JPS609897A - Manufacture of alumite substrate with high corrosion resistance for magnetic disk - Google Patents

Abstract

PURPOSE:To improve the corrosion resistance of a substrate without carrying out pore sealing treatment by anodically oxidizing the substrate in sulfuric acid, mirror-finishing the surface of the resulting alumite layer, and carrying out anodic oxidation again at DC or AC voltage in an aqueous soln. of a specified pH contg. specified anions. CONSTITUTION:An Al substrate for a magnetic disk is anodically oxidized in sulfuric acid as an anodically oxidizing soln., and the substrate is polished while feeding water to provide a mirror finished surface. Fe is sputtered on the surface, and oxidation and reduction treatments are carried out as usual. Finally, the substrate is anodically oxidized again at DC or AC electrolytic voltage in a noncorrosive aqueous soln. of 2-12pH contg. one or more kinds of anions selected among OH<->, BO3<-3> and COOH<->.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a method for manufacturing a highly corrosion-resistant alumite magnetic disk substrate used as a magnetic recording medium of a magnetic disk device, and particularly to a method for manufacturing a highly corrosion-resistant alumite magnetic disk substrate, such as a high recording density magnetic disk substrate. The present invention relates to a method for manufacturing an alumite substrate that provides high corrosion resistance and high heat resistance even in an alumite substrate that cannot be sealed after anodizing treatment.

[Prior art and its problems]

Magnetic disk devices used in data processing equipment, etc.
In recent years, recording densities and capacities have rapidly increased, and at the same time, the flying height of magnetic heads has become extremely small, making it even more necessary to make magnetic disk surfaces smoother. In order to meet this requirement, alumite treatment has conventionally been carried out using the method shown in FIG. That is, (using sulfuric acid as a 1,1 anodizing solution, an aluminum substrate is anodized to form an alumite gap of about 3 to 5+ um).

(2) Next, while supplying water, the surface of the anodic oxide film is mirror-finished by boring.

(Aged at about 31320℃ (Corp))
Remove distortion and dry.

(4) Sputtering Fe on top of it to form α-shaped Fez
Form O3.

(5) Next, reduction treatment is performed in a hydrogen furnace heated to 350°C to obtain Fe3O4.

(6) This is oxidized in an atmospheric furnace heated to 350° C. to form γ-shaped FezO3, which is a magnetic film.

The sulfuric acid alumite thus obtained exhibits high hardness and stable properties. However, as mentioned above, in order to form a magnetic film on the surface of the alumite substrate, the alumite substrate must be heated to a high temperature of about 350°C during the oxidation and reduction steps when sputtering Fe to form α-shaped FezO*. It won't happen.

When an acid such as sulfuric acid, phosphoric acid or oxalic acid is used as an anodizing solution to manufacture this alumite substrate,
A highly corrosive acid remains in the current-carrying micropores formed during the formation of the anodic oxide film, and the heating in the oxidation and reduction steps corrodes the anodic oxide film, and furthermore, the γ-shaped FezO film, which is a magnetic film, is also damaged. There is a problem of corrosion and destruction.

Further, between the aluminum layer and the alumite layer, a thin film having intermediate properties between aluminum and alumite is formed, which is called a barrier layer and is generated during the alumite production process.

However, when heated during the oxidation and reduction processes, the remaining acid reacts to produce aluminum sulfide, which interacts with the water that entered during the polysosh process to form aluminum hydroxide, liberating hydrogen sulfide and causing corrosion distortion. , aluminum sulfide is hydrolyzed at an accelerated rate. As a result, the barrier layer that connects the aluminum layer and the alumite layer is likely to peel or crack.

On the other hand, it is also possible to improve the corrosion resistance of the alumite substrate by washing and sealing the acid remaining in the energized micropores after anodization, but during high-temperature heating during the oxidation and reduction steps, Crank occurs in the anodic oxide film layer,
Because it causes bit errors in magnetic recording media,
Nor can you do this.

That is, as shown in FIG. 2, when the aluminum substrate 1 is anodized, the conductive holes 2 are formed, but when this is sealed in water at 100°C, the conductive holes 2 are formed as shown in FIG. T-81203 Boehmai 1-5 consisting of HzO
is occluded by In the alumite substrate sealed in this way, the difference in linear thermal expansion coefficient between the aluminum substrate 1 and the anodic oxide film 3 is about five times different, so in the heat treatment of the oxidation and reduction steps, the difference shown in FIG. bend like a bell,
It is thought that crack 6 is generated. However, if the sealing treatment is not performed, the current-carrying hole 2 will remain as shown in FIG. 2, and the difference in thermal linear expansion coefficient between the aluminum substrate 1 and the anodized skin l*3 will increase as shown in FIG. It is considered that even if deformation (shrinkage stress) occurs, it is absorbed by the current-carrying holes 2 and no cracks occur. For the above reasons, alumite substrates for magnetic disk substrates cannot be sealed.

[Purpose of the invention]

The purpose of the present invention is to improve the corrosion resistance of the alumite substrate for magnetic disks to which sealing cannot be applied, to prevent corrosion from spreading to the magnetic film layer, and to improve the corrosion resistance of the alumite substrate without sealing. The objective is to strengthen the barrier layer, which is easy to peel off.

