JP3277649B2 - Method for producing acicular alloy magnetic particle powder containing iron as a main component - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing acicular alloy magnetic particle powder containing iron as a main component and suitable as a material for a magnetic recording medium. It is an object of the present invention to provide a needle-shaped alloy magnetic particle powder containing iron as a main component, which is good, has a high coercive force and a large saturation magnetization, and has a good dispersibility in a vehicle.

[0002]

2. Description of the Related Art As the size and weight of magnetic recording / reproducing devices have been reduced, the need for higher performance for magnetic recording media such as magnetic tapes and magnetic disks has been increasing. That is,
There is a demand for high-density recording, high-output characteristics, and particularly improvement in frequency characteristics. In order to obtain a magnetic recording medium having such properties, it is required that the magnetic particle powder used has a high coercive force, a large saturation magnetization, and a good dispersibility in a vehicle. .

In recent years, magnetic particle powders suitable for high output and high density recording, that is, magnetic particle powders having high coercive force and large saturation magnetization, have been actively developed. Acicular iron oxide hydroxide particles or acicular iron oxide particles are used as starting material particles, and acicular alloy magnetic particles containing iron as a main component obtained by heating and reducing the starting material particles in a reducing gas are practically used. Have been.

[0004] Recently, demands for improving the characteristics of magnetic recording media have been increasing, and accordingly, it has been strongly required to further improve various characteristics of acicular alloy magnetic particles containing iron as a main component. Has been requested.

That is, the noise level of the magnetic recording medium refers to the particle size of the acicular alloy magnetic particle powder containing iron as a main component used in the manufacture of the magnetic recording medium, the primary particle diameter constituting one particle, in other words, Therefore, there is a close relationship with the size of the X-ray particle size, and the smaller the particle size or the size of the X-ray particle size, the lower the noise level tends to be. Because of its higher coercive force, there is a need for acicular alloy magnetic particle powder that is fine particles and has a good acicular shape as a main component.

However, in order to obtain fine needle-like alloy magnetic particles containing iron as a main component, fine needle-like hydrous iron oxide particles or needle-like iron oxide particles are used as starting material particles.
When the starting material particles are heat-reduced, the surface activity is large due to the fine particles, so that sintering and shape collapse occur during the heat-reduction, and a needle-shaped alloy mainly composed of iron having a good needle-like shape is obtained. It is difficult to obtain magnetic particle powder.

Conventionally, an object of the present invention is to provide a needle-like alloy magnetic particle powder containing iron as a main component which is fine and has a good needle-like shape while preventing sintering and shape collapse of the particles during heat reduction. Among them, various technical means have been proposed. Among them, a method in which acicular iron oxide hydroxide particles or acicular iron oxide particles are coated in advance with a boron compound and then reduced by heating (see, for example, JP-A-57459, JP-B-54-42832, JP-A-58-48611, JP-A-58-46607, and JP-A-59-56.
No. 03, JP-A-61-174304, JP-B-59-32881, JP-A-61-186410, JP-A-2-197503, JP-A-2-25
0902, JP-A-3-12902, JP-A-3-232201) are considered to be effective.

[0008]

SUMMARY OF THE INVENTION Needles mainly composed of iron, which are fine particles, have a good needle shape, have a high coercive force and a large saturation magnetization, and have a good dispersibility in a vehicle. The magnetic alloy particles are most demanded at present, but those obtained by the above-mentioned known methods have a problem that the dispersibility in a vehicle is insufficient as shown in the following Reference Examples.

Therefore, the present invention relates to a needle containing iron as a main component, which is a fine particle, has a good needle shape, has a high coercive force and a large saturation magnetization, and has a good dispersibility in a vehicle. It is a technical object to provide powdery alloy particles.

[0010]

The above technical objects can be achieved by the present invention as described below.

That is, the present invention comprises, as a main component, iron containing boron obtained by treating the particle surface of acicular iron oxide hydroxide particle powder or acicular iron oxide particle powder with a boron compound and reducing it by heating. to acicular alloy magnetic particles, under inert gas atmosphere, boron content remaining ventilation treatment with alcohol vapor at a temperature and less than 100 ° C. Fe to
It performed Te until reduced to 1% by weight or less in terms of B, then
A method for producing acicular alloy magnetic particle powder containing iron as a main component, characterized in that aeration treatment with steam is performed in an inert gas atmosphere.

