JP2970699B2 - 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
(Small axis diameter), and the particle size is more uniform and dendritic particles are not mixed. As a result, the coercive force distribution is excellent, and the individual particles are independent. The present invention relates to a method for producing acicular magnetic iron oxide particles.

[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.

[0003] The characteristics of magnetic material particles required to satisfy the above requirements for a magnetic recording medium are as follows:
High coercive force, excellent dispersibility, and excellent coercive force distribution.

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. Is clear from the description.

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.

In order to increase the recording density and output of a magnetic recording medium, the above-mentioned “Development of Magnetic Materials and Technology for Highly Dispersing Magnetic Powder”, p. The condition is that high output characteristics can be maintained with low noise for short wavelength signals.
And the residual magnetization Br must be large, and the thickness of the coating film must be thinner. "On page 310 of the same document," The obtained magnetic tape has improved coercive force Hc and squareness (Br / Bm). As a result, the magnetic recording medium needs to have a high coercive force, a large residual magnetization Br and a square shape,
For that purpose, it is required that the magnetic particle powder has a high coercive force and is excellent in dispersibility in a vehicle, orientation and filling in a coating film.

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.

[0008] Magnetic iron oxide particles such as acicular magnetite particles, acicular maghemite particles, and the like, which are currently used as magnetic particles for magnetic recording, or these particles are C
The needle-like magnetic iron oxide particles powder denatured by o or denatured by Co and Fe, utilizing anisotropy derived from its shape,
That is, a relatively high coercive force is obtained by increasing the axial ratio (major axis diameter / minor axis diameter).

These known magnetic particle powders are obtained by reducing goatite particles as a starting material or hematite particles obtained by heat-treating the particles at 300 to 700 ° C. in an oxidizing atmosphere or an inert atmosphere to reduce reducing particles such as hydrogen. 300-500 in gas
C. to reduce to magnetite particles, or then oxidize the magnetite particles in air at 200 to 500 ° C. to form maghemite particles.

The known acicular magnetic iron oxide particles modified with Co or modified with Co and Fe use acicular magnetite particles or acicular maghemite particles as precursor particles. 0.5-15.0 atom%
Is obtained by dispersing the above-mentioned precursor particles in an alkali suspension containing cobalt hydroxide or cobalt hydroxide and ferrous hydroxide so as to contain Co, and subjecting the dispersion to heat treatment.

The residual magnetization Br and the square shape of the magnetic recording medium are as follows:
It depends on the dispersibility of the magnetic particle powder in the vehicle, the orientation in the coating film, and the filling property. To improve these properties, the magnetic particle powder dispersed in the vehicle has a large axial ratio (long length). (Shaft diameter / short axis diameter), and the particle size is uniform, dendritic particles are not mixed, and sintering between particles and particles is prevented and each particle is independent. Is required.

This fact is described in the above-mentioned “Development of Magnetic Materials and Technology for Highly Dispersing Magnetic Powder” on page 317, “Magnetic Particles for Magnetic Tape, which are easily dispersed in a vehicle and easily dispersed in a coating film. The nature of the orientation is most important.The subject of research on the method of synthesizing the highly dispersed and highly oriented acicular γ-Fe ₂ O ₃ particles is to form acicular particles in which individual particles can move independently. Was obtained. "

As described above, magnetic particle powders having a large axial ratio (major axis diameter / minor axis diameter), uniform particle size, no mixture of dendritic particles, and dispersed particles. Is currently the most required, and in order to obtain magnetic particle powder having such properties, goethite particle powder as a starting material has a large axis ratio (long axis diameter / short axis diameter). Further, it is necessary that the particles have a uniform particle size, do not contain dendritic particles, and sintering between particles and particles in the subsequent heat treatment step is prevented as much as possible.

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 amount or more of an alkali hydroxide aqueous solution to a ferrous salt aqueous solution is used. 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 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 perform an oxidation reaction. (Japanese Unexamined Patent Publication No.
0-80999) and the like.

