JPH10134346A - Production of magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high-characteristic magnetic disk which is useful for making a capacity higher and density higher and has high coercive force and small coercive force distribution by specifying an etching rate in electrolytic etching treatment to a ratio of a specific range with respect to a conductive substrate weight. SOLUTION: The electrolyte to be used for electrolytic etching includes aq. solns. of, for example, sulfuric acid, nitric acid, hydrochloric acid, etc. Electrolysis conditions are specified to a liquid temp. 10 to 70 deg.C, average current density 0.5 to 45mA, electrolysis time 2 to 200 seconds and quantity of electricity 50 to 800mA.sec/cm<2> . The electrolyte etching rate is so regulated as to attain 0.05 to 0.025% of the conductive substrate weight. If the etching rate is below 0.015%, the higher coercive force and the improvement in coercive force distribution are insufficient. When the etching rate exceeds 0.025%, the coercive force distribution improves but on the contrary, the coercive force degrades. The electrolyte etching is preferably executed by impressing AC voltages in an acidic soln in such a manner that the currents flowing in the substrate has specific waveforms, i.e., square waves.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a magnetic recording medium, and more particularly to a method for reducing the in-plane coercive force distribution of a magnetic recording medium by optimizing the amount of electrolytic etching of a conductive substrate.

[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 with the increase in density, and recently, about 0.15 μm. It is as follows. 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 such a magnetic head from crashing or sticking, a surface processing (hereinafter referred to as a polishing process) for forming a fine groove on the surface of a magnetic disk substrate after polishing (polishing) the surface of the magnetic disk substrate has been conventionally performed. , Texture processing). However, due to the reduction in the flying height of the head, the average surface roughness Ra of the processed substrate is also reduced in this texture processing (reduction of Ra).
≦ 20 ° in some cases.

[0006] Texture processing is particularly effective in reducing the contact resistance between the magnetic head and the surface of the magnetic disk. Although the floating processing of the head on the magnetic disk is improved by the texturing, the recent flying height of the head has been reduced. The performance required for small magnetic disks is still insufficient.

[0007] Japanese Patent Application Laid-Open No. 4-95221 discloses that
In order to meet the above demand, it has been proposed to wash the substrate after the texture processing and then perform electrolytic etching to perform surface treatment.

[0008]

In order to increase the capacity and density of the magnetic disk, the coercive force (Hc) of the magnetic disk must be increased and the Hc distribution in the disk surface (each point on the disk surface) must be increased. The difference in Hc of the magnetic disk is required to be minimized. However, the recent reduction in the flying height of the head has led to a reduction in the Ra of the texture processing, and in particular, the Hc on the outer periphery of the magnetic disk has been reduced, so that the in-plane of the disk has been reduced. There is a problem that the Hc distribution deteriorates.

The present invention solves the above-mentioned conventional problems and provides Hc
It is an object of the present invention to provide a method of manufacturing a high-performance magnetic disk having a high Hc distribution and a small Hc distribution in the disk surface.

[0010]

According to a method of manufacturing a magnetic recording medium of the present invention, there is provided a method of manufacturing a magnetic recording medium having a step of electrolytically etching a conductive substrate. It is characterized by being 0.015 to 0.025% with respect to the substrate weight.

That is, the present inventors have conducted intensive studies to solve the above-mentioned conventional problems, and as a result, have found that the Hc distribution of the disk is drastically reduced by optimizing the amount of electrolytic etching, and to complete the present invention. It has arrived.

According to the present invention, by setting the amount of electrolytic etching to 0.015 to 0.025% of the weight of the conductive substrate, the Hc distribution can be reduced while maintaining the Hc of the magnetic disk high.

It is preferable that this etching process is performed after polishing or texturing.

[0014]

Embodiments of the present invention will be described below.

As the conductive substrate of the magnetic disk in the present invention, a disk-shaped substrate made of an aluminum alloy is generally used. Usually, the aluminum alloy substrate is processed to a predetermined thickness, and the surface is mirror-finished. From
A nonmagnetic metal, for example, a Ni-P alloy or a Ni-Cu-P alloy is applied by electroless plating to form a surface layer having a thickness of about 5 to 20 m. Next, a surface processing is performed on this surface layer to form a surface processed layer finished to a specific surface roughness. As the surface processing, usually, the surface layer is polished (polished) and then subjected to texturing, and then the substrate surface is subjected to electrolytic etching in an electrolytic solution according to the method of the present invention. Note that the etching treatment may be performed after the polishing.

