JPH10194787A - Glass substrate for recording medium, and production of recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a glass substrate for a recording medium, equalized in the depths of compression strain layers on the front and back surfaces of the glass substrate to correct the curvature of the substrate, and excellent in flatness by chemically reinforcing again an already chemically reinforced glass substrate different in the depths of the compression strains on the front and back surfaces. SOLUTION: When a glass substrate different in the depths of compression strain layers on the front and back surfaces is again chemically reinforced, the permeation rate or amount of relatively larger diameter ions permeated from an ion exchange treatment liquid into the surface layer portion of the glass substrate is excellent in comparison with a case the ions are permeated into a surface layer portion on the side large in the depth of the compression strain layer. When the front and back surfaces of the glass substrate are thereby again chemically reinforced in the same conditions, the depths of the compression strain layers on the front and back surfaces are equalized. The curvature of the again chemically reinforced glass substrate is preferably <=5μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a glass substrate for a recording medium, a method for manufacturing a recording medium, and the like.

[0002]

2. Description of the Related Art Aluminum substrates have been widely used as substrates for magnetic recording media such as magnetic disks. However, as magnetic disks have become smaller and thinner and recording density has increased, the strength and flatness of aluminum substrates have been reduced. Is gradually being replaced by a glass substrate with excellent properties.

[0003] This is because glass substrates have characteristics such as having sufficient hardness to cope with recent small-diameter and thinner hard disks, have excellent physical and chemical durability, and have a comparative surface. Can be easily formed with high plane accuracy.
Therefore, it is more suitable for realizing high-density recording that the magnetic head has such a property that the spacing can be reduced and the magnetic head can easily be operated at a low flying height.

[0004] Generally, in glass substrates for recording media such as magnetic disks, the surface of the glass substrate is often subjected to chemical strengthening treatment in order to improve the strength of the glass substrate.

More specifically, when a glass substrate is used as a magnetic disk substrate, the surface of the glass substrate is kept at a low temperature in order to improve the shock resistance and vibration resistance and to prevent the substrate from being damaged by shock or vibration. In many cases, chemical strengthening treatment is performed by an ion exchange method.

The chemical strengthening treatment is performed, for example, by using L in glass.
i, Na ions, etc., are replaced by Na, K ions, etc., having a relatively large ionic radius by ion exchange,
This is a process for generating a strong compressive stress in the glass surface layer to increase the strength.

The substrate may be polished to improve the smoothness of the substrate after the chemical strengthening process or to remove impurities adhering to the substrate during the chemical strengthening.

[0008]

As described above, when the substrate is polished again after the chemical strengthening, the glass substrate is warped. This is because the chemically strengthened substrate is balanced because a compressive strain layer (compressive stress layer) is formed on the surface of the substrate and a tensile stress layer is formed inside the substrate.
This is because the re-polishing after the chemical strengthening causes a difference in the depth of each of the compression strain layers on the front surface and the back surface of the substrate, and as a result, the substrate is warped.

In order to solve such a problem, a method of controlling the amount of polishing on the front surface and the back surface of the substrate has been proposed as disclosed in Japanese Patent Application Laid-Open No. Hei 7-134823. It was difficult to remove.

A similar problem also occurs in the case of recycling (reproducing) a glass substrate for a magnetic disk. That is, when the completed magnetic disk becomes defective, the thin film such as the magnetic layer is peeled off and the surface of the glass substrate on which the thin film is formed is polished again. The depth of the compression-strained layer on the polished front surface becomes shallower than that on the rear surface, and warpage occurs.

The present invention has been made under the above-mentioned background, and has as its first object to provide a glass substrate for a recording medium having a small flatness and excellent flatness.

It is a second object of the present invention to provide a recording medium in which the substrate is less warped and has excellent flatness.

[0013]

Means for Solving the Problems In order to achieve the above object, the present inventors have conducted intensive studies and as a result, the depth of the compressively strained layer is different between the front surface and the back surface of a chemically strengthened glass substrate. When the glass substrate is chemically strengthened again, ions having a relatively large ionic radius that enter the surface layer of the glass substrate from the ion exchange treatment liquid enter the surface layer on the side where the depth of the compressively strained layer is shallow. Is superior in speed or amount to the case where the depth of the compressively strained layer enters the deeper surface layer portion, and when the front and back surfaces of the glass substrate are chemically strengthened again under the same conditions, the depth of the compressively strained layer becomes larger. Are equalized,
The inventors have found that the warpage of the glass substrate can be corrected, and have completed the present invention.

