JPS61233416A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the title medium having excellent durability, a high output and excellent erasing characteristic and random orientation by jointly using hexagonal ferrite magnetic powder and acicular ferromagnetic powder. CONSTITUTION:Magnetic powder having <=5 squareness ratio and <600 Oe coercive force is selected as the hexagonal ferrite magnetic powder, ferromagnetic powder having <=4 acicular ratio, >=100emu/g saturation magnetization and <=700Oe coercive force is selected as the ferromagnetic powder. Less than 70pts. wt. hexagonal ferrite magnetic powder is used with 300-100pts.wt. ferromagnetic powder and more preferably about 5-70wt% ferromagnetic powder. Besides, the hexagonal ferrite magnetic powder having about 400-600Oe coercive force and the ferromagnetic powder having about 500-700Oe coercive force are preferably used in consideration of the erasing characteristic.

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-Fears 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, a so-called perpendicular magnetic recording type magnetic recording medium has been proposed to solve this drawback.
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).

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 Oe or less, and ferromagnetic powder with The acicular ratio is 4 or less, and the saturation magnetism (Hi is 100 emu
/g or more and has a coercive force of 700 Oe or less, and the ratio of the hexagonal ferrite magnetic powder having the above characteristics to the ferromagnetic powder having the above characteristics is 30 to 100 parts by weight of the latter to 100 parts by weight of the former. If it is set to 70 parts by weight or less,
It has been discovered that a highly durable and 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. The proportion of the powder is preferably 70% by weight or less, and even more preferably, the proportion of the ferromagnetic powder is about 30 to 95% by weight and the hexagonal ferrite magnetic powder is about 5 to 70% by weight.

Furthermore, in order to improve the dispersibility of the magnetic paint, it is desirable that the ratio of the hexagonal ferrite magnetic powder and the ferromagnetic powder be as described above, but it is not sufficient to consider this mixing ratio alone. In other words, it is necessary to consider the plate-like ratio of the hexagonal ferrite magnetic powder and the needle-like ratio of the ferromagnetic powder.
For example, if the plate ratio of hexagonal ferrite magnetic powder becomes too large, magnetic agglomeration becomes strong and the dispersibility of the magnetic paint deteriorates. It is important that the acicular ratio of the magnetic powder is 4 or less. Furthermore, considering not only the dispersibility but also the orientation of the magnetic paint, the plate-like ratio of hexagonal ferrite magnetic powder should be about 1 to 5, and the needle-like ratio of ferromagnetic powder should be about 1 to 4. is desirable.

Furthermore, when the plate ratio of the hexagonal ferrite magnetic powder is as described above, the hexagonal ferrite magnetic powder also acts as an abrasive, and the durability of the magnetic layer is improved. It will be good. That is, by keeping the plate ratio of the hexagonal ferrite magnetic powder as above,
This greatly extends the time it takes for methylation to occur.

Further, the hexagonal ferrite magnetic powder has a coercive force of 600 Oe or less, more preferably about 400 to 600 Oe, and the ferromagnetic powder has a saturation magnetization of 10,100 e/
From the viewpoint of erasing characteristics, it is desirable that the coercive force be 700 Oe or less, more preferably about 500 to 700 Oe.

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 550 Oe, saturation magnetization 57 emu)
/ g, average particle size 0.2 pm) 50 parts by weight, metallic iron magnetic powder (acicular ratio 3, coercive force 680 oersted, saturation magnetization 10105e/g, average particle size 0.2 pm) 50
Parts by weight, 25 parts by weight of binder, 1 part by weight of dispersant, 4 parts by weight of abrasive
A mixture of 5 parts by weight of carbon black, 1 part by weight of a lubricant, and 300 parts by weight of a solvent is thoroughly cross-dispersed to make a magnetic paint, and a hardening agent is added to this magnetic paint before being applied onto a non-magnetic substrate such as polyethylene terephthalate. The magnetic tape is coated, dried, calendered, and slit to a width of W inches to obtain a magnetic tape.

[Example 2] In Example 1, the plate ratio was 3, the coercive force was 550 Oe, the saturation magnetization was 57 emu/g, and the average grain size was 0.2 μm.
Also, using barium ferrite magnetic powder, the acicular ratio is 3,
Coercive force 600 oersted, saturation magnetization 10105e/g
A magnetic tape is obtained by carrying out the same procedure using metallic iron magnetic powder having an average particle size of 0.2 μm.

[Examples 3 to 5] In Example 1, the amounts of barium ferrite magnetic powder and metal iron magnetic powder were changed to 5 parts by weight and 95 parts by weight (Example 3,
30 parts by weight and 70 parts by weight (Example 4).

The same procedure was carried out using 70 parts by weight and 30 parts by weight (Example 5) to obtain a magnetic tape.

[Examples 6 to 9] In Examples 1, 3, and 4.5, instead of making a magnetic tape, a floppy disk was punched out with a diameter of 3.5 inches.

