JPH01133218A - Production of aluminum substrate for magnetic disk - Google Patents

Abstract

PURPOSE:To prevent generation of a characteristic change and crack by high- temp. heating and to increase hardness by subjecting an aluminum substrate material to an anodic oxidation treatment to form a hard oxide film thereon, then subjecting the film to a post-stage anodic oxidation treatment using a chromic acid electrolyte. CONSTITUTION:While the aluminum substrate material is not particularly limited, an alloy which consists of high-purity aluminum having >=99.99% purity as a base and is added with 4-5wt.% Mg is preferably used. The substrate material 1 is subjected to the fore-stage anodic oxidation treatment to form the hard oxide film 2 thereon. The oxalic acid anodic oxidation treatment is preferable as said treatment and the film thickness thereof is preferably set at 5-20mum. The film is then subjected to the post-stage anodic oxidation treatment by using the chromic acid electrolyte by which the heat resistance of the film 2 is improved. The boundary face to the base material is roughened and the crack at the time of heating is prevented by the chromic acid-anodized film 3 formed by the post-stage anodic oxidation treatment. The surface of such substrate material is polished to form the finished substrate.

Description

[Detailed Description of the Invention] Industrial Application Field This invention relates to a method for manufacturing an aluminum substrate constituting a magnetic disk as a magnetic recording medium in a computer, etc., and in particular a method for depositing a magnetic film in the form of a thin film by sputtering or the like. The present invention relates to a method of manufacturing an aluminum substrate suitable for magnetic disks of this type.

Conventional technology Conventionally, so-called coated type magnetic disks have been used, in which a magnetic medium is coated on the surface of an aluminum substrate, but with this coated type disks, the thickness of the magnetic film is unavoidable. Therefore, there is a limit to the ability to meet the recent demands for higher recording densities on magnetic disks.

Therefore, magnetic disks in which a magnetic medium is deposited as a thin film on the surface of an aluminum substrate by sputtering or the like have been developed and provided.

The aluminum substrate used in such magnetic disks is generally coated with a base film layer for the purpose of improving surface hardness and adhesion to a magnetic film.

Conventionally, an electroless N1-P plating film, a sulfuric acid anodic oxide film, or a chromic acid anodic oxide film has been employed as the base film, but these have the following drawbacks.

The problem to be solved by the invention is that when the magnetic film to be formed on the surface of the base film is, for example, an oxide thin film, 30%
Heat treatment is performed at a temperature of about 0 to 400°C, but if the base film is an electroless N1-P plating film, heating above about 200°C will cause it to crystallize and become magnetic, making it suitable for application to magnetic disks. The drawback was that the range was limited. In addition, since the sulfuric acid anodic oxide film has poor heat resistance, the thickness of the film was reduced to 3 μm to prevent cracks from occurring during heating.
Although it is necessary to limit the thickness to the following, there is a drawback that if the film thickness is made thin, sufficient hardness cannot be obtained. Furthermore, although the chromic acid anodic oxide film has relatively good heat resistance, it has a maximum hardness of about 350 Hv, which is not as hard as the N1-P plating film, so it has the disadvantage of poor C8S properties. Ta. Moreover, the chromic acid anodic oxidation film has poor film formation efficiency, and it takes a processing time of about 90 minutes to form a film with a thickness of 15 μm, for example, resulting in high costs.

The present invention was made in view of this technical background, and aims to provide an aluminum substrate that does not cause characteristic changes or cracks due to high temperature heating and has a base film that has high hardness. .

Means for Solving the Problems With this objective in mind, the inventor conducted various experiments and research, and as a result of conducting various experiments and research, the inventor applied a first-stage anodic oxidation treatment to form a hard oxide film on the base film, and a second-stage anodization process using a chromic acid electrolyte. The inventors have discovered that the above object can be achieved by sequentially performing oxidation treatments, and have completed the present invention.

That is, the present invention provides an aluminum substrate for a magnetic disk, which is characterized in that an aluminum substrate material is subjected to a first-stage anodization treatment to form a hard oxide film, and then a second-stage anodic oxidation treatment is performed using a chromic acid electrolyte. The gist is the manufacturing method.

The composition of the aluminum substrate material is not particularly limited, but a preferred composition is based on high-purity aluminum with a purity of 99.99% or more, and Mg: 4 to 4.
It is preferable to use an alloy containing 5%. In this case, Mg is an element that provides strength to withstand high-speed rotation as a magnetic disk, and its content is 4vt%.
If it is less than 5vt%, the effect will be poor, and if it exceeds 5vt%, workability, mechanical properties, and surface smoothness will deteriorate. Furthermore, the reason why high-purity aluminum is used as a base is to prevent the precipitation of Fe5Sl, which adversely affects magnetic properties, as much as possible.

