JPH06345439A - Granulated substance for magnetic iron oxide particle for magnetic recording, production thereof and production of magnetic iron oxide granular powder for magnetic recording with the use of the granulated substance - Google Patents

Abstract

PURPOSE:To provide a granulated substance for magnetic iron oxide particle for magnetic recording composed of needle-like granulated substance of iron(III) oxide hydrate or needle-like granulated substance of iron(III) oxide and to provide a production method capable of obtaining the granulated substance on an industrial scale. CONSTITUTION:Needle-like particles of iron(III) oxide hydrate or needle-like particles of iron(III) oxide is suspended in water. Semisynthetic starch or semisynthetic cellulose, which is soluble in water or hot water, is added to a suspension in the ratio of 0.1-5.0wt.% to the needle-like particles of iron(III) oxide hydrate or the needle-like particles of iron(III) oxide. After mixing of the liquid, a cake is obtained by press-dehydration and this is granulated to obtain the granulated substance for magnetic iron oxide particles for magnetic recording. The granulated substance has an average granulated size of 1-7mm, an apparent density of >=0.3g/cm<3> and a powder ratio of <=40%. This is reduced under heating in a reducing gas to obtain needle-like magnetite particles or thereafter further oxidized to obtain needle-like maghemite particles. The objective magnetic iron oxide granular powder for magnetic recording is obtained from either of those particles, optionally after the modification with Co or Co and Fe<2+>.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In recent years, with the progress of miniaturization and weight reduction of magnetic recording / reproducing equipment, there is an increasing need to improve the performance of recording media such as magnetic tapes and magnetic disks. That is, high recording density, high sensitivity characteristics and high output characteristics are required. The characteristics of the magnetic particle powder required to satisfy the above requirements for the magnetic recording medium are to have a high coercive force and to minimize the distribution width of the coercive force between the particles.

That is, in order to increase the sensitivity and output of the magnetic recording medium, it is necessary for the magnetic particle powder to have as high a coercive force as possible. "Development of materials and high-dispersion technology of magnetic powder" (1982), page 310, "The direction of improving magnetic tape performance was to improve sensitivity and output.
The emphasis was on increasing the coercive force of the acicular γ-Fe ₂ O ₃ particle powder. ".

In order to increase the output of the magnetic recording medium,
Japanese Unexamined Patent Publication No. 63-26821 shows "FIG. 1 is a diagram showing the relationship between the SFD measured on the above-mentioned magnetic disk and the recording / reproducing output. As is clear from Fig. 1, the relationship between the recording and reproducing output is a straight line, which means that the recording and reproducing output can be increased by using a ferromagnetic powder having a small SFD. In order to increase the recording / reproducing output, it is desirable that the SFD is small, and in order to obtain an output higher than usual, it is 0.6
The following S. F. D. is necessary. As stated,
The S. F. D. (Switching F
The field distribution is required to be small, and for that purpose, the coercive force distribution width between particles of the magnetic particle powder is required to be small.

As is well known, the magnitude of coercive force of magnetic particle powder is shape anisotropy. It depends on any one of crystal anisotropy, strain anisotropy and exchange anisotropy, or their interaction.

Magnetic iron oxide particle powders such as acicular magnetite particle powders and acicular maghemite particle powders currently used as magnetic particle powders for magnetic recording are compared by utilizing anisotropy derived from their shape. It has a very high coercive force.

These known magnetic particle powders are obtained by reducing goethite particles as a starting material or needle-like hematite particles obtained by heating and dehydrating the goethite particles in a reducing gas such as hydrogen to obtain magnetite particles. Further, it is obtained by oxidizing the magnetite particles in air to form maghemite particles.

Known acicular magnetic iron oxide particles modified with Co or modified with Co and Fe ²⁺ are prepared by using acicular magnetite particles or acicular maghemite particles as precursor particles. It is obtained by dispersing body particles in an alkaline suspension containing cobalt hydroxide or an alkaline suspension containing cobalt hydroxide / ferrous hydroxide and subjecting the dispersion to heat treatment.

The most important step that influences various characteristics of the obtained magnetic iron oxide particle powder is the heating and firing step of the starting raw material. As the firing apparatus used in the heating and firing, the starting raw material is rolled. A rotary firing furnace for heating and firing, a fluidization firing furnace for heating and firing while flowing a starting material, and the like are known.

When magnetic iron oxide particles are produced by heating and firing acicular goethite particles or acicular hematite particles as a starting material, the starting material is tumbled or fluidized when a rotary firing furnace or a fluidized firing furnace is used. By doing so, a uniform mixed state of the firing atmosphere is obtained, so that the reaction proceeds uniformly. However, on the other hand, since the starting material rolls or flows, collision or friction occurs between the raw material particles or between the raw material particles and the reactor wall, so that sintering between particles or collapse of the shape of particles occurs in the firing process. It has a drawback that it is liable to occur and the magnetic properties of the particles are accordingly deteriorated.

Therefore, it is necessary to use, as a starting material, a desired granulated molded product which is less likely to generate fine powder due to collision or friction between the raw material particles or between the raw material particles and the reactor wall.

As a method of granulating the starting material in advance,
In the technical field of producing metal magnetic powder, for example, a method of obtaining granulated powder by supplying α-Fe ₂ O ₃ particles that are finely pulverized products and water sprayed at a predetermined ratio to a granulator. (Japanese Patent Application Laid-Open No. 63-88807) or fine needle-shaped iron oxide powder is dispersed in water, and the water content is 60 by a filter press.
To 80 wt% and dehydrated, and molded into a lump (Japanese Patent Application Laid-Open No. 57-54205, Japanese Patent Application Laid-Open No. 57-11670).
No. 6 publication) and the like are known.

[0013]

The industrial and economical production of magnetic iron oxide particles having a high coercive force and a small coercive force distribution width among the particles is currently under way.
Although most demanded, when a granulated product according to the above-mentioned known method is used as a starting material using a rotary type or fluidized type firing furnace, the coercive force distribution width between particles is large. It is not possible to obtain magnetic iron oxide particles that sufficiently satisfy various characteristics.

In the case of heating and calcination using a rotary type or fluidized type calcination furnace, the distribution width of the coercive force between the particles of the obtained magnetic iron oxide particles becomes large because the starting material is a granulated product in which fine powder is easily generated. Because it is used.

That is, since the above-mentioned conventional granules use water as a binder, they become weak granules.
Granules vibrate slightly under the conditions of relatively high aeration gas linear velocity adopted to increase the oxidation / reduction efficiency during heating and firing, and fine powder is generated due to friction between granules with weak strength. In addition, when starting materials before heating and firing are transferred (transferred) into the heating and firing furnace, and due to thermal expansion during heating and the like, pulverization occurs and fine powder is generated. In this way, when a granulated product with weak strength is used as a starting material and fine particles generated when heated and fired in a rotary or fluidized firing furnace are locally present in the layer, the pressure loss in that portion becomes large. As a result, aeration gas drifts, the progress of oxidation / reduction of the particles to be treated becomes non-uniform, and the oxidation / reduction efficiency is also very poor, resulting in a distribution of magnetic properties between particles (coercive force and saturation magnetization Each distribution) becomes a magnetic iron oxide particle having a large width.

Therefore, it is a technical object of the present invention to obtain a magnetic iron oxide particle powder for magnetic recording which has a high coercive force and has a distribution width of coercive force between particles as small as possible.

