JPS63106921A - Manufacture of magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the durability and the corrosion resistance by polishing the surface of a non-magnetic protective layer formed on a recording magnetic layer, and thereafter, bringing the surface to an oxidation processing. CONSTITUTION:A recording magnetic layer 11 and a non-magnetic protective layer 12a are formed on a substrate 10, a projection 21 existing on the surface of a disk is eliminated by polishing, and thereafter, an oxidation of the surface is executed. Subsequently, a projection on the surface of the non-magnetic protective layer formed on the recording magnetic layer of a metallic thin film is eliminated by polishing, and thereafter, by providing an oxidation processing process of the surface, a dust supply from the medium itself is eliminated without deteriorating the corrosion resistance, a damage of the medium caused by an entrainment of dust between the medium and the head is prevented, the durability is improved, and a variance of the durability can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing a magnetic recording medium having a recording magnetic layer made of a metal thin film.

(Prior Art) Perpendicular magnetic recording has many excellent features as a high-density recording technology, and intensive research is being conducted in various places to put it into practical use. Recording medium used for perpendicular magnetic recording (hereinafter referred to as
Perpendicular magnetic recording media) include those whose recording magnetic layer is an oxide thin film having a magnetoplumbite crystal structure such as Ba-ferrite, and Co-Cr5Co-V.
S.C.

In recent years, research has mainly been carried out on recording magnetic layers made of metal thin films such as -Cr-Rh. In particular, the latter metal thin film type media, which can be formed at a lower temperature than Ba-ferrite thin film, is possible because it can be formed at a temperature that allows the use of flexible resin film substrates used in floppy disks, etc. is seen as promising as a perpendicular magnetic recording medium.

Metal thin film type perpendicular magnetic recording media are conventionally used coated media, such as γ-Fe2O3 and Co-γ-F.
Because it has a completely different structure from a magnetic recording medium in which ferromagnetic particles such as e2O3 are dispersed in a binder and coated on a substrate,
When put into practical use, new issues will arise that did not arise with coated media. A typical example of this is maintaining the ability of the medium to withstand environments such as high temperature and high humidity, that is, maintaining corrosion resistance.
The objective is to ensure the properties that can withstand the contact running of the magnetic head, that is, the durability.

In order to improve the durability of metallic thin-film media, conventional methods have been considered, such as forming a non-magnetic protective layer on the recording magnetic layer and further providing a lubricating layer using liquid or solid lubricant thereon. However, it can be said that the improvement in durability achieved by these methods is still insufficient from a practical standpoint. This can be seen in the fact that the results of durability evaluation vary.

In other words, while there are media with high durability, there are also media with low durability. An effective measure to solve this problem is to remove the protrusions that exist on the surface of the metal thin film media, which is one of the causes of decreasing durability. By polishing, etc., it was possible to eliminate variations in durability and improve the overall durability level.However, polishing peels off the protective layer on the protruding parts and exposes the magnetic layer. , a new problem has arisen in that the corrosion resistance of the exposed portion of the magnetic layer may deteriorate. Therefore, in order to improve the reliability of the medium, it is necessary to take measures to improve the durability of the medium while maintaining corrosion resistance.

(Problems to be Solved by the Invention) As described above, even if conventional manufacturing techniques for metal thin film magnetic recording media such as providing a protective layer or a lubricant layer are used, variations in the durability of the media occur. Because of the large size, it has been difficult to obtain a magnetic recording medium that can be put to practical use. Also,
The introduction of a method of polishing the surface of the medium, which is effective for suppressing variations in durability, has been insufficient in terms of improving reliability because it may worsen corrosion resistance.

Accordingly, an object of the present invention is to provide a method for manufacturing a magnetic recording medium having a magnetic recording layer made of a metal thin film that has high durability, small variations in durability, and excellent corrosion resistance.

[Structure of the Invention (Means for Solving the Problems)] The present invention provides a method for improving the surface of a non-magnetic protective layer formed on a recording magnetic layer made of a metal thin film formed on a substrate by removing protrusions on the surface. The above object is achieved by performing an oxidation treatment step on the surface after polishing to remove it.

(Function) If there are protrusions on the surface of the recording magnetic layer or the non-magnetic protective layer, when the magnetic head runs in contact with the medium, the recording magnetic layer or non-magnetic protective layer at the protruding parts is scraped away, causing dust to form. occurs. When this dust is caught between the medium and the head, it causes destruction of the medium and impairs its durability.

If the protrusions on the surface of the non-magnetic protective layer are removed by polishing in advance based on the present invention, the supply of dust from the medium itself is eliminated, thereby suppressing damage to the medium due to dust entrained between the medium and the head. , durability is improved.

