JPH0361307A - Manufacture of metallic magnetic powder for magnetic recording - Google Patents

Abstract

PURPOSE:To industrially and stably manufacture metallic magnetic powder for magnetic recording by heating under condition of the specific atmosphere and temp. after coating combining the specific Al compound and B compound on surface of fine ferrous oxide. CONSTITUTION:Powder of water containing iron oxide of extremely fine FeOOH, etc., having >=55m<2>/g specific surface area or iron oxide of fine Fe2O3, Fe3O4, etc., having >=40m<2>/g specific surface area, is charged into suspension of B compound of boric acid, ammonium borate, etc., and Al(OH)3 to form mixed coating layer of the B compound and Al(OH)3 on the surface of water containing iron oxide and iron oxide particles. After heating this at 550-900 deg.C in the air, this is heated and reduced under reducing atmosphere of hydrogen gas stream, etc., and successively, cooled in N2 gas and after dipping this in toluene, the toluene is vaporized at the room temp. to manufacture the ferrous fine powder being suitable to the magnetic recording.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing iron-based metal magnetic powder suitable for magnetic recording.

[Technical background of the invention and its problems]

2. Description of the Related Art In recent years, there has been an increasing trend toward improving the recording density of magnetic recording media and making them smaller and with higher performance. Accordingly, iron or iron-based metal magnetic powders (hereinafter referred to as metal magnetic powders), which have higher saturation magnetization and coercive force than iron oxide-based magnetic powders, are attracting attention as magnetic powders for magnetic recording. Metal magnetic powder is
Practical applications for digital audio tapes, 8 mm video tapes, etc. are being attempted, and recently there are even more expectations for its application to high-performance recording media such as high-quality video tapes and high-density disks.

In particular, when the metal magnetic powder for high-performance magnetic recording media is, for example, acicular particles, it is usually required to be fine and non-sintered, with a long axis of about 0.5 μm, or even 0.3 μm or less, and When this material is used as a magnetic coating material, it is desired to have even better dispersibility, orientation in the coating film, filling property, and surface smoothness. For this purpose, it is desired that the starting raw materials, such as hydrated iron oxide and iron oxide, have fine particles and a good particle size distribution. however,
The finer the starting material is, the more likely it is that its needle-like shape changes due to particle sintering or crosslinking or coarsening occurs due to interparticle sintering during the reduction process to the target product. This will significantly adversely affect the magnetic properties of the target object.

In order to solve the above-mentioned problems, various methods have been proposed in the past. For example, silicon compounds, aluminum compounds,
A method is known in which a boron compound or the like is deposited and then heated and reduced.

However, although these methods can improve particle shape collapse and interparticle sintering to some extent, there are still many problems that still need to be solved, such as the progress of the reduction reaction being easily inhibited.

[Purpose of the invention]

An object of the present invention is to provide a method for manufacturing metal magnetic powder for magnetic recording with industrial advantage by eliminating the above-mentioned problems.

[Structure of the invention]

The present inventors have been conducting various studies to solve the above-mentioned problems for some time, and prior to heat reduction treatment of hydrated iron oxide or a metal compound mainly composed of iron oxide, a specific aluminum compound and By applying a boron compound in combination and heat-treating this material under a specific atmosphere at a specific temperature, the reduction reaction can be easily carried out, and particle shape collapse and interparticle sintering can be virtually avoided. The present invention was completed based on the knowledge that the metal magnetic powder obtained can easily form dense crystals, and that this powder can be extremely suitable for high-density magnetic recording media. That is, in the present invention, (1) a hydrous oxide of aluminum and a boron compound are deposited on the surface of hydrated iron oxide or iron oxide particles, and then a 550 to 900
1. A method for producing a metal magnetic powder for magnetic recording, which comprises heating at a temperature of 0.degree. C. and then subjecting it to a heat reduction treatment.

2) A hydrated oxide of aluminum and a boron compound are deposited on the surface of hydrated iron oxide or iron oxide particles, a boron compound is further added to the deposited product, and then heated to 550°C under a non-reducing atmosphere. A method for producing metal magnetic powder for magnetic recording, which comprises heat treatment at ~900°C and then heat reduction treatment.

3) In claim 1 or 2, a boron compound adsorbed on a hydrated argonium oxide is added to the hydrated iron oxide or iron oxide suspension to prepare the hydrated iron oxide or iron oxide. A method for producing a metal magnetic powder for magnetic recording, which comprises depositing a hydrous oxide of aluminum and a boron compound on the surface of the particles.

