JP2000207730A - Glass substrate of magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a disk substrate made of glass at low costs for improving the flatness of a chemically reinforced disk substrate made of glass, and for achieving the low floating of a magnetic head. SOLUTION: In a method for manufacturing a glass substrate for a magnetic recording medium, the main surface of the chemically reinforced glass substrate is ground, and the strengthened layer is removed, and the reinforced layer is allowed to remain only at the edge face parts of the inner and outer peripheries, and the inner tensile stress value of chemical reinforcing processing is 0-4.5 kg/mm2 or less, desirably, 0-0.5 kg/mm2 or less, and surface roughness Ra is 1.00 μm or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glass disk substrate for a magnetic recording medium.

[0002]

2. Description of the Related Art Conventionally, substrates for magnetic recording media have been provided by aluminum substrates, carbon substrates, polycarbonate substrates, and the like. Glass substrates have attracted attention because they have the potential to meet this demand and can be expected to have low costs. As the surface smoothness of the glass substrate has no crystal grain boundaries due to the development of the polishing technology, it is theoretically possible to reduce the surface roughness to the atomic level. In addition, the flying height of the read magnetic head can be further reduced along with the decrease in the disk flatness, and the recording density per unit area increases, which leads to an increase in the recording capacity.

However, in order to increase the recording capacity, a further reduction in the flying height of the head is required. In particular, the flatness of the disk substrate depends on the writing of the recorded magnetic recording,
There is a need for a glass disk substrate that is important during reading and that undergoes a strengthening process without losing the advantages of the current disk substrate.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned conventional problems and achieve a low flying height of a magnetic head and to provide a glass disk substrate at low cost. .

[0005]

The magnetic disk glass substrate of the present invention, which has been made to achieve the above object, is provided on the main surface of the substrate other than the inner and outer peripheral end surfaces of the toughened doughnut-shaped glass substrate. The compression stress value of the main surface of the substrate is reduced to almost zero by polishing and removing the reinforcing layer.

In particular, a glass disk substrate needs to be strengthened because it is a brittle material. However, this strengthening process is performed by polishing the substrate after strengthening and touch polishing to remove the strengthening salt,
It is a known fact that the thickness of the reinforcing layers existing on the upper and lower surfaces of the main surface of the disk varies, thereby deforming the disk and deteriorating the flatness.

[0007] This phenomenon is because the balance between the tensile and compressive stress inside the glass substrate is lost due to the difference in thickness of the compressive stress layer of the main surface reinforcing layer. Further, it is very difficult to match the polishing amounts of the upper and lower surfaces on the order of microns, and the production cost is extremely high, if not impossible. Originally, the strengthening process of a glass disk is a process performed in order to prevent breakage in handling at the time of assembling a drive or at the time of sputtering a magnetic recording medium.
However, all of the damages in this case are damages due to crack progress or contact from the inner peripheral end face portion of the substrate, and there are very few cases in which the origin is generated on the main surface and is damaged.

That is, it can be said that the portion of the glass disk substrate that needs to be strengthened is located particularly at the inner and outer peripheral end surfaces. Therefore, the present invention is characterized in that the reinforcing layer on the main surface of the substrate except for the inner and outer peripheral end faces is removed by polishing.

[0009]

Next, the present invention will be described in detail.

The present inventor pays particular attention to the flatness of the glass disk substrate, and maintains the flatness before the substrate reinforcement by polishing and removing the reinforcing layer on the main surface of the substrate in the polishing step after the substrate reinforcement. Further, it has been found that the remaining of the reinforcing layer on the inner and outer peripheral end faces of the disk substrate can suppress breakage due to an external force, thereby achieving the present invention. In other words, the present invention relates to a method for manufacturing a magnetic recording glass disk in which a glass disk substrate is chemically strengthened and then a reinforcing layer is removed by polishing, and a magnetic recording glass disk substrate manufactured by the method.

