JPS62275028A - Ferromagnetic iron oxide powder containing cobalt and its production - Google Patents

Abstract

PURPOSE:To obtain the titled powder excellent in dispersion properties in an organic binder by using a spray dryer in the drying process after coating Co compd. in case of producing ferromagnetic ion oxide powder contg. Co by coating Co compd. on the surfaces of magnetic iron oxide particles. CONSTITUTION:Magnetic iron oxide is treated in an aq. medium with Co salt or Co salt and the other metallic salt and alkali and thereby a metallic compd. contg. Co is coated on the surfaces of magnetic iron oxide particles. Ferromag netic iron oxide powder contg. Co is produced by filtering and water-washing it or furthermore heating or drying it. The following ferromagnetic iron oxide powder contg. Co is obtained by performing the drying of this case by means of a spray dryer. It is spherical powder having 5-200mum diameter wherein fine particles of ferromagnetic iron oxide contg. Co having >=30m<2>/g specific surface area measured by a BET method are converged, has <=35 degrees angle of repose of powdery material, is excellent in dispersion properties in an organic binder, and has excellent characteristics as a magnetic recording material.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Technical Field of the Invention] The present invention provides a ferromagnetic oxidized material useful as a recording material for a magnetic recording medium (a ferromagnetic oxidized material having improved dispersibility in an organic binder). This invention relates to iron powder and its manufacturing method.

[Technical background of the invention and its problems 1 Huvart-containing ferromagnetic iron oxide has a high coercive force, and when used as a recording element of a magnetic recording medium, high-density recording is possible and it has excellent sensitivity in the high frequency region. It is used in the field of magnetic recording, such as for video, because it has characteristics such as .

As a recent trend, with the trend towards high-quality magnetic recording media such as video tapes, the cobalt-containing ferromagnetic iron oxide used as the recording element is becoming increasingly finer. As the fine particle magnetic powder becomes finer, it becomes difficult to disperse it uniformly into the paint when mixed with various organic binders to prepare magnetic paints, and it also becomes difficult to disperse the fine particles evenly in the paint when mixed with various organic binders. There may be a problem that the effect cannot be extracted.

On the other hand, in the recent manufacturing method of magnetic recording media, firstly, a high degree of smoothness is imparted to the surface of the magnetic recording medium by highly filling and highly oriented magnetic powder with high coercive force, and by uniformly dispersing the magnetic powder. This is important in obtaining excellent magnetic properties, and for this purpose, it is necessary to disperse the magnetic powder close to the primary particles without destroying the magnetic powder during the preparation of the magnetic paint. However, magnetic powders obtained by conventional manufacturing methods tend to have large particles that aggregate to form agglomerates.
When preparing magnetic paint, it was difficult to disperse mainly near the primary particles.

Various proposals have already been made to solve these problems. For example, before preparing magnetic paint, the surface of magnetic powder particles is coated with a surfactant that is compatible with the binder (Japanese Patent Publication No. 53-19120, Japanese Patent Application Laid-Open No. 54-372).
97, JP-A-53-141196, JP-A-54-823
54, JP-A-54-85397) and a method of adding a surfactant as a dispersant during the preparation of magnetic paint (JP-A-55-85397).
151068, JP-A-55-151069), or a method of loosening agglomerates using mechanical dispersion means during the preparation of magnetic paint (JP-A-50-22297, JP-A-55-15721)
6, Japanese Unexamined Patent Publication No. 10903 (1983)) have been attempted.

However, even these conventional methods are ineffective due to problems with the resin selectivity of the surfactant, and problems such as decreased strength of the magnetic tape, bleeding, and powder dropout (a phenomenon in which magnetic powder peels off due to wear of the tape) occur. However, depending on the degree of mechanical dispersion, reaggregation may occur.

In particular, as the magnetic powder is made into finer particles, these defects become more noticeable, making it extremely difficult to improve the dispersibility.

In the process of manufacturing cobalt-containing ferromagnetic iron oxide by depositing a cobalt compound on the surface of magnetic iron oxide particles, the dryer used in the drying process after depositing the cobalt compound is generally an air-flow box dryer. , fluidized type dryers, rotary type ventilation dryers, etc., but these are the main methods, and there have been no proposals for devising the drying process to improve dispersibility.