4) The method for producing a metal magnetic powder for magnetic recording according to any one of claims 1 to 3, wherein the specific surface area of the hydrated iron oxide is 55 m2/g or more.

5) The method for producing a metal magnetic powder for magnetic recording according to any one of claims 1 to 3, wherein the iron oxide has a specific surface area of 40 m/g or more.

There are various types of hydrated iron oxide or iron oxide used as the base particles in the present invention. Typical examples of hydrated iron oxide include iron oxyhydroxide, such as α-Fe0011,
β-FeO011, T-Fe0011, etc. may be mentioned.

Further, as iron oxide, for example, α-FezO,,,Fe
,0. , γ-Fe, 03, and bertolide compounds obtained by partial reduction of γ-FezO= can be used. The particle shape of the above-mentioned hydrous iron oxide or iron oxide is typically acicular, but various other shapes can be used. For example, spindle-shaped, rice grain-shaped, rod-shaped, plate-shaped,
It is dice-shaped, etc.

Among these base particles, acicular α-Fe is particularly desirable.
It is lon. Further, the base particles have a specific surface area of 55i
Fine particles such as acicular hydrated iron oxide with a particle size of 40 m/g or more or acicular iron oxide with a particle size of 40 m/g or more are preferable. The base particles may include, for example, (dehydration in the case of al-iron oxyhydroxide, phosphorus compounds as sintering inhibitors in the firing process, silicon compounds, etc.) (b) cobalt compounds, chromium, which contribute to improving the magnetic properties of the target object. Compounds etc. (C) Others Mn, Ni,
Cu, Ag, cti, pb, Ca+ Mg+
sr, Zn, Sn+W.

It does not prevent the inclusion of various additives such as Zr compounds.

In the present invention, the hydrated oxide of aluminum and the boron compound can be deposited on the surface of the particles of the hydrated iron oxide or the metal compound mainly composed of iron oxide by various methods. Regarding the adhesion process, a typical process will be described using an example in which acicular α-FeOOll (goethite) is used as the base particle.

First, an aqueous suspension of fine goethite is prepared.

This suspension is prepared with an alkaline compound such as sodium hydroxide, potassium hydroxide, ammonia, etc. or an acidic compound such as sulfuric acid, hydrochloric acid, etc., as necessary, to bring the ρn to 6.
It is best to adjust it to 0 to 9.0. Further, if necessary, a suitable dispersant such as a phosphate or a polyacrylate may be added to this suspension to improve the dispersion of goethite. Sodium hexametaphosphate as phosphate,
When sodium pyrophosphate or the like is used, the preferable addition amount is usually 0.1 to 3% (weight % in terms of P) based on goethite.

Next, a hydrous oxide of aluminum and a boron compound can be applied to the aqueous suspension containing the base particles by various methods, such as (a)
Alkali or acid is added to a solution of acidic salts of aluminum such as aluminum nitrate, aluminum sulfate, and aluminum chloride, or basic salts of aluminum such as sodium aluminate to neutralize it and precipitate a hydrous oxide of aluminum. Alternatively, in the process of hydrolyzing a solution of an organoaluminum compound such as an aluminum alkoxide or an alkyl aluminum compound to precipitate a hydrous oxide of aluminum, to the reaction liquid system during the precipitation precipitation, and further to the reaction system after the precipitation precipitation,
A boron compound, such as a metal salt such as boric acid, ammonium borate, or zinc borate, or a solution, suspension, or powder of an organic boron compound such as a boric acid ester or boron alkoxide, is added to a mixture of 11, The added boron compound is adsorbed into the precipitated product of aluminum hydrous oxide, and the treated product thus prepared is used as a modified modifier and a predetermined amount of this is mixed and dispersed into the aqueous suspension containing the substrate particles. (b) By adding a salt solution of aluminum or a solution of an organoaluminum compound to the aqueous suspension of the base particles, the hydrous oxide of aluminum and the boron compound are closely adhered to the particle surface of the base particles. In this treatment system, aluminum This can be carried out by neutralizing salts or hydrolyzing an organic aluminum compound to precipitate a hydrous oxide of aluminum onto the surface of the substrate particles, and at the same time adsorbing a boron compound thereto.

