JPH07225945A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the surface characteristics of an underlayer and to obtain a medium excellent in levitation characteristics, lubricity and wear resistance by placing cathodes on both sides of each textured substrate so that they confront each other and carrying out electrolysis. CONSTITUTION:Cathodes 2 are parallel placed on both sides of each textured substrate 1 so that they confront each other and electrolysis is carried out in an acidic electrolytic soln. 3 while impressing prescribed voltage on the substrate 1 from a DC power source 4. Protrusions and burrs on the surface of the substrate 1 are removed by electrolytic etching and the substrate 1 is finished to a smooth state. The pref. interval between the substrate 1 and each of the cathodes 2 is 5-30mm, the electrolytic soln. is preferably an aq. phosphoric acid soln. having 0.5-40wt.% concn. and current. density is preferably 0.1-25mA/cm<2>. An underlayer and a magnetic layer are then formed on the substrate 1 and the objective medium having a smooth surface is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a magnetic recording medium. In detail, improve the surface characteristics by performing the surface processing on the substrate using a specific method,
The present invention relates to a method of manufacturing a magnetic recording medium having excellent flying characteristics, lubricity and wear resistance.

[0002]

2. Description of the Related Art In recent years, with the development of information processing technology for computers and the like, magnetic recording media such as magnetic disks have been used as external storage devices. Conventionally, as a magnetic recording medium, an aluminum alloy substrate is subjected to alumite treatment or Ni-
A non-magnetic plating treatment such as P plating is applied, followed by coating an underlayer such as Cr, then a magnetic thin film layer of a Co-based alloy, and a carbonaceous protective film. .

With the increase in density of the magnetic recording medium (magnetic disk), the distance between the magnetic disk and the magnetic head, that is, the flying height, has become smaller and smaller.
It is about m or less. As described above, since the flying height of the magnetic head is extremely small, a protrusion on the magnetic disk surface may cause a head crash, which may damage the disk surface. Further, even minute protrusions that do not lead to head crashes are likely to cause various errors when reading and writing information.

On the other hand, magnetic disks are being miniaturized in parallel with the increase in capacity and density, and motors for spindle rotation are becoming smaller and smaller. For this reason, the torque of the motor is insufficient, and the phenomenon that the magnetic head does not fly while being fixed to the magnetic disk surface is likely to occur. As a means for preventing the sticking of the magnetic head by reducing the contact between the magnetic head and the surface of the magnetic disk, a surface treatment called texturing for forming fine grooves on the substrate surface of the magnetic disk is performed. ing.

Further, Japanese Patent Application Laid-Open No. 4-95221 proposes that texturing is performed, cleaning is performed, and then chemical etching is performed. Furthermore, JP-A-5-12850
No. 6 discloses that abnormal projections on the substrate surface are selectively removed by performing electrolytic polishing treatment on the textured substrate surface.

[0006]

However, when only the above-mentioned texture processing is used, although the floating characteristics of the magnetic disk are improved, it cannot be said to be sufficient. Further, in the method by chemical etching described in JP-A-4-95221, it is difficult to control the processed surface state by selecting the etching conditions, and
Since the etching state is likely to be non-uniform and local corrosion is likely to occur, a satisfactory surface state has not yet been obtained, and it is desired to improve the floating characteristics of the magnetic disk.

Furthermore, when the method described in Japanese Patent Laid-Open No. 5-128506 is used on an industrial scale, that is, when a plurality of substrates are electrolytically treated at the same time, the etching amounts of the substrates due to the electrolytic treatment are different from each other and are the same. Even in the case of a substrate, the amount of etching varies in the in-plane direction, which affects the floating characteristics of the surface of the substrate.

[0008]

DISCLOSURE OF THE INVENTION The inventors of the present invention have made earnest studies to further improve the levitation characteristics of the above-mentioned magnetic disk, and as a result, after texturing the substrate, the substrate surface is treated with an acidic electrolytic solution. Among them, it has been found that the surface characteristics of the substrate are improved and the above object is achieved by performing the direct current electrolytic treatment using a specific apparatus, and the present invention has been completed.

