JPH0755828B2 - Magnetic particle powder and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magnetic particle powder having excellent dispersibility, which is suitable as a magnetic particle powder for high density recording, and a method for producing the same.

[Conventional technology]

In recent years, as the size and weight of magnetic recording / reproducing devices have been reduced, there has been an increasing demand for high performance and high density recording of magnetic recording media such as magnetic tapes and magnetic disks.

In order to improve the performance and the recording density of the magnetic recording medium, it is necessary to improve the residual magnetic flux density Br. The residual magnetic flux density Br of the magnetic recording medium depends on the dispersibility of the magnetic particle powder in the vehicle, the orientation in the coating film, and the filling property.

Various attempts have been made to improve the dispersibility of magnetic particle powders, for example, JP-A-55-83207 and JP-A-57-569.
JP 04, JP 61-63921 JP, JP 60-217529 JP, JP 62-89226 JP, JP 58-60506 JP,
As described in JP-A-58-161725 and JP-A-59-23505, there is a method of modifying the particle surface of a magnetic particle powder by coating the particle surface with a Si compound or an Al compound. is there.

[Problems to be solved by the invention]

Magnetic particle powders having excellent dispersibility are currently most demanded, but it is hard to say that they are particles having excellent dispersibility by the above-mentioned known method. The reason why particles with excellent dispersibility have not yet been obtained by the known method is, for example, "Magnetic paint from the viewpoint of researchers of magnetic recording materials" (powder powder metallurgy "7th Ferrite Summer Seminar Lecture Summary") (52) pp. 14-16), p. 16, "In general, obtaining a high degree of dispersion is a fairly difficult problem even in the case of ordinary non-magnetic pigments. The effect further complicates the phenomenon. "
This is because the aggregates are formed by the interaction due to magnetism, and thus the surface is covered with the aggregates as they are.

In particular, in the case of hexagonal ferrite particle powder having an easy axis of magnetization in the direction perpendicular to the plate surface, the particles are strongly aggregated by the interaction of magnetism, and the aggregated particles are individually separated by only mechanical treatment. Separation into particles is difficult.

Therefore, in order to obtain a magnetic particle powder having more excellent dispersibility,
There is a strong demand for establishment of a technical means for coating the particle surface of magnetic particle powder.

[Means for solving problems]

The present inventor has reached the present invention as a result of various studies on a method of coating the particle surface of the magnetic particle powder in order to obtain a magnetic particle powder having more excellent dispersibility.

That is, the present invention is a hydrated alumina having a boehmite structure between a magnetic particle surface and an oxide layer or a hydroxide layer containing Al or Si or Al and Si which coats the particle surface. PH 6.5 by adding an acid or alkali aqueous solution to a mixed suspension of pH 9 or more or 4 or less containing magnetic particle powder consisting of magnetic particles in which particles are present and magnetic particles and hydrated alumina particles having a boehmite structure By adjusting to ~ 8.5, the hydrated alumina particles are deposited on the surface of the magnetic particles, and then an aqueous alkali solution is added to the suspension containing the magnetic particles on which the hydrated alumina particles are deposited. After the suspension having a pH of 10 or more, a compound containing Al or a compound containing Si or both compounds is added to the suspension, and then an acid is added to adjust the pH to 6.5 to 8.5. Hydrated alumina particles settle A method for producing magnetic particles consists in generating the oxide layer or hydroxide layer containing either Al or Si or Al and Si on the particle surfaces of the magnetic particles are.

[Action]

First, the most important point in the present invention is to have a boehmite structure on the magnetic particle surface in advance before coating the particle surface of the magnetic particle with Al or Si or an oxide or hydroxide containing either Al and Si. The fact is that when hydrated alumina particles are deposited, magnetic particle powders with more excellent dispersibility can be obtained.

The reason why the magnetic particle powder having excellent dispersibility is obtained in the present invention is not yet clear, but the present inventor thinks as follows.

