JPS6258604A - Manufacture of magnetic iron powder for magnetic recording - Google Patents

Abstract

PURPOSE:To obtain excellent needle-like ferromagnetic fine powder containing iron carbide by a method wherein a vapor phase contact carbonizing reaction is performed under the state in which the mixed gas of carbon monoxide and reducing gas is flowing at the linear speed of 2cm/sec. or more. CONSTITUTION:The needle-like iron oxyhydroxide fine particles deposited and modified on a configulation retaining part are formed into ferromagnetic reducing iron powder by performing a vapor phase reducing reaction using the reducing gas having hydrogen as the main component. Then, said iron powder is formed into ferromagnetic cementite by the vapor phase contact carbonic reaction using the mixed gas of carbon monoxide and reducing gas. The above- mentioned vapor phase contact carbonic reaction is performed under the state wherein the flow speed of the mixed gas of carbon monoxide and reducing gas is maintained at the linear speed of 2cm/sec. or more using an agitative fludized floor or the reactor of a fluidized substance system. As a result, excellent cementite containing needle-like ferromagnetic fine particles can be obtained.

Description

[Detailed description of the invention] The present invention relates to a magnetic material and a method for manufacturing the same.

The wood can be suitably used as a magnetic material in magnetic recording media suitable for high-density recording mainly for audio and video.

Magnetic powders useful for magnetic tapes and magnetic recording media were once mainly composed of r-iron oxide. In recent years, there has been a demand for high-density recording media for TR and high-end audio, and metallic iron or cobalt, which is obtained by gas-phase catalytic reduction reaction of iron oxyhydroxide or iron oxide-based powder with reducing gas, has become desirable. Alternatively, magnetic powders having a high coercive force and mainly composed of an alloy of nickel and iron have come to be used. The coercive force of metal magnetic fine particles has strong shape anisotropy, so it depends on the particle size, acicularity, etc., but for tape recording, it is necessary to have an appropriate coercive force in balance with the capabilities of the playback head and erase head. It is. Magnetic recording media, whether used for audio or video, are required to have high output and low noise over a wide recording frequency band. That is, the shape of magnetic powder tends to become finer. In addition, it is desired to further improve the affinity and dispersibility with paint resins, as well as the orientation and filling properties of coating films, and research is needed to improve binder resins and various additives, as well as paint dispersion and media processing technology. [For example, Akashi Okabe [Advances in Magnetic Tape J, Japanese Journal of Applied Magnetics, 7 (3), 185 (1983)]].

Therefore, increasing the (-1 cm) value and making the magnetic powder as fine as possible within the allowable range are extremely rate-limiting elemental technologies for realizing high-density recording.

In the case of acicular metal powder particles containing iron as the main component, although there is room for large variations depending on the manufacturing method,
Overall, the long axis diameter (L) and short axis diameter (D > or the value of the axial ratio (L/D)) -1c- value are almost fixed, for example, L/D: around 10. In the above acicular fine particle system, L: around 1 μ) -1c- value: 500 to 70
About 00e, L20° around 5μ Te Hc-value: 1000
About 12000e or L: 140 at around 0.1μ
A value of about 0 to 160,000 is usually put into practical use.

Conventionally, the techniques for reducing the particle size while maintaining the shape of magnetic powder and having an appropriate holding force were: (1) designing an extremely low axial ratio; (2) using a large amount of N.
A method for producing alloyed fine particles based on the introduction of an i-component, and (3) a method for producing semimetallic alloyed particles based on the introduction of Si, B, P, C, UN, etc. are known.

In (1), by reducing the shape anisotropy,
The principle is to suppress the ferromagnetism expression mechanism, and also <2)
This is a method that actively utilizes the fact that the magnetic anisotropy decreases due to magnetic dilution caused by lattice substitution of the body-centered cubic (BCC) formed by the Ni and Fe components. However, when processed into a tape medium, sufficient orientation cannot be achieved, and the residual magnetic flux density (Sr) and maximum magnetic flux density (B
There is a drawback that the ratio (Br/Bm-value), that is, the squareness ratio, is greatly reduced.

In (3), the starting material is various iron oxyhydroxides, and even if a compound containing B, Si, and P is surface-modified, the gas-phase catalytic reaction mainly using hydrogen gas will stop the reaction until the oxide is reached. Therefore, their introduction is impossible. A gas phase catalytic reaction using expensive borane gas, silane gas, and phosphine gas will be performed.

