JPH11265506A - Glass substrate for magnetic disk and magnetic disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a dust evolution due to fine breakings of the end face of a glass substrate by chamfering end parts of the inner periphery and the outer periphery of the substrate and stipulating the angle formed by this end face and the chamfered surface to be within a prescribed range. SOLUTION: The width (a) of a disk end face is made to be equal to or larger than 0.05 mm and to be equal to or smaller than 0.35 mm. When the width (a) is smaller than 0.05 mm, a frequency in which the end face is breaked is increased by the concentration of stresses at the time of a contact with a jig because the width of the disk end face is small. Moreover, when the width (a) exceeds 0.35 mm, since the width (a) becomes wide, a contact area with the jig is increased and a dust evolution from the disk end face is increased. Moreover, the angle θ formed by the disk surface of the disk substrate and the chamfered surface of the end face is made to be equal to or larger than 48 deg. and to be equal to or smaller than 80 deg.. When the angle θ is smaller than 48 deg., since the angle between the end face and the chamfered surface is too sharp, an dust evolution from the part is not a few. Furthermore, when the angle θ exceeds 80 deg. since the effect of the chamferring is lessened in itself, the preventing of an dust evolution from the disk end face becomes impossible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a glass substrate for a magnetic disk used for a hard disk or the like. More specifically, the present invention relates to a glass substrate for a magnetic disk suitable for high-density recording using an MR head or a GMR head.

[0002]

2. Description of the Related Art As a substrate for magnetic recording, an aluminum substrate has been conventionally used in many cases. In recent years, a glass substrate which can easily obtain a smoothness and can be made thinner is used as a magnetic disk becomes smaller and thinner. The percentage is increasing. As a glass material used for a magnetic disk substrate, it is common to use tempered glass or crystallized glass having a high mechanical strength as a base material. The magnetic disk glass substrate is obtained by processing and polishing these base materials to form a smooth surface.

The glass substrate for a magnetic disk is flat,
In addition to being smooth, it is a necessary condition that there is no attached matter such as dust. Recently, with the adoption of MR heads and GMR heads, the necessity thereof has been increasing, and even a small amount of dust has become a problem.

For this reason, efforts have been made to sufficiently remove dust from the glass substrate for a magnetic disk, but there has been a problem that the dust cannot be completely removed. As a result of investigating the cause, it was found that dust was generated from the glass substrate itself, and that the dust adhered to the glass substrate surface. Further, when the dust generation from the glass substrate was examined, it was found that the end face was mainly rubbed, and minute chips were generated, and dust was generated.

[0005] By the way, when the glass substrate is transported, or when the glass substrate is taken in and out of the storage case, the end surface is rubbed to cause minute chipping and dust may be generated. Has been proposed (Japanese Patent Laid-Open No.
124323). However, merely etching the end face is not enough to prevent even minute dust generation which is a problem in high-density recording.

Actually, it has been found that when a magnetic film is formed on a glass substrate by sputtering, minute defects occur in the magnetic film, and these minute defects cause a problem in the high-density recording. As a result of the investigation, it was found that the minute chipping on the glass end face was caused by adhesion to the substrate surface. Then, it was found that when the magnetic film was sputtered on the glass substrate, the jig and the end face of the glass substrate were brought into contact with each other to generate minute chips, which adhered to the substrate surface.

In this case, minute chips are generated even if the glass substrate is thoroughly washed before sputtering. Even if the chips can be removed by washing well after sputtering, the minute chips are not adhered. The portion which has been turned into a defective portion without a magnetic film. In addition, since the sputtering process is close to the final process of manufacturing the magnetic disk medium, a decrease in the yield due to the occurrence of the defect significantly increases the manufacturing cost of the magnetic disk medium.

