JPH0766541B2 - Magnetic recording body - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium suitable for perpendicular magnetic recording.

[Technical Background of the Invention and Problems Thereof] Magnetic recording is generally performed by a method in which a recording medium in which a magnetic powder such as acicular Co—γFe ₂ O ₃ is coated on a support is used to magnetize in-plane longitudinal direction. (The shortest recording wavelength is about 1.2 μm).

However, in the recording method using the magnetization in the in-plane longitudinal direction, if the recording density is increased, the demagnetizing field in the recording medium increases, which makes it difficult to achieve high density recording.

In recent years, as a magnetic recording method that eliminates such inconvenience,
A perpendicular magnetization recording method using the perpendicular magnetization of a recording medium has been proposed.

In this perpendicular magnetization recording method, the demagnetizing field in the recording medium decreases as the recording density increases, and thus it can be said that the recording method is essentially suitable for high density recording.

By the way, in this perpendicular magnetization method, the recording medium needs to have an easy axis of magnetization in a direction perpendicular to the surface thereof, and a Co—Cr sputtered film has been developed as this type of recording medium.

However, this Co-Cr film is easily worn by friction (sliding) with the head, and the recording medium layer itself is poor in flexibility and difficult to handle, and further its manufacturing is complicated in operation.
Moreover, since Co-Cr is chemically unstable, there is a problem in reliability as a recording medium. In particular, this recording medium needs to be prepared by using a vacuum process such as sputtering or vapor deposition, and has a disadvantage that it cannot be prepared by a conventionally used coating method.

By the way, conventionally known as a hard magnetic material,
For example, a hexagonal ferrite such as BaFe ₁₂ O ₁₉ has a flat plate shape, and the easy axis of magnetization is also perpendicular to the plane of the flat plate. Therefore, if this hexagonal ferrite can be used as a magnetic powder for a recording medium, It is considered that the recording medium layer can be formed by the coating method, and the above-mentioned inconvenience can be eliminated.

However, the above-mentioned hexagonal ferrite has a high coercive force iHc (usually 5000 oersted or more), and therefore, there is a problem that recording and erasing cannot be performed with the currently used head material made of ferrite, sendust, amorphous or the like. Even if recording and erasing were possible, particles could easily aggregate in the film-forming process by the coating method, and in fact, a high-density magnetic recording medium by the coating method using hexagonal ferrite as magnetic powder could be used. I couldn't get it.

[Object of the Invention] As a result of intensive research conducted by the present inventors to eliminate such conventional defects, Fe constituting a hexagonal ferrite is formed.
By substituting some of the atoms with elements that reduce the coercive force, the coercive force can be recorded and erased with the current head material, and can be adjusted to a value suitable for the coating method. It has been found that a high-density magnetic recording medium can be obtained.

That is, as the hexagonal ferrite, the general formula AFe ₁₂ O ₁₉ (or AO.6Fe ₂ O ₃ ) (where A is Ba, Cr,
It is known that one of more than one element selected from Pb) is represented, but this hexagonal ferrite has 8 out of 12 Fe ³⁺ ions in one molecule, Four of them have anti-parallel magnetic efficiencies such as downward, and have so-called ferrimagnetism, but by substituting a part of these 8 Fe ³⁺ ions with other metal ions, the coercive force is increased. It can be reduced.

The present invention has been made on the basis of such findings, and it is an object of the present invention to provide a magnetic recording body capable of high-density recording and easily manufactured by a coating method without agglomerating magnetic fine powder in a film forming process. To do.

SUMMARY OF THE INVENTION That is, the manufacturing method of a high-density magnetic recording medium of the present invention have the general formula _{AFe (12-X) M X} O 19 (A is one or more elements selected Ba, Sr, and Pb To M
Represents one or more atoms or a combination of atoms of In, Zn-Ge, Zn-Nb, Zn-V, Co-Ti, and Co-Ge, and X represents a positive number of 1 to 2.5). And the average particle size is 0.01
A magnetic coating material containing hexagonal ferrite powder having a particle size of 0.3 μm is applied on a support, and the hexagonal ferrite fine powder is oriented by applying a magnetic field before drying.

When the element that reduces the coercive force is represented by M, the above-mentioned hexagonal ferrite is represented by the following general formula.

AFe _(12-X) M _X O ₁₉ (1) (where A represents one or more elements selected from Ba, Sr, and Pb, and X represents a positive number smaller than 12) Such an element that reduces the coercive force is a metal element that has an ionic radius similar to that of Fe ³⁺ ions and that maintains the electrical neutrality of the hexagonal ferrite crystal even after substitution. Is desirable.

