JP2970706B2 - Method for producing acicular magnetic iron oxide particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a uniform particle size, no mixture of dendritic particles, a large axial ratio (major axis diameter / minor axis diameter), and a coercive force distribution. It is an object of the present invention to provide a needle-like magnetic iron oxide particle powder which is excellent in a square shape and a degree of orientation.

[0002]

2. Description of the Related Art In recent years, as the size and weight of magnetic recording / reproducing devices have been reduced, the need for higher performance for recording media such as magnetic tapes and magnetic disks has been increasing. That is, high recording density, high sensitivity characteristics, high output characteristics, and the like are required. The characteristics of the magnetic material particles required to satisfy the above requirements for the magnetic recording medium are to have high coercive force and excellent dispersibility.

That is, in order to increase the sensitivity and output of a magnetic recording medium, it is necessary that the magnetic particle powder has a coercive force as high as possible. "Development of Magnetic Materials and Technology for Highly Dispersing Magnetic Powder" (1982), p. 310, "Improvement of magnetic tape performance was driven by high sensitivity and high output."
The emphasis was on increasing the coercive force の of the acicular γ-Fe ₂ O ₃ particles. ".

In order to achieve a high recording density of a magnetic recording medium, the aforementioned “Development of Magnetic Materials and Technology for Highly Dispersing Magnetic Powder”, No. 3
The condition for high-density recording on a coated tape is to be able to maintain high output characteristics with low noise for a short wavelength signal on page 12, and for this purpose, both the coercive force Hc and the residual magnetization Br are high. It is necessary for the magnetic recording medium to have a high coercive force and a large remanent Br, and for that purpose, the magnetic particle powder must be used. It is required to have a high coercive force and excellent dispersibility in a vehicle, orientation in a coating film, and filling property.

In order to increase the output of a magnetic recording medium,
FIG. 1 of JP-A-63-26821 shows the relationship between the SFD measured for the above magnetic disk and the recording / reproducing output. 1, the relationship between the recording and reproduction output becomes a straight line, which indicates that the recording and reproduction 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.
The following S. F. D. is necessary. "
S. of magnetic recording medium F. D. (Switching F
It is necessary that the field distribution is small, and for that purpose, the distribution width of the coercive force of the magnetic particle powder needs to be small.

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

At present, magnetic iron oxide particles such as acicular magnetite particles and acicular maghemite particles used as magnetic particles for magnetic recording use the anisotropy derived from the shape thereof. By increasing the axial ratio (major axis diameter / minor axis diameter), a relatively high coercive force is obtained.

These known magnetic particle powders are obtained by reducing goethite particles as a starting material or acicular hematite particles obtained by heat-treating the goethite particles into magnetite particles in a reducing gas such as hydrogen. By and
It is obtained by oxidizing the magnetite particles in the air to form maghemite particles.

The known acicular magnetic iron oxide particles modified with Co or modified with Co and Fe are prepared by using acicular magnetite particles or acicular maghemite particles as precursor particles. 0.5 to 15.
The precursor particles are dispersed in an alkaline suspension containing cobalt hydroxide or an alkaline suspension containing cobalt hydroxide and ferrous hydroxide so as to contain 0 atomic% of Co, and the dispersion is heated. It is obtained by processing.

The residual magnetization Br of the magnetic recording medium depends on the dispersibility of the magnetic particle powder in the vehicle, the orientation in the coating film, and the filling property. It is required that the magnetic particles to be dispersed in the powder have a uniform particle size, do not contain dendritic particles, and have a large axial ratio (major axis diameter / minor axis diameter).

[0011] As described above, the particle size is uniform, dendritic particles are not mixed, and the large axial ratio (long axis diameter /
Magnetic particle powder having a short axis diameter) and having excellent squareness and degree of orientation is currently the most required, and in order to obtain a magnetic particle powder having such characteristics, It is required that the starting material, goethite particle powder, has a uniform particle size, does not contain dendritic particles, and has a large axis ratio (major axis diameter / minor axis diameter).

Conventionally, as a method for producing goethite particle powder as a starting material, a suspension containing a ferrous hydroxide colloid obtained by adding an equivalent or more of an aqueous alkali hydroxide solution to a ferrous salt aqueous solution has a pH of 11 or less. A method of producing needle-like goethite particles by passing an oxygen-containing gas at a temperature of 80 ° C. or lower to carry out an oxidation reaction (Japanese Patent Publication No.
No. 5610), spindle-shaped goethite particles are formed by passing an oxygen-containing gas through a suspension containing FeCO ₃ obtained by reacting an aqueous ferrous salt solution and an aqueous alkali carbonate solution to carry out an acid reaction. Generation method (Japanese Unexamined Patent Publication No.
No. 80999) and an oxygen-containing gas is passed through a ferrous hydroxide colloid or a ferrous salt aqueous solution containing iron carbonate obtained by adding an equivalent amount or less of an aqueous alkali hydroxide solution or an aqueous alkali carbonate solution to a ferrous salt aqueous solution. By performing an oxidation reaction to generate needle-like goethite core particles, and then to an aqueous ferrous salt solution containing the needle-like goethite core particles, an equivalent amount or more with respect to the amount of Fe ²⁺ in the aqueous ferrous salt solution. A method of growing the acicular goethite nucleus particles by adding an aqueous alkali hydroxide solution and then passing an oxygen-containing gas therethrough (Japanese Patent Publication No. 59-4876).
No. 6, JP-A-59-128293 and JP-A-5-128293.
JP-A-9-128294, JP-A-59-128295 and JP-A-60-21818) are known.

