JPH04317421A - Production of acicular magnetic iron oxide granular powder - Google Patents

Abstract

PURPOSE:To provide the method for producing acicular magnetic iron oxide granular powder which has a large aspect ratio, uniform particle size without coexisting of branched particles, and thereby has excellent coercive force distribution and each particle is independent from another. CONSTITUTION:A suspension of >=pH 11 containing ferrous oxide is prepared by the reaction of an aq. ferrous salt soln. and an alkali soln. Preliminarily, a water-soluble silicate and a water-soluble aluminum salt are added into the suspension, into which oxygen-contg. gas is introduced to cause the oxidation reaction and to produce acicular goethite particlar powder containing Si and Al. Then these particles are reduced to obtain acicular magnetite particles, or further the particles are oxidized to obtain acicular maghemite particles, or both of particles are modified with Co to obtain acicular magnetic iron oxide particles. Since the production amt. of goethite is increased to >=6.3g/l/ hour by this method, magnetic oxide particles can be obtd. advantageously in industry and economics.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention has a large axial ratio (major axis diameter/
Furthermore, the particle size is more uniform and dendritic particles are not mixed, resulting in an excellent coercive force distribution and 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 magnetic recording and reproducing equipment has become smaller and lighter, there has been an increasing need for recording media such as magnetic tapes and magnetic disks to have higher performance. That is, high recording density, high sensitivity characteristics, high output characteristics, etc. are required.

[0003] The properties of magnetic material particles required to satisfy the above requirements for magnetic recording media are as follows:
It has 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 for the magnetic particles to have as high a coercive force as possible. ``Development of Magnetic Materials and Highly Dispersed Magnetic Powder Technology'' (1982), page 310, ``The aim to improve magnetic tape performance was to increase sensitivity and output.
The emphasis was on increasing the coercive force of acicular γ-Fe2O3 particles. It is clear from the statement ``.

As is well known, the magnitude of the coercive force of magnetic particles depends on shape anisotropy, crystal anisotropy, strain anisotropy, exchange anisotropy, or their interaction. There is.

[0006] In addition, in order to increase the recording density and output of magnetic recording media, it is necessary to refer to ``Development of magnetic materials and high dispersion technology of magnetic particles'', p. 312, ``For high-density recording in coated tapes''. The condition for this is to be able to maintain high output characteristics with low noise for short wavelength signals;
"The obtained magnetic tape has improved coercive force Hc and squareness (Br/Bm)," p. 310 of the same document. As stated in ``The magnetic recording medium must have a high coercive force, a large residual magnetization Br, and a square shape.''
For this purpose, it is required that the magnetic particles have a high coercive force, and have excellent dispersibility in a vehicle, and excellent orientation and filling properties in a coating film.

[0007] Furthermore, in order to increase the output of magnetic recording media,
JP-A No. 63-26821 states, ``Figure 1 is a diagram showing the relationship between S.F.D. and recording/reproduction output measured for the above-mentioned magnetic disk. As is clear from Fig. 1, the relationship between ferromagnetic powder and recording/reproducing output is a straight line, which shows that the recording/reproducing output can be increased by using ferromagnetic powder with a small S.F.D. In order to increase the recording and playback output, it is desirable that the S.F.D.
The following S. F. D. is necessary. ” As stated,
S. of magnetic recording media. F. D. (Switching
It is necessary that the coercive force distribution width of the magnetic particles be small.

Magnetic iron oxide particles such as acicular magnetite particles and acicular maghemite particles, which are currently used as magnetic particles for magnetic recording, or these particles are
The acicular magnetic iron oxide particle powder metamorphosed with o or Co and Fe can utilize the 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 particles are made by heating goethite 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 a reducible material such as hydrogen. 300-500 in gas
It is obtained by reducing the magnetite particles at 0.degree. C. to obtain magnetite particles, or by oxidizing the magnetite particles in air at 200 to 500.degree. C. to obtain maghemite particles.

In addition, the known acicular magnetic iron oxide particle powder modified with Co or modified with Co and Fe uses acicular magnetite particles or acicular maghemite particles as precursor particles, and the Fe of the precursor particles is 0.5 to 15.0 at%
It can be obtained by dispersing the precursor particles in an alkaline suspension containing cobalt hydroxide or cobalt hydroxide and ferrous hydroxide so as to contain Co, and heat-treating the dispersion.

