JPS636807A - Manufacture of fine particles of acicular iron for magnetic recording - Google Patents

Abstract

PURPOSE:To easily prepare high dispersive magnetic paint by drying oxyhydroxide iron or iron oxide, or surfacemodified oxyhydroxide iron or iron oxide in the state flocculated in liquid. CONSTITUTION:Oxyhydroxide iron or iron oxide, or surfacemodified oxyhydroxide iron or iron oxide is suspended in liquid. Then, hydrogen ion concentration of suspension is so controlled as to become suspended flocculation range to be flocculated, and then dried. Then, it is converted to ferromagnetic iron fine particles by vapor contact reducting reaction with reducing gas. Thus, the secondary coagulation lump strength of the magnetic fine particles in ferromagnetic metal fine particles are much weakened. Accordingly, the fluidity of organic solvent slurry is very improved to extremely accelerate paint dispersion.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for producing ferromagnetic metal powder particles as a magnetic material for high-density magnetic recording media mainly used for audio and video.

<Prior art> Magnetic powder useful for magnetic tapes and magnetic recording media has traditionally been mainly T-iron oxide, but in recent years, high-density recording media for VTRs and high-end audio have become desirable.
A metal with high coercive force that is mainly made of metallic iron, cobalt, or an alloy of nickel and iron, which is obtained by subjecting powder mainly composed of iron oxyhydroxide or iron oxide to a vapor phase catalytic reduction reaction using a reducing gas. Magnetic particles have come to be used. The coercive force of metal magnetic fine particles has strong shape anisotropy, so it depends on particle size, acicularity, etc., but appropriate coercive force and residual magnetic flux density are required for tape recording, for example.

Magnetic recording media, whether used for audio or video, are required to have high output and low noise over a wide recording frequency band.
In order to respond to the demand for coughs, the shape of magnetic powders is becoming increasingly finer, and it is desired to further improve the affinity and dispersibility with paint resins, as well as the orientation and filling properties of paint films. , improvement of binder resins and various additives, and coating dispersion/
Research to improve media processing technology has been carried out (for example, Akashi Sanbe ``Advances in magnetic tape'', Journal of the Japan Society of Applied Magnetics, 7 (3).
), 185 (1983), ).

However, in general, when particles become finer, their surface energy increases, and therefore, secondary agglomeration becomes stronger. In other words, in the case of magnetic powder, the finer the primary particles of the material are made to meet the demands for higher output and lower noise, the more their surface energy increases, and conversely the agglomeration and sintering between particles increases. This results in a trade-off problem in that the particles become more intense and it becomes difficult to easily disperse the paint.

Fine metal particles as a magnetic material tend to aggregate because of their larger saturation magnetization (σS) compared to γ-iron oxide, etc., and when produced by vapor phase catalytic reduction of surface-modified iron oxyhydroxide,
Sintering between particles may occur, making dispersion operations difficult. Therefore, it is possible to reduce the secondary agglomeration of magnetic metal fine particles or to control the secondary agglomeration strength of magnetic metal fine particles.
In other words, techniques to reduce surface contact (aggregates) of primary particles and limit line contact (aggrega tes) have become important (for example, see Hiroto Ando's ``Pigment Dispersion'' Printing Ink Advanced Course - Printing Inks and Coverings). Collection of printed assignment summaries).

Therefore, it has been proposed to treat iron oxyhydroxide or iron oxide with various organic substances such as resins and fatty acids in the raw material process, and to perform calcination and reduction (Japanese Patent Publication No. 56-17291, Japanese Patent Publication No. 59-51725). No., JP-A-60-74405).

In addition, chemical treatments such as surface treatment of magnetic powder with a camping agent, adsorption on the surface active side, polymerization resin treatment of organic monomers, microencapsulation treatment, so-called surface modification, and mechanical dispersion treatment using a homomixer, disper, etc. (For example, Masumi Koishi and Mitsuo Tsunoda, "Surface Chemistry of Powder," Nikkan Kogyo Shimbun).