Further, in the above-mentioned method, a method of adding a water-soluble silicate during the reaction to improve the particle size of the acicular goethite particles produced (JP-B-55-8461, JP-B-55-32652). Japanese Patent Application Laid-Open No. Sho 55 (1993)], a method of adding a water-soluble silicate and a water-soluble zinc salt during the reaction in order to improve the particle size and the axial ratio (major axis diameter / minor axis diameter) of the resulting needle-like goethite particles. No. 6575, Japanese Patent Publication No. 55-6576) and the like.

[0016]

SUMMARY OF THE INVENTION A large axial ratio (long axis diameter /
Magnetic particle powders having a short axis diameter), a uniform particle size, no dendritic particles, and scattered particles are currently most demanded. In the case of the above-mentioned method of producing goethite particle powder, needle-like goethite particles having an axial ratio (major axis diameter / minor axis diameter) of 10 or more are generated, but dendritic particles are mixed, Also, in terms of the particle size, it is difficult to say that the particles have a uniform particle size.

In the case of the above-mentioned method, spindle-shaped particles having a uniform particle size and containing no dendritic particles are formed, but the axial ratio (major axis diameter / minor axis) 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.

According to the above method, acicular goethite particles having a uniform particle size and containing no dendritic particles are produced, but the axial ratio (major axis diameter / minor axis diameter) is at most about 9 at most. As the amount of the water-soluble silicate increases, the particle size becomes uniform and dendritic particles are not mixed, but the axial ratio (major axis diameter / minor axis diameter) tends to decrease rapidly. is there. Further, at the time of heat reduction, it is difficult to sufficiently prevent sintering between the particles and the particles, and it is difficult to say that the individual particles are independent.

According to the above method, acicular goethite particles having a large axis ratio (major axis diameter / minor axis diameter) are produced, but the effect of improving the axis ratio (major axis diameter / minor axis diameter) is not obtained. The addition of the water-soluble zinc salt has a non-uniform particle size, which makes it easier for dendritic particles to be mixed together, and furthermore, it is difficult to sufficiently prevent sintering between the particles and the particles during heat reduction. Are hardly independent. In addition, there is a problem that the production efficiency is reduced due to a decrease in the production amount per unit time / unit volume (hereinafter, referred to as production amount), which is not industrial and economical.

Therefore, the present invention provides a large axis ratio (major axis diameter /
(Small axis diameter), the particle size is more uniform, and dendritic particles are not mixed. As a result, the coercive force distribution is excellent, and sintering between particles and particles is further prevented. Accordingly, it is a technical object to obtain acicular magnetic iron oxide particle powder in which individual particles are independent.

[0021]

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

That is, the present invention provides a p-containing ferrous hydroxide obtained by reacting an aqueous ferrous salt solution with an aqueous alkaline solution.
In generating needle-like goethite particles by oxidizing a suspension containing H11 or more by passing an oxygen-containing gas into the suspension,
The water-soluble silicate is 0.1 to 0.7 atomic% in terms of Si in any one of the suspensions before the oxidation reaction is performed by passing the alkaline aqueous solution and the oxygen-containing gas. The water-soluble aluminum salt is added to Fe in any of the suspensions before the oxidation reaction is performed by passing the ferrous salt aqueous solution, the alkaline aqueous solution, and the oxygen-containing gas. On the other hand, 0.1 to 3.0 atomic% in terms of Al
By adding, acicular goethite particles containing Si and Al are generated, and then the acicular goethite particles containing Si and Al or the particles are 300 to 70.
The needle-like hematite particles containing Si and Al obtained by heat treatment at 0 ° C. are reduced by heating in a reducing gas to obtain needle-like magnetite particles containing Si and Al, or if necessary, further oxidized. To obtain acicular maghemite particles containing Si and Al, or, if necessary, acicular magnetite particles containing Si and Al or acicular maghemite particles containing Si and Al as precursor particles. Used, 0.5 to 0.5 of Fe of the precursor particles
The precursor particles are dispersed in an alkali suspension containing cobalt hydroxide or cobalt hydroxide and ferrous hydroxide so as to contain 15.0 atomic% of Co, and the dispersion is subjected to heat treatment. A method for producing acicular magnetic iron oxide particle powder comprising obtaining acicular magnetite particles containing Si and Al modified with Co or Co and Fe ²⁺ or acicular maghemite particles containing Si and Al. .

