JPS6194226A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the Y-S/N, C-S/N, reproduction output and traveling performance by forming a magnetic layer contg. magnetic powder and magnetic powder of hexagonal ferrite having <=600Oe coercive force, >=5 aspect ratio and a regulated particle size in a specified mixing ratio. CONSTITUTION:A magnetic layer contg. 100pts.wt. magnetic powder having >=70emu/g saturation magnetization and <=5pts.wt. magnetic powder of hexagonal ferrite having an axis of easy magnetization in the direction of the c-axis, <=600Oe coercive force, >=5 aspect ratio and 0.2-0.5mum particle size is formed. The resulting magnetic recording medium can attain high reproduction output when a ringlike magnetic head of ferrite is used, and the medium is suitable for high density recording. The reproduction output of a magnetic recording medium in a high frequency region is improved by using a small amount of magnetic powder of hexagonal ferrite mixed with a large amount of needlelike ferromagnetic powder, and the medium can be adapted to high density recording. The reproduction output in a low frequency region is improved by the horizontal magnetizable component of the needlelike ferromagnetic powder. The medium has improved Y-S/N, C-S/N, reproduction output, traveling performance, still characteristics and resistance to repeated reproduction.

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-pe2oz magnetic powder on a non-magnetic substrate, and then oriented the magnetization in the in-plane longitudinal direction by an orientation treatment such as mechanical orientation or magnetic field orientation. The main type is horizontal magnetic recording.

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.
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 the configuration is as follows, the dispersibility of the magnetic coating material will be improved, and thus a magnetic recording medium with good magnetic properties will 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 magnetic recording media that can obtain large playback output using ring-shaped ferrite magnetic heads that are currently incorporated in recording and playback devices, and can also handle high-density recording. , saturation magnetization 70 e
Hexagonal crystal system with magnetic powder of mu / g or more, easy axis of magnetization in the C-axis direction, coercive force of 600 oersted or less, plate ratio of 5 or more, and particle size of 0.2 to 0.5 μm. A magnetic recording medium that includes ferrite magnetic powder in a magnetic layer and has a ratio of 5 parts by weight or less of the hexagonal ferrite magnetic powder to 100 parts by weight of the magnetic powder has a large reproduction output with a ring-type ferrite magnetic head. It has been found that this method is suitable for high-density recording.

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, increasing the reproduction output in the high frequency range. In addition, since the horizontal magnetization component of the acicular ferromagnetic powder can be effectively used, the reproduction output in the low frequency region is improved.

In order to be able to perform recording and reproduction with good running performance, still characteristics, recording density, and S/N, especially in the high frequency range,
For example, the average particle diameter of hexagonal ferrite magnetic 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 about 0.
It is desirable that the thickness be 2 to 0.5 μm.

In addition, in terms of C/N improvement in the high frequency range, the coercive force of the hexagonal ferrite magnetic powder is approximately 600 oersted or less,
More preferably, it is about 400 to 600 oersted.

In addition, in order to improve the C/N in the high frequency range, it is necessary that the hexagonal ferrite magnetic powder not only has a coercive force of about 600 oersted or less, but also a plate ratio of about 5 or more. More preferably, the platelet ratio is about 5 to 12.

In addition, the content ratio of hexagonal ferrite magnetic powder is also an extremely important factor for improving C/N in the high frequency range.
Since the C/N tends to decrease as the amount of hexagonal ferrite magnetic powder increases, the hexagonal ferrite magnetic powder should be about 5 parts by weight or less per 100 parts by weight of the acicular ferromagnetic powder.
Even more preferably, the amount is about 0.1 parts by weight or more and less than 5 parts by weight.

Examples of magnetic powders with a saturation magnetization of about 708 mu/g or more include 7-Ft, Oz, Co-coated 7-Peso,
, Fe504, CrCh, Fe6, or alloy powders are needle-shaped (acicularity ratio is preferably about 5 to 15) ferromagnetic powders, and the saturation magnetization of such magnetic powders is about 70 emu/g.
Otherwise, the reproduction output in the low frequency region will decrease.

[Example 1] Hexagonal barium ferrite magnetic powder (saturation magnetization Ms approximately 5
4emu/g, Homori force Hc about 5500e, average particle size 0
．． 4 μm, plate-like specific 7) 1 to 5 parts by weight, Co-containing r-F
Ezes magnetic powder (Ms approx. 75 emu/g, He approx. 6000e, average particle size 0.2 μm, needle-like ratio 10)
100 parts by weight, vinyl chloride-vinyl acetate copolymer 25
A mixture of 10 parts by weight of nitrocellulose, 8 parts by weight of carbon black, 1 part by weight of oleic acid-modified amine, 1.5 parts by weight of oleic acid, 160 parts by weight of toluene, and 160 parts by weight of methyl ethyl ketone was mixed and dispersed in a sand mill for a predetermined time. to make magnetic paint.

