JPH0785301B2 - Magnetic powder for magnetic recording and magnetic recording medium using the same - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to magnetic powder for magnetic recording and a magnetic recording medium using the magnetic powder.

[Technical background of the invention and its problems]

In recent years, there has been a demand for miniaturization, large capacity, and high quality of magnetic recording devices, but in order to achieve such technical problems, it is essential to improve the recording density of magnetic recording media.
Conventionally used coating media using acicular magnetic particles of γ-Fe ₂ O ₃ and CrO ₂ are approaching their limits for improving recording density. In order to further increase the recording density in the future, it is necessary to develop new magnetic recording media to replace them.

As a new magnetic recording medium, a magnetic recording medium coated with hexagonal ferrite has been considered. However, since coercive force (Hc) is usually too high for hexagonal ferrite to allow magnetic recording, it is necessary to replace some of the constituent atoms with specific atoms to reduce Hc. Become.

However, when the above replacement operation is performed, for example, Co
The -Ti substitution type Ba ferrite and the like had a drawback that the saturation magnetization (Vs) of the substitutional Ba ferrite was lowered as compared with that before substitution.

By the way, it is known that Vs is improved in the substitutional solid solution of Ba ferrite (for example, see Tohoku University Institute of Scientific and Instrument Research Vol. 18, No. 2-3, pp. 61-69, 1969). The Fe ³⁺ ions of BaFe ₁₂ O ₁₉ are converted into In ³⁺ , (Zn ²⁺ −Ge ⁴⁺ ),
(Zn ²⁺ −V ⁵⁺ ), (Zn ²⁺ −Nb ⁵⁺ ) or (Zn ²⁺ −T
The substitution solid solution obtained by substituting with a ⁵⁺ ) has higher Vs than before substitution. However, the improvement in Vs can be clearly observed under the temperature condition below room temperature, and Vs decreases as the temperature rises. Therefore, it is unsuitable to use these substituted solid solutions for magnetic powder for magnetic recording which requires high Vs at room temperature or high temperature.

Therefore, regarding hexagonal ferrite, it is strongly desired that Hc is controlled to an appropriate value and that Vs is high.

[Object of the Invention]

The present invention maintains an appropriate coercive force (Hc) and saturation magnetization (Vc
An object of the present invention is to provide a magnetic powder for magnetic recording having a high s) and a magnetic recording medium having improved electromagnetic conversion characteristics, particularly reproduction output, by using the magnetic powder.

[Outline of Invention]

First, the first invention is that the average particle diameter is 0.01 to 0.3 μm and the coercive force is 2
It consists of a hexagonal ferrite of 00 to 2000 Oe, and the hexagonal ferrite contains at least Fe, O, Co, 0.05 to 0.5 of Zn in the number of atoms per one chemical formula, and Ba as essential components. Is a magnetic powder for magnetic recording.

That is, in the ferrite of the above invention, Hc is controlled to an appropriate value by substituting with Co, and further by partially substituting with Zn, a high Vs that cannot be obtained only by Co substitution
Can be realized.

The reason for limiting the average particle size, the coercive force, and the substitution amount of Zn as described above is as follows. That is,
If the average particle size is less than 0.01 μm, it does not exhibit ferromagnetism,
If it exceeds 0.3 μm, a multi-domain structure is formed, which is not preferable. Further, when Hc is less than 200 Oe, it becomes difficult to hold the recording signal, and when it exceeds 2000 Oe, the head magnetic field causes a saturation phenomenon and recording becomes difficult. Regarding the substitution amount of Zn, when the amount is less than 0.05, the improvement of Vs is insufficient, and when it exceeds 0.5, Vs is rather decreased.

Examples of the hexagonal ferrite applicable to the present invention include M type (magnetoplumbite type) and W type.
_{It can be represented by α} Fe _{12- (X + Y + Z)} Co _X Zn _Y M _Z O _{18 + α-β} . A represents at least one element selected from the group consisting of Ba, Sr, Ca and Pb, X, Y and Z represent substitution amounts (atoms) per one chemical formula of Co, Zn and M ions, and α Is greater than 0 and 1
The following number, β, is the number of [X + Y + (3-m) Z] / 2, and m represents the valence of M ion. Considering the easiness of crystallization, the M type with α = 1 and β = 0 in the above formula is particularly preferable.