The polishing is carried out, for example, by sandwiching the substrate between polishing pads having free abrasive grains attached to and impregnated on the surface thereof, and supplying a polishing solution such as an aqueous solution of a surfactant. In a normal case, the substrate surface is polished by about 2 to 5 μm, and the average surface roughness Ra of the substrate surface is 30 °.
Hereafter, it is desirably mirror-finished to 20 ° or less. Here, as the free abrasive grains, typically, alumina-based slurries DL-3471 and DL-4479 (both are registered trademarks of Fujimi Incorporated), diamond-based slurries, SiC-based slurries, and the like are used. As the polish pad, urethane foam such as Surfin018 and SurfinXXX-5 (both are registered trademarks of Fujimi Incorporated) is typically used.

The texture processing is carried out, for example, in the case where the average particle size is 0.
Using a buff tape carrying 1 to 3 μm diamond slurry, pressing the buff tape against the polished substrate surface with a processing roller, the average surface roughness Ra in the circumferential direction of the substrate is 5 to 60 °, Preferably 5-4
Fine grooves or irregularities in the range of 0 °, more preferably in the range of 5 ° to 20 °, are formed with high precision. By this texture processing, adsorption between the magnetic head and the magnetic disk can be prevented, and the CSS characteristics can be improved. Furthermore, the magnetic anisotropy of the magnetic disk is improved.

After texturing, the surface of the substrate is subjected to electrolytic etching, and then an underlayer and a magnetic layer are formed by a thin film forming process.

In the method of the present invention, the electrolytic solution used for electrolytic etching may be, for example, 0.5 to 1 or a combination of two or more of sulfuric acid, nitric acid, hydrochloric acid, chromic acid, phosphoric acid, oxalic acid and acetic acid. 40% by weight, preferably 1 to 30
An aqueous solution having a concentration in the range of% by weight is exemplified, and an aqueous phosphoric acid solution is particularly preferable. The conditions for the electrolytic treatment are as follows:
0 to 70 ° C., an average current density of 50 mA / cm ² or less, preferably 0.1~50mA / cm ^2, more preferably 0.5~45mA / cm ^2, the electrolysis time is 1 to 400 seconds,
Preferably, a range of 2 to 200 seconds and a quantity of electricity (product of average current density and electrolysis time) of 10 to 1000 mA · sec / cm ² , preferably 50 to 800 mA · sec / cm ² are selected. The etching is performed so that the electrolytic etching amount is 0.015 to 0.025% of the substrate weight immediately before processing. Here, if the amount of electrolytic etching is less than 0.015% of the weight of the conductive substrate, the increase in Hc and the improvement in Hc distribution are not sufficient, and if it exceeds 0.025%, the Hc distribution becomes good, but Hc tends to decrease. There is.

In the present invention, the electrolytic etching is preferably performed by applying an alternating voltage in an electrolytic solution of an acidic solution so that the current flowing through the substrate has a specific waveform, that is, a rectangular wave.

On the substrate surface subjected to the electrolytic etching treatment, Cr is formed as a second underlayer by sputtering. The thickness of the Cr underlayer is usually 100 to 100.
0 ° range. As the metal magnetic thin film layer formed on the Cr underlayer of such a substrate, Co—Cr, Co—
Ni, Co-Cr-X, Co-Ni-X, Co-W-X
A magnetic layer of a Co-based alloy represented by, for example, is preferable. Here, X is Li, Si, Ca, Ti, V, Cr, N
i, As, Y, Zr, Nb, Mo, Ru, Rh, Ag,
Sb, Hf, Ta, W, Re, Os, Ir, Pt, A
One, two or more elements selected from the group consisting of u, La, Ce, Pr, Nd, Pm, Sm and Eu. The magnetic layer made of such a Co-based alloy is usually formed on the Cr underlayer of the substrate by means such as sputtering.
It is formed with a thickness of 00 to 1000 °.