[Object of the Invention] An object of the present invention is to solve the problems of the prior art described above, and to provide a cobalt-containing ferromagnetic iron oxide powder useful as a recording material, which has excellent dispersibility in an organic binder, and a method for producing the same. It is in.

[Summary of the Invention 1] As a result of various studies to achieve the above object, the inventors of the present invention have developed a process for producing cobalt-containing ferromagnetic iron oxide by depositing a cobalt compound on the particle surface of magnetic iron oxide powder. By using a spray dryer in the drying process after coating the cobalt compound, a spherical powder with a diameter of 5 to 200 μm, which is an aggregate of fine particles of cobalt-containing magnetic iron oxide, is produced. The present invention was completed based on the knowledge that a magnetic powder with extremely excellent dispersibility that can be easily dispersed into primary particles before aggregation can be obtained. That is, the first aspect of the present invention is a spherical powder with a diameter of 5 to 200 μm, which is made up of fine particles of cobalt-containing ferromagnetic iron oxide having a specific surface area of 30 m2/g or more according to the BET method. This is a cobalt-containing ferromagnetic iron oxide powder characterized by an angle of 35 degrees or less.

The second aspect of the present invention is to treat magnetic iron oxide with a cobalt salt or a cobalt salt and other metal salts and an alkali in an aqueous medium to deposit a cobalt-containing metal compound on the surface of the particles, and then A method for producing cobalt-containing ferromagnetic iron oxide powder by filtering, washing with water, or further heating and drying the magnetic iron oxide, characterized in that the drying is carried out by spray drying. This is a method for producing powder.

Cobalt-containing ferromagnetic iron oxide having a specific surface area of 30 m2/g or more according to the BET method can be manufactured by various methods, and the manufacturing method is not particularly limited, but usually magnetite (γ-Fe20.), Magnetite (Fe-
0,), hellide-based compounds (FeOx, 1.33<
x < 1.5) in an aqueous medium,
A cobalt-containing metal compound is coated on the surface of the particles by treatment with a cobalt salt or a cobalt salt and other metal salts and an alkali, and then the magnetic iron oxide is filtered, washed with water, or further heat-treated. It will be done. The shape of this substance is typically acicular crystals with an average particle size (major axis length) of 0.08-0.
．． 3μm uniaxial ratio is 3-15 and specific surface area is 3030-7O
/g, preferably 35 to 70 m2/g, but in addition to the above-mentioned needle-shaped particles, for example, spindle-shaped,
Fine particles having various shapes such as rice grains and having a specific surface area within the above range may be used. Examples of the other metal salts mentioned above include salts of metals such as ferrous iron, manganese, zinc, vanadium, barium, and magnesium.

The effects of the present invention are particularly remarkable in fine particle magnetic iron oxide having the above-mentioned specific surface area. The reason is that as the specific surface area increases, the interparticle cohesive force increases1).
This is thought to be due to the fact that the agglomeration state of the dried particles progresses rapidly during drying.

In the case of magnetic iron oxide having a small specific surface area (less than 30 m'/g), agglomeration during drying does not pose much of a problem, and the effects of the present invention are not so noticeable.

The magnetic powder of the present invention retains the shape of a droplet, and has a diameter consisting of fine particles of cobalt-containing ferromagnetic iron oxide having a specific surface area of 30 m"/g or more measured by the BET method. It has a spherical shape of 5 to 200 μm.This material has excellent fluidity, and the angle of repose, which is often used as a measure of the fluidity of powder, is 35 degrees or less. (measured using a dryer) is significantly lower than that obtained using a normal drying device, such as a hot air circulation type or fluidized flow type drying device. The angle of repose, which is a property of powder related to fluidity, is 35 degrees or less, preferably 30 degrees.
degree or less. Magnetic powders with an angle of repose exceeding 35 degrees have poor dispersibility and also have poor magnetic properties such as squareness ratio and orientation of magnetic recording media. Powders with a temperature exceeding 35 degrees generally have strong adhesion and agglomeration properties, and therefore are undesirable because they tend to cause adhesion and clogging in pneumatic transportation equipment, storage equipment, etc., and pose problems in handling the powder. The degree of compaction, which is sometimes used as another property of powders related to flowability, is believed to be less than 0.25, preferably less than 0.20.