In the former method, the material is burned during the calcination and reduction process,
This is advantageous because it hardly remains as it is in the magnetic powder due to thermal decomposition or carbonization, and it has the effect of reducing contact between particles and avoiding sintering, but there are some concerns about surface-treated iron powder. The turbid cake tends to take on an agglomerated structure due to the organic matter being treated, making it difficult to disperse and often resulting in a significant drop in paint properties. extremely difficult.

In the latter method, metal magnetic fine particles produced by reduction of surface-modified iron oxyhydroxide are essentially porous particles, so compared to iron oxide-based magnetic powders such as γ-Fe, O, etc. , has strong mechanical strength, and since it is a metal powder, there is a high risk of ignition. Therefore, various surface modifications! The operation, especially the atomization treatment for converting the agglomerates into primary particles, must be performed with extreme caution.

<Problems to be solved by the invention> Acicular metal magnetic fine particles used as magnetic materials for high-density magnetic recording media mainly intended for audio and video have high agglomeration and sintering properties, and are basically 7- Paint dispersion is difficult compared to FezOy or cobalt-containing γ-Fez03. Furthermore, in order to achieve higher output and lower noise, particles tend to become smaller and finer, but in order to sufficiently disperse them, it is necessary to extend the paint dispersion time and use powerful mechanical dispersion, and as a result, the metal magnetic The acicular shape of the fine particles may not be maintained, or undispersed aggregates may remain, resulting in poor magnetic properties and poor media surface smoothness when the paint is processed into a medium. As a result, although the particles of the magnetic material themselves were made sufficiently fine, when a tape or the like was actually formed, it was not possible to obtain the intended high-output, low-noise electromagnetic conversion characteristics.

In addition, the surface has been modified so that paint can be easily dispersed! The remaining magnetic metal powder is susceptible to particle disintegration due to the combined atomization treatment, that is, the mechanical loosening of aggregated particles. It is very difficult to achieve the original purpose of atomization treatment, as it tends to cause a decrease in the magnetic properties of magnetic powder, especially the coercive force, and a decrease in the squareness ratio (Br/8m) when processing media. Met.

As a result of intensive studies to solve the above problems, the present invention has been developed to facilitate the production of ultrafine magnetic metal particles by intentionally producing raw material powder with extremely weak secondary aggregation in an intermediate process. The inventors discovered that it is possible to produce magnetic metal fine particles that can be used to prepare highly dispersed magnetic paints, and completed the present invention.

Means for Solving Problems> As described above, the gist of the present invention is to synthesize fine acicular iron oxyhydroxide fine particles by a well-known wet method, and then to modify the adhesion using a shape-retaining component. By applying a method of processing, washing as necessary, coagulating the suspension, and then drying and pulverizing it, subsequent gas phase contact with a reducing gas mainly composed of hydrogen gas can be achieved. The fine particles subjected to the reduction reaction can exhibit an acicular shape well inherited from that of the coarse raw material iron oxyhydroxide fine particles without being damaged or destroyed, and the secondary shape of the fine particles thus obtained can be Cohesion is extremely weak and easily loosens in solvents.
It has the characteristics that there is little interparticle sintering and it can be easily dispersed in paint.

That is, the present invention provides a method for producing ferromagnetic iron fine particles by subjecting iron oxyhydroxide or iron oxide, or surface-modified iron oxyhydroxide or iron oxide, to a vapor phase catalytic reduction reaction with a reducing gas. , an acicular ferromagnetic metallic iron fine particle zodiac characterized by drying the iron oxyhydroxide or iron oxide, or the surface-modified iron oxyhydroxide or iron oxide in an agglomerated state in a liquid. This is a production method, in particular, in which iron oxyhydroxide or iron oxide, or surface-modified iron oxyhydroxide or iron oxide, is suspended in a liquid, and the hydrogen ion concentration of the suspension is adjusted by adjusting the hydrogen ion concentration of the suspension. This is a method for producing acicular ferromagnetic metallic iron fine particles, which are controlled in an agglomeration region, agglomerated, dried, and further made into ferromagnetic iron fine particles by a gas phase catalytic reduction reaction using a reducing gas.

