JPS61217932A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium which has good surface smoothness, a good frequency characteristic over the entire range from a low to high frequency range, permits easy production and is low in cost 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 <=4 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 latter with respect to 80-100pts.wt. the former, then the magnetic recording medium having high density and high output is obtd. at a low cost. 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, magnetic recording media have been produced by applying a magnetic paint containing acicular γ-Felos magnetic powder onto a non-magnetic substrate, and then applying an orientation process such as mechanical orientation or magnetic field orientation to orient the magnetization in the in-plane longitudinal direction. 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 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 7-elite powder with an average particle size of 0.2 μm or less 5 to 1
00 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. Proposal (JP-A-58-203625
No.) has been done.

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 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 less and a coercive force of 600 oersted or less, and as ferromagnetic powder, we selected The acicular ratio is 4 or less, 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 amount is 20 parts by weight or less, a high-density, high-output magnetic recording medium can be obtained at low cost.

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 relative amount of the ferromagnetic powder and the hexagonal ferrite magnetic powder is In other words, depending on the relative amounts of these, the dispersibility of the magnetic paint is poor, making it impossible to produce high-performance magnetic recording media with good productivity. It is desirable that the proportion of the powder be 20% by weight or less, and even more preferably, the proportion of the ferromagnetic powder should be about 80-95% by weight and the hexagonal ferrite magnetic powder should be about 20-5% by weight.

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 Oe or less, more preferably about 400 to 600 Oe. and the saturation magnetization of the ferromagnetic powder is 60 to 10100e/
g and coercive force of less than 700 oersteds, more preferably about 500 to 700 oersteds.

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.

In addition, by using a hexagonal ferrite magnetic powder whose platelet ratio is 5 or less, preferably about 1 to 5, and a ferromagnetic powder whose acicular ratio is 4 or less, preferably about 1 to 4, the magnetic paint can be The dispersibility is improved, random orientation can be obtained, and high output in the high frequency region can be achieved.

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 3, coercive force 528 oersted, saturation magnetization 56 emu)
/ g, average particle size 0.17 μm) 10 parts by weight, C
O adhered to - Fetrs magnetic powder (acicular ratio 3, coercive force 571
Else.

Ted, saturation magnetization 74 emu/gs average grain size 0.2 μm
), 25 parts by weight of binder, 1 part 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. A curing agent is added to the magnetic paint, and then applied onto a nonmagnetic substrate made of polyethylene terephthalate, dried, calendered, and slit into i-inch widths to obtain a magnetic tape.

[Example 2] The same procedure as in Example 1 was carried out except that 15 parts by weight of the barium ferrite magnetic powder and 85 parts by weight of the Co-coated FetOx magnetic powder were used to obtain a magnetic tape.

[Comparative Examples 1 and 2] In Example 1, 30 parts by weight of barium ferrite magnetic powder, 70 parts by weight of Co-coated FetCh magnetic powder (Comparative Example 1), 50 parts by weight of barium ferrite magnetic powder, C
o Adhesion - 50 parts by weight of Fee's magnetic powder (Comparative Example 2)
Perform the same procedure as above to obtain a magnetic tape.

[Comparative Examples 3 to 6] In Example 1, the plate ratio was 8, the coercive force was 528 oersted, the saturation magnetization was 56 emu/g, and the average grain size was 0.17/Am.
barium ferrite magnetic powder with an acicular ratio of 10°, a coercive force of 571 oersted, and a saturation magnetization of 74 emu/g.
Using Co-coated Fears with an average particle size of 0.2 μm, 10 parts by weight of the barium ferrite magnetic powder,
and 90 parts by weight of the Co-coated γ-Fe*Os magnetic powder (
Comparative Example 3), 15 parts by weight of the barium ferrite magnetic powder and 85 parts by weight of the CO-coated γ-Fe*Os magnetic powder (Comparative Example 4), 30 parts by weight of the barium ferrite magnetic powder
Part by weight, and the Co-adhered γ-F e! The same procedure was carried out using 70 parts by weight of the Os magnetic powder (Comparative Example 5), 50 parts by weight of the barium ferrite magnetic powder, and 50 parts by weight of the CO-coated γ-Fe*Os magnetic powder (Comparative Example 6). Get the tape.

〔Characteristic〕

The relationship between the dispersion time of the magnetic paint and the maximum magnetic flux density for the magnetic paints prepared on each side was investigated as shown in the drawings.

According to this, the magnetic paint used in the production of the magnetic tape of this example has a large dispersion progress at the initial stage of dispersion, that is, a product exhibiting a large maximum magnetic flux density can be obtained even with a short time of dispersion, thereby increasing productivity. While magnetic tapes can be produced well, the comparative example cannot produce a product with a large maximum magnetic flux density without long hours of dispersion work, and therefore the comparative example has poor productivity, or Only low-performance magnetic tape can be obtained. That is, by setting the ratio of the barium ferrite magnetic powder to the ferromagnetic powder as in the present invention, and setting the plate-like ratio of the barium ferrite magnetic powder and the needle-like ratio of the ferromagnetic powder as in the present invention, good quality can be obtained. This allows magnetic recording media to be manufactured with high productivity.

Furthermore, when examining the color S/N of the magnetic tapes on each side, it is +2.3 dB for Example 1 and +2.1 dB for Example 2, whereas it is +2.1 dB for Comparative Example 1.
+0.8 dB for those of Comparative Example 2, -0 for those of Comparative Example 2
, 3dB, -0.1dB for Comparative Example 3, Comparative Example 4
-0.8d B for the sample and -1 for the sample from Comparative Example 5.
,2dB.

The value of Comparative Example 6 was -1.5 dB, indicating that the magnetic tape of this example had good color S/N.

That is, by keeping the ratio of barium ferrite magnetic powder to ferromagnetic powder, the plate-like ratio of barium ferrite magnetic powder, and the needle-like ratio of ferromagnetic powder as in the present invention, color S
/N can be obtained.

Furthermore, when examining the surface roughness (center line average roughness Ra) of the magnetic layer surface of the magnetic tape on each side, it was found that in Example 1, R
a is 0.007 μm1 In Example 2, Ra is o, o
o s μm, whereas in Comparative Example 1, Ra
is 0.010 μm, and in Comparative Example 2, Ra is 0:'0
12μm1012μm1 comparison is Ra is 0.011μm1
In Comparative Example 4, Ra is 0.013 μm; in Comparative Example 5, Ra is 0.015 μm; and in Comparative Example 6, R
It can be seen that a is 0.016 μm, and the magnetic tape of this example has good surface properties. That is, by keeping the ratio of the barium ferrite magnetic powder to the ferromagnetic powder, the plate-like ratio of the barium ferrite magnetic powder, and the needle-like ratio of the ferromagnetic powder as in the present invention, the surface properties are good and S
A magnetic tape with good /N can be obtained.

〔effect〕

It has good surface smoothness, good frequency characteristics over the entire range from low frequencies to high frequencies, and is easy to manufacture and low cost.

[Brief explanation of drawings]

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 less and a coercive force of 600 Oe or less, and a ferromagnetic powder with an acicular ratio of 4 or less, 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.