By applying the present invention, it is possible to prevent the flatness of the disk substrate from deteriorating, promote the low flying height of the magnetic head, and further improve the productivity and reduce the cost. The composition of the glass substrate is not particularly limited, and the surface roughness of the disk substrate before the strengthening treatment is not limited. However, in view of the productivity in the disk polishing process, it is desirable that the surface roughness Ra is preferably not more than 1.00 μm. This is because, in the polishing step after the strengthening treatment, in the case of a disk having Ra = 1.00 μm or more, the polishing time is extremely long in order to make the Ra of the disk surface of the final finish 3 ° or less, which leads to a decrease in productivity.

The chemical strengthening treatment for a glass disk substrate varies depending on the composition of the substrate, the thickness of the work at the time of the strengthening treatment, or the processing conditions. In the present invention, the surface of the final polished product (super polished product) is used. Since it is characterized by making the stress almost zero, it can be said that it is a technology that can be applied to any chemically strengthened disk product, but in order to introduce a sufficient reinforcing layer thickness to the inner and outer peripheral end surfaces of the disk substrate, The thickness of the reinforcing layer over the entire disk substrate is preferably introduced to a thickness of 30 μm or more and 200 μm or less, and the main surface of the disk substrate is preferably polished to a thickness of 30 μm or more and 200 μm or less. From 0 to 4.5 kg / mm ² ,
It is desirable to set it to 0 to 0.5 kg / mm ² .

By removing the reinforcing layer on the main surface of the disk substrate, there is no variation in the tensile stress and the compressive stress in the thickness direction of the disk, and the deformation of the disk can be avoided. Therefore, it is possible to start the step of sputtering the magnetic recording medium while maintaining a very good flatness.

In the past, when a tempered glass disk substrate was damaged in the handling step or the sputtering step, the compressive stress on the surface was alleviated at once, so that the substrate was broken into pieces. Although it was very difficult, when using the substrate of the present invention, since the stress is almost zero on the main surface of the glass disk substrate, it is considered that the work is unnecessary and leads to an increase in productivity. Can be

[0015]

EXAMPLES (Example 1) Aluminosilicate glass was mixed with 9
Cut out into a 5mmφ disk, thickness 1mm, surface roughness Ra =
A disk substrate adjusted to 0.3 μm was used as a sample. The disk substrate was immersed in a molten salt at 360 ° C. in which potassium nitrate and sodium nitrate were mixed at a weight ratio of 8: 2 for 60 minutes to perform ion exchange strengthening treatment.
Both surfaces of the disk substrate were polished to a predetermined thickness, and the flatness of the substrate surface with respect to the polishing amount, the presence or absence of the remaining reinforcing layer, and the residual tensile stress value inside the substrate were measured. The results are shown in Table 1.

[0016]

Example 2 The same disk substrate as in Example 1 was used as a sample, and the disk substrate was heated at 380 ° C.
Of potassium nitrate and sodium nitrate in a weight ratio of 8: 2
After immersion in a molten salt mixed at a ratio of 60 minutes for ion exchange strengthening treatment, both surfaces of the disk substrate are polished to a predetermined thickness, the flatness of the substrate surface with respect to the polishing amount, the presence or absence of a residual reinforcing layer, The residual tensile stress value inside the substrate was measured. The results are shown in Table 2.

[0018]

Example 3 The same disk substrate as in Example 1 was used as a sample, and the disk substrate was heated at 400 ° C.
Of potassium nitrate and sodium nitrate in a weight ratio of 8: 2
After immersion in a molten salt mixed at a ratio of 60 minutes for ion exchange strengthening treatment, both surfaces of the disk substrate are polished to a predetermined thickness, the flatness of the substrate surface with respect to the polishing amount, the presence or absence of a residual reinforcing layer, The residual tensile stress value inside the substrate was measured. Table 3 shows the results.

[0020]

Example 4 The same disk substrate as in Example 1 was used as a sample.
Of potassium nitrate and sodium nitrate in a weight ratio of 8: 2
After immersion in a molten salt mixed at a ratio of 60 minutes for ion exchange strengthening treatment, both surfaces of the disk substrate are polished to a predetermined thickness, the flatness of the substrate surface with respect to the polishing amount, the presence or absence of a residual reinforcing layer, The residual tensile stress value inside the substrate was measured. Table 4 shows the results.

