JPH10287444A - Crystallized glass substrate for magnetic disk, and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a crystallized glass substrate that can be easily formed into a substrate for zone-textured magnetic disks adaptable to a low-levitation CSS system by merely grinding the entire surface of the substrate, and also to provide a method for producing the crystallized glass substrate. SOLUTION: This crystallized glass substrate is made to vary the density of crystallization for every substrate zone, so as to have a varying surface roughness Ra for every zone, e.g. 7.0 nm>=Ra >=1.5 nm in the landing zone and 1.5 nm>Ra >=0.6 nm in the record reproduction zone, by merely grinding the entire surface of the substrate. For this purpose, nucleation for the crystallized glass is controlled differently zone by zone, e.g. the substrate surface is irradiated with a varying quantity of ultraviolet ray for a specific zone, or the nucleation is effected at varying temperature zone by zone, for a specific nucleating agent used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a crystallized glass substrate from which a zone-textured magnetic disk can be easily obtained, and a method for manufacturing the same.

[0002]

2. Description of the Related Art A magnetic disk device used as an external storage device of a computer or the like is a recent computer or
With the advancement of S, the demand is expanding, and the magnetic disk incorporated therein is rapidly increasing in recording capacity and recording density. Conventionally, as one type of this magnetic disk, one having a structure in which a magnetic layer for recording signals is formed on a crystallized glass substrate is known.

[0003] Most of the current magnetic disk devices employ a CSS (contact start / stop) system. According to this system, the magnetic head is in contact with the magnetic disk when the system is stopped. When the apparatus is operated, the magnetic disk starts to rotate, and the magnetic head rubs against the disk surface until sufficient buoyancy is obtained by the airflow generated by the rotation of the magnetic disk, and then floats up, and then rises up from the disk surface. Records and reproduces signals. Therefore, if the surface of the magnetic disk is too smooth, the contact area between the magnetic disk and the magnetic head when the apparatus is stopped becomes large, the frictional force acting between them increases, and the magnetic head is attracted to the surface of the magnetic disk. . When operating the device in such a state,
There is a possibility that the disk itself, or a head support system or a disk drive system member may be damaged or malfunction.

For the purpose of preventing the magnetic disk and the magnetic head from being attracted to each other, the surface of the magnetic disk substrate is conventionally made to have a moderately rough surface. The surface of the substrate is subjected to a texture treatment using large abrasive grains such as cerium oxide having an average particle diameter of 1 to 3 μm, and a surface roughness Ra of 1.5 to 7.0 is applied.
It is common to have a rough surface of about nm. Or,
JP-A-6-329440 discloses that a raw glass having a specific composition is heat-treated to control the crystal particle size.
A crystallized glass substrate in which the surface roughness Ra after polishing is controlled in the above range is disclosed.

In recent years, in a CSS type magnetic disk drive, in order to respond to the above-mentioned increase in recording capacity, the flying height of a magnetic head is reduced to increase the recording density of a magnetic disk. I have. As the flying height of the magnetic head becomes smaller, it is required that the surface of the magnetic disk be smoother in order to accurately record and reproduce signals. For example, when the flying height of the magnetic head is reduced to 100 nm or less, a rough surface as obtained by the conventional texture processing for a magnetic disk becomes too rough. In other words, the surface of the magnetic disk is
There are two contradictory requirements, that is, a smoother surface from the viewpoint of signal recording and reproduction and a rough surface from the viewpoint of preventing magnetic head adsorption.

As one of the techniques to meet such a demand, a zone texture technique has been developed. In this method, texturing is not performed on the entire surface of the magnetic disk, but is performed only on the landing zone (usually, the inner peripheral side of the disk) of the surface of the magnetic disk where CSS is performed. This is a technique for making the recording / reproducing zone smooth.

[0007]

However, it is technically difficult to apply a zone texture treatment to a crystallized glass substrate, and if it is to be performed, there is a problem that the process is complicated. For example, Japanese Patent Application Laid-Open No. Hei 7-2449
According to the disclosure of Japanese Patent No. 47, a crystallized glass substrate that has been subjected to zone texture processing is obtained through a complicated process in which various polishing texture techniques are devised and combined. As described above, although the polishing texture technique is generally used for an aluminum disk, it is not easy to apply it directly to a crystallized glass substrate. Moreover, since the surface of the landing zone roughened by the zone texture is lower than the recording / reproducing zone,
A problem may occur when the head is moved. On the other hand, in the case of film texture using spatter,
Although it is easy to apply it to the entire surface of the crystallized glass substrate, it is difficult to apply it partially because there are many restrictions in terms of equipment and cost. Therefore, it was not suitable as a means for zone texture.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem in zone texture with respect to a conventional crystallized glass substrate, and a magnetic disk substrate in which zone texture is obtained only by polishing the entire surface of the substrate under a single condition. It is an object of the present invention to provide a crystallized glass substrate and a method for manufacturing the same, which can be easily obtained.

