JPH07220268A - Method of manufacturing magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve a floating characteristic, lubricity and wear resistance by subjecting the surface of a substrate to two stages of texturing to maintain the substrate surface to a specific shape, then subjecting this substrate surface to an electrolytic treatment in an acidic electrolyte. CONSTITUTION:Ruggedness and line trace patterns are formed by two stages of texturing on the front surface layer of the substrate 1. The substrate surface subjected to the texturing is subjected to the electrolytic treatment while voltage is applied to the substrate 1 in the electrolyte of an acidic soln. The projections, burrs, etc., remaining on the front surface of the substrate 1 after the texturing are etched away and the front surface of the substrate 1 has a smooth surface state. The floating characteristic and CSS characteristic of the head are greatly improved.

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, by performing a specific surface processing on the substrate, the surface characteristics are improved, the floating characteristics,
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. Has been.
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]

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, have performed two-step texture processing on the substrate to specify the substrate surface. The inventors have found that the above problems can be solved by electrolytically treating the surface of the substrate in an acidic electrolytic solution after maintaining the shape, and completed the present invention.

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. The surface average roughness Ra of the substrate is processed into a surface shape of 20 to 150Å by texturing,
Next, after subjecting the substrate surface having the maximum protrusion height Rp of 400 Å or less on the substrate surface by the second stage texturing to electrolytic treatment in an electrolytic solution of an acidic solution while applying a voltage to the substrate, an underlayer and A method of manufacturing a magnetic recording medium is characterized by forming a magnetic layer.

The present invention will be described in more detail below.
As the 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 thereof is mirror-finished, and then a non-magnetic metal,
For example, a Ni-P alloy, a Ni-Cu-P alloy, or the like formed as a surface layer having a thickness of about 5 to 20 m by electroless plating is used. It is common to subject the surface layer of the above-mentioned substrate to a polishing treatment and then to perform a texture treatment. The polishing process is performed, for example, by sandwiching the substrate between polishing pads which are impregnated with free abrasive grains on the surface, and polishing the liquid while supplying a polishing solution such as a surfactant aqueous solution. The surface is mirror-finished to have an average surface roughness Ra of 50 Å or less, preferably 30 Å or less. The free abrasive grains are typically alumina slurry polypla 700 or polypla 103 (both are registered trademarks of Fujimi Incorporated), diamond slurry, S.
iC-based slurry or the like is used. As a polishing pad, typically, Surfin 100 or Surfin
A urethane foam such as XXX-5 (both are registered trademarks of Fujimi Incorporated) is used.

In the present invention, specific unevenness and streak patterns are formed on the surface layer of the above-mentioned substrate by two-step texturing. First, in the first stage texturing, the surface layer of the substrate is ground by slurry grinding using a polishing tape and free abrasive grains, or tape grinding using a polishing tape carrying abrasive grains, and the average roughness of the substrate surface is ground. Ra is 20 ~
150 Å, preferably 40 to 100 Å, and the maximum protrusion height Rp is 100 to 1000 Å, preferably 200 to 400
The angle (cross angle) θ at which the unevenness of Å intersects with the formed scratches is preferably 10 to 40 °, more preferably 1
Form a surface profile of 0 to 30 °. By forming the cross pattern striations on the substrate surface, the adsorption property of the substrate surface can be improved.

A buff tape such as nylon pile or polyester pile is preferably used as the polishing tape used for the above slurry grinding, and a free abrasive grain of 0.
Diamond-based abrasive grains of 3 to 4 μm are used, and the loose abrasive grains are used as a liquid slurry in which a dispersant is suspended in a liquid (water or a water-based liquid). An example of the above texture processing will be described in detail with reference to FIG. In FIG. 1, four polishing tapes 2 are pressed by contact rollers 3 on both the front and back surfaces of a disk-shaped substrate rotating in the direction of arrow A to perform polishing. The contact roller 3 presses the polishing tape against both surfaces of the substrate 1 with a predetermined force by the roller pressing cylinder 4. The polishing tape is running in the direction of arrow B, and a new tape surface is always in contact with the surface of the substrate for polishing. Further, the polishing tape can be reciprocated (vibrated) in the direction of arrow C by the reciprocating motion of the contact roller 3 to polish the entire surface of the substrate, and the scratches A formed by polishing with the polishing tape on the substrate intersect. Angle (cross angle)
The angle θ is usually 10 to 40 °. Further, in the case of slurry grinding, the polishing liquid in which the above-mentioned free abrasive grains are suspended is supplied from the polishing nozzle 5 to the polishing surface side of the polishing tape. As the conditions for the slurry grinding, the number of rotations of the disk is 30 to 450 rpm, the frequency of the polishing tape (reciprocating motion) is 60 to 3000 times / minute,
Cylinder pressing pressure is 1.0 to 3.0 kg / cm ² , and polishing time is 5 to 30 seconds.

