US20010024932A1

US20010024932A1 - Substrate for magnetic recording media, manufacturing method for the same, and magnetic recording media

Info

Publication number: US20010024932A1
Application number: US09/784,272
Authority: US
Inventors: Takashi Shimada
Original assignee: Individual
Current assignee: Fuji Electric Co Ltd
Priority date: 2000-03-24
Filing date: 2001-02-15
Publication date: 2001-09-27
Also published as: JP2001266336A

Abstract

A substrate surface polishing step in the manufacturing method for a magnetic recording medium glass substrate uses a polishing solution consisting of a mixture solution of water and abrasive grains with potassium hydroxide. One embodiment of the invention uses only a mixture solution of water and potassium hydroxide to manufacture a glass substrate with very fine surface roughness. A second embodiment uses a two-step process in which the glass substrate is first polished using water, abrasive grains and potassium hydroxide, and is then again polished using water and potassium hydroxide, but omitting abrasive grains. A glass substrate, produced according to the invention, results in the manufacture of a magnetic recording medium with excellent high recording density.

Description

BACKGROUND TO THE INVENTION

The present invention relates to a glass substrate as a non-magnetic substrate for a magnetic recording medium mounted onto various magnetic recording devices such as an external memory device for computers and the like. The present invention also relates to a manufacturing method for the same, and to a magnetic recording medium.

For the substrate used in thin film magnetic recording media (henceforth referred to as media), in order to achieve high recording density, surface shape accuracy and mechanical properties must be maintained through a high degree of precision processing and precision polishing. With increased recording volume of the magnetic recording device, low-floating magnetic heads are needed, and the necessity for high precision is even greater.

In recent years, instead of the aluminum alloy substrate that is largely used in the prior art, glass substrates that are stronger and have little surface shaking during high speed rotation is becoming more mainstream as the medium substrate.

For manufacturing glass substrates, a polish processing is generally conducted for polishing the surface. In general, polish processing is a method for polishing the substrate surface, wherein two platens are placed one on top of the other as a unit; pads are attached to the surfaces where the lower and upper platens contact each other; polishing solution such as slurry and the like is poured between the upper and lower pads while rotating the platens; a substrate is anchored by a carrier between the upper and lower pads, and the substrate surface is polished. This is a total surface contact processing where the polishing is conducted by having the entire surface of the substrate contacted at the same time by the pads that are the processing members. On top of the glass substrate that has been surface polished, a Cr under layer, Co alloy magnetic layer, and a carbon protective film and the like are formed by a sputtering method. On top of this, a liquid lubricant layer is coated, thereby forming the medium.

The glass substrate used for the medium, polished as described above, has a very fine surface roughness. A polishing solution, for example a mixture solution of polishing abrasive grains of cerium oxide abrasive grains and water, is used for polish processing. However, adherence of abrasive grains to the substrate surface and small scratches by the abrasive grains cannot be avoided.

In recent years, the need for higher recording volume for magnetic recording devices is even greater, and there is demand for increasing the recording density of media. As a result, magnetic heads have become low-floating, and there is demand for further reduction in surface roughness of the substrate used by media.

By decreasing the amount of abrasive grains in the polishing solution used for polish processing the glass substrate, the amount of adhesion of the abrasive grains to the substrate surface is reduced, and the generation of small scratches by the abrasive grains is reduced. For example, when using cerium oxide grains as the polishing abrasive grains, the concentration of the abrasive grains in the prior art has been generally 10 weight % to 20 weight %. By reducing this concentration, the amount of adhesion of cerium oxide to the substrate surface is reduced, and the small scratches by the abrasive grains is reduced. However, this is not a fundamental solution, and there is also the disadvantage of a reduced amount of processing.

OBJECTS AND SUMMARY OF THE INVENTION

Upon considering the above points, the object of the present invention is to provide a glass substrate with very low surface roughness and a manufacturing method for the same. A further object is to provide a medium that uses this substrate to attain an excellent high recording density.

The present invention is used for manufacture of a glass substrate used as a non-magnetic substrate for a magnetic recording medium that comprises a sequential layering of at least a non-magnetic under layer, a magnetic layer, a protective layer, and a liquid lubricant layer on top of the non-magnetic substrate. The above objective is solved by using a mixture solution of water, polishing abrasive grains, and potassium hydroxide for the polishing solution of the surface polishing step in the manufacturing method for the above glass substrate.

By having the polishing solution contain potassium hydroxide, a substrate with very fine surface roughness is obtained without reducing the amount of processing. This is due to the potassium hydroxide which has an etching effect and also has the effect of reducing friction during processing.

