JPS6063723A - Manufacture of magnetic recording medium - Google Patents

Abstract

PURPOSE:To sufficiently improve the corrosion resistance of a magnetic recording medium, by loading a base body on which a ferromagnetic metallic thin layer is formed with the base body being faced to a plasma generating electrode and installing another electrode to the vicinity of the loaded base body, and then, performing plasma oxidizing or plasma nitriding while a voltage is applied to the second mentioned electrode. CONSTITUTION:When plasma processing is performed by introducing oxygen gas or nitrogen gas from a gas introducing pipe 6 after a DC electrode 10 is installed very closely to and just below a cylindrical can 4 and connected with a power source 11 so that a voltage can be applied to the electrode 10, plasma is produced by means of an AC electrode 9 for generating plasma and the voltage is simultaneously applied to the electrode 10. When plasma processing is made in such a way, the plasma processing can be performed quickly under an excellent condition and the surface of a ferromagnetic metallic thin film is efficiently oxidized or nitrided and, as a result, a magnetic recording medium having an excellent corrosion resistance is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a magnetic recording medium having a ferromagnetic metal thin film layer as a magnetic recording layer, and more particularly to a method for manufacturing the above-mentioned magnetic recording medium having excellent corrosion resistance.

A magnetic recording medium whose magnetic recording layer is a ferromagnetic metal thin film layer is
It is usually made by bonding metals or their alloys onto a base film by vacuum deposition, etc., and has characteristics suitable for high-density recording, but on the other hand, it is easily oxidized by oxygen in the air, and this oxidation can cause There are drawbacks such as deterioration of magnetic properties such as magnetic flux density.

For this reason, the surface of the ferromagnetic metal thin film layer has been oxidized or nitrided to improve its corrosion resistance.
For example, using a plasma processing apparatus as shown in FIG. 1, a polyester film 1 on which a ferromagnetic metal thin film layer is formed is moved from a raw roll 3 in a vacuum chamber 2 along the circumferential side of a cylindrical can 4. Oxygen gas or nitrogen gas is introduced into the vacuum chamber 2 maintained at a predetermined degree of vacuum by an exhaust system 7 through a gas introduction pipe 6 attached to the vacuum chamber 2. However, the surface of the ferromagnetic metal thin film layer is subjected to plasma oxidation or plasma nitridation by applying a voltage to the AC electrode 9 using the AC power source 8.

However, in this method, since the plasma potential in plasma treatment is weak, the rate of oxidation or nitridation by plasma treatment is slow, the treatment time must be lengthened, and corrosion resistance cannot be sufficiently improved.

As a result of various studies in view of the current situation, the inventors formed a ferromagnetic metal thin film layer made of metal or an alloy thereof on a substrate, and then formed a substrate on which this ferromagnetic metal thin film layer was 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 disposed near the loaded substrate;
When plasma oxidation or plasma nitridation is performed while applying a voltage to an electrode placed near this substrate, the plasma potential becomes stronger, making it possible to apply a voltage to the surface of the ferromagnetic metal thin film layer, which was previously at ground potential. The same effect as shown in FIG. 1 is obtained, oxidation or nitridation by plasma treatment is performed quickly and well, the surface of the ferromagnetic metal thin film layer is well oxidized or nitrided, and a magnetic recording medium with sufficiently improved corrosion resistance can be obtained. They discovered this and came up with this invention.

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

FIG. 2 shows an example of a plasma processing apparatus used in the present invention. This plasma processing apparatus includes a raw fabric roll 3, a cylindrical can 4, a take-up roll 5, and an AC power source in a vacuum chamber 2. It is the same as the conventional plasma processing apparatus shown in FIG. 1 in that a plasma generation AC electrode 9 connected to A DC electrode 10 is disposed directly under the can 4 in the vicinity of grinding, and is connected to a power source 11 so that a voltage can be applied to the DC electrode 10. However, according to this plasma processing apparatus, when performing plasma processing by introducing oxygen gas or nitrogen gas from the gas introduction pipe 6, plasma is generated at the plasma generation AC electrode 9, and at the same time, the DC electrode 1
A voltage is applied to the surface of the ferromagnetic metal thin film layer, which has the same effect as applying a voltage to the surface of the ferromagnetic metal thin film layer. As a result, a magnetic recording medium with excellent corrosion resistance can be obtained.

The DC electrode 10 disposed in the immediate vicinity of the cylindrical can 4 is preferably made of stainless steel or molybdenum to avoid sputtering, and is moved along the circumferential surface of the cylindrical can 4. The distance from the surface of the ferromagnetic metal thin film layer on the substrate 1 varies depending on the pressure of the gas such as oxygen gas and nitrogen gas introduced into the vacuum chamber 2.
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. Further, this DC electrode 10 is disposed very close to and directly under the cylindrical can 4, and is disposed within 1 cm from the surface of the ferromagnetic metal thin film layer on the base 1 that moves along the circumferential side of the cylindrical can 4. Therefore, a mesh type is preferably used so that oxygen gas or nitrogen gas can flow well between the DC electrodes 10.

