JPH0756692B2 - Magnetic disk substrate and manufacturing method thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic disk substrate used for hard disks and flexible disks, and particularly to a magnetic disk substrate suitable for a metal continuous thin film type recording medium and a method for manufacturing the same. .

[Prior Art] Magnetic recording media using metal magnetic thin films typified by Co-Cr alloys and Co-Ni alloys are attracting attention as high-density recording media because of their high saturation magnetic density and surface smoothness. Practical application has been widely studied. In particular, Co-Cr, which has perpendicular magnetic recording characteristics, has a linear recording density of 200 KBPI. Co-Ni is also reported to have a linear recording density of 70 KBPI when used in a thin film horizontal magnetic recording medium of about 500 Å.

Each of the above magnetic recording media is far superior to the linear recording density of 15 to 20 KBPI of the γ-Fe ₂ O ₃ coating medium which has been widely put into practical use at present.

However, such a continuous thin film type recording medium having excellent magnetic recording characteristics has not been widely put into practical use at present. One of the factors that hinder practical application is the problem of the sliding characteristics between the magnetic head and the medium.

That is, since the surface of the metal continuous thin film type recording medium is smooth, in the case of a hard disk, the magnetic head crashes due to the adsorption of the magnetic head and the medium, and in the case of a flexible disk, the friction coefficient due to the difficulty of holding the lubricant is The magnetic head is apt to crash due to an increase in sliding.

In order to solve these problems, conventionally, a mechanical texture treatment, that is, a surface treatment for making line groove-like scratches on the substrate surface by sandpaper or the like has been attempted. Figure 13 is a differential interference micrograph showing the surface texture of the substrate after mechanical texture treatment (magnification 400x),
The figure shows 248 × 248 μm of the same tissue by laser interference type Asara meter
It is the perspective view which expanded the range of.

[Technical problem to be solved] Although this mechanical texture processing is effective to some extent, in a medium requiring a high recording density, bit errors increase due to the density (depth) of the texture (line groove) and mass production. It is difficult to control at the level. That is,
When the track width of magnetic recording is narrowed to about 10-20 μm,
If the width of the texture is not reduced to about one tenth, the modulation (variation in reproduction output when various recording currents are changed) exceeds 10%. Also, when the texture depression exceeds 200Å, the head output will decrease by 10% or more, and the modulation will increase. Even if a texture that meets these requirements is created, if the number of units per unit area is small, the sliding area of the magnetic head will be 0.5 m.
Since it is as large as mx 4 mm, it causes a problem of adsorption. Due to irregular irregularities such as burrs due to the mechanical texture, the head and the magnetic recording medium cannot be sufficiently close to each other, and it is difficult to increase the recording density due to spaceing loss. In particular, on a hard disk, irregular irregularities are generated as dust during CSS operation and adhere to the head and medium, causing a head crash.

The present invention has been made to solve the above problems, and the first invention is that the regularity of the pores of alumite, that is, the pore diameter and the pore spacing (cell diameter) are minute, and these and the pore distribution are Focusing on the uniformity, by utilizing the difference in the etching rate between the substrate and the material in the state where the material is filled in the pores of alumite, the etching process creates regular two-dimensional fine irregularities on the substrate surface. By doing so, it is intended to provide a substrate for obtaining a magnetic disk having sliding characteristics that does not cause a magnetic head crash.

The second invention is to provide a method for manufacturing a magnetic disk substrate having the above-mentioned fine irregularities on the surface.

[Problem Solving Means and Functions and Effects] A magnetic disk substrate according to the first invention comprises a substrate body, an alumite coating layer formed on the surface of the substrate body, and a filling material filled in the pores of the alumite coating layer. In the magnetic disk substrate having the above, the filling material is characterized in that a small amount is projected or a small amount is depressed from the surface of the alumite coating layer to form fine irregularities on the surface of the alumite coating layer.

Therefore, the diameter and spacing of each unevenness are equal to the diameter and spacing of the alumite pores, and the distribution is very uniform, and by setting the depth of the unevenness appropriately, the magnetic characteristics and friction coefficient suitable for the magnetic head can be improved. Therefore, it is possible to provide a magnetic disk having sliding characteristics that does not cause magnetic head crash.

The magnetic disk substrate manufacturing method according to the second invention, the pores of the alumite film formed on the surface of the substrate, a step of filling a filling material different in etching rate from the alumite coating, and the surface of the substrate filled with the filling material And polishing the surface of the polished substrate, until the filling material protrudes from the surface of the alumite coating,
Alternatively, it is characterized in that it comprises a step of etching treatment to form fine irregularities on the surface of the substrate until the depression.

