JPH06101115B2 - Zirconia magnetic disk substrate and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magnetic disk substrate in which a zirconia substrate is used as a support for a magnetic disk and void defects on the substrate surface are eliminated.

The invention also relates to the process for obtaining this substrate.

[Prior art and problems]

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 and plating, the magnetic recording medium is made thinner and the surface accuracy is improved, and the demand is being met. 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 of the substrate is coated with a thickness of about 2 μ. This alumite layer increases the hardness of the substrate surface. However, since the thickness of this hard alumite layer is small and the aluminum alloy and alumite have different thermal expansion coefficients, the substrate is likely to be distorted as the substrate temperature rises. That is, when a magnetic recording medium is formed on a substrate by sputtering, sputtered particles and electrons collide with the substrate, so that the collision energy raises the substrate temperature, and the magnetic energy of γ-Fe ₂ O ₃ In the case of a recording medium, the 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.

Furthermore, the magnetic disk device arranges a plurality of magnetic disks on the same rotary shaft and rotates them at a high speed of about 1000 to 3000 rpm to perform read and write data processing. If it is formed, 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 it is desired to solve such writing error and reading error. It was

Moreover, a magnetic disk substrate made of an aluminum alloy usually has a void (void) of 2 to 3 μ all over one surface of the substrate surface even if the surface is anodized.
Since there are 100 or more magnetic disk devices for high-density recording, there is also a problem that accurate writing and reading cannot be performed due to this void defect, and a magnetic disk substrate material with few void defects is desired. It was

In addition to the alumite treatment, it has been proposed to subject the surface of an aluminum substrate to a Ni-P undercoat treatment by plating, but the production yield is poor due to void defects and uneven plating, and practical application is difficult.

[Object of the Invention]

The present invention has been completed in order to solve all of the above-mentioned difficulties, and its purpose is to prevent the substrate from being distorted by sputtering or heat treatment, and to apply the centrifugal force to the substrate to the substrate itself. It is another object of the present invention to provide a magnetic disk substrate capable of writing and reading suitable for high density magnetic recording without void defects on the surface of the substrate.

A further object of the present invention is to provide a manufacturing method for obtaining the above-mentioned excellent magnetic disk substrate.

[Means for solving problems]

According to the present invention, there is provided a zirconia magnetic disk substrate comprising a zirconia sintered body containing a stabilizer and unavoidable impurities and having an average void diameter of 1 μm or less.

Further, according to the present invention, a raw material containing zirconia as a main component and containing a stabilizer and unavoidable impurities is molded into a disk shape, and the green body is fired by HIP treatment to reduce the average void diameter to 1 μm or less. A method for manufacturing a magnetic disk substrate made of zirconia is provided.

Hereinafter, the present invention will be described in detail.

The magnetic disk substrate of the present invention reduces void defects such as those generated in an aluminum alloy substrate, and when manufacturing a zirconia (ZrO ₂ ) substrate, HIP (Hot Isostatic Pre)
ssing, hot isostatic pressing).

That is, as described below, the HIP-treated zirconia substrate had almost no voids, and even if voids were generated, the diameter was extremely small.

The inventor repeatedly performed an experiment and found that the average void diameter was 1 μm or less, and the production condition was set to be 0.
The diameter and the content of voids can be reduced to 5 μ or less, and further to 0.3 μ or less, even when compared with the HIP-treated alumina sintered body. This results in a high-density magnetic disk substrate that can be written and read accurately.

Zirconia (ZrO ₂ ) has a monoclinic tetragonal transition point of 10
The temperature is close to 00 ° C, and a sudden volume change occurs during this transition, which causes the sintered body to break.

In the present invention Y ₂ O _3, MgO, added per se known stabilizer such CeO _2, CaO in the base material, partially stabilized zirconia or stabilized by the formation of tetragonal solid solution during sintering As zirconia, it has improved mechanical strength such as transverse strength and toughness.

In particular, in partially stabilized zirconia, the toughness characteristics are remarkably improved by the martensitic transformation, and the bending strength is further improved as compared with the alumina sintered body.