The above technical problems can be achieved by the present invention as follows. That is, in the present invention, the average grain size is 1 to 7
mm, the bulk density is 0.3 g / cm ³ or more,
Further, a granular material for magnetic iron oxide particles for magnetic recording comprising a needle-shaped ferric oxide hydroxide granule or a needle-shaped ferric oxide granule having a pulverization rate of 40% or less, and a needle-shaped hydrous hydroxide fraction. Needle-like ferric hydroxide particles or needle-shaped ferric oxide particles or needle-shaped particles of semi-synthetic starch or semi-synthetic cellulose soluble in water or warm water in a suspension prepared by suspending ferric oxide particles or acicular ferric oxide particles in water. 0.1 for ferric oxide particles
˜5.0 wt% is added and stirred, and then compression-dewatering is performed to granulate and form a cake, and a method for producing a granulated product for magnetic iron oxide particles for magnetic recording, needle-shaped hydrous hydroxide Magnetically characterized in that iron granules or acicular ferric oxide granules are heated and reduced in a reducing gas to obtain acicular magnetite particles, or further oxidized to acicular maghemite particles. A method for producing a magnetic iron oxide particle powder for recording and the acicular magnetite particles or acicular maghemite particles as precursor particles, the precursor particles being an alkali suspension containing cobalt hydroxide or cobalt hydroxide / hydroxide no. To obtain acicular magnetite particles or acicular maghemite particles modified with Co or modified with Co and Fe ²⁺ by dispersing in an alkaline suspension containing iron and subjecting the dispersion to heat treatment. Characterized by magnetism It is a manufacturing method of the recording magnetic iron oxide particles.

Next, various conditions for carrying out the present invention will be described. The acicular hydrous ferric oxide particles used in the present invention have an average major axis diameter of 0.1 to 1.0 μm,
Α-FeOOH having an axial ratio (major axis diameter / minor axis diameter-the same applies below) of 3 or more, preferably about 0.2 to 0.6 μm,
β-FeOOH or γ-FeOOH particles can be used.
Further, as the acicular ferric oxide particles, acicular hematite particles obtained by heating and dehydrating the acicular hydrous ferric oxide particles at a temperature of about 300 ° C and acicular hydrous ferric oxide particles are obtained. Densified needle-like hematite particles obtained by heat treatment in a temperature range of 300 to 850 ° C. in a non-reducing atmosphere, and
Needle-shaped maghetite particles, bertolide compound ( FeO x
Any of Fe ₂ O ₃ and 0 <x <1) can be used.

The acicular hydrous ferric oxide particles or acicular ferric oxide particles used in the present invention are usually used to improve various properties of the magnetic iron oxide particles.
One or more kinds of different elements other than Fe, such as 1, Ni, Co, B, Zn, P and Si, may be used in combination and contained in the inside of the particle, or may be coated on the surface of the particle.

The acicular particles in the present invention refer to particles having an axial ratio of 3 or more, and the shape thereof is not limited to acicular, and includes spindle-shaped, rice granular and strip-shaped particles.

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

In the present invention, examples of the semi-synthetic starch to be added include soluble starch, positive starch, starch substituted with a hydrophilic group (carboxymethyldialdehyde, etc.), and the semi-synthetic cellulose includes viscose and hydrophilic. Groups (methyl,
Examples thereof include cellulose substituted with ethyl, hydroxy ether, carboxyl, etc., and these are soluble in water or warm water.

The amount of the semi-synthetic starch or semi-synthetic cellulose added is in the range of 0.1 to 5.0% by weight based on the acicular ferric hydroxide particles or acicular ferric oxide particles. Industrially, a small amount is preferable as long as the effect of addition can appear, but
If it is less than 0.1% by weight, the effect of the present invention cannot be exhibited. If it exceeds 5.0% by weight, the adverse effect of the residual organic matter on the reduction remarkably appears, and the coercive force and the saturation magnetization are lowered, and further the reduction takes a long time, which is not preferable.

As means for granulating the acicular hydrous ferric oxide particles or acicular ferric oxide particles in the present invention, there are various types such as rolling granulation, compression granulation, crush granulation, extrusion granulation and the like. However, after adding and stirring the semi-synthetic starch or semi-synthetic cellulose in a suspension containing acicular hydrous ferric oxide particles or acicular ferric oxide particles, compression dehydration is performed by a filter press. A method of granulating the cake obtained by extrusion by a granulation method is industrially preferable.

