JPH10105949A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium which permits to sufficiently correspond to wave-length shortening and is excellent in running and output characteristics, by adopting a surface roughness except relative large swelling of a medium as a specific range. SOLUTION: This medium is a magnetic recording medium having a holder and a magnetic layer formed on the holder and a surface roughness (Ra) of 4-6nm measured by a laser microscope type interferometer but the surface roughness (RaF) is made to be read as 1-1.5nm when measured by the laser microscope type interferometer through a high-pass filter. The surface roughness through the high-pass filter is relative small irregularity excluding large swelling of the medium, and since a track width is small in such a short-wave recording as a shortest recording wavelength is 0.4μm or less, the surface roughness through the high-pass filter within the above-mentioned irregularity has a little influence and improves an output characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a magnetic recording medium. More specifically, the present invention relates to a magnetic recording medium having excellent running properties and output characteristics.

[0002]

2. Description of the Related Art In recent years, magnetic recording is in the direction of high-density recording, and a magnetic recording medium having excellent high-frequency characteristics is demanded. Conventionally, a so-called coating type magnetic recording medium in which magnetic powder is dispersed in an appropriate binder and coated on a support is the mainstream, and various improvements have been made to meet the demand for high-density recording. Is approaching.

A so-called metal thin film type magnetic recording medium having a magnetic layer in which a magnetic metal is adhered to a support by vapor deposition or the like has been developed as a magnetic recording medium which can be expected to have a performance exceeding that of a coating type magnetic recording medium. Metal thin-film type magnetic recording media are considered to be promising for high-density recording because the magnetic layer does not contain a binder and can increase the density of a magnetic material. As the metal thin film type magnetic layer, Co, Co
-Ni, Co-Ni-P, Co-O, Co-Ni-O,
Co-Cr, Co-Ni-Cr and the like have been studied. A vacuum deposition method is most suitable as a manufacturing method when a metal thin film type magnetic recording medium is put into practical use.
Hi8 VTR tapes having a magnetic layer made of i-O and DVC (digital video cassette) tapes having a magnetic layer made of Co-O have already been put to practical use.

[0004]

In a magnetic recording medium of the metal thin film type, a magnetic layer is formed by depositing a metal material on a support by vapor deposition or the like. Exists. Such unevenness of the magnetic layer can be measured as surface roughness by, for example, a laser microscope-type interferometer, and is one of important characteristics that affect the traveling properties and output characteristics of the magnetic recording medium. In addition, a plastic film such as a PET film is usually used for the support, but depending on the characteristics of the film to be used or the stress of the formed metal thin film,
Distortion (undulation) occurs throughout the medium, but if the undulation is too noticeable, it affects the running properties and output characteristics of the medium.

As described above, the surface roughness and distortion of a metal thin film type magnetic recording medium are factors that greatly contribute to the running properties and output characteristics, and it is important to properly maintain both of them in order to perform good magnetic recording. However, studies from such a viewpoint have not been sufficiently advanced. In particular, it is thought that the recording wavelength will be shortened in order to achieve higher density recording in the future, but no magnetic recording medium having a surface roughness or undulation sufficient to cope with this is known.

[0006]

In view of the above situation, the present inventors can sufficiently cope with the shortening of the wavelength by setting the surface roughness excluding a relatively large waviness of the medium to a specific range. The present inventors have found that a magnetic recording medium having excellent running properties and output characteristics can be obtained, and have completed the present invention.

That is, the present invention relates to a magnetic recording medium having a support and a magnetic layer formed on the support, and having a surface roughness (Ra) of 4 to 6 nm measured by a laser microscope type interferometer. The surface roughness (Ra _F ) measured by applying a high-pass filter with the laser microscope interferometer is 1 to 1.
A magnetic recording medium having a thickness of 5 nm is provided.