Note that the most preferred embodiment of the present invention is as follows:
α-Iron oxyhydroxide or P5Al-, Ti, Cr, Mn, with a specific surface area of 20 to 150 m''/gr.
B is added to α-iron oxyhydroxide co-precipitated with at least one element selected from Co, Nt, Zn, etc. to avoid Sakai formation, maintain shape, control coercive force, and improve corrosion resistance.
, Kg, AI, 5iSPs Tis ZnSCrS
Mn5 Co, Ni, Cu, Zr, Sn, Pb,
At least one element selected from elements such as Ca5Ba is deposited on the surface, washed with water, suspended in the liquid, and the hydrogen ion concentration (pi) is controlled with various mineral acids, organic acids, or alkalis, and the mixture is aggregated. After drying and pulverizing the agglomerated state while maintaining its agglomerated state, and calcining at 300 to 800°C as necessary to obtain surface-modified α-iron oxide, it is heated to 300 to 800°C using a reducing gas mainly containing hydrogen gas. Metal magnetic fine particles mainly composed of iron are produced by subjecting the particles to a gas phase catalytic reduction reaction at 500°C.

The iron oxyhydroxide or iron oxide used in the present invention has a major axis diameter of 0.1 to 1.0μ and a minor axis diameter of 0.01 to 0.1.
It can be considered to be a so-called colloidal particle having an axial ratio (L/El) of 4 to 30.

The main feature of the present invention is that iron oxyhydroxide or iron oxide, or surface-modified iron oxyhydroxide or iron oxide is dried in a liquid in an "agglomerated state". Here, in the present invention, "in an aggregated state" means
A state in which a suspension of iron oxyhydroxide or iron oxide, or a surface-modified iron oxyhydroxide or iron oxide, easily separates into two phases, with an aqueous phase at the top and an iron gel phase at the bottom. In contrast, "in a non-agglomerated state" means that the suspension is in a "dispersed state". Alternatively, it means that the iron oxide suspension does not easily separate into two phases and remains in a phase state for a long time, that is, it appears to be in an upper half milky state. That is, according to the findings of the present inventors, the suspension has two distinct appearances: the "agglomerated region" in the agglomerated state and the "dispersed region" in the dispersed state. It is the one that can take on the state of the realm.

These two regions can be displayed using, for example, viscosity, rj:, and falling height. In other words, the agglomerated region has a higher viscosity and a lower sedimentation height than the dispersed region. Therefore, it cannot be unambiguously determined because it varies depending on the manufacturing method of iron oxyhydroxide, the amount of coprecipitation, the amount of coprecipitation, the method of surface modification, the amount of surface-modified species, and the amount of surface-modified species. The above-mentioned viscosity and sedimentation height were measured by changing the hydrogen ion concentration (pH) of
By plotting the latter on the vertical axis and the former on the horizontal axis, these two areas can be determined on the graph as shown in Examples below. For example, in Figure 1, the range of approximately pH 3 to pH 7 is the aggregation region, and the range of pH 8 to pH 7 is the aggregation region.
It can be seen that the range of 12 is the dispersion area. Alternatively, particle aggregation and dispersion can also be determined by measuring the ζ potential of a dilute suspension and measuring the pH near the isoelectric point.

For example, in the case of α-iron oxyhydroxide suspension, the pH is usually 7.
The vicinity is defined as a boundary region, below which it is dispersed, and above it is agglomerated; however, in the case of surface-modified α-iron oxyhydroxide, the aggregation region may be reversed, and cannot be determined exactly, so it is preferable to determine it experimentally.

Rather than further suspending and flocculating the surface-modified iron oxyhydroxide after washing with water, if the pH of this flocculation region is determined experimentally in advance, the pH of the flocculation region can be lowered by acid or alkali.
It is also possible to control the agglomeration state by washing with water adjusted to H, and it is more preferable to use a volatile acid such as nitric acid or a volatile alkali such as ammonia. It is possible to obtain a raw material powder with less bunch-like lumps and less contact between particles.

