JPS6089820A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having excellent durability without affecting adversely the electromagnetic conversion characteristic thereof by forming a thin ferromagnetic metallic film on a base body, forming a plasma- polymerized protective film of an org. compd. on the film surface and oxidizing or nitriding the surface of the protective film. CONSTITUTION:A thin ferromagnetic film 8 of a metal such as Co, Ni, Fe or the alloy thereof is formed on a base body 1 consisting of a polyester film, etc. A protective film 9 by plasma polymn. of hydrocarbon, fluorine org. compd. such as C2F4 or silicon org. compd. such as tetremethylsilane is formed on the surface of the film 8. The surface of the film 9 is then exposed to gaseous nitrogen or O2 and high-frequency or DC plasma is generated to form a nitride or oxide film 10. The surface of the film 9 is thus made to the dense hard film 10 by which the magnetic recording medium having improved wear resistance and excellent durability is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium having a ferromagnetic metal thin film layer as a magnetic recording layer, and an object thereof is to provide the above-mentioned magnetic recording medium having excellent durability. .

Ferromagnetic metal thin 1! A magnetic recording medium in which the ii layer is a magnetic recording layer is made by depositing metals or their alloys on a base film by vacuum deposition, etc., and has characteristics suitable for high-density recording. It has the disadvantage that it has a large coefficient of friction with the magnetic head and is easily subject to wear and damage, making it difficult to obtain good durability.

For this reason, durability has been conventionally improved by providing various protective film layers on the ferromagnetic metal thin film layer, and in recent years, plasma polymerized protective film layers of organic compounds have been replaced with ferromagnetic metal thin film layers. It has been proposed and proposed that it be installed on top.

However, although the plasma polymerized protective film layer of this self-organized compound improves the durability, it is still not sufficient, and especially when the deposition rate is increased by increasing the gas pressure during plasma polymerization, plasma polymerization with a relatively low molecular weight Polymerized and hard protection! ! There was a ffllt point where an i-layer could not be obtained and good wear resistance could not be obtained.

As a result of conducting various inspections in view of the current situation, the inventors first formed a plasma polymerized protective film layer of an organic compound on the surface of a ferromagnetic metal thin film layer, and then, at least on the surface of this plasma polymerized protective film layer. When oxidized or nitrided, the crosslinking density of the plasma-polymerized protective film layer increases and becomes hard, and a relatively hard oxide or nitride film layer of the plasma-polymerized protective film is formed to sufficiently improve wear resistance. It was discovered that a magnetic recording medium with excellent durability can be obtained, and this invention was made.

In this invention, the plasma polymerized protective film layer is formed on the ferromagnetic metal thin film layer in a treatment tank using a hydrocarbon compound,
It is formed by plasma polymerizing monomer gases such as fluorine-based organic compounds and silicon-based compounds using high frequency waves and depositing them on ferromagnetic gold. Examples of the 7-mer gases used to form include propane,
Monomer gas of hydrocarbon compounds such as ethylene and propylene, monomer gas of fluorine-based compounds such as C2p4 and C3FG, and monomer gas of silicon-based organic compounds such as tetramethylsilane, octamethylcyclotetrasiloxane, and hexamethyldisilazane. etc. are preferably used, and radicals are generated from the monomer gas of these organic compounds by high frequency, and the generated radicals react and polymerize to become the test material. This radical is more likely to be generated when these organic compounds have double bonds or triple bonds, are metal salt compounds with a metal element at the end, or have a functional group such as an OH group. , those having these unsaturated bonds, metal elements, functional groups, etc. are more preferably used.

Also, when plasma polymerizing these monomer gases, if a carrier gas such as argon gas, helium gas, or oxygen gas is present, the monomer gases will be deposited at a rate 3 to 5 times faster than when plasma polymerizing them alone. It is preferable to use these carrier gases together. When coexisting with these carrier gases, the composition ratio of the carrier gas to the monomer gas of the organic compound is 1.
It is preferable to coexist in a ratio of 1:1 to 20:1; if the carrier gas is too small, the deposition rate will decrease, and if it is too large, the monomer gas will be too small, which will interfere with the plasma polymerization reaction. Note that when using a monomer gas of a hydrocarbon compound, it is not preferable to use oxygen gas as a carrier gas because an oxidation reaction will occur if oxygen gas is used as a carrier gas.

