JPS60237626A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium which is extremely stable and has excellent corrosion resistance on account of Co2O3 by forming a thin ferromagnetic metallic film layer consisting of Co or contg. Co on a substrate and subjecting the surface of said layer to plasma oxidation thereby forming a protective layer consisting of Co2O3 thereon. CONSTITUTION:The substrate 4 consisting of a polyester film, etc. is moved along the peripheral side surface of a cylindrical can 3 from a stock film roll 5 and while the substrate is taken up on a take-up roll 8, gaseous O2 is introduced through an introducing pipe 9 into a vacuum chamber 1. A voltage is impressed to an AC electrode 10 for generation of plasma provided in the lower part of the vessel 1 and a voltage is impressed to a DC electrode 11 provided right under the can 3 in extreme proximity thereto at the same instant to oxide the surface of the thin ferromagnetic metallic film 14 consisting of Co or contg. Co, thereby forming the protective layer 5 consisting of Co2O3. The Co2O3 has excellent corrosion resistance and since the layer 15 exhibits substantial corrosion resistance at about 10-100Angstrom , the recording medium A having a small spacing loss and excellent durability is obtd.

Description

[Detailed description of the invention] [Technical field and purpose] The present invention relates to a magnetic recording medium having a ferromagnetic metal thin film layer made of cobalt or a ferromagnetic material containing cobalt as a recording layer. The object of the present invention is to provide an excellent magnetic recording medium.

[Background technology]

A magnetic recording medium whose magnetic recording layer is a ferromagnetic metal thin film layer made of cobalt or a ferromagnetic material containing cobalt is usually made by depositing cobalt or a cobalt alloy on a base film by vacuum deposition, etc. Although it has characteristics suitable for density recording, it has the disadvantage that it is easily oxidized by oxygen in the air, and this oxidation deteriorates magnetic properties such as maximum magnetic flux density.

For this reason, the surface of a ferromagnetic metal thin film layer made of this type of cobalt or a ferromagnetic material containing cobalt has been oxidized to improve its corrosion resistance. Co by exposing it to oxygen plasma.

with a protective layer consisting of
No. 8-41439) has been proposed, but the protective layer formed by this method is composed of unstable Coo and Co3O4, and has the disadvantage that oxidation progresses further because it contains Coo, and the results are still sufficiently satisfactory. has not been obtained.

[Summary of the invention]

This invention was developed as a result of various studies in view of the current situation.
The surface of a ferromagnetic metal thin film layer made of cobalt or a ferromagnetic material containing cobalt formed on a substrate is turned into plasma M with an extremely strong plasma potential, and the cobalt is oxidized to trivalent cobalt oxide, which is extremely stable. Co2O3
This was developed based on the discovery that a magnetic recording medium with sufficiently improved corrosion resistance could be obtained by forming a protective layer consisting of cobalt or a ferromagnetic material containing cobalt. It is characterized by being provided on the surface of a ferromagnetic metal thin film layer consisting of.

In this invention, the formation of a protective layer made of Co2O3 on the surface of a ferromagnetic metal thin film layer made of cobalt or a ferromagnetic material containing cobalt is performed on a substrate on which a ferromagnetic metal thin film layer made of cobalt or a ferromagnetic material containing cobalt is formed. ,
The substrate is loaded in a plasma processing apparatus equipped with a plasma generation electrode so as to face the plasma generation electrode, and an electrode is further placed near the loaded substrate, and a voltage is applied to the electrode placed near the substrate. This is done by plasma oxidation. When such plasma oxidation is performed, the effect is similar to that of applying a voltage to the surface of the ferromagnetic metal thin film layer, which was previously at ground potential, and the plasma oxidation is rapid and good due to the extremely strong plasma potential. The cobalt on the surface of the ferromagnetic metal thin film layer is oxidized until it becomes trivalent cobalt oxide, resulting in extremely stable Co2
A protective layer made of O3 is formed, and a magnetic recording medium with sufficiently improved corrosion resistance is obtained.

The present invention will be described below with reference to the drawings.

Figure 1 shows an example of a plasma processing apparatus used when forming a protective layer made of Co203 on the surface of a ferromagnetic metal thin film layer made of cobalt or a ferromagnetic material containing cobalt. is a vacuum chamber, and the inside of this vacuum chamber is evacuated by an exhaust system 2 and maintained in a vacuum. 3 is a cylindrical can disposed in the center of the vacuum chamber l, and the polyester film 4 on which a ferromagnetic metal thin film layer made of cobalt or a ferromagnetic material containing cobalt is formed is transferred from a raw roll 5 to a guide roll 6. Through this cylindrical can 3
The paper moves along the circumferential side of the paper and is wound onto a winding roll 8 via a guide roll 7.

