JP3981374B2 - 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 of a predetermined size, for example, there is a method of cutting out a glass disk from a glass material formed into a plate shape by a float process. Non-Patent Document 1 below describes a plate-like glass obtained by a float method. Moreover, 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.
For reference, as prior art documents relating to a glass substrate for a magnetic disk, for example, Japanese Patent No. 2785906, Japanese Patent Application Laid-Open No. 2-92837, Japanese Utility Model Publication No. 57-23452, Japanese Patent Publication No. 55-6584, Japanese Patent Publication No. No. 35095, Japanese Patent Publication No. 55-29019, etc.

Japanese Patent No. 2973354 Sakuo Sakuo and two others, “Glass Handbook”, first edition, 8th edition, Asakura Shoten Co., Ltd., November 20, 1985, p. 412-413

  However, when a glass disk is cut out by heating after forming a cut line on the main surface of the sheet glass produced by the float process, the glass disk cannot be separated or cut out from the sheet glass. There is a problem that chips, scratches, cracks, etc. are generated on the end face of the glass disk, resulting in defective products, and the yield is low.

Recently, HDDs have been required to have an information recording density of 60 Gbit / inch ² (1 inch is 25.4 mm) or more. This is partly related to the fact that HDDs have been installed in personal digital assistants (PDAs), mobile phones, digital cameras, car navigation systems, etc., in addition to the need for conventional computer storage devices. There is. In these mobile applications, the housing space for mounting the HDD is significantly smaller than that of a computer, so it is necessary to reduce the size of the HDD. For this purpose, it is necessary to reduce the diameter of the magnetic disk mounted on the HDD. For example, a 3.5 (inch) type or 2.5 (inch) type magnetic disk could be used in a computer application, but in the case of the mobile application, a smaller diameter, for example, 0.8 (inch). ) Type to 1.8 (inch) type small-diameter magnetic disks are used. Conventionally, when such a small-diameter glass disk is cut out from the plate glass, there is a problem that the ratio of defective products is particularly high. Conventionally, even if the glass substrate for a magnetic disk has a diameter larger than that of the 2.5 (inch) type, the circular hole formed in the central portion has a small diameter. In the case of cutting out, there is also a problem that defective products having defects in the circular hole portions are likely to occur.

  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, and the magnetic disk surface can be made extremely smooth. Thus, the flying height of the magnetic head can be significantly reduced. For example, the flying height of the magnetic head is 10 nm or less. In addition, the LUL type HDD has an advantage that the recording / reproducing area of the magnetic disk can be expanded because it is not necessary to provide a CSS contact sliding area as compared with the conventional CSS type HDD. As described above, since the LUL system can effectively use the area of the magnetic disk surface, there is an advantage that a small disk area can be effectively used particularly in a small-diameter magnetic disk mounted on a small HDD.

  By the way, with the LUL method, the flying height of the magnetic head is much narrower than before, so the magnetic disk mounted on the HDD or the glass substrate for the magnetic disk has been conventionally allowed. Even cracks, scratches, and other defects are prone to serious failures (eg, thermal asperity failures). In particular, in a small-diameter magnetic disk mounted on a small HDD, particularly in a 1.0 (inch) small-diameter magnetic disk having an outer diameter of 30 mm or less, for example, 27.4 mm or less, or a glass substrate for a small-diameter magnetic disk, The problem of the above obstacle becomes even more serious. This is because such a small-diameter magnetic disk and a small-diameter magnetic disk glass substrate having an outer diameter of 30 mm or less are mounted on HDDs for mobile use such as the above-mentioned personal digital assistant (PDA), cellular phone, digital camera, This is because such a mobile HDD is used in an environment where there is always a striking force such as a drop, a collision, and a vibration, so that the occurrence of a failure is a particular concern.

