JPH036643B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a fine hexagonal ferrite powder used in a magnetic recording medium, and particularly to a fine hexagonal ferrite powder for a magnetic recording medium suitable for a perpendicular magnetic recording medium. [Technical background of the invention and its problems] Magnetic recording generally uses a recording medium in which a support is coated with magnetic powder such as acicular Co-γFe ₂ O ₃ and is magnetized in the in-plane longitudinal direction. (Shortest recording wavelength approx.
1.2 μm). However, this recording method using magnetization in the in-plane longitudinal direction has the 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, a perpendicular magnetic recording method that uses magnetization in the perpendicular direction of a recording medium has been proposed as a magnetic recording method that overcomes these difficulties. In this perpendicular magnetization recording method, as the recording density increases, the demagnetizing field within the recording medium decreases, and the density 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 a direction perpendicular to its surface, and a Co--Cr sputtered film has been developed as this type of recording medium. However, this Co-Cr film is easily worn out due to friction (sliding) with the head, and the recording medium layer itself has poor flexibility and is difficult to handle.Furthermore, its manufacture is complicated, and the Co-Cr film is difficult to handle. Since it is chemically unstable, there is also a problem with its reliability as a recording medium. 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, hexagonal ferrite, such as BaFe ₁₂ O ₁₉ , which has been conventionally known as a hard magnetic material, has a flat plate shape, and the axis of magnetic ease is perpendicular to the plane of the flat plate. If ferrite based ferrite can be used as a magnetic powder for recording media, it will be possible to form a recording media layer by a coating method, and it is thought that the above-mentioned disadvantages can be eliminated. However, the hexagonal ferrite mentioned above has a coercive force
There is a problem in that recording and erasing cannot be performed with currently used head materials such as ferrite, sendust, and amorphous, which have a high iHc (usually 5000 oersted or more). Furthermore, even if recording and erasing were possible, due to the high coercive force iHc, the particles tend to aggregate with each other during the film formation process using the coating method. It was not possible to obtain a magnetized recording medium of high density. [Purpose of the Invention] As a result of intensive research aimed at solving these conventional drawbacks, the present inventors have succeeded in replacing some of the Fe atoms in hexagonal ferrite with an element that reduces its coercive force. It has been found that by doing this, the coercive force can be adjusted to a value suitable for the coating method, and thereby a high-density magnetized recording material can be obtained by the coating method. In other words, hexagonal ferrite is represented by the general formula AFe ₁₂ O ₁₉ (or AO・6Fe ₂ O ₃ ) (where A represents one or more elements selected from Ba, Sr, and Pb). This hexagonal ferrite has magnetic efficiencies that are antiparallel to each other, with 8 of the 12 Fe ³⁺ ions in one molecule pointing upward and 4 pointing downward. Although it has magnetism, the coercive force can be reduced by replacing some of these eight Fe ³⁺ ions with other metal ions. The present invention was made based on these findings, and aims to provide a fine hexagonal ferrite powder for magnetic recording materials that does not agglomerate during the film-forming process and can be easily manufactured by a coating method. It is something to do. [Summary of the invention] That is, the hexagonal ferrite fine powder for magnetic recording media of the present invention has _the general formula AFe _{(12-X) M} One or more selected elements, M is 1/2zn + 1/2Ge, 2/3Zn + 1/3
Nb, 2/3Zn+1/3V, 1/2Co+1/2Ti, 1/2Co+1/
One or more substitution elements or combinations of elements of 2Ge,
Furthermore, x represents a positive number from 1 to 2.5), and the average particle size is 0.01 to 0.3 μm.
By substituting some of the Fe atoms, the coercive force of hexagonal ferrite can be adjusted to the extent that it does not aggregate during the coating process, and the recording of magnetic recording media can be improved.
It can be adjusted to match the characteristics of the magnetic head used for reproduction. Generally, when some of the Fe atoms in hexagonal ferrite are replaced with a combination of the above-mentioned elements, the coercive force is reduced. In order to record and reproduce data with currently used magnetic heads, the coercive force of magnetic powder must be
It is preferably in the range of 200 to 2000 oersteds, and therefore the number of substituted atoms X in the above general formula is set so that the coercive force of the resulting magnetic powder falls within this range. The above range of X varies depending on the element or combination of elements used, but generally a range of X=1 to 2.5 is appropriate. If the number of atoms of the substituent element 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 so low that it will be difficult to obtain the required performance as a recording medium. Further, when two or more types of atoms are used as A in the above general formula (1), it is desirable that the total number of these atoms as a whole satisfies the formula AFe _(12-X) MxO ₁₉ . Generally, when increasing the recording density in the longitudinal direction, it is necessary to shorten the recording wavelength, but the average particle size of the substituted hexagonal ferato fine powder of the present invention can be smaller than the recording wavelength for this magnetic recording medium. is necessary. Since the average particle size of the hexagonal ferrite fine powder of the present invention depends on the intended recording wavelength, the particle size cannot be determined unconditionally, but it needs to be in the range of 0.01 to 0.3 μm. If the average particle size is less than 0.01μm, it will not exhibit the required ferromagnetism;
