JPH11219520A - Production of magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for producing a magnetic recording medium having the high intra-surface uniformity of an electrolysis quantity. SOLUTION: The process for producing the magnetic recording medium having a stage for subjecting the surface of a substrate or medium to an electrolysis treatment is characterized in that the electrolysis described above is executed by using a pair of approximately disk-shaped terminal electrodes 20 disposed to face the surface of the substrate 21 or medium on the side not facing the other substrate or medium and the bore of the terminal electrodes 20 is larger than the bore of the substrate 2 or the medium and the outside diameter is smaller than the outside diameter of the substrate 2 or the medium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for manufacturing a magnetic recording medium. More specifically, the present invention relates to a method for manufacturing a magnetic recording medium having excellent flying characteristics, lubricity, and abrasion resistance by improving the surface characteristics of the magnetic recording medium by performing a surface processing treatment.

[0002]

2. Description of the Related Art In recent years, with the development of information processing technology such as computers, magnetic recording media such as magnetic disks have been used as external storage devices. Conventionally, as a magnetic recording medium, an alumite treatment or Ni
A non-magnetic substrate that has been subjected to a non-magnetic plating process such as -P plating is coated with a base layer such as Cr, then coated with a magnetic thin film layer of a Co-based alloy, and further coated with a carbonaceous protective film. in use.

In the above-mentioned magnetic recording medium (hereinafter referred to as a magnetic disk), the distance between the magnetic disk and the magnetic head, that is, the flying height of the head is becoming smaller and smaller in recent years. It has become. With such a small flying height, if a protrusion exists on the surface of the magnetic disk, there is a possibility that a head crash may sometimes occur and the disk surface may be damaged. Also, the presence of minute projections that do not lead to a head crash can cause various errors when reading and writing information.

On the other hand, magnetic disks are being miniaturized in parallel with their large capacity and high density, and drive motors for rotating spindles are becoming increasingly smaller. For this reason, the torque of the drive motor may be insufficient, and a phenomenon that the magnetic head does not fly while fixed to the magnetic disk surface is likely to occur. Conventionally, in order to prevent the magnetic head from crashing or sticking, a surface processing (hereinafter referred to as texture processing) for forming fine grooves on the disk surface after polishing the surface of the magnetic disk has been conventionally performed. Is being done. Texture processing is particularly effective in reducing the contact resistance between the magnetic head and the surface of the magnetic disk.

As described above, although the flying characteristics of the head in a magnetic disk have been improved by texture processing, the performance required of the magnetic disk has not yet been sufficiently met. Incidentally, Japanese Patent Application Laid-Open No. Hei 4-95221 proposes a surface treatment technique for cleaning a magnetic disk and performing chemical etching subsequent to texture processing in order to meet the above demand.

However, in the treatment by chemical etching, it is generally difficult to control the surface state accurately by selecting the etching conditions, and there is a problem that the surface after etching tends to be non-uniform.

The present applicants have conducted intensive studies to further improve the flying characteristics of the head on the magnetic disk. As a result, after subjecting the substrate surface to texturing, the substrate surface is subjected to electrolytic treatment (electrolytic treatment). They have found that the surface is improved, and have proposed this in JP-A-7-225945 and JP-A-8-171719, respectively.

[0008]

However, when these methods are carried out industrially, there are problems to be solved. That is, the former (JP-A-7-225)
No. 945) is a method in which a DC potential is applied to the electrolytic treatment. When the counter electrode is disposed on both sides of the substrate, the cost of the electrode is increased when the method is carried out on an industrial scale, and the treatment efficiency is not necessarily improved. There is a situation that is not good. Further, the latter method (Japanese Patent Laid-Open No. Hei 8-171719) is to improve the former problem. In the method, an AC potential is applied to the electrolytic treatment, and the substrates are used as opposite electrodes. Although only one side of the substrate can be subjected to electrolytic treatment, it is conceivable to use the substrates at both ends in reverse each time, but the operation is complicated and not always advantageous.