That is, the method of manufacturing a glass substrate for a recording medium according to the present invention is a method of manufacturing a glass substrate for a recording medium which has been chemically strengthened. The difference between the depths is reduced by re-chemical strengthening.

In another method of manufacturing a glass substrate for a recording medium according to the present invention, the main surface of the glass substrate is ground and polished, then chemically strengthened, polished again, and then the surface of the glass substrate is chemically strengthened. And the difference in depth of each of the compression-strained layers formed on the back surface is reduced by re-chemical strengthening.

Further, the method of manufacturing a glass substrate for a recording medium according to the present invention is further characterized in that the thin film is peeled off from the chemically strengthened glass substrate on which the thin film is formed, polished, and then the front and back surfaces of the glass substrate are chemically strengthened. The difference in the depth of each of the compression-strained layers formed in each of the above is reduced by re-chemical strengthening.

Further, the method for producing a glass substrate for a recording medium of the present invention is the same as the above method for producing a glass substrate for a recording medium, wherein the warpage of the glass substrate is 5 μm or less.

Further, the method for producing a recording medium according to the present invention comprises:
At least a recording layer is formed on the glass substrate for a recording medium manufactured by the method for manufacturing a glass substrate for a recording medium of the present invention.

[0019]

According to the present invention, the depth of the compression-strained layer is equalized by chemically strengthening again the glass substrate which is a chemically strengthened glass substrate in which the depth of the compression-strained layer is different between the front surface and the back surface. Thus, the warpage of the glass substrate can be corrected. Therefore, a glass substrate for a recording medium having less warpage of the substrate and excellent flatness can be obtained.

Hereinafter, the present invention will be described in detail.

The present invention is characterized in that the difference in the depth of each of the strained layers formed on the front and back surfaces of the glass substrate by chemical strengthening is reduced by re-chemical strengthening.

Here, the origin of the glass substrate in which the depth of the compressively strained layer is different between the front surface and the rear surface is not particularly limited, and may be caused by any cause. Such a glass substrate is usually generated by polishing a chemically strengthened glass substrate. For example, it occurs when the main surface of a glass substrate is ground and polished, then chemically strengthened, and then polished again.
It also occurs when the thin film is peeled from the chemically strengthened glass substrate on which the thin film is formed, polished and recycled.

The depth of the compression-strained layer formed on the front and back surfaces by the first chemical strengthening, the value of the compression stress, and the like are not particularly limited. Further, the glass composition of the chemically strengthened glass substrate is not particularly limited.

In the present invention, the chemical strengthening may be performed again by appropriately selecting and controlling the chemical strengthening conditions (chemical strengthening solution, temperature, time, etc.). The re-chemical strengthening may be under the same conditions as the first chemical strengthening or under different conditions.

Since there is a correlation between the difference in the depth of the compression-strained layers on the front and back surfaces and the warpage of the substrate, the difference in the depths of the compression-strained layers on the front and back surfaces is preferably zero or close to zero.
This is because the difference in the depth of the compressive strain layers on the front and back surfaces after the re-chemical strengthening is preferably zero in order to minimize the warpage of the substrate. If the difference is close to zero, the warpage of the substrate is substantially small and there is no practical problem.

The warpage of the glass substrate after the re-chemical strengthening is preferably 3 μm or less, more preferably 1 μm or less.

In the present invention, the chemical strengthening method in the first chemical strengthening and re-chemical strengthening is not particularly limited as long as it is a conventionally known chemical strengthening method.

The chemical strengthening of the glass substrate is performed, for example, by immersing the glass substrate in a heated chemical strengthening solution and ion-exchanging ions on the surface layer of the glass substrate with ions in the chemical strengthening solution.

Here, as the ion exchange method, a low-temperature type ion exchange method, a high-temperature type ion exchange method, a surface crystallization method, a dealkalization method of a glass surface, and the like are known. It is preferable to use a low-temperature ion exchange method in which ion exchange is performed in a region not exceeding a transition temperature.