Next, I will explain the manufacturing process of aluminum substrates.
First, an aluminum substrate having a desired thickness, chamfer shape, and surface accuracy is manufactured by subjecting an aluminum plate of a predetermined shape to diamond turning, boring, rough turning, and the like.

Next, the substrate material is subjected to a preliminary anodic oxidation treatment. This anodizing treatment is for forming a hard anodic oxide film. Examples of the hard oxide film include an oxalic acid film and other organic acid films, and as a preliminary treatment for forming this, organic acids such as oxalic acid, sulfosalicylic acid, cresol sulfonic acid, phenolsulfonic acid, and sulfophthalic acid are used as an electrolyte. An example of this is anodizing using an acid. Among these, anodic oxidation treatment using an oxalic acid method is preferred. Preferred electrolytic conditions for this oxalic acid anodization treatment are as follows: oxalic acid concentration: 1 to 5 wt%, current density: 1.5 A
In order to obtain good constant current electrolytic treatment around /dd and to form a harder film, it is preferable to set the liquid temperature at 0 to 20°C. In addition to the oxalic acid film, the thickness of the hard oxide film formed by the pre-treatment is preferably set to 5 to 20 μm. 5 μm
If it is less than 20 μm, the hardness of the film may not be sufficient, and if it exceeds 20 μm, the heat resistance of the base film may be deteriorated, and depending on the temperature conditions, there is a risk of cracking the film.

The latter stage anodic oxidation treatment using chromic acid as an electrolyte is carried out to improve the heat resistance of the film. The conditions for electrolytic treatment using this chromic acid method are not particularly limited, but the preferred conditions for achieving even better heat resistance of the film are: liquid concentration: 1 to 10 wt%; liquid temperature;
A constant voltage electrolytic treatment at 5 to 45° C. and a voltage of 70 to 120 V can be used, and the film thickness is preferably 0.5 to 5 μm.

The surface of the aluminum substrate material that has undergone two stages of anodizing treatment, front and rear, is polished to form a finished product. An example of polishing is puff polishing in which alumina particles are used as an abrasive.

Note that manufacturing a magnetic disk using the aluminum substrate obtained above is generally performed by forming a magnetic film on the surface of the substrate by sputtering or the like, and further forming a protective layer thereon.

Incidentally, the reason why the heat resistance of the film is improved by performing the post-stage anodizing treatment using the chromic acid method is presumed to be due to the following reason. That is, as shown in FIG. 1, a porous hard oxide film (2) of a predetermined thickness is formed on the surface of the aluminum substrate material (1) due to the anodizing treatment in the previous stage, but as shown in FIG. As shown, due to the formation of a chromic acid anodic oxide film (3) in the subsequent anodizing process, the film becomes similar to the substrate material (
It is thought that the surface becomes rough at the interface with 1). Cracks occur in sulfuric acid anodic oxide films, etc. when heated at high temperatures, due to the difference in thermal expansion coefficient between the substrate material and the film. It is presumed that heat resistance improves as a result of reducing internal stress and preventing the occurrence of cracks.

Effects of the Invention Since the present invention is as described above, it is possible to provide a magnetic disk substrate having an anodic oxide film having excellent hardness and heat resistance on its surface as a base film.

Therefore, during the production of magnetic disks, the magnetic film coated on the surface of the undercoating film has a 300 to 400%
Even if it is a type that needs to be heated and maintained at 0℃,
Since no cracks or changes in properties occur in the base film due to heating, it can be coated without any problems, and the range of applications as a magnetic disk substrate can be expanded. Moreover, in addition to the base film itself having excellent hardness,
Since there is no need to reduce the thickness of the base film in order to improve its heat resistance, the film can be thick enough and have excellent hardness, which reduces head crashes of the magnetic film. The durability of the magnetic film can be improved. Furthermore, since the chromic acid anodic oxidation treatment is not the only treatment, the film can be formed in a short time and the film formation efficiency is good, which makes it possible to provide a low-cost aluminum substrate.

Example [Example 1] AQ-based aluminum with a purity of 99.99%
Donut-shaped aluminum plate made of 4νt%Mg alloy (
Outer diameter 95mm, inner diameter 25InI11, plate thickness 1.3mm)
A plurality of sets were prepared, and the surfaces of the alloy plates were smoothed and then cleaned with a non-erosive cleaning agent to produce aluminum substrate materials.

