JPH11134630A - Substrate for magnetic disk and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the breakage and deformation of a substrate for a magnetic disk even if the substrate is thinned and to attain high magnetic recording density by using ceramics having a specified Young's modules, a specified deflective strength and a specified average void diameter. SOLUTION: Stock power for ceramics having >=30 GPa Young's modulus, >=700 MPa deflective strength and <=0.3 μm average void diameter is compacted in a prescribed shape by centrifugal compacting. Since the stock powder can be filled to the closest state, a sintered compact having very small voids is obtd. without carrying out any special treatment. When a substrate 1 for a magnetic disk is formed from the ceramics, high density recording is enabled and the deformation and breakage of the substrate 1 are not caused because of high rigidity and high strength of the ceramics even if the substrate 1 is thinned. Since the stock powder can be filled to the closest state, sinterability is improved, firing temp. is lowered and the grain diameter of the sintered compact is reduced. The amt. of a grain boundary phase existing at grain boundaries can be made very small.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a substrate for a magnetic disk used as a medium in a magnetic recording apparatus and a method for manufacturing the same.

[0002]

2. Description of the Related Art Among external storage devices of a computer, a magnetic disk device occupies a central position as a large-capacity, high-speed, random-access memory. Also,
Like the LSI, the magnetic disk device has also been increased in capacity and density, and more specifically, the recording density has been improved by about 60% per year.

This magnetic disk device is composed of a magnetic disk having a magnetic film as a magnetic recording layer formed on a substrate, and a magnetic head for slightly recording and reproducing information on the magnetic disk. .

[0004] With the increase in the recording density, the flying height of the magnetic head must be reduced. In order to reduce the flying height and achieve stable flying, a magnetic disk substrate processed with high shape accuracy and dimensional accuracy is indispensable.

The characteristics required of such a magnetic disk substrate for high recording density include non-magnetic properties, durability against deformation and distortion during high-speed rotation (3600 to 10000 rpm), high strength and high strength. It has toughness, no void defects, high hardness, low thermal expansion coefficient, physical and chemical stability and durability that do not impair the function during the manufacturing and use process of magnetic disks. Corrosion resistance, required shape accuracy,
That surface accuracy can be ensured.

In response to these requirements, Ni-P plated aluminum alloys are generally used as magnetic disk substrates currently used, and glass and the like are also used. The applicant of the present application has already proposed the use of various ceramics as a material for the magnetic disk substrate (Japanese Patent Publication Nos. 6-22055 and 7-4035).
0, Japanese Patent Publication No. 6-101115, etc.).

[0007]

However, the magnetic disk substrates made of the above-mentioned various materials have not completely satisfied the above-mentioned required characteristics.

For example, a substrate made of an aluminum alloy or glass has a problem that hardness, rigidity and heat resistance are low. That is, since the Vickers hardness of the aluminum alloy or glass is as low as about 4 to 7 GPa, there is an inconvenience that the substrate is easily damaged or deformed when it comes into contact with the magnetic head during use or carrying. In addition, it is necessary to make the substrate thinner with the increase in recording density, but aluminum alloy or glass has low rigidity, so it is easily deformed during processing, mounting, or use of the substrate, and is suitable for high-density recording. There was a disadvantage that accurate data processing could not be performed. Further, the film formation temperature of the magnetic film is increased to increase the capacity of the magnetic recording layer. Some of the films are formed at a temperature exceeding 600 ° C., such as a granular film. Not applicable due to heat resistance.

On the other hand, in a magnetic disk substrate made of ceramics, it is inevitable that voids are generated as internal defects, and it cannot be used as a substrate as it is. In order to eliminate this void, hot isostatic pressing (HI
P) Although a treatment or the like can be performed, there is a problem that the manufacturing process is troublesome. Although a glaze layer can be formed on the ceramic surface, there is a problem that hardness, strength and heat resistance are reduced.

[0010] Further, since ceramics generally have lower strength than metal materials, there is a problem that the substrate is easily broken when the substrate is made thinner. In this regard, ceramics having high strength, such as zirconia ceramics, have a low Young's modulus and are therefore easily deformed. As described above, the ceramic magnetic disk substrate could not satisfy both the strength and the rigidity.

[0011]

SUMMARY OF THE INVENTION Accordingly, the present invention is directed to a method of molding a ceramic material powder by centrifugal force generated by injecting a slurry in which ceramic material powder is dispersed into a mold having a predetermined shape and rotating the mold. The method is characterized in that a substrate for a magnetic disk is manufactured from a step of molding the obtained molded body and firing the obtained molded body.

That is, by forming the ceramic raw material into a predetermined shape by using centrifugal force (hereinafter, referred to as centrifugal forming), the raw material powder can be packed most closely, and the density of the formed body can be increased. As a result, without any special processing,
A sintered body with extremely small voids can be obtained. In addition, since the sinterability can be improved by being able to close-pack the raw material powder, the firing temperature can be reduced to reduce the crystal grain size, and the existence of the grain boundary phase in the crystal grain boundaries can be extremely reduced. As a result, a sintered body having high mechanical properties such as strength and rigidity can be obtained.