The surface roughness (Ra) of the magnetic recording medium is measured by a laser microscope type interferometer (for example, model 570 manufactured by Zygo).
0), and Ra is 4-6n.
m. In the present invention, the surface roughness (Ra _F ) is further measured by applying a high-pass filter (Hi-Pass filter) with a laser microscope-type interferometer, and the value is determined to be 0.5 to 0.5 μm.
It needs to be in the range of 1.5 nm. The surface roughness with the high-pass filter measures relatively small irregularities excluding a large waviness of the medium. In short wavelength recording where the shortest recording wavelength is 0.4 μm or less, since the track width is small, if the surface roughness with the high-pass filter is in the above range, the influence of the unevenness is extremely reduced, and the output characteristics are improved. . When a model 5700 manufactured by Zygo is used as a laser microscope type interferometer, a micro Fizeau objective lens or a Mirau objective lens having an appropriate magnification is used as an objective lens. In this apparatus, the surface roughness (Ra) of the medium can be measured by turning off the filter mode, and a high-pass filter (Hi-Pass filter)
By setting the mode to / FFT (fast Fourier transform) mode, the surface roughness (Ra _F ) with a filter can be measured.

On the other hand, it is desirable for the running property of the medium to have a certain degree of undulation. In the present invention, sufficient running property can be secured if the surface roughness (Ra) measured without a filter is 4 to 6 nm. As a method of forming undulations on the support, for example, a method of applying a larger tension than usual to the support during film formation by vapor deposition and heating the support is used.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The magnetic recording medium of the present invention has a surface roughness Ra of 4 to 6 measured by a laser microscope type interferometer.
nm, surface roughness measured with a high-pass filter Ra _F
Is in the range of 0.5 to 1.5 nm, the magnetic layer and other structures are not particularly limited. Specific examples are shown below.

In the magnetic recording medium of the present invention, the magnetic layer is preferably of a metal thin film type. The metal thin film is formed by a usual method such as evaporation or sputtering. Examples of the magnetic material for forming the metal thin film type magnetic layer include ferromagnetic metal materials used in the manufacture of ordinary metal thin film type magnetic recording media. For example, ferromagnetic metals such as Co, Ni, and Fe; Fe-Co, Fe-Ni, Co-Ni, Fe-Co
-Ni, Fe-Cu, Co-Cu, Co-Au, Co-
Y, Co-La, Co-Pr, Co-Gd, Co-S
m, Co-Pt, Ni-Cu, Mn-Bi, Mn-S
b, Mn-Al, Fe-Cr, Co-Cr, Ni-C
and ferromagnetic alloys such as r-Fe-Co-Cr and Ni-Co-Cr. Further, nitrides, carbides, and oxides of these metals or metal alloys are also preferable.

For high-density recording, the magnetic layer of the magnetic recording medium is preferably formed on a substrate by oblique evaporation. The method for oblique deposition is not particularly limited, and follows a conventionally known method. The degree of vacuum at the time of vapor deposition is 10 ^-4 to 10 ^-7 Torr
It is about. The magnetic layer formed by vapor deposition may have either a single layer structure or a multilayer structure. In particular, by introducing an oxidizing gas to form an oxide on the surface of the magnetic layer, the durability can be improved.

The thickness of the magnetic layer depends on the total thickness of the medium.
000-3000 °, more preferably 150
0-2000 °.

Furthermore, a back coat layer can be further formed on the concave curved surface of the support. The back coat layer is coated with a coating material in which carbon black or the like and a binder are dispersed.
It may be formed by coating so as to have a thickness of about 1.0 μm (after drying). At that time, in addition to carbon black, Si
Ceramic fine particles such as O ₂ , Al ₂ O ₃ , and CaCO ₃ may be added. Alternatively, a metal or semimetal may be attached to a support by vapor deposition or the like. Various metals can be used as the back coat layer.
Cu, Zn, Sn, Ni, Ag and the like and alloys thereof are used, and a Cu-Al alloy is preferable. Further, ceramics such as an oxide film and a carbonized film which have been subjected to an oxidation reaction, a carbonization reaction, and the like at the time of vapor deposition are also suitable. Further, as the semimetal forming the back coat layer, Si, Ge, A
s, Sc, Sb, etc. are used, and Si is preferred. The thickness of the metal thin film type back coat layer is 0.05 to 1.0.
It is about μm. When the metal thin film type back coat layer is formed, it is necessary to take into consideration the rigidity with the metal forming the magnetic layer so as not to cause cupping of the support.

