JPS61154110A - Acicular particulates of cementite for magnetic recording and manufacture thereof - Google Patents

Abstract

PURPOSE:To enable to make high density of magnetic recording medium by a method wherein acicular ferromagnetic cementite particulates are made as a main constituent. CONSTITUTION:Acicular ferro-hydroxide particulates are prepared and are designated as acicular ferromagnetic reduced iron powder class by adhesion and denaturalization, sintering and reduction process and secondly, acicular ferromagnetic iron carbide particulates of Fe3C is designated as molecular species by carbonization process. According to the working of this ferromagnetic particulates, particle's size, which is indicated by the same Hc value as the particulates mentioned later, can be designed in fully small in comparison with alpha-Fe particulates. Moreover, even if said particulates are contained carbon more than stoichometry, as Fe3C is formed as a molecular species, saturated magnetization is not lowered largely. This face is extremely favarorable. As a result of this fact, the system which magnetic property is hardly changed, can be realized using particulates system being microminiaturized as raw material powder at the time of medium processing work.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to ferromagnetic iron carbide fine particles as a magnetic material in magnetic recording media suitable for high-density recording mainly intended for audio and video, and the production thereof. Regarding the method.

<Prior art> In order to achieve high output and low noise in a wide recording wavelength range, magnetic materials for magnetic recording are made of highly uniform fine particles, have high coercive force (He), and have low saturation magnetization (He). Both σS) and residual magnetization (σr) are large, and the squareness ratio (Rs=σr/
σ8) is also basically required to have as large a magnetic property as possible,
Furthermore, the affinity and dispersibility with paint resins, the orientation and
It is desired that the media have excellent filling properties, and that the media has a sufficient life span to ensure reliability. In recent years, there has been a social demand for high-density recording, and a wide range of improvement research has been carried out, including magnetic powder as a material powder, binder resin, various additives, and even media processing methods (:
For example, see Okabe Akashi, "Advances in Magnetic Tape," Journal of the Japan Society of Applied Magnetics, 7 (3), 185 (1983). , efforts have been made to make the magnetic powder finer and increase the coercive force He- value (for example, Yasube Imaoka, "Magnetic Tape Technology", Electronics, March 1980 issue, p. 259).
. However, although a large Hc-value is basically required, there is generally a limit on the relationship with the characteristics of the material constituting the magnetic head, and it cannot be increased unnecessarily.

Therefore, increasing the He value as much as possible within the allowable range of magnetic powder and making it finer are extremely rate-limiting elemental technologies for realizing high-density recording.

In recent years, regarding magnetic powder as a magnetic material, ferromagnetic metal powder has first been put to practical use as a material for audio magnetic tapes due to its excellent magnetic properties, and is expected to be used as a video material in the near future. Hc-(direct and σ
The excellent magnetic potential based on a sufficiently high S-value is utilized, but in the case of acicular metal powder particles whose main component is iron, the main factor for the manifestation of ferromagnetism is the so-called shape. It is anisotropic and therefore its ferromagnetism is influenced by the particle geometry, i.e. its external size and its internal structure.

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,
Broadly speaking, the above-mentioned Ha-value is almost determined by the values of the major axis diameter (:L) and minor axis diameter (:D) or their axial ratio (:L/D), for example, L/D: 10 For acicular fine particle systems of around 1 μm or more, L: around 1μ and He-value: 500 to 70.
About 00e, L: around 0.5μ, Ha-value: 1000
About 12000e to 1400 at L:o, around 1μ
A value of about 16,000e to 16,000e is normally achieved.

Therefore, if the acicular metal powder particles containing iron as the main component are made finer for the purpose of achieving high-density recording as mentioned above, the Ha- value will inevitably increase, and if a normal magnetic head is mounted. It is no longer applicable to magnetic recording devices that have been modified, and is no longer practical. Therefore, we investigated the particle size and magnetic properties, especially He-
There has become a need for form design technology that can independently control M.

Conventionally, this type of morphology design technology includes (1) a method of designing an extremely low axial ratio, (2) a method of alloying fine particles based on the introduction of a large amount of Ni-component, and (3) a method of designing the surface layer of fine particles. In addition to methods of modification using organic substances, (4) a method using iron nitride is also known.

The principle of (1) is to suppress the ferromagnetism expression mechanism by reducing the shape anisotropy (for example,
Soshin Chikakumi, “Physics of Ferromagnetic Materials”, Shokabosha edition, p15
．． (1978).

In reality, there is a lot of room for variation depending on the manufacturing method, but
For example, in a needle-like fine particle system with iron as the main component and L/D: about 5, a system with L: about 0.5μ has a He-value of 600.
In an acicular fine particle system containing iron as a main component and having an L/D of about 3 and an L/D of about 3, the Ha-value will be about 500 to 600o.

However, in the case of longitudinal/coated magnetic recording media mainly used for audio and video, electromagnetic conversion characteristics over a wide band, especially high output, are required, and the residual magnetic flux density of the medium (: One of the essential factors is that the ratio between Br) and the maximum magnetic flux density (:Bm), that is, the squareness ratio, is sufficiently large (for example, Sango Muramatsu [Video and Audio ``Recent Advances in Magnetic Tapes'', Nikkei Electronics, May 1976 issue, p. 82), whereas sufficient orientation cannot be achieved with fine particle systems with small axial ratios (e.g., JP-A-110999-1999). Further, see application No. 59-209748 by the present inventors), which is inappropriate for this purpose.

