JPS62128928A - Production of magnetic powder for magnetic recording - Google Patents

Abstract

PURPOSE:To produce hexagonal series barium ferrite magnetic powder in case of producing barium ferrite in a coprecipitation method by heating immediately an aq. soln. contg. a coprecipitate without filtering and water-washing it and evaporating water content, drying and calcining it and thereafter washing water soluble metallic salt to remove it. CONSTITUTION:A coprecipitate is formed by mixing 8-12mol chloride or sulfate of Fe as Fe ion and an aq. soln. contg. 0.8-3mol ion of Ba, Sr, Ca, Pb wherein one or two kinds or above of chloride or nitrate of Ba, Sr, Ca and Pb are dissolved and an alkaline aq. soln. contg. hydroxide or carbonate of alkali metal such as NaOH, Na2CO3, NH4OH and (NH4)2CO3. pH of this coprecipitate- contg. aq. soln. is regulated to >=5 and heated at >=70 deg.C in the presence or nonpresence of one or two kinds or above of compds. such as NaCl, KCl, BaCl2 and SrCl2 to evaporate water content and dried. Hexagonal barium ferrite magnetic powder preferable for high-density magnetic recording medium is easily produced by successively calcining it at 600-1,200 deg.C for 0.5-5hr.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for producing magnetic powder for magnetic recording, and more specifically to a hexagonal ferrite magnetic powder consisting of fine particles suitable for use in high-density magnetic recording media. This invention relates to a method for easily manufacturing.

(Prior Art) In recent years, with the demand for higher density magnetic recording, perpendicular magnetic recording methods that record a magnetic field in the thickness direction of a magnetic recording medium have been attracting attention.

By the way, ferrite having hexagonal uniaxial magnetization anisotropy, such as barium ferrite, is known to be a magnetic powder suitable for the above-mentioned perpendicular magnetic recording method, and has a coercive force (
Ha) is at an appropriate level (400 to 20,000θ), the saturation magnetization (σ8) is as high as possible, the particles are small (generally 0.3 μm or less) and uniform, there is no agglomeration or sintering of particles, and there is good dispersibility. something is desired.

Conventionally, various methods are known for producing barium ferrite, such as a coprecipitation method, a flux method, a hydrothermal synthesis method, and a glass crystallization method. Publication, JP-A-56-60002
No. 1, JP-A-58-2223, JP-A-60-1
This method has been proposed in Publication No. 15204 and the like.

(Problems to be Solved by the Invention) The production of barium ferrite by the coprecipitation method allows for very good mixing with various metals added in small amounts for coercive force control and other purposes, resulting in uniform ferrite. Since the coprecipitate is a microcrystalline powder, it has many advantages such as being able to form hepteraite at a relatively low temperature. However, there are major drawbacks such as the particle size of the magnetic powder obtained is relatively large, at least 0.15 μm, and the sintering of the fine particles progresses during the firing process, resulting in very poor dispersibility. For this purpose, a method of adding a water-immiscible organic solvent to the coprecipitate and subjecting it to azeotropic dehydration (
(see Japanese Patent Application Laid-Open No. 60-115204) and coprecipitates.
A method of hydrothermal treatment under pressure and heating (Unexamined Japanese Patent Publication No. 56-1
60328) have been proposed, but they are still not sufficient.

(Means for Solving the Problems) In view of the above circumstances, the present inventors have developed a material with uniform and small particle size, no agglomeration or sintering of particles, good dispersibility, and good magnetic properties. As a result of intensive research with the aim of producing excellent hexagonal ferrite magnetic powder, we found that an aqueous solution containing a coprecipitate obtained by a normal coprecipitation method was prepared in the conventional manner (the coprecipitate was washed door to door, washed with water, etc.). The inventors have discovered that the above object can be achieved by immediately heating the product to 70°C or higher to evaporate the moisture, sintering it, and then washing and removing the water-soluble metal salt, and have completed the present invention. .