In the magnetic recording medium of the present invention,
An appropriate protective layer may be formed on the magnetic layer. The protective layer is preferably made of diamond-like carbon, graphite, diamond, silicon oxide, aluminum oxide, silicon carbide, carbon nitride, or the like. In particular, when forming a metal thin film type magnetic layer, it is preferable to form a protective layer made of a diamond-like carbon thin film. The diamond-like carbon thin film can be formed by a general-purpose method such as an RF plasma CVD method or an ECR plasma CVD method. The thickness of the protective layer made of a diamond-like carbon thin film is preferably 50 to 200 °.

Further, in the magnetic recording medium of the present invention,
A lubricant layer made of a suitable lubricant may be formed on the magnetic layer or the protective layer. The lubricant layer may be formed by applying a solution obtained by dissolving a lubricant in an appropriate solvent, or may be formed by spraying the lubricant in a vacuum. When the lubricant is formed by spraying, it is preferable to spray the lubricant onto the magnetic layer formed on the support with a sprayer equipped with an ultrasonic oscillator (hereinafter, referred to as an ultrasonic sprayer). As the lubricant, a fluorine-based lubricant such as perfluoropolyether is preferable in any case of coating or spraying. Specifically, the perfluoropolyether has a molecular weight of 2,000 to 500.
0 is preferable, for example, “FOMBLIN Z
DIAC] [Carboxyl group modification, Montecatini
Co., Ltd.), "FOMBLIN Z DOL" [alcohol-modified, Montecatini Co., Ltd.] "Demnum SA"
A product commercially available under the trade name of (Daikin Industries) can be used. The spray amount of the lubricant may be appropriately determined in consideration of the use of the magnetic recording medium, the type of the lubricant, and the like. The thickness of the formed lubricant layer is about 5 to 100 °.

In the present invention, the material of the support is
Polyesters such as polyethylene terephthalate and polyethylene naphthalate; polyolefins such as polyethylene and polypropylene; cellulose derivatives such as cellulose triacetate and cellulose diacetate; polycarbonates; polyvinyl chloride; polyimides; The thickness of the support depends on the total thickness of the medium, but is preferably 2 to 5.5 μm.

An example of a method for manufacturing the magnetic recording medium of the present invention will be described with reference to FIG. FIG. 1 is a schematic view of a main part of a vapor deposition apparatus for manufacturing a metal thin film type magnetic recording medium. FIG.
Among them, 1 is a film, 2 is an unwind roll, 3 is a can roll, 4 is a take-up roll, 5 is a bombarding means, 6,
6 'is an expander roll, 7 is an oxygen gas introduction pipe, 8
Is a shielding plate for regulating the area of metal vapor, 9 is an electron gun, 10
Denotes a crucible, which contains a magnetic metal such as Co or Fe. These are arranged in a vacuum vessel not shown,
The inside of the vacuum vessel is maintained at a degree of vacuum of about 1 × 10 ^{−4 to} 5 × 10 ⁻⁷ Torr. Film 1 is unwinding roll 2
Is transported to a take-up roll 4 via a can roll 3. An electron beam was irradiated from an electron gun 9 onto a magnetic metal housed in a crucible 10 to vaporize the magnetic metal and form a magnetic layer on the film 1 conveyed on the can roll 3. Further, oxygen gas can be introduced from the oxygen gas introduction pipe 7 into the deposition region to control the specific magnetic properties and oxidize the surface of the magnetic metal.

In the present invention, in order to adjust the undulation of the magnetic recording medium, a film is applied with a tension larger than usual, for example, about twice, and the can roll is heated to about 100 ° C. to perform vapor deposition. This causes large undulations in the film. By changing this condition, the degree of undulation can be adjusted. Alternatively, a base film having undulation from the beginning may be used.