In the second invention, the physical and chemical properties are different from those of the alumite coating on the substrate due to the coating process utilizing the electrodeposition process and heating / cooling in the pores of the porous alumite of the substrate, or the sputter process when the pore size is large. Materials such as Cu, Sn, Ni, Zn, NiO, resin, and Ni-Sn are deposited or permeated and filled. In this case, it is not always necessary to enter the bottom of the pore. In the case of the sputtering process or the coating process, the selected material is arbitrary. In the case of an organic coating agent containing oxide powder, after coating, reduction treatment may be performed to deposit metal (IBM Technical Disclosur
e Bulletin Vol.11 No.3 Known from issued in August 1968). The pore diameter and cell diameter can be freely controlled within the range of 100 to 400Å and 400 to 2000Å depending on the alumite treatment voltage and the pore dissolution treatment condition.

The substrate that has been subjected to the filling process is then polished to make the surface smooth and then subjected to an etching process. The etching method is preferably chemical etching, but may be a physical method such as sputtering. By this etching treatment, a texture structure composed of regular two-dimensional fine irregularities based on the pore distribution is formed on the substrate surface. Further, since the unevenness is not irregular unlike the mechanical texture processing and the surface is uniform, the noise level of the magnetic material is reduced to about one half.

The surface may be soft depending on the type of material filled in the pores. In this case, it is preferable to harden the surface by coating a hard film by electroless plating or sputtering. Since the hard film grows following the unevenness of the surface, the two-dimensional texture structure is retained.

A magnetic recording medium is completed by attaching a magnetic material to the surface of the substrate thus prepared by sputtering or plating and coating a protective film on the magnetic material.

It is advisable to hold the liquid lubricant on the irregularities of the surface, if necessary.

As described above, the method of the present invention utilizes the difference in the etching rate between the material filled in the pores of alumite and the substrate to form the unevenness due to the difference in the etching rate. It is extremely easy and mass production of a disk substrate of uniform quality is possible, and by attaching a magnetic material to the surface of this substrate, the problem of bit error due to texture processing does not occur.

[Embodiment] Next, an embodiment of the present invention will be described.

[Example I] (When the filling material is Cu) The thickness of the glass plate used as the substrate was 1 μm by vapor deposition.
m aluminum film is generated, and this substrate is applied voltage 48
Anodizing treatment is performed in a 3% V oxalic acid bath, and the pore size is 250
Å, After forming an alumite film with a cell diameter of 1100Å, electrolytically plating this substrate in a CuSO ₄ bath to deposit and fill Cu in the pores, and then use 0.8 μm diameter alumina powder on the surface of this substrate Then, the surface was smoothed by polishing for 5 minutes, and the alumite film thickness was adjusted to 0.5 μm.

Then, the substrate after the polishing was subjected to etching treatment. One of the substrates was chemically etched in a 4% NaOH solution so that the etching rate of alumite was higher than that of Cu. As a result, as shown in the surface structure of FIG. 1 (a), needle-like Cu was projected from the surface of the alumite Al to generate two-dimensional unevenness on the surface of the substrate.

FIG. 2 is a differential interference microscope photograph (400 ×) of the metal structure showing the surface condition of the substrate after the etching treatment. FIG. 3 is an enlarged perspective view of the same tissue in a range of 248 × 248 μm by a laser interference type roughness meter. By comparing with FIG. 13 and FIG. 14, it is understood that the difference in roughness is clear and how the unevenness of the substrate of the present invention is uniform.

The other substrate is sputter gas Ar and the degree of vacuum is 10 ^-3.
Under the conditions of Torr and applied voltage of 600 V, sputter etching treatment was performed so that the etching rate of Cu was larger than that of alumite. As a result, as shown in the surface structure of FIG. 1B, the upper end of the needle-shaped Cu was recessed from the surface of the alumite Al, and the same uniform two-dimensional unevenness was generated on the substrate surface.

Subsequently, the surface of the obtained substrate was coated with a magnetic material to form a magnetic disk, and the relationship between the uneven depth of the magnetic disk and the friction coefficient was examined. The magnetic material was coated under the following conditions.

Substrate temperature 130 ° C. Underlayer Cr 1,100Å Magnetic layer Co-Ni 600Å Protective layer C 200Å The results are shown in FIG. The magnetic head used for the measurement has a load of 15 g and a moving speed of 0.2 m / sec.