[0013]

The particle size is uniform, dendritic particles are not mixed, and a large axial ratio (long axis diameter / short axis diameter) is excellent, and the coercive force distribution is excellent. Needle-like magnetic iron oxide particles powder which is more excellent in squareness and degree of orientation is currently the most required,
In the case of the above-mentioned method for producing goethite particle powder as a starting material, needle-like goethite particles having a large axial ratio (major axis diameter / minor axis diameter), especially 10 or more, are produced, but dendritic particles are obtained. Are mixed, and it cannot be said that the particles have a uniform particle size in terms of the particle size.

In the case of the above-mentioned method, spindle-shaped particles having a uniform particle size and containing no dendritic particles are produced. On the other hand, an axial ratio (major axis diameter / minor axis) is obtained. Diameter)
Has a drawback that particles having a large axial ratio (major axis diameter / short axis diameter) are difficult to generate. In particular, this phenomenon becomes more pronounced as the major axis diameter of the formed particles decreases. There is a tendency. Various attempts have been made to increase the axial ratio (major axis diameter / minor axis diameter) of goethite particles having a spindle shape, but at most about 17-18, which is not yet satisfactory.

The above-mentioned method is characterized by various properties of the acicular goethite particles obtained by each of the above-mentioned methods and
That is, although it is intended to improve the particle size, the axial ratio (major axis diameter / minor axis diameter), and the presence or absence of dendritic particles, goethite particle powder having sufficiently satisfactory properties has not yet been obtained.

The acicular magnetic iron oxide particles obtained by using these acicular goethite particles as starting material particles are also uniform in particle size and free of dendritic particles.
It is hard to say that it has a large axis ratio (major axis diameter / short axis diameter).

Therefore, the present invention provides a uniform particle size without dendritic particles, a large axial ratio (major axis diameter / minor axis diameter), and excellent coercive force distribution. It is another technical object of the present invention to obtain needle-like magnetic iron oxide particles having an excellent squareness and a high degree of orientation.

[0018]

The above technical objects can be achieved by the present invention as described below. That is, the present invention is obtained by reacting an aqueous solution of ferrous salt with an aqueous solution of an alkali hydroxide or an aqueous solution of an alkali carbonate or an aqueous solution of an alkali hydroxide / alkali carbonate which is less than the equivalent to Fe ²⁺ in the aqueous solution of a ferrous salt. The ferrous hydroxide colloid or the iron-containing precipitate colloid is oxidized by passing an oxygen-containing gas through the ferrous hydroxide reaction solution or the ferrous salt-containing reaction solution containing the iron-containing precipitate colloid. After forming the core-like goethite core particles, the ferrous salt reaction solution containing the acicular goethite core particles is maintained at a temperature of 75 ° C. or higher, and then cooled to 60 ° C. or lower. It held below, subsequently, by passing an oxygen-containing gas after the addition of more equivalents of aqueous alkali carbonate solution to Fe ²⁺ in the ferrous salt reaction solution, carrying out the growth reaction of the acicular goethite nucleus particles More needle-like goethite particles are generated, and then the needle-like goethite particles or needle-like hematite particles obtained by heat-treating the particles at 300 to 700 ° C. are reduced by heating in a reducing gas to obtain needle-like magnetite particles. To obtain acicular maghemite particles, if necessary, or to obtain acicular maghemite particles, or, if necessary, using the acicular magnetite particles or acicular magmite particles as precursor particles, and adding 0.1 to the Fe of the precursor particles. The precursor particles are dispersed in an alkaline suspension containing cobalt hydroxide or an alkaline suspension containing cobalt hydroxide and ferrous hydroxide so as to contain 5 to 15.0 atomic% of Co. acicular magnetic iron oxide which consists in obtaining acicular magnetite particles or acicular maghemite particles modified with the been or Co and Fe ²⁺ and modified with Co by heating the dispersion A method for producing a child powder.

Next, various conditions for implementing the method of the present invention will be described. As the aqueous ferrous salt solution used in the present invention, an aqueous ferrous sulfate solution, an aqueous ferrous chloride solution, or the like can be used.

The aqueous solution of alkali hydroxide used in the production reaction of the acicular goethite particles of the present invention includes an aqueous solution of sodium hydroxide and potassium hydroxide, and the aqueous solution of alkali carbonate includes an aqueous solution of sodium carbonate and an aqueous solution of potassium carbonate. Ammonium carbonate or the like can be used.

The amount of the aqueous alkali hydroxide solution or the aqueous alkali carbonate solution or the aqueous alkali hydroxide / alkali carbonate solution is less than the equivalent of Fe ²⁺ in the aqueous ferrous salt solution. In the case of the equivalent amount or more, goethite particles having an uneven particle size and mixed with dendritic particles are obtained. Also,
Granular magnetite particles are mixed.

In the present invention, the abundance of the acicular goethite core particles is 10 to 90 mol% based on the produced goethite particles.
Is preferable. If the content is less than 10 mol%, the needle-like goethite particles intended for the present invention cannot be obtained. If the content exceeds 90 mol%, the ratio of iron carbonate to the acicular goethite core particles becomes small, so that the reaction becomes nonuniform and the particle size of the obtained goethite particles becomes uneven.

