JPS62207900A - Production of substrate for magnetic recording medium - Google Patents

Abstract

PURPOSE:To produce an alumite substrate for a magnetic recording medium suitable for high density magnetic recording by anodically oxidizing the surface of an Al or Al alloy plate as a substrate for a magnetic recording medium under specified conditions. CONSTITUTION:When a substrate for a high density magnetic recording medium is produced with Al or an Al alloy, an Al or Al alloy plate is immersed in a treating soln. having 1.5-3% concn. of CrO3 at 15-30 deg.C and 60-75V voltage is applied to anodically oxidize the surface of the Al or Al alloy plate. Thus, a smooth alumite substrate for a magnetic recording medium suitable for high density magnetic recording is obtd. The alumite substrate has <120Angstrom average surface roughness Ra and >350kg/mm<2> Vickers hardness Hv.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a substrate for a magnetic recording medium, and in particular to an electrolytic treatment method for forming a hard alumite film with a smooth surface on an aluminum or aluminum alloy material. Regarding.

[Conventional technology]

As magnetic recording density increases, recording media become thinner, and substrates are required to have smoothness and strength, so it was proposed to form an alumite film on the surface of an aluminum alloy substrate (
JP-A No. 51-48303).

This anodizing treatment was carried out at 20℃ using a 10% sulfuric acid bath.
~l 5 V, l A/dm".

In addition, in order to provide an alumite film with superior smoothness, heat resistance, and strength, a treatment using a chromic acid bath has been proposed in Japanese Patent Laid-Open Nos. 59-85895 and 60-164927. The former uses a bath containing hexavalent chromium ions to obtain a film with a thickness of 5 mg/d+w" (approximately 0.117 m) or more, and the latter uses a bath with a chromic acid concentration of 1.5 to 15%. This is a method in which the film is treated at a temperature of 35 to 50° C. and a voltage of 60 to 100 V to form a film with a thickness of 10 μm or more.

[Problem that the invention seeks to solve]

As an alumite base film used for substrates for magnetic recording media such as magnetic disks, ■) It has good surface hardness and strength because it can withstand contact with the magnetic head when starting and stopping the disk (C3S resistance). 2) The surface must be smooth to prevent head crashes (this is achieved through a polishing process, but the smoother it is before polishing, the better the finish); 3) The crank must be smooth on the magnetic head. 300~ to prevent smooth ascent and cause missing records.
It is required that no cranking occurs during heat treatment of magnetic materials at 400°C.

In the method described in JP-A-51-48303, the film thickness must be 3 μm or less in order to prevent cracks from occurring at 350° C., which is the heat treatment temperature for magnetic materials. At 3 μm, the film strength such as C8S resistance is insufficient for practical use.

JP-A-59-85895 and JP-A-60-16
According to the chromic acid bath treatment described in Publication No. 4927,
The heat resistance has been improved, and even with a thicker film thickness, no cranking occurs during heat treatment, making it possible to increase the film strength, but it is still sufficiently smooth (average surface roughness Ra <
100 people) and hard (Vickers hardness Hv > 32
0kg/mm”) No film was obtained.

[Means and effects for solving the problems] The present inventors solved the above problems and achieved an average surface roughness of Ra S 12
As a result of our intensive efforts to develop a method to obtain a hard film with a smooth surface that exhibits Ra < IQQ and Vickers hardness Hv > 350 kg/mm2, we have developed an alumite-formed anode in a low-temperature chromic acid bath. They discovered that this can be achieved by performing oxidation treatment, and completed the present invention.

That is, in the present invention, aluminum or aluminum alloy material is heated at a temperature of 15% in a bath with a chromic acid concentration of 1.5% to 3%.
A method of manufacturing a substrate for a magnetic recording medium includes forming an alumite film on the surface of the substrate by anodizing the substrate at a temperature of 30° C. and a voltage of 60 to 75 V.

Lowering the bath temperature and increasing the voltage improves the hardness of the film, but the surface becomes rougher. In the present invention, a bath temperature of 15 to 30°C is utilized. If the bath temperature is higher than 30°C, no effect of improving the hardness of the film will be observed, and if it is lower than 15°C, the formation rate will be too slow to be practical. A suitable voltage is 60 to 75V; if it is less than 60V, the strength of the film will be insufficient, and if it exceeds 75V, the film will become porous, which is undesirable or undesirable.

Although the film thickness is not limited, it is preferably 10 μm or more and 20 μm or less in order to have strong adhesion, wear resistance, and toughness. The film thickness can be adjusted by selecting the processing time. Because this film is treated in a chromic acid bath, as mentioned above,
Even with a film thickness of 10 μm or more, no cracks occur when the magnetic material is heat-treated at 300 to 400°C. When the chromic acid concentration is less than 1.5%, the surface becomes uneven, and when it exceeds 3%, a hard film cannot be obtained.

Thus, the alumite anodic oxide film obtained by processing according to the method of the present invention has a high hardness of Hv > 350 kg/+u+'', a smoothness of Ra < 120, and a hardness of 3.
It has an excellent property of not generating cranks even when heat treated at 50°C or higher.

If the surface roughness of the film is Ra < 100, it can be used for practical use as is without polishing, and Ra > 1.
Even in the case of 00 people, the smoothness can be further improved by lightly polishing the surface. For example, conventional tape polishing (rubbing with a tape coated with alumina powder having an average particle size of 5 μm) may be used, and the degree of polishing may be less than that of the conventional method. Also,
Polishing the surface has the effect of improving surface hardness, and in that sense polishing is preferable. This is because in the alumite film forming reaction, the alumina production reaction and alumina dissolution reaction compete, so the surface of the film formed is somewhat soft.
By polishing the surface, a harder and smoother coating can be obtained.

〔Example〕

JI with a diameter of 95 mm and a thickness of 1.3 +n+w as a substrate
S 5058 aluminum alloy plate was used. The aluminum alloy plate has a maximum surface roughness R by precision turning and puff polishing.
The surface was finished to a surface roughness of max-0.10 μm or less and was washed to a mirror surface.

This substrate was anodized using a chromic acid bath with a chromic acid concentration of 1.7% under various conditions as shown in Table 1, varying the bath temperature, voltage, and treatment time. The thickness of the resulting film was lO~16μ. The hardness and surface roughness of the resulting film were measured.

The hardness is Vickers hardness according to JIS B7725.

The surface roughness was measured according to JIS 80601.

For samples No. 5, No. 6, and No. 8, the surface roughness of the obtained film was Ra > 100, so the surface was polished by approximately 0.1 AIm using a tape polishing device, and the hardness and surface roughness before and after polishing were measured. did. These results are also shown in Table 1.

From the results shown in Table 1 below, it can be seen that in the case of the present invention, a positive scratched oxide film with an extremely smooth surface and a hard surface can be obtained.

(Effect of the invention) According to the present invention, Ra < 120 people, preferably Ra < 100 people smoothness and Hv > 350 kg/
Provided is an alumite substrate for a magnetic recording medium suitable for high-density magnetic recording, which has a hardness of "m+w" and does not generate cranking even at 300 to 400° C., which is the heat treatment temperature for magnetic materials. Even in this case, the smoothness can be improved simply by light polishing, and the hardness can also be further improved by polishing.

Claims (1)

[Claims] 1. Aluminum or aluminum alloy material is heated in a bath with a chromic acid concentration of 1.5 to 3% at a temperature of 15 to 30°C and a voltage of 6.
1. A method of manufacturing a substrate for a magnetic recording medium, comprising forming an alumite film on the surface of the substrate by anodizing the substrate at 0 to 75V.