JPS61217930A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having good vertical orientability with good productivity by making combination use of hexagonal ferrite magnetic powder and acicular ferromagnetic powder. CONSTITUTION:The hexagonal ferrite magnetic powder having >=5 plate ratio and <=600 oersted coercive force is selected. The ferromagnetic powder having >=4 acicular ratio, 600-100emu/g saturation magnetization and <=700 oersted coercive force is selected. The ratio of the hexagonal ferrite magnetic powder and the ferromagnetic powder is made <=80pts.wt. the latter with respect to 20-100pts.wt. the former, then the magnetic recordingmedium having a good erasing characteristic, good high-frequency characteristic, high density and high output is obtd. The ratio of the ferromagnetic powder is more preferably about 80-5wt% with respect to about 20-95wt% the hexagonal ferrite magnetic 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 is applicable to magnetic tapes, floppy disks, or diskettes for use in audio, video, computers, etc.
It relates to magnetic recording media such as hard disks.

[Prior art and its problems]

Conventionally, as a magnetic recording medium, acicular γ-Fe! O
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 5 to 1
00 parts by weight of a ferromagnetic powder having a saturation magnetization of 70 e m u/g or more and an average particle size larger than the average particle size of the hexagonal ferrite powder, which are dispersed in a resin binder. Suggested by the medium (Japanese Unexamined Patent Publication No. 58-203
No. 625 has been issued.

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 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 100 e
m u/g and 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 20 to 100 parts by weight of the former. If the latter is kept at 80 parts by weight or less,
It has been found that a magnetic recording medium with good erasing properties, good high frequency properties, 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. In addition, 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 ratio of the ferromagnetic powder to the hexagonal ferrite magnetic powder The reproduction output decreases greatly, and therefore, when the hexagonal ferrite magnetic powder is 20 to 1
The ratio of ferromagnetic powder to 00% by weight is 80% by weight or less,
Even more preferably, the hexagonal ferrite magnetic powder is about 20
It is desirable that the proportion of ferromagnetic powder be about 80 to 5% by weight to about 95% by weight.

The coercive force of the ferromagnetic powder is 600 Oe/g or less, more preferably about 400 to 600 Oe/g, and the ferromagnetic powder has a saturation magnetization of 60 to 10100 e/g.
It is desirable that the coercive force is less than 700 oersted, more preferably about 500 to 700 oersted.

Further, 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 the reproduction output characteristics but also from the viewpoint of the 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 538 oersted, saturation magnetization 57 emu/
g, average particle size 0.17 μm) 65 parts by weight, Co coating
Fe*Os magnetic powder (acicular ratio 6, coercive force 586 oersted, saturation magnetization 75 emu/g, average powder diameter 0.2 μm) 3
5 parts by weight, 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,
A magnetic paint is prepared by thoroughly cross-dispersing a mixture of 250 parts by weight of a solvent, a curing agent is added to this magnetic paint, and the paint is applied onto a non-magnetic substrate such as polyethylene terephthalate. After drying, it is calendered and slit into an i-inch width. and obtain magnetic tape.

[Example 2] The same procedure as in Example 1 was repeated except that 50 parts by weight of the barium ferrite magnetic powder and 50 parts by weight of the Co-coated Fezes magnetic powder were used to obtain a magnetic tape.

[Example 3] In Example 1, CrCh magnetic powder having an acicular ratio of 10, a coercive force of 625 oersted, a saturation magnetization of 72 emu/g, and an average particle size of 0.2 μm was used instead of the Co-adhered Fetus magnetic powder. Perform the same procedure to obtain a magnetic tape.

[Example 4] In Example 1, instead of the Co-adhered Fe*Os magnetic powder, metal magnetic powder with an acicular ratio of 10, a coercive force of 680 oersted, a saturation magnetization of 90 emu/gs, and an average particle size of 0.15 μm was used. Perform the same procedure using a magnetic tape to obtain a magnetic tape.

[Example 5] In Example 1, instead of making a magnetic tape by slitting it to a width of i inch, a floppy disk is obtained by punching it to a diameter of 5.25 inches.

[Example 6.7] In Example 1, 50 parts by weight of barium ferrite magnetic powder, 50 parts by weight of CO-coated Fetus magnetic powder (Example 6), 70 parts by weight of barium ferrite magnetic powder, and 50 parts by weight of CO-coated Fetus magnetic powder were used. A floppy disk was obtained in the same manner as in Example 7 using 30 parts by weight of the Fears magnetic powder to be adhered.

[Comparative Example 1] A magnetic tape is obtained by carrying out the same procedure as in Example 1 except that 10 parts by weight of the barium ferrite magnetic powder and 90 parts by weight of the CO-coated Fetus magnetic powder were used.

[Comparative Example 2] A magnetic tape was obtained in the same manner as in Example 1 except that 15 parts by weight of the barium ferrite magnetic powder and 85 parts by weight of the Co-coated Fears magnetic powder were used.

[Comparative Example 3] In Example 1, barium ferrite magnetic powder with a plate ratio of 3, a coercive force of 638 oersted, a saturation magnetization of s7 emu/g, and an average particle size of 0.1 μm was used, and a barium ferrite magnetic powder with an acicular ratio of 3 and a coercive force of 62
0 oersted, saturation magnetization 75 emu/g.

A magnetic tape is obtained by carrying out the same procedure using Co-coated Fe*Os magnetic powder having an average particle size of 0.2 μm.

[Comparative Example 4] The procedure of Example 1 was repeated except that the barium ferrite magnetic powder was not used and 100 parts by weight of CO-coated Fe*03 magnetic powder was used to obtain a floppy disk instead of a magnetic tape.

[Comparative Example 5] A floppy disk was obtained by carrying out the same procedure as in Example 1 except that 10 parts by weight of the barium ferrite magnetic powder and 90 parts by weight of the Co-coated -Fe=Os magnetic powder were used.

[Characteristics] For the magnetic tapes of Examples 1 to 4 and Comparative Examples 1 to 3, when an FM signal is input and the frequency characteristics of the reproduced output are examined, the results are as shown in the drawings.

According to this graph, the reproduction output of the magnetic tape of this example is high overall in both the high frequency region and the low frequency region, whereas the magnetic tape of Comparative Example 1.2 has a high reproduction output. The reduction in reproduction output in the high frequency region is severe, and although the magnetic tape of Comparative Example 3 does not have a large decrease in reproduction output in the high frequency region like the magnetic tape of Comparative Example 1.2, the overall reproduction output It can be seen that the magnetic tape of the present invention is suitable for high-density recording.

In addition, the floppy disks of Examples 5, 6.7 and Comparative Examples 4 and 5
'If you look into the modulation of the disc,
1.2% for Example 5, 1.2% for Example 6,
Although the modulation characteristics are good, such as 5% and 1.0% for Example 7, the modulation characteristics are 8.8% for Comparative Example 4 and 5.4% for Comparative Example 5. The ration characteristics are poor.

〔effect〕

It has good reproduction output over the entire range from low frequencies to high frequencies.

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. Patent applicant: Victor Japan Co., Ltd. d+: Masato Yuyo, Katsu Uko,
,/

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. A magnetic recording medium, wherein the ferromagnetic powder is contained in a magnetic layer in an amount of 80 parts by weight or less relative to 20 to 100 parts by weight of the hexagonal ferrite magnetic powder.