JP2735382B2 - 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) Generally, a coated magnetic recording medium is a non-magnetic support (substrate) such as a polyethylene terephthalate film.
And a magnetic layer provided on the surface of the support and having a magnetic powder and a resin binder as main components.

As the magnetic powder, conventionally, γ-Fe ₂ O ₃ ,
Acicular ferromagnetic powders such as —Fe ₂ O ₃ , Co-doped γ-Fe ₂ O ₃ , CrO ₂ , and Fe powder are widely used, and magnetic recording uses magnetization in a longitudinal direction in a plane. Recently, a magnetic recording medium capable of perpendicular magnetic recording using magnetization in a direction perpendicular to the support has been desired in order to greatly improve the magnetic recording density. Researches using ultrafine magnetic powder of crystalline ferrite have been studied, and some of them are being put to practical use.

(Problems to be Solved by the Invention) Incidentally, hexagonal ferrite generally has a property that the coercive force increases with an increase in temperature near normal temperature. That is, the temperature coefficient of the coercive force (the gradient of the coercive force with respect to the temperature near room temperature) is positive. However, in a magnetic recording medium, if the temperature coefficient of the coercive force is large, the electromagnetic conversion characteristics fluctuate due to temperature, and the characteristics such as recording, reproduction, and erasing are deteriorated, and particularly the overwrite characteristics are hindered. Problems arise. for that reason,
In a magnetic recording medium, the temperature coefficient of the coercive force is -2 to +
It is desired to be in the range of 2 Oe / ° C.

In response to such demands, for example, an attempt has been made to replace a part of the Fe component with Sn. There is a problem that the function required as a medium cannot be sufficiently performed.

The present invention has been made in response to such problems.
The object of the present invention is to provide a magnetic powder for magnetic recording that not only has a temperature coefficient of coercive force in a range of approximately −2 to +2 Oe / ° C. but also has a required saturation magnetization as a magnetic recording medium and is suitable for high-density magnetic recording. .

[Constitution of the Invention] (Means for Solving the Problems) The magnetic powder for magnetic recording of the present invention has a general formula: AO · n / 6 (Fe _12-xyz B _x Ni _y C _z O _18-α ) or AO・ N / 6 ｛Fe _{12−x−y−z / 2} B _x Ni _y C ′
_{z / 2} O _18-α ｝ (where A is at least one element selected from Ba, Sr, Ca and Pb, and B is at least one divalent element selected from Co and Zn) C is at least one tetravalent element selected from Ti, Sn and Ge, and C 'is Nb, V, Ta, Sb
Represents at least one pentavalent element selected from the group consisting of α = (x + yz) / 2, 7.2 <n ≦ 12.
0, 0.5 ≦ x ≦ 1.5, 0.2 ≦ y ≦ 1.6, 0.7 ≦ x + y ≦ 2.7,
It is characterized by being composed of a hexagonal ferrite powder represented by 0 ≦ z <2.0, 0.34 <α ≦ 1.0).

The hexagonal ferrite according to the present invention includes, for example, M-type (Magnetoplumbite tipe) or W-type hexagonal Ba ferrite, Sr ferrite, Pb ferrite, Ca ferrite, a solid solution thereof, or an ion substitute. .

In the hexagonal ferrite according to the present invention, the element B,
The reason why the substitution amounts of Ni, C and C ', that is, the ranges of values of x, y and z, and n and α are limited as described above, is as follows.

That is, when n takes a value of 6, a perfect hexagonal ferrite is formed, but practically it is preferably in the range of 6.1 to 12.0. At this time, desired magnetic properties such as coercive force and saturation magnetization are obtained. The obtained hexagonal ferrite powder is obtained. If n is less than 6.1 to 7.2, the saturation magnetization is small, and 7.
When it is 2 or more, it has a desired saturation magnetization.

Further, an element B which is a substitution component for controlling the coercive force
When the coercive force x of the obtained hexagonal ferrite powder is less than 0.5, the coercive force of the hexagonal ferrite powder exceeds 2,000 Oe, the head magnetic field causes a saturation phenomenon, and magnetic recording becomes difficult. The coercive force of the obtained hexagonal ferrite powder is less than 200 Oe, and it is difficult for a magnetic recording medium formed using the same to retain a recording signal.

