JPH0778875B2 - Texture processing method for amorphous carbon substrate for magnetic disk - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a texture processing method for an amorphous carbon substrate for a magnetic disk, which is texture-processed to prevent an adsorption phenomenon between a magnetic head levitating surface and a magnetic disk surface. .

[0002]

2. Description of the Related Art Conventionally, a magnetic disk is constructed by forming a magnetic film on an Al substrate coated with a Ni--P plating material or the like. In the magnetic disk reproducing apparatus, a floating magnetic head is arranged on the magnetic disk, and the magnetic head is levitated by rotating the magnetic disk, and writing or reproducing to or from the magnetic disk is performed by this magnetic head. To do. However, when writing to or reproducing from a magnetic disk, adsorption may occur between the magnetic head levitation surface and the magnetic disk surface when the disk is stationary. This adsorption phenomenon is caused when the magnetic head levitation surface and the magnetic disk surface are extremely smooth and both face each other with a minute gap, and the gap is filled with molecules such as O ₂ , N ₂ or H ₂ O. This is due to the large adsorption force generated by the interfacial tension. When such an adsorption phenomenon occurs, it causes a disadvantage that a large amount of electric power is consumed when the motor that drives the magnetic disk is started.

Therefore, in order to prevent the above-mentioned adsorption phenomenon,
In the Al substrate for a magnetic disk, before the magnetic film is deposited, the substrate surface is once mirror-finished and then subjected to a texture treatment to adjust the surface roughness. The following texture processing methods are available. That is, while the Al substrate (Ni-P plated material) is rotated, the polishing tape is moved in the radial direction of the Al substrate while the polishing tape is pressed against the Al substrate by the roller to make contact with the Al substrate. Silicon carbide as polishing tape,
Use those to which abrasive grains such as alumina or diamond are attached. By performing the mechanical texture treatment in this way, it is possible to form a concentric circular striation on the surface of the Al substrate for a magnetic disk and obtain a rough surface in which the striation is oriented in the circumferential direction.

Incidentally, as another conventional magnetic disk substrate, an amorphous carbon substrate (Kobe Steel Technical Report, Vol.
9, No. 4, pages 35 to 38, issued in 1989) is proposed. This amorphous carbon substrate is lightweight and has high strength, is excellent in heat resistance and surface accuracy, and can improve the recording density of the magnetic disk as compared with the Al substrate.

[0005]

However, it is extremely difficult to adjust the surface roughness to an appropriate value in the conventional method of texture-treating an Al substrate for a magnetic disk, and it tends to be unnecessarily rough. In order to increase the recording density of the magnetic disk, it is preferable to further reduce the flying height (spacing) of the magnetic head. However, as described above, if the surface roughness of the Al substrate for the magnetic disk becomes larger than necessary, The flying height of the magnetic head increases,
The recording density of the magnetic disk cannot be improved.
Further, the conventional amorphous carbon substrate has a problem that the surface roughness itself has not been sufficiently examined from the viewpoint of preventing the magnetic head from adsorbing and improving the magnetic recording characteristics.

The present invention has been made in view of the above problems. It is possible to prevent the magnetic head from sticking to the magnetic disk, improve the characteristics of the magnetic film, and make the flying height of the magnetic head smaller than before. It is an object of the present invention to provide a texture processing method for an amorphous carbon substrate for a magnetic disk, which can obtain a textured surface that can be obtained.

[0007]

A method of texturing an amorphous carbon substrate for a magnetic disk according to the present invention has a surface roughness Ra of 5 to 50Å by polishing the surface of the amorphous carbon substrate, Polishing step for increasing the ratio Ra ₂ / Ra ₁ of the surface roughness Ra ₁ in the radial direction to the surface roughness Ra ₂ in the radial direction to 1.50 or more, and a heating step for heating the surface-polished amorphous carbon substrate in the presence of oxygen. And having.

[0008]

The present inventors paid attention to the properties of the amorphous carbon substrate and conducted various studies on the texture processing method. As a result, after the amorphous carbon substrate is polished to a predetermined surface roughness, the amorphous carbon substrate is heat-treated at a predetermined temperature in an oxidizing atmosphere to process the amorphous carbon substrate to a suitable surface roughness for a magnetic disk. I found that I can do it.