That is, the gist of the present invention is a method for manufacturing a magnetic recording medium in which an underlayer and a magnetic layer are sequentially formed on the surface of a textured non-magnetic substrate. Install the cathode opposite to
A method for producing a magnetic recording medium is characterized in that a DC voltage is applied to the substrate in an acidic electrolytic solution to perform an electrolytic treatment, and then an underlayer and a magnetic layer are formed.

The present invention will be described in more detail below.
As the non-magnetic substrate of the magnetic recording medium in the present invention, a disk-shaped substrate generally made of an aluminum alloy is processed to a predetermined thickness, and then the surface is mirror-finished, and then a non-magnetic metal such as Ni-P alloy, Alternatively, a Ni-Cu-P alloy or the like formed as a surface layer having a thickness of about 5 to 20 μm by electroless plating or the like is used.

It is general that the surface layer of the above-mentioned substrate is subjected to polishing and then textured. The polishing process is performed, for example, by sandwiching the substrate between polishing pads that are impregnated with free abrasive grains on the surface, and polishing the liquid while supplying a polishing solution such as a surfactant aqueous solution. Average surface roughness Ra is 50 Å or less, preferably 30 Å
The mirror finish is given below. As the loose abrasive grains, typically, alumina-based slurry polyplastics 700 and polyplastics 1 are used.
03 (both are registered trademarks of Fujimi Inc.), diamond-based slurry, SiC-based slurry 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.

The texture processing is, for example, 2
The average surface roughness Ra is 20 Å or more, preferably on the surface of the substrate subjected to the above-mentioned polishing by tape grinding using a polishing tape carrying alumina abrasive grains of about 500 to 6000 # or slurry grinding using loose abrasive grains. 30 ~
300 Å, more preferably 50-150 Å, the angle of intersection of the formed striations is preferably 10-40 °, more preferably 10-30 ° to form fine grooves or irregularities with high precision, It is preferable to form a cross pattern striation on the base surface of the substrate because the adsorption property is improved. Further, in order to remove abnormal protrusions on the substrate surface, a second stage texture may be applied by slurry grinding using loose abrasive grains. By this texture processing,
Adhesion between the magnetic head and the magnetic recording medium can be prevented, and CS
The S characteristic is improved and the magnetic anisotropy is improved.

In the present invention, the surface of the textured substrate is preferably in the acidic electrolyte at a current density of 0.1 to 25 mA / cm ² , more preferably 0.1 to 25 mA / cm ² .
Within the range of 10 mA / cm ² , a DC voltage is applied to the substrate for electrolytic treatment. As the electrolysis time, a range of 1 to 400 seconds, preferably 2 to 200 seconds is used, and the amount of electricity, that is, the product of current density and electrolysis time is 2000 mA · sec / cm ² or less, preferably 50 to 1500 mA · sec / c
A range of m ² is used. The temperature in the electrolytic solution is not particularly limited, but is usually in the range of 10 to 70 ° C.

As the above-mentioned electrolytic solution, for example, sulfuric acid, nitric acid, hydrochloric acid, chromic acid, phosphoric acid, oxalic acid, acetic acid and the like are used, or a combination of two or more thereof is used, and the concentration thereof is 0.5 to 40 weight. %, Preferably used as an aqueous solution in the range of 1 to 30% by weight. Phosphoric acid is suitable as the electrolytic solution.

When phosphoric acid is used as the electrolyte,
The phosphoric acid concentration is 0.5 to 40% by weight, preferably 1 to 20
It is in the range of% by weight. The electrolytic treatment condition is a liquid temperature of 10
In the electrolyte solution of the above phosphoric acid aqueous solution at ˜70 ° C., the current density is 0.1 to 25 mA / cm ² , preferably 0.1 to 10 m.
A / cm ² , more preferably 1 to 5 mA / cm ² , and electrolysis time is 10 to 400 seconds, preferably 10 to 2 seconds.
It is in the range of 00 seconds.