Further, when the substitution amount y of Ni is less than 0.2, the temperature coefficient of the coercive force of the obtained hexagonal ferrite powder becomes as large as +2 Oe / ° C. or more, which impairs the overwriting characteristics of the recording medium. Conversely, when the ratio exceeds 1.6, the squareness ratio of the obtained hexagonal ferrite powder becomes small, and the value of the residual magnetization expressed by squareness ratio × saturation magnetization becomes small, so that the output characteristics of the recording medium are greatly reduced. Would.

Further, when the value of x + y is less than 0.7, the coercive force of the obtained hexagonal ferrite powder exceeds 2000 Oe, the head magnetic field saturates, and magnetic recording becomes difficult. The coercive force of the obtained hexagonal ferrite powder is less than 200 Oe, and it is difficult for a magnetic recording medium formed using the same to retain a recording signal.

Further, when the substitution amount z of the elements C and C ′ exceeds 2.0, the saturation magnetization and the coercive force of the obtained hexagonal ferrite powder become small, respectively, and the output characteristics of the recording medium are greatly reduced.

Further, when the value of α (α = (x + yz) / 2), which depends on the substitution amounts of the elements B, Ni, C, and C ′, exceeds 1.0, the obtained hexagonal ferrite powder has a square shape. The ratio becomes smaller, and the output characteristics of the recording medium deteriorate more.

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. That is, if the average particle size is less than 0.02 μm,
When the magnetization and coercive force decrease, the reproduction output of the magnetic recording medium decreases, and when it exceeds 0.2 μm, a multi-domain structure is formed,
At the time of high density recording, noise at the time of reproduction becomes remarkable. The coercive force is desirably in the range of 200 to 2000 Oe.

The magnetic powder for magnetic recording according to the present invention can be produced, for example, as follows. That is, the oxides and carbonates of the respective elements necessary to form the hexagonal ferrite having the desired composition formula are first heated and melted together with a glass-forming substance such as boric acid, silicic acid, and phosphoric acid. . Next, the obtained melt is rapidly cooled to be amorphized (vitrified), and then the obtained glass body is subjected to a heat treatment at a predetermined temperature to obtain a desired hexagonal ferrite crystal powder. Precipitate. The powder thus obtained can be easily obtained by washing with a dilute acid such as phosphoric acid or acetic acid to dissolve and remove the glass component. Of course, besides the above glass crystallization method,
Although it can be obtained by a coprecipitation-firing method or a hydrothermal method, it is particularly preferable to employ a glass crystallization method.

The hexagonal ferrite powder according to the present invention is usually applied to the surface of a nonmagnetic support together with a binder resin, and is used as a magnetic recording medium. Here, as the binder resin constituting the magnetic layer together with the magnetic powder, for example, a vinyl chloride-vinyl acetate copolymer, a vinylidene chloride-based copolymer, an acrylate-based copolymer, a polyvinyl butyral-based resin, a polyurethane-based resin, Polyester-based resins, cellulose derivatives, epoxy resins, and the like,
These can be used alone or in combination of two or more. Further, in the magnetic layer composed of the hexagonal ferrite powder and the binder resin, additives such as a dispersant, a lubricant, an abrasive, and an antistatic agent can be appropriately contained as needed.

(Function) In the magnetic powder according to the present invention, a part of Fe atoms constituting ferrite is replaced with Co and / or Zn atoms, so that the magnetic powder for magnetic recording has a required coercive force and high saturation magnetization. In addition, since some of the Fe atoms are also replaced by Ni atoms, the temperature coefficient of the coercive force is also close to zero,
Stable against temperature changes. Therefore, by using the magnetic powder according to the present invention, a magnetic recording medium having high recording density and reproduction output can be manufactured.

(Example) Hereinafter, an example of the present invention will be described.

Examples 1 to 6 In the Ba ferrite represented by the chemical formula, BaO · n / 6 {Fe _12-xyz (Co / Zn) _x Ni _y C _z O _18-α }, C is Ti alone and Sn
With respect to the single case, Ba ferrite having a composition in which the substitution amounts x, y, z, n, and α of the respective elements have the values shown in Table 1 was produced.