In the figure, the △ mark has an uneven depth of 200Å, the □ mark is 300Å,
The ◇ mark is a 500 Å substrate. 20 for a substrate with a depth of 100 Å
It was the same as the 0Å substrate. In the figure, the ones that have not been subjected to the etching treatment, that is, those that have no unevenness are also shown in contrast by the circles. The crosses indicate the depth of unevenness.
This is the case of a substrate that holds a liquid lubricant on the surface of a 200Å object.

As a result of such a measurement, it was found that the one having an uneven depth of 50 to 5000 Å exhibited a friction coefficient within an allowable range.

Further, with respect to the magnetic disk obtained as described above, changes in friction coefficient depending on environmental conditions were measured by a high humidity standing test and a high temperature rotation test.

In the high humidity storage test, two types of substrates, each having a surface with a 200 Å carbon coat and an uneven depth of 100 Å and 300 Å, were used. The results of this test are shown in FIG. 5, and the friction coefficient changes very little under normal use conditions.

The high-temperature rotation test uses a magnetic disk with an uneven depth of 200 Å and 200 Å with a carbon coat.
Performed at 3600 rpm. The results of this test are as shown in FIG. 6, and it can be seen that the coefficient of friction is low and very stable regardless of the number of days left.

[Example II] (When the filling material is Ni) An aluminum film having a thickness of 1 μm is formed on the surface of a glass plate as a substrate by vapor deposition, and this substrate is anodized in an oxalic acid 3% bath with an applied voltage of 48 V. Done, film thickness 0.5μ,
After forming an alumite film with a pore diameter of 250Å and a cell diameter of 1100Å, this substrate is electrodeposited in NiSO ₄ 30 g / solution until Ni overflows from the pores in the bath, and then the surface of this substrate is 0.3 μm in diameter. The surface was smoothed by polishing with alumina powder of No. 3 until the film thickness became 0.3 μm.

Then, the substrate after the above polishing is mixed with 10% phosphoric chromic acid mixed solution.
A chemical etching treatment was performed in the solution. As a result, unevenness depths of 100 Å, 200 Å, 300 Å, 500 on the substrate surface
Two-dimensional unevenness of Å was generated.

A magnetic material was sputtered on the substrate after the etching treatment under the following conditions.

Substrate temperature 150 ℃ Underlayer Cr 1,000 Å Magnetic layer Co-Ni 600 Å Protective layer C 200 Å Figure 7 is an electron micrograph of the metallographic structure showing the surface condition of the substrate after the pores were filled with Ni and then subjected to chemical etching. FIG. 8 is an electron micrograph (tilt angle 70 °) of a state in which a magnetic material was sputtered on the same substrate and a carbon protective layer was applied on the same substrate (tilt angle 70 °).

[Example III] (When the filling material is Sn) An Al-4% Mg alloy was used as a substrate, and this substrate was applied with an applied voltage.
Anodizing treatment is performed in a 48 V oxalic acid 3% bath to obtain a film thickness of 10
After forming an alumite film with μm, pore diameter 250 Å, cell diameter 1100 Å, this substrate is SnSO ₄ 30 g / solution
Electrodeposited and filled until n overflows, and then the surface of this substrate is polished using alumina powder of 0.3 μm diameter as primary polishing until the film thickness becomes 10 μ, and subsequently silica powder of 0.1 μm diameter is used as secondary polishing. Was used to smooth the surface by polishing the film thickness from 7 μ to 6 μ.

Then, the substrate after the above polishing is mixed with 10% phosphoric chromic acid mixed solution.
Chemical etching is performed in the solution, and two-dimensional unevenness with unevenness depths of 100Å, 200Å, 300Å, 500Å is generated on the substrate surface as in Example II, depending on the immersion time. did.

A magnetic material was sputtered on the substrate after the etching treatment under the following conditions.

Substrate temperature 100 ° C Underlayer Cr 1,000Å Magnetic layer Co-Ni 600Å Protective layer C 200Å Fig. 9 is an electron micrograph of the same substrate with a magnetic material sputtered and a carbon protective layer applied (tilt angle 70 °). Is.

[Example IV] (when the filling material is Teflon) An Al-4% Mg alloy substrate was anodized in a 3% oxalic acid bath with an applied voltage of 48 V to obtain a film thickness of 10 µm, a pore diameter of 250 Å,
After forming an alumite film with a cell diameter of 1100Å, immerse this substrate in a H ₃ PO ₄ 1% solution for 10 minutes to perform pore expansion treatment to obtain a pore diameter of 600Å and a cell diameter of 1,100Å, and melt this at 350 ° C. Dip in Teflon, fill the pores with Teflon by heat infiltration treatment, and after this Teflon coating, polish the surface of this substrate with alumina powder of 0.3 μm diameter until the film thickness becomes 0.5 μm. The surface was smoothed.