That is, when an amorphous carbon substrate polished to a predetermined surface roughness is heated to a predetermined temperature, C + O
The oxidation reaction of ₂ → CO ₂ occurs, carbon is gasified, and fine irregularities are formed on the polished surface. Therefore, by controlling the heat treatment conditions such as the treatment temperature and time, the amorphous carbon substrate can be easily treated to have an appropriate surface roughness, and the surface is not roughened more than necessary. As a result, the magnetic disk head adsorption can be prevented, the characteristics of the magnetic film formed on the amorphous carbon substrate can be improved, and the flying height of the magnetic head can be made smaller than before.

Next, the surface roughness Ra and the surface roughness Ra in the circumferential direction of the amorphous carbon substrate after surface polishing.
_The reason for limiting the ratio Ra ₂ / Ra ₁ of ₁ to the surface roughness Ra ₂ in the radial direction will be described.

If the surface roughness (average surface roughness) Ra of the amorphous carbon substrate after surface polishing is smaller than 5Å, the magnetic head is apt to be attracted when it is practically used as a magnetic disk. On the other hand, when the surface roughness Ra exceeds 50Å,
It becomes difficult to make the flying height of the magnetic head smaller than in the past. Therefore, the surface roughness Ra of the amorphous carbon substrate after surface polishing is set to 5 to 50 Å.

The main purpose of texturing an amorphous carbon substrate for a magnetic disk is to prevent adsorption of a magnetic head. However, when the directionality of the texture with respect to the substrate surface is made into a concentric circular orientation, that is, the surface roughness of the amorphous carbon substrate is roughened. When Ra is made larger in the radial direction than in the circumferential direction, the coercive force and the squareness ratio in the circumferential direction can be improved by 20 to 30% as compared with those in the radial direction. Since the magnetic head moves in the circumferential direction relative to the magnetic disk during recording and reproduction, if the texture is oriented in the circumferential direction as described above, the magnetic characteristics of the magnetic film in the circumferential direction are significantly increased. Can be improved. Therefore, it is not necessary to improve the magnetic characteristics of the magnetic film by adding an expensive element such as Pt or Ta to the magnetic film (media layer).

The circumferential orientation of this texture is determined by surface polishing before heat treatment. However, the ratio Ra ₂ of the surface roughness Ra ₁ in the circumferential direction and the surface roughness Ra ₂ in the radial direction of the amorphous carbon substrate after surface polishing.
When / Ra ₁ is less than 1.50, the circumferential orientation of the texture is insufficient and the magnetic properties of the media layer in the circumferential direction are insufficiently improved. Therefore, the ratio Ra ₂ / Ra ₁ of the surface roughness Ra ₁ in the circumferential direction and the surface roughness Ra ₂ in the radial direction of the amorphous carbon substrate after the surface polishing is set to 1.50 or more.

As described above, the amorphous carbon substrate for a magnetic disk according to the present invention can reduce the flying height of the magnetic head, and can form a medium layer without adding an expensive element such as Pt or Ta. Since the magnetic characteristics can be improved, it is particularly suitable for use in a low-cost magnetic disk.

[0015] Note that the amorphous carbon substrate in the present invention, by performing the ultra-high temperature HIP (hot isostatic pressing) process to amorphous carbon, a density almost abolished pores high as 1.80 g / cm ³ or more However, it is made of high-density amorphous carbon whose characteristics are close to those of graphite.

Next, a polishing method for polishing the amorphous carbon substrate to the above-mentioned surface roughness will be described.

