JPH1079120A - Manufacturing method of magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize stabilization of magnetic property and electromagnetic conversion characteristics, by cutting a metallic magnetic thin film on a non- magnetic support web in the longitudinal direction to form a pancake-like roll having a predetermined width, and storing the roll in an atmosphere rich in oxygen for a predetermined time. SOLUTION: A metallic magnetic thin film is continuously formed on a non-magnetic support web, when cut in the longitudinal direction, and wound up with a width less than 20mm so as to form a pancake-like roll. This roll is stored in an atmosphere richer in oxygen than the ambient atmosphere, for example, in an mixed gas atmosphere of oxygen gas and nitrogen gas, for a predetermined time. After that, an anticorrosive agent is applied. Therefore, oxidation of the metallic magnetic thin film proceeds mainly from the cut surface of the pancake-like roll, and the coercive force significantly affecting the magnetic property, particularly the electromagnetic conversion characteristics, is saturated early. An Fe alloy and a Co alloy may be used as the material of the metallic magnetic thin film, and a polyester resin and a polycarbonate resin are used as the non-magnetic support. Thus, the magnetic property and electromagnetic conversion characteristics are stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magnetic recording medium in which a metal-based magnetic thin film is formed on a non-magnetic support, and more particularly, to a thin-film type magnetic material having little change over time in magnetic characteristics and electromagnetic conversion characteristics. The present invention relates to a method for manufacturing a recording medium.

[0002]

2. Description of the Related Art In the field of information recording by magnetic recording, the amount of information to be recorded is increased, the size of a magnetic recording device is reduced,
Alternatively, high-density recording has been demanded in view of trends such as a reduction in the relative speed between the magnetic recording medium and the magnetic head. Along with this, instead of a coating type magnetic recording medium in which magnetic particles are dispersed in an organic binder also in a magnetic recording medium, a metal-based magnetic thin film is formed by plating or a vacuum thin film forming technique, that is, vacuum evaporation, sputtering or ion plating. Thin-film magnetic recording media for film formation are becoming mainstream. Above all, it is known that a thin-film magnetic recording medium employing a metal-based magnetic thin film mainly composed of Co is excellent in various magnetostatic properties such as coercive force, squareness ratio and residual magnetic flux density. Further, since it is not necessary to mix a non-magnetic organic binder in the magnetic layer as in the case of the coating type magnetic recording medium, it is possible to reduce the thickness of the magnetic layer for obtaining the required amount of magnetic flux. Since the magnetism is small, it also has excellent electromagnetic conversion characteristics in a short wavelength region from this aspect.

In a thin-film magnetic recording medium used for a helical scan video tape recorder (VTR), a digital audio tape recorder (DAT), or the like,
In order to increase the magnetic anisotropy in the longitudinal direction of the tape and achieve higher output at shorter wavelengths, a thin film type magnetic recording medium by oblique deposition has been proposed and put to practical use. In the oblique deposition, a magnetic layer is formed on a non-magnetic support web made of a polymer material such as polyester which moves and travels by an electron beam deposition or the like oblique to the traveling direction. In a thin film type magnetic recording medium formed by oblique evaporation, magnetic particles are obliquely oriented with respect to the surface of the nonmagnetic support in the fine structure. Therefore, high-density recording is possible as compared with a conventional magnetic tape in which magnetic particles are uniaxially oriented in the longitudinal direction of the plane of the nonmagnetic support. The axis of easy magnetization of a thin-film magnetic recording medium formed by oblique vapor deposition that is currently in practical use is generally inclined at about 20 ° with respect to the surface of the nonmagnetic support.

In a thin film type magnetic recording medium formed by oblique evaporation, Co or Co- is generally used as a metal-based magnetic thin film material.
Ni alloy system is adopted. In order to form these metal-based magnetic thin films on a non-magnetic support web, Co or Co-Ni
A manufacturing method in which oblique deposition is performed on a moving non-magnetic support web while an alloy is used as an evaporation source and a small and fixed amount of oxygen gas is introduced into a deposition apparatus is usually used. By this oblique deposition step, the metal-based magnetic thin film becomes α-Co (or Co-N
i) magnetic particles and Co-
O (or Co-Ni-O) is mixed.
The reason for introducing oxygen into the metal-based magnetic thin film is to reduce the medium noise by reducing the size of the magnetic particles and to increase the oblique shape anisotropy by forming the metal-based magnetic thin film into a columnar particle structure. That's why. In addition to the oblique deposition, there is a method of forming a metal-based magnetic thin film by a sputtering method using Co or a Co-Ni alloy as a target.

