JP2956841B2 - Magnetic powder for magnetic recording - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a magnetic powder for magnetic recording particularly suitable for high-density magnetic recording. (Prior Art) A coating type magnetic recording medium is composed of a non-magnetic support such as polyethylene terephthalate and a magnetic layer provided on the support and mainly composed of a magnetic powder and a resin binder. . As magnetic powder, conventionally, γ-Fe ₂ O ₃ , CrO ₂ , Co-γF
Acicular magnetic powders such as e ₂ O ₃ are widely used. Recently, there has been a strong demand for a magnetic recording medium capable of perpendicular magnetic recording in order to greatly improve the magnetic recording density, and ultrafine magnetic powder of hexagonal ferrite has been used as a suitable magnetic recording medium. Have been studied, and it has been found that high-density recording is possible. (Problems to be Solved by the Invention) However, hexagonal ferrite itself usually has too high a coercive force (Hc) to perform magnetic recording. It is necessary to reduce the magnetic force (Hc). However, when such a replacement operation is performed, for example, the saturation magnetization (σ _S ) of the Co—Ti substitution type Ba ferrite or the like becomes lower than that before the substitution. It had the drawback of lowering. By the way, it is known that the saturation magnetization (σ _s ) of the substituted solid solution of Ba ferrite is improved as compared with the non-substituted solid solution.
No. 2-3, Showa 44, pp. 61-69). That is,
Ba ferrite (BaFe ₁₂ O ₁₉ ) Fe ³⁺ ion is ^converted to In ³⁺ , (Zn
^{2 +} -Ge ⁴⁺ ), (Zn ²⁺ -Nb ⁵⁺ ) or (Zn ²⁺ -Ta ⁵⁺ ), the substitutional solid solution obtained has a higher saturation magnetization (σ _S ) than before substitution. I have. However, in such a substituted solid solution, the improvement in saturation magnetization (σ _S ) can be clearly observed under a temperature condition of room temperature or lower, and the saturation magnetization (σ _S ) decreases as the temperature increases. Therefore, it has been inappropriate to use these substituted solid solutions as magnetic powders for magnetic recording requiring high saturation magnetization (σ _S ) at room temperature or high temperature. The present invention has been made to solve such a conventional problem, and the saturation magnetization (σ _S ) of the hexagonal ferrite and the coercivity (Hc) of the hexagonal ferrite have been improved so as to be in a range suitable for magnetic recording. It is an object of the present invention to provide a reduced magnetic recording magnetic powder. [Configuration of the Invention (Means for solving the problems) for magnetic recording magnetic powder of the present invention have the general _{formula: AO · Fe 2N-2X Co} X (D 1-Y Zn Y) X O 3N-α ( In the formula, A represents Ba, Sr, Pb or Ca, D represents one or more selected from Ti and Ge, N = 5.5 to 10.0, 0.6 ≦ X ≦
1.3, 0 <Y ≦ 0.75, 0 <α <1) It is characterized by comprising a hexagonal ferrite magnetic powder represented by the following formula. The hexagonal ferrite used in the present invention includes, for example, M-type (Magnetoplumbite type), W-type hexagonal Ba,
Ferrite, Sr ferrite, Pb ferrite, Ca ferrite or a solid solution thereof, or an ion-substituted product is included. In the present invention, the substitution amount of N, X, Y such as Zn, Ti, Ge, etc.
Is limited as described above for the following reason. That is, when N takes a value of 6, a perfect hexagonal ferrite is formed, but in a practical use, a hexagonal ferrite powder having desired properties sufficiently in the range of 5.5 to 10.0 is obtained. If X is less than 0.6, the coercive force of the obtained hexagonal ferrite powder exceeds 2,000 Oe, the head magnetic field saturates, and magnetic recording becomes difficult, and conversely,
The coercive force of the obtained hexagonal ferrite exceeding 1.3
This is because it becomes less than 00 Oe and it becomes difficult for a magnetic recording medium using this to hold a recording signal. The magnetic powder having a higher saturation magnetization (σ _s ) can be obtained as the value of Y indicating the amount of Zn substitution increases. Therefore, 0
It is desirable that the value of Y is large in the range of <Y ≦ 0.75, preferably 0.1 <Y ≦ 0.6. In the magnetic powder of the present invention, the average particle size of the hexagonal ferrite crystal is desirably in the range of 0.02 to 0.2 μm. If it is less than 0.02 μm, the magnetization and coercive force decrease, and the reproduction output of the magnetic recording medium decreases.
Is exceeded, a multi-domain structure is formed and noise during reproduction becomes remarkable during high-density recording. For the reasons described above, the coercive force of the hexagonal ferrite powder of the present invention is desirably in the range of 200 to 2000 Oe. As a method for producing the magnetic powder of the present invention, for example, an oxide of each element necessary to form a desired hexagonal ferrite, a carbonate is melted together with a glass-forming substance such as boric acid to obtain The obtained melt is quenched to form a glass, and then the glass is heat-treated at a predetermined temperature to precipitate a desired ferrite crystal powder, and finally, a glass crystallization method of removing a glass component by an acid treatment. , A coprecipitation-firing method, a hydrothermal method and the like can be applied, and among them, a glass crystallization method is particularly preferable. The hexagonal ferrite magnetic powder of the present invention is usually applied to a support surface together with a binder resin and used as a magnetic recording medium. Examples of the binder resin constituting the magnetic layer together with the magnetic fine particles include vinyl chloride-vinyl acetate copolymer, vinylidene chloride-based copolymer, acrylate-based copolymer, polyvinyl butyral-based resin, polyurethane-based resin, and polyester-based resin. A resin, a cellulose derivative, an epoxy resin, or a mixture of two or more thereof is used. Further, in addition to the magnetic powder and the binder resin, additives such as a dispersant, a lubricant, an abrasive, and an antistatic agent can be appropriately contained in the magnetic layer as needed. (Operation) The magnetic powder of the present invention has a coercive force and high saturation magnetization suitable as magnetic powder for magnetic recording since a part of Fe atoms constituting ferrite is replaced by Co and Zn. (Example) Next, an example of the present invention will be described. Examples 1 to 4 and Comparative Examples 1, 5, 6 Formula: in ferrite represented by _{AO · Fe 12-2X Co X (Ti} 1-Y Zn Y) X O 3N-α, and A and Ba, X = Three types (Example 1, Example 2, Comparative Example 1) with Y = 0.10, 0.50, and 1.0 as 1.0, and X = 0.60 and 1.30 with Y = 0.5
And Co-Ti-Zn-substituted and Co-Zn-substituted Ba ferrites having the chemical formula: AO.Fe
_12-2X Co _X (Ti / Sn _1-Y Zn _Y ) _X O In a ferrite represented by _18-α , A is Ba, x = 0.95, Y = 0.50,
Two types of Co-T (Comparative Examples 5 and 6) with Ti / Sn = 0.5 and 0.2
i-Sn-Zn-substituted Ba ferrite was prepared by a glass crystallization method. Among the above magnetic powders, the Co-Ti-Zn-substituted Ba ferrite magnetic powder of the example was produced as follows. First B ₂ O ₃ · BaO glass formulated to constitute the Ba ferrite composition BaO, in addition Fe ₂ O _3, CoO, and TiO _2, ZnO simultaneously, melted at 1350 ° C., and rolled quenched A glass containing the above components was produced. Next, this glass was heated at 800 ° C. for 4 hours to precipitate Co—Ti—Zn-substituted Ba ferrite in the matrix. Finally, the glass was washed with acetic acid to remove Co-Ti-
A Zn-substituted Ba ferrite magnetic powder was obtained. The saturation magnetization (σ _S ) of each of the obtained magnetic powders is 59 to 65.
emu / g. The average particle size was as fine as about 800 mm. The coercive force (Hc), saturation magnetization (σ
Table 1 shows the values of _s ). Comparative Examples 2, 3, 4, 7, and 8 Ba ferrites prepared by setting X such that Co-Ti-substituted and Co-Ti-Sn-substituted Ba ferrites can obtain almost the same coercive force as in the examples. Table 1 and Table 2 show the values of the coercive force (Hc) and the saturation magnetization (σ _s ). In the Co-Ti-Zn substituted Ba ferrite, the squareness ratio (σr / σs) of the Ba ferrite manufactured by changing X and changing Y so that a coercive force (Hc) of about 750 Oe is obtained.
Is shown in the drawing. The measurement was performed at a constant 10 kOe. As is clear from the figure, when the value of Y is larger than 0.6, the squareness ratio decreases and the medium output decreases. In addition, in addition to the above examples, even when ferrite using Sr, Pb, or Ca as A, a high saturation magnetization value can be obtained by substituting D with Zn regardless of any combination of the above-described elements as the D component. [Effects of the Invention] As is clear from the above examples, the magnetic powder of the present invention not only has a fine particle size and enables high-density recording, but also has an improved saturation magnetization (σ _s ). In addition, the magnetic powder has a coercive force (Hc) in an appropriate range as the magnetic powder for magnetic recording, and can effectively improve the temperature characteristics of the magnetic powder and the coercive force of the recording medium using the same.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the relationship between the Zn substitution amount and the squareness ratio of Co—Ti—Zn substituted Ba ferrite magnetic powder.