The purpose of the present invention is to (1) contain at least 8 to 12 moles of It's ions and J
An aqueous solution containing one or more metal ions selected from the group consisting of 3a ions, Br ions, Ca ions, and Pb ions in a molar ratio of 0.8 to 3 mol and an alkaline aqueous solution are mixed. The aqueous solution containing the coprecipitate is mixed with one or two compounds selected from the group consisting of sodium chloride, potassium chloride, barium chloride, strontium chloride, sodium sulfate, potassium sulfate, and lithium sulfate. Heat to 70°C or higher in the presence or absence of water to evaporate moisture, then dry for 600-1200'
By washing and drying after baking with O, (2) at least 8 to 12 moles of Fs ions and 3a
ion,! A compound obtained by mixing an aqueous solution containing 1s or two or more metal ions selected from the group consisting of 3r ions, Ca ions, and Pb ions in a molar ratio of 0.8 to 3 mol and an alkaline aqueous solution. The pH of the aqueous solution containing the precipitate is adjusted to below the pH of the υ prokaryotic aqueous solution by adding hydrochloric acid and/or sulfuric acid, and the aqueous solution is mixed with sodium chloride, potassium chloride, barium chloride, strontium chloride, sodium sulfate, potassium sulfate, and lithium sulfate. In the presence or absence of one or two compounds selected from the group consisting of: heating to 70"C or higher to evaporate moisture, followed by baking at 600 to 1200"C followed by washing and drying. achieved by

According to the present invention, treatment with a large amount of organic solvent as described in JP-A-60-115204 or coprecipitate under high pressure as described in JP-A-56-160328 There is no need to perform complicated treatments such as hydrothermal treatment under heating.Fe ion, Ba ion SB used in the present invention
r ions, Ca ions, Pb ions, and various metal ions (for example, Mg, Sc, Y, 'V, Ta) that may be added in small amounts as desired to control magnetic properties or for other purposes.

Mo, W, Re, Ru, ○s, Rh, Engineering r, Pd, Pt
, Ag, Hg.

Ga, Go, As, To, C! o, Ni, Mn, Zn,
Ti, Eng.

Nb, Sm, Nd, Zr, Or, La, Ou, Cd, A
4. Tj.

si, sn, p, sb, Bt, so, ce, pr, 'r
b, Ga, yb.

To prepare an aqueous solution containing one or more metal ions selected from Th, σ, etc., water-soluble metal salts of each metal, such as nitrates, sulfates, chlorides, ammonium salts, carbonates, etc. Examples include salts, acid anhydrides, condensed acids, etc. 0 In particular, the raw material for FlI ions is chloride or sulfate, and Ba ions, Br ions, CI! It is preferable that the raw materials for L ions and Pb ions are chlorides or nitrates. Even in this case, there are no particular restrictions on the raw materials for various metal ions added in small amounts to control magnetic properties, etc. In order to obtain the desired magnetic powder in the present invention, at least 8 to 12 moles of Fe ions and Ba ion, Br ion, Ca ion, and Pb ion in a molar ratio of 0.8 to 3 mol.

In addition, when adding small amounts of various metal ions for the purpose of controlling magnetic properties, etc., the total of these added metal ions is preferably 3 moles or less at the above molar ratio. This means that each metal ion is Excellent magnetic properties (coercive force 400 to 2
0000e and saturation magnetization of 40 emu79 or higher).

Further, the concentration of the metal ions in the aqueous solution is preferably such that the total amount of metal ions is 10 mol/l or less, more preferably 1 mol/z or less.

On the other hand, the alkaline component used in the alkaline aqueous solution may be any water-soluble one, such as alkali metal hydroxides, carbonates, ammonia, ammonium carbonate, etc.
For example, NaOH, KOH, Na2CO3゜NaHCO3
，'! -2CO3, KHCO3, NH4OH, (NH4
)zC! 03 etc. are used, and a combination of hydroxide and carbonate is particularly preferred.

The concentration of the alkaline aqueous solution is such that the total amount of alkali metal ions and/or ammonium ions is preferably 25m01/
I! More preferably, it is 10 mo1/j or less.

In the method of the present invention, the metal ion aqueous solution and the alkaline aqueous solution are mixed to obtain an aqueous solution containing a coprecipitate. In this case, the aqueous alkaline solution may be added to the aqueous metal ion solution, or conversely, the aqueous metal ion solution may be added to the aqueous alkaline solution, but the latter is preferred.

In the present invention, the pH of the aqueous solution containing the coprecipitate is not particularly limited, but from the viewpoint of the magnetic properties and powder properties of the magnetic powder, preferably the pH is 5 or higher at a liquid temperature of 25°C, more preferably 5.
It ranges from 5 to 13.

Conventionally, this pH value is generally said to be 10 or more, preferably 12 or more (for example, JP-A-58-56303), and specifically, it is practiced at 13.0 or more. By the way, the amount of alkali required for adjusting the pH value increases significantly from pH 9, which exceeds 13. For this reason, known methods require large amounts of alkaline components. In the present invention, it is acceptable if the H value (at a liquid temperature of 25°C) is 5 or more (this makes it possible to significantly reduce the amount of alkaline components used. This is an improvement not found in conventional manufacturing methods, such as easier selection of materials and ease of handling due to reduced toxicity to the human body.

