JPH0833992B2 - Method of manufacturing magnetic recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a magnetic recording medium having a ferromagnetic metal thin film as a magnetic recording layer, and more particularly to a protective film having excellent durability on the magnetic recording layer. It relates to a method of forming.

(Prior Art) Conventionally, a magnetic recording body using a ferromagnetic metal thin film as a magnetic recording layer is formed by vacuum-depositing a ferromagnetic metal material on a non-magnetic metal disk substrate or tape substrate or by using a ferromagnetic metal material as a resin matrix. It is produced by spin coating an emulsion in which is dispersed.

However, although the ferromagnetic metal thin film has excellent characteristics for high-density recording, it has the drawback that it is easily worn or damaged by contact with the head, and that it is oxidized or corroded in the air to change its characteristics.

Therefore, durability and corrosion resistance have been improved by forming various protective films on the ferromagnetic metal thin film, and as one example thereof, forming the above protective film by plasma polymerization has been attracting attention in recent years. . By using this plasma polymerization method, a thin film can be easily formed, and the obtained thin film has various characteristics such as excellent uniformity.

However, the protective film obtained by the conventional plasma polymerization method has a large friction coefficient, and in the case of a magnetic disk, the CSS test results show that the film surface is not damaged when repeated contact with the magnetic head is repeated many times. As seen, it was inferior in durability and wear resistance.

The inventors of the present invention have a method of manufacturing a magnetic recording medium by first providing a protective film by plasma polymerization on the surface of a ferromagnetic metal thin film and then performing heat treatment to improve the above drawbacks (Japanese Patent Application No. 61-127644). And a method (Japanese Patent Application No. 61-217216) of heat-treating the protective film in an atmosphere of a reactive gas such as oxygen.

In addition, when the protective film is applied to the substrate by plasma polymerization while heating the substrate, the smoothness and adhesiveness of the film can be greatly improved (Japanese Patent Application No. 61-234459).
No.) was also proposed.

However, even if such a method is individually performed, a protective film having sufficient mechanical properties cannot be obtained.

(Problems to be Solved by the Invention) As a result of intensive studies in view of the present situation, the present invention has a small friction coefficient and does not suffer any damage to the surface even if the magnetic head is frequently contacted. This is a method for forming a strong protective film and manufacturing a magnetic recording medium having excellent running properties.

(Means for Solving Problems) The method of the present invention is a method for producing a magnetic recording medium by forming a protective film on the surface of a magnetic recording layer provided with a ferromagnetic metal thin film on a substrate, wherein After providing the magnetic metal thin film, while heating the substrate to 50 to 300 ° C., the surface of the ferromagnetic metal thin film is vaporized at room temperature and atmospheric pressure to protect the solid sublimable organic compound by plasma polymerization. It is characterized in that a film is formed and then heat treatment is performed.

It should be noted that, in order to improve the physical properties such as the density and the like of conventional crystalline polymers and amorphous heat-resistant polymers, the atmospheric temperature for expressing the microstructure and the polymerization temperature of the polymers are changed, and the molded articles of the polymers obtained. Although various heat treatments have been performed on these, these methods are intended for bulk samples.

The method of the present invention is completely different from these methods, and focuses on the surface effects peculiar to the thin film in the protective film, that is, changes in surface physical properties such as adhesion, friction coefficient, and smoothness.

In the method of the present invention, the plasma-polymerized organic thin film is formed while heating the substrate to prevent oxidation and damage of the ferromagnetic metal thin film, improve adhesion with the ferromagnetic metal thin film, and form a smooth and strong film. This is to obtain a magnetic recording medium having a small friction coefficient and excellent running property.

The method of the present invention is to heat the substrate first, but the temperature depends on the type of organic monomer and the reaction conditions. Usually 50 ° -300 ° C, preferably 80 °
~ 250 ° C is desirable. If this temperature is less than 50 ° C, a strong and smooth protective film cannot be obtained, and if it exceeds 300 ° C, the adhesion of the ferromagnetic metal thin film is poor and the hardness of the protective film decreases. Is.

The heating method may be any method as long as it can supply heat to the substrate, such as heating with a resistance heater or infrared radiation.

Further, as the organic compound used in the method of the present invention,
Sublimable aromatic organic compounds such as naphthalene, anthracene, diphenyl, dibenzyl and diphenylacetylene, which are solid at room temperature and atmospheric pressure, are used.

The present invention, after forming a protective film by the above-mentioned plasma polymerization, further heat in an oxygen atmosphere to make the film structure stronger and to make the surface of the protective film smoother, thereby improving durability and abrasion resistance. Is intended.

As a flat plate to which heat is applied, any method can be used as long as it can provide heat to the protective film, such as resistance heating, high frequency heating, laser heating, infrared heating, and heating in an open state. It does not matter whether it is in active gas or air.

The heating temperature range is 50 to 300 ° C, preferably 80 to 250 ° C. If the heating temperature is too low, the film structure and the film surface cannot be modified, and if the heating temperature is too high, the protective film and the ferromagnetic metal thin film are adversely affected.

Further, when heat is applied, the thickness of the protective film usually changes with the change of the film structure. It is desirable to perform heat treatment so that the change rate of the film thickness is within ± 20% in order to improve the surface structure of the film.

The heating temperature range of the plasma polymerization protective film is as described above.
Although the temperature is 50 to 300 ° C, the heating time is short when the temperature is high, and long when the temperature is low, but it is about 10 seconds to 120 minutes. If the time is too short, the predetermined performance cannot be obtained, and if it is too long, the predetermined performance cannot be obtained or it is uneconomical.