In the polishing step, an abrasive material such as a tape polisher used when mechanically texture-processing a conventional Al substrate for a magnetic disk is effective. That is, while the polishing material is brought into contact with the amorphous carbon substrate while the amorphous carbon substrate is rotated, the polishing material is moved in the radial direction of the amorphous carbon substrate, for example, from the outer peripheral portion of the substrate toward the inner peripheral portion. . A polishing tape to which fine powdery abrasive grains are attached can be used as the polishing material. Abrasive grains having hardness equal to or higher than that of an amorphous carbon substrate and industrially inexpensive, for example, diamond, alumina, SiC, Zr
O ₂ , cerium oxide, SiO ₂ or the like is used. As a result, the surface of the amorphous carbon substrate is cut by the abrasive grains as it rotates. Therefore, by appropriately selecting the number of rotations of the substrate, the number of the polishing tape to be used, the moving speed of the polishing tape, etc., the surface roughness Ra of the amorphous carbon substrate after the surface polishing is set to 5 to 50 Å and the The ratio Ra ₂ / Ra ₁ of the surface roughness Ra ₁ and the surface roughness Ra ₂ in the radial direction can be 1.50 or more, and concentric circular scratches can be formed on the surface of the amorphous carbon substrate.

[0018]

EXAMPLES A method of texturing an amorphous carbon substrate for a magnetic disk according to examples of the present invention and comparative examples which depart from the scope of the claims of the present application will be described below.

First, a mixed resin of a thermosetting resin that becomes amorphous carbon after carbonization and firing and a phenol-formaldehyde resin is molded into a magnetic disk shape by hot pressing, and this molded body is subjected to about 1450 in an N ₂ gas atmosphere.
It was preheated by heating to a temperature of ° C. Then, the pre-fired body is heated to about 2350 using a hot isostatic pressing (HIP) device.
HIP by applying isotropic pressure of about 1800 atm while heating to ℃
Treated. As a result, an amorphous carbon substrate (untreated) was obtained.

Next, using a 16B double-side polishing machine manufactured by Speed Fam Co., rough polishing was performed on an untreated amorphous carbon substrate with a cast iron surface plate while dropping SiC abrasive grains as a slurry. In this rough polishing, the abrasive grain concentration
The weight was 35% by weight, the work load was 300 g / cm ² , the lower platen rotation speed was 100 rpm, the slurry dropping amount was 600 ml / min, and the polishing time was 45 minutes.

Then, the amorphous carbon substrate after the rough polishing was ultrasonically cleaned to sufficiently remove the abrasive grains for the rough polishing.
After that, the amorphous carbon substrate after rough polishing was fixed to the substrate rotating shaft, and while this was rotated at 300 to 500 rpm, the polishing tape was brought into contact with the amorphous carbon substrate, and the polishing tape was put inside from the outer peripheral portion of the substrate. Moved to the circumference. In this way, the amorphous carbon substrate after the rough polishing was subjected to the final polishing to form concentric polishing marks on the surface of the amorphous carbon substrate. As the polishing tape, diamond, SiC,
It is preferable to use those having abrasive grains such as Al ₂ O ₃ , SiO ₂ and ZrO ₂ attached thereto and having a count of 6000 or more.

By the above-mentioned finish polishing, the surface roughness Ra of the amorphous carbon substrate and the surface roughness Ra ₁ in the circumferential direction are obtained.
Examples 1 to 4 and Comparative Examples 1 to 3 with different ratios Ra ₂ / Ra ₁ between the surface roughness Ra ₂ and the surface roughness Ra ₂ in the radial direction.
And Then, with respect to the amorphous carbon substrates according to the example and the comparative example, the surface roughness Ra after finish polishing was measured using a surface roughness meter, respectively, and the surface roughness Ra ₁ in the circumferential direction and the surface roughness Ra in the radial direction were measured. is the ratio _Ra 2 / Ra with Ra ₂
I asked for ₁ . The results are shown in Table 1 below. The surface roughness Ra after the finish polishing was limited to 5 Å, and a mirror surface higher than that could not be obtained. Also,
As the surface roughness meter, TALISTEP (trade name) manufactured by Lanktera Hobson Co. was used, and measurement was performed under the following conditions. Stylus: 0.2 μm Measurement length: 1 mm Cutoff: 0.08 mm Magnification: Vertical x 1000000 Next, the amorphous carbon substrate after finish polishing was heat-treated in air (in the presence of oxygen) at a predetermined temperature for a predetermined time. Thus, the amorphous carbon substrates for magnetic disks according to Examples 1 to 4 and Comparative Examples 1 to 3 were manufactured.