[0022]

Example 5 The same disk substrate as in Example 1 was used as a sample, and the disk substrate was heated at 480 ° C.
Of potassium nitrate and sodium nitrate in a weight ratio of 8: 2
After immersion in a molten salt mixed at a ratio of 60 minutes for ion exchange strengthening treatment, both surfaces of the disk substrate are polished to a predetermined thickness, the flatness of the substrate surface with respect to the polishing amount, the presence or absence of a residual reinforcing layer, The residual tensile stress value inside the substrate was measured. Table 5 shows the results.

[0024]

Tables 1 to 5 show the change in flatness and the change in internal compressive stress value when the sample was polished when the strengthening treatment was performed at each temperature for 60 minutes. From the tables from Tables 1 to 5, in the process of polishing the reinforcing layer stepwise, temporary deterioration of flatness and reduction of internal stress are seen,
When the polishing is performed until the internal stress becomes almost zero, that is, when the introduced reinforcing layer is removed by polishing, it is observed that the flatness is maintained at the value after the initial strengthening.

Example 6 Table 6 shows the time of the strengthening treatment at each temperature, the thickness of the strengthening layer introduced at that time, and the internal tensile stress value when the disk substrate is strengthened by ion exchange.

[0027]

The mark * in Table 6 indicates that the internal stress was lower than that of the sample treated for a short time at each temperature because the reinforcing layer was introduced too much and the internal stress was relaxed. Generally, chemical strengthening treatment is performed at a temperature higher than the glass transition point,
It has been known that by performing an unnecessarily long treatment on the glass composition, a deep reinforcing layer is introduced, while the compressive stress value on the surface decreases.

It can be seen that in the aluminosilicate glass of the example, stress relaxation occurs from about 100 μm on one side. Although the reinforcing layer is introduced into both the main surface and the edge of the disk, stress relaxation occurs as a whole. However, the surface of the sample with reduced internal stress marked with * is close to the strength of the unreinforced treated sample, so the impact resistance to the contact at the time of handling the inner and outer peripheral end surfaces of the disk originally intended is reduced. Resulting in.

That is, in a silicate-based glass such as aluminosilicate, aluminoborosilicate, soda lime, or borosilicate, after a strengthening treatment is performed to such an extent that the compression stress on the surface is not relaxed, the reinforcing layer on the main surface is polished. It is important to remove with.

The surface compressive stress value is 4.5 kg / m
If it exceeds m ² , the compressive stress value of the disc before polishing is 4.5 k, particularly because the breakage is remarkable in the subsequent polishing step.
g / mm ² or less, desirably 0.5 kg / mm ² or less.

Further, since the compressive stress finally remains only at the inner and outer diameter edges, a large stress difference occurs at the boundary between the edge and the main surface. For this reason, if there is a possibility of causing a breakage, further polishing this boundary portion to make the edge portion round also leads to a reduction in broken work.

As described above, in accordance with the method of manufacturing a glass substrate for a magnetic recording medium of the present invention, the glass substrate after polishing the main surface of the glass substrate after chemical strengthening and polishing and removing the reinforcing layer on the main surface is as follows. The flatness of the surface of the glass substrate is maintained at the initial value after strengthening, the recording density of the information recording medium formed on the glass substrate is increased, and the glass substrate capable of increasing the recording capacity can be provided. Reliability can be dramatically improved.

Claims (4)

[Claims] 1. A method of manufacturing a disk substrate made of glass for a magnetic recording medium, wherein a polishing process is performed, particularly after chemical strengthening, to remove a reinforcing layer on the main surface of the disk substrate. 2. A glass disk substrate for a magnetic recording medium, wherein the reinforcing layer is left only on the inner and outer peripheral end surfaces. 3. The glass disk substrate for a magnetic recording medium according to claim 1, wherein the internal tensile stress value of the chemical strengthening treatment is 0 to 4.5 kg / mm ² or less, preferably 0 to 0.5 kg / mm ^2.
mm ² or less of the disk substrate. 4. The glass disk substrate for a magnetic recording medium according to claim 2, wherein the surface roughness Ra is 1.00 μm or less.