JPS6033392A - Preparation of alumite substrate for magnetic recording medium - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an alumite substrate for magnetic recording media such as magnetic disks, and more specifically, a magnetic recording medium that is substantially free of black spot defects, has excellent mechanical strength, and has excellent heat resistance. The present invention relates to a method of manufacturing an alumite substrate for use.

For magnetic recording media substrates such as magnetic disks, an aluminum alloy material (hereinafter referred to as AZOMITE IGETA) with an alumite layer formed on its surface is used.

The reason why alumite substrates are used in this way is that alumite is harder than alumite alloys, has excellent wear resistance, and has good abrasiveness, so it is easy to obtain a smooth surface with a high Ml. This is because it is possible to form a thin magnetic M layer. 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 a black spot defect, in which impurities such as iron and silicon present in the aluminum or aluminum alloy base material crystallize as intermetallic compounds, which are dotted on the surface of the base material, and when the alumite substrate is anodized, these defects occur. This is an extremely small missing part of the alumite film, and this missing part is initially a very small part on the order of submicrons, but expands as the alumite film grows, and becomes 5μ.
For an alumite layer with a film thickness of m or more, the thickness is 5 to 10 μm.
This number of small bit-like defects is large in magnetic recording media. This is undesirable as it increases signal errors.

In addition, when the alumite substrate is used as a high-density magnetic recording FG body, α-1! 'e205i or F
A thin film of θ 304 is deposited by sputtering or other methods, and then heated to 300-400°C to obtain γ
-Fθ203 is carried out, but when such high temperature heating is carried out, cracks occur in the alumite, which tends to cause product defects.

This is based on the difference in thermal expansion coefficient between the aluminum base material and the aluminium)17M, and therefore the aluminium)IN film j
1 to 3 μm, and the processing temperature was 31 μm.
The temperature must be kept below about 0°C to avoid cracking. However, such a thin alumite layer cannot substantially take advantage of the hardness of alumite, which causes a decrease in the head crushing resistance of the magnetic recording medium, and the formation of r-Fe203 is slow due to insufficient temperature, which is not desirable. Ta.

Therefore, it has been desired to develop an alumite substrate that has a flat alumite layer and does not crack when heated at high temperatures.

In order to solve the above-mentioned drawbacks, the inventors conducted research on 1. As a result,
When a chromic acid solution is used as the alumite treatment solution and the alumite treatment is performed by the constant voltage method, it is possible to prevent small defects in the alumite film, increase the thickness of the alumite layer, and improve heat resistance. It was found that there is an effect. However, this method also has its limitations, and the alumite film is
It has good heat resistance up to about 10 μm, but if the rP is higher than that, cracks will occur in the alumite layer when heated, so there was a problem in practical use with a certain kettle that had an alumite IIM of 10 μm or more. .

In the present invention, of course, if the film thickness is 118 m or less,
An excellent heat-resistant alumite manufacturing method that can be used even when the alumite film has an alumite film of m or more. Secondary electrolytic treatment by applying voltage in an electrolytic solution containing The purpose is to prevent the occurrence of sunspots by applying JfQ and to produce anodized aluminum plate without cracking during heating.

That is, the present invention uses a chromic acid solution having a concentration of 1.5 to 15% by weight on an aluminum or aluminum alloy substrate and applies a pressure higher than 6 OV, preferably 70 to
After performing alumite treatment at a voltage of 100V, the cloth is washed with water using a conventional method, and then subjected to secondary electrolysis in an electrolytic solution containing Sn salt to form alumite)1.
This causes Sn to precipitate in the holes for η and ♀ of 1, and also generates countless fine cracks in the barrier 1 (support) at the bottom of the alumite micropores, and these fine cracks are a barrier to magnetic film formation. This is to prevent the occurrence of cracks of an inconvenient size in the alumite layer during heating of the magnetic recording medium.

The alumite treatment conditions used are the same as those of the conventional Gutsard method, and the 'lF' of the chromic acid solution = % p'; 1
, 5 to 15 vehicles, constant voltage at a liquid temperature of 35 to 50"C, but the voltage is higher than the 40 V of the Gutsard method.
Alumite treatment is carried out at a voltage higher than ioV, preferably between 70 and 100V. At that time, a small amount of sulfuric acid may be added to the chromic acid-acid M solution to increase the mineral properties of the solution. After the alumite treatment, the bowl material "fr" is taken out of the electrolytic cell, washed with water in the usual manner, and purified as necessary. washing with water]- may also be used.