That is, if x = 1.1, y = 0.6, Z = 0.7, α = 0.50, Z
Co-Ni-Ti substituent without n atom (Example 1), Zn-Ni-Ti substituent without Co atom (Example 2) and Co =
Three types of Co-Zn-Ni-Ti substitution products (Example 3) with 0.54 / Zn = 0.56, x = 0.9 (Co = 0.5 / Zn = 0.4), y = 1.
6, Co-Zn-Ni-T with z = 0.5, α = 1.0 (Example 4)
i-substitute, X = 1.10 (Co = 0.54 / Zn = 0.56), y = 0.
6, Co-Zn-Ni-S with z = 0.7 and α = 0.5 (Example 6)
The n-substituted product was produced by a glass crystallization method.

Manufacturing first, the B ₂ O ₃ · BaO _{glass, BaO, Fe 2 O 3,} CoO,
ZnO, each component of NiO and TiO _2, added formulated to constitute a Ba ferrite of the composition, was melted by heating at a temperature of 1350 ° C., non-comprising quench rolled to the above components by a twin roll A crystalline body (glass) was formed.

Next, this glass was heated at 800 ° C. for 4 hours to precipitate Ba ferrite crystals such as Co—Zn—Ni—Ti substitution in the matrix, and then washed with dilute acetic acid and pure water to form a glass. The components were removed and the Ba ferrite was extracted, followed by drying treatment to obtain respective magnetic powders.

Each of the magnetic powders obtained above has an average particle size of about
It was as fine as 500 mm.

Comparative Examples 1 to 7 and the substitution amount y of the 14 Ni atom was α = 0, 0.6, 1.8, and α = 0, 0.
Coercive force (Hc) at 50 is almost the same as in Example 1 etc.
The value of x is set so as to obtain a Co-Ti substitute of Ba ferrite having the composition ratio shown in Table 1 (Comparative Example 1),
-Ni-Ti substituent (Comparative Example 2), Co-Zn-Ti substituent (Comparative Example 3) and Co-Zn-Ni-Ti substituent (Comparative Example 4), α
= 1.10, 0.50, z = 0.3, 2.0, a Co-Zn-Ni-Ti substitution product having the composition ratio shown in Table 1 (Comparative Examples 5 and 6);
0.3 of Co-Zn-Ni-Sn substitution (Comparative Example 7) and α = 0.30
And a Co-Zn-Ni-Ti substitution product (Comparative Example 14) were produced by a glass crystallization method in the same manner as in Example 1 and the like.

Examples 1 to 6 and Comparative Examples 1 to 7 obtained above, respectively.
The values of the coercive force (Hc), the saturation magnetization (σ _s ), the squareness ratio SQR (σ _ν / σ _s ), and the temperature coefficient of coercive force (δHc) of Table 2 shows the results of the measurements.

Note that Example 6 and Comparative Example 7 are cases where Sn was used instead of Ti.

Examples 7 to 10 Chemical formula, BaO · n / 6 ｛Fe _{12-xy-z / 2} (Co / Zn) _x Ni _y Nb _{z / 2}
In the Ba ferrite represented by O _18-α量, the substitution amount x of each element,
Ba having a composition in which y, z, and n and α have the values shown in Table 1.
Ferrite was manufactured.

That is, when x = 1.1, y = 0.6, z = 0.7 and α = 0.50, Z
Co-Ni-Nb substitution not containing n atom (Example 7), Zn-Ni-Nb substitution not containing Co atom (Example 8) and Co =
Three types of Co-Zn-Ni-Nb substituted products (Example 9) with 0.54 / Zn = 0.56, x = 0.9 (Co = 0.5 / Zn = 0.4), y = 1.
6, Co-Zn-Ni-N with z = 0.5 and α = 1.0 (Example 10)
b-substituted product was produced by a glass crystallization method.

Manufacturing first, the B ₂ O ₃ · BaO _{glass, BaO, Fe 2 O 3,} CoO,
Each component of ZnO, NiO and Nb ₂ O ₅ was mixed and added so as to constitute the Ba ferrite of the above composition, heated and melted at a temperature of 1350 ° C., and then quenched and rolled with twin rolls to obtain the above components. An amorphous body (glass) containing the same was formed.

