JPH07335417A - Magnetic powder - Google Patents

Abstract

PURPOSE:To obtain magnetic powder with which dispersion processes are easy and a degree of dispersion is excellent by a method wherein at least a group IIa element and a group IIIb element exist on a surface of a hexagonal ferrite magnetic powder. CONSTITUTION:A magnetic powder surface is coated with a group IIIb element and a group IIa element. Incidentally, the group IIa element is selected out of Be, Mg, Ca, Sr, Ra and Ba. Further, it is possible to enhance a wetting characteristic and affinity between magnetic powder and a solvent without reducing attraction activation marks enhancing a dispersion easiness of magnetic powder. As a result, it is possible to enhance not only a dispersion easiness but also a degree of dispersion, an orientation and an electric characteristic.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic powder for a coating type magnetic recording medium which can be easily dispersed and has a good degree of dispersion.

[0002]

2. Description of the Related Art A coating type magnetic recording medium is a non-magnetic support made of polyethylene terephthalate or the like, and a magnetic coating prepared by coating a ferromagnetic coating with a magnetic paint uniformly dispersed in a resin binder solution. It is composed of layers and. Needle-shaped ferromagnetic powder such as γ-Fe ₂ O ₃ has been used as the magnetic powder, but in recent years, one using ultrafine magnetic powder of hexagonal ferrite has been developed aiming at improvement of recording density. It is being done and is being put to practical use.

Generally, as factors that control the dispersion behavior of magnetic powder in a resin binder solution, progress of aggregation due to magnetostatic interaction between magnetic powder particles and the like, and magnetic powder surface and binder solution The progress of dispersion due to the interfacial chemical interaction with

The interfacial chemical interaction between the binder liquid and the surface of the powder is considered to occur in proportion to the surface area of the powder. Particularly when using a resin containing an acidic group such as a sulfone group, a carboxyl group, a phosphoric acid ester group, and a sulfuric acid ester group, which has been frequently used recently, a magnetic powder surface capable of adsorbing and interacting with the acidic group of the resin binder. The existence of the base point of is important.

For example, an oxide of a Group IIIb element, or
It is well known that the amorphous group IIIb element functions as a solid acid, so that the wetting property and affinity with a solvent are improved, and as a result, the ease of dispersion is improved. However, the presence of the solid acid reduces the number of adsorption active points (mainly base points), leading to a decrease in orientation and dispersibility.
For this reason, improvement in electrical characteristics could not be expected.

By the way, when hexagonal ferrite fine particles are used for magnetic powder, magnetic interaction is large because the shape of the fine particles is plate-like, and each magnetic powder is single crystal and polycrystal. It has been pointed out that it is difficult to disperse due to the fact that it is difficult to form a fine structure such as irregularities on the powder surface as compared with the conventional acicular particles formed of the above-mentioned aggregate, and lack of dispersion stability. For this reason, the surface of the medium obtained by coating is often not finished with a surface precision suitable for high density recording.

[0007] In response to such a point, conventionally, a surface treatment with an organic coating has been proposed, but a sufficient effect has not been found.

[0008]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a hexagonal ferrite magnetic powder for a coating type magnetic recording medium which is easy to disperse and has a good degree of dispersion.

[0009]

The present inventors have found that at least the group IIa element and the group IIIa element are present on the surface of the hexagonal ferrite magnetic powder.
The present inventors have completed the present invention by finding that the presence of the b-group element facilitates the dispersion treatment and provides a magnetic powder for a coating type magnetic recording medium having a good dispersity.

That is, the present invention is a magnetic powder characterized in that at least the group IIa element and the group IIIb element are present on the surface of the hexagonal ferrite magnetic powder.

In the present invention, the hexagonal ferrite has a crystal structure represented by BaFe ₁₂ O _{19 in} which iron or an iron-substituted metal has an average valence of 3 and its basic composition is an M-type magnetoplumbite hexagonal system. Ferrite; 2
BaM ₂ Fe ₁₆ O ₂₇ containing a valent metal (hereinafter referred to as M)
Crystal structure or the basic composition is W-type magnetoplumbite hexagonal ferrite represented by; BaMFe ₆ O ₁₁ crystal structure or basic composition represented is Y-type magnetoplumbite hexagonal ferrite; Ba ₃ M ₂ Fe ₂₄ O ₄₁
Z-type magnetoplumbite hexagonal ferrite whose crystal structure or basic composition is typified by; and so-called composite type hexagonal ferrite in which spinel ferrite is epitaxially compounded on the surface of these hexagonal ferrites is used. To be

Here, M in the composition formula of hexagonal ferrite,
Examples of the divalent metal that constitutes the spinel ferrite include Co, Fe, Ni, Mn, Mg, Cu and Zn.