When performing plasma polymerization, the higher the gas pressure and the higher the high frequency output, the higher the deposition rate, but on the other hand, the monomer gas is plasma polymerized with a relatively low molecular weight, making it difficult to obtain a hard protective film layer. If the gas pressure is lowered and the high frequency output is increased, the deposition rate will be slower, but at the same time a relatively hard protective film layer made of polymer will be obtained. However, if the gas pressure is lowered and the high frequency output is kept high, the monomer gas will turn into powder. If the plasma polymerized protective film layer is not formed, the gas pressure should be reduced to 0.
．． Within the range of 0.03 to 5 torr, and the high frequency output is 0.03
It is preferable to set the gas pressure in the range of ~I W/cIil, the gas pressure to be 0.05 to 1 Torr, and the high frequency output to be 0.05 to 1 Torr.
More preferably, it is within the range of 0.3 W/cnT. Plasma polymerization protection of organic compounds precipitated by plasma polymerization in this way! i! The layer is dense and has a small coefficient of friction, so when the plasma polymerized protective film 1- of this organic compound is formed, the wear resistance is improved. The film thickness of such a plasma polymerized protective film layer of an organic compound is 20 to 10
If the film thickness is too thin, the durability effect of this protective film layer will not be fully exhibited, and if it is too thick, the spacing loss will be too large and the electromagnetic conversion characteristics will deteriorate. No adverse effects.

The surface of the plasma-polymerized protective film layer thus formed is oxidized by exposing the plasma-polymerized protective film layer to oxygen gas plasma generated by a high-frequency electrode, an AC electrode, or a DC electrode in a treatment tank. This is done by bringing plasma-formed oxygen gas into contact with the plasma-polymerized protective film layer, and when the plasma-formed oxygen gas is brought into contact with the plasma-polymerized protective film layer, the plasma-formed oxygen gas has high energy. Therefore, the surface of the plasma-polymerized protective film layer is oxidized well, and a dense film grows from the surface, so that a dense oxide film layer made of the oxide of the plasma-polymerized protective film is well formed. If the thickness of the oxide film layer formed in this way is made thinner than 3 Å, the hardness of the plasma polymerized protective film layer will not be sufficiently improved and the wear resistance will not be sufficiently improved, so it is preferable to make it 3 Å or more. , the entire plasma polymerized protective film layer may be blue oxidized. In addition, when plasma-formed oxygen gas is brought into contact with the surface of the metal thin film layer, the gas pressure of the oxygen gas in the processing tank is lower than If it is lower than 3 torr, it will not cause a discharge, and if it is higher than 3 torr, it will not have an adverse effect on the plastic film used as the substrate, so it is preferable to keep it within the range of lXl0-5 to 31 torr. When generating a plasma of 3.times.10-5 Torr, it is preferable to keep the value within the range of 3.times.10-5 to 5 Torr, since if it is lower than 3.times.10-Torr, no discharge will occur, and if it is higher than 5 Torr, it will have an adverse effect on the plastic film. Note that if this oxidation of the plasma polymerized protective film layer is performed on a plasma polymerized protective film layer formed using a monomer gas of a hydrocarbon compound and a fluorine-based organic compound, the plasma polymerized protective film layer may be decomposed or It is not desirable because

In addition, nitriding the surface of the plasma polymerized protective film layer can be performed by exposing the plasma polymerized protective film layer to nitrogen gas plasma generated by a high frequency electrode, an AC electrode, or a DC electrode. This is done by bringing gas into contact with the plasma polymerized protective film layer, and when nitrogen gas that has been turned into plasma in this way is brought into contact with the plasma polymerized protective film layer, the nitrogen gas that has been turned into plasma becomes high energy, similar to the case of the oxidation described above. Since the plasma-polymerized protective film has a nitride, the surface of the plasma-polymerized protective film is well nitrided, a dense film grows from the surface, and a nitride film layer made of the nitride of the plasma-polymerized protective film is well formed on the surface.