In addition, by performing an oxidation treatment process on the surface after polishing, an effective oxide film can be formed on the surface of the metal magnetic layer where the non-magnetic protective layer has been peeled off due to polishing, and the remaining protective layer can be removed. Since no new oxide film is formed in the area where the layer exists, the increase in the overall protective layer thickness can be suppressed compared to the case where a new protective layer is formed, which results in an increase in spacing loss during recording and playback. Deterioration of corrosion resistance can be prevented without any damage.

(Embodiment) FIG. 1 is a diagram illustrating the present invention using a floppy disk as an example. The disk has a recording magnetic layer 11 on a substrate 1o.
In addition, a nonmagnetic protective layer 12a is formed (FIG. 1-a). The protrusions 21 present on the disk surface are removed by polishing (FIG. 1-b). This prevents the protrusions from being destroyed by the head, eliminates the generation of dust, suppresses damage to the medium caused by dust getting caught between the medium and the head, and improves durability, but the non-magnetic protective layer peels off. Corrosion may occur from the damaged parts.

For this reason, after polishing, the following surface oxidation treatment was performed (Figure 1-c).

FIG. 2 shows the basic configuration of an apparatus for oxidizing the surface of a polished medium. An electrode 62 is provided inside the vacuum chamber 61, and the electrode 62 is connected to a high frequency power source 63 installed outside the vacuum chamber 61. The medium 55 that has been polished and cleaned as necessary is held by the electrode 62. The vacuum chamber 61 is connected to the vacuum pump 6 via the vacuum valve 64.
6 and is also connected to an oxygen supply source 67 via a vacuum valve 65.

The polished medium 55 was set in this device, and after the device was once evacuated to a high vacuum, oxygen was introduced until the pressure reached 5 Pa. Thereafter, the high frequency power source was turned on to perform high frequency discharge in an oxygen atmosphere. As a result, the medium 55 was exposed to oxygen plasma, and a thin film of oxide of the element constituting the metal thin film was formed only in the portion where the protective layer was removed and the metal layer was exposed.

As a result, the oxidized layer 12b of the metal was formed only in the portion where the magnetic metal layer was exposed by polishing, and as a result, corrosion in a high temperature and high humidity environment was suppressed, and deterioration of corrosion resistance could be prevented. Therefore, by performing polishing as in the present invention and oxidizing the surface, an effective oxide film can be formed on the exposed magnetic metal thin film layer after the protective layer has been removed.
Durability can be greatly improved while maintaining corrosion resistance.

3A and 3B are diagrams for explaining a polishing process in an embodiment of the present invention. A center hub 2 is attached to the center of a magnetic recording medium 1 manufactured in the form of a floppy disk, and this center hub 2 is connected to a motor 3. When the magnetic recording medium 1 is rotated by the motor 3, the medium 1 is pressed against the surface of the polishing tape 4 with a force f.

Further, the polishing tape 4 is fed at a constant speed as shown by an arrow 5. As a result, the surface of the magnetic recording medium 1 is polished. Also, protrusions on the surface are removed. As the polishing tape 4, for example, Aj2203 is applied as an abrasive on a tape-shaped base.
The one coated with #10,000 particles is used.

On the other hand, in order to remove the fragments removed by this polishing, the cleaning tape 6 is sent in the direction indicated by the arrow 7 while being in contact with the surface of the magnetic recording medium 1 in the same manner as the polishing tape 4. The polishing tape 4 and the cleaning tape 6 are also movable in the radial direction of the magnetic recording medium 1 as shown by arrows 8 and 9 so that at least the entire recording surface of the magnetic recording medium 1 can be polished and cleaned. ing.

FIG. 4 is an enlarged view showing how the surface of the magnetic recording medium 1 is polished by the polishing tape 4, and the base substrate 10 is
This is a case where the surface of a medium on which a recording magnetic layer 11 and a nonmagnetic protective layer 12 are laminated is polished.

The recording magnetic layer 11 and the nonmagnetic protective layer 12 are, for example, a fifth layer.
It is possible to form the film using a continuous thin film forming apparatus as shown in the figure. A supply roll 41 and a heating roller 43a supplying the flexible resin film base 42 into the vacuum chamber 4o.
A take-up roll 44 for winding up the s43bs and the base body 42 is provided. Note that guide rollers and the like are omitted in the figure.

For example, Co--Cr alloy targets 45a and 145b are provided around the heating rollers 43a and 43b, and these targets 45a and 45b are supplied with electric power from external power sources 46a and 46b.

