JPH0887740A - Magnetic recording medium - Google Patents

Abstract

PURPOSE: To obtain a magnetic recording medium capable of ensuring satisfac tory overwriting characteristics and electromagnetic transducing. characteristics and fit for high density digital signal recording. CONSTITUTION: A magnetic layer is formed on one side of a filmlike nonmagnetic substrate. The thickness of the magnetic layer is regulated to 0.1-0.3μm and Fe-based magnetic powder having 160-200emu/g of saturation magnetization σs and 0.05-0.2μm major axis size is used as magnetic powder contained in the magnetic layer. The saturation magnetic flux density Bm of the magnetic layer in the longitudinal direction is regulated to 3,500-5,000G and the coercive force Hc of the magnetic layer in the longitudinal direction is regulated to 1,800-2,100Oe.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, particularly to a magnetic recording medium suitable for high density digital signal recording.
It is an object of the present invention to provide a magnetic recording medium that can obtain good reproduction output over the entire band even when the magnetic layer is thinned to obtain good overwrite characteristics.

[0002]

2. Description of the Related Art In recent years, in magnetic recording, the form of recorded signals is shifting from analog to digital. In magnetic recording of digital signals, the mainstream method is to overwrite the recorded signal without overwriting it once when recording the signal on the recorded medium again (overwriting). Is.

[0003]

As a means for improving the overwrite characteristic, it is effective to reduce the thickness of the magnetic layer of the recording medium. However, when the magnetic layer is made thin, there is a problem in that the reproduction output is reduced, especially in the low range. In order to improve the reproducing characteristics, the coercive force Hc of the magnetic layer
It is effective to raise the value, but the increase in the coercive force Hc causes deterioration of the overwrite characteristic.

The magnetic layer has a small thickness (0.1 to 0.3 μm).
(About a certain thickness), in order to improve various recording characteristics,
It has been proposed to provide a non-magnetic layer between the magnetic layer and the support. However, providing a large number of layers having different compositions on the support causes non-uniform distribution of liquid additives such as lubricants, resulting in a great reliability problem.

As described above, in the conventional magnetic recording medium, it was not possible to achieve both sufficient reproduction output and good overwrite characteristics. The present invention, even when the thickness of the magnetic layer is thin to obtain good overwrite characteristics,
It is an object of the present invention to provide a magnetic recording medium capable of obtaining a good reproduction output over the entire band (having a high electromagnetic conversion characteristic).

[0006]

In order to solve the above problems, the present invention provides a magnetic recording medium having a magnetic layer on one surface of a film-like non-magnetic support, and the magnetic property contained in the magnetic layer. The powder is a metal-based powder having Fe as a main component, a saturation magnetization σs of 160 emu / g or more and 200 emu / g or less, and a major axis length of 0.05 μm or more and 0.2 μm or less, and the magnetic layer has a thickness of Is 0.1 μm or more and 0.3 μ
The magnetic flux has a saturation magnetic flux density Bm of 3500 G or more and 5000 G or less in the main magnetic recording medium running direction at the time of recording, and a coercive force Hc of 1800 Oe or more and 2100 Oe or less in the main magnetic recording medium running direction during recording. A recording medium is provided.

[0007]

EXAMPLES The present inventors have made intensive studies on magnetic tapes for recording digital signals in order to solve the above problems. As a result, the thickness of the magnetic layer on the film-shaped non-magnetic support was 0.1 μm or more and 0.3 μm or less, the magnetic powder contained in the magnetic layer was Fe as a main component, and the saturation magnetization σs was 1
60emu / g or more and 200emu / g or less, major axis length is 0.05μ
m to 0.2 μm, the saturation magnetic flux density Bm in the longitudinal direction of the magnetic layer (the running direction of the magnetic tape during recording) is 3500 G to 5000 G, and the coercive force Hc in the longitudinal direction of the magnetic layer is 1800 Oe. 2100 Oe
It has been found that the following is suitable for solving the problem.

In order to realize high electromagnetic conversion characteristics, it is effective to use fine magnetic powder having excellent magnetic characteristics. Therefore, here, the saturation magnetization σs is 160 emu / g or more and 200 emu / g or more.
Hereinafter, a metal-based magnetic powder having a major axis length of 0.05 μm or more and 0.2 μm or less was used. When σs was less than 160 emu / g, a sufficient saturation magnetic flux density Bm could not be obtained when the magnetic tape was used (the thickness of the magnetic layer was 0.1 μm to 0.3 μm).
If it is as thin as m, the output particularly in the low frequency range is reduced). σs is 2
If it exceeds 00emu / g, the corrosion resistance of the magnetic powder deteriorates significantly,
The handling at the time of making a magnetic tape was extremely bad, and the magnetic tape could not be completed.