The residual magnetization Br and the square shape of the magnetic recording medium are as follows:
It depends on the dispersibility of the magnetic particles in the vehicle, the orientation and filling properties in the coating film, and in order to improve these properties, the magnetic particles dispersed in the vehicle must have a large axial ratio (axis diameter/minor axis diameter), 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.

[0012] This fact is explained in the above-mentioned ``Development of Magnetic Materials and Technology for Highly Dispersing Magnetic Particles'', p. The orientation property is the most important.The main objective of research on the synthesis method of highly dispersed and highly oriented acicular γ-Fe2O3 particles is to obtain acicular particles in which each particle can move independently. This is as stated in the following statement.

As mentioned above, magnetic particle powder has a large axial ratio (major axis diameter/minor axis diameter), has uniform particle size, does not contain dendritic particles, and has discrete particles. is currently in the greatest demand, and in order to obtain magnetic particles with such characteristics, the starting material, goethite particles, must have a large axial ratio (major axis diameter/minor axis diameter). Moreover, it is necessary that the particle size is uniform, that dendritic particles are not mixed, and that sintering between particles and particles is prevented as much as possible in the subsequent heat treatment step.

[0014] Conventionally, the method for producing goethite particles as a starting material is as follows: (1) Adding an equivalent or more aqueous alkali hydroxide solution to an aqueous ferrous salt solution to obtain a suspension containing ferrous hydroxide colloid; A method of producing acicular goethite particles by carrying out an oxidation reaction by passing an oxygen-containing gas at a temperature of 80°C or lower at a pH of 11 or higher
(No. 5610), ■ goethite particles that have a spindle shape by performing an oxidation reaction by passing an oxygen-containing gas through a suspension containing FeCO3 obtained by reacting an aqueous ferrous salt solution with an aqueous alkali carbonate solution. There is a known method for generating .

[0015] In addition, in the method (1) above, a water-soluble silicate is added during the reaction in order to improve the particle size of the acicular goethite particles produced (Japanese Patent Publication No. 55-8461, Japanese Patent Publication No. 55-84). -32652 Publication), ■ A method of adding water-soluble silicate and water-soluble zinc salt during the reaction to improve the particle size and axial ratio (major axis diameter/minor axis diameter) of the acicular goethite particles produced ( Japanese Patent Publication No. 55-6575, Japanese Patent Publication No. 55-6576), etc. are known.

[0016]

[Problem to be solved by the invention] Large axial ratio (major axis diameter/
At present, magnetic particles with uniform particle size, no dendritic particles mixed in, and dispersed particles are most in demand; In the case of the above-mentioned method (2) for producing goethite particle powder, acicular goethite particles with an axial ratio (major axis diameter/minor axis diameter) of 10 or more are produced, but dendritic particles are mixed. Furthermore, in terms of particle size, it is difficult to say that the particles have a uniform particle size.

[0017] In the case of method (2) above, spindle-shaped particles with uniform particle size and no dendritic particles are produced, but on the other hand, the axial ratio (long axis diameter/short axis diameter shaft diameter)
is about 7 at most, and it has the disadvantage that it is difficult to produce particles with a large axial ratio (major axis diameter/minor axis diameter), and this phenomenon is said to become especially pronounced as the major axis diameter of the produced particles becomes smaller. There is a tendency.

[0018] In the case of the method (2) above, acicular goethite particles with uniform particle size and no dendritic particles are produced, but the axial ratio (major axis diameter/minor axis diameter) is about 9 at most. As the amount of water-soluble silicate added increases, the particle size becomes uniform and dendritic particles are no longer mixed, but on the other hand, the axial ratio (major axis diameter/minor axis diameter) tends to decrease rapidly. It is in. Furthermore, it is difficult to sufficiently prevent sintering between particles and particles during thermal reduction, and it is difficult to say that individual particles are independent.

In the case of method (2) above, acicular goethite particles having a large axial ratio (major axis diameter/minor axis diameter) are produced, but the effect of improving the axial ratio (major axis diameter/minor axis diameter) is Addition of a water-soluble zinc salt having a It is difficult to say that particles are independent. In addition, there is a problem that the production efficiency is lowered due to a decrease in the production amount per unit time/unit volume (hereinafter referred to as production amount), which is not industrially or economically viable.