In addition, the plasma generation electrode is not limited to the AC electrode 9, but may be a DC electrode or a high frequency electrode. Depending on which electrode is used, the oxygen gas and nitrogen gas introduced into the vacuum chamber 2 can be Although the gas pressure is slightly limited, in order to perform plasma oxidation and plasma nitridation quickly and well, the gas pressure of the oxygen gas and nitrogen gas introduced into the vacuum chamber 2 should be within the range of lXl0-' to 3 Torr. It is preferably within the range of 0.03 to 041 Torr, and more preferably within the range of 0.03 to 041 Torr. In this way, the vacuum l! When the gas pressure of oxygen gas and nitrogen gas introduced into 2 is within the range of 0.03 to 0.1 Torr, the distance between the DC electrode 10 and the surface of the ferromagnetic metal thin film layer on the substrate 1 is preferably within l'cm.

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 1o may be 10 or - in the case of oxidation, but - in the case of nitridation.
It is necessary to apply a voltage of

As described above, oxygen gas or nitrogen gas plasma is generated with the plasma generation AC electrode 9, and the DC electrode 1
When a voltage is applied to 0 and the ferromagnetic metal thin film layer is brought into contact with ionized oxygen gas or ionized nitrogen gas,
The plasma potential is also strong, and the ionized oxygen and nitrogen gases have high energy, so they easily penetrate the surface of the ferromagnetic metal thin film layer to perform oxidation or nitridation, and a dense film grows from the surface. An oxide film layer or a nitride film layer made of a ferromagnetic metal oxide or nitride can be formed satisfactorily without creating an interface. In particular, in this method, a DC electrode 10 is disposed within a distance of 1 cm from the surface of the ferromagnetic metal thin film layer on the base 1 that moves along the circumferential side of the cylindrical can 4, and Since the plasma treatment is performed by applying a voltage, the surface of the ferromagnetic metal thin film layer is quickly and efficiently oxidized or nitrided, resulting in a magnetic recording medium with even better corrosion resistance.

The formation of a ferromagnetic metal thin film layer on the substrate can be performed using co, Fe, N
i, Co-Ni alloy, Co-Cr alloy, Co-P alloy,
This is accomplished by depositing a ferromagnetic material such as a Co--N1--P alloy onto a substrate by means such as vacuum evaporation, ion blasting, sputtering, or plating.

Next, embodiments of the invention will be described.

Example I A polyester film with a thickness of 10 μm was loaded into a vacuum evaporation apparatus, and the cobalt was heated to evaporate under a residual gas pressure of 5×10 −5 μl of oxygen gas pressure to form a polyester film with a thickness of 1000 μm on the polyester film. A ferromagnetic metal thin film layer was formed. Next, using a plasma processing apparatus in which the distance between the cylindrical can 4 and the DC electrode 10 shown in FIG.
is moved along the circumferential side of the cylindrical can 4 from the raw fabric roll 3 in the vacuum chamber 2, set to be wound up on the take-up roll 5, and oxygen gas is introduced from the gas introduction pipe 6 for 200 seconds.
Oxidation was carried out at various treatment times, with an oxygen gas pressure of 0.1 torr, a voltage of 600 V for the AC electrode 9 for plasma generation, and a voltage of 100 V for the DC electrode 10. Thereafter, it was cut to a predetermined rlJ to make a large number of magnetic tapes.

Figure 3 shows the magnetic tape obtained in this way at 60°C.
The magnetic tape was left under conditions of 90% RH, and the deterioration rate of the maximum magnetic flux density over time was measured, with the maximum magnetic flux density of the magnetic tape before being left as 100%, and the relationship between the deterioration rate and the plasma processing time was determined. Graph A shows the results obtained in Example 1.

Example 2 In the plasma treatment of Example 1, a large number of magnetic tapes were processed in the same manner as in Example 1, except that the treatment time was 10 seconds and the voltage of the DC electrode was variously varied. The graph shows the relationship between the deterioration rate of the maximum magnetic flux density of the thus obtained magnetic tape measured in the same manner as in Example 1 and the voltage applied to the DC electrode.

Example 3 In the plasma treatment of Example 1, the gas pressure of oxygen gas was changed from 0.1 Torr to 0.01 Torr, and the voltage applied to the plasma generation AC electrode 9 was changed from 600V to 1ooov.
A large number of magnetic tapes were made in the same manner as in Example 1 except that the following was changed. Graph B in FIG. 3 graphically represents the relationship between the deterioration rate of the maximum magnetic flux density of the magnetic tape thus obtained, measured in the same manner as in Example 1, and the plasma processing time.

Example 4 In the plasma treatment of Example 1, instead of oxygen gas,
Nitrogen gas was introduced at a flow rate of 200 sec, and the voltage of the plasma generation AC electrode 9 was set to 600 m at a nitrogen gas pressure of 0.1 torr.
A large number of magnetic tapes were produced in the same manner as in Example 1, except that the nitriding was carried out at a voltage of 10V and a DC electrode 10 voltage of 100V and various treatment times. The graph in FIG. 5 graphically represents the relationship between the deterioration rate of the maximum magnetic flux density of the magnetic tape thus obtained, measured in the same manner as in Example 1, and the plasma processing time.