The granulated product for magnetic iron oxide particles for magnetic recording in the present invention has an average particle size of 1 to 7 mm, a bulk density of 0.3 g / cm ³ or more, and a pulverization rate of 40%. Must be:

When the average particle size of the granulated material for magnetic iron oxide particles for magnetic recording is less than 1 mm, the granulated particles start to flow largely due to the flow of aeration gas, causing collision and friction between particles, It is not preferable because sintering of particles or deformation of the shape of primary particles occurs, and finely pulverized particles scatter out of the system to become dust and cause clogging of exhaust gas filter, which is not preferable in terms of equipment Occurs.

On the other hand, when it exceeds 7 mm, it takes a long time for the aeration gas, especially the reducing gas, to reach the inside of the particles, and at the same time, the diffusion of water vapor in the granulated particles which controls the reduction reaction becomes slow. Therefore, the reduction time becomes long, the productivity is deteriorated, and the magnetic characteristics are deteriorated, which is not preferable.

When the bulk density of the granulated material for magnetic iron oxide particles for magnetic recording is less than 0.3 g / cm ³ , the strength of the granulated material becomes weak and the pulverization rate tends to be large, so that fine powder is generated. It is liable to occur, which makes the particles more likely to sinter and deteriorates the magnetic properties, which is not preferable.

Further, when the pulverization rate of the granulated material for magnetic iron oxide particles for magnetic recording exceeds 40%, the starting raw material is transferred into the firing furnace or the like, and heated or oxidized. In the reduction process, pulverization occurs due to friction due to slight vibration of the granulated product, thermal expansion due to heating, etc., and fine powder is easily generated.

Using such a granulated product as a starting material,
When heating and oxidizing / reducing in a rotary or fluidized firing furnace, the generated fine powder is locally present in the bed, and since the pressure loss at that portion is large, a drift of the aeration gas occurs and The progress of oxidation / reduction of treated particles becomes non-uniform,
The reduction efficiency is also very poor, and magnetic iron oxide particles having a wide magnetic property distribution width between particles are obtained, which is not preferable.

The heat reduction temperature in the present invention can be carried out in the range of 300 to 500 ° C. by a conventional method. Also,
The oxidation temperature can be set in the range of 200 to 500 ° C. by a conventional method.

Co of the magnetic iron oxide particle powder in the present invention
Alternatively, the transformation of Co and Fe ²⁺ can be carried out by a conventional method, for example, Japanese Patent Publication No. 52-24237 and Japanese Patent Publication No. 5-5.
The precursor particles contain cobalt hydroxide, or cobalt hydroxide / ferrous hydroxide, as described in JP-A No. 2-24238, JP-B-52-36571 and JP-B-52-36863. It is carried out by dispersing in an alkaline suspension and heat-treating the dispersion.

The cobalt hydroxide in the present invention can be obtained by using a water-soluble cobalt salt such as cobalt sulfate or cobalt chloride and an aqueous alkali hydroxide solution such as sodium hydroxide or potassium hydroxide.

The ferrous hydroxide in the present invention is obtained by using a water-soluble ferrous salt such as ferrous sulfate and ferrous chloride and an aqueous alkali hydroxide solution such as sodium hydroxide and potassium hydroxide. .

Upon conversion of Co or Co and Fe ²⁺ ,
The conditions for the heat treatment are 50 to 1 in a non-oxidizing atmosphere.
It is preferable to carry out in the temperature range of 00 ° C.

The temperature of the transformation of Co or Co and Fe ²⁺ is
It is related to the treatment time, and if the temperature is 50 ° C. or lower, it is difficult to generate magnetite particles or maghemite particles modified with Co or modified with Co and Fe ²⁺ , and even if it is generated, the treatment is extremely long. Need.

The amount of the water-soluble cobalt salt modified in the present invention is 0.5 to 15.0 atomic% in terms of Co based on Fe. If it is less than 0.5 atom%, the effect of improving the coercive force of the obtained acicular magnetite particles or maghemite particles cannot be sufficiently achieved. 1
If it exceeds 5.0 atomic%, the effect of reducing the coercive force distribution of the obtained acicular magnetite particles or maghemite particles is not sufficient.

Almost all of the added water-soluble cobalt salt is used for the transformation of the magnetic iron oxide particles on the particle surface.

