the glass substrate for magnetic discs of the structure 1 or 2 characterized by the above-mentioned.

(Structure 4) The method for producing a glass substrate for a magnetic disk according to any one of Structures 1 to 3, wherein an end face of the cut-out disk-shaped glass substrate is chamfered.
(Structure 5) The glass for magnetic disk according to any one of Structures 1 to 4, wherein the glass substrate is a glass substrate used for a magnetic disk mounted in a load / unload magnetic disk device. A method for manufacturing a substrate.

(Configuration 6) 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 any one of configurations 1 to 5.

According to the present invention, after a predetermined score is formed on a sheet glass, the score is advanced, and then etched using a solution having an etching action on the glass along the score. Since the plate-like glass is divided, it is possible to stably produce a good glass substrate for a magnetic disk with high end face quality, and increase the production yield.

In addition, by manufacturing a magnetic disk using the glass substrate for magnetic disk obtained by the manufacturing method of the present invention, the processing quality of the end surface of the glass substrate for magnetic disk is high, so that reliability that does not cause thermal asperity failure etc. Therefore, it is possible to reduce the manufacturing cost of the magnetic disk because the manufacturing yield of the magnetic disk glass substrate is high.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a cross-sectional view showing a process of cutting out a disk-shaped glass substrate according to the present invention.
The method for manufacturing a glass substrate for a magnetic disk according to the present invention includes a step of cutting out a disk-shaped glass substrate from a plate-shaped glass, and in the cutting step, the magnetic surface is magnetically applied to the main surface of the plate-shaped glass. After forming a cutting line that draws a curve that forms a substantially peripheral edge of a region to be a glass substrate for a disk, a straight line is formed in the thickness direction of the plate glass, and then the cutting line is advanced, and then a solution having an etching action is used. Then, the plate glass is divided along the cut lines, and a disk-shaped glass substrate is cut out.

Examples of the type of glass of the plate glass for producing the magnetic disk glass substrate in the present invention include aluminosilicate glass and soda lime glass. Aluminosilicate glass is preferable because it can be made of chemically strengthened glass because high rigidity can be obtained.
Such glass, for _example, SiO 2: 58-75 _{wt%, Al} 2 O 3: _{5~23 wt%,} Li 2 O: 3 to 10 _wt%, Na 2 O: 4 to 13 wt% of the main It is preferable to consist of an aluminosilicate glass contained as a component.

Furthermore, the composition of the _glass, SiO 2: 62 to 75 _{wt%, Al} 2 O 3: _{5~15 wt%,} Li 2 O: _{4~10 wt%,} Na 2 O: _4~12 wt%, ZrO ₂ : 5.5-15 mass% as a main component, the mass ratio of Na ₂ O / ZrO ₂ is 0.5-2.0, and the mass ratio of Al ₂ O ₃ / ZrO ₂ is 0.4-2. Aluminosilicate glass of .5 is preferred.
Further, in order to eliminate protrusions on the surface of the glass substrate caused by the undissolved material of ZrO ₂ , SiO ₂ is 57 to 74%, ZrO ₂ is 0 to 2.8%, Al ₂ O ₃ is 3 in terms of mol%. It is preferable to use a glass for chemical strengthening containing ˜15%, LiO ₂ ˜7-16% and Na ₂ O 4˜14%.
In addition, examples of the method for forming the glass sheet include a float method, a press method, a fusion method, and the like. The plate forming method is not particularly limited as long as it is plate-like, but a float method capable of obtaining a smooth surface is preferable.

FIG. 1A is a cross-sectional view of the sheet glass 1. Usually, the sheet glass is cut in advance to an appropriate size that allows a disk having a desired size to be cut out. The plate-like glass 1 shown here is cut into a square having an appropriate size.
For example, in the case of plate glass manufactured by the float process, since the molten glass is formed into a plate shape on the molten metal, the main surface (hereinafter referred to as the following) that contacts the molten metal (generally molten tin) in the manufacturing stage. In the case of the sheet glass 1 shown in FIG. 1 (a), it is possible to distinguish between a “bottom surface” and a main surface on the side facing the bottom surface (hereinafter referred to as “top surface”). The upper main surface is the top surface 1A, and the lower main surface is the bottom surface 1B. A metal diffusion layer having a thickness of about 10 to 50 μm is inevitably formed on the bottom surface 1B side. On the other hand, the molten metal is not directly in contact with the top surface 1A in the manufacturing stage, but the metal vaporized in the atmosphere may permeate to form a metal diffusion layer. However, even if a metal diffusion layer is formed on the top surface 1A side, the thickness is at most about several μm.