In general, the hydrated oxide of aluminium deposited on the surface of the base particle of hydrated iron oxide or a metal compound mainly composed of iron oxide is retained on the surface of the base particle during the subsequent heating and dehydration process; During the thermal reduction process, it is easy to segregate from the particle surface or peel off from the particle surface, and as a result, the particle shape of the obtained metal magnetic powder is unavoidable. However, in the case of the present invention, it is easy to avoid the segregation and peeling of the adherend as described above, and in particular, the method (a) above uniformly spreads the hydrous oxide of aluminum that has adsorbed a necessary and sufficient amount of boron compound. It is relatively easy to apply and is therefore more desirable.

In the above deposition treatment, the amount of the hydrous oxide of aluminum deposited is at least 0.5% by weight, preferably 2 to 6% by weight, as A 1 /Fe, based on the iron in the base particles, and The amount of the compound deposited is at least 0.2% by weight, preferably 0.5 to 3% by weight, based on B/Fe based on the iron in the base particles.

If the amount of these deposits is less than the above, the desired effect will not be brought about, and if the amount of deposit is too much than the above, it will take a long time to reduce the target object or the saturation magnetization of the target object will decrease. I don't like doing that. Note that when a boron compound is adsorbed on a hydrous oxide of aluminum, it is usually B///! (weight ratio) 0.05 to 2, preferably 0
．． 1 to 1.5.

If the B/A f value is too low, the desired effect will not be obtained, and if the B/A p value is too high, the saturated adsorption of hydrous oxides of aluminum will be exceeded, resulting in subsequent filtration and water washing. Boron compounds are removed from the system during the process, which is economically unfavorable. The treatment system in which the hydrous oxide of aluminum and the boron compound are deposited on the surface of the base particles as described above is adjusted to have a pi of 6 to 9 using an acid or an alkali. The above-mentioned adhesion treatment step may be carried out at room temperature, but may be carried out under heating if necessary. In the present invention, the hydrated oxide of aluminum refers to hydroxide of argonium, hydrated oxide of aluminum, etc. A general term for oxides, hydrated oxyoxides, partial hydrates of oxides, etc.

In the present invention, the surface of the hydrous iron oxide or iron oxide base particles coated with the hydrous oxide of aluminum and the boron compound as described above is separated from the suspension and reduced to produce metal magnetic material. Although powder can be produced,
In the present invention, the base particles coated with the hydrous oxide of aluminum and the boron compound before reduction have a particle size of 550 to
It is essential to carry out the heat treatment at 900°C, preferably 600-850°C, in a non-reducing atmosphere, for example in air or in an inert gas atmosphere such as nitrogen. Through this heat treatment, a close composite oxide of aluminum and boron is generated at 600°C or higher and retained on the surface of the base particle, which has a remarkable effect on sintering and deformation of the particle shape, and on goethite particles. is baked and becomes dense, making it possible to further suppress sintering and collapse of particle shape during reduction.

If the heat treatment temperature is too high than the above range, α-Fe
, 03, deterioration of acicularity and coarsening occur due to intra-particle and inter-particle sintering, which is not preferable. On the other hand, if it is too low than the above range, many pores remain in the particles and the particles themselves are not dense crystals, resulting in significant shape deterioration in the subsequent reduction step, making it impossible to obtain the desired effect.

The object of the present invention is obtained by reducing the heat-treated product of goethite coated with the hydrous oxide of aluminum and a boron compound. Various well-known methods can be used for this reduction. Generally, substantially all of the iron oxide can be reduced to metallic iron by treatment at 350 to 600°C using, for example, hydrogen as the reducing gas. When the metal magnetic powder obtained by reduction in this way comes into contact with the atmosphere, it may ignite or α
-Fe20 = and the saturation magnetization decreases,
Generally, various known methods are used to stabilize the material before it is taken out into the atmosphere. For example, methods include stabilizing by immersing the toluene in an organic solvent such as toluene and then slowly evaporating the toluene, stabilizing by passing an oxygen-containing gas into the liquid or gas phase of toluene, and various other methods. There is a method in which the above-mentioned method is used in combination with an oxidation-inhibiting film treatment.

In addition, in the above method, if the boron content in the goethite of the base particles coated with the boron compound adsorbed on the hydrous oxide of aluminum is less than the desired amount, the goethite treated with the above coating may be filtered. By adding and mixing a boron compound to the washed cake, a more excellent metal magnetic powder can be obtained as described later.

It is usually advantageous from an industrial and effective point of view to heat-treat the hydrated oxide of aluminum and the boron compound as described above after the adhesion treatment, but in some cases, hydrated iron oxide may be heated to a temperature of about 500°C, for example. Iron oxide (α
-Fe203), this aqueous suspension may be prepared, and a hydrous oxide of aluminum and a boron compound may be deposited on the surface of the iron oxide particles according to the above-described deposition treatment method.