Using the above-described device, the flexible resin film base 42 sent out from the supply roll 41 is transferred to the first heating roller 4.
3a, a recording magnetic layer made of a Co-Cr alloy thin film is first formed on one surface of the base 42 by sputtering, and then when the base 42 passes around the surface of the second heating roller 43b, Then, a recording magnetic layer made of a Co--Cr alloy thin film was formed on the other surface of the base 42 in the same manner. After recording magnetic layers are thus formed on both sides, the base body 42 is wound up on a winding roll 44.

Next, a nonmagnetic protective layer made of oxide was formed on the recording magnetic layer to a thickness of 0.02 μm by sputtering an oxide target such as SiO2. Then, the substrate on which the recording magnetic layer and the nonmagnetic protective layer were formed was punched out into a disk shape with a diameter of 3.5 inches.

Table 1 shows the main specifications of the 3.5 inch floppy disk thus produced.

Forty Co--Cr floppy disks thus formed were prepared, and the surface of the medium was polished to remove protrusions using the apparatus shown in FIG. 2 of these
For the 0th sheet, treatment was performed in oxygen plasma using the surface oxidation treatment apparatus shown in FIG. 2 described above. 2 left
0 sheets were left as is. Next, 20 pieces each, total 4
After cleaning the surface of 0 Co--Cr floppy disks, the same lubrication treatment was performed.

A durability test was conducted on these two different groups of 620 floppy disks under the same conditions using the same magnetic head (Mn-Zn phyllite head, radius of curvature 50R). The disk life was defined as the point in time when the reproduction output decreased to 70% of the initial output, and the number of times the disk was run (buses) until reaching that state was defined as the durability. The results of the durability test are shown in Figure 6. The horizontal axis in Figure 6 is durability, and the vertical axis is the percentage of media showing each durability.
(a) shows a disk polished after forming a non-magnetic protective layer, (
b) shows the results for a disk in which the surface was oxidized after polishing to form an oxide film again in the area where the protective layer had been removed.

As is clear from FIG. 7, the variation in durability is small for both the disks subjected to polishing after forming the nonmagnetic protective layer and the disks subjected to polishing and then formed with the nonmagnetic protective layer. That is, none of them have a durability of 4 million buses or less, and a high proportion of them have a high durability of IQ 1,000,000 buses or more.

Next, a 3.5-inch floppy disk having the specifications shown in Table 2 was produced by the same process as above.

Thereafter, 20 identical floppy disks were prepared in the same manner as described above, and subjected to the same polishing treatment using the apparatus shown in FIG. Ten of them were left as they were, and the remaining ten were subjected to a step of oxidizing their surfaces using the apparatus shown in FIG. Thereafter, missing pulses were measured for a total of 20 floppy disks, 10 each, which had been subjected to the same lubrication treatment. The track width is 120μ. The results are shown in FIG. (a) shows the results of a disk without surface oxidation treatment, and (b) shows the results of a disk whose surface was treated with the surface oxidation treatment apparatus shown in FIG. 2 after polishing.

Next, each of the 10 disks on which the missing pulse measurement was performed was placed at a temperature of 80°C and a humidity of 90% Rh for 16 minutes.
It was left for 8 hours. Thereafter, missing pulses were measured for each of the 10 disks. The results are shown in FIG.

(a) Disc as polished after protective film formation, (b)
This is a disk that has been subjected to the surface oxidation treatment described above after polishing.

As is clear from FIGS. 7 and 8, the disks subjected to surface oxidation treatment after polishing according to the present invention show almost no increase in the number of missing pulses even when left in a high temperature and high humidity environment. Corrosion resistance is good. On the other hand, the number of missing pulses increases in the as-polished disk, indicating that the recording magnetic layer has deteriorated. That is, the corrosion resistance is insufficient.

The reason why durability is improved while maintaining sufficient corrosion resistance by performing surface oxidation treatment after polishing based on the present invention is that protrusions on the disk surface are removed by polishing, and the surface treatment This is because an effective oxide film is formed on the surface of the metal thin film in the area where the protective layer is removed, and the exposure of the magnetic layer to the outside air can be suppressed.

As shown in FIG. 9(a), the protrusion 21 on the disk surface breaks while the magnetic head 23 is in contact with it and travels, as shown in FJ, and dust 22 is generated. Become. The dust generated in this way will not be caught between the disk head and the disk when the head is running stably, but when the head moves in the radial direction of the disk, due to thermal expansion of the disk, or when the device It is easy to get caught between the disk head in an unbalanced state such as vibration. Dust caught between disk heads has a non-negligible probability of destroying the disk.