In the low-temperature ion exchange method, alkali ions in glass are replaced with alkali ions having a larger ionic radius in a temperature range not higher than the glass transition temperature Tg.
This is a method in which a strong compressive stress is generated in the glass surface layer by increasing the volume of the ion exchange section, thereby strengthening the glass surface.

As the chemical strengthening solution, potassium nitrate (K
Molten salts such as NO ₃ ), sodium nitrate (NaNO ₃ ) and potassium carbonate (K ₂ CO ₃ ), and molten salts of a mixture of these salts (KNO ₃ + NaNO ₃ , KNO ₃ + K ₂ CO ₃ ); Alternatively, Cu, Ag, Rb, C
Examples thereof include a molten salt of a mixture of salts of ions such as s. Note that the chemical strengthening solution may be a solution of the above salt instead of the molten salt.

The heating temperature of the chemical strengthening solution is 280-66.
0 ° C, particularly 300-400 ° C, is preferred.

The immersion time is preferably several hours to several tens of hours.

It is preferable that the glass substrate is preheated before immersing the glass substrate in the molten salt.

The glass substrate is not particularly limited as long as it can be chemically strengthened. Further, the size, thickness, and the like of the glass substrate are not particularly limited.

The thickness of the glass substrate is 0.1 to 20.
mm, and more preferably about 0.635 to 0.889 mm.

Examples of the material of the glass substrate include aluminosilicate glass, soda lime glass, sodaaluminosilicate glass, aluminoborosilicate glass,
Examples thereof include borosilicate glass, quartz glass, chain silicate glass, and glass ceramics such as crystallized glass. In addition, aluminosilicate glass is
It is particularly preferable because it has excellent impact resistance and vibration resistance.

As the aluminosilicate glass, Si
O ₂ : 62 to 75% by weight, Al ₂ O ₃ : 5 to 15% by weight,
Li ₂ O: 4 to 10% by weight, Na ₂ O: 4 to 12% by weight,
ZrO _2: 5.5 to 15 with containing by weight% as the main component, the weight ratio of Na ₂ O / ZrO ₂ is 0.5 to 2.
0, Al ₂ O ₃ / weight ratio of ZrO ₂ of glass for chemical strengthening is 0.4 to 2.5 is preferred.

In order to eliminate projections on the glass substrate surface caused by undissolved ZrO ₂ , 57% to 74% of SiO ₂ , 0% to 2.8% of ZnO ₂ ,
The Al ₂ O ₃ 3~15%, the LiO ₂ 7~16%, Na ₂ O
It is preferable to use glass for chemical strengthening containing 4 to 14%.

Such an aluminosilicate glass is
By chemically strengthening, the three factors of compressive stress, tensile stress, and depth of compressive stress layer can be controlled in a well-balanced manner, and the bending strength and heat resistance are excellent, and there is no precipitation of Na even in a high temperature environment. In addition, it maintains flatness and has excellent Knoop hardness.

The method of polishing (including re-polishing) the chemically strengthened glass substrate is not particularly limited, and a known polishing technique can be used.

Examples of the polishing method include polishing with a polishing pad (polishing powder) such as a soft polisher and a hard polisher, polishing with an abrasive (abrasives and the like), and mechanical polishing such as brush polishing. In addition, these mechanical polishing,
In order to obtain a mirror surface having a required surface roughness, different types of mechanical polishing, or mechanical polishing using different types of polishers, different particle sizes, or the like can be appropriately combined.

Here, as the soft polisher, for example,
Suedes and velours are used as materials. Examples of the hard polisher include hard velours, urethane foam, and pitch impregnated suede. Cerium oxide (CeO ₂ ), alumina (γ-
Al ₂ O ₃ ), bran (Fe ₂ O ₃ ), chromium oxide (Cr
₂ O ₃ ), zirconium oxide (ZrO ₂ ), titanium oxide (TiO ₂ ) and the like.

The grinding and polishing steps of the main surface of the glass substrate (indicating the surface on which the recording layer is formed, indicating one or both sides) are not particularly limited, and known grinding and polishing steps can be used.