Therefore, the present invention has a large axial ratio (major axis diameter/
In addition, the particle size is more uniform and dendritic particles are not mixed, resulting in an excellent coercive force distribution and better prevention of sintering between particles and between particles. The technical problem is to obtain acicular magnetic iron oxide particles in which individual particles are independent.

[0021]

[Means for Solving the Problems] The above technical problems can be achieved by the present invention as follows.

That is, the present invention provides a p-containing compound containing ferrous hydroxide obtained by reacting an aqueous ferrous salt solution with an aqueous alkaline solution.
In producing acicular goethite particles by passing an oxygen-containing gas through a suspension of H11 or higher to oxidize it,
Water-soluble silicate is added in an amount of 0.1 to 0.7 atomic % based on Fe in terms of Si in any of the suspensions before the aqueous alkali solution and oxygen-containing gas are passed through to perform the oxidation reaction. A water-soluble aluminum salt is added to Fe in any of the suspensions before the ferrous salt aqueous solution, the alkaline aqueous solution, and the oxygen-containing gas are passed through the suspension to perform the oxidation reaction. 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
The acicular hematite particles containing Si and Al obtained by heat treatment at 0°C are thermally reduced in a reducing gas to obtain acicular magnetite particles containing Si and Al, or further oxidized if necessary. to obtain acicular maghemite particles containing Si and Al, or, if necessary, using the acicular magnetite particles containing Si and Al or the acicular maghemite particles containing Si and Al as precursor particles. 0.5 to 1 with respect to Fe of the precursor particles.
By dispersing the precursor particles in an alkaline suspension containing cobalt hydroxide or cobalt hydroxide and ferrous hydroxide so as to contain 5.0 atom% of Co, and heat-treating the dispersion. This is a method for producing acicular magnetic iron oxide particle powder, which comprises obtaining acicular magnetite particles containing Si and Al modified with Co or Co and Fe2+, or acicular maghemite particles containing Si and Al.

[0023]

[Function] First, the most important point in the present invention is that an oxygen-containing gas is passed through a suspension containing ferrous hydroxide and having a pH of 11 or higher, which is obtained by reacting a ferrous salt aqueous solution and an alkaline aqueous solution. In producing acicular goethite particles by oxidation, a water-soluble silicate containing Fe is added to any of the suspensions before the oxidation reaction is carried out by passing the alkaline aqueous solution and oxygen-containing gas through the aqueous alkali solution and oxygen-containing gas. 0 in terms of Si
．． 1 to 0.7 atomic % is added, and the ferrous salt aqueous solution, the alkaline aqueous solution and the oxygen-containing gas are aerated into any of the suspensions before the oxidation reaction is carried out. The water-soluble aluminum salt is 0.0% in terms of Al relative to Fe.
When 1 to 3.0 at% is added, it has a large axial ratio (major axis diameter/minor axis diameter) and contains Si and Al with a more uniform particle size and no dendritic particles. It is said that the acicular goethite particles containing Si and Al are sufficiently prevented from sintering between the particles and each other in the heat reduction process, and each particle is independent. It is a fact.

[0024] The present inventor has ascertained the reason why acicular goethite particles having a large axial ratio (major axis diameter/minor axis diameter), uniform particle size, and no dendritic particles are obtained in the present invention. As shown in the comparative example below, in any method in which water-soluble silicate or water-soluble aluminum salt is added alone in the goethite particle production reaction, the desired acicular goethite particles cannot be produced. Since it cannot be produced, it is thought that this is due to the synergistic effect of water-soluble silicate and water-soluble aluminum salt.

In the present invention, the reason why acicular magnetic iron oxide in which each particle is independent is obtained is as follows. When acicular goethite particles are heat-reduced, the square shape is not good in any case, so due to the synergistic effect of Si and Al contained in acicular goethite particles, the particles and the inter-particles are reduced in the heat-reduction process. We believe that this has sufficiently prevented sintering.

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

[0027] Conventionally, there is a method described in JP-A-64-33019 in which a silicon compound and an aluminum compound are added in the reaction for producing acicular goethite particles. This method supplies oxygen-containing gas while adding a silicon compound and an aluminum compound to a suspension containing ferrous hydroxide, which tends to produce dendritic particles with asymmetric particle sizes. This becomes more pronounced as the production amount of acicular goethite particles increases, especially through high-concentration reactions, and its effects are completely different from those of the present invention.

