JPH0323224A - Production of complex-type ferritic magnetic powder - Google Patents

Abstract

PURPOSE:To obtain the magnetic powder excellent in dispersibility and saturation magnetization, reduced in temp. change of coercive force and electric resistance, and useful for magnetic recording material for high-density recording by applying specific treatment to a fine particles having magnetoplumbite-type crystalline structure. CONSTITUTION:Fine particles composed of hexagonal magnetoplumbite-type ferrite represented, preferably, by a formula (where A means Ba, Sr, and Pb, M means Co, Ni, Zn, Cu, Bi, Ti, Zr, Sn, Nb, V, Mo, and W, and the symbols n, x, and alpha stand for 0.9-1.2, >0-<4, and -2-0, respectively) and having a magnetoplumbite-type crystalline structure in which particle size is regulated to <=0.1mu are suspended in water. Subsequently, an aqueous solution containing ions of one or more metals selected from Co, Ni, Zn, and Cu and Fe<2+> and aqueous alkali (e.g. NaOH) are added to the resulting suspension to form a mixed suspension, which is subjected to heating treatment at 50-200 deg.C, washed, filtered, and then subjected to heat treatment at 100-500 deg.C in a nonoxidizing atmosphere, such as N2.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a composite ferrite magnetic layer.

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 rd/
g, the coercive force is 200 to 2000 oe, the saturation magnetization is dramatically improved compared to conventional ones, the coercive force changes less with temperature, the electrical resistance of the powder is small, and the powder has excellent dispersibility. The present invention relates to a method for producing composite ferrite magnetic powder.

In recent years, with the demand for higher density magnetic recording, the development of perpendicular magnetic recording methods 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 (20
0 to 20000e), the saturation magnetization is as high as possible, the coercive force changes little with temperature, the electrical resistance is small, and the dispersibility is good.

(Prior art and its problems) Conventionally, various methods have been known for manufacturing magnetoplumbite type ferrite magnetic materials, such as coprecipitation method, glass crystallization method, hydrothermal synthesis method, etc. The crystallization method is described in Japanese Patent Publication No. 60-15575, and the hydrothermal synthesis method is described in, for example, 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 a low saturation magnetization of 60 emu/g or less, a large temperature change in coercive force, and poor dispersibility. ．． On the other hand, the magnetoplumbite type ferrite magnetic powder is similar to the conventional Go-γ-Fe. Since the electrical resistance of the powder is higher than that of O, a large amount of conductive substance must be added when making it into a coating medium, which causes the problem of deterioration of the IIT magnetic conversion characteristics. 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 disclose Ferrai l-
It has been proposed to coat the surface of IF powder with spinel type ferrite.

Although the ferrite magnetic powder obtained by this method actually has improved various properties described above, these properties deteriorate due to changes over time, which poses a practical problem.

(Objective of the Invention) The object of the present invention is to solve the above-mentioned problems, and to obtain fine particles with a specific surface area of 20 to 70 rd/g and a coercive force of 200 to 200 rd/g.
00e, the saturation magnetization has been dramatically improved compared to conventional ones, the temperature change in coercive force is small, the electrical resistance of the powder is small, and the powder has excellent dispersibility, and these characteristics remain unchanged over time. An object of the present invention is to provide a method for producing composite ferrite magnetic powder that does not change.

(Means for Solving the Problems) The present invention involves suspending fine particles having a magnetoplumbite crystal structure in water, and adding one or more metal ions selected from Co, Ni, Zn, and Cu to the fine particles. An aqueous solution containing ``Fe'' and an aqueous alkaline solution were added, and the resulting mixed suspension was heat-treated at 50 to 200''C, washed and filtered, and then heat-treated at 100 to 500℃ in a non-oxidizing atmosphere. This article relates to a method for producing composite ferrite magnetic powder characterized by the following. Examples of the fine particles having a magnetoplumbite crystal structure in the present invention include magnetoplumbite ferrite represented by the general formula A○・n(Fe+z1MxO..α), and in particular particles having a hexagonal plate shape and a particle diameter of 0. ．． The thickness is preferably 1 μm or less.

A in the general formula represents one or more elements selected from Ba, Sr and Pb, and M represents CoSNi, Z
n, Cu, Bi, Ti, Zr, Sn, Nb,
V. ．． Indicates one or more elements selected from Mo and W, n = 0. 9-1. It is a numerical value of 2, 0 x 4. In addition, α is α=(
m-3) A numerical value expressed as x/2, where -2≦α≦0
, preferably -1.5≦α≦-0. It is 1.