That is, both magnetic particles and hydrated alumina particles are negatively charged in a mixed suspension of pH 9 or more, and both magnetic particles and hydrated alumina particles are negatively charged in a mixed suspension of pH 4 or less. It is positively charged, and an electric repulsive force is generated between both particles in any suspension of pH 9 or higher or pH 4 or lower, and this repulsive force is larger than the cohesive force due to the magnetism of the magnetic particles. , The mutual aggregation of magnetic particles is loosened. Then, by adjusting the pH to 6.5 to 8.5, the magnetic particles remain negatively charged when a suspension of pH 9 or higher is used, whereas the hydrated alumina particles are positively charged. On the other hand, when using a suspension of pH 4 or less, the hydrated alumina particles remain positively charged, whereas the magnetic particles are negatively charged and both particles have opposite charges. Since the particles are charged, the hydrated alumina particles are deposited on the surface of the magnetic particles and the subsequent re-aggregation is prevented. As a result, in the subsequent step of coating Al or Si or an oxide or hydroxide containing Al and Si, individual particles can be coated instead of the aggregate of magnetic particles.

Next, various conditions for carrying out the present invention will be described.

Examples of the magnetic particle powder in the present invention include maghemite particle powder, magnetite particle powder, magnetic iron oxide particle powder such as a beltride compound ( FeO x · Fe ₂ O ₃ , 0 <x <1),
Particles containing different magnetic metals such as Co other than Fe in these magnetic iron oxide particle powders or particles obtained by depositing Co on these magnetic iron oxide particles, metallic magnetic particles containing iron as a main component, and hexagonal ferrite Any of particles and the like can be used.

The hydrated alumina in the present invention may have any particle morphology as long as it has a boehmite structure, and may be commercially available or may be produced by hydrothermal treatment of an alkaline aqueous solution containing an Al salt. .

The amount of hydrated alumina added is 0.05 to 5.0% by weight in terms of Al ₂ O _{3 based on the} magnetic particle powder. If the amount is less than 0.05% by weight, the desired effect of the present invention cannot be obtained. 5.0% by weight
If it exceeds the above range, the effect aimed at by the present invention can be obtained, but it is not preferable because the saturation magnetization is lowered due to the increase of hydrated alumina which is not involved in magnetism. Considering the dispersibility and saturation magnetization of the magnetic particle powder, 0.1 to 3.0% by weight is preferable.

The pH of the mixed suspension of magnetic particles and hydrated alumina particles having a boehmite structure in the present invention is 9 or more or 4 or less. When the pH is between 4 and 9, the magnetic particles and the hydrated alumina particles are charged with opposite charges or the repulsive charge is weak, resulting in insufficient electric repulsion and Cannot be separated into particles. Equipment having shearing force when creating a mixed suspension of pH 9 or more or pH 4 or less, for example,
By performing mechanical treatment using a homomixer, a line mill, a sand grind mill, etc., a more excellent dispersion effect can be obtained.

Deposition of hydrated alumina on the surface of magnetic particles in the present invention is performed by adding an acid or alkali aqueous solution to a mixed suspension having a pH of 9 or more and 4 or less to adjust the pH to 6.5 to 8.5. By adjusting the pH, almost all of the added hydrated alumina particles are deposited. Near this pH, the hydrated alumina has a positive charge and the magnetic particle powder has a negative charge, so that electrical coupling occurs and the hydrated alumina particles are deposited on the surface of the magnetic particles. Sulfuric acid, hydrochloric acid, acetic acid, nitric acid or the like can be used as the acid for adjusting the pH, and sodium hydroxide, potassium hydroxide, aqueous ammonia or the like can be used as the alkali.

In the present invention, the suspension containing the magnetic particles in which the hydrated alumina particles are deposited is adjusted to pH 10 or more by adding an alkaline aqueous solution, and then a compound containing Al or a compound containing Si or both the compounds are added. The pH is set to 10 or more so that the magnetic particles in which the hydrated alumina is deposited are in a dispersed state and uniformly mixed with the added compound.