The pulverized powder is calcined at 300 to 800°C as necessary to form surface-modified α-Fe, O, and then charged into a reduction furnace.
300 to 50 by reducing gas mainly composed of hydrogen gas
A weakly agglomerated metal magnetic powder can be obtained by carrying out a gas phase catalytic reduction reaction at 0°C.

The metal magnetic fine particles obtained in this way are composed of extremely fine particles, have very high activity, are easily oxidized, and spontaneously ignite in the atmosphere and return to iron oxide, which is a well-known phenomenon in itself. It is desirable to form an oxide film on the surface and stabilize it by the method described above.

In the agglomeration region, the fine particles are thought to form a secondary agglomerate in the liquid, but the strength of the secondary agglomerate obtained by drying the metal magnetic fine particles is Probably because it is relatively weak and easily loosens, good fluidity can be obtained when soaked in an organic solvent, and it can also be quickly and evenly mixed with various additives added to improve affinity and dispersibility with the binder resin. As a result, the magnetic coating material can be easily made into a magnetic coating material, and as a result, the surface smoothness of the coating medium is particularly improved.

The most important feature of the present invention is that, contrary to conventional thinking, fine particles in an aggregated state are dried.

Those skilled in the art would probably think that drying fine particles in a dispersed state would yield dry fine particles in a more dispersed state, but surprisingly, drying fine particles in a dispersed state If this happens, on the other hand, extremely strongly bonded secondary aggregates will be newly formed during the drying process. On the other hand, if the material is dried to some degree in agglomerated state from the beginning, secondary agglomerates in a weakly bonded state are likely to be produced, so that the object of the present application can be suitably achieved.

[For production]

A feature of the ferromagnetic metal fine particles obtained by the method of the present invention is that the secondary agglomerate strength of the magnetic fine particles is much weaker than that of conventional ones. It is thought that the secondary agglomerates are easily loosened in an organic solvent, and therefore, the fluidity of the organic solvent slurry of the ferromagnetic metal fine particles is very good, and the coating dispersibility is extremely fast.

In particular, when pre-calcination or gas phase catalytic reduction reaction is performed by controlling the agglomeration of dry powder of iron oxyhydroxide, which is the raw material and whose surface has been modified, interparticle sintering is small (the produced magnetic The fluidity and paint dispersibility of the organic solvent slurry of metal fine particles are also improved, which is extremely preferable.

In addition, in recent years there has been a trend to make magnetic fine particles even finer, especially in 8m/m video applications, etc., which require the use of acicular metal fine particles with a major axis diameter of 0.3μ or less. The method for producing ferromagnetic metal fine particles of the present invention can be an extremely useful means.

As a result, when media processing is performed, it becomes possible to use finer particles as the material powder, and it becomes possible to create a system with almost no change in magnetic properties. As a direct result of this, the surface smoothness of the media increases,
Furthermore, the magnetic recording characteristics, that is, the tUt conversion characteristics (=sensitivity/output) in the high frequency range, and the noise are significantly improved [Example] Hereinafter, the method of the present invention will be explained with reference to Examples and Comparative Examples. and effects in detail.

Examples 1 to 2 The present examples are examples showing a summary of the method of the present invention and its effects regarding ferromagnetic metal fine particles containing metal iron as a main component for so-called audio metal positions.

<Manufacture of raw material powder> By the method described in JP-A-57-106527 and JP-A-57-96504, P, Ni and Si components were mixed in a weight ratio of P/Fe.0.3/100, Ni/Fe=1.
5/100, and acicular iron oxyhydroxide fine particles containing Si/Fe=1.5/100 were synthesized and washed with water.

The shape of the fine particles has a specific surface mc:sA) of 39.2 m''/gr calculated from the adsorption characteristics of nitrogen gas, and a major axis diameter (=shi) calculated from a transmission electron microscope image of 60,000 to 90,000 times. and the short axis diameter (:D), that is, the axial ratio (:L/D) is 1
It was 5.

