JP2001266336A - Substrate for magnetic recording medium, method of manufacturing the same and magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glass substrate for magnetic recording medium having ultra fine surface roughness and its manufacturing method and to provide a magnetic recording medium excellent in high recording density by using the glass substrate obtained. SOLUTION: The glass substrate having ultra fine surface roughness is manufactured by using a mixed liquid of water, abrasive grains and potassium hydroxide and further a mixed liquid of water and potassium hydroxide as a grinding liquid in a stage for grinding the surface of the substrate included in the method for manufacturing the glass substrate for magnetic recording medium, and the magnetic recording medium excellent in recording density is manufactured by using the glass substrata.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a glass substrate as a non-magnetic substrate used for a magnetic recording medium mounted on various magnetic recording devices such as an external storage device of a computer, a method of manufacturing the same, and a magnetic recording medium.

[0002]

2. Description of the Related Art In order to obtain a high recording density, a substrate used for a thin-film magnetic recording medium (hereinafter, also simply referred to as a medium) needs to have high precision processing and precision polishing to secure surface shape accuracy and mechanical characteristics. You. As the recording capacity of a magnetic recording device increases, the flying height of a magnetic head is required, and the necessity is increasing.

In recent years, as a medium substrate, a glass substrate having higher strength and less surface runout at the time of high-speed rotation is becoming mainstream in place of an aluminum-based alloy substrate which has been mainly used in the past. When manufacturing glass substrates,
Polishing is generally performed for surface polishing. Polishing is generally performed by laminating two surface plates to form a set, attaching a pad to the surfaces of the upper and lower surface plates that contact each other, and pouring a polishing liquid such as slurry between the upper and lower pads while rotating the surface plate. In this method, the entire surface of the substrate is simultaneously polished by simultaneously contacting the pad, which is a processing member, by polishing the surface of the substrate fixed by the carrier between the upper and lower pads. A Cr underlayer, a Co alloy magnetic layer, a carbon protective film, and the like are formed on the glass substrate after the surface polishing by a sputtering method, and a liquid lubricant layer is applied thereon to form a medium.

[0004]

As described above, a glass substrate used as a medium is polished by polishing to have an extremely fine surface roughness. Polishing liquid for polishing,
For example, a mixed solution of cerium oxide abrasive grains and water is used as the abrasive grains, but it is unavoidable that the abrasive grains adhere to the substrate surface and minute scratches are generated by the abrasive grains.

[0005] In recent years, the demand for increasing the recording capacity of a magnetic recording apparatus has become stronger and stronger, and it is required to increase the recording density of a medium. For this reason, the flying height of the magnetic head has been reduced, and it has been required to further reduce the surface roughness of a substrate used for a medium. By reducing the amount of the abrasive grains of the polishing liquid used for polishing the glass substrate, the amount of the abrasive grains attached to the substrate surface can be reduced, and the occurrence of minute scratches due to the abrasive grains can also be reduced. For example, when using cerium oxide abrasive grains as abrasive grains,
Conventionally, the concentration of abrasive grains is generally set at 10% by weight to 20% by weight. By lowering the concentration, the amount of cerium oxide abrasive grains attached to the substrate surface can be reduced, and the generation of minute scratches by the abrasive grains Can be reduced, but this is not a fundamental solution, but on the other hand, there is an adverse effect that the amount of processing is reduced.

The present invention has been made in view of the above points, and provides a glass substrate having an extremely fine surface roughness and a method for manufacturing the same, and using the substrate to provide an excellent medium having a high recording density. The purpose is to provide.

[0007]

According to the present invention, there is provided a magnetic recording medium comprising at least a non-magnetic underlayer, a magnetic layer, a protective film and a liquid lubricant layer sequentially laminated on a non-magnetic substrate. It is preferably used in the production of a glass substrate used as a non-magnetic substrate, by using a mixed solution of water, abrasive grains and potassium hydroxide as a polishing liquid in the surface polishing step included in the glass substrate production method Will be resolved.