With respect to the amorphous carbon substrates for magnetic disks according to the above-mentioned Examples and Comparative Examples, the surface roughness Ra after the texture treatment was measured using a surface roughness meter, respectively, and the surface roughness Ra ₁ in the circumferential direction was measured. And radial surface roughness R
was determined the ratio Ra ₂ / Ra ₁ and a _2. The results are also shown in Table 1 below.

[0024]

[Table 1] Next, after precisely cleaning the amorphous carbon substrates for magnetic disks according to Examples and Comparative Examples, a media layer (magnetic film) made of CoNiCr and a carbon protective film were formed on the amorphous carbon substrates by using a magnetron sputtering device. Films were sequentially formed, and a lubricant was applied to the surface of the film to manufacture a magnetic disk.

Then, a square sample piece having a side of 5 mm was cut out from each of the magnetic disks according to the examples and comparative examples, and the magnetostatic characteristics of the sample piece were measured. The magnetostatic characteristics were measured in the circumferential direction of the magnetic disk and the radial direction orthogonal to this. Further, with respect to the magnetic disks according to Examples and Comparative Examples manufactured in the same manner, recording / reproducing was performed using a disk certifier (trade name) manufactured by Proquip Co., Ltd., and the occurrence of head crash was evaluated. The results are also shown in Table 1 above. The head flying height between the magnetic disk and the MIG (Metal In Gap) head was set to about 0.15 μm.

As is apparent from Table 1, the magnetic disks according to Examples 1 to 4 all have a head flying height of about 1.
Even if it was as low as 0.15 μm, head crash did not occur, and its coercive force Hc in the circumferential direction was excellent.

On the other hand, the surface roughness Ra after finish polishing is 61Å
In the magnetic disk according to Comparative Example 1, the surface roughness Ra after the texture treatment is unnecessarily rough, so that a head crash occurs during recording and reproduction, and it is difficult to put the head into practical use at a low head flying height. Ra ₂ / Ra ₁ after finish polishing
Is less than 1.50, the magnetic disks according to Comparative Examples 2 and 3 are
The improvement of the coercive force Hc in the circumferential direction was insufficient.

[0028]

As described above, according to the present invention, the surface roughness Ra of the amorphous carbon substrate for a magnetic disk is adjusted to 5 to 50Å and the surface roughness Ra in the circumferential direction is polished. ₁ and surface roughness R in the radial direction
Since the ratio Ra ₂ / Ra ₁ with respect to a ₂ is set to 1.50 or more and then heat-treated in the presence of oxygen, the texture can be circumferentially oriented and the surface roughness can be made appropriate. Therefore, the magnetic head can be prevented from being attracted to the magnetic disk, and the flying height of the magnetic head can be made smaller than in the prior art, and the magnetic characteristics in the circumferential direction of the magnetic film can be remarkably improved.

Therefore, the amorphous carbon substrate for a magnetic disk according to the present invention is particularly suitable as a low-cost magnetic disk substrate in which an expensive element such as Pt or Ta is not added to the media layer.

Claims (2)

[Claims] 1. The surface roughness Ra of the amorphous carbon substrate is adjusted to 5 to 50 Å by polishing the surface, and the surface roughness Ra ₁ in the circumferential direction and the surface roughness R in the radial direction are obtained.
An amorphous carbon substrate for a magnetic disk, comprising: a polishing step for making a ratio Ra ₂ / Ra ₁ with respect to a ₂ 1.50 or more; and a heating step for heating a surface-polished amorphous carbon substrate in the presence of oxygen. Texture processing method. 2. In the polishing step, while the amorphous carbon substrate is being rotated, a polishing material is brought into contact with the amorphous carbon substrate and moved in the radial direction thereof to form concentric scratches on the surface of the amorphous carbon substrate. The method for texture treatment of an amorphous carbon substrate for a magnetic disk according to claim 1, wherein