The magnetic powder of the present invention, which has excellent fluidity, has the advantage of being easily handled as a powder. The main powder is easily dispersed close to the primary particles when preparing magnetic paint, so it not only greatly shortens the dispersion time, but also makes it possible to use it to create magnetic recording media such as magnetic tape. In addition to the glossiness of the magnetic recording medium, the squareness ratio (B
It also improves magnetic properties such as r/8m) and orientation (OR).

The present invention is a method for producing spherical cobalt-containing ferromagnetic iron oxide powder, which includes the following steps.

That is, in the present invention, magnetic iron oxide is placed in an aqueous medium and treated with Fval Y salt or cobalt salt, other metal salts, and alkali to coat the surface of the particles with a metal compound containing cobalt. Then, this magnetic iron oxide is separated by filtration, washed with water,
Alternatively, a method for producing a cobalt-containing ferromagnetic iron oxide powder by further heating and drying is characterized in that the drying is performed by spray drying.

A spray dryer is a device that atomizes liquid raw materials such as solutions, colloids, pastes, and slurries, and dries them in seconds by contacting them with a high-temperature air stream. , or Q. There are various types of spraying methods, but any type can be used in the present invention. A cross-sectional view of an example of a spray dryer is shown in Figure 1.

The concentration of the magnetic iron oxide slurry supplied to the spray dryer is not particularly limited as it can be atomized using a pressure nozzle format or a disk format depending on its properties, but it is usually 30 to 400 g.
/ρ, preferably about 150 to 300 g/f. If the concentration of magnetic iron oxide is too high, it will interfere with pumping and atomization, resulting in insufficient droplet formation for spherical particles.

Furthermore, for the purpose of removing moisture by drying, if the concentration is too low, it will be economically inefficient, so the concentration usually used industrially is preferably 150 g/ρ or more.

There are various appropriate conditions for the discharge pressure during atomization depending on the spray type, supply pump type, and capacity, but it is usually 2 to 30
Kg/am", preferably about 10 to 25 Kg/cm2.

The inlet temperature of the hot air as a drying heat source is usually 150°C or higher, but the outlet temperature increases depending on the inlet temperature, and when using a bag filter as a method for collecting spray-dried products, the filtration The upper temperature limit is regulated based on the heat resistance of the fabric.

In the case of magnetic iron oxide, if it is heated to a temperature above 200'C during drying, its magnetic properties and dispersion properties tend to deteriorate, so it is better to set the inlet temperature so that the outlet temperature does not exceed 200'C. . Also, if the outlet temperature is too low, the moisture content after drying will be too high, and the spherical particle state will be destroyed when additional drying is performed, or the influence of additional drying equipment will be greater, making it difficult to spray dry. This is not preferable because the characteristics of improved dispersibility are small and the drying efficiency deteriorates. Therefore, the drying outlet temperature is usually 6
0 to 200'' C1, preferably about 70 to 200°C.

By appropriately combining the above-mentioned ranges of magnetic iron oxide concentration, discharge pressure, and drying outlet temperature depending on the model and capacity of the spray dryer, magnetic powder having a spherical particle diameter of 5 to 200 μm can be obtained.

As the drying atmosphere, a non-oxidizing atmosphere of 1 tvf is not required, and air may be used. A non-oxidizing atmosphere is sometimes required as a drying atmosphere for cobalt-containing ferromagnetic iron oxide.
This is generally to prevent Fe in the cobalt-containing ferromagnetic iron oxide from being oxidized. In the method of the present invention, the oxidation reaction of Fe" is difficult to proceed, perhaps because drying is instantaneous. Therefore, in the method of the present invention, in the case of magnetic iron oxide, which requires a non-oxidizing atmosphere in a normal dryer, However, it is advantageous in terms of cost since it is not necessary to adjust the atmosphere to be non-oxidizing and drying can be done in air.

[Example] Next, an example of the present invention will be shown. In addition, comparative examples are also listed for reference.

Cobalt-containing ferromagnetic iron oxide (
(hereinafter abbreviated as magnetic iron oxide) has an average particle diameter (major axis length) of 0.1
8μ, axial ratio 8, Hc3800e, ffs71emu/
g, γ-F e with a specific surface area of 50 m”/g
203 as a core crystal, a cobalt-containing magnetic iron oxide layer was formed on the core crystal using an aqueous solution of cobalt sulfate, ferrous sulfate, and an aqueous solution of caustic soda, and the layer was filtered and thoroughly washed with water. Note that the contents of cobalt and ferrous iron are 3.5% and 3.7%, respectively, on a dry weight basis.