The amount of the aqueous alkali carbonate solution used in the growth reaction of the acicular goethite core particles of the present invention is at least equivalent to Fe ²⁺ in the remaining aqueous ferrous salt solution. When the amount is less than the equivalent, the particle size of the obtained goethite particles becomes uneven, and spherical magnetite particles are mixed.

The oxidizing means in the present invention is carried out by passing an oxygen-containing gas (for example, air) through the liquid, and may be accompanied by stirring by a mechanical operation or the like, if necessary.

The reaction temperature in the present invention may be usually at a temperature of 60 ° C. or less at which goethite particles are formed. 6
When the temperature exceeds 0 ° C., granular magnetite particles are mixed in the acicular goethite particles.

In the present invention, the reaction for producing goethite nucleus particles and the reaction for growing the goethite nucleus particles can be carried out using the same reaction tower, and the present invention can be applied to the case where separate reaction towers are used. Goethite particles are obtained.

In the present invention, after the ferrous salt reaction solution containing acicular goethite core particles is maintained at a temperature of 75 ° C. or higher, 6
The temperature is lowered to 0 ° C. or lower, and if necessary, is maintained at 60 ° C. or lower in a non-oxidizing atmosphere. When the holding temperature is lower than 75 ° C., the squareness and the degree of orientation of the obtained magnetic iron oxide particles cannot be further improved. In order to form a non-oxidizing atmosphere, an inert gas such as N ₂ gas is passed through the liquid, or the gas is agitated by mechanical operation or the like. When the temperature exceeds 60 ° C., granular magnetite particles are mixed in the subsequent process of generating an acicular goethite particle by passing an oxygen-containing gas.

In the present invention, one of Co compounds, Ni compounds, Zn compounds, Al compounds, P compounds, Si compounds and the like usually added during the reaction for forming goethite particles in order to improve the properties of the magnetic particles. Seeds or two or more kinds may be added, and in this case, the acicular goethite particle powder of the present invention can be obtained.

In the present invention, if necessary, the starting material particles may be converted into S by a well-known method prior to the heat reduction treatment.
It may be coated in advance with a substance having an effect of preventing sintering, such as an i compound, an Al compound, or a P compound.
This coating treatment prevents sintering between the particles and the particles, retains and inherits the particle shape and the axial ratio (major axis diameter / minor axis diameter) of the starting material particles, and obtains individual magnetic iron oxide particles individually. It will be easier.

The oxidation temperature in the present invention is 2
It can be performed at 00 to 500 ° C.

In the present invention, the magnetic iron oxide particles powder of Co
Metamorphosis can be performed by a conventional method.
JP-A-2-24237, JP-B-52-24238, JP-B-52-36651, and JP-B-52-3.
As described in Japanese Patent No. 6863, precursor particles are dispersed in cobalt hydroxide or an alkaline suspension containing cobalt hydroxide and ferrous hydroxide, and the dispersion is subjected to heat treatment. Will be

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

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

In the conversion of Co, the heat treatment is preferably performed in a non-oxidizing atmosphere at a temperature of 50 to 100 ° C.

The temperature of the Co transformation is related to the treatment time. If the temperature is set to 50 ° C. or lower, magnetite particles or maghemite particles transformed by Co or transformed by Co and Fe ²⁺ are hardly formed. Even if it is generated, an extremely long process is required.

The conversion amount of the water-soluble cobalt salt in the present invention is 0.5 to 15.0 atomic% in terms of Co with respect to Fe. If it is less than 0.5 atomic%, 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 denaturation on the surface of the magnetic iron oxide particles.

When considering the coercive force and coercive force distribution of acicular magnetite particles or maghemite particles, 2.0 to 1
3.0 at% is preferred.

[0039]

First, the most important point in the present invention is that an aqueous solution of ferrous salt and an aqueous solution of alkali hydroxide or an aqueous solution of alkali carbonate or alkali hydroxide / carbonate which are less than equivalent to Fe ²⁺ in the aqueous solution of ferrous salt are used. An oxygen-containing gas is passed through the ferrous hydroxide colloid or iron-containing precipitate colloid containing a ferrous hydroxide colloid or an iron-containing precipitate colloid obtained by reacting with an alkaline aqueous solution. After the precipitate colloid is oxidized to form needle-like goethite core particles, the ferrous salt reaction solution containing the needle-like goethite core particles is maintained at a temperature of 75 ° C. or higher, and then cooled to 60 ° C. or lower. by passing an oxygen-containing gas after the addition of more equivalents of aqueous alkali carbonate solution to Fe ²⁺ in said ferrous salt reaction solution, when performing growth reaction of the acicular goethite nucleus particles, the particle Are homogeneous, do not contain dendritic particles, and have a large axial ratio (major axis diameter / minor axis diameter), in particular, acicular goethite particle powder of 20 or more. The acicular magnetic iron oxide particles obtained using the particles as starting material particles are also uniform in particle size, do not contain dendritic particles, and have a large axial ratio (long axis diameter /
Particles having a short axis diameter) are obtained. And it is a fact that the needle-like magnetic iron oxide particles having these various properties have more excellent squareness and degree of orientation.