In addition, in the present invention, the temperature during coprecipitation is 0 to 100'C.
In the present invention, the solution containing the coprecipitate obtained in this way is then heated to a temperature of 70°C or higher to evaporate and dry the water in the solution. is finally obtained by heating in the presence of 11 or more compounds selected from the group consisting of sodium chloride, potassium chloride, barium chloride, strontium chloride, sodium sulfate, potassium sulfate and lithium sulfate. The powder characteristics of the magnetic powder, particularly the particle size and thickness of the magnetic powder, can be reduced.

These compounds may be added to any aqueous solution containing metal ions such as Fa ions and J3a ions, alkaline aqueous solutions, or aqueous solutions containing coprecipitates, and are added in an amount of 0.01 to 10% by weight based on the final magnetic powder obtained. times, preferably 0.
05 to 3 times the weight is added.

Further, the effect of the present invention is that 1) H of the aqueous solution containing the coprecipitate is
is adjusted to an arbitrary range below the pH of the aqueous solution before addition of the acid by adding hydrochloric acid and/or sulfuric acid, and this aqueous solution is
The dispersibility of the magnetic powder is further improved by heating to 0° C. or higher to evaporate water. During heating, the presence of one or more of the metal chlorides and metal sulfates enhances the effects of the present invention. These compounds may be added to the aqueous solution containing the coprecipitate before pH adjustment, to the aqueous solution containing the metal ions of the present invention, or to the alkaline bath solution, or 1) to the aqueous solution containing the coprecipitate after H adjustment. It may be added to an aqueous solution containing a coprecipitate. The amount of the compound added is the same as above.

The aqueous solution containing the coprecipitate thus obtained is heated to 70° C. or higher to evaporate and dry the water in the solution. Although a drum dryer, a spray dryer, or the like may be used to evaporate the water, the easiest method is to boil down the solution containing the coprecipitate at 70° C. or higher in an evaporator. That is, the solution containing the coprecipitate is placed in an evaporator and heated with steam or direct flame while stirring to evaporate most of the water. In the present invention, the temperature at which water is evaporated must be 70° C. or higher. If this temperature is below 70°C, the average particle size of the magnetic powder obtained will be 0.25 μm or more. It is better to evaporate water sufficiently, but there is no problem even if it is insufficient. After most of the moisture has been evaporated in this way, it is dried at an appropriate temperature, usually 100 to 300° C., to evaporate the remaining moisture.

This dried product may be fired as is, but for the purpose of more uniform firing, it may be powdered, molded with a hammer, or extruded at +500 to 1200°C.
Preferably it is fired at 650 to 950°C. Baking time is 0
．． A suitable firing time is 5 to 50 hours, and the firing atmosphere may be either a nitrogen atmosphere or an oxygen atmosphere, but it is usually preferable to perform the firing in an air atmosphere. In addition, preliminary firing may be performed during the firing.

The fired product fired at 600 to 1200"C is then washed and dried.Washing removes metal chlorides, metal sulfates, metal nitrates, other alkali metal ions, and excess hydroxide contained in the fired product. Any method may be used as long as it can sufficiently remove impurities such as barium.Water, acetic acid, nitric acid, hydrochloric acid, etc. can be used as the cleaning liquid.The fired product that has been sufficiently washed is then dried, but the drying method is not particularly limited.

(Effect of the invention) The hexagonal ferrite magnetic powder obtained by the present invention is
It consists of uniform particles with an average particle diameter of CL25 μm or less, each of which is individually dispersed. In addition, this magnetic powder has good dispersibility (coercive force of 400-20000e and coercive force of 40e
It exhibits a saturation magnetization of mu/l or more.

The coercive force can be freely controlled by adding various elements (eg Co, Ti, etc.).

The invention will be explained in more detail with reference to Examples below. The coercive force and saturation magnetization in the examples were determined by filling a glass test tube with an inner diameter of SMS and a length of 5 mm with the obtained magnetic powder, using a DC magnetization characteristic measuring machine, and measuring the maximum applied magnetic field of 3500 yen.
I went with 0e. The average particle diameter was calculated by measuring the maximum diameter of 400 particles from a photograph taken with a transmission electron microscope and calculating the arithmetic average. X-ray diffraction was performed on the Examples and Comparative Examples listed here, and in both cases, the crystal phase of the magnetic powder was hexagonal ferrite with a magnetobrambite structure. The empirical formula for powder uses the atomic ratio of metals at the time of raw material preparation. The representation of oxygen in the ferrite component has been omitted for the sake of brevity.