Example 1 An aqueous slurry with a magnetic iron oxide concentration of 195 g/I2 was prepared using a spray dryer (Ashizawa Niro Atomizer K) which is stable at an air hot air inlet temperature of 300°C and an outlet temperature of IQQ'C.
Magnetic powder (manufactured by K, AN-12,5CN/CR type) with a nozzle discharge pressure of 15 kg/am2 and dried to produce spherical particles with a moisture content of 0.2% by weight and an average diameter of approximately 85 μm.
A) was obtained.

Example 2 Hot air inlet temperature is 400 ``C1 outlet temperature is ISO''
The same procedure as Example 1 was carried out except that C was used, and the moisture content was 0.
．． 1% by weight spherical particles Magnetic powder with an average diameter of about 83 μm (B
) was obtained.

Example 3 The procedure was the same as in Example 1 except that the hot air inlet temperature was 250°C and the outlet temperature was 75°C, and the moisture content was 5.
A magnetic powder containing 0% by weight was obtained. This was further dried at 120"C in nitrogen gas with a moisture content of 0.1 using an airflow box dryer.
% by weight, and the average diameter of the spherical particles is approximately 8.
A magnetic powder (C) of 0 μm was obtained.

Comparative Example 1 The same magnetic iron oxide slurry as that used in the example was dehydrated and made into a cake shape, and dried at 120'C in nitrogen gas using an air-flow box dryer to give a moisture content of 0.1% by weight. Magnetic powder (D) was obtained.

Comparative Example 2 The same magnetic iron oxide cake as in Comparative Example 1 was dried at 120°C in nitrogen gas using a fluidized fluid dryer to obtain magnetic powder (E) with a water content of 0.1% by weight.

Comparative Example 3 The same magnetic iron oxide cake as in Comparative Example 1 was dried at 120°C in nitrogen gas using a rotary ventilation dryer to reduce the water content to 0.
A 1% by weight magnetic powder (F) was obtained.

Comparative Example 4 The same magnetic iron oxide cake as in Comparative Example 1 was dried in an air flow box dryer 1) at 120°C in the atmosphere to a moisture content of 0.1.
A magnetic powder (G) of % by weight was obtained.

The coercive force (Hc) and saturation magnetization (GS) of the above samples (A) to (G) were measured by conventional methods. Mainly, QFej+ content (
% by weight) was measured.

Furthermore, the angle of repose, loose apparent specific gravity and hardened apparent specific gravity were measured using a Hosokawa powder tester, and the results are shown in Table 1.

How to measure the angle of repose: Vibrate a standard sieve (710 μm opening), pass the sample through the funnel, and deposit the powder in a table cup using the injection method. When the powder spills out and the angle of repose is constant, Measure the crest line (the diagonal line when looking at the powder from the front) using a protractor to calculate the angle.

Method for measuring loose apparent specific gravity: Vibrate a standard sieve (710 μm mesh size), drop the sample through the chute, and place in a specified container (inner volume 100 cm).
Allow the powder to enter c) for about 20 to 30 seconds until it becomes a heap, then hold the blade vertically, scrape the surface of the powder, weigh it with a top balance, and calculate the weight of the powder ÷ 100. Calculate the slack apparent specific gravity value.

Method for measuring apparent specific gravity after solidification Add a cap to a specified container (inner volume 100cc), place it in the tapping holder, fill the cap with powder up to the top, cover the cap, and tap (1 time/second) once.
After 80 times, play Y (same as the loose apparent specific gravity value))) Cut and weigh, harden by dividing the weight of the powder by 100, and calculate the apparent specific gravity value.

Further, for each sample, a compound was prepared according to the following compounding ratio and dispersed in a ball mill to produce a magnetic paint.

(1) Cobalt-containing ferromagnetic iron oxide powder 100.0 parts by weight (2) Surfactant 3
．． 8 (3) Vinyl chloride-vinyl acetate copolymer resin 8
．． 0 (4) Polyurethane resin 35
．． 5 //(5) Methyl ethyl ketone
108,1 /1(6) Toluene
108.1 //(7) Cyclohexanone 36.0 /7 Next, each magnetic paint was applied to a polyester film by a normal method,
After orientation and drying, a magnetic tape having a magnetic coating film with a thickness of about 9 μm was prepared. For each tape, the coercive force (He), squareness ratio (Br/8m), orientation (OR), switching field distribution (SFD), and coating film gloss (60
゜-60' Gloss) was measured. The result is the first
Shown in the table.