As the alkaline aqueous solution for adjusting the pH to 10 or more, sodium hydroxide, potassium hydroxide, aqueous ammonia, etc. can be used. As the compound containing Al, alkali aluminate such as sodium aluminate and potassium aluminate, aluminum salt such as aluminum sulfate, aluminum chloride and aluminum nitrate can be used.

The addition amount of the compound containing Al is Al ₂ O based on the magnetic particle powder.
It is 0.01 to 5.0% by weight in terms of ₃ . If it is less than 0.01% by weight, the effect of the present invention cannot be obtained. Even if the amount exceeds 5.0% by weight, the effect of the present invention can be obtained, but the saturation magnetization is lowered due to the increase of Al-containing compounds not involved in magnetism, which is not preferable. Considering the dispersibility and saturation magnetization of the magnetic particle powder, 0.05 to 3.0% by weight is preferable.

As the compound containing Si, sodium silicate, potassium silicate, colloidal silica or the like can be used.

The addition amount of the compound containing Si is SiO _{2 with} respect to the magnetic particle powder.
It is 0.01 to 5.0% by weight in conversion. If it is less than 0.01% by weight, the effect of the present invention cannot be obtained. Even when the amount exceeds 5.0% by weight, the effect of the present invention can be obtained, but the saturation magnetization is lowered due to the increase of the compound containing Si that is not involved in magnetism, which is not preferable. Considering the dispersibility and saturation magnetization of the magnetic particle powder, 0.1 to 2.0% by weight is preferable.

When adding a Si compound and an Al compound in the present invention, the total amount of Al ₂ O ₃ conversion and SiO ₂ conversion is 0.01 to 5.0% by weight, preferably 0.1 to 3.0% by weight, with respect to the magnetic iron oxide particles. .

With a Si compound added to a suspension having a pH of 10 or more in the present invention
By adjusting the pH of the suspension to 6.5 to 8.5, the Al compound is deposited on and deposited on the surface of the magnetic particles as Si, Al oxides and hydroxides, and the coating film is formed. .

As the acid for adjusting the pH, sulfuric acid, hydrochloric acid, acetic acid, nitric acid or the like can be used.

〔Example〕

 Next, the present invention will be described with reference to Examples and Comparative Examples.

Incidentally, the evaluation of the dispersibility in the present invention, in the case of acicular magnetic iron oxide particles powder, the residual magnetic flux density B when taped
In the case of tabular Ba ferrite fine particle powder, the saturation magnetic flux density Bm, the square shape (Br / Bm), and the square shape (Br / Bm) of It shows by showing each value of glossiness, and it means that the dispersibility is improved as any of the above values is increased.

In addition, the value of the square shape when made into a tape by using plate-like Ba ferrite fine particles is measured by measuring the square shape (Br / Bm) in the vertical direction of the magnetic tape in which the magnetic field is oriented in the direction perpendicular to the tape surface, The values are shown after demagnetizing field correction.

The magnetic properties of the magnetic particle powder are described in "Vibration sample magnetometer VSM-3S
-15 "(manufactured by Toei Industry Co., Ltd.) under an external magnetic field of 10KOe.
It is the result of measurement under KOe (5 KOe when maghemite particles are used).

The surface gloss of the coating film is an incident angle of 60 manufactured by Nippon Denshoku Industries Co., Ltd.
It is the value measured with a gloss meter at
The value when 89.0% is shown in%.

<Surface Treatment of Magnetic Particle Powder> Examples 1 to 9, Comparative Examples 1 to 9, Reference Examples 1 to 3; Example 1 Long axis 0.22 μm, axial ratio (major axis: minor axis) 7.5: 1 Co-coated acicular γ-Fe ₂ O ₃ particles with a magnetic force of 635 Oe (Co / total amount =
3.29% by weight) and 500 g of the particles and hydrated alumina AS-520 having a boehmite structure (manufactured by Nissan Chemical Industries, Ltd., the amount of Al corresponds to 20.8% by weight in terms of Al ₂ O ₃ ) 24 g (Co It corresponds to 1.0% by weight in terms of Al ₂ O _{3 with} respect to the adherend γ-Fe ₂ O _3. )
And were added to and mixed with 5 liters of water, sodium hydroxide was added to obtain a mixed suspension having a pH of 11.3.