The potassium hydroxide concentration contained in the polishing solution is preferably in the range of 0.1 weight % or greater and 15 weight % or less. If the concentration is less than 0.1 weight %, the required etching effect is barely achieved, and if the concentration exceeds 15 weight %, the etching becomes too strong, and negative effects such as pitting results.

Furthermore, as the abrasive grains mixed in the polishing solution, cerium oxide abrasive grains generate few scratches and are suitable.

As the method for surface polishing, the polish processing method, which is a total surface contact processing method wherein polishing is conducted by simultaneous contacting of the entire substrate surface to the processing member, is used.

Furthermore, for the surface polishing method, if a partial contact processing method, wherein polishing is conducted by having one section of a processing member that moves in one direction contact one section of a rotating substrate surface, clogging or deterioration of the pad is eliminated, and a very fine surface roughness is easily obtained. The contact surface area where the processing member contacts the substrate surface is preferably 2% or greater and 30% or less of the entire substrate surface area. If it is less than 2%, too much time is needed for processing, and if it exceeds 30%, a very fine surface roughness is harder to obtain.

Furthermore, for the polishing solution, if abrasive grains such as cerium oxide and the like are not added and a polishing solution in which only water and potassium hydroxide are added is used, a surface roughness of a center line average roughness Ra of 0.2 nm or less is obtained. This is a very fine surface roughness that is not seen in the prior art.

If the glass substrate is a chemically strengthened glass substrate, the above polishing method is suitable for the surface polishing prior to chemical strengthening as well as for polishing in order to remove surface irregularities generated by chemical treatment after the chemical strengthening treatment.

A substrate for a magnetic recording medium is created with the manufacturing method containing one of the polishing steps as described above. By creating a magnetic recording medium using this substrate, a medium with excellent high recording density is obtained.

As the surface polishing step in the manufacturing method for the glass substrate, a standard lapping of the glass substrate surface is conducted.

Next, after lapping, in order to have an even finer surface roughness, fine surface polishing is conducted on the glass substrate surface.

For the fine surface polishing, polish processing, which is a processing method wherein there is polishing by simultaneous contact of the entire surface of the substrate surface by the processing member that conducts polishing, is used. In polish processing, a device having a construction of the standard polish processing device is suitable. In the standard polish processing device, two platens are placed one on top of the other as a unit; pads are attached to the surfaces where the lower and upper platens contact each other; polishing solution is supplied between the upper and lower pads while rotating the platens; a substrate is anchored by a carrier between the upper and lower pads, and the substrate surface is polished.

Or else, instead of polish processing, a partial contact processing, wherein polishing is conducted by contacting one section of a rotating substrate surface with one section of a processing member that moves in one direction, is used. The surface area of the contact of the processing member to the substrate surface is 2% or greater and less than 30% of the substrate surface area.

In order to conduct partial contact processing, for example, a polishing device shown principally in FIG. 1 is suitable. FIG. 1( a) is a front view, and FIG. 1(b) is a side view. Referring to FIG. 1, a substrate 1 rotates in the direction of arrow A. Polishing members 2 are each pressed into contact with the two sides of substrate 1 by forcing jigs 3. While each of polishing members 2 is moving in the direction of arrow B, polishing solution is supplied to the contact surface by nozzles 4, and the substrate surface is polished. Polishing members 2 have a width sufficient for covering the width that is to be processed in the radial direction of substrate 1. The shape of the surface of forcing jigs 3 contacting the substrate surface and the pushing force of forcing jigs 3 is selected as appropriate depending on the surface roughness that is to be achieved for the substrate.

For the polishing solution, a mixture solution in which potassium hydroxide is added to a mixture solution of water and abrasive grains to obtain a potassium hydroxide concentration of 0.1 weight % to 15 weight % is used. By using this polishing solution, a substrate with a very fine surface roughness is achieved. For the abrasive grains, any of the standard types of grains is used, but in order to reduce scratching, cerium oxide is preferably used.

Furthermore, in the surface polishing step described above, by using a polishing solution of a mixture solution that has only water and potassium hydroxide and does not contain abrasive grains, a very fine surface roughness is achieved.

By using a glass substrate manufactured in this manner, a medium with excellent high recording density is achieved.