In the present invention, when the surface of the textured substrate is subjected to electrolytic treatment in an acidic electrolytic solution, cathodes are installed on both sides of the substrate so as to face each other in parallel, and a DC voltage is applied to the substrate. Apply and electrolyze. An example of the embodiment of the present invention will be described with reference to FIG.

In FIG. 1, a cathode (2) is installed so as to face both sides of a substrate (anode) (1) in parallel, and a predetermined voltage is applied from a DC power source (4) in an acidic electrolytic solution (3). Is applied to the substrate (1) for electrolytic treatment to remove protrusions and burrs on the surface of the substrate by electrolytic etching to finish the substrate surface into a smooth surface state. The substrate (1) and cathode (2)
It is preferable that the distance between the electrodes and is in the range of 5 to 30 mm, preferably 10 to 20 mm, because the etching amount becomes uniform. As the cathode, stainless steel, aluminum carbon, or the like is used, and as the shape thereof, a disk having a size similar to that of the substrate or a donut shape is used. In order to make the etching amount in the in-plane direction of the substrate uniform during the electrolytic treatment, the current density, the distance between the electrodes, the shape of the cathode and the size thereof are appropriately adjusted.

By the above electrolytic treatment method, projections, burrs and the like on the substrate surface after texture processing are uniformly removed by electrolytic etching, the substrate surface becomes a smooth surface state, and the levitation characteristics and CSS characteristics are greatly improved.

After completion of the electrolytic treatment, if necessary, prior to laminating the underlayer and the magnetic layer, loose abrasive grains are adhered and impregnated on the surface of a substrate such as a cellulose nonwoven fabric, or an abrasive such as alumina. You may perform the finishing process which presses the tape etc. which carry comparatively fine grain | grains on a board | substrate surface, and performs a texture process again. Chromium is formed as a secondary underlayer by sputtering on the surface of the substrate that has been subjected to the electrolytic treatment. The thickness of the chromium underlayer is usually 50 to
It is in the range of 2000Å.

As the metal magnetic thin film layer formed on the Cr underlayer of such a substrate, Co--Cr, Co--Ni,
A magnetic thin film layer of a Co-based alloy represented by Co-Cr-X, Co-Ni-X, Co-W-X or the like is suitable. Here, X is 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,
Examples include one or more elements selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, and Eu.

The metal magnetic thin film layer made of such a Co-based alloy is usually deposited and formed on the underlayer of the substrate by means such as sputtering. The film thickness of the metal magnetic thin film layer is usually in the range of 100 to 1000Å. The protective thin film layer formed on the metal magnetic thin film layer is preferably a carbonaceous film, and the carbonaceous protective thin film layer is usually argon,
In a rare gas atmosphere such as helium or in the presence of a small amount of hydrogen, an amorphous carbon film, a hydrogenated carbon film or the like is deposited by sputtering with carbon as a target. The thickness of the protective thin film layer is usually 50 to 50.
It is set in the range of 0Å. Further, in order to reduce the friction coefficient, a lubricating film may be further formed on the protective thin film layer.

[0022]

EXAMPLES Next, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

Example 1 The surface of a 3.5-inch aluminum alloy disk-shaped substrate plated with Ni-P to a thickness of about 15 μm by electroless plating has a surface average roughness (Ra) of about 20 by polishing. A film surface having a thickness of -30 Å was formed, and then fine grooves were formed by texturing with a polishing tape to have a surface average roughness (Ra) of about 100 Å. Next, as shown in FIG. 1, 10 disk substrates and 11 stainless steel cathodes having the same shape as the disk substrate were arranged in parallel with the disk surfaces facing each other with a distance between electrodes of 12 mm, and 10 wt% phosphorus. Electrolytic treatment was carried out by applying a DC voltage to the substrate in an acid aqueous solution at a liquid temperature of 20 ° C., a current density of ² mA / cm ² , and an electrolysis time of 100 seconds. Electrolysis time 2 for substrates that have been similarly textured
The electrolytic treatment was performed under the conditions of 00 seconds and 600 seconds. For each of the obtained substrates, the weight change (etching amount) of the disk substrate before and after electrolytic etching was measured, and this etching amount was plotted against the position of 10 disks for each electrolysis time and is shown in FIG. .