<Dispersion/coagulation of iron oxyhydroxide> The above-mentioned washing paste was diluted with water and stirred, and the hydrogen ion concentration (pH) of the iron oxyhydroxide slurry (5wtX) was adjusted with nitric acid and aqueous ammonia. The viscosity of each slurry is B
The results measured using a viscometer are shown in Figure 1.The washing paste was diluted and stirred with water, and its pH was diluted with nitric acid/ammonia water.
Iron oxyhydroxide slurry with controlled H (0.2wtZ)
and measured the sedimentation height after 24 hours.
As shown in the figure. From this result, it was found that the slurry coagulated and opened at around pH 3 to 7. Therefore, while kneading IKg of the paste (containing iron oxyhydroxide, !20 et $) in a rice cooker, it was mixed with nitric acid to pH 4 and 5, respectively. (Example 1) and pH 5.5 (Example 2), kneaded for an additional 2 hours, dried in a box-type hot air dryer at 120°C for 18 hours, and crushed in a Nara type free crusher. It was powdered.

<Manufacture of reduced iron powder> The pulverized powder thus obtained was charged into a fixed bed reduction furnace, and subjected to a gas phase catalytic reduction reaction (:is, a7s) using hydrogen gas.
°C, gas space velocity = 20 Nl! 13-H2/nig −
It was made into reduced iron powder using Fe, )Ir).

Next, after thoroughly soaking the fine particles in toluene, the fine particle slurry was transferred onto an enamel vat to a thickness of about 1c11, and subjected to toluene scattering treatment in the atmosphere.

When the smell of the solvent disappeared, the magnetic powder was collected and made into air-dried metal iron powder.

When the shape of the air-dried metallic iron powder is observed with an electron microscope at a magnification of 30,000 to 90,000 times, it appears that it closely follows the shape of the primary raw material, iron oxyhydroxide, and shows signs of fracture order, fracture, and interparticle sintering. was hardly seen.

The magnetic properties of the air-dried metallic iron powder were measured using a sample vibrating magnetometer VSM-111 manufactured by Toei Kogyo Co., Ltd., and the specific surface area was calculated from the nitrogen gas adsorption properties and is shown in the table.

<Evaluation of the dispersion type of air-dried metal iron powder> 60g of the air-dried metal iron powder was collected and used together with the following materials in a 4-tube sand grinder MODEL manufactured by Igarashi Kikai Manufacturing ■.
Pour 4TSG-1/4 into a pot with an internal volume of 800 ml and disperse at a rotation speed of 1500 rpm.
, 60.120m1n, 30g of paint was extracted from fi.

Glass beads with a diameter of 1.5 mm were used as the dispersion media.

・UCC made salt-vinyl acetate poly? -VAG)I:6. Og
r. Polyurethane NL-2448 manufactured by Mitsui Toatsu Chemical Co., Ltd.: 6. Ogr-1 container Toluene: 85gr, MEK: 85gr
.

Next, the dispersion media was separated to obtain a magnetic paint, which was coated onto a 13μ thick polyester film (Nilmirror 13W-QO6S) manufactured by Toshi Co., Ltd. using an applicator in a precision coater equipped with magnetic tape. After drying, the gloss of the coating film was measured using a digital variable angle gloss meter UGV-50 (large incident angle 60°) manufactured by Suga Test Instruments Co., Ltd. without calendering and rolling treatment.The results are shown in the table. From this, it was found that the dispersion speed was faster and the attainment of dispersion was also higher than in Comparative Example-1 described below.

<Conversion of air-dried metallic iron powder into paint, coating, and evaluation of sheets> 10g of the air-dried metallic iron powder was collected and placed in a pot with an internal volume of 550 ml along with the following materials.
Mixing and dispersion continued for 6 hours using a DeVille paint shaker. Alumina beads of 2.0Llalφ were used as the dispersion media.

- Salt vinyl acetate poly v manufactured by UCC - VAGH: 0.8gr
・Mitsui Toatsu (Polyurethane NL-2448 manufactured by W Gakusha: 0.8 gr ・Phosphate ester AP-13 manufactured by Daihe Kagakusha: 0.5 gr
.

