JPS6194227A - 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 <=0.2mum 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 horizontally magnetizable component of the needlelike ferromagnetic powder. The medium has improved Y-S/N, C-S/N can C/N.

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, as magnetic recording media, acicular γ-F·e, 0. 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.
A magnetic recording medium is proposed in which 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 is dispersed in a resin binder. No. 1983-203625).

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 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 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 70em
Magnetic powder of u/g or more, ring metal that is easily magnetized in the C-axis direction, coercive force of 600 Oe or more, and plate ratio of 5.
In the above, a hexagonal ferrite magnetic powder having a particle size of 0.2 μm or less is included in the magnetic layer, and the magnetic powder 100 is
A magnetic recording medium containing the hexagonal ferrite magnetic powder in a ratio of 5 parts by weight or less to parts by weight is capable of obtaining a large reproduction output with a ring-type ferrite magnetic head1), and is also suitable for high-density recording. I found it to be suitable.

In other words, 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, improving the reproduction output in the high frequency range. However, since it is compatible with high-density recording, and 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 improve the playback output, especially in the high frequency range, we are using vertical 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. It is necessary to strengthen the magnetization component, and it is desirable that the coercive force of such a hexagonal ferrite magnetic powder is about 600 Oe or more, more preferably about 600 to 1000 Oe.

Further, in order to improve the C/N in the high frequency range, it is necessary that the plate ratio of the hexagonal ferrite magnetic powder is about 5 or more, and more preferably the plate ratio is about 5 to 12. It is desirable that the

In addition, the content of the orthogonal ferrite magnetic powder is an extremely important factor in terms of C/N improvement in the high frequency range. Crystalline ferrite magnetic powder is acicular magnetic powder 10
Desirably, the amount is about 5 parts by weight or less, more preferably about 0.1 parts by weight or more and less than 5 parts by weight relative to 0 parts by weight.

In addition, the particle size of the hexagonal ferrite magnetic powder is also greatly involved in improving the C/N in the high frequency range, and when the average particle size of the hexagonal ferrite magnetic powder exceeds 0.2 μm, the C/N increases. Therefore, it is desirable that the average particle size of the hexagonal ferrite magnetic powder is about 0.2 μm or less, more preferably about 0.05 μm or more and less than 0.2 μm.

Examples of magnetic powders with a saturation magnetization of about 70 emu/g or more include r-Few 03, Co-coated r-Fe
! 03, Fe, 04. Acicular (acicularity ratio is preferably about 5 to 15) ferromagnetic powder such as Crux, Fe 6 or alloy powder, the saturation magnetization of such magnetic powder is about 70
If it is not more than emu/g, the reproduction output in the low frequency region will decrease.

[Examples 1 to 10] 5 parts by weight or less of hexagonal barium ferrite magnetic powder shown in Table 1 below, CO-containing -Fe2Om magnetic powder (saturation magnetization Ms about 75 emu/g, coercive force Hc about 6000e, average particle size 0.2 μm, needle-like ratio 10) 100 parts by weight, 25 parts by weight of vinyl chloride-vinyl acetate copolymer, 10 parts by weight of nitrocellulose, 8 parts by weight of carbon black, 1 part by weight of oleic acid-modified amine, 1.0 parts by weight of oleic acid. A magnetic paint is prepared by mixing and dispersing a mixture of 5 parts by weight, 160 parts by weight of toluene, and 160 parts by weight of methyl ethyl ketone in a sand mill for a predetermined period of time.

15 parts by weight of polyincyanate (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) is added to this magnetic paint, and this is applied to a base film, which is then dried, calendered, and slit to form a video magnetic tape. Configured a floppy disk.

Table 1 [Example 11] Hexagonal barium ferrite magnetic powder (Ms approximately 54 emu
/g, He about 7000e, average particle size 0.1 μm, plate ratio about 7) 3 parts by weight, CrO, magnetic powder (Ms about 70e
mu/g, He about 6300e, average particle size 0.2/Am
, needle-like ratio 10) 10 parts by weight, 30 parts by weight of vinyl chloride-vinyl acetate copolymer, 5 parts by weight of butyl polyacrylate, 8 parts by weight of carbon black, 1 part by weight of oleic acid-modified amine, 2 parts by weight of oleic acid. A magnetic paint was prepared using 200 parts by weight of butyl acetate and 100 parts by weight of methyl isobutyl ketone, and a video magnetic tape and a floppy disk were constructed in the same manner as in Example 1.

[Example 12] 3 parts by weight of the hexagonal barium ferrite magnetic powder of Example 11, Fe-Co-Ni alloy magnetic powder (Ms approx. 125
emu/g, He about 7500e, average particle size 0.2μ
m, acicular ratio 10) 100 parts by weight, 10 parts by weight of vinyl chloride-vinyl acetate copolymer, 20 parts by weight of polyurethane resin, 1 part by weight of oleyl/acid-modified amine, 0.5 part by weight of silicone resin, 165 parts by weight of methyl ethyl ketone A magnetic paint was prepared using 165 parts by weight of methyl in butyl ketone, and a video magnetic tape and a floppy disk were constructed in the same manner as in Example 1.

[Example 13] In Example 1, Ms about 54 emu/g, Hc about 7
A video magnetic tape and a floppy disk were constructed in the same manner using 1 to 5 parts by weight of hexagonal substituted barium ferrite magnetic powder having a particle size of 10 Oe, an average particle size of 0.1 μm, and a platelet ratio of about 7.