Only the remaining N and C are inexpensive and can be introduced into iron by gas phase catalytic reaction, but since ammonia is used as a nitriding agent to introduce N, special manufacturing equipment is required. It was necessary to take measures against corrosion, which was impractical when considering industrial production.

To independently control the particle niceness and magnetic properties, especially the coercive force 1-(c-value), of acicular magnetic powder as a magnetic material for high-density magnetic recording media mainly used for audio and video. The 81 technology is one of the ultimate elemental technologies related to magnetic powder.It can be positioned as one of the most desired industrial technologies for increasing density.

The inventors of the present invention have already proposed a method for removing iron carbide fine particles by subjecting reduced iron to a gas phase catalytic reaction with a carbonizing gas. However, in this technique, it was necessary to complete the reduction of iron oxyhydroxide as much as possible in a step prior to the carbonization reaction.

If the reduction is not completed, iron oxide and carbon are generated as a side reaction during the carbonization reaction due to unreduced iron oxyhydroxide in the carbonization process, and it is not possible to efficiently lower the coercive force while maintaining a high σS. was there.

Furthermore, if the reduction temperature is increased or the reduction time is prolonged due to fear of incomplete reduction, sintering between metal fine particles will occur, causing a decrease in tape properties (Sr /Bm >), which is extremely undesirable.

In order to solve the above-mentioned problems, the present inventors conducted various studies and while continuing to research improvements in the characteristics, they decided to use a reducing gas in addition to the carbonizing gas in the carbonization process. It was discovered that by entraining iron carbide, it was possible to produce iron carbide suitable as a magnetic material with a small amount of iron oxide and carbon produced, and the technology was proposed in Japanese Patent Application No. 60-36533.This method allows the carbonization reaction to be carried out efficiently. As a result, the coercive force (HC) can be lowered by about 8000 e)2 depending on the degree of carbonization, and the saturation magnetization (σS) can also be kept high. In other words, even if finer particles are controlled to be reduced to an appropriate HC level, the output of the electromagnetic conversion characteristics of the media tape can be minimized, while noise can be dramatically reduced. This is what we found.

That is, the gist of the invention is that, as a first step, acicular metal powder particles containing iron as a main component for magnetic recording are produced, and then, as a second step, the metal powder particles are carbonized and reduced. It consists of establishing a

In this case, the first step of producing acicular metal powder particles containing iron as a main component for magnetic recording is basically obtained by a well-known method. For example, specific surface area 20-150
m2/c+r, α-iron oxyhydroxide, if <Al
, Ti, Cr, Mn, Co, Ni, Zn, etc. are co-precipitated into α-iron oxyhydroxide, which has properties such as sintering avoidance, shape retention, coercive force control, and corrosion resistance. For improvement etc., B, Al, Si, P, Ti, Zn,
Cr, Mn, Co, Ni, Cu, Zr, Sn
The dried surface-modified α-iron oxyhydroxide is coated with at least one element selected from elements such as , Pb, Ca, and 3a, and the dried surface-modified α-iron oxyhydroxide is pulverized and, if necessary, calcined at 300 to 800°C to surface-modify the surface. After forming α-iron oxide, it is subjected to a gas phase catalytic reduction reaction at a temperature of about 300 to 500°C using a reducing gas mainly composed of hydrogen gas to form a body-centered cubic system (bcc) crystallographically. It is possible to produce α-Fe powder.

The completion of the reduction reaction is usually determined by setting the hydrogen flow temperature and time, or by analyzing the water concentration of the exhaust gas from the reactor system, for example, by measuring the dew point.

After stopping the reduction, a portion of the material was taken out in a nitrogen gas atmosphere and the magnetic properties were measured. The saturation magnetization (σS) was 150 to 200 e.
mu / (lr), and the saturation magnetization of pure iron (σ
S) 217. Oemu/gr indicates a lower value.