It is also conceivable to use the substrates at both ends as terminal electrodes, but they need to be replaced frequently because the thickness of the underlying Ni-P plating layer is thin, which complicates the operation and causes loss of the substrate. It is not an advantageous method from the point of view. On the other hand, when a counter electrode proposed in the former, for example, a stainless steel electrode is used as a terminal electrode, Ni-P
Due to the difference in electrical resistance between the layer and the stainless steel, current does not easily flow through the stainless steel electrode, which results in insufficient electrolytic etching of the conductive substrate at both ends facing the stainless steel electrode. Can not.

Further, when a Ni metal having an electric resistance close to that of the Ni-P layer of the substrate is used as the terminal electrode, electrolytic etching of the substrate surface facing the Ni electrode is performed in the same manner as other substrates. It has been found that there is a problem that the substrate surface is contaminated by electrolytic etching of the Ni electrode itself. In view of the above situation, the present invention provides a method for manufacturing a magnetic recording medium that can be implemented on an industrial scale and at a low cost while obtaining a good quality substrate surface for post-processing the texture processing of the substrate of the magnetic recording medium. The aim is to provide a method.

[0011]

Means for Solving the Problems In the manufacture of the above-mentioned magnetic recording medium, the present inventors have made intensive studies to solve the problems in performing electrolytic treatment of a substrate after texture processing on an industrial scale. As a result of the superposition, the above-mentioned problems are improved by using a specific shape as the above-mentioned terminal electrode,
The inventors have found that the above objects can be achieved, and have completed the present invention.

That is, the gist of the present invention is to provide a method for manufacturing a magnetic recording medium having a step of electrolyzing the surface of a substrate or a medium, wherein the electrolysis is not performed on another substrate or medium of the substrate or the medium. Performed using a pair of substantially disc-shaped terminal electrodes provided so as to face the surface, and the inner diameter of the terminal electrode is larger than the inner diameter of the substrate or medium, and the outer diameter is smaller than the outer diameter of the substrate or medium. A method for manufacturing a magnetic recording medium is characterized in that:

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail based on preferred embodiments. The substrate of the magnetic recording medium in the present invention is not particularly limited, and a known material such as an aluminum alloy, glass, and carbon can be used. However, at the time of performing the electrolytic treatment, the substrate surface needs to be covered with a conductor such as a metal film. Currently N on the surface
Since a substrate obtained by electroless plating an i-P alloy or a Ni-Cu-P alloy is widely used, a case in which this substrate is used will be described in detail below.

Before forming a metal thin film such as a magnetic layer, the plating layer is subjected to surface processing to form a surface processed layer finished to a specific surface roughness. As the surface processing, first, for example, the surface layer is polished, and then the texture processing is performed.

Here, the polishing is carried out, for example, by sandwiching the substrate between polishing pads having free abrasive grains adhered to the surface and impregnating the polishing pad, while supplying a polishing liquid such as a surfactant aqueous solution. Usually, a polishing process of about 2 to 5 μm is performed to make the surface of the substrate have an average surface roughness Ra.
Is less than 50 ° (angstrom), preferably 30 °
Mirror finish below. As the loose abrasive, typically, an alumina slurry polyplastic 700 or polyplastic 1 is used.
03 (both are registered trademarks of Fujimi Incorporated), diamond-based slurries, SiC-based slurries, and the like. As a polish pad, typically,
Urethane foams such as Surfin 100 and SurfinXXX-5 (both are registered trademarks of Fujimi Incorporated) are used.

As texture processing, for example,
Using a polishing tape carrying alumina abrasive grains of about 2,500 to 6000 #, the polishing tape is pressed against the polished substrate surface by a processing roller, and the average surface roughness in the circumferential direction of the substrate is obtained. Ra is 20 ° or more, preferably 30 to 300 °, and more preferably 50 to 15 °. Fine grooves or irregularities are formed with high precision. By this texture processing, a gap between the magnetic head and the magnetic recording medium is formed. Adsorption can be prevented, CSS characteristics are improved, and the magnetic anisotropy of the magnetic recording medium is improved.