[0005] Thereafter, a conductive back coat layer is provided on the back surface of the non-magnetic support web as required, and a lubricant or rust inhibitor is applied on the metal-based magnetic thin film. Then, it is made into a pancake-shaped roll, and stored in a container such as a cassette to complete a magnetic recording medium.

[0006]

By the way, when a magnetic recording medium using such a metal-based magnetic thin film is stored in the air for a long time, the magnetic characteristics may change. This phenomenon is considered to be because oxidation of the metal-based magnetic thin film proceeds to some extent because the metal-based magnetic thin film is not covered with the organic binder, unlike the coating type magnetic recording medium. In particular, the change in the coercive force is remarkable in the comparative example, and starts to increase immediately after the deposition of the metal-based magnetic thin film, and after about 200 days, increases by 20 to 30% and finally reaches the saturation value.
After that it hardly changes. FIG. 2 is a graph showing how the coercive force changes. The figure shows the results of measurement when a magnetic recording medium with a 180-nm-thick metal-based magnetic thin film formed by oblique deposition using pure Co metal as an evaporation source and slit to a width of 8 mm was stored in the atmosphere. It is. As is clear from the figure, the coercive force was 2% after the deposition of the metal-based magnetic thin film.
It rises about 27% in 00 days, reaches a saturation value and stabilizes.
The example of FIG. 2 is an example of a magnetic recording medium slit to a width of 8 mm. However, when the recording medium is slit to a wider width or stored without slitting, it takes a longer time until the magnetic characteristics are saturated. It is.

Since it takes a long time for the coercive force to stabilize, when the magnetic recording medium is supplied to the user during this time and used, the mismatch between the recording current and the bias current is reduced. Therefore, there is a possibility that the original characteristics of the magnetic recording medium cannot be exhibited, such as a decrease in the reproduction output. An object of the present invention is to provide a method of manufacturing a magnetic recording medium capable of supplying a thin-film magnetic recording medium having no change in magnetic characteristics to a user and stably exhibiting the original electromagnetic conversion characteristics of the magnetic recording medium. .

[0008]

The method of manufacturing a magnetic recording medium according to the present invention is proposed to achieve the above-mentioned object, and at least a metal-based magnetic thin film is continuously formed on a non-magnetic support web. The non-magnetic support web on which the metal-based magnetic thin film has been formed is cut in the longitudinal direction by 20 m.
m and a width of less than m
The pancake roll is stored for a predetermined time in an oxygen-rich atmosphere than the atmosphere.

In the method for manufacturing a magnetic recording medium of the present invention, the pressure of the atmosphere rich in oxygen than the atmosphere is desirably substantially atmospheric pressure. The atmosphere richer in oxygen than the atmosphere is preferably a mixed gas atmosphere of oxygen gas and nitrogen gas or an oxygen gas atmosphere. The predetermined time for storing the pancake-shaped roll in an oxygen-rich atmosphere than the atmosphere is a time until the coercive force of the metal-based magnetic thin film increases and reaches a substantially saturated value. This time varies between several days and several tens of days depending on the storage atmosphere.

Further, in the method of manufacturing a magnetic recording medium of the present invention, it is preferable that after the step of storing for a predetermined time in an oxygen-rich atmosphere than the atmosphere, a rust inhibitor is applied to the metal-based magnetic thin film.

The material of the metal-based magnetic thin film in the present invention is not particularly limited, and any material can be used as long as it is a magnetic material used for a normal thin-film magnetic recording medium. For example, Fe,
Simple ferromagnetic metals such as Co and Ni, and Fe-Co and F
e-Co-Ni, Fe-Co-Cr, Fe-Co-Ni
-Cr, Fe-Cr, Fe-based alloys such as Fe-Cu, C
o-Ni, Co-Fe-Ni, Co-Pt, Co-C
Co-based alloys such as r and Co-Cu are preferably exemplified.
The material layers of these metal-based magnetic thin films may contain impurities such as oxygen, nitrogen, and carbon. The metal-based magnetic thin film may have a single layer or a laminated structure. Further, an underlayer or an intermediate layer may be provided between the non-magnetic support and the metal-based magnetic thin film or between layers in the case of a laminated structure for controlling the adhesion and coercive force.

The non-magnetic support employed in the present invention includes:
Examples include polyester resins such as PET (Polyethylene terephthalate), and organic polymers such as polyolefin resins, vinyl resins, polyimide resins, polyamide resins, and polycarbonate resins.