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

Ferrous salts used in the present invention include aqueous ferrous sulfate solutions and aqueous ferrous chloride solutions.

[0030] Examples of the alkaline aqueous solution used in the present invention include a sodium hydroxide aqueous solution and a potassium hydroxide aqueous solution.

The water-soluble silicates used in the present invention include sodium and potassium silicates. The amount of water-soluble silicate added is 0.1 to 0.7 atomic % based on Fe in terms of Si. If it is less than 0.1 atomic %, it is difficult to produce acicular goethite particles with uniform particle size and no dendritic particles, which is the objective of the present invention. If it exceeds 0.7 at %, acicular goethite particles having a large axial ratio (major axis diameter/minor axis diameter) cannot be obtained.

[0032] The water-soluble silicate used in the present invention is involved in the particle size and the form of dendritic particles of the acicular goethite particles produced, so the timing of its addition is determined by aerating oxygen-containing gas to carry out the oxidation reaction. It is necessary to add it to either an alkaline aqueous solution or a suspension containing ferrous hydroxide.

Water-soluble aluminum salts used in the present invention include aluminum sulfate, sodium aluminate, and aluminum chloride. The amount of water-soluble aluminum salt added is 0.1 to 3.0 atomic % based on Fe in terms of Al. If it is less than 0.1 atomic %, it is difficult to produce acicular goethite particles with uniform particle size and no dendritic particles, which is the objective of the present invention. If the content exceeds 3.0 at %, the desired effects of the present invention can be obtained, but the saturation magnetization of the acicular magnetic iron oxide particles obtained using the produced acicular goethite particles decreases.

The water-soluble aluminum salt in the present invention is involved in the axial ratio (major axis diameter/minor axis diameter), particle size, and particle morphology such as dendritic particles of the acicular goethite particles produced. The timing of addition must be before the oxidation reaction is carried out by passing in oxygen-containing gas, and the addition time must be before the oxidation reaction is carried out by aerating oxygen-containing gas. It can be added inside.

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

The heating 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 are treated with 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, or P compounds. This coating treatment further prevents sintering between particles and particles, and improves the particle shape and axial ratio (major axis diameter/minor axis diameter) of the starting material particles.
This makes it easier to obtain individually independent magnetic iron oxide particles.

The oxidation temperature in the present invention is set to 2 by a conventional method.
It can be carried out at a temperature of 00 to 500°C.

Co of the magnetic iron oxide particles in the present invention
Metamorphosis can be carried out by conventional methods, for example,
2-24237, Japanese Patent Publication No. 52-24238, Japanese Patent Publication No. 52-36751, and Japanese Patent Publication No. 52-36
As described in Japanese Patent No. 863, precursor particles are dispersed in an alkaline suspension containing cobalt hydroxide or cobalt hydroxide and ferrous hydroxide, and the dispersion is heat-treated. be exposed.

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.

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. .

[0042] For Co modification, the heat treatment is preferably carried out in a non-oxidizing atmosphere at a temperature in the range of 50 to 100°C.

[0043] The temperature of Co metamorphosis is related to the treatment time; if the temperature is set to 50°C or lower, magnetite particles or maghemite particles metamorphosed with Co or Co and Fe2+ are difficult to form, and even if they are formed, they are Requires extremely long processing time.

[0044] Co modification is carried out in a non-oxidizing atmosphere because
This is because metamorphosis occurs only when cobalt and ferrous hydroxide are present, and this is to prevent oxidation of cobalt hydroxide and ferrous hydroxide in the dispersion.

The modified amount of the water-soluble cobalt salt in the present invention is 0.5 to 15.0 atomic % based on Fe in terms of Co. If it is less than 0.5 at %, the effect of improving the coercive force of the obtained acicular magnetite particles or maghemite particles cannot be sufficiently achieved. 15
．． If it exceeds 0 atomic %, the effect of reducing the coercive force distribution of the obtained acicular magnetite particles or maghemite particles will not be sufficient.

Almost all of the added water-soluble cobalt salt is utilized for denaturing 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.