On the magnetic layer, a protective layer preferably made of a carbonaceous film is formed. The carbonaceous protective layer is usually made of A
It is formed by sputtering using carbon as a target in a rare gas atmosphere such as r or He or in the presence of a small amount of hydrogen in addition thereto, and is formed as an amorphous carbon film or a hydrogenated carbon film. The thickness of this protective layer is usually in the range of 50 to 500 °.

In order to further reduce the coefficient of friction,
A lubricating film may be further formed on this protective layer.

[0024]

The present invention will be described more specifically below with reference to examples and comparative examples.

EXAMPLE 1 A 10 μm-thick NiP surface layer was formed on a disk-shaped substrate made of an aluminum alloy by electroless plating according to a conventional method, and polished to obtain an average surface roughness Ra.
After processing to 20 °, texture processing was performed to obtain an average surface roughness Ra of 15 °, and then electrolytic etching was performed in a 3% by weight phosphoric acid aqueous solution at 23 ° C. and an average current density of 40 mA / cm ² . . In this electrolytic etching treatment, the amount of electrolytic etching was adjusted to 1.5 mg, 3.0 mg, or 5.0 mg by adjusting the electrolytic time. For comparison, one without electrolytic etching (electrolytic etching amount 0 mg) was also prepared. In the case of the electrolytic etching amount of 1.5 mg, the ratio of the electrolytic etching amount to the substrate weight after texture processing is 0.010%, and in the case of the electrolytic etching amount of 3.0 mg, the ratio of the electrolytic etching amount to the substrate weight is 0. In the case of 0.020% and the amount of electrolytic etching of 5.0 mg, the ratio of the amount of electrolytic etching to the substrate weight is 0.034%.

For each substrate, a 700 ° -thick Cr
After the formation of the underlayer, a CoCrTa alloy magnetic layer having a thickness of 440 ° was formed, and a carbonaceous protective layer having a thickness of 100 ° was further formed to manufacture a magnetic disk. The Hc of the obtained magnetic disk was measured.

The measurement point of Hc is a radius 21 mm from the center, 3
At points of 3 mm and 45 mm, 12 points on one side and 24 points on the front and back surfaces at 90 ° intervals, the average value of Hc of each of the five disks (24 × 5 = average value of 120 points) was obtained.
It was shown to. The standard deviation σ of Hc is shown in FIG. 2 as Hc in of the inner circumference measurement point (average value of n = 40 at a position of a radius of 21 mm from the center) and Hc _in of the outer circumference (n = 40 at a position of a radius of 45 mm from the center). The difference from Hc _out of (average value of 40) is shown in FIG. FIG. 1 shows that Hc shows the maximum value when the etching amount is 3 mg.

2 and 3, at low Ra, Hc at the outer periphery is lower than Hc at the inner periphery, and the σ and Hc difference (Hc _in -Hc _out ) tend to decrease with an increase in the etching amount. From the results of FIGS. 1 to 3, it can be seen that in order to minimize the high Hc and the Hc distribution, it is preferable that the etching amount in the substrate of the present example is 3 ± 0.5 mg.

[0029]

As described in detail above, according to the method of manufacturing a magnetic recording medium of the present invention, the Hc is high and the Hc distribution is small, and therefore, the high characteristics which are useful for increasing the capacity and density of the magnetic disk. A magnetic disk can be manufactured.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between an average Hc and an etching amount in Example 1.

FIG. 2 is a graph showing a relationship between a standard deviation σ of Hc and an etching amount in Example 1.

FIG. 3 shows the difference in Hc (Hc _in −Hc _out ) _in Example 1.
4 is a graph showing the relationship between the amount of etching and the amount of etching.

Claims (2)

[Claims] 1. A method for manufacturing a magnetic recording medium comprising a step of electrolytically etching a conductive substrate, wherein the amount of etching in the electrolytic etching is 0.015 to 0.025% based on the weight of the conductive substrate. A method for manufacturing a magnetic recording medium, comprising: 2. The method according to claim 1, wherein the etching process is performed after a polishing process or a texturing process.