Further, in the method for manufacturing a magnetic recording medium of the present invention, after forming a protective film by plasma polymerization, the protective film is subjected to heat treatment in an oxygen atmosphere. This makes it possible to modify the surface of the protective film and obtain a magnetic recording medium having a small friction coefficient and excellent running properties. Further, such surface treatment also improves the adhesion between the ferromagnetic metal thin film and the protective film.

The case where the method of the present invention is applied to, for example, the production of a magnetic disk is as follows.

First, a chemical plating layer such as Ni-P is brought into close contact with an aluminum substrate to be a substrate, and post-treatment such as polishing is performed, and then a ferromagnetic metal thin film is formed on the surface by a physical or chemical method.

Next, as shown in the drawing, the magnetic disk main body 1 is set in a counter electrode type plasma polymerization apparatus, that is, the magnetic disk main body 1 is sandwiched between the electrodes 2A and 2B and inserted into the electrode 2A.
To 50 to 300 ° C, and plasma polymerization is performed while heating.

In addition, 3 is a bell jar, 4 is a table, 5 is a vacuum pump for vacuuming the inside of the bell jar 3, 6 is an absolute vacuum gauge, 7 is a high frequency power source connected to the electrodes 2A and 2B, 8 is a resistance heating body for solid monomer, 9 is a resistance heating element for solid organic compounds, 10
Is a power source for the resistance heating element, 11 is a carrier gas source, 12 is a nozzle, 13 is a heating element, and 14 is a heating source.

Further, the plasma generator is not limited to the above, and may be any one provided with a high frequency oscillator such as an induction coil type or a waveguide type.

When plasma polymerization is performed with high frequency, the energy density is 0.2 to 4 W / cm due to the high frequency output and the size of the electrode area.
² Desirably to be in the range of 0.5 to ³ W / cm ² , and to obtain a hardened protective film by maintaining the output of the high frequency power supply at 300 to 500 W, preferably 100 to 450 W and performing as high output as possible. Can be done. The high frequency power source normally has an oscillation frequency of 13.56 MHz, but the frequency is not particularly limited to this frequency and any frequency from direct current to microwave may be used.

In the bell jar, 0.005 to 3 Torr, preferably 0.01 to 1.5T
It is preferable to set the pressure to orr, and the reaction time depends on the kind of the monomer, the electrode arrangement, etc., but usually 5 seconds to 10 minutes, preferably 10 seconds to 3 minutes to obtain a desired film thickness. You can get it.

The film thickness by plasma polymerization is usually 10 to 1000Å and preferably 80 to 600Å. It is preferable that the film thickness is thinner than 10Å, durability and abrasion resistance are poor, and conversely 1000
If it is thicker than Å, the spacing loss becomes large and the read characteristics of recording are adversely affected.

(Example) A 3.5-inch magnetic disk in which a Ni-Cr-Co ternary ferromagnetic metal thin film was provided on an aluminum substrate was set in the plasma polymerization apparatus shown in the drawing and heated to about 210 ° C to make the disk surface uniform. While heating, deposit a protective film by plasma polymerization on the surface of the ferromagnetic metal thin film, and then in an oxygen atmosphere for 20 minutes.
Heat treatment was performed at 0 ° C. for 5 minutes to obtain a magnetic recording medium according to the method of the present invention.

Thus, dibenzyl was used as the monomer and pure argon was used as the carrier gas. The inner pressure of the bell jar just before starting the plasma polymerization was 0.1 Torr, and the thickness of the obtained protective film became a constant value depending on the amount of the monomer.
Further, for vaporization of the monomer, an electric current was passed through a small boat for vapor deposition to heat the boat to a temperature of about 80 ° C.

Regarding the magnetic recording medium thus obtained according to the method of the present invention
CSS durability, coefficient of friction, and corrosion resistance were measured. The results are shown in Table 1.

For comparison with the magnetic recording medium according to the method of the present invention, after providing a ferromagnetic metal thin film on the surface of an aluminum substrate, it is possible to perform heat treatment without heating the substrate in depositing a protective film by plasma polymerization. A magnetic recording medium (Comparative Example) was manufactured without performing the measurement, and its performance was measured in the same manner as in the Example, and is also shown in Table 1.

(Effect) As described above in detail, according to the method of the present invention, the protective film of the magnetic recording medium can be excellent in durability, corrosion resistance and friction coefficient. It is extremely useful industrially such that it can be used over a long period of time.

[Brief description of drawings]

The drawings are schematic explanatory views showing an example of an apparatus for depositing a protective film by plasma polymerization on a substrate in the method for producing a magnetic recording medium of the present invention. DESCRIPTION OF SYMBOLS 1 ... Magnetic disk main body, 2A, 2B ... Opposing electrodes, 3 ... Bell jar, 4 ... Table, 5 ... Vacuum pump, 6 ... Absolute vacuum gauge, 7 ... High frequency power supply, 8 ... Resistance heating body, 9 ... Resistance heating body, 10 ... Power source, 11 ... Carrier gas source, 12 ... Nozzle, 13
… Heating body.

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Claims (1)

[Claims] 1. A method for producing a magnetic recording medium by forming a protective film on the surface of a ferromagnetic metal thin film provided on a substrate, wherein the ferromagnetic metal thin film is provided on the substrate and then the substrate is changed to 50 to 30.
While heating at 0 ° C., a solid sublimable organic compound is vaporized at room temperature and atmospheric pressure on the surface of the ferromagnetic metal thin film to perform plasma polymerization to form a protective film, and then heat treatment is performed in an oxygen atmosphere. A method of manufacturing a magnetic recording medium, characterized by: