JP3087804B2 - A granulated product for iron alloy magnetic particles for magnetic recording, a method for producing the same, and a method for producing iron alloy magnetic particles for magnetic recording using the granulated product. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a granulated material for iron alloy magnetic particles which is suitable as a starting material for producing magnetic particles for magnetic recording and a method for producing the same. And a method for producing iron alloy magnetic particles for magnetic recording.

[0002]

2. Description of the Related Art In recent years, long-time recording, miniaturization and lightening of magnetic recording / reproducing devices for video and audio have been intensified. In particular, VTRs (video tape recorders) have been remarkably popularized in recent years. 2. Description of the Related Art VTRs aiming at time recording and reduction in size and weight have been actively developed. On the other hand, there is an increasing demand for higher performance of a magnetic tape as a magnetic recording medium, that is, an improvement in output characteristics.

[0003] This characteristic of a magnetic recording medium is closely related to the magnetic particles used in the magnetic recording medium, and in recent years, it has a higher coercive force and a larger saturation magnetization than conventional iron oxide magnetic particles. Attention is focused on iron alloy magnetic particles having
It is used for magnetic recording media such as digital audio tape (DAT), 8 mm video tape, Hi-8 tape, and video floppy, and has been put to practical use.

In recent years, the demand for improving the properties of these iron alloy magnetic particles has not stopped, and from the viewpoint of improving the output characteristics of the magnetic recording medium, the distribution of coercive force and saturation magnetization between the particles of the iron alloy magnetic particles has been increased. It is strongly required that the width be as small as possible.

As is well known, iron alloy magnetic particles include acicular goethite particles, acicular hematite particles obtained by heating and dehydrating the acicular goethite particles at a temperature of about 300 ° C., or non-reducing 300-850 ° C under atmosphere
The needle-shaped hematite particles which have been densified by heating in the above temperature range are used as a starting material, and the starting material is heated and reduced under a flow of a reducing gas such as hydrogen gas.

[0006] The most important step that determines the properties of the obtained iron alloy magnetic particles is the step of heating and reducing the starting material. The heating and reducing apparatus used in the heating and reduction is performed while rolling the starting material. There are known a rotary furnace reduction device for performing heat reduction, a fluidized bed reduction device for performing heat reduction while flowing a starting material, and a fixed bed reduction device for fixing and heating and reducing a starting material.

In producing iron alloy magnetic particles by heating and reducing acicular goethite particles or acicular hematite particles as a starting material, when a rotary furnace reduction device or a fluidized bed reduction device is used, the starting material is tumbled or fluidized. By doing so, a uniform mixing state of the reducing atmosphere is obtained, so that the reaction proceeds uniformly. However, on the other hand, the starting material rolls or flows, causing collisions or friction between the raw material particles or between the raw material particles and the reactor wall. This has the disadvantage that the magnetic properties of the particles are easily reduced and the magnetic properties of the particles are accordingly reduced. On the other hand, when a fixed bed reduction device is used, the starting material particles are heated and reduced almost in a stationary state, so that sintering of the particles or deformation of the primary particles due to collision or friction between the material particles due to rolling or flowing are performed. Is less likely to occur. As described above, when heat reduction is performed by the fixed bed reduction device, in order to prevent the starting material from flowing against the gas flow rate, a starting material obtained by granulation using various means is used.

[0008] Conventionally, in the production of iron alloy magnetic particles, a method using a fixed bed reduction apparatus is disclosed in JP-B-61-36.
No. 048, Japanese Patent Publication No. 1-52441, Japanese Patent Publication No. 1
Japanese Patent Application Laid-Open Nos. 52524/1994, 52443/1994, 52444/1994 and 62915/1979, and the like.

[0009] As a method of granulating the starting material in advance,
For example, α-Fe ₂ O ₃ particles, which are finely pulverized powder, and water sprayed at a predetermined ratio are supplied to a granulator at a predetermined ratio to obtain granulated powder (Japanese Patent Application Laid-Open No. 63-88807). A method of dispersing fine iron oxide powder in water into water, compressing and dehydrating the powder to a water content of 60 to 80 wt% by a filter press, and forming a block (JP-A-57-54205, JP-A-57-205205)
-116706) and the like.

[0010]

SUMMARY OF THE INVENTION An iron alloy magnetic particle having a high coercive force and a large saturation magnetization and having a small distribution width of the coercive force and the saturation magnetization between particles is industrially and economically advantageous. Production is currently the most demanded, but when a granulated material according to the above-mentioned known method is used as a starting material using a fixed bed reduction device, coercive force and saturation magnetization between particles are used. Since each distribution width is large, it is not possible to obtain iron alloy magnetic particles that sufficiently satisfy the above-mentioned characteristics.

In the case of heating reduction using a fixed bed reduction apparatus, the distribution width of the coercive force and the saturation magnetization between the obtained iron alloy magnetic particles is increased because the granulated material from which fine powder is easily generated is a starting material. It is because it is used as.

That is, since the above-mentioned conventional granulated product uses water as a binder, it becomes a granulated product having low strength.
Under conditions of relatively high aeration gas linear velocity used to increase the reduction efficiency during heating reduction, fine vibrations occur in the granulated material, and fine powder is generated due to friction between granulated materials having low strength. In addition, powdering occurs due to thermal expansion or the like at the time of charging (transferring) the starting material into the fixed bed reducing device before the heat reduction, and also at the time of heating, thereby generating fine powder. When the granulated material having such a weak strength is used as a starting material and reduced by a fixed bed reduction device, fine powder generated is locally present in the bed, and the pressure loss in that portion increases. Is generated, the degree of reduction of the particles to be treated becomes non-uniform, the reduction efficiency is very poor, and as a result, an iron alloy having a large magnetic characteristic distribution (each distribution of coercive force and saturation magnetization) between particles. It becomes magnetic particles.

In view of the above, the present invention provides a method of producing iron alloy magnetic particles using a fixed bed reduction apparatus, in which iron alloy magnetic particles having a distribution width of coercive force and saturation magnetization between particles as small as possible can be obtained. It is a technical object to provide a granulated material for recording iron alloy magnetic particles.

The above technical object can be achieved by the present invention as described below. That is, the present invention relates to a needle-shaped hydrous ferric oxide.
Applicable to water or hot water for particle powder or acicular iron oxide particle powder
Granulate by adding soluble semi-synthetic starch or semi-synthetic cellulose.
Average granulation diameter at Te is a 1 to 5 mm, a bulk density of 0.
Magnetic recording reduced by forming a fixed layer comprising acicular hydrous ferric oxide granules or acicular iron oxide granules of 5 g / cm ³ or more and a powdering ratio of 40% or less. Granules for magnetic particles for iron alloy, needle-like hydrous ferric oxide particles or a suspension of needle-like iron oxide particles in water, semi-synthetic starch or semi-synthetic soluble in water or hot water Cellulose is added in an amount of 0.1 to 5.0 with respect to the acicular ferric hydroxide oxide particles or the acicular iron oxide particles.
After wt% added and stirring, the preparation of the magnetic recording granules for iron alloy magnetic particles, characterized in that the granule compression obtained by dehydration cake and granulated for said magnetic recording iron alloy magnetic particles A method for producing iron alloy magnetic particles for magnetic recording, comprising forming a fixed layer of particles and heating and reducing the particles in a reducing gas to obtain iron alloy magnetic particles.

Next, various conditions for implementing the present invention will be described. Needle-like hydrous used in the present invention
As ferric particles, the average major axis diameter is 0.05 to 1.0 μm
m, preferably about 0.05 to 0.5 μm, and α-FeOOH having an axial ratio (major axis diameter / minor axis diameter-the same applies hereinafter) of 3 or more;
β-FeOOH or γ-FeOOH particles can be used. In addition, as the acicular iron oxide particles, about 3
The needle-like hematite particles and the needle-like hydrous ferric oxide particles obtained by heating and dehydrating at a temperature of 00 ° C.
Densified acicular hematite particles obtained by heat treatment in a temperature range of 0 to 850 ° C., acicular maghemite particles, and a beltride compound ( FeO x .Fe ₂ O ₃ , 0
Any one of <x <1) and needle-like magnetite particles obtained by heating and dehydrating the needle-like hydrous ferric oxide particles at a temperature of about 300 ° C. can be used.

Further, the acicular hydrous used in the present invention
Ferric oxide particles or acicular iron oxide particles include Al, N which are usually used to improve various properties of iron alloy magnetic particles.
One or more kinds of different elements other than Fe such as i, Co, B, Zn, P, and Si may be used in combination in the inside of the particle or coated on the surface of the particle. Incidentally, the acicular particles in the present invention refers to particles having an axial ratio (major axis diameter / minor axis diameter) of 3 or more,
The shape is not limited to a needle shape, and includes a spindle shape, a rice grain shape, and a strip shape.

The granules for magnetic particles of iron alloys for magnetic recording according to the present invention are prepared by adding acicular hydrous ferric oxide particles or acicular iron oxide particles to a suspension of water in water or hot water. After adding and stirring a soluble semi-synthetic starch or a semi-synthetic cellulose, the cake obtained by compression dehydration is granulated and obtained.

In the present invention, examples of the semi-synthetic starch to be added include soluble starch, positive starch, starch substituted with a hydrophilic group (such as carboxymethyldialdehyde), and the like.
And then the semi-synthetic cellulose, viscose, hydrophilic groups (methyl, ethyl, hydroxy ether, carboxyl, etc.) cellulose substituted with, and these are water Moshiku
Is soluble in warm water.

The amount of the semisynthetic starch or semisynthetic cellulose is in the range of 0.1 to 5.0 wt% with respect to acicular ferric oxide particles or acicular iron oxide particles. Industrially, a small amount is preferable as long as the effect of addition can be exhibited.
If the amount is less than 10% by weight, the effects of the present invention cannot be exhibited. If the content exceeds 5.0% by weight, undesired adverse effects on the reduction due to the residual organic matter appear, causing problems such as a reduction in coercive force and saturation magnetization and a long time required for the reduction.

Means for granulating and shaping the acicular hydrous ferric oxide particles or the acicular iron oxide particles in the present invention include various methods such as rolling granulation, compression granulation, crushing granulation, and extrusion granulation. However, after adding and stirring the semi-synthetic starch or semi-synthetic cellulose in a suspension containing acicular hematite particles, the cake obtained by compression dehydration by a filter press is extruded and granulated by a granulation method. The method is industrially preferred.

The granules for magnetic particles of the iron alloy for magnetic recording according to the present invention have an average grain size of 1 to 5 mm, a bulk density of 0.5 g / cm ³ or more, and a powdering ratio of 40%. Must be:

If the average granulated particle size of the granulated product is less than 1 mm, the granulated particles begin to flow largely due to the reducing gas flow, causing collisions and friction between the particles, sintering of the particles and primary particles. This is not desirable because the shape of the particles is distorted, and undesired phenomena occur in terms of equipment such as finely divided particles scattered outside the system and become dust, causing clogging of the exhaust gas filter.

On the other hand, when the distance exceeds 5 mm, it takes time for the reducing gas to pass through the inside of the particles, and at the same time, the diffusion of water vapor in the granulated particles that controls the reduction reaction becomes slow. , The productivity is inferior, and the magnetic properties deteriorate, which is not preferable.

When the bulk density of the granulated material is less than 0.5 g / cm ³ , the strength of the granulated material tends to be weak and the powdering ratio tends to be large, so that fine powder is liable to be generated. Since the weight of one material is reduced, if the gas flow rate is increased for the purpose of increasing the reduction efficiency, the granulated material becomes easier to flow, and the sintering of the particles and the shape of the primary particles due to friction and collision between the granulated materials Collapse easily occurs.

Further, when the powdered ratio of the granulated material exceeds 40%, the fine particles of the granulated material are transferred at the time of transferring the starting material into the fixed bed reducing device or during the heat reduction process. Powdering occurs due to friction due to vibration, thermal expansion due to heating, and the like, and fine powder is easily generated.

Using such granules as starting materials,
When reducing with a fixed bed reduction device, the generated fine powder is locally present in the bed, and the pressure loss in that portion is increased, so that the aeration gas drifts and the reduction of the particles to be treated progresses. This is not preferable because iron alloy magnetic particles having a nonuniform degree and a very low reduction efficiency and a large magnetic property distribution width between particles can be obtained.

[0027] The iron alloy magnetic particles for magnetic recording according to the present invention are prepared by adding acicular ferric hydroxide particles or acicular iron oxide particles to a suspension of water in water or hot water-soluble half-water. After adding and stirring synthetic starch or semi-synthetic cellulose, the cake obtained by compression dehydration is granulated and formed to have an average granulated particle size of 1 to 5 mm and a bulk density of 0.5 g / cm ^3. Above, it can be obtained by heating and reducing a needle-like hydrous ferric oxide granule or a needle-like iron oxide granule having a powdering ratio of 40% or less in a reducing gas.

