JPS6176699A - Manufacture of alumite substrate for high density magnetic recording material - Google Patents

Abstract

PURPOSE:To shorten the treatment time and to improve the work efficiency without deteriorating the superior characteristics of an alumite film when an alumite substrate for a high density magnetic recording material is manufactured by anodic oxidation with chromic acid, by adding a specified org. acid or a salt thereof to a chromic acid soln. CONSTITUTION:When an alumite substrate for a high density magnetic recording material as a magnetic recording substrate for a magnetic disk or the like is manufactured by anodic oxidation with chromic acid, an Al or Al alloy material is immersed in a soln. contg. 15-150g/l chromic acid and one or more kinds of compounds selected among sulfonic acid, sulfonates, sulfamic acid and sulfamates. The concn. of the compounds is 1/100-1/4 time the concn. of chromic acid. The Al or Al alloy material is anodically oxidized in the soln. by supplying electric current. An alumite film having superior hardness, smoothness and heat resistance and free from black spots can be formed on the surface of the Al or Al alloy material in a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method of manufacturing an alumite substrate for high-density magnetic recording material using a chromic acid anodization method.

[Conventional technology]

Alumite treatment is used because it has excellent abrasion resistance, which is required for magnetic recording substrates such as magnetic disks, has good abrasiveness, makes it easy to obtain a highly accurate smooth surface, and can easily form a thin magnetic layer on the surface. Coated aluminum or aluminum alloys are used. However, in this alumite substrate, impurities such as iron and silicon that are present in the aluminum or aluminum alloy material crystallize as intermetallic compounds, and these impurities are dotted on the surface of the material and during alumite treatment, these parts become a very small alumite film. Defects called so-called black spot defects occur, and these defects are initially very small on the submicron scale, but expand as the alumite film grows, and in an alumite layer with a film thickness of 5 μm or more, 5 μm. The larger the number of pit-like micro defects of ~10 μm, the more signal errors will occur in the magnetic recording material, which is not preferable.

α-Fag O, is deposited by sputtering or other methods and heated to 300-400°C to form
However, when such high-temperature heating is performed, cracks occur in the alumite film, which tends to cause product defects. Therefore, the thickness of the alumite layer must be extremely thin, on the order of 1 to 3 .mu.m, which causes a decrease in the head crush resistance of the alumite substrate.

As a means to solve these problems, we have previously proposed a method of alumite treatment of aluminum or aluminum alloy materials in a chromic acid solution at a voltage higher than the electrolytic voltage normally used in the constant voltage method (Japanese Patent Application No. 1983- 44364). However, in this method, the current density is low; for example, in the sulfuric acid alumite method that uses a sulfuric acid bath, it takes 20 to 35 minutes to obtain a film with a thickness of 10 μm, whereas in the chromic acid alumite method, it takes 20 to 35 minutes to obtain a 10 μm thick film. The problem was recognized that the rate of formation of the alumite film was slow, requiring 70 to 200 minutes. However, in order to increase the current density,
It is necessary to increase the applied voltage or raise the bath temperature to facilitate the flow of current.

The chromic acid alumite method requires a high voltage t'', preferably higher than bov, and if the voltage is increased further, the film will break, so there is a limit to how much the voltage can be increased. Increasing the amount of heat has a remarkable effect on film formation, but the film becomes soft and has insufficient strength as a sputtering base, so this also has a limit and is rarely used.

[Problem that the invention seeks to solve]

This is an attempt to solve the long processing time, which is a drawback of the method of manufacturing an alumite substrate for high-density magnetic recording using the chromic acid anodization method.

[Means for solving problems]

As a result of repeated research in order to obtain a method that can shorten the processing time while retaining the advantages of chromic acid, the present inventors have discovered that one of sulfonic acid, sulfonate, sulfamic acid, and sulfamate is added to chromic acid solution. species or two or more species (hereinafter referred to as
It's called an additive. ) The present invention was completed by discovering that the object could be achieved by adding the following.

That is, in the second aspect of the present invention, the concentration of aluminum or aluminum alloy material is 1/100 or more relative to the chromic acid concentration.

15-150P/ containing additives with a concentration of 1/4 or less
This is a method for producing an alumite substrate for a high-density magnetic recording material, which is characterized by carrying out an alumite treatment in a chromic acid solution of No. 43.