In addition to the above methods, the present invention provides techniques that further improve these methods. That is, after or before coating the particle surface of hydrous iron oxide or iron oxide base particles with a hydrous oxide of aluminum and a boron compound, a reduction accelerator is applied to the surface of the coated product or the base particles. A method for producing a metal magnetic powder for magnetic recording according to items (1) to (5), in which the time required for reduction to the target product can be shortened,
This makes the present invention even more preferred industrially.

Examples of the reduction accelerator include nickel, copper, cobalt, silver, and calcium compounds, with nickel compounds being one of the preferred ones. Taking as an example the case where a nickel compound is used, a typical treatment method will be explained. The nickel compound can be treated by immersing the base particles in a solution such as a nickel salt aqueous solution, or by adding an alkali such as caustic soda after contact with a nickel sulfate, nickel chloride, or nickel nitrate aqueous solution to precipitate nickel hydroxide. Known methods such as coating on substrate particles and heating and hydrolysis of nickel acetate are used.Industrially, salts such as nickel sulfate are used in aqueous systems because it is easy to control the amount of nickel treated. Preference is given to neutralizing methods.

For example, when depositing a nickel compound, the amount of the reduction accelerator to be deposited is 0.1 to 0.1% by weight of Nt/Fe.
It is about 5% by weight.

The present invention will be further explained below by giving Examples and Comparative Examples.

[Example of the present invention]

Method for creating a boron compound adsorbed on aluminum hydroxide A-1 = aluminum chloride (AlCl2-6) 120)
72.04 g, boric acid 57.56 g dissolved in deionized water to give 1600 mj! Then, while stirring, add 4N ammonia water to about 2°5mj! The pH was adjusted to 7.5 by adding at a rate of 1/min over 2 hours, and the aluminum hydroxide suspension was maintained for 30 minutes to obtain an aluminum hydroxide suspension adsorbing boron compounds.

Δ-2: Using 900- of the aluminum hydroxide suspension adsorbing boron compounds obtained in A-1, this was filtered and washed with water to obtain a wet cake of aluminum hydroxide adsorbing boron compounds ( 2% by weight as Aff).

8-3 = Sodium aluminate (NaA I Oz) 12
．． 15 g was dissolved in 900 ml of deionized water, 28.78 g of boric acid was added, and then IN hydrochloric acid was added over 1 hour at a rate of about 1 ml of boric acid with stirring to adjust the pH.
7.5 and then held for 30 minutes to obtain an aluminum hydroxide suspension adsorbing boron compounds.

Example 1 As a base particle, acicular α-Fe00111 with a specific surface area (BET method) of 90 m/g, an average major axis diameter of 0.18 μ, and an axial ratio of 9
After suspending 20g in 1.5β water and adding 15g (5% by weight of nickel) to nickel chloride with stirring, IN
of ammonia water was added at a rate of about 1 ml and 11 minutes, and the pH was adjusted to 7.
, 5 was neutralized. To this suspension, aluminum hydroxide suspension 88 which adsorbed the boron compound prepared in the previous stage A-1 was added.
0 ml was added and then held for 1 hour, filtered and washed with water.

Next, this wet cake was heat-treated in a Matsufuru furnace at 740° C. for 2 hours in the atmosphere.

After that, 50 g of the α-Fezes was placed in a stainless steel vertical fixed bed reduction reactor (inner diameter: 43 mmφ, height:
500 mm), and the exhaust gas was reduced at 425° C. under a hydrogen stream at a linear velocity of about 10 cm/sec until the dew point of the exhaust gas reached -20° C.

The time required for reduction was 185 minutes. The obtained reduced product was cooled under a nitrogen stream and then immersed in toluene, and then the toluene was gradually evaporated at room temperature to form a metal magnetic powder (sample A).
I got it.

Example 2 Completely the same as in Example 1 except that 187.5 g of the aluminum hydroxide wet cake adsorbed with the boron compound prepared in A-2 above was used instead of ^-1 above. A metal magnetic powder (sample B) was obtained.

Example 3 In Example 1, the aluminum hydroxide suspension adsorbing the boron compound prepared in ^-3 above was used instead of A-1, and the heat treatment temperature was 720°C. was treated in exactly the same manner as in the same example to obtain metal magnetic powder (sample C).

Example 4 A metal magnetic powder (sample D) was obtained by processing in exactly the same manner as in Example 1, except that nickel chloride was not added (the time required for reduction was 345
).