Next, these substrate materials were mixed with oxalic acid concentration: 1.5 νt% and liquid temperature:
Current density in oxalic acid electrolyte at 10°C: 1°5A/dTIt
First, a preliminary anodic oxidation treatment was carried out by constant current electrolysis treatment under conditions of electrolysis time of 26 minutes to form an oxalic acid film with a thickness of 10 μm. Next, as a subsequent anodic oxidation treatment, chromic acid concentration: 3 wt%, liquid? m: A constant voltage electrolytic treatment was performed in a chromic acid electrolyte at 30° C. at a bath voltage of 100 V to form a chromic acid film with a thickness of 1 μm, thereby obtaining an aluminum substrate according to the present invention.

On the other hand, pre- and post-stage anodizing treatments were performed under the same conditions as above, except that the processing time of the pre-processing was changed appropriately to obtain aluminum substrates with oxalic acid coatings having thicknesses of 3 μm, 6 μm, and 20 μm.

[Comparative Example 1] Using the same aluminum substrate material as in Example 1, oxalic acid concentration:
Oxalic acid alone was anodized by direct current constant current electrolytic treatment in an oxalic acid electrolyte with a temperature of 1.5 vt% and a liquid temperature of 10°C, with a current density of 1.5 A/dm and various electrolytic times. and film thickness 3μms 6μm, 10μm 120μm
Various types of substrates were obtained. In addition, in this process, processing time 2
Film thickness: 10. czm, the film thickness reached 15 μm in 40 minutes.

[Comparative Example 2] Using the same aluminum substrate material as in Example 1, sulfuric acid concentration:
In a sulfuric acid electrolyte containing 15 wt% and a liquid temperature of 15°C, anodic oxidation treatment using sulfuric acid alone was carried out by direct current constant current electrolysis treatment at a current density of 1.5 A/dTd and various electrolysis times. Various substrates with film thicknesses of 3 μm, 6 μm, 10 μm, and 120 μm were obtained. Note that in this process, the processing time is 26
The film thickness reached 10 μm in minutes and 15 μm in 40 minutes.

[Comparative Example 3] Using the same aluminum substrate material as in Example 1, electrolysis time was increased at a current density of +0.8 A/dH in an anhydrous chromic acid electrolyte with a chromic acid concentration of 3 vt% and a liquid temperature of 40°C. Instead of various types, we carried out anodizing treatment using chromium acid alone using DC constant current electrolytic treatment, resulting in film thicknesses of 3 μm, 6 μm, and 10 μm.
, 20 μm various substrates were obtained. In this process,
Film thickness: 10 μm after 60 minutes, 15 μm after 90 minutes
reached.

In order to examine the heat resistance of the aluminum alloy substrate obtained above, the film surface was polished and then heated in an electric furnace to temperatures of 200°C, 1300°C, and 400°C, respectively, and the presence or absence of cracks was visually observed. Observed.

Furthermore, the hardness of the surface film before heating was measured using a microhardness meter.

The results are shown in Table 1.

[Blank below] As is clear from the above results, it was confirmed that the product implementing the present invention was superior to the comparative product in both heat resistance and hardness of the substrate surface.

[Brief explanation of the drawing]

Figure 1 is an enlarged partial sectional view schematically showing the vicinity of the interface between the film and the substrate material after the first-stage anodizing treatment, and Figure 2 is a schematic diagram showing the vicinity of the interface between the film and the substrate material after the second-stage anodizing treatment. FIG. 3 is an enlarged partial cross-sectional view shown in FIG. (1)...Aluminum substrate material, (2)...Hard film, (3)...Chromic acid film. that's all

Claims (5)

[Claims] (1) Manufacture of an aluminum substrate for a magnetic disk, which is characterized in that the aluminum substrate material is subjected to a first-stage anodizing treatment to form a hard oxide film, and then a second-stage anodic oxidation treatment is performed using a chromic acid electrolyte. Method. (2) The aluminum substrate material is based on high-purity aluminum with a purity of 99.99% or more, and Mg: 4 to 5 wt.
Claim 1, which has a composition containing %
A method for manufacturing an aluminum substrate for a magnetic disk as described in . (3) The method for manufacturing an aluminum substrate for a magnetic disk according to claim 1 or 2, wherein the hard oxide film has a thickness of 5 to 20 μm. (4) The method for manufacturing an aluminum substrate for a magnetic disk according to any one of claims 1 to 3, wherein the anodizing treatment in the first stage is performed using an oxalic acid electrolyte. (5) The method for manufacturing an aluminum substrate for a magnetic disk according to claim 4, wherein the temperature of the oxalic acid electrolyte is 0 to 20°C.