The magnetoplumbite type ferrite is produced by a coprecipitation method, a glass crystallization method, a hydrothermal coalescence method, etc. below,
A method for producing magnetoplumbite barium ferrite using a hydrothermal coalescence method is described.

As a starting material, 1 gram atom of barium, 1 to 12 gram atom of iron per atom, 12-x gram atom of iron,
Using a compound of each element in which M is a proportion of is added to form a precipitate, and the slurry containing the precipitate is hydrothermally treated at 130 to 300°C. A flux is mixed to the raw precipitate, and the mixture is heated to a temperature of 700 to 950°C.
By annealing with C, the magnetoplumbite type ferrite is obtained.

As the barium compound, barium nitrate, barium chloride, barium hydroxide, etc. are used. The amount of barium used is preferably such that the barium concentration is in the range of 0.03 to 0.50 mol/l in order to obtain hexagonal particles with good crystallinity.

Ferric nitrate, ferric chloride, etc. are used as iron compounds. The amount of iron used is 1 to 1 gram atom of barium.
It is a 12 gram atom. If the amount of iron is too small, the amount of magnetoplumbite barium ferrite produced will be small and the crystallinity will be poor. Furthermore, if the amount of iron is too large, hematite may be produced as a by-product, and barium ferrite particles may become large, resulting in poor magnetic properties.

Examples of compounds of M include CO, N+. ．． Zn, Cu,
For Bi, TLZr and Nb, their chlorides,
For V, Mo and W, their ammonium salts are generally used. As the alkali hydroxide, sodium hydroxide, potassium hydroxide, etc. are used. The amount of alkali hydroxide used must be such that the alkali hydroxide concentration in the solution after mixing the alkali hydroxide is 3 mol/l or more, and 4 to 8 mol/l.
A range of l is preferred.

If the amount of alkali hydroxide is too small, the particles will become large, the particle size distribution will become wide, and hematite will be damaged. Further, it is not economical to increase the amount of alkali hydroxide excessively.

There is no particular restriction on the method of mixing the alkali hydroxide into the aqueous solution of the starting material, but for example, there are methods of directly adding the alkali hydroxide or adding an aqueous solution of the alkali hydroxide to the aqueous solution of the starting material. . Alternatively, there is a method of adding a barium compound to the aqueous solution of alkali hydroxide and mixing this with an aqueous solution containing iron.

Furthermore, a small amount of water-soluble compounds such as Si and Ca, such as silicic acid, sodium silicate, calcium nitrate, and calcium chloride, can be added in advance to the aqueous solution of the starting material or the aqueous solution of alkali hydroxide. These additives are preferred for controlling particle shape.

By hydrothermally treating the slurry containing the precipitate of the starting material, fine crystals of barium ferrite are generated and precipitated. The temperature of the hydrothermal treatment is 130-300'C, preferably 140-280'C. If the temperature is too low, crystal growth will not be sufficient, and if the temperature is too high, the particle size of the final barium ferrite powder will become large, which is not preferable. The hydrothermal treatment time is usually about 0.5 to 20 hours, and an autoclave is usually used for the hydrothermal treatment. After washing the fine crystal precipitate produced by the hydrothermal treatment with water to remove free alkali, a fluxing agent is mixed with the obtained precipitate. At least one of sodium chloride, barium chloride, potassium chloride, strontium chloride, and sodium fluoride is used as the flux. The amount of flux used is based on the precipitate (dry basis).
10-180% by weight, especially 30-120% by weight is preferred. If the amount of flux is too small, sintering of the particles will occur, and if it is too large, there will be no advantage to increasing the amount and it is not economical. Precipitation: There is no particular restriction on the method of mixing the R material and the flux. For example, the flux may be added to a slurry of the precipitate and wet-mixed, and then the slurry may be dried, or the precipitate may be dried, and then the flux may be mixed. may be added and dry mixed.

Next, the resulting mixture is annealed to completely crystallize the barium ferrite.

