JPS6050323B2 - High density recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a high-density magnetic recording medium, particularly a high-density magnetic recording medium suitable for perpendicular magnetic recording.

[Technical background of the invention and its problems]

Magnetic recording generally uses acicular Co-γFe.

This method uses a recording medium in which magnetic powder such as No. 03 is coated on a support and magnetizes it in the longitudinal direction of the surface (shortest recording wavelength is about 1.2 μm).

However, in this recording method using magnetization in the longitudinal direction in the plane, there is a disadvantage that if the recording density is increased, the demagnetizing field within the recording medium increases, making it difficult to achieve high density recording.

In recent years, magnetic recording methods have been developed to eliminate these inconveniences.
A perpendicular magnetization recording method that uses perpendicular magnetization of a recording medium has been proposed.

In this perpendicular magnetization recording method, as the recording density increases, the demagnetizing field within the recording medium decreases, and the recording state becomes more stable.

Therefore, it can be said that this recording method is essentially suitable for high-density recording. However, in this perpendicular magnetization method, it is necessary for the recording medium to have an axis of easy magnetization in the direction perpendicular to its surface.
r sputtered film has been developed.

However, this Co-Cr film is easily worn out due to friction (sliding) with the head, the recording medium layer itself has poor flexibility and is difficult to handle, and furthermore, the manufacturing process is complicated, and the Co-Cr film is difficult to handle. Since Cr is chemically unstable, its reliability as a recording medium is problematic.

In particular, this recording medium has the disadvantage that it must be produced using a vacuum process such as sputtering or vapor deposition, and cannot be produced by conventional coating methods.
By the way, there is a material that has been known as a hard magnetic material.
For example, BaFel.

Hexagonal ferrite such as Ol9 has a flat plate shape, and the axis of easy magnetization is perpendicular to the plane of the flat plate. Therefore, if this hexagonal ferrite can be used as a magnetic powder for recording media, it can be applied by coating. It is possible to form a recording medium layer, and it is considered that the above-mentioned disadvantages can be eliminated. However, the above-mentioned hexagonal ferrite has a high coercive force IHc (usually 5000 Oe or more).
There is a problem in that recording and erasing cannot be performed with currently used head materials such as ferrite, sendust, and amorphous.

Furthermore, even if recording and erasing were possible, due to the high coercive force of 1Hc, particles tend to agglomerate with each other during the film formation process using the coating method, and in reality, the coating method using hexagonal ferrite as magnetic powder It was not possible to obtain a magnetized recording medium with high density. Also BaFel.

In addition to Ba ferrite represented by Ol9, various ion-substituted products in which Fe atoms are replaced with other elements are also known. However, all of these relate to sintered bodies or magnetic powders with large particle sizes adjusted by firing, and none are known to relate to substituted fine particles.

In sintered bodies of Ba ferrite and in cases where the grain size is large, a multi-domain structure and crystal structure are observed. Therefore, the magnetic properties of the magnetic powders are very different, and it has not been possible to obtain magnetic powders with coercive force and magnetization suitable for magnetic recording. In addition, Japanese Patent Publication No. 46-3545 describes BaF due to so-called hydrothermal properties.
In the synthesis method of el2Ol9, CO. ．． Zn i. It has been suggested that there is a possibility that ions may be contained, but in this hydrothermal method, it is not possible to replace trivalent Fe ions in a sufficient amount with these divalent -f ions; is an extremely small amount of impurity level, and is practically BaFel2
Because it is not possible to control the magnetic properties of Ol9, particularly the coercivity and force, within a range suitable for current head materials, it has not been possible to put it into practical use as a high-density magnetic recording medium.

[Purpose of the Invention] The present inventors discovered that in minerals having general ionic crystals, a pair of ions have a relationship such that changes in cation valence cancel each other out even if the ions have different valences. We focused on the fact that ion replacement occurs when a combination of BaFel and BaFel is used.