  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. In particular, small magnetic disks with an outer diameter of 65 mm or less, especially with an outer diameter of 30 mm or less, and magnetic disks mounted on LUL HDDs are more prone to failure than conventional, so scratches and cracks are possible. As described above, in the conventional method for manufacturing a glass substrate for a magnetic disk, defects such as scratches and cracks are likely to occur at the stage of cutting out the glass disk. It was sometimes difficult to produce a glass substrate for a magnetic disk mounted on a LUL HDD with high yield and stability.

  Therefore, the object of the present invention is to provide a method for producing a glass substrate for a magnetic disk capable of increasing the yield when producing a glass substrate for a magnetic disk by cutting out a glass disk from a plate glass produced by a float process, and An object of the present invention is to provide a method of manufacturing a magnetic disk using the glass substrate for magnetic disk.

  The present inventor examined the cause of the problem, and in the case of a sheet glass manufactured by the float process, there are a surface (bottom surface) in contact with molten tin and a surface on the opposite side (top surface). In addition, a tin diffusion layer having a thickness of about 10 to 50 μm is inevitably formed on the bottom surface side, and the tin diffusion layer formed on the bottom surface side cuts out a predetermined glass disk from the plate glass. If found to be involved in the occurrence of defective products.

As a result of further diligent research to solve the above problems based on the obtained knowledge, the inventor obtained a top surface on the opposite side to the bottom surface on the side in contact with the molten tin of the sheet glass produced by the float process. After forming a predetermined cut line on the surface, the cut line is advanced to cut out a disk-shaped glass substrate, whereby a non-defective glass disk for a magnetic disk can be stably manufactured and manufactured by the float process. It has been found that the yield in the case of manufacturing a glass substrate for a magnetic disk by cutting out a glass disk from the plate-like glass can be increased.
That is, the present invention has the following configuration.

(Configuration 1) A method of manufacturing a glass substrate for a magnetic disk having a step of cutting out a disk-shaped glass substrate from a glass material formed into a plate shape on a molten metal, the side contacting the molten metal of the glass material After forming a scoring line that draws a curved line that forms a substantially peripheral edge of a region of the glass material that is to be a glass substrate for a magnetic disk with respect to the main surface that faces the main surface of the disc, A method for producing a glass substrate for a magnetic disk, comprising cutting out a glass substrate.
(Configuration 2) A method of manufacturing a glass substrate for a magnetic disk, comprising a step of cutting a disk-shaped glass substrate from a glass material formed into a plate shape on a molten metal, wherein the glass substrate for a magnetic disk has a circular shape at the center. A main surface opposite to the main surface of the glass material that is in contact with the molten metal, and a substantially peripheral edge on the inner peripheral side of a region of the glass material to be a glass substrate for a magnetic disk. A method of manufacturing a glass substrate for a magnetic disk, comprising: forming a cut line that draws a curve to be formed, and then forming the circular hole in the center of the disk-shaped glass substrate by advancing the cut line is there.

(Structure 3) The method for producing a glass substrate for a magnetic disk according to Structure 1 or 2, wherein the cut line is formed obliquely with respect to a thickness direction of the glass material.
(Configuration 4) After forming the score on the main surface of the glass material, the glass material is heated or cooled, and the score is advanced toward the main surface of the glass material in contact with the molten metal. 4. A method for manufacturing a glass substrate for a magnetic disk according to any one of configurations 1 to 3, wherein:
(Structure 5) The glass substrate for a magnetic disk according to any one of Structures 1 to 4, wherein the glass substrate is a small glass substrate for a magnetic disk having a diameter of 65 mm or less. .

(Structure 6) The glass substrate for a magnetic disk according to any one of Structures 1 to 5, wherein the glass substrate is a glass substrate used for a magnetic disk mounted in a load / unload magnetic disk device. It is a manufacturing method.
(Structure 7) 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 6.