The firing temperature is 700-950'C, preferably 80'C.
The temperature is 0 to 930°C. If the temperature is too low, crystallization will not proceed and the saturation magnetization will become low. Furthermore, if the temperature is too high, the particles become large and sintering occurs, which is not preferable. Appropriate baking 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,
Barium ferrite magnetic powder is obtained.

The cleaning may be carried out by any method as long as impurities such as flux and excess barium in the fired product can be sufficiently removed. As the cleaning liquid, water, inorganic acids such as nitric acid and hydrochloric acid, and organic acids such as acetic acid and propionic acid can be used.

In the present invention, the fine particles having the magnetoplumbite crystal structure are made to become cloudy in water, and Co, N
Add an aqueous solution containing one or more metal ions selected from i, Zn and Cu and an alkaline aqueous solution, heat the resulting mixed suspension at 50 to 200'C, wash and filter, Then, in a non-oxidizing atmosphere,
A composite ferrite magnetic powder is obtained by heat treatment at 0 to 500°C.

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. In the present invention, first, fine particles having a magnetoplumbite crystal structure are sufficiently dispersed in water to prepare a suspension solution, an aqueous solution of the compound is added to this in a non-oxidizing atmosphere, and then an alkali solution is prepared. Add an aqueous solution to deposit hydroxide on the surface of the microparticles. Alternatively, the order of addition of the aqueous solution of the compound and the aqueous alkaline solution may be reversed. Then, the obtained mixed suspension was heated to 50 to 200'C.
Heat-treated with In this case, it is preferable to add an oxidizing agent to promote the survival of Subinel.

As the oxidizing agent, air may be circulated, or an oxidizing agent such as potassium nitrate, sodium nitrate, or hydrogen peroxide may be used.

By heat treatment, the general formula MxFe”y04eto3(
However, M is Go. ．． One or more metal elements selected from Ni, Zn and Cu, O<x≦1, O≦y<1
, 0<x+y≦1. ) Composite Subinel type ferrite is formed on the surface of the fine particles.

If the heat treatment is insufficient, the amount of composite Subinel type ferrite produced will decrease, and if it is excessively heated, the properties will not be improved. It is preferable to leave 4. The amount of the fine particles having the magnetoplumbite crystal structure of the composite spinel ferrite deposited on the surface is 5 to 50% by weight, particularly 10 to 40% by weight, based on the fine particles. Preferably. Outside this range, the saturation magnetization is high, the temperature change in coercive force is small, and the electrical resistance of the powder is small.
A product with 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.

Next, the obtained powder was heated to 100-50% in a non-oxidizing atmosphere.
The heat treatment is carried out at 00'C, preferably from 150 to 400'C.The non-oxidizing atmosphere is preferably an inert gas such as nitrogen or helium, or a vacuum.

In the present invention, by depositing composite Subinel type ferrite on the surface of fine particles having a magnetoplumbite type crystal structure, the saturation magnetization is high, the temperature change in coercive force is small, the electrical resistance is small, and the dispersibility is excellent. By heat-treating this magnetic powder in a non-oxidizing atmosphere, it is possible to prevent various improved properties from deteriorating over time.

Although it is not yet clear why the various improved properties of the composite ferrite magnetic powder obtained by the present invention do not change over time, it is possible to construct a composite spinel ferrite by heat-treating the magnetic powder in a non-oxidizing atmosphere. It is thought that a part of the metal elements moving into the interior forms a kind of solid solution at the interface between the surface of the fine particles having a magnetoplumbite crystal structure and the composite Subinel type ferrite, and as a result, It is believed that the various improved properties will not change over time.

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.

Furthermore, dispersants, lubricants, hardeners, abrasives, 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 Crt's and A.
bCh, (r-FezOs, 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 processing. (Examples) Examples and comparative examples are shown below to explain the present invention in more detail. Reference example l Ferric nitrate [Fe(NOs)] was added to 1800 m of deionized water.
c9H, 013. 189 mol, cobalt nitrate [CO
(NO!) 16LO] 0.18+4++ol, Nickel nitrate [Ni (NOs) g'68zO] 0.06
1 mol, titanium tetrachloride [TiCL] 0. 123mo
l and zinc nitrate [Zn(NOs)16HtO] 0.1
Separately, barium hydroxide [Ba(OR) 18Hz zO ]0.23sol was dissolved in 2000d of deionized water.
460 mol and 37 mo of caustic soda (NaOH)
1 was 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 145°C for 8 hours. Next, the obtained precipitate was thoroughly washed with water, filtered and dried, and a flux of NaCl and BaClz.2HtO was added in a weight ratio of 1:1.
100% by weight of the mixture was added to the precipitate and mixed. This mixture was annealed at 860°C for 2 hours under an air atmosphere. After thoroughly washing the obtained burnt bottom with water, it was filtered and dried to obtain barium ferrite magnetic powder. As a result of X-ray powder diffraction spectrum and compositional analysis, the obtained barium ferrite magnetic powder was found to have BaO.(Fe+ e.
acoo. Jio. zZno. aTio. 4
01 t. 6), and was of the magnetoplumbite type.

