JPS6127477B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a magnetic disk medium,
In particular, the present invention relates to a method of manufacturing a magnetic disk medium that does not cause damage such as cracks to the surface due to subsequent high heat treatment when the surface is mirror-finished. Magnetic disks used in data processing equipment and the like are made of an Al substrate coated with a ferrite thin film. In this case, in order to make the surface of the magnetic disk flat, the Al substrate is polished to make it mirror-like and smooth, and then ferrite paint is applied on top of it and the surface is polished again to make it a mirror-like surface. . However, recently there has been a demand to improve the recording density of data stored on magnetic disks. For example, when using the ferrite thin film mentioned above, it is 4000 ~
Although a recording density of only about 6,000 BPI (pits per inch) can be obtained, there is a demand for increasing this to around 20,000 BPI. In order to increase the recording density in this manner, the flying height of the head must also be made very small, so that the smoothness of the magnetic disk surface is even more required. Therefore,
If an Al substrate is smoothed for a long time, the Al substrate will become undulated and cannot be flattened, making it impossible to reduce the flying height of the magnetic head. Therefore, research is being carried out on treating the surface of an Al substrate to harden the surface as alumite, polishing it to make it mirror-finished, and forming a magnetic film on it. In this case, in order to form a magnetic film on the surface of the alumite, Fl is sputtered to form α-shaped Fl ₃ O ₄ on the surface, and this is turned into γ.
In this _case , it is necessary to heat the alumite substrate to a high temperature of about 350° to 400°C in the _oxidation -reduction process. However, the coefficient of thermal expansion of Al on the substrate and the alumite on the surface is significantly different, with Al having a coefficient of thermal expansion approximately five times larger than that of alumite. Therefore, even if the alumite surface is mirror-finished, cracks may appear on the surface during the step of forming the magnetic film, and this poses a problem in that it cannot be used as a magnetic disk. That is, as shown in FIG. 1, when an Al substrate 1 is immersed in an electrolytic solution and energized, a barrier layer 2 of alumite Al ₂ O ₃ is first formed on the surface of the Al substrate 1 as shown in FIG. This barrier layer 2 is a semiconducting layer. Next, as shown in 2, corrosion points 3, 3, etc. occur on the barrier layer 2, and as shown in 3, as the electrolysis progresses, this alumite Al ₂ O ₃ becomes thicker and thicker, and this barrier layer 2 is lowered downward. Moving. And as electrolysis progresses, 4
A porous alumite 4 having a large number of holes 5 is formed as shown in FIG. In FIG. 1, A is a sectional view thereof, and B is a partial plan view thereof. When the alumite hole 5 constructed as shown in FIG. 1 is heated in 100°C water as shown in FIG. 1, γ-Al ₂ O ₃ H ₂ is formed in the hole 5. A sealing portion 6 is formed. As a result, the hole 5 is sealed and normal alumite is obtained.