(2) shows that in the alloy-based fine particles produced by the so-called evaporation method with Fe as the host metal component, the Ni-component is 40%.
In the composition range up to about 100% by weight, we actively reduce the magnetic anisotropy due to magnetic dilution accompanying the lattice substitution of the body-centered cubic crystal (bibcc) formed by the Fe-component due to Ni. (For example, Tasaki, Takao, Hoki et al.) Magnetic Properties of F
erromagnetic Metal A11oy
Fine ParticlesPrepared by
Evaporation in Inert Gas
*a, IIJ, Jpn, J, Appl, Phys,
13(2), 271 (1974) (Although it is certainly possible to control the magnetic properties to some extent independently of the acicular particle size by this method, FeNi co-precipitation by a wet method that does not depend on the evaporation method When manufacturing coarse raw materials and then manufacturing alloyed fine particles using a gas phase catalytic reduction reaction method, the uniform magnetic dilution of the bcc-phase is limited to about 20% by weight of the Ni-component at most. For example, if H
c-(The amount of direct reduction is about 2000e. Therefore, L/
D: Needle-like fine particles of around 10 or more, L: '0.
If it is around 5μ, Hc-(direct: 800 to 1000oe
It is difficult to go below that level. In systems with a higher Ni content, face-centered cubic crystals (: fc
e) occurs as a side effect: As a result, the apparent value is 8000e.
Although the He- value is reduced to a certain extent, when the medium is processed, the squareness ratio is greatly reduced, and this method can only be applied within a limited range.

(3) is a method first discovered and proposed by the present inventors (application filed 179300/1982).

Acicular iron oxyhydroxide fine particles as a crude raw material are coated and modified with an acrylic organic substance and then reduced with hydrogen at 300 to 475°C.
It was discovered and proposed that a decrease in the Ha value of about 5,000e occurs without destroying the shape of the particles. It can be said to be an extremely effective method with a wide range of applications.

(4) is a method mainly using acicular Fe4N fine particles, and is a method reported by one of the inventors (Tasaki, Tagawa, Kita et al. Recording Tapes
UsingIron Ni tride Fine
PowdsrJ, IEKE, Trans, Fil
lmg, MAG-17(6), Nov, 302
6 (1981)). This example is also an extremely effective manufacturing method that allows particle size and magnetic properties to be designed independently by controlling the degree of nitriding, but since ammonia is used as the nitriding agent, the production equipment It was necessary to take special anti-corrosion measures, which was impractical when considering industrial production.

Looking back at the prior art, it can be seen that there are surprisingly few manufacturing methods that independently control particle size and magnetic properties over a wide range and are practical for industrial production.

Problems to be Solved by the Present Invention> Regarding acicular magnetic powder as a magnetic material for high-density magnetic recording media mainly intended for audio and video, the particle size and magnetic properties, especially the coercive force He The design technology that independently controls the magnetic powder value is the ultimate elemental technology for magnetic powder, and can be positioned as one of the most awaited industrial technologies for increasing density.

The present invention aims to address the above-mentioned basic problem, which is still largely unsolved in the field, by providing a completely new industrial manufacturing method and a new magnetic powder based thereon.

Means for Solving the Problems> In order to solve the above problems, the present inventors have conducted various studies, and as a result, the present inventors have developed a method of fine acicular oxyhydroxidation using a well-known wet method. Fine iron particles are synthesized, then subjected to adhesion modification treatment using a shape-retaining component, and then washed, dried, crushed, and calcined as necessary, and then subjected to a gas phase catalytic reduction reaction using a reducing gas mainly composed of hydrogen gas. After that, a powder system subjected to a vapor phase catalytic carbonization reaction using a carbonizing gas mainly composed of carbon oxide gas has a shape similar to that of the iron oxyhydroxide fine particles used as the crude raw material without damaging or destroying it. We discovered that it can exhibit inherited acicular properties, and at the same time have magnetic properties that depend on the conditions of the gas phase catalytic carbonization reaction.In particular, we discovered that the coercive force He- value decreases by about 200 to 800 oe depending on the degree of carbonization. invention has been achieved.

That is, the method of the present invention includes, as a first step, producing acicular metal powder particles containing iron as a main component for magnetic recording, and then, as a second step, carbonizing the metal powder particles. configured.

Acicular metal powder fine particles containing iron as a main component for magnetic recording can basically be produced by well-known methods, but for example, the method disclosed by the present inventors can be used. It is possible to implement it by

That is, ferrous sulfate is neutralized with caustic soda, and then an oxidizing gas such as air is introduced to oxidize and crystallize the neutralized hydrogel to form acicular iron oxyhydroxide fine particles. Synthesize. Various methods can be used to control the shape of the acicular fine particles that develop, but the so-called coprecipitation method, in which water-soluble salts of various metal components are introduced as subcomponents, is simple and industrially practical. be.