[Comparative Examples 1 to 3] The same procedures as in Examples 1, 11, and 12 were carried out without using the hexagonal barium ferrite magnetic powder to construct video magnetic tapes and floppy disks.

[Comparative Example 4] In Example 1, Ms about 54 emu/g, H
The same procedure was carried out using 1 to 10 parts by weight of hexagonal barium ferrite magnetic powder having an e of about 7000 e, an average particle size of 0.1 μm, and a platelet ratio of about 3, to construct a video magnetic tape and a floppy disk.

[Comparative Examples 5 and 6] The same procedure as in Examples 2 and 13 was carried out using 10 parts by weight of the hexagonal ferrite magnetic powder to construct a video magnetic tape and a floppy disk.

[Comparative Example 7] In Example 1, Ms about 54 emu/g, He about 7
A video magnetic tape and a floppy disk were constructed in the same manner using hexagonal barium ferrite magnetic powder having an average particle size of 0.3 μm and a platelet ratio of about 7.

[Comparative Example 8] The same procedure as in Example 1 was carried out using hexagonal barium ferrite magnetic powder having an Ms of about 54 emu/g, a He of about 5500 e, an average particle size of 0.1 μm, and a plate ratio of about 7. magnetic tape and floppy disk.

〔Characteristic〕

Regarding the magnetic tape obtained as above, its Y
-8/N and C-8/N were measured to be 6D as shown in Table 2, and frequency characteristics and input/output characteristics (4 MHz) were measured as shown in FIGS. 1 and 2.

Table 2 According to this table, the magnetic properties such as pY-8/N and C-8/N are improved by using a small amount of hexagonal ferrite magnetic powder, and this effect is particularly 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 range.Also, as can be seen from Figure 2, when the recording voltage is high, the hexagonal ferrite magnetic powder The effect of the addition appears.

In addition, the plate ratio of hexagonal ferrite magnetic powder and 4.5MHz
C/ of 1MHz near the carrier when recording and reproducing the signal of
The relationship with N is as shown in FIG. When the C/N of the magnetic tapes of Examples 1 to 4 and Comparative Example 4 was measured, it was as shown in Fig. 3. When the plate ratio of the hexagonal ferrite magnetic powder was greater than 5, the C/N was in the high frequency region. C/ in
An improvement in N was observed, and if it was too large, C/N
The improvement effect also began to decline, and as particles agglomerated when oriented in the longitudinal direction, the plate ratio was approximately 5 to 5.
12 is desirable.

Furthermore, when the relationship between the average particle diameter of hexagonal ferrite magnetic powder and the C/N, that is, the C/N of the magnetic tapes of Examples 2, 5.6 and Comparative Example 7, was measured, the results were as shown in Figure 4. It is shi.

According to this, when the average particle size of the hexagonal ferrite magnetic powder becomes larger than 0.2 μm, the C/N decreases significantly, so the average particle size of the hexagonal ferrite magnetic powder is about 0.
．． It is desirable that the thickness be as small as 2 μm.

Also, 4.5 MHz using a ring ferrite head
, 5 MHz, and 6 MHz signals are recorded and reproduced, and the relationship between the C/N of IMHz near the carrier and the coercive force of the hexagonal ferrite magnetic powder is shown in FIG. 5. In other words, when measuring the C/N of the magnetic tapes of Examples 2, 7.8 and Comparative Example 8, it is as shown in Figure 5. According to this, when signals in the high frequency region are used for recording, the Hc It can be seen that a larger coercive force is preferable, that is, it is preferable from the viewpoint of high-density recording that the coercive force of the hexagonal ferrite magnetic powder is about 600 oersted or more.

Moreover, when the relationship between the 2F output of the floppy disk and the amount of hexagonal ferrite magnetic powder was investigated, that is, Examples 2 and 9.
Examining the 2F output of Comparative Examples 1 and 4.5, it is shown in Figure 6.1) According to this, the plate ratio of the hexagonal ferrite magnetic powder is about 5 or more, It can be seen that the content is desirably about 5 parts by weight or less per 100 parts by weight (11 parts) of the acicular ferromagnetic powder.

Furthermore, for the magnetic tapes of Examples 2, 9, and 10 and Comparative Example 5, when a 4 MHz signal was recorded and reproduced, the C/N of IMHz near the carrier was measured as shown in FIG. 7.
This also shows that the content of the hexagonal ferrite magnetic powder is desirably about 5 parts by weight or less per 100 parts by weight of the acicular magnetic powder.

In addition, a similar tendency is observed in the case of hexagonal substitution type barium ferrite magnetic powder. When C/N was measured for the magnetic tapes of Example 13 and Comparative Example 6, the C/N ratio was as shown in Fig. 8. However, it can be seen that it is desirable to use less than about 5 parts by weight.

〔effect〕

Y-8/N, C-8/N, C/N, excellent reproduction output, and compatible with high-density recording.

[Brief explanation of the drawing]

1 to 8 are explanatory diagrams of characteristics of magnetic recording media. i″ 1st 74th For 75 fJ(0s 6EI Barish la7g Kunoto λ4 raw #t (ttJ) off eye

Claims (1)

[Claims] A hexagonal ferrite having a 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 more, a plate ratio of 5 or more, and a particle size of 0.2 μm or less. 1. A magnetic recording medium comprising a magnetic powder in a magnetic layer, wherein the hexagonal ferrite magnetic powder is contained in a ratio of 5 parts by weight or less to 100 parts by weight of the magnetic powder.