JPH0622055B2 - Magnetic disk manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a magnetic disk using an alumina ceramic substrate as a support.

The magnetic disk device plays a central role of information storage in the information processing system of a computer, but recently, since this magnetic recording tends to have a high density and a large capacity,
By using thin film technology such as sputtering, the magnetic recording medium has been made thinner and the surface accuracy has been improved, and it is trying to meet the demand.

An aluminum alloy is used for a substrate on which such a magnetic recording medium is formed, and an alumite layer obtained by oxidizing the surface thereof is coated with a thickness of 2 μ to 15 μ, and the hardness of the substrate surface is large due to the alumite layer. Has become
Since the thickness of this coin alumite layer is small and the aluminum alloy and alumite have different thermal expansion coefficients,
As the substrate temperature increased, the substrate was likely to be distorted. That is, when forming a magnetic recording medium on a substrate by sputtering, since the sputtering particles and electrons impinging on the substrate, the substrate temperature is increased by the collision energy, further consisting of γ-Fe ₂ O ₃ magnetic In the case of a recording medium, heat treatment is usually performed at 300 ° C. or higher, and the aluminum substrate is likely to be distorted due to the temperature rise of the substrate. When a magnetic recording medium is formed in and used for high density magnetic recording, there is a problem that it is difficult to perform accurate writing and reading.

Further, the magnetic disk device arranges a plurality of magnetic disks on the same rotating shaft and rotates them at a high speed of about 1000 to 3000 rmp to perform read and write data processing. If the substrate is made of an aluminum alloy, the substrate itself tends to expand due to centrifugal force, and this also makes it impossible to perform accurate writing and reading suitable for high-density magnetic recording, and to solve such writing errors and reading errors. Was wanted.

In addition, the aluminum alloy magnetic disk substrate,
Normally, the surface is anodized, but it is used even if there are about 10 voids with a maximum of 5μ. Therefore, the magnetic disk device for high-density recording has a problem that accurate writing and reading cannot be performed due to the void defect, and a magnetic disk substrate material having few void defects has been desired.

Further, although plastics and glass have been studied as other materials for disk substrates, it is said that the plastics have high moisture permeability, the glass is easily broken, and the risk of breaking is high, which is the greatest weakness. There is. When a substrate made of a plastic material is rotated at a high speed, the Young's modulus is small and the substrate itself tends to expand due to centrifugal force, which causes the same problem as described above.

Further, although it is considered to use ceramics as the magnetic disk substrate, the ceramic substrate has
There was a problem that many pores of 20 μm existed. Therefore, when a magnetic thin film having a thickness of 0.5 μm or less is formed, it causes a film defect, or the distance between the head and the magnetic film becomes long, so that the recording density is lowered.

The present invention has been completed in order to eliminate all the above-mentioned difficulties, and the purpose thereof is to prevent any distortion in the substrate due to sputtering or heat treatment, and to prevent the centrifugal force applied to the substrate from affecting the substrate itself. There is no elongation at all,
Another object of the present invention is to provide a magnetic disk substrate capable of writing and reading suitable for high-density magnetic recording by using a material having few void defects on the substrate surface.

The method of manufacturing a magnetic disk according to the present invention has an average particle size of 1
Alumina raw material powder with a purity of 97% or more at a size of less than μm is molded into a predetermined shape, fired, and then subjected to HIP treatment at a pressure of at least 1000 atm to obtain an average void diameter of 1.0 μ or less and 0.01 μm
It comprises the steps of producing an alumina ceramic substrate having the following centerline average roughness and forming a magnetic film on the substrate.

The method for producing a magnetic disk made of the polycrystalline alumina of the present invention will be described in detail below.

The magnetic disk substrate of the present invention is manufactured by HIP (Hot Isostatic Pressing) when manufacturing the alumina disk substrate in order to reduce defects such as those generated in the aluminum alloy substrate.
Hot isostatic pressing).

That is, as described below, the HIP-treated alumina disk substrate had significantly less voids and the diameter of the voids was further reduced, and when the present inventor repeatedly performed the experiment, the average void diameter was reduced to 1.0 μm or less. I was able to. As a result, a high-density magnetic disk substrate capable of accurate writing and reading is obtained.

Since the alumina disk substrate of the present invention has a significantly smaller elastic modulus than metals such as aluminum and plastics, even if the substrate is rotated at a high speed of 3000 rpm, the substrate itself is stretched due to the centrifugal force applied to the substrate. There was no.

Furthermore, according to the present invention, the waviness of the plate surface caused by the high-speed rotation of the magnetic disk substrate can be completely prevented by increasing the hardness of the substrate itself. 21 as indicated by Vickers hardness Hv
The value of 00kg / mm ² is obtained.

The magnetic disk substrate of the present invention has a center line average roughness (R
With a), a surface roughness of 0.01μ or less can be achieved, and as a result, even if the magnetic recording medium formed by sputtering etc. becomes extremely thin, the surface roughness of the substrate surface causes unevenness on the surface of the recording medium. It has been found that it is a substrate for a magnetic disk that is suitable for high-density magnetic recording with almost no occurrence.

Furthermore, in using the magnetic disk substrate of the present invention, before applying the magnetic recording medium to the substrate surface,
There is no problem in providing an intervening layer effective for high density magnetic recording.

Next, a method for manufacturing the magnetic disk substrate of the present invention will be described.