After washing the acicular iron oxyhydroxide fine particles, a modification treatment with a shape-retaining component mainly consisting of zinc oxalate is applied.
Then, if necessary, it is washed, dried, and crushed to obtain a raw material for reduction (Japanese Patent Application Laid-Open No. 58-48612).

The raw material is charged into a steel pipe reactor equipped with a preheater for the raw material gas for reaction and whose temperature can be controlled from the outside, and heated for 30 minutes.
By introducing a reducing gas, mainly hydrogen gas, at around 0 to 500°C and continuing the reduction reaction, α-F6 powder, which forms a body-centered cubic system (bce) in crystallography, is produced. I can do things.

The next carbonization reaction step can be carried out as follows. That is, when the above-mentioned reduction reaction is completed, the supply of reducing gas, mainly hydrogen gas, is stopped, and after setting the reaction temperature to a predetermined temperature, a mixed gas of carbon monoxide gas and nitrogen gas is introduced.

The end point of the reduction reaction can be determined by on-line analysis of the water concentration of the reactor system exhaust gas, such as dew point measurement.

□The appropriate temperature for the carbonization reaction is 200 to 500°C.

If the reaction temperature is lower than 200° C., carbonization will not substantially proceed and the object of the present invention will not be met. If the temperature exceeds 500°C, although the carbonization reaction itself will proceed, the acicular fine particles will be severely sintered, making the powder unsuitable as a magnetic powder for magnetic recording.

As the carbonizing material in the carbonization reaction, -carbon oxide is preferred because it has the highest carbonization ability and enables low-temperature carbonization. Carburizing materials commonly used in the steel industry such as methane, ethane, propane, and butane can also be used, but in this case, carbonates of Group II metals of the periodic table, such as barium carbonate, can be used as carbonization accelerators. By adding such substances in the above-mentioned adhesion modification step, it is necessary to move the carbonization reaction caused by these carbonizing materials, which usually does not proceed unless it is extremely high temperature, to a temperature below 500° C. as described above.

The carbonization reaction when carbon monoxide gas is used is extremely fast, and since it is necessary to control the degree of carbonization, it is effective to entrain it with an inert gas such as nitrogen gas.

- The amount of oxidizing gas entrained is preferably about 50% by volume or less from the viewpoint of controlling the degree of carbonization. If the entrained amount is more than this, the carbonization reaction progresses very quickly, and it becomes increasingly difficult to quantitatively control the degree of carbonization.

The supply amount and speed of the reaction gas are determined by the gas hourly space velocity (:G
H8V) is 0.1 to 100, preferably 10 to
A range of 30 NI Co/g'r-F*/Hr is suitable. Below this range, although the carbonization reaction progresses,
This rate is extremely slow and impractical, and if it exceeds this range, the pressure drop in the reaction system will increase, which is not preferable as a reaction operation.

Since the carbonization reaction in the present invention is a gas-solid-liquid reaction, the overall reaction rate is determined by two factors: the surface reaction rate and the diffusion rate. Therefore, in order to accurately control the degree of carbonization, it is necessary to quantitatively understand these two factors. However, as a more practical method, the degree of carbonization can be controlled by considering that it is determined by two factors: the apparent contact amount of the carbonized material and the reaction efficiency. In this case, the former can be calculated online from the reaction gas supply rate and cumulative reaction time. The latter amount is a complex function of the reactor type, reaction conditions (temperature, reaction gas species and composition, supply amount and speed, etc.), and the form of the reduced iron powder (composition, size, particle size, etc.). However, it can be easily evaluated experimentally by conducting a series of preliminary experiments, and can be prepared as a diagram. By attaching a dedicated small computer to the reactor system and establishing a program control system in advance, although it is not possible to actually measure the degree of carbonization, its control becomes fully possible industrially.

When the predetermined carbonization degree of X of FeCx reaches about 0.1 to 0.5, the supply of the carbonizing gas is stopped, switched to an inert gas such as nitrogen, heating of the reactor is also stopped, and the temperature is lowered to room temperature. do. Since the carbonized reaction powder is composed of extremely fine particles, there is a possibility that it will spontaneously ignite in the atmosphere and return to iron oxide, so the sample for analysis is sealed in nitrogen gas. Otherwise, the material is collected in an organic solvent such as toluene and preserved by immersion. Thereafter, it is possible to make a stabilized dry powder by air-drying it as needed and applying slow oxidation treatment, and then it can be made into a paint, coated, and cut according to a prescribed formulation to form the desired shape. It is possible to use a coating medium having the following properties.

In this way, acicular iron oxyhydroxide fine particles are used as the primary raw material, and through a gas phase catalytic reduction reaction, acicular reduced iron powder is produced.
Carbonized powder can be produced by gas phase catalytic carbonization reaction. As mentioned above, the gas-phase catalytic carbonization reaction in the second stage can use the same reactor system that carries out the gas-phase catalytic reduction reaction in the first stage, and since carbon monoxide is used as the carbonizing agent, the reaction equipment can be easily used. Problems such as corrosion do not occur, which is extremely convenient.