The electrolytic treatment in the present invention can be performed, for example, following the texturing. The present invention is characterized by an electrode used for performing the electrolytic treatment. FIG. 1 is a diagram showing an electrolysis apparatus to which the electrolysis according to the present invention can be applied. In the figure, the terminal electrodes 20, 21
And a plurality of substrates 1 and 2 are disposed in the electrolyte 3 respectively.

In this figure, when a plurality of substrates are subjected to electrolytic treatment, the substrates are arranged in the electrolytic solution by sequentially arranging the substrates in a direction perpendicular to the substrate surface, and terminal electrodes are disposed outside the conductive substrates at both ends. By sequentially applying an alternating voltage between the odd-numbered conductive substrate and the even-numbered substrate from the terminal electrode,
The case where each substrate is treated in an electrolytic solution is shown.

The terminal electrode used in the present invention has an inner diameter larger than that of a donut-shaped substrate.
In addition, a material whose outer diameter is smaller than that of the substrate is used. The shape of the terminal electrode will be further described with reference to FIG. 4. The inner diameter ratio (inner diameter of terminal electrode (D ₂ ′) / inner diameter of substrate (D ₂ )) is in the range of 1.05 to 1.5, more preferably 1 to 1.5. 0.1 to 1.4, and the outer diameter ratio (outer diameter of the terminal electrode (D ₁ ′) / outer diameter of the substrate (D ₁ )) is 0.7 to 0.7.
It is preferably in the range of 0.95, more preferably in the range of 0.8 to 0.9. By using such a terminal electrode, the in-plane distribution of the etching amount is reduced, and uniform etching can be performed.

The mechanism of the present invention is considered as follows. The etching speed depends on the density of the electric flux lines reaching the substrate surface, and the electric flux lines are also generated from the end face of the terminal electrode or the surface of the terminal electrode not facing the substrate. Therefore, 'or if is equal to or smaller than the inner diameter of the substrate (D _2), the outer diameter of the terminal electrode (D ₁ the inner diameter of the terminal electrode (D _2)' If) is the outer diameter (D ₁₎ or more substrate, electrical The flow of the force line wraps around the inner peripheral space of the terminal electrode and the outer space from the outer periphery and locally contacts the inner peripheral side and the outer peripheral side of the opposing substrate, and The density of lines of electric force at the outer peripheral portion increases. Therefore, it is considered that the amount of electrolytic etching increases, and the in-plane distribution of the amount of electrolytic etching becomes nonuniform on the inner and outer peripheral sides of the substrate.

In the present invention, the ratio of the inner and outer diameters of the terminal electrode to the substrate is increased by increasing the ratio of the inner diameter to the substrate, and the ratio of the outer diameter is reduced, so that the area around the lines of electric force from the inside and outside of the terminal electrode is reduced. The in-plane distribution of the amount of electrolytic etching is made uniform by increasing the area to be filled.

The thickness ratio of the terminal electrode to the substrate (the thickness of the terminal electrode (H ₁ ′) / the thickness of the substrate (H ₁ )) is 0.5 to 2, Desirably 0.8 ~
The range of 1.1 is preferable from the viewpoint of the uniformity of the etching amount.

The distance between the terminal electrode and the electrode is preferably in the range of 3 to 30 mm, and more preferably in the range of 5 to 15 mm from the viewpoint of the uniformity of the electrolytic etching amount.

It is preferable that the resistance value of the terminal electrode is substantially the same as the electric resistance of the portion to be etched. That is, when etching the Ni-P plating layer,
It is desirable to use a terminal electrode made of a material having the same electric resistance value as Ni-P.

Further, as the material of the terminal electrode, a metal having more corrosion resistance than the substrate is preferable. Examples of such a material include titanium and platinum. The terminal electrode is most easily made of a metal plate, but can have any structure as needed.

