JPH03232726A - Composite ferrite magnetic powder and production thereof - Google Patents

Abstract

PURPOSE:To obtain the subject magnetic powder having a suitable coercive force, low in the temperature dependence thereof, excellent in dispersibility and suitable for a magnetic recording medium for a high-density recording by depositing a spinel type ferrite on the surface of a ferrite magnetic powder occluding zinc in the inside of the particle and having a magnetoplumbite-type crystal structure. CONSTITUTION:A ferrite magnetic powder having a magnetoplumbite-type crystal structure is suspended in an aqueous zinc salt solution and an alkali hydroxide is added thereto to deposit a zinc hydroxide on the surface of the powdery magnetic particles. After filtration and drying, calcination is carried out at 700-950 deg.C to obtain a magnetic powder occluding zinc in the inside of the particle. The resultant ferrite magnetic powder is suspended in water and an aqueous solution containing a metallic ion of Co, Ni, Zn, Cu, etc., and Fe<2+> and an aqueous alkaline solution are added thereto. The obtained mixture is subjected to aging, washing and filtration and subsequently dried in a non-oxidative atmosphere, thus obtaining the objective composite ferrite magnetic powder having a spinel-type ferrite deposited on the particle surface, having 20-70m<2>/g specific surface area and 200-20000 Oe coercive force.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a composite ferrite magnetic powder and a method for producing the same.

More specifically, the present invention is suitable for use in magnetic recording media for high-density recording, and has a specific surface area of 20 to 70 rrf/g.
The present invention relates to a method for producing a composite ferrite magnetic powder having a coercive force of 200 to 20,000 e, a small temperature change in the coercive force, a small electrical resistance of the powder, and excellent dispersibility.

In recent years, with the demand for higher density magnetic recording, development of perpendicular magnetic recording systems using magnetoplumbite-type ferrite magnetic powder as a magnetic recording medium has been progressing.

The magnetoplumbite type ferrite magnetic powder used in the perpendicular magnetic recording system has a coercive force of an appropriate value (200
~20,000e), with small temperature changes in coercive force, low electrical resistance, and good dispersibility.

(Prior art and its problems) Conventionally, various methods have been known for producing magnetoplumbite-type ferrite magnetic powder, such as coprecipitation, glass crystallization, and hydrothermal synthesis. Regarding the chemical synthesis method, see Japanese Patent Publication No. 60-15575, and regarding the hydrothermal synthesis method, see Japanese Patent Publication No. 59-175707, Japanese Patent Publication No. 60-12973, and Japanese Patent Publication No. 60-15576.
This method has been proposed in Japanese Patent Application Laid-Open No. 60-137002, etc.

However, the magnetoplumbite type ferrite magnetic powder obtained by any of the above methods has drawbacks such as large temperature changes in coercive force and poor dispersibility.

On the other hand, magnetoplumbite-type ferrite magnetic powder has a higher electric resistance than conventional Co7FezO3, so a large amount of conductive substance must be added when making it into a coating medium. There was a problem that the conversion characteristics deteriorated.

As a method to solve these problems, JP-A-62-1
No. 39122, No. 62-139124, No. 6
No. 2-265122, No. 63-144118, and No. 63-144119 propose coating the surface of ferrite magnetic powder with spinel type ferrite.

The ferrite magnetic powder obtained by this method actually improves the various properties mentioned above, but when the surface of the ferrite magnetic powder is coated with spinel ferrite, the coercivity of the ferrite magnetic powder is affected by the coercive force of the spinel ferrite. Since the magnetic force fluctuates greatly, it has been difficult to control the coercive force.

(Objective of the Invention) The object of the present invention is to solve the above-mentioned problems, and to obtain fine particles having a specific surface area of 20 to 70 m/g and a coercive force of 200 to 20 m/g.
It can be easily controlled within the range of 000e, the temperature change in coercive force is small, and the electrical resistance of the powder is small.
An object of the present invention is to provide a composite type ferrite magnetic powder with excellent dispersibility and a method for producing the same.

(Means for Solving the Problems) The present invention is characterized in that zinc is solidly dissolved inside particles of ferrite magnetic powder having a magnetoplumbite crystal structure, and spinel ferrite is adhered to the surface of the particles. The present invention relates to a composite ferrite magnetic powder and a method for producing the same.