Then, 15 parts by weight of polyisocyanate (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) was added to this magnetic paint, and this was applied to the base film, dried, calendered, and then slit to a width of 100 inches to form a video magnetic tape. Also, a floppy disk was constructed by punching it out to a predetermined diameter.

[Example 2] 1 to 5 parts by weight of the hexagonal barium ferrite magnetic powder,
CrOz magnetic powder (Ms approx. 70 emu/g, Hc approx. 6
300e, average particle size 0.2μm, needle-like ratio 10) 1
00 parts by weight, 30 parts by weight of vinyl chloride-vinyl acetate copolymer, 5 parts by weight of polybutyl acrylate, 8 parts by weight of carbon black, 1 part by weight of oleic acid-modified amine, 2 parts by weight of oleic acid, 200 parts by weight of butyl acetate, A magnetic paint was prepared by mixing and dispersing a mixture of 100 parts by weight of methyl in butyl ketone for a predetermined period of time, and polyincyanate was added thereto in the same manner as in Example 1, and a video magnetic tape and a floppy disk were constructed in the same manner.

[Example 3] 1 to 5 parts by weight of the hexagonal barium ferrite magnetic powder,
Fe-Co-Ni alloy magnetic powder (Ms approx. 125 emu/g
, Hc about 6100e, average particle size 0.2 μm, needle shape 10) 100 parts by weight, vinyl chloride-vinyl acetate copolymer 10 parts by weight, polyurethane resin 20 parts by weight, oleic acid modified amine 1 part by weight, silicone A magnetic paint was prepared by mixing and dispersing a mixture of 0.5 parts by weight of resin, 165 parts by weight of methyl ethyl ketone, and 165 parts by weight of methyl imbutyl ketone for a predetermined period of time. Polyisocyanate was added to this in the same manner as in Example 1, and the same procedure was carried out. Video magnetic tapes and floppy disks were constructed using this technology.

[Example 4] In Example 1, Ms about 54 emu/g, Hc 5
A magnetic tape and a floppy disk were constructed in the same manner using hexagonal barium ferrite magnetic powder having a particle size of 50 to 5600e, an average particle size of 0.2 to 0.5 μm, and a platelet ratio of about 7.

[Example 5] In Example 1, Ms about 54 emu/g, He about 550 to 5600e, average particle size 0.4 μm, plate ratio 5
The same procedure was carried out using ~15 hexagonal barium ferrite magnetic powders to construct magnetic tapes and floppy disks.

[Example 6] In Example 1, Ms about 54 emu/g, He about 5
50-6000e, average particle size 0.4μm, plate ratio approximately 7
The same procedure was carried out using hexagonal barium ferrite magnetic powder to construct magnetic tapes and floppy disks.

[Example 7] The same procedure as in Example 1 was carried out using hexagonal substituted barium ferrite magnetic powder having Ms approximately 54 emu/g, Hc approximately 5600e, average particle diameter 0.4 μm, and plate ratio approximately 7. , magnetic tape and floppy disk.

[Comparative Examples 1 to 3] In Examples 1 to 3, the hexagonal barium ferrite magnetic powder was changed to zero, and the other conditions were the same, and 1. composed the Sufu.

[Comparative Examples 4 to 5] In Example 4, Ms about 54 emu/g, Hc about 5
50-5600e, average particle size 0.1μm or 0.7μm
A video magnetic tape and a floppy disk were constructed in the same manner using 3 parts by weight of hexagonal barium ferrite magnetic powder having a plate ratio of about 7.

[Comparative Example 6] In Example 5, Ms about 54 emu/g, Hc
A video magnetic tape and a floppy disk were constructed in the same manner using 3 parts by weight of hexagonal barium ferrite magnetic powder having a diameter of about 550 to 5600 e, an average particle diameter of 0.4 μm, and a platelet ratio of 3.

[Comparative Examples 7 to 8] In Example 6, 3 parts by weight of hexagonal barium ferrite magnetic powder having an Ms of about 54 emu/g, a Hc of about 7000e or 7600e, and an average particle size of 0.4 μm and a plate ratio of about 7 was used. A video magnetic tape and a floppy disk were constructed in the same manner.

[Comparative Example 9] In Example 1, Ms about 54 emu/g, HC
A video magnetic tape and a floppy disk were constructed in the same manner using 1 to 10 parts by weight of hexagonal barium ferrite magnetic powder having a diameter of about 5,500 e, an average particle diameter of 0.4 μm, and a platelet ratio of about 3.

