JPS6139934A - Aluminum substrate for magnetic disk and its production - Google Patents

Abstract

PURPOSE:To obtain an underlying film which obviates the generation of cracking, etc. as a result of heating in the stage of forming a magnetic layer and permits the easy working to smooth the surface thereof by using an Al blank material which is anodized in a sulfosalicylic acid bath as the substrate for a magnetic disk. CONSTITUTION:The Al blank material consisting of an Al-Mg alloy, etc. is anodized in an electrolyte contg. the sulfosaicylic acid to form an alumite film on the surface. The material formed in such a manner is used as the substrate for the magnetic disk. A sulfuric acid is further incorporated into the electrolytic bath by which the anodizing rate can be increased to about 1.5 times the anodizing rate of the case in which the sulfuric acid is not incorporated into said bath. Even if the alumite film formed in the above-mentioned way is formed to about >=5mu thickness, the generation of cracking, etc. by the heating in the stage of forming the magnetic layer is obviated and the alumite underlying film having excellent heat resistance is formed with easy polishing. For example, an Fe3O4 film is formed on such underlying layer and thereafter the film is converted to a gamma-Fe2O3 film at 300-350 deg.C in atm. air, by which the easy manufacture of the thin film magnetic recording medium at a low cost is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an aluminum substrate for magnetic disks and a method for manufacturing the same, and particularly an aluminum substrate having a so-called alumite film obtained by anodizing an aluminum material, and such an aluminum substrate. The present invention relates to a method for advantageously manufacturing.

BACKGROUND OF THE INVENTION Conventionally, magnetic disks for external storage devices of electronic computers have a structure in which a magnetic recording medium is formed on the surface of an aluminum substrate obtained by polishing. As this magnetic recording medium, an r-Fe203 fine particle coating film (coating film) formed on the surface of an aluminum substrate has been widely used.
Recently, a γ-Fe203 continuous thin film medium has been studied as a high-density magnetic recording medium to replace the γ-Fe,03 fine particle coating film. At present, it is not possible to directly form this γ-Fe203 continuous thin film on an aluminum substrate, so a peao film is first formed on an aluminum substrate, and then 300 to 35
By oxidizing at a temperature of 0°C, the Fe3O4 film is
-Change into Fe203 film and target γ-Fe2
We manufacture magnetic disks on which thin film magnetic recording media made of O3 are formed.

By the way, in the case of conventional coated magnetic disks in which a magnetic recording medium is coated, a polished aluminum plate was sufficient as the substrate, but a substrate with a thickness of 0.3 μm
In the case of the r-Fe2o3 thin film described above, the aluminum plate as the substrate has a surface roughness: R of 0.
．． A surface with a smoothness of 0.3 μm or less is required. Therefore, polishing the aluminum plate alone is not enough.
Such high machining accuracy cannot be obtained.

Therefore, some kind of base treatment is applied to the surface of the aluminum plate, but in conventional N1-P plating, the magnetism is recovered by heating at 300 to 350°C to form the r-Fe203 film as described above. Unfortunately, this is not a method that can be adopted at all.

However, the following performance is generally required of the base film of an aluminum substrate for a magnetic disk.

a) Be non-magnetic; b) The surface is smooth; C) The surface is hard.

On the other hand, Japanese Patent Publication No. 54-26439 discloses a method for manufacturing an aluminum substrate having an anodic oxide film (alumite film) formed of an alumite substrate that satisfies the performance as a base film. According to this manufacturing method of an aluminum substrate for a magnetic disk, an aluminum plate is alumite-treated to form an alumite film with a thickness of 3 μm or less, and then this alumite plate is heat-treated at 150 to 350°C, and then polished. processing and then further forming a thin film magnetic recording medium.