Next, various conditions for implementing the present invention will be described.

[0013] The acicular iron oxide hydroxide particles powder is α-FeOO.
H, β-FeOOH, γ-FeOOH and the like can be used.
α-FeOOH can be obtained by wet oxidation of a neutralized precipitate suspension produced by mixing a ferrous salt with an alkali hydroxide or an alkali carbonate. Here, needle-like refers to particles having an axis ratio (major axis diameter / minor axis diameter) of 4 or more,
Needle-shaped as well as spindle-shaped, strip-shaped,
Rice grains and the like can be used. The average major axis diameter is 0.0
5 to 0.3 μm particles having an axial ratio ( major axis diameter / minor axis)
Larger (diameter ), especially 5 or more are preferable.

The needle-like iron oxide particles are composed of α-Fe ₂ O ₃ ,
γ-Fe ₂ O ₃ , Fe ₃ O ₄ , a beltride compound ( F
_{eO X · Fe 2 O 3 (} 0 <x <1)) and the like can be used.
α-Fe ₂ O ₃ can be obtained by heating and dehydrating needle-like hydrous iron oxide α-FeOOH, and Fe ₃ O ₄ is α-FeO
It can be obtained by heating and reducing ₂ O ₃ . γ-Fe ₂ O ₃
Can be obtained by heating and oxidizing Fe ₃ O ₄ . The belt-ride compound is obtained by heating and oxidizing Fe ₃ O ₄ to obtain γ-Fe ₂ O ₃ in a state where it is not completely oxidized, or by heating and reducing α-Fe ₂ O ₃ to obtain Fe ₃ O 4. _Four
Can be obtained on the way. Here, the needle shape refers to particles having an axial ratio (major axis diameter / short axis diameter) of 4 or more, and a needle shape obtained by an ordinary method, a spindle shape, a strip shape, a rice grain shape, or the like can be used. The average major axis diameter is 0.05 to 0.3.
It is preferable that the particles have a large axial ratio ( major axis diameter / short axis diameter), particularly 5 or more.

The acicular hydrous iron oxide particles or acicular iron oxide particles include Al, Ni, and C which are commonly used to improve various properties of acicular alloy magnetic particles containing iron as a main component.
Different elements other than Fe, such as o, Zn, P, Nd, Si, and Ca, may be present.

The boron compound used in the present invention is boron oxide, boric acid, metaboric acid, potassium metaborate, ammonium borate, zinc borate and the like.

A method for coating a boron compound is, for example, a so-called wet method (Japanese Patent Laid-Open Publication No. Hei 10-260,078) in which an aqueous solution containing boron is mixed with acicular iron oxide hydroxide particles or acicular iron oxide particles, stirred, filtered, and dried. No. 2-197503), a so-called dry method of mixing and dispersing acicular hydrated iron oxide particle powder or acicular iron oxide particle powder and boron oxide or borate with a grinder or the like (JP-A-58-48611). Etc.).

The amount of boron added in the coating treatment with the boron compound is about 1.5 to 10 mol% in terms of B with respect to Fe.

The heat reduction in the present invention may be performed by a conventional method, and the reduction temperature is 300 to 500 ° C. 30
When the temperature is lower than 0 ° C., the reduction reaction is insufficient, and it is not possible to obtain needle-like alloy magnetic particles having iron having a large saturation magnetization as a main component. If the temperature exceeds 500 ° C., sintering occurs between the particles and the shape of the particles is broken, so that the coercive force of the acicular alloy magnetic particles containing iron as a main component is reduced.

The needle-like alloy magnetic particles containing iron as a main component after the heat reduction in the present invention are acicular or spindle-shaped, have an average major axis diameter of 0.05 to 0.3 μm, and have an axial ratio ( length). Shaft diameter
/ Short axis diameter ) in the range of 5 to 20. Further, the boron content is about 5% by weight or less in terms of B with respect to Fe .