[Structure of the invention]

5- The technical measures taken by the present invention to solve this technical problem include the step of anodizing an aluminum substrate for a magnetic disk with a sulfuric acid-based anodizing solution, and mirror-finishing the anodized film. Step + -3- and after these steps, 0■, BO3, C00I
A method is employed that includes a step of performing anodization treatment again at a direct current or alternating current electrolytic voltage using a non-corrosive aqueous solution with a pH of 2 to 12 containing some or all of the positive anions.

[Embodiments of the invention]

Next, examples will be used to explain how the method of manufacturing a highly corrosion-resistant alumite magnetic disk substrate according to the present invention is actually implemented. In the case of the present invention, as shown in Fig. 1, an aluminum substrate is anodized using sulfuric acid, then polished while supplying water to give a mirror finish, and Fe is sputtered thereon, followed by oxidation and reduction treatment. What you do is the same as before.

In the present invention, after these steps, anodization treatment is performed again. This first anodic oxidation treatment is called a second alumite treatment. This second alumite treatment is carried out using a non-corrosive bath composition. That is, (a) Bath composition-3-1 ■ Anions contained: 011, BO3, C0OH ■ pH 1 ~
12 ■Aqueous solution (b) of the above ■■ Electrolysis conditions ■Electrolysis voltage (current): DC or AC ■Cathode: pb
, carbon anode Nialuminum substrate Non-corrosive bath compositions that satisfy the above conditions include aqueous acetic acid (pH 2,8), boric acid, citric acid, sodium hydroxide, and the like.

When alumite is treated with such a non-corrosive bath composition, a current flows for a very short period of about 10 seconds, and then no current flows. In other words, the barrier layer has properties intermediate between aluminum, which is a conductor, and alumite, which is an insulator, and exhibits conductivity, but since this barrier layer is oxidized in the second alumite treatment and becomes an insulator, No current flows (no current flows.Moreover, the barrier layer is marked 7 in FIGS. 2 to 5.
As shown in Figure 2, the extremely thin layer is formed only at the bottom of the current-carrying hole, and since a non-corrosive bath composition is used, oxidation does not proceed any further, and the second alumite treatment is completed in a short time of about 10 seconds. Complete.

In this way, the barrier layer 7 is oxidized and turned into alumite,
Since a non-corrosive bath composition is used, oxidation does not proceed further, the barrier layer is strengthened and corrosion resistance is improved.

Furthermore, the gas (oxygen) pressure instantaneously generated by the anode reaction cleans the inside of the current-carrying hole, and the remaining corrosive sulfuric acid is pushed out into the bath composition. Since the aluminum substrate serves as an anode, neutralization is performed by concentration of 011 ions.

In addition, the oxygen gas pressure generated on the aluminum substrate of the anode and the adsorption of anions prevent water from being supplied, thereby preventing corrosive distortion and hydrolysis.

Next, an example of the second alumite treatment that was actually performed will be described.

(11 As the bath composition, an acetic acid aqueous solution (pl+ 2.8) was used, and it was treated with AC electrolysis at 100 (V) for 5 minutes.

(2) As a bath composition, a mixed solution of boric acid and citric acid (pl
+4 to 5), and 60 (V) direct current electrolytic treatment was performed for 5 minutes.

(3) As the bath composition, a mixture of boric acid, citric acid, and sodium hydroxide (pl+9 to 1'O) was used, and 40
(V) DC electrolytic treatment was performed for 5 minutes.

As a result, no problems occurred in terms of heat resistance and corrosion resistance in any of the above cases. Note that when the pH exceeds 12, alumite dissolves.

[Effects of the Invention] As described above, according to the alumite treatment method of the present invention, an aluminum substrate for a magnetic disk is anodized with sulfuric acid,
After polishing the alumite layer to a mirror finish, the alumite layer is polished using a non-corrosive aqueous solution of PL (2 to 12) containing some or all of the anions of Oll, BO3, Coo). We use a method of alumite treatment using direct current or alternating current electrolytic voltage.
The barrier layer is oxidized and strengthened, and the corrosive sulfuric acid is expelled from the current-carrying holes by the gas pressure generated during oxidation, so that corrosion within the current-carrying holes does not progress. Furthermore, the generated gas prevents the alumite from being hydrated, and since a non-corrosive bath composition is used, corrosion is reliably prevented. Moreover, the processing method is extremely simple and can be processed in a short time.

[Brief explanation of drawings]

Fig. 1 is a process diagram showing a method for manufacturing an alumite magnetic disk substrate, Fig. 2 is a sectional view showing an alumite substrate after anodization, and Fig. 3 is a sectional view showing an alumite substrate sealed by a conventional method. , FIG. 4 is a sectional view showing a state in which a crank has occurred in the alumite substrate of FIG. 3 during the heat treatment process, and FIG. 5 is a sectional view showing a state in which the alumite substrate without sealing treatment is heated. In the figure, 1 is an aluminum substrate, 2 is a current-carrying microhole, and 3 is an aluminum substrate.
4 indicates a residual acid, 6 indicates a crack, and 7 indicates a barrier layer. Patent applicant Fujitsu Ltd. agent Patent attorney Minoru Aoyagi 10-

Claims (1)

[Claims] A step of anodizing an aluminum substrate for a magnetic disk with a sulfuric acid-based anodizing solution, a step of mirror-finishing the anodized film, and after these steps-3-1, 011, B(h), a high-temperature oxidation process characterized by comprising a step of re-anodizing at a DC or AC electrolytic voltage using a non-corrosive aqueous solution with a pH of 2 to 12 containing some or all of the anions of CQOII. A method for manufacturing a corrosion-resistant alumite magnetic disk substrate.