JPH0512662A - Production of titanium magnetic disk substrate - Google Patents

Abstract

PURPOSE:To provide the process for production of the titanium magnetic disk substrate which can form this magnetic disk substrate to <=0.025mum surface roughness Rmax. CONSTITUTION:The surface roughness Rmax of a titanium plate prior to an anodic oxidation treatment is set at <=0.04mum at the time of producing the titanium magnetic disk substrate by subjecting a bland material for the titanium magnetic disk substrate to the anodic oxidation treatment. The voltage at the time of the anodic oxidation treatment is set at 4 to 12V and further, the current density at the end of of the anodic oxidation treatment is set at <=5X10<-4>A/mm<2>.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a titanium magnetic disk substrate used for high density recording / reproducing.

[0002]

2. Description of the Related Art In recent years, magnetic disks have been increased in capacity and recording density.
Therefore, attempts have been made to reduce the thickness of the magnetic film (magnetic medium) formed on the magnetic disk substrate and to reduce the distance between the magnetic head and the magnetic film (lower the flying height).

By the way, aluminum alloys have been conventionally used as the magnetic disk substrate, but in recent years, it has been attempted to use titanium as the magnetic disk substrate instead of aluminum alloy. This is because titanium is superior to aluminum alloys in terms of heat resistance, a wide range of magnetic films can be formed by sputtering, and the characteristics of the magnetic film can be improved.

However, in order to use titanium as a magnetic disk substrate, there is a big problem that it is necessary to improve its surface roughness. The surface roughness becomes a problem when titanium is used as a magnetic disk substrate for the following reason.

Titanium magnetic disk substrates have many advantages in that they have sufficient cleanliness and that the limitation of the sputtering temperature of the magnetic film when NiP plating is applied to the surface is removed. The surface of the crystal titanium is used as it is, and the NiP plating on the surface of the aluminum alloy magnetic disk substrate is not applied. However, the current distance between the magnetic head and the magnetic disk (head flying height)
Has been attempted to be 0.05 μm, and in order to satisfy this low floating condition, the surface roughness of the magnetic disk substrate must be 0.025 μm or less over the entire surface. The substrate cannot satisfy such a value. In other words, the surface of the aluminum alloy magnetic disk substrate becomes NiP amorphous, and uniform polishing is possible, and the entire surface can be 0.025 μm or less. However, the surface of the titanium magnetic disk substrate remains polycrystalline. Therefore, the crystal grain step due to the difference in the polishing rate of the crystal plane is inevitably left, and the R
_It is virtually impossible to obtain _max of 0.03 μm or less.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a method of manufacturing a titanium magnetic disk substrate whose surface roughness R _max is 0.025 μm or less. ..

[0007]

In order to solve the above problems, the present invention provides a titanium magnetic disk substrate for producing a titanium magnetic disk substrate by subjecting a titanium magnetic disk substrate material to anodizing treatment. In the manufacturing method, the surface roughness R _max of the titanium plate before anodizing treatment is 0.
It is not more than 04 μm, and the voltage at the time of anodizing treatment is 4 to 1
2V and the current density at the end of anodizing treatment is 5 ×
10 ^-4 A / mm ² There is provided a method for manufacturing a titanium magnetic disk substrate, which is characterized below.

The inventors of the present application have conducted various studies to improve the surface roughness of the titanium magnetic disk substrate, and as a result,
It was newly found that the crystal grain steps remaining in the conventional titanium-made magnetic disk substrate as mirror-polished can be reduced by the anodic oxidation treatment under specific conditions, whereby a sufficiently good surface roughness can be easily obtained. The present invention was made based on such knowledge.

That is, when a titanium plate processed to have a surface roughness of a certain value or less by mirror polishing is anodized, an anodized layer having a different thickness depending on the crystal orientation is formed on the surface. As a result, the steps of crystal grains remaining on the titanium magnetic disk substrate that has been mirror-polished can be reduced. In other words, titanium is easily oxidized, and the polishing property is improved by the oxidation. Therefore, the mirror polishing rate becomes larger as the crystal surface that is more likely to be oxidized and the specific crystal surface becomes a recess, but the mirror surface polishing gives a certain surface roughness. In the anodic oxidation treatment after processing, the thickness of the anodic oxide film increases on the surface that is more likely to be oxidized, and as a result, the crystal steps in the two steps cancel each other out, making titanium magnetic A disk substrate will be obtained.

An example of incorporating titanium anodic oxidation into a magnetic disk is found in Japanese Patent Laid-Open No. 56-71821. This invention prevents the diffusion of atoms between the magnetic medium and the substrate without defects on the substrate by forming an anodizable film containing titanium on the substrate by sputtering or the like and then polishing it. It is intended to form a surface.
However, in the technique disclosed in Japanese Patent Laid-Open No. 56-71821, unlike the present invention, the surface roughness of the anodic oxide film is not good and it cannot be controlled.
This is apparent from the fact that the polishing is performed after the anodizing treatment in JP-A-56-71821.