The steps of grinding and polishing a glass substrate are usually
It can be roughly divided into (1) rough grinding (rough grinding), (2) sanding (fine grinding, lapping), (3) first polishing (polishing), (4) second polishing (final polishing, polishing)
Of each process.

The surface roughness of the glass substrate is preferably R
max: 0.01 to 2 μm, Ra: 0.001 to 1 μm
Less, more preferably, Rmax: 0.01-1 μm
m, Ra: 0.001 to 0.8 μm, more preferably Rmax: 0.01 to 1 μm, Ra: 0.001
０．５0.5 μm.

The above-described glass substrate for a recording medium of the present invention can be used as a glass substrate for a magneto-optical disk and a disk substrate for an electro-optical disk such as an optical disk, in addition to a glass substrate for a magnetic recording medium.

Next, a method for manufacturing the recording medium of the present invention will be described.

The method for producing a recording medium of the present invention is characterized in that at least a recording layer is formed on a glass substrate for a recording medium obtained by the above-mentioned method of the present invention.

In the present invention, since a glass substrate for a recording medium having less warpage of the substrate and excellent flatness is used, a recording medium having less warpage of the substrate and excellent flatness can be obtained.

Hereinafter, a method for manufacturing a recording medium according to the present invention will be described by taking a magnetic recording medium as an example.

The magnetic recording medium is usually manufactured by sequentially laminating an underlayer, a magnetic layer, a protective layer and a lubricating layer on a glass substrate for a magnetic disk. In the present invention, a glass substrate for a recording medium obtained by the above-described method of the present invention is used.

The underlayer in the magnetic recording medium is selected according to the magnetic layer.

As the underlayer, for example, Cr, Mo, T
a, an underlayer made of at least one material selected from nonmagnetic metals such as Ti, W, V, B, and Al. In the case of a magnetic layer containing Co as a main component, it is preferable to use Cr alone or a Cr alloy from the viewpoint of improving magnetic properties. The underlayer is not limited to a single layer, and may have a multilayer structure in which the same or different layers are stacked. For example, Cr / Cr, Cr / CrMo, Cr / CrV, Cr
V / CrV, Al / Cr / CrMo, Al / Cr / C
r, a multilayer base layer of Al / Cr / CrV, Al / CrV / CrV and the like.

The material of the magnetic layer in the magnetic recording medium is not particularly limited.

As the magnetic layer, for example, CoPt, CoCr, CoNi, CoNiCr, C
oCrTa, CoPtCr, CoNiPt, CoNi
CrPt, CoNiCrTa, CoCrTaPt, Co
A magnetic thin film such as CrPtSiO may be used. The magnetic layer is made of a non-magnetic film (for example, Cr, CrMo, Cr).
V, etc. to reduce noise (for example, CoPtCr / CrMo / CoPtCr, CoC
rTaPt / CrMo / CoCrTaPt).

As a magnetic layer corresponding to a magnetoresistive head (MR head) or a large magnetoresistive head (GMR head), Y, Si, rare earth elements, Hf, G
An impurity element selected from e, Sn, and Zn, or an element containing an oxide of these impurity elements is also included.

As the magnetic layer, in addition to the above, magnetic particles such as Fe, Co, FeCo, and CoNiPt are dispersed in a non-magnetic film made of ferrite, iron-rare earth, SiO ₂ , BN, or the like. It may be a granular structure or the like. Further, the magnetic layer may have any of an inner surface type and a perpendicular type recording format.

The protective layer in the magnetic recording medium is not particularly limited.

Examples of the protective layer include a Cr film, a Cr alloy film, a carbon film, a zirconia film, and a silica film. These protective films can be continuously formed with an underlayer, a magnetic layer, and the like by an in-line type sputtering apparatus. Also,
These protective films may have a single-layer structure or a multilayer structure composed of the same or different films.

In the present invention, another protective layer may be formed on the above protective layer or in place of the above protective layer. For example, instead of the above-mentioned protective layer, colloidal silica fine particles are dispersed and applied to a Cr film after diluting tetraalkoxylan with an alcohol-based solvent, and then fired to form a silicon oxide (SiO ₂ ) film. It may be formed.