After stirring and mixing the above mixed suspension, sulfuric acid was added to adjust the pH.
After adjusting to 7.2, hydrated alumina particles were deposited on the surface of the Co-adhered γ-Fe ₂ O ₃ particles.

A part of the reaction solution was taken out, filtered by a conventional method, washed with water, and dried to obtain a brownish brown particle powder. As a result of fluorescent X-ray analysis, the Co-adhered γ-Fe ₂ O ₃ particles were present on the surface. Al
The amount was 0.98% by weight in terms of Al ₂ O ₃ .

Sodium hydroxide was added to the suspension containing the brown precipitate particles to adjust the pH to 10.9, and then No. 3 water glass (manufactured by Tokuyama Soda Co., Ltd., the Si content corresponds to 29.0 wt% in terms of SiO ₂ ). ) 34.5 g (Co-deposited γ-Fe ₂ O ₃ is 2.0 in terms of SiO ₂₎
Corresponds to% by weight. ) Was added, followed by stirring and mixing, and then sulfuric acid was added to adjust the pH to 7.9 to obtain brownish brown precipitate particles in which a SiO ₂ film was deposited on the surface of the brownish brown precipitate particles.

The suspension containing the brown-colored precipitated particles is filtered by a conventional method,
It was washed with water and dried.

The amount of SiO ₂ present on the surface of the obtained brown particle powder is
As a result of a fluorescent X-ray analysis, it was 1.99% by weight in terms of SiO ₂ .

Example 2 Using the same Co-coated acicular γ-Fe ₂ O ₃ particles (Co / total amount = 3.29% by weight) as in Example 1, 500 g of the particles and hydrated alumina AS-520 having a boehmite structure (Nissan Chemical Industry Co., Al
The amount corresponds to 20.8% by weight in terms of Al ₂ O ₃ . ) 12.0 g (corresponding to 0.5% by weight in terms of Al ₂ O _{3 with} respect to Co-adhered γ-Fe ₂ O ₃ ) was added to 5 liters of water and mixed, and sodium hydroxide was added to adjust the pH to 10 A mixed suspension of 0.8 was obtained.

After stirring and mixing the above mixed suspension, sulfuric acid was added to adjust the pH.
After adjusting to 7.1, hydrated alumina particles were deposited on the surface of the Co-adhered γ-Fe ₂ O ₃ particles.

A part of the reaction solution was taken out, filtered by a conventional method, washed with water, and dried to obtain a brownish brown particle powder. As a result of fluorescent X-ray analysis, the Co-adhered γ-Fe ₂ O ₃ particles were present on the surface. Al
The amount was 0.49% by weight in terms of Al ₂ O ₃ .

Sodium hydroxide was added to the suspension containing the brown precipitate particles to adjust the pH to 11.8, and sodium aluminate (Yoneyama Yakuhin Kogyo Co., Ltd., the amount of Al was 62% by weight in terms of Al ₂ O ₃ ). 16.1 g (corresponding to 2.0% by weight in terms of Al ₂ O _{3 with} respect to Co-deposited γ-Fe ₂ O ₃ ), and then stirring,
After mixing, sulfuric acid was added to adjust the pH to 7.0 to obtain brownish brown precipitate particles having an aluminum hydroxide film deposited on the surface of the brownish brown precipitate particles.

The suspension containing the brown-colored precipitated particles is filtered by a conventional method,
It was washed with water and dried.

The amount of Al in the obtained brown particle powder was 2.46% by weight in terms of Al ₂ O _{3 as} a result of fluorescent X-ray analysis.
1.97 obtained by subtracting the amount of Al existing in the deposited γ-Fe ₂ O _3.
Weight% is the amount of Al in terms of Al ₂ O ₃ in the sodium hydroxide coating.

