JPS61123023A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording having good color S/N and reproduced output by incorporating a small amt. of hexagonal ferrite magnetic powder into a large amt. of needle-like ferromagnetic powder mixture. CONSTITUTION:The magnetic recording medium which contains the magnetic powder having >=70emu/g satd. magnetization and the hexagonal ferrite mag netic powder having the axis of easy magnetization in the c-axis direction and having >=600 oersted coercive force, >=5 planar ratio and 0.2-0.5mum particle size in the magnetic layer and in which the hexagonal ferrite magnetic powder is incorporated at 4h5pts.wt. by 100pts.wt. the magnetic powder is formed. The vertically magnetizable component of the hexagonal ferrite magnetic pow der is effectively utilized, by which the reproduced output in a high-frequency region is improved and the recording medium is made adaptable to high-density recording. The horizontally magnetizable component of the needle-like ferromag netic powder is effectively utilized, by which the reproduced output in a low-fre quency region is improved.

Description

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

[Prior art and its problems]

Conventionally, magnetic recording media have been produced by coating a magnetic paint containing acicular γ-Fe*Os magnetic powder on a non-magnetic substrate, and then oriented the magnetization in the in-plane longitudinal direction by an orientation process such as mechanical orientation or magnetic field orientation. The main type is the so-called horizontal magnetic recording method.

However, this type of horizontal magnetic recording type magnetic recording medium is
If the recording signal has a short wavelength, the self-demagnetizing effect will increase and the reproduction output will decrease.

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 ferromagnetic powder with 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. No. 58-203625).

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 this configuration is adopted, the dispersibility of the magnetic coating material will be improved, and thus a magnetic recording medium with good magnetic properties can 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 been conducting research on a magnetic recording medium that can obtain a large reproduction output using a ring-shaped ferrite magnetic head that is currently incorporated in recording and reproduction devices, and can also handle high-density recording. , saturation magnetization 70e
Hexagonal crystal system with magnetic powder of mu/g or more, easy axis of magnetization in the C-axis direction, coercive force of 600 Oe or more, platelet ratio of 5 or more, and particle size of 0.2 to 0.5 μmn. A magnetic recording medium containing a ferrite magnetic powder in a magnetic layer and having a ratio of the hexagonal ferrite magnetic powder to 100 parts by weight of the magnetic powder at a ratio of 5 helicoids or less can produce a large reproduction output with a ring-shaped ferrite magnetic head. It has been found that this method is suitable for high-density recording.

In other words, by mixing a small amount of hexagonal ferrite magnetic powder with a large amount of acicular ferromagnetic powder, the perpendicular magnetization component of the hexagonal ferrite magnetic powder can be effectively used, improving the reproduction output in the high frequency range. However, it becomes compatible with high-density recording, and the horizontal magnetization component of the acicular ferromagnetic powder can be effectively used, improving the reproduction output in the low frequency region.

In order to perform recording and reproducing with a good S/N ratio especially in the high frequency range and to improve running performance, for example, barium ferrite magnetic powder, strontium ferrite magnetic powder, calcium ferrite magnetic powder, lead ferrite magnetic powder, etc. , or the average particle size of the substituted barium ferrite magnetic powder and the hexagonal ferrite magnetic powder is about 0.2 to 0.
．． It is desirable that the thickness is 5 μm.

In order to improve the reproduction output in the high frequency range, it is necessary to strengthen the perpendicular magnetization component of the hexagonal ferrite magnetic powder, and from this plane the coercive force of the hexagonal ferrite magnetic powder is approximately 600 oersted or more. , more preferably about 600 to 1000 oersteds. In other words, by doing so, high-density recording and high output are possible.

In addition, in order to improve the reproduction output in the O/N and high frequency regions, select a hexagonal ferrite magnetic powder with a plate ratio of about 5 or more, more preferably 5 to 15, and The content of ferrite magnetic powder is acicular ferromagnetic powder 10
It is desirable from the viewpoint of dispersibility that the amount is about 5 parts by weight or less, more preferably about 0.1 parts by weight or more and less than 5 parts by weight, relative to 0 parts by weight.

Further, examples of the magnetic powder having a saturation magnetization of about 7 Q em u / g or more include r Fe! rs, Co-adhered r
FeOs, Fes Oa, 0rOz, Fe
Or acicular powder such as alloy powder (acicular ratio is preferably about 5 to
15) There is a ferromagnetic powder, and unless the saturation magnetization of such magnetic powder is about 70 emu/g or more, the reproduction output in the low frequency region will decrease.

[Example 1] Orthogonal barium ferrite magnetic powder (saturation magnetization Ms approximately 5
4emu/g, coercive force He about 6200e, average grain madness 0
．． 3 μm, plate ratio approx. 6) 4 parts by weight, Co deposited r Fe!
O3 magnetic powder (Ms approx. 75 emu/g, Hc approx. 5760
e, average grain size 0.2 μm, acicular ratio 10) 96 parts by weight, binder 24 parts by weight, dispersant 1 part by weight, abrasive 12
A magnetic paint is prepared by mixing and dispersing a mixture of 1 part by weight, 8 parts by weight of carbon black, 1 part by weight of a lubricant, and 280 parts by weight of a solvent for a predetermined period of time using a sand mill. - This magnetic paint was applied onto a polyethylene terephthalate film, subjected to magnetic field orientation treatment, drying treatment, and calendering treatment, and then slit to -inch width to construct a video magnetic tape.