On the other hand, as in the present invention, by polishing and then oxidizing the surface, a non-magnetic protective layer, which is an oxide of the elements constituting the metal thin film, is formed on the exposed part of the metal thin film layer. As shown in FIG. 10, protrusions on the disk surface are removed, dust generation is eliminated, and durability can be greatly improved while maintaining corrosion resistance.

In the figure, 10 is a substrate, 11 is a recording magnetic layer, 12a is a nonmagnetic protective layer, and 12b is a nonmagnetic protective layer formed after polishing.

The present invention is not limited to the embodiments described above, and can be implemented with various modifications without departing from the scope of the invention.

For example, in the examples, polishing and forming the nonmagnetic protective layer were performed after punching, but polishing and forming the nonmagnetic protective layer by surface oxidation treatment can be performed sequentially. As shown in FIG. 11, a device for continuously polishing a medium includes a take-up roll 111 and a delivery roll 1.
12 and polishing tape 113, cleaning tape 11
4 may be used. In addition, surface oxidation treatment after polishing preserves 1 [11! For formation, the apparatus shown in 2nd rlA may be used.

Further, in the embodiment, cleaning was performed after the polishing process, but the cleaning process may be omitted as long as the effect of the cleaning tape 6 explained in FIG. 2 is sufficient.

Furthermore, in the durability test mentioned above, the recording magnetic layer was C.

- This is an example of a case of a Cr alloy thin film, and a case of a medium in which a nonmagnetic protective layer is formed on a recording magnetic layer,
The polishing treatment for removing surface protrusions according to the present invention is effective when the recording magnetic layer is other metal thin film or when the non-magnetic coercive WL is CL
For example, Aj! other than O2! It is also effective for media that are oxide thin films such as 203 and ZrOz, oxide thin films such as 5t-0-N, nitride thin films, carbide thin films, and carbon films.

For surface oxidation treatment, it is preferable to use oxygen plasma to improve corrosion resistance and durability.
The bias voltage, oxygen pressure, etc. and atmosphere can be selected according to requirements, but other methods such as thermal oxidation and other methods are also possible.

This is especially worth considering in hard disks whose substrates are hard, such as A2 or glass.

Note that the plasma atmosphere may not be pure oxygen, but may be an oxygen atmosphere or a mixed atmosphere.

[Effects of the Invention] According to the present invention, protrusions on the surface of the nonmagnetic protective layer formed on the recording magnetic layer made of a thin metal film are removed by polishing,
After that, a surface oxidation treatment process eliminates dust supply from the media itself without reducing corrosion resistance, prevents damage to the media caused by dust getting caught between the media and the head, and improves durability. Gender variation can be suppressed.

[Brief explanation of the drawing]

Figure 1 is a diagram for explaining the polishing process and non-magnetic protective layer formation in the present invention, and Figure 2 is a diagram showing an example of a surface treatment apparatus used to perform surface oxidation treatment on a medium punched into a floppy disk shape. , FIG. 3 is a front view and side view showing the configuration of a polishing apparatus for explaining the polishing process in an embodiment of the present invention, and FIG. 4 is an enlarged view showing the state of polishing.
FIG. 5 is a diagram showing an example of a continuous thin film forming apparatus used for forming the recording magnetic layer and the non-magnetic protective layer, FIG. Figure 7 shows an example of the results of missing pulse measurements on polished media, Figure 8 shows an example of the results of missing pulse measurements on media left in a high temperature and high humidity environment after polishing, and Figure 9. 10 is a diagram for explaining the mechanism of durability deterioration caused by surface protrusions of a magnetic recording medium having a recording magnetic layer made of a thin metal film, and FIG. FIG. 11, which is a diagram for explaining film formation, is a diagram showing an example of the configuration of a polishing apparatus that continuously performs polishing processing in the present invention.

Claims (4)

[Claims] (1) A method for manufacturing a magnetic recording medium in which a recording magnetic layer made of a metal thin film is formed on a nonmagnetic substrate, and then a protective thin film layer is formed on the surface of the nonmagnetic protective layer formed on the recording magnetic layer. A method for manufacturing a magnetic recording medium, comprising the steps of: polishing to remove protrusions on the surface; and then oxidizing the surface. (2) After polishing the surface of the nonmagnetic protective layer formed on the recording magnetic layer, the method further comprises a step of cleaning the surface, and a step of oxidizing the surface. A method for producing a magnetic recording medium as described in . (3) After polishing the surface of the nonmagnetic protective layer formed on the recording magnetic layer, the method further comprises the steps of oxidizing the surface and lubricating the surface. A method of manufacturing the magnetic recording medium described above. (4) The method for manufacturing a magnetic recording medium according to claim 1, wherein the recording magnetic layer is made of an alloy containing at least one of Co and Cr as a main component.