Such metal elements include InZn-Ge, Zn-Nb, Zn-
There are elements such as V, Co-Ti, and Co-Ge, or combinations of elements. Each of these substituting elements and the like may be one kind or a combination of two or more kinds.

In the present invention, by substituting a part of Fe atoms with these elements or a combination of these elements, the coercive force of the hexagonal ferrite is matched with the characteristics of the current head material,
In addition, it can be adjusted so as not to agglomerate during the film formation process by the coating method.

It is desirable that the average valence per atom of the substitution atom be the same as the valence 3 of the Fe atom to be substituted. Therefore,
The trivalent metal such as In may be replaced by itself, but the divalent metal such as Co and Zn may be replaced by the tetravalent metal such as Ti and Ge.
It is desirable to adjust the valence by substitution with a pentavalent metal such as Nb or V for substitution.

When substitution is performed with a combination of a divalent metal and a tetravalent metal, for example, 1/2 to 1/2 of both metals per Fe atom.
It can be used in an atomic ratio of, and when substituting with a combination of a divalent metal and a pentavalent metal, 1/2 to 2/5 respectively.
Alternatively, it may be used at an atomic ratio of 1: 1/5.

Further, in the present invention, other substitutional elements may be contained as long as they do not impair the hexagonal crystal structure.

Generally, if a part of Fe atoms of hexagonal ferrite is replaced with each atom or combination of atoms described above, the coercive force is reduced.

In order to match the characteristics of the current head material, the coercive force of the magnetic powder is preferably in the range of 200 to 2000 Oersted, and therefore the number of substituted atoms X in the above general formula is X.
Is set such that the coercive force of the obtained magnetic powder is in this range.

The above range of X varies depending on the atom or combination of atoms used, but generally a range of X = 1 to 2.5 is suitable. If the number of substitutional atoms X is less than 1, the effect of reducing coercive force will be small, and if it exceeds 2.5, the coercive force will be low and it will be difficult to obtain the required performance as a recording medium.

Further, when two or more kinds of atoms are used as A in the general formula (1), the total number of these atoms as a whole is
It is desirable that the number satisfies the formula of AFe _(12-X) M _X O ₁₉ .

Generally, when the recording density is increased, the recording wavelength needs to be shortened, but the average particle size of the substituted hexagonal ferrite fine powder of the present invention needs to be smaller than the recording wavelength for this magnetic recording medium. . Thus, since the average particle size of the hexagonal ferrite fine powder of the present invention depends on the target recording wavelength, the particle size cannot be unconditionally determined, but 0.01 to
It is preferably in the range of 0.3 μm. Particle size is 0.01μ
If it is less than m, it will not exhibit the required ferromagnetism, and conversely,
If it exceeds 0.3 μm, a large number of magnetic domains will be present in a single crystal, the signal-to-noise ratio will be deteriorated, and it will be difficult to make high-density recording advantageous.

The magnetic recording medium of the present invention comprises hexagonal ferrite fine powder which is magnetic particles and a binder containing a thermoplastic or thermosetting resin as a main component, an auxiliary agent such as a lubricant, an abrasive, an antistatic agent or a dispersant. It can be obtained by applying a magnetic coating material dissolved or dispersed in an organic solvent on a support such as a film or sheet made of polyethylene terephthalate and heating and curing the binder.

The magnetic recording medium layer may be a uniform single layer, or may have a multi-layer structure in which two or more magnetic layers having different magnetic properties or different magnetic particle contents are stacked.

In addition to the support and the layer of the magnetic recording medium, in order to increase the adhesive strength of the magnetic recording medium layer to the support, an undercoat layer may be provided directly on the support or a back coat may be provided on the side opposite to the magnetic layer of the support. A layer may be provided, a protective layer may be provided on the magnetic layer to protect the magnetic layer, and a multilayer structure in which these layers are combined may be used if necessary.

The coating layer of the magnetic paint is usually subjected to orientation treatment before drying.

The orientation treatment may be carried out by passing a support coated with a magnetic coating in a direction crossing the magnetic flux in a magnetic field to orient the easy axis of magnetization of the hexagonal ferrite fine particles in the direction of the magnetic flux, or rolling the coating layer. You may perform by doing.

After that, the support coated with the magnetic coating material is sent to a drier and dried to obtain the magnetic recording material of the present invention.