The lubricating layer in the magnetic recording medium is not particularly limited.

The lubricating layer is prepared, for example, by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a solvent such as Freon, and applying the diluted solution to the medium surface by dipping, spin coating, or spraying. It is formed by performing heat treatment.

[0064]

EXAMPLES The present invention will be described below more specifically based on examples.

Embodiment 1

Production of Glass Substrate On the front and back surfaces, a strength of 20 kg / mm ² at a depth of 100 μm
, A chemically strengthened glass substrate having a thickness of 0.6 mm and an outer diameter of 65 mmφ having a tensile stress of 3 kg / mm ² inside was prepared.

As a glass substrate, in terms of mol%, SiO ₂ is 57 to 74%, ZnO ₂ is 0 to 2.8%,
The Al ₂ O ₃ 3~15%, the LiO ₂ 7~16%, Na ₂ O
For chemical strengthening comprising an aluminosilicate glass containing 4 to 14% as a main component (for example, mol%
As shown, SiO ₂ : 67.0%, ZnO ₂ : 1.0%, A
l ₂ O ₃ : 9.0%, LiO ₂ : 12.0%, Na ₂ O: 1
Glass for chemical strengthening containing 0.0% as a main component) was used. Chemical strengthening is performed by potassium nitrate (60%)
And a nitric acid solution (40%) were prepared, and the chemically strengthened solution was heated to 400 ° C.
The cleaning was performed by immersing the cleaned glass substrate preheated to a temperature of about 4 hours.

Next, in order to improve the flatness of the surface on which the thin film is formed, both main surfaces of the glass substrate prepared above were polished by 1 to 2 μm. At this time, the flatness deteriorated to 4 microns.

Next, the polished glass substrate was immersed in a chemical strengthening treatment solution for about 2 hours (about half the processing time of the first chemical strengthening treatment). It was confirmed that the flatness was improved to 1 micron by the re-chemical strengthening treatment, and the chemically strengthened glass substrate was restored to a state before polishing.

Manufacture of Magnetic Disk A texture layer, a Cr underlayer, a CrMo underlayer, and a CoPtCrTa magnetic layer were formed on both surfaces of a glass substrate for a magnetic disk obtained through the above-described steps by using an in-line sputtering apparatus. A layer and a C protective layer were sequentially formed to obtain a magnetic disk.

The flatness of the obtained magnetic disk was 1 μm.

When a glide test was performed on the obtained magnetic disk, a hit (the head touches a protrusion on the surface of the magnetic disk) and a crash (the head collides with a protrusion on the surface of the magnetic disk) were recognized. Did not.

Example 2 Production of Glass Substrate On the front and back surfaces, a strength of 20 kg / mm ² at a depth of 100 μm
And a chemically strengthened glass substrate having a thickness of 0.6 mm and an outer diameter of 65 mm having a tensile strain of 3 kg / mm ² inside was prepared.

As the glass substrate, in terms of mol%, SiO ₂ is 57 to 74%, ZnO ₂ is 0 to 2.8%,
The Al ₂ O ₃ 3~15%, the LiO ₂ 7~16%, Na ₂ O
For chemical strengthening comprising an aluminosilicate glass containing 4 to 14% as a main component (for example, mol%
As shown, SiO ₂ : 67.0%, ZnO ₂ : 1.0%, A
l ₂ O ₃ : 9.0%, LiO ₂ : 12.0%, Na ₂ O: 1
Glass for chemical strengthening containing 0.0% as a main component) was used. Chemical strengthening is performed by potassium nitrate (60%)
And a nitric acid solution (40%) were prepared, and the chemically strengthened solution was heated to 400 ° C.
The cleaning was performed by immersing a washed glass substrate that had been preheated to ° C.

Manufacture of Magnetic Disk A texture layer, a Cr underlayer, a CrMo underlayer, and a CoPtCrTa magnetic layer were formed on both surfaces of a glass substrate for a magnetic disk obtained through the above-described steps by using an in-line type sputtering apparatus. A layer and a C protective layer were sequentially formed to obtain a magnetic disk.

