JPH0713841B2 - Texturing method of carbon substrate for magnetic disk - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] When writing to or reproducing from a magnetic disk, the magnetic head levitation surface and the magnetic disk surface may stick to each other when the disk is stationary. In order to prevent this adsorption phenomenon, after the surface of the magnetic disk substrate is polished, a texture treatment for roughening the surface is performed. The present invention relates to such a texture processing method for a magnetic disk substrate, and more particularly to a texture processing method for a carbon substrate.

[Conventional technology]

When the magnetic head levitation surface and the magnetic disk surface are extremely smooth and face each other at a minute interval, the adsorption phenomenon as described above is filled with molecules such as O ₂ , N ₂ , H ₂ O, etc. This is because a large attraction force is generated due to the tension. When this head adsorption occurs, there arises a problem that a large amount of electric power is consumed when starting the motor.

In order to prevent such adsorption phenomenon, prior to forming a magnetic film on the substrate, the surface of the substrate is once mirror-finished and then textured to roughen the surface and adjust to an appropriate surface roughness. Is being done. Conventionally, the following method has been adopted as this texture processing method.

That is, using a polishing tape to which abrasive grains of silicon carbide, alumina, or diamond are adhered, while the NiP plated substrate is rotated, while the polishing tape is pressed from the back side of the tape with a roll, contact movement is made in the substrate radial direction. ,
Concentric stripes are attached to the surface of the substrate to obtain a so-called textured substrate.

[Problems to be Solved by the Invention]

However, the above-mentioned conventional method has a problem that it is difficult to adjust the surface of the substrate to an appropriate surface roughness to roughen the surface, and the surface tends to be unnecessarily rough. Therefore, in the magnetic disk using the substrate roughened by the conventional texture processing method, the flying height (spacing) of the magnetic head for coping with the increase in recording density cannot be made smaller.

By the way, a carbon substrate (amorphous carbon substrate) has been proposed as a substrate having high hardness, heat resistance, excellent surface accuracy, and lightness, which are characteristics required for a magnetic disk substrate in order to improve the recording density. (Kobe Steel Technical Report, Vol.39, No4, pp. 35-38, 1989).

Under these circumstances, the inventors of the present invention have conducted extensive research on texture treatment methods while paying attention to the properties of the carbon substrate, and as a result, heat-treating the carbon substrate at a predetermined temperature in an oxidizing atmosphere. The inventors have found that the above problems can be solved and arrived at the present invention.

That is, the present invention provides a method for texture-treating a carbon substrate for a magnetic disk, which can easily roughen the surface of the carbon substrate for a magnetic disk whose surface has been polished to an appropriate surface roughness without making the surface rougher than necessary. For the purpose of providing.

[Means for Solving the Problems]

In order to achieve the above object, the method for texturing a carbon substrate for a magnetic disk according to the present invention comprises heat-treating a surface-polished carbon substrate for a magnetic disk at a temperature of 400 to 700 ° C. in an oxidizing atmosphere. Thus, the surface of the carbon substrate is roughened.

[Work]

400 carbon surface polished in oxidizing atmosphere
When heated to a temperature above ℃, C + O ₂ CO ₂ , C + 1 / 2O ₂ C
O, CO + 1 / 2O ₂ CO ₂ , C + CO ₂ 2CO oxidation reaction occurs, carbon is gasified, and fine wavy irregularities are formed on the polished surface. This makes it possible to easily and moderately roughen the surface-polished carbon substrate surface without making the surface of the carbon substrate roughened more than necessary by selecting the heat treatment conditions.

Further, in the present invention, the heat treatment temperature is suitably in the range of 400 to 700 ° C. This is because if the temperature is lower than 400 ° C, it takes a long time to roughen the surface of the carbon substrate, and if it exceeds 700 ° C, the surface roughness tends to be too rough.

〔Example〕

 The present invention will be described below based on examples.