Next, in the second step, a mixed gas of carbon monoxide gas and hydrogen gas is introduced in the carbonization reaction process, or a mixed gas of carbon monoxide gas, hydrogen gas, and an inert gas is introduced, and the carbonization and By allowing the reduction reaction to proceed simultaneously, it becomes possible to suppress the production of iron oxide and carbon, and iron carbide-containing ferromagnetic fine particles can be obtained. - The mixing ratio of carbon oxide and hydrogen gas (CO:H) is limited to 1:30000, and a larger amount of CO may be added. Although it is possible to use helium gas, argon gas, and carbon dioxide gas as the inert gas to be entrained with the mixed gas, nitrogen gas, which is relatively inexpensive and fiffi, is most preferable. The volume ratio of the mixed gas (CO:N ratio of 1:] to 1:500 is appropriate, and the purpose is mainly to control the reaction rate of the carbonization reaction. If the reaction rate of the carbonization reaction is too fast, M separation will occur. of carbon is produced, and if it is too slow, it is not economical, so this composition range is appropriate.

As explained above, this invention can be positioned as a promising industrial technology that can independently control the particle size and magnetic properties of acicular magnetic powder, especially the coercive force H+ value, and is suitable for mass production. However, in the second stage of the carbonization reaction of metal powder particles of the present invention, we found that the activity of CO is extremely large and the carbonization reaction of metal powder particles tends to be non-uniform.

In order to solve the above-mentioned problems, the present inventors investigated a method for uniformly proceeding the carbonization reaction of metal powder particles with CO on an industrial scale, and completed the present invention.

According to the present invention, acicular iron oxyhydroxide fine particles that have been deposited and modified with a shape-retaining component are made into ferromagnetic reduced iron powder by a gas phase catalytic reduction reaction using a reducing gas mainly composed of hydrogen, and then converted into ferromagnetic reduced iron powder with carbon monoxide. In a method for producing acicular ferromagnetic particles containing iron carbide, which involves producing ferromagnetic iron carbide through a vapor phase catalytic carbonization reaction using a mixed gas with a reducing gas, the vapor phase catalytic carbonization reaction is carried out using a stirred fluidized bed or a fluidized bed method. Using a reactor, the flow rate of the mixed gas of carbon monoxide and reducing gas was set at 20 m/
A method for producing iron carbide-containing acicular ferromagnetic particles is provided, which is characterized in that the production is carried out under conditions of a linear velocity of 580 or higher.

The present inventors conducted a study on scaling up the gas phase catalytic carbonization reaction of ferromagnetic reduced iron powder using a fixed bed reactor. In this case, under the conditions of 300 to 500°C in a H2 gas flow and a C-C0 deepness of 1000 ppm or less, almost all of the amount of CO contributes to the carbonization reaction, and the CO deepness in the reactor outlet gas is almost 0. It was recognized that the carbonization reaction was extremely active.

Furthermore, it was found that in a fixed bed reactor, as shown in Comparative Example 4, carbonization concentrates on the upstream side of the scum, making it extremely difficult to carry out a uniform reaction. On the other hand, if the carbonization reaction is carried out while fluidizing the ferromagnetic reduced iron powder using a 'e, vJ bed reactor,
It was found that the problem of non-uniformity of carbonization reaction in fixed bed reactor can be avoided.

In order to uniformly fluidize ferromagnetic reduced iron powder in a fluidized bed reactor, a gas linear velocity of 2 cm/sec or more is required. Further, it is more preferable to mechanically stir the ferromagnetic reduced iron powder at 2 to 12 Orpm using a stirring blade while flowing the gas at a linear gas velocity of 2 cm/sec or more.

Ferromagnetic)! There is no particular limit to the layer height of the original iron powder, and basically it is sufficient to provide a gas linear velocity that is higher than the flow start velocity of the ferromagnetic reduced iron powder, specifically a linear velocity of 2 cm/sec or higher. do it. There are no particular restrictions on the structure of the fluidized bed or stirred fluidized bed reactor, but a dispersion plate made of a sintered metal or ceramic plate with micropores of about 5 to 50 μm is installed to disperse gas and improve ferromagnetic properties. It is preferable to provide both functions of retaining reduced iron powder. In addition to the above, a dispersion plate having a large number of holes of about 1 to 5 111/m at an appropriate pitch may also be used. In this case, the hole pitch is 20
It is easy to operate around mm.

Hereinafter, the present invention will be specifically explained with reference to Examples and Comparative Examples.

Example 1 (1) Goethite synthesis Fe SOa 7H 2050 kfJ was melted in 10001 water, and the liquid temperature was 40°C (,: To adjust, this was dissolved in solution T.
). Also, NaOH'1.5! J water 5001
The solution temperature was adjusted to 35° C. (this will be referred to as solution ①).