In the present invention, the anodizing voltage in the anodizing process is controlled to 4 to 12V. This is a control factor necessary for achieving the surface roughness R _{max of} 0.025 μm or less. If the anodic oxidation voltage is less than 4 V, it is not possible to form an anodic oxide film having a thickness sufficient to cover the crystal steps, and thus it becomes impossible to achieve sufficient surface roughness. On the other hand, when the anodic oxidation voltage is higher than 12 V, an anodic oxide film having a thickness larger than that required to cover the crystal step is formed. That is, an anodized film that is thicker than other crystal faces is formed on the crystal surface that has become a concave portion after mirror polishing, and becomes a convex portion after anodizing treatment. Also in this case, it becomes impossible to achieve sufficient surface roughness.

The surface roughness of the substrate before the anodizing treatment is defined as R _max.
To 0.04 μm or less. This is because the effect of the depth of the recess in the mirror-polished before anodization (R _max) is too large when the surface roughness by anodic oxidation process improvement does not reach, R _max for the first time below 0.04μm A surface roughness of 0.025 μm or less will be achieved.

The current density at the end of the anodizing treatment is 5 × 10 5.
^-4 A / mm ² It is specified below. This is for the following reason. The thickness of the anodic oxide film and its characteristics depend on the anodic oxidation voltage in equilibrium, but in a transient state reaching equilibrium, the film thickness etc. is affected by the electrode lead-out position, inter-electrode distance, etc. It depends on the location. The current density decreases due to the progress of formation of the insulating anodic oxide film, but it is possible to achieve uniform surface roughness only when the current density at the end of the treatment is 5 × 10 ^-4 A / mm 2 or less. ..

As described above, according to the present invention, the titanium plate having the surface roughness defined by the mirror-polishing to have a constant and good value,
By performing the controlled anodic oxidation treatment, a better surface roughness can be obtained, and the flying height of the magnetic head can be reduced.

It is needless to say that the titanium plate referred to here is not limited to pure titanium, but can be applied to various titanium alloys, pure titanium plates subjected to surface hardening treatment, and various titanium alloy plates.

[0016]

Embodiments of the present invention will be described below.

A 3.5 inch pure titanium magnetic disk substrate material having a plate thickness of 1.27 mm and a surface roughness of R _max of 0.029 to 0.100 μm was anodized under various conditions. The electrolytic solution was a 1.0 vol% phosphoric acid aqueous solution, the cathode was a pure titanium plate, and the distance from the pure titanium magnetic disk substrate material to be anodized was 2 cm.

The anodizing voltage is 0 to 50 V, the anodizing finish current density is 1 × 10 ^-1 to 1 × 10 ^-6 A / mm 2.
Changed. The surface roughness is measured using a non-contact roughness meter.
Evaluation was performed by randomly measuring 50 points on the substrate. In addition,
Surface roughness R ^max here Is the average of 50 measurement points. Regarding the uniformity of the magnetic disk, the standard deviation σ _R of the measured surface roughness was determined. If σ _R was smaller than 0.001 μm, it was uniform, and if it was 0.001 μm or more, it was not uniform. The results are shown in Table 1.

[0019]

[Table 1]

As is apparent from Table 1, the surface roughness before the anodizing treatment is 0.04 μm or less, and the anodizing voltage is 4
~ 12V, current density at the end of anodization is 5 x 10
^-4 A / mm ² If it is below, surface roughness R ^max Is 0.025
It was confirmed that a magnetic disk substrate having a thickness of less than μm and good uniformity was obtained.

[0021]

According to the present invention, the surface roughness R of the substrate is
A titanium magnetic disk substrate having a _max of 0.025 μm or less and easily obtaining a titanium magnetic disk substrate having good uniformity is provided. Therefore, it becomes possible to easily and inexpensively provide a recording medium having characteristics capable of high-density recording, which has a great effect on the information processing apparatus industry.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenji Morita, 1-2, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Masanori Omura, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Main Steel Pipe Co., Ltd.

Claims (1)

Claim: What is claimed is: 1. A method for manufacturing a titanium magnetic disk substrate, which comprises subjecting a titanium magnetic disk substrate material to anodization treatment to manufacture a titanium magnetic disk substrate, wherein titanium before anodization treatment is used. The surface roughness R _{max of the} plate is 0.04 μm or less, the voltage during the anodizing treatment is 4 to 12 V,
And the current density at the end of anodizing treatment is 5 × 10 ^-4 A / m
m ² A method of manufacturing a magnetic disk substrate made of titanium characterized by the following.