Considering the coercive force and coercive force distribution of needle-shaped magnetite particles or maghemite particles, 2.0 to 1
3.0 atom% is preferable.

[0040]

First of all, the most important point in the present invention is that the acicular hydrous ferric oxide particles or acicular ferric oxide particles are suspended in water and are soluble in water or warm water. The semi-synthetic starch or semi-synthetic cellulose is added to the acicular hydrous iron oxide particles or acicular ferric oxide particles in an amount of 0.1 to 5.0% by weight, stirred, and then compressed and dehydrated to obtain a cake. When granulated, the average particle size is 1 to 7 mm and the bulk density is 0.3 g.
/ Cm ³ or more, yet is that the magnetic recording magnetic granules for iron oxide particles powdering of not more than 40% is obtained.

By adding the above-mentioned semi-synthetic starch or semi-synthetic cellulose, it is possible to strengthen the bond between the acicular hydrous ferric oxide particles or acicular ferric oxide particles and to strengthen the strength of the particles. The occurrence can be effectively prevented.
As a result, it is possible to prevent the drift of the aeration gas in the firing furnace, and the degree of progress of the oxidation / reduction of the granulated material (particles to be treated) becomes uniform. As a result, the magnetic characteristic distribution width between particles can be reduced. It is possible to obtain small magnetic iron oxide particles.

The bulk density of the granulated product is 0.3 g / cm ^3.
When the bulk density is higher than, the distance between the primary particles forming the granulated product becomes short, so that the diffusion rate of water generated by the reduction inside the granulated product becomes slow. This means that the steam partial pressure inside the granulated product is easily maintained in a high state. Therefore, generally, when the bulk density becomes high, it becomes difficult to control the partial pressure of water vapor inside the granulated product, which causes a problem that sintering between particles is likely to occur.

However, by the method according to the invention,
After adding and stirring semi-synthetic starch or semi-synthetic cellulose soluble in water or warm water into a suspension obtained by suspending acicular hydrous ferric oxide particles or acicular ferric oxide particles in water, compressing After dehydration, if the cake obtained by compression dehydration is granulated,
Even in the case of a high bulk density granulated product having a bulk density of 0.3 g / cm ³ or more, the problem is solved because the added semi-synthetic starch or semi-synthetic cellulose maintains an appropriate primary interparticle distance.

It is to be noted that, unlike the conventional technique for producing magnetic iron oxide particles, a method similar to semi-synthetic starch or semi-synthetic cellulose used for producing iron alloy magnetic particles is disclosed in JP-A-55-82408. There is a method described in Japanese Patent Publication. This method is a method in which starch is used as a reducing agent, and the acicular hydrous ferric oxide particles or acicular ferric oxide particles are soluble in water or warm water before heating and oxidizing / reducing semi-synthetic starch or semi-synthetic starch. The present invention differs from the present invention in which granulation and molding are performed using synthetic cellulose in the purpose, constitution and effect.

[0045]

The present invention will be described below with reference to Examples and Comparative Examples. The major axis and 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 the numerical values measured from electron micrographs. The magnetic characteristics of the magnetic iron oxide particles were measured by using an "oscillating sample magnetometer VSM-3S-15" (manufactured by Toei Industry Co., Ltd.) with an external magnetic field of 10 KOe.

The pulverization rate is a value measured by the following method. 100 g of acicular hydrous ferric oxide granules or acicular ferric oxide granules having a particle size of more than 1 mm
2.5gφ steel ball 200g and inner diameter 8.
The mixture is put into a steel container having a size of 5 cm, a height of 8.5 cm and an internal volume of 482 cm ³ , and then mixed at a peripheral speed of 50 rpm for 1 hour. Next, the acicular hydrous ferric oxide granules or acicular ferric oxide granules having a particle size of less than 1 mm are weighed in a steel container. (Weight of acicular hydrous ferric oxide granules or acicular ferric oxide granules less than 1 mm / acicular ferric hydroxide ferric oxide granules or acicular ferric oxide granule weight before measurement) (100g)) x 10
0 = pulverization rate (%)

Example 1 36 aqueous solution of ferrous sulfate containing Fe ²⁺ 1.50 mol / l
0 l of 4.6-N N previously prepared in the reactor
Add to 540 liters of aOH aqueous solution, pH 13.2, temperature 45
Generation of ferrous hydroxide particles was carried out at ° C. continue,
Air-oxidation gave goethite particles in the form of needles having a major axis of 0.3 μm and an axial ratio of 14.