As the alcohol used in the present invention, alcohol compounds having a volatility of less than 100 ° C., such as methanol, ethanol, propyl alcohol, butyl alcohol and amyl alcohol, can be used.

The inert gas used in the aeration treatment with alcohol vapor of the present invention includes nitrogen gas, argon gas, helium gas and the like. The temperature at the time of the aeration treatment with the alcohol vapor of the present invention is less than 100 ° C. 10
When the temperature exceeds 0 ° C., the magnetic properties such as a decrease in coercive force are adversely affected. In addition, as the temperature decreases, it takes a long time to remove the boron component, from an industrial point of view,
It is preferable to carry out at 50 ° C. or higher.

In the present invention, the aeration treatment with alcohol vapor in an inert gas atmosphere is performed until the amount of boron remaining on the particle surface becomes about 1% by weight or less with respect to Fe in terms of B.

The above-mentioned inert gas may be used as the inert gas used in the aeration treatment with steam of the present invention. The temperature of the ventilation treatment is preferably less than 100 ° C. in order to suppress the adverse effect on the magnetic properties.

In the aeration treatment with steam of the present invention, the concentration of steam is preferably in the range of 1 g / Nm ^{3 to} 50 g / Nm ³ . (Here, g / Nm ³ is a value converted to a concentration g / m ³ in a standard state (0 ° C., 1 atm).)

In the present invention, the aeration treatment with water vapor in an inert gas atmosphere is preferably performed until the carbon content remaining on the particle surface becomes about 0.1% by weight or less.
Further, it is more preferable to carry out until the carbon content remaining on the particle surface becomes about 0.05% by weight or less.

In the present invention, the aeration treatment with alcohol vapor in an inert gas atmosphere and the aeration treatment with water vapor in an inert gas atmosphere are carried out by using a reduction vessel as it is after heat reduction, or by reducing. Needle-like alloy magnetic particles containing iron as a main component can be transferred to another reactor in an inert gas atmosphere.

In the present invention, the ventilation with alcohol vapor in an inert gas atmosphere and the ventilation with water vapor in an inert gas atmosphere are performed by introducing alcohol vapor or water vapor from a device for generating alcohol vapor or water vapor. And at the same time, into the reactor.

When taking out the needle-like alloy magnetic particle powder containing iron as a main component after the aeration treatment into the air, an oxide film is formed on the surface of the needle-like alloy magnetic particle powder containing iron as a main component by a conventional method. Form. In other words, the formation of the oxide film is achieved by increasing the oxygen content in the inert gas after replacing the atmosphere with the inert gas after the ventilation treatment with the alcohol vapor and the steam treatment in the inert gas atmosphere. Finally, it can be carried out by a method of gradually oxidizing with air or the like. However, when the oxide film is formed, it is preferable to control the air content, the air flow rate, and the air flow time and to perform the oxidation under the mildest possible oxidation conditions. When the maximum heat generation temperature exceeds 200 ° C., the saturation magnetization and the coercive force are significantly reduced.

[0030] Immediately after the reduction, an oxide film is formed, and then each aeration treatment can be performed.

The iron-based acicular alloy magnetic particle powder after the aeration treatment in the present invention is acicular or spindle-shaped, has an average major axis diameter of 0.05 to 0.3 μm, and has an axial shape. The ratio ( major axis diameter / short axis diameter ) is 5 to 20. Further, the remaining boron content is about 1% by weight or less in terms of B with respect to Fe , and the remaining carbon content is about 0.1% by weight or less.

[0032]

The most important point in the present invention is that a needle-like alloy magnetic particle powder containing iron as a main component containing boron is subjected to an aeration treatment with an alcohol vapor at a temperature lower than 100 ° C. in an inert gas atmosphere. Residual boron content relative to Fe
It performed Te until reduced to 1% by weight or less in terms of B, then
This is a fact that when aeration treatment with water vapor is performed in an inert gas atmosphere, a needle-like alloy magnetic particle powder containing iron as a main component and having good dispersibility in a vehicle can be obtained. The present inventor considers this phenomenon as follows.