By including potassium hydroxide in the polishing liquid, a substrate having an extremely fine surface roughness can be obtained without reducing the amount of processing due to the etching effect of potassium hydroxide and the effect of reducing friction during processing. The concentration of potassium hydroxide contained in the polishing liquid is preferably in the range of 0.1% by weight to 15% by weight. If the amount is less than 0.1% by weight, the required etching effect is hardly obtained. If the amount exceeds 15% by weight, the etching becomes too strong, and adverse effects such as generation of pits occur.

[0009] Further, as polishing abrasive grains mixed with the polishing liquid, cerium oxide abrasive grains are suitable because they generate less scratches. As the surface polishing method, a so-called polishing processing method in which a processing member simultaneously contacts and polishes the entire surface of the substrate, that is, a so-called polishing processing method can be employed. In addition, when a partial contact processing method in which a part of a processing member moving in one direction is brought into contact with a part of a rotating substrate surface and polished is adopted as a surface polishing method, clogging and deterioration of a pad can be eliminated. It is preferable because fine surface roughness can be easily obtained. At this time, it is preferable that the contact area of the processing member in contact with the substrate surface is 2% or more and 30% or less of the total surface area of the substrate. If it is less than 2%, processing takes a long time, and if it exceeds 30%, it becomes difficult to obtain an extremely fine surface roughness.

When a polishing liquid containing only potassium hydroxide added to water without adding abrasive grains such as cerium oxide is used as the polishing liquid, the surface roughness is reduced to a center line average roughness _Ra of 0.1.
It is possible to obtain an unprecedented ultrafine surface roughness of 2 nm or less. When the glass substrate is a chemically strengthened glass substrate, the above-described polishing method is suitable not only for surface polishing before the chemical strengthening treatment but also for polishing for removing surface abnormalities caused by the chemical treatment after the chemical strengthening treatment.

By manufacturing a magnetic recording medium substrate by a manufacturing method including any of the above-described polishing steps and manufacturing a magnetic recording medium using the same, it is possible to obtain a medium excellent in high recording density. It becomes possible.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION As a surface polishing step in a method of manufacturing a glass substrate, a normal lapping process is performed on the surface of the glass substrate. Subsequently, the surface of the glass substrate after the lapping is polished to obtain a finer surface roughness.

For the fine surface polishing, a processing method in which a processing member to be polished is brought into simultaneous contact with the entire surface of the substrate and polished, for example, polishing is employed. For polishing, a normal polishing machine, for example, two sets of surface plates are stacked to form a set, and pads are attached to the surfaces of the upper and lower surface plates that are in contact with each other, and polishing is performed between the upper and lower pads while rotating the surface plates. An apparatus having a structure in which a liquid is supplied and the surface of a substrate fixed by a carrier between upper and lower pads is polished is preferably used.

Alternatively, in place of the polishing, a partial contact process in which a part of the processing member moving in one direction is brought into contact with a part of the surface of the rotating substrate and polished is employed. The contact area of the processed member with the substrate surface is 2% or more of the substrate surface area 30
%. In order to perform the partial contact processing, for example, a polishing apparatus and a polishing method as shown in principle in FIG. 1 are suitably used. FIG. 1A is a front view, and FIG. 1B is a side view. In FIG. 1, a polishing member 2 is pressed against both surfaces of a substrate 1 rotating in the direction of arrow A, and is brought into press contact with a jig 3. The polishing liquid is applied by a nozzle 4 while running the polishing member 2 in the direction of arrow B. It is supplied to the contact surface to polish the substrate surface. The polishing member 2 has a width sufficient to cover the width of the substrate 1 to be processed in the radial direction. The shape of the contact surface of the pressing jig 3 against the substrate surface and the pressing pressure are appropriately selected according to the surface roughness of the substrate to be obtained.

As the polishing liquid at this time, a mixed liquid in which potassium hydroxide is further added to a concentration of 0.1% by weight to 15% by weight to a mixed liquid obtained by adding abrasive grains to water is used. A substrate with a fine surface roughness is obtained. As the abrasive grains, any of the commonly used types of abrasive grains may be used, but cerium oxide is preferably used for the purpose of reducing the occurrence of scratches.