According to the first aspect of the present invention, when manufacturing a glass substrate for a magnetic disk by cutting out a glass disk from a glass material made into a plate shape on a molten metal, a good glass substrate for a magnetic disk is stably manufactured. It can be manufactured and the manufacturing yield can be increased.
According to the second aspect of the present invention, when a glass disk for a magnetic disk is manufactured by cutting out a glass disk from a glass material formed into a plate shape on a molten metal, the magnetic disk glass substrate is at the center. It has a circular hole, and this small-diameter circular hole can also be cut out from the glass material, and as a result, a good glass substrate for a magnetic disk can be manufactured stably and the manufacturing yield is increased. be able to.

According to the invention of claim 3, after forming the cut line on the main surface of the glass material, the glass material is heated or cooled, and the cut line is brought into contact with the molten metal of the glass material. By proceeding toward the main surface on the side, a glass disk for a magnetic disk can be manufactured by cutting out a glass disk from the glass material, so that a non-defective glass substrate for a magnetic disk can be manufactured stably. , Manufacturing yield can be increased.
In addition, according to the invention of claim 4, a small glass substrate for a magnetic disk having a diameter of 65 mm or less can be stably manufactured from the glass material, and the product yield can be increased. Particularly, it is suitable for manufacturing a small glass substrate for a magnetic disk.

According to the invention described in claim 5, a glass substrate used for a magnetic disk mounted on a load / unload type magnetic disk device can be stably manufactured from the glass material, and the product yield is increased. be able to.
In addition, according to the invention described in claim 6, by producing a magnetic disk using the magnetic disk glass substrate obtained by the production method of the present invention, the production yield of the magnetic disk glass substrate is high. The manufacturing cost of the magnetic disk can be reduced.

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 glass material formed into a plate shape on a molten metal, and in the cutting step, the melting of the glass material A cut line is formed on the main surface opposite to the main surface on the side in contact with the metal, which forms a curved line that forms a substantially peripheral edge of a region of the glass material to be a glass substrate for a magnetic disk. It is characterized by cutting out a disk-shaped glass substrate.

A plate-like glass material (hereinafter referred to as “plate glass”) for producing the magnetic disk glass substrate in the present invention is produced by a float process. Examples of the glass 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: 62-75 _{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%.

FIG. 1A is a cross-sectional view of the sheet glass 1. Usually, the sheet glass manufactured by the float process is cut in advance to an appropriate size capable of cutting out a disk having a desired size. The plate-like glass 1 shown here is cut into a square having an appropriate size.
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 on the side in contact with the molten metal (generally molten tin) in the manufacturing stage (hereinafter referred to as “ In the case of the sheet glass 1 shown in FIG. 1 (a), it can be distinguished from the main surface (hereinafter referred to as "top surface") on the side facing the bottom 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.

  A cut line is formed on the top surface 1A of the plate-like glass 1 to draw a curve that forms a substantially peripheral edge of a region to be a glass substrate for a magnetic disk. In the present embodiment, as shown in FIGS. 1B and 2, the outer peripheral side and the inner peripheral side of the region formed as the magnetic disk glass substrate on the top surface 1 </ b> A of the plate-like glass 1 with a glass cutter. Circular cut lines 2 and 3 each depicting the periphery were formed. 2 is a plan view showing a state in which a cut line is formed on the top surface of the sheet glass 1, and FIG. 1B is a cross-sectional view taken along the line II of FIG.

  In this case, the cut lines 2 and 3 on the outer peripheral side and the inner peripheral side are formed obliquely with respect to the plate thickness direction. Further, in the present embodiment, the cut lines 2 and 3 are formed obliquely outward from the top surface 1A to the bottom surface 1B side of the sheet glass 1, and when viewed in the cross-sectional view of FIG. The cut lines 2 and 2 and the cut lines 3 and 3 are formed in a C shape. By forming a cut line on the top surface of the sheet glass obtained by the float method obliquely with respect to the plate thickness direction, if this cut line is advanced and the inner part surrounded by the cut line is extracted, chipping, cracking A good glass disk free from defects such as scratches can be obtained stably. FIG. 3 is an enlarged cross-sectional view showing a state in which a cut line is formed. The angle when the cut line is formed obliquely is not particularly limited, but the angle (α) (see FIG. 3) formed by the cut line and the direction orthogonal to the top surface 1A is in the range of, for example, about 5 to 45 degrees. It is preferable to form in the inside.

