JPS61217928A - 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, >=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 <=30pts.wt. the latter with respect to 70-100 pts.wt. the former, then the magnetic recording medium of which the magnetic characteristics are less deteriorated with time (for example, the reproduced output is less decreased with time) and which has a good high-frequency characteristic, high density and high output is obtd. The ratio of the ferromagnetic powder is more preferably about 30-50wt% with respect to about 70-95wt% 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 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, a magnetic paint containing acicular γ-Fetus 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. 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 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 emu/g or more and an average particle size larger than that of the hexagonal ferrite powder are dispersed in a resin binder. Proposal (Japanese Unexamined 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 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 a hexagonal ferrite magnetic powder with a platelet ratio of 5 or less and a coercive force of 600 oersted or more. The acicular ratio is 4 or less, and the saturation magnetization is 10100e/
g or more and has a coercive force of 700 oersted or more, and the ratio of the hexagonal ferrite magnetic powder having the above characteristics to the ferromagnetic powder having the above characteristics is 70 to 100 parts by weight for the former and 70 to 100 parts by weight for the latter. If the amount is 30 parts by weight or less, there will be little change in magnetic properties over time (for example, less decline in FM output due to changes over time), good high frequency properties, and a high-density, high-output magnetic recording medium will be obtained. I found it.

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 relative amount of the ferromagnetic powder to the hexagonal ferrite magnetic powder is If the amount is too large, the deterioration of the magnetic properties will be severe, for example, the FM output will decrease significantly due to aging, and the reproduction output in the high frequency region will also decrease significantly. The ratio of ferromagnetic powder to ~100% by weight is 30% by weight or less1. Even more preferably, the ratio of the hexagonal ferrite magnetic powder is about 70 to 95% by weight and the ferromagnetic powder is about 30 to 5% by weight.

Furthermore, it is desirable that the ratio of the hexagonal ferrite magnetic powder to the ferromagnetic powder be as described above, not only in terms of the magnetic properties but also in terms of the frequency characteristics of the reproduced output. In order to improve the reproduction output characteristics in this high frequency range, it is necessary to not only improve the ratio of hexagonal ferrite magnetic powder to ferromagnetic powder, but also to increase the coercive force of hexagonal ferrite magnetic powder to 600%.
Oersted or more, more preferably about 700 to 15
00 Oe/g, and the saturation magnetization of the ferromagnetic powder is 10,100 e/g or more, and the coercive force is 700 Oe/g or more, more preferably about 700 to 150 Oe/g.
It is desirable that it be 0 oersted.

Furthermore, 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, random orientation can be achieved. This makes it possible to achieve high output in the high frequency region.

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 850 oersted, saturation magnetization 57 emu/
85 parts by weight of metal iron magnetic powder (acicularity ratio 3, coercive force 1000 oersted, saturation magnetization 125 emu/g, average particle size 0.2 μm), 25 parts by weight of binder 1 part by weight of dispersant, 4 parts by weight of abrasive, 5 parts by weight of carbon black, 1 part by weight of lubricant, and 300 parts by weight of solvent to make a magnetic paint. After adding the mixture, it is coated on a non-magnetic substrate such as polyethylene terephthalate, dried, calendered, and slit into 1-inch widths to obtain a magnetic tape.

[Example 2.3] 95 parts by weight of the barium ferrite magnetic powder in Example 1, 5 parts by weight of the metal iron magnetic powder (Example 2), 90 parts by weight of the barium ferrite magnetic powder, and 10 parts by weight of the metal iron magnetic powder A magnetic tape was obtained in the same manner as in Section (Example 3).

[Embodiment 4] In Embodiment 1, instead of slitting the magnetic tape to a width of 1 inch to obtain a magnetic tape, it is punched out to a diameter of 5.25 inches to obtain a floppy disk.

[Comparative Example 1] A magnetic tape is obtained by carrying out the same procedure as in Example 1 using barium ferrite magnetic powder having a plate ratio of 3, a coercive force of 500 oersted, a saturation magnetization of 57 emu/g, and an average particle size of 0.1 μm.

[Comparative Example 2] In Example 1, the acicular ratio was 3, the coercive force was 680 oersted, the saturation magnetization was 125 emu/gs, and the average grain size was 0.
A magnetic tape is obtained in the same manner using 2 μm metal iron magnetic powder.

[Comparative Example 3] A magnetic tape is obtained by carrying out the same procedure as in Example 1 except for using 100 parts by weight of metal iron magnetic powder instead of using barium ferrite magnetic powder.