In the present invention, after the ferrous salt reaction solution containing acicular goethite core particles is maintained at a temperature of 75 ° C. or higher,
When the temperature is lowered to 0 ° C. or lower and further kept in a non-oxidizing atmosphere, needle-like magnetic iron oxide particles having more excellent coercive force distribution while maintaining more excellent squareness and orientation degree can be obtained.

When an aqueous solution of alkali hydroxide is used in place of the aqueous solution of alkali carbonate in the growth reaction of the goethite core particles, or when an aqueous solution of an alkali hydroxide or an alkali carbonate in an equivalent amount or more is used in the reaction of forming the core particles of goethite, As shown in the Comparative Examples, the target particle size of the present invention is uniform, dendritic particles are not mixed, and the acicular goethite particles having a large axial ratio (major axis diameter / minor axis diameter) are I can't get it.

[0042]

Next, the present invention will be described with reference to examples and comparative examples. In addition, the major axis diameter and the axial ratio (major axis diameter / minor axis diameter) of the particles in the following Examples and Comparative Examples are all shown as average values of the numerical values measured from electron micrographs.

The particle size distribution of the particles was represented by a geometric standard deviation (σg) obtained by the following method. That is, the major axis diameter of 350 particles shown in a 120,000-fold electron micrograph was measured, and the logarithmic normal was calculated from the actual major axis diameter and the number of particles calculated from the measured value according to a statistical method. The horizontal axis on the probability paper plots the major axis diameter of the particles, and the vertical axis plots the cumulative number of particles belonging to each of the major axis diameter sections at equal intervals in percentage. Then, the value of the major axis diameter corresponding to 50% and 84.13% of the number of particles was read from this graph, and the major axis diameter (μm) when the number of particles was 50% was counted to 84.1%.
It was shown by the value divided by the major axis diameter (μm) at 3%.

The magnetic properties and the coating properties of the magnetic iron oxide particles were measured using a vibrating sample magnetometer VSM-3S-15 (manufactured by Toei Kogyo Co., Ltd.), and the acicular magnetite particles and acicular maghemite were used. The particle powder was measured at an external magnetic field of 5 KOe, and the Co-modified magnetic iron oxide particle powder was measured at an external magnetic field of 10 KOe.

The squareness of the coating film and S.I. F. D. Was measured using a sheet sample obtained by the method of Example 16 described later. Also, S.I. F. D. Was obtained by using a differentiating circuit of the magnetometer to obtain a differential curve of a demagnetization curve of a magnetic hysteresis curve, measuring a half width of the curve, and dividing this value by a coercive force.

<Production Method of Acicular Goethite Particle Powder> Examples 1 to 3, Reference Example 1, Comparative Examples 1 to 6; Example 1 Ferrous sulfate aqueous solution 1 containing 1.50 mol / l of Fe ²⁺
2.8 l and 0.60-N NaOH aqueous solution 32.0
1 (corresponding to 0.50 equivalents to Fe ²⁺ in the aqueous ferrous sulfate solution) to form an aqueous ferrous sulfate solution containing Fe (OH) ₂ at pH 7.2 and a temperature of 38 ° C. Was performed. 130 l of air per minute was passed through the aqueous ferrous sulfate solution containing Fe (OH) ₂ at a temperature of 40 ° C. for 3.0 hours to produce goethite core particles.

An aqueous ferrous sulfate solution containing the above goethite core particles (the amount of goethite core particles corresponding to 50 mol% based on the produced goethite particles) was maintained at a temperature of 80 ° C. for 1 hour, and then cooled to 45 ° C. Then 4.7-N of N
7.0 l of a ₂ CO ₃ aqueous solution (corresponding to 1.7 equivalents with ^respect to Fe ²⁺ in the remaining aqueous ferrous sulfate solution) was added, and the pH was adjusted.
9.6, 130 liters of air per minute at a temperature of 45 ° C.
Vent for a period of time to produce goethite particles. The produced goethite particles were separated by filtration, washed with water and dried by a conventional method.

The obtained goethite particle powder was observed by electron microscopy to be uniform in particle size, free of dendritic particles, and had a major axis of 0.37 μm and an axial ratio (major axis diameter / short axis). Needle-shaped particles having an axial diameter of 32). Σg was 0.792.

Example 2 Ferrous sulfate aqueous solution 1 containing 1.50 mol / l of Fe ²⁺
2.8 l and 0.54-N NaOH aqueous solution 32.0
1 (corresponding to 0.45 equivalents to Fe ²⁺ in the aqueous ferrous sulfate solution) to form an aqueous ferrous sulfate solution containing Fe (OH) ₂ at pH 7.0 and a temperature of 38 ° C. Was performed. 100 l of air per minute was passed through the aqueous solution of ferrous sulfate containing Fe (OH) ₂ at 35 ° C. for 3.5 hours to produce goethite core particles.

An aqueous ferrous sulfate solution containing the above goethite core particles (the abundance of goethite core particles corresponds to 45 mol% with respect to the produced goethite particles) at a temperature of 80 ° C.
After holding for 5 hours, the temperature was lowered to 48 ° C., and then 4.8-N
Of Na ₂ CO ₃ aqueous solution (corresponding to 1.6 equivalents to Fe ²⁺ in the residual aqueous ferrous sulfate solution)
130 liters of air per minute was passed for 4 hours at H9.5 and a temperature of 48 ° C. to produce goethite particles. The produced goethite particles were separated by filtration, washed with water and dried by a conventional method.