As described above, in the magnetic recording medium of the present invention, the recording medium layer is mainly composed of uniaxial substituted hexagonal ferrite fine powder, and this fine powder has a plate-like shape having a hexagonal C plane. The orientation of the C plane is easy in the coating step because it has the following characteristics. By applying a magnetic coating material containing this as a main component to a support and then applying a magnetic field before drying or by mechanically rolling in a fixed direction. The easy axis of magnetization can easily be oriented perpendicular to the plane of the support.

Moreover, some of Fe atoms are In, Zn-Ge, Zn-Nb, Zn-V, Co
-Ti, Co-Ge, etc., and adjusted to have a coercive force iHc of about 200 to 2000 Oersted, so that it can be matched with the characteristics of the current head material,
High density recording by perpendicular magnetization becomes possible. It is also possible to prevent the aggregation due to the magnetic field orientation and perform the production by the coating method. Therefore, in the magnetic recording medium of the present invention, the dispersibility of the magnetic particles is extremely good, and also from this point, good high density recording characteristics are exhibited.

Furthermore, since the recording material according to the present invention can be easily formed (configured) by a coating method, it is suitable for mass production, and therefore the manufacturing cost can be reduced.

Further, in the high-density recording material of the present invention, the hexagonal ferrite fine powder is uniformly dispersed, and when the orientation treatment is not performed, the magnetization component perpendicular to the medium and the in-plane longitudinal magnetization component of the medium are Since both of them exist, they can be used as a recording medium capable of both perpendicular magnetization recording and longitudinal longitudinal recording by drying and curing without orientation treatment.

[Effect of the Invention] According to the present invention, a high-density magnetic recording medium can be realized by a conventionally used coating method without requiring a complicated means such as sputtering.

Examples of the Invention Example 1 Barium, iron and indium nitrates in a molar ratio of 1 to 2.
A coprecipitate was obtained by dropping an alkaline aqueous solution into an aqueous solution containing 11: 1. The coprecipitate was washed with water to remove alkali, dried, and heated at 950 ° C. to obtain fine powder of partially substituted indium of barium ferrite. According to electron microscopic observation, this fine particle powder was a plate having an average particle size of 0.1 to 0.2 μm, a coercive force iHc of 2000 oersted and a magnetization σg of 50 emu / g.

The magnetic powder obtained above and an auxiliary agent such as a binder are dispersed or dissolved in an organic solvent, mixed, and then applied to the surface of a polyethylene terephthalate film for magnetic field orientation (orientation condition: vertical direction 3500 O _e magnetic field application). After that, it was dried and heated to cure the binder, thereby providing a magnetic medium layer having perpendicular anisotropy.

FIG. 1 is a magnetization curve of the thus obtained substituted hexagonal ferrite fine powder magnetic recording medium in a direction perpendicular to the medium surface, and FIG. 2 is a general formula of average BeFe ₁₂ O ₁₉ as magnetic fine powder. Magnetization curve of the magnetic medium of Comparative Example 1 manufactured in the same manner as in Example 1 except that the hexagonal ferrite fine powder having No. 3 was used, and FIG. 3 shows needle-like shapes in the magnetic medium layer of the conventional video tape.
9 is a magnetization curve in a direction perpendicular to the medium surface of a magnetic recording body of Comparative Example 2 manufactured in the same manner as in Example 1 using Co—γFe ₂ O ₃ powder.

From each of these figures, in the recording medium layer of the recording medium of the present invention, the substituted hexagonal ferrite fine powder was well dispersed, and as a result, the particles were vertically oriented, the magnetization curve was square, and the coercive force was It can be seen that the current head material shows an appropriate value that allows recording and erasing.

When the magnetic recording medium thus constructed was applied to perpendicular magnetization recording, the demagnetizing field in the recording medium layer (in-plane) was small, and high density and good recording could be performed. The following table shows the results of recording and playback tests.

Medium / head relative speed 3.76 m / sec Recording head: Auxiliary magnetic pole excitation perpendicular recording head (main magnetic pole thickness 3 μm, winding number 15 turns) Reproducing head: Ring head (gap 0.2 μm, track width 35 μm, winding number 18)
Turn) In the above, the barium salt was kept constant, and the ratio of iron salt to indium salt was changed to a ratio (molar ratio) of 9.5 to 2.5 (980 ° C).
When heat-treated with, instead of indium salt
1 / 2Zn ＋ 1 / 2Ge type salt, 2 / 3Zn ＋ 1 / 3Nb type salt or 2 / 3Zn ＋ 1/3
The same magnetic fine particle powder was obtained when the V-based salt was used, and the same result was observed when the magnetic recording medium was constructed.

