JPS61220131A - Production of vertical magnetic recording medium - Google Patents

Abstract

PURPOSE:To prevent the generation of cracks by forming a low-coercive force film consisting essentially of iron and nickel on a substrate of an org. polymer by ion-plating and then forming a vertically magnetized film on the film. CONSTITUTION:The low-coercive force film to be used consists essentially of iron and nickel and manganese, molybdenum, chromium, copper, etc., can be incorporated to reduce the coercive force and increase the permeability. The low-coercive force film is formed by ion-plating and hence a uniform low- coercive force film without any cracks and having an excellent magnetic characteristic can be formed on a substrate at low temp. The vertically magnetized film has magnetic anisotropy vertical to the film surface. A uniform vertical magnetic recording medium having excellent magnetic characteristic and without generating any cracks is thus obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a perpendicular magnetic recording medium. More specifically, the present invention relates to a method of manufacturing a thin-film perpendicular magnetic recording medium having a perpendicular magnetization film and a low coercive force film mainly made of iron and nickel.

[Conventional technology]

As perpendicularly magnetized films constituting perpendicular magnetic recording media, alloy thin films of cobalt and other metals, such as cobalt-chromium, cobalt-rhodium, and cobalt-vanadium, are known as representative films.

These perpendicularly magnetized films are usually formed on a substrate by sputtering or vacuum deposition. However, a cobalt alloy film formed by sputtering has a slow film formation rate.

Furthermore, the method of electron beam evaporation of cobalt alloys has a problem in that it is difficult to control the alloy composition.

In addition, both methods are used to obtain films with good magnetic properties.

There is a drawback that the substrate must be heated to a high temperature of about 150° C. to 500° C., which is a major obstacle, especially when using a plastic substrate.

As a method to improve this problem, a method of obtaining a perpendicularly magnetized film made of cobalt and cobalt oxide on a cooled substrate has been proposed (Collection of Abstracts of the 7th Academic Conference of the Japan Society of Applied Magnetics).

Furthermore, the present inventors have previously proposed a method for obtaining a perpendicularly magnetized film mainly composed of iron and iron oxide on a cooled substrate.

A low coercive force film was provided between the substrate and the perpendicular magnetization film.

A so-called two-layer recording medium is known as a method that has a higher reproduction output than a single-layer recording medium having only a perpendicular magnetization film, and can greatly improve the writing/recording/reproduction characteristics.

As a low coercive force film, 1. In addition to having excellent magnetic properties, the evaporation vapor pressures of the containing compositions are almost the same.

Iron and nickel were used as the main materials because they can be used to create films with no compositional fluctuations over long periods of time by vacuum deposition. A vacuum-deposited film of so-called permalloy is known.

[Problem that the invention seeks to solve]

However, when a low coercive force film made mainly of iron and nickel is formed by vacuum evaporation, cracks occur and the coercive force increases, so in order to prevent cracks from occurring, the temperature of the substrate must be raised to 200°C or higher. It was necessary to increase the amount of coercivity and form a low coercive force film consisting primarily of iron and nickel. For this reason, there has been an industrially important problem that a perpendicular magnetic recording medium having a uniform low coercive force film cannot be produced on an organic polymer substrate that does not have sufficient heat resistance.

The present inventors have conducted extensive studies on perpendicular magnetic recording media equipped with a low coercive force film and a perpendicular magnetization film that do not generate T-cracks and have uniform and good magnetic properties without heating an organic polymer substrate to high temperatures. The present invention has now been achieved.

[Failure to solve the problem]

That is, 1) the present invention forms a low coercive force film mainly made of iron and nickel on a substrate made of a V-mechanical combination by ion plating; This is a method for manufacturing a perpendicular magnetic recording medium characterized by forming a perpendicularly magnetized film having orientation.

Organic polymers that can be used for the substrate in the present invention include polyesters such as polyethylene terephthalate, polyethylene naphthalate, and polyethylene dicarboxylate, polyolefins such as polyethylene, polypropylene, and polybutene, polymethyl methacrylate, polycarbonate, polysulfone, and polyamide. , aromatic polyamide.