One example of a particularly preferred embodiment of the present invention is shown in FIG.
This will be described with reference to FIG. FIG. 1 is an elevational view of the inside of an electrolytic cell viewed in a substrate surface direction, schematically showing a state in which a substrate is subjected to electrolytic treatment. In FIG. 1, reference numeral 1 denotes an odd-numbered substrate counted sequentially from the left side in the drawing, and reference numeral 2 denotes an even-numbered substrate. A large number of the substrates 1 and 2 are arranged in an electrolytic bath 5 filled with the electrolytic solution 3 in a direction orthogonal to the substrate surface. Reference numeral 20, as the terminal electrode,
21 are provided. Reference numeral 4 denotes an AC power supply, of which one line 6 is connected to each odd-numbered substrate 1 and the other line 7 is connected to each even-numbered substrate 2 via a support member (not shown). Outputs an alternating voltage composed of a rectangular wave of a predetermined frequency (for example, 20 Hz). Accordingly, the odd-numbered substrate 1 and the even-numbered substrate 2 opposite thereto function alternately as anode or cathode electrode plates, and an alternating current flows between the opposing substrates 1 and 2 so that the respective substrates 1 and 2 2 is possible. By this electric field treatment, protrusions and burrs on the substrate surface are removed by etching, and the substrate surface is finished to a smooth surface state.

FIG. 2 is a front view of the substrate viewed in a direction perpendicular to the substrate surface, showing a state of supporting the substrate in the electrolytic cell. FIG. 3 is a view taken along the line AA ′ in FIG. is there. FIG. 2 is drawn as a diagram common to the odd-numbered and even-numbered substrates 1 and 2, and each of the disk-shaped substrates 1 and 2 is separated from each other in the circumferential direction of the disk so as to receive it. The three supporting members 11, 12, and 13 are supported at three points on the outer peripheral edge of the disk. The number of support members is two or more, and an arbitrary number is selected, but three or more points are preferable for convenience of handling such as insertion and removal of a substrate.

The first and second support members 11 and 12
Each of them is configured as a conductive support member, for example, a metal member. As shown in FIG. 3, a conductive support rod 14 extending in the arrangement direction of the substrate near the outer peripheral portion of the substrate, It is composed of a first locking member 15 that is supported while being in contact with each other, and a second locking member 17 that is supported while being electrically insulated by the conductive support rod 14. Each of the locking members 15 and 17 is made of, for example, a metal material, is formed in a substantially soloban ball shape, has a hollow hole inserted into the conductive support rod 14, and has an outer peripheral surface formed as an annular groove 18. The bottom of the annular groove 18 abuts against the outer peripheral surfaces of the substrates 1 and 2 to support the conductive substrates 1 and 2 in the vertical and horizontal directions and to make electrical contact therewith.

The first locking member 15 is electrically and mechanically connected to the conductive support rod 14 by a screw 19. The second locking member 17 is supported by the conductive support rod 14 while being insulated from the conductive support rod 14 via an insulating material 16 such as Teflon. The third support member 13 shown in FIG. 2 is an insulative support member having a conductive support rod similar to the conductive support members 11 and 12 and a second locking member. 1 and 2 are merely mechanically supported.

The current from the AC power supply 4 flows through the support rod 14 of the first conductive support member 11, for example, to the first locking member 15 which is in electrical contact with the support rod 14. Then, it is provided to the odd-numbered conductive substrate 1 from the corresponding outer peripheral edge via the surface of the annular groove 18 of the first locking member. Next, from the even-numbered substrates 2 facing each other via the electrolytic solution, the second conductive support members 1 are similarly formed.
Reflux to AC power via 2. When the voltage polarity is inverted, the current flows in the opposite direction. As described above, the odd-numbered substrate 1 and the even-numbered substrate 2 facing the odd-numbered substrate 1 constitute opposing electrodes facing each other. Thereby, the electrolytic treatment of each substrate becomes possible.