Next, the present invention will be described in more detail regarding the magnetoplumbite type ferrite.

The basic formula of magnetoplumbite ferrite is AFe ₁₂ O ₁₉
It is represented by. Here, A represents at least one element selected from the group consisting of Ba, Sr, Ca and Pb. The Fe ³⁺ ion of AFe ₁₂ O ₁₉ is replaced with Co ²⁺ and Zn ²⁺ , but it is necessary to perform valence compensation in order to replace the ions having different valences. As ions for valence compensation, Ti ⁴⁺ , Ge
⁴⁺ , Zr ⁴⁺ , Nb ⁵⁺ , Ta ⁵⁺ , V ⁵⁺ . In this case, Go-Z
n-substituted magnetoplumbite ferrite is AFe
It becomes _{12- (X + Y + Z)} Co _X Zn _Y M _Z O ₁₉ . Here, M represents a valence compensation ion, and X, Y, and Z represent substitution amounts (atoms) per one chemical formula of Co, Zn, and M ions. Here, if the valence of M ion is n, in order to compensate the valence, Must be met.

In the present invention, the substitution amount Y of Zn is set in the range of 0.05 to 0.5, and the substitution amount X of Co is Hc of 200 above.
It is determined to be in the range of up to 2000 Oe, and specifically, it is preferably in the range of 0.5 to 1.2. Further, Z is determined by the above formula (1).

As the method for producing the magnetic powder of the present invention, for example, an oxide of each element necessary to form the target hexagonal ferrite, a carbonate is melted with a glass-forming substance such as boric acid, The resulting melt is rapidly cooled to form a glass, which is then heat-treated at a predetermined temperature to precipitate the target barium ferrite crystal powder, and finally the glass component is removed by an acid bath to form a glass crystal. In addition to the chemical method, a coprecipitation-firing method, a hydrothermal synthesis method and the like can be applied.

The magnetic recording medium of the present invention using the magnetic powder of the second invention comprises a supporting base and a magnetic layer, and the magnetic layer is composed of the magnetic powder and a binder resin. Additives such as a dispersant, a lubricant, a curing agent and an abrasive may be added.

Examples of the binder resin include vinyl chloride-vinyl acetate copolymer, nitrocellulose, and polyurethane resin, examples of the dispersant include lecithin, and examples of the lubricant include higher fatty acid and fatty acid ester. Examples of the curing agent include bifunctional or higher functional isocyanate compounds, and examples of the polishing agent include Cr ₂ O ₃ , Al ₂ O ₃ , and α-Fe ₂ O ₃ .

On the other hand, as the supporting substrate, for example, a polyethylene terephthalate film, a polyamide resin film, a polyimide resin film or the like is used.

As a method for producing a magnetic recording medium, for example, magnetic powder, a binder resin, and an additive are kneaded together with a solvent to produce a magnetic coating material, and the magnetic coating material is applied to a supporting substrate and then subjected to orientation treatment / drying treatment, etc. The usual method of completing the magnetic recording medium by the method is applied.

Example of Invention

In the chemical formula AFe _{12- (X + Y + Z)} Co _X Zn _Y M _Z O ₁₉ , A = Ba, M = Nb
Or Ta, X = 0.7 and Y is 0.05, 0.20, 0.30, 0.50 and 4
8 kinds of Co-Zn-Ta substitution or Co
Ba Zn ferrite substituted with -Zn-Nb was prepared by the glass crystallization method.

First, to B ₂ O ₃ · BaO glass, at the same time, BaO, Fe ₂ O ₃ , CoO, ZnO, Nb ₂ O ₅ or Ta ₂ O ₅ prepared to constitute the above Ba ferrite composition was added at 1350 ° C. The glass containing the above components was prepared by melting and rolling and quenching.