Accordingly, in a glass substrate used for a magnetic disk for high-density recording, dust is prevented from being generated due to minute chipping of an end face, thereby preventing generation of defects and improving the yield of magnetic disk production. It is strongly desired that a magnetic disk with few defects can be manufactured by using a simple glass substrate.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in order to solve such a problem, and it is possible to prevent the generation of dust due to minute chipping of the end face of a glass substrate, thereby reducing the occurrence of defects. It is an object of the present invention to provide a glass substrate capable of improving the production yield of a magnetic disk and a magnetic disk with few defects.

[0010]

According to the present invention, there is provided a glass substrate for a magnetic desk according to the present invention, wherein an inner or outer edge of the glass substrate is chamfered. Outer end face width is 0.05
mm or more and 0.35 mm or less, and the angle formed by the chamfered surface of the edge with respect to the plate surface of the substrate is 48 ° or more and 80 ° or more.
° or less. Further, the glass substrate for a magnetic desk according to the present invention is characterized in that an end surface of an inner peripheral portion or an outer peripheral portion of the glass substrate is subjected to a chemical strengthening treatment after polishing. Further, a magnetic desk according to the present invention is characterized in that a magnetic recording layer is provided on the magnetic disk substrate. The glass material used as the base material of the glass substrate used in the present invention is a glass material which can obtain the flatness, smoothness, high hardness, corrosion resistance and heat resistance required for the glass substrate and can form the end shape of the present invention. If there is, there is no particular limitation. Examples of such a glass material include aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, sodaaluminosilicate glass, quartz glass, soda-lime glass, and the like. Among them, crystallized glass and a glass material that can be chemically strengthened by ion exchange are preferable because high strength can be obtained. As a glass material that can be chemically strengthened, aluminosilicate glass is particularly preferable because it has a high softening point and a remarkable effect of chemical strengthening.

The method for producing the glass substrate and the magnetic disk of the present invention is not particularly limited, and can be produced, for example, by the following steps.

First, the above glass base material is subjected to press molding, plate molding, and the like, and is further subjected to diamond processing to form a donut disk shape. Next, lapping of the upper and lower surfaces is performed so that the thickness of the disk falls within a specified range, and the parallelism of the upper and lower surfaces of the substrate is obtained.

Next, the inner circumference and the outer circumference are processed. First, grinding and lapping of the inner periphery and outer periphery are performed, and then chamfering of the inner periphery or the outer periphery is performed.

Thereafter, the upper and lower surfaces and, if necessary, the inner and outer periphery are polished to finish the surface. When the glass of the base material is a glass for chemical strengthening, a chemical strengthening treatment of immersing in a molten salt and performing ion exchange is performed.

The chemical strengthening treatment method used in the present invention is not particularly limited, but a method capable of performing ion exchange at a relatively low temperature is preferably used. And as the alkali molten salt used for chemical strengthening, potassium nitrate,
Sodium nitrate or a mixed nitrate thereof is preferably used.

The magnetic disk of the present invention is manufactured by sequentially laminating an underlayer, a magnetic layer, a protective layer and, if necessary, a lubricating layer on a glass substrate which has been subjected to the above processing. As the underlayer, a metal such as Cr, Mo, TiTa, W, or Al, or a combination of these metals is used. For the magnetic layer, Co
CoPtCr, CoCrT, which are alloys mainly composed of
a, CoNiCrTa and the like. Examples of the protective film include a C (carbon) film, a SiO ₂ , ZrO ₂ , Cr, or Cr alloy film. As the lubricating layer, a lubricant such as perfluoropolyether or tetraalkoxysilane can be used as needed.

FIG. 1 is a schematic sectional view of a disk end according to the present invention. In the drawing, the width a of the disk end face is 0.
It is not less than 05 mm and not more than 0.35 mm. If the width a of the disk end surface is less than 0.05 mm, the width of the disk end surface is small, and the frequency of chipping of the end surface increases due to concentration of stress when the disk comes into contact with the jig. In assembling the magnetic disk drive, the chucking area for fixing to the spindle is reduced, so that the substrate is easily warped due to the fixing stress. The width a of the disk end face is 0.05
If it exceeds mm, the width of the end face of the disk is increased, so that the contact area with the jig is increased. In this case as well, dust generation from the end face of the disk is increased. More preferably, the width a of the disk end face is 0.1 mm or more and 0.3 mm or less.