・Sumitomo Chemical α, alumina AKP-300,0,56
r.

・Solvent Toluene: 15gr, MEK: 15gr.

Next, the dispersion media was separated to obtain a magnetic paint, which was coated onto a 13 μm thick polyester film manufactured by Toray (Lumirror 13W-QO6S) using an applicator in a precision coater equipped with magnetic tape.

Thereafter, the coated film surface was smoothed by calendering to form a magnetic sheet.

The magnetic properties and glossiness of the magnetic sheet were measured using the above-mentioned measuring device, and the surface roughness of the sheet was determined by the center line average roughness 2R.
a) ■ Universal surface shape measuring device MODEL manufactured by Koita Institute
From the results shown in the table below, it was found that the surface smoothness of the magnetic sheet was improved compared to Comparative Example-1.

Comparative Example-1 While co-firing the water-washed paste in a Raikai machine, ammonia water was used to adjust the pH to the dispersion region, which is outside the agglomeration region.
The production of raw material powder, the production of reduced iron powder, and the evaluation of dispersion of air-dried metal iron powder were performed in the same manner as in Example-1, except that the powder was adjusted to 9.0, and the results are shown in the table. When iron powder was observed under an electron microscope, bundles or agglomerates, which appeared to be sintering between particles, were observed. It was also found that the surface smoothness of the magnetic sheet was inferior to Examples 1 and 2.

Examples 3 to 4 The present examples are examples showing an overview of the method of the present invention and its effects regarding ferromagnetic metallic iron fine particles containing metallic iron as a main component for so-called 8 mm video.

<Manufacture of raw material powder> By the same method as in Example-1, the co and Mn components were adjusted to a weight ratio of Co/Fe-2,0/100, Mn/Fe=
Acicular iron oxyhydroxide fine particles containing only 2.0/100 were synthesized and washed with water.

The specific surface area (SA) of the fine particles is 86.7 m"/gr,
Also, the axial ratio calculated from the transmitted electron U4'R1 and the mirror image (:L/
D) was 18.

The washed paste was diluted with water and stirred, and after adjusting the pH to 10.0 with an aqueous NaOH solution, sodium hexametaphosphate,
Using No. 3 water glass, sodium aluminate, and 1-7 Kel of nitric acid, the weight ratio was P/Fe=0.8/100, St/
Fe-2,0/ioo, AI/Fe-2,0/100
And Ni/Fe=6.0/100 was deposited on the surface, filtered, and washed with water.

Dispersion and aggregation of iron oxyhydroxide> Figure 2 shows the results of measuring dispersion and aggregation using the same method as in Example-1.
It was found that the vicinity was a cohesive area, so paste 1
While kneading each g in a rice cooker, add nitric acid to pH 5 (
Example 3) and pH 7 (Example 4) were controlled (containing iron oxyhydroxide: 1120 wt), mixed for another 2 hours, and then dried in a box-type hot air dryer at 120'C for 118 hours. It was crushed using a crusher to obtain raw material powder.

In the production of reduced iron powder, raw material powder is calcined at 700℃,
The process was carried out in the same manner as in Example 1, except that reduction was carried out at a temperature of 425°C with fluidization using a stirring type (lrpm) reduction furnace, and the results are shown in the table. The organic solvent slurry had a black appearance and had good fluidity. When the shape of the air-dried metallic iron powder is observed with an electron microscope at a magnification of 30,000 to 90,000 times, it appears that the shape closely follows that of the primary raw material, iron oxyhydroxide, and there is no damage, destruction, or interparticle sintering. It was hardly seen. From the table,
The dispersion speed and reach are high, and the magnetic properties of the magnetic sheet (Br/8m) are sufficiently high, and the surface smoothness (gloss, center line average roughness) is also improved compared to the comparative example described below. I found out what to do.

Comparative Example-2 Water washing paste manufactured by the same method as Example-3 (30.2X as iron oxyhydroxide, pH 9.0)
Example except that it was directly dried and pulverized to make the raw material powder.
The results are shown in the table.