Moreover, as a glass cutter used for forming such an oblique cut line, a wheel cutter is suitable, for example, and a diamond cutter can also be used. In this case, cutters with different left and right blade angles with respect to the cutter ridgeline may be used, but the left and right blade angles may be used to make the angle of contact with the sheet glass oblique. Good.
In addition, since it grinds and polishes after cutting out a glass disk and finishes to a predetermined outer diameter and inner diameter dimension, each circular cut line 2 that draws the outer peripheral side and the substantially peripheral edge of the inner peripheral side of the region to be a glass substrate for magnetic disk , 3 is preferably determined in consideration of the margin.

  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 or cooling the glass 1 is preferred. By heating or cooling the plate glass 1, a difference in thermal expansion occurs in the plate thickness direction of the plate glass 1, and the plate glass 1 is deformed so as to have a convex shape upward or downward. The cut lines 2 and 3 instantaneously reach the bottom surface 1B.

  When heating or cooling the sheet glass 1, the entire sheet glass 1 may be heated or cooled using a heating device such as an oven or a cooling device, but in particular, one side of the sheet glass 1 is heated or cooled. Is preferred. This is because the cut line advances more reliably by heating or cooling one side of the plate glass 1. In this case, one side of the sheet glass 1 may be heated or cooled as a whole, or one side may be partially heated or cooled. For example, when heating or cooling one side of the sheet glass 1 as a whole, the top surface 1A side on which the cut lines 2 and 3 are formed is heated, or the top surface on which the cut lines 2 and 3 are formed. It is preferable to cool the bottom surface 1B side on the opposite side. Moreover, when partially heating or cooling the one surface side of the sheet glass 1, it is preferable to heat the area | region outside the said cut line, or to cool the area | region inside the said cut line.

Next, as shown in FIG. 1 (d), the inner regions 10 a and 10 b surrounded by the incision 2 are extruded downward using a means such as an appropriate push bar, and further, the incision 3 is surrounded by the incision 3. By extruding the region 10b, a glass disk (disk-shaped glass substrate) 10 having a circular hole in the center is obtained.
In the present embodiment, first, the cut lines 2 and 3 are formed on the top surface 1A of the plate glass 1 so as to draw the outer peripheral side and the inner peripheral side of the region to be the magnetic disk glass substrate. These scissors are advanced to the bottom surface 1B side to obtain the glass disk 10. However, the present invention is not limited to this. First, the perforation 2 on the outer peripheral side is first formed, and this is advanced. The entire enclosed inner region is cut out from the plate-like glass 1, and then a cutout 3 on the inner peripheral side is formed at the center of the cut out glass disk, and this is advanced to form a circular hole surrounded by the cutout 3. By doing so, the glass disk 10 may be obtained.

In addition, in the case of a small glass substrate for a magnetic disk whose outer diameter is 65 mm or less, the inner diameter is very small with a diameter of 20 mm or less. A glass disk for a magnetic disk can be stably produced by cutting a glass disk from a plate glass, so that the yield can be increased.
Further, in the present embodiment, the cut lines 2 and 3 are formed obliquely outward from the top surface 1A of the sheet glass 1 toward the bottom surface 1B side. However, the present invention is not limited thereto, and for example, the top of the sheet glass 1 The cut lines 2 and 3 are formed obliquely inward from the surface 1A toward the bottom surface 1B, and the left and right cut lines 2 and 2 and the cut lines 3 and 3 are seen in a cross-sectional view as shown in FIG. May be formed in a reverse C shape, and this cut line may be advanced so that the inner part surrounded by the cut line is extracted upward.
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 shifted, it is possible to cut out the disk-shaped glass substrate by moving the cut line. Further, the cut line does not have to be a continuous curve. For example, a cut line is formed by drawing 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 form a disk shape. It is possible to cut out the glass substrate.