The ferrite magnetic powder having a magnetoplumbite crystal structure in the present invention has the general formula A 0-n (Fe
Ferrite magnetic powder represented by
Preferably, the thickness is 0.1 μm.

A in the general formula represents one or more elements selected from Ba, Sr, and pb, and M represents Co, Ni,
Zn, Cu, old, Ti, Zr, Sn, Nb, ■,
Indicates one or more elements selected from MO and W, n =
It is a numerical value of 0.9 to 1.2.0<x<4. Also, α
When the average valence of M is m, α=(m-3)x/
2, and −2≦α≦0.

In addition, as a spinel type ferrite, the general formula MXFe
2''', 048zO8 (M is C01Ni, Z
One or more metal elements selected from n and Cu, and 0
<x≦1.0≦y<1, Q<x+y≦1.

) Composite spinel type ferrites can be mentioned.

The amount of the ferrite magnetic powder of the composite spinel type ferrite deposited on the particle surface is 5 to 40% by weight based on the magnetic powder.
, particularly preferably 10 to 30% by weight. Outside this range, a powder with small temperature change in coercive force, small electrical resistance, and excellent dispersibility cannot be obtained.

Further, in the present invention, the coating layer of the composite spinel ferrite may partially contain an oxide of a metal element constituting the composite spinel ferrite.

In the present invention, by coating composite spinel type ferrite on the particle surface of ferrite magnetic powder, ferrite magnetic powder with small temperature change in coercive force, small electrical resistance, and excellent dispersibility can be obtained.

Furthermore, by dissolving zinc inside the particles of the ferrite magnetic powder, fluctuations in coercive force are suppressed, so the coercive force of the ferrite magnetic powder can be easily controlled. In particular, some of the iron is C.

The effect is remarkable in the case of ferrite magnetic powder substituted with Ti and Ti.

The solid solution amount of zinc is 0.1 to 10% by weight based on the magnetic powder,
Particularly preferred is 0.3 to 6% by weight. If the solid solution amount is less than 0.1% by weight, the effect of zinc cannot be obtained, and 10% by weight
Even if it is increased, there is no advantage to increasing it, and it is not economical.

The composite ferrite magnetic powder of the present invention is produced by suspending ferrite magnetic powder having a magnetoplumbite crystal structure in an aqueous solution containing zinc, and adding alkali hydroxide to deposit zinc hydroxide on the particle surface. After that, filter and dry, 70
A first step of obtaining ferrite magnetic powder in which zinc is solidly dissolved inside the particles by firing at 0 to 950°C, and the ferrite magnetic powder obtained in the first step is suspended in water, and Co, Co, An aqueous solution containing one or more metal ions selected from Ni, Zn, and Cu and an aqueous alkaline solution containing "Fe" are added, and the resulting mixed suspension is aged, washed, filtered, and dried in a non-oxidizing atmosphere. By doing so, the second step produces ferrite magnetic powder in which spinel-type ferrite is adhered to the particle surface.

Each step will be explained in detail below.

[First Step] As the ferrite magnetic powder having a macnetobrambite crystal structure, those manufactured by conventionally known coprecipitation methods, glass crystallization methods, hydrothermal synthesis methods, etc. are used.

First, this ferrite magnetic powder is suspended in an aqueous solution containing zinc, and alkali hydroxide is added to deposit zinc hydroxide on the particle surface.

As the aqueous solution containing zinc, halides such as zinc chloride, zinc bromide, and zinc iodide, zinc nitrate, zinc sulfate, zinc acetate, and the like are used.

As the alkali hydroxide, sodium hydroxide, potassium hydroxide, aqueous ammonia, etc. are used.

Next, the particles are filtered, dried, and fired at 700 to 950''C to obtain ferrite magnetic powder in which zinc is solidly dissolved inside the particles.

In the present invention, it is preferable to mix a flux with the ferrite magnetic powder and then sinter the mixture. As the flux, at least one of sodium chloride, barium chloride, potassium chloride, strontium chloride, and sodium fluoride is used. The amount of flux used is preferably 10 to 180% by weight, particularly 30 to 120% by weight, based on the magnetic powder. If the amount of flux is too small, sintering of the particles will occur, and if it is too large, there will be no benefit from increasing the amount and it is not economical. There are no particular restrictions on the method of mixing the magnetic powder and the flux; for example, the flux may be added to a slurry of magnetic powder, mixed wet, and then the slurry may be dried, or the magnetic powder may be dried and then the flux may be added. It may be dry mixed.

