JPH0997425A - Production of magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance certifying (error) yield as well as to efficiently remove abnormal protrusions by carrying out a vanishing process for reducing the height of abnormal protrusions existing on the surface of a protective layer by anodic oxidation in an electrolytic soln. SOLUTION: In this vanishing process, a substrate is put in an electrolytic soln. and protrusions on the surface of a protective layer are anodically oxidized. At this time, abnormal protrusions are preferentially oxidized and removed. Various conditions in the anodic oxidation are desirably regulated so as to attain 5-100Å, preferably 5-30Å Ra (center line average roughness) and 10-500Å, preferably 10-200Å Rp (center line peak height). In the case of >500Å Rp, it becomes difficult to reduce the extent of levitation of a head and spacing loss is caused to reduce recording density.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magnetic recording medium. More specifically, it relates to a magnetic recording medium represented by a hard disk in which a magnetic layer is formed on a non-magnetic substrate by a method such as dry plating.

[0002]

2. Description of the Related Art In a magnetic disk system, when reproduction output is taken into consideration, it is advantageous that the distance (flying height) between the magnetic recording medium and the magnetic head is small, that is, the spacing loss is small. In other words, it is desirable that the magnetic disk surface be smooth.

However, in general, a magnetic disk has an "abnormal protrusion" on its surface after forming a protective layer or applying a lubricant.
Since there exist minute protrusions called "," these are removed with a polishing tape to appropriately lower the height of the protrusions and finish the surface. Such an operation of removing the abnormal protrusion on the disk surface by a physical means is usually called "burnish".

The burnishing process using a polishing tape is basically performed by applying an appropriate pressure to the surface of the magnetic disk with a polishing tape in which abrasive grains such as amylna and diamond are provided on a flexible support by an organic binder. It is carried out by bringing them into contact with each other and running the disk and the polishing tape. As such a burnishing process, for example, in the manufacturing process of a magnetic disk medium, after the surface of the magnetic disk medium is processed using a polishing tape, a polishing tape is used in order to effectively remove only minute projections existing on the surface. Using a medium peripheral speed of 250 m / min or more, tape processing pressure of 50 g
/ Mm ² or less, a method of manufacturing a magnetic disk medium is proposed (Japanese Patent Laid-Open No. 59-148134, Japanese Patent Publication No. 2-104).
No. 86). Further, there is also proposed a method in which after the texture is formed, the substrate is subjected to direct current electrolysis in an electrolytic solution to remove abnormal protrusions on the surface, and then a magnetic layer is formed (JP-A-7-
No. 225945).

[0005]

However, in the burnishing process using a polishing tape, since the abrasive grains in the polishing tape are not uniform in grain size but have a distribution (unevenness) in the grain size, the abrasive grains having a large grain size are large. There is a problem in that the abrasive grains dropped from the tape or the tape damage the disk surface and cause an error, resulting in a decrease in yield. Further, if polishing powder or grinding powder generated by polishing remains on the disk surface, it collides with the head to reduce sliding durability and damages the magnetic layer and the protective layer. Moreover, if the polishing powder or the grinding powder remains on the disk surface, the liquid lubricant or water is gathered around the remaining particles due to the capillary phenomenon, which causes head adsorption. Further, if the abnormal protrusions are continuously removed after the texture is formed as in Japanese Patent Laid-Open No. 7-225945, the abnormal protrusions that grow during the formation of each recording medium layer have no effect and a problem remains.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide an excellent burnishing method capable of solving the above-mentioned problems of burnishing with a polishing tape when removing abnormal protrusions on the surface of a magnetic recording medium. As a result of earnest research, the present inventors have found that a chemical burnishing method by anodic oxidation in an electrolytic solution is used instead of a physical burnishing method like burnishing with a conventional polishing tape. The inventors have found that these requirements are met and have completed the present invention.

That is, according to the present invention, at least a step of forming a magnetic layer on a non-magnetic substrate, a step of forming a protective layer on the magnetic layer, and a bar for reducing the height of abnormal protrusions existing on the surface of the protective layer. A method for manufacturing a magnetic recording medium having a nishishing step, wherein the burnishing step is performed by anodic oxidation in an electrolytic solution.

In a usual hard disk manufacturing process, a substrate is textured (the surface is appropriately roughened), washed, a magnetic layer is formed on the substrate, and then a protective layer is formed on the magnetic layer. After that, a burnishing process is performed to remove abnormal protrusions on the disk surface and adjust the height to an appropriate height. In such a manufacturing process, a step of providing an underlayer under the magnetic layer, a lubricating layer on the protective layer, and the like is added if necessary. The manufacturing method of the present invention is characterized in that a so-called burnishing step is performed by anodic oxidation in a known manufacturing step.