In the above description, it is conceivable that the second locking member 17 itself for insulation is formed of an insulating material such as Teflon. However, in this case, bubbles are generated in the locking member 17 during the electrolytic treatment. It adheres, and the substrate surface near the support member is masked by the bubbles, which causes etching unevenness, which is not preferable.

In the method of the present invention, as described above, an alternating voltage is applied so that the current flowing through the substrate has a specific waveform, preferably in an electrolytic solution of an acidic solution, so that the surface of the textured substrate is treated. An electrolytic treatment is performed. Here, as the electrolytic solution, for example, sulfuric acid, nitric acid, hydrochloric acid, chromic acid,
0.5 to 40% by weight, preferably 1 to 30% by weight of one or a combination of two or more of phosphoric acid, oxalic acid and acetic acid
An aqueous solution having a concentration in the range described above is used, and a phosphoric acid aqueous solution is particularly preferable. The conditions of the electrolytic treatment are as follows:
0 ° C., an average current density of 50 mA / cm ² or less, preferably 1~50mA / cm ^2, more preferably 5~45mA
/ Cm ² , the electrolysis time is 1 to 400 seconds, preferably 2 to 2 seconds.
00 seconds, quantity of electricity (product of average current density and electrolysis time) is 10
１０００1000 mA · sec / cm ² , preferably 50-600
A range of mA · sec / cm ² is selected.

The current used for the electrolytic etching may be a positive or negative polarity, that is, an alternating current that alternately changes the polarity of the anode and the cathode, for example, a sinusoidal single-phase alternating current or a rectangular wave.
Alternating currents such as triangular waves and trapezoidal waves are mentioned. The frequency of the alternating current is in the range of 0.5-100 Hz, preferably 1-50 Hz.

When the above-described electrolytic treatment is performed after the texturing treatment, it is general to form a thin film after washing and drying. In such a case, Cr is usually used as the second underlayer.
An underlayer is formed in a thickness of 50 to 2000 °, and then a metal magnetic thin film layer and a protective layer are formed. Although there is no particular limitation on the magnetic thin film layer, Co—Cr, Co—Ni, C
A magnetic thin film layer of a Co-based alloy represented by o-Cr-X, Co-Ni-X, Co-WX or the like is preferable. Where X
Are Li, Si, Ca, Ti, V, Cr, Ni,
As, Y, Zr, Nb, Mo, Ru, Rh, Ag, S
b, Hf, Ta, W, Re, Os, Ir, Pt, Au,
One or more elements selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, and Eu. The thickness of the metal magnetic thin film layer is generally 100 to 1
In the range of 000 °.

On the metal magnetic thin film, a protective thin film layer preferably made of a carbonaceous film is formed. The carbonaceous protective thin film layer is usually formed by sputtering using carbon as a target in an atmosphere of a rare gas such as argon (Ar) or helium (He) or in the presence of a small amount of hydrogen in addition to the amorphous. It is formed as a carbon film or a hydrogenated carbon film. The thickness of this protective thin film layer is usually in the range of 50 to 500 °. Further, in order to further reduce the friction coefficient, a lubricating film may be further formed on the protective thin film.

The surface treatment by the electrolytic treatment can be arbitrarily adopted not only after the texturing but also during the manufacturing process of the magnetic disk, and the application of the present invention is not limited to the electrolytic treatment following the texturing.

[0037]

Next, the present invention will be further described with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention. (Example 1) Ni-P plating was performed by one
2. Made of an aluminum alloy with a thickness of about 5 μm
A substrate for a 5-inch disk was prepared. The surface of the substrate is polished to have an average surface roughness (Ra) of about 20.
Then, a fine groove was formed by texturing using a polishing tape. Further, the disk was subjected to a texturing process using free abrasive grains, so that the surface was finished so that the average surface roughness (Ra) was about 60 °.