[0048]

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

The particle size distribution of the particles was expressed by the geometric standard deviation value (σg) determined by the following method. In other words, the major axis diameters of 350 particles shown in an electron micrograph at 120,000 times magnification were measured, and the actual major axis diameter and number of particles calculated from the measured values were calculated using a logarithmic normal method using a statistical method. On probability paper, the long axis diameter of the particle is plotted on the horizontal axis, and the cumulative number of particles belonging to each of the long axis diameter sections taken at equal intervals on the vertical axis is plotted as a percentage. Then, from this graph, the values of the major axis diameter corresponding to 50% and 84.13% of the particles are read, and the geometric standard deviation value (σg) = major axis diameter when the number of particles is 50% (μm)/ Long axis diameter (μm) when number of pieces is 84.13%
It is shown as a value calculated according to the following.

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

The magnetic properties and coating film properties of the magnetic iron oxide particles were measured using a "vibrating sample magnetometer VSM-3S-15" (manufactured by Toei Kogyo Co., Ltd.). The measurement was performed by applying an external magnetic field of up to 5 KOe for the powder particles, and an external magnetic field of up to 10 KOe for the Co-transformed magnetic iron oxide particles.

[0052] The square shape of the coating film and the S.I. F. D. The measurement was carried out using a sheet sample piece obtained by the method of Example 35 below. Also, S. F. D. was determined by obtaining a differential curve of the demagnetization curve of the magnetic hysteresis curve using the differential circuit of the magnetometer, measuring the half-width of this curve, and dividing this value by the coercive force.

<Production of acicular goethite particles> Examples 1 to 4 Comparative Examples 1 to 4; Example 1 Sulfuric acid obtained by adding aluminum sulfate to contain 1.0 atomic % in terms of Al/Fe Ferrous iron 1.5mol/l
Sodium silicate (No. 3) (SiO2 28.55 wt%) 3 was added to 24 liters of aqueous solution so as to contain 0.50 at% in terms of Si/Fe, which was prepared in advance in a reactor.
6.7-N NaOH aqueous solution 2 obtained by adding 7.8 g (corresponding to 0.50 at% in terms of Si/Fe)
6 l, pH 13.1, temperature 50°C
An aqueous solution containing e(OH)2 and Al(OH)3 was obtained.

[0054] The above Fe(OH)2 and Al(OH)3
100 per minute at a temperature of 50°C to an aqueous solution containing
1 of air was aerated for 9 hours to produce acicular goethite particles. The production amount was 7.1 g/l/hour. The end point of the oxidation reaction was determined by the presence or absence of a blue coloring reaction of Fe2+ using a 1% hydrochloric acid red blood salt solution. The resulting particles were washed with water, filtered, dried, and pulverized using conventional methods. The acicular goethite particles contained 0.61 atomic % of Si/Fe and 1.0 atomic % of Al/Fe.

[0055] Furthermore, the electron micrograph shown in Fig. 1 (×30
000), the average value of the major axis is 0.46μ
m, an axial ratio (major axis diameter/minor axis diameter) of 25, a geometric standard deviation value of 0.78, uniform particle size, and no dendritic particles were present.

Examples 2 to 4 The type of ferrous salt aqueous solution, Fe2+ concentration, concentration of NaOH aqueous solution, type, amount and timing of addition of water-soluble aluminum salt, and amount of water-soluble silicate added were varied. Acicular goethite particles were produced in the same manner as in Example 1 except for this. The main manufacturing conditions at this time are shown in Table 1, and the various characteristics are shown in Table 2. As a result of electron microscopic observation, the acicular goethite particles obtained in Examples 2 to 4 all had a large axial ratio (major axis diameter/minor axis diameter) and did not contain dendritic particles,
The particles were uniform in particle size and had a geometric standard deviation value of 0.70 or more. In addition, the production amount is 6.3g/l/hour in both cases.
Preferably, it was 6.5 g/l/hour or more, and the production efficiency was excellent.

Comparative Example 1 Acicular goethite particles were produced in the same manner as in Example 4 except that water-soluble aluminum salt and water-soluble silicate were not added. The main manufacturing conditions at this time are shown in Table 1, and the various characteristics are shown in Table 2. The obtained acicular goethite particles are shown in the electron micrograph (×30,000) shown in Figure 2.
As shown in the figure, dendritic particles were mixed, and the particle size was asymmetric with a geometric standard deviation value of 0.52.