The appearance of the air-dried metallic iron powder is granulated and has a silvery gray color. !
Even when immersed in a solvent, the fluidity was poor. In addition, the magnetic properties and surface area of air-dried metallic iron powder are almost the same as in Examples 3 and 4.
However, it was found that the dispersion layering, reachability, magnetic properties and surface smoothness of the sheet were inferior. While kneading in a Laikai machine, control the pH to 10, which is the dispersion range, with aqueous ammonia (content of iron oxyhydroxide: 20-Lχ), kneading for another 2 hours, and then kneading at 120°C in a box-type hot air dryer. The process was carried out in the same manner as in Example 3, except that it was dried for 18 hours and then ground using a Nara-type free grinder to obtain a raw material powder.The results are shown in the table below. Bundles or agglomerates, which were thought to be caused by sintering between particles, were observed. It was also found that the surface smoothness of the magnetic sheet was inferior to Examples 3 and 4.

Examples 5 to 6 P/
Fe-0,05/100 and AI/Re-1,2/10
Acicular iron oxyhydroxide fine particles containing only 0 were synthesized and washed with water. The surface area (SA) of the fine particles is 82.6 m”/g
r, and the axial ratio calculated from the electron microscope image (: L/D
) was 12.

Furthermore, Si/Fe=0.
8/100, AI/Fe=2.5/100 and Ni
/Fe=0.6/100 surface deposition was performed.

The suspension was separated, filtered, and the paste obtained by washing with water was used in Example-
Dispersion and aggregation were measured using the same method as in 1. The results are shown in Figure 3. From this result, it was found that the agglomeration region was around pH 7.0 to 10.0, so the suspension was dispersed and the pH
Washing was performed with water adjusted to p) 8.0 (Example 5) and p) 19.0 (Example 6).

In the production of reduced iron powder, calcination is performed using nitrogen gas in a reducing furnace (temperature: 450°C, gas space velocity: 1ONm'-H
z/Kgr-Fe, Hr,) L, except that a gas phase catalytic reduction reaction using hydrogen gas (: 4 degrees, 420°C, gas hourly space velocity, 2ONm'-H1/Kgr-Fe, Hr,) was subsequently performed. was carried out in the same manner as in Example 1, and the results are shown in the table. When the shape of the air-dried metal powder was observed with an electron microscope at a magnification of 30,000 to 90,000 times, it appeared that the primary raw material, iron oxyhydroxide, The shape was good (inherited), and there was almost no damage, destruction, or interparticle sintering.

From the table, the speed and reach of dispersion are high, the magnetic properties of the magnetic sheet (Br/8m) are also sufficiently high, and the surface smoothness (gloss, center line average roughness) is also as good as the comparative example described below. Example 7 in which it was found that the results were improved compared to Example 7 In the same manner as in Example 3, iron oxyhydroxide was synthesized, adhered to the surface, filtered, and washed with pure water.

The water washing paste (25.3X as iron oxyhydroxide, p
H7,9) was dried and pulverized, and then the calcined, reduced, and air-dried iron powder was evaluated for its dispersibility in the same manner as in Example-5.The results are shown in the table, and the shape of the air-dried metal iron powder was 30,000 to 9
Ten thousand times more electronic i! When observed with an IM mirror, the shape of the primary raw material iron oxyhydroxide was observed to be good (inherited), and there was almost no damage, destruction, or interparticle sintering. The magnetic properties of the magnetic sheet (B
r/8m) is sufficiently high, and the surface smoothness (gloss,
It was also found that the center line average roughness) was also improved compared to the comparative example described below.