During this time, oxygen gas is introduced from the gas inlet tube 9 attached to the vacuum chamber 1, while the gas is placed at the bottom of the vacuum chamber 1 facing the polyester film 4 moving along the circumferential side of the cylindrical can 3. A voltage is applied to the AC electrode 10 for plasma generation, and at the same time, a voltage is applied to the DC electrode 11 disposed in the immediate vicinity of the cylindrical can 3 to perform plasma oxidation. In addition, in the figure, 12 is an AC power supply, and 13 is a DC power supply.

However, according to this plasma processing apparatus, the gas introduction pipe 9
When plasma treatment is performed by introducing oxygen gas from the plasma generating AC electrode 10, a voltage is applied to the DC electrode II at the same time as the plasma is formed at the plasma generation AC electrode 10, and a voltage is applied to the surface of the ferromagnetic metal thin film layer. The same effect is achieved. As a result, high-energy oxygen gas ionized by an extremely strong plasma potential penetrates the surface of the ferromagnetic metal thin film layer and oxidizes it. A dense film grows from the surface, and trivalent cobalt Co oxidized to an oxide of
A protective layer made of 2O3 is well formed without forming an interface, and a magnetic recording medium with even better corrosion resistance can be obtained. The thickness of the protective layer made of Co2O3 thus formed is preferably within the range of 10 to 100 layers, and if it is thinner than 10 layers, the desired effect may not be obtained.

DC electrode 11 disposed directly under the cylindrical can 3
is preferably made of stainless steel or molybdenum to avoid sputtering, and the DC electrode 11
A mesh-like material is preferably used so that oxygen gas can circulate well between the materials. Further, the distance between the DC electrode 11 and the surface of the ferromagnetic metal thin film layer on the base 4 that moves along the circumferential side of the cylindrical can 3 varies depending on the gas pressure of the oxygen gas introduced into the vacuum chamber 1. If it is larger than 1 cm, the effect will be weak or there will be no effect, so it is preferably within 1 cm.

In addition, the electrode for plasma generation is limited to the AC electrode 1o, but either a DC electrode or a high frequency electrode may be used. Depending on which electrode is used, the gas pressure of the oxygen gas introduced into the vacuum chamber l will be Although slightly different, in order to perform plasma oxidation quickly and well, the gas pressure of the oxygen gas introduced into the vacuum chamber 1 is preferably within the range of lXl0' to 0°3 Torr, and 0.03 to 0.03 Torr. More preferably, it is within the range of 0.1 Torr.

In addition, the voltage applied to the plasma generation electrode is preferably within the range of 300 to IKV so that plasma can be generated satisfactorily under such gas pressure conditions. It is preferable to apply a voltage in the range of 50 to 400 V, because if the voltage is lower than 50 V, the desired effect will not be obtained, and if it is higher than 400 V, sputtering will occur. Note that the voltage applied to the DC electrode 11 may be 10 or -.

Materials for forming the ferromagnetic metal thin film layer include Co, Co-N
Cobalt or ferromagnetic materials containing cobalt, such as i-alloy, Co-Cr alloy, Go-PXCo-Ni-P, are used, and ferromagnetic metal thin film layers made of these ferromagnetic materials can be formed by vacuum evaporation, ion blating, It is deposited and formed on the substrate by means such as sputtering and plating.

In addition, as magnetic recording media, polyester film,
Various types of structures that come into sliding contact with magnetic heads, such as magnetic tapes based on synthetic resin films such as polyimide films, magnetic disks and magnetic drums based on disks and drums made of synthetic resin films, aluminum plates, glass plates, etc. includes.

Next, embodiments of the invention will be described.