When the particle shape of the carbonized powder is observed under an electron microscope with a magnification of 30,000 to 90,000 times, it appears to be exactly the same as the particle shape of the fine powder particles formed in the previous reaction, that is, the reduced metal powder containing iron as the main component. That is, its shape has an acicular outer shape that closely follows the shape of the iron oxyhydroxide fine particles used as the primary raw material, and it has a spherical ultrafine particle (about 100 to 300A).
(referred to as crystallites, microcrystals, crystallinotes, grains, etc.) are assembled in large numbers to constitute each needle-shaped carbonized powder skeleton particle. In addition, there is almost no damage, destruction, or interparticle bonding, that is, sintering. :D should be 0.1μ or less and its axial ratio:L/D should be 10 to 30. If the shape size is larger than this size, processing it into a magnetic medium and measuring its electromagnetic conversion characteristics will result in extremely high noise, making it unsuitable. If the axial ratio is less than 10, as described above, when processed into a magnetic medium, the magnetic squareness ratio will not be large enough, and the material will not be suitable. Furthermore, if the axial ratio is 30 or more, the rate of damage caused by the dispersion media in the coating process becomes extremely high, making it ineffective.

The acicular carbonized powder can be carefully subjected to chemical analysis to determine the ratio of iron to carbon without exposing it to the atmosphere. F
When expressed as eCx, the X-value is 0.1 to 0.
5 is appropriate. If the X-value is less than this value, the desired ferromagnetic properties, especially the Ha-value, will decrease by 2000e.
Stay below. Also, if the X-value exceeds 0.5, He-
Although the decrease in value is large, the saturation magnetization (σ8) value, which is one of the factors regulating the residual magnetic flux density (Br) value when processed into a magnetic medium, is extremely reduced, and the magnetic properties of the magnetic recording medium are reduced. It is no longer suitable as a material powder.

The acicular carbonized powder is subjected to powder method X-ray diffraction measurement,
When identified from the diffraction angle of the crystalline diffraction peak group, Tokorun Cementite species: Fe5C is detected.

α-F phase is detected simultaneously only when the degree of carbonization is low. It was confirmed that even though the degree of carbonization progressed, other iron carbide tanks, such as Fe 2 C, were not formed under the carbonization reaction conditions of the present invention. Carbon in an amount greater than the stoichiometric amount acts to reduce the crystallinity of Fe5C, and is therefore presumed to mainly distort the cementite crystal lattice.

The magnetic properties of the acicular iron carbide powder have an Ha value of 50.
00@ or more, σS-value is 100 emu/gr,
The above is appropriate. Below this value, the desired high output
High-density magnetic recording cannot be achieved. These magnetic properties can be controlled by the morphology and modification recipe of the iron oxyhydroxide fine particles that serve as the secondary raw material, the characteristics of the reduced iron powder that serves as the secondary raw material, and especially the conditions of the subsequent carbonization reaction.

[Effect]

Iron carbide itself is a well-known chemical species, and it is also known that it can be obtained by carbonizing α-Fe with carbon monoxide gas (for example: H, A, Bahr, etc.).
xyd-8paltung an Eisenoxy
d und EisenJ, Berichte, 66
゜1238 (1933)). There are many well-known facts about its carbonization mechanism, but most of its uses have conventionally been in so-called carburizing treatment for designing the phase structure of steel sheets and improving mechanical hardness.

Little is known about synthesizing iron carbide as fine particles and utilizing its ferromagnetic properties as magnetic material powder for magnetic recording media, and only a few US patents: USP 3,572,
993 (Mar, 1971: D, B, Rogers). According to the patent specification, a fine particle type X-phase is obtained by thermally decomposing an iron carbonyl compound (=especially Fe(CO)s) in a hydrogen and carbon oxide gas atmosphere at a temperature of 280 to 340°C. The X-phase is a species called iron carbide of H'agg, and is expressed as Fe2C.According to the description in the patent specification, the particle shape of is 0.005 to 0
．． It is a spherical ultrafine particle of 16μ, and its magnetic properties are Ha
-fO! is said to be about 200 to 10,000e, and the 6m value is about 85 to 100 smu/gr.

There are almost no known examples of using bulk iron carbide as a magnetic material in the field of magnetic recording, and this is only found in JP-A-53-26218. In the Japanese Patent Application Laid-open No. 2003-120023, an iron-based alloy containing 0.5 to 5.0% carbon is melted, and the melt is rapidly cooled by centrifugation to form a ribbon-shaped sample with a thickness of about 3 μm.

Next, the rapidly cooled sample was heated to 800°C at a heating rate of 100°C/H.
Heat to ℃ and then cool down to room temperature at the same rate.

It has been shown that this heat treatment increases the saturation magnetization of the ribbon-shaped sample.

As a method for synthesizing iron carbide fine particles, thermal decomposition of an iron-cyanide compound in a non-oxidizing atmosphere (= JP-A-5O-22
000), a method by evaporation of iron metal in a low-pressure active gas (=Japanese Patent Application Laid-Open No. 52-84179), a method by gas spraying of a melt (=Japanese Patent Application Laid-Open No. 54-29305), etc. are known.

In the method of the present invention, acicular iron oxyhydroxide fine particles are prepared, and are converted into acicular ferromagnetic reduced iron powder through a modification treatment with a shape-retaining component, calcination, and reduction process, followed by a carbonization process. Therefore, the molecular species is F*3C, which is acicular ferromagnetic iron carbide fine particles.