The characteristics of this barium ferrite magnetic powder are the particle size
0. 0 6 2μm Plate ratio 7.8 Specific surface area 55.3bo/g Coercive force 4200e Saturation magnetization 60emu/g Temperature change in coercive force 1. O O e /"The electrical resistance of the shaped body of C powder was 1.2 x 10'Ω.Reference example 2 3.189 mol of ferric nitrate in 1800 d of deionized water
, cobalt nitrate 0. 123 mo1, nickel nitrate 0.
123wol, zinc nitrate 0. 184s+ol and 0.061sol of titanium chloride were dissolved, and separately, 0.460++ol of barium hydroxide and 37mof of caustic soda were dissolved in 2000ml of deionized water, and both solutions were mixed to remove the precipitate. Next, barium ferrite magnetic powder was obtained in the same manner as in Reference Example 1. As a result of X-ray powder diffraction spectrum and compositional analysis, the obtained barium ferrite magnetic powder was found to be BaO・(Fe+ a1
cOo. Jio. aZna. hTio. *0+
L4) and was of the magnetoplumbite type.

The characteristics of this barium ferrite magnetic powder are the particle size
0. 0 5 8μm Plate ratio 6.5 Specific surface area 57.3rrf/g Coercive force 5500e Saturation magnetization 61.5emu/g Temperature change in coercive force 1. The electrical resistance of the bottom body of 20 e/''C powder was 1.8 x 10' Ωcm. Reference Example 3 3.312 mo of ferric nitrate was added to 1800 ad of deionized water.
[, 0.246 mol of cobalt nitrate and 0.246 mol of titanium tetrachloride. Dissolve 123 mol and add 2000 ml of deionized water separately.
0.460 mol of barium hydroxide and 37 mol of caustic soda were dissolved in d, and both solutions were mixed to form a precipitate.

Next, barium ferrite magnetic powder was obtained in the same manner as in Example 1. As a result of X-ray powder diffraction spectrum and compositional analysis, the obtained barium ferrite magnetic powder had BaO° (Fe+ a.
sCoo. sTio. 401? ．． I) and was of the magnetoplumbite type.

The characteristics of this barium ferrite magnetic powder are the particle size
0. 0 5 2μm Plate ratio 3.5 Specific surface area 32.1bo/g Coercive force 6 6 00e Saturation magnetization 54emu/g Temperature change in coercive force 2. 8 0 e/' Electrical resistance of C powder cylindrical body 4. OX]-0'Ω・c
It was m.

Example 1 Barium ferrite obtained in Reference Example 1 [100 g
was dissolved in 1N water, and separately, cobalt chloride [
CoCj! z'6To0] 22g and ferrous chloride [FeC
J! After adding a solution containing 62 g of caustic soda I. 7tmo I water 3
After adding the solution dissolved in 00 td and incubating it at 80°C in a nitrogen atmosphere, air was removed to 150 ad! /+min for 5 hours to perform oxidation. After washing and filtering the resulting slurry, the powder was heat treated at 400°C for 1 hour in a nitrogen atmosphere. When the obtained ferrite magnetic powder was observed with a transmission electron microscope, the particle size was found to be slightly larger.

Table 1 shows the results of measuring the magnetic properties, specific surface area, and electrical resistance of this ferrite magnetic powder.

Further, using this ferrite magnetic powder, a magnetic paint having the following composition was prepared.

Magnetic powder 100 parts by weight Vinyl chloride vinyl acetate copolymer 10 parts by weight Polyurethane resin
10 parts by weight Lecithin 2 parts by weight Stearic acid 2 parts by weight Methyl ethyl ketone 70 parts by weight Methyl isobutyl ketone 70 parts by weight Cyclohexanone 70 parts by weight The obtained magnetic paint was applied to the surface of a polyethylene terephthalate film, and the gloss of the obtained coating medium We measured the degree of The results are shown in Table J.