Further, regarding the substrate subjected to the electrolytic treatment under the condition of the electrolysis time of 600 seconds, the etching depths (A) to (D) shown in FIG. Fig. 4 shows the result of measuring Å) by the following method.

<Method of Measuring Etching Depth> An imide tape having a width of 1 mm was attached in the radial direction at four positions A to D on the disk substrate before electrolytic treatment. After performing electrolytic treatment in this state, it was washed and dried, and the adhesive component on the tape adhering portion was wiped off with isopropyl alcohol. The step of the sample manufactured as described above is measured by Talystep (Tay
The etching depth (Å) was determined by measurement with a lon-Hobson model, ST-200S). From Figure 3,
It can be seen that there is almost no change in the etching amount between the disk substrates and it is constant. Further, it can be seen from FIG. 4 that the etching depth is almost constant regardless of the distance from the center of the disk.

Comparative Example 1 Four disc substrates textured in the same manner as in Example 1 were attached to an inner circumference hanging jig shown in FIG. 6, and a 10 wt% phosphoric acid aqueous solution was used by using the apparatus shown in FIG. In this, direct current electrolysis treatment was performed under the conditions of a liquid temperature of 20 ° C., a current density of ² mA / cm ² , and an electrolysis time of 45 seconds. Similarly, as shown in FIG. 6, 6 and 25 disk substrates subjected to texture processing were attached to an inner circumference hanging jig and subjected to electrolytic treatment.
The etching amount was measured for each of the obtained substrates, and the sample No. shown in FIG. Plotted against Figure 7
Shown in.

Comparative Example 2 Four disc substrates were treated in the same manner as in Comparative Example 1 except that the electrolytic treatment was carried out under the condition of electrolysis time of 600 seconds, and the obtained disc was treated in the same manner as in Example 2. 8 shows the result of measuring the etching depth (Å) by etching.

[0028]

By electrolytically treating the substrate surface using the method of the present invention, the substrate surface is uniformly etched, abnormal projections and burrs are selectively removed, and a smooth surface condition is obtained. It is possible to provide a magnetic recording medium having significantly improved characteristics and CSS characteristics.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of disk surfaces A to D in measurement of in-plane distribution of etching amount.

FIG. 3 shows an etching amount distribution of each disk of Example 1.

FIG. 4 shows an in-plane distribution of an etching amount in Example 2.

FIG. 5 is an explanatory diagram showing a comparative example of the present invention.

FIG. 6 is an inner circumference hanging jig (made of SUS316) in FIG.
It is an enlarged view of (6).

7 shows an etching amount distribution of each disk of Comparative Example 1. FIG.

8 shows an in-plane distribution of etching amount in Comparative Example 2. FIG.

[Explanation of symbols]

 1 substrate (anode) 2 cathode 3 electrolyte 4 DC power supply 5 electrolysis tank 6 inner circumference jig

Claims (4)

[Claims] 1. A method of manufacturing a magnetic recording medium in which an underlayer and a magnetic layer are sequentially formed on the surface of a textured non-magnetic substrate, and a cathode is opposed to both sides of the textured substrate. A method for producing a magnetic recording medium, which comprises placing the substrate, applying a DC voltage to the substrate in an acidic electrolytic solution to subject the surface to electrolytic treatment, and then forming an underlayer and a magnetic layer. ^2. The method for producing a magnetic recording medium according to claim 1, wherein the electrolytic treatment is performed under the condition that the current density is in the range of 0.1 to 25 mA / cm ² . 3. The method for producing a magnetic recording medium according to claim 1, wherein a 0.5-40 wt% phosphoric acid aqueous solution is used as the electrolytic solution. 4. The method for producing a magnetic recording medium according to claim 1, wherein the distance between the substrate and the cathode is in the range of 5 to 30 mm.