If m is exceeded, a large number of magnetic domains will exist in a single crystal, which will deteriorate the signal-to-nozzle ratio and make it difficult to advantageously perform high-density recording. In order to produce a magnetic recording medium using the hexagonal ferrite fine powder of the present invention, a binder, a lubricant, an abrasive, an antistatic agent, or a dispersant mainly composed of a thermoplastic or thermosetting resin is required. A magnetic recording medium layer can be formed by dissolving or dispersing the binder in a binder and an organic solvent to form a magnetic coating, coating this on a support such as a film or sheet made of polyethylene terephthalate, and curing the binder by heating. 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 layer is provided on the opposite side of the support from the magnetic layer. or a protective layer may be provided on the magnetic layer to protect the magnetic layer, and if necessary, a multilayer structure may be formed in which these are combined. The applied layer of magnetic paint is usually subjected to an orientation treatment before drying. Orientation treatment may be carried out 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 in a certain direction with a certain pressure. Thereafter, the support coated with the magnetic paint is sent to a dryer and dried and hardened to obtain a magnetic recording medium. As explained above, since the substituted hexagonal ferrite fine powder of the present invention has a plate-like shape with a hexagonal C-plane, the C-plane can be easily oriented in the coating process, and a magnetic paint containing this as a main component After being applied to a support and before drying, the easy magnetization axis can be easily oriented perpendicular to the surface of the support by applying a magnetic field or mechanically rolling it in a certain direction. Moreover, some of the Fe atoms can be converted into Zn−Ge, Zn−Nb,
Substituted by Zn-V, Co-Ti, Co-Ge, etc.
Since the coercive force iHc is adjusted to an appropriate range,
Aggregation due to magnetic field orientation can be prevented. Therefore, the hexagonal ferrite fine powder of the present invention has extremely good dispersibility and can perform high-density recording by perpendicular magnetization well. Thus, the hexagonal ferrite fine powder of the present invention can easily form (constitute) a magnetic recording medium layer by a coating method, and is therefore suitable for mass production and can reduce manufacturing costs. Furthermore, the hexagonal ferrite fine powder of the present invention is
Since the average particle size is small, if orientation treatment is not performed, both magnetization components perpendicular to the medium and magnetization components in the plane of the medium will exist, and perpendicular magnetization recording can be achieved by drying and hardening without orientation treatment. It can be used as a magnetic recording medium capable of both in-plane longitudinal recording and in-plane longitudinal recording. [Effects of the Invention] In the hexagonal ferrite fine powder of the present invention, a part of the Fe atoms are replaced with a combination of two types of elements whose ratio is adjusted according to the valence, and the coercive force is adjusted to an appropriate range. Therefore, a perpendicularly magnetized magnetic recording medium capable of homogeneous, high-density recording can be manufactured by a conventional coating method without requiring complicated means such as sputtering. Furthermore, since the average particle size is minute, those fixed on a support without orientation can be used as a magnetic recording medium capable of both perpendicular magnetization recording and in-plane longitudinal recording. [Embodiments of the Invention] Example 1 An alkaline aqueous solution was added dropwise to an aqueous solution containing nitrates of barium, iron, zinc, and niobium in a molar ratio of 1:11.35:2/3×0.65:1/3×0.65. Got a precipitate. This coprecipitate was washed with water to remove the alkali, then dried and heat-treated at 950°C to obtain fine powder of barium ferrite partially substituted with zinc and niobium. According to electron microscopic observation, this fine particle powder has a plate shape with an average particle size of 0.1 to 0.2 μm, a coercive force iHc of 2000 oersted, and a magnetization σg62emu/
It was hot at 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 (alignment condition: magnetic field attraction of 4000 Oe in the vertical direction). (a)), dried, calendered to smooth the surface, and heated to harden the binder to form a magnetic medium layer having perpendicular magnetic anisotropy. Figure 1 shows the magnetization curve of the magnetic recording material of the substituted hexagonal ferrite powder obtained in this way.
Figure 2 shows the magnetic recording of the hexagonal ferrite powder of Comparative Example 1, which was produced in the same manner as in Example 1, except that hexagonal ferrite fine powder with an average molecular formula of BaFe ₁₂ O ₁₉ was used as the magnetic powder. magnetization curve of the body,
Figure 3 shows the needle-like shape used in conventional videotapes.
2 is a magnetization curve in a direction perpendicular to the medium surface of a magnetic recording medium of Comparative Example 2 manufactured using Co-γFe ₂ O ₃ powder. These figures show that the substituted hexagonal ferrite fine powder of the present invention is well dispersed, so that the particles are vertically oriented, the magnetization curve is square, and the coercive force is an appropriate value for a recording medium. I understand that. When the magnetic recording body manufactured in this way was applied to perpendicular magnetization recording, it was found that within the recording medium layer (in-plane)
The demagnetizing field was also small, allowing high-density and good recording. The results of the recording/reproduction test are shown in the attached table.