[0023]

First, the most important point in the present invention is that an oxygen-containing gas is passed through a suspension of ferrous hydroxide containing pH 11 or more obtained by reacting an aqueous ferrous salt solution with an aqueous alkaline solution. In producing needle-like goethite particles by oxidizing the aqueous solution, a water-soluble silicate is added to any of the suspensions before the oxidation reaction is performed by passing the alkaline aqueous solution and the oxygen-containing gas through Fe. Of the ferrous salt solution, the alkali aqueous solution and the oxygen-containing gas before the oxidation reaction is carried out by adding 0.1 to 0.7 atomic% in terms of Si with respect to Si. When a water-soluble aluminum salt is added to Fe in an amount of 0.1 to 3.0 atomic% in terms of Al with respect to Fe, a large axis ratio (major axis diameter / minor axis diameter) is obtained. In addition, the particle size is more uniform and dendritic particles are mixed. Acicular goethite particles can be produced a containing and non Si and Al, the S
Acicular goethite particles containing i and Al are the fact that the particles and the particles are sufficiently prevented from sintering in the heat reduction step and the individual particles are independent.

In the present invention, the reason why the needle-like goethite particles having a large axis ratio (major axis diameter / minor axis diameter) and having a more uniform particle size and containing no dendritic particles can be obtained is as follows. As shown in the comparative examples described later, in any case where each of the water-soluble silicate and the water-soluble aluminum salt is independently added in the reaction for producing goethite particles, the target acicular goethite particles are used. It is thought that the synergistic effect of the water-soluble silicate and the water-soluble aluminum salt is attributable to the inability to produce.

In the present invention, the reason why an acicular magnetic iron oxide in which individual particles are independent can be obtained is as follows. As shown in a comparative example, the present inventor has proposed a needle containing only Si and Al alone. When the goethite particles are heat-reduced, the squareness is not good in any case, so that the synergistic effect of Si and Al contained in the acicular goethite particles causes the particles and the particles to interoperate in the heat-reduction step. It is considered that the sintering of sintering was sufficiently prevented.

In the present invention, the production amount of acicular goethite particles containing Al and Si can be increased to 6.3 g / l / h, preferably 6.5 g / l / h or more, so that industrial, Magnetic iron oxide particles can be obtained economically advantageously.

Conventionally, as a method for adding a silicon compound and an aluminum compound in the reaction for producing acicular goethite particles, there is a method described in JP-A-64-33019. This method is to supply an oxygen-containing gas while adding a silicon compound and an aluminum compound to a suspension containing ferrous hydroxide. Is particularly remarkable as the production amount of needle-like goethite particles is increased by a high-concentration reaction, and the operation and effect are completely different from those of the present invention.

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

The ferrous salt used in the present invention includes an aqueous ferrous sulfate solution and an aqueous ferrous chloride solution.

Examples of the aqueous alkali solution used in the present invention include an aqueous sodium hydroxide solution and an aqueous potassium hydroxide solution.

The water-soluble silicate used in the present invention includes sodium and potassium silicates. The addition amount of the water-soluble silicate is 0.1 to 0.7 atomic% in terms of Si with respect to Fe. When the content is less than 0.1 atomic%, it is difficult to produce a needle-like goethite particle powder in which the target particle size of the present invention is uniform and does not contain dendritic particles. If it exceeds 0.7 atomic%, needle-like goethite particles having a large axis ratio (major axis diameter / minor axis diameter) cannot be obtained.