As a basic configuration of the magnetic recording medium of the present invention,
In addition to the nonmagnetic support and the metal-based magnetic thin film, a back coat layer, a lubricant layer, a protective layer, or the like may be formed as necessary. The materials and forming methods of these layers may be the same as those used in conventional thin-film magnetic recording media.

According to the method of manufacturing a magnetic recording medium of the present invention, the number of days conventionally required for about 200 days until the magnetic characteristics are stabilized can be reduced from several days to several tens of days. By storing the magnetic recording medium cut to a width of less than 20 mm in an oxygen-rich atmosphere, the oxidation of the metal-based magnetic thin film mainly proceeds from the cut surface of the pancake-shaped roll, and greatly increases the magnetic characteristics, particularly the electromagnetic conversion characteristics. The effecting coercive force reaches saturation early. The cutting width may be determined for each intended use of the magnetic recording medium. For example, 19.05 mm in Umatic format, 12.7 mm in VHS format, 8.0 m in 8 mm video format
m and 3.81 in compact cassette format
mm or the like. By cutting to a width of less than 20 mm in this way, rather than storing the roll with the full width of the non-magnetic support web, that is, as a jumbo roll, or storing with a pancake-shaped roll slit to a width of several tens of mm, Magnetic characteristics can be stabilized in a short time. Further, after storage, it can be immediately stored in a cassette without going through a slitting step.

Further, by storing at atmospheric pressure, the storage container or storage does not need to adopt a pressure-resistant structure, which contributes to simplification of the apparatus. An atmosphere richer in oxygen than the atmosphere can be formed by adding oxygen gas to air, so that the cost is low. Of course, if an atmosphere of 100% oxygen gas is used,
Magnetic characteristics can be stabilized in a short time. After the step of storing for a predetermined time in such an atmosphere, if a rust preventive is applied on this metal-based magnetic thin film, the subsequent change in magnetic properties can be almost completely prevented.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. First, an example of a continuous vapor deposition apparatus employed in the method for manufacturing a magnetic recording medium of the present invention will be described with reference to a schematic sectional view shown in FIG.

The apparatus shown in FIG. 3 is a general reel-to-reel type continuous vapor deposition apparatus. That is, a supply roll 1 for supplying a non-magnetic support web such as a PET film and a non-magnetic support web are wound in a vacuum chamber 9 in which the inside is evacuated by a vacuum pump (not shown). The cooling can 2 that rotates in synchronization
A take-up roll 3 for winding a non-magnetic support web on which a metal-based magnetic thin film is deposited is provided. on the other hand,
The vacuum evaporation means deflects and scans an electron beam 5 generated from an electron gun 4 by a magnet 6, irradiates the electron beam to a ferromagnetic metal such as Co in a hearth 7, and dissolves and evaporates this. . In order to regulate the incident angle of the oblique deposition, a shielding plate 8 is provided near the cooling can 2. An automatic supply device (not shown) for supplying pellets or wires of ferromagnetic metal such as Co into the hearth.
And the liquid level of the molten metal accompanying evaporation can be maintained at a constant level.

Hereinafter, the method for manufacturing a magnetic recording medium of the present invention will be described in more detail. Example 1 A metal-based magnetic thin film was continuously formed on a non-magnetic support web under the following conditions, for example, using the continuous vapor deposition apparatus shown in FIG. The non-magnetic support web has a thickness of 10 μm,
A 250-mm-wide PET film is used, and water-soluble latex particles containing acrylic ester as a main component are applied on the surface thereof to a particle density of 10 ⁷ particles / mm ² and dried. Metal-based magnetic thin film condition condition Pellet Co metal 100% Incident angle 40-90 ° O ₂ flow rate 330 sccm Vacuum degree during evaporation 7 × 10 ^-2 Pa Line speed during evaporation 0.17 m / sec Thickness of metal-based magnetic thin film 180 nm

After the continuous deposition, the non-magnetic support web is
If necessary, a back coat layer was formed on the back surface, and a lubricant such as perfluoropolyether was applied to the surface of the metal-based magnetic thin film. Thereafter, the mixture was cut into a width of 8 mm to form a pancake-shaped roll, and the mixed gas of O ₂ : N ₂ = 5: 5 (volume ratio) was stored as it was in a storage in an atmosphere in which a small flow rate was flown. A recording medium sample was used. The pressure in the storage was always at atmospheric pressure.

Example 2 A sample of a magnetic recording medium of Example 2 was prepared in accordance with Example 1, except that the atmosphere in the storage was changed to O ₂ : N ₂ = 8: 2 (volume ratio).