The inventor of the present invention carried out various experiments to change the boron content of the acicular alloy magnetic particle powder containing iron as a main component, in which the amount of boron contained in the coating treatment was changed. It was found that the dispersibility in the vehicle was relatively good. However, when the boron content to be coated is reduced, sintering of the particles during heating reduction, shape collapse, etc. occur, and the magnetic properties are not good,
An acicular alloy magnetic particle powder containing iron as a main component and having excellent magnetic properties and excellent dispersibility in a vehicle was not obtained.

The present inventor believes that the boron remaining on the surface of the acicular alloy magnetic particles containing iron as a main component is present in the form of boron oxide or boric acid. The present inventor has found that this residual boron content is a factor that deteriorates dispersibility in a vehicle when a needle-shaped alloy magnetic particle powder containing iron as a main component is used as a magnetic recording medium,
This phenomenon occurs because the acidity of the surface of the acicular alloy magnetic particle powder containing iron as a main component increases due to the presence of boron that exhibits acidity. It is thought that repulsive force is generated due to the same polarity between the acidic resin having a sulfonic acid group and the like.

The inventor of the present invention has described that acicular alloy magnetic particles containing iron as a main component and containing boron are added under an inert gas atmosphere.
Further, when aeration treatment with alcohol vapor was performed at a temperature lower than 100 ° C., it was confirmed that the boron content before the treatment was reduced after the treatment.

The inventor of the present invention has reported that boron, which is considered to be present on the surface of the acicular alloy magnetic particles containing iron as a main component in the form of boron oxide or boric acid, forms a borate ester by the above-mentioned aeration treatment with alcohol vapor. However, it is considered that boron is removed by being evaporated because it is volatile.

However, the dispersibility in the vehicle of the needle-like alloy magnetic particle powder containing iron as a main component from which the boron content has been removed by the above-mentioned aeration treatment with alcohol vapor was not yet satisfactory. Then, when the particle powder after the treatment was examined, it was confirmed that the carbon amount was increased as compared with before the treatment. For this reason, the inventor
It is considered that the increased carbon content is due to an alkoxyl group formed on the surface of the needle-shaped alloy magnetic particles containing iron as a main component when the borate is formed. Then, it was found that the alkoxyl group formed on the surface of the particles had an adverse effect on the dispersibility in the vehicle.

As a result of extensive studies, the present inventor has conducted aeration treatment with alcohol vapor, and subsequently aeration with water vapor in an inert gas atmosphere to modify the particle surface and disperse the particles in the vehicle. It has been found that the properties are significantly improved. Further, it was confirmed that the amount of carbon remaining in the acicular alloy magnetic particles containing iron as a main component before the treatment was considerably reduced after the treatment.

The inventor of the present invention concluded that the reason why the dispersibility in the vehicle is improved is that the hydroxyl groups suitable for the dispersibility in the vehicle are hydrolyzed by hydrolyzing the alkoxyl groups on the particle surface which adversely affect the dispersibility in the vehicle. It is considered that the formation of the group causes the alkoxyl group to evaporate, resulting in a decrease in the carbon amount due to the alkoxyl group, thereby improving the dispersibility in the vehicle.

The above two processes have no effect on the magnetic properties of the needle-like alloy magnetic particles containing iron as a main component.

The method described in Japanese Patent Application Laid-Open No. 3-232201 mentioned above mainly uses boron-containing iron for the purpose of ensuring safety in removal from the air after reduction and oxidation resistance during storage. This is to remove the boron content by subjecting the needle-like alloy magnetic particle powder as a component to heat-contact treatment with a hydroxyl-containing organic compound, but not to improve the dispersibility in the vehicle.

[0042]

EXAMPLES The effects of the present invention will be described in more detail with reference to the following examples.

The magnetic characteristics of the acicular alloy magnetic particles containing iron as a main component are described in "Vibration sample magnetometer VSM-3S-1".
5 "(manufactured by Toei Industry Co., Ltd.) and an external magnetic field of 10 kO
e.

Further, the specific surface area is “Monosorb MS-1”.
1 "(manufactured by Cantachrome Co., Ltd.) and measured by the BET method using nitrogen gas.