Polyphenylene sulfide + 'tf'J Phenylene oxide, polyamideimide, polyimide, polyvinyl chloride, polyvinylidene chloride, polyvinylidene fluoride, polytetrafluoroethylene, cellulose acetate, methyl cellulose, ethyl cellulose, epoxy resin, urethane resin, or these Mixtures, copolymers, etc. are suitable.

In particular, biaxially stretched films and sheets are most suitable for their superior flatness and one-dimensional stability, among which polyester,
Polyphenylene sulfide, aromatic polyamide, etc. are most suitable.

The shape of the base is drum-shaped or disk-shaped.

It can be in sheet form, tape form, card form, etc.

The thickness is also not particularly limited. Sheet form.

In the case of a tape shape, card shape, etc., the thickness is preferably in the range of 2 to 500 μm, particularly 4 to 200 μm, from the viewpoint of workability and dimensional stability.

Prior to the formation of the low coercive force film described later, the substrate used in the present invention is prepared to provide easy adhesion, flatness improvement9, coloration, antistatic properties,
Various surface treatments, pretreatments, and formation of a base layer may be performed for the purpose of imparting wear resistance and the like.

The low coercive force film used in the present invention is mainly made of iron and nickel, and has a low coercive force.

Manganese and molybdenum for the purpose of increasing magnetic permeability.

It may also contain chromium, copper, etc. In particular, the addition of molybdenum or copper is highly desirable since it has the effect of reducing coercive force and increasing magnetic permeability. Iron and nickel have a weight ratio of 20:8
A combination of around 0 and around 50:50 is preferable because it reduces the coercive force and increases the magnetic permeability.

Additions of elements other than iron and nickel include 21.2 iron, 778.5 nickel, 10.3 manganese, and
15.7 Iron/790 Nickel 15.0 Molybdenum 10.
6 manganese, 18.0 iron/75.0 nickel/2.0 chromium 15.0 copper, 17.7 iron/7B, 5 nickel/6,
8 chromium, 16.0 iron/80.0 nickel 74.0 molybdenum, 14.0 iron/77.0 = 75.
A composition close to 0 copper/4.0 molybdenum is preferable.

In order to enhance the interaction with the head and the perpendicularly magnetized film and improve the recording and reproducing characteristics, the coercive force in the direction parallel to the film surface of the low coercive force film is 35 oersted or less.

Preferably less than 20 oersteds, most preferably 10
It is desirable that it is less than Oersted.

The thickness of the low coercive force film has an optimum range in terms of the strength of interaction with the head and the perpendicularly magnetized film, and the saturation magnetic moment per unit area of the low coercive force film is within the range per unit area of the perpendicularly magnetized film. The thickness of the low coercive force film is preferably one quarter or more and ten times or less of the saturation magnetic moment. It is further preferable that the above value is 1/6 or more and 6 times or less.

It is most preferable that the above-mentioned value is 1/2 or more, above, and 4 times or less.

As a method for forming such a low coercive force film.

In the present invention, it is important to use an ion plater, which makes it possible to form a low coercive force film on a low-temperature substrate that is free from cracks and has uniform, good magnetic properties.

The ion plating used in the present invention refers to a method in which part or all of the particles that fly onto a substrate and adhere to the substrate to form a thin film are ionized to a monovalent or higher valence using a vacuum deposition method.

Ion plating methods include glow discharge method, hot cathode excitation method, radio frequency excitation method, cluster ion beam method,
An ion beam method or the like can be used.

Among these, in the present invention, the hot cathode excitation method, radio frequency excitation method, and cluster ion beam method are advantageous in that they can form a high-performance low coercive force film at high speed under high vacuum, and in particular, the ionization efficiency can be increased. The hot cathode excitation method, the radio frequency excitation method, and a combination thereof are most preferred.

Methods for vaporizing materials include electron beam heating, induction heating,
There are methods using heating such as resistance heating and laser heating, and methods using elimation using ion bombardment, but methods using heating are preferable because the degree of formation of 1M shape is rapid.