Next, using the apparatus shown in FIGS. 1 to 3, 20 disk substrates and a titanium electrode 2 having the shape shown in Table 1 were used.
As shown in FIG. 1, the disc substrates (20 and 21) were arranged at a distance between the electrodes of 6.2 mm, and the titanium electrodes 20 and 21 were arranged outside the disc substrates at both ends. Next, in a 3 wt% phosphoric acid aqueous solution as an electrolytic treatment solution,
The electrolysis treatment was performed by controlling the alternating voltage applied between the odd-numbered substrate and the even-numbered substrate so that the supplied current became an alternating current of a rectangular wave. As the conditions for the electrolytic treatment, a liquid temperature of the electrolytic solution of 20 ° C., an average current density of 20 mA / cm ² , a frequency of 5 Hz, and an electrolytic time of 20 seconds were employed.

The in-plane distribution of the electrolytic etching depth was measured for the opposite surfaces of the substrates at both ends obtained by the electrolytic treatment, which face the titanium electrodes. (Measurement method) Two directions that intersect at the center of the substrate and are orthogonal to each other (that is, 0 degree, 90 degree, 180
(In the direction of 270 degrees), an etching process is performed by applying a mask having a predetermined width, and the mask is removed after the etching. Using a tally step (a stylus roughness meter) at a predetermined radius position, the step between the portion where the radius position is masked by 8 points and the etched portion in each of the four directions viewed from the center of the substrate is measured. The distribution of the etching depth is measured by observing the variation in the measured step value at the radial position. It was determined that there was no unevenness when the previous data was included within plus or minus 10% of the measured step average value. The measurement results of Example 1 are shown in FIG.

Comparative Examples 1 to 4 The same procedure as in Example 1 was carried out except that a titanium electrode having the shape shown in Table 1 was used as a terminal electrode. As a result, FIG. 5B (Comparative Example 1) and FIG. 5C (Comparative Example 2)
As shown in Table 1 and Table 1, those having an in-plane distribution of the etching depth on the inner peripheral side were obtained, and it was found that local electrolytic etching unevenness occurred on the inner peripheral side of the substrate.

[0041]

[Table 1]

[0042]

As described above, according to the present invention,
By using a terminal electrode having a specific shape, the etching depth can be made uniform even on the outermost surface of the magnetic disk.

[Brief description of the drawings]

FIG. 1 is a diagram showing a main configuration of an electrolytic etching apparatus.

FIG. 2 is a diagram showing an example of a substrate support configuration in an electrolytic cell.

FIG. 3 is a sectional view of FIG. 2;

FIG. 4 is a view showing dimensions of a substrate and a terminal electrode.

FIG. 5 is a diagram showing etching depth measurement results in Examples and Comparative Examples.

[Explanation of symbols]

 1, 2 substrate 3 electrolytic solution 4 AC power supply 5 electrolytic cell 20, 21 terminal electrode

Claims (4)

[Claims] 1. A method for manufacturing a magnetic recording medium comprising a step of subjecting a surface of a substrate or a medium to electrolysis, wherein the electrolysis is performed so as to face a surface of the substrate or medium that does not face another substrate or medium. The method is performed using a pair of substantially disk-shaped terminal electrodes provided on the substrate, and the inner diameter of the terminal electrode is larger than the inner diameter of the substrate or the medium, and the outer diameter is smaller than the outer diameter of the substrate or the medium. Of manufacturing a magnetic recording medium. 2. The inner diameter of the terminal electrode is 1.05 to 1.5 with respect to the inner diameter of the substrate or medium, and the outer diameter is 0.7 to 0.95 with respect to the outer diameter of the substrate or medium. The method for manufacturing a magnetic recording medium according to claim 1, wherein: 3. The method for manufacturing a magnetic recording medium according to claim 1, wherein the terminal electrode is a metal electrode having substantially the same electric resistance value as the substrate and having corrosion resistance more than the substrate. 4. The electrolytic processing step comprises: arranging a plurality of conductive substrates in an electrolytic solution by sequentially arranging the plurality of conductive substrates in a direction perpendicular to the substrate surface, and sequentially counting odd-numbered conductive substrates and even-numbered conductive substrates. 4. The method according to claim 1, wherein an alternating voltage is applied between the magnetic recording media.