The X-ray particle size (D ₁₁₀ ) represents the size of a crystal particle measured by the X-ray diffraction method, and represents the thickness of the crystal particle in a direction perpendicular to the (110) crystal plane. 11
0) It is a value calculated from the diffraction peak curve of the crystal plane using the following Scherrer equation.

D ₁₁₀ = Kλ / βcos θ where β = half-width (in radians) of a true diffraction peak corrected for the mechanical width caused by the apparatus K = Scherrer constant (0.9) λ = X-ray wavelength (1) .935 °) θ = diffraction angle

Further, the residual amount of boron was measured using a “high frequency plasma emission spectrometer ICAP-575” (manufactured by Nippon Jarrell Ash Co., Ltd.).
"Carbon and sulfur in metal analyzer EMIA-2200" that burns carbon in an oxygen stream and detects it with an infrared spectrometer
(Manufactured by Horiba, Ltd.).

The evaluation of the dispersibility of the needle-shaped alloy magnetic particles containing iron as a main component in the vehicle was performed by the following method.

First, the magnetic particle powder was mixed with a binder resin and a solvent and kneaded at a solid content of 76% by weight using a plast mill for 30 minutes. Thereafter, a predetermined amount of the kneaded material is taken out, added to a glass bottle together with an abrasive, glass beads and a solvent, and mixed for 3 hours with a paint conditioner.
Dispersion was performed. At that time, in order to evaluate the dispersibility, the paint was sampled at each of 0.5 hours, 1 hour and 3 hours during the dispersion.

The magnetic paint extracted at each dispersion time is applied on a polyethylene terephthalate film having a thickness of 14 μm to a thickness of 55 μm using an applicator, and then oriented by a magnetic field of 10 kOe and dried. As a result, a sheet sample piece (1) was obtained. The dispersibility was measured by measuring the surface gloss of the sheet sample (1). The higher the rate of increase in the surface gloss and the value of the surface gloss at 3 hours, the better the dispersibility. . In addition,
The surface gloss of the coating film is a value measured with a gloss meter “UGV-5D” (manufactured by Suga Test Instruments Co., Ltd.) at an incident angle of 45 °, and the value when the standard plate gloss is set to 86.3% is indicated in%. It is shown by.

Next, in order to prepare a magnetic tape, the magnetic paint mixed and dispersed for 3 hours was added with a lubricant and a curing agent, and then mixed and dispersed for another 15 minutes. The composition of the magnetic paint at this time was as follows. Magnetic particle powder 100 parts by weight Vinyl chloride-vinyl acetate copolymer resin having sodium sulfonate group 10 parts by weight Polyurethane resin having sodium sulfonate group 10 parts by weight Abrasive 10 parts by weight Lubricant 2.5 parts by weight Hardener 5 parts by weight Part Cyclohexanone 52.5 parts by weight Methyl ethyl ketone 130.5 parts by weight Toluene 78.3 parts by weight The obtained magnetic paint was applied to a polyethylene terephthalate film having a thickness of 14 μm by using an applicator at 55 μm.
, And then oriented by a magnetic field of 10 kOe, followed by drying to obtain a sheet sample (2). After calendering the obtained sheet sample piece, a curing reaction was performed at 60 ° C. for 24 hours, and a 0.5-inch width slit was obtained to obtain a magnetic tape.

The surface roughness Ra of the magnetic tape is set to “Sur
fcom-575A "(manufactured by Tokyo Seimitsu Co., Ltd.). The smaller the value of the surface roughness, the better the dispersibility of the magnetic particle powder in the vehicle.

The magnetic properties of the magnetic tape were the same as in the case of the magnetic particle powder, "Vibrating sample magnetometer VSM-3S
-15 "(manufactured by Toei Industry Co., Ltd.)
It was measured by applying up to kOe.

Example 1 An acicular α-FeOOH particle powder (major axis diameter: 0.21 μm, axial ratio: 11.0) was coated with an aluminum compound and a cobalt compound, followed by filtration and washing with water to obtain an acicular needle. α-Fe
The OOH cake was mixed and stirred in a 1.5 wt% boric acid aqueous solution, filtered and filtered to obtain acicular α-Fe containing 0.7 wt% boric acid in terms of B with respect to acicular α-FeOOH solids.
An OOH cake was obtained. Next, the obtained acicular α-Fe
The OOH cake was formed into a column having a diameter of 2 to 3 mm and a length of 4 to 8 mm, and dried. Further, this was heated and dehydrated to obtain a molded product composed of acicular α-Fe ₂ O ₃ particles.

