JPS6149400B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of manufacturing an alumite substrate for magnetic recording media such as magnetic disks, and more particularly, to a method of manufacturing an alumite substrate for magnetic recording media that is substantially free of black spot defects, has excellent mechanical strength, and has excellent heat resistance. It is something. 2. Description of the Related Art Aluminum or aluminum alloy materials (hereinafter referred to as alumite substrates) with an alumite layer formed on the surface are used for magnetic recording medium substrates such as magnetic disks. The reason why alumite substrates are used in this way is that alumite is harder and has better wear resistance than alumite alloys, and also has good abrasiveness, so it is easy to obtain a highly precise smooth surface, and it is easy to coat the surface with a thin magnetic layer. This is because it is possible to form . By the way, this alumite substrate also has the following drawbacks, and these are obstacles to increasing the recording density of magnetic recording media. One of them is called black spot defects, where impurities such as iron and silicon present in the aluminum or aluminum alloy base material crystallize as intermetallic compounds, which are scattered on the surface of the base material and are removed during alumite treatment. This is an extremely small missing part of the alumite film. Initially, this missing part is extremely small on the order of submicrons, but as the alumite film grows, it expands to a size of 5 μm.
For alumite layers with a film thickness of 5 to 10μ
m pit-like minute defects, so the larger the number, the more signal errors occur in the magnetic recording medium, which is undesirable. In addition, when using an alumite substrate as a high-density magnetic recording medium, a thin film of α-Fe ₂ O ₃ or Fe ₃ O ₄ is deposited on the alumite substrate by sputtering or other methods, and then heat-treated at 300 to 400°C. However, when such high _- temperature _heating is performed, cracks occur in the alumite film, which tends to cause product defects. This is based on the difference in the coefficient of thermal expansion between the aluminum base material and the alumite layer. Therefore, the thickness of the alumite layer must be extremely thin, approximately 1 to 3 μm, and the processing temperature must be approximately 310°C or lower to avoid cracking. Must. However, with such a thin alumite layer, the hardness of alumite cannot be effectively utilized, which causes a decrease in the head crushing resistance of the magnetic recording medium.
- Fe ₂ O ₃ formation was slow and unfavorable. Therefore, it has been desired to develop an alumite substrate that has a thick alumite layer and does not crack when heated at high temperatures. The inventors conducted extensive research to solve the above drawbacks, and found that when a chromic acid solution was used as the alumite treatment solution and the alumite treatment was carried out by the constant voltage method, it was possible to prevent black spot defects on the alumite film and improve the alumite treatment. It was found that this method has a considerable effect on thickening the layer and improving heat resistance. However, this method also has its limits; heat resistance is good up to an alumite film of around 10 μm, but if the film is thicker than that, cracks will occur in the alumite layer during heating, so it is not practical.
There were problems in manufacturing substrates with an alumite layer of 10 μm or more. The present invention can be used not only for film thicknesses of 10 μm or less, but also for film thicknesses of 10 μm or less.
This is a method for manufacturing an alumite substrate with excellent heat resistance that can be applied to cases with an alumite film of less than μm. During alumite treatment, an alumite film is formed by a constant voltage method in a chromic acid solution, and then an electrolytic film containing Sn salt is applied. 2 by applying voltage in solution
The purpose is to prevent the generation of sunspots and to produce an alumite substrate that does not generate cracks during heating by performing a subsequent electrolytic treatment. That is, in the present invention, an aluminum or aluminum alloy base material is anodized using a chromic acid solution having a concentration of 1.5 to 15% by weight using a constant voltage method at a voltage higher than 60V, preferably at a voltage of 70 to 100V. Afterwards, after washing with water or the like using a conventional method, Sn is added into the micropores of the alumite layer by performing a secondary electrolytic treatment in an electrolytic solution containing Sn salt.
At the same time, it causes numerous fine cracks to be generated in the barrier layer at the bottom of the alumite micropores, and when heated to form a magnetic film, these fine cracks form in the alumite layer to a size that is inconvenient for use as a magnetic recording medium. This prevents the occurrence of cracks. The alumite treatment conditions used are the same as the conventional Butsard method, with a chromic acid solution concentration of 1.5 to
The alumite treatment is carried out at a constant voltage of 15% by weight and a liquid temperature of 35 to 50°C, but the voltage is higher than 40V in the Butssard method and exceeds 60V, preferably between 70 and 100V. At this time, a small amount of sulfuric acid may be added to increase the conductivity of the chromic acid electrolyte. After the alumite treatment, take out the base material from the electrolytic bath,
It may be washed with water by a conventional method and, if necessary, with pure water. After that, 2
Next electrolyze. The electrolytic solution for secondary electrolysis may be any salt that precipitates Sn into the fine pores of the alumite layer. For example, use stannous sulfate, and add mineral acid to a concentration of 3 to 15 g/min.
Add organic acid, etc., adjust the pH to about 0.5-2, and lower the temperature.
It can be conveniently used at a temperature of 20 to 30°C.
It is also possible to add tartaric acid as a chelating agent and use it as a weak acid to neutral Sn salt-containing solution. An alumite substrate on which a chromic acid alumite layer has already been formed is immersed in the above solution, and electricity is applied to the electrolytic solution for about 20 seconds to 10 minutes, preferably 30 seconds to 8 minutes, using an alternating current or a waveform similar to alternating current. The alumite substrate obtained by the above treatment has almost no black spots and has excellent heat resistance even with a film thickness of 10 μm or more. Furthermore, the α-Fe ₂ O ₃ thin film deposited on the film _is Cracks do not occur even when heat treatment is applied to form an O ₃ thin film. Next, experiments conducted by the inventors in completing the present invention will be described. Table 1 shows aluminum alloy materials (A1-3 weight% Mg
Voltage and appearance of black spots on the alumite substrate when alumite treatment was performed using a DC constant voltage method in a 5 wt % chromic acid solution stored at a liquid temperature of 40°C, and the occurrence of cracks after heating at 350°C for 2 hours. and coating hardness related to head crushing resistance. The thickness of the alumite film at that time is 5μ
m and 15 μm. In addition, in Table 1, evaluation of sunspots is performed in a microscopic field of view (0.36 mm ² ), 〇 is 2.5 μm or less, and △ is 3.5 μm.
μm or less, × indicates one or less black dots of 5 μm or less, and evaluation of cracks is based on microscopic observation of the alumite substrate after heat treatment. ○ indicates no cracks at all, △ indicates partial cracks. , × indicates that cracks occurred on the entire surface, and hardness evaluation is the result of using a microhardness meter. 〇 indicates 250H _v or more, △ indicates 200 to 250H _v , ×
indicates 200H _v or less. The measurement samples for black spots, cracks, and hardness were made by grinding the surface of the film by 2 μm.