Example 1 BaO/2.2H200.55 mol, Ti0j40.
575 mol, CoC/2 6H200,375 mol, and FeCl3 6H205.25 mol-qlo-e
c) N
17.5 mol aOH and 20034.72 mol Na
52 in distilled water at room temperature, and this was used as Solution B. 50
After gradually adding Solution A to Solution B heated to .degree. C., the mixture was stirred at 50.degree. C. for 1 hour. The pH after stirring was 10.9. The aqueous solution containing the coprecipitate thus obtained was transferred to an evaporating dish, boiled to about 100°C using an electric heater, and then stirred and mixed to evaporate water until the water content reached 50%. After further drying the cake-like coprecipitate at 150"O,
This was fired in an electric furnace at a firing temperature of 850°C for 2 hours. This baked product was washed with water until no soluble matter was removed, filtered and dried, and B "11pe1α5COα75T1
Barium ferrite magnetic powder represented by α75 was obtained.

The fine particle powder thus obtained has an average particle size of 0.17 μm1
It was plate-like with a thickness of 0.045 μm, and each particle was separate and had a neat shape. When the magnetic properties were measured, 'f(a) was 8290e, and σG was 57 emu/?〇Example 2 Hydrochloric acid was added to the aqueous solution containing the coprecipitate of Example 1 to adjust the pH to 1.
Barium ferrite was produced in exactly the same manner as in Example 1, except that the value was 0.0. The obtained barium ferrite fine particle powder has an average particle size of 0.14 μm and a thickness of 0.03 μm.
It had a plate shape of 2 μm, and each particle was arranged separately and had a beautiful shape. The magnetic properties are Ha
was 8110eS #s was 57 emu/liter.

Example 3 Nap/2002 was added to the aqueous solution containing the coprecipitate of Example 1.
Barium ferrite was produced in exactly the same manner as in Example 1, except that . The obtained barium ferrite fine particles had an average particle size of 0.11 μm.

It was plate-like with a thickness of 0.028 μm, and each particle was arranged in a uniform manner, and had a nice shape. The magnetic properties are 8050e1#6 for HC and 58e mu/
f! Met.

Example 4 Barium ferrite was produced in the same manner as in Example 1, except that 500 t of NIL2SO4 was added to liquid A in Example 1. The obtained barium ferrite fine particles were as follows:
The particles were plate-shaped with an average particle size of 0512 μm and a thickness of 0.0215 μm, and each particle was arranged separately and had a nice shape. Magnetic properties: Ha, 8460e
, eg was 58 emu/7.0 Example 5 Hydrochloric acid was added to the aqueous solution containing the coprecipitate of Example 1 to bring the pE to 1.
After setting it to 0.0, Na2SO4200? Barium ferrite was produced in exactly the same manner as in Example 1, except that . The obtained barium ferrite fine particle powder had a plate shape with an average particle diameter of 0.12 μm and a thickness of 0.029 μnl, and each particle was arranged separately and had a neat shape. The magnetic properties are Ha, 7860e, a
B was 55 smu/P.

Example 6 He-C12001 was added to the aqueous solution containing the coprecipitate of Example 1.
was added, and then sulfuric acid was added to adjust the pH to 85.
Barium ferrite was produced in exactly the same manner.

The obtained barium ferrite fine particle powder has an average particle size of 0.
．． It was plate-shaped with a thickness of 15 μm and a thickness α of 27 μm. Each particle was arranged separately and had a nice shape.0 Magnetic properties: Hc is 7980e, ms is 57
It was emu/7.

Example 7 NaC/100P, BaC/2・2H in the B solution of Example 1
Barium ferrite was produced in exactly the same manner as in Example 1, except that 20502 was added. The obtained barium ferrite fine particle powder has an average particle size of 0.16 μm and a thickness of 0.1 μm.
The magnetic properties of the 018 μm plate-shaped particles were uniform, with each particle being uniform, and had a neat shape.
HC was 7930e, and σθ was 56 emu/7.