Therefore, it is possible to solve all the problems of voids, rigidity, and strength described above as problems of the ceramic magnetic disk substrate.

According to the above-mentioned production method, the present invention provides a resin having a Young's modulus of 300 GPa or more and a flexural strength of 700 MPa or more.
The magnetic disk substrate has an average void diameter of 0.3 μm or less.

That is, by performing the above-described centrifugal molding, it is possible to obtain a ceramic having both high strength and high rigidity. In particular, ceramics having a Young's modulus of 300 GPa or more and a bending strength of 700 MPa or more can be obtained for the first time by a centrifugal molding method, and satisfying such characteristics can be suitably used as a magnetic disk substrate.

In addition, the centrifugal molding method makes it possible to make the void extremely small without performing special treatment. In particular, when the average void diameter is 0.3 μm or less, it can be suitably used as a substrate for a magnetic disk.

[0017]

Embodiments of the present invention will be described below.

As shown in FIG. 1, a substrate 1 for a magnetic disk is a disk-shaped body having a through hole 1a in the center, and various magnetic films are formed on a main surface 1b to form a magnetic recording layer. A magnetic disk substrate is used. Then, a magnetic head is arranged so as to float slightly from the magnetic recording layer of the magnetic disk substrate, and information is recorded / reproduced from the magnetic head to constitute a magnetic recording apparatus.

The substrate 1 is formed of a ceramic such as alumina. In general, the ceramic substrate 1 is excellent in nonmagnetic properties, hardness, heat resistance, corrosion resistance, rigidity, and the like, but has a problem that it has many voids and low strength. Therefore, in the present invention, the substrate 1 is manufactured using a centrifugal molding method.

In this centrifugal molding method, as shown in FIG. 2 (a), a ceramic raw material powder is dispersed in a solvent such as water, and the obtained slurry 21 is poured into a molding die 20, and then, in a direction indicated by an arrow in FIG. The mold 20 is rotated so that a centrifugal force is applied. Then, as shown in FIG. 2B, the ceramic raw material powder and the solvent in the slurry 21 are centrifuged, and the ceramic raw material powder is settled and deposited at the lower part of the molding die 20 to form a molded body 22, and the solvent is molded. The supernatant liquid 23 is formed on the upper part of the mold 20. Then, after the rotation is stopped, the supernatant liquid 23 is removed as shown in FIG. 2C, and the remaining molded body 22 is taken out, whereby the molded body 20 can be molded into a shape conforming to the shape of the molding die 20. .

According to such a centrifugal molding method, the ceramic raw material can be packed most closely, and an extremely dense molded body 22 can be obtained. Therefore, a sintered body having a very small void diameter can be obtained without performing any special treatment only by firing under predetermined conditions.

In addition, sinterability can be improved by being able to close-pack the ceramic raw material. As a result, the firing temperature can be lowered to reduce the crystal grain size, and the sintering aid component can be reduced, so that the grain boundary phase of the crystal grain boundaries can be extremely reduced. As described above, by reducing the crystal grain size and the grain boundary phase, mechanical properties such as strength and rigidity can be improved, and ceramics having high rigidity and strength that cannot be obtained by the conventional method can be obtained. Obtainable.

Further, in the present invention, ceramics having such excellent characteristics can be obtained by simply baking them under normal pressure after centrifugal molding, and there is no need to perform special treatment such as HIP. It can be simplified. It goes without saying that voids can be further reduced by performing an HIP treatment after the above-mentioned firing.

For example, general alumina ceramics have a firing temperature of 1500 to 1750 ° C., a large average crystal grain size of 2 to 15 μm, a void size of about 0.5 to 10 μm, and a transverse rupture strength of 200 to 400 MPa. It is low.

On the other hand, in the present invention, when the raw material powder has an Al ₂ O ₃ content of 99.9% by weight or more, the powder has an average particle size (measured by a microtrack method) of 0.1 to 0.1%
Using the 0.5 μm high-purity fine powder raw material, molding was performed by the centrifugal molding method described above. The obtained molded body is 1200 to 1300
The sintered body obtained has an extremely small temperature of 0.5 to 1.0 μm and has an average void diameter of 0.3 μm or less. It was extremely small, had a Young's modulus representing rigidity of 300 GPa or more, and a transverse rupture strength of 700 MPa or more, exhibiting excellent mechanical properties. It should be noted that ceramics having a Young's modulus of 300 GPa or more and a flexural strength of 700 MPa or more have not heretofore been obtained, but are first obtained by centrifugal molding.

Therefore, when the substrate 1 for a magnetic disk is formed from the ceramics obtained in this way, high density recording is possible due to extremely small voids, and the substrate 1 has high rigidity and strength. Can be prevented from being deformed or damaged.