Example 5 0.858 g of boric acid was added to 60 g of the wet cake obtained in Example 1 (24 g as α-FeOOH), heated to 50°C, mixed with a spatula, and heated in a Matsufuru furnace at 720°C in the atmosphere. A metal magnetic powder (sample E) was obtained by processing in exactly the same manner as in the same example, except that the powder was fired for 2 hours.

Example 6 In Example 5, 1.85 g of boric acid was replaced with 0.858 g.
Except that the weight was 716 g and the heat treatment temperature was 690°C, the process was carried out in exactly the same manner as in the same example.
A metal magnetic powder (sample F) was obtained.

Comparative Example 1 In Example 1, except that aluminum hydroxide prepared without adding boric acid was used when creating A-1,
A metal magnetic powder (Sample X) was obtained by processing in exactly the same manner as in the same example.

Comparative Example 2 In Example 1, the firing temperature in the Matsufuru furnace was changed to 500°C.
A metal magnetic powder (Sample Y) was obtained by processing in exactly the same manner as in the same example except that

Comparative Example 3 In Example 5, the firing temperature in the Matsufuru furnace was set to 500°C.
A metal magnetic powder (Sample Z) was obtained by processing in exactly the same manner as in the same example except that

The magnetic properties of each of the metal magnetic powder samples obtained in the Examples and Comparative Examples described above were measured by a conventional method. In addition, using these samples, a magnetic paint was prepared by mixing and dispersing the following compounded composition, and then a dry film [10 μm thick was applied, and a magnetic tape prepared by drying after orientation treatment was prepared using a conventional method. The magnetic properties were measured by

Magnetic powder 5 Weight part dispersant
0.25 ・Polyurethane tree JJ
R(30%:8?(I) 2.96
"Mixed solvent" 13.4
〃'')
4.5/1) These magnetic properties, namely coercive force (I
lc: Oe), saturation magnetization (tys: emu/
g), saturation magnetic flux density (Bm: Gauss), squareness ratio (
RS, 5 ports), orientation ratio (Or), reversal magnetic field distribution (S
FD) and further evaluate oxidative stability.
The sample powder was heated at a temperature of 60°C and a relative humidity of 80%,
After leaving it for a week, the accelerated change over time in σS was measured, and the deterioration rate ΔσS (%) of saturation magnetization was determined by the following formula.

(In the formula, σs0 is σS before aging, and σS is σS after aging.) Also, for each of the above magnetic tapes, 60°-6
0' gloss was measured. These results are shown in the table.

〔Effect of the invention〕

The method of the present invention, in which the surface of hydrated iron oxide or iron oxide particles is coated with a hydrated oxide of aluminum that has adsorbed a boron compound, is then subjected to high-temperature dehydration and densification treatment, which eliminates the heat dehydration treatment and densification treatment seen in conventional adhesion treatments. Combustion within and between particles and particle shape deviation are suppressed without causing any problems during thermal reduction treatment, and the dispersibility in the magnetic recording medium is good, with excellent squareness ratio, orientation ratio, etc. It is possible to efficiently produce fine metal magnetic powder suitable for high-density recording, and is a very industrially advantageous method.

Claims (1)

[Claims] 1). A hydrous oxide of aluminum and a boron compound are deposited on the surface of hydrated iron oxide or iron oxide particles, then heat treated at 550 to 900°C in a non-reducing atmosphere, and then heated and reduced. A method for producing metal magnetic powder for magnetic recording. 2). A hydrous aluminum oxide and a boron compound are deposited on the surface of hydrous iron oxide or iron oxide particles, a boron compound is further added to the deposited product, and then heated at 550 to 900°C in a non-reducing atmosphere. 1. A method for producing a metal magnetic powder for magnetic recording, the method comprising heat treatment followed by a heat reduction treatment. 3). In claim 1 or 2, a boron compound adsorbed on a hydrous oxide of aluminum is added to the hydrous iron oxide or iron oxide suspension to form aluminum on the surface of the hydrous iron oxide or iron oxide particles. A method for producing metal magnetic powder for magnetic recording, which comprises depositing a hydrous oxide and a boron compound. 4). 4. The method for producing a metal magnetic powder for magnetic recording according to claim 1, wherein the specific surface area of the hydrated iron oxide is 55 m^2/g or more. 5). 4. The method for producing a metal magnetic powder for magnetic recording according to claim 1, wherein the iron oxide has a specific surface area of 40 m^2/g or more.