Next, a suspension is prepared by suspending acicular goethite particles in water, and the acicular goethite particle suspension is
A solution in which the solid content concentration was adjusted to 8% by weight, and the positive starch substituted with the aliphatic tertiary amine was dissolved in the suspension (corresponding to 1 wt% of the positive starch amount with respect to the needle-shaped goethite particles). Was added and stirred, and then compressed and dehydrated by a filter press to obtain a cake having a water content of 35% by weight, followed by extrusion molding using a molding screen having a pore size of 3 mm, followed by drying at a temperature of 105 ° C. and needle. A granular hydrous ferric oxide granule was obtained. The obtained acicular hydrous iron oxide granules had an average particle diameter of 3.7 mm and a bulk density of 0.35 g / cm.
³ , and the pulverization rate was 30%.

Examples 2 to 6 and Comparative Examples 1 to 5 As Example 1 except that the starting material type, heating temperature, type and addition amount of semi-synthetic starch or semi-synthetic cellulose, and the pore size of the molding screen were variously changed. In the same manner, a granulated product for magnetic iron oxide particles for magnetic recording was manufactured. Table 1 shows the main manufacturing conditions and various characteristics at this time.

[0050]

[Table 1]

In Example 6, needle-shaped hematite particles were used instead of the needle-shaped goethite particles as the object to be treated.

<Production of acicular goethite particles or acicular maghemite particles> Examples 7 to 13 and Comparative Examples 6 to 10;

Example 7 The acicular hydrous ferric oxide granulated product 1300 obtained in Example 1
g was heat-treated in air at 400 ° C. to obtain a needle-shaped hematite particle granulated product.

Next, the obtained acicular hematite particle granulated product was put into a retort reduction vessel, and H ₂ gas was aerated at a rate of 2 l / min while being driven and rotated, and the reduction temperature was 400 ° C.
To obtain a needle-shaped magnetite particle granulated product.

The obtained needle-shaped magnetite particle granulated product was sieved with a sieve having an opening of 1 mm to obtain a needle-shaped magnetite particle granulated product of 1 mm or more and less than 1 mm.

In the obtained acicular magnetite particle granules, the coercive force Hc of the acicular magnetite particle granules having a size of 1 mm or more is 445 Oe and the saturation magnetization σs is 8.
4.8 emu / g, transfer P / T is 57.5 dB, erasing property is 53.5 dB, and coercive force Hc of acicular magnetite particle granules having a size of less than 1 mm is 430O.
e, the saturation magnetization σs was 83.5 emu / g, the transfer P / T was 55.9 dB, and the erasing characteristic was 52.6 dB. The distribution widths of coercive force and saturation magnetization of both needle-shaped magnetite particles were small.

Further, the magnetic properties of the acicular magnetite particle powder obtained by pulverizing the acicular magnetite particle granules before the sieving by a usual method have coercive force Hc of 441 O.
e, the saturation magnetization σs was 84.3 emu / g, the transfer P / T was 57.3 dB, and the erasing property was 53.1 dB.

Further, the magnetic paint prepared by adding the obtained acicular magnetite particle powder, resin and solvent in the following proportions and mixing and dispersing for 2 hours with a paint conditioner was applied to a polyethylene terephthalate film having a thickness of 25 μm. A magnetic tape was obtained by applying a film having a thickness of 40 μm using an applicator, then orienting it in a magnetic field of 1650 Gauss and then drying it.

