JPH103660A - Production of magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for production which enables the execution of vapor deposition without the deformation of a base film by thermal radiation even if this base film is as thin as <=6μm. SOLUTION: A crucible 7 which is a ferromagnetic material evaporating source is arranged below a cooling can roll 3 and the position in its horizontal direction (x) is variable from a position (-1) where the normal erected at the center of the evaporating surface of the crucible 7 aligns to the revolving shaft of a cylindrical can to a position (1) where this normal is tangent with the cylindrical can on the carrying-in side of the base film. The base film 4 is made to travel onto the cooling can roll 3 from an un-winding roll 5 after a prescribed vacuum atmosphere is maintained in a chamber 2. The power P(kW) of the electron beam cast from the electron gun 8 to the cobalt in the crucible 7 is controlled in accordance with 3a>=P>=a (where a=50-tx/2), according to the position of the crucible 7 along an (x) direction and the temp. t ( deg.C) of the cooling can roll 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of manufacturing a magnetic recording medium, and more particularly to a novel method of manufacturing a magnetic recording medium suitable for depositing a ferromagnetic thin film on a thin base film.

[0002]

2. Description of the Related Art An evaporation type, which is manufactured by irradiating an electron beam to a ferromagnetic material evaporation source and heating it to form a metal thin film on a base film conveyed on a cylindrical can. A magnetic recording medium has a high filling ratio of a magnetic substance and thus has a thin film and a large saturation magnetization and a large coercive force as compared with a coating type magnetic recording medium and the like, and is used in various application fields as suitable for high-density recording. Regarding the manufacturing technology of such a vapor deposition type magnetic recording medium, for example, a video tape or an 8 mm video tape, many improvements have been proposed for the purpose of improving the characteristics. As an example, Japanese Patent Publication No. 41-19389 discloses that a magnetic layer having an oblique column structure is obtained by using a so-called oblique deposition technique, thereby increasing the coercive force and improving the output. .
Japanese Patent Publication No. 60-10370 discloses that the center of the evaporation surface of a ferromagnetic material evaporation source is shifted from the rotation axis of the cylindrical can to the side where the base film is carried in, thereby increasing the coercive force of the obtained magnetic film. doing.

[0003]

A non-magnetic support such as a plastic such as polyethylene terephthalate is used as a base film of a magnetic recording medium. Its thickness is 16μ for VHS type video tape, for example.
m, about 9 μm for an 8 mm video tape, and about 6.3 μm for a digital video cassette (DVC),
With the demand for high-density recording, miniaturization and lengthening of the magnetic recording medium, and hence the thickness of the base film, tend to become thinner. In such a case, if the above conventional technique is applied as it is, there is a problem that the base film is damaged by heat radiation from the ferromagnetic material evaporation source.
In particular, recently, the use of an extremely thin base film having a thickness of 6 μm or less has been studied. In these cases, such a problem is particularly serious. That is, the base film is deformed by heat loss, and the resulting magnetic recording medium may have a deteriorated envelope waveform or a poor running.

Japanese Patent Publication No. Sho 60-10370 discloses that the distance between a ferromagnetic material evaporation source and a cylindrical can is reduced within a range where the pace film is not damaged by heat radiation, and evaporation from a cylindrical can rotating shaft is performed. It is described that it is preferable to increase the shift of the plane center. However, this does not take into account the differences caused by the thickness of the base film, nor does it take into account the relationship between these distances and other parameters. This merely teaches the common-sense matter of bringing the cylindrical can and the evaporation source closer to each other as long as the conventional base film does not lose heat, and further consideration is needed when dealing with thinning of the base film. It is.

[0005]

According to the method of manufacturing a magnetic recording medium provided by the present invention, a magnetic recording medium is provided on a base film conveyed through a cylindrical can in a vacuum atmosphere in the same manner as in the conventional method. The ferromagnetic metal thin film layer is deposited through electron beam scanning heating of a magnetic material evaporation source. However, in the present invention, the power of the electron beam, that is, the power of the electron gun for irradiating the electron beam, is controlled in accordance with the position of the ferromagnetic material evaporation source with respect to the cylindrical can and the temperature of the cylindrical can. As described above, by controlling the power of the electron gun in accordance with the temperature of the cylindrical can and the position of the ferromagnetic material evaporation source, it is possible to perform optimal vapor deposition while avoiding damage to the base film.