The water-soluble silicate according to the present invention is involved in the particle size of the needle-like goethite particles to be formed and the form of dendritic particles. It needs to be before the reaction, and can be added to any liquid in the suspension containing the aqueous alkali solution and ferrous hydroxide.

The water-soluble aluminum salt used in the present invention includes aluminum sulfate, sodium aluminate, aluminum chloride and the like. The addition amount of the water-soluble aluminum salt is 0.1 to 3.0 atomic% in terms of Al with respect to Fe. When the content is less than 0.1 atomic%, it is difficult to produce acicular goethite particle powder in which the target particle size of the present invention is more uniform and does not contain dendritic particles. When the content exceeds 3.0 atomic%, the desired effects of the present invention can be obtained, but the saturation magnetization of the acicular magnetic iron oxide particles obtained by using the acicular goethite particles produced decreases.

The water-soluble aluminum salt according to the present invention is involved in the axial ratio (major axis diameter / minor axis diameter), particle size, and morphology of particles such as dendritic particles of the acicular goethite particles. The addition time must be before the oxygen-containing gas is passed to cause the oxidation reaction, and any of the ferrous salt aqueous solution, the alkaline aqueous solution and the suspension containing ferrous hydroxide may be used. It can be added inside.

The oxidizing means in the present invention is carried out by passing an oxygen-containing gas (for example, air) through the liquid.

The heat reduction temperature in the present invention can be carried out at 300 to 500 ° C. by a conventional method.

In the present invention, if necessary, the starting material particles may be converted to 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 i, Al, and P compounds. By this coating treatment, sintering between the particles and the particles is further prevented, the particle shape and the axial ratio (major axis diameter / minor axis diameter) of the starting material particles are retained and inherited, and the magnetic iron oxide particles which are individually independent are formed. It is easier to obtain.

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 No. 6863, the 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 or cobalt chloride and an aqueous alkali hydroxide solution such as sodium hydroxide or potassium hydroxide.

The ferrous hydroxide in the present invention can be 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. .

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

The temperature of Co alteration is related to the treatment time. If the temperature is set to 50 ° C. or less, magnetite particles or maghemite particles altered by Co or Co and Fe ²⁺ are less likely to be formed. However, it requires extremely long processing.

Performing the Co transformation under a non-oxidizing atmosphere is as follows.
This is because the transformation occurs for the first time when cobalt and ferrous hydroxide are hydroxides, in order to prevent oxidation of cobalt hydroxide and ferrous hydroxide in the dispersion.

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.

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

[0048]

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. On the probability paper, the horizontal axis represents the major axis diameter of the particles, and the vertical axis represents 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 that of 50% and 84.13% of the number of particles is read from this graph, and the geometric standard deviation value (σg) = the major axis diameter (μm) / 50% number of particles / μm / Long axis diameter when the number is 84.13% (μm)
It was shown by the value calculated according to.

The amounts of Si and Al contained in the acicular goethite particles were measured by X-ray fluorescence analysis.

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 the S.I. F. D. Was measured using a sheet sample obtained by the method of Example 35 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 of Acicular Goethite Particle Powder> Examples 1 to 4 Comparative Examples 1 to 4; Example 1 Sulfuric acid obtained by adding aluminum sulfate so as to contain 1.0 atomic% in terms of Al / Fe. Ferrous iron 1.5mol / l
Sodium silicate (No. 3) (SiO ₂ 28.55 wt%) 37.8 was prepared so that 24 l of the aqueous solution was prepared in advance so as to contain 0.50 atomic% in terms of Si / Fe prepared in the reactor.
g (corresponding to 0.50 atomic% in terms of Si / Fe) of a 6.7-N NaOH aqueous solution 26 obtained.
at a pH of 13.1 and at a temperature of 50 ° C.
An aqueous solution containing H) ₂ and Al (OH) ₃ was obtained.