  In the present embodiment, for example, a scoring line is formed on the top surface 1A of the plate-like glass 1 that draws a curve that forms a substantially peripheral edge of a region to be a glass substrate for magnetic disks. In the present embodiment, as shown in FIG. 1 (b), the outer peripheral side and the inner peripheral side of the region to be the glass substrate for a magnetic disk are drawn on the top surface 1A of the sheet glass 1 with a glass cutter. Circular cut lines 2 and 3 were formed respectively.

In this case, the cut lines 2 and 3 on the outer peripheral side and the inner peripheral side are both formed substantially straight in the thickness direction. Conventionally, if a glass disk is cut out by heating after forming a cut line perpendicular to the main surface of the sheet glass, the glass disk cannot be separated well from the sheet glass or the cut glass disk Since there are many defective products due to chipping, scratches, cracks, etc. on the end surface, for example, the cut lines 2 and 3 are obliquely inclined outward from the top surface 1A to the bottom surface 1B side of the sheet glass 1. The left and right cut lines 2 and 2 and the cut lines 3 and 3 were formed in a C shape (see FIGS. 2A and 2B). Then, the cut line formed obliquely with respect to the thickness direction was advanced (see FIG. 2C), and the inner part surrounded by the cut line was extracted to obtain the glass disk 10 (FIG. 2D). )), The problems with such a method are as described above.

In the present embodiment, both the outer peripheral side and inner peripheral cut lines 2 and 3 are formed substantially straight in the plate thickness direction, but the cut lines are advanced, and then a solution having an etching action is used. Since the glass sheet is divided along the cut line, it is possible to cut out a glass disk free from the occurrence of chipping or cracks on the end face. In addition, since the end face is cut out substantially perpendicularly to the main surface, the burden of subsequent chamfering and the like can be reduced.

Moreover, as a glass cutter used for forming such a cutting line, a wheel cutter is suitable, for example, and a diamond cutter can also be used.

  Next, as shown in FIG. 1C, the cut lines 2 and 3 formed on the top surface 1A of the sheet glass 1 are advanced toward the bottom surface 1B. Thereby, the inner region 10 a surrounded by the cut line 2 is separated from the sheet glass 1. Further, the inner portion 10 b surrounded by the cut line 3 is separated from the region 10 a surrounded by the cut line 2. As means for advancing the cut lines 2 and 3 formed on the top surface 1A of the sheet glass 1 in this way toward the bottom surface 1B side, means for causing a difference in thermal expansion in the sheet glass 1, for example, a sheet shape A method of heating the glass 1 is preferred. By heating the glass sheet 1, a difference in thermal expansion occurs in the thickness direction of the glass sheet 1, and the glass sheet 1 is deformed so as to have a convex shape upward or downward. The streaks 2 and 3 instantaneously reach the bottom surface 1B.

When the plate glass 1 is heated, the whole plate glass 1 may be heated using a heating device such as an oven, but it is particularly preferable to heat one side of the plate glass 1. This is because the cut line advances more reliably by heating one side of the sheet glass 1. In this case, one side of the sheet glass 1 may be heated as a whole, or one side may be partially heated. For example, when heating one side of the sheet glass 1 as a whole, it is preferable to heat the top surface 1A side on which the cut lines 2 and 3 are formed.