Thereafter, secondary electrolysis is performed in an electrolytic solution containing Sn salt. 2
The electrolytic solution for the next electrolysis may be a crucible that precipitates Sn into the fine pores of the alumite layer, for example, using stannous nitrate at a concentration of 3.
If the pH is adjusted to about 0.5 to 2 by adding ore layers, hydration, etc. to ~15 R/1, and the pH is adjusted to ~(9)C, it can be used for phlegm. In addition, tartarite C stage is used as a chelating agent [-・
In addition, if you use it as a weak acid to neutral 5nP4-containing solution, you can also do seven things.Immerse an alumite substrate on which a chromic acid alumite layer has already been formed in the above solution, and use a waveform that changes to alternating current or alternating current for Δ) seconds to About 1 () minutes, 3 minutes if you like it
The alumite substrate obtained by the process of passing electricity through an electrolytic solution for 0 seconds to 8 seconds has almost no #1 minute black spots, and even with a skin thickness of 10 μm or more, +i
] - I It has excellent heat resistance, and even when the α-Fe2.03 thin film deposited on the skin 11q is subjected to heat treatment to form a 1-Fa203 thin film, no cracks occur.

Next, the experiments conducted by the inventors in completing the present invention will be described.

m1 table shows aluminum alloy material (AI-3iN band (f, J
Voltage and appearance of black spots when alumite (aluminum alloy) is alumite treated by direct current constant voltage method in a 5 weight ratio chromic acid solution stored at a liquid temperature of 40'C, 350
The appearance of cracks after heating at °C for 12 hours and the thickness of the skin IIa with respect to head crushing resistance are shown. The thickness of the alumite film at that time was 5/1 m and 15 μm.

In addition, in Table 1, the evaluation of sunspots is in the microscopic field (0,
36ryrm"),
△ indicates that there is no more than 3.5 μm, Y indicates that there is no more than 1 black spot of 5 μm or less, crack evaluation is based on microscopic observation of the alumite substrate after heat treatment, 0 indicates that there are no cracks, Δ indicates that there is no crack at all. Items with partial cracks are shown, and A indicates items with full cracks.Furthermore, the hardness is evaluated to be very small. As a result of using courage, ○ke 250 Hv
Above, △ke 200-250 Hv, yke 200 Hv
It also shows the following. Note that the measurement samples for black spots, cracks, and hardness were made on samples whose coating surfaces were ground by 2/1 m.

ptr, ■ Fuck (1) Alumite film thickness 5μm0 t2i 1 15 μm.

(3) Sn is deposited at 5 μm by secondary electrolytic treatment.

t41 #15μm11, 8n deposited (51cu deposited.

15μm (Note) Secondary electrolysis conditions (31,14i 5nS0.5F/
/-1 pH 1,2 electrolyte solution, AC HIV, 3 minutes of electricity.

For sunspots, use alumite lightning, pressure higher than 60 V, preferably (at 70 to 100 V, film thickness 5 nm, 1F+
When a μm skin MN k is formed, a product without black spots can be obtained regardless of the presence or absence of secondary electrolysis.

For comparison, sulfuric acid coatings made using the conventional method are also shown, but black spots occur in both cases. For high-density magnetic recording media: Unsuitable as a board. Only alumite film with a crack thickness of 5 μm is present.
Although it is fine to a certain extent, cracks occur when the film thickness exceeds 1011 m. However, if the secondary electrolytic treatment is performed in an electrolytic solution containing Sn salt, no cracks will 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.

Table 2 also uses an aluminum alloy base material as in the MI table, and after anodizing at 85V using a chromic acid solution at the same temperature and concentration using the DC constant voltage method, an additional 5nSO. Secondary electromagnetic waves were carried out by applying an alternating current voltage of 1 V in a solution containing lightning at a temperature of 5-°C.For comparison, a case containing Cu5O is also shown.This method Created SnJ or Cu'?: Crack occurrence situation and before heating when the substrate deposited in the alumite micropores was heated at a temperature range of 300 to 400"C and held at this temperature for 2 hours each. The appearance of sunspots,
The film hardness related to head crush resistance is shown below.

The evaluation criteria for black spots and film hardness in Table 2 are the same as in Table 1.

From the results in Tables 1 and 2, the following was found.

That is, as in the present invention, a substrate is anodized using a chromic acid solution at a voltage higher than 6()■ using a DC constant voltage method, and then subjected to secondary electrolysis in an electrolytic solution containing Sn salt. In particular, there are no sunspots or cracks caused by heating, and almost no cracks are observed.Also, to the face of the original team, the film thickness has been increased to improve the sodo-crash resistance. No blackening or cracking was observed even when However, as shown in the example of the ratio axis (1 including Cu salt)
BahT! 2 snowstorms in solution.

If you have free time, alumite skin 11W with a diameter of 10μm or more
Cracks were observed in I'W.