The aqueous solution containing Fe (OH) ₂ and Al (OH) ₃ was air-flowed at a temperature of 50 ° C. at a rate of 100 l / min for 9 hours to produce acicular goethite particles. The yield was 7.1 g / l / h. The end point of the oxidation reaction is
A 1% hydrochloric acid red blood salt solution was used to determine the presence or absence of Fe ²⁺ blue color reaction. The produced particles were washed with water, separated by filtration, dried and pulverized by a conventional method. The acicular goethite particles are Si
/ Fe was 0.61 at% and Al / Fe was 1.0 at%.

The electron micrograph (× 30) shown in FIG.
000), the average value of the major axis was 0.46 μm.
m, the axis ratio (major axis diameter / minor axis diameter) was 25, and the geometric standard deviation was 0.78. The particles were uniform in particle size and did not contain dendritic particles.

Examples 2 to 4 Various types of ferrous salt aqueous solution, Fe ²⁺ concentration, NaOH aqueous solution concentration, type of water-soluble aluminum salt, amount and timing of addition, amount of water-soluble silicate varied. Except having been performed, needle-like goethite particles were produced in the same manner as in Example 1. The main manufacturing conditions at this time are shown in Table 1, and various characteristics are shown in Table 2. Each of the acicular goethite particle powders obtained in Examples 2 to 4 has a large axial ratio (major axis diameter / minor axis diameter) as a result of observation with an electron microscope, and does not contain dendritic particles.
Particles having a geometric standard deviation value of 0.70 or more were uniform in particle size. In addition, the amount of production was 6.3 g / l / hour,
Preferably, it was 6.5 g / l / hour or more, and the production efficiency was excellent.

Comparative Example 1 A needle-like goethite particle powder was produced in the same manner as in Example 4 except that the water-soluble aluminum salt and the water-soluble silicate were not added. The main manufacturing conditions at this time are shown in Table 1, and various characteristics are shown in Table 2. The obtained needle-like goethite particle powder is an electron micrograph (× 30000) shown in FIG.
As shown in Fig. 7, dendritic particles were mixed, and the geometric standard deviation was 0.52, and the particles were uneven in particle size.

Comparative Example 2 Sodium silicate (No. 3) without adding a water-soluble silicate
Acicular goethite particle powder was produced in the same manner as in Example 4 except that (SiO _2: 28.55 wt%) was changed to 0.50 atomic% in terms of Si / Fe. The main manufacturing conditions at this time are shown in Table 1, and various characteristics are shown in Table 2. The obtained acicular goethite particle powder was obtained by an electron micrograph (× 3000) shown in FIG.
As shown in 0), the particles had a small axial ratio (major axis diameter / short axis diameter).

Comparative Example 3 A needle was prepared in the same manner as in Example 4 except that the water-soluble silicate was not added, the addition amount of aluminum sulfate was changed to 1.0 atomic% in terms of Al / Fe, and the addition time was changed. A goethite particulate powder was produced. The main manufacturing conditions at this time are shown in Table 1, and various characteristics are shown in Table 2. The obtained acicular goethite particle powder is
As shown in the electron micrograph (× 30000) shown in FIG. 4, dendritic particles are mixed, and the geometric standard deviation value is 0.
The particles had an irregular particle size of 52.

Comparative Example 4 A production reaction was carried out in the same manner as in Example 1 except that the method of adding the water-soluble aluminum salt and the water-soluble silicate was changed. The main manufacturing conditions at this time are shown in Table 1, and various characteristics are shown in Table 2. The particle powder obtained in Comparative Example 4 was an asymmetric particle having a geometric standard deviation of 0.57. In addition, the production amount was 3.6 g / l / hour, and the production efficiency was extremely poor.