The thin film was removed from the magnetic disk obtained above by etching and returned to the glass substrate, and both main surfaces of the glass substrate were polished by 2 to 3 μm. The flatness at this time deteriorated to 5.38 microns on average.

Next, the polished glass substrate was immersed in a chemical strengthening treatment solution for about 4 hours. By this re-chemical strengthening treatment, the flatness is improved to 3.21 microns on average,
It was confirmed that the glass substrate that had been chemically strengthened was restored to a state before polishing.

Manufacture of Magnetic Disk A texture layer, a Cr underlayer, a CrMo underlayer, and a CoPtCrTa magnetic layer were formed on both sides of a glass substrate for a magnetic disk obtained through the above-described steps by using an in-line type sputtering apparatus. A layer and a C protective layer were sequentially formed to obtain a magnetic disk.

The flatness of the obtained magnetic disk was about 3 μm on average.

When a glide test was performed on the obtained magnetic disk, a hit (the head touches a protrusion on the surface of the magnetic disk) and a crash (the head hits a protrusion on the surface of the magnetic disk) were recognized. Did not.

Examples 3-4 Glass for magnetic disks was prepared in the same manner as in Example 1 except that soda lime glass (Example 3) and soda aluminosilicate glass (Example 4) were used instead of aluminosilicate glass. A substrate and a magnetic disk were obtained.

The same test as in Example 1 was performed on the obtained magnetic disk, and the same effect as in Example 1 was confirmed.

Example 5 On both sides of the glass substrate for a magnetic disk obtained in Example 1, Al (film thickness 50 Å) / Cr (100
0 Å / CrMo (100 Å), CoPtCr (120 Å) / CrMo (50 Å) / Co
A magnetic layer made of PtCr (120 Å),
A Cr (50 Å) protective layer was formed by an in-line type sputtering apparatus.

The above substrate is immersed in an organic silicon compound solution (a mixed solution of water, IPA and tetraethoxysilane) in which fine silica particles (particle size: 100 Å) are dispersed,
A protective layer having a texture function made of SiO ₂ is formed by firing, and a dip treatment is performed on the protective layer with a lubricant made of perfluoropolyether to form a lubricating layer. Got a disc.

As a result of performing the same test as in Example 1 on the obtained magnetic disk, the same effect as in Example 1 was confirmed.

Example 6 The underlayer was made of Al / Cr / Cr, and the magnetic layer was made of CoNiCr.
A magnetic disk for a thin film head was obtained in the same manner as in Example 5 except that Ta was used.

The same thing as Example 5 was confirmed for the above magnetic disk.

Although the present invention has been described with reference to the preferred embodiments, the present invention is not necessarily limited to the above embodiments.

For example, the type of the glass substrate and the type of the recording layer such as the magnetic layer are not limited to those of the embodiment.

[0090]

As described above, according to the present invention, a glass substrate which is chemically strengthened and whose compression strain layer has a different depth between the front surface and the back surface is chemically strengthened again. The depth of the strained layer is equalized, and the warpage of the glass substrate can be corrected. Therefore, a glass substrate for a recording medium and a recording medium which are less warped and excellent in flatness can be obtained.

Claims (5)

[Claims] 1. A method for manufacturing a chemically strengthened glass substrate for a recording medium, wherein the difference in depth between the compression-strained layers formed on the front and back surfaces of the glass substrate by chemical strengthening is re-chemically strengthened. A method for producing a glass substrate for a recording medium, characterized in that the method comprises: 2. The main surface of the glass substrate is ground and polished, then chemically strengthened, polished again, and then the depth of each of the compressively strained layers respectively formed on the front and back surfaces of the glass substrate by chemical strengthening. Characterized in that the difference between the two is reduced by re-chemical strengthening. 3. The thickness difference between the compression-strained layers formed on the front and back surfaces of the glass substrate by chemical strengthening after peeling and polishing the thin film from the chemically strengthened glass substrate on which the thin film is formed. Is reduced by re-chemical strengthening, thereby producing a glass substrate for a recording medium. 4. The glass substrate for a recording medium according to claim 1, wherein the warpage of the glass substrate is 5 μm or less. 5. A method for manufacturing a recording medium, comprising: forming at least a recording layer on the glass substrate for a recording medium according to claim 1.