The above α-Fe ₂ O ₃ molded product was charged into a fixed-bed reactor, and was heated at 400 ° C. and 3.5 in a hydrogen stream.
The mixture was reduced by heating for a period of time to obtain a molded product comprising needle-like alloy magnetic particles containing iron as a main component and containing boron.

The obtained needle-like alloy magnetic particles containing iron as a main component were cooled in a nitrogen stream, and then methanol vapor and nitrogen gas at 30 ° C. were introduced into a fixed-bed reactor to conduct the reaction at 70 ° C. under a nitrogen gas atmosphere. For 2 hours. Next, water vapor and nitrogen gas are introduced into the reactor, and the water vapor having a dew point of 9 ° C. is used at 95 ° C. in a nitrogen gas atmosphere.
For 2 hours.

Thereafter, the inside of the reactor was sufficiently replaced with nitrogen, and then gradually oxidized with air while gradually increasing the oxygen content in the nitrogen gas to form an oxide film on the particle surfaces. .

The characteristics of the obtained magnetic particle powder mainly composed of iron are as follows: major axis diameter 0.16 μm, axial ratio 10.1, specific surface area 53 m ² / g, X-ray particle diameter 162 °, residual boron amount 0 .9
5 wt%, carbon residual amount 0.024 wt%, coercive force 160
9 Oe, saturation magnetization 130 emu / g.

The surface gloss of the sheet sample (1) at 3 hours was 142.2%. Further, each characteristic of the magnetic tape prepared by using the obtained needle-like alloy magnetic particle powder containing iron as a main component has a surface roughness Ra of 10.4 n.
m, coercive force 1606 Oe, squareness ratio 0.75, degree of orientation 1.
60.

Example 2 A needle-like alloy containing iron as a main component was prepared in the same manner as in Example 1 except that the temperature for aeration treatment with methanol vapor in a nitrogen gas atmosphere was changed to 90 ° C. Particle powder was obtained.

The characteristics of the magnetic particles are as follows.
14 μm, axial ratio 8.7, specific surface area 53 m ² / g, X-ray particle size 161 °, residual boron content 0.93 wt%, residual carbon content 0.032 wt%, coercive force 1606 Oe, saturation magnetization 13
It was 0 emu / g.

The surface gloss of the sheet sample piece (1) prepared in the same manner as in Example 1 was 3 hours at 14 hours.
2.5%. Further, each characteristic of the magnetic tape prepared by using the magnetic particle powder has a surface roughness Ra of 10.4 n.
m, coercive force 1598 Oe, squareness ratio 0.74, degree of orientation 1.
55.

Comparative Example 1 Needle-like alloy magnetic particles containing iron as a main component were obtained in the same manner as in Example 1 except that aeration treatment with water vapor was not performed in a nitrogen gas atmosphere.

The characteristics of the magnetic particles are as follows.
16 μm, axial ratio 9.2, specific surface area 52 m ² / g, X-ray particle size 161 °, residual amount of boron 0.98 wt%, residual amount of carbon 0.337 wt%, coercive force 1610 Oe, saturation magnetization 13
It was 1 emu / g.

The surface gloss at 3 hours of the sheet sample (1) prepared in the same manner as in Example 1 was 84.
It was 0%. Further, each characteristic of the magnetic tape prepared using the magnetic particle powder has a surface roughness Ra of 18.8 nm,
Coercive force 1597 Oe, squareness ratio 0.70, degree of orientation 1.38
Met.

COMPARATIVE EXAMPLE 2 In a nitrogen gas atmosphere, the temperature of the aeration treatment with methanol vapor was set to 150 ° C., and the subsequent aeration treatment with a nitrogen gas containing water vapor was not performed. Thus, acicular alloy magnetic particle powder containing as a main component was obtained.

