JPH08315348A - Magnetic recording medium - Google Patents

Abstract

PURPOSE: To obtain a magnetic recording medium having low demagnetizability and satisfactory reproduction output. CONSTITUTION: This magnetic recording medium has two magnetic layers formed by diagonal vapor deposition. The upper layer is thinner than the lower layer and the angle of the columns of the upper layer is smaller than that of the lower layer. The angle of the columns of the upper layer is preferably <=30 deg. and that of the lower layer is 30-70 deg.. The thickness of the upper layer is 1/5-1/10 of that of the lower layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vapor-deposited magnetic recording medium, and more particularly to a high output magnetic recording medium in which demagnetization hardly occurs.

[0002]

2. Description of the Related Art Evaporation type magnetic recording media are thin films and have a large saturation magnetization as compared with coating type magnetic recording media due to their high filling rate of magnetic material, and are suitable for high density recording in various application fields. It's being used. In manufacturing such a vapor deposition type magnetic recording medium, for example, a video tape or an 8 mm video tape, it is common to use a so-called oblique vapor deposition technique in order to increase the coercive force Hc. Various improvements have been made such that the magnetic layer has a multilayer structure in order to obtain magnetic characteristics.

For example, Japanese Patent Application Laid-Open No. 6-111267 of the present applicant discloses a magnetic recording medium having a plurality of magnetic layers formed by oblique vapor deposition, and the growth direction of the column structure of each magnetic layer is toward the upper layer. It is disclosed that it becomes more vertical. The magnetic layer of such a magnetic recording medium as a whole has a column structure conforming to the shape of the lines of magnetic force from the magnetic head, which maintains a high coercive force by oblique vapor deposition and also meets the demand for high density recording. be able to. However, when the column in the upper layer is close to vertical, the overwrite characteristic is good, but the demagnetizing field increases as the recording frequency becomes higher, and the reproduction output decreases, so that high output characteristics are required. Has a problem that the coercive force must be increased.

[0004]

The characteristics required for magnetic recording media include various characteristics from a magnetic, electrical or mechanical viewpoint, but these are not necessarily all magnetic recording media. Is not common to. For example, if it is a video tape that is repeatedly used for recording / playback in a normal home VCR, it is considered necessary to have good degaussing characteristics and be able to overwrite without significantly increasing the input signal to the magnetic head. However, even if the video tape is also used for a home VCR, such a characteristic is not necessary for a so-called soft tape for reproduction in which a movie or the like is recorded and sold in advance. On the contrary, for such soft tapes, it is preferable that the demagnetizing field is small and the reproduction output is high, even if the overwrite characteristics are poor. It is prudent to separate the areas in consideration of the characteristics required for the recording medium.

From this point of view, the magnetic recording medium as disclosed in, for example, Japanese Patent Laid-Open No. 6-111267 mentioned above is used as a so-called blank tape for recording / reproducing by utilizing its characteristics, while the magnetic recording medium for reproducing only is used. Regarding recording media, it is considered rational to seek high reproduction output for soft tapes without considering overwrite characteristics.
From this standpoint, the present inventors have aimed to obtain a magnetic recording medium suitable for so-called soft tape.

[0006]

According to the present invention, a magnetic recording medium has two magnetic layers consisting of a lower layer and an upper layer continuously formed on a base film by oblique vapor deposition, wherein the upper layer is It is thinner than the lower layer, and the column angle of the upper layer is smaller than that of the lower layer. Here, the column angle is a columnar structure forming the magnetic layer, that is, the growth direction of the column structure is
It is an angle formed with respect to the plane of the base film or the plane of the magnetic recording medium. The column angle is indicated by θ in FIG. 3 for both the case where the column structure is curved and the case where it is linear.
The column angle of the upper layer is preferably much smaller than the column angle of the lower layer. Specifically, the column angle of the upper layer is 30 ° or less,
For example, from 10 ° to 25 °, and the column angle of the lower layer is from 30 °
It is preferably in the range of 70 °. Also, the upper layer is much thinner than the lower layer, and preferably the thickness of the upper layer is 1 / the thickness of the lower layer.
It is in the range of 5 to 1/10. More specifically, the upper layer has a thickness of about 100Å to 1500Å, and the lower layer has a thickness of about 500Å to 10000Å. With such a structure, it is possible to reduce the demagnetizing field and prevent the reproduction output from decreasing.

In such a magnetic recording medium, a lower magnetic layer is obliquely vapor-deposited at a first incident angle on a base film running in a vacuum atmosphere, and then a second incident angle larger than the first incident angle. It can be manufactured by obliquely depositing the upper magnetic layer at a corner.