Comparative Example 2 No water-soluble silicate was added, and sodium silicate (No. 3) (
Acicular goethite particles were produced in the same manner as in Example 4, except that SiO2 (28.55 wt%) was 0.50 atomic % in terms of Si/Fe. The main manufacturing conditions at this time are shown in Table 1, and the various characteristics are shown in Table 2. The obtained acicular goethite particles are shown in the electron micrograph (×3000
As shown in 0), the particles had a small axial ratio (major axis diameter/minor axis diameter).

Comparative Example 3 A needle was prepared in the same manner as in Example 4, except that no water-soluble silicate was added, the amount of aluminum sulfate added was 1.0 atomic % in terms of Al/Fe, and the timing of addition was changed. Goethite particle powder was produced. The main manufacturing conditions at this time are shown in Table 1, and the various characteristics are shown in Table 2. The obtained acicular goethite particle powder is
As shown in the electron micrograph (×30000) shown in Figure 4, dendritic particles are mixed, and the geometric standard deviation value is 0.5.
2, the particles were asymmetric in particle size.

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 the various characteristics are shown in Table 2. The particles obtained in Comparative Example 4 were asymmetric particles with a geometric standard deviation of 0.57. Also, the amount of production is 3
．． The production efficiency was 6 g/l/hour, which was extremely poor.

<Production of acicular magnetite particles> Examples 5 to 11, Comparative Examples 5 to 8; Example 5 The acicular goethite particles containing Si and Al obtained in Example 1 and filtered and washed with water 9.5 kg of paste (corresponding to about 2.8 kg of acicular goethite particles containing Si and Al) was suspended in 50 l of water. The pH at this time was 9.4. Next, 200 ml of an aqueous solution containing 19.6 g of sodium hexametaphosphate was added to the above suspension.
(P for acicular goethite particles containing Si and Al)
This corresponds to 0.54 wt% as O3. ) was added and stirred for 30 minutes, filtered and dried to obtain acicular goethite particles containing Si and Al coated with a P compound. S whose particle surface is coated with a P compound
Acicular goethite particles containing i and Al are heated in air at 320°C to obtain S coated with a P compound.
Acicular hematite particles containing i and Al were obtained.

Acicular hematite particle powder 600 containing Si and Al, the particle surface of which is coated with a P compound
g into a retort reduction container, and while driving and rotating H2 gas was aerated at a rate of 2 liters per minute until the reduction temperature was 4.
Si and A coated with P compound after reduction at 00°C
Acicular magnetite particle powder containing 1 was obtained.

As a result of electron microscopic observation, the obtained acicular magnetite particles coated with the P compound and containing Si and Al have an average value of 0.27 μm on the major axis and an axial ratio (major axis diameter/minor axis diameter). diameter) 7.2, and the geometric standard deviation value is 0.6
The particle size of No. 2 was uniform, and dendritic particles were not mixed therein. Each particle existed independently. Also, as a result of magnetic measurement, the coercive force Hc was 457
Oe and saturation magnetization σs were 83.1 emu/g.

Examples 6 to 11, Comparative Examples 5 to 8 Example 5 except that the type of starting material, presence or absence of coating treatment with P compound, presence or absence of heat treatment in air, and heating temperature were varied.
Acicular magnetite particle powder was obtained in the same manner as above. Table 3 shows the main manufacturing conditions and characteristics of the particles at this time. As a result of electron microscopy, the acicular magnetite particles obtained in Examples 6 to 11 were all found to have uniform particle sizes and no dendritic particles were present.

<Production of acicular maghemite particles> Examples 12 to 18, Comparative Examples 9 to 12; Example 12 The particle surface obtained in Example 5 contains Si and Al and 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 and whose particle surface was coated with a P compound.

As a result of electron microscopy observation, the obtained acicular maghemite particles containing Si and Al whose particle surfaces are coated with a P compound have a long axis of 0.27 μm and an axial ratio (
The major axis diameter/minor axis diameter) is 7.0, and the geometric standard deviation value is 0.
The particles had a uniform particle size of 60 and had no dendritic particles mixed therein. Each particle existed independently. In addition, as a result of magnetic measurement, the coercive force Hc was 44
3 Oe, and the saturation magnetization σs was 73.3 emu/g.

