JPS60181297A - Manufacture of alumite substrate for high density magnetic recording material - Google Patents

Abstract

PURPOSE:To obtain an alumite substrate for a high density magnetic recording material having no black spots, superior smoothness and heat resistance in a shortened treatment time by treating an Al material in a chromic acid soln. contg. a specified amount of oxalic acid. CONSTITUTION:An Al or Al alloy plate is immersed in a soln. contg. chromic acid by 15-150g/l and oxalic acid by 1g/l or <1/5 of the amount of chromic acid, and it is treated at constant voltage and prescribed current density to form an opaline smooth alumite film. By this method, an alumite substrate for a high density magnetic recording material provided with a film having superior hardness and preventing cracking is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an alumite substrate for high-density magnetic recording, which can shorten the alumite treatment time using the chromic acid alumite method, has no black spot defects, and has excellent smoothness and heat resistance. be.

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. 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. A defect called a so-called black spot defect occurs, and this defect is initially very small on the submicron scale, but expands as the alumite film grows and becomes 5Rn or more in the alumite layer of the film ring. Since the pit-like minute defects are 10 μm in size, the larger the number, the more signal errors in the magnetic recording material will occur, which is not preferable. Also, when making a high-density magnetic recording plate, on an alumite substrate.

α-Fe=04 was deposited by sputtering or other method and heated to 300-400°C to form 1-Pe tube Os.
However, when such high-temperature heating is performed, there is a problem that cracks occur in the alumite film, which can easily cause product defects. As a means to solve these problems, we first applied a constant voltage method to aluminum or aluminum alloy materials in a chromic acid solution. We proposed a method for alumite treatment at a voltage higher than the commonly used electrolytic voltage. (Patent application 1973-44364)
However, in this method, the current rating is low,
For example, in the sulfuric acid alumite method, which uses a sulfuric acid bath, it takes 20 to 35 minutes to obtain a 100% thick film, whereas in the chromic acid alumite method, it takes 70 to 200 minutes to form an alumite film. The problem of slow production speed was recognized. 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, but the chromic acid alumite method requires a high voltage, preferably 60 V or more,
Furthermore, there is a limit to how much voltage can be raised because the film will break if the voltage is increased, and although raising the bath temperature is very effective, the film becomes soft and its strength as a sputtering base is insufficient. Therefore, this also had its limits.

As a result of repeated research to find a method that could shorten the processing time while retaining the advantages of using chromic acid, the present inventors found that the objective could be achieved by adding an appropriate amount of 7-niu shavings to the chromic acid solution. The present invention was made in recognition of the above.9 The present invention is based on the following: Al minilum or aluminum alloy material containing oxalic acid in an amount not exceeding 115 tons per 1 g/l to chromic acid. This is a method for manufacturing an alumite substrate for high-density magnetic recording in which alumite treatment is performed in a 150 g/l chromic acid solution.

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.

In addition, as a chlorination bath for alumite, chromic acid solution is
The concentration of oxalic acid used should be within the range of 15 to 150 g/l; outside this range, the effects of the present invention cannot be fully exhibited, and the concentration of oxalic acid to be mixed should be 1 f.
It is used in an amount that does not exceed i/l or 115 of chromic acid; if the oxalic acid content is less than 1971, the effect of addition is small, and if the amount of chromic acid is added in an amount of 175 or more, the hardness of the alumite film increases. Vickers hardness is 40
If it exceeds 0Hv, thermal cracks are likely to occur, so it is preferable.
C
Alumite treatment was carried out in a rα509/1 bath with varying amounts of oxalic acid added, while changing the bath temperature and keeping the voltage constant at 100V. The results of the measurements are shown in the table below.The thickness of the alumite film is 1.
The thickness was set to 0 μm. However, at 30°C without the addition of oxalic acid, a film thickness of only 5 μm can be obtained even after 200 minutes of electrolysis.
I stopped here.

(5) As shown in the table above, 2. In the constant voltage chromic acid alumite method called the usual Gutsard method.

The bath temperature is 35 to 50°C, but if the bath temperature is high, the film will soften, but by adding oxalic acid, the film hardness can be increased at the same bath temperature. If it is sufficient to obtain a film with a certain degree of hardness, the bath temperature can be increased.