【table】

【table】

[Table] In this alumite production process, Table 1 shows the following:
The type of electrolyte, the thickness A of the barrier layer 2 formed by it, the diameter B of the hole 5, and the thickness C of the cell wall.
(See Figure 1 C). Table 2 also shows the types of electrolytes and the holes 5
An example of the number of holes, that is, the number of small holes is shown below. Therefore, even if the surface of alumite that has been sealed in this way is treated to a mirror finish, the sealed portion remains, and when this is heat-treated to form a magnetic film,
As shown in FIG. 2B, since the Al substrate 1 has a large coefficient of thermal expansion, it curves as shown by the arrow, and it is thought that the sealing portions 6 are strongly pressed against each other, causing the crack. For this reason, as shown in Japanese Unexamined Patent Publication No. 55-85694, an aluminum plate is alumite-treated, heat-treated at 150 to 350°C, and then polished to prevent the occurrence of cracks. Methods have been proposed to reduce this. However, when polishing the substrate to make it smooth and then washing it with water to remove polishing powder, a large amount of moisture adheres to the back surface of the substrate and inside the hole 5, so it is simply heated. If only a portion is evaporated, a large amount of γ-Al ₂ O ₃ H ₂ O will be formed due to the remaining water, and a large amount of the sealing portion 6 will be formed. Therefore, as described above, there is a problem in that cracks occur when heat treatment is performed to form a magnetic film. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method for manufacturing a magnetic disk medium that does not cause cracks on its surface even when heated at high temperatures by solving these problems. To this end, in the method for manufacturing a magnetic disk medium according to the present invention, an alumite layer is provided on the surface of an aluminum substrate, and after dehydration and drying treatment is performed, a heat treatment is performed to form a magnetic film. The alumite layer is polished to a thickness of 8 μm or less, washed with water, and then subjected to vacuum dehydration, centrifugal dehydration, or water displacement treatment using a solvent, followed by dehydration and drying treatment. shall be. Embodiments of the present invention will be described below with reference to FIGS. 3 and 4. FIG. 3 shows an embodiment of the present invention, and FIG. 4 is an explanatory diagram illustrating the reason why cracks do not occur in the magnetic disk medium manufactured according to the present invention. Example-1 (1) First, in (1) of FIG. 3A, alumite having a large number of holes is formed on an Al substrate as shown in FIGS. 1 (1) to (4). In this case, the thickness of the alumite film may be any number of micrometers, but since mirror polishing must be performed later to reduce the thickness to 8 micrometers or less, it is desirable that the film thickness be as thin as possible, taking into account the polishing allowance. (2) Next, the aluminum substrate on which alumite is formed (hereinafter referred to as an alumite substrate) is washed with water to remove the electrolyte. When manufacturing a magnetic disk from this alumite substrate, it is necessary to mirror the surface to make it flat, so the alumite portion is polished to a thickness of 8 μm or less. (3) Next, the alumite substrate polished to 8 μm or less is washed with water, centrifugally dehydrated using a centrifugal dehydrator, a certain amount of moisture remaining in the holes 5 is removed, and the substrate is further dried at 100°C or higher. The water in the hole is completely dehydrated. (4) The alumite substrate from which the moisture in the holes has been completely removed is stored in a dry state so that no moisture is present in the holes until it is manufactured as a magnetic disk. (5) Then sputter Fl onto this dried alumite substrate. (6) It is then reduced to form a film of Fl ₃ O ₄ as described above. (7) Then, by oxidizing this to γ-Fe ₂ O ₃ , a magnetic film can be formed on the surface of the alumite substrate. Example 2 (1) First, as shown in FIG. 3B (1), alumite having a large number of holes is formed on an Al substrate as shown in FIGS. 1 (1) to (4). In this case, the alumite film is formed to have a thickness of 8 μm or less. (2) Next, the alumite substrate is thoroughly washed with water, immersed in a hydrophilic organic solvent such as ethyl alcohol for water displacement treatment, and further dried at 100°C or higher to completely remove water from the alumite pores. (3) The alumite substrate from which the moisture in the holes has been completely removed is stored in a dry state so that no moisture is present in the holes until it is manufactured as a magnetic disk. (4) When manufacturing a magnetic disk from this alumite substrate, the surface needs to be mirror-finished and flat, so the alumite portion is polished. In this case, dry polishing using wrapping tape can also be performed. (5) After being polished in this manner to form a mirror surface, this is washed and dried again. (6) Fe is then sputtered onto this dried alumite substrate. (7) This is then reduced to form a Fe ₃ O ₄ film as described above. (8) This can then be oxidized to form γ-Fe ₂ O ₃ to form a magnetic film on the surface of the alumite substrate. Example-1 (6), (7) and Example-2 (7), (8)
Although the alumite substrate is heated to approximately 400°C during this process, no cracks occur on the surface of the alumite substrate.