In the present invention, the burnishing step is carried out by immersing the support in an electrolytic solution and performing anodizing treatment. That is, at least the support on which the magnetic layer and the protective layer are formed is immersed in an electrolyte aqueous solution such as NaOH,
Using this as an anode, a voltage is applied between the cathode and the reference electrode. Thereby, in an aqueous solution, OH ⁻ , ClO ⁻ ,
Discharge of oxidizing ions such as SO ₄ ⁻ and CO ₃ ⁻ occurs. As a result, the atoms constituting the protective layer of the support of the anode, for example, carbon in the case of a carbon thin film, reacts with the oxidizing ions to combine with each other, resulting in CO ₂ , CO, Na ₂ CO _3, etc. To do. This removes the protrusions of the protective layer. Although the support is an anode in the present invention, the material of the cathode is not limited.

The electrolyte aqueous solution used in the burnishing process may be an acid or alkali aqueous solution, and may be 0.1
A concentration of -100% by weight, preferably 1-60% by weight is used. Examples of the acid used include inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, hydrofluoric acid and perchloric acid, and organic acids such as oxalic acid and formic acid. Examples of the alkali include NaOH and KOH, and two or more kinds of these may be blended and used. In consideration of burnish efficiency and corrosion of the electrolytic bath, it is preferable to use an alkaline aqueous solution. Moreover, you may mix | blend the additive for burnish efficiency and rust prevention property provision.

The current waveform to be used is, for example, direct current, alternating current such as single-phase alternating current and three-phase alternating current, pulse wave such as rectangular wave and triangular wave, single-phase half-wave, two-phase half-wave, three-phase half-wave, and six-phase half-wave. Special waveforms such as single-phase full-wave and three-phase full-wave are used. These waveforms may be used in combination. From the viewpoint of productivity, three-phase alternating current is desirable. Since the obtained burnish shape also changes when the electrolytic waveform is changed, it is desirable to select / combine the current waveforms according to the desired burnish shape.

Regarding the current density at the time of anodic oxidation, considering the uniformity of burnishing treatment, productivity and equipment load,
1 to 200 mA / cm ² is preferable, and more preferably 5
Is about 100 mA / cm ² . That is, if the current density is too low, the productivity tends to decrease, and conversely, if the current density is too high, the uniformity of the burnishing tends to decrease.

The voltage at the time of anodic oxidation is preferably 1 to 100 V, more preferably 2 to 50 V in view of the uniformity of burnishing treatment, productivity, and equipment load.
V. That is, if the voltage is too low, the required current density cannot be obtained, and the productivity is lowered. On the contrary, if it is too high, the electric field tends to be biased, and uniform roughening tends not to be performed.

The current and voltage during anodic oxidation may be set to be constant during the treatment, or may be changed during the process. Regarding the treatment time of anodization, considering the degree and uniformity of burnishing treatment, 1 second to 1
Time is preferable. More preferably, it is about 5 seconds to 20 minutes. That is, if the treatment time is too short, it is difficult to obtain the desired burnishing effect, and conversely, if the treatment time is too long, it tends to be difficult to obtain the desired burnishing effect.

The temperature at which anodic oxidation is performed is 1 to 100 ° C.
Degree is fine. Generally, the temperature may be around room temperature, but it may be appropriately selected depending on the type of electrolytic solution.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION In the method of manufacturing a magnetic recording medium of the present invention, the steps other than the burnishing step by anodic oxidation can be performed according to the conventional manufacturing method. That is, in the present invention, the basic structure of the magnetic recording medium is already formed before the step of removing the abnormal protrusion existing on the surface by anodic oxidation. For example, a step of providing a magnetic layer on a carbon substrate by dry plating means such as vapor deposition or sputtering, a dry plating means such as vapor deposition or sputtering, or providing a protective layer on the magnetic layer by dipping or spin coating. A magnetic recording medium is configured through steps and the like, and an operation of removing an abnormal protrusion existing on the surface is performed on such a magnetic recording medium. Further, it is possible to include a step of providing an underlayer on the carbon substrate by a dry plating means such as vapor deposition or sputtering means before the magnetic layer is provided.