[Comparative Example 10] The same procedure as in Example 1 was carried out using 10 parts by weight of hexagonal barium ferrite magnetic powder to construct a video magnetic tape and a floppy disk.

[Comparative Example 11] The same procedure as in Example 7 was carried out using 10 parts by weight of the hexagonal substituted barium ferrite magnetic powder to construct a video magnetic tape and a floppy disk.

〔Characteristic〕

The Y-8/N and C-8/N of the magnetic tape obtained as described above (in the example, the amount of hexagonal ferrite magnetic powder added was 3 parts by weight) was as shown in the table. Reeds, frequency characteristics and input/output characteristics (4MH
When z) was measured, the results were as shown in FIGS. 1 and 2.

Table According to this table, magnetic properties such as Y-8/N and C-S/N can be improved by using a small amount of hexagonal ferrite magnetic powder, and this effect is especially noticeable in the 3x mode. As can be seen from Figure 1, the reproduction output is high, and the reproduction output improvement effect is particularly remarkable in the high frequency region.Also, as can be seen from Figure 2, as the recording voltage increases, the hexagonal ferrite magnetism The effect of adding powder appears.

In addition, the plate ratio of hexagonal ferrite magnetic powder and 4.5MHz
C/ of IMHz near the carrier when recording and reproducing the signal of
The relationship with N is as shown in FIG. In other words, when measuring the C/N of the magnetic tapes of Example 5 and Comparative Example 6, the C/N in the high frequency region is as shown in FIG. When the C/N ratio becomes too large, the C/N improving effect begins to decrease, and when the longitudinal direction is oriented, agglomeration of particles is observed.
Preferably.

Further, the relationship between the average particle size of the hexagonal ferrite magnetic powder and the coefficient of dynamic friction is shown in FIG. 4 when the coefficients of dynamic friction of the magnetic tapes of Example 4 and Comparative Examples 4 and 5 are measured.

According to this, it can be seen that the larger the average particle diameter of the hexagonal ferrite magnetic powder is, the more effective it is in terms of runnability.

-Also, when we measured the still characteristics (time until still out when paused and played back at -5°C), we found that the average particle size of the hexagonal ferrite magnetic powder was larger, as shown in Figure 5. It can be seen that this is desirable.

Furthermore, as shown in Figure 6, when we examine how repeated regenerative demagnetization is affected by the average particle size of hexagonal ferrite magnetic powder, we find that a larger average particle size is desirable. Recognize.

However, as the average particle size of hexagonal ferrite magnetic powder increases, it becomes undesirable in terms of recording density, and the degree of improvement in the above characteristics also decreases. A thickness of .2 to 0.5 μm is desirable.

Furthermore, the relationship between the IMHz C/N near the carrier and the coercive force of hexagonal ferrite magnetic powder when recording and reproducing a 4 MHz signal using a ring-type ferrite head is shown in Figure 7. . Tsumashi, Example 6 and Comparative Examples 7 and 8
Figure 7 shows that the C/N tends to decrease as the coercive force increases, and therefore the coercive force of the macrogonal ferrite magnetic powder is approximately A value of 600 Oersted or less is desirable.

Furthermore, when we examine the relationship between the 2F output of the floppy disk and the amount of hexagonal ferrite magnetic powder, that is, when we examine the 2F output of Example 1 and Comparative Examples 1 and 9.10, we find the normal cycle shown in Figure 8. According to this, it is desirable that the plate ratio of the hexagonal ferrite magnetic powder is about 5 or more, and the content ratio is about 5 parts by weight or less per 100 parts by weight of the acicular ferromagnetic powder. I understand that. “ Also, for the magnetic tapes of Example 1 and Comparative Examples 1 and 10, the C near the carrier when a 4 MHz signal was recorded and reproduced.
/N was measured as shown in Figure 9, and from this it is also desirable that the content of hexagonal ferrite magnetic powder is about 5 parts by weight or less per 100 parts by weight of acicular ferromagnetic powder. Recognize.

Furthermore, a similar tendency exists in the case of hexagonal substitution type barium ferrite magnetic powder, that is, when measuring the C/N of the magnetic tapes of Example 7 and Comparative Example 11, the C/N is 10th.
The results shown in the figure indicate that it is preferable to use less than about 5 parts by weight.

〔effect〕

It is excellent in Y-8/N, C-8/N, reproduction output, running performance, still characteristics, repeated reproduction demagnetization, etc., and is also compatible with high-density recording.

[Brief explanation of drawings]

1 to 10 are explanatory diagrams of characteristics of magnetic recording media. T! Surrounding cap J [IIL (Mfb) T 2nd Takahiro FL (V)

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 less, 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.