[Example 2] In Example 1, Ms about 54 emu/g, H
A video magnetic tape was constructed in the same manner using hexagonal barium ferrite magnetic powder having e of about 7300 e, average grain size of 0.3 μm, and platelet ratio of about 6.

[Comparative Example 1] In Example 1, 10 layers of hexagonal barium ferrite magnetic powder and 90 layers of Co-adhered Fears magnetic powder were used.
A video magnetic tape was prepared in the same manner as the weight part.

[Comparative Example 2] In Example 1, Ms about 54 emu/g,
A video magnetic tape was constructed in the same manner using hexagonal barium ferrite magnetic powder having a Hc of about 6200e, an average grain size of 0.3 μm, and a platelet ratio of 3.

[Comparative Example 3] In Example 1, Ms about 54 emu/g, He about 6
A video magnetic tape was constructed in the same manner using hexagonal barium ferrite magnetic powder having characteristics of 200e, average grain size of 0.6 μm, and platelet ratio of about 6.

[Comparative Example 4] In Example 1, Ms about 54 emu/g, Hc about 6
The same procedure was carried out using hexagonal barium ferrite magnetic powder having characteristics of 200e, average grain size of 0.1 μm, and platelet ratio of about 6 to construct a video magnetic tape.

[Comparative Example 5] In Example 1, MS approximately 54 e In u / g
A magnetic tape for video was constructed in the same manner using hexagonal barium ferrite magnetic powder having characteristics of HC of about 5500e, average grain size of 0.3 μm, and platelet ratio of about 6.

[Comparative Example 6] A video magnetic tape was constructed in the same manner as in Example 1 except that the Co-adhered pf40s magnetic powder was not used and 100 parts by weight of hexagonal barium ferrite magnetic powder was used.

〔Characteristic〕

The relationship between the dispersion time and the magnetic flux density of the magnetic paint used in the magnetic layer structure of the magnetic recording media of Examples and Comparative Examples is shown in FIG.

According to this, when the content of barium ferrite magnetic powder is high, the dispersibility is poor and the magnetic flux density is low. It is preferable.

In addition, when measuring the color S of the examples and comparative examples containing barium ferrite magnetic powder,
4.5 dB in Example 1 and 4 in Example 2.
．． 7dB, compared to Comparative Example 1, it was 4.0dB.

4.5 dB for Comparative Example 2, 3 dB for Comparative Example 3
．． 5dB, 3.8dB for Comparative Example 4, Comparative Example 5
4.3dB for Comparative Example 6, 2.4dB for Comparative Example 6.
dB, and it can be seen that the product of this example also has excellent color 8/N characteristics.

In other words, even if the barium ferrite magnetic powder content is the same, as the particle size of the barium ferrite magnetic powder increases, the color S/N decreases, and conversely, if the particle size is too small, the color S/N decreases, and the barium ferrite magnetic powder The average particle size of the magnetic powder is preferably about 0.2 to 0.5 μm.

Furthermore, the frequency characteristics of the magnetic recording media of Examples and Comparative Examples were measured using a current ring-type ferrite magnetic head, and the results were as shown in FIG.

According to this, the coercive force of barium ferrite magnetic powder is 6
When it becomes smaller than 00 oersted, the reproduction output decreases rapidly, and when the content of barium ferrite magnetic powder increases, it was thought that the reproduction output in the short wavelength region would improve, but contrary to expectations, it decreased. Therefore, it is desirable that the barium ferrite magnetic powder has a coercive force of 600 Oe or more, and that the content of the barium ferrite magnetic powder is about 5% by weight or less based on the acicular ferromagnetic powder. or,
As the plate ratio of barium ferrite magnetic powder decreases, the reproduction output also decreases.In other words, when the plate ratio decreases, the reproduction output in the high frequency region is low, probably because the vertical orientation decreases, and therefore the plate of barium ferrite magnetic powder It is desirable that the shape ratio is larger than 5.

〔effect〕

It has a good color S/N, a good reproduction output over a wide frequency range, especially in a short wavelength region, and has good dispersion, so it can be made at low cost.

[Brief explanation of the drawing]

FIGS. 1 and 2 are graphs showing the characteristics of magnetic recording media.

Claims (1)

[Claims] Magnetic powder with a saturation magnetization of 70 emu/g or more, an axis of easy magnetization in the c-axis direction, a coercive force of 600 Oe or more, a plate ratio of 5 or more, and a particle size of 0.2 to 0.5.
A magnetic recording medium, characterized in that the magnetic layer contains a hexagonal ferrite magnetic powder of μm size, and the hexagonal ferrite magnetic powder is present in a ratio of 5 parts by weight or less to 100 parts by weight of the magnetic powder.