A reactor with an internal volume of 3M3 equipped with a stirrer was charged with the solution (2), and then the solution (2) was added all at once, stirred and mixed for 5 minutes to complete the neutralization reaction, and then air was blown at a feed rate of 15M3/min to oxidize. As a result, yellowish brown goethite was obtained as precipitated particles.

When the Gusai 1~ was washed with water and filtered, and a part of the r-filtration cake was separated and analyzed, the Gusai 1~ had an axial ratio of 14 and a specific surface area of 85 m2/! ] (the Gary 1- is referred to as Gl).

(2) Slurry 1001, which was prepared by adjusting the weight ratio of goethite and water to 100, was charged into a container equipped with a stirrer. Next, ■ 52g of sodium metaphosphate to 1 portion of water! An aqueous solution in which 1.13 klJ of No. 03 water glass stock solution was dissolved in 51 water, ■N1 (NOs)2 ・6H + 01.57 k (l was dissolved in water 5
1 aqueous solution dissolved in 1, 1 normal NaOH aqueous solution, and 1 normal HNO! An aqueous solution was prepared, and to the above slurry, (1) was first added, and then (2) and (2) were added simultaneously over 1 hour each. When adding (2) and (2), (2) was added appropriately so that the I)H of the liquid did not fall below 8. Finally, the pH of the slurry was adjusted to 8 using (1) or (2), and the slurry was washed with water and dried.

When a portion of the dry powder was separated and analyzed, the adhering powder had a weight ratio of Ni/Fe-9.5/100. P/Fe=0
．． 45/100. Si/Fe =4.7/100. Met.

(3) Calcining, reduction and CO treatment The adhered powder obtained in (2) above was dried and pulverized to pass through a 16-mesh sieve, and calcined in air at 650°C for 4 hours to give a bulk density of 0.55. A fired powder of a/cc was obtained.

5 kg of this sintered powder was placed in a metal sintered reactor with an inner diameter of 200 mm and an inner volume of 60 mm, which was constructed with 20 μm micropores at the bottom of the reactor for the purpose of holding the filled powder and uniformly dispersing the gas. Pour the powder into a stirred fluidized bed reactor with a plate installed and a powder stirring sound installed inside the reactor,
While supplying N2 at 8ONm 3/H, the stirring blade was set to E2rp.
The reaction temperature was maintained at 400° C. for 3 hours to carry out the reduction.

After 3 hours at 400℃, the dew point of the reactor outlet gas is ~5
It was found that the reduction reaction was improved. Continue to add 10% CO to 8ONm 3/H of N2 gas.
The mixture was mixed to a concentration of 0 ppI11, maintained at 4.degree. 0.degree. C. for 1 hour, and the reduced iron powder was subjected to co-treatment.Then, the gas was switched to N2 and the mixture was allowed to cool to ambient temperature. In addition, gas chromatography analysis of the reactor outlet gas during CO treatment revealed that CO was 1 p.
pm or less, and CO2 had increased by about 50 ppm.

Next, the reduced powder is collected and immersed in toluene, spread on a flat plate, and brought into contact with air to form an oxide film on the surface of the reduced powder to stabilize it, and finally to form a dry magnetic iron powder. 3.3 kg was obtained.

(4) Evaluation of magnetic iron powder [Powder physical properties] The powder physical properties of the magnetic iron powder were measured in terms of magnetic properties and specific surface area, and the following values were obtained. The magnetic properties were measured using a vibrating sample magnetometer (VSM) at a measurement magnetic field of 10 KOe.

Hc1540 Qe (fs 1 26 emtJ/g σr /σSo, 51 Specific surface area 58 m2/g In addition, when the C concentration in the magnetic iron powder was analyzed, lff1
The ratio rc/Fe-0.07/100.

[Measurement of sheet physical properties J 300 parts of magnetic iron powder, VAGH (vinyl hydrochloride polymer, UCC)
After stirring and dispersing a mixture of 45 parts (product name), 175 parts of toluene, and 175 parts of methyl isobutyl ketone in a ball mill for 24 hours,
7 (Urethane prepolymer, Narita Pharmaceutical product name) 2 parts,
15 parts of toluene and 15 parts of methyl isobutyl ketone were added to a hole mill and stirred and dispersed for 1 hour to prepare a magnetic coating material.