  In order to achieve high recording density of the magnetic disk, it is necessary to improve the smoothness of the glass substrate surface. The glass substrate for a magnetic disk is manufactured by grinding and polishing the surface of the glass disk 10 cut into a predetermined size from the plate glass obtained by the float method 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. Because it has more remarkable effects, it is a small magnetic disk of 2.5 (inch) or smaller type that is often used as a HDD for mobile applications (outer diameter 65mm, inner diameter in the case of 2.5 (inch)) 20 mm), the present invention that can stably manufacture a glass substrate for a magnetic disk that has high impact resistance and enables high recording density is highly useful. Preferably, the glass substrate for a small magnetic disk of 1.8 (inch) type (outer diameter 48 mm, inner diameter 12 mm) or less, more preferably 30 mm or less, for example, 1.0 (inch) type (outer diameter 27.4 mm, A glass substrate for a small magnetic disk having an inner diameter of 7 mm or less.
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 following (1) cutting step, (2) shape processing step, (3) fine lapping step (fine grinding step), (4) end face polishing step, (5) main surface polishing step, and (6) chemical strengthening step. After that, the magnetic disk glass substrate of this example was manufactured.

(1) Cutting process A glass plate made of aluminosilicate glass having a thickness of 1.5 mm manufactured by the float method is cut into a square of a predetermined size, and a glass cutter is used on its top surface for a magnetic disk. Circular cut lines each describing the substantially peripheral edge on the outer peripheral side and the inner peripheral side of the region to be the glass substrate were formed. The cut lines in this case were formed obliquely outward with respect to the plate thickness direction on both the outer peripheral side and the inner peripheral side, and the aforementioned inclination angle α was about 10 degrees. As the aluminosilicate _glass, SiO 2: _{58~75 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 top surface side of the sheet glass on which the cut line is formed is heated with a heater as a whole, the cut line is advanced to the bottom surface side of the sheet glass, and a glass disk having a circular hole in the center portion Was cut out. The outer diameter of the cut glass disk exceeded 65 mm.

(2) Shape processing step Next, after grinding the outer peripheral end surface and the inner peripheral end surface to an outer diameter of 65 mmφ and an inner diameter (diameter of a circular hole in the central portion) of 20 mmφ, a predetermined amount is applied to the outer peripheral end surface and the inner peripheral end surface. Chamfered. The surface roughness of the end surface of the glass disk at this time was about 4 μm in Rmax. In general, a 2.5 (inch) type HDD (hard disk drive) uses a magnetic disk having an outer diameter of 65 mm.

(3) Precision lapping step Next, by lapping the surface of the glass disk using alumina abrasive grains having a particle size of # 1000 with a double-sided lapping device, the surface roughness is about 2 μm in Rmax and about 0.2 μm in Ra. did. 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.
(4) End face polishing step Next, the surface roughness of the end face (inner circumference, outer circumference) of the glass disk was polished to about 1 μm at Rmax and about 0.3 μm at Ra while rotating the glass disk by brush polishing. And the surface of the glass disk which finished the said end surface grinding | polishing was water-washed.

(5) 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 cerium oxide (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.

(6) Chemical strengthening process Next, the glass disk which finished the said washing | cleaning was chemically strengthened. For chemical strengthening, a chemical strengthening solution in which potassium nitrate and sodium nitrate were mixed was prepared, 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 the above (1) cutting step, all 100 glass disks cut out from the sheet glass produced by the float process were all free from defects such as chips, cracks and scratches.