In particular, in W-type and composite-type hexagonal ferrites, since there are few alkaline metals and transition metals and oxygen are abundant in the bulk composition or the composition of the powder surface, the acid of the powder surface and the binder -The surface chemical interaction by the base becomes poor, and both systems have a large amount of magnetization and are rich in magnetic cohesive force. The present invention is
It works particularly effectively for such systems.

The particle size of the magnetic powder used in the present invention varies depending on the recording density, but is 100 to 1000Å, preferably 150 to 800Å, more preferably 300 to 600Å.
Is. If the particle diameter is less than 100 Å, the amount of magnetization is significantly reduced, so that it is not suitable for a recording medium, and if it exceeds 1000 Å, a noise component becomes large and it is not suitable for high density recording.

On the other hand, the plate-like ratio represented by the ratio of the particle size to the particle thickness is 2 to 10, preferably 3 to 7, and more preferably 3 to 5. If the ratio is less than 2, it is difficult to produce the magnetic powder, and if it exceeds 10, the magnetic cohesive force is more dominant than the dispersive force, which makes the dispersion difficult.

The hexagonal ferrite may be produced by any method such as a glass crystallization method, a hydrothermal synthesis method, a coprecipitation method and a flux method. In any of the methods, it is important to find a condition where the shape distribution and the particle size distribution are sharp in order to achieve high density.

IIa to be deposited on the surface of the magnetic powder of the present invention
The group element is at least one element selected from Be, Mg, Ca, Sr, Ra and Ba.
Mg, Ca, Sr and Ba are preferably used.

Similarly, the group IIIb elements are B, Al, and G.
At least one element selected from a, In, and Tl, and among these, preferably B, Al, Ga, and I
n, particularly preferably Al, Ga or In is used.

As the deposition method, after the hexagonal ferrite produced by the above method and the salts of the IIa group element and the IIIb group element are uniformly mixed in water, NaOH is added thereto, and the IIa group element and the IIIb group element are added. Element IIa and IIIb elements are added to the glass matrix by the coprecipitation method in which the elements are deposited as hydroxides on the powder surface and then filtered, washed with water, dried, and heat-treated in order, or by the glass crystallization method. When growing and then removing the glass matrix by washing with water, there is a method of leaving a part of the glass.

The amount of the magnetic powder deposited on the surface of the magnetic powder is 0.1 to 5.0 parts by weight, preferably 0.1 to 5.0 parts by weight as an oxide of the IIa group element and the IIIb group element, relative to 100 parts by weight of the magnetic powder.
˜4.0 parts by weight, particularly preferably 1.0 to 3.0 parts by weight.

If the amount is less than 0.1 parts by weight, the dispersibility is insufficient, and if it exceeds 5.0 parts by weight, the amount of magnetization is decreased and the electrical characteristics of the medium are deteriorated.

Due to the presence of the oxide of the group IIa element, the adsorption interaction occurring between the binder and the surface of the powder is remarkably active, and as a result, the amount of the group IIa element can be small. The coprecipitation method is generally adopted because the control of the deposition amount, particularly the control of the important amount of the group IIa element is easy.

An isocyanate compound is used for the purpose of three-dimensionally cross-linking the binders with each other to improve the mechanical properties of the magnetic coating film. As a result, the magnetic properties of the resulting magnetic powder, the mechanical properties of the magnetic coating film, and the surface properties of the powder become insufficient. Therefore, it is enough to supply the adsorption site of the binder.
It is important to introduce the amount of the group IIa element, and the amount of the group IIa element deposited is preferably 1 part by weight or less as an oxide.

Using the magnetic powder of the present invention, the conventional binder composition, dispersion process, and coating orientation technology can be used as they are, and magnetic properties and powder suitable for sufficiently high-density recording can be obtained without impairing the mechanical properties of the magnetic coating film. It is possible to manufacture a magnetic recording medium having the above surface characteristics and electrical characteristics.

According to the present invention, by introducing a group IIa element together with a group IIIb element on the surface of the magnetic powder, an adsorption active point (mainly a base point) for improving the ease of dispersion of the magnetic powder.
It is possible to improve the wetting property and affinity between the magnetic powder and the solvent without reducing the number, and as a result, it is possible to improve the dispersibility, the orientation and the electrical properties as well as the ease of dispersion.

[0026]

EXAMPLES AND COMPARATIVE EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples. In the examples and comparative examples, the magnetic coating materials were evaluated by the following test methods.

[Evaluation of Magnetic Paint] (1) Dispersibility (Ease of Dispersion and Dispersion) Test The binder, lubricant, abrasive and solvent shown in Table 2 were added to the treated magnetic powder, and the dispersion operation was carried out for 1 hour. went. In addition, B
The method of treating a ferrite powder, the dispersing operation, and Table 2 will be described in detail in Examples. Using an applicator with a gap of 30 μm, a magnetic coating film was prepared from the obtained magnetic coating material by hand. The gloss value (incident angle and reflection angle of 60 degrees) of the obtained coating film was measured using a gloss meter, and this gloss value was regarded as dispersibility. Therefore, the larger this value, the better the dispersibility and the dispersibility represented by the degree of dispersion.