It is preferable to accelerate the ionized particles and make them incident on the substrate in order to prevent the occurrence of cracks and to reduce the coercive force.

On the other hand, when two particles are accelerated, the amount of heat flowing into the base increases,
Substrates made of organic polymers are more susceptible to thermal damage. Therefore, the accelerating voltage is.

-5kV to -300V range is preferred, -3kV
V i)h is more preferably in the range of 400v y=2k
A range of 15 oov from v is most preferred.

FIG. 1 shows an example of an apparatus for carrying out the method of the present invention. C is a vacuum chamber, D is a drum-shaped substrate holder that controls the temperature while running the substrate at a predetermined speed, E is a substrate made of an organic polymer, I is a crucible, and G is an evaporation material made of iron and nickel. .

J is an electron beam that heats the evaporation material, and F is a shielding plate. The iron and nickel particles evaporated from the crucible and headed toward the drum D collide with electrons emitted from the filament K and are ionized. The ionized particles are accelerated by the mesh-like accelerating electrode 0 and are incident on the base E that is in close contact with the drum D. L is a power source for heating the filament, N is a bias power source for emitting electrons from the filament, and P is a power source for accelerating ions.

When forming a low coercive force film, the temperature of the substrate is controlled by a substrate holder in contact with the substrate.

The temperature of the substrate holder, which cools or heats the substrate by closely contacting the surface of the substrate, prevents thermal deformation of the organic polymer substrate during formation of the low coercive force film, and also prevents thermal expansion between the substrate, inorganic film, and low coercive force film. A lower value is preferable in order to prevent the coercive force of the low coercive force film from increasing due to stress caused by the difference in coefficients.

Ion plating can prevent cracks from occurring, so there is no need to heat the substrate.
Even if the substrate temperature is increased, the effect of ion derating is not impaired. For this reason, the temperature of the basic holder when forming a low coercive force film is -30°C or more and 180°C or less, preferably
-20°C or higher and 150°C or lower, most preferably -20°C
It is desirable that the temperature is between 130°C and 130°C.

The perpendicularly magnetized film used in the present invention is mainly composed of cobalt, cobalt oxide and/or iron and iron oxide, and has magnetic anisotropy in the direction perpendicular to the substrate surface.

The perpendicularly magnetized film having magnetic anisotropy in the direction perpendicular to the film plane in the present invention is defined as second-order.

The magnetic properties of the perpendicular magnetization film are as per JIS C-2561.
It can be measured using the vibrating magnetometer method shown in or the self-recording magnetometer method. That is, the magnetization (M) of the sample is measured while applying an external magnetic field (H) to the perpendicularly magnetized film, which is the t sample.

FIG. 2 schematically shows the results of this measurement. First, the external magnetic field (H) is gradually increased from the 00 state (point 0), and when the magnetization (M) of the sample is saturated (point A), the external magnetic field (H) is decreased and further Apply a magnetic field in the opposite direction. When the magnetization in the opposite direction is saturated (point B), reduce the external magnetic field (H), and then apply the external magnetic field (H) in the initially applied direction until the magnetization (M) of the sample is saturated (
Point A).

The curve A→B −+ A obtained in this way is.

This is called a hysteresis loop. Magnetic properties such as coercive force and saturation magnetization can be measured from this hysteresis loop. When used for magnetic recording media.

The larger the area (S) surrounded by this hysteresis loop is, the larger the recording capacity is, and it is suitable for high-density recording.

In a perpendicular magnetic recording medium equipped with a low coercive force film, the hysteresis loop of the low coercive force film is measured in advance, and after forming the perpendicular magnetic film, the hysteresis loop of the low coercive force film is calculated from the measured hysteresis loop. By subtracting it, the hysteresis loop of only the perpendicularly magnetized film can be found.

S is the area surrounded by the hysteresis loop measured while applying an external magnetic field in the perpendicular direction to the perpendicularly magnetized film surface of the sample.
= If the area of the hysteresis loop when an external magnetic field is applied in a direction parallel to the perpendicularly magnetized film surface is Sl, +
When SL is larger than Sl, it can be said that the magnetic recording medium is suitable for perpendicular magnetic recording.