The heat reduction in a reducing gas can be performed in a temperature range of 350 to 550 ° C. under a flow of hydrogen gas.

In the present invention, the heat-reduced iron alloy magnetic particles are prepared by a known method, for example, immersion in an organic solvent such as toluene, and after the atmosphere of the reduced iron alloy magnetic particles is once replaced with an inert gas. Alternatively, it can be taken out into the air by a method such as gradually oxidizing by gradually increasing the oxygen content in the inert gas into air while gradually increasing the oxygen content.

[0030]

First, the most important point in the present invention is that a semi-synthetic material soluble in water or warm water is added to a suspension of needle-like hydrous ferric oxide particles or needle-like iron oxide particles in water. Starch or semi-synthetic cellulose is added to acicular hematite particles in an amount of 0.1%.
When the cake obtained by compressing and dehydrating after adding and stirring the mixture by granulation is formed with an average particle diameter of 1 to 5 mm and a bulk density of 0.5 g / cm ³ or more, The point is that a granulated product for iron alloy magnetic particles for magnetic recording having a powdering ratio of 40% or less can be obtained.

Further, when the granules for magnetic particles of iron alloy for magnetic recording are heat-reduced in a reducing gas, they have a high coercive force and a large saturation magnetization, and have a high coercive force between particles. The point is that iron alloy magnetic particles having a small distribution width of saturation magnetization can be obtained.

In the present invention, the reason why iron alloy magnetic particles having small distribution widths of coercive force and saturation magnetization between particles can be obtained is as follows. The present inventor adds needles by adding semi-synthetic starch or semi-synthetic cellulose. Jo hydrous oxide to ferric <br/> strongly binding particles or acicular iron oxide particles each other, it is possible to increase the intensity, it is possible to prevent generation of fine powder effectively. As a result, it is possible to prevent the drift of the ventilation gas in the fixed bed, and the progress of the reduction of the granulated material (particles to be treated) is also uniform. As a result, the iron having a small magnetic characteristic distribution width between the particles is obtained. We believe that alloy magnetic particles can be obtained.

The bulk density of the granulated product is 0.5 g / cm ³
If the bulk density is higher than the above, the distance between the primary particles forming the granulated material becomes short, so that the diffusion rate of the moisture generated by the reduction inside the granulated material becomes slow. This means that the water vapor partial pressure inside the granules is easily maintained in a high state. Therefore, in general, when the bulk density becomes large, it becomes difficult to control the partial pressure of water vapor inside the granulated material, and there is a problem that sintering between particles is easily caused.

However, according to the method according to the present invention, a semi-synthetic starch or semi-synthetic soluble in water or warm water is introduced into a suspension of acicular ferric hydroxide oxide particles or acicular iron oxide particles suspended in water. After adding and stirring cellulose, compressing and dewatering, and then compressing and dehydrating the cake, when the cake obtained is granulated and formed, even if the bulk density is 0.5 g / cm ³ or more, the granulated product has a high bulk density. The problem is solved because the added semi-synthetic starch or semi-synthetic cellulose keeps the distance between the primary particles at an appropriate level.

Conventionally, a method similar to semi-synthetic starch or semi-synthetic cellulose for producing iron alloy magnetic particles is described in JP-A-55-82408. This method is a method using starch as a reducing agent, and uses a semi-synthetic starch or a semi-synthetic cellulose in which needle-like hydrous ferric oxide particles or needle-like iron oxide particles are soluble in water or hot water before heat reduction. The present invention is different from the present invention in which granulation is performed by its purpose, configuration and effect.

[0036]

Next, the present invention will be described with reference to examples and comparative examples. In addition, the major axis and the axial ratio (major axis diameter / minor axis diameter) of the particles in the following Examples and Comparative Examples are shown by the average value of numerical values measured from an electron micrograph. The magnetic properties of the iron alloy magnetic particles were measured using an "oscillating sample magnetometer VSM-3S-15" (manufactured by Toei Industry Co., Ltd.) under an external magnetic field of 10 KOe.