For the purpose of replacing the Fe atom of Ol9 with another element and controlling its coercive force to a value suitable for magnetic recording, a single ion or ion radius whose ionic radius and ion valence are approximately equal to that of the Fe ion) is almost equal to that of Fe ions and the valence when combined is equal to that of Fe ions. O
Many substitutions by replacing the Fe ion of l9? As a result of conducting experiments to create fine ferrite particles, we discovered the type and amount of substitution elements that can control the coercive force value of substituted ferrite particles to a value suitable for magnetic recording. The present invention has been made based on such knowledge, and provides a magnetic recording medium that can be easily manufactured by a coating method without causing agglomeration of magnetic fine powder during film formation, and that can perform high-density recording. This is what I am trying to do.

[Summary of the invention]

That is, the high-density magnetic recording body of the present invention has the general formula AF'e
(12-X)MxOl9(1) (wherein A is Ba, Sr,
Any one or more elements of Pb, M is In. ．． Zn-
E. ．． Zn-Nb. ．． Zn-■, CO-Ti. ．． CO-
One or more elements or a combination of elements of Ge, X is 1
The present invention is a high-density magnetic recording body characterized by comprising a magnetic recording medium layer containing hexagonal ferrite fine powder represented by a positive number less than 2.

In the hexagonal ferrite represented by general formula (1),
In and Zn-E. substituting part of Fe. ．． Zn-N
b. ．． Zn-V. sCO-Ti. ．． Each substituting element of CO-α may be used alone or in combination of two or more.

In the present invention, by substituting some of the Fe atoms with these elements or a combination of elements, the coercive force of the hexagonal ferrite is adjusted to such an extent that it does not agglomerate during the coating process, and magnetic recording is achieved. It can be adjusted to match the characteristics of the magnetic head used for recording and reproducing data on the body.

The average valence per substituted atom is
It is desirable to match the valence of the atom to 3.

Therefore, In, which is a trivalent metal, may be substituted alone, but CO, which is a divalent metal, may be substituted alone. ．． Zn is a tetravalent metal Ti. ．． It is desirable to adjust the valence and replace by combining with Ge, etc., and Nbl, which is a pentavalent metal, etc. When performing substitution with a combination of a divalent metal and a tetravalent metal, it is sufficient to use both metals in an atomic ratio of 1 h to 112 per Fe atom, and the divalent metal and the 5
When replacing with a combination of valent metals, 1 for each
It may be used at an atomic ratio of h:215 or 1:115.

Furthermore, in the present invention, it is not necessary to strictly match the above composition as long as the hexagonal crystal structure is not impaired; either one of the components may be increased or decreased, or other substituent elements may be included. It's okay.

Generally, when some of the Fe atoms in hexagonal ferrite are replaced with the above-mentioned elements or combinations of elements, the coercive force is reduced. Recorded using currently used magnetic heads,
For regeneration, the magnetic powder must have a holding power of 200 to 200
It is preferably in the range of 0 oersteds, and therefore the number of substituted atoms X in the above general formula is set so that the coercive force of the obtained magnetic powder falls within this range. The above range of X varies depending on the atoms or combinations of atoms used, but generally a range of X=1 to 2.5 is suitable.

If the number of substituted atoms, In addition, the above general formula (1
), when two or more types of atoms are used as A,
The total number of these atoms as a whole is AFe, 2-o) M
．． It is desirable that the number satisfies the formula of XOl9.

Generally, when increasing the recording density in the longitudinal direction, it is necessary to shorten the recording wavelength, but the average particle diameter of the substituted hexagonal ferrite fine powder of the present invention can be smaller than the recording wavelength for this magnetic recording medium. is necessary.

As described above, since the average particle size of the hexagonal ferrite fine powder of the present invention depends on the intended recording wavelength, the average particle size cannot be determined unconditionally, but it is within the range of 0.01 to 0.3 μm. It is preferable that If the particle size is less than 0.01 μm, it will not exhibit the required ferromagnetism;
If it exceeds .mu.m, a large number of magnetic domains will exist in a single crystal, deteriorating the signal-to-noise ratio and making it difficult to advantageously perform high-density recording. The high-density magnetic recording material of the present invention consists of hexagonal ferrite fine powder, which is a magnetic particle, and a binder, a lubricant, an abrasive, an antistatic agent, a dispersant, etc. mainly composed of a thermoplastic or thermosetting resin. It can be obtained by applying a magnetic coating material in which a binder is dissolved or dispersed in an organic solvent onto a support such as a film or sheet made of polyethylene terephthalate, and then heating and curing the binder.