If the thickness of the nitride film layer formed in this way is made thinner than 3 layers, as with the oxide film layer, the hardness of the plasma polymerized protective film layer will not be sufficiently improved and the wear resistance will not be sufficiently improved. , 3 Å or more, and the entire plasma polymerized protective film layer may be nitrided. In addition, when bringing the plasma-formed nitrogen gas into contact with the surface of the plasma-polymerized protective film layer, the gas pressure of the nitrogen gas used in the treatment tank is controlled by a high-frequency electrode, similar to the case of oxygen gas during oxidation. When generating a plasma of ■×10'
If it is lower than 1 Torr, no discharge will occur, and if it is higher than 3 Torr, it will not have an adverse effect on the plastic film used as the base. When generating nitrogen gas plasma with electrodes and DC electrodes, if the temperature is lower than 3X10-5 Torr, no discharge will occur, and if the temperature is higher than 5 Torr, it will have a negative effect on the plastic film.
It is preferable to keep it within the range of toll.

Examples of materials for forming the ferromagnetic metal thin film layer include Co, Fe, and N.
Ferromagnetic materials such as Co-Ni alloy, Co-Cr alloy, Co-P alloy, and Co-N1-P alloy are used, and the ferromagnetic metal thin film layer consisting of these ferromagnetic phases can be formed by vacuum deposition,
It is deposited on the substrate by means such as ion blasting, 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 device, and cobalt was heated and evaporated under a vacuum of 1×10° and 5 torr to form a ferromagnetic metal thin film layer of cobalt with a thickness of 1000 μm on the polyester film. did. Then,
Using the plasma processing apparatus shown in FIG.
Set it on the bottom surface of the substrate 3 placed in the upper part of the
Tetramethylsilane monomer gas was introduced at a flow rate of 50 scn+ from the gas introduction pipe 4 attached to the gas inlet, and the gas pressure was set to 0.51-rel, and 150 W of high frequency of 13.56 M1lz was applied at the electrode 5 for plasma polymerization for 1 minute. A plasma polymerized protective film layer was formed. Next, using the same device, nitrogen gas was introduced from the gas introduction pipe 4, and 100 WEII of high frequency waves were applied by the electrode 5 at a nitrogen gas pressure of 0.1 Torr, and the plasma polymerization protection 11 troubled surface was nitrided by varying the treatment time. . The thickness of the plasma polymerized protective film layer at this time is 30
There were 0 people. Thereafter, a ferromagnetic metal thin film layer 8, a plasma polymerized protective film layer 9, and an oxide film layer 10 of the plasma polymerized protective film are sequentially laminated on the polyester film 1 which is cut into a predetermined size as shown in FIG. He made a large number of magnetic tapes. In the figure, 6 is an exhaust system for reducing the pressure inside the processing tank 2, and 7 is a high frequency power source for applying high frequency to the electrode 5.

A sliding test was performed on a large number of the magnetic tapes thus obtained using a sliding testing machine, and the number of sliding movements until the surface of the ferromagnetic metal thin film layer of the magnetic tape was scratched was measured. Figure 3 shows the results in a graph.As is clear from this graph, when the surface of the plasma-polymerized protective film layer is nitrided, the treatment time becomes longer (as the number of sliding increases, the durability increases. It can be seen that the abrasion resistance is improved too much. Also, the number of times of sliding increases rapidly until the treatment time reaches 1 minute, indicating that it is preferable to carry out the nitriding treatment for 5 minutes or more.