The above results are shown in the following table.

Note that FIG. 4 is a curve diagram showing the relationship between the indium substitution amount and the coercive force iHc for the indium substitution system of barium ferrite.

Example 2 Barium, iron, cobalt and titanium (1 / 2Co + 1 / 2Ti)
Alkali was added to an aqueous solution containing the nitrate of 1 in a molar ratio of 1: 10.6: 0.7: 0.7 to obtain a coprecipitate. This coprecipitate is washed with water to remove alkali and dried, then 950
By heat treatment at ℃, barium ferrite fine particles of cobalt-substituted titanium particles were obtained. According to electron microscopic observation, this fine particle powder was a plate having an average particle diameter of about 0.1 μm, a coercive force of iHc1000 oersted, and a magnetization of σg58emu / g.

A magnetic recording medium was constructed in the same manner as in Example 1 using the magnetic powder obtained above. When this recording medium was applied to perpendicular magnetization recording, good recording was possible with high density as shown in the following table.

Further, the coercive force iHc was measured for each barium ferrite-substitute fine particle powder obtained under the same conditions except that the barium salt was kept constant and the ratio of iron salt to cobalt salt-titanium salt was changed, as shown in FIG. Such a tendency was recognized.

Furthermore, in the above, instead of 1 / 2Co + 1 / 2Ti type salt, 1 / 2Co + 1
The average particle size, coercive force, and magnetization of the magnetic powder obtained in the same manner using the / 2Ge-based salt were as follows.

In the above, the case of the barium ferrite substitute is exemplified, but the same results were obtained also in the case of the strontium ferrite substitute and the lead ferrite substitute as shown in the following table.

[Brief description of drawings]

1 is a magnetization curve diagram of a substituted hexagonal ferrite fine powder recording medium layer of Example 1 of the present invention, and FIG. 2 is a magnetization curve diagram of a hexagonal ferrite fine powder recording medium layer of Comparative Example 1. The figure shows the magnetization curve diagram of the Co—γFe ₂ O ₃ powder recording medium of Comparative Example 2,
FIG. 4 is a curve diagram showing the relationship between the coercive force and the amount of indium substitution for the indium substitution product of barium ferrite according to the present invention, and FIG. 5 is the coercive force and cobalt for the cobalt-titanium substitution product of barium ferrite according to the present invention. FIG. 6 is a curve diagram showing the relationship with the titanium substitution amount.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Osamu Kubo 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Toshiba Research Institute Ltd. (72) Inventor Masanobu Umewa Komukai-shi, Kawasaki, Kanagawa 1 Toshiba Corp. Research Institute (56) References JP-A-55-86103 (JP, A) JP-A-53-20596 (JP, A) JP-A-50-32498 (JP, A) JP-B-46 -3545 (JP, B1) "THE PHYSICS OF MA GNETIC RECORDING" (1964) NORTH-HALLLAND PUBLISHING COMPANY P. 177, P.I. 205-207 JAPANESE JOURNAL OF APPLIED PHYSICS vol. 12, No. 3, MARCH, 1973.P. 355-360 Tohoku University Institute of Scientific Measurement Vol. 21, No. 1, 1-12 (1972) FERRITES: Proceedings of the International Conference, Jul 1970, Japan P. 380 to 382 LANDOT-BORN STEIN, Neu Series ▲ III ▼ / 4b (1970) P.I. 571, 576, 577 J. Appl. Phys. vol. 34, no. 4, APRIL 1963 P. 1271-1272

Claims (3)

[Claims] 1. A general formula AFe _(12-x) M _X O ₁₉ (A represents one or more elements selected from Ba, Sr, and Pb as M
Represents one or more atoms or a combination of atoms of In, Zn-Ge, Zn-Nb, Zn-V, Co-Ti, and Co-Ge, and X represents a positive number of 1 to 2.5). And the average particle is 0.01
Magnetic recording containing hexagonal ferrite powder of ˜0.3 μm is applied on a support, and a magnetic field is applied before drying to orient the fine hexagonal ferrite powder for high-density magnetic recording. Medium manufacturing method. 2. The coercive force of the hexagonal ferrite fine powder is 200.
The method for manufacturing a magnetic recording medium according to claim 1, wherein the magnetic recording medium is 2,000 to 2000 oersteds. 3. The method for producing a magnetic recording medium according to claim 1, wherein the support is a flexible film.