JPS61217934A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium which has good color S/N and reproduced output characteristic and erasing characteristic over a wide frequency range and is suitable for high-density recording by making combination use of hexagonal ferrite magnetic powder and acicular ferromagnetic powder. CONSTITUTION:The hexagonal ferrite magnetic powder having >=5 platy ratio and <=600 oersted coercive force is selected. The ferromagnetic powder having >=5 acicular ratio, 60-100emu/g saturation magnetization and <=700 oersted coercive force is selected. The ratio of the hexagonal ferrite magnetic powder and the ferromagnetic powder is made <=20pts.wt. the former with respect to 800-100pts.wt. the latter, then the magnetic recording medium which has the good color S/N and has the good erasing characteristic, high frequency characteristic, high density and high output is obtd. The ratio of the hexagonal ferrite magnetic powder is more preferably about 20-5wt% with respect to about 80-95wt% ferromagnetic powder. The average grain sizes of both the hexagonal ferrite magnetic powder and ferromagnetic powder are about <=0.3mum.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium such as a magnetic tape, a floppy disk, or a hard disk for use in audio, video, or computers.

[Prior art and its problems]

Conventionally, as a magnetic recording medium, acicular γ-FetOsil
The main method is the so-called horizontal magnetic recording method, in which a magnetic paint containing magnetic powder is applied onto a non-magnetic substrate, and the magnetization is oriented in the in-plane longitudinal direction by an orientation treatment such as mechanical orientation or magnetic field orientation.

However, this type of horizontal magnetic recording type magnetic recording medium is
If the recording signal has a short wavelength, the self-demagnetizing effect increases and the reproduction output decreases, so it is not suitable for high-density recording.

Therefore, as a solution to these drawbacks, a so-called perpendicular magnetic recording type magnetic recording medium has been proposed.
For example, ferromagnetic powder and hexagonal ferrite magnetic powder, especially hexagonal ferrite powder with an average particle size of 0.2 μm or less.
A magnetic recording medium is proposed in which 100 parts by weight of a ferromagnetic powder having a saturation magnetization of 70 emu/g or more and an average particle size larger than the average particle size of the hexagonal ferrite powder are dispersed in a resin binder. (Unexamined Japanese Patent Publication No. 58-20362
No. 5).

In other words, the technical idea of this proposal is that simply using ferromagnetic powder and hexagonal ferrite magnetic powder would result in a decrease in magnetic properties due to poor dispersibility of the magnetic paint. It is stated that if the structure is configured as follows, the dispersibility of the magnetic coating material will be improved, and a magnetic recording medium with good magnetic properties can therefore be obtained.

However, according to research conducted by the present inventors, it has been found that even this proposed magnetic recording medium is not fully satisfactory for high-density recording.

[Disclosure of the invention]

The present inventor has discovered that a combination of hexagonal ferrite magnetic powder and ferromagnetic powder, such as barium ferrite magnetic powder, strontium ferrite magnetic powder, calcium ferrite magnetic powder, lead ferrite magnetic powder, or substituted barium ferrite magnetic powder, is mixed. While researching and developing magnetic recording media, we selected hexagonal ferrite magnetic powder with a platelet ratio of 5 or more and a coercive force of 600 oersted or less, and as ferromagnetic powder, The acicular ratio is 4 or more, and the saturation magnetization is 60 to 10100e.
/g and has a coercive force of 700 oersted or less, and the ratio of the hexagonal ferrite magnetic powder having the above characteristics to the ferromagnetic powder having the above characteristics is 80 to 100 parts by weight for the latter and 80 to 100 parts by weight for the former. It has been found that if the content is 20 parts by weight or less, a magnetic recording medium with good color S/N, good erasing characteristics, and good high frequency characteristics, and high density and high output can be obtained. .

In other words, by using hexagonal ferrite magnetic powder and acicular ferromagnetic powder together, the perpendicular magnetization component of hexagonal ferrite magnetic powder can be effectively used, improving reproduction output in the high frequency range and achieving high-density recording. Although the horizontal magnetization component of the acicular ferromagnetic powder can be effectively used and the reproduction output in the low frequency range is improved, the amount of ferromagnetic powder and hexagonal ferrite magnetic powder The color S/N ratio is poor and the playback output is greatly reduced. Therefore, the ratio of hexagonal ferrite magnetic powder is 20% by weight or less compared to 80 to 100% by weight of ferromagnetic powder, and more preferably ferromagnetic powder. It is desirable that the hexagonal ferrite magnetic powder be in a proportion of about 20 to 5% by weight to about 80 to 95% by weight of the hexagonal ferrite magnetic powder.

Furthermore, in order to improve the frequency characteristics, not only the ratio of the hexagonal ferrite magnetic powder and the ferromagnetic powder but also the coercive force of the hexagonal ferrite magnetic powder is 600 Oersteds or less, more preferably about 400 to 600 Oersteds. It is desirable that the ferromagnetic powder has a saturation magnetization of 60 to 10,100 e/g and a coercive force of 700 oersted or less, more preferably about 500 to 700 oersted.

Furthermore, it is desirable that the coercive force of the hexagonal ferrite magnetic powder and the ferromagnetic powder be as described above not only from the viewpoint of improving frequency characteristics but also from the viewpoint of erasing characteristics.

Further, by using a hexagonal ferrite magnetic powder whose platelet ratio is 5 or more, preferably about 7 to 15, and a ferromagnetic powder whose acicular ratio is 4 or more, preferably about 6 to 15, mechanical orientation can be achieved. Easy processing and improved frequency characteristics.

Further, it is desirable that both the hexagonal ferrite magnetic powder and the ferromagnetic powder used above have an average particle size of about 0.3 μm or less.