[Table] Media: Head relative speed 3/75 m/sec Recording head: Auxiliary magnetic pole excitation perpendicular recording head (main pole thickness 3 μm, number of turns, 15 turns) Playback head: Ring head (gap 0/2 μm, track width 35 μm, number of turns 18
In addition, in the above case, when the barium salt is kept constant and the ratio of iron salt: 2/3 zinc + 1/3 niobium salt is changed to a ratio (molar ratio) of 9.5: 2.5 and heat treated at 980℃, 2/3 Zn + 1/3 Nb Similar magnetic fine particle powders were obtained when 1/2Zn+1/2Ge-based salts and 2/3Zn+1/3V-based salts were used instead of the system salts, and similar results were observed when magnetic recording bodies were constructed. The above results are shown in the table below.

[Table] Example 2 Baurim, iron, cobalt and titanium (1/2Co
+1/2Ti) nitrate in a molar ratio of 1:10.6:0.7:0.7
An alkali was added to an aqueous solution containing the following ratio 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 barium ferrite substituted with cobalt and titanium. These fine particles are plate-shaped with an average particle size of approximately 0.1 μm as observed by electron microscopy, and have a coercive force
iHc1000 oersted, magnetization σg 58emu/g. A 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.

[Table] (Recording and playback conditions are the same as in Example 1) Also, barium ferrite substituted 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. When the coercive force iHc was measured for each, a tendency as shown in FIG. 2 was observed. Furthermore, the average particle diameter, coercive force, and magnetization of magnetic powder obtained in the same manner as above using 1/2Co+1/2Ge salt instead of 1/2Co+1/2Ti salt were as shown in the following table.

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

【table】

【table】 [Brief explanation of the drawing]

FIG. 1 is a magnetization curve diagram of a recording layer using substituted hexagonal ferrite fine powder of Example 1 of the present invention, and FIG. 2 is a magnetization curve diagram of a recording layer using hexagonal ferrite fine powder of Comparative Example 1. Magnetization curve diagram, Figure 3 is of Comparative Example 2.
Magnetization curve of recording medium using Co-γFe ₂ O ₃ powder,
Figure 4 shows the coercive force and cobalt-titanium substituted barium ferrite of Example 2 of the present invention.
It is a curve diagram showing the relationship with the amount of titanium substitution.

Claims (1)

[Claims] 1 General formula AFe _{( 12 -X)} M 3Zn+1/3
Nb, 2/3Zn+1/3V, 1/2Co+1/2Ti, 1/2Co+1/
One or more substitution elements or combinations of elements of 2Ge,
A fine hexagonal ferrite powder for a magnetic recording medium, characterized in that x represents a positive number from 1 to 2.5) and has an average particle size of 0.01 to 0.3 μm. 2. The hexagonal ferrite fine powder for magnetic recording media according to claim 1, which has a coercive force of 200 to 2000 oersteds.