[Table] Example-1 (1), (2), (3) and Example-2 (1),
The thickness of the alumite obtained by (2) is 1 to 10 μm
The alumite plate was then heated at 400℃ for 1 hour, and then tested for cracks.
The results shown in the table were obtained. As is clear from this, when the thickness of the alumite is less than 8 μm, the occurrence of cracks can be prevented by performing dehydration and drying treatment.
It has also been found that when the thickness of the alumite is 1 μm or less, cracks do not occur even without dehydration treatment. However, when polishing alumite to give it a mirror finish, a considerable amount of the alumite film is polished, so it is quite difficult to obtain the desired mirror finish with an alumite film thickness of 1 μm. Also, first 8
If you need an alumite film of μm or more,
After the alumite treatment, it is necessary to immediately polish it to a thickness of 8 μm or less and perform dehydration and drying treatment. By dehydrating and drying in this way, when water is present in the pores of the elongated alumite, this water turns into crystal water and becomes γ-Al ₂ O ₃ H ₂ O or γ-
It is possible to prevent Al ₂ O ₃ .3H ₂ O from being formed and causing volumetric expansion, which would easily cause cracks. In addition, in the explanation of Examples 1 and 2, in the case of drying treatment, examples of heat drying and water replacement treatment with a hydrophilic organic solvent were explained. It is also possible to perform water displacement treatment using a surfactant-containing organic solvent in which a surfactant is added to the solvent. Vacuum dehydration can also be performed instead of centrifugal dehydration. If the sputtering step (5) is performed immediately after the step (3) in Example-1, then (4) is of course unnecessary. Further, if the polishing step (4) is performed immediately after the step (2) of Example-2, the step (3) is naturally unnecessary. The reason why cracks do not occur in the present invention is that, as shown in FIG. 4, the holes 5 remain in the alumite substrate 1 because the holes are not sealed by dehydration and drying. Figures 4A and 4B show cross-sectional views of the alumite film during high-temperature treatment. The reason why cracks do not occur in the present invention is that, as shown in FIG. 4, the holes 5 remain in the alumite substrate 1 because no sealing process is performed by dehydration and drying, as shown in FIG. It is thought that even if the alumite film is thin (less than 8 μm) and deformation (shrinkage stress) occurs due to the difference in thermal expansion coefficients, it is absorbed by the holes 5 and no cracks occur. On the other hand, since the alumite film in FIG. 4B is thick (8 μm or more), the shrinkage stress in the upper layer of the alumite film is greater than that in FIG. 4A, and it is thought that cracks occur. (For the sake of understanding, the right side of Fig. 4B shows the tips of the upper layer of alumite touching each other, but in reality, cracks may occur before they come into contact with each other.) As explained above, according to the present invention, For the Al substrate,
We can provide a highly heat-resistant alumite substrate with anodized aluminum that does not cause cracks due to high-temperature processing, so if used as a base material for magnetic disks, it is possible to manufacture magnetic disks with high recording density and high track density. becomes.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the manufacturing state of conventional alumite.
FIG. 2 is an explanatory diagram of the problems of conventional alumite, FIGS. 3A and 3B are explanatory diagrams of an embodiment of the present invention, and FIG. 4 is an explanatory diagram of the features of the present invention. In the figure, 1 is an Al substrate, 2 is a barrier layer, 3 is a corrosion point, 4 is alumite, 5 is a hole, and 6 is a sealing part.

Claims (1)

[Claims] 1. A method for manufacturing a magnetic disk medium in which an alumite layer is provided on the surface of an aluminum substrate, dehydrated and dried, and then heat treated to form a magnetic film, the method comprising polishing the alumite layer to a thickness of 8 μm or less. A method for manufacturing a magnetic disk medium, which comprises performing a dehydration/drying process in which, after washing with water, vacuum dehydration, centrifugal dehydration, or water displacement treatment using a solvent is performed, and then drying is performed.