(2) Dispersion attainment test The same test as the dispersibility test was conducted except that the dispersion operation was carried out for 3 hours, and the gloss value of the obtained coating film was taken as the dispersion attainment ratio. Therefore, the larger this value is, the better the dispersibility is.

(3) Orientation test The magnetic coating material, which had been subjected to the dispersion operation for 3 hours, was naturally dried under a direct current magnetic field of 8 kOe to obtain a magnetic coating film. VSM (Vibrating Sample magne
and the residual magnetization amount / saturation magnetization amount ratio was taken as the degree of orientation. Therefore, the larger this value is, the larger the degree of orientation is and the better.

(4) Measurement of Reactivity between Isocyanate Compound and Surface of Magnetic Powder Magnetic powder coated with the above-mentioned dispersion operation for 3 hours was treated with an isocyanate compound [Coronate L, manufactured by Nippon Polyurethane Co., Ltd.] Magnetic powder 100 It was added at a ratio of 3 parts by weight to parts by weight. Immediately after the addition of the isocyanate compound, this magnetic paint was allowed to stand in an environment of a temperature of 20 ° C. and a relative humidity of 60% so that the N
The temporal change of the infrared absorption spectrum based on the CO stretching motion was measured by an infrared spectrophotometer to determine the amount of unreacted isocyanate compound remaining in the paint. The residual ratio of the isocyanate compound was defined as the ratio of the residual amount of the compound 5 hours after the reaction to the initial amount of the isocyanate compound added. It is shown that the larger the residual ratio, the better the delay in the reaction between the isocyanate compound and the Group IIa element.

(5) 5 MHz C / N measurement 5 MHz C / N means the relative speed between the head and tape is 3.7.
It is set to 7 m / s, and the ratio between the signal strength of 5 MHz and the modulation noise of 4 MHz is displayed in dB. In addition, the sample of Comparative Example 1 described later using untreated magnetic powder is used as a reference.

Examples 1 to 8 BaOFe _14.44 Co _0.78 Ni by the glass crystallization method
_A plate-shaped particle of Ba ferrite powder (coercive force 1110 Oe, saturation magnetization 61 emu / g, specific surface area 35 m ² / g) having a basic composition represented by _1.0 Zn _1.0 Ti _0.78 O ₂₄ was W type magnetoplumbite was prepared. Then, 300 g of the untreated magnetic powder thus obtained was well dispersed in 3000 ml of water to obtain a slurry. Further, chlorides containing the treatment elements consisting of the IIa group elements and the IIIb group elements were mixed as the oxides of these elements in the amount shown in Table 1 with respect to 100 parts by weight of the untreated magnetic powder and added to the above slurry. The combination of the group IIa element and the group IIIb element used is Mg / Al.
System, Ba / Al system and Ba / In system. After sufficiently stirring the slurry, 2 times equivalent amount of NaOH was added to the above chloride, and the IIa group element and the I group were added on the surface of the magnetic powder.
The Group IIb element oxide was deposited. The obtained precipitate is
The treated magnetic powder was obtained by processing in the order of filtration, washing with water and drying.

[0033]

[Table 1]

A magnetic coating material was prepared by adding 100 parts by weight of the obtained treated magnetic powder with a binder, a lubricant, an abrasive and a solvent in the respective amounts shown in Table 2. The dispersion was performed for 3 hours with a pot type sand grinder using glass beads having a diameter of 0.8 mm.

[0035]

[Table 2]

The magnetic coating material obtained as described above was evaluated according to the test method described above. Table 3 shows the evaluation results of the Mg / Al based paints, Table 4 shows the same results of the Ba / Al based paints, and B
The same results for the a / In system are shown in Table 5, respectively. Ba / Al
For the system examples, the magnetic coating was applied to a polyethylene terephthalate support film, oriented, then mirror finished and the C / N at 5 MHz was measured and the results are also shown in Table 4.

[0037]

[Table 3]

[0038]

[Table 4]

[0039]

[Table 5]

Although the Mg / Al system and the Ba / Al system show similar behaviors, the Ba / Al system has a larger residual ratio of isocyanate than the Mg / Al system when the coating amount is the same. Also, the degree of dispersion is large. It is considered that this is because the Ba element has a larger atomic weight and is heavier than the Mg element. In addition,
Regarding the degree of dispersion, the Ba / Al system is Mg / Al
It is slightly lower than the system.

On the other hand, in the Ba / In system, although the cause is unknown although the atomic weights of the In element and the Al element are different, the behavior is similar to that of the Ba / Al system.