[0020]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Example 1 (1) Production of Magnetic Tape A PET film having a thickness of 6 μm was set in the apparatus shown in FIG.
While introducing oxygen gas (350 SCCM), Co was deposited to form a magnetic layer having a thickness of 1600 °. The deposition conditions at this time were a film running speed of 20 m / min, an electron gun power of 40 kW, a can roll temperature of 100 ° C., and a film tension of 8 kgf / 300 mm. Next, a protective layer made of a diamond-like carbon thin film having a thickness of 100 ° was formed on the magnetic layer by ECR plasma CVD. Further, a lubricant layer was formed by attaching a perfluoropolyether having a -OH group which is a polar group (manufactured by Daikin Industries, Ltd .: Demnum SA) on the protective layer so as to have a thickness of 20 °. A back coat layer was formed on the surface of the film opposite to the surface on which the magnetic layer was formed. The back coat layer was formed by applying a binder containing carbon having a diameter of 20 to 30 nm to a film so that the thickness after drying was 0.5 μm, and drying the film. The film obtained above, on which the magnetic layer, the diamond-like carbon protective layer, the fluorine-based lubricating layer and the back coat layer were formed, was cut into a width of 6.35 mm and loaded into a cassette case to obtain a video tape.

(2) Performance Evaluation The frequency characteristics and the friction coefficient of the output of the video tape obtained above were measured by the head tester method.
The output was a relative evaluation using Comparative Example 2 described later as a reference (0 dB). In addition, the surface roughness of the medium was measured using a filter (H) using a laser microscope interferometer (manufactured by Zygo, model 5700, objective lens: Micro Fizeau 40 ×).
i-Pass filter, filter type: FFT)
Both the surface roughness (Ra _F ) with and without the filter (Ra) were measured. Each surface roughness is an average value measured at 10 locations. Table 1 shows the results.

Example 2 In Example 1, the film tension was changed to 10 kgf /
6.35 in the same manner as in Example 1 except that the distance was 300 mm.
mm tape was prepared and evaluated in the same manner as in Example 1. Table 1 shows the results.

Example 3 In Example 1, the film traveling speed was 35 m / min, the electron gun power was 40 kW, and the amount of introduced oxygen gas was 530 SCC.
After forming a Co magnetic layer (lower layer) having a thickness of 900 mm, the film was rewound around the winding side, and a Co magnetic layer having a thickness of 900 mm was formed on the magnetic layer (lower layer) under the same conditions. Otherwise, the same evaluation as in Example 1 was performed in the same manner as in Example 1. Table 1 shows the results.

Example 4 In Example 1, the thickness of the PET film was set to 4.5 μm.
A 6.35 mm tape was produced in the same manner as in Example 1 except that the film tension was changed to 5 kgf / 300 mm, and the same evaluation as in Example 1 was performed. Table 1 shows the results.

Comparative Example 1 A 6.35 mm tape was produced in the same manner as in Example 1 except that the can roll temperature was changed to -20 ° C., and the same evaluation as in Example 1 was performed. Table 1 shows the results.
Shown in

Comparative Example 2 A 6.35 mm tape was produced in the same manner as in Example 1 except that the can roll temperature was set to 0 ° C. and the film tension was changed to 2 kgf / 300 mm. An evaluation was performed. Table 1 shows the results.

[0028]

[Table 1]

[0029]

According to the present invention, a magnetic recording medium exhibiting good output characteristics and running properties can be obtained, and its effect is not impaired even in high-frequency recording where the shortest recording wavelength is 0.4 μm or less.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a vapor deposition apparatus for manufacturing a magnetic recording medium of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Film 3 Can roll 9 Electron beam gun 10 Crucible

Claims (5)

[Claims] 1. A magnetic recording medium comprising a support and a magnetic layer formed on the support, wherein the surface roughness (Ra) of the magnetic recording medium measured by a laser microscope interferometer is 4 to 6 nm. A magnetic recording medium characterized by having a surface roughness (Ra _F ) of 1 to 1.5 nm measured by a high-pass filter using a laser microscope interferometer. 2. The magnetic recording medium according to claim 1, wherein the total thickness is 6 μm or less. 3. The magnetic recording medium according to claim 1, which is used for a magnetic recording system having a minimum recording wavelength of 0.4 μm or less. 4. The magnetic recording medium according to claim 1, wherein said magnetic layer is a metal thin film type magnetic layer. 5. The magnetic recording medium according to claim 1, further comprising a protective layer and / or a lubricant layer on the magnetic layer.