The characteristics of the magnetic particles are as follows.
15 μm, axial ratio 8.3, specific surface area 50 m ² / g, X-ray particle size 161 °, residual boron content 0.86 wt%, residual carbon content 0.398 wt%, coercive force 1588 Oe, saturation magnetization 12
It was 7 emu / g.

The surface gloss of the sheet sample (1) prepared in the same manner as in Example 1 was 3 hours at 10 hours.
6.0%. Further, each characteristic of the magnetic tape prepared by using the magnetic particle powder has a surface roughness Ra of 16.4n.
m, coercive force 1584 Oe, squareness ratio 0.70, degree of orientation 1.
37.

Reference Example Aeration treatment with methanol vapor in an inert gas atmosphere,
In addition, needle-like alloy magnetic particles containing iron as a main component were obtained in the same manner as in Example 1 except that aeration treatment with water vapor was not performed in an inert gas atmosphere.

The characteristics of the magnetic particles are as follows.
16 μm, axial ratio 8.5, specific surface area 52 m ² / g, X-ray particle size 161 °, residual boron content 1.23 wt%, residual carbon content 0.034 wt%, coercive force 1608 Oe, saturation magnetization 12
It was 9 emu / g.

The surface gloss at 3 hours of the sheet sample prepared in the same manner as in Example 1 was 128.7%.
Met. The magnetic tape produced using the magnetic particle powder had the following characteristics: surface roughness Ra of 18.0 nm, coercive force of 1610 Oe, squareness ratio of 0.71, and degree of orientation of 1.46.

Table 1 shows the properties of the iron-based acicular alloy magnetic particle powders obtained in the above Examples, Comparative Examples and Reference Examples, and the magnetic tapes prepared using the magnetic particle powders. It summarizes each characteristic.

[0073]

[Table 1]

From Table 1, Examples 1 and 2 show Comparative Example 1,
Since the value of the surface roughness is very low as compared with Comparative Example 2 and Reference Example, it can be seen that the dispersibility in the vehicle of the magnetic particle powder obtained by the present invention is remarkably improved. Further, in Examples 1 and 2, the dispersibility in the vehicle was remarkably improved because the squareness ratio and the degree of orientation in the tape properties were clearly improved as compared with Comparative Examples 1 and 2 and Reference Example. You can see that there is.

Time-dependent changes in surface gloss when the iron-based needle-like alloy magnetic particles obtained in Examples 1 and 2 and Comparative Examples 1 and 2 and Reference Example were mixed and dispersed in a vehicle. It is shown. 1. In FIG. 1, .largecircle. Represents the time change of the surface glossiness in the vehicle of Example 1, .DELTA. Represents the Example 2, Δ represents the Comparative Example 1, ▲ represents the Comparative Example 2, and ● represents the Reference Example. I have.

As shown in FIG. 1, Examples 1 and 2 are Comparative Examples 1 and 2.
2 and the rise rate of the surface glossiness is larger than that of the reference example,
Further, since the value of the surface gloss after 3 hours is also large, it can be seen that the dispersibility in the vehicle of the magnetic particle powder obtained by the present invention is remarkably improved.

[0077]

According to the present invention, as described in the previous embodiment, the particles are fine, have a high coercive force and a large saturation magnetization,
In addition, it is possible to obtain needle-like alloy magnetic particle powder containing iron as a main component for magnetic recording media with good dispersibility in the vehicle, so that the most demanded for high density recording, high output, and low noise level at present. It is suitable as a magnetic particle powder for use.

[Brief description of the drawings]

FIG. 1 shows a change over time of the surface gloss when a needle-like alloy magnetic particle powder containing iron as a main component is mixed and dispersed in a vehicle.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B22F 9/22 B22F 1/00

Claims (1)

(57) [Claims] An acicular iron-containing iron-containing powder obtained by treating a particle surface of acicular iron oxide hydroxide particles or acicular iron oxide particles with a boron compound and then reducing by heating. Under the inert gas atmosphere,
And performing aeration treatment with alcohol vapor at a temperature of less than 100 ° C. until the remaining boron content is reduced to 1% by weight or less with respect to Fe , and then performing aeration treatment with steam in an inert gas atmosphere. A method for producing acicular alloy magnetic particle powder containing iron as a main component.