The obtained magnetic paint was applied to a polyester film with a thickness of 16 μm so that the dry Jl was 3 μm, the metal powder was oriented in a magnetic field, and then dried. Then, the surface of the magnetic layer was sharpened by calendering. The sample was then cut to a predetermined width to obtain a specimen.

The sample was measured with a VSM at a measurement magnetic field of 10 KOe to obtain the following sheet properties.

Hc1450 0e Br2150 Gauss Br /am 0.74 Examples 2 to 6 Example 1 except for changing the reduction conditions and co98 processing conditions
Magnetic iron powder was obtained in the same manner. The evaluation results for each magnetic iron powder are shown in the table below. Incidentally, the C0yA degree at the reactor outlet during CO treatment in each example was 1 ppm or less.

Example 7 In Example 1, 10 kg of calcined powder was placed in a stirred fluidized bed reactor.
o During filling and reduction and CO treatment (7) Hr
Approximately 6.8 kg of magnetic iron was obtained by the same operation as in Example 1 except that the material was changed to 16ONn+3/H.

The properties of the magnetic R powder are: HCl535 0e as 125 emu/+ ;) σr/σS0.51 Specific surface area 571R2/g, and the sheet properties are: HCl440 0e Br 2150 Gauss Sr /Bu 0.74. It was recognized that the properties were almost the same as in Example 1.

Comparative Example 1 Magnetic iron powder was obtained by carrying out the same operations as in Example 1, except that the CO treatment in Example 1 was omitted, and after reduction, the treatment was immediately switched to N2 and allowed to cool.

The powder characteristics of the magnetic iron powder are: Hc1660 0e σS 125 emu/g σr/σs0.51 Specific surface area 59m2/Q And the sheet physical properties are Hc1540 0e Br2080 Gauss 3r/Bm o, 74 Met.

In addition, the physical properties of the sheet 1-1 are at the i3r level, which is satisfactory for 3mm video applications, but the sheet 1-1c is 1430.
-1500, making the magnetic iron powder unsuitable.

Comparative Examples 2 and 3 By omitting the CO treatment in Examples 2 and 3)! Magnetic iron powder was obtained by carrying out the same operations as in Examples 2 and 3, except that immediately after death, the atmosphere was changed to N2 and allowed to cool.

The evaluation results for each magnetic iron powder are as shown in the table below.

Comparative Example 4 A fixed bed reactor was filled with the calcined powder soog of Example 1,
Reduction was carried out at 380° C. in a hydrogen stream of 13 Nm 3 /H. still,
The bed height of the fixed bed was 8 Qcm at the time of filling. After 5.5 hours, the dew point of the reactor outlet gas reached =50°C, at which point 1100 pp of CO was added to the H2 stream, and after treatment for 1 hour, it was allowed to cool to room temperature in a N2 stream. Incidentally, the C0W4 degree at the reactor outlet when CO was added was below Q, 1 pt)l.

Next, 50 g of the reduced powder was carefully collected from the top, and each portion was stabilized to obtain magnetic iron powder. The preparative samples are numbered S-1 and S-2 in order from the top of the reactor.
It was set to -9. In addition, half of each of S-1 to S-9 was uniformly mixed using a powder mixer to obtain 5-10. The magnetic properties of each sample are as shown in the table below. Also, C'
As shown in the following table, the elemental analysis results for the III-degree reactor showed that the upper part of the reactor was at a height of m degrees.

From the above, it can be seen that in CO treatment, the reaction activity between Co and magnetic iron powder is extremely low, so a fixed bed reactor cannot be used industrially.

Claims (1)

[Claims] The acicular iron oxyhydroxide fine particles that have been modified with a shape-retaining component are made into ferromagnetic reduced iron powder by a gas phase catalytic reduction reaction using a reducing gas mainly composed of hydrogen, and then converted into ferromagnetic reduced iron powder with carbon monoxide and a reducing gas. In a method for producing acicular ferromagnetic fine particles containing iron carbide, which comprises producing ferromagnetic iron carbide through a gas phase catalytic carbonization reaction using a mixed gas, the gas phase catalytic carbonization reaction is carried out in a stirred fluidized bed or a fluidized bed type reactor. A method for producing acicular ferromagnetic particles containing iron carbide, characterized in that the process is carried out under conditions where the flow rate of a mixed gas of carbon monoxide and a reducing gas is set to a linear velocity of 2 cm/sec or more.