Subsequently, as shown in FIG.1 (d), the said plate glass is immersed in a hydrofluoric acid solution. Since hydrofluoric acid has an etching action on the glass, the solution having an etching action penetrates into the cut lines 2 and 3, and the glass is etched in the cut lines 2 and 3. As the width increases, the corresponding portion that becomes the disk substrate is cut off from the cut-off portion.
As the solution having an etching action for dividing, a hydrofluoric acid solution is preferable from the viewpoint of the etching rate, but any solution having a glass etching action such as a silicon hydrofluoric acid solution may be used. A solution containing hydrofluoric acid (HF) or silicic hydrofluoric acid (H ₂ SiF ₆ ) as a main component may be used. The concentration is arbitrary as long as the etching action of the glass is suitably obtained. Further, hydrofluoric acid is the main component, and an acid such as sulfuric acid, nitric acid or hydrochloric acid may be mixed in an appropriate amount in order to further increase the etching power.

A glass disk having a circular hole at the center by taking out the inner regions 10a and 10b surrounded by the cut line 2 and extruding the region 10b surrounded by the cut line 3 of the plate glass thus cut. A (disk-shaped glass substrate) 10 is obtained (see FIG. 1 (e)).

Thus, the end surface of the glass disk formed by etching along the cut line has a surface roughness (surface roughness) suitable as an end surface of the glass substrate for magnetic disks, and has a surface free from processing cracks. In addition, the cut line is formed substantially perpendicular to the substrate, and as a result, the end surface is substantially perpendicular to the main surface of the glass disk, so that it can be used as the side wall surface 12a of the end surface 12 of the glass disk 10. it can. Therefore, the chamfering and polishing of the side wall surface 12a are not required in the subsequent process, and only the chamfering and polishing of the chamfered surface 12b may be performed, so that the burden of end face processing is greatly reduced and the side wall surface 12a is processed. Since there are no cracks (polishing marks), the processing quality of the end face is improved, and the occurrence of chipping and cracking during handling in the subsequent steps can be suitably suppressed.

In addition, the conventionally performed method can be arbitrarily applied to the chamfering processing of the chamfered surfaces 12b and 12b of the glass disk thus formed and the subsequent polishing processing.
Moreover, in this Embodiment, although the cut lines 2 and 3 are formed with respect to the top surface 1A of the said plate-like glass 1, for example, it is not restricted to this, With respect to the bottom surface 1B of the plate-like glass 1 Thus, the cut lines 2 and 3 may be formed.

  In the present embodiment, the cut line is a closed curve that draws a substantially peripheral edge of a region to be a glass substrate for a magnetic disk, but it may not be a complete closed curve. For example, even when the starting point and the ending point of the cut line are slightly deviated, it is possible to advance the cut line and cut out a disk-shaped glass substrate by etching with a solution having an etching action. Further, the cut line does not have to be a continuous curve. For example, a cut line is drawn which draws a substantially peripheral edge of a region to be a glass substrate for a magnetic disk in a broken line shape, and the cut line is advanced to perform an etching action. It is possible to cut out a disk-shaped glass substrate by etching with a solution having the same.

  In order to achieve high recording density of the magnetic disk, it is necessary to improve the smoothness of the main surface of the glass substrate. The glass substrate for a magnetic disk is manufactured by grinding and polishing the main surface of the glass disk 10 cut into a predetermined size from the plate glass as described above. Usually, this grinding process is performed using a lapping device and using abrasive grains of a predetermined grain size in order to improve the dimensional accuracy and shape accuracy of the glass disk 10. Further, this polishing step uses a polishing apparatus, and as a preferred embodiment, in order to remove scratches and distortion remaining in the grinding step, a hard polisher is used as a polisher, and the first polishing step is used to polish the glass substrate surface. And a second polishing step of polishing the glass disk surface with a soft polisher in place of the hard polisher in order to finish a smoother mirror surface while maintaining the flat surface obtained in the first polishing step.

Moreover, the glass substrate which finished the grinding | polishing process may give chemical strengthening. When the glass type is particularly aluminosilicate glass, the strength of bending is increased by the chemical strengthening, the depth of the compressive stress layer is deep, and the Knoop hardness is excellent. The chemical strengthening method is not particularly limited as long as it is a conventionally known chemical strengthening method, but chemical strengthening by a low-temperature ion exchange method is preferable in practice.
Moreover, you may form in the main surface of a glass substrate the texture for providing magnetic anisotropy to the magnetic layer formed on a glass substrate. As a method for forming such a texture, for example, a method by tape polishing is mentioned, and the glass substrate and the tape are relatively moved while pressing the tape against the main surface of the glass substrate and supplying the polishing liquid. Thus, a circumferential texture can be formed on the main surface of the glass substrate.