Next, the following film formation process was performed on the magnetic disk glass substrate obtained in this example to obtain a magnetic disk.
A seed layer, an underlayer, a magnetic layer, a protective layer, and a lubricating layer were sequentially formed on the glass substrate using a single wafer sputtering apparatus.
As the seed layer, a first seed layer made of a CrTi thin film (film thickness: 30 nm) and a second seed layer made of an AlRu thin film (film thickness: 40 nm) were formed. The underlayer was a CrW thin film (film thickness: 10 nm) and was provided in order to improve the crystal structure of the magnetic layer. In addition, this CrW thin film is comprised by the composition ratio of Cr: 90at% and W: 10at%.

The magnetic layer is made of a CoPtCrB alloy and has a thickness of 20 nm. The contents of Co, Pt, Cr, and B in this magnetic layer are Co: 73 at%, Pt: 7 at%, Cr: 18 at%, and B: 2 at%.
The protective layer is for preventing the magnetic 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.
[Reliability evaluation]
When the obtained magnetic disk was evaluated for glide characteristics, the touchdown height was 4.5 nm. The touchdown height decreases the flying height of the flying head in order (for example, lowering the rotational speed of the magnetic disk), finds the flying height that starts to contact the magnetic disk, and determines the flying height of the magnetic disk. In order to measure the capability, normally, an HDD that requires a recording density of 60 Gbit / inch ² or more is required to have a touchdown height of 5 nm or less.

In addition, when the head flying height was set to 10 nm and tested for LUL durability by repeatedly loading and unloading the head in an environment of 70 ° C. and 80% RH, even after 600,000 consecutive LUL tests, No thermal asperity failure or head crash failure occurred. It is said that normally used HDDs need to be used for about 10 years in order to exceed 600,000 LUL times. From this, it can be seen that the magnetic disk of this embodiment can guarantee high reliability.
In this embodiment, the flying posture and flying height of the magnetic head were stable.

(Example 2)
In this example, a glass substrate for a magnetic disk having an outer diameter of 27.4 mm, an inner diameter of 7 mm, and a plate thickness of 0.381 mm for mounting on a 1.0 (inch) type HDD was manufactured. Therefore, the magnetic disk glass of this example is the same as that of Example 1 except that in the (1) cutting process of Example 1, the size of the glass disk cut out from the sheet glass manufactured by the float process is different. A substrate was manufactured. In this example, good products free from defects such as chips, cracks and scratches were obtained from 100 glass disks cut out from the sheet glass in the (1) cutting step.

  Next, using the magnetic disk glass substrate obtained in this example, a film forming process was performed in the same manner as in Example 1 to obtain a magnetic disk. When the reliability of the obtained magnetic disk was evaluated, the touchdown height was 4.5 nm. In the LUL durability test, the durability was 600,000 times, and no thermal asperity failure or head crash failure occurred. Therefore, it was found that the magnetic disk of this example can guarantee high reliability.

(Comparative Example 1)
In the cutting process of Example 1 (1), each of the circular cut lines describing the substantially peripheral edges on the outer peripheral side and the inner peripheral side of the region to be the glass substrate for the magnetic disk on the bottom surface of the sheet glass manufactured by the float process. A glass disk having a circular hole in the center by heating the bottom surface side of the sheet glass on which the score line is formed with a heater and advancing the score line toward the top surface side of the sheet glass. Was cut out. The cut lines in this case were formed obliquely outward with respect to the plate thickness direction on both the outer peripheral side and the inner peripheral side, and the aforementioned inclination angle α was set to about 10 degrees as in the first embodiment.

  Except that the glass disk was cut out from the plate-like glass as described above, the outer diameter for mounting on the 2.5 (inch) type HDD was 65 mm and the inner diameter was the same as in the first embodiment. Produced a glass substrate for a magnetic disk having a thickness of 20 mm and a thickness of 0.635 mm. In the case of this comparative example, in the (1) cutting process, 8 out of 100 glass disks cut out from the sheet glass were defective products having defects such as chipping, cracks, and scratches.