<Production of Acicular Magnetite Particle Powder> Examples 5 to 11, Comparative Examples 5 to 8; Example 5 The filtered and washed acicular goethite particles containing Si and Al obtained in Example 1 were prepared. 9.5 kg of paste (corresponding to about 2.8 kg of acicular goethite particles containing Si and Al) were suspended in 50 l of water. P at this time
H was 9.4. Then, 200 ml of an aqueous solution containing 19.6 g of sodium hexametaphosphate in the suspension.
(P with respect to acicular goethite particles containing Si and Al
It corresponds to 0.54 wt% as O ₃ . 3)
After stirring for 0 minutes, the resultant was separated by filtration and dried to obtain a powder of acicular goethite particles containing Si and Al coated with a P compound. Si whose particle surface is coated with a P compound
And the Al-containing acicular goethite particle powder is heat-treated at 320 ° C. in air to be coated with a P compound.
And Al-containing acicular hematite particles were obtained.

Needle-like hematite particle powder 600 containing Si and Al whose particle surface is coated with a P compound
g of H ₂ gas was introduced into the retort reduction vessel and H ₂ gas was passed at a rate of 2 liters per minute while being driven to rotate.
The resultant mixture was reduced at a temperature of ° C to obtain acicular magnetite particles containing Si and Al coated with a P compound.

As a result of observation with an electron microscope, the obtained acicular magnetite particle powder containing Si and Al coated with the P compound was found to have a major axis of 0.27 μm and an axial ratio (major axis diameter / minor axis). Diameter) 7.2, and the geometric standard deviation value is 0.6
The particles of No. 2 were uniform in particle size and did not contain dendritic particles. And each particle existed independently. As a result of the magnetic measurement, the coercive force Hc was 457.
Oe and the saturation magnetization s were 83.1 emu / g.

Examples 6 to 11 and Comparative Examples 5 to 8 The same procedures as in Example 5 were carried out except that the types of the starting materials, the presence or absence of the coating treatment with the P compound, the presence or absence of the heat treatment in the air, and the heating temperature were variously changed. Thus, acicular magnetite particles were obtained. Table 3 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, the acicular magnetite particle powders obtained in Examples 6 to 11 were all uniform in particle size and did not contain dendritic particles.

<Production of Acicular Maghemite Particle Powder> Examples 12 to 18, Comparative Examples 9 to 12; Example 12 The particles obtained in Example 5 contain Si and Al whose surface is coated with a P compound. Acicular magnetite particle powder 3
00g was oxidized in air at 300 ° C. for 60 minutes to obtain maghemite particle powder containing Si and Al whose particle surfaces were coated with a P compound.

The obtained acicular maghemite particles containing Si and Al whose particle surfaces are coated with a P compound were observed by an electron microscope to have a major axis of 0.27 μm and an axial ratio (major axis diameter / minor axis). The diameter was 7.0, the particles were uniform in particle size with a geometric standard deviation of 0.60, and did not contain dendritic particles. And each particle existed independently. As a result of magnetism measurement, the coercive force Hc was 443 Oe, and the saturation magnetization s was 73.3 emu / g.

Examples 13 to 18 and Comparative Examples 9 to 12 Acicular maghemite particles were obtained in the same manner as in Example 12, except that the type of the acicular magnetite particles was variously changed. Table 4 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 maghemite particles containing Si and Al obtained in Examples 13 to 18 were all uniform in particle size and did not contain dendritic particles. And each particle existed independently.

<Manufacture of Acicular Magnetite Particle Powder Modified with Co> Examples 19 to 26, Comparative Examples 13 to 16; Example 19 Si obtained by coating the particle surface obtained in Example 5 with a P compound. 0.085 mol of cobalt using cobalt sulfate and ferrous sulfate while preventing the incorporation of air as much as possible into 100 g of acicular magnetite particles containing Al and Al
And 0.179 mol of ferrous iron are dissolved in 1.0 liter of water and dispersed until a fine slurry is formed. Then, 102 ml of an 18-N NaOH aqueous solution is poured into the dispersion, and water is further added. In addition, the total volume was adjusted to 1.3 l to prepare 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, dried at 60 ° C., and containing Si and Al modified with Co. Needle-like magnetite particles were obtained.