The diameter size of the glass substrate for a magnetic disk according to the present invention is not particularly limited, but the present invention relates to the production of a glass substrate for a small diameter magnetic disk obtained by forming a cut line that draws a circular closed curve with a small curvature. There are more remarkable effects.
The thickness of the magnetic disk glass substrate according to the present invention is preferably about 0.1 mm to 0.65 mm. In particular, in the case of a magnetic disk constituted by a thin substrate of about 0.1 mm to 0.4 mm which is difficult to cut out, the present invention is highly useful and suitable.

By forming at least the magnetic layer on the magnetic disk substrate obtained by the present invention, a magnetic disk suitable for increasing the recording density can be obtained. If a Co-based alloy magnetic layer having an hcp crystal structure is used as the magnetic layer, the coercive force (Hc) is high, which can contribute to an increase in recording density.
If necessary, it is also preferable to form a base layer between the substrate and the magnetic layer in order to control crystal grains and orientation of the magnetic layer.
In manufacturing a magnetic disk, it is preferable to form at least a magnetic layer by DC magnetron sputtering using a stationary facing film forming method.

In addition, it is preferable to provide a protective layer on the magnetic layer. By providing the protective layer, the surface of the magnetic disk can be protected from the magnetic recording head flying over the magnetic disk. As a material for the protective layer, for example, a carbon-based protective layer is suitable. Further, it is preferable to further provide a lubricating layer on the protective layer. By providing the lubricating layer, wear between the magnetic recording head and the magnetic disk can be suppressed, and the durability of the magnetic disk can be improved. As a material for the lubricating layer, for example, PFPE (perfluoropolyether) is preferable.
According to the present invention, a glass substrate used for a magnetic disk mounted on a load / unload type magnetic disk apparatus advantageous for increasing the recording density is stably manufactured from a plate-like glass obtained by a float process. be able to. In addition, by manufacturing a magnetic disk using the magnetic disk glass substrate obtained by the manufacturing method of the present invention, the manufacturing yield of the magnetic disk glass substrate is high, so that the manufacturing cost of the magnetic disk can be reduced. It becomes possible.

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
The magnetic disk glass of the present embodiment is subjected to the following (1) cutting process (etching cutting process), (2) lapping process, (3) chamfering process, (4) main surface polishing process, and (5) chemical strengthening process. A substrate was manufactured.

(1) Cutting process (etching cutting process)
A glass plate made of aluminosilicate glass with a thickness of 0.95 mm manufactured by the float method is cut into a square of a predetermined size (80 mm x 80 mm), and two abacus balls are formed on one main surface. Rotate while pressing the cutter wheel to form circular cut lines (distances from the center of rotation of 10mm and 32.5mm) that draw the outer periphery and inner periphery of the area to be the magnetic disk glass substrate. did. The cut lines in this case were formed substantially straight in the thickness direction on both the outer peripheral side and the inner peripheral side. As the aluminosilicate _glass, SiO 2: 58 to 75 _{wt%, Al} 2 O 3: _{5~23 wt%,} Li 2 O: 3 to 10 _wt%, Na 2 O: containing 4-13 wt% Glass for chemical strengthening was used. Next, the surface of the sheet glass on which the cut line was formed was heated to 300 ° C. with a heater as a whole, and the cut line was advanced to the surface on the opposite side of the sheet glass.

Next, the plate glass is immersed in a hydrofluoric acid solution having a concentration of 3 mol / liter and a temperature of 40 ° C. for 2 minutes, the glass is divided along the cut line, and a glass disk having a circular hole at the center. Was cut out.

(2) Lapping step Next, by lapping the glass disk surface with alumina abrasive grains having a particle size of # 1000 by a double-sided lapping apparatus, the flatness is 3 μm, the surface roughness is about 2 μm in Rmax, and 0 in Ra. About 2 μm. The flatness was measured with a flatness measuring device, and Rmax and Ra were measured with an atomic force microscope (AFM). The glass disk which finished the said lapping process was immersed in each washing tank (ultrasonic application) of neutral detergent and water sequentially, and ultrasonic cleaning was performed.

