JPH11322374A - Production of glass substrate for magnetically recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the surface smoothness and flatness of glass substrate excellent without impairing the effect of chemical strengthening treatment, by polishing the surface of a glass disk to conduct chemical strengthening, by removing formed surface projections to attain a specific surface roughness without reducing a compressive stress layer. SOLUTION: The purpose of this invention is achieved by the following steps: (1) polishing the surface of a disk molded from glass base by means of an abrasive such as cerium oxide; (2) chemically strengthening treatmenting this disk wherein the disk is dipped in a fused salt to replace the ions (e.g. Li<+> , Na<+> ) near the glass surface with ions in the fused salt, larger in their ionic radius than that of the ions near the glass surface, and e.g. Li<+> is displaced with Na<+> and Na<+> is displaced with K<+> . This treatment forms a compressed layer in the surface of the disk and strengthens the disk; (3) preferentially removing peaking formed on the disk surface due to the chemically strengthening treatment by floating polish, etc., to attain the average surface roughness Ra of the disk, surface of <=0.5 nm, the maximum height Ry of the peaking of <=5.0 nm and the average flatness of <=3 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a glass substrate for a magnetic recording medium used for a magnetic disk or the like.

[0002]

2. Description of the Related Art A magnetic disk device used as an external storage device of a computer or the like has been developed in accordance with recent advances in computer software and operating systems.
With the rapid increase in capacity, the recording density of magnetic disks, which are recording media, is being increased.

Most of the current magnetic disk drives are CS
The S (contact start / stop) method is employed, and according to this method, the magnetic head is in contact with the magnetic disk when the apparatus stops. However, when the apparatus starts operating and the disk starts rotating, buoyancy is generated by airflow, and the magnetic head flies. Recording and reproduction are performed on the CSS type magnetic disk with the magnetic head flying above.

In such a magnetic disk device, the flying height of a magnetic head has been reduced to increase the recording density. As the flying height of the magnetic head becomes smaller, for accurate recording and reproduction of signals,
It has become necessary for the magnetic disk surface to be smoother and more flat.

Recently, as the size of magnetic disks has been reduced, glass substrates have been used as magnetic disk substrates. Since a glass substrate can easily obtain good smoothness and good planarity as compared with an aluminum alloy substrate, it is suitable as a substrate for a magnetic recording medium aiming at high density. However, glass has a drawback in strength, which is generally more brittle than aluminum alloys.
When used for a magnetic recording medium substrate, it is common practice to perform a strengthening process to increase the strength of the glass.

As a method of strengthening the glass substrate, for example, a chemical strengthening method by ion exchange (Japanese Patent Publication No. 3-52130) can be mentioned. In this method, after polishing a glass substrate, the glass substrate is held in a potassium nitrate melt for several hours, and exchange of Na ⁺ ions in the glass with K ⁺ ions in the potassium nitrate melt to generate a compressive stress on the glass surface. It is intended to increase the strength of the glass substrate.

However, when the glass substrate is chemically strengthened by the above-mentioned method, the strength of the glass is improved, but the surface property is deteriorated. If the surface property is impaired, it becomes difficult to use the magnetic head as a substrate for low flying height.

Therefore, as one of the methods for solving the above-mentioned difficulties, a glass substrate is polished to have a surface roughness (Rmax) of 50 nm.
After the following, after performing a chemical strengthening treatment by ion exchange, by performing polishing again so that the reduction in thickness due to polishing is larger than 0.7 μm on one side,
There is a method of improving the surface properties while improving the strength of a glass substrate (Japanese Patent Application Laid-Open No. 8-124153).

[0009]

However, in this method, although the surface smoothness of the glass substrate is improved, a part of the compressive stress layer very close to the substrate surface caused by the chemical strengthening treatment by ion exchange is re-used. Because of the removal by the polishing process, the effect of the chemical strengthening process is impaired, and the balance between the stresses between the front and back surfaces of the glass is broken, causing a new problem that the substrate is warped and the flatness is reduced. Was. Such a decrease in flatness appears remarkably in a glass substrate having a thickness of 1 mm or less, and becomes a fatal defect particularly in a glass substrate having a thickness of 0.7 mm or less.

The present invention has been made on the basis of the above circumstances. In a glass substrate which has been subjected to a chemical strengthening treatment, both the surface smoothness and the flatness are good without impairing the effect of the chemical strengthening treatment, and It is an object of the present invention to provide a method of manufacturing a glass substrate for magnetic recording suitable for use in a magnetic disk compatible with a low flying head.

[0011]

According to the present invention, there is provided a method of manufacturing a glass substrate for a magnetic recording medium, comprising the steps of: forming a glass base material into a disk; polishing the surface of the disk; The method is characterized by including a step of performing a chemical strengthening treatment and a step of removing a protrusion generated on the surface of the disk by the chemical strengthening treatment and substantially not reducing the compressive stress layer.

Further, in the method of manufacturing a glass substrate for a magnetic recording medium according to the present invention, a step of forming a glass base material into a disk, a step of polishing the surface of the disk, and a step of chemically strengthening the disk And a step of removing protrusions on the surface of the disk caused by the chemical strengthening treatment and substantially not reducing the compressive stress layer, thereby reducing the average surface roughness Ra of the disk surface to 0.5 nm or less, The maximum height Ry is 5.0 nm or less, and the flatness is 3 μm or less.

Here, the amount Ra indicating the surface roughness is JIS.
The arithmetic average roughness, Ry, defined in standard B0601 is the maximum height also defined in JIS standard B0601. Further, the flatness is a magnitude of deviation from a geometrically correct plane, and in the present invention, a value obtained by using a Fizeau interferometer is defined as the magnitude of the flatness.