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Shunji Kurisu               1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa               Inside Toshiba Research Institute (72) Inventor Osamu Kubo               1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa               Inside Toshiba Research Institute (72) Inventor Tadashi Well               1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa               Inside Toshiba Research Institute                (56) References JP-A-62-55904 (JP, A)                 JP-A-57-212623 (JP, A)                 JP-A-63-307122 (JP, A)                 JP-A-64-10604 (JP, A)

Claims (1)

(57) [Claims] General formula: AO · Fe _2N-2X Co _X (D _1-Y Zn _Y ) _X O _3N-α (where A represents Ba, Sr, Pb or Ca, and D represents 1 selected from Ti and Ge. More than species, N = 5.5-10.0, 0.6 ≦ X ≦
1.3, 0 <Y ≦ 0.75, 0 <α <1) A magnetic powder for magnetic recording, comprising a hexagonal ferrite magnetic powder represented by the following formula: 2. The hexagonal ferrite magnetic powder has an average particle size of 0.02 to
3. The magnetic powder for magnetic recording according to claim 1, wherein the magnetic powder has a coercive force of 0.02 [mu] m and 200 to 2000 Oe. 3. 3. The magnetic recording magnetic powder according to claim 1, wherein the hexagonal ferrite magnetic powder is a magnetoplumbite ferrite.