Then, the substrate after the above polishing is treated with 3% phosphoric acid chromic acid mixed solution.
A chemical etching treatment was performed in the solution. This allows
As in the case of Example II, the unevenness on the substrate surface was
Two-dimensional unevenness of 100Å, 200Å, 300Å, 500Å was generated.

A magnetic material was sputtered on the substrate after the above etching treatment under the same conditions as in the previous example.

[Example V] (When the filling material is an acrylic resin) An Al-4% Mg alloy substrate was anodized in an oxalic acid 3% bath with an applied voltage of 48 V to obtain a film thickness of 9 μm and a pore diameter of 250 Å.
After forming an alumite film with a cell diameter of 1100 Å, immerse this substrate in H ₃ PO ₄ 1% solution for 10 minutes to make a pore diameter of 600 Å and a cell diameter of 1,100 Å, which is a water-soluble acrylic resin with a solid content of 20%. Soak for 1 minute, drain for 3 minutes, apply dip coating, and bake for 10 minutes at 180 ° C. Then, coat the surface of this substrate with a 0.3 μm diameter alumina powder. Polishing was performed until the thickness became 8 μm.

Then, the polished substrate is treated with a phosphoric chromic acid mixed solution (5:
5) Chemical etching was performed in a 10% solution, and the depth of the unevenness was 100 and 20 respectively on the substrate surface as in Example II.
Two-dimensional unevenness of 0,300,500Å was generated.

A magnetic material was sputtered on the substrate after the etching treatment under the same conditions as in Example III. However, the substrate temperature is 130
It is ゜.

[Example VII] (In the case of filling by reduction treatment) An Al-4% Mg alloy substrate was anodized in a 3% oxalic acid bath with an applied voltage of 48 V to obtain a film thickness of 10 μm, a pore diameter of 250 Å,
After forming an alumite film with a cell diameter of 1100 Å, immerse this substrate in a H ₃ PO ₄ 1% solution for 10 minutes to obtain a pore diameter of 850 Å and a cell diameter of 1,100 Å, on which Nicl ₂ 600 g, H ₂ O 1000 cc, Dextr
After applying in30 g of the coating material, heat reduction treatment was performed in H _{2 at} 450 ° C. for 10 minutes, and then the surface of this substrate was polished with alumina powder having a diameter of 0.1 μm until the film thickness became 9 μm.

Then, the polished substrate is treated with a phosphoric chromic acid mixed solution (5:
5) Chemical etching was performed in a 10% solution to form two-dimensional unevenness with unevenness depths of 100, 200, 300, 500Å.

A magnetic material was sputtered on the substrate after the etching treatment under the same conditions as in Example VI.

The magnetic disk substrates obtained in the above Examples II to VII were tested for the relationship between the uneven depth and the friction coefficient, and the friction coefficient was changed according to the environmental conditions by the high humidity standing test and the high temperature rotation test. When measured under the same conditions as in Example I, almost the same results as in Example I were obtained.

Next, a recording / reproducing characteristic test was conducted on the magnetic recording media obtained in each of the above examples.

FIGS. 10A to 10C show the magnetic disk (horizontal magnetized film of the filling Ni and the magnetic material Co--Ni) of Example II for the Mn-Zn monolithic magnetic head (product code) manufactured by Matsushita Electric Industrial Co., Ltd. The measurement results when using M556 (head gap 0.5μm, track width 15μm, flying height 0.1μ
m).

FIG. 10A shows the relationship between the current applied to the magnetic head when recording on the medium at 2.5 MHz and 5 MHz, the output voltage obtained on the magnetic head when reproducing the medium, and the output attenuation at the time of overwriting. It is a recording / reproducing characteristic figure. In any recording wavelength, a stable head output can be obtained regardless of the recording current.

FIG. 10B is an output waveform diagram showing the fluctuation state of the maximum value and the minimum value of the head output.

FIG. 10C is a frequency characteristic diagram showing the relationship between the head output and the recording frequency. The output value is almost constant from 100 KHz to 2 MHz, and about 20 mV can be obtained even at 5 MHz. The numbers in the recording density column mean the recording densities corresponding to the upper frequencies.

11A to 11C show the product code M515 for the magnetic disk (filler Sn, magnetic body Co--Ni) according to Example III.
10A to 10C respectively when measured under the same measurement conditions using the magnetic head of FIG.

