JPH03290904A - Production of metallic magnetic powder - Google Patents

Abstract

PURPOSE:To prepare fine metallic magnetic powder superior in dispersibility by carrying out a shape holding processing of the metallic magnetic powder while dispersing the powder using a dispersing apparatus in the process of preparing the metallic magnetic powder, wherein needle goethite, or the like is used as raw material, wherein the shape holding processing is applied to the metallic magnetic powder, followed by reduction of the powder. CONSTITUTION:In the process of preparing the metallic magnetic powder, wherein a needle goethite or a needle goethite modified using metal other than iron is used as raw material, wherein the shape holding processing is applied to the metallic magnetic powder, followed by reduction thereof, and then the shape holding processing is carried out while dispersing the powder using a dispersing apparatus. As such, although metallic magnetic powder superior in dispersibility is obtained by reducing the processed powder after the shape holding processing is carried out while dispersing the powder using a dispersing apparatus, when the reduction is interrupted during the step of producing magnetite and then the shape holding processing is again carried out while dispersing it using a dispersing apparatus, more effective dispersibility is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing metal magnetic powder used for magnetic recording, and particularly relates to a method for manufacturing metal magnetic powder used for magnetic recording, and in particular, metal magnetic powder having a large specific surface area, high coercive force, and excellent dispersibility. This invention relates to a method for producing powder.

[Problems to be solved by conventional techniques and inventions] In recent years,
There have been remarkable developments in various recording methods, and among them, the progress in making magnetic recording and reproducing devices smaller and lighter has been remarkable. Along with this, there is an increasing demand for higher performance in magnetic recording media such as magnetic tapes and magnetic disks.

In order to satisfy these requirements for magnetic recording, magnetic powders with high coercivity and high saturation magnetization are required. Conventionally, acicular magnetite or magnetite or these magnetic iron oxide powders modified with cobalt, so-called cobalt-containing iron oxides, have been used as magnetic powders for magnetic recording, but in order to obtain higher output media, Ferromagnetic metal powders with higher coercive force and saturation magnetization, so-called metal magnetic powders, are beginning to be used.

Various methods have been proposed for producing metal magnetic powder, but generally speaking, due to its economical advantages, acicular goethite or iron oxide particles obtained by heating and dehydrating it are processed using hydrogen, etc. A method is used in which iron is heated in a reducing gas atmosphere to reduce it to metallic iron.

However, since reduction is carried out at high temperatures in this method, it is easy to cause particle fusion and shape collapse, making it impossible to obtain fully satisfactory performance.Therefore, various proposals have been made. Examples include one in which goethite is treated with water glass and then reduced by firing (Japanese Patent Publication No. 63-49722), and one in which goethite is dehydrated by heating and then a silicon compound is attached to its surface and then reduced by heating. (Japanese Unexamined Patent Publication No. 59-80901), and one in which goethite is coated with aluminum phosphate and subjected to thermal reduction (Japanese Unexamined Patent Publication No. 63-67705).

However, these proposals can only solve the problem when the particle size is relatively large, and are not satisfactory in the case of fine metal magnetic powder with a specific surface area close to 60 m''/g, which corresponds to recent high-density recording. It's not possible.

The present invention aims to provide a method for producing metal magnetic powder with excellent dispersibility by preventing particles from sintering together during the production stage of such fine-grained metal magnetic powder.

[Means to solve the problem]

As a result of studying the process of obtaining metal magnetic powder from goethite, the present inventors found that reduction was interrupted at the stage of magnetite produced during reduction, and the magnetite was subjected to shape-maintaining treatment. , found that it is easy to prevent sintering during reduction and maintain the shape, and has filed a patent application (Japanese Patent Application No. 1-119134). However, as a result of further study, it was decided that the shape-maintaining treatment should be carried out under specific conditions. The present inventors have discovered that the dispersibility is even more excellent.

That is, the present invention uses acicular goethite or acicular goethite modified with a metal other than iron as a raw material, performs shape maintenance treatment, and then reduces it to produce metal magnetic powder. The present invention relates to a method for producing fine metal magnetic powder with excellent dispersibility, which is characterized by carrying out shape maintenance treatment while dispersing.