[0006] In particular, the production method of the present invention is extremely effective when the base film is thinned as described above and the thickness is 6 μm or less. In such a case, the power of the electron beam, that is, the output P (kW) of the electron gun is 3a ≧ P
It is selected within the range of ≧ a. However, in this case, a = 50
−tx / 2, t is the temperature (° C.) of the cylindrical can, x is −1, the position where the normal set at the center of the evaporation surface of the ferromagnetic material evaporation source coincides with the rotation axis of the cylindrical can, and −1. This is a number where the position that is tangent to the cylindrical can on the loading side is 1. If the film is formed within such a range,
It can cope well with thinning of base film,
Thus, it is possible to preferably respond to the demand for high density. In other words, this range provides good deposition without undesired deformation of the base film for a given can roll temperature and a given location of a ferromagnetic material evaporation source, typically a crucible. It is possible to easily obtain an electron beam power that can be used.

According to another aspect of the present invention, the position of the ferromagnetic material evaporation source is variable within a range of -1 ≦ x ≦ 1. Although this position affects the characteristics of the ferromagnetic thin film to be formed, it is changed and adjusted within a range that satisfies the above-described predetermined relationship, so as to cope with the thinning of the base film. Attempts can be made to obtain films with excellent magnetic properties.

In the method for producing a magnetic recording medium of the present invention, polyethylene terephthalate is preferred as the base film. However, besides, polyesters such as polyethylene naphthalate; polyolefins such as polyethylene and polypropylene; cellulose derivatives such as cellulose triacetate and cellulose diacetate; polycarbonates; polyvinyl chloride; polyimides; The thickness of these supports can generally be up to about 50 μm, but in the present invention, the use of those having a thickness of 6 μm or less is particularly practical. In particular, polyethylene terephthalate, polyethylene naphthalate or the like having a thickness of about 2.5 to 6 μm can be used.

In the present invention, examples of the magnetic material used for forming the magnetic metal thin film layer include ferromagnetic metal materials used for manufacturing a usual metal thin film type magnetic recording medium. For example, ferromagnetic metals such as Co, Ni, Fe, or
Fe-Co, Fe-Ni, Co-Ni, Fe-Co-Ni, Fe-Cu, Co-C
u, Co-Au, Co-Y, Co-La, Co-Pr, Co-Gd, Co-S
m, Co-Pt, Ni-Cu, Mn-Bi, Mn-Sb, Mn-Al, Fe-C
r, ferromagnetic alloys such as Co-Cr, Ni-Cr, Fe-Co-Cr, and Ni-Co-Cr. In particular, a ferromagnetic alloy mainly composed of iron, cobalt, and nickel, and at least one selected from nitrides and carbides thereof are preferable. In addition, the durability can be improved by introducing an oxidizing gas when forming the magnetic layer by vapor deposition and forming an oxide on the surface of the magnetic layer. The magnetic layer may have a single-layer structure or a multilayer structure.
In order to cope with high frequency recording, it is preferable to use a multilayer, and as a practical range, two to three layers are appropriate. The thickness of the magnetic layer is about 1000 to 3000 mm, and in the case of two layers, the lower layer is 200
The upper layer is preferably about 100 to 1000 mm at about 2000 mm, and the lower layer is about 200 to 2000 mm and the middle layer is 200 to 1000 in the case of three layers.
The upper layer is preferably about 100 to 1000 mm.

Further, for the purpose of improving the characteristics such as corrosion resistance and durability of the magnetic recording medium, after forming a magnetic layer according to the present invention, a protective layer of a high hardness thin film can be provided thereon. Such a protective layer is made of a nonmagnetic material, for example, diamond-like carbon, or various carbides, nitrides, oxides such as boron carbide, silicon carbide, boron nitride, silicon nitride, silicon oxide, and aluminum oxide. Or by a PVD method. further,
For example, a lubricating layer made of a suitable lubricant can be formed to a thickness of about 5 to 50 ° by applying a fluorine-based lubricant in the air or spraying it on the magnetic layer in a vacuum. On the side opposite to the magnetic layer, a back coat layer may be provided on the base film, which may be formed by a conventional method, for example, by applying a back coat paint containing carbon black, or forming a metal in a vacuum. Alternatively, it can be formed by attaching a metalloid. The thickness is 0.1 ~
The thickness is about 1.0 μm, and about 0.05 to 1.0 μm in the case of vapor deposition.