Problems However, in the surface treatment of aluminum plates using the alumite method, the sulfuric acid alumite method using a sulfuric acid bath is used as the alumite method.
Further, the thickness of the alumite film to be formed is limited to 3 μm or less, and in an alumite film exceeding 3 μm, cranking is said to occur during heating to form the aforementioned γ-Fe20B film. The thin thickness of the alumite film as the base film means that it is difficult to polish the alumite substrate, which is performed after the base treatment in order to manufacture magnetic disks. Moreover, in the conventional manufacturing method of anodized aluminum substrates for magnetic disks described above, heat treatment (post-treatment) is required prior to polishing treatment, which lengthens the manufacturing process and makes the process complicated. However, there are inherent problems such as increasing production costs and increasing production costs.

Solution The present invention has been made to solve such conventional problems, and its gist is to provide a base treatment for the surface on which a magnetic recording medium made of aluminum material is formed. The aluminum material is anodized in a sulfosalicylic acid bath, and for the aluminum substrate on which such a sulfosalicylic acid alumite film is formed, the thickness of the alumite film is 5 μm.
The aluminum substrate exhibits good heat resistance even when the thickness is 10 μm or more, preferably 10 μm or more, does not cause any cranking when heated at high temperatures, and can be easily polished after surface treatment as an aluminum substrate for magnetic disks. .

By the way, as the aluminum material used in the present invention, any plate material made of an aluminum-based alloy that has been conventionally used as a material for aluminum substrates for magnetic disks can be used, such as AN-Mg. A type alloy plate is used from the viewpoint of strength and workability. Then, such an aluminum material is previously subjected to a polishing process similar to the conventional method, and then anodization treatment using a sulfosalicylic acid bath according to the present invention is performed.

For the anodizing treatment using this sulfosalicylic acid bath, the method known as the natural coloring electrolytic method for building materials is applied as is. So, H)C
This is a method of anodic oxidation using direct current using an electrolytic bath containing OOH.

The conditions for such anodic oxidation treatment will be determined appropriately depending on the aluminum material used and the thickness of the alumite film to be formed, but generally about 100 to 150 g/J is added to the electrolytic bath. of sulfosalicylic acid is present, and at a voltage of about 30 to 80 V,
A method of direct current electrolysis at a current density of about 0.1 to 4 A/drd will be adopted.

In addition, the bath temperature during this electrolysis is generally 20 to 4
Temperatures of the order of 0° C. are preferably employed, while bath temperatures that are too low are desirably avoided.

However, if the bath temperature is lower than 20° C., cranks are likely to occur in the alumite film when subjected to heat treatment.

Furthermore, in such anodizing treatment, it is desirable that the sulfosalicylic acid bath contain sulfuric acid or aluminum sulfate, and the presence of such sulfuric acid or aluminum sulfate will reduce the alumite film formed on the surface of the aluminum material. The production rate is effectively increased, and the film has better heat resistance. In addition, the amount of sulfuric acid present in the electrolytic bath (
The amount added is generally about 1 to 10 g/42, and the amount of aluminum sulfate is generally 0.5 to 5 g/j! The degree will be adopted.

The sulfosalicylic acid alumite film formed on the surface of the aluminum material in this way has all the characteristics required as the base film of the magnetic disk described above, and it depends on the degree of the subsequent polishing treatment. Generally, the thickness is at least 5 μm, preferably 10 to 40 μm.
It will be formed to a certain thickness. In this way, by increasing the thickness and thickness of the alumite film, the subsequent polishing process can be made easier, and in the method of the present invention, such a thick alumite film can be processed with equal consideration to the occurrence of cracks. However, the sulfuric acid alumite film in the conventional method has the inherent problem that cranking occurs when the film thickness exceeds 3 μm. In particular, the sulfosalicylic acid alumite film according to the present invention can withstand heating at 350° C. for 3 hours even if the thickness is 1011 m.

In addition, the aluminum substrate formed by forming the sulfosalicylic acid alumite film as a base film on the surface of the aluminum material is then subjected to a polishing treatment, in other words, mechanical treatment, in the same manner as the conventional magnetic disk manufacturing method. Alternatively, a chemical surface smoothing treatment is performed, and then a thin film magnetic recording medium is formed on the smooth surface to form the intended magnetic disk.