If the major axis length of the magnetic powder is less than 0.05 μm,
The dispersibility of the magnetic powder when producing the magnetic tape was poor, and the orientation when the magnetic field was applied was poor. When the major axis length exceeds 0.2 μm, the reproduction output in C / N and the high frequency range is lowered.

Even if the magnetic powder having the saturation magnetization amount σs and the major axis length within the above-mentioned preferable ranges is used, good reproduction output is obtained when the saturation magnetic flux density Bm in the longitudinal direction of the magnetic layer after mediumization is less than 3500G. Couldn't get Also, Bm is 50
If it exceeds 00 G, so-called powder drop such as lack of magnetic powder occurs, and the magnetic layer cannot be provided on the support.

Coercive force Hc in the longitudinal direction of the magnetic layer after mediumization
With respect to the above, when it was less than 1800 Oe, the reproduction output in the high frequency range deteriorated, and when it exceeded 2100 Oe, the reproduction output in the low frequency range and the overwrite characteristic deteriorated.

With respect to the thickness of the magnetic layer, if the thickness is less than 0.1 μm, the reproduction output is lowered over the entire area, and if it exceeds 0.3 μm, the waveform distortion at the time of recording / reproducing a pulse signal is increased and the overwrite characteristic is deteriorated.

From the above, the thickness of the magnetic layer is 0.1 μm.
m or more and 0.3 μm or less, the magnetic powder contained in the magnetic layer is Fe as a main component, and the saturation magnetization σs is 160 emu / g
Or more and 200 emu / g or less, the major axis length is 0.05 μm or more and 0.
2 μm or less, the saturation magnetic flux density Bm in the longitudinal direction of the magnetic layer is 3500 G or more and 5000 G or less, and the coercive force Hc in the longitudinal direction of the magnetic layer is 1800 Oe or more and 2100 Oe.
By the following, it was concluded that good overwrite characteristics and good reproduction output can both be achieved.

Further, the inventor has found that the surface roughness S of the magnetic layer is
It has been found that Ra is more preferably 2 nm or more and 5 nm or less. If the surface roughness SRa is less than 2 nm, the running property, still resistance, etc. are extremely deteriorated. When the surface roughness SRa exceeds 5 nm, the space loss between the magnetic head and the medium at the time of signal recording / reproduction increases, and the reproduction output particularly in the high frequency range is lowered.

Next, concrete examples will be described in comparison with comparative examples. [Production Method of Magnetic Tape Sample] First, a mixture of the following components is mixed and dispersed by a sand mill to prepare a magnetic coating material. Magnetic powder 100 parts by weight Vinyl chloride copolymer 10 parts by weight Urethane resin 10 parts by weight α-alumina 3 parts by weight Isocyanate 4 parts by weight Palmitic acid 2 parts by weight Methyl ethyl ketone 100 parts by weight Cyclohexanone 100 parts by weight

As the magnetic powder, 12 of a to l shown in Table 1 are used.
Different types of magnetic powder were prepared. (Note that ↓ in the table indicates a value less than the preferred range and ↑ indicates a value greater than the preferred range. The same applies to the following tables.)

[0017]

[Table 1]

A magnetic paint was prepared for each magnetic powder (total 1
2 types), magnetic tape. In the process of forming a magnetic tape, the thickness of the magnetic layer and the surface roughness of the magnetic layer were controlled by adjusting the coating conditions and the calendering conditions of the magnetic coating material on the film-like non-magnetic support. Magnetic tapes of Examples 1 to 10 and Comparative Examples 1 to 9 were prepared. Table 2 also shows the saturation magnetic flux density Bm and the coercive force Hc in the longitudinal direction of the magnetic layer. As the film-shaped non-magnetic support, PET (polyethylene terephthalate) having a thickness of 6 μm was used, and the back surface of the support had a thickness of 0.5 μm.
Back coat layer (mainly composed of carbon black)
Was set up. The width of the magnetic tape stock thus obtained is 3.81 m.
A magnetic tape (DAT tape) for recording digital audio signals was cut into m. The magnetic tape was manufactured by the same method as the conventional method.