Examples 3 to 9 Type of powder to be treated, pH of mixed suspension, type of hydrated alumina in treatment step with hydrated alumina, addition amount and adjusted pH, Al or Si or oxidation containing Al and Si. PH and Al after adjustment in the production process of the oxide layer or hydroxide layer
A brownish brown particle powder was obtained in the same manner as in Example 1 except that the kind of the compound containing Si or the compound containing Si, the addition amount, and the adjusted pH were variously changed.

Table 1 shows the main production conditions at this time and various characteristics of the obtained brownish brown particle powder.

Comparative Examples 1 to 9 Example 1 except that the treatment step with hydrated alumina was omitted.
Brown powders were obtained in the same manner as in Nos. 9 to 9.

Reference Examples 1 to 3 Treatment with only hydrated alumina was performed in the same manner as in Examples 1, 4 and 5 to obtain magnetic particle powder in which hydrated alumina was deposited on the surface of magnetic particles.

<Production of Magnetic Tape> Examples 10 to 18, Comparative Examples 10 to 18, Reference Examples 4 to 6; Example 10 The particle surface obtained in Example 1 and the aluminum hydroxide layer coated on the particle surface. Using Co-coated acicular γ-Fe ₂ O ₃ particle powder in which hydrated alumina particles are present, an appropriate amount of a dispersant, a vinyl chloride vinyl acetate copolymer, a thermoplastic polyurethane resin and toluene, A mixed solvent composed of methyl ethyl ketone and methyl isobutyl ketone was mixed in a constant composition, and then mixed and dispersed in a ball mill for 8 hours to obtain a magnetic paint.

The above-mentioned mixed solvent was added to the obtained magnetic paint to adjust it to an appropriate paint viscosity, which was applied, oriented and dried on a polyester resin film by a usual method to produce a magnetic tape.

The residual magnetic flux density Br of this magnetic tape was 1550 Gauss, the square type (Br / Bm) was 0.84, and the orientation degree was 2.39.

Examples 11 to 13, Comparative Examples 10 to 13, Reference Examples 4 and 5 The acicular magnetic iron oxide particle powders obtained in Examples 2 to 4, Comparative Examples 1 to 4 and Reference Examples 1 and 2 were used. except,
A magnetic tape was manufactured in the same manner as in Example 10.

When hexagonal ferrite particle powder is used as the magnetic powder, a magnetic paint whose paint viscosity has been adjusted is applied on a polyester resin film, which is then oriented in the direction perpendicular to the film and dried to produce a magnetic powder. A tape was manufactured.

Table 2 shows various characteristics of this magnetic tape.

Examples 14-18, Comparative Examples 14-18, Reference Example 6 Examples except that the plate-like Ba ferrite fine particles obtained in Examples 5-9, Comparative Examples 5-9, and Reference Example 3 were used, respectively. A magnetic tape was manufactured in the same manner as in 10.

Table 3 shows various characteristics of this magnetic tape.

[Effects of the Invention] The magnetic particle powder according to the present invention is suitable for high-density recording because it has excellent dispersibility as shown in the above-mentioned Examples.

Claims (2)

[Claims] 1. A hydrated alumina particle having a boehmite structure between the surface of a magnetic particle and an oxide layer or a hydroxide layer containing Al or Si or Al and Si that coats the surface of the particle. Magnetic particle powder consisting of magnetic particles present in. 2. A mixed suspension of pH 9 or more or 4 or less containing magnetic particles and hydrated alumina particles having a boehmite structure is adjusted to pH 6.5 to 8.5 by adding an acid or alkali aqueous solution. After depositing the hydrated alumina particles on the surface of the magnetic particles, and then adding an alkaline aqueous solution to the suspension containing the magnetic particles on which the hydrated alumina particles are deposited to form a suspension having a pH of 10 or more. By adding a compound containing Al or a compound containing Si or both compounds to the suspension and then adding an acid to adjust the pH to 6.5 to 8.5, the hydrated alumina particles are deposited. A method for producing magnetic particle powder, which comprises forming an oxide layer or a hydroxide layer containing Al or Si or either Al and Si on the surface of magnetic particles.