The magnetic recording medium layer may be a homogeneous single layer, or may have a multilayer structure in which two or more magnetic layers having different magnetic properties or different magnetic particle contents are laminated.

In addition to the support and magnetic recording medium layer, in order to increase the adhesive strength of the magnetic recording medium layer to the support, an undercoat layer is provided directly above the support, and a back coat is provided on the opposite side of the support from the magnetic layer. A protective layer may be provided on the magnetic layer to protect the magnetic layer, and if necessary, a multilayer structure may be formed by combining these layers.

The applied layer of magnetic paint is usually subjected to an orientation treatment before drying. Orientation treatment may be performed by passing a support coated with magnetic paint in a direction transverse to the magnetic flux in a magnetic field to orient the axis of easy magnetization of the hexagonal ferrite fine particles in the direction of the magnetic flux. It may be carried out by rolling.

Thereafter, the support coated with the magnetic paint is sent to a dryer and dried to obtain the magnetic recording medium of the present invention.

As explained above, the high-density magnetic recording body of the present invention has a recording medium layer mainly composed of uniaxial substituted hexagonal ferrite fine powder, and this fine powder is a plate having a hexagonal C-plane. Because it has a cylindrical shape, it is easy to orient the C-plane during the coating process, and after applying a magnetic paint containing this as a main component to a support, a magnetic field is applied before drying, or mechanically rolled in a certain direction. By doing so, the axis of easy magnetization can be easily oriented perpendicular to the surface of the support body.

Moreover, some of the Fe atoms are In, . Zn-α, Zn-Nb
lZn-■, CO-Ti. ．． Coercive force 1HC of about 200 to 2000 Oe by substitution with CO-α etc.
Since the magnetic head is adjusted to have the following properties, it is possible to prevent agglomeration due to magnetic field orientation, and moreover, it is possible to perform recording and reproduction using current magnetic heads used for recording and reproduction of magnetic recording bodies.

Therefore, in the magnetic recording medium of the present invention, the dispersibility of magnetic particles is extremely good, and high-density recording by perpendicular magnetization can be performed satisfactorily.

Thus, the recording medium according to the present invention can be easily formed (structured) by a coating method, and is therefore suitable for mass production, and can reduce manufacturing costs.

In addition, in the high-density recording body of the present invention, hexagonal ferrite fine powder is uniformly dispersed, and if no orientation treatment is performed, the magnetization component perpendicular to the medium and the magnetization component in the in-plane longitudinal direction of the medium are Since both exist, it can be dried and hardened without any orientation treatment and used as a recording medium capable of both perpendicular magnetization recording and in-plane longitudinal magnetization recording.

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

[Examples of the Invention] Example 1 A solution of alkaline water was dropped into an aqueous solution containing nitrates of barium, iron, and indium in a molar ratio of 1:11:1 to obtain a coprecipitate.

This coprecipitate was washed with water to remove the alkali, then dried and heat-treated at 950° C. to obtain fine particle powder of an indium moiety substituted product of barium ferrite. This fine particle powder has an average particle size according to electron microscopic observation. 0.1~
It had a plate shape of 0.2 μm, a coercive force Hc of 2000 Oe, 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 coated on the surface of a polyethylene terephthalate film and oriented in a magnetic field (alignment conditions: applying a magnetic field of 35,000 e in the vertical direction). ), then dry, smooth the surface by super calendering,
Heat was applied to cure the binder and provide a magnetic media layer with perpendicular anisotropy. Figure 1 shows the magnetization curve of the thus obtained substituted hexagonal ferrite fine powder magnetic recording material in the direction perpendicular to the medium surface, and Figure 2 shows the average B of the magnetic fine powder.
aFel.