Although polyethylene terephthalate is preferable as the base film, various polyester and polyolefin materials can be used in addition to the above, and the thickness thereof is about 3 to 50 μm. Examples of the magnetic material forming the magnetic layer include ferromagnetic metal materials used in the production of ordinary metal thin film type magnetic recording media. For example, in addition to metals such as Fe, Co, and Ni, Co--Ni alloys, Co-Pt alloy, Co-Ni-Pt alloy, Fe-Co alloy, Fe-Ni alloy, Fe-Co-Ni alloy, Fe-Co
-B alloy, Fe-Co-Ni-B alloy, Co-Cr alloy, or Al, Ta, Pt, Au, Ti, V, Cr, Mn, Cu, Mg, Z
n, Ni, W, La, Ce, Pr, Nd, Pm, Sm, Eu, Li, Si,
Magnetic alloys containing one or more elements selected from the group consisting of B, Ca, As, Y, Zr, Nb, Mo, Ru, Rh, Ag, Sb, and Hf can be given. In addition to metals, O, N, C,
Fe-N type, Fe-O type, Fe-NC- containing B, Si, etc.
O-based, Fe-Ni-N-based, Co-Ni-N-based compounds and the like may be used. In addition, an oxidizing gas can be introduced during vapor deposition to improve coercive force and durability. The degree of vacuum during vapor deposition
It is about 10 ⁻⁴ to 10 ⁻⁷ Torr. The coercive force Hc is usually 900
Set to about 2000 Oe. Further, a back coat layer, a lubricating layer, a protective layer and the like can be provided according to a conventional method.

[0009]

FIG. 1 shows an example of an apparatus used for manufacturing the magnetic recording medium of the present invention. The base film 1 made of PET is conveyed from an unwinding roll 2 to a winding roll 3 via an intermediate roll 4-6 in a vacuum chamber (not shown), and vapor deposition between the intermediate rolls 4 and 5 and 5 and 6 is performed. A magnetic layer is deposited in regions 7 and 8. In the vapor deposition region 7, the lower magnetic layer is formed of a ferromagnetic metal evaporated from the crucible 9 by the electron beam ε, and its incident angle is α. In the vapor deposition region 8, the upper magnetic layer is also formed of a ferromagnetic metal vaporized from the crucible 10 by the electron beam ε, and its incident angle is β. In this case, for example, as shown by the arrow 11, the incident angle β in the vapor deposition region 8
Can be adjusted by changing the positions of the intermediate roll 6 and the shield plate and oxygen supply nozzle associated therewith. With the same structure, the incident angle α in the vapor deposition region 7 can be made variable. According to the invention, α <β, which means that the lower and upper layers have a column structure grown obliquely at corresponding angles.

Example 1 Using the apparatus of FIG. 1, crucibles 9 and 10 were filled with cobalt. After the vacuum chamber was evacuated to 10 ^-6 Torr, the electron gun was used to irradiate the electron beams to the cobalt in the crucibles 9 and 10 at 5 kW in the vapor deposition region 7 and 20 kW in the vapor deposition region 8 to melt and vaporize, and to form a vapor deposition atmosphere did. Transfer the PET film 1 with a thickness of 6.5 μm from the unwinding roll 2 to the winding roll 3.
Oxygen gas was introduced at 40 SCCM and 120 SCCM from a nozzle in each of the vapor deposition regions 7 and 8 by running at a speed of m / min, and a 1500 Å lower layer and a 200 Å upper layer were formed by oblique vapor deposition. The lower column angle is 60 ° and the upper column angle is 25 °
It was °. Coercive force Hc is 1480 Oe, saturation magnetic flux density Bs
Was 6200 G and the squareness ratio Br / Bs was 0.81.

Then, in a chamber separate from that obtained, E
Microwave power 600W by CR plasma CVD method
Then, a diamond-like carbon (DLC) layer was formed at 70 Å. Fluorine-based lubricant (trade name FOMBLI on this protective layer
NAM2001) with a thickness of 20Å and a back coat layer of aluminum 0.2 μm on the back side of the PET film.
It is attached by the vacuum evaporation method with the thickness of, and cut into 8 mm width,
The cassette was loaded to make an 8 mm video cassette.
FIG. 2 shows a conceptual diagram of the column structure of this 8 mm video tape.

The 8 mm video cassette obtained in Example 1 was connected to a commercially available signal oscillator to obtain a high band 8 mm VT.
It was put in the R deck and the signal from the signal oscillator was input. Output from the thus obtained 8 mm video cassette, Y-
S / N and C-S / N (AM, PM) were measured using a video noise meter. The results are shown in Table 1. In Table 1, the output is a relative value based on Comparative Example 3.

Example 2 A magnetic layer having a lower column angle of 30 ° and an upper column angle of 10 ° was formed in the same manner except that the incident angles α and β were adjusted in the apparatus shown in FIG. Lower layer is 1500Å, upper layer is 150
Was Å. Coercive force Hc is 1540 Oe, saturation magnetic flux density Bs
Was 6000 G and the squareness ratio Br / Bs was 0.84. After that, an 8 mm video cassette was manufactured under the same conditions as in Example 1.

A signal is input to the obtained 8 mm video cassette in the same manner as in Example 1, and output, Y-S / N, C-
The S / N (AM, PM) was measured. The results are shown in Table 1.