(3) Chamfering step Next, a hard urethane pad is attached to the hemispherical metal fitting, and the end face (inner and outer circumference) of the glass disk is pressed and chamfered while flowing a cerium oxide abrasive having an average particle diameter of about 1.2 μm. (Chamfered surface processing) was performed. In addition, the above-mentioned etching-cut end face was used as a side wall face as it was. And the surface of the glass disk which finished the said chamfering process was washed with water.

(4) Main surface polishing step Next, a first polishing step for removing scratches and distortions remaining in the lapping step described above was performed using a double-side polishing apparatus. In a double-side polishing apparatus, a glass disk held by a carrier is closely attached between an upper and lower polishing surface plate to which a polishing pad is attached, and the carrier is engaged with a sun gear and an internal gear, and the glass disk is vertically polished. Clamp with a platen. Thereafter, a polishing liquid is supplied and rotated between the polishing pad and the polishing surface of the glass disk, whereby the glass disk revolves while rotating on the polishing surface plate to simultaneously polish both surfaces. Specifically, a hard polisher (hard foamed urethane) was used as the polisher, and the first polishing step was performed. As polishing conditions, the polishing liquid was RO water in which cerium oxide (average particle size 1.3 μm) was dispersed as an abrasive, and the polishing time was 15 minutes. The glass disk after the first polishing step was immersed in a cleaning bath of neutral detergent, pure water, pure water, IPA (isopropyl alcohol), and IPA (steam drying) sequentially, ultrasonically cleaned, and dried. .

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 soft polisher (suede). In this second polishing step, for example, mirror polishing for finishing the surface roughness of the glass disk main surface to a smooth mirror surface with an Rmax of about 8 nm or less while maintaining the flat surface obtained in the first polishing step described above. It is processing. The polishing conditions were RO water in which colloidal silica (average particle size 0.8 μm) was dispersed as the polishing liquid, and the polishing time was 5 minutes. The glass disk which finished the said 2nd grinding | polishing process was immersed in each washing tank of neutral detergent, a pure water, a pure water, IPA, and IPA (steam drying) one by one, ultrasonically cleaned, and dried.

(5) Chemical strengthening step Next, chemical strengthening was performed on the glass disk that had been cleaned. For chemical strengthening, a chemical strengthening solution in which potassium nitrate and sodium nitrate were mixed was prepared, this chemical strengthening solution was heated to 380 ° C., and the cleaned and dried glass disk was immersed for about 4 hours for chemical strengthening treatment. The glass disk after chemical strengthening was sequentially immersed in each washing tank of sulfuric acid, neutral detergent, pure water, pure water, IPA, and IPA (steam drying), ultrasonically cleaned, and dried.

Further, when the surface roughness of the main surface of the glass disk obtained through the above steps was measured with an atomic force microscope (AFM), an ultra-smooth surface with Rmax = 2.13 nm and Ra = 0.20 nm was obtained. I got a glass disk with it. The obtained glass disk had an outer diameter of 65 mm, an inner diameter of 20 mm, and a plate thickness of 0.635 mm.
Thus, a glass substrate for magnetic disk of this example was obtained. In addition, from the 10000 glass disks obtained as described above, non-defective products having no defects such as chipping, cracks, and scratches were obtained. Further, the surface was in a clean mirror surface state, and there was no foreign matter that hindered the flying of the magnetic head or foreign matter that would cause thermal asperity failure.

Next, the following film formation process was performed on the magnetic disk glass substrate obtained in this example to obtain a magnetic disk.
On the glass substrate, an adhesion layer made of a Cr alloy, a soft magnetic layer made of a CoTaZr alloy, an underlayer made of Ru, a perpendicular magnetic recording layer made of a CoCrPt alloy, a protective layer, and a lubricating layer were sequentially 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 having a thickness of 5 nm, and wear resistance is obtained. The lubricating layer is formed by perfluoropolyether liquid lubricant by dipping and has a thickness of 0.9 nm.