Firing temperature is 700-950℃1 preferably 800-93℃
It is 0°C. If the temperature is too low, solid solution of zinc inside the particles will not be sufficient. Furthermore, if the temperature is too high, the particles become large and sintering occurs, which is not preferable. Appropriate firing time is about 10 minutes to 30 hours. The firing atmosphere is not particularly limited, but an air atmosphere is generally convenient.

By washing, filtering and drying the obtained baked product,
Ferrite magnetic powder in which zinc is solidly dissolved inside the particles is obtained.

[Second step] The ferrite magnetic powder obtained in the first step is suspended in water,
To this, an aqueous solution containing one or more metal ions selected from Co, Ni, Zn, and Cu and Fe'' and an alkaline aqueous solution are added.

As compounds of Co, Ni, Zn, and Cu, those soluble in water such as their nitrates, chlorides, and sulfates are used, and as compounds of Fe, ferrous sulfate and ferrous chloride are generally used. used.

As for the addition method, an aqueous solution of the compound may be added to a suspension solution of ferrite magnetic powder in a non-oxidizing atmosphere, and then an aqueous alkaline solution may be added to coat the hydroxide on the particle surface. The order of addition of the aqueous solution and aqueous alkaline solution may be reversed.

The resulting mixed suspension is then aged. The aging temperature is preferably room temperature to 200°C.

Due to aging, general 2 M, Fe”, ()Fe, 03 (
However, M is one or more metal elements selected from Co, Ni, Zn, and Cu, and O<x≦1.0≦y<1
．． 0<x+y≦1. ) is formed on the particle surface.

Next, after washing and filtering, the particles are dried in a non-oxidizing atmosphere to obtain ferrite magnetic powder in which spinel-type ferrite is adhered to the particle surface.

The non-oxidizing atmosphere is preferably an inert gas such as nitrogen or helium, or a vacuum.

Drying is carried out at room temperature to 500°C, preferably 100 to 500°C.
1. It is particularly desirable to conduct the reaction at a temperature in the range of 150 to 400°C.

Furthermore, a magnetic recording medium can be obtained by applying the composite ferrite magnetic powder obtained according to the present invention to the surface of a support together with a binder resin.

As the binder resin, for example, vinyl chloride-vinyl acetate copolymer, cellulose derivative, polyurethane resin, epoxy resin, etc. are used. Further, as the support, for example, a polyethylene terephthalate film, a polyamide resin film, a polyimide resin film, etc. are used.

Further, a dispersant, a lubricant, a hardening agent, an abrasive, etc. can also be added. Examples of dispersants include lecithin, lubricants include higher fatty acids and fatty acid esters, hardeners include bifunctional or higher-functional isocyanate compounds, and polishing agents include CrzO, Af, etc.
zOi, (r-Fe203, etc.) are used.

The method for producing magnetic recording media is the usual method, for example, by kneading magnetic powder, binder resin, and additives with a solvent to produce a magnetic paint, applying this magnetic paint to a support, and then performing an orientation treatment and drying. Examples include methods of performing treatments and the like.

(Example) The present invention will be explained in more detail by showing Examples and Comparative Examples below.

Reference Example 1 Ferric nitrate [Fe(NOs)] was added to 550 d of deionized water.
s'9HzO] 472.8g, cobalt nitrate [Co(N
Os) t・61bO] 30.4 g and titanium tetrachloride [T
Dissolve 119.8 g of 1Cf and separately add 103 g of deionized water.
5d, barium chloride [BaCjz・2HzO] 36.
2 g and 693 g of caustic soda [NaOH] were dissolved and both solutions were mixed to form a precipitate.

The resulting slurry containing the precipitate was placed in an autoclave;
Hydrothermal treatment was performed at 250° C. for 3 hours to obtain a precipitate of barium ferrite fine particles.

Example 1 [First step] After thoroughly washing the precipitate obtained in Reference Example 1 with water, acetic acid was added while stirring to adjust the pH to 4.5, and zinc nitrate [Zn(NOs)z・68zO] After adding an aqueous solution in which 19.7 g was dissolved, the mixture was neutralized with aqueous ammonia.