The polishing tape used for the above-mentioned tape grinding has a grain size of # 3000 (grain size 3 μm) to # 10000.
Polishing tape carrying alumina abrasive grains (particle diameter 0.5 μm) or SiC abrasive grains, preferably WA # 4000 to WA #
A polishing tape carrying 8000 white alumina abrasive grains is used, and it is carried out using the same apparatus as in FIG. As the polishing conditions for the above-mentioned tape grinding, general conditions can be adopted, and the rotation speed of the disk is usually 30 to 200 rpm,
Vibration frequency (reciprocating motion) of the polishing tape is 80 to 300 times /
Min., Cylinder pressing pressure is 1.0 to 2.0 kg / c
m ² and a polishing time of 5 to 30 seconds are used.

The surface average roughness Ra of the substrate after the first-stage texture processing is 20 to 150Å, and 20Å
If it is lower, the CSS characteristics deteriorate, while Ra is 150Å
If it is higher than this, the floating characteristics are deteriorated, which is not preferable. Next, a second layer is formed on the surface of the substrate after the first-step texture processing.
We give technic processing processing of step. In the texturing of the second step, it is preferable to perform slurry grinding using a polishing tape and specific loose abrasive grains, and without substantially changing the surface average roughness Ra and the cross angle in the first step, The protrusions such as burrs and burrs on the surface are selectively polished and removed, and the maximum protrusion height Rp of the surface is 400 Å or less,
Preferably, the surface shape of 100 to 250Å is formed.

The polishing tape used for the second-stage texturing has sufficient porosity so that the following liquid slurry can penetrate into the polishing tape, for example, a non-woven tape such as nylon, cellulose or rayon, a buff tape, Woven tape or the like is preferably used, and as the free abrasive grains, for example, white alumina-based abrasive grains of 0.3 to 6 μm are used, and the free abrasive grains together with a dispersant in a water-based liquid. The suspended liquid slurry is used as a polishing liquid. The loose abrasive grains in the polishing liquid are trapped in the contact area between the polishing tape and the disc and pressed against the disc surface to realize a desired polishing action. As the second stage texture device, a device similar to that shown in FIG. 1 is used. The conditions for the slurry grinding in the second-stage texturing are not particularly limited, and are usually a disk rotation speed of 50 to 400 rpm, a polishing tape vibration frequency (reciprocating frequency) of 50 to 200 times / min, and a cylinder rotation speed. A pressing pressure of 1.0 to 3.0 kg / cm ² and a polishing time of 3 to 20 seconds are used. The maximum protrusion height Rp after the second-stage texture processing is 400 Å or less, but 40
If it is higher than 0Å, the floating characteristics are deteriorated, which is not preferable.

The substrate obtained by the two-step texture processing of the present invention has a surface average roughness Ra of 20 to 150.
Å, preferably 40 to 100Å, maximum protrusion height Rp is 1
Unevenness of 0 to 400Å, preferably 100 to 250Å, and an Rp / Ra ratio of 5 or less, and a cross angle θ of 1
It has a shape of 0 to 40 °, preferably 10 to 30 °.
By performing the two-step texture processing of the present invention, adsorption of the magnetic head and the magnetic recording medium can be prevented, and the CSS
The characteristics are improved and the magnetic anisotropy is improved.

In the present invention, texture processing is applied.
The surface of the substrate is immersed in an electrolytic solution of an acidic solution and a voltage is applied to the substrate.
Electrolyte while applying. As the above electrolyte, for example,
For example, sulfuric acid, nitric acid, hydrochloric acid, chromic acid, phosphoric acid, oxalic acid, vinegar
0.5 to 40 weight of one or a combination of two or more acids
%, Preferably 1 to 30% by weight of the aqueous solution
It is used, and phosphoric acid is particularly preferable. Electrolytic treatment conditions
For liquid temperature 10-70 ° C, current density 0.1-50mA /
cm², Preferably 0.5 to 45 mA / cm²,further
Preferably 1.0 to 25 mA / cm², Electrolysis time 1-4
00 seconds, preferably 2 to 200 seconds, quantity of electricity (current density and
Product of electrolysis time) 10 to 1000 mA · sec / cm², Preferred
50 to 600 mA · sec / c ²Carried out within
It

As the potential used in the electrolysis treatment in the present invention, an alternating waveform current in which direct current or positive and negative polarities are alternately converted can be mentioned, and an alternating waveform current is particularly preferable. Examples of the alternating waveform current include waveform currents such as sine wave single-phase alternating current, sine wave three-phase alternating current, rectangular wave, triangular wave, and trapezoidal wave. The frequency of the alternating waveform current is preferably 0.1 to less than 500 Hz, more preferably 0.1 to 30 Hz.
It is carried out in the range 0 Hz, particularly preferably in the range 0.5 to 200 Hz. The ratio (QA) of the amount of electricity at the anode (QA) and the amount of electricity at the cathode (QA) when the alternating waveform current is used.
/ QC) is 0 to 2.0, preferably 0.8 to 1.
5, more preferably 0.9 to 1.1.

