JPH0371423A - Alumite substrate for magnetic disk and its production - Google Patents

Abstract

PURPOSE:To prevent deformation or ruggedness of the surface of a substrate during heating for degassing or sputtering, by forming priorly larger grains in the substrate and eliminating the growth of the grains during heated for degassing. CONSTITUTION:The aluminum alloy substrate covered with an anodized film has average grain size of 50 - 500mum. Growth of the grains can be inhibited even when this substrate is heated for degassing of sputtering. Thereby, deformation of the substrate caused by growth of grains or ruggedness of the surface due to various again height on the substrate can be avoided. The obtd. disk has excellent dimensional precision and surface roughness, and has advantages for low-height floating of a head without causing head crash.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to an alumite substrate constituting a magnetic disk as a magnetic recording medium in a computer, etc., and a method for manufacturing the same, in particular a method for depositing a magnetic film in the form of a thin film by sputtering. The present invention relates to an alumite substrate used in a sputter type magnetic disk and a method for manufacturing the same.

Conventional technology Conventionally, so-called coated type magnetic disks have been used, in which a magnetic medium is coated on the surface of an aluminum substrate, but with this coated type disks, the thickness of the magnetic film is unavoidable. Therefore, there is a limit to the ability to meet the recent demands for higher recording densities on magnetic disks.

Therefore, sputter-type magnetic disks in which a magnetic medium is deposited as a thin film on the surface of an aluminum substrate by sputtering have been developed and provided.

As an aluminum substrate for such a Subaddha type magnetic disk, an alumite substrate having an anodic oxide film formed on its surface is generally used for the purpose of improving surface hardness and adhesion with a magnetic film.

Problems to be Solved by the Invention By the way, with two pairs of alumite substrates, the second step after polishing is due to degassing treatment to remove water and CO2 from the anodic oxide film.
There is a method in which the substrate is subjected to heat treatment at a temperature of about 00 to 400 degrees Celsius. Further, during sputtering for subsequent formation of a magnetic film, the substrate may be heated to a temperature of around 400° C. or higher for the purpose of improving the coercive force of the magnetic film.

However, there have been disadvantages in that the substrate is deformed by heating during degassing or heating during sputtering, and further, unevenness occurs on the substrate, resulting in subtle unevenness on the surface of the magnetic film. Such drawbacks have led to problems such as causing head crashes in magnetic disks and hindering lower flying height of the head.

The present invention has been made in view of the above technical background, and an object of the present invention is to provide an alumite substrate that does not cause deformation or surface unevenness even when heated during degassing or during heating with a lid. purpose.

Means for Solving the Problems In order to achieve the above-mentioned object, the present invention is based on the fact that the deformation and unevenness of a substrate due to heating are caused by the growth of crystal grains of the substrate during heating. By making the grains larger in advance, it is possible to eliminate the growth of crystal grains during degassing and heating, thereby eliminating the above-mentioned drawbacks.

That is, the gist of the present invention is an alumite substrate for a magnetic disk, characterized in that the average crystal grain size of the aluminum alloy substrate on which an anodized film is formed is defined to be 50 to 500 μm; Also, an aluminum alloy substrate is heated at a temperature of 400°C or higher, the temperature of the substrate at the time of sputtering, but 500°C or lower, and a time of 1 minute to 10 hours. The gist of this paper is a method of manufacturing an alumite substrate for magnetic disks.

First, as an aluminum alloy substrate, the film contains an A base-Mg alloy, an A, Q-Mg-Cu alloy, specifically Mg: about 3 to 5 vt%, or further Cu:
A material containing about 4 vt% of Q, Q5 to Q, and the remainder consisting of aluminum and unavoidable impurities is used. More preferably, the balance composition is 1 with a purity of 99.99%. In the above composition, Mg is an element that provides strength to withstand high-speed rotation as a magnetic disk.

However, if the content is less than 3 wt%, the effect will be poor, and if it exceeds 5 wt%, there is a risk that processability, mechanical properties, and surface smoothness will deteriorate. In addition, Cu also contributes to improving the strength of the substrate, but if it is less than 0.05wt%, it has no effect, and if it exceeds 0.4wt%, there is a risk of demerits such as workability and surface smoothness. There is.

The average grain size of the aluminum alloy substrate is 50 to 500μ
m is specified because if it is less than 50 μm, crystal grains will still grow during heating of the alumite substrate for degassing or during sputtering, and surface irregularities due to non-negligible deformation of the substrate and generation of grain boundary steps will occur. This is because it occurs. On the other hand, if the average crystal grain size exceeds 500 μm, the crystal grains are too coarse, and the roughness of the substrate surface may be reduced after turning, grinding, diamond turning, etc. are applied to the aluminum alloy substrate itself before anodizing treatment. Deteriorate. Particularly preferably, the thickness is 150 to 300 μm.

The type of anodic oxide film formed on the surface of the aluminum alloy substrate is not particularly limited, but an oxalic acid film is preferable because it has excellent hardness and heat resistance. Film thickness is 5-20μ on one side
It is best to set it to about m.