Next, this glass is heated at 800 ° C. for 4 hours to precipitate Ba ferrite crystals such as Co—Zn—Ni—Nb substitution in the matrix, and then washed with dilute acetic acid and pure water to form a glass. The components were removed and the Ba ferrite was extracted, followed by drying treatment to obtain respective magnetic powders.

Each of the magnetic powders obtained above has an average particle size of about
It was as fine as 500 mm.

Comparative Examples 8 to 13, the substitution amount y of the 15 Ni atom is y = 0, 0.6, 1.8 and α = 0, 0.
In Example 50, the value of x was set so as to obtain substantially the same coercive force (Hc) as in Example 7 and the like, and the Co-Nb-substituted Ba ferrite having the composition ratio shown in Table 3 (Comparative Example) 8), Co-Ni-Nb-substituted product (Comparative Example 9), Co-Zn-Nb-substituted product (Comparative Example 10), and Co-Zn-Ni-Nb-substituted product (Comparative Example 1)
1) and a Co—Zn—Ni—Nb-substituted product having a composition ratio shown in Table 3 where α = 1.10, 0.50, 0.30, z = 0.3, 2.0, 0.7 (Comparative Example
12, 13 and 15) were produced by the glass crystallization method in the same manner as in Example 7 and the like.

Examples 7 to 10 and Comparative Examples 8 to 1 obtained above, respectively.
For the magnetic powders of Nos. 3 and 15, the values of coercive force (Hc), saturation magnetization (σ _s ), squareness ratio SQR (σ _ν σ _s ), and temperature coefficient of coercive force (δHc) were measured using the vibrating sample magnetic force, respectively. Table 4 shows the results of the measurements.

As can be seen from Tables 2 and 4, the magnetic powders of the examples according to the present invention have a coercive force of an appropriate magnitude for high-density recording and a saturation magnetization of 56 to 59 emu / g.
Shows a high value. The temperature coefficient of the coercive force is -2 to +20.
It is close to zero, e / ° C., and is not only stable against temperature changes, but also has a sufficiently large squareness ratio.

Accordingly, the Ba ferrite powder according to the present invention is mixed with a binder resin, a lubricant, a dispersant, and an abrasive to prepare a magnetic paint, for example, applied to a non-magnetic support surface such as a polyethylene terephthalate film, and subjected to an orientation treatment.
When a magnetic recording medium is formed by performing a drying process, a calendering process, or the like, excellent recording / reproducing characteristics are always maintained and exhibited.

[Effects of the Invention] As is clear from the above description, the magnetic powder according to the present invention has a fine particle diameter, enables high-density magnetic recording, and has a required coercive force and saturation magnetization. I have. In addition, since the coercive force is stable against temperature changes, when a recording medium is used, a decrease in overwrite characteristics is prevented, and a magnetic recording medium having both high S / N characteristics and reproduction output is obtained. Can be.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tadashi Ido 1 Toshiba-cho, Komukai-shi, Kawasaki-shi, Kanagawa Prefecture Inside Toshiba Research Institute, Inc. (72) Inventor Osamu Kubo 1 Toshiba-cho, Komukai-ku, Kawasaki-shi, Kanagawa Address Toshiba Research Institute, Inc. (56) References JP-A-63-307122 (JP, A) JP-A-1-100027 (JP, A) JP-A-62-216920 (JP, A)

Claims (1)

(57) [Claims] (1) AO · n / 6 (Fe _12-xyz B _x Ni _y C _z O _18-α ) or AO · n / 6 (Fe _{12-x-y-z / 2} B _x Ni _y) C ′ _{z / 2} O _18-α ) wherein A is at least one element selected from Ba, Sr, Ca and Pb, and B is at least one element selected from Co and Zn. C is a divalent element, C is at least one tetravalent element selected from Ti, Sn, and Ge; and C 'is Nb, V, Ta, Sb.
Represents at least one pentavalent element selected from the group consisting of α = (x + yz) / 2, 7.2 <n ≦ 12.
0, 0.5 ≦ x ≦ 1.5, 0.2 ≦ y ≦ 1.6, 0.7 ≦ x + y ≦ 2.7,
A magnetic powder for magnetic recording, comprising a hexagonal ferrite powder represented by the following formula: 0 ≦ z <2.0, 0.34 <α ≦ 1.0).