As the aluminum or aluminum alloy material used in the present invention, ordinary plate materials can be used, but from the viewpoint of black spot defects, those containing less iron, silicon, etc. are preferable.

Furthermore, as an electrolytic bath for alumite, a chromic acid solution should be used with a concentration in the range of 15 to 150 f/J3, and the effects of the present invention cannot be fully exhibited outside this range. be.

The sulfonic acids referred to in the present invention include benzenesulfonic acid, toluenesulfonic acid, etc., and the sulfonic acid salts are salts thereof. The reason why sulfonic acids were limited to specific ones is that it is necessary that they do not have any adverse effects when added to the chromic acid bath. When it has a hydroxyl group (-OH), Cr'+ in chromic acid is reduced to Cr3+, making it difficult to electrolyze and also causing the bath itself to turn black. Carboxyl group (-
Even if it contains COOH, it cannot be added because it has a structure corresponding to 10H.

The concentration of the additive is 1/100 or more of the concentration of chromic acid, 1
74 or less, and if the additive is placed too small, the effect of the addition will be poor, and if it is too large, the electrolytic current value will decrease and the electrolytic behavior will become unstable. .

~ [Function] When additives are added to the chromic acid bath, re-dissolution of the generated alumite is suppressed and pore expansion is small, so BL
The hardness of the film is improved. On the other hand, in the chromic acid anodization method, the bath temperature has a large effect on the current value, and increasing the bath temperature is the most effective way to increase the current, but increasing the bath temperature may cause re-dissolution of sialumite. This will cause a noticeable decrease in film hardness. As a result, by adding the additive, it is possible to increase the current value while suppressing a decrease in film hardness.

〔Effect of the invention〕

The hardness of the film of conventional chromic acid alumite.

Processing time can be shortened without degrading excellent properties such as black spot defects, smoothness, and heat resistance.

The following will be explained in detail with reference to examples.

Example 1 Aluminum alloy for high-density magnetic recording substrate (A-19-4
A 1-piece alloy (75 pieces in inner diameter, 200 pieces in outer diameter, 2 pieces in thickness) was subjected to a prescribed surface polishing, then cleaned with a non-erosive cleaning agent, and subjected to anodization. Toluenesulfonic acid was added to chromic acid and used as an anodizing bath. This mixed acid bath did not undergo discoloration due to reduction of chromic acid. Table 1 shows the bath components and electrolytic conditions used in the experiment.

Table 1 An alumite of about 10 μm was produced with electrolytic neutrality as shown in Table 1, and the surface condition of the obtained test piece was examined for microvitskas hardness 1. The current density during electrolysis was also measured.

These results are shown in Table 2.

Table 2 Note) 1) Unit of electric density A/da+"2) Hardness is measured from the surface finish Hma3) Surface condition no: *Good Δ: Large defect p As is clear from the results in Table 2 In order to obtain the same hardness, it is better to add toluenesulfonic acid, which allows treatment at high temperatures.
At that time, by increasing the current density, the processing time to obtain a predetermined film thickness could be significantly shortened.

In addition, after further heating this film at 350°C for 2 hours,
When observed under a microscope, there were no cracks at all.

Example 2 Example 1. Alumite was applied to the same test material in a bath containing chromic acid and sulfamic acid. Furthermore, the completed test piece was tested in Example 1. The same measurements and observations were carried out. The processing conditions are shown in Table 3.

The results are shown in Table 4.

Table 3 Table 4 Example 1. got the same conclusion.

Example 5 Example 1. Alumite was applied to a sample material similar to the above to a thickness of about 10 μm in a bath containing benzenesulfonic acid and sodium benzenesulfonate added to chromic acid.

The electrolysis voltage was 70V. Furthermore, the completed test piece was used in Example 1. The same measurements and observations were carried out.

The treatment conditions and results are shown in Table 5.

Claims (1)

[Claims] 15 containing one or more of sulfonic acid, sulfonate, sulfamic acid, and sulfamate at a concentration of 1/100 or more and 1/4 or less of the chromic acid concentration in aluminum or aluminum alloy material ~150g
1. A method for producing an alumite substrate for a high-density magnetic recording material, characterized by carrying out an alumite treatment in a chromic acid solution of /l.