The magnetization curve of the magnetic medium of Comparative Example 1 manufactured in the same manner as in Example 1 except that hexagonal ferrite fine powder having the chemical formula of ``Ol9'' was used. Figure 3 shows the magnetization curve of the magnetic medium of Comparative Example 1. - Magnetization curves in the direction perpendicular to the medium surface of the magnetic recording body of Comparative Example 2 manufactured in the same manner as in Example 1 using -γFe2O3 powder.From these figures, it can be seen that the recording medium layer of the recording body of the present invention Inside, as a result of the well-dispersed substituted hexagonal ferrite fine powder, the particles are vertically oriented, exhibiting a magnetization curve or angular shape, and the coercive force shows an appropriate value for a recording medium. .

When the magnetic recording body thus constructed was applied to perpendicular magnetization recording, the demagnetizing field within the recording medium layer (in-plane) was small, and high-density and good recording could be performed.

The results of the recording and playback tests are shown in the table below. Media/head relative speed 3.75n1/Sec Recording head Auxiliary magnetic pole excitation perpendicular recording head (Main pole thickness 3μm 1 turn 15 turns) Reproduction head Nilling head (gap 0.2μm 1 track width 3.5μm 1 turn 1
8 turns) In the above, when the barium salt is kept constant and the ratio of iron salt to indium salt is changed to a ratio (molar ratio) of 9.5 to 2.5 and heat treated at 980'C, 112Zn+112Ge salt, 213Z
n+113Nb salt or 2137. Similar magnetic fine particle powder can be obtained when using n+113■ series salt,
Similar results were observed when a magnetic recording medium was constructed.

The above results are shown in the table below. FIG. 4 is a curve diagram showing the relationship between the amount of indium substitution and the coercive force 1Hc for an indium substitution system of barium ferrite.

Example 2 Baurim, iron, cobalt and titanium (112C0+1
1 liver 1) nitrate in molar ratio 1:10, 6:0.7:0
．． An alkali was added to an aqueous solution containing 7 parts to obtain a coprecipitate.

This coprecipitate was sequentially washed with water to remove alkali, dried, and then heated at 950°C to obtain fine powder of cobalt and titanium substituted barium ferrite. According to electron microscope observation, this fine particle powder has an average particle size of approximately 0.1 μm.
It was plate-shaped, had a coercive force of 1 Hc1000 Oe, and a magnetization σG of 58 emu/g. A high-density magnetic recording body 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 at high density was possible as shown in the following table. (The regeneration conditions are the same as in the examples.) In addition, the barium ferrite substitute fine particle powder obtained under the same conditions as above except that the barium salt was kept constant and the ratio of iron salt to cobalt salt to titanium salt was changed, had a coercive force of 1Hc.
When these were measured, a tendency as shown in FIG. 5 was observed.

Furthermore, the average particle size, coercive force and magnetization of magnetic powder obtained in the same manner as above using 112C0+112Ge type salt instead of 112C0+112T1 type salt were as follows.

In the above, the case of a barium ferrite substituted product was exemplified, but similar results were obtained with a strontium ferrite substituted product and a lead ferrite substituted product as shown in the following table.

[Brief explanation of drawings]

FIG. 1 shows the magnetization curve of the substituted hexagonal ferrite fine powder recording medium layer of Example 1 of the present invention, FIG. 2 shows the magnetization curve of the hexagonal ferrite fine powder recording medium layer of Comparative Example 1, and FIG. The magnetization curve of the CO-γFe2O(1) 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-substituted barium ferrite according to the present invention, and FIG. FIG. 2 is a curve diagram showing the relationship between coercive force and cobalt-titanium substitution amount for a barium ferrite substituted with cobalt-titanium according to the present invention.

Claims (1)

[Claims] 1 General formula AFe_(_1_2_-_x_)MxO_1
_9 (However, A is one or more elements selected from Ba, Sr, and Pb, and M is In, Zn-Ge, Zn-Nb, Z
n-V, Co-Ti, Co-Ge, and X represents a positive number from 1 to 2.5, respectively), and the average particle size is 0. .01~0.
A high-density recording medium comprising a magnetic recording medium layer containing 3 μm hexagonal ferrite fine powder. 2 The coercive force of hexagonal ferrite fine powder is 200 to 20
2. The high-density recording medium according to claim 1, which is 0.00 Oersted.