[Table] For sunspots, the alumite voltage is higher than 60V.
Preferably at 70-100V, film thickness 5μm, 15μm
When a film is formed, a film without black spots can be obtained regardless of the presence or absence of secondary electrolysis. For comparison, conventional sulfuric acid films are also shown, but all of them produce black spots and are unsuitable as substrates for high-density magnetic recording media. Regarding cracks, an alumite film alone with a thickness of about 5 μm is sufficient, but a film thickness of 10 μm or more will cause cracks. However, if a secondary electrolytic treatment is performed in an electrolytic solution containing Sn salts, cracks will not occur even if the film thickness is 10 μm or more. However, cracks occur during secondary electrolysis using an electrolytic solution containing Cu salt. There is almost no difference in hardness as shown in Table 1 above, but as the film becomes thicker, the alumite treatment time becomes longer, so the surface of the film is more dissolved by the treatment liquid, and the hardness tends to decrease. In addition, Table 2 uses an aluminum alloy base material as in Table 1, and after anodizing at 85V using the DC constant voltage method using a chromic acid solution at the same temperature and concentration, SnSO 2 using AC voltage 10V in an electrolytic solution containing ₄ at a temperature of 25°C.
Next electrolysis was performed. For comparison, _CuSO4
It also shows the case where it is included. created using this method
A substrate with Sn or Cu deposited in alumite micropores is heated by varying the heating temperature in the temperature range of 300 to 400℃.
The appearance of cracks when this temperature was maintained for 2 hours, the appearance of black spots before heating, and the film hardness related to head crack resistance are shown. The evaluation criteria for black spots and film hardness in Table 2 are the same as in Table 1.