The obtained goethite particle powder had a σg of 0.3 as shown in the electron micrograph (× 30000) of FIG.
The particles had a uniform particle size of 800 and did not contain dendritic particles. Further, they were needle-like particles having a major axis of 0.28 μm and an axial ratio (major axis diameter / minor axis diameter) of 27.

Example 3 Ferrous chloride aqueous solution 1 containing 1.5 mol / l of Fe ²⁺
2.8 l and 35.5 of 0.60-N NaOH aqueous solution
1 (corresponding to 0.5 equivalent to Fe ²⁺ in the aqueous ferrous chloride solution) to form an aqueous ferrous chloride solution containing Fe (OH) ₂ at a pH of 7.2 and a temperature of 38 ° C. Was performed. 130 liters of air per minute was passed through the aqueous ferrous chloride solution containing Fe (OH) ₂ at a temperature of 35 ° C. for 3.0 hours to produce goethite core particles.

An aqueous ferrous chloride solution containing the above goethite core particles (the amount of goethite core particles corresponding to 50 mol% based on the produced goethite particles) was maintained at a temperature of 90 ° C. for 1 hour, and then cooled to 45 ° C. Continued at 0.83c per second
It was kept at a temperature of 45 ° C. for 2 hours while being kept in a non-oxidizing atmosphere by flowing N ₂ gas at a rate of m ³ . Then, 7.0 l of a 4.7-N Na ₂ CO ₃ aqueous solution (corresponding to 1.7 equivalents to Fe ²⁺ in the remaining ferrous chloride aqueous solution) was added, and the mixture was heated at pH 9.6 and at a temperature of 44 ° C. 1 per minute
Goethite particles were produced by bubbling 30 l of air for 4 hours. The generated goethite particles are separated by filtration, washed with water,
Dried.

The obtained goethite particle powder had a σg of 0.3 as shown in the electron micrograph (× 30000) of FIG.
The particles were particles having a uniform particle size of 836, and no dendritic particles were present. Further, the particles were needle-like particles having a major axis of 0.31 μm and an axial ratio (major axis diameter / minor axis diameter) of 30.

Reference Example 1 An aqueous ferrous sulfate solution containing goethite core particles was heated at 80 ° C. for 1 hour.
Goethite particles were produced in the same manner as in Example 1 except that the time was not maintained. The generated goethite particle powder is
As a result of observation with an electron microscope, the particles were needle-like particles having a major axis of 0.36 μm and an axial ratio (major axis diameter / minor axis diameter) of 30, and σg was 0.785.
Met.

COMPARATIVE EXAMPLE 1 7.0 l of a 4.7-N NaOH aqueous solution was replaced with 7.0 l of a 4.7-N Na ₂ CO ₃ aqueous solution (based on Fe ²⁺ in the remaining ferrous sulfate aqueous solution). Goethite particle powder was obtained in the same manner as in Example 1 except that 1.7 equivalents were used. The obtained goethite particle powder had an uneven particle size and a mixture of dendritic particles as shown in the electron micrograph (× 30000) of FIG. The σg of this goethite particle powder was 0.511.

COMPARATIVE EXAMPLE 2 32.0 l of a 0.60-N aqueous solution of Na ₂ CO ₃ was replaced with 32.0 l of an aqueous solution of 0.60-N NaOH (0 ^% of Fe ²⁺ in an aqueous solution of ferrous sulfate). .50 corresponds to eq.) as well as use of 4.7-N Na ₂ CO ₃
The procedure was carried out except that 7.0 l of a 4.7-N NaOH aqueous solution (corresponding to 1.7 equivalents to Fe ²⁺ in the remaining ferrous sulfate aqueous solution) was used instead of 7.0 l of the aqueous solution. Example 1
In the same manner as in Example 1, goethite particle powder was obtained. The obtained goethite particle powder was obtained by an electron microscope photograph (× 3000) shown in FIG.
As shown in 0), the particle size was uneven and dendritic particles were mixed. The σg of this goethite particle powder was 0.516.

Comparative Example 3 Ferrous sulfate aqueous solution containing 1.0 mol / l of Fe ²⁺ 7.
5 l and 24.2 l of an aqueous solution of 1.3-N Na ₂ CO ₃
(Corresponding to 2.1 equivalents with ^respect to Fe ²⁺ in the aqueous ferrous sulfate solution) to produce FeCO ₃ at a pH of 9.9 and a temperature of 42 ° C. 100 l of air per minute was passed through the aqueous solution containing FeCO ₃ at 45 ° C. for 5 hours to produce spindle-shaped goethite particles.

To the aqueous solution containing the spindle-shaped goethite particles, 8.3 l of an aqueous ferrous sulfate solution containing 1.8 mol / l of Fe ²⁺ and 10 l of an aqueous 13-N NaOH solution were added.
(Corresponding to 4.4 equivalents with respect to Fe ²⁺ in the added aqueous ferrous sulfate solution) and stirring and mixing (the spindle-shaped goethite particles are 33 mo relative to the produced goethite particles).
1%. ) And then at 50 ° C for 1 minute
The growth reaction of goethite was carried out by passing 50 l of air for 3 hours.