Examples 2 to 4 Ferrite magnetic powder was obtained in the same manner as in Example 1, except that the coating conditions were changed as shown in Table 1.

Obtained Ferai] [For the powder, Example 1 and
] Table 1 shows the results of measurements of magnetic properties, specific surface area, electrical resistance, and gloss.

Example 5 100g of barium ferrite magnetic powder obtained in Reference Example 2
was suspended in 1 i of water, and to this was added 1.7 a+ of caustic soda.
After adding a solution prepared by dissolving 300 g of cobalt chloride and 62 g of ferrous chloride in 200 d of water and thoroughly dispersing it, a solution of 22 g of cobalt chloride and 62 g of ferrous chloride was added to 200 d of water and mixed thoroughly. After aging in the air, 2001
d/win was introduced for 7 hours to perform oxidation. After washing and filtering the obtained slurry, the powder was heated for 300' in a nitrogen atmosphere.
It was heat-treated at C for 2 hours.

The magnetic properties, specific surface area, electrical resistance, and gloss of the obtained ferrite magnetic powder were measured in the same manner as in Example 1, and the results are shown in Table 1.

Examples 6 to 8 Ferrite magnetic powder was obtained in the same manner as in Example 5, except that the coating conditions were changed as shown in Table 1. The magnetic properties, specific surface area, electrical resistance, and gloss of the obtained ferrite magnetic powder were measured in the same manner as in Example 1, and the results are shown in Table 1.

Comparative Examples 1 to 3 Ferrite magnetic powder was obtained in the same manner as in Example 1, except that the coating conditions were changed as shown in Table 1.

The magnetic properties, specific surface area, electrical resistance, and gloss of the obtained ferrite magnetic powder were measured in the same manner as in Example 1, and the results are shown in Table 1.

Example 9 The ferrite obtained in Example 1 was mixed with 6
It was stored in an oven maintained at 0°C for 168 hours, and changes in magnetic properties and electrical resistance over time were measured.

The results are shown in Table 2. Comparative Example 4 100g of barium ferrite magnetic material obtained in Reference Example 1
Suspend it in water IC and add 200m of water! cobal chloride}
After adding a solution of 22g of ferrous chloride and 62g of ferrous chloride and mixing thoroughly, add 1.7mol of caustic soda to 30g of water.
After adding a solution dissolved in a 0-proof solution and aging in a nitrogen atmosphere at 80° C., oxidation was performed by introducing air at 150 d/win for 5 hours.

After washing and filtering the resulting slurry, the powder was heat treated at 80°C for 5 hours in a nitrogen atmosphere. The obtained ferrite l-
Regarding the monomorphic powder, changes over time in magnetic properties and electrical resistance were measured in the same manner as in Example 9.

The results are shown in Table 2.

(Effects of the Invention) The composite ferrite hm material obtained by the present invention has dramatically improved saturation magnetization compared to conventional ones, has small temperature change in coercive force, and has low electrical resistance of powder. It is small, has excellent dispersibility, and these properties do not change over time, so it is suitable for use as a magnetic recording material for high-density recording.

Claims (2)

[Claims] (1) Fine particles having a magnetoplumbite crystal structure are suspended in water, and an aqueous solution and an alkaline aqueous solution containing one or more metal ions selected from Co, Ni, Zn, and Cu and Fe^2^+ are added. is added, the resulting mixed suspension is heat-treated at 50-200°C, washed and filtered, and then heat-treated at 100-500°C in a non-oxidizing atmosphere. How to make powder. (2) Fine particles having a magnetoplumbite crystal structure have the general formula AO・n(Fe_1_2_-_xM_xO_
1_8_+α) (However, A represents one or more elements selected from Ba, Sr, and Pb, and M represents Co, Ni,
Zn, Cu, Bi, Ti, Zr, Sn, Nb, V, Mo
and one or more elements selected from W, n=0.9
~1.2, 0<x<4, -2≦α≦0. )
2. The method for producing a composite ferrite magnetic powder according to claim 1, wherein the powder is a hexagonal plate-like magnetoplumbite type ferrite represented by the following formula and has a particle size of 0.1 μm or less.