The powdering ratio is shown by a value measured by the following method. Acicular ferric oxide granules or acicular oxide Tetsuzo Tsububutsu 100g and 12.5mmφ steel ball 200 having a granulation diameter size of more than 1mm
g, 8.5 cm inside diameter, 8.5 cm height, 48 internal volumes
After putting into a 2cm ³ steel container, the peripheral speed is 50rpm
Mix for 1 hour at m. Next, acicular hydrous oxyhydroxide having a particle size of less than 1 mm in a steel container.
Weigh ferric granulation or acicular oxide Tetsuzo grain product. (1
acicular ferric oxide granules or acicular oxide Tetsuzo Tsububutsu weight / measurement before the acicular ferric oxide granules of less than mm or acicular oxide Tetsuzo Tsububutsu weight (100 g)) × 100 = powdering rate (%)

<Manufacture of Granules for Iron Alloy Magnetic Particles for Magnetic Recording> Examples 1 to 15, Comparative Examples 1 to 5; Example 1 A long particle surface coated with an Al compound, a Co compound and a B compound. Needle-like goethite particles having an axis of 0.23 μm and an axis ratio (major axis diameter / short axis diameter) of 11 (Al = 1.
(0% by weight, Co = 4.6% by weight, B = 0.9% by weight) in air at 400 ° C. to obtain acicular hematite particles.

Next, the obtained acicular hematite particles were finely pulverized using a wet pulverizer to obtain a dispersion of acicular hematite particles.

Next, the needle-like hematite particle suspension obtained above was adjusted to a solid concentration of 8% by weight, and a solution obtained by dissolving a positive starch substituted with an aliphatic tertiary amine in the suspension ( After adding and stirring, the mixture was compressed and dewatered by a filter press to obtain a cake having a water content of 35% by weight. After extrusion molding using the same, drying was performed at a temperature of 100 ° C. to obtain an acicular iron oxide granulated product. The obtained acicular iron oxide granulated product has an average granulated particle size of 2.
5 mm, the bulk density is 0.58 g / cm ³ ,
The powdering rate was 33%.

Examples 2 to 15, Comparative Examples 1 to 5 Types of needle-like goethite particles, types and amounts of additional elements, presence or absence of heat treatment and heating temperature, types and amounts of semi-synthetic starch or semi-synthetic cellulose, and A granulated product for iron alloy magnetic particles was produced in the same manner as in Example 1 except that the pore size of the molding screen was variously changed. Table 1 shows the main manufacturing conditions and various characteristics at this time. The object to be treated in Example 14 was acicular goethite particles, and the object to be treated in Example 15 was needles obtained by heating and dehydrating acicular goethite particles at a temperature of 400 ° C., and then reducing by heating at a temperature of 300 ° C. Magnetite particles

<Production of Iron Alloy Magnetic Particles> Examples 16 to 30, Comparative Examples 6 to 10; Example 16 5 kg of the acicular iron oxide granules obtained in Example 1 was applied to an inner diameter of 16 kg.
0 mm fixed bed reduction device, followed by 200 Nl
Per minute, and hydrogen reduction was performed at a temperature of 410 ° C. to obtain iron alloy magnetic particle granules. The reduction time was 20 hours.

The obtained iron alloy magnetic particle granules in the fixed layer were immersed in toluene and taken out, and the iron alloy magnetic particle granules were sieved with a sieve having an opening of 1 mm, and sieved with 1 mm or more and 1 mm or more.
An iron alloy magnetic particle granulated product having a diameter of less than 1 mm was obtained. Next, a thin stable oxide film was formed on the surface while evaporating toluene.

In the obtained iron alloy magnetic particle granules,
The coercive force Hc of the iron alloy magnetic particles having a size of 1 mm or more is 1610 Oe, and the saturation magnetization s is 158 em.
u / g, and the coercive force Hc of the iron alloy magnetic particles having a size of less than 1 mm is 1595 Oe and the saturation magnetization σ
s was 156 emu / g. The distribution widths of the coercive force and the saturation magnetization of the ferromagnetic particles were small.

Examples 17 to 30, Comparative Examples 6 to 10 When the granules for iron alloy magnetic particles obtained in Examples 2 to 15 and Comparative Examples 1 to 5 were heat-reduced, various reduction temperatures and reduction times were used. Except having changed, it carried out similarly to Example 16, and manufactured the iron alloy magnetic particle granule. Table 2 shows the main manufacturing conditions and various characteristics at this time.

The distribution widths of the coercive force and the saturation magnetization between the particles of the iron alloy magnetic particles obtained in Examples 17 to 30 were small, but were obtained in Comparative Examples 6 to 10. The distribution width between the particles of the obtained iron alloy magnetic particle granules was large.