Example 2 In the formation of the plasma-polymerized protective film layer in Example 1, the same amount of hexamethyldisilazane monomer gas was used in place of the tetramedylsilane monomer gas, and the same amount of hexamethyldisilazane monomer gas was used in the nitriding treatment, except that nitriding was performed for 5 minutes. A plasma polymerized protective film layer was formed in the same manner as in Example 1 to produce a magnetic tape. At this time, the thickness of the plasma polymerized protective film layer was 250, and the thickness of the nitride film layer on the surface of the plasma polymerized protective film was 200.
It was a person.

Example 3 In Example 2, the nitridation of the plasma polymerized protective film layer was changed to oxidation, oxygen gas was introduced from the gas introduction pipe 4 to set the oxygen gas pressure to 0.1 Torr, and high frequency power of 100 W was applied using the electrode 5. A plasma polymerized protective M layer was formed in the same manner as in Example 2, except that oxidation was performed for 1 minute, and a magnetic tape was produced. Plasma polymerization protection at this time I9! ! The thickness of the layer is 250, and the thickness of the oxide film layer on the surface of the plasma polymerized protective film is 20.
It was a person.

Example 4 Plasma polymerization protection in Example 2 115! A plasma-polymerized protective film layer was formed in the same manner as in Example 2, except that the same amount of propane monomer gas was used in place of the hexamethyldisilazane heptanomer gas in the formation of the layer, and a magnetic tape was produced. The thickness of the plasma-polymerized protective film layer at this time was 250 mm, and the thickness of the nitride film layer on the surface of the plasma-polymerized protective film layer was 2 () mm.

Comparative Example 1 A magnetic tape was produced in the same manner as in Example 1 except that the nitriding treatment of the plasma polymerized protective film layer was omitted.

Comparative Example 2 A magnetic tape was produced in the same manner as in Example 2, except that the nitriding treatment of the plasma polymerized protective film layer was omitted.

Comparative Example 3 A magnetic tape was produced in the same manner as in Example 4, except that the nitriding treatment of the plasma polymerized protective film layer was omitted.

Comparative Example 4 A magnetic tape was produced in the same manner as in Example 1 except that the formation of the plasma polymerized protective film layer and the nitriding treatment of the plasma polymerized protective film layer were omitted.

Regarding the magnetic tapes obtained in each example and comparative example,
The friction coefficient was measured and durability was tested.

The durability test was carried out by subjecting the obtained magnetic tape to a sliding test using a sliding testing machine and measuring the number of sliding movements until the surface of the ferromagnetic metal thin film layer was scratched.

The table below shows the results.

As is clear from the above table, the magnetic tapes obtained in this invention (Examples 2 to 4) are all the same as Comparative Examples 1 to 4.
Compared to the magnetic tape obtained by the present invention, the coefficient of friction is smaller and the number of times of sliding is greater, which indicates that the magnetic recording medium obtained by the present invention has further improved durability.

[Brief Description of the Drawings] Fig. 1 is a schematic cross-sectional view showing an example of a plasma processing apparatus used for forming a plasma polymerized protective film layer and oxidizing or nitriding the plasma polymerized protective film layer. FIG. 3 is a partially enlarged sectional view of the magnetic tape obtained according to the present invention, and is a diagram showing the relationship between the nitriding treatment time and the number of times of sliding of the magnetic tape obtained according to the present invention. DESCRIPTION OF SYMBOLS 1... Polyester film (substrate), 8... Ferromagnetic metal thin film layer, 9... Plasma polymerization protective film layer, IO.
...Oxidation 1! ii layer (nitride film layer), A...Magnetic tape (magnetic recording medium) Patent applicant Hitachi Maxell Ltd. Figure 1 Figure 3I2I Nitriding treatment time (minutes)

Claims (1)

[Claims] 1. Form a ferromagnetic metal thin film layer made of a metal or an alloy thereof on a substrate, form a plasma polymerized protective film layer of an organic compound on this ferromagnetic metal thin film layer, and form a plasma polymerized protective film layer of this plasma polymerized protective film. A magnetic recording medium with at least the surface oxidized or nitrided