In the method of US Pat. No. 3,572,993, ferromagnetic spherical ultrafine particles are formed by thermal decomposition of an iron carbonyl compound in a reducing atmosphere, and the molecular species thereof is Fe2C. Therefore, the present invention can be said to be a completely different system from the patented technology system. In the method of the present invention, one of the key points is the use of specific acicular fine particles, which cannot be omitted due to the characteristics of the magnetic medium.

The technique described in JP-A-53-26218 is a manufacturing recipe for improving the ferromagnetic properties of iron carbide, and is completely different from the present invention in terms of purpose and effect.

Furthermore, JP-A-50-22000.52-84179.5
No. 4-29305 and the like are methods for producing spherical particles, and it can be said that the technical idea is different from the present invention.

As seen above, the method of the present invention is completely different from conventional related technology systems, and provides a novel magnetic material powder that has never been seen before in the field of magnetic recording technology. I understand that it is something.

The action of acicular ferromagnetic fine particles whose molecular species is expressed as Fe3C is shown in comparison with α-Fe powder fine particles. Furthermore, even if more than the stoichiometric amount of carbon is contained, Fe5C is formed as the molecular species within the scope of the present invention, so the above-mentioned F 111 C Unlike the case, the saturation magnetization does not decrease significantly, which is extremely convenient.

As a result, when media processing is performed, it is possible to use finer particles as the raw material powder while creating a system with almost no change in magnetic properties. As a direct result of this, the magnetic recording characteristics that are strongly controlled by the particle size of the magnetic powder, that is, the high magnetic conversion characteristics (sensitivity and output) in the high range and the noise, are greatly improved.

In particular, for acicular iron carbide fine particles with a major axis diameter of about 0.1μ, if it is α-Fe powder, the Ha value is 150.
00e, which can be used as so-called 8m/m video powder, is HC-(1iL, which is around 8000e, making it optimal as a high band magnetic powder in current home video systems. .

〔Example〕

Hereinafter, the method and effects of the present invention will be described in detail with reference to Examples and Comparative Examples. In this example, test results will not be specifically described regarding the evaluation of video characteristics as a high band system, as the hardware itself of the relevant video deck is not completely completed at this time, but the test results for the evaluation of audio characteristics will be Since the high-frequency characteristics of the magnetic tape based on acicular ferromagnetic iron carbide powder obtained by the method of the present invention are remarkably good, it is assumed that the magnetic tape has sufficiently high video characteristics. It is estimated.

[Example-1] This example is an example showing an overview of the method of the present invention and its effects on acicular ferromagnetic fine particles containing iron carbide as a main component for so-called high-position audio applications. be.

Production of Reduced Iron Powder> By the method described in JP-A-57-106527 and JP-A-57-96504, P, Si, and a Ni component as a coprecipitated component were mixed in a weight ratio of P/Fe=0.3/100. Si/Fe=
Acicular iron oxyhydroxide fine particles containing only 1.5/100 and 3.9/100 of Ni/Fe were synthesized.

The shape of the fine particles has a specific surface area (SA) of 40.5 m''/gr s calculated from the adsorption characteristics of nitrogen gas and a major axis diameter (L
) and the minor axis diameter (=D), that is, the axial ratio (L/D) was 15.

Next, adhesion modification treatment with zinc borate was applied using the method described in JP-A-58-48612 (B/Fe-0, 6/1).
0 weight ratio), after drying and pulverization process, gas phase catalytic reduction reaction with hydrogen gas (temperature = 375°C, gas hourly space velocity =
2ONm3-C/kgr Fe/Hr, ) to obtain reduced iron powder.

A portion of the iron powder was extracted under a nitrogen gas atmosphere, and the specific surface area and magnetism were evaluated using a vibrating magnetic property measuring device (Model VSM-III, manufactured by Toei Kogyo Co., Ltd.) using the nitrogen gas method, and 5A = 40. 1m/gr,, Hc=11820e
, ffs=182emu/gr, Rs=0.48
It was 7.

Carbonization reaction〉 The magnetic iron powder is heated with a mixed gas of carbon monoxide and nitrogen (volume ratio 1:
1) Gas phase catalytic carbonization reaction (=temperature=450°C, gas space velocity=20 Nm mlxed gas/k
The carbonization reaction was carried out for 5 hours using gr-pe/Hr.

When a part of the fine particles was extracted under a nitrogen gas atmosphere and analyzed for carbon and iron, the weight ratio C/Fe=8.9/
100 (F e CO4).

Next, after thoroughly immersing the fine particles in toluene, the fine particle slurry was transferred onto an enamel vat to a thickness of about 1 crrL, 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 iron powder.

When the physical properties of the air-dried iron carbide powder were evaluated, 5A=35
．． 2m7/gr, Hc=8320s, σg=
116 emu/gr, Rs=0.456.

Evaluation of coating/coating and tape properties of air-dried iron carbide powder> 10 gr of the air-dried iron carbide powder was collected and placed in a pot with an internal volume of 550 m1 along with the following materials. Mixing and dispersion continued for 5 hours on a paint shaker. As the dispersion media, 2 m/α-alumina beads were used.