In order to obtain the magnetic disk substrate of the present invention, it is important to set the primary average particle diameter and the purity of the alumina raw material powder within a predetermined range. That is, as a result of repeated experiments conducted by the present inventor, although it is related to other various manufacturing conditions, the average primary particle size is 1 μm or less and the purity is 97% or less.
If HIP treatment is performed using alumina raw material powder of which the content is at least 100%, the average void diameter on the disk substrate surface can be reduced to 1.0 μ or less.

WAX emulsion, PV using such alumina raw material powder
Add organic binders such as A and PEG, and sintering aids such as SiO ₂ and MgO, mix thoroughly, and then dry and granulate with a spray dryer. Then, it is press-molded into a disc shape at a pressure of 0.6 kg / cm ² or more, and firing is performed for 2 to 6 hours in an atmosphere set within a temperature range of 1450 to 1750 ° C. The fired product is subjected to HIP treatment in a nitrogen or argon atmosphere at a pressure of 1000 to 2000 atm (gauge pressure) within a temperature range of 1300 to 1800 ° C for 0.5 to 3 hours.

The HIP-treated alumina sintered body thus obtained shows a clearer transparency than the unsintered alumina sintered body. This HI
The P-treated product is lapped, polished and polished to obtain a magnetic disk substrate of the present invention.

Further, the magnetic recording medium provided on the above-mentioned substrate may be any known per se, and its film forming means may be any, but in the present invention, the magnetic film is continuously formed by sputtering or plating. It is preferably provided in the form of a thin film.

Next, examples of the present invention will be described.

[Example 1] 0.2% by weight of alumina powder (first average particle size: 0.6 µ, purity: 99.7%) and sintering aid MgO together with an organic binder.
In addition, after milling, it was dried and granulated with a spray dryer. This powder hydraulic press (pressure 1.2ton / cm ² )
A donut-shaped disc (outer diameter 114 mm, inner diameter 30 mm, thickness 2.4
mm). This molded product was baked at a temperature of 1600 ° C. for 3 hours to obtain a disk-shaped baked product. After that, HIP treatment was performed in an argon atmosphere at 2000 atm at 1500 ° C for 1 hour, and a magnetic disk substrate (95 mm outer diameter, 25 mm inner diameter, 2 m thickness)
m) got.

When this substrate was polished with a diamond grindstone (# 220), a surface roughness of 3 to 6S was obtained. Then, the surface of this substrate was polished by lapping and polishing, and a center line average roughness (Ra) of 0.01 μ was obtained.

Thus obtained magnetic disk substrate of the present invention, the average number of voids generated on the surface of one side, the average void occupation area ratio, the average void diameter and the maximum void diameter was measured by an image analyzer, 55 in each order,
0.002%, 0.8 μ and 1.2 μ, the conventional aluminum substrate has 100 or more voids of 2 to 3 μ on one side, and the disk substrate made of alumina polycrystal without HIP treatment has a maximum void diameter of about 50 μ. The void defects are remarkably improved as compared with the average void diameter of about 15 μm.

Furthermore, the disk substrate of the present invention has a Vickers hardness of 2100 kg.
/ mm ² , flexural strength 60kg / mm ² and HIP-free substrate for alumina polycrystalline disk (Vickers hardness 1800kg / mm ² ,
The bending strength was 33 kg / mm ² ) and the strength and hardness were much higher, and the waviness of the plate surface caused by the high speed rotation of the disk substrate did not occur at all.

This example will be described in more detail. On the magnetic disk substrate of the present invention, an α-Fe ₂ O ₃ film (thickness 0.2 μm) was deposited by reactive sputtering targeting Fe containing Co, Then, as it is reduced at 320 ℃ in hydrogen atmosphere, it is converted into Fe ₃ O ₄ film, oxidized in air at 320 ℃ and converted into γ-Fe ₂ O ₃ film. I made a disc. For the magnetic disks thus obtained, when the head was levitated at a flying height of 0.2 μ, the head did not collide with the magnetic disk, and the signal error was confirmed for each, and it was found that high-density recording was practically used. , I found that there was no problem.

[Example 2] The primary average particle diameter and purity of the alumina raw material powder in Example 1 were as shown in Table 1, and the others were completely Example 1.
A substrate for an alumina disk was manufactured in the same manner as in. And the average void diameter of these substrates was measured.

As is clear from Table 1, since the sample Nos. 1, 2, and 4 used the predetermined alumina raw material powder, the average void diameter could be set to 1.0 μ or less. As a comparative example, sample number 3,
In Nos. 5 and 6 , the average void diameter was large and was close to the average void diameter of the aluminum substrate, and the object of the present invention could not be achieved.

As described above, in the magnetic disk substrate of the present invention, the substrate itself is not distorted due to the formation of the magnetic recording medium, and the substrate itself is not elongated by the centrifugal force applied to the substrate. The surface roughness can be as low as 0.01μ or less in the line average roughness (Ra), and the void defects appearing on the surface are significantly smaller than those of the aluminum alloy substrate, resulting in accurate high density recording. It is possible to provide a highly reliable magnetic disk substrate capable of writing and reading.

Claims (1)

[Claims] 1. An alumina raw material powder having an average particle size of 1 μm or less and a purity of 97% or more is molded into a predetermined shape and fired, and then 1000
Alumina ceramic substrate with average void diameter 1.0μm or less and center line average roughness (Ra) 0.01μm or less was prepared by HIP treatment under pressure higher than atmospheric pressure, and magnetic A method of manufacturing a magnetic disk, which comprises the step of forming a film.