[Comparative Example 4] The same procedure as in Example 1 was carried out except that the barium ferrite magnetic powder was used in an amount of 30 parts by weight, and the metal iron magnetic powder was added in an amount of 70 parts by weight.
Get magnetic tape.

[Comparative Example 5] 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 metal iron magnetic powder were used to obtain a magnetic tape.

[Comparative Example 6] The same procedure as in Example 1 was carried out except that the barium ferrite magnetic powder was used in 65 parts by weight and the metal iron magnetic powder was used in 35 parts by weight.
Get magnetic tape.

[Comparative Example 7] In Example 1, the plate ratio was 12, the coercive force was 850 oersted, the saturation magnetization was 7 emu/g, and the average grain size was 0.
A magnetic tape is obtained by carrying out the same procedure using 1 μm barium ferrite magnetic powder.

[Comparative Example 8] In Example 1, the acicular ratio was 10. Coercive force 1000 oersted, saturation magnetization 125 emu/g, average grain size 0.2 μ
A magnetic tape is obtained in the same manner using m metal iron magnetic powder.

[Comparative Example 9] In Example 3, the plate ratio was 12, the coercive force was 850 oersted, the saturation magnetization was 57 emu/gs, and the average grain size was 0.
A floppy disk was obtained by performing the same procedure using 1 μm barium ferrite magnetic powder.

[Comparative Example 10] In Example 3, the acicular ratio was 10, the coercive force was 1000 oersted, and the saturation magnetization was 125 emu/g1, and the average grain size was 0.2 μ.
A floppy disk is obtained by carrying out the same procedure using m metal iron magnetic powder.

[Comparative Examples 11 to 13] In Example 3, the amounts of barium ferrite magnetic powder and metal iron magnetic powder were 0 parts by weight and 100 parts by weight (Comparative Example 11)
, 50 parts by weight and 50 parts by weight (Comparative Example 12), and 65 parts by weight and 35 parts by weight (Comparative Example 13) to obtain floppy disks.

[Comparative Example 14] In Example 3, the plate ratio was 3, the coercive force was 500 oersted, the saturation magnetization was 57 emu/g, and the average grain size was 0.1 μ.
The same procedure was carried out using m barium ferrite magnetic powder,
Get a floppy disk.

[Comparative Example 15] A floppy disk was obtained by carrying out the same procedure as in Example 3 using metal iron magnetic powder having an acicular ratio of 3, a coercive force of 680 oersted, a saturation magnetization of 125 emu/g, and an average particle size of 0.2 μm.

〔Characteristic〕

Regarding the magnetic tapes of Examples 1 to 3 and Comparative Examples 3 to 6, the magnetic tapes were placed in an atmosphere with a temperature of 40°C and a humidity of 80% RH, and how the FM output of the magnetic tapes changed over time. The first result is
As shown in the figure.

According to this, the FM output of the example has a small decrease, whereas the FM output of the comparative example has sharply decreased in a short period of time, and the magnetic recording medium of the present invention has magnetic characteristics. It can be seen that there is little deterioration in , and the durability is high.

FIG. 2 shows the results of examining the frequency characteristics of the reproduced FM signals for the floppy disks of Example 4 and Comparative Examples 9 to 15 after a long period of time.

According to this, the magnetic recording medium of the present invention has a high reproduction output in the high frequency region, whereas the reproduction output of the comparative example has a low reproduction output in the high frequency region, and the magnetic recording medium of the present invention is suitable for high-density recording. I can see that it is something.

FIG. 3 shows the results of examining the frequency characteristics of the magnetic tapes of Example 1.2 and Comparative Examples 1, 2, 3, and 7.8.

According to this, the magnetic recording medium of the present invention has a high output in the high frequency region, whereas the comparative example has a low output in the high frequency region, indicating that the magnetic recording medium of the present invention is suitable for high-density recording. I understand that there is something.

〔effect〕

It has a high output in the high frequency range, and is highly durable with little deterioration in magnetic properties.

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]

1 to 3 are graphs showing the characteristics of magnetic recording media. Hats off to patent applicant Japan Victor Co., Ltd. t+rhlf-! +0 da
IOFM 4 report (mon Hsu'13rfl

Claims (1)

[Claims] A hexagonal ferrite magnetic powder with a plate ratio of 5 or less and a coercive force of 600 Oe or more, and a ferromagnetic powder with an acicular ratio of 4 or less, a saturation magnetization of 100 emu/g or more, and a coercive force of 700 Oe or more are magnetic. A magnetic recording medium, wherein the ferromagnetic powder is contained in a layer in an amount of 30 parts by weight or less relative to 70 to 100 parts by weight of the hexagonal ferrite magnetic powder.