Comparative Example 1 The same procedure as in Example 1 was carried out except that the plasma processing apparatus shown in FIG. 1 was used instead of the plasma processing apparatus shown in FIG. 2, and the voltage application to the DC electrode 10 was omitted. He made a large number of magnetic tapes. The graph in FIG. 6 is a graph showing the relationship between the deterioration rate of the maximum magnetic flux density and the plasma processing time, which was measured in the same manner as in Example 1 of the magnetic tape thus obtained.

Comparative Example 2 In the plasma treatment of Comparative Example I, instead of oxygen gas,
Nitrogen gas was introduced at a flow rate of 200 scn+, and the voltage of the plasma generation AC electrode 9 was 60 at a nitrogen gas pressure of 0.1 Torr.
A large number of magnetic tapes were produced in the same manner as in Comparative Example 1, except that the nitriding was performed at 0 V and for various treatment times. The graph in FIG. 7 is a graph showing the relationship between the deterioration rate of the maximum magnetic flux density and the plasma processing time, which was measured in the same manner as in Example 1 of the magnetic tape thus obtained.

As is clear from the graphs in FIGS. 3, 5 to 7 showing the relationship between the deterioration rate of the maximum magnetic flux density of the magnetic tape obtained in each Example and each Comparative Example and the processing time, the present invention Magnetic tape obtained by the manufacturing method (graph A in Figure 3)
, B, Fig. 5) are all significantly shorter than magnetic tapes obtained by conventional manufacturing methods (Figs. 6 and 7), and the deterioration rate of maximum magnetic flux density with processing time is This shows that according to the manufacturing method of the present invention, a magnetic recording medium with excellent corrosion resistance can be obtained. Furthermore, as is clear from the graph in FIG. 4 showing the relationship between the deterioration rate of the maximum magnetic flux density of the magnetic tape obtained in Example 2 and the voltage applied to the DC electrode, the maximum The rate of deterioration of magnetic flux density has decreased significantly, and from this reason, the voltage applied to the DC electrode in the manufacturing method of this invention is 50V.
It can be seen that the above is preferable.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view of a conventional plasma processing apparatus, and FIG. 2 is a schematic sectional view of a plasma processing apparatus used in the manufacturing method of the present invention.
A schematic cross-sectional view showing an example, FIGS. 3 and 5 are graphs showing the relationship between the deterioration rate of the maximum magnetic flux density of the magnetic tape obtained by this invention and plasma processing time, and FIG. The relationship between the deterioration rate of the maximum magnetic flux density of the tape and the voltage applied to the DC electrode, Figures 6 and 11gl show the relationship between the deterioration rate of the maximum magnetic flux density of the magnetic tape obtained by the conventional manufacturing method and the plasma processing time. It is a diagram. DESCRIPTION OF SYMBOLS 1...Base body, 2...Vacuum chamber, 4...Cylindrical can, 6...Gas introduction tube, 9...AC voltage +a for plasma generation (electrode for plasma generation), 10... DC electrode patent applicant Hitachi Maxell Ltd. Figure 3 Q5101520 Plasma treatment time (seconds) Figure 4 0 100 200 300 400 DC electrode voltage (V) Figure 5 Plasma treatment time (seconds) Figure 6 0 12345 Plasma treatment Time (minutes)

Claims (1)

[Claims] 1. Substrate: 2. A ferromagnetic metal thin film layer made of metal or an alloy thereof is formed on the substrate, and then the substrate on which the ferromagnetic metal thin film layer is formed is equipped with a plasma generation electrode. The plasma processing device is loaded facing the plasma generation electrode, and further electrodes are arranged near the loaded substrate, and a voltage is applied to these electrodes to generate oxygen gas or nitrogen introduced into the plasma processing device. Method 2 for producing a magnetic recording medium characterized by oxidizing or nitriding the surface of a 1% lW ferromagnetic metal thin film formed on a substrate by plasma treating a gas, wherein the electrode disposed near the substrate is Method 3 of manufacturing a magnetic recording medium according to claim 1, wherein the magnetic recording medium is disposed within Icm from a ferromagnetic metal thin film layer formed thereon, and the ferromagnetic metal thin film layer is disposed near the substrate on which the ferromagnetic metal thin film layer is formed. A method for manufacturing a magnetic recording medium according to claims 1 and 2, wherein the voltage applied to the electrode is within the range of 50 to 400 V, and the method is disposed near a substrate on which a ferromagnetic metal thin film layer is formed. A method 5 for producing a magnetic recording medium according to claims 1 to 3, wherein the electrodes are made of stainless steel or molybdenum, and the electrodes are arranged in the vicinity of a substrate on which a ferromagnetic metal film layer is formed. Claim 1 IJ consisting of
to the method for manufacturing a magnetic recording medium according to item 4;