[Example 1] Barium ferrite magnetic powder whose C axis is the axis of easy magnetization (plate ratio 8, coercive force 517 oersted, saturation magnetization 56 emu/
g, average particle size 0.22 μm) 10 parts by weight, Co coating
Fears magnetic powder (acicular ratio 10. Coercive force 588 oersted, saturation magnetization 77 emu/gs, average particle size 0.
23 μm), 25 parts by weight of binder, 2 parts by weight of dispersant, 5 parts by weight of abrasive, 5 parts by weight of carbon black, 1 part by weight of lubricant, and 280 parts by weight of solvent were sufficiently cross-dispersed to form a magnetic paint. After adding a curing agent to this magnetic paint, it is applied onto a non-magnetic substrate such as polyethylene terephthalate, dried, calendered, and slit to the width of the fin to obtain a magnetic tape.

[Example 2] In Example 1, 15 parts by weight of barium ferrite magnetic powder was coated with Co-Fe! The same procedure was carried out using 85 parts by weight of rs magnetic powder to obtain a magnetic tape.

[Comparative Example 1.2] In Example 1, 30 parts by weight of barium ferrite magnetic powder, 70 parts by weight of Co-coated Fetus magnetic powder (Comparative Example 1), 40 parts by weight of barium ferrite magnetic powder, C
O deposited - 60 parts by weight of Fe*Os magnetic powder (Comparative Example 2)
Perform the same procedure as above to obtain a magnetic tape.

[Comparative Example 3] In Example 1, barium ferrite magnetic powder with a plate ratio of 4, a coercive force of 517 oersted, a saturation magnetization of 56 emu/g, and an average particle size of 0.22 μm was used; 588)-, Rusted, saturation magnetization 77 emu/g
, average particle size 0.23 μm', Co-coated 1-FexOs
A magnetic tape is obtained by carrying out the same procedure using magnetic powder.

[Comparative Example 4] A magnetic tape is obtained in the same manner as in Example 2 using magnetic powder having the same characteristics as the magnetic powder used in Comparative Example 3.

[Comparative Example 5] In Example 1, barium ferrite magnetic powder having a plate ratio of 8, a coercive force of 930 oersted, a saturation magnetization of 56 emu/gs, and an average particle size of 0.22 μm was used, and an acicular ratio of 10,
Coercive force 1030 oersted, saturation magnetization 77emu/
g. The same procedure was carried out using metal magnetic powder with an average particle size of 0.23 μm instead of the C6-coated γ-Fears magnetic powder,
Get magnetic tape.

[Comparative Example 6] In Example 2, the plate ratio was 8, the coercive force was 880 oersted, the saturation magnetization was 56 emu/gs, and the average grain size was 0.22.
Using barium ferrite magnetic powder of μm, the needle ratio is 10. Coercive force 910 oersted, saturation magnetization 77 e
Co-coated 1 Fe with mu/g, average particle size 0.23 pm
*A magnetic tape is obtained by carrying out the same procedure using Os magnetic powder.

〔Characteristic〕

When examining the color S/N of the magnetic tapes of Example 1.2 and Comparative Examples 1 and 2, the color S/N of Example 1 was +2.0.
dB, whereas that of Example 2 is +1.2 dB,
Comparative example 1 is -0.3 dB, comparative example 2 is -1
, 1dB, and the magnetic tape of this example has a color S/N.
You can see that it is a good product. That is, by setting the ratio of barium ferrite magnetic powder to ferromagnetic powder as in the present invention, a magnetic tape with good color S/N can be obtained.

Further, when the frequency characteristics of the reproduced outputs of the magnetic tapes of Example 1.2 and Comparative Example 3.4 were examined, they were as shown in the drawings.

According to this graph, the reproduction output of the magnetic tape of this example is high in both the low frequency region and the high frequency region, whereas the reproduction output of the magnetic tape of the comparative example is significantly reduced in the high frequency region. That is, it is not possible to obtain a satisfactory magnetic tape by only considering the ratio of the barium ferrite magnetic powder and the ferromagnetic powder. It can be seen that it is important to adjust the plate-like ratio and needle-like ratio as well in accordance with the present invention.

Further, when examining the erasing characteristics of the magnetic tapes of Example 1.2 and Comparative Example 5.6, it was found that the erasing characteristics of the magnetic tapes of Example 1 were 62 d.
B, 61 dB in Example 2, 41 dB in Comparative Example 5, and 45 dB in Comparative Example 6.
Therefore, the magnetic tape of this example has good erasing characteristics. In other words, it is not enough to consider only the ratio of barium ferrite magnetic powder to ferromagnetic powder, the plate-like ratio and the needle-like ratio of the magnetic powder, and by also considering the saturation magnetization and coercive force of these magnetic powders. It is important that the coercive force and saturation magnetization of these magnetic powders be as desirable as those of the present invention.

〔effect〕

It has good color S/N, reproduction output characteristics over a wide frequency band, and erasing characteristics, and is suitable for high-density recording.

Further, a magnetic recording medium with good vertical alignment can be obtained without special magnetic field alignment treatment, and can be manufactured with high productivity.

[Brief explanation of the drawing]

The drawing is a graph showing the characteristics of a magnetic recording medium.

Claims (1)

[Claims] A hexagonal ferrite magnetic powder with a plate ratio of 5 or more and a coercive force of 600 Oe or less, and a ferromagnetic powder with an acicular ratio of 4 or more, a saturation magnetization of 60 to 100 emu/g, and a coercive force of 700 Oe or less. The ferromagnetic powder 8 contained in the magnetic layer
A magnetic recording medium characterized in that the amount of the hexagonal ferrite magnetic powder is 20 parts by weight or less relative to 0 to 100 parts by weight.