Example 3 The atmosphere in the storage was changed to O ₂ : N ₂ = 10: 0, that is,
A magnetic recording medium sample of Example 3 was manufactured according to Example 1, except that oxygen gas was set to 100%.

Comparative Example A magnetic recording medium sample of a comparative example was prepared according to Example 1, except that the atmosphere in the storage was O ₂ : N ₂ = 1: 4 (volume ratio), that is, ordinary air was used. .

Examples 1 to 3 produced as described above,
For the magnetic recording medium samples of Comparative Examples, a part thereof was taken out of the storage at 10, 40, 70, 100, 150, and 200 days after the deposition of the metal-based magnetic thin film, and the coercive force was measured. The coercive force was measured by a sample vibration type magnetometer. The measurement results are shown in [Table 1].

[0024]

[Table 1]

The measurement results are shown in the graphs of FIGS.

As is clear from Table 1 and FIGS. 1 and 2, the higher the oxygen concentration, the shorter the coercive force reaches the saturation value in a short time, and the storage at 100% oxygen (Example 3) is 10 days. It can be seen that the saturation is almost reached. O ₂ : N ₂ =
In 8: 2 (Example 2), about 40 days, O ₂ : N ₂ = 5: 5
In the first embodiment, the coercive force is saturated in 100 days. On the other hand, it can be seen that in the case of O ₂ : N ₂ = 1: 4, that is, in the case of ordinary air, it takes 200 days to reach the saturation value.

In the magnetic recording medium whose magnetic properties reach saturation in a short time as described above, the change with time after that is extremely small, but thereafter, by applying a rust preventive to the metal-based magnetic thin film, The stability of the magnetic properties can be made almost perfect.

As described above, the magnetic recording medium of the present invention has been described in detail with reference to three examples and comparative examples. However, the present invention can be implemented in various embodiments other than these examples. For example, the pancake roll is stored at room temperature, but may be stored at an elevated temperature within a range that does not cause a shape defect in the magnetic recording medium.

Although pure Co metal is used as the metal-based magnetic thin film, similar good results can be obtained by using various Co alloys or other ferromagnetic metals as described above. Good results can also be obtained when the present invention is applied to a perpendicular magnetic recording medium utilizing perpendicular magnetic anisotropy such as a Co-Cr alloy.

Further, in the embodiment, a method for producing a metal-based magnetic thin film by vapor deposition is exemplified, but a sputtering method or an ion plating method may be used.

[0031]

As is clear from the above description, by employing the method for manufacturing a magnetic recording medium of the present invention, it is possible to provide a magnetic recording medium with stable magnetic characteristics and electromagnetic conversion characteristics.

[Brief description of the drawings]

FIG. 1 is a graph showing a change over time of a coercive force of a magnetic recording medium of an example.

FIG. 2 is a graph showing a change over time of a coercive force of a magnetic recording medium of a comparative example.

FIG. 3 is a schematic sectional view of a continuous vapor deposition apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Supply roll, 2 ... Cooling can, 3 ... Take-up roll, 4 ... Electron gun, 5 ... Electron beam, 6 ... Magnet, 7 ... Hearth, 8 ... Shielding plate, 9 ... Vacuum chamber, 10
... O ₂ nozzle, 11 ... O ₂ pipe

Claims (6)

[Claims] 1. A method for producing a magnetic recording medium comprising a step of continuously forming at least a metal-based magnetic thin film on a non-magnetic support web, comprising: A longitudinally cut width of less than 20 mm to form a take-up pancake roll, wherein the pancake roll is stored for a predetermined time in an oxygen-rich atmosphere from the atmosphere. Production method. 2. The method for manufacturing a magnetic recording medium according to claim 1, wherein the pressure of the oxygen-rich atmosphere is substantially atmospheric pressure. 3. The method according to claim 1, wherein the atmosphere richer in oxygen than the atmosphere is a mixed gas atmosphere of oxygen gas and nitrogen gas. 4. The method according to claim 1, wherein the atmosphere richer in oxygen than the atmosphere is an oxygen gas atmosphere. 5. The predetermined time for storing the pancake-shaped roll in an oxygen-rich atmosphere than the atmosphere is a time until the coercive force of the metal-based magnetic thin film increases and reaches a substantially saturated value. The method for manufacturing a magnetic recording medium according to claim 1. 6. The method for manufacturing a magnetic recording medium according to claim 1, wherein a rust preventive is applied on the metal-based magnetic thin film after the step of storing the metal-based magnetic thin film in an oxygen-rich atmosphere for a predetermined time. .