In FIG. 1, the angle .theta. Formed by the chamfered surface of the end of the disk substrate according to the present invention with respect to the plate surface is not less than 48.degree. If θ is less than 48 °, the angle between the end surface and the chamfered surface is sharp, so that dust generation from that portion is not small. The ratio of the chamfered portion to the area of the recording surface of the substrate cannot be ignored. Also, if θ exceeds 80 °, the effect of chamfering itself decreases,
Therefore, dust generation from the end of the disk cannot be prevented. It is more preferable that the angle θ formed by the chamfered surface of the end portion with respect to the plate surface of the disk substrate is 50 ° or more and 75 ° or less.

The above-described chamfering according to the present invention is preferably performed on the inner peripheral end portion and the outer peripheral end portion. However, it is also effective to perform the chamfering only on any part where the jig contacts.

Next, the operation of the present invention will be described.

According to the present invention, minute chipping at the edge of the glass substrate is prevented, so that dust generation during the process is reduced. As a result, by using the substrate of the present invention, the defects of the manufactured magnetic disk can be reduced. At this time, the inner and outer circumferences of the glass substrate are polished and then subjected to chemical strengthening treatment, thereby removing irregularities on the inner and outer peripheral surfaces, which are easily chipped, and improving the surface strength. Prevention of dust generation due to chipping of the part becomes more reliable.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be specifically described below based on examples.

(Example 1) As a glass composition, Si was used.
O ₂ : 65% by weight, Al ₂ O ₃ : 14% by weight, Li
₂ O: 6% by weight, Na ₂ O: 11% by weight, ZrO ₂ : 4
A weight-% aluminosilicate glass pressed to a diameter of 68 mm and a thickness of 1.8 mm was used as a base material. Next, the upper and lower surfaces were ground using a rough diamond grindstone to a thickness of 1.0 mm. Next, Speed Fam 16
Using a polishing machine B, lapping of the upper and lower surfaces was performed using # 500 silicon carbide as an abrasive.

Next, a prepared hole was formed on the inner periphery, and the inner and outer peripheral surfaces were machined using an inner and outer peripheral processing machine. Thereafter, the inner and outer peripheral edges were chamfered, and the shape of the edge was a = 0.3 mm and the chamfer angle θ = 52 °.

Next, the upper and lower surfaces, the inner periphery, and the outer periphery were polished with # 1000 alumina abrasive grains. Subsequently, primary polishing of the upper and lower surfaces was performed using cerium oxide as an abrasive, and a polyurethane pad (Rodelnitta M) as a polisher.
HC14B). MR head and GM
In order to obtain a smoothness suitable for R head running, secondary polishing is performed using cerium oxide as an abrasive and a foamed polyurethane pad (Polytex manufactured by Rodel Nitta) as a polisher to obtain a surface roughness of 0.35 μm and flatness. 1.5 μm
I got The surface roughness is measured by an atomic force microscope (AFM), and the flatness is a value measured by a laser interferometer.

Thereafter, the polished glass substrate is preheated, and potassium nitrate 60% and sodium nitrate 40%
After performing chemical strengthening treatment by immersing in a 400 ° C. mixed melt for 4 hours, precision cleaning was performed.

The glass substrate thus obtained was placed in a substrate case, and the glass substrate was vibrated through a vibrating sieve for 15 minutes. After that, the surface of the substrate was inspected.

Further, a Cr underlayer, a CoPtCr magnetic layer, and a carbon protective layer were sequentially laminated on both surfaces of the glass substrate obtained in the above-described process, to obtain a magnetic disk. In this step, when the process was carried out after repeating the attachment and detachment to and from the jig when performing sputtering on the glass substrate three times, no defect was found in the obtained magnetic disk.