In the present invention, a perpendicularly magnetized film having magnetic anisotropy in the direction perpendicular to the film surface is defined by the area S= of a hysteresis loop against an external magnetic field perpendicular to the film surface, and the hysteresis against an external magnetic field in a direction parallel to the film surface. Area of the loop S1. The magnetic anisotropy coefficient (S on/S1.) calculated by is larger than 1,
Preferably it is 1.2 or more, most preferably 1.4 or more.

There is no particular limit to the thickness of the perpendicular magnetization film, but it is practically 0.
．． A range of 0.02μm to 5μm is best, especially 0.08μm.
A range of m to 6 μm, particularly 0.1 μm to 2 μm, is most preferable in terms of flexibility and good head touch.

The perpendicular magnetization film is mainly composed of cobalt and C00°CO
□0, + Cobalt oxides such as CosO4 and/or iron and FeO, Pe20. , Fe
, 04 and other iron oxides. Other examples of cobalt oxide include Co0X (X is a number between 0 and 2)
Also included are non-stoichiometric oxides and peroxides represented by In addition to this, iron oxides include Fe0x (x is 0 to 2
Also included are non-stoichiometric oxides and peroxides represented by numbers in between.

The perpendicularly magnetized film contains cobalt, cobalt oxide, and elements or compounds other than iron and iron oxide, such as nickel copper, chromium, aluminum, carbon, silicon, vanadium, titanium, and zinc.

Manganese, metal oxides, metal nitrides, metal hydroxides, and the like may be contained within the range that does not impair vertical magnetic anisotropy.

Vacuum deposition methods such as vacuum evaporation, ion plating, and sputtering can be used to form such a perpendicularly magnetized film, but vacuum evaporation is particularly preferred since the temperature rise of the substrate is small and the film formation rate is high.

The pressure of the oxygen-containing atmosphere in the tank during vacuum deposition is set to 1x in order to improve the magnetic properties of the perpendicularly magnetized film mainly composed of cobalt and cobalt oxide and/or iron and iron oxide.
A range of 10) Torr to 1×10 Torr is desirable.

When forming a perpendicularly magnetized film, it is desirable to cool the temperature of the substrate to 50° C. or less in order to increase the magnetic anisotropy coefficient of the perpendicularly magnetized film. In addition, the angle between the cobalt and/or iron vapor and the normal to the substrate surface is 45 degrees or less.
It is preferable to provide a mask that blocks incident particles exceeding 5 degrees in order to increase the magnetic anisotropy coefficient of the perpendicularly magnetized film.

An example of the method for manufacturing the perpendicular magnetic recording medium of the present invention having the structure of organic polymer substrate/low coercive force film/perpendicular magnetization film is shown below, but the method is not limited thereto.

The base is a biaxially stretched polyethylene terephthalate film with a thickness of 50 μm. After evacuating the vacuum chamber to 1 x 10-6 Torr, the weight ratio of iron and nickel was 17:8.
6 by electron beam vacuum evaporation using an alloy of 3 as a deposition material.
A low coercivity film approximately 0.25 μm thick is formed on the above substrate at a deposition rate of 0 μl 1115+.

At this time, in the apparatus shown in Fig. 1, the output of the insulator source (N) for electron irradiation is -50V, and the output of the ion accelerating electrode (0) is -50V.
A voltage of oov is applied to ionize particles flying onto the substrate and accelerate these ions, respectively. At this time, the holder is in close contact with the back side of the base.

Cooled to below 20°C. After evacuation to 1x101-1 again, oxygen was introduced at 10 to 1000α per minute, and
Cobalt and cobalt oxide were deposited on the low coercive force magnetic film by electron beam vacuum evaporation at a rate of 10 μm/min in a vacuum chamber at a pressure of 0 to 1 O-2) Torr. A perpendicularly magnetized film mainly consisting of is formed.At this time, the back surface of the substrate is

A shielding plate is installed between the evaporation source and the substrate so that the cobalt vapor is cooled to -10°C or lower, and the angle between the incident vapor and the normal direction of the substrate is 45° or less when the cobalt vapor is incident on the film substrate. Place.