[0011]

FIG. 1 shows an example of a vapor deposition apparatus 1 suitable for carrying out a method for manufacturing a magnetic recording medium according to the present invention. This is a vacuum source, for example, a vacuum chamber 2 connected to a vacuum pump, a cylindrical can provided in the vacuum chamber 2, ie, a cooling can roll 3, and a base such as a PET film on the cooling can roll 3. An unwind roll 5 and a take-up roll 6 for running the film 4 are included. A crucible 7 is disposed below the cooling can roll 3 as an evaporation source. The crucible 7 contains a ferromagnetic material, for example, cobalt.
An electron gun 8 is disposed in the vacuum chamber 2 and irradiates an electron beam toward the crucible 7 to evaporate cobalt in the crucible 7. The space between the crucible 7 and the cooling can roll 3 is evaporated by an electron beam and
A shielding plate 9 is provided to limit the incident range of the vapor of the ferromagnetic material from the air to the cooling can roll 3 in an oblique direction. A nozzle 10 for supplying oxygen gas is arranged between the cooling can roll 3 and the shielding plate 9.

According to the present invention, the crucible 7, which is a ferromagnetic material evaporation source, is disposed below the cooling can roll 3, and its horizontal position (x) is set at the center of the evaporation surface of the crucible 7. The position where the line coincides with the rotation axis of the cylindrical can (-
From 1), this normal line is variable to a position (1) (the crucible is indicated by 7 ') at which the normal line becomes the tangent line of the cylindrical can on the base film loading side. The mechanism that makes this variable is
Any known one can be used. The distance between the lowermost end of the cooling can roll 3 and the crucible 7 is generally equal to or less than the radius of the cooling can roll 3. In the illustrated example, this distance is equal to the radius of the cooling can roll 3.

In order to manufacture a magnetic recording medium according to the present invention using the vapor deposition apparatus 1, the inside of the chamber 2 is set to a predetermined vacuum atmosphere by a vacuum source, and then the base film 4 is unloaded from the unwind roll 5 to the cooling can roll 3 Run up. The cooling can roll 3 is generally cooled to about -30 ° C by a cooling chiller. The crucible 7 is, for example, x in FIG.
= 0, the power of the electron beam irradiated from the electron gun 8 to the cobalt in the crucible 7 is controlled according to this position and the temperature t (° C.) of the cooling can roll 3. According to the above equation, the power P is in the range of 150 ≧ P ≧ 50 (kW) when x = 0. In this manner, the oblique vapor deposition is performed on the base film 4 by performing the melt evaporation by the electron beam irradiation, for example, in the presence of oxygen supplied from the nozzle 10. The processed film thus obtained is taken up on a take-up roll 6. In the case of forming two or more layers, the processing film wound up in this way is rewound onto the unwinding roll 5, and the operation of vapor deposition using the apparatus of FIG. 1 is repeated again by the number of magnetic layers. . After the required number of magnetic layers are formed, a protective layer (for example, a high-hardness thin film such as diamond-like carbon or SiO ₂ ) is provided on the magnetic layer as necessary. Then, a lubricating layer is formed on the uppermost layer by applying, for example, a fluorine-based lubricant in the air as described above, or by spraying the magnetic layer in a vacuum. Prior to or after the formation of the magnetic layer, a back coat layer is formed on the base film 4 opposite to the magnetic layer. As described above, this may also be formed by applying a back coat paint containing, for example, carbon black, or by attaching a metal or metalloid in a vacuum.
After the formation of the necessary layers is completed, slitting, winding, assembling into a cassette, and the like are performed by a general method, and the product is commercialized as an 8-mm video tape, for example.