1.5 mmφ glass beads 100 g Needle-like magnetite particle powder 15 g Toluene 5.6 g Phosphate ester (GAFAC RE-610 manufactured by Toho Kagaku) 0.6 g Lecithin 0.6 g Vinyl chloride vinyl acetate copolymer resin (Vinyllite VAGH Union Car) Bite Co., Ltd.) 3.75 g Butadiene acrylonitrile rubber (Hycar 1432J Nippon Zeon Co., Ltd.) 0.75 g Methyl isobutyl ketone: Methyl ethyl ketone: Toluene = 3: 1: 1 mixed solution 40.5 g

The coercive force Hc of this magnetic tape is 420 O
e, the squareness ratio Rs is 0.80, and the S. F. D. Was 0.44.

Example 8 The acicular hydrous ferric oxide granulated product 1300 obtained in Example 1
g was heat-treated in air at 400 ° C. to obtain a needle-shaped hematite particle granulated product.

Next, the obtained needle-shaped hematite particle granulated product was put into a retort reduction vessel, and H ₂ gas was aerated at a rate of 2 l / min while being driven and rotated, and the reduction temperature was 400 ° C.
To obtain a needle-shaped magnetite particle granulated product.

The obtained acicular magnetite particle granules were oxidized in air at 300 ° C. for 60 minutes to obtain acicular maghemite particle granules.

The obtained acicular maghemite particle granules are sieved with a sieve having an opening of 1 mm and the acicular maghemite particle granules having a size of 1 mm or more and less than 1 mm and the acicular maghemite particle granules before sieving are usually used. The powder was pulverized by the above method to obtain a needle-shaped maghemite particle powder.

A magnetic tape was manufactured in the same manner as in Example 7 using the obtained acicular maghemite particle powder.

Table 2 shows the main manufacturing conditions and various characteristics at this time.

Examples 9 to 13 and Comparative Examples 6 to 10 Needle-shaped maghematite was prepared in the same manner as in Example 8 except that the kinds of the starting granules, dehydration temperature, reduction temperature and oxidation temperature were variously changed. A granulated product or acicular maghemite particle powder was obtained. Also, a magnetic tape was manufactured. Table 2 shows the main manufacturing conditions and various characteristics at this time.

[0068]

[Table 2]

<Production of acicular magnetite particle powder or acicular maghemite particle powder modified with Co or Co and Fe ²⁺ > Examples 14-18, Comparative Examples 11-12;

Example 14 800 g of the acicular magnetite particle powder obtained in Example 7
0.41 mol of cobalt and ferrous iron using cobalt sulfate and ferrous sulfate while preventing air from entering as much as possible.
It is poured into 8 l of water in which 43 mol is dissolved and dispersed until it becomes a fine slurry, and then 18-
1650 ml of an aqueous NaOH solution of N was added, and water was further added to make the total volume 13 l to obtain a dispersion liquid having an OH group concentration of 2 mol / l. The temperature of the dispersion was raised to 100 ° C., the slurry was taken out after stirring for 5 hours at this temperature, filtered, washed with water, dried at 60 ° C., and needle-shaped denatured with Co and Fe ^2+. Magnetite particles Particle powder was obtained.

Regarding the magnetic characteristics of the obtained particles, the coercive force Hc was 748 Oe, the saturation magnetization σs was 84.7 emu / g, the transfer P / T was 58.9 dB, and the erasing characteristic was 53.5 dB.

A magnetic tape was manufactured in the same manner as in Example 7 using the obtained acicular magnetite particles powder modified with Co and Fe ²⁺ . Table 3 shows the magnetic characteristics at this time.

Examples 15 to 18 and Comparative Examples 11 to 12 Co or Co and Fe were prepared in the same manner as in Example 14 except that the type of precursor, the amount of Co added, and the amount of Fe ²⁺ added were variously changed.
^A powder of acicular maghemite particles modified with ²⁺ was obtained. Also, a magnetic tape was manufactured. Table 3 shows the main manufacturing conditions and various characteristics at this time.