The obtained particles were observed by an electron microscope.
Si whose precursor particles are coated with a P compound
And the shape and particle size of the magnetite particles containing Al and Al are inherited, the major axis is 0.26 m, the axial ratio (major axis diameter / minor axis diameter) is 6.3, and the geometric standard deviation is 0.59. Were uniform particles. As a result of the magnetic measurement, the coercive force H
c is 825 Oe, saturation magnetization s is 84.0 emu / g.
Met.

Examples 20 to 26, Comparative Examples 13 to 6 Precursor type, cobalt addition amount, Fe ²⁺ addition amount, assuming that the amount of magnetite particles as the precursor is 100 g and the total volume of the processing solution is 1.3 l. And Co or Co and F in the same manner as in Example 19, except that the addition amount of NaOH and NaOH was variously changed.
Acicular magnetite particles containing Si and Al modified by e ²⁺ were obtained. Table 5 shows the main manufacturing conditions and characteristics at this time.

<Manufacture of Acicular Maghemite Particle Powder Modified with Co> Examples 27 to 34, Comparative Examples 17 to 20; Example 27 Si obtained by coating the surface of the particles obtained in Example 12 with a P compound. 0.085 mol of cobalt using cobalt sulfate and ferrous sulfate while preventing as much as possible air from mixing 100 g of the acicular maghemite particles containing Al and Al.
1.0 l in which 0.179 mol of ferrous iron is dissolved
Into water and disperse until it becomes a fine slurry,
Then, 102 ml of an 18-N NaOH solution was poured into the dispersion, and water was further added to make the total volume 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, separated by filtration, dried at 60 ° C., and contained Si and Al modified with Co. Needle-like maghemite particles were obtained.

The obtained particles were observed by an electron microscope.
Si whose precursor particles are coated with a P compound
And the shape of acicular maghemite particles containing Al,
The particles inherited the particle size, had a major axis of 0.26 μm, an axial ratio (major axis diameter / minor axis diameter) of 6.1, and had a geometric standard deviation of 0.58. As a result of the magnetic measurement, the coercive force Hc was 765 Oe, and the saturation magnetization s was 77.1 em.
u / g.

Examples 28 to 34, Comparative Examples 7 to 20 Precursor type, Co addition amount, Fe ²⁺ addition, with the amount of acicular maghemite particles as precursor being 100 g and the total volume of the treatment liquid being 1.3 l. Amount, the amount of NaOH aqueous solution added, the temperature, and the time were changed in various ways in the same manner as in Example 27.
Acicular maghemite particles containing Si and Al modified with o or Co and Fe ²⁺ were obtained. Table 6 shows the main manufacturing conditions and characteristics at this time.

<Production of Magnetic Tape> Examples 35 to 64, Comparative Examples 21 to 36; Example 35 A 140 cc glass bottle containing Si and Al whose particle surfaces obtained in Example 5 were coated with a P compound. After adding the needle-like magnetic iron oxide particles powder, resin and solvent in the following proportions, the magnetic paint prepared by mixing and dispersing with a paint conditioner for 2 hours is applied to an applicator on a 25 μm-thick polyethylene terephthalate film. To a thickness of 40 μm and then 1450
It was obtained by orienting in a magnetic field of Gauss and then drying.

1.5 mmφ glass beads 100 g Magnetic iron oxide 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
4. Coercive force Hc is 382 Oe, residual magnetic flux density Br is 1
620 Gauss, square Br / Bm was 0.83.

Examples 36 to 64, Comparative Examples 21 to 36 Example 35 except that the type of the magnetic particle powder was variously changed.
A magnetic tape was manufactured in the same manner as described above. The acicular maghemite particles were oriented in a magnetic field of 1450 Gauss, and the Co-modified magnetic iron oxide particles were oriented in a magnetic field of 1900 Gauss. Tables 7 to 10 show various properties of the magnetic tape.