Example 3 In the apparatus of FIG. 1, incident angles α and β were adjusted, and otherwise the same procedure was performed to form a magnetic layer having a lower column angle of 70 ° and an upper column angle of 30 °. Lower layer is 1500Å, upper layer is 300
Was Å. Coercive force Hc is 1390 Oe, saturation magnetic flux density Bs
Was 6400 G and the squareness ratio Br / Bs was 0.73. After that, an 8 mm video cassette was manufactured under the same conditions as in Example 1.

A signal was input to the obtained 8 mm video cassette in the same manner as in Example 1, and output, Y-S / N, C-
The S / N (AM, PM) was measured. The results are shown in Table 1.

Comparative Example 1 In the apparatus shown in FIG. 1, incident angles α and β were adjusted, and otherwise the lower layer and the upper layer were formed as magnetic layers having the same column angle of 45 °. The lower layer was 900Å and the upper layer was 900Å. Coercive force Hc is 1500 Oe, saturation magnetic flux density Bs is 590
The squareness ratio, Br / Bs, was 0G and 0.82. Then, Example 1
An 8 mm video cassette was produced under the same conditions as above.

A signal was input to the obtained 8 mm video cassette in the same manner as in Example 1 and output, Y-S / N, C-
The S / N (AM, PM) was measured. The results are shown in Table 1.

Comparative Example 2 A magnetic layer having a lower column angle of 60 ° and an upper column angle of 30 ° was formed in the same manner as above except that the incident angles α and β were adjusted. However, in this case, the lower layer is 500
Å, the upper layer was 1000Å. The coercive force Hc was 1550 Oe, the saturation magnetic flux density Bs was 6000 G, and the squareness ratio Br / Bs was 0.86.
After that, an 8 mm video cassette was manufactured under the same conditions as in Example 1.

A signal was input to the obtained 8 mm video cassette in the same manner as in Example 1 and output, Y-S / N, C-
The S / N (AM, PM) was measured. The results are shown in Table 1.

Comparative Example 3 A magnetic layer having a lower column angle of 30 ° and an upper column angle of 60 ° was formed in the same manner except that the incident angles α and β were adjusted in the apparatus shown in FIG. Lower layer is 1500Å, upper layer is 300
Was Å. Coercive force Hc is 1570 Oe, saturation magnetic flux density Bs
Was 6100 G and the squareness ratio Br / Bs was 0.85. After that, an 8 mm video cassette was manufactured under the same conditions as in Example 1.

A signal was input to the obtained 8 mm video cassette in the same manner as in Example 1 and output, Y-S / N, C-
The S / N (AM, PM) was measured. The results are shown in Table 1.

[0023]

[Table 1]

[0024]

As can be understood from the results of Examples and Comparative Examples, the magnetic recording medium according to the present invention has a high reproduction output, and is therefore effective as, for example, a Head to Head type dubbing tape.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of an apparatus that can be used for manufacturing a magnetic recording medium of the present invention.

2 is a schematic cross-sectional view for explaining the column structure of the magnetic recording medium of the present invention obtained in Example 1. FIG.

FIG. 3 is a schematic diagram for explaining a column angle both when the column structure is curved and when it is linear.

[Explanation of symbols]

 1 Base Film 2 Unwinding Roll 3 Winding Roll 4, 5, 6 Intermediate Roll 7, 8 Deposition Area 9, 10 Crucible

Front page continuation (72) Inventor Katsumi Sasaki 2606 Akabane Akabane, Kaiga-cho, Haga-gun, Tochigi Prefecture, Kao Institute of Stock Companies (72) Inventor Yuzo Matsuo 2606 Akabane Kai-cho, Haga-gun, Tochigi, Institute of Kao Corporation (72) Inventions Person Akira Shiga 2606, Akabane, Kai-cho, Haga-gun, Tochigi Prefecture, Kao Institute of Stock Companies (72) Inventor, Junko Ishikawa 2606, Akabane, Kai-cho, Haga-gun, Tochigi Institute, Kao Corporation

Claims (4)

[Claims] 1. A magnetic recording medium having a two-layer magnetic layer consisting of a lower layer and an upper layer continuously formed by oblique vapor deposition on a base film, wherein the upper layer is thinner than the lower layer and the column angle of the upper layer is the column of the lower layer. A magnetic recording medium characterized by being smaller than a corner. 2. The magnetic recording medium according to claim 1, wherein the column angle of the upper layer is 30 ° or less and the column angle of the lower layer is in the range of 30 ° to 70 °. 3. The thickness of the upper layer is 1/5 to 1 of the thickness of the lower layer.
The magnetic recording medium according to claim 1, which is in a range of / 10. 4. A lower magnetic layer obliquely deposited at a first incident angle on a base film running in a vacuum atmosphere, and then obliquely evaporated at a second incident angle larger than the first incident angle. And a magnetic recording medium having an upper magnetic layer thinner than the lower magnetic layer.