Stabilizers such as Y ₂ O ₃ , MgO, CeO ₂ and CaO are generally 2 to 55 mol% per zirconia sintered body and an amount sufficient to partially stabilize or stabilize zirconia. Use alone or in combination. The specific amount used varies depending on the kind of the stabilizer, but is, for example, as follows. If the component ratio of Y ₂ O ₃ to the zirconia sintered body is in the range of 2 mol% or more and less than 9 mol%, it will be partially stabilized zirconia, and in the range of 9 to 55 mol%, it will be stabilized zirconia.

Also, the composition ratio of CaO to the zirconia sintered body is 8 to 12 m.
If it is in the range of ol%, it will be preferable partially stabilized zirconia, and in the range of 16 to 29 mol%, it will be stabilized zirconia.
If the composition ratio of MgO to the zirconia sintered body is in the range of 16 to 26 mol%, it will be a partially stabilized zirconia.

Furthermore, this zirconia sintered body was
One or more of O ₂ , Fe ₂ O ₃ , Na ₂ O, and HfO ₂ may be mixed as unavoidable impurities, but the maximum content of each is determined within the range that does not affect the zirconia characteristics of the magnetic disk substrate. To be

According to the zirconia sintered body of the present invention, in addition to the combination of zirconia and the stabilizer, a firing accelerator such as alumina or titania may be blended within a range that does not impair the effects of the present invention.

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

The ZrO ₂ raw material powder used in the present invention has a smaller primary average particle size, which is better, and 0.5 μ or less is preferable. Alternatively, zirconium hydroxide or the like may be changed to ZrO ₂ powder upon calcination.

Stabilizers have an average particle size of 2μ or less, preferably 1μ
The following should be used.

Furthermore, a stabilizer coprecipitated ZrO ₂ powder in which a predetermined amount of the stabilizer is added may be used, and when this powder is used, the stabilizer and the ZrO ₂ component are in a more densely and uniformly distributed mixed state,
It has an advantage that the crystal grain size of the sintered body is made uniform.

According to the present invention, the stabilizer is added to the ZrO ₂ powder as described above and mixed well to homogeneity.

This mixed powder is dried and granulated to form a disk, and pre-baked. This pre-baking is generally performed at a temperature of 1250 to 1600 ° C. for 1 to 4 hours. Next, the pre-sintered body is HIP processed. Pre-baking is not essential, and the disk-shaped molded body may be sealed and subjected to HIP treatment.

The HIP device is characterized in that it performs hydrostatic compression and heating at the same time, and can be roughly classified into a part for compressing an inert gas as a pressure medium, a high-pressure container containing a heating part, and a temperature / pressure control part. Of these, the gas pressure generation method is mechanical compression, and He, A, which is chemically stable as an inert gas, is used.
Use r.

The pre-baked body is placed inside the HIP device, and an inert gas is press-fitted therein and heated. At this time, generally, pressurization of 1500 to 2000 atm and heating to 1250 to 1600 ° C. are effective.

The HIP-treated zirconia substrate thus obtained is used as a magnetic disk substrate by using a polishing treatment means such as lapping and polishing.

〔Example〕

An organic binder of wax emulsion was added to ZrO ₂ powder containing ₃ mol% of Y ₂ O ₃ prepared by the coprecipitation method and sufficiently mixed, and then dried and granulated by a spray dryer.
Next, this powder was subjected to a hydraulic press (pressure 1.5 ton / cm ² ) to obtain a molded body which was a donut-shaped disc (outer diameter 180 mm, inner diameter 52 mm, thickness 4 mm). This compact was fired at a temperature of 1500 ° C. for 3 hours to obtain a disc-shaped fired product.

A plurality of the above-mentioned disc-shaped fired products were manufactured, and some of the fired products were HIP-treated to obtain two types of magnetic disk substrates depending on the presence or absence of the HIP treatment.

In both cases, polishing is performed in the order of lapping and polishing.
The final product has an outer diameter of 130 mm, an inner diameter of 40 mm, and a thickness of 1.9 mm, and has a flatness of 3μ, surface roughness of 0.01Ra, coaxiality of 10μ, and parallelism.
A 5.25 inch magnetic disk substrate with an accuracy of 10μ was obtained.

