JPH06231453A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve surface characteristics and to obtain a magnetic recording medium excellent in floating characteristic, lubricant property, and wear resistance by treating the surface of the substrate in a short time. CONSTITUTION:A nonmagnetic substrate is subjected to texturing, and a base coating layer and a magentic layer are successively formed on the surface of the substrate. The surface of the substrate after textured is subjected to electrolysis under conditions of <=25mA/cm<2> current density and DC voltage in an acid soln. Then the base coating layer and the magnetic layer are formed.

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. Specifically, the surface characteristics are improved by performing surface processing on the substrate in a short time.
The present invention relates to a method of manufacturing a magnetic recording medium having excellent 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 processing called texture processing for forming fine grooves on the substrate surface of the magnetic disk is performed. ing. Further, Japanese Patent Laid-Open No. 4-95221 proposes that texture processing is performed, cleaning is performed, and then chemical etching is performed.

[0005]

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.

[0006]

Means for Solving the Problems 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 was found that the substrate surface characteristics are improved and the above-mentioned object is achieved by performing the electrolytic treatment under specific conditions, and the present invention has been completed.

That is, the gist of the present invention is to provide a method for manufacturing a magnetic recording medium in which a non-magnetic substrate is textured, and an underlayer and a magnetic layer are sequentially formed on the surface of the non-magnetic substrate. In the electrolyte of acidic solution,
A method for producing a magnetic recording medium is characterized in that a voltage is applied to the substrate under the condition of a current density of 25 mA / cm ² 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 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
A polishing tape carrying alumina abrasive grains of about 500 to 6000 # is pressed against the surface of the polished substrate by a processing roller so that the average surface roughness Ra in the circumferential direction of the substrate is 20 Å or more, preferably 30. ~ 300 Å, more preferably 30 ~ 150 Å fine grooves or irregularities are processed with high accuracy, this texturing can prevent the magnetic head and the magnetic recording medium from adsorbing, CSS characteristics are improved, Further, the magnetic anisotropy becomes good.

In the present invention, the textured substrate surface is subjected to a current density of 25 mA in an electrolytic solution of an acidic solution.
/ Cm ² or less, preferably 0.1 to 25 mA / cm ² , and more preferably 0.1 to 10 mA / cm ² within the range of applying a voltage to the substrate for electrolytic treatment. The electrolysis time is 1 to
A range of 400 seconds, preferably 2 to 200 seconds is used,
The quantity of electricity, that is, the product of current density and electrolysis time is 10
~ 1000mA · sec / cm ² or less, preferably 50-60
A range of 0 mA · sec / cm ² is used. The electrolytic treatment of the present invention is carried out by direct current electrolysis, and the temperature in the electrolytic solution is not particularly limited, but is usually carried out in the range of 10 to 70 ° C.

As the above-mentioned electrolytic solution, for example, one or a combination of two or more of sulfuric acid, nitric acid, hydrochloric acid, chromic acid, phosphoric acid, oxalic acid, acetic acid and the like is used, and its concentration is 0.5 to 40 weight. %, Preferably 1 to 30% by weight as an aqueous solution. Phosphoric acid is suitable as the electrolytic solution. When using phosphoric acid as the electrolyte,
Phosphoric acid concentration is 0.5-40wt%, preferably 1-20wt%
% Range. The electrolytic treatment conditions include a liquid temperature of 10 to 7
The current density is 0.1 in the electrolyte solution of the phosphoric acid aqueous solution at 0 ° C.
-25 mA / cm ² , preferably 0.1-10 mA / c
The electrolysis time is in the range of 10 to 400 seconds, preferably 10 to 200 seconds, in the range of m ² , more preferably 1 to 5 mA / cm ² .

In the present invention, when the current density in the electrolytic treatment is higher than the above range, the protrusions, burrs and the like on the substrate surface are insufficiently removed and the flying characteristics and CSS characteristics of the head are insufficiently improved, which is preferable. Absent. By the above electrolytic treatment, protrusions, burrs, and the like on the substrate surface after texture processing are removed by etching, the substrate surface becomes a smooth surface state, and the floating characteristics and CSS characteristics are greatly improved.

After completion of the electrolytic etching treatment, if necessary, prior to laminating the underlayer and the magnetic layer, loose abrasive grains are adhered and impregnated on the surface of a base material such as a cellulose nonwoven fabric, or alumina or the like. A finishing process may be performed in which a tape or the like carrying relatively fine abrasive grains is pressed against the substrate surface and the texture process is performed 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 in the range of 50 to 2000 Å.

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 He 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 500.
It is set in the range of Å. Further, a lubricating film may be further formed on the protective thin film layer in order to reduce the coefficient of friction.