〔Effect of the invention〕

The method of manufacturing a perpendicular magnetic recording medium of the present invention can produce a perpendicular magnetic recording medium that is uniform without cracking and has good magnetic properties.

The reason why it is possible to obtain a low coercive force film mainly made of iron and nickel on an organic polymer substrate by vacuum deposition that does not crack even at low substrate temperatures by using ion plating has not been fully elucidated. This is presumably because the energy possessed by the ionized and accelerated particles has the effect of relaxing the internal stress of the low coercive force film during growth.

As a result, it is possible to obtain a perpendicular magnetic recording medium with good head touch and less wear and detachment due to contact with the magnetic head or guide portion. Also.

The combination of vacuum deposition and low substrate temperature makes it possible to obtain perpendicular magnetic recording media at high speeds on plastic substrates with low heat resistance.

The perpendicular magnetic recording medium obtained by the present invention is a tape.

It can be widely used for magnetic recording of audio, video, digital signals, etc. in the form of sheets, cards, disks, drums, etc.

[Measurement method and evaluation criteria of characteristics]

(1) Coercive force vibrating sample magnetometer (manufactured by Riken Electronics Co., Ltd., BHV-30
) to apply an external magnetic field parallel to the film surface and record the hysteresis loop. From this hysteresis loop, the coercive force is determined based on the definition of JIS C2560.

〔Example〕

Example 1 A biaxially stretched polyethylene terephthalate film (Lumirror" manufactured by Toshiku Co., Ltd.) having a thickness of 75 μm was used as a substrate.

Using an alloy of iron and nickel in a weight ratio of 17:83 as the deposition material, the film was deposited to a thickness of approximately 0.25 μm by electron beam vacuum deposition at a deposition rate of 60 μm/min in an atmosphere of 1×10 TOrr.
A low coercive force film of m was formed on the substrate.

At this time, in the apparatus shown in FIG. 1, a voltage of -50 V was applied to the bias power supply N for electron irradiation, and a voltage of -1 kV was applied to the ion accelerating electrode 0. The substrate was placed in close contact with a cooled holder, and the temperature of the holder was maintained at 20°C.

No cracks were observed in the low coercive force film thus obtained. Moreover, the coercive force in the direction parallel to the film surface was 6 oersted.

Next, cobalt was evaporated by electron beam vacuum evaporation by introducing oxygen gas at a rate of 550 mm per minute and setting the pressure inside the vacuum chamber to 8 x 10 Torr, to form cobalt and cobalt oxide with a thickness of about 0.25 μm at a deposition rate of 10 μm/min. A perpendicularly magnetized film mainly consisting of a film was formed on a low coercive force film.

The substrate was placed in close contact with a holder cooled to 5°C.
A water-cooled shielding plate for blocking incident particles exceeding 45 degrees is placed on the front surface of the substrate so that the angle between the cobalt vapor and the normal to the surface of the substrate is 45 degrees or less.

The thus obtained perpendicular magnetic recording medium showed no cracks at all and had good wear resistance.

Example 2 The same polyethylene terephthalate film as in Example 1 was used as the substrate. A low coercive force film made of iron and nickel was formed on the substrate in the same manner as in Example 1 except that a voltage of -5 oov was applied to the ion accelerating electrode 0.

No cracks were observed in the low coercive force film thus obtained. The coercive force in the direction parallel to the film surface was 7 Oersteds.

Next, a perpendicularly magnetized film mainly composed of iron and iron oxide was formed on the low coercive force film.

That is, a mixed gas of oxygen and nitrogen with a partial pressure of 60:40 was introduced at 550 μ/min, the pressure inside the vacuum chamber was set to 8×10 Torr, and iron was evaporated by electron beam vacuum evaporation.
A perpendicularly magnetized film consisting primarily of iron and iron oxide with a thickness of approximately 0.25 μm was formed on the low coercive force film at a deposition rate of μffi/min.