Further, FIG. 2 shows the results of investigating the relationship between the ball mill dispersion time and the gloss of the magnetic tape coating for the magnetic powder (A) and the magnetic powder (D).

From the results in Table 1, it can be seen that the cobalt-containing ferromagnetic iron oxide powder obtained by the present invention has high fluidity, and the gloss, squareness ratio and It can be seen from the orientation value that it has excellent dispersibility. In addition, although hot air was used, the Fe
content, indicating that the oxidation reaction of Fe is difficult to proceed.

From FIG. 2, it can be seen that the dispersion time required to obtain a coating gloss value equivalent to that obtained using a conventional dryer is greatly reduced, and the dispersion time obtained by the present invention is significantly reduced. It can be seen that the magnetic powder has been improved to have the advantage of reducing the cost by a large amount.

It can be seen from the results of Example 3 that if the moisture value of the dry product is insufficient, additional drying is sufficient. This additional drying
The difference between the desired moisture value and the residual moisture content (Φru 1) may be an auxiliary means to remove a small amount of moisture.It is not desirable if the moisture value of the dried waste product is too high (approximately 10% or more). , 5
%, the characteristics of the magnetic powder produced by the spray dryer will not be lost even if a normal dryer is used.

Electron micrograph (30,000x) showing the crystal structure of cobalt-containing ferromagnetic iron oxide particles used in Examples and Comparative Examples, and micrograph @It (40x) showing the particle structure of magnetic powder A and magnetic powder. ) are attached in order as Figures 3 to 5. 1 The magnetic powder obtained by the present invention (magnetic powder A) has a particle size of 5 to 200 J.
It is clearly a spherical powder with a particle diameter of III.

[Effects of the Invention] The present invention achieves the following various excellent effects in addition to the above-described structure.

In other words, ■ This magnetic powder is made up of cobalt-containing ferromagnetic iron oxide particles, which are large particles, aggregated with a relatively gentle cohesive force, so it is easily dispersed to near primary particles during the preparation of magnetic paint, and the dispersion time is short. Shorten to a large width. Therefore, it leads to lower costs in industrial operations.

■ When magnetic recording media such as magnetic tapes are made using this magnetic powder, not only the gloss of the coating film but also the magnetic properties such as squareness ratio and orientation are greatly improved.

(2) The cobalt-containing ferromagnetic iron oxide powder of the present invention is highly fluid and has many advantages in handling as a powder. For example, clogging and crosslinking phenomena can be prevented during powder transportation.

■ In conventional products, dispersibility is slightly improved by crushing after drying, but this magnetic powder has excellent dispersibility even without crushing, so repeated crushing is not necessary. .

(2) According to the method of the present invention, even in the case of magnetic iron oxide, which requires a non-oxidizing atmosphere during drying, there is no need to adjust the atmosphere to non-oxidizing, and it is industrially advantageous in terms of cost.

[Brief explanation of the drawing]

Figure 1 is a sectional view showing an example of a spray dryer, and Figure 2 is a diagram showing the relationship between dispersion time in a resin binder and coating gloss for the magnetic powders obtained in Example 1 and Comparative Example 1. , FIG. 3 is an electron micrograph (30,000
4 and 5 are micrographs showing the particle structure of the magnetic powder obtained in Example 1 and the magnetic powder obtained in Comparative Example 1, respectively, and the magnification is 40 times. In FIG. 2, curve 1 shows the case of the magnetic powder of Example 1, and curve 2 shows the case of the magnetic powder of Comparative Example 1.

Claims (1)

[Scope of Claims] 1) A spherical powder with a diameter of 5 to 200 μm made up of fine particles of cobalt-containing ferromagnetic iron oxide having a specific surface area of 30 m^2/g or more according to the BET method; A cobalt-containing ferromagnetic iron oxide powder having an angle of repose of 35 degrees or less. 2) Magnetic iron oxide is treated with cobalt salt or cobalt salt and other metal salts and alkali in an aqueous medium to deposit a cobalt-containing metal compound on the surface of the particles, and then the magnetic iron oxide is filtered. A method for producing a cobalt-containing ferromagnetic iron oxide powder by separately washing with water or further heating and drying the cobalt-containing ferromagnetic iron oxide powder, the drying being carried out by spray drying.