The area of the substrate thus obtained was measured using an image analyzer (Luzex 500) and a metallurgical microscope (400x).
As a result of examining the voids over 8.0 × 10 ⁵ μm ² , the results are shown in Table 1.

In Table 1, the equivalent circle diameter of the void represents the size of the diameter obtained by converting the areas of various shapes into areas corresponding to the circle.

As is clear from Table 1, the HIP-treated magnetic disk substrate of the present invention showed no voids of 0.3 μm or more.

〔The invention's effect〕

As described above, the magnetic disk substrate of the present invention has a size of 1 μm or more,
It is desirable to provide a magnetic disk substrate that eliminates voids of 0.5 μm or more and is suitable for high density recording of a thin film magnetic recording medium.

Since this substrate also has the following effects, it is apparent that it is more preferably a magnetic disk substrate.

Even if a small amount of magnetism is present in the periphery of the substrate other than the magnetic recording medium, it may cause signal loss and noise, but the substrate of the present invention is non-magnetic and enhances the reliability of the magnetic disk device.

With HIP treated zirconia substrate, Vickers hardness Hv is 1400k
Since it has a high hardness characteristic of g / mm ^2, it does not require alumite treatment or Ni-P undercoating unlike an aluminum substrate, and can directly form a magnetic recording medium by plating or sputtering. Thus, the manufacturing cost can be reduced.

Due to its high rigidity, the substrate itself is less likely to be deformed when it is processed, and even if it is rotated at a high speed of 3000 rpm or more, the elongation generated on the substrate itself due to the centrifugal force applied to the substrate itself is small. The head cannot follow the disk surface, which is greatly deformed when the disk is clamped or rotated, which causes signal disturbance or head crash, but this problem is completely eliminated.

Magnetic recording media tend to become thinner with higher density recording.
0.3μ or less is common. Even if such a thin film is directly formed on the zirconia substrate, it can withstand CSS (Contact-Start-Stop) up to tens of thousands of times with the head.

It is manufactured by ultra-precision machining and has excellent shape accuracy. By polishing the substrate surface, the center line average roughness (Ra) can be as low as 0.01μ or less, and as a result, it is formed by sputtering or plating. Moreover, even if the magnetic recording medium becomes extremely thin, the surface roughness of the substrate hardly causes unevenness on the surface of the recording medium, which is suitable for high-density magnetic recording.

With respect to an aluminum substrate such as an alumite-treated aluminum substrate which has been subjected to a surface treatment, crack generation due to a difference in thermal expansion coefficient between the alumite layer and the aluminum substrate has been a problem. It is one material, and such a problem does not occur.

Generally, when forming a magnetic recording medium by sputtering, it is possible to increase the film formation rate by increasing the substrate temperature during sputtering, and the heat treatment temperature after film formation is high when forming the γ-Fe ₂ O ₃ film. The one with better magnetic properties can be obtained, but the Ni-P-primed aluminum substrate is 280
This temperature is the limit because it exhibits magnetism above ℃, and the heat resistance limit of the alumite-treated substrate is about 350 ℃ at most. On the other hand, the substrate of the present invention is further excellent in heat resistance, and a magnetic recording medium having excellent magnetic characteristics can be formed by high speed film formation.

Since it is a substrate with excellent corrosion resistance, it can be cleaned using acid or alkali. Further, since it is a non-conductor, electrochemical corrosin does not occur between the metal magnetic medium and the substrate, noise and signal errors resulting from this can be eliminated, and long-term reliability can be improved.

Since a magnetic disk is required to have a very high degree of reliability, cracks or damage should never occur.
According to the substrate of the present invention, when partially stabilized zirconia is used, the toughness can be remarkably improved and the long-term reliability can be sufficiently satisfied.

Claims (2)

[Claims] 1. A magnetic disk substrate made of zirconia, comprising a zirconia sintered body containing a stabilizer and unavoidable impurities, and having an average void diameter of 1 μm or less. 2. A zirconia-based raw material containing a stabilizer and unavoidable impurities is molded into a disc shape, and the green body is fired by HIP treatment to reduce the average void diameter to 1 μm or less. A characteristic method for manufacturing a magnetic disk substrate made of zirconia.