The produced goethite particle powder is prepared by a conventional method.
Filtration, washing with water and drying. As shown in the electron micrograph (× 30000) in FIG. 5, the obtained goethite particle powder has a uniform particle size and does not contain dendritic particles, but has an axial ratio (major axis diameter / minor axis diameter). Were small and strip-shaped particles. The σg of this goethite particle powder is 0.
841.

Comparative Example 4 Ferrous sulfate aqueous solution 1 containing 1.3 mol / l of Fe ²⁺
2.8 l and 30.2 l of 2.4-N NaOH aqueous solution
(Corresponding to 2.2 equivalents to Fe ²⁺ in the aqueous ferrous sulfate solution) to produce Fe (OH) ₂ at pH 13.2 and at a temperature of 40 ° C. The above Fe (OH) ₂
130 l / min of air was passed through the aqueous solution containing at 15 ° C for 15 hours at a temperature of 45 ° C to produce needle-like goethite particles. The resulting goethite particles were filtered and washed with water in a conventional manner.

To 27.5 liters of the aqueous solution containing 586 g of the acicular goethite particles, 12.5 liters of an aqueous ferrous sulfate solution containing 1.0 mol / l of Fe ²⁺ and 3.8-N Na ₂ C
10 l of O ₃ aqueous solution (F in aqueous ferrous sulfate solution
This corresponds to 1.5 equivalents to e ²⁺ . ) And stirred and mixed (acicular goethite particles correspond to 35 mol% with respect to the produced goethite particles), and 130 l / min of air is passed through at a temperature of 42 ° C. for 4 hours to carry out the growth reaction of goethite. went.

The resulting goethite particle powder is prepared by a conventional method.
Filtration, washing with water and drying. The obtained goethite particle powder was uneven in particle size and mixed with dendritic particles, and had a small axial ratio (major axis diameter / short axis diameter) of 10. Σg of this goethite particle powder was 0.512.

Comparative Example 5 An aqueous solution of ferrous sulfate containing 1.5 mol / l of Fe ²⁺ 10
and 33 l of a 2.1-N aqueous solution of NaOH (corresponding to 2.3 equivalents to Fe ²⁺ in an aqueous solution of ferrous sulfate).
_Two colloids were produced. The suspension containing the colloidal Fe (OH) ₂ was aerated at a temperature of 42 ° C. at a rate of 13 l / min for 15 hours to produce acicular goethite particles. The resulting goethite particle powder was filtered, washed with water, and dried by a conventional method. As shown in the electron micrograph (× 30000) of FIG. 6, the obtained goethite particle powder had an uneven particle size and a mixture of dendritic particles. Σg of this goethite particle powder was 0.510.

Comparative Example 6 An aqueous solution of ferrous sulfate containing 1.5 mol / l of Fe ²⁺ 10
1 and 33 liters of a 1.8-N Na ₂ CO ₃ aqueous solution (corresponding to 2.0 equivalents to Fe ²⁺ in an aqueous ferrous sulfate solution) at pH 9.8 and a temperature of 45 ° C. F
eCO ₃ was produced. 100 liters of air per minute was passed through the aqueous solution containing FeCO ₃ at a temperature of 50 ° C. for 5 hours to produce goethite particles. The resulting goethite particle powder was filtered, washed with water, and dried by a conventional method. The obtained goethite particle powder was obtained by an electron micrograph (× 30) shown in FIG.
000), it had a spindle shape, and the axial ratio (major axis diameter / minor axis diameter) 7 and the axial ratio were small. Σg of this goethite particle powder was 0.829.

<Production of powder of acicular magnetite particles> Examples 4 to 6, Reference Example 2, Comparative Examples 7 to 12; Example 4 Paste 5 of needle-like goethite particles obtained in Example 1 and separated by filtration and washed with water. 0.3Kg (acicular goethite particles about 1.6K
g. ) Was suspended in 28 l of water. The pH at this time was 8.0. Then, 240 ml of an aqueous solution containing 24 g of sodium hexametaphosphate in the above suspension
(1.15 wt% of PO ₃ as needle-like goethite particles
%. ) Was added and stirred for 30 minutes, followed by filtration and drying to obtain a needle-like goethite particle powder coated with the P compound. The acicular goethite particle powder having the particle surface coated with the P compound was heat-treated at 660 ° C. in air to obtain an acicular hematite particle powder coated with the P compound.

1000 g of acicular hematite particle powder whose particle surface is coated with a P compound is charged into a retort reduction vessel, and H ₂ gas is supplied at 2 l / min while being driven to rotate.
Then, the mixture was reduced at a reduction temperature of 360 ° C. to obtain a powder of acicular magnetite particles coated with a P compound.

As a result of observation with an electron microscope, the obtained acicular magnetite particle powder coated with the P compound was found to have a major axis of 0.30 μm on average and an axial ratio (major axis diameter / minor axis diameter) of 8.0. Yes, the particles were uniform in particle size with a geometric standard deviation value of 0.67, and did not contain dendritic particles. As a result of the magnetic measurement, the coercive force Hc was 406 Oe and the saturation magnetization σ was σ.
s was 82.7 emu / g.