・Salt vinyl acetate polymer manufactured by UCC VAGH: 1.2
gr'・Polyurethane NL- manufactured by Mitsui Toatsu Chemical Co., Ltd.
2448: 0.8gr, phosphate ester manufactured by Oiri Kagaku Co., Ltd. AP-13: 0.1gr, α-alumina manufactured by Sumitomo Chemical Co., Ltd. AKP-30: 0.2gr, solvent Toluene:
13 gr., MEK: 13 gr.

Next, the dispersion media was separated to obtain a magnetic paint, which was coated onto a 12μ thick polyester film (Nilmirror 12B-LIO) manufactured by Toshi Co., Ltd. using an applicator in a precision coater equipped with magnetic tape. After that, the coating surface was smoothed by calender roll treatment and 50'C
A heat treatment was applied for 2 days to complete the polyurethane curing reaction. The sheet was cut into 3.81i+thickness to produce a magnetic tape of the current cassette specification size.

The magnetic properties of the magnetic tape are measured using the measuring device described above.
After evaluation, Ha-7050s, Br=2850Gauss,
Br/Bm=0.772, indicating sufficient characteristic values.

Evaluation of audio characteristics> Tape tester manufactured by Nippon Columbia: DENON-031
Audio characteristics were measured and evaluated using an RGC standard Type II tape using an RGC (equipped with an IEC standard head) according to the measurement method described in Japan Magnetic Tape Standard: MTS-0101 ('72).

Low frequency sensitivity (: 333 Hz sensitivity) is +3.5 dB, high frequency sensitivity (: 12.5 kHz sensitivity) is +3.5 dB, maximum output (=3XMOL) is +7.5 dB, saturated output (:
10kHz, 5QL) is -2.5dB, and AC bias noise (:Nae) after auditory correction is -57.5
It was dB. As will be made clear in the comparative examples described later, this characteristic shows sufficient high-frequency sensitivity and saturation output, and provides a uniquely low noise.

[Example-2] This example is for metal position audio applications.
This is an example showing an overview of the method of the present invention and its effects regarding acicular fine particles containing iron carbide as a main component.

Production of Reduced Iron Powder> By the method described in JP-A-57-106527 and JP-A-57-96504, p, st and N i - component as coprecipitated component were mixed in a weight ratio of P/Fe=0.7/100. Si/Fe=1
．． 5/100 and N i /Fe, = 8.0/
Acicular iron oxyhydroxide fine particles containing only 100% of iron oxyhydroxide were synthesized.

The shape of the fine particles has an SA of 73. Oyj/gr,
, and L/D was 12 from a transmission electron microscope image. Next, after passing through a drying and pulverizing process, calcination (temperature = 725°C)
) and gas phase catalytic reduction reaction using hydrogen gas (temperature=42
5℃, gas space velocity -2oN, "-Hg, /kgr-
Fe, 4(r,)t was used to obtain reduced iron powder.

When a part of the iron powder was extracted under a nitrogen gas atmosphere and magnetic properties were evaluated using SA and the above-mentioned apparatus, it was found that 5A=6
0.5m'/gr,, Hc=14320e, 7FI=1
54 emu/gr, Rs = 0.502.

Carbonization reaction〉 The magnetic iron powder is heated with a mixed gas of carbon monoxide and nitrogen (volume ratio 1:
1) Gas phase catalytic carbonization reaction (: temperature = 380°C, gas space velocity = zoN, '-mix@d gas/kg
r Fs.

The carbonization reaction was carried out for 8 hours using Hr, ).

When a part of the fine particles was extracted under a nitrogen gas atmosphere and analyzed for carbon and iron, the weight ratio C/Fe was 3.6/1.
00 (FeCo, 17).

Next, the fine particles were sufficiently immersed in toluene, and then the fine particle slurry was transferred onto an enamel vat to a thickness of about 1 cIL, and subjected to toluene scattering treatment in the atmosphere. When the solvent odor disappeared, the magnetic powder was collected and used as air-dried iron carbide powder.

When the physical properties of the air-dried iron carbide powder were evaluated, 5A=53
．． 4774/gr,, Hc=13000e, σg=13
4emu/gr.

Rm = 0.492.

<Evaluation of coating, coating, and tape properties of air-dried iron carbide powder> Take 10 gr of the air-dried iron carbide powder and add it together with the following materials to make an internal volume of 550+1! The mixture was poured into a small pot, and mixed and dispersed for 5 hours using a paint shaker manufactured by Red Devil Co., Ltd., USA. As a distributed media, 2111If α
- using alumina beads.

- Salt vinyl acetate polymer manufactured by UCC Co., Ltd. VAGH: 1. Og
r.Mitsui Toatsu Chemical Co., Ltd. polyurethane NL-2448:
1. Ogr/Oiri Kagakusha phosphate ester AP 1
3: 0.21r α-alumina AK manufactured by Sumitomo Chemical Co., Ltd.
P30: 0.2gr・Solvent Toluene: 1'
4 gr., MEK: 14 gr.

Next, the dispersion media was separated to obtain a magnetic paint, which was coated onto a 12μ thick polyester film (Nilmirror 12B-LIO) manufactured by Toshi Co., Ltd. using an applicator in a precision coater equipped with magnetic tape.