Next, the obtained magnetic disk was evaluated as follows.
For the obtained magnetic disk, a head crash test was carried out by flying over the magnetic disk using an inspection head having a flying height of 8 nm. As a result, in the magnetic disk of this example, the magnetic head was There was no contact and no crash failure occurred.
Next, a recording / reproducing test by a perpendicular magnetic recording method was performed using a magnetic head in which the reproducing element portion was a magnetoresistive element, the recording element portion was a single magnetic pole element, and the flying height was 8 nm. However, it was confirmed that information was recorded and reproduced normally. At this time, recording / reproduction could be performed at 200 gigabits per square inch without detecting a thermal asperity signal as a reproduction signal.
As a result of finally examining the occurrence rate of chipping of the outer diameter of 10,000 magnetic disks by visual inspection, the chipping rate was very small at 0.02%.

(Comparative example)
In the cutting-out process of Example 1 (1), using the asymmetric cutter wheel on the plate-like glass surface produced by the float method, the outer peripheral side and the inner peripheral side of the region to be the glass substrate for magnetic disk Each of the circular cut lines for drawing the outer peripheral side and the inner peripheral side was formed obliquely outward (inclination angle of about 10 degrees) with respect to the plate thickness direction. Heat is applied at 300 ° C. to the outer diameter cut portion of the sheet glass on which the cut lines are formed, the cut lines are permeated to the opposite surface of the substrate, and further separated and cut out by expansion of the substrate. Cut out. Further, in the (3) chamfering step of Example 1, since the end face is cut obliquely, the chamfered surface and the side wall surface are simultaneously processed with a rotating grindstone, and subsequently, made of nylon and having an average wire diameter of 0.2 mm. Using a polishing brush, the polishing allowance was 30 μm or more, and the chamfered surface and the side wall surface were mirror finished.
Except for the above, a magnetic disk glass substrate and a magnetic disk were produced in the same manner as in Example 1.
As a result of visual inspection of the incidence of chipping of the outer diameter of 10,000 magnetic disks manufactured in the manufacturing process of the comparative example in this way, the chipping rate was as high as 0.2%, and even in the head crush test similar to the example. The incidence of crash failures was high.

It is sectional drawing which shows the process of cutting out a disk-shaped glass substrate from the plate-shaped glass by this invention. It is sectional drawing which shows the process of cutting out a disk-shaped glass substrate from the plate-shaped glass by the conventional method. It is sectional drawing which shows the end surface shape of a glass substrate.

Explanation of symbols

1 Sheet glass 2, 3 Cutting line 10 Disc-shaped glass substrate (glass disc)
11 Main surface 12 End surface

Claims (6)

Have a step of cutting the glass substrate disk-shaped plate-like glass, a process for producing a glass substrate for a magnetic disk which have a and the side wall surface and the chamfered surface as the end surface,
After forming a cutting line that draws a curve that forms a substantially peripheral edge of a region to be a glass substrate for a magnetic disk with respect to the main surface on one side of the plate glass, substantially straight in the plate thickness direction of the plate glass, The cutting line is advanced until it reaches the main surface on the other side of the plate-like glass , and then a solution having an etching action on the glass is infiltrated into the advanced cutting line, that by causing etching to divide the plate glass along the cut muscle, and cut out the glass substrate of the disk-shaped, and the side wall surface of the end face part of the formed surface by its excision A method for producing a glass substrate for a magnetic disk.   The cut glass formed in the sheet glass is advanced, and then the plate glass is divided in the hydrofluoric acid solution to divide the plate glass along the cut line. Item 2. A method for producing a glass substrate for a magnetic disk according to Item 1.   After forming the cut line on the main surface on one side of the sheet glass, the sheet glass is heated as a whole, and the cut line is advanced toward the main surface on the other side of the plate glass. The method for producing a glass substrate for a magnetic disk according to claim 1 or 2.   The method for producing a glass substrate for a magnetic disk according to any one of claims 1 to 3, wherein the end surface of the cut-out disk-shaped glass substrate is chamfered.   The said glass substrate is a glass substrate used for the magnetic disk mounted in the magnetic disk apparatus of a load / unload system, The manufacturing of the glass substrate for magnetic discs as described in any one of Claim 1 thru | or 4 characterized by the above-mentioned. Method. 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.

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