The present invention has been made based on the finding that the decrease in surface properties after the chemical curing treatment is due to the generation of minute projections.
This is based on the idea that the surface property can be restored by removing only these minute projections.

In the present invention, the composition of the glass material used as the substrate is not particularly limited. For example, a glass material such as aluminosilicate glass or soda glass, which can be subjected to a chemical strengthening treatment, may be used. Can be used. For example, Li ⁺ and Na ⁺ as alkali ions
And a glass containing 50% by weight or more of SiO ₂ and 10% by weight or more of Al ₂ O ₃ can be suitably used.

In the present invention, as a method of the polishing treatment performed before the chemical strengthening treatment, a general method of manufacturing a glass substrate can be adopted. For example, polishing performed using cerium oxide, silica, colloidal silica, aluminum oxide, or the like as an abrasive, under conditions of a surface pressure of 0 to 100 g / cm ² and a processing time of about 0.5 to 30 minutes can be employed. .

In the present invention, the method of chemical strengthening treatment is as follows:
Immersing the glass substrate in a molten salt by an ion exchange treatment to replace ions near the surface of the glass with ions of a molten salt having a larger ionic radius;
For example, a glass substrate having Li ⁺ and Na ⁺ is
I was immersed in ₃ and mixed molten salt of KNO ₃ and Li ⁺ Na
⁺ , And a compressed layer is formed on the surface by replacing Na ⁺ with K ⁺ .

In the present invention, there is no particular limitation on the method of removing the projections after the chemical strengthening treatment. For example, the reduction in the thickness direction of the glass substrate by polishing may be 0.05% on one side.
A method performed in a range of less than μm, more preferably in a range of less than 0.02 μm can be used.

Further, as a method for removing the projections after the chemical strengthening treatment of the present invention, a method of fluid floating polishing (floating polishing) can be suitably used. If this method is used, the polishing tool floats through the fluid containing the abrasive, so that it does not directly contact the surface of the disk, and the fluid containing the abrasive runs in the direction of the disk surface. It can be carried out.

As a method for removing the protrusions after the chemical strengthening treatment of the present invention, varnish widely used in a finishing step of a magnetic disk can be applied. By this method, the glass disk is rotated at a high speed, and the blade can be brought close to the disk surface to remove only the protrusions.

According to the present invention, only the protrusions on the surface of the glass substrate after the chemical strengthening treatment are removed, which is different from the prior art in which the surface layer is widely removed, thereby impairing the effect of the chemical strengthening treatment. Can be prevented. In addition, it is possible to prevent a part of the glass substrate surface having a compressive stress from being removed, thereby preventing the balance between the compressive stresses of the two surfaces from being lost and impairing the flatness.

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

According to the present invention, it has been found that the surface property of the glass substrate surface after the chemical strengthening treatment is reduced by the minute projections, and only the protrusions on the glass substrate surface after the chemical strengthening treatment are removed. It does not polish the entire surface of the substrate after the chemical strengthening treatment as in the prior art, and removes only the protrusions, so that the effect of the chemical curing treatment is lowered or the warpage occurs. Deterioration of flatness is avoided.

[0024]

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

EXAMPLE An aluminosilicate glass substrate was formed into a disk having a diameter of 65 mm and a thickness of 0.635 mm according to a conventional method, and polished with cerium oxide. The result of measuring the surface properties of the polished disk-shaped glass substrate is shown by symbol 1 in FIG.

The glass substrate was placed in a potassium nitrate melt for 4 hours.
The chemical strengthening treatment was performed by holding for a time. The result of measuring the surface properties after the chemical strengthening treatment is shown by symbol 2 in FIG. Surface roughness Ra after chemical strengthening treatment is 0.45 nm, Ry is 30.6
nm and the flatness were 0.8 μm.

Next, the glass substrate was polished to remove protrusions. The result of measuring the surface properties after removing the protrusions is shown as symbol 3 in FIG. The polishing amount during the polishing treatment was approximately 0 μm. The surface roughness Ra of the substrate after removing the protrusions is 0.30 nm, Ry is 3.0 nm, and the flatness is 0.8.
μm and no change.

[0028]

According to the present invention, the problem of deterioration in surface properties and flatness due to the strengthening of the glass substrate by the chemical strengthening treatment is solved, and it becomes possible to manufacture a glass substrate having high strength and good surface properties and flatness. Was. By using the glass substrate manufactured by this manufacturing method, a low head flying height can be achieved in the magnetic disk device, which can contribute to further increase in the density and capacity of the magnetic disk device.

[Brief description of the drawings]

FIG. 1 is a diagram showing the surface roughness of a disk surface before a chemical strengthening process, after a chemical strengthening process, and after removing surface protrusions.

[Description of Signs] 1... Disk surface before chemical strengthening treatment 2... Disk surface after chemical strengthening treatment 3... Disk surface after removal of surface protrusions

Claims (2)

[Claims] 1. A step of forming a glass base material into a disk, a step of polishing a surface of the disk, a step of chemically strengthening the disk, and a surface of the disk produced by the chemical strengthening processing. Removing the projections and substantially not reducing the compressive stress layer. 2. A step of forming a glass base material into a disk, a step of polishing the surface of the disk, a step of chemically strengthening the disk, and a surface of the disk produced by the chemical strengthening processing. By removing the projections and substantially not reducing the compressive stress layer, the average surface roughness Ra of the disk surface is 0.5 nm or less, the maximum height Ry is 5.0 nm or less, and the flatness is reduced. A method for producing a glass substrate for a magnetic recording medium, wherein the glass substrate has a thickness of 3 μm or less.