Therefore, it is possible to increase the current density and shorten the processing time. Namely.

When processing at a constant voltage and bath temperature, the current density increases significantly due to the addition of oxalic acid in a relatively low temperature range such as around 30°C, so it is necessary to keep the bath temperature constant and increase the processing time. It can be shortened to width (6). In addition, when the bath temperature is 35°C or higher, the current density does not change much, but the effect of increasing film hardness becomes obvious. If there is no need to increase the current density, for example, by keeping the voltage constant and increasing the bath fRW from 35°C to 40°C, it is possible to increase the current density by about 1.5 times (the processing time is approximately inversely proportional to the current density). Therefore, the processing time can be greatly shortened without reducing the hardness. Thus, the bath temperature can be selected within the range of 30 to 50°C depending on whether the objective is to increase the hardness or shorten the time by 9 hours. In addition, the voltage is higher than 40V for the Gutsard method and is 60℃ or higher, and 70 to 100V.
It is preferable that

In the alumite substrate obtained in this way, no minute sunspots were observed, and even when the film was grown to a thickness of 10 or more in order to improve head crushing resistance, no large sunspots were found. or.

Excellent heat resistance, 300-400℃ for forming magnetic film
Cracks did not occur even when heated and held at a temperature of Compared to when using German chromic acid bath, film hardness and black spot defects were improved.

without reducing good properties such as smoothness and heat resistance.
Excellent effects have been recognized, such as the ability to shorten processing time and the ability to significantly increase hardness.

Next, nine examples of the method of the present invention will be described.

Example 1 An aluminum alloy for high-density magnetic recording (AJ-4% Mg alloy, inner diameter 755 m, outer diameter 200 mm, thickness 2 m+) was subjected to a specified surface polishing, and then washed with a non-erosive cleaning agent for 30 minutes. The anode was immersed in a bath containing 10 g/l of oxalic acid added to a 50 g/l chromic acid solution heated to 0.degree. C., and the voltage was kept constant at 100 V for alumite treatment.

A smooth milky white alumite film was formed.

The current density at this time is 030 A/.

The treatment time was 190 minutes.

The Vickers hardness of the obtained film was 351 Hv.

When observed under a microscope, no sunspot defects were observed.

After this film was further heated to 350° C. for 2 hours, it was observed under a microscope, and no cracks were observed.

Comparative Example Alumite treatment was carried out in a solution containing only chromic acid under the same conditions as in Example 1 without adding oxalic acid. The current density at this time was 0.16'/dm-.

Even when the treatment time was 200 minutes, a film thickness of only 5IHn was obtained.

Although the Vickers hardness of the obtained film could not be measured due to insufficient film thickness, no abnormalities such as black spot defects and cracks were observed during various observations.

Example 2 Alumite treatment was carried out in the same manner as in Example 1, except that the amount of oxalic acid added was 59% and the bath temperature was 40°C. The current density at this time was 0.651 Vdm·, and the treatment time was 75 minutes.

The Vickers hardness of the obtained film was 351Hv.
No abnormalities such as black spot defects or cracks were observed (9).

Comparative Example 2 Alumite treatment was performed in a solution containing only chromic acid in the same manner as in Example 1 except that oxalic acid was not added and the bath temperature was 35°C. The current density at this time is 0.43 k/
dm'' and the treatment time was 110 minutes.

The Vickers hardness of the obtained film was 359Hv,
No abnormalities such as black spot defects and cracks were observed.

Comparative Example 3 Alumite treatment was performed in a solution containing only chromic acid in the same manner as in Example 1, except that oxalic acid was not added and the bath temperature was 40°C. The current density at this time is 0.66 A
Jdm, and the treatment time was 73 minutes, but the Vickers hardness of the obtained film was 2481 (v), which was low.

Patent applicant: Nippon Light Metal Co., Ltd. (10)

Claims (1)

[Claims] 1) For high-density magnetic recording, characterized in that aluminum or aluminum alloy material is alumite-treated in a chromic acid solution of 15 to 150 fl containing an amount of oxalic acid not exceeding 115 to 1 to chromic acid. A method for manufacturing an alumite substrate.