In the present invention, the electrolytic treatment described above removes the protrusions, burrs, and the like remaining on the substrate surface after the texturing by etching, so that the substrate surface becomes a smooth surface state, and the flying characteristics and CSS characteristics of the head are improved. Greatly improved. In particular, the use of an alternating waveform current is preferable because in addition to the above improvement, the occurrence of pits (pitting corrosion) on the substrate surface can be suppressed and the magnetic characteristics such as coercive force are improved. Also, after the electrolytic etching treatment, if necessary,
Prior to lamination of 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,
Alternatively, a finishing process may be performed in which a tape carrying relatively fine abrasive grains such as alumina is pressed against the surface of the substrate and the texture process is performed again.

On the surface of the substrate that has been subjected to the electrolytic treatment, chromium is formed as a secondary underlayer by sputtering.
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 alloy is
Usually, it is deposited and formed on the base layer 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.

A carbonaceous film is preferable as the protective thin film layer formed on the metal magnetic thin film layer, and the carbonaceous protective thin film layer is usually in the atmosphere of a rare gas such as argon or He or in the presence of a small amount of hydrogen. Then, an amorphous carbon film, a hydrogenated carbon film or the like is deposited by sputtering using carbon as a target. The thickness of the protective thin film layer is
It is usually in the range of 50 to 500Å. Further, a lubricating film may be further formed on the protective thin film layer in order to reduce the coefficient of friction.

[0020]

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 3 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 30Å is formed, and then fine grooves are formed by the first-step texturing performed under the conditions shown in Table 1, and the disk is subjected to the second-step texturing using loose abrasive grains. Treated, average surface roughness (Ra) of about 60Å
And the maximum protrusion height (Rp) of 270Å. Next, 10 wt. % Aqueous solution of phosphoric acid, electrolysis was carried out under the conditions shown in Table 2 at a liquid temperature of 20 ° C. while applying a voltage to the disk substrate so that the current had an alternating rectangular waveform. Surface average roughness (Ra) of the obtained disk
Was 63Å, and the maximum protrusion height (Rp) was 240Å.
Then, on the surface layer of the substrate, a general Cr underlayer, Co-
A magnetic disk was manufactured by sequentially sputter-coating a magnetic layer made of a Cr-Ta alloy and a protective film made of a carbon film. Surface shape of the obtained disk (R
a and Rp), glide flying characteristics, and CSS characteristics were evaluated by the following methods. The results are shown in Table 2.

Evaluation method Surface shape (surface average roughness (Ra), maximum projection height (R
p)): The surface length was measured with a surface roughness meter (“ET-30HK” manufactured by Kosaka Laboratory) having a 0.5 μm conical stylus with a measurement length of 250 μm. As a measuring method, the surface on an arbitrary straight line on the circumference of the substrate was measured in the radial direction, and the surface average roughness Ra and the maximum protrusion height Rp were obtained. Glide flying characteristics: RG550 manufactured by Hitachi DECO was used to detect the collision of the head and the protrusion of the disk with the PZT element, and was evaluated as the flying height of the external head. CSS characteristics A disk was incorporated into an actual drive, and start and stop were repeated. After performing CSS20000 times, the static friction coefficient between the head and the disk was evaluated. Comparative Examples 1 and 2 Magnetic disks were manufactured in the same manner as in Examples 1 to 3 except that the first-stage texturing was performed under the conditions shown in Table 1 and the electrolytic treatment with phosphoric acid was not performed. Table 2 shows the evaluation results of the obtained disks.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

The surface treatment of the substrate according to the method of the present invention makes it possible to provide a magnetic recording medium which is excellent in floating characteristics, lubricity and wear resistance, and thus has high industrial utility value. .

[Brief description of drawings]

FIG. 1 (a) is a partial schematic front view of components of a texture processing apparatus used in the present invention. (B) It is a schematic side view of (a).

[Explanation of symbols] 1 substrate 2 polishing tape 3 contact roller 4 roller pressing cylinder 5 polishing nozzle

Claims (4)

[Claims] 1. A method of manufacturing a magnetic recording medium, wherein a substrate is textured, and an underlayer and a magnetic layer are sequentially formed on the surface of the substrate. Average roughness Ra of 20 to 150Å
The surface shape of the substrate is set to 400 Å or less by the second step texturing, and the maximum protrusion height Rp of the substrate surface is 400 Å or less. A method of manufacturing a magnetic recording medium, comprising forming an underlayer and a magnetic layer after the treatment. 2. The method for producing a magnetic recording medium according to claim 1, wherein the second-step texturing is performed by slurry grinding using loose abrasive grains. 3. The surface of the substrate after the texturing of the second step has irregularities in which the ratio of the maximum protrusion roughness (Rp) to the average surface roughness (Ra) is 5 or less, and is formed on the substrate surface. 3. The method for manufacturing a magnetic recording medium according to claim 1, wherein the intersecting angle of the scratches is in the range of 10 to 40 °. 4. The method for producing a magnetic recording medium according to claim 1, wherein the electrolytic treatment is performed while applying a voltage to the substrate so that an electric current has an alternating waveform.