Examples 13 to 18, Comparative Examples 9 to 12 Acicular maghemite particles were obtained in the same manner as in Example 12, except that the type of acicular magnetite particles was varied. Table 4 shows the main manufacturing conditions and characteristics of the particles at this time. As a result of electron microscopy, the acicular maghemite particles containing Si and Al obtained in Examples 13 to 18 were all found to have uniform particle sizes and no dendritic particles. Each particle existed independently.

<Production of acicular magnetite particles modified with Co> Examples 19 to 26, Comparative Examples 13 to 16; Example 19 Si particles obtained in Example 5 whose surfaces are coated with a P compound and 0.085 mol of cobalt using cobalt sulfate and ferrous sulfate while preventing the incorporation of air as much as possible from 100 g of acicular magnetite particle powder containing Al.
and 1.0 l with 0.179 mol of ferrous iron dissolved
water and dispersed until it becomes a fine slurry. Then, 102 ml of 18-N NaOH aqueous solution was added to the dispersion, and water was further added to bring the total volume to 1.3 liters.
A dispersion liquid with a base concentration of 1.0 mol/l was prepared. The temperature of the dispersion was raised to 100°C, and after 5 hours while stirring at this temperature, the slurry was taken out, washed with water, filtered, and dried at 60°C to form a slurry containing Co-modified Si and Al. Acicular magnetite particles were obtained.

As a result of electron microscopy observation of the obtained particles,
Si precursor particle surface coated with P compound
It inherits the shape and particle size of magnetite particles containing Al and has a long axis of 0.26 m, an axial ratio (long axis diameter / short axis diameter) of 6.3, and a geometric standard deviation value of 0.59. The particles were uniform in particle size. In addition, as a result of magnetic measurement, the coercive force H
c is 825 Oe, saturation magnetization σs is 84.0 emu/
It was g.

Examples 20 to 26, Comparative Examples 13 to 6 The amount of magnetite particles as a precursor was 100 g, the total volume of the treatment liquid was 1.3 liters, and the type of precursor, amount of cobalt added, amount of Fe2+ added, and NaOH Co or Co and Fe was prepared in the same manner as in Example 19, except that the amount of
Acicular magnetite particles containing 2+ modified Si and Al were obtained. Table 5 shows the main manufacturing conditions and characteristics at this time.

<Production of acicular maghemite particles modified with Co> Examples 27 to 34, Comparative Examples 17 to 20; Example 27 Si particles obtained in Example 12 whose surfaces are coated with a P compound 0.085 mo of cobalt using cobalt sulfate and ferrous sulfate while preventing air incorporation as much as possible from 100 g of acicular maghemite particles containing Al.
l and 0.179 mol of ferrous iron are dissolved in 1.0
1 of water and dispersed until it becomes a fine slurry, then 102 ml of 18-N NaOH solution was added to the dispersion.
and then add water to bring the total volume to 1.3 l.
A dispersion liquid with an H group concentration of 1.0 mol/l was prepared. The temperature of the dispersion was raised to 100°C, and after 5 hours while stirring at this temperature, the slurry was taken out, washed with water, filtered, and dried at 60°C to obtain a slurry containing Co-modified Si and Al. Acicular maghemite particles were obtained.

As a result of electron microscopy observation of the obtained particles,
Si precursor particle surface coated with P compound
and the shape of acicular maghemite particles containing Al,
The particles were uniform in particle size, with a long axis of 0.26 μm, an axial ratio (long axis diameter/short axis diameter) of 6.1, and a geometric standard deviation value of 0.58. Also, as a result of magnetic measurement, the coercive force Hc is 765 Oe, and the saturation magnetization σs is 77.1e.
It was mu/g.

Examples 28 to 34, Comparative Examples 7 to 20 The amount of acicular maghemite particles as a precursor was 100 g, the total volume of the treatment liquid was 1.3 liters, and the type of precursor, amount of Co added, F
Acicular maghemite particles containing Si and Al modified with Co or Co and Fe2+ were prepared in the same manner as in Example 27, except that the amount of e2+ added, the amount of NaOH aqueous solution added, temperature, and time were varied. Obtained. Table 6 shows the main manufacturing conditions and characteristics at this time.