The average grain size of the aluminum alloy substrate is 50 to 500μ
Although the method for manufacturing the alumite substrate described above is not particularly limited, the manufacturing method according to the present invention can be cited as a preferred manufacturing method ε. First, the average crystal grain size is 50μ
In order to specify the temperature to be at least m, an aluminum alloy substrate processed into a predetermined shape is heated at 400° C. or higher for 1 minute or more. 40
If the temperature is less than 0° C. or less than 1 minute, the crystal grains will not grow, and the crystal grains will re-grow due to subsequent heating during degassing or sputtering, resulting in deformation of the substrate and fine irregularities. In addition, if the heating temperature of the substrate during sputtering exceeds 400°C, the aluminum alloy substrate must be heated at a temperature higher than the substrate temperature during sputtering in order to suppress the regrowth of crystal grains during sputtering heating. There is. On the other hand, in order to specify the average crystal grain size of the aluminum alloy substrate to be 500 μm or less, the aluminum alloy substrate must be heated at a temperature of 500° C. or less. Also, the heating time is 10
It must be less than an hour. This is because if the heating time exceeds 10 hours, precipitates within the substrate will grow on the surface and cause film defects during the anodizing treatment.

After the above heating, the aluminum alloy substrate is subjected to turning, grinding, and diamond turning.
An anodic oxidation treatment is performed to form an anodic oxide film of about 5 to 20 μm on one side on the surface of the substrate to obtain an alumite substrate. The anodizing treatment is preferably performed by the oxalic acid method as described above.

Specific oxalic acid treatment methods include constant current electrolysis treatment in an oxalic acid electrolytic bath, and a particularly preferred electrolytic treatment method is the current recovery method, in which the treatment is carried out in two stages, one before and the other, and the second stage treatment is rapidly lowered from the first stage treatment voltage. One example is a method in which the voltage is applied at a constant voltage.

The surface of the alumite substrate produced as described above is then polished to such an extent that the anodic oxide film has a thickness of 5 to 110 liters on one side, and then the 200 to B coating is degassed. Since the substrate is heated in advance before the anodizing treatment to grow the average crystal grain size to 50 μm to 500 μm, regrowth of the crystal grains due to this degassing heating is suppressed.

Thereafter, a magnetic thin film is deposited on the substrate surface by sputtering. In order to achieve high recording density, the substrate is heated and maintained at 300 to 450° C. during sputtering, but in this case as well, regrowth of crystal grains in the substrate is suppressed.

Effects of the Invention As described above, the present invention provides an aluminum alloy substrate having an anodic oxide film formed on its surface with an average crystal grain size of 50 to 50.
Since it is 0 .mu.m, even if this alumite substrate is subsequently heated during degassing or during a snok lid, the growth of crystal grains on the substrate is no longer suppressed. Therefore, it is possible to avoid deformation of the substrate due to the growth of crystal grains and generation of minute irregularities on the substrate surface due to grain boundary steps. As a result, dimensional accuracy,
A magnetic disk with excellent surface roughness, which does not cause head/socket crashes and is advantageous for lowering the flying height of the head, can be obtained.

In addition, the aluminum alloy substrate is heated at a temperature of 400°C or higher and the temperature of the substrate during sputtering but not higher than 500°C.
By heating under the conditions of time = 1 minute to 10 hours and then anodizing, it is possible to reliably produce an alumite substrate having an average crystal grain size of 50 to 500 μm.

Example Next, the present invention will be explained in detail.

After preparing a plurality of aluminum alloy substrates (outer diameter 95mm, inner diameter 25m, plate thickness 1.3m) made of AjJ-4wt%Mg-0,1,wt%Cu alloy, and smoothing the surface of the substrate, Heating was performed under the conditions shown in Table 1. Then, when we measured the average crystal grain size on the substrate surface after heating, we found that the first
It was as shown in the table.

Next, each of the aluminum substrates was subjected to an oxalic acid anodic oxidation treatment to form an oxalic acid film on the surface. Note that the anodizing treatment was performed in accordance with the following. That is, oxalic acid concentration: ], 5νt%,
Liquid temperature: Current density 1.5A/dr in oxalic acid electrolyte at 30℃
lt, electrolysis time: 30 minutes, firstly, a preliminary anodization treatment by direct current electrolysis treatment was performed. Next, after the electricity was turned off at one end, a subsequent anodization process was performed by direct current electrolytic treatment at a constant voltage of 36 V in the same electrolytic solution. The film thickness was 10 μm on one side.

Next, the various alumite substrates obtained above were heated at the temperatures shown in Table 1, and changes in the flatness of the substrates before and after heating were examined. The results are also shown in Table 1.

[Margins below] As is clear from the results in Table 1, the products of the present invention maintain good flatness even when heated after anodizing treatment, and therefore suppress deformation of the substrate and surface unevenness, and reduce scales. I was able to confirm that.

that's all

Claims (2)

[Claims] (1) An alumite substrate for a magnetic disk, characterized in that the aluminum alloy substrate has an anodic oxide film formed on its surface and has an average grain size of 50 to 500 μm. (2) The aluminum alloy substrate is heated at a temperature of 400°C or higher, higher than the temperature of the substrate during sputtering and 500°C or lower, for 1 minute to 10 hours, and then anodized. A method for manufacturing an alumite substrate for magnetic disks.