[0074]

[Table 3]

[0075]

The granules for magnetic iron oxide particles for magnetic recording according to the present invention have an average particle size of 1 as shown in the above-mentioned Examples.
Needle-shaped ferric oxide hydrous granules or acicular ferric oxide granules having a bulk density of 0.3 g / cm ³ or more and a pulverization rate of 40% or less. Therefore, when using a rotary type or fluidized type firing furnace, generation of fine powder is small,
Therefore, the uneven flow of the ventilation gas in the layer at the time of heating and firing does not occur, and the progress of the oxidation / reduction of the granulated product (processed object) becomes uniform, so that the coercive force currently required most is obtained. It is suitable as a starting material for obtaining magnetic iron oxide particles for magnetic recording having a small coercive force distribution width between particles.

According to the method for producing the magnetic iron oxide particle powder for magnetic recording according to the present invention, as shown in the above-mentioned Examples, the specific needle-shaped ferric oxide hydroxide granules or needles described above are used as the starting material. Since a granular ferric oxide granules are used, when a rotary type or fluidized type firing furnace is used, generation of fine powder is small, and accordingly, aeration gas in the layer during heating and firing does not occur, and Since the progress of oxidation / reduction of particles (objects to be treated) is also uniform, it has the most required coercive force at present and has a small distribution width of coercive force between particles. Since iron oxide particles can be obtained, it is suitable as a magnetic particle powder for high recording density, high sensitivity, and high output.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kunihiro Kawachi Inventor, Kunihiro, 4-1-2, Funarinami, Naka-ku, Hiroshima City, Toda Kogyo Co., Ltd. (72) Inventor, Hiroki Kamon, Naka-ku, Hiroshima City, Hiroshima Prefecture 4-1-2 Fununairi Minami Toda Industry Co., Ltd. Creative Center

Claims (4)

[Claims] 1. A needle-shaped material having an average grain size of 1 to 7 mm, a bulk density of 0.3 g / cm ³ or more, and a pulverization rate of 40% or less measured by the following measuring method. A granule for magnetic recording magnetic iron oxide particles, comprising a ferric oxide hydrate granule or acicular ferric oxide granule. 100 g of acicular hydrous ferric oxide granules or acicular ferric oxide granules having a particle size of more than 1 mm
2.5gφ steel ball 200g and inner diameter 8.
The mixture is put into a steel container having a size of 5 cm, a height of 8.5 cm and an internal volume of 482 cm ³ , and then mixed at a peripheral speed of 50 rpm for 1 hour. Next, the acicular hydrous ferric oxide granules or acicular ferric oxide granules having a particle size of less than 1 mm are weighed in a steel container. (Weight of acicular hydrous ferric oxide granules or acicular ferric oxide granules less than 1 mm / acicular ferric hydroxide ferric oxide granules or acicular ferric oxide granule weight before measurement) (100g)) x 10
0 = pulverization rate (%) 2. A semi-synthetic starch or semi-synthetic cellulose soluble in water or warm water is added to a suspension obtained by suspending acicular hydrous ferric oxide particles or acicular ferric oxide particles in water. 0.1 to 5 relative to the ferric oxide-containing ferric oxide particles or acicular ferric oxide particles.
2. The method for producing a granulated product for magnetic iron oxide particles for magnetic recording according to claim 1, wherein the cake obtained by adding 0% by weight and stirring and then compressing and dehydrating is granulated. 3. The needle-shaped hydrous ferric oxide granules or the acicular ferric oxide granules according to claim 1 are heated and reduced in a reducing gas to obtain acicular magnetite particles, or A method for producing a magnetic iron oxide particle powder for magnetic recording, which is characterized by further oxidizing to obtain acicular maghemite particles. 4. The acicular magnetite particles or acicular maghemite particles obtained by the method according to claim 3 are used as precursor particles, and the precursor particles are used as an alkaline suspension containing cobalt hydroxide or cobalt hydroxide. Needle-like magnetite particles or needle-like maghemite particles modified with Co or modified with Co and Fe ²⁺ by dispersing the solution in an alkaline suspension containing ferrous hydroxide and heating the dispersion. For producing magnetic iron oxide particle powder for magnetic recording, characterized in that