(Comparative Example 2)
In this comparative example, a magnetic disk glass substrate having an outer diameter of 27.4 mm, an inner diameter of 7 mm, and a plate thickness of 0.381 mm for mounting on a 1.0 (inch) type HDD was manufactured. That is, in the cutting process of Comparative Example 1 (1), a glass substrate for a magnetic disk was manufactured in the same manner as in Comparative Example 1, except that the size of the glass disk cut out from the plate glass manufactured by the float process was different. . In the case of this comparative example, (1) In the cutting process, 19 out of 100 glass disks cut out from the sheet glass were defective products having defects such as chipping, cracking, and scratches.

From the comparison of the results of Examples 1 and 2 and Comparative Examples 1 and 2, the following can be seen. That is, in the comparative example in which a predetermined cut line is formed on the bottom surface side of the sheet glass that is in contact with the molten metal in the manufacturing process by the float method, and the glass disk is cut out from the sheet glass by moving the cut line. Since the incidence of defective products having defects such as chipping, cracking and scratching is increased, the production yield of the magnetic disk glass substrate is lowered. Moreover, in the case of the comparative example, the smaller the diameter of the disk, the higher the incidence of defective products when cutting out from the sheet glass.
On the other hand, a predetermined cut line is formed on the top surface side of the sheet glass that is not in direct contact with the molten metal in the manufacturing process by the float method, and the glass disk is cut out from the sheet glass by moving the cut line. In the embodiment of the present invention, a good glass disk free from defects such as chips, cracks, scratches, etc. can be obtained. Thus, a small-diameter glass substrate for a magnetic disk having an outer diameter of 65 mm or less can be stably produced. It is possible to increase the manufacturing yield. That is, according to the present invention, a more remarkable effect can be obtained in manufacturing a small-diameter disk.

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 a top view which shows the state which formed the cut line in the main surface of sheet glass. It is sectional drawing which expands and shows the state which formed the cut line in the main surface of sheet glass.

Explanation of symbols

1 Sheet glass 2, 3 Cutting line 10 Disc-shaped glass substrate (glass disc)

Claims (6)

A method for producing a glass substrate for a magnetic disk comprising a step of cutting out a disk-shaped glass substrate from a glass material formed into a plate shape on a molten metal,
A scoring line that draws a curve that forms a substantially peripheral edge of a region of the glass material that is to be a glass substrate for a magnetic disk with respect to a main surface that faces the main surface of the glass material that is in contact with the molten metal. A method of manufacturing a glass substrate for a magnetic disk, comprising: forming a disk-shaped glass substrate by advancing the cut line after forming the layer obliquely with respect to the plate thickness direction. A method for producing a glass substrate for a magnetic disk comprising a step of cutting out a disk-shaped glass substrate from a glass material formed into a plate shape on a molten metal,
The magnetic disk glass substrate has a circular hole in the center,
A scoring line that draws a curve that forms a substantially peripheral edge on the inner peripheral side of a region of the glass material that is to be a glass substrate for a magnetic disk, with respect to the main surface that faces the main surface of the glass material that is in contact with the molten metal. Is formed obliquely with respect to the plate thickness direction of the glass material, and then the cut line is advanced to form a circular hole in the center of the disk-shaped glass substrate. A method for manufacturing a substrate.   After forming the cut line on the main surface of the glass material, the glass material is heated or cooled, and the cut line is advanced toward the main surface of the glass material in contact with the molten metal. The manufacturing method of the glass substrate for magnetic discs of Claim 1 or 2.   4. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the glass substrate is a small glass substrate for a magnetic disk having a diameter of 65 mm or less.   5. The method of manufacturing a glass substrate for a magnetic disk according to claim 1, wherein the glass substrate is a glass substrate used for a magnetic disk mounted on a load / unload type magnetic disk device. 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 claim 1.

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