Examples 5-6, Reference Example 2, Comparative Examples 7-12 Needle-like magnetite particles were prepared in the same manner as in Example 4, except that the kind of the starting material and the heating temperature in the air heat treatment were variously changed. I got Table 1 shows the main production conditions and the characteristics of the particle powder at this time. As a result of observation with an electron microscope, the acicular magnetite particle powders obtained in Examples 5 to 6 were all uniform in particle size and did not contain dendritic particles.

<Production of acicular maghemite particle powder> Examples 7 to 9, Reference Example 3, Comparative Examples 13 to 18; Example 7 Acicular particles obtained in Example 4 whose surface is coated with a P compound. 300g of magnetite particle powder in air at 300 ℃
For 60 minutes to obtain acicular maghemite particle powder whose particle surface is coated with a P compound.

As a result of observation with an electron microscope, the obtained acicular maghemite particle powder having the particle surface coated with the P compound was found to have a major axis of 0.29 μm and an axial ratio (major axis diameter / minor axis diameter) of 7.8.
The particles having a geometric standard deviation of 0.67 were particles having a uniform particle size, and did not contain dendritic particles. Also,
As a result of the magnetic measurement, the coercive force Hc was 380 Oe, and the saturation magnetization s was 71.5 emu / g.

Examples 8-9, Reference Example 3, Comparative Examples 13-1
8. Acicular maghemite particle powder was obtained in the same manner as in Example 7, except that the type of acicular magnetite particle powder was variously changed. Table 2 shows the main production conditions and the characteristics of the particle powder at this time.
Shown in As a result of observation with an electron microscope, all the acicular maghemite particles obtained in Examples 8 to 9 were uniform in particle size and did not contain dendritic particles.

<Production of Acicular Magnetite Particle Powder Modified with Co> Examples 10 to 12, Reference Example 4, Comparative Examples 19 to 24; Example 10 The surface of the particles obtained in Example 7 was coated with a P compound. 100 g of the prepared needle-like magnetite particle powder is dissolved in an amount of 0.085 mol of cobalt using cobalt sulfate and ferrous sulfate and 0.179 mol of ferrous iron while preventing mixing of air as much as possible. 1N water and dispersed until a fine slurry is obtained.
An OH aqueous solution (102 ml) was added, and water was further added to adjust the total volume to 1.3 liter, thereby obtaining a dispersion having an OH group concentration of 1.0 mol / l. The temperature of the dispersion was raised to 100 ° C., and after 5 hours with stirring at this temperature, the slurry was taken out, washed with water, filtered, and dried at 60 ° C. to obtain a powder of acicular magnetite particles modified with Co. Was.

The obtained particles were observed by an electron microscope.
The surface and the particle size of the magnetite particles whose precursor particles are coated with a P compound are inherited,
The particles had an axial ratio (major axis diameter / minor axis diameter) of 9 μm and a geometric standard deviation of 0.66, and were uniform in particle size. Also,
As a result of the magnetic measurement, the coercive force Hc was 851 Oe, and the saturation magnetization s was 85.3 emu / g.

Examples 11 to 12, Reference Example 4, Comparative Example 19
２４24 The same procedure as in Example 10 was carried out except that the amount of the magnetite particles as the precursor was 100 g and the total volume of the treatment liquid was 1.3 l, and the type of the precursor was variously changed.
Acicular magnetite particles modified with o and Fe ²⁺ were obtained.
Table 3 shows the main manufacturing conditions and characteristics at this time.

<Production of Coated Modified Acicular Maghemite Particle Powder> Examples 13 to 15, Reference Example 5, Comparative Examples 25 to 30; Example 13 The surface of the particles obtained in Example 10 was coated with a P compound. 0.085 mol of cobalt using cobalt sulfate and ferrous sulfate and 0.179 mol of ferrous iron while preventing as much as possible air from mixing 100 g of the acicular maghemite particles powder.
Is poured into 1.0 l of water in which is dissolved, and dispersed until a fine slurry is formed. Then, 102 ml of an 18-N NaOH solution is poured into the dispersion, and water is further added to adjust the total volume to 1. A dispersion having an OH group concentration of 1.0 mol / l was prepared as 3 l. The temperature of the dispersion was raised to 100 ° C., and after 5 hours with stirring at this temperature, the slurry was taken out, washed with water,
It was filtered off and dried at 60 ° C. to obtain needle-shaped maghemite particles modified with Co.

The obtained particles were observed by an electron microscope.
It has inherited the shape and particle size of acicular maghemite particles whose precursor particles are coated with a P compound, and has a major axis of 0.27 μm and an axial ratio (major axis / minor axis diameter) of 7.0. ,
Particles having a geometric standard deviation of 0.67 were uniform in particle size.
As a result of the magnetic measurement, the coercive force Hc was 820 Oe and the saturation magnetization s was 78.5 emu / g.

Examples 14 to 15, Reference Example 5, Comparative Example 25
The amount of the precursor, the amount of Co added, the amount of Fe ²⁺ added, the amount of added NaOH aqueous solution, the temperature, and the time were set assuming that the amount of the acicular maghemite particles as the precursor was 100 g and the total volume of the treatment liquid was 1.3 l. Except that various changes were made, C
Acicular maghemite particles modified with o or Co and Fe ²⁺ were obtained. Table 4 shows the main manufacturing conditions and characteristics at this time.