Moreover, in the present invention, the ceramic magnetic disk substrate 1 having such excellent characteristics can be obtained only by baking at normal pressure after centrifugal molding, and it is necessary to perform a special treatment such as HIP. Therefore, the manufacturing process can be simplified.

Although the above description has been made using alumina ceramics as an example, the same applies to other ceramics such as zirconia, silicon carbide and silicon nitride.

[0029]

Next, embodiments of the present invention will be described.

The raw material powder has an Al ₂ O ₃ content of 9
A ceramic raw material of 9.99% by weight, the balance being unavoidable impurities, having an average particle size of 0.2 μm and a particle size distribution in the range of 0.15 to 0.3 μm was prepared. A slurry was prepared by adding 30% of water and 1% of a dispersing agent, and mixing them in a pot mill for 24 hours.

As shown in FIG. 2, after this slurry 21 is poured into a molding die 20, the molding die 20 is set on a rotor (not shown) in a centrifuge, and the rotor is rotated to 15000.
A centrifugal acceleration of G was applied. As a result, the ceramic particles in the slurry 21 settled down at the bottom of the mold 20 by the centrifugal action and solidified to form a compact 22. At this time, the air in the slurry 21 was effectively exhausted to the outside, and the ceramic particles were closest packed by centrifugal force, so that a very high-density compact 22 was obtained.

In this case, the centrifugal acceleration is set to 15,000 G.
However, it was found that centrifugal molding can be effectively performed at 5000 G or more. However, in order to shorten the molding time, it is preferable to set the centrifugal acceleration high.

The molded body 22 obtained in this manner is taken out of the molding die 20, and the molded body 22 is prepared using a Kanthal super furnace.
It was fired at 30 to 1280 ° C. to obtain a sintered body. A 3 × 4 × 35 mm test piece was cut out from the sintered body obtained here,
A three-point bending test was performed according to JIS rules to measure the bending strength, and the Young's modulus was measured by an ultrasonic pulse method, and other characteristics were measured in the same manner. Further, the average crystal grain size was measured by a cord method.

The results are shown in Table 1 in comparison with comparative examples of glass, aluminum alloy and conventional alumina ceramics.

From these results, the alumina ceramic of the present invention has a small average crystal grain size of 0.6 to 0.7 μm, a Young's modulus of 400 GPa, a transverse rupture strength of 700 MPa or more,
A maximum of 1200 MPa or more, which was extremely high in rigidity and strength as compared with the comparative example, was obtained.

As described above, the flexural strength of the present invention refers to a three-point bending strength of a test piece based on JIS rules. May be cut out and subjected to a bending test. When a test piece having the above dimensions cannot be cut out from the substrate 1, a bending test can be performed using a test piece cut into a predetermined shape, and the value can be converted by a known method.

[0037]

[Table 1]

Next, the sintered body obtained above was ground and processed into the shape of a substrate 1 having a diameter of 25.4 mm and a thickness of 0.3 mm, followed by polishing to obtain a final product. For this substrate 1, a scanning electron microscope (SEM:
(1500 times, 10000 times), the diameter and the number of voids were measured over a measurement area of 540 μm ² at arbitrary several places.

As a comparative example, the same measurement was performed on the substrate 1 made of the conventional easily sinterable alumina. In addition, in the comparative example, since the void was large, the magnification was set to 1500 times, so that a void of less than 0.3 μm could not be measured.

As shown in Table 2, the comparative example had many voids exceeding 0.3 μm which were regarded as fatal defects, whereas the substrate 1 of the present invention had voids exceeding 0.3 μm. Did not exist.

[0041]

[Table 2]

[0042]

As described above, according to the present invention, a ceramic material having a Young's modulus of 300 GPa or more, a flexural strength of 700 MPa or more, and an average void diameter of 0.3 μm or less is formed by forming a ceramic material by centrifugal molding. A disk substrate can be obtained by a simple process, and a magnetic disk substrate capable of further increasing the magnetic recording density without a risk of breakage or deformation even when the substrate is thinned can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a magnetic disk substrate of the present invention.

FIGS. 2A to 2C are views for explaining a method of manufacturing a magnetic disk substrate according to the present invention.

[Explanation of symbols]

 1: substrate 11: through hole 12: main surface 20: molding die 21: slurry 22: molded body 23: supernatant

Claims (2)

[Claims] (1) a Young's modulus of 300 GPa or more and a bending strength of 70
A magnetic disk substrate comprising a ceramic having a pressure of 0 MPa or more and an average void diameter of 0.3 μm or less. 2. A slurry in which the ceramic raw material powder is dispersed is poured into a molding die having a predetermined shape, and the ceramic raw material powder is molded by centrifugal force generated by rotating the molding die. A method for manufacturing a magnetic disk substrate, comprising a step of firing.