First of all, the production of a carbon substrate for a magnetic disk will be described. After phenol-formaldehyde resin, which is a thermosetting resin that becomes vitreous carbon after carbonization and firing, is hot-press molded into a magnetic disk shape, and then this is subjected to N ₂ gas atmosphere Preheated by heating to a temperature of 1500 ° C. Then
This is subjected to HIP treatment by applying an isotropic pressure of 1800 atm while being heated to 2600 ° C using a hot isostatic press (HIP). The obtained molded body was subjected to predetermined end surface processing and surface mirror finishing to obtain a 3.5 inch diameter carbon substrate for a magnetic disk having a surface roughness Ra20 to 23Å.

Next, the 25 carbon substrates contained in the stainless steel tray were placed in an electric furnace, and 25 carbon substrates were heated in the atmosphere at each heat treatment temperature and heat treatment time shown in Table 1 below. , Texture processing was performed. For comparison, a carbon substrate, which was also mirror-finished to have a surface roughness of Ra20 to 23Å, was textured using the above-mentioned polishing tape. The texture treatment conditions with this polishing tape were as follows: polishing tape: No. 6000, pressing pressure: 2 kg / cm ² , substrate rotation speed: 800 rpm, roll hardness: 90, processing time: 2 minutes.

After the texture treatment, the surface roughness Ra of the carbon substrate was measured. The results are shown in Table 1.

As can be seen from Table 1, according to the texture treatment according to the present invention, the heat treatment temperature is set in the range of 400 to 700 ° C., and the heat treatment time is appropriately selected so that the range shown by the thick line is shown. The surface roughness of the mirror-polished carbon substrate could be adjusted to the range of Ra30 to 100Å. When the texture treatment is performed at a relatively low temperature of about 400 ° C., the oxygen concentration may be increased to shorten the treatment time.

Next, a magnetic disk was produced using the textured carbon substrate, and an adsorption test (sticking test) between the magnetic head levitating surface and the magnetic disk surface was conducted using a dynamic friction tester. That is, 500 ° C. × 60 minutes, 600 ° C. × 10 minutes, 70 ° C. on a mirror-polished carbon substrate.
Texture treatment is performed under each heat treatment condition of 0 ° C x 5 minutes, and then each of the texture-treated carbon substrates is subjected to a Cr underlayer having a thickness of 1500Å and CoNiC having a thickness of 600Å.
A magnetic disk and a C protective film having a thickness of 500Å were sequentially formed by a sputtering method to manufacture a magnetic disk. For comparison, a magnetic disk for comparison was prepared by forming the same films as above on a carbon substrate that was texture-treated using a polishing tape and a carbon substrate that was not texture-treated, and was similarly absorbed. The test was conducted.

The results of the adsorption test are shown in Table 2. As can be seen from Table 2, in the magnetic disk using the carbon substrate textured by the conventional method using the polishing tape, the adsorption phenomenon did not occur under the conditions of this example, but the magnetic head floated. The height could only be achieved up to 0.2 μm.

On the other hand, in the magnetic disk using the carbon substrate subjected to the texture treatment according to the present invention, the flying height of the magnetic head is set to 0 without causing magnetic head adsorption.
It could be 1 μm or less.

〔The invention's effect〕

As described above, in the method for texture-treating a carbon substrate for a magnetic disk according to the present invention, the surface-polished carbon substrate for a magnetic disk is treated in an oxidizing atmosphere.
Since the heat treatment is performed at a temperature of 0 to 700 ° C., carbon is gasified by this heat treatment to form fine wavy irregularities on the polished surface, and the surface of the surface-polished carbon substrate is unnecessarily increased. It can be easily roughened to a suitable surface roughness without roughening. In addition, this texture processing method is industrially very simple and has the effect of being superior in mass productivity to the conventional method.

As a result, according to the present invention, the magnetic disk manufactured by using the carbon substrate subjected to the texture treatment according to the present invention can have a magnetic head flying height of 0.1 μm or less when applied to a magnetic disk device.
This can contribute to higher recording density.

Claims (1)

[Claims] 1. A surface-polished carbon substrate for a magnetic disk is heat-treated at a temperature of 400 to 700 ° C. in an oxidizing atmosphere to roughen the surface of the carbon substrate. And a method of texture-treating a carbon substrate for a magnetic disk.