<Production of Magnetic Tape> Examples 16 to 27, Reference Examples 6 to 9, Comparative Examples 31 to 54; Example 16 A 140 cc glass bottle was coated with the surface of the particles obtained in Example 4 with a P compound. After adding the acicular magnetite particle powder, the resin and the solvent at the following ratios, the magnetic paint prepared by mixing and dispersing for 2 hours with a paint conditioner was applied to a 25 μm-thick polyethylene terephthalate film having a thickness of 40 μm using an applicator. It was obtained by coating to a thickness, then orienting in a magnetic field of 1450 Gauss and drying.

1.5 mmφ glass beads 100 g Needle-like magnetite particle powder 15 g Toluene 5.6 g Phosphate ester (GAFACRE-610 Toho Chemical Co., Ltd.) 0.6 g Lecithin 0.6 g Vinyl acetate vinyl copolymer resin (vinylite VAGH Union) 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 S.V. F. D. Is 0.4
5. Coercive force Hc is 380 Oe, residual magnetic flux density Br is 1
640 Gauss, square Br / Bm was 0.85, and degree of orientation was 2.81.

Examples 17 to 27, Reference Examples 6 to 9, Comparative Examples 31 to 54 Example 16 except that the type of the magnetic particles was changed in various ways.
A magnetic tape was manufactured in the same manner as described above. The acicular magnetite particle powder and the acicular maghemite particle powder were 1450.
Gauss, Co-modified magnetic iron oxide particle powder is 1900G
Orientation was performed in an auss magnetic field. Tables 5 to 8 show various properties of the magnetic tape.

[0083]

[Table 1]

[0084]

[Table 2]

[0085]

[Table 3]

[0086]

[Table 4]

[0087]

[Table 5]

[0088]

[Table 6]

[0089]

[Table 7]

[0090]

[Table 8]

[0091]

According to the method for producing acicular magnetic iron oxide particles according to the present invention, the particle size is uniform and dendritic particles are not mixed, Acicular magnetic iron oxide particles having a large axis ratio (major axis diameter / minor axis diameter), excellent coercive force distribution, and excellent squareness and degree of orientation can be obtained. It is suitable as magnetic particles for high recording density, high sensitivity and high output.

[0092]

[Brief description of the drawings]

FIG. 1 is an electron micrograph (× 30000) showing the particle structure of the acicular goethite particle powder obtained in Example 2.

FIG. 2 is an electron micrograph (× 30000) showing the particle structure of the acicular goethite particle powder obtained in Example 3.

FIG. 3 is an electron micrograph (× 30000) showing the particle structure of the goethite particle powder obtained in Comparative Example 1.

FIG. 4 is an electron micrograph (× 30000) showing the particle structure of the goethite particle powder obtained in Comparative Example 2.

FIG. 5 is an electron micrograph (× 30000) showing the particle structure of the goethite particle powder obtained in Comparative Example 3.

FIG. 6 is an electron micrograph (× 30000) showing the particle structure of the goethite particle powder obtained in Comparative Example 5.

FIG. 7 is an electron micrograph (× 30000) showing the particle structure of the goethite particle powder obtained in Comparative Example 6.

Claims (3)

(57) [Claims] 1. An aqueous solution of a ferrous salt obtained by reacting an aqueous solution of a ferrous salt with an aqueous solution of an alkali hydroxide, an aqueous solution of an alkali carbonate or an aqueous solution of an alkali hydroxide / alkali carbonate, which is less than the equivalent of Fe ²⁺ in the aqueous solution of a ferrous salt. The ferrous hydroxide colloid or the iron-containing precipitate colloid is oxidized by passing oxygen-containing gas through the ferrous hydroxide reaction solution containing the ferrous hydroxide colloid or the iron-containing precipitate colloid. After generating goethite core particles, the ferrous salt reaction solution containing the acicular goethite core particles is maintained at a temperature of 75 ° C. or higher, and then heated to 60 ° C.
The temperature was lowered below, and then the Fe ²⁺ in the ferrous salt reaction solution was
After adding an equivalent amount or more of an aqueous alkali carbonate solution, aeration of an oxygen-containing gas is performed to generate acicular goethite particles by performing a growth reaction of the acicular goethite core particles,
Next, the acicular goethite particles or the particles are mixed with 300 to 7 particles.
Needles obtained by heating and reducing needle-like hematite particles obtained by heat treatment at 00 ° C. in a reducing gas to obtain needle-like magnetite particles, or further oxidizing to obtain needle-like maghemite particles. For producing magnetic iron oxide particles. 2. The ferrous salt reaction solution containing acicular goethite core particles is maintained at a temperature of 75 ° C. or higher, then cooled to 60 ° C. or lower, and further maintained at 60 ° C. or lower in a non-oxidizing atmosphere. For producing needle-like magnetic iron oxide particles. 3. A needle-like magnetite particle or a needle-like magmite particle obtained by the method according to claim 1 or 2 is used as a precursor particle, and 0.5 to 15.0 based on Fe of the precursor particle. The precursor particles are dispersed in an alkaline suspension containing cobalt hydroxide or an alkaline suspension containing cobalt hydroxide and ferrous hydroxide so that the dispersion contains at least atomic% of Co, and the dispersion is subjected to heat treatment. And obtaining acicular magnetite particles or acicular maghemite particles modified with Co or modified with Co and Fe ²⁺ .