[0009]

In the production of crystallized glass, crystal nuclei are usually generated first, and then crystallization and crystal growth are performed centering on the crystal nuclei. In some cases, it is known that precipitated crystals growing therefrom become coarse. Then, when the crystallized glass containing the coarsened precipitated crystals is polished, the surface roughness of the crystallized glass obtained becomes large because the influence of the crystal grain boundaries is large. The present invention controls the size of the precipitated crystals by controlling the state of crystal nuclei formation during the production of crystallized glass for each zone, thereby controlling the surface roughness of the crystallized glass after polishing for each zone. Is what I tried.

That is, the crystallized glass substrate for a magnetic disk of the present invention is characterized in that the crystal density of the crystallized glass is different for each zone, and the surface roughness Ra after the entire surface polishing is different for each zone. . The surface roughness Ra after the entire surface polishing is 1.5 nm in the landing zone.
It is a further feature of the present invention that the thickness is not less than 7.0 nm and not more than 0.6 nm and less than 1.5 nm in the recording / reproducing zone. If the Ra is less than 1.5 nm in the landing zone, the effect of preventing the head from being attracted by the texture is not sufficient, and if the Ra exceeds 7.0 nm, the height difference between the zones becomes large, which hinders the movement of the head, which is not preferable. On the other hand, if Ra is 1.5 nm or more in the recording / reproducing zone, there is a high risk that a head crash will occur when the magnetic head is brought close to the substrate.
Since it is difficult to make it smaller than nm, both are not preferable.

In the method of manufacturing a crystallized glass substrate for a magnetic disk according to the present invention, the nucleation of crystallized glass is controlled in each zone of the substrate surface, and then the crystallized glass substrate surface obtained by heat treatment is formed. It is characterized in that the entire surface is polished so that the surface roughness Ra of the substrate surface is different for each zone.

In the present invention, as a means for controlling the state of formation of crystal nuclei for each zone, for example, a crystal nucleating agent for forming nuclei by irradiating ultraviolet rays is added to the crystallized glass composition so that the landing zone on the substrate surface can be controlled. There is a method of irradiating a different amount of ultraviolet rays for each zone from the recording / reproducing zone to control the nucleation of crystallized glass for each zone on the substrate surface. Examples of the crystal nucleating agent that forms nuclei by ultraviolet irradiation include Au, AgCl, and Cu ₂ O. Adjustment of the amount of UV irradiation requires special equipment, for example, by applying a mask with a film with low UV transmittance to the part where the crystal density is to be reduced, that is, the part of the landing zone where the surface roughness is to be increased. And can be easily implemented. Also,
As a film with low UV transmittance, UV cut,
Anything that has UV resistance can be used,
For example, a material obtained by mixing a predetermined amount of an ultraviolet absorbing material with a synthetic resin composition so as to obtain a desired ultraviolet transmittance and then forming a film according to a conventional method is suitable.

In the present invention, other means for controlling the state of formation of crystal nuclei for each zone include:
A method of controlling the nucleation of crystallized glass for each zone on the substrate surface by including a crystal nucleating agent for performing nucleation by heat treatment and causing the landing zone and the recording / reproducing zone to perform crystal nucleation at different temperatures, respectively. can give. Crystal nucleating agents that form nuclei by heat treatment include:
Examples include P ₂ O ₅ , TiO ₂ , and ZrO ₂ . The heat treatment temperature for crystal nucleus formation is adjusted, for example, by bringing a heat insulating material or a heat absorbing member made of, for example, thick ceramic into contact with a portion where the crystal density is to be reduced, that is, a landing zone portion where the surface roughness is to be increased. Therefore, the present invention can be easily implemented without requiring a special device or the like. Alternatively, a heating element manufactured so that the temperature is different for each zone may be brought into contact. In addition,
When the heat insulating material is brought into contact, the landing zone is made lower than the nucleation temperature during the first heat treatment to inhibit nucleation during the first heat treatment, and the heat insulating material is removed during the second heat treatment to rapidly grow crystals. This causes a difference in the crystal grain size. Therefore, it is necessary that the temperature difference is generated by contacting the heat insulating material such that when the recording / reproducing zone is heated to the nucleation temperature, the landing zone is maintained at a temperature at which nucleation does not proceed. The temperature difference is in the range of about several tens of degrees C to 100 degrees C. However, since the nucleation temperature range varies depending on the glass composition, the temperature difference cannot be determined unconditionally. However, care must be taken because if the temperature difference is too large, the glass may be broken.

As described above, by adding to the crystallized glass composition either a crystal nucleating agent that forms a nucleus by irradiation with ultraviolet light or a crystal nucleating agent that forms a nucleus by heat treatment, the nucleus of the crystallized glass is increased. While the formation is well controllable, nucleation can be better controlled by using both crystal nucleating agents. That is, if both the crystal nucleating agent is contained in the crystallized glass composition and the heat treatment is performed after irradiating different amounts of ultraviolet rays to the landing zone and the recording / reproducing zone, crystal nucleus formation by ultraviolet irradiation is insufficient. Non-uniform crystallization that may occur in some cases can be prevented.