Next, it is washed, filtered, dried, and Na(
A mixture of 1 g of J and 1 g of BaC/2 HzO in a weight ratio of 1=1 was added to the magnetic powder in an amount of 100% by weight and mixed. This mixture was calcined at 860° C. for 2 hours under an air atmosphere.

[Second step] After thoroughly washing the baked product obtained in the first step with water, a solution of 90 g of caustic soda dissolved in 5001 d of water was added,
Separately, add cobalt sulfate [Co50a・7Ht] to 500jd of water.
O] 15.5g and ferrous sulfate [FeSO4H*0]
After adding a solution containing 90g and mixing thoroughly, add 1
The sample was aged at 00°C in a nitrogen atmosphere to perform a cobalt ferrite deposition reaction.

After washing and filtering the obtained slurry, the filter cake was dried at 150° C. for 10 hours in a nitrogen atmosphere.

Table 1 shows the results of measuring the powder properties of the composite ferrite magnetic powder obtained.

Example 2 In Example 1, 15.5 g of cobalt sulfate in the cobalt ferrite adhesion reaction in the second step was replaced with cobalt sulfate) 11.
A composite ferrite magnetic powder was obtained in the same manner as in Example 1, except that 6 g of zinc sulfate and 4.0 g of zinc sulfate [ZnSO44H*0] were used.

Table 1 shows the results of measuring the powder properties of the composite ferrite magnetic powder obtained.

Comparative Example 1 The precipitate obtained in Reference Example 1 was washed, filtered, and dried, and a mixture of NaCl and Ba1J2.2H20 in a weight ratio of 1:1 was added thereto as a flux at 100% by weight based on the magnetic powder. Mixed. This mixture was calcined at 860° C. for 2 hours under an air atmosphere.

After thoroughly washing the obtained baked product with water, add caustic soda 9
Add a solution of 0g dissolved in 5001d of water, and separately add 5001d of water.
A solution containing 5.5 g of cobalt sulfate and 90 g of ferrous sulfate was added to Oi and thoroughly mixed, and then aged at 100° C. in a nitrogen atmosphere to perform a cobalt ferrite adhesion reaction.

After washing and filtering the resulting slurry, the filter cake was dried at 150''C for 10 hours in a nitrogen atmosphere.

Table 1 shows the results of measuring the powder properties of the composite ferrite magnetic powder obtained.

Comparative Example 2 The precipitate obtained in Reference Example 1 was washed, filtered, and dried, and a mixture of Na (J and Ba (J, 2) 20 in a weight ratio of 1:1 as a fluxing agent was added to it as a magnetic powder. The mixture was added in an amount of 100% by weight and mixed.This mixture was fired at 860° C. for 2 hours in an air atmosphere.

The obtained fired product was thoroughly washed with water, filtered, and dried to obtain a composite ferrite magnetic powder.

Table 1 shows the results of measuring the powder properties of the composite ferrite magnetic powder obtained.

(Effects of the Invention) The composite ferrite magnetic powder obtained by the present invention has a small temperature change in coercive force, a small electrical resistance of the powder, excellent dispersibility, and can easily have a coercive force in the range of 200 to 20,000e. Since it can be controlled, it is suitably used as a magnetic recording material for high-density recording.

Claims (2)

[Claims] (1) A composite ferrite magnetic powder characterized in that zinc is solidly dissolved inside the particles of ferrite magnetic powder having a magnetoplumbite crystal structure, and spinel ferrite is adhered to the surface of the particles. . (2) suspending ferrite magnetic powder having a magnetoplumbite crystal structure in an aqueous solution containing zinc, adding alkali hydroxide to deposit zinc hydroxide on the particle surface, filtering and drying; A first step of obtaining ferrite magnetic powder in which zinc is solidly dissolved inside the particles by firing at 700 to 950°C, and the ferrite magnetic powder obtained in the first step is suspended in water, and Co, Co, An aqueous solution and an alkaline aqueous solution containing one or more metal ions selected from Ni, Zn, and Cu and Fe^2^+ are added, and the resulting mixed suspension is aged, washed, filtered, and placed in a non-oxidizing atmosphere. 2. The method for producing a composite ferrite magnetic powder according to claim 1, further comprising a second step of drying the powder in a drying medium to obtain a ferrite magnetic powder in which spinel-type ferrite is adhered to the surface of the particles.