Comparative Example 1 BaOFe _14.44 Co _0.78 Ni by the glass crystallization method
_A plate-shaped particle of Ba ferrite powder (coercive force 1110 Oe, saturation magnetization 61 emu / g, specific surface area 35 m ² / g) having a basic composition represented by _1.0 Zn _1.0 Ti _0.78 O ₂₄ was W-type magnetoplumbite was prepared. The coating material was evaluated in the same manner as in Example 1 except that the IIa group element and the IIIb group element were not deposited. The results are shown in Table 6.

Comparative Examples 2 and 3 BaOFe _14.44 Co _0.78 Ni by glass crystallization method
_A plate-shaped particle of Ba ferrite powder (coercive force 1110 Oe, saturation magnetization 61 emu / g, specific surface area 35 m ² / g) having a basic composition represented by _1.0 Zn _1.0 Ti _0.78 O ₂₄ was W-type magnetoplumbite was prepared. This was obtained by subjecting Ba to 100 parts by weight of untreated magnetic powder in terms of oxide so as to be 0.1 (comparative example 2) and 0.5 (comparative example 3) parts by weight. The magnetic coating material was evaluated in the same manner as in Example 1. The results are shown in Table 6.

Comparative Examples 4 and 5 BaOFe _14.44 Co _0.78 Ni by the glass crystallization method.
_A plate-shaped particle of Ba ferrite powder (coercive force 1110 Oe, saturation magnetization 61 emu / g, specific surface area 35 m ² / g) having a basic composition represented by _1.0 Zn _1.0 Ti _0.78 O ₂₄ was W-type magnetoplumbite was prepared. This was obtained by subjecting Al to an amount of 0.1 (Comparative Example 4) and 0.5 (Comparative Example 5) parts by weight based on 100 parts by weight of untreated magnetic powder in terms of oxide. The magnetic coating material was evaluated in the same manner as in Example 1. The results are shown in Table 6.

Comparative Examples 6 and 7 BaOFe _14.44 Co _0.78 Ni by glass crystallization method
_A plate-shaped particle of Ba ferrite powder (coercive force 1110 Oe, saturation magnetization 61 emu / g, specific surface area 35 m ² / g) having a basic composition represented by _1.0 Zn _1.0 Ti _0.78 O ₂₄ was W-type magnetoplumbite was prepared. This was obtained by subjecting Zr to an amount of 0.1 (Comparative Example 6) and 0.5 (Comparative Example 7) parts by weight based on 100 parts by weight of untreated magnetic powder in terms of oxide. The magnetic coating material was evaluated in the same manner as in Example 1. The results are shown in Table 6.

Comparative Examples 8 and 9 BaOFe _14.44 Co _0.78 Ni by glass crystallization method
_A plate-shaped particle of Ba ferrite powder (coercive force 1110 Oe, saturation magnetization 61 emu / g, specific surface area 35 m ² / g) having a basic composition represented by _1.0 Zn _1.0 Ti _0.78 O ₂₄ was W-type magnetoplumbite was prepared. Add sodium silicate solution to this
i is converted to oxide based on 100 parts by weight of untreated magnetic powder,
After adding 0.1 (Comparative Example 8) and 0.5 (Comparative Example 9) parts by weight to the magnetic powder slurry, hydrochloric acid was added until the pH of the slurry became 4. Then, the treated powder was obtained by filtering, washing with water and drying, and evaluated in the same manner as in Example 1.
The results are shown in Table 6.

[0047]

[Table 6]

[0048]

As is apparent from the above examples, the magnetic powder of the present invention has improved dispersibility and good dispersibility by depositing the IIa group element and the IIIb group element on the surface.
In addition to its excellent electrical properties, it is a magnetic powder that can delay the reaction with isocyanate compounds, which is important during mass production.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Etsuji Ogawa 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Incorporated Toshiba Research and Development Center

Claims (3)

[Claims] 1. A magnetic powder characterized in that at least a Group IIa element and a Group IIIb element are present on the surface of a hexagonal ferrite magnetic powder. 2. The hexagonal ferrite magnetic powder has a crystal structure or basic composition of M-type magnetoplumbite hexagonal ferrite, W-type magnetoplumbite hexagonal ferrite, Y-type magnetoplumbite hexagonal ferrite,
The magnetic powder according to claim 1, which is a hexagonal ferrite of Z-type magnetoplumbite or a composite type hexagonal ferrite in which spinel ferrite is epitaxially compounded on the surface of these hexagonal ferrites. 3. The IIa group element is Be, Mg, Ca, Sr,
The magnetic powder according to claim 1 or 2, which is at least one element selected from Ra and Ba, and the Group IIIb element is at least one element selected from B, Al, Ga, In, and Tl.