Further, in the above-described surface polishing step, an ultrafine surface roughness can be obtained by using a mixed solution of only water and potassium hydroxide without containing abrasive grains as a polishing solution. By using the glass substrate manufactured in this way, an excellent medium having a high recording density can be obtained.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described. Example 1 Lapping is performed on a disk-shaped glass substrate having a diameter of 2.5 inches, and polishing is performed on the substrate after the lapping.
A urethane foam pad is used as a polishing member, and a mixed solution obtained by adding 1% by weight of cerium oxide abrasive grains having an average particle size of 1.5 μm and 5% by weight of potassium hydroxide to water is used as a polishing liquid. The surface roughness before polishing was 10 nm or more in Ra, whereas the surface roughness after processing was as fine as 0.4 nm in Ra.

Example 2 The polished substrate obtained in Example 1 was polished using the polishing apparatus shown in FIG. A polishing tape made of urethane foam is used as the polishing member, the contact area of the polishing member with respect to the substrate surface area is 20%, the pressure applied to the surface of the substrate is 40 g / cm ² , and the rotation speed of the substrate is 200 rpm.
Cerium oxide abrasive grains were not used as the polishing liquid, and a mixture of water and 5% by weight of potassium hydroxide was used.

Atomic surface roughness of the processed substrate
Investigated by Force Microscope (AFM). The surface image is shown in FIG. Surface roughness is Ra before processing
Was 0.4 nm while Ra was 0.2 nm after processing.
A very fine surface roughness of nm was obtained.

[0020]

According to the present invention, a fine surface roughness can be obtained by using a polishing solution containing potassium hydroxide in the surface polishing step included in the method of manufacturing a glass substrate used as a non-magnetic substrate of a magnetic recording medium. Can be produced, and further, a substrate having an ultrafine surface roughness can be produced by using a mixed solution of only water and potassium hydroxide without containing abrasive grains as a polishing solution. By using a suitable substrate, an excellent medium having a high recording density can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of an example of a polishing apparatus and a polishing method used for partial contact processing according to the present invention.

FIG. 2 is a surface image diagram by AFM of a substrate surface obtained in Example 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Polishing member 3 Pressing jig 4 Nozzle

Claims (10)

[Claims] 1. A method for manufacturing a glass substrate used for a magnetic recording medium, wherein a mixed solution of water, abrasive grains and potassium hydroxide is used as a polishing liquid used in a surface polishing step included in the method for manufacturing a glass substrate. A method for manufacturing a substrate for a magnetic recording medium, comprising: 2. The method for manufacturing a substrate for a magnetic recording medium according to claim 1, wherein the concentration of potassium hydroxide contained in the polishing liquid is in the range of 0.1% by weight to 15% by weight. 3. The method for manufacturing a substrate for a magnetic recording medium according to claim 1, wherein the polishing liquid contains cerium oxide abrasive grains as abrasive grains. 4. The polishing liquid according to claim 1, wherein the polishing liquid does not contain abrasive grains and is a mixed liquid of water and potassium hydroxide.
The manufacturing method of the substrate for magnetic recording media according to the above. 5. The method for manufacturing a substrate for a magnetic recording medium according to claim 1, wherein the surface polishing is a full-surface contact processing method in which a processing member simultaneously contacts and polishes the entire surface of the substrate. 6. A partial contact processing method for polishing by bringing a part of a processing member moving in one direction into contact with a part of a rotating substrate surface for surface polishing.
The manufacturing method of the substrate for magnetic recording media according to the above. 7. The method for manufacturing a substrate for a magnetic recording medium according to claim 6, wherein the contact area of the processed member with the substrate surface during surface polishing is 2% or more and less than 30% of the total surface area of the substrate. 8. The magnetic recording medium according to claim 1, wherein the glass substrate is a chemically strengthened glass substrate, and the surface of the glass substrate is subjected to the polishing method according to claim 1 before or after the chemical strengthening treatment. Method of manufacturing substrates. 9. A substrate for a magnetic recording medium, which is manufactured by the manufacturing method according to claim 1. 10. A magnetic recording medium comprising a magnetic recording medium substrate according to claim 9, wherein at least a magnetic layer and a protective film are sequentially laminated.