Comparative Example 1 The coprecipitate was separated from the aqueous solution containing the coprecipitate obtained by the same method as in Example 1, and thoroughly washed with water. The coprecipitate thus obtained was dried at 150'C, and then fired in an electric furnace at a firing temperature of 850C for 2 hours. This fired product was washed with water, filtered and dried to obtain Bat+ Fe1CL5.
G! O[L75 Ti (L75) '' ferrite was produced. The obtained barium ferrite fine particles had an average particle size of 0.41 μm and a thickness of 0.085 μm.
The particles were in the shape of a μη plate, but several particles were strongly aggregated (many were seen), and the particle size was widely distributed from large particles of 0.7 μn1 or more to particles of about 0.15 μm. The magnetic properties were H
O was 8500e, and σ6 was \32θmu/7.

Comparative Example 2 An aqueous solution containing a coprecipitate was injected into liquid nitrogen and frozen,
Barium ferrite was produced in the same manner as in Example 1, except that this was freeze-dried at −5° C. under reduced pressure. The obtained barium ferrite fine particle powder has an average particle size of 0.43μ
〃1. It was plate-shaped with a thickness of about 0092 μm. Also, Ha was 32 smu/y for 5B60e and 6e.

Comparative Example 3 Barium ferrite was produced in the same manner as in Example 1, except that the aqueous solution containing the coprecipitate was dried at 60°C. The magnetic properties of the obtained barium ferrite fine particles were similar to those in Example 1, but the average particle size was 0.35 μm.
1 Thickness was 0.057 μm and the particles were large 〇Examples 8 to 16 Examples 8 to 16 Examples except that the type and amount of Naczt or the equivalent substance used and the firing conditions were changed as shown in Table 1. 5
Barium ferrite was produced in the same manner. Compared to Comparative Example 1, each of the obtained fine powder particles had individual particles that were uniform and had a neat shape. The average particle diameter, thickness, coercive force, and saturation magnetization of each are as shown in Table 1. Example 17 BrC12.6FI2 on BaCl2-2H20
A 5r-7 elite represented by 5rtI Fetas coays Ti (L75) was produced in the same manner as in Example 1 except that 0 f was used.

This fine particle powder is plate-shaped with an average particle size of 0.18 μm,
Ha was 9550s, #8 was 55 emu/70 Example 18 Instead of BaC/212H200,55 mol, BaC
J2-2H20 and E3rQ12・6H20 were each 0.
Ba(L555r(L55 Fe1 [L5 coll
A Ba-8r-ferrite designated Lys TirL75 was produced.

This fine particle powder was plate-shaped with an average particle size of 0.17μ〃1, HC was 8760s, and σe was 57 smu/y.

Example 19 BaCl2.2H20f CaCl2 in Example 1
Or C in the same manner as in Example 1 except for using PbCl2.
A-ferrite and Pb-ferrite were produced. The properties of these ferrites were equivalent to Ba-ferrite. In addition, the particles were uniform and dispersed one by one, and had good dispersibility.

Claims (3)

[Claims] (1) At least 8 to 12 moles of Fe ions and 0.0 moles of one or more metal ions selected from the group consisting of Ba ions, Br ions, Ca ions, and Pb ions.
A coprecipitate is obtained by mixing an aqueous solution containing an alkaline aqueous solution in a molar ratio of 8 to 3 moles, and the aqueous solution containing the coprecipitate is mixed with sodium chloride, potassium chloride, barium chloride,
In the presence or absence of one or two compounds selected from the group consisting of strontium chloride, sodium sulfate, potassium sulfate and lithium sulfate, water is evaporated and dried by heating to 70°C or higher, and then at 600 to 1200°C. 1. A method for producing magnetic powder for magnetic recording, which comprises firing the powder, followed by washing and drying. (2) At least 8 to 12 moles of Fe ions and 0.0 to 0.0 moles of one or more metal ions selected from the group consisting of Ba ions, Br ions, Ca ions, and Pb ions.
p of an aqueous solution containing a coprecipitate obtained by mixing an aqueous solution and an alkaline aqueous solution containing a molar ratio of 8 to 3 moles.
The pH of the original aqueous solution is adjusted by adding H to hydrochloric acid and/or sulfuric acid.
the aqueous solution in the presence or absence of one or two compounds selected from the group consisting of sodium chloride, potassium chloride, barium chloride, strontium chloride, sodium sulfate, potassium sulfate and lithium sulfate, Heat to 70°C or higher to evaporate moisture, then dry at 60°C.
A method for producing magnetic powder for magnetic recording, which comprises firing at a temperature of 00 to 1200°C, followed by washing and drying. (3) Fe ion raw material is chloride or sulfate and Ba
2. The method for producing magnetic powder for magnetic recording according to claim 1, wherein the raw material for the ions, Br ions, Ca ions, and Pb ions is chloride or nitrate.