[0078]

[Table 1]

[0079]

[Table 2]

[0080]

[Table 3]

[0081]

[Table 4]

[0082]

[Table 5]

[0083]

[Table 6]

[0084]

[Table 7]

[0085]

[Table 8]

[0086]

[Table 9]

[0087]

[Table 10]

[0088]

According to the method for producing acicular magnetic iron oxide particles according to the present invention, as described in the above embodiment, the particles have a large axis ratio (major axis diameter / minor axis diameter) and a higher particle size. Since it is uniform and does not contain dendritic particles, as a result, it is possible to obtain a needle-like magnetic iron oxide particle powder having an excellent coercive force distribution and in which individual particles are independent. ,
It is suitable as a magnetic particle powder for high recording density, high sensitivity, and high output which is currently most required.

In the present invention, the amount of goethite produced as a starting material can be increased to 6.3 g / l / hour, preferably 6.5 g / l / hour or more, so that it is industrially and economically advantageous. This also has the effect that needle-like magnetic iron oxide particles can be obtained.

[0090]

[Brief description of the drawings]

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

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

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

FIG. 4 is an electron micrograph (× 30000) showing the particle structure of the acicular goethite particles obtained in Comparative Example 3.

FIG. 5 is an electron micrograph (× 30000) showing the particle structure of the acicular goethite particles obtained in Comparative Example 4.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshiro Okuda 4-1-2, Funariminami, Naka-ku, Hiroshima-shi, Hiroshima Examiner, Toda Kogyo Co., Ltd. Creative Center Hitoshi Misaki (56) References JP-A-64-33019 (JP, A) JP-A-4-204949 (JP, A) JP-A-2-167829 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C01G 49/00-49 / 08 H01F 1/11

Claims (3)

(57) [Claims] An acicular goethite particle by passing an oxygen-containing gas through a suspension containing ferrous hydroxide and having a pH of 11 or more, which is obtained by reacting an aqueous ferrous salt solution and an aqueous alkaline solution, to oxidize the suspension. In producing the water-soluble silicate, the water-soluble silicate is added to any of the suspensions before the oxidation reaction is performed by passing the alkaline aqueous solution and the oxygen-containing gas.
0.1 to 0.7 atomic% in terms of Si with respect to e, and the suspension before the oxidation reaction is performed by passing the aqueous ferrous salt solution, the alkaline aqueous solution and the oxygen-containing gas. Water soluble aluminum salt in any of the
By adding 0.1 to 3.0 atomic% in terms of Al with respect to e, acicular goethite particles containing Si and Al are generated, and then acicular goethite particles containing Si and Al or Acicular hematite particles containing Si and Al obtained by heat-treating the particles at 300 to 700 ° C. are heated and reduced in a reducing gas to obtain acicular magnetite particles containing Si and Al. A method for producing acicular magnetic iron oxide particles. 2. The Si obtained by the method according to claim 1.
And oxidizing acicular magnetite particles containing Al and Al
A method for producing acicular magnetic iron oxide particles, wherein acicular maghemite particles containing i and Al are obtained. 3. Si obtained by the method according to claim 1.
Magnetite particles containing Al and Al.
Needle-like maghemite particles containing Si and Al obtained by the method described above are used as precursor particles, and the precursor particles contain 0.5 to 15.0 atomic% of Co with respect to Fe of the precursor particles. The body particles are dispersed in cobalt hydroxide or an alkaline suspension containing cobalt hydroxide and ferrous hydroxide, and the dispersion is subjected to a heat treatment to thereby ^convert Si or Al modified with Co or Co and Fe ^2+. A method for producing acicular magnetic iron oxide particles, characterized by obtaining acicular magnetite particles containing Si or Al and acicular maghemite particles containing Si and Al.