As in the method of the present invention, metal magnetic powder with excellent dispersibility can be obtained by performing shape maintenance treatment while dispersing with a disperser and then reducing, but the reduction is interrupted at the magnetite stage and the disperser is used again. Even better effects can be achieved if the shape maintenance treatment is performed while dispersing the particles.

It is not clear why the performance of metal powder improves when shape maintenance treatment is performed while dispersing with a dispersion machine, but by performing shape maintenance treatment in the presence of dispersion force, the treatment agent adheres more uniformly and works more effectively. It is assumed that one of the reasons for this is that it is easier to do so.

Generally, when preparing a slurry by mixing a powder with a liquid,
Operations to homogenize powder and liquid, expressed by terms such as dispersion, mixing, and stirring, are performed, but in the present invention, ``dispersion by a dispersing machine'' does not simply refer to mixing and stirring, but rather refers to slurry units. It refers to the application of power above a certain value per liquid volume.In other words, it refers to the application of power above a certain value per liquid volume.
In stirring, the stirring power (P/V value) per unit liquid volume of slurry is 0.1 to 10 kW/1T: For some noni, in "dispersion using a disperser", P/V is preferably IXIO' kh/- or more. is a value greater than or equal to IXIO"kga/va".

Here, P: stirring power (kW) of stirrer, disperser, etc. v:
For stirring, the amount of liquid in the tank is [-], and for dispersion, it is the amount of hold-up in the dispersion section [1].

It is sufficient for the dispersing machine used in the present invention to have a dispersion mechanism using shearing force generated by high-speed rotation, but it is more preferable if it has a dispersion mechanism using ultrasonic waves in addition to shearing force. Further, although the dispersing machine can be installed within the reaction tank, it is more efficient to provide a circulation line outside the reaction layer and installing the dispersing machine in the middle of this line.

The axial ratio and size of the acicular goethite used in the present invention may be as long as it can be used as a raw material for a numerically sized metal magnetic powder, but the effect of the present invention is most noticeable when the particle size is small. become.

The goethite referred to in the present invention is a powder mainly composed of hydrated iron oxide represented by the general formula Fe00H, and has a lattice spacing of 4.18±
It has a main peak of X-ray diffraction at a position corresponding to 0.05.2.69 ± 0.05.2.45 ± 0.05 angstroms, and a weight loss of approximately 12% occurs when heated in the atmosphere, and hematite This refers to those that produce iron, and may contain a small amount of metal elements other than iron. In addition, the magnetite referred to in the present invention is an oxide mainly composed of iron oxide, and the interplanar spacing is 2.97±0.05.2.53±0.05.
It has a main peak of X-ray diffraction at a position corresponding to 2.10 ± 0.05 angstroms, and when heated in the atmosphere,
．． X&! means something that causes a weight increase of 5% or more This refers to a state in which substantially no diffraction peaks corresponding to goethite, hematite, or metallic iron are observed in diffraction.

The X-ray diffraction patterns of these typical powders are shown in FIG. In FIG. 1, (A) is a diffraction pattern diagram of goethite, (B) is a diffraction pattern diagram of magnetite, and (C) is a diffraction pattern diagram of metallic iron.

Shape maintenance treatment for goethite and magnetite as used in the present invention is to prevent fusion and shape collapse that occur when goethite is reduced to magnetite or metallic iron, and further when magnetite is reduced to metallic iron. It is a general term for the treatments described above, and is also referred to as sintering prevention treatment or fusion prevention treatment.

Si+AL is used to maintain the shape of acicular goethite.
Treatment using compounds such as Zr, Ti, Sn+ Mg, Ca+ B+ P, etc. alone or in combination is used, and is carried out by precipitation of insoluble matter from a solution state, deposition of colloidal compounds, etc. Specific examples include a method in which insoluble hydroxides are precipitated by adding an aqueous solution of water-soluble compounds such as water glass, sodium alkyl phosphate, and magnesium sulfate to a slurry of goethite, and then adjusting the pH of the system; The methods used include precipitating insoluble salts such as salts and balates, and adding metal alkoxides such as triisopropoxyaluminum, tetraethoxysilane, and tetraisopropoxytitanium to goethite slurry to precipitate hydrolysates. . In addition, as the Si compound, silicon resin,
Silicone oil can also be used.