In addition, the amount of Sn precipitated by dividing the second-order rQi solution is 70 my/m2 in 2 seconds and 70 my/m2 in 1 minute.
In 5 minutes, it was 250 my/m2 rod. -! i
In addition, in the case of an acidic electrolytic solution containing increased Sn during secondary melting, extremely fine cracks of approximately several + A are formed at the bottom of the alumite pores, and during heating, the precipitated S and N are melted in the bath, and from the cracks. Since Cu penetrates into the layer and thereby modifies the layer, cracks do not occur.On the other hand, since Cu has a high melting point, it is thought that such a phenomenon does not occur.

As described above, in the method of manufacturing an alumite substrate for high-density magnetic recording media according to the method of the present invention, problems such as generation of black spots, generation of cracks during high-temperature heating, and film hardness related to head crushing resistance, which have been problems in the past, can be solved. It can be said that this invention is excellent in terms of T industry because it can solve the problems at the same time.

Next, examples of the present invention will be shown below.

Example 1 Aluminum alloy base material for high-density magnetic recording (A1.-3% by weight Mg alloy, inner diameter 100 mm, outer diameter 210 mm, width 2 m
m)′f! : After the specified surface was polished, it was 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 with direct current as an anode. The voltage was 85 V-U, and a milky white smooth alumite film with a thickness of 1 μm was obtained after about 150 minutes of electrolysis.

Next, the alumite-treated alloy base was taken out of the electrolytic bath, washed with water and purified water, and then carbon was used as the counter electrode.
Secondary electrolysis was performed by applying an alternating current of V. The composition of the electrolytic solution at that time is as follows.

Sulfuric acid No. (fil+ S rlrJOa 5f //- Sulfuric acid 1 (2S0.5q/l.

Ammonium sulfate ("4'hSOa 7 f//
.

Water pH 1,2'αtiT solution 1Vl Temperature 25°C Electrolysis time m seconds, 40 seconds, 1 minute, 3 minutes, 5 minutes After secondary electrolysis, wash and dry, grind 2ttm to remove the surface of the alumite film. When the specimens were heated at 350° C. for 12 hours and observed under a microscope, the occurrence of cracks did not subside in all cases.

Furthermore, the surface roughness before and after heating was measured and compared using a stylus probe n1 (Talysurf).
The deterioration of the surface roughness due to the 4111 constant error is 1 force. Therefore, according to the present invention, the alumite hole bottom has a force of 11 F to form a magnetic thin film of γ-Fe2O3.
It was found that it had sufficient heat resistance in 70 processes.

For comparison, only sn So4 of the above composition was
When secondary electrolysis was performed using an electrolytic solution in place of uso, (7yet) and the others under the same conditions, cracks were observed in all cases, and substrate 17 for high-density magnetic recording media was unsuitable.

Example 2 The surface of the alumite substrate formed by the method shown in Example 1 was further polished to a thickness of 3 μm.
, 6.5μ, and 12μ, respectively, and a 0.17ttm thick 1-Fe2O3 magnetic f! If
m was formed. The tip diameter is mμ on the surface of this magnetic recording medium.
The entire load of the diamond bottle i1~; U() was pushed and scratched with 7, and the depth of the scratch mark was measured using a surface roughness meter. Surface hardened glass plate and approx. δ for comparison
A γ-Fθ2osW+x thin film was formed on an aluminum alloy substrate whose surface was hardened with a μm thick N1-P plating.

Figure 1 shows the load dependence of scratch retention.

As shown in Figure 1, when an alumite substrate is used, the scratch depth decreases with the furnace force n of the alumite, and when a 12 μm thick alumite substrate is used, the scratch depth ld decreases when the surface hardens. The # is improved to the same level as when glass or N1-P plated substrates are used.

This is because when the alumite (aluminum) H is thin, the alumite layer does not substantially play the role of surface hardening, and FIJ deformation occurs in the underlying aluminum alloy even under relatively low loads.
This is because if the alumite is thick, the surface hardening effect will appear on the noodles. Therefore, the alumite substrate produced by the method of the present invention has a thicker alumite layer without reducing the hardness Hv of the alumite layer, compared to the conventional 1 to 3 μm hardness.
The mechanical strength is improved compared to the alumite substrates up to m, indicating 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 drawings]

Figure 1 shows the technical content of the present invention, in which a 17 μm thick γ-Fe203 magnetic thin film of gold is coated on the surface of anodized aluminum with a thickness of 3 μm, 6.5 μm, and 12 μm. , and a graph showing the relationship between load and scratch depth for surface hardened glass and N1-P plating for comparison. Patent issued by Nippon Telegraph Corporation Nippon Light Metal Co., Ltd.

Claims (1)

[Claims] Aluminum or aluminum alloy base material from 1.5 to 1
60% by constant voltage method by dipping in 5% chromic acid solution.
After performing alumite treatment on the surface of aluminum or aluminum alloy base material at a voltage higher than V, secondary electrolysis is performed in an electrolytic solution containing Sn salt, and Sn is added to the alumite layer.
1. A method for producing an alumite substrate for a magnetic recording medium, the method comprising depositing.