Examples 8 to 9 Slurry produced in the same manner as in Example 5 was filtered and washed with pure water to form a surface-adhering washing paste, and the agglomeration rate was increased while mixing and kneading in the same manner as in Example 1. The same method as in Example 5 was carried out except that the pH was adjusted to pH 8.0 (Example 8) and pH 9.0 (Example 9), which is the page area, and dried and pulverized. The results are shown in the table. When the shape of air-dried metallic iron powder is observed with an electron microscope at a magnification of 30,000 to 90,000 times, it appears that it closely follows the shape of the primary raw material, iron oxyhydroxide, and there is almost no damage, destruction, or interparticle sintering. I couldn't see it. It was also found that the dispersion rate and reach of the air-dried metallic iron powder were high, and the magnetic properties of the magnetic sheet were sufficiently high (and the surface smoothness was also improved compared to the comparative example described below).

Comparative Examples 4 to 5 A surface-adhering water washing paste produced in the same manner as in Example 8 was mixed and kneaded in the same manner as in Example 1, and its dispersion slope was adjusted to pH 4.0 (Comparative Example 4). ) and 6.0 (Comparative Example 5), and the same method as in Example 8 was carried out except that drying and pulverization were performed, and the results are shown in the table.

When air-dried metallic iron powder was observed under an electron microscope, bundles or agglomerates, which appeared to be sintering between particles, were observed. In addition, the magnetic properties of the air-dried metallic iron powder are almost the same as those of the air-dried metallic iron powder of Examples-5 to 9, but the magnetic properties and surface smoothness of the magnetic sheet are inferior to those of Examples-5 to 9. Understood.

[Results]

The effects and effects of the present invention can be summarized as follows from the results of Examples and Comparative Examples.

That is, in acicular ferromagnetic metallic iron-coated particles as a magnetic recording material suitable for high-density magnetic recording, reducing properties can be improved by agglomerating and post-drying acicular iron oxyhydroxide fine particles that have been modified by adhesion. By producing ferromagnetic reduced iron fine particles through a gas phase catalytic reduction reaction with gas, (11) the metallic iron fine particles themselves exhibit an acicular shape well inheriting the shape of iron oxyhydroxide, which is the raw material; The strength of the secondary agglomerates became extremely weak, and the fluidity of the organic solvent slurry of the metallic iron fine particles was greatly improved. It has been found that sexual performance improves.

In addition to the above, the present invention provides a method for producing fine ferromagnetic metal particles that significantly improves quality without changing most of the conventional M manufacturing process and equipment.

Patent applicant Mitsui Toatsu Chemical Co., Ltd. Figure 1 Hydrogen ion concentration τ/PH) Hydrogen ion olfactory CPHI Procedural amendment (method) (% formula % 1, case indication 1985 Patent Application No. 149450 2
, Title of the invention: Method for manufacturing acicular iron fine particles for magnetic recording 3, Relationship with the person making the amendment Patent applicant address: 3-2-5-4 Kasumigaseki, Chiyoda-ku, Tokyo Date of amendment order: August 1988 On the 26th (shipment), page 30 of the statement is corrected as shown in the attached sheet (no changes are made to the contents except for the matters stated in the column subject to amendment).

:Attachment) The present invention provides a method for producing magnetic metal fine particles.

[Brief explanation of the drawing]

FIGS. 1 to 3 are graphs showing the relationship between the hydrogen ion concentration of a suspension of iron oxyhydroxide, the viscosity of the suspension, and the sedimentation height.

Claims (2)

[Claims] (1) In a method for producing ferromagnetic iron fine particles by subjecting iron oxyhydroxide or iron oxide, or surface-modified iron oxyhydroxide or iron oxide, to a vapor phase catalytic reduction reaction with a reducing gas, A method for producing acicular ferromagnetic metallic iron fine particles characterized by drying iron hydroxide or iron oxide, or surface-modified iron oxyhydroxide or iron oxide in a coagulated state in a liquid. . (2) Iron oxyhydroxide or iron oxide, or surface-modified iron oxyhydroxide or iron oxide, is suspended in a liquid, and the hydrogen ion concentration of the suspension is adjusted to a concentration area of the suspension. The suspension is agglomerated under controlled conditions, and then dried.
The method according to claim 1, wherein ferromagnetic iron particles are further produced by a gas phase catalytic reduction reaction using a reducing gas.