[0019]

[Table 2]

[Evaluation of each sample tape] The DAT deck (XD)
-Z505: manufactured by Victor Company of Japan),
The overwrite characteristics and running properties were evaluated.

The electromagnetic conversion characteristics and the overwrite characteristics were evaluated by modifying the deck. The magnetic head is made of iron nitride, and a signal is directly supplied to the magnetic head from the outside so that the reproduction output of the magnetic head can be directly measured.

Regarding the electromagnetic conversion characteristics, sine waves of 1 MHz (low range) and 7 MHz (high range) were recorded,
The reproduction output was measured. Overwrite characteristic is 1M
After recording the Hz signal, the 7 MHz signal was overwritten on the same track without erasing the signal, and the decrease in the reproduction output of the 1 MHz signal was measured. The larger the decrease, the better the overwrite property.

The runnability was evaluated by repeatedly running 100 times in an environment of a temperature of 25 ° C. and a humidity of 60%. Table 3 shows the evaluation results of Examples 1 to 10 and Comparative Examples 1 to 9. In Table 3, the reproduction output (electromagnetic conversion characteristics) at 1 MHz and 7 MHz is shown with the value obtained in Example 1 as the reference value (0 dB). In addition, the running property is × when stopped during repeated running, Δ when there was no stop in the middle but the magnetic tape was damaged, and the running was completed without problems such as stopping halfway or tape damage What was done was shown as ○.

[0024]

[Table 3]

Next, the evaluation results shown in Table 3 will be analyzed. In Comparative Example 1, the coercive force Hc is too high (2100 Oe
Therefore, the overwrite characteristics are extremely poor. On the contrary, in Comparative Example 3, the coercive force Hc is too low (1800
Since it is smaller than Oe (see Table 2), the reproduction output in the high frequency range is low.

In Comparative Example 2, the saturation magnetization σ of the used magnetic powder f is
s is low (less than 160 emu / g, see Table 1), the saturation magnetic flux density Bm as a medium is insufficient (less than 3500 G, see Table 2), and the reproduction output is lowered over the entire area.

In Comparative Example 4, the major axis length of the magnetic powder h used was too short (less than 0.05 μm, see Table 1), and the saturation magnetic flux density Bm as a medium was insufficient (less than 3500 G, see Table 2). , The playback output has decreased over the entire area. There is also a problem with drivability. In Comparative Example 5, the major axis length of the magnetic powder 1 used was too long (greater than 0.2 μm, see Table 1), and the reproduction output in the high frequency range decreased.

In Comparative Example 6, the surface roughness SRa of the magnetic layer is too small (less than 2 nm, see Table 2), and the surface is too smooth, so the running property is poor. Comparative Example 7 has a surface roughness SR of the magnetic layer.
Since a is too large (greater than 5 nm, see Table 2), the space loss with the magnetic head increases, so the reproduction output in the high frequency range is reduced.

In Comparative Example 8, since the thickness of the magnetic layer is too thin (less than 0.1 μm, see Table 2), the reproduction output is lowered particularly in the low range, and the running property is also problematic. In Comparative Example 9, the overwrite property was deteriorated because the thickness of the magnetic layer was too thick (greater than 0.3 μm, see Table 2).

On the other hand, Examples 1 to 10 satisfying each of the numerical conditions show good results in reproduction output, overwrite characteristics, and running performance.

[0031]

As described above, the magnetic recording medium of the present invention can achieve both good overwrite characteristics and good electromagnetic conversion characteristics. Therefore, since the thickness of the magnetic layer can be reduced while maintaining both characteristics as good characteristics, this magnetic recording medium has a long recording time in a magnetic tape wound and stored in a limited space. It is also suitable for Further, the magnetic recording medium according to claim 2 is excellent in running property.

Claims (2)

[Claims] 1. In a magnetic recording medium having a magnetic layer on one surface of a film-shaped non-magnetic support, the magnetic powder contained in the magnetic layer contains Fe as a main component and a saturation magnetization σs of 160 emu / g. Above 200emu / g, major axis length above 0.05μm and above 0.2μ
The magnetic layer has a thickness of 0.1 μm or more and 0.3 μm or less, and has a saturation magnetic flux density Bm of 3500 in the running direction of the present magnetic recording medium during recording.
A magnetic recording medium, wherein the coercive force Hc in the running direction of the magnetic recording medium is 1800 Oe or more and 2100 Oe or less. 2. The magnetic recording medium according to claim 1, wherein the surface roughness SRa of the magnetic layer is 2 nm or more and 5 nm or less.