The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements. [0026]

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. [0027] 1(a) and 1(b) are explanatory drawings of a model of one example of a polishing device and polishing method using the partial contact processing relating to the present invention.
FIG. 2 is a surface image by AFM (atomic force microscope) of the substrate surface obtained by Embodiment 2.[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Concrete embodiments of the present invention is described below. [0029]
Embodiment 1 [0030]
Lapping was conducted on a circular glass substrate with a diameter of 2.5 inches. After lapping, polish processing of the substrate was conducted. A foam urethane pad was used as the polishing member. For the polishing solution, a mixture solution was used, in which 1 weight % of cerium oxide abrasive grains with an average grain size of 1.5 micrometers and 5 weight % of potassium hydroxide was added to water. The surface roughness Ra prior to polish processing was 10 nm or greater. After processing, the surface roughness was finer at 0.4 nm. [0031]
[0032] Embodiment 2
With the polish processed substrate obtained in Embodiment [0033] 1, polishing was conducted using the polishing device shown in FIG. 1. A polishing tape of a foam urethane pad was used as the polishing member. The contact surface area of the polishing member with respect to the substrate surface area was 20%. The pressure applied to the surface of the substrate was 40 g/cm². The rotation speed of the substrate was 200 rpm. The polishing solution omitted cerium oxide abrasive grains.
After processing, the surface roughness of the substrate was examined with an Atomic Force Microscope (AFM). Referring to FIG. 2, the surface image is shown. The surface Ra prior to processing was 0.4 nm. In contrast, after processing, a very fine surface roughness of 0.2 nm was achieved. [0034]
According to the present invention, in the surface polishing step of the manufacturing method for the glass substrate used as the non-magnetic substrate of a magnetic recording medium, a polishing solution containing potassium hydroxide is used. As a result, a substrate with a finer surface roughness is manufactured. Furthermore, by using a mixture solution that does not contain abrasive grains and contains only water and potassium hydroxide as the polishing solution, a substrate with a very fine surface roughness is manufactured. By using this substrate, a medium with excellent high recording density is obtained. [0035]
There exist circumstances in which the polishing using [0036] only embodiment 2 is satisfactory. That is, polishing with an alkali solution but without the use of cerium oxide grains. This is effective for removing slight surface projections on the chemically strengthened surface. When only embodiment 1 is used, a relatively rough surface is attained, and at least some cerium oxide grains remain on the surface after polishing is completed. Thus, for a smoother surface (about 1 nm) the polishing of embodiment 2 may follow the polishing of embodiment 1. When this is done, residual cerium oxide grains are removed, and the surface smoothness is improved.
Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims. [0037]

Claims

What is claimed is:

1. A manufacturing method for a glass substrate for a magnetic recording medium, comprising:

mixing a polishing solution of water and abrasive grains with potassium hydroxide; and

polishing a surface of said glass substrate with said polishing solution.

2. A manufacturing method according to

claim 1

, wherein:

a concentration of potassium hydroxide in said polishing solution is from about 0.1 weight % to about 15 weight %.

3. A manufacturing method according to

claim 1

, wherein said abrasive grains are cerium oxide.

4. A manufacturing method according to

claim 2

, wherein said abrasive grains are cerium oxide.

5. A manufacturing method for a substrate for a magnetic recording medium:

mixing a polishing solution containing at least water and potassium hydroxide;

polishing a surface of said magnetic recording medium by a total surface contact processing method wherein polishing is conducted by simultaneous contact of a processing member with an entire surface of said substrate surface.

6. A manufacturing method for a substrate for a magnetic recording medium, comprising:

mixing a polishing solution containing at least water and potassium hydroxide;

surface polishing a surface of said substrate using said polishing solution;

said surface polishing is by a partial contact processing method wherein polishing is conducted by having a first section of a rotating substrate surface contact a second section of a processing member that is moving.

7. A manufacturing method for a substrate for a magnetic recording medium, according to

claim 6

, wherein:

during surface polishing, a contact surface area of said first section is from about 2% to about 30% of a total surface area of said substrate.

8. A manufacturing method for a substrate for a magnetic recording medium, comprising:

mixing a polishing solution containing at least water and potassium hydroxide;

surface polishing a surface of said substrate using said polishing solution;

and then chemically strengthening said glass substrate.

9. A substrate for a magnetic recording medium having a surface polished using a mixture of water and at least potassium hydroxide.

10. A magnetic recording medium, comprising:

a magnetic recording medium substrate having a polished surface polished using a mixture of water and at least potassium hydroxide;

sequential layering of at least a magnetic layer on said surface;

layering at least a protective layer on said magnetic layer.

11. A manufacturing method for a glass substrate for a magnetic recording medium, comprising:

mixing a polishing solution of water and potassium hydroxide; and

polishing a surface of said glass substrate with said polishing solution.

12. A manufacturing method for a glass substrate for a magnetic recording medium, comprising:

mixing a first polishing solution of water, potassium hydroxide and an abrasive;

polishing a surface of said glass substrate with said first polishing solution;

mixing a second polishing solution of water and potassium hydroxide; and

polishing said surface with said second polishing solution until a residue of said abrasive is substantially removed, and a desired surface smoothness is attained.