The crystallized glass substrate produced by the above-described method of the present invention can obtain different surface roughness for each zone only by polishing. Polishing in this case does not require a special technique or process, and lapping is performed using a method known as a general polishing method for optical glass, for example, using an abrasive such as alumina or zirconia having an average particle size of about 5 to 15 μm. After that, the polishing can be easily performed by a method such as polishing with cerium oxide or the like.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described more specifically with reference to examples. Table 1 shows the glass composition of each example.

[0017]

[Table 1] Example 1 A glass having the composition shown in Table 1 was prepared, and
It was shaped into a disk-shaped hard disk substrate of 5 mm (2.5 inches) and 0.635 mm thick. In this glass composition, Au is included as a crystal nucleating agent for forming nuclei by irradiation with ultraviolet rays. Next, a film having an ultraviolet transmittance of 30% was attached to a portion corresponding to the landing zone, and then the entire substrate was irradiated with ultraviolet light using a high-pressure mercury lamp to form nuclei. This film was obtained by mixing a polyurethane resin with an ultraviolet absorber Tinuvin (trade name, manufactured by Ciba Geigy).

Thereafter, a heat treatment was performed at 520 ° C. for 30 minutes, and a heat treatment was further performed at 820 ° C. for 4 hours to crystallize the glass. Further, the crystallized substrate was polished. Polishing was performed by lapping using alumina having an average particle size of 5 to 15 μm, and then polishing with cerium oxide having an average particle size of 1 to 3 μm.

The surface roughness of the substrate thus obtained was Ra 3.0 nm in the landing zone and Ra 1.3 nm in the recording / reproducing zone. The surface roughness was measured using a stylus type surface profiler with a scan length of 500 μm.
I went in.

Example 2 A glass having the composition shown in Table 1 was prepared, and was formed into the same hard disk substrate shape as in Example 1. The glass composition contains P ₂ O ₅ as a crystal nucleating agent for forming nuclei by heat treatment. Next, a ceramic heat insulating material having a thickness of 40 mm was brought into contact with a portion corresponding to the landing zone, and heat treatment was performed at 520 ° C. for 30 minutes to form crystal nuclei. Thereafter, the heat insulating material is removed and another 80 is removed.
Heat treatment was performed at 0 ° C. for 1.5 hours to crystallize. Further, the crystallized substrate was polished in the same manner as in Example 1.

The surface roughness of the substrate thus obtained was Ra 3.0 nm in the landing zone and Ra 1.3 nm in the recording / reproducing zone. In addition, the measurement of the surface roughness was performed using the stylus type surface shape measuring device in the same manner as in Example 1.

Example 3 Glass having the composition shown in Table 1 was prepared and molded into the same hard disk substrate shape as in Example 1. In this glass composition, Au is included as a crystal nucleus forming agent for forming nuclei by ultraviolet irradiation, and P ₂ O ₅ is included as a crystal nucleating agent for forming nuclei by heat treatment. Next, after a film having an ultraviolet transmittance of 0% was attached to a portion corresponding to the landing zone, the entire substrate was irradiated with ultraviolet light using a high-pressure mercury lamp to form nuclei. Then, at 820 ° C., 1.5
The glass was crystallized by performing a heat treatment for a time. further,
The crystallized substrate was polished in the same manner as in Example 1.

The surface roughness of the substrate thus obtained was 4.0 nm in the landing zone and 1.3 nm in the recording / reproducing zone. In addition, the measurement of the surface roughness was performed using the stylus type surface shape measuring device in the same manner as in Example 1.

[0024]

As described above, according to the present invention, there is provided a crystallized glass substrate and a method for manufacturing the same, in which a magnetic disk substrate having a zone texture can be easily obtained only by polishing the entire surface of the substrate.

[0025]

Claims (5)

[Claims] 1. A crystallized glass substrate for a magnetic disk, wherein the crystal density of the crystallized glass is different for each zone, and the surface roughness Ra after overall polishing is different for each zone. 2. The method according to claim 1, wherein the surface roughness Ra after the entire surface polishing is 1.5 nm or more and 7.0 nm or less in the landing zone and 0.6 nm or more and less than 1.5 nm in the recording / reproducing zone. The crystallized glass substrate for a magnetic disk according to claim 1. 3. The nucleation of the crystallized glass is controlled by each zone on the substrate surface, and thereafter, the entire surface of the crystallized glass substrate obtained by heat treatment is polished to obtain a surface roughness Ra of the substrate surface.
The method for producing a crystallized glass substrate for a magnetic disk, wherein the method is different for each zone. 4. The crystallized glass composition contains a crystal nucleating agent that forms nuclei by irradiating ultraviolet rays, and irradiates a different amount of ultraviolet rays to each zone of the substrate surface to reduce the nucleation of the crystallized glass on the substrate surface. 4. The method according to claim 3, wherein the control is performed for each zone. 5. The crystallized glass composition contains a crystal nucleating agent that forms nuclei by heat treatment, and nucleation is performed at different temperatures for each zone on the substrate surface, so that the nucleation of the crystallized glass is reduced on the substrate surface. 5. The method for manufacturing a crystallized glass substrate for a magnetic disk according to claim 3, wherein the control is performed for each zone.