Next, this glass was heated at 850 ° C. for 4 hours to precipitate Ba ferrite substituted with Co, Zn, Nb or Ta in the matrix. Finally, it was washed with acetic acid to obtain Co, Zn, Nb or Ta-substituted Ba ferrite magnetic powder.

The average particle size of the obtained magnetic powder is 0.06 to 0.07 μm
Met. The measurement results of Hc and Vs are shown in Tables 1 and 2 (Examples 1 to 4 and 5 to 8).

As a comparative example, a Co—Nb, Co—Ta-substituted Ba ferrite BaFe _{12- (X + Z)} Co _X M _Z O ₁₉ (M = Nb or
In Ta), Hc and σs of the samples produced by setting X and Z are also shown in Tables 1 and 2 so that the coercive force is almost equal to that of the example. (Comparative Examples 1 to 4 and 5 to 8) As is clear from the above results, the substitution amount Y of Zn is 0.05 to
Magnetic powder of the present invention controlled in the range of 0.5 (Examples 1 to 8)
In, it is understood that a higher σs is obtained than the magnetic powder having the same coercive force and not containing Zn (Comparative Examples 1 to 8).

Next, among the magnetic powders obtained as described above, the following four types of BaFe _10,5 Co _0,7 Zn _0,3 Nb _0,5 O ₁₉ ... Example 9 BaFe _10,5 Co _0.7 Zn _0,2 Ta _0,45 O ₁₉ …… Example 10 BaFe _10.72 Co _0.85 Nb _0.43 O ₁₉ …… Comparative Example 9 BaFe _10.72 Co _0.85 Ta _0.43 O ₁₉ …… Using Comparative Example 10, a magnetic recording medium was _prepared by a conventional method. Was produced.

The components and blending amount of the magnetic paint that constitutes the magnetic layer It was prepared as shown in Table 3 and kneaded with a sand grinder to obtain a magnetic coating material.

The obtained magnetic coating was applied to the surface of a polyethylene terephthalate film, and the film was subjected to an alignment treatment in a vertical alignment magnetic field of 4000 Oe and then dried to prepare a magnetic recording medium.

The reproduction output of these magnetic recording media at a recording wavelength of 0.95 μm was measured using a ring type ferrite head (gap width 0.2 μm, track width 35 μm, winding number 18 turns), and the results are shown in Table 3.

〔The invention's effect〕

As described above, as is apparent from the examples of the invention, the magnetic powder of the present invention has improved saturation magnetization in a state of having an appropriate coercive force, and therefore, the magnetic recording medium using the magnetic powder of the present invention. , A high reproduction output is obtained, and its industrial value is great.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadashi Izu 1 Komukai Toshiba-cho, Kouki-ku, Kawasaki City, Kanagawa Prefecture, Toshiba Corporation Research Institute (56) Reference JP-A-57-212623 (JP, A) JP Sho 59-151339 (JP, A)

Claims (3)

[Claims] 1. An average particle diameter of 0.01 to 0.3 μm and a coercive force of 200 to 20.
A hexagonal ferrite of 00 Oe, characterized in that the hexagonal ferrite contains at least Fe, O, Co, 0.05 to 0.5 in terms of the number of atoms per chemical formula, and Zn and Ba as essential constituent components. And magnetic powder for magnetic recording. 2. The magnetic powder for magnetic recording according to claim 1, wherein the hexagonal ferrite is a magnetoplumbite type ferrite. 3. A magnetic recording medium comprising a supporting base and a magnetic layer provided on the supporting base, wherein the magnetic powder in the magnetic layer is a hexagonal crystal having an average particle size of 0.01 to 0.3 μm and a coercive force of 200 to 2000 Oe. A magnetic recording comprising a system ferrite, wherein the hexagonal ferrite contains at least Fe, O, Co, 0.05 to 0.5 in terms of the number of atoms per chemical formula, and Ba as essential constituent components. Medium for use.