[0047]

[Table 1]

[0048]

[Table 2]

[0049]

According to the present invention, the granulated material for iron alloy magnetic particles for magnetic recording according to the present invention has an average granulated particle size of 1 as described in the above embodiment.
５5 mm, a bulk density of 0.5 g / cm ³ or more, and a powdered ratio of 40% or less .
Since iron granules or acicular oxide Tetsuzo grain product, when used in a fixed bed reduction apparatus, it generates less fines, therefore without drift also occurs vent gas in the layer during the heat-reduction,
Since the degree of reduction of the granulated material (workpiece) is also uniform, it has the most required high coercive force and large saturation magnetization at present, and furthermore, each of the coercive force and saturation magnetization between particles. It is suitable as a starting material for obtaining iron alloy magnetic particles having a small distribution width.

[0050] Further, according to the manufacturing method of the magnetic recording iron alloy magnetic particles according to the present invention, as shown in supra embodiment, specific acicular ferric oxide granules described above as starting materials or Since the needle-shaped iron oxide granules are used, when used in a fixed bed reduction apparatus, the generation of fine powder is small, and thus the aeration gas in the bed is not deviated during heating and reduction. Since the degree of reduction of the processed material is also uniform, an iron alloy having the most required high coercive force and large saturation magnetization at present, and having a small distribution width of the coercive force and saturation magnetization between particles. Since magnetic particles can be obtained, they are suitable as magnetic particles for high density recording.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI C01G 49/06 C01G 49/06 A G11B 5/706 G11B 5/706 H01F 1/06 H01F 1/06 L (72) Masayuki Kami 4-1-2, Funairi Minami, Naka-ku, Hiroshima City, Hiroshima Prefecture Inside the Creative Center of Toda Kogyo Co., Ltd. (72) Inventor Hiroo Mishima 4-1-2, Funamiri Minami, Naka-ku, Hiroshima City, Hiroshima Hiroshima Prefecture Toda Kogyo Co., Ltd. Examiner in the center Hitoshi Misaki (56) References JP-A-57-116716 (JP, A) JP-A-63-88807 (JP, A) JP-A-4-62906 (JP, A) JP-A-4-144208 (JP, A) JP-A-54-33258 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01G 49/02-49/06 B22F 1/00, 9/00

Claims (3)

(57) [Claims] Claims: 1. A needle-like hydrous ferric oxide particle powder or a needle-like acid
Semi-synthetic starch soluble in water or warm water in iron fossil particles or
The average granulated particle diameter obtained by adding and granulating semi-synthetic cellulose is 1 to 5 mm, the bulk density is 0.5 g / cm ³ or more, and the powdering ratio measured by the following measurement method is A granulated material for magnetic particles of an iron alloy for magnetic recording, which is reduced by forming a fixed layer of a needle-shaped hydrous ferric oxide granulated material or a needle-shaped iron oxide granulated material of 40% or less. 100 g of a needle-like hydrous ferric oxide granulation or a needle-like iron oxide granulation having a granulated particle size of more than 1 mm and 200 g of 12.5 mmφ steel balls were prepared with an inner diameter of 8.5 cm and a height of 8. 5 cm, put in a steel container with an inner volume of 482 cm ³ ,
Mix for 1 hour at 0 rpm. Next, a needle-like hydrous ferric oxide granule or a needle-like iron oxide granule having a granulated particle size of less than 1 mm in a steel container is weighed.
(Weight of needle-like hydrous ferric oxide granules or needle-like iron oxide granules less than 1 mm / weight of needle-like hydrous ferric oxide granules or needle-like iron oxide granules before measurement (100 g)) × 100 = powdering rate (%) 2. A method in which a needle-like hydrous ferric oxide particle or a needle-like iron oxide particle is suspended in water, and a semi-synthetic starch or a semi-synthetic cellulose soluble in water or hot water is acicular. The cake obtained by adding and stirring 0.1 to 5.0% by weight of ferric oxide particles or needle-like iron oxide particles, and then compressing and dewatering the resulting product is granulated. Production method of iron alloy magnetic particles for magnetic recording. 3. A magnetic recording material according to claim 1, wherein the granules for magnetic particles of iron alloy for magnetic recording are formed in a fixed layer and reduced by heating in a reducing gas to form magnetic particles of iron alloy. Manufacturing method of iron alloy magnetic particles.