Effects of the Invention As described above, according to the present invention, a thick sulfosalicylic acid alumite film with good heat resistance is formed as a base film on the surface of a magnetic recording medium made of aluminum material, and as a result, The subsequent polishing process could be easily carried out, and since the heat resistance of the alumite film was improved, heat treatment as in conventional methods was no longer necessary. Therefore, there is no problem such as an increase in production costs.

Moreover, the sulfosalicylic acid alumite film formed on the surface of the aluminum material according to the present invention can be easily formed by anodizing using a sulfosalicylic acid electrolytic bath, which has been conventionally used as a naturally coloring electrolytic bath for building materials. In forming such an alumite film, no particular problems arise.

EXAMPLES Below, some examples will be shown to clarify the present invention in more detail, but it goes without saying that the present invention is not limited in any way by the description of these examples. . Note that the percentages in the examples are expressed on a weight basis unless otherwise specified.

Example I Aβ-Mg alloy plate, for example, alloy composition of AA5086 standard, that is, Mg: 4.2%, Fe: 0.18%, Si: 0
．． 06%, Mn: 0.37%, Cr: 0.08%, Cu
:0.04%, Ti:0.03%, and Zn:0.01
% or less, and the balance is AA, 10
In an electrolytic bath containing 0 g/A of sulfosalicylic acid,
At a current density of L A/d rrf, bath temperature: 6 at 25°C
Anodic oxidation was performed for 0 minutes to form an alumite film with a thickness of 10 μm on the surface of the AJ alloy plate. Next, this alumite-treated A11 alloy plate was subjected to a heat treatment at 350° C. for 3 hours, and the heat resistance of the alumite film formed on its surface was evaluated.

This heat resistance evaluation was performed by copper sulfate precipitation test and surface observation using an optical microscope, but no cracks were observed in the sulfosalicylic acid alumite film obtained by anodizing using a sulfosalicylic acid bath. It has become clear that its heat resistance is excellent.

Note that the copper sulfate precipitation test is a test consisting of observing copper precipitation in a copper sulfate solution acidified with hydrochloric acid.

Comparative Example 1 An A4 alloy plate similar to that of Example 1 was anodized in the same manner in a sulfuric acid electrolytic bath with a concentration of 150 g/A, and the plate was made to a thickness of 10
A sulfuric acid alumite film of μm thickness was formed.

Next, the A4 alloy plate having the sulfuric acid alumite film was subjected to a heating test similar to that in Example 1, and its heat resistance was evaluated. As a result of the heat treatment, cranks were generated in the sulfuric acid alumite film, and some cracks were observed. It was observed that the alumite film had peeled off. Therefore,
As a result, the sulfuric acid alumite film was judged to be inferior in heat resistance (1).

Example 2 Sulfuric acid was added at a rate of 1.8 g/g to the sulfosa IJ tylic acid electrolytic bath used in Example 1.
When anodizing was carried out in the same manner as above, the film formation rate was 1.5 (i) compared to the case without additives.

Then, when a heating test similar to that described above was conducted on the obtained /1 alloy plate having the sulfosalicylic acid alumite film, no cracking was observed.

Example 3 Ig/
When β aluminum sulfate was added and anodic oxidation was performed in the same manner as in Example 1, the formation rate of the alumite film was 1.5 times that of the case without the addition. In addition, the produced alumite skin M Aoi did not cause any cracks or cracks in the heating test.

Claims (5)

[Claims] (1) A method for producing an aluminum substrate for a magnetic disk, which comprises anodizing the aluminum material in a sulfosalicylic acid bath as a surface treatment for the surface on which the magnetic recording medium is formed. (2) The manufacturing method according to claim 1, wherein the sulfosalicylic acid bath contains sulfuric acid. (3) The manufacturing method according to claim 1, wherein the sulfosalicylic acid bath contains aluminum sulfate. (4) An aluminum substrate for a magnetic disk having a base film obtained by anodizing in a sulfosalicylic acid bath on the surface on which a magnetic recording medium is to be formed. (5) The aluminum substrate according to claim 4, wherein the base film is formed to have a thickness of at least 5 μm.