To reduce goethite to magnetite or metallic iron, goethite after shape maintenance treatment is reduced to 250 to 50% in a hydrogen stream, for example.
This is done by maintaining the temperature at 50"C. At this time, heating and dehydration may be performed in air prior to shape maintenance treatment and reduction, but the final result is better if heating and dehydration is performed in a reducing atmosphere. The magnetic properties of the metal magnetic powder become better.

Si is used to maintain the shape of magnetite.

AI, Zr, Ti, Sn, Mg, Ca+ B
In addition to treatments with compounds such as, treatments with thermosetting resins such as phenol resins and furan resins are also effective. Si,
AlZr, Ti+ Sn, F! Ig, Ca,
For treatment with compounds such as B, the same method as for goethite is used, and an example of treatment with a thermosetting resin is to add a solution of these resins in a water-soluble organic solvent (acetone, ethanol, etc.) to a slurry of magnetite. This is done by making it insoluble. Of course, these processing agents may be used alone or in combination.

The reduction of magnetite to metal magnetic powder after the shape maintenance treatment may also be maintained at 300 to 550°C in a hydrogen stream.

[Examples] Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples.

Example 1 As shown in FIG. 2, an apparatus having a circulation line with a pipeline dispersion machine Milder 2 (manufactured by Ebara Corporation) installed outside the reaction tank 1 was used to collect goethite (major axis diameter: 0. 1
8 m, axial ratio: 8) After dispersing 1 kg in 3% solution 11 of Poise 530 (polycarboxylic acid oligomer manufactured by Kao ■) for about 1 hour, 70 g of No. 3 Keiso (SiOz content 29%) was added, and for another 1 hour. continued to disperse. Further, while continuing dispersion, dilute nitric acid was added to lower the pH of the system to 6.5, and dispersion was continued for 1 hour, followed by filtration, washing, and drying to obtain goethite having a silicon compound layer.

In addition, in FIG. 2, 3 is a dripping tank, and 4 is a dripping pump.

This silicon compound-treated goethite was heated to 300°C at 2.5°C/min in a retort furnace (inner volume 301) while flowing hydrogen/nitrogen = 1/1 mixed gas at 501/min. C, and reduction was carried out until the peaks of goethite and hematite were no longer seen in X-ray diffraction to obtain magnetite. While this magnetite was being dispersed again using the above device, 60 g of Keiso No. 3 was added for 1 hour, dilute nitric acid was added to bring the pH of the system to 6.5, and the mixture was further dispersed for 1 hour.

Thereafter, it was filtered, washed, and dried to obtain magnetite with a new silicon compound layer formed thereon. This magnetite was reduced in a retort furnace at 350''C in a hydrogen stream to obtain metal powder 1.

When the shape of the metal powder was observed using a transmission electron microscope (hereinafter abbreviated as TEM), it was found that the acicular shape of the raw goethite was maintained. Table 1 shows the magnetic properties of metal powder 1 along with other examples.
Shown below.

Next, the following paint composition was mixed for 6 hours in a Bunch type sand mill, 2.5 parts by weight of Coronate (manufactured by Nippon Polyurethane Industries) was added to the mixture, and after further mixing for 15 minutes, it was filtered. The glass beads were separated and a magnetic paint was prepared.

Apply this paint to a 10μ thick PE↑ film with a dry film thickness of 3
PET
A magnetic layer was formed on the film. Next, a mirror finish was obtained by calendering to obtain a coating film 1.

The magnetostatic properties of the obtained coating films are shown in Table 2 along with other examples.

Paint formulation> Metal powder 1100 parts by weight Lecithin 2 Carbon black 3 γ-Algos 5 VAGH" 15 Niraporan 2304" 2 10 Methyl ethyl ketone
150 parts by weight Toluene 50 Cyclohexanone 75 (Note) ml: Union Carbide vinyl chloride/
Vinyl acetate/polyvinyl alcohol copolymer *2 Polyurethane resin manufactured by Nippon Polyurethane Kogyo Co., Ltd. Example 2 Goethite containing a silicon compound layer obtained in the same manner as in Example 1 was reduced to obtain magnetite.