[Ratio/bite example 1] In Example 1, plate ratio 8, coercive force 550 Oe, saturation magnetization 57 emu/gs, average grain size 0.2 μ
The same procedure was carried out using m barium ferrite magnetic powder,
Get magnetic tape.

[Comparative Example 2] In Example 1, the plate ratio was 15, the coercive force was 550 Oe, the saturation magnetization was 57 emu/gs, and the average grain size was 0.2.
A magnetic tape is obtained in the same manner using μm barium ferrite magnetic powder.

[Comparative Example 3] The same procedure as in Example 1 was carried out except that 90 parts by weight of barium ferrite magnetic powder and 10 parts by weight of metal iron magnetic powder were used.
Get magnetic tape.

[Comparative Example 4] In Example 1, the acicular ratio was 3, the coercive force was 980 Oe, the saturation magnetization was 10105 e/g, and the average particle size was 0.2 p.
A magnetic tape is obtained in the same manner using m metal iron magnetic powder.

[Comparative Example 5] In Example 1, the acicular ratio was 3, the coercive force was 1200 Oe, the saturation magnetization was 10105 e/g, 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 6] In Comparative Example 8, a floppy disk was obtained by punching out a 3.5-inch diameter instead of a magnetic tape.

〔Characteristic〕

The relationship between the maximum magnetic flux density and the amount of barium ferrite magnetic powder in this magnetic chip ζ and the maximum magnetic flux density and the plate of barium ferrite magnetic powder when the dispersion time of the magnetic paint used to produce the magnetic tape on each side is 20 hours. The relationship with the shape ratio is as shown in FIGS. 1 and 2.

According to this, that is, according to FIG. 1, when the proportion of barium ferrite magnetic powder is up to about 50% by weight, the maximum magnetic flux density shows a tendency to increase, and as it exceeds about 50% by weight, it gradually reaches a maximum. The magnetic flux density shows a decreasing tendency,
Then, it rapidly decreases after reaching about 70% by weight.

In other words, barium ferrite magnetic powder is more likely to cause magnetic agglomeration than needle-shaped ferromagnetic powder. It is understood that it is important to keep the amount below % by weight.

Moreover, according to FIG. 2, it is understood that the plate ratio of the barium ferrite magnetic powder also has a great influence on the maximum magnetic flux density. That is, even if the amount of the barium ferrite magnetic powder is within the above-mentioned desirable range, if the plate ratio of the barium ferrite magnetic powder is too thick, the maximum magnetic flux density will sharply decrease, which is not preferable. And about 150
A maximum magnetic flux density of about 0 Gauss, that is, a high maximum magnetic flux density when the amount of barium ferrite magnetic powder is about 70% by weight or less is shown when the plate ratio of barium ferrite magnetic powder is about 5 or less. I understand. That is,
In order to obtain good dispersibility of the magnetic paint and improve its magnetic properties, the barium ferrite magnetic powder must not only be about 70% by weight or less, but also have a platelet ratio of about 5 or less.

In addition, after recording the color par signal on the magnetic tape on each side, the time required for the output to completely go down (still out) by playing back the still image is determined, and the plate ratio of the barium ferrite magnetic powder and the still time are calculated. When we examine the relationship between the two, we find that it is as shown in Fig. 3.

According to this, the plate ratio of barium ferrite magnetic powder is
It can be seen that it not only has a large effect on the magnetic properties but also has a large effect on the durability of the magnetic layer.

It can also be seen that when the platelet ratio of the barium ferrite magnetic powder is about 5 or less, the durability of the magnetic layer is also excellent.

Further, when the erasing characteristics of the magnetic tapes on each side are examined, the results are as shown in FIG.

According to this, the coercive force of barium ferrite magnetic powder is 6
00 oersted or less, coercive force of acicular ferromagnetic powder is 700
It can be seen that the erasing characteristics are good in the case of Oersted or less.

Further, when a 2 MHz signal is recorded on the floppy disk and reproduced, the reproduced output is examined as shown in FIG. 5.

According to this, since the reproduction output decreases as the amount of barium ferrite magnetic powder increases, it can be seen that the content of barium ferrite magnetic powder is desirably about 70% by weight or less.

〔effect〕

It is highly durable, has high output, and has good erasing characteristics.

In addition, a magnetic recording medium with good random orientation can be obtained and can be manufactured in a short time and with high productivity.

[Brief explanation of drawings]

1 to 5 are graphs showing the characteristics of magnetic recording media. Patent Applicant: Victor Company of Japan Co., Ltd.

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 100 emu/g or more, and a coercive force of 700 Oe or less are magnetic. The ferromagnetic powder 30 contained in the layer
A magnetic recording medium characterized in that the amount of the hexagonal ferrite magnetic powder is 70 parts by weight or less relative to 100 parts by weight.