Thereafter, the coating surface was smoothed by calender roll treatment, and heat treatment was applied at 50° C. for 2 days to complete the polyurethane curing reaction. The sheet was cut to 3.81 mm to produce a magnetic tape having the size specified by the current cassette.

The magnetic properties of the magnetic tape are measured using the measuring device described above.
As a result of evaluation, Hc=12090e, Br=2890 Gauas,
Br/Bm=0.806, showing sufficient characteristic values.

Evaluation of audio characteristics> In the same manner as in Example-1, IEC standard T'ype-IV
We measured and evaluated audio characteristics based on tape.

Low frequency sensitivity (:333Hz sensitivity) is +1.2 dB, high frequency sensitivity (:20kHz sensitivity) is +3.5dB, maximum output (:3%MOL) is +7.5dB, saturated output (:10
kHz, 5QL) is +1.5 a B, and after auditory correction AC bias noise (:Nac) is -58.0 dB
Met.

As will be made clear in the comparative examples described later, this characteristic shows sufficient high-frequency sensitivity and saturation output, and provides a uniquely low noise.

[Comparative Example-1] This comparative example is a ferromagnetic metal powder that is the main component of iron for high-position audio applications, and when the axial ratio (:L/D) of the raw material α-iron oxyhydroxide is short. This is an example.

Production of reduced iron powder> By the method described in JP-A-57-106527 and JP-A-57-96504, P, Si and a Ni component as a coprecipitated component were mixed in a weight ratio of P/Fs=0.3/100. Si/Fe=0.
Acicular iron oxyhydroxide fine particles containing Ni/Fs=1.5/100 and Ni/Fs=1.5/100 were synthesized.

Regarding the shape of the fine particles, SA was 28.0i/gr, and L/D was 5 from a transmission electron microscope image. Then,
Zinc borate adhesion modification treatment was added by the method described in JP-A-58-48612 (B/F e =0.6/100
Weight ratio), after drying and pulverization process, gas phase catalytic reduction reaction with hydrogen gas (temperature = 375°C, gas hourly space velocity =
2 ONm H2/kgr-Fe, Hr) to obtain reduced iron powder.

A portion of the iron powder was extracted under a nitrogen gas atmosphere and evaluated for magnetism using SA and the above-mentioned apparatus, and it was found that 5A=2
2.0m”/gr,, Hc=7870e, (Fg=18
5 emu/gr, Rs = 0.450.

Air Drying of Reduced Iron Powder> After the fine particles were sufficiently immersed in toluene, the fine particle slurry was transferred onto an enamel vat to a thickness of about 1 cIn, 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 iron powder.

When the physical properties of the air-dried iron powder were evaluated, 5A=21.5
m/gr, , Ha =8200s, 0g =
165 emu/gr-rRs = 0.444.

<Evaluation of coating/coating and tape properties of air-dried iron powder> 10g of the air-dried iron powder was collected, a coating was prepared in the same manner as in Example-1, and coating/film smoothing/heat treatment/ After cutting, it was made into a magnetic tape of the current cassette specification size.

The magnetic properties of the magnetic tape are measured using the measuring device described above.
As a result of evaluation, He-6530e, Br=2760 Gauss,
The characteristic value was Br/Bm=0.611.

Evaluation of audio characteristics> In the same manner as in Example-1, audio characteristics were measured and evaluated using IEC standard Type-II tape as a reference.

Low range sensitivity (=333Hz333Hz feeling, 4 dB1 high range sensitivity (: 12.5kHz sensitivity) is +3.0 dB, maximum output (: 3% MOL) is +7.5 dB, saturated output (:
10kHz, 5QL) is -3.5d B, and after auditory correction, the intersection bias noise (:Nac) is -54.0d
It was B.

[Comparative Example-2] This comparative example is an example of a ferromagnetic metal powder whose main components are an alloy of iron and nickel for high-position audio applications.

Production of reduced iron powder> By the same method as in Example-2, the weight ratio of P/Fe was 5.
5/100. Si/Fe=1.5/Zoo and Ni/F
Acicular α-iron oxyhydroxide fine particles containing only e=36/100 were synthesized.

The shape of the fine particles is as follows: SA is 31.1 m/g r;
, and L/D was 15 from a transmission electron microscope image. Next, after passing through a drying and pulverizing process, calcination (temperature = 725°C)
), and temperature = 425 for gas phase catalytic reduction reaction with hydrogen gas.
°C, gas space velocity -2ONm3-Hffi/kgr-F
e, Hr,) to obtain reduced iron powder.

A portion of the iron powder was extracted under a nitrogen gas atmosphere and evaluated for magnetism using SA and the above-mentioned apparatus, and it was found that 5A=2
8.2 m/gr, , Hc = 7620e, σg = 149゜emu/gr, , Rs = 0.452.

Air Drying of Reduced Iron Powder> After thoroughly immersing the fine particles in toluene, the fine particle slurry was transferred onto an enamel vat to a thickness of about 1 cm, 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 iron powder.

When the physical properties of the air-dried iron powder were evaluated, 5A=27.5
77//gr,, Hc=7820e, σs=124e
mu/gr.

Rs = 0.447.