This magnetite was again dispersed in a 3% solution of Boyds 530 for 1 hour. Add Resin M (Maruzen Petrochemical ■) to this slurry.
A solution prepared by dissolving 50 g of a phenolic resin (manufactured by the company) in 0.31 g of ethanol was added dropwise and stirred for 1 hour, followed by filtration, washing, and drying to obtain magnetite coated with a phenol resin.

This magnetite was reduced in a retort furnace at 350° C. in a hydrogen stream to obtain metal powder 2 and coating film 2.

Observation by TEM showed that the acicularity was well maintained.

Comparative Example 1 Ikg of goethite used in Example 1 was dispersed in 10ffi of a 3% solution of Boyz 530, and after dispersing and stirring for about 1 hour using a TK homomixer SL model (manufactured by Tokushu Kika Kogyo ■),
Add 70g of No. Keiso (Si (h content 29%) and add 1
Continued time distribution. Thereafter, dilute nitric acid was added to lower the pH of the system to 6.5, and after stirring for 1 hour, the mixture was filtered, washed, and dried to obtain goethite having a silicon compound layer.

This silicon compound-treated goethite was reduced in the same manner as in Example 1 to obtain magnetite. This magnetite was again dispersed in a 3% solution of Boyds 530, 60 g of No. 3 Keiso was added and dispersed for 1 hour, and then dilute nitric acid was added to adjust the pH of the system to 6.5.
After stirring for 1 hour, the mixture was filtered, washed and dried to obtain magnetite with a new silicon compound layer formed thereon, and reduced in the same manner as in Example 1 to obtain metal powder 11. In observation by TEH, neither particle fusion nor shape collapse was observed.

Furthermore, coating 811 was obtained using this metal powder 11 in the same manner as in Example 1.

Example 3 Example except that in place of the No. 3 diaphragm and dilute nitric acid in Example 1, an aqueous sulfuric acid solution (AI□03 min 2.1%) 6f and an ammonia aqueous solution were used to adjust the pH of the system to 7.0. Goethite having an aluminum compound layer was obtained in the same manner as in Example 1. Next, it was reduced in a retort furnace to form magnetite in the same manner as in Example 1, and then processed in the same manner as in Example 1 to form magnetite with a silicon compound layer formed thereon, and then reduced in the same manner as in Example 1 to obtain metal powder 3 and Coating film 3 was obtained.

Comparative Example 2 Comparative Example except that in place of No. 3 Keiso and dilute nitric acid in Comparative Example 1, 6ff of sulfuric acid band aqueous solution (Al□03 min 2.1%) and ammonium aqueous solution were used to adjust the pH of the system to 7.0. After obtaining goethite having an aluminum compound layer in the same manner as in Comparative Example 1, the magnetite was reduced to magnetite in a retort furnace in the same manner as in Comparative Example 1, and then a silicon compound layer was formed by the same treatment as in Comparative Example 1. After that, it was reduced in the same manner as in Comparative Example 1 to obtain metal powder 12 and coating film 12.

The magnetic properties of the metal powders and coating films obtained in Examples 1 to 3 and Comparative Examples 1 to 2 are shown in Tables 1 and 2, respectively.

Table 1 Table 2 P.S.

[Brief explanation of drawings]

FIG. 1 shows the x1 diffraction patterns of goethite, magnetite, and metallic iron; (A) shows the diffraction pattern of goethite, (B) shows the diffraction pattern of magnetite, and (C) shows the diffraction pattern of metallic iron. FIG. 2 is a schematic diagram of a circulation line with a disperser used in Example 1. 1: Reaction tank 2: Milder 3: Dripping tank 4: Dripping pump

Claims (2)

[Claims] 1. The raw material is acicular goethite or acicular goethite modified with metals other than iron, and after undergoing shape maintenance treatment,
A method for manufacturing metal magnetic powder, which comprises performing shape maintenance treatment while dispersing the metal magnetic powder using a disperser when reducing the metal magnetic powder. 2. The metal magnetic powder according to claim 1, characterized in that the goethite that has been subjected to a shape-maintaining treatment while being dispersed with a disperser is turned into magnetite, and then the metal magnetic powder is reduced by performing a shape-maintaining treatment while being dispersed with a disperser again. Production method.