Incidentally, it is preferable to employ dry plating means for film formation. That is, the dry plating means is more likely to obtain a high-quality magnetic film than the wet plating means. Further, the composition of the magnetic film can be easily changed, and the design of the magnetic film can be easily changed.

In the burnishing process of the present invention, as described above, the protrusions on the surface of the protective layer are anodized by arranging the substrate in the electrolytic solution. At that time, abnormal protrusions are preferentially oxidized. Are removed. The height (degree of oxidation) of the abnormal protrusions to be removed can also be precisely controlled by adjusting the oxidation conditions (current density, electrolysis time, type of electrolytic solution, etc.). Therefore, in the present invention, as the constituent material of the protective layer, any material can be used as long as it can be vaporized and decomposed by anodic oxidation and does not adversely affect the disk manufacturing process at that time. Particularly in the present invention, the protective layer is preferably a layer mainly composed of carbon such as diamond-like carbon, glassy carbon and graphite, or a metal or a metal thin film subjected to surface oxidation.
These protective layers are formed by a conventionally known method, for example, dry plating such as sputtering, and have a thickness of 5 to 25 n.
m.

The conditions for the anodizing treatment are that the Ra (center line average roughness) of the magnetic recording medium after the burnishing treatment is 5-1.
It is desirable to adjust it so that it is 00Å, preferably 5 to 30Å, and Rp (maximum height of center line) is 10 to 500Å, preferably 10 to 200Å. If Rp exceeds 500 Å, it is difficult to reduce the flying height of the head, resulting in spacing loss, which is not preferable in terms of improving recording density.

A lubricant is usually applied to the surface of the magnetic recording medium. This lubricant is usually only provided by applying a lubricant solution, and the surface profile (projections) does not change before and after the lubricant is applied. Work to remove the protrusion is performed. Although the work of removing the abnormal protrusion may be performed after applying the lubricant, in consideration of the fact that the lubricant is wiped off by this work, the lubricant must be applied again. Absent. Therefore, normally, the work of removing the abnormal protrusion is performed before the lubricant is provided.

The magnetic recording medium from which the abnormal projections are removed according to the present invention can reduce the flying height of the magnetic head and reduce the spacing loss, which is preferable in terms of reproduction output.

Further, in the present invention, the conventional technology is used as it is for the structure of the magnetic layer on the substrate. That is, the conventional techniques can be used as they are for the structure of the underlying layer (underlying film), the magnetic layer (magnetic film), the protective layer (protective film), the lubricating layer (lubricating film) and the like provided on the substrate.
For example, JP-A-5-18952 and 5-1.
The techniques described in Japanese Patent No. 37822, Japanese Patent Application Laid-Open No. 5-212169, Japanese Patent Application Laid-Open No. 5-289494, etc. can be used.

The substrate used in the present invention comprises, for example, carbon such as glassy carbon, tempered glass, crystallized glass, aluminum and aluminum alloys, titanium and titanium alloys, ceramics, resins, or composite materials thereof. Is mentioned. Among these, glassy carbon is particularly preferable, and for example, those described in JP-A-60-35333 can be used.

[0024]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Examples 1 to 4 and Comparative Examples 1 to 2 Film Forming Step As a substrate, the diameter is 1.8 inches, 25 mils, and the specific gravity is 1.5.
A glassy carbon substrate of No. 1 was prepared.

Ar gas pressure of 2 mTor was applied on these substrates.
A Ti layer having a thickness of 100 nm was formed by DC magnetron sputtering under the conditions of r and the substrate temperature of 250 ° C. Then, a 20 nm thick Al-Si alloy (Al: Si = 95 :) was formed on the Ti layer by DC magnetron sputtering under the conditions of Ar gas pressure of 2 mTorr and substrate temperature of 260 ° C.
5 / wt%) layer was formed. These layers form unevenness (texture) on the substrate.

Next, a 25 nm thick amorphous carbon (diamond-like carbon) layer was formed on the Al-Si alloy layer by DC magnetron sputtering under the conditions of Ar gas pressure of 2 mTorr and substrate temperature of 260 ° C. Next, Ar gas pressure 2 mTorr, substrate temperature 20
Using a DC magnetron sputtering device under the condition of 0 ° C., a thickness of 100 nm is formed on the amorphous carbon layer.
A Ti layer of 40 nm thick, and then a 40 nm thick C layer is formed on the Ti layer.
An r layer was provided.

Further, a 400 nm thick Co-Cr-Pt layer was formed on the Cr layer by DC magnetron sputtering under the conditions of Ar gas pressure of 2 mTorr and substrate temperature of 260 ° C.
A -B type magnetic layer was provided.