[0014]

【Example】

Examples 1 to 5 A ferromagnetic material composed of 100% cobalt was put in a crucible 7 using the apparatus shown in FIG. After the inside of the vacuum chamber was evacuated to 10 ^-6 Torr, the cobalt metal in the crucible 7 was irradiated with an electron beam by the electron gun 8 to form a vapor deposition atmosphere. Crucible 7
In the x direction, the temperature t of the cooling can roll 3
(° C.) and the power (kW) of the electron gun 8 are as shown in Table 1 below. As the base film 4, a PET film having a thickness (μm) shown in Table 1 was run at a speed of 40 (m / min), and a magnetic layer was formed by oblique evaporation. Next, on the opposite side of the magnetic layer, a backcoat layer containing carbon black and a binder resin was applied on the PET film to form a backcoat layer having a thickness of 0.5 μm. A protective layer made of diamond-like carbon was formed on the magnetic layer by microwave plasma CVD, and a lubricant made of perfluoropolyether was coated to form a lubricating layer. The obtained one was cut into a width of 8 mm and loaded into a cassette to produce an 8 mm video cassette.

Comparative Examples 1 and 2 The same conditions as described for the embodiment were used, except that the position of the crucible 7 in the x direction, the temperature t (° C.) of the cooling can roll 3, and the power (kW) of the electron gun 8 were used. The thickness (μm) of the PET film was changed to the numerical values shown in Table 1.

With respect to the magnetic tapes obtained in Examples and Comparative Examples, the envelope characteristics of output waveforms were measured by using a device modified from a commercially available 8 mm VTR device. In this case, it is ideal that an envelope characteristic as shown in FIG. 2A is obtained, but in reality, as shown in FIG. 2B, a waveform lacks due to a head touch failure or the like. Will happen. Here, the chipping rate was determined by subtracting the higher chipping rate of the front chipping or the rear chipping from 100% at the time of measurement. For example, if the higher chip rate is 5%, the envelope is 95%. The results are shown in Table 1.

The running performance of these tapes was evaluated by the coefficient of friction. The coefficient of friction is measured as follows. That is, at a temperature of 20 ° C. and a humidity of 50%, the diameter is 2 mm,
With the magnetic tape wrapped around a SUS pin with a surface roughness of 0.2S by 90 °, apply a tension of 0.1 from the unwinding side.
N, sends out the tape at a speed of 14.3 mm / s. The tension is also measured on the winding side, and the loss due to the friction pin is calculated from the difference from the tension (0.1 N) on the unwinding side according to Euler's equation to determine the friction coefficient of the magnetic tape.

[0018]

[Table 1]

[0019]

As is clear from the above embodiments, according to the manufacturing method of the present invention, even if the thickness of the base film is small, the power of the electron beam can be controlled to an optimum value. Thus, it is possible to obtain a magnetic recording medium free from defects due to heat loss of the base film.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing an example of an apparatus capable of implementing a manufacturing method of the present invention.

FIG. 2 is a schematic diagram for explaining a method of measuring an envelope in an example of the present invention and a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Deposition apparatus 2 Vacuum chamber 3 Cooling can roll 4 Base film 5 Unwind roll 6 Take-up roll 7, 7 'crucible 8 Electron gun 9 Shield plate 10 Nozzle

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Osamu Yoshida, Inventor 2606, Kabane-cho, Akaga-cho, Haga-gun, Tochigi Prefecture.

Claims (3)

[Claims] 1. A method of manufacturing a magnetic recording medium, comprising: depositing a ferromagnetic metal thin film layer on a base film conveyed through a cylindrical can in a vacuum atmosphere through electron beam scanning heating of a ferromagnetic material evaporation source. A method for manufacturing a magnetic recording medium, comprising: controlling a power of the electron beam according to a position of the ferromagnetic material evaporation source with respect to the cylindrical can and a temperature of the cylindrical can. 2. The method according to claim 1, wherein the thickness of the base film is 6 μm or less, and the power P (kW) of the electron beam is 3a ≧ P ≧
a (where a = 50−tx / 2, t is the temperature (° C.) of the cylindrical can, x is the position where the normal set to the center of the evaporation surface of the ferromagnetic material evaporation source coincides with the rotation axis of the cylindrical can The method for manufacturing a magnetic recording medium according to claim 1, wherein -1 is given by 1 and a position at which a tangent of the cylindrical can is tangential on the base film loading side is 1). 3. The position of the ferromagnetic material evaporation source is -1 ≦
3. The method of manufacturing a magnetic recording medium according to claim 2, wherein the variable is within a range of x ≦ 1.