[Table] From the results in Tables 1 and 2, the following was found. That is, in the case of a board that has been alumite treated at a voltage higher than 60V using a chromic acid solution using a DC constant voltage method as in the present invention, and then subjected to secondary electrolysis in an electrolytic solution containing Sn salts, black spots may occur. No or almost no cracks were observed due to heat or heating, and even when the film thickness was increased to improve the board's head crushing resistance,
No sunspots or cracks were observed. However, as shown in the comparative example, 2
When the subsequent electrolysis was performed, cracks were observed in alumite coatings with a thickness of 10 μm or more. The amount of Sn deposited during secondary electrolysis is 20 mg/m ² in 20 seconds, 70 mg/m 2 in 1 minute, and 70 mg/m ² in 5 minutes.
It was ^about 250mg/m2. Also, during secondary electrolysis
In an acidic electrolytic solution containing Sn salts, countless extremely fine cracks of several angstroms in size are generated at the bottom of the alumite pores, and when heated, the precipitated Sn melts and penetrates into the barrier layer through the cracks, thereby modifying the barrier layer. On the other hand, it is thought that such a phenomenon does not occur because Cu has a high melting point. As described above, the method of manufacturing an alumite substrate for high-density magnetic recording media according to the method of the present invention simultaneously solves the conventional problems of black spots, cracks during high-temperature heating, and film hardness related to head crush resistance. This can be said to be an industrially excellent invention. Next, examples of the present invention will be shown below. Example 1 Aluminum alloy base material for high-density magnetic recording (A1
-3 wt% Mg alloy, inner diameter 100 mm, outer diameter 210 mm, thickness 2 mm) was subjected to specified surface polishing, then cleaned with a non-erosive cleaning agent, and anodized. For the alumite treatment, the aluminum material was immersed in a 5% by weight chromic acid solution heated to 40°C, and electrolytically treated using direct current as an anode. The voltage was kept constant at 85 V, and a milky white smooth alumite film with a thickness of 20 μm was obtained after approximately 150 minutes of electrolysis. Next, the alumite-treated alloy base material was pulled out of the electrolytic cell, washed with water and purified water, and then subjected to secondary electrolysis by applying 10 V alternating current with carbon as the counter electrode. The composition of the electrolytic solution at that time is as follows. Stannous sulfate SnSO ₄ 5g / Sulfuric acid H ₂ SO ₄ 5g / Ammonium sulfate (NH ₄ ) ₂ SO ₄ 7g / Water Balance PH 1.2 Electrolyte solution temperature 25℃ Electrolysis time 20 seconds, 40 seconds, 1 minute, 3 minutes, 5 minutes After secondary electrolysis, washing with water and drying, the surface of the alumite film was smoothed by grinding by 2 μm, heated at 350° C. for 2 hours, and observed under a microscope. No cracks were observed in any case. Furthermore, the surface roughness was measured and compared before and after heating using a stylus roughness meter (Talysurf), but no deterioration in surface roughness due to the heating treatment was detected within the measurement error. Therefore, it was found that the alumite substrate produced according to the present invention has sufficient heat resistance in the heating process for forming a magnetic thin film of γ-Fe ₂ O ₃ . For comparison, only SnSO ₄ of the above composition was used.
When secondary electrolysis was performed using an electrolytic solution in place of CuSO ₄ (7 g/) under the same conditions, cracks were observed in all cases, making them unsuitable as substrates for high-density magnetic recording media. Example 2 The surface of the alumite substrate formed by the method shown in Example 1 was further polished to create an alumite layer with a thickness of 3 μm, 6.5 μm, and 12 μm, and a 0.17 μm thick layer was applied on top of the alumite layer. A γ-Fe ₂ O ₃ magnetic thin film was formed. A diamond pin with a tip diameter of 20 .mu.m was pressed against the surface of the magnetic recording medium under a load of 1 to 30 g, and the depth of the scratch mark was measured using a surface roughness meter. For comparison, γ-Fe ₂ O ₃ was deposited on a surface-hardened glass substrate and an aluminum alloy substrate surface-hardened with a Ni-P plating layer of approximately 25 μmV thickness.
A magnetic thin film formed thereon was used. Figure 1 shows the load dependence of the scratch depth. As shown in Figure 1, when an alumite substrate is used, the scratch depth decreases as the alumite layer increases, and when an alumite substrate with a thickness of 12 μm is used, the scratch depth decreases when surface-hardened glass or Ni - Improved to almost the same level as when using a P-plated board. This is because when the alumite thickness is thin, the alumite layer does not substantially play the role of surface hardening, and plastic deformation occurs in the underlying aluminum alloy even under relatively low loads, whereas when the alumite thickness is thick, This is because the effect of surface hardening becomes noticeable. Therefore, the alumite substrate made by the method of the present invention can have a thick alumite layer without reducing the hardness _Hv of the alumite layer, and as a result has improved mechanical strength compared to conventional alumite substrates with a thickness of 1 to 3 μm. This shows that the problem of head crush resistance, which was a drawback of conventional substrates, has been successfully improved to a large extent.

[Brief explanation of the drawing]

Figure 1 shows the technical content of the present invention, and shows the alumite thicknesses of 3 μm, 6.5 μm, and 12 μm.
A graph showing the relationship between load and scratch depth is shown for a case where a γ-Fe ₂ O ₃ magnetic thin film with a thickness of 0.17 μm is deposited on the surface of Toshiro, as well as surface hardened glass and Ni-P plating for comparison. be.

Claims (1)

[Claims] 1 Aluminum or aluminum alloy base material
After applying alumite treatment to the surface of the aluminum or aluminum alloy base material at a voltage higher than 60V by immersing it in a 1.5 to 15% by weight chromic acid solution using a constant voltage method, it is subjected to secondary electrolysis in an electrolytic solution containing Sn salt, A method for manufacturing an alumite substrate for a magnetic recording medium, characterized by precipitating Sn in an alumite layer.