Then, using a facing target type sputtering apparatus equipped with a glassy carbon target, the interior of the chamber was evacuated, and Ar was adjusted to a gas pressure of 2 mTorr.
A gas was introduced to perform sputtering, and a protective layer made of amorphous carbon having a thickness of 20 nm was provided on the magnetic layer.

Burnishing Process The substrate on which various films were formed as described above was subjected to a burnishing treatment by anodic oxidation under the conditions (counter electrode: carbon) shown in Table 1. The tape burnish of Comparative Example 1 was carried out by pressing the polishing tape against a rotating roll with a rubber roll, under the following conditions. Abrasive tape: WA # 10000 Relative speed: 100 m / sec Time: 1 sec Roll hardness: 25 Shore hardness Roll pressing pressure: 0.8 kgf Comparative example 2 uses the same carbon substrate as in example 1,
A surface having a surface roughness of Ra = 37Å and Rp = 270Å is formed by texturing using a polishing tape of WA # 6000, and direct current electrolysis is performed in a 10% sulfuric acid aqueous solution to remove abnormal protrusions, and Ra = 35Å , Rp = 190Å was obtained. After that, a recording medium layer was subsequently formed in the same manner as in Example 1, but the burnishing treatment after forming the protective layer was not performed.

Thereafter, a perfluoropolyether type lubricant (Fomblin manufactured by Montecatini Co., Ltd. was used by a conventional method.
AM2001) solution was applied so that the thickness after drying was 17 Å to form a lubricant layer on the protective layer.

Characteristic Evaluation The magnetic disk obtained as described above was evaluated for the following characteristics. Table 1 shows the results.

(I) Ra (center line average roughness) and Rp
(Maximum height of center line) Ra and Rp are stylus roughness gauges (manufactured by TENCOR,
The measurement was performed under the following conditions according to model P2). Ra and Rp were measured before and after the burnishing process. Stylus diameter: 0.6 μm (needle curvature radius) Stylus pressing pressure: 7 mg Measurement length: 250 μm x 8 places Trace speed: 2.5 μm / sec Cut-off: 1.25 μm (low pass filter) (ii) Appearance inspection Bright illumination Visual inspection was performed under the following conditions to check for scratches and scratches, and those having an appearance with no problem in practical use were regarded as acceptable and evaluated according to the following criteria. S: Pass rate is 80% or more to 100% A: Pass rate is 50% to less than 80% B: Pass rate is 30% to less than 50% C: Pass rate is 0% to less than 30% (iii) It was performed using a MG150T device manufactured by GHT Proquip, using a 50% slider head. The following evaluation was made based on the passing rate at a flying height of 1.5 μ inches. S: Passage is 90% or more A: Passage is 70% or more and less than 90% B: Passage is 50% or more and less than 70% C: Passage is 30% or more and less than 50% D: Passage is 30 Less than% (iv) MCF (error characteristic) The error characteristic was measured using a MG150T device manufactured by Proquip, using a 70% slider head, and a recording density of 51 KF.
It was evaluated under the conditions of CI. Slice level is 70%,
The number of missing errors of less than 16 bits was counted and evaluated as follows. S: 50% or more of the evaluation disks have 0 to 5 errors. A: The number of errors is 6 to 15 in 50% or more of the evaluation disks
Individual. B: The number of errors is 16 to 4 in 50% or more of the evaluation disks
There are five. C: 50% or more of the evaluation disks have 46 or more errors.

[0034]

[Table 1]

As can be seen from these results, it can be seen that the magnetic recording medium produced by the manufacturing method of the present invention effectively removes the abnormal protrusions on the surface and is less likely to cause an error.

[0036]

According to the manufacturing method of the present invention, abnormal protrusions on the surface of a magnetic recording medium can be effectively removed, the certifying (error) yield is improved, and the appearance defect is significantly reduced.

Claims (2)

[Claims] 1. At least a step of forming a magnetic layer on a non-magnetic substrate, a step of forming a protective layer on the magnetic layer, and a burnishing step of reducing the height of abnormal protrusions present on the surface of the protective layer. In the method of manufacturing a magnetic recording medium having
A method of manufacturing a magnetic recording medium, wherein the burnishing step is performed by anodic oxidation in an electrolytic solution. 2. The method for producing a magnetic recording medium according to claim 1, wherein the main constituent component of the protective layer is carbon, a metal or a metal subjected to surface oxidation.