The substrate was placed in close contact with a holder cooled to 5°C, and the angle between the iron vapor and the normal to the substrate surface was 45 degrees or less.
A water-cooled shielding plate that shields incident particles above 45 degrees is placed in front of the substrate.

The thus obtained perpendicular magnetic recording medium showed no cracks at all and had good wear resistance.

Example 3 A low coercive force film made of iron and nickel was formed on a polyethylene terephthalate film substrate in the same manner as in Example 2. No cracks were observed in the low coercive force film thus obtained. The coercive force of the low coercive force film in the direction parallel to the film surface was 7 oersteds.

A perpendicularly magnetized film mainly composed of cobalt, iron, and oxides thereof was formed on the low coercive force film.

In other words, a mixed gas of oxygen and nitrogen with a partial pressure of 70:30 was introduced at a rate of 500 cc per minute, the pressure inside the vacuum chamber was set to 7×10 Torr, and an alloy of cobalt and iron with a weight ratio of 80:20 was evaporated with an electron beam. A perpendicularly magnetized film mainly composed of cobalt, iron, and oxides thereof having a thickness of about 0.6 μm was formed on the low coercive force film at a deposition rate of 10 μrn/min.

The substrate was placed in close contact with a holder cooled to 5°C, and a water-cooled shielding plate was installed to block incident particles exceeding 45 degrees so that the angle between the metal vapor and the normal to the substrate surface was 45 degrees or less. Place it on the front of the base.

The thus obtained perpendicular magnetic recording medium showed no cracks at all and had good wear resistance.

Example 4 The same polyethylene terephthalate film as in Example 1 was used as the substrate.

A low coercive force film made of iron and nickel was formed on the substrate in the same manner as in Example 1 except that the voltage applied to the ion accelerating electrode 0 was -300V.

Although some of the low coercive force films obtained in this way had minute racks, they were improved compared to those in which ionization and ion acceleration were not performed.

The coercive force in the direction parallel to the film surface was 26 oersted, which was smaller than that in the case where ionization and ion acceleration were not performed.

A perpendicularly magnetized film mainly made of cobalt and cobalt oxide was formed on the low coercive force film in the same manner as in Example 1.

The thus obtained perpendicular magnetic recording medium had almost no cracks in the perpendicular magnetization film and had good wear resistance.

Comparative Example 1 The same polyethylene terephthalate film as in Example 1 was used as the substrate.

A low coercive force film made of iron and nickel was formed on the substrate in the same manner as in Example 1 except that ionization and ion acceleration were not performed.

In the thus obtained low coercive force film, many fine racks were generated, the film became cloudy, and some peeling occurred.

The coercive force in the direction parallel to the film surface was 40 oersteds.

A perpendicularly magnetized film mainly made of cobalt and cobalt oxide was formed on the low coercive force film in the same manner as in Example 1.

In the thus obtained perpendicular magnetic recording medium, cracks also occurred in the perpendicular magnetization film, and the film easily came off due to contact with the head or guide portion.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of an apparatus for carrying out the present invention, and FIG. 2 is an explanatory diagram showing an example of measuring a hysteresis loop. C: Vacuum chamber D = Heating or cooling drum E: Substrate made of organic polymer F: Shielding plate G: Evaporation material made of iron and nickel: Crucible J: For electron beam for heating evaporation material: Filament L: For heating filament Power supply N: Bias power supply for electron emission 0: Ion acceleration electrode P: Power supply for ion acceleration A, B:
Saturation point H: External magnetic field M: Magnetization of sample Patent applicant Toshi Co., Ltd. Figure 2

Claims (2)

[Claims] (1) A low coercive force film mainly made of iron and nickel is formed on a substrate made of an organic polymer by ion plating, and then magnetically anisotropic in the direction perpendicular to the film surface on the low coercive force film. 1. A method of manufacturing a perpendicular magnetic recording medium, the method comprising forming a perpendicularly magnetized film having a magnetic field. (2) The method of manufacturing a perpendicular magnetic recording medium according to claim 1, wherein the perpendicular magnetization film mainly consists of cobalt and cobalt oxide and/or iron and iron oxide.