Comparative Example 1 A glass substrate was prepared in the same process as in Example 1, except that the width a of the end face after chamfering was set to 0.03 and the chamfer angle θ was set to 60 °. Further, an underlayer, a magnetic layer, a protective layer, and a lubricating layer were sequentially laminated on this substrate to produce a magnetic disk. When a vibration test was performed on the manufactured glass substrate under the same conditions as in Example 1, foreign substances were found to adhere to the substrate surface. In addition, when a test for attachment and detachment to and from a jig was performed when sputtering was performed under the same conditions as in Example 1, defects were found in the obtained magnetic disk. As a result of the investigation, it was found that all of the causes were due to the generation of fine chips at the tip of the end portion and the generation of dust.

Comparative Example 2 A glass substrate was prepared in the same process as in Example 1 except that the width a of the end face after chamfering was 0.40 and the chamfer angle θ was 60 °. Further, an underlayer, a magnetic layer, a protective layer, and a lubricating layer were sequentially laminated on this substrate to produce a magnetic disk. When a vibration test was performed on the manufactured glass substrate under the same conditions as in Example 1, foreign substances were found to adhere to the substrate surface. In addition, when a test for attachment and detachment to and from a jig was performed when sputtering was performed under the same conditions as in Example 1, defects were found in the obtained magnetic disk. As a result of the investigation, it was found that all of the causes were caused by minute chipping on the end face and dust generation.

Comparative Example 3 A glass substrate was prepared in the same process as in Example 1, except that the width a of the end face after chamfering was 0.25 and the chamfer angle θ was 30 °. Further, an underlayer, a magnetic layer, a protective layer, and a lubricating layer were sequentially laminated on this substrate to produce a magnetic disk. When a vibration test was performed on the manufactured glass substrate under the same conditions as in Example 1, foreign substances were found to adhere to the substrate surface. In addition, when a vibration test for attaching and detaching the jig when performing sputtering under the same conditions as in Example 1 was performed, a defect was recognized in the obtained magnetic disk. As a result of the investigation, it was found that all of the causes were due to generation of fine chips at the edges between the end face and the chamfered face, and generation of dust.

Comparative Example 4 A glass substrate was prepared in the same process as in Example 1 except that the width a of the end face after chamfering was 0.25 and the chamfer angle θ was 85 °. Further, an underlayer, a magnetic layer, a protective layer, and a lubricating layer were sequentially laminated on this substrate to produce a magnetic disk. When a vibration test was performed on the manufactured glass substrate under the same conditions as in Example 1, foreign substances were found to adhere to the substrate surface. In addition, when a vibration test for attaching and detaching the jig when performing sputtering under the same conditions as in Example 1 was performed, a defect was recognized in the obtained magnetic disk. As a result of the investigation, it was found that all of the causes were due to the generation of fine chips at the edges of the upper and lower surfaces and the chamfered surfaces.

[0033]

As described in detail above, according to the present invention, dust generation due to minute chipping of the end surface of the glass substrate can be prevented, so that the occurrence of defects is small and the production yield of the magnetic disk is improved. The obtained glass substrate for a magnetic disk can be provided. Further, by manufacturing a magnetic disk using this glass substrate, defects of the magnetic disk can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing the shape of an end of a glass substrate of the present invention.

[Explanation of symbols]

1 ... glass substrate, 2 ... end face, 3 ... chamfered part,
4 ... upper surface of glass substrate 5 ... lower surface of glass substrate

Claims (3)

[Claims] 1. A glass substrate for a magnetic disk comprising a glass composition, wherein the inner or outer edge of the glass substrate is chamfered, and the width of the inner or outer edge is 0.05 mm or more. 35 mm or less, and
The angle between the edge and the chamfered surface with respect to the plate surface of the substrate is 48.
A glass substrate characterized by being at least 80 ° and at most 80 °. 2. The glass substrate for a magnetic disk according to claim 1, wherein an end surface of an inner peripheral portion or an outer peripheral portion of the glass substrate made of the glass composition is subjected to a chemical strengthening process after polishing. . 3. A magnetic disk, wherein a magnetic recording layer is provided on the glass substrate for a magnetic disk according to claim 1.