[0017]

EXAMPLES Next, the present invention will be described more specifically by way of examples, but the present invention is not limited to the following examples unless it exceeds the gist. Examples 1 to 8 The surface average roughness (Ra) of the aluminum alloy disk-shaped substrate, which was Ni-P plated to a thickness of about 15 μm by electroless plating, was about 2 by polishing.
A film surface of 0 to 30 Å is formed, and then fine grooves are formed by texturing with a polishing tape to obtain an average surface roughness (Ra) of 1
About 00Å (Examples 1 to 5) or about 70Å (Example 6)
~ 8). Next, the disk substrate was subjected to direct current electrolytic treatment in an acidic aqueous solution at a liquid temperature of 35 ° C. under the conditions shown in Table 1. Further, the disc was subjected to a finishing treatment in which texturing using loose abrasive grains was performed. The surface average roughness of the obtained disk was as shown in Table 1.
Then, on the surface layer of the substrate, a general Cr underlayer, Co-
A magnetic layer made of a Cr—Ta alloy and a protective film made of a carbonaceous material were sequentially sputter coated to manufacture a magnetic disk. The surface average roughness, glide floating characteristics, CSS characteristics, coercive force, and surface shape of the obtained magnetic disk were evaluated by the following methods. The results are shown in Table 1.

Comparative Example 1 A magnetic disk was manufactured in the same manner as in Examples 6 to 8 except that the electrolytic treatment was not performed, and each characteristic was evaluated. The results are shown in Table 1.

Evaluation Method (Examples 1 to 8 and Comparative Example 1) Surface Average Roughness Ra: Surface Roughness Gauge (“ET-30HK” manufactured by Kosaka Laboratory) having a stylus with a 0.5 μm conical tip.
Was measured with a measurement length of 250 μm. As a measuring method, a surface on an arbitrary straight line on the inner peripheral portion of the substrate was measured in the radial direction to obtain a surface average roughness Ra.

Glide levitation characteristics: Hitachi DECO R
The collision between the head and the protrusion of the disk was detected by the PZT element using X-2000 and evaluated as the flying height of the external head. CSS (Contact Start and Stop) characteristics: The disk was incorporated into an actual drive, and start and stop were repeated, and the static friction coefficient between the head and the disk after CSS 20,000 times was evaluated.

Measurement of coercive force: Using a BH meter (GMZ-2 manufactured by Glory Industry Co., Ltd.), the coercive force at a position 33 mm from the center of the disk was measured. Surface shape: The surface shape uses a scanning electron microscope SEM (JSM-5400 manufactured by JEOL Ltd.) and a magnification of 500.
Photographs were taken at 0 and 10000 times and visually observed.
At that time, A indicates that the burr was completely removed by etching, B indicates that the burr was removed but was incomplete and had a fluffy surface, and a large number of burr was not removed. What was shown was evaluated as C.

Examples 9 and 10 and Comparative Example 2 The surface of an 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 10 μm by polishing. Two
A film surface of 0 to 30 Å is formed, then fine grooves are formed by texturing using a polishing tape, and the disk is subjected to texturing using loose abrasive grains.
The average surface roughness (Ra) was finished to about 60Å. Next, the disk substrate was placed in a 10 wt% phosphoric acid aqueous solution,
Direct current electrolysis was performed under the conditions shown in Table 2 at a liquid temperature of 20 ° C. The surface average roughness of the obtained disk was as shown in Table 2. Then, on the surface layer of the substrate, a general Cr underlayer film, a magnetic layer made of a Co—Cr—Ta alloy, and a protective film made of a carbon film were sequentially sputter-coated,
A magnetic disk was manufactured. The surface shape, glide floating characteristics and coercive force of the obtained disk were evaluated by the following methods. The results are shown in Table 2.

Comparative Example 3 A magnetic disk was manufactured in the same manner as in Examples 9 and 10 except that no DC potential was applied. Table 2 shows the evaluation results of each characteristic.

Evaluation method (Examples 9 and 10 and Comparative Example 2,
3) Surface shape (average surface roughness Ra, peak count Pc
And SEM evaluation): Surface average roughness Ra and SEM evaluation were performed in the same manner as the evaluation methods of Examples 1 to 8 and Comparative Example 1. Further, a count level parallel to the center line was provided at 200 Å above the center line of the roughness curve, and the peak count at a measurement length of 250 μm was measured, which was designated as Pc200.

Glide levitation characteristics: Hitachi DECO R
The collision between the head and the protrusion of the disk was detected by the PZT element using G550, and evaluated as the flying height of the external head. Measurement of coercive force: The coercive force was measured in the same manner as in Examples 1 to 8 and Comparative Example 1.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

Industrial Applicability Since the surface treatment of the substrate by the method of the present invention can provide a magnetic recording medium excellent in floating characteristics, lubricity and wear resistance, it has high industrial utility value.

Claims (1)

[Claims] 1. A non-magnetic substrate is textured,
In a method of manufacturing a magnetic recording medium in which an underlayer and a magnetic layer are sequentially formed on this surface, the textured substrate surface is subjected to a current density of 25 mA / cm 2 in an electrolytic solution of an acidic solution.
^{2. A} method for producing a magnetic recording medium, comprising forming an underlayer and a magnetic layer after applying a voltage to the substrate for electrolytic treatment under the conditions of ² or less.