Example 1 A polyester film with a thickness of 10 μm was loaded into a vacuum evaporation apparatus, and cobalt was heated and evaporated under a residual gas pressure of 5Xl'0-5 torr to deposit cobalt on the polyester film with a thickness of 100 μm. A ferromagnetic metal thin film layer was formed. Next, the cylindrical can 3 shown in FIG.
Using a plasma processing device with a distance of 4 mm from the DC electrode 11, the polyester film 4 on which the ferromagnetic metal thin film layer was formed was transferred from the raw roll 5 in the vacuum chamber 1 to the guide roll 6.
1 m/min along the circumferential side of the cylindrical can 3 through
was moved at a speed of
Oxygen gas pressure o, o5 torr, AC electrode for plasma generation 1
Plasma oxidation was carried out at a voltage of 700 mm at 0, while varying the voltage applied to the DC electrode 11. After that, the prescribed 1
A large number of magnetic tapes A were made by cutting the tape into J-shaped pieces, forming a ferromagnetic metal thin film layer 14 made of cobalt on a polyester film 4, and then laminating a protective layer N15 on top of the polyester film 4, as shown in FIG. Ta. The protective layer 15 of the obtained magnetic tape A was subjected to x'pζ (X-ray photoelectron spectroscopy, hereinafter xps
As a result of the investigation, it was found that the protective layer 15 was CO
It was found that it was a cobalt oxide consisting of □03.

Figure 3 shows the magnetic tape obtained in this way at 60°C.
The deterioration rate of the maximum magnetic flux density after being left standing for one week under the condition of 190% RH was measured with the maximum magnetic flux density of the magnetic tape before being left standing as 100%, and the deterioration rate and the deterioration rate of the DC electrode 11 were measured. This is a graph showing the relationship with applied voltage.

Example 2 The ferromagnetic metal til of Example 1! ! In forming the layer, cobalt-nickel alloy (weight ratio 8:2) was used instead of cobalt.
) was used in the same manner as in Example 1, and a ferromagnetic metal thin film layer made of a cobalt-nickel alloy with a thickness of 1000 μm was formed on a polyester film, and in the plasma treatment, the voltage of the DC electrode 11 was changed to 100 μm. Plasma oxidation was performed in the same manner as in Example 1 except that magnetic tape A was
I made it. The protective layer 15 of the obtained magnetic tape A was
As a result of an investigation using S, it was found that the protective layer 15 was made of cobalt oxide consisting of CO2O3.

Comparative Example 1 The same procedure as in Example 1 was carried out except that a plasma processing apparatus without a DC electrode as shown in Fig. 4 was used in place of the plasma processing apparatus shown in Fig. 1, and the voltage application to the DC electrode was omitted. A magnetic tape was made in the same manner as in Example 1. As a result of examining the protective layer of the obtained magnetic tape by XPS, it was found that the protective layer was a composite oxide consisting of Coo and Co3O4.

Comparative Example 2 The same procedure was carried out as in Example 2, except that a plasma processing apparatus without a DC electrode as shown in Fig. 4 was used instead of the plasma processing apparatus shown in Fig. 1, and the voltage application to the DC electrode was omitted. A magnetic tape was made in the same manner as in Example 2. As a result of examining the protective layer of the obtained magnetic tape by xPS, it was found that the protective layer was a composite oxide consisting of Coo and Co3O4.

Regarding the magnetic tapes obtained in Example 2 and each comparative example, the deterioration rate of maximum magnetic flux density was measured in the same manner as in Example 1.

The table below shows the results.

〔Effect of the invention〕

Example 1 As is clear from the graph in Figure 3 showing the relationship between the deterioration rate of the maximum magnetic flux density of the obtained magnetic tape and the voltage applied to the DC electrode, the maximum magnetic flux density decreases when the voltage of the DC electrode is 50V or higher. The deterioration rate is greatly reduced, and this shows that the products obtained by applying the voltage to the DC electrode of 50 V or more according to the present invention have an extremely small deterioration rate of maximum magnetic flux density and are excellent in corrosion resistance. Furthermore, as is clear from the above table, the magnetic tape obtained in this invention (Example 2
) compared to the magnetic tapes obtained in Comparative Examples 1 and 2,
The rate of deterioration of the maximum magnetic flux density is small, which indicates that the magnetic recording medium obtained by the present invention has excellent corrosion resistance.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a plasma processing apparatus used in the manufacturing method of the present invention, FIG. 2 is a partially enlarged cross-sectional view of a magnetic tape obtained by the present invention, and FIG. FIG. 4 is a schematic cross-sectional view of a conventional plasma processing apparatus. 4... Polyester film (substrate), 14... Ferromagnetic metal thin film layer, 15... Protective layer, A... Magnetic tape (magnetic recording medium) Patent applicant Hitachi Maxell, Ltd. Iζ° ~ No. Figure 1 ↓ Figure 3 0 100 200 Applied voltage (V) Figure 4

Claims (1)

[Claims] (2) A magnetic recording medium characterized in that a ferromagnetic metal thin film layer made of cobalt or a ferromagnetic material containing cobalt is formed on a substrate, and a protective layer made of Co2O3 is provided on the surface of this ferromagnetic metal thin film layer.