<Manufacture of magnetic tape> Examples 35 to 64, Comparative Examples 21 to 36; Example 35 A 140 cc glass bottle contains Si and Al particles obtained in Example 5 whose surfaces are coated with a P compound. After adding acicular magnetic iron oxide particle powder, resin and solvent in the proportions shown below, the prepared magnetic paint was mixed and dispersed in a paint conditioner for 2 hours, and then applied with an applicator onto a 25 μm thick polyethylene terephthalate film. to a thickness of 40 μm, then 1450 μm
It was obtained by orienting it in a Gauss magnetic field and then drying it.

1.5mmφ glass beads
10
0g magnetic iron oxide particles powder

15g toluene

5.6g phosphoric acid ester (GAFACRE-610 manufactured by Toho Chemical Co., Ltd.)
0.6g lecithin

0.6g PVC vinyl acetate copolymer resin (Vinyrite VAGH Union Carbide Co., Ltd.
made))

3.75g Butadiene acrylonitrile rubber (Hycar 1432J manufactured by Nippon Zeon Co., Ltd.)

0.75g Methyl isobutyl ketone: methyl ethyl ketone: toluene = 3:1:1
mixed solution

40.5g

[0076] The S. F.
D. is 0.44, coercive force Hc is 382 Oe, residual magnetic flux density Br is 1620 Gauss, square Br/Bm is 0
．． It was 83.

Examples 36 to 64 and Comparative Examples 21 to 36 Magnetic tapes were produced in the same manner as in Example 35, except that the type of magnetic particles was varied. 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. Various properties of the magnetic tape are shown in Tables 7 to 10.

[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]

Effects of the Invention: According to the method for producing acicular magnetic iron oxide particles according to the present invention, as shown in the above-mentioned examples, the acicular magnetic iron oxide particles have a large axial ratio (major axis diameter/minor axis diameter) and a particle size of It is possible to obtain acicular magnetic iron oxide particles that are uniform and do not contain dendritic particles, and as a result, have an excellent coercive force distribution and each particle is independent. ,
It is suitable as a magnetic particle powder for high recording density, high sensitivity, and high output, which are currently most required.

In the present invention, the production amount of goethite, which is a starting material, is 6.3 g/l/hour, preferably 6.3 g/l/hour.
．． Since it can be increased to 5 g/l/hour or more, it also has the effect that acicular magnetic iron oxide particles can be obtained industrially and economically advantageously.

[0090]

[Brief explanation of the drawing]

1 to 5 are "Example 1" and "Comparative Example 1", respectively.
These are electron micrographs (×30,000) showing the particle structures of acicular goethite particles obtained in “Comparative Example 4”.

Claims (3)

[Claims] Claim 1: Acicular goethite particles are produced by blowing an oxygen-containing gas through a suspension containing ferrous hydroxide and having a pH of 11 or more obtained by reacting an aqueous ferrous salt solution with an aqueous alkaline solution to oxidize it. In producing the aqueous alkaline solution and oxygen-containing gas, water-soluble silicate is added to any of the suspensions before the oxidation reaction is carried out by passing the aqueous alkali solution and oxygen-containing gas through the aqueous alkali solution and the oxygen-containing gas. 0.7 atomic % of the ferrous salt aqueous solution, the alkaline aqueous solution, and the suspension before the oxidation reaction is carried out by passing through the aqueous ferrous salt solution, aqueous alkali solution, and oxygen-containing gas. Aluminum salt F
By adding 0.1 to 3.0 atomic % in terms of Al 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 heating the particles at 300 to 700°C are reduced by heating in a reducing gas to obtain acicular magnetite particles containing Si and Al. A method for producing acicular magnetic iron oxide particles. [Claim 2] S obtained by the method according to Claim 1
A method for producing acicular magnetic iron oxide particles, the method comprising oxidizing acicular magnetite particles containing i and Al to obtain acicular maghemite particles containing Si and Al. [Claim 3] S obtained by the method according to Claim 1
Acicular magnetite particles containing i and Al or acicular maghemite particles containing Si and Al obtained by the method according to claim 2 are used as precursor particles, and Fe of the precursor particles is 0.5 to 0. By dispersing the precursor particles in an alkaline suspension containing cobalt hydroxide or cobalt hydroxide and ferrous hydroxide so as to contain 15.0 atom% of Co, and heat-treating the dispersion. A method for producing acicular magnetic iron oxide particle powder, characterized by obtaining acicular magnetite particles containing Si and Al modified with Co or Co and Fe2+, or acicular maghemite particles containing Si and Al.