As is clear from comparing FIG. 11B with FIG. 10B, Ni was used as the filling material, and a horizontal magnetic layer of Co--Ni or Co--Cr was used as the magnetic material to weaken the magnetic coupling. Although the output is somewhat lowered, the head output is hardly changed (modulated) regardless of the magnitude of the recording current, and high stability can be obtained. It is presumed that this is due to the interaction between the lower perpendicular magnetic film and the upper horizontal magnetic film of the substrate.

Furthermore, the result of the signal-to-noise test of the magnetic disk obtained by the chemical texture method according to the present invention was compared with the result of the signal-to-noise test of the conventional mechanical texture method. FIG. 12A shows the test results of the magnetic disk according to the present invention, and FIG. 12B shows the test results of the conventional product. Line B in the figure
N is the background noise of the test equipment, line S is the signal, and the area between BN and S shows the magnitude of the noise. Therefore, it is understood that the use of the magnetic disk substrate according to the present invention reduces noise by half compared with the conventional product.

The following conclusions were obtained as a result of the chemical texture treatment with the above various materials.

The mechanical properties of the magnetic disk (friction coefficient, humidity test, lubricity) are determined by the texture depth.

b. When a magnetic material (Ni) is used as the filling material for the pores and the upper magnetic body is horizontally magnetized, the modulation becomes small due to the interaction between the lower vertically magnetized layer and the upper horizontally magnetized layer.

These measurement results show that the magnetic disk substrate and the manufacturing method thereof according to the present invention are capable of controlled texture processing and have desired sliding characteristics, unlike conventional mechanical textures. , Its industrial effect is extremely large.

[Brief description of drawings]

FIG. 1 is a partially enlarged cross-sectional view showing a surface structure of a substrate according to the present invention after etching treatment, and FIG. 2 is a differential interference microscope photograph of a metal structure showing a surface state of the substrate after etching treatment, FIG. Is an enlarged perspective view of the surface texture of the substrate by a laser interference type roughness meter, FIG. 4 is a graph showing the relationship between various uneven depths of the substrate surface and the friction coefficient, and FIGS. 5 and 6 are the friction coefficient depending on environmental conditions. 5 is a graph showing changes, FIG. 5 shows the result of a high humidity storage test, and FIG. 6 shows the result of a high temperature rotation test. Fig. 7 is an electron micrograph of the metal structure showing the surface condition of the substrate after Ni filling and chemical etching treatment, and Fig. 8 shows the surface condition of the substrate after magnetic sputtering and carbon protective layer coating on the same substrate. The electron micrograph of the metal structure shown in FIG. 9 is an electron micrograph of the metal structure showing the surface condition of the substrate after Sn filling, etching treatment, magnetic sputtering and carbon coating. 10A to 10C show the recording / reproducing characteristics of the magnetic disk according to one embodiment, FIG. 10A is a recording / reproducing characteristic diagram, FIG. 10B is an output waveform diagram, and FIG. 10C is a frequency characteristic diagram.
11A to 11C are graphs showing similar recording / reproducing characteristics of magnetic disks according to other examples. 12A and 12B are graphs showing the results of the signal-to-noise test of the magnetic disk of the present invention and the conventional product, respectively. FIG. 13 is a differential interference microscope photograph of a metal structure showing a surface state of a substrate by a conventional mechanical texture, and FIG. 14 is an enlarged perspective view of the surface structure of the substrate by a laser interference type roughness meter.

Claims (6)

[Claims] 1. A magnetic disk substrate having a substrate body, an alumite coating layer formed on the surface of the substrate body, and a filling material filled in the pores of the alumite coating layer, wherein the filling material is the A magnetic disk substrate, wherein minute protrusions or recesses are formed on the surface of the alumite coating layer to form minute irregularities on the surface of the alumite coating layer. 2. The magnetic disk substrate according to claim 1, wherein the depth of the unevenness on the surface is 50 to 5000 Å. 3. The magnetic disk substrate according to claim 1 or 2, wherein a magnetic material is used as a material filled in the pores. 4. A magnetic disk substrate according to claim 1 or 2, wherein a non-magnetic material is used as a material filled in the pores. 5. A magnetic disk substrate according to claim 1, wherein the surface of the substrate is coated with a hard material. 6. A method of manufacturing a magnetic disk substrate comprising the following steps. a. A step of filling the pores of the alumite film formed on the surface of the substrate with a filling material having an etching rate different from that of the alumite film. b. A step of polishing the surface of the substrate filled with the filling material to make the surface smooth. c. A step of etching the polished substrate until the filling material protrudes from the surface of the alumite coating or forms a recess, to form fine irregularities on the surface of the substrate.