Making paint from air-dried iron powder, coating, and evaluation of tape properties〉 10 gr of the air-dried iron powder was collected, and a paint was prepared in the same manner as in Example-1, followed by coating, smoothing of the coating, and heat treatment.・
After cutting, it was made into a magnetic tape of the current cassette specification size.

The magnetic properties of the magnetic tape are measured using the measuring device described above.
As a result of evaluation, Hc=6930e, Br=1824 Gauss,
The characteristic value was Br/Bm=0.698.

Evaluation of Audio Characteristics> In the same manner as in Example-1, the audio characteristics were measured and evaluated using the IEC standard Type-II tape as a reference.

Low frequency sensitivity ('333Hz sensitivity) is +2.0 a B,
High frequency sensitivity (: 12.5kHz sensitivity) is +3.0 dB
, the maximum output (: 3% MOL) is +5.5 d B1 saturation output (: 10 kHz, 5QL) is -3.5 dB1, and the AC bias noise (2 Nae) after auditory correction is -5
It was 5.5 dB.

[Comparative Example-3] This comparative example is an example of a ferromagnetic metal powder containing iron as a main component for metal position audio applications.

Preparation of Reduced Iron Powder Since the particle shape and magnetic properties of the reduced iron powder described in Example 1 are suitable as magnetic powder for current metal position audio applications, this powder was used.

Air Drying of Reduced Iron Powder> After thoroughly immersing the fine particles in toluene, the fine particle slurry was transferred onto an enamel vat to a thickness of about 1 cWL, 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 iron powder.

When the physical properties of the air-dried iron powder were evaluated, 5A = 33.5
g/g, r,, Hc=12950e, ffs=1
54 emu/gr.

Rs=0.491.

Making paint from air-dried iron powder, coating, and evaluation of tape properties> 10g of the air-dried iron powder was collected, a paint was prepared in the same manner as in Example-2, and coating, smoothing of the coating film, heat treatment, After cutting, it was made into a magnetic tape of the current cassette specification size.

When the magnetic properties of the magnetic tape were measured and evaluated using the above-mentioned measuring device, Hc=l 2000e, Br=3010 Gauss
, Br/Bm=0.805.

Evaluation of Audio Characteristics> In the same manner as in Example-2, the audio characteristics were measured and evaluated using the IEC standard Type-IV tape as a reference.

Low frequency sensitivity (:333Hz sensitivity) is +1.3 dB, high frequency sensitivity (:20kHz sensitivity) is +2.8 dB, maximum output (=3%MOL) is 7.0dB, saturated output (:10
kHz, 5QL) is +1.0 dB.

Furthermore, the alternating current bias noise (Nac) after auditory correction was -56.0 dB.

〔effect〕

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

That is, in the case of acicular ferromagnetic fine particles as a magnetic recording material suitable for high-density magnetic recording, the fine particles are mainly iron-based fine particles containing a predetermined amount of carbon, and the acicular ferromagnetic fine particles are coated with modified acicular ferromagnetic particles. By converting iron hydroxide fine particles into ferromagnetic reduced iron through a gas phase catalytic reduction reaction using a reducing gas, and then into ferromagnetic iron carbide fine particles through a gas phase catalytic carbonization reaction using a carbonizing gas, (1) Regarding the iron carbide fine particles themselves: exhibits an acicular shape that closely follows the shape of iron oxyhydroxide, the raw material.

(2) It is possible to control the magnetic property values, especially the coercive force Hc value, over a wide range according to the degree of carbonization, and (3) the magnetic powder particles are fine and have appropriate magnetic properties (coercive force Hc value). magnetic force,
(4) The manufacturing equipment uses ferromagnetic metal powder made from iron oxyhydroxide as raw material. It was found that the manufacturing equipment can be used as is.

As described above, the substance of the present invention is a magnetic material with remarkable characteristics for use in audio and video applications, and provides a method for producing the same.

Claims (7)

[Claims] (1) A magnetic material for magnetic recording media mainly consisting of acicular ferromagnetic iron carbide fine particles. (2) The magnetic material according to claim 1, wherein the value of x in iron carbide composition FeCx is in the range of 0.1 to 0.5. (3) The long axis diameter of iron carbide fine particles is 1μ or less, and the short axis diameter is 0.
1. 2. The magnetic material according to claim 1, wherein the magnetic material is less than μ and has an axial ratio of 10 to 30. (4) Magnetic property values are 500 Oe or more as coercive force and 100 emu/gr as saturation magnetization. A magnetic material according to claim 1, comprising ferromagnetic iron carbide fine particles exhibiting the above. (5) The acicular iron oxyhydroxide particles modified with a shape-retaining component are made into ferromagnetic reduced iron powder through a gas phase catalytic reduction reaction using a reducing gas, and then strengthened through a gas phase catalytic carbonization reaction using a carbonizing gas. A method for producing magnetic iron carbide fine particles for magnetic recording, which are acicular and exhibit ferromagnetism. (6) The manufacturing method according to claim 5, wherein the reducing gas is a gas mainly composed of hydrogen, and the gas phase catalytic reduction reaction is carried out at 300 to 500°C. (7) The manufacturing method according